Stem Cells Faulty in Duchenne Muscular Dystrophy

Stem Cells Faulty in Duchenne Muscular Dystrophy

Thursday, 18 December 2014

Like human patients, mice with a form of Duchenne muscular dystrophy undergo progressive muscle degeneration and accumulate connective tissue as they age. Now, researchers at the Stanford University School of Medicine have found that the fault may lie at least partly in the stem cells that surround the muscle fibres.

They've found that during the course of the disease, the stem cells become less able to make new muscle and instead begin to express genes involved in the formation of connective tissue. Excess connective tissue – a condition called fibrosis – can accumulate in many organs, including the lungs, liver and heart, in many different disorders. In the skeletal muscles of people with muscular dystrophy, the fibrotic tissue impairs the function of the muscle fibres and leads to increasing weakness and stiffness, which are hallmarks of the disease.

The researchers discovered that this abnormal change in stem cells could be inhibited in laboratory mice by giving the animals a drug that is already approved for use in humans. The drug works by blocking a signalling pathway involved in the development of fibrosis. Although much more research is needed, the scientists are hopeful that a similar approach may one day work in children with muscular dystrophy.

"These cells are losing their ability to produce muscle, and are beginning to look more like fibroblasts, which secrete connective tissue," said Thomas Rando, MD, PhD, professor of neurology and neurological sciences.

"It's possible that if we could prevent this transition in the muscle stem cells, we could slow or ameliorate the fibrosis seen in muscular dystrophy in humans."

A paper describing the researchers' findings will be published Dec. 17 in Science Translational Medicine. Rando, the paper's senior author, is director of the Glenn Laboratories for the Biology of Aging and founding director of the Muscular Dystrophy Association Clinic at Stanford. Former postdoctoral scholar Stefano Biressi, PhD, is the lead author. Biressi is now at the Centre for Integrative Biology at the University of Trento in Italy.

A devastating disease

Duchenne muscular dystrophy is a devastating disease that affects about 1 in every 3,600 boys born in the United States. Patients usually experience severe, progressive muscle weakness that confines them to a wheelchair in early adolescence and eventually leads to paralysis. It's caused by mutations in the dystrophin gene, which encodes the dystrophin protein. The dystrophin protein serves to connect muscle fibres to the surrounding external matrix. This connection stabilizes the fibres, enhancing their strength and preventing injury. Sufferers are nearly always boys because the dystrophin gene is located on the X chromosome. (Girls would need to inherit two faulty copies, which is unlikely because male carriers often die in early adulthood.)

Under normal conditions, muscle stem cells respond to muscle damage by dividing into cells, one of which becomes new muscle, while the other remains a stem cell. However, in the mice missing the dystrophin gene, the muscle stem cells slowly assume a different fate. They begin to resemble fibroblasts instead of muscle-making machines.

To conduct the research, Biressi and Rando used a strain of laboratory mice in which the muscle stem cells were engineered to glow with a fluorescent light when treated with a drug called tamoxifen. They then bred the mice with another strain in which the dystrophin gene is mutated, and followed the fate of the cells over time.

The researchers found that the expression of myogenic genes, which are associated with the regeneration of muscle in response to injury, was nearly completely lacking in many of the muscle stem cells in the mice after just 11 months, while the expression of fibrotic genes had increased compared with that of control animals. The cells from the dystrophic animals were also oddly located: Rather than being nestled next to the muscle fibres, they had begun to move away into the spaces between tissues.

The role of a signalling pathway

Rando and Biressi knew that a similar, but much less pronounced, accumulation of connective tissue in muscle fibres occurs during normal aging. That process is governed by signalling proteins, which include the Wnt and TGF-beta protein families. Wnt plays a critical role in embryonic development and cancer; TGF-beta controls cell division and specialization. They wondered whether blocking the Wnt/TGF-beta pathway in the dystrophic mice would inhibit fibrosis in the animals' muscles.

The researchers turned to a drug called losartan, which is used to treat high blood pressure. Losartan inhibits the expression of the genes for TGF-beta types 1 and 2. The researchers thought it would probably interrupt the signalling pathway that leads the muscle stem cells astray.

Treating the mice with losartan, they found, did in fact prevent the muscle stem cells from expressing fibrosis-associated genes and partially maintained their ability to form new muscle.

"This scar tissue, or fibrosis, leaves the muscle less elastic and impairs muscle function," Rando said.

"So we'd like to understand why it happens, and how to prevent it. It's also important to limit fibrosis to increase the likelihood of success with other possible therapies, such as cell therapy or gene therapy."

Next steps

Because TGF-beta type 1 plays many roles throughout the body, the researchers are now working to find ways to specifically inhibit TGF-beta type 2, which is involved in the transition of the muscle stem cells. They're also interested in learning how to translate the research to other diseases.

"Fibrosis seems to occur in a vicious cycle," Rando said.

"As the muscle stem cells become less able to regenerate new muscle, the tissue is less able to repair itself after damage. This leads to fibrosis, which then further impairs muscle formation. Understanding the biological basis of fibrosis could have a profound effect on many other diseases."

Source: Stanford University Medical Center

Contact: Krista Conger

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iPS Cells Used to Correct Genetic Mutations that Cause Muscular Dystrophy

iPS Cells Used to Correct Genetic Mutations that Cause Muscular Dystrophy

Thursday, 27 November 2014

This image shows immunofluorescence staining

of skeletal cells differentiated from DMD-iPS

cells. Untreated DMD skeletal cells do not

express dystrophin (green) due to the deletion of

exon 44. However, after any of the three

correction strategies are applied to iPS cells,

differentiation into skeletal cells results in normal

dystrophin expression. Scale bar, 50 μm.

Credit: Dr. Akitsu Hotta, Kyoto University.

Researchers at the Center for iPS Cell Research and Application (CiRA), Kyoto University, show that induced pluripotent stem (iPS) cells can be used to correct genetic mutations that cause Duchenne muscular dystrophy (DMD). The research, published in Stem Cell Reports, demonstrates how engineered nucleases, such as TALEN and CRISPR, can be used to edit the genome of iPS cells generated from the skin cells of a DMD patient. The cells were then differentiated into skeletal muscles, in which the mutation responsible for DMD had disappeared.

DMD is a severe muscular degenerative disease caused by a loss-of-function mutation in the dystrophin gene. It inflicts 1 in 3500 boys and normally leads to death by early adulthood. Currently, very little is available in terms of treatment for patients outside palliative care. One option gaining interest is genomic editing by TALEN and CRISPR, which have quickly become invaluable tools in molecular biology. These enzymes allow scientists to cleave genes at specific locations and then modify the remnants to produce a genomic sequence to their liking. However, programmable nucleases are not pristine and often mistakenly edit similar sequences that vary a few base pairs from the target sequence, making them unreliable for clinical use because of the potential for undesired mutations.

For this reason, induced pluripotent stem cells (iPS cells) are ideal models, because they provide researchers an abundance of patient cells on which to test the programmable nucleases and find optimal conditions that minimize off-target modifications. CiRA scientists took advantage of this feature by generating iPS cells from a DMD patient. They used several different TALEN and CRISPR to modify the genome of the iPS cells, which were then differentiated into skeletal muscle cells. In all cases, dystrophin protein expression was convalesced, and in some cases, the dystrophin gene was fully corrected.

One key to the success was the development of a computational protocol that minimized the risk of off-target editing. The team built a database that all possible permutations of sequences up to 16 base pairs long. Among these, they extracted those that only appear once in the human genome, i.e. unique sequences. DMD can be caused by several different mutations; in the case of the patient used in this study, it was the result of the deletion of exon 44. The researchers therefore built a histogram of unique sequences that appeared in a genomic region that contained this exon. They found a stack of unique sequences in exon 45.

to Akitsu Hotta, who headed the project and holds joint positions at CiRA and the Institute for Integrated Cell-Materials Sciences at Kyoto University:

"Nearly half the human genome consists of repeated sequences. So even if we found one unique sequence, a change of one or two base pairs may result in these other repeated sequences, which risks the TALEN or CRISPR editing an incorrect region. To avoid this problem, we sought a region that hit high in the histogram".

With this target, the team considered three strategies to modify the frame-shift mutation of the dystrophin gene: exon skipping by connecting exons 43 and 46 to restore the reading frame, frame shifting by incorporating insertion or deletion (indel) mutations, and exon knock-in by inserting exon 44 before exon 45. All three strategies effectively increased dystrophin synthesis in differentiated skeletal cells, but only the exon knock-in approach recovered the gene to its natural state. Importantly, editing showed very high specificity, suggesting that their computational approach can be used to minimize off-target editing by the programming nucleases.

Moreover, the paper provides a proof-of-principle for using iPS cell technology to treat DMD in combination with TALEN or CRISPR. The group now aims to expand this protocol to other diseases.

First author Lisa Li explains: "We show that TALEN and CRISPR can be used to correct the mutation of the DMD gene. I want to apply the nucleases to correct mutations for other genetic-based diseases like point mutations".

Source: Center for iPS Cell Research and Application - Kyoto University

Contact: Akemi Nakamura

Reference:

Precise correction of the DYSTROPHIN gene in Duchenne Muscular Dystrophy patient-derived iPS cells by TALEN and CRISPR-Cas9

Hongmei Lisa Li, Naoko Fujimoto, Noriko Sasakawa, Saya Shirai, Tokiko Ohkame, tetsushi Sakuma, Michihiro tanaka, Naoki Amano, Akira Watanabe, Hidetoshi Sakurai, Takashi Yamamoto, Shinya Yamanaka, and Akitsu Hotta

Stem Cell Reports, November 26, 2014, DOI: http://dx.doi.org/10.1016/j.stemcr.2014.10.013

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Cardiac Stem Cell Therapy may Heal Heart Damage Caused by Duchenne Muscular Dystrophy

Late-breaking basic science research presented at American Heart Association Scientific Sessions shows stem cell treatment restores heart function damaged by muscular disease

Tuesday, 18 November 2014

Researchers at the Cedars-Sinai Heart Institute have found that injections of cardiac stem cells might help reverse heart damage caused by Duchenne muscular dystrophy, potentially resulting in a longer life expectancy for patients with the chronic muscle-wasting disease.

The study results were presented today at a Breaking Basic Science presentation during the American Heart Association Scientific Sessions in Chicago. After laboratory mice with Duchenne muscular dystrophy were infused with cardiac stem cells, the mice showed steady, marked improvement in heart function and increased exercise capacity.

Duchenne muscular dystrophy, which affects 1 in 3,600 boys, is a neuromuscular disease caused by a shortage of a protein called dystrophin, leading to progressive muscle weakness. Most Duchenne patients lose their ability to walk by age 12. Average life expectancy is about 25. The cause of death often is heart failure because the dystrophin deficiency leads to cardiomyopathy, a weakness of the heart muscle that makes the heart less able to pump blood and maintain a regular rhythm.

"Most research into treatments for Duchenne muscular dystrophy patients has focused on the skeletal muscle aspects of the disease, but more often than not, the cause of death has been the heart failure that affects Duchenne patients," said Eduardo Marbán, MD, PhD, director of the Cedars-Sinai Heart Institute and study leader.

"Currently, there is no treatment to address the loss of functional heart muscle in these patients."

During the past five years, the Cedars-Sinai Heart Institute has become a world leader in studying the use of stem cells to regenerate heart muscle in patients who have had heart attacks. In 2009, Marbán and his team completed the world's first procedure in which a patient's own heart tissue was used to grow specialized heart stem cells. The specialized cells were then injected back into the patient's heart in an effort to repair and regrow healthy muscle in a heart that had been injured by a heart attack. Results, published in The Lancet in 2012, showed that one year after receiving the experimental stem cell treatment, heart attack patients demonstrated a significant reduction in the size of the scar left on the heart muscle.

Earlier this year, Heart Institute researchers began a new study, called ALLSTAR, in which heart attack patients are being infused with allogeneic stem cells, which are derived from donor-quality hearts.

Recently, the Heart Institute opened the nation's first Regenerative Medicine Clinic, designed to match heart and vascular disease patients with appropriate stem cell clinical trials being conducted at Cedars-Sinai and other institutions.

"We are committed to thoroughly investigating whether stem cells could repair heart damage caused by Duchenne muscular dystrophy," Marbán said.

In the study, 78 lab mice were injected with cardiac stem cells. Over the next three months, the lab mice demonstrated improved pumping ability and exercise capacity in addition to a reduction in heart inflammation. The researchers also discovered that the stem cells work indirectly, by secreting tiny fat droplets called exosomes. The exosomes, when purified and administered alone, reproduce the key benefits of the cardiac stem cells.

Marbán said the procedure could be ready for testing in human clinical studies as soon as next year. The process to grow cardiac-derived stem cells was developed by Marbán when he was on the faculty of Johns Hopkins University. Johns Hopkins has filed for a patent on that intellectual property and has licensed it to Capricor, a company in which Cedars-Sinai and Marbán have a financial interest. Capricor is providing funds for the ALLSTAR clinical trial at Cedars-Sinai.

The Cedars-Sinai Heart Institute has been at the forefront of developing investigational stem cell treatments for heart attack patients.

Source: Cedars-Sinai Medical Center

Contact: Sally Stewart

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Successful Regeneration of Human Skeletal Muscle in Mice Enables Accelerated Research in Muscular Dystrophy

Kennedy Krieger researchers develop valid and accurate model for FSHD

Tuesday, 28 January 2014

Researchers at the Kennedy Krieger Institute recently announced study findings showing the successful development of a humanized preclinical model for facioscapulohumeral muscular dystrophy (FSHD), providing scientists with a much needed tool to accelerate novel therapeutic research and development.

Published in Human Molecular Genetics, the study outlines the validity of a unique model that, for the first time, mirrors the gene expression and biomarker profile of human FSHD tissue. Previously, there has been no accepted preclinical model for FSHD, a complex and rare neuromuscular disorder that affects approximately 4 - 7 per 100,000 individuals. As a result, therapeutic development for the disorder has been stymied.

“The inability to mimic the FSHD’s genetic mechanism in preclinical models has been an ongoing challenge for the research community. Without an accurate model, making the leap to clinical research commonly fails,” said Kathryn Wagner MD, PhD, director of the Center for Genetic Muscle Disorders at the Kennedy Krieger Institute in Baltimore, MD.

“We believe this unique model will open the door to studying muscle regeneration over time and help better predict clinical response to therapeutic drugs.”

Inspired by cancer preclinical models developed with human tumour tissue, Dr. Wagner and her research team leveraged both basic science and clinical research resources available at Kennedy Krieger to successfully regenerate grafted muscle within the models. Human bicep muscle biopsies transplanted into models survived for over 41 weeks and retained features of normal and diseased tissue.

“This model is not only applicable to genetic muscle diseases for which we lack appropriate research models, but for other acquired muscle conditions,” said Wagner.

“Now there will be more research possibilities related to the overall impact of age and disease on the regenerative and growth capacity of human skeletal muscle.”

Source: Kennedy Krieger Institute 

Contact: Jennifer Burke

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Researchers Develop New Muscular Dystrophy Treatment Approach Using Human Stem Cells

Researchers Develop New Muscular Dystrophy Treatment Approach Using Human Stem Cells

Saturday, 05 May 2012

Researchers from the University of Minnesota's Lillehei Heart Institute have effectively treated muscular dystrophy in mice using human stem cells derived from a new process that – for the first time – makes the production of human muscle cells from stem cells efficient and effective.

The research, published today in Cell Stem Cell, outlines the strategy for the development of a rapidly dividing population of skeletal myogenic progenitor cells (muscle-forming cells) derived from induced pluripotent (iPS) cells. iPS cells have all of the potential of embryonic stem (ES) cells, but are derived by reprogramming skin cells. They can be patient-specific, which renders them unlikely to be rejected, and do not involve the destruction of embryos.

This is the first time that human stem cells have been shown to be effective in the treatment of muscular dystrophy.

According to U of M researchers – who were also the first to use ES cells from mice to treat muscular dystrophy – there has been a significant lag in translating studies using mouse stem cells into therapeutically relevant studies involving human stem cells. This lag has dramatically limited the development of cell therapies or clinical trials for human patients.

The latest research from the U of M provides the proof-of-principle for treating muscular dystrophy with human iPS cells, setting the stage for future human clinical trials.

"One of the biggest barriers to the development of cell-based therapies for neuromuscular disorders like muscular dystrophy has been obtaining sufficient muscle progenitor cells to produce a therapeutically effective response," said principal investigator Rita Perlingeiro, Ph.D., associate professor of medicine in the Medical School's Division of Cardiology.

"Up until now, deriving engraftable skeletal muscle stem cells from human pluripotent stem cells hasn't been possible. Our results demonstrate that it is indeed possible and sets the stage for the development of a clinically meaningful treatment approach."

Upon transplantation into mice suffering from muscular dystrophy, human skeletal myogenic progenitor cells provided both extensive and long-term muscle regeneration which resulted in improved muscle function.

To achieve their results, U of M researchers genetically modified two well-characterized human iPS cell lines and an existing human ES cell line with the PAX7 gene. This allowed them to regulate levels of the Pax7 protein, which is essential for the regeneration of skeletal muscle tissue after damage. The researchers found this regulation could prompt naïve ES and iPS cells to differentiate into muscle-forming cells.

Up until this point, researchers had struggled to make muscle efficiently from ES and iPS cells. PAX7 – induced at exactly the right time – helped determine the fate of human ES and iPS cells, pushing them into becoming human muscle progenitor cells.

Once Dr. Perlingeiro's team was able to pinpoint the optimal timing of differentiation, the cells were well suited to the regrowth needed to treat conditions such as muscular dystrophy. In fact, Pax7-induced muscle progenitors were far more effective than human myoblasts at improving muscle function. Myoblasts, which are cell cultures derived from adult muscle biopsies, had previously been tested in clinical trials for muscular dystrophy, however the myoblasts did not persist after transplantation.

"Seeing long-term maintenance of these cells without major adverse side effects is exciting," said Perlingeiro.

"Our research proves that these differentiated stem cells have real staying power in the fight against muscular dystrophy."

According to John Wagner, M.D., scientific director of clinical research at the University's Stem Cell Institute and renowned blood and marrow transplant expert,

"This research is a phenomenal breakthrough. Dr. Perlingeiro and her collaborators have overcome one of the most significant obstacles to moving stem cell therapies into the treatment of children with devastating and life threatening muscular dystrophies."

The U of M researchers say alternative methods of Pax7 induction will need to be investigated before this study can be turned into a human clinical trial. Their method of delivering the Pax7 protein involved genetic modification of cells with viruses and because viruses sometimes cause mutations, they add risk to a clinical trial. But the U of M researchers are committed to developing a safe and effective clinical protocol, and are actively testing alternate methods of delivering Pax7.

Source: University of Minnesota Academic Health Center 

Contact: Caroline Marin

Reference:

Human ES- and iPS-Derived Myogenic Progenitors Restore DYSTROPHIN and Improve Contractility upon Transplantation in Dystrophic Mice

Radbod Darabi, Robert W. Arpke, Stefan Irion, John T. Dimos, Marica Grskovic, Michael Kyba, Rita C.R. Perlingeiro

Cell Stem Cell, Volume 10, Issue 5, 610-619, 4 May 2012, 10.1016/j.stem.2012.02.015

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Gene Mutations in Patients with Becker Muscular Dystrophy

Gene Mutations in Patients with Becker Muscular Dystrophy Thursday, 14 January 2010 Investigators in The Research Institute at Nationwide Children's Hospital have identified a link between specific modifications of the dystrophin gene and the age of cardiac disease onset in patients with Becker muscular dystrophy (BMD). This information could help clinicians provide early cardiac intervention for BMD patients based on genetic testing results performed on a blood sample. These findings are a result of analysis of the largest number of BMD patients to date and are published in the December issue of the journal Circulation: Cardiovascular Genetics. Becker muscular dystrophy is a genetic disorder that usually begins in adolescence causing progressive muscle weakness of the legs and pelvis. Most patients – more than 70 percent – will also develop cardiac disease that is likely to go unnoticed until it has reached an advanced stage. To date, clinicians cannot predict when cardiac disease will occur and which patients would most benefit from early heart screenings. "Our study findings revealed areas of gene mutation most associated with early onset of heart disease," said the study's lead author, Rita Wen Kaspar, BSN, RN, a PhD student at The Ohio State University College of Nursing who conducted this research at the Center for Gene Therapy in The Research Institute at Nationwide Children's Hospital. "By identifying which dystrophin mutations are most likely to cause early-onset heart conditions, our research could help clinicians identify at-risk patients, provide early intervention and ultimately prolong patient survival." Investigators collected data from 78 patients with BMD or X-linked dilated cardiomyopathy from Nationwide Children's Hospital, The Ohio State University, the Utah Dystrophinopathy Project, the Leiden Open Variation Database and published case reports. They then correlated genetic mutations with the onset age of heart disease. Federica Montanaro, PhD, the study's corresponding author and a principal investigator in the Center for Gene Therapy at Nationwide Children's, described the study as an important example of collaboration between basic scientists and clinicians. "The results from this study are important at two levels," explained Dr. Montanaro, also a faculty member of The Ohio State University College of Medicine. "First, as genetic screening becomes more widely available, clinicians will now be able to use this information to deliver more personalized care to BMD patients. Second, our findings provide new clues as to the functions of dystrophin in the heart. These clinical findings are now being brought back to the research laboratory to help design more effective treatments for heart disease in BMD patients as well as in children that suffer from the more severe form of this disease known as Duchenne Muscular Dystrophy." ......... ZenMaster

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Stem Cell Breakthrough Gives New Hope to Sufferers of Muscle-wasting Diseases

Stem Cell Breakthrough Gives New Hope to Sufferers of Muscle-wasting Diseases Saturday, 07 March 2009 An experimental procedure that dramatically strengthens stem cells' ability to regenerate damaged tissue could offer new hope to sufferers of muscle-wasting diseases such as myopathy and muscular dystrophy, according to researchers from the University of New South Wales (UNSW). The world-first procedure has been successfully used to re-grow muscles in a mouse model, but it could be applied to all tissue-based illnesses in humans such as in the liver, pancreas or brain, the researchers say. The research team, which is based at UNSW and formerly from Sydney's Westmead Children's Hospital, adapted a technique currently being trialled in bone marrow transplantation. Adult stem cells are given a gene that makes them resistant to chemotherapy, which is used to clean out damaged cells and allow the new stem cells to take hold. A paper detailing the breakthrough appears in the prestigious journal Stem Cells this week. The ability of adult stem cells to regenerate whole tissues opens up a world of new possibilities for many human diseases, according to the lead authors of the paper, Professor Peter Gunning, Professor Edna Hardeman and Dr Antonio Lee, from UNSW's School of Medical Sciences. "The beauty of this technique is that chemotherapy makes space for stem cells coming into muscle and also gives the stem cells an advantage over the locals. It's the first strategy that gives the good guys the edge in the battle to cure sick tissues," Professor Gunning said. "What has been the realm of science fiction is looking more and more like the medicine of the future," he said. The procedure solves one of the major hurdles involving stem cell therapy – getting the cells to survive for more than an hour or so after inserting them into damaged tissue. "In muscle, most stem cells die in the first hour or are present in such low numbers that they are not much help," Professor Gunning said. "Until now, the new healthy cells had no advantage over the existing damaged tissue and were getting out-competed.” While trials of the procedure are at the pre-clinical stage, researchers are looking to launch human trials treating specific forms of muscular dystrophy such as oculopharyngeal muscular dystrophy within the next three to five years. ......... ZenMaster

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Single Adult Muscle Stem Cell Can Self Renew

Single Adult Muscle Stem Cell Can Self Renew Monday, 15 December 2008 The first demonstration that a single adult stem cell can self-renew in a mammal was reported at the American Society for Cell Biology (ASCB) 48th Annual Meeting, Dec. 13-17, 2008 in San Francisco. The transplanted adult stem cell and its differentiated descendants restored lost function to mice with hind limb muscle tissue damage. The adult stem cells used in the study, conducted at Stanford University, were isolated from a mixed population of satellite cells in the skeletal muscle of mice. The skeletal adult muscle stem cells (MusSC), which live just under the membrane that surrounds muscle fibres, normally respond to tissue damage by giving rise to progenitor cells that become myoblasts, fusing into myofibers to repair the tissue damage. The scientists transplanted the MusSC into special immune-suppressed "nude" mice whose muscle satellite cells had been wiped out in a hind limb by irradiation. The mice would only be able to repair injury if the transplanted MuSC "took." The scientists, Alessandra Sacco and Helen Blau, had genetically engineered the transplanted MusSC to express Pax7 and luciferase proteins. As a result, every transplanted cell glowed under ultraviolet light and was easy to trace. "To be able to detect the presence of the cells by bioluminescence was really a breakthrough," says Blau. "It taught us so much more. We could see how the cells were responding, and really monitor their dynamics." Through luminescent imaging as well as quantitative and kinetic analyses, Sacco and Blau tracked each transplanted stem cell as it rapidly proliferated and engrafted its progeny into the irradiated muscle tissue. The scientists then injured the regenerated tissue, setting off massive waves of muscle cell growth and repair, and subsequently showed that the MuSC and descendents rescued the second animal's lost muscle healing function. After isolating the luciferase-glowing muscle stem cells from the transplanted animal, the scientists duplicated, or cloned, the cells in the lab. Like the original MuSC, the cloned copies were intact and capable of self-renewal. "We are thrilled with the results," says Sacco. "It's been known that these satellite cells are crucial for the regeneration of muscle tissue, but this is the first demonstration of self-renewal of a single cell." The ability to isolate and then transplant skeletal adult muscle stems cells could have a wide impact in treating not only a variety of muscle wasting diseases such as muscular dystrophy but also severe muscle injuries or loss of function from aging and disuse. In other experiments, the researchers transplanted between 10 and 500 luciferase-tagged MuSC into the leg muscles of mice. These cells also proliferated and engrafted, forming new myofibers and fusing with injured fibres. Unlike tumour cells, the transplanted stem cells achieved homeostasis, growing to a stable, constant level and ceasing replication. After demonstrating that the transplanted stem cells proliferated and fully restored the animal's lost function, Sacco and Blau recovered new stem cells from the transplant with full stem cell potency, meeting the final "gold standard" test for adult multipotent stem cells. ......... ZenMaster

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Neurons and Muscle Cells Need Stabilizing Force for Effective Communication

Neurons and Muscle Cells Need Stabilizing Force for Effective Communication Thursday, 09 October 2008 You cannot raise a finger without your brain directing muscle cells, and scientists have figured out another reason that usually works so well. A neuron sends a message, or neurotransmitter, to the muscle cell to tell it what to do. To get the message, the receiving cell must have a receptor. Oddly, the unstable protein rapsyn is responsible for anchoring the receptor so it is properly positioned to catch the message. Medical College of Georgia scientists have found what keeps rapsyn in proper conformation. It is a heat shock protein, one of a large family of molecular chaperones that make sure proteins get where they are needed and do what they should, says Dr. Lin Mei, chief of developmental neurobiology at MCG and Georgia Research Alliance Eminent Scholar in Neuroscience. Hsp90β helps stabilize rapsyn so receptors can get and stay where needed, according to research published in the Oct. 9 issue of Neuron. Dr. Mei suspects that other hsp siblings have a similar caretaker role in neuron-to-neuron communication in the brain. Scientists knew rapsyn's role in getting neuromuscular receptors to aggregate and stay where needed, but they didn't know what stabilized it. "It makes you wonder how to control this naughty boy which is very important," says Dr. Mei, the study's corresponding author. They found hsp90β wherever rapsyn clustered in muscle cells. When they disrupted its activity or expression, they realized hsp90β's stabilizing role in forming and maintaining receptor clusters, says Dr. Shiwen Luo, postdoctoral fellow in Dr. Mei's lab and the study's first author. Rapsyn and the receptor apparently interact, and then hsp90β comes along to help stabilize the relationship. Rapsyn mutations have been implicated in muscular dystrophies including congenital myasthenia gravis. MCG researchers are looking now to see if a mutated rapsyn still interacts with hsp90β. They used a type of acetylcholine nicotinic receptor at the neuromuscular junction as a model for their studies of brain development and communication. The junction is 1,000 times larger than connections, or synapses, between two neurons but structurally similar. Fundamentals include presynaptic terminals that release neurotransmitters picked up by receptors on the postsynaptic side. Terminals and receptors must be lined up well, whether it's a muscle cell or neuron getting the message. "In central nervous system synapses and at the neuromuscular junction, receptors have to be concentrated at the right spot to receive the neurotransmitter released," says Dr. Mei. If receptors are in the wrong place, the message can be weak or even lost. At the neuromuscular juncture, communication is usually straightforward, with primarily one neurotransmitter and one principal receptor. "Whenever you tell a muscle to move, it moves. If you want your muscles to think, you wouldn't be able to pick up a pin," says Dr. Mei. In the brain, where neurons have thousands of synapses, it is more of a negotiation. "Signals have to be integrated in the neuron for it to decide what to do." ......... ZenMaster

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Disease-Specific Induced Pluripotent Stem Cells

Scientists replicate diseases in the lab with new stem cell lines Thursday, 07 August 2008 A set of new stem cell lines will make it possible for researchers to explore ten different genetic disorders — including muscular dystrophy, juvenile diabetes, and Parkinson's disease — in a variety of cell and tissue types as they develop in laboratory cultures. Researchers led by Howard Hughes Medical Institute investigator George Q. Daley have converted cells from individuals with diseases into stem cells with the same genetic errors. These newly created stem cells will allow researchers to reproduce human tissue formation in a Petri dish as it occurs in individuals with any of the ten diseases, a vast improvement over current technology. Like all stem cells, these disease-specific stem cells grow indefinitely, and scientists can coax them into becoming a variety of cell types. Daley, who is at Children's Hospital Boston, worked with researchers from Harvard Medical School, Massachusetts General Hospital, and the University of Washington to create the disease-specific stem cell strains. The scientists will make the cell lines available to scientists worldwide through a core facility funded by the Harvard Stem Cell Institute. Daley and his colleagues published the details of the disease-specific stem cell lines in an advanced online publication of the journal Cell on August 7, 2008. "Researchers have long wanted to find a way to move a patient's disease into the test tube, to develop cells that could be cultured into the many tissues relevant to diseases of the blood, the brain and the heart, for example," he says. "Now, we have a way to do just that — to derive pluripotent cells from patients with disease, which means the cells can make any tissue and can grow forever. This enables us to model thousands of conditions using classical cell culture techniques." Daley's team has created disease-specific stem cell lines for Duchenne muscular dystrophy; Becker muscular dystrophy; juvenile-onset (type I) diabetes; Parkinson's disease; Huntington's disease; Down's syndrome; ADA severe combined immunodeficiency (a form of the disorder commonly known as "boy-in-the-bubble disease"); Shwachman-Bodian-Diamond syndrome (which causes bone marrow failure and a predisposition to leukaemia); Gaucher disease (an inherited metabolic disorder in which a fatty substance accumulates in several of the body's organs); and Lesch-Nyhan syndrome (an enzyme deficiency that causes a build-up of uric acid in body fluids). Many more cell lines are possible. For years, researchers have grown human cells in the laboratory in an attempt to mimic various genetic diseases, but the available techniques had significant shortcomings. Cells taken directly from affected patients typically have a limited lifespan when grown in laboratory dishes, restricting the types of studies for which they can be used. Researchers often turn to cells that have been modified to make them live in a dish forever, but altering cells to make them immortal changes their physiology and can cast doubt on a study's results. Recently, Daley's lab and others have demonstrated that adult cells can be converted to stem cells by introducing a set of genetic "reprogramming factors." To produce the disease-specific stem cells, Daley and his colleagues mixed cells from patients with the ten disorders with benign viruses to introduce the reprogramming factors into the cells. The resulting stem cells harboured the genetic diseases of the donors. Once the researchers isolated the disease-specific stem cells, they analyzed the genes and confirmed that the stem cells had the same disease-causing defects as the original donor cells. The researchers also made sure that the stem cells were pluripotent — able to differentiate into many different tissue types. Daley says that in many cases these new stem cell cultures will mimic human disease more reliably than animal models. Despite the vast genetic similarities between humans and mice, physiological differences invariably affect the course of disease in a mouse. In some cases, the genetic defect that produces a disorder in humans — such as Down's syndrome — does not cause the same symptoms in mice. Therefore, human cell cultures are an essential complement to research with animal models, Daley says. The most immediate application of the disease-specific stem cells will be to reproduce human diseases in culture to explore their development in different tissues, Daley says. The technique will even enable researchers to compare how the same disease varies among people, by generating disease-specific stem cell cultures from many individuals. The cells will also offer a proving ground for screening drugs to treat disease. Over the longer term, Daley expects the technique will be applied clinically. For example, it may allow scientists to develop therapies using a patient's own cells — reengineering the cells to correct a disease-causing defect then re-introducing them into the body. The Harvard Stem Cell Institute will make the stem cell lines available to the scientific community as quickly as possible, Daley says. The institute will also continue to work to generate cell lines for other diseases. Daley and his colleagues' techniques for reprogramming adult cells are readily available so other researchers can generate their own disease-specific stem cell lines. "Stem cells are quite finicky," Daley cautions. "They don't grow like weeds; they're more like orchids. You really have to tend to them." Therefore, he plans to collaborate with researchers at other institutions to help produce stem cell lines for the diseases they want to study.

The new iPS lines, developed from the cells of patients ranging in age from one month to 57-years-old and suffering from a range of conditions from Down Syndrome to Parkinson's disease, will be deposited in a new HSCI "core" facility being established at Massachusetts General Hospital (MGH), HSCI co-director Doug Melton announced yesterday. The operations of the iPS Core will be overseen by a faculty committee, which Daley will chair. "We wanted to produce a large number of disease models for ourselves, our collaborators, and the stem cell research community to accelerate research," Daley said. "The original embryonic stem cell lines are generic, and allow you to ask only basic questions. But these new lines are valuable tools for attacking the root causes of disease. Our work is just the beginning for studying thousands of diseases in a Petri dish," he said. Melton said that the HSCI iPS Core will serve as a repository for iPS cells produced by HSCI scientists. "The Core will also function as a technical laboratory to produce these disease- specific lines for use by scientists around the world," Melton said. He went on to say that "the suite of iPS cell lines reported by the Daley group marks an important achievement and a very significant advance for patients suffering from degenerative diseases. These disease-specific iPS cells are invaluable tools that will allow researchers to watch the development diseases in Petri dishes, outside of the patients. And we have good reason to believe that this will make it possible to find new treatments, and eventually drugs, to slow or even stop the course of a number of diseases. In years ahead, this report will be seen as opening the door to a new approach to develop therapies." "One of our goals in creating the NIH Director's Pioneer Award programs was to enable exceptionally creative scientists to move quickly in promising new directions, thereby speeding the intellectual and technical breakthroughs needed to address major challenges in biomedical or behavioural research," said National Institutes of Health Director Elias A. Zerhouni, M.D. "This is certainly the case for Drs. Daley and Hochedlinger, who deployed their Director's award resources to advance our ability to use induced pluripotent stem cells for disease-specific studies and drug development." Reference: Disease-Specific Induced Pluripotent Stem Cells In-Hyun Park, Natasha Arora, Hongguang Huo, Nimet Maherali, Tim Ahfeldt, Akiko Shimamura, M. William Lensch, Chad Cowan, Konrad Hochedlinger, and George Q. Daley Cell ......... ZenMaster

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Stem Cells Restore Muscle in Muscular Dystrophy

Muscle stem cell transplant boosts diseased muscle function and replenishes stem cell pool Friday, 11 July 2008 Researchers at the Joslin Diabetes Center have demonstrated for the first time that transplanted muscle stem cells can both improve muscle function in animals with a form of muscular dystrophy and replenish the stem cell population for use in the repair of future muscle injuries. By injecting purified stem cells isolated from adult skeletal muscle, researchers have shown they can restore healthy muscle and improve muscle function in mice with a form of muscular dystrophy. Those muscle-building stem cells were derived from a larger pool of so-called satellite cells that normally associate with mature muscle fibers and play a role in muscle growth and repair. In addition to their contributions to mature muscle, the injected cells also replenished the pool of regenerative cells normally found in muscle. Those stem cells allowed the treated muscle to undergo subsequent rounds of injury repair, they found. "I'm very excited about this," said lead author Amy J. Wagers, Ph.D., Principal Investigator in the Joslin Section on Developmental and Stem Cell Biology, principal faculty member at the Harvard Stem Cell Institute and Assistant Professor of Stem Cell and Regenerative Biology at Harvard University. "This study indicates the presence of renewing muscle stem cells in adult skeletal muscle and demonstrates the potential benefit of stem cell therapy for the treatment of muscle degenerative diseases such as muscular dystrophy." "Our work shows proof-of-concept that purified muscle stem cells can be used in therapy," said Wagers, noting that in some cases the stem cells replaced more than 90 percent of the muscle fibers. Such an advance would require isolation of stem cells equivalent to those in the mouse from human muscle, something Wagers said her team is now working on. The study was designed to test the concept that skeletal muscle precursor cells could function as adult stem cells and that transplantation of these cells could both repair muscle tissue and regenerate the stem cell pool in a model of Duchenne muscular dystrophy, she said. Duchenne muscular dystrophy is the most common form of the disease and is characterized by rapidly progressing muscle degeneration. The disease is caused by a genetic mutation and there is currently no cure. The data from this new study demonstrate that regenerative muscle stem cells can be distinguished from other cells in the muscle by unique protein markers present on their surfaces. The authors used these markers to select stem cells from normal adult muscle and transferred the cells to diseased muscle of mice carrying a mutation in the same gene affected in human Duchenne muscular dystrophy. Satellite cells were first described decades ago and have since generally been considered as a homogeneous group, Wagers said. While anatomically they look similar under a microscope, they nonetheless show considerable variation in their physiology and function. In a previous study, Wagers' identified a set of five markers that characterize the only subset of satellite cells responsible for forming muscle, which they also refer to as skeletal muscle precursors or SMPs. In the new study, the researchers analyzed the stem cell and regenerative properties of those SMPs. When engrafted into muscle of mice lacking dystrophin, purified SMPs contributed to up to 94 percent of muscle fibers, restoring dystrophin expression and significantly improving muscle structure and contractile function, they report. (The dystrophin gene encodes a protein important for muscle integrity. Mice lacking dystrophin, also known as mdx mice, are a model for Duchenne muscular dystrophy, the most prevalent form of muscular dystrophy.) "Importantly, high-level engraftment of transplanted SMPs in mdx animals shows therapeutic value — restoring defective dystrophin gene expression, improving muscle histology, and rescuing physiological muscle function," the researchers said. "Moreover, in addition to generating mature muscle fibers, transplanted SMPs also re-seed the satellite cell niche and are maintained there such that they can be recruited to participate in future rounds of muscle regeneration.” "Taken together, these data indicate that SMPs act as renewable, transplantable stem cells for adult skeletal muscle. The level of myofiber reconstitution achieved by these myogenic stem cells exceeds that reported for most other myogenic cell populations and leads to a striking improvement of muscle contraction function in SMP-treated muscles. These data thus provide direct evidence that prospectively isolatable, lineage-specific skeletal muscle stem cells provide a robust source of muscle replacement cells and a viable therapeutic option for the treatment of muscle degenerative disorders." Wagers noted however that there may be complications in the delivery of cell therapy in humans, particularly for those with conditions influencing skeletal muscle throughout the body. Even so, the new findings present an "opportunity to understand what happens [to these regenerative cells] in disease and identify factors and pathways that may boost their activity," she said. "We may get a handle on drugs that could target muscle impairment" not only in those with muscular dystrophies, but also in elderly people suffering from the muscle wasting that comes with age. "Once the healthy stem cells were transplanted into the muscles of the mice with muscular dystrophy, they generated cells that incorporated into the diseased muscle and substantially improved the ability of the treated muscles to contract," said Wagers. "At the same time, the transplantation of the healthy stem cells replenished the formerly diseased stem cell pool, providing a reservoir of healthy stem cells that could be re-activated to repair the muscle again during a second injury." According to the paper, these cells provide an effective source of immediately available muscle regenerative cells as well as a reserve pool that can maintain muscle regenerative activity in response to future challenges. "This work demonstrates, in concept, that stem cell therapy could be beneficial for degenerative muscle diseases," Wagers said. Wagers also said the study will lead to other studies in the near-term that will identify pathways that regulate these muscle stem cells in order to figure out ways to boost the normal regenerative potential of these cells. These could include drug therapies or genomic approaches, she said. In the long-term, the idea will be to replicate these findings in humans. "This is still very basic science, but I think we're going to be able to move forward in a lot of directions. It opens up many exciting avenues," she said. The Wagers Lab at Joslin studies both hematopoietic stem cells, which constantly maintain and can fully regenerate the entire blood system, as well as skeletal muscle stem cells, involved in skeletal muscle growth and repair. The work is aimed particularly at defining novel mechanisms that regulate the migration, expansion, and regenerative potential of these two distinct adult stem cells. About Joslin Diabetes Center Joslin Diabetes Center is the world's largest diabetes clinic, diabetes research center and provider of diabetes education. Joslin is dedicated to ensuring people with diabetes live long, healthy lives and offers real hope and progress toward diabetes prevention and a cure for the disease. Founded in 1898 by Elliott P. Joslin, M.D., Joslin is an independent non-profit institution affiliated with Harvard Medical School. Reference: Highly Efficient, Functional Engraftment of Skeletal Muscle Stem Cells in Dystrophic Muscles Massimiliano Cerletti, Sara Jurga, Carol A. Witczak, Michael F. Hirshman, Jennifer L. Shadrach, Laurie J. Goodyear, and Amy J. Wagers Cell, Vol 134, 37-47, 11 July 2008 ......... ZenMaster

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Embryonic Stem Cell Transplantation Improves Muscular Dystrophy in Mice

Embryonic Stem Cell Transplantation Improves Muscular Dystrophy in Mice Sunday, 20 January 2008 Using embryonic stem cells from mice, UT Southwestern Medical Center researchers have prompted the growth of healthy – and more importantly, functioning – muscle cells in mice afflicted with a human model of Duchenne muscular dystrophy. The study represents the first time transplanted embryonic stem cells have been shown to restore function to defective muscles in a model of muscular dystrophy. The researchers’ newly developed technique, which involves stringent sorting to preserve all stem cells destined to become muscle, avoids the risk of tumour formation while improving the overall muscle strength and coordination of the mice, the researchers found. The mice used in the study lacked dystrophin, the same protein that humans with the fatal wasting disease also are missing. The study, headed by Dr. Rita Perlingeiro, assistant professor of developmental biology and molecular biology, is available online today and in the February issue of Nature Medicine. “We envision eventually developing a stem-cell therapy for humans with muscular dystrophy, if we are able to successfully combine this approach with the technology now available to make human embryonic stem cells from reprogrammed skin cells,” Dr. Perlingeiro said. “These cells can be transplanted into the muscle, and they cause muscle regeneration resulting in stronger contractility.” The study represents a major step in the field, she said, because the researchers were able to tease out exactly the cells they wanted. “The problem had been that embryonic stem cells make everything,” Dr. Perlingeiro said. “They make a great variety of cells. The trick is to pull out only the one type you want.” The UT Southwestern researchers focused on manipulating genes that are active in the very early stages as embryonic stem cells start to develop into more specialized cells. At first, they activated a gene called Pax3, which is involved in creating muscle cells, and then injected those cells into the animals’ muscles. Those cells caused tumours containing many different types of cells, indicating that there were still residual undifferentiated embryonic stem cells in the cultures at the time of implantation. “Even if there are 10 undesirable cells, that’s too many,” Dr. Perlingeiro said. The researchers then began using fluorescent dyes to sort cells depending on whether some surface markers were turned on while others were turned off. By analogy, it was as if they were dealing with a crowd of people and wanted to pull out only those with red hair, green scarves and blue coats, while those with red hair, green scarves and no coats would be disqualified. The final selection of cells, containing only one type, was again injected into the animals’ hind-limb muscles. After a month, the fluorescent dyes showed that the cells had deeply penetrated the muscle, an indication that they were growing and reproducing as desired, and many of the muscle fibres also contained dystrophin, the key protein lacking in muscular dystrophy. After three months, the mice also showed no signs of tumours. Tests of isolated muscles showed that the treated muscles were significantly stronger than untreated mice lacking dystrophin, although not quite as strong as those of normal mice. The treated mice also were tested for coordination. Again, their performance was better than that of untreated mice, but not as good as that of normal mice. “The improved coordination is significant because it shows the embryonic stem cells have benefited the animal’s quality of life, not simply caused an isolated growth with no overall improvement,” Dr. Perlingeiro said. The researchers will next investigate whether these transplanted cells can make “muscle stem cells,” which are partially developed cells in muscle tissue that serve as a reserve to replenish muscles. They also are testing their implantation approach in animal models of other types of muscular dystrophy. ......... ZenMaster

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Stem cells for Duchenne muscular dystrophy?

Reprogrammed human adult stem cells rescue diseased muscle in mice Wednesday, 12 December 2007 Scientists report that adult stem cells isolated from humans with muscular dystrophy can be genetically corrected and used to induce functional improvement when transplanted into a mouse model of the disease. The research, published by Cell Press in the December issue of Cell Stem Cell, represents a significant advance toward the future development of a gene therapy that uses a patient’s own cells to treat this devastating muscle-wasting disease. Duchenne muscular dystrophy (DMD) is a hereditary disease caused by a mutation in the gene that codes for a muscle protein called dystrophin. Dystrophin is a key structural protein that helps to keep muscle cells intact. DMD is characterized by a chronic degeneration of skeletal muscle cells that leads to progressive muscle weakness. Although intense research has focused on finding a way to replace the defective dystrophin protein, at this time there is no cure for DMD. A research group led by Dr. Yvan Torrente from the University of Milan used a combination of cell- and gene-based therapy to isolate adult human stem cells from DMD patients and engineer a genetic modification to correct the dystrophin gene. “Use of the patient’s own cells would reduce the risk of implant rejection seen with transplantation of normal muscle-forming cells,” explains Dr. Torrente. Muscle stem cells, identified by expression of the CD133 surface marker, were isolated from normal and dystrophic human blood and skeletal muscle. The isolated human muscle progenitors were implanted into the muscles of mice and were successfully recruited into muscle fibers. As expected, the CD133+ cells isolated from DMD patients expressed the mutated gene for dystrophin and gave rise to muscle cells that resembled muscle fibers in DMD patients. The researchers then used a sophisticated genetic technique to repair the mutated dystrophin gene in the isolated DMD CD133+ cells so that dystrophin synthesis was restored. Importantly, intramuscular or intra-arterial delivery of the genetically corrected muscle cell progenitors resulted in significant recovery of muscle morphology, function, and dystrophin expression in a mouse model of muscular dystrophy. “These data demonstrate that genetically engineered blood or muscle-derived CD133+ cells represent a possible tool for future stem cell-based autograft applications in humans with DMD,” says Dr. Torrente. The authors caution that significant additional work needs to be done prior to using this technology in humans. “Additional research will substantially enhance our understanding of the mechanisms underlying this effect and may lead to the improvement of gene and cell therapy strategies for DMD.” ......... ZenMaster

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microRNA scan uncovers reasons behind muscle dystrophies

Massive microRNA scan uncovers leads to treating muscle degeneration Thursday, 18 October 2007 Researchers have discovered the first microRNAs – tiny bits of code that regulate gene activity – linked to each of 10 major degenerative muscular disorders, opening doors to new treatments and a better biological understanding of these debilitating, poorly understood, often untreatable diseases. The study, to be published online this week by the Proceedings of the National Academy of Sciences, was led by Iris Eisenberg, PhD, of the Program in Genomics at Children’s Hospital Boston. Louis Kunkel, PhD, director of the Program in Genomics and an investigator with the Howard Hughes Medical Institute, was senior investigator. The disorders include the muscular dystrophies (Duchenne muscular dystrophy, Becker muscular dystrophy, limb girdle muscular dystrophies, Miyoshi myopathy, and fascioscapulohumeral muscular dystrophy); the congenital myopathies (nemaline myopathy); and the inflammatory myopathies (polymyositis, dermatomyositis, and inclusion body myositis). While past studies have linked them with an increasing number of genes, it's still largely unknown how these genes cause muscle weakness and wasting, and, more importantly, how to translate the discoveries into treatments. For instance, most muscular dystrophies begin with a known mutation in a “master gene”, leading to damaged or absent proteins in muscle cells. In Duchenne and Becker muscular dystrophies, the absent protein is dystrophin, as Kunkel himself discovered in 1987. Its absence causes muscle tissue to weaken and rupture, and the tissue becomes progressively non-functional through inflammatory attacks and other damaging events that aren’t fully understood. “The initial mutations do not explain why patients are losing their muscle so fast,” says Eisenberg. “There are still many unknown genes involved in these processes, as well as in the inflammatory processes taking place in the damaged muscle tissue.” She and Kunkel believe microRNAs may help provide the missing genetic links. Their team analyzed muscle tissue from patients with each of the ten muscular disorders, discovering that 185 microRNAs are either too abundant or too scarce in wasting muscle, compared with healthy muscle. Discovered in humans only in the past decade, microRNAs are already known to regulate major processes in the body. Therefore, Eisenberg believes microRNAs may be involved in orchestrating the tissue death, inflammatory response and other major degenerative processes in the affected muscle tissue. The researchers used bioinformatics to uncover a list of genes the microRNAs may act on, and now plan to find which microRNAs and genes actually underlie these processes. The findings raise the possibility of slowing muscle loss by targeting the microRNAs that control these “cascades” of damaging events. This approach is more efficient than targeting individual genes. The team also defined the abnormal microRNA “signatures” that correspond to each of the ten wasting diseases. They hope these will shed light on the genes and disease mechanisms involved in the most poorly understood and least treatable of the degenerative disorders, such as inclusion body myositis. “At this point, it’s very theoretical, but it’s possible,” says Eisenberg. Article: Distinctive patterns of microRNA expression in primary muscular disorders Iris Eisenberg et al. Proc. Natl. Acad. Sci. USA, 10.1073/pnas.0708115104 ......... ZenMaster

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