Wednesday, 22 October 2014
Human Skin Cells Reprogrammed Directly into Brain Cells
Wednesday, 22 October 2014
Scientists have described a way to convert human skin cells directly into a specific type of brain cell affected by Huntington's disease, an ultimately fatal neurodegenerative disorder. Unlike other techniques that turn one cell type into another, this new process does not pass through a stem cell phase, avoiding the production of multiple cell types, the study's authors report.
The researchers, at Washington University School of Medicine in St. Louis, demonstrated that these converted cells survived at least six months after injection into the brains of mice and behaved similarly to native cells in the brain.
"Not only did these transplanted cells survive in the mouse brain, they showed functional properties similar to those of native cells," said senior author Andrew S. Yoo, PhD, assistant professor of developmental biology.
"These cells are known to extend projections into certain brain regions. And we found the human transplanted cells also connected to these distant targets in the mouse brain. That's a landmark point about this paper."
The work appears Oct. 22 in the journal Neuron.
The investigators produced a specific type of brain cell called medium spiny neurons, which are important for controlling movement. They are the primary cells affected in Huntington's disease, an inherited genetic disorder that causes involuntary muscle movements and cognitive decline usually beginning in middle-adulthood. Patients with the condition live about 20 years following the onset of symptoms, which steadily worsen over time.
The research involved adult human skin cells, rather than more commonly studied mouse cells or even human cells at an earlier stage of development. In regard to potential future therapies, the ability to convert adult human cells presents the possibility of using a patient's own skin cells, which are easily accessible and won't be rejected by the immune system.
To reprogram these cells, Yoo and his colleagues put the skin cells in an environment that closely mimics the environment of brain cells. They knew from past work that exposure to two small molecules of RNA, a close chemical cousin of DNA, could turn skin cells into a mix of different types of neurons.
In a skin cell, the DNA instructions for how to be a brain cell, or any other type of cell, are neatly packed away, unused. In past research published in Nature, Yoo and his colleagues showed that exposure to two microRNAs called miR-9 and miR-124 altered the machinery that governs packaging of DNA. Though the investigators still are unravelling the details of this complex process, these microRNAs appear to be opening up the tightly packaged sections of DNA important for brain cells, allowing expression of genes governing development and function of neurons.
Knowing exposure to these microRNAs alone could change skin cells into a mix of neurons, the researchers then started to fine tune the chemical signals, exposing the cells to additional molecules called transcription factors that they knew were present in the part of the brain where medium spiny neurons are common.
"We think that the microRNAs are really doing the heavy lifting," said co-first author Matheus B. Victor, a graduate student in neuroscience.
"They are priming the skin cells to become neurons. The transcription factors we add then guide the skin cells to become a specific subtype, in this case medium spiny neurons. We think we could produce different types of neurons by switching out different transcription factors."
Yoo also explained that the microRNAs, but not the transcription factors, are important components for the general reprogramming of human skin cells directly to neurons. His team, including co-first author Michelle C. Richner, senior research technician, showed that when the skin cells were exposed to the transcription factors alone, without the microRNAs, the conversion into neurons wasn't successful.
The researchers performed extensive tests to demonstrate that these newly converted brain cells did indeed look and behave like native medium spiny neurons. The converted cells expressed genes specific to native human medium spiny neurons and did not express genes for other types of neurons. When transplanted into the mouse brain, the converted cells showed morphological and functional properties similar to native neurons.
To study the cellular properties associated with the disease, the investigators now are taking skin cells from patients with Huntington's disease and reprogramming them into medium spiny neurons using the approach described in the new paper. They also plan to inject healthy reprogrammed human cells into mice with a model of Huntington's disease to see if this has any effect on the symptoms.
Contact: Julia Evangelou Strait
Generation of human striatal neurons by microRNA-dependent direct conversion of fibroblasts
Victor MB, Richner M, Hermanstyne TO, Ransdell JL, Sobieski C, Deng PY, Klyachko VA, Nerbonne JM, Yoo AS
Neuron. Oct. 22, 2014, Volume 84, Issue 2, p311–323
For more on stem cells and cloning, go to CellNEWS athttp://cellnews-blog.blogspot.com/
Tuesday, 21 October 2014
Is beauty, brains, or health most important?
Tuesday, 21 October 2014
|Human egg cell.|
Homero Flores, MD and coauthors from Reproductive Medicine Associates of New York and Icahn School of Medicine at Mount Sinai (New York, NY) reviewed the requests of ovum donor recipients over a 5-year period and assessed their preferences for donor traits, categorizing them by appearance, ethnicity, intellect, ability, and mental health. The authors documented statistically significant increases and decreases in the different categories over the years, with more "practical traits" that would improve offspring's overall quality of life tending to increase compared to "self-reflective" traits.
"As social acceptance of ovum donation has increased, and donor selection has become more sophisticated, couples are changing their preferences for what donor characteristics they value most for their future offspring," says Susan G. Kornstein, MD, Editor-in-Chief of Journal of Women's Health, Executive Director of the Virginia Commonwealth University Institute for Women's Health, Richmond, VA, and President of the Academy of Women's Health.
Contact: Kathryn Ryan
Beauty, Brains or Health: Trends in Ovum Recipient Preferences
Flores Homero, Lee Joseph, Rodriguez-Purata Jorge, Witkin Georgia, Sandler Benjamin, and Copperman Alan B.
Journal of Women's Health. October 2014, 23(10): 830-833. doi:10.1089/jwh.2014.4792
Friday, 10 October 2014
From human embryonic stem cells to billions of human insulin producing cells
Giant step toward new diabetes treatment
Friday, 10 October 2014
Harvard stem cell researchers today announced that they have made a giant leap forward in the quest to find a truly effective treatment for type 1 diabetes, a condition that affects an estimated three million Americans at a cost of about $15 billion annually: With human embryonic stem cells as a starting point, the scientists are for the first time able to produce, in the kind of massive quantities needed for cell transplantation and pharmaceutical purposes, human insulin-producing beta cells equivalent in most every way to normally functioning beta cells.
Doug Melton, who led the work and who twenty-three years ago, when his then infant son Sam was diagnosed with type 1 diabetes, dedicated his career to finding a cure for the disease, said he hopes to have human transplantation trials using the cells to be underway within a few years.
"We are now just one pre-clinical step away from the finish line," said Melton, whose daughter Emma also has type 1 diabetes.
A report on the new work has today been published by the journal Cell.
Felicia W. Pagliuca, Jeff Millman, and Mads Gurtler of Melton's lab are co-first authors on the Cell paper. The research group and paper authors include a Harvard undergraduate.
"You never know for sure that something like this is going to work until you've tested it numerous ways," said Melton, Harvard's Xander University Professor and a Howard Hughes Medical Institute Investigator.
"We've given these cells three separate challenges with glucose in mice and they've responded appropriately; that was really exciting.”
"It was gratifying to know that we could do something that we always thought was possible," he continued, "but many people felt it wouldn't work. If we had shown this was not possible, then I would have had to give up on this whole approach. Now I'm really energized."
The stem cell-derived beta cells are presently undergoing trials in animal models, including non-human primates, Melton said.
Elaine Fuchs, the Rebecca C. Lancefield Professor at Rockefeller University, and a Howard Hughes Medical Institute Investigator who is not involved in the work, hailed it as "one of the most important advances to date in the stem cell field, and I join the many people throughout the world in applauding my colleague for this remarkable achievement.”
"For decades, researchers have tried to generate human pancreatic beta cells that could be cultured and passaged long term under conditions where they produce insulin. Melton and his colleagues have now overcome this hurdle and opened the door for drug discovery and transplantation therapy in diabetes," Fuchs said.
And Jose Oberholtzer, M.D., Associate Professor of Surgery, Endocrinology and Diabetes, and Bioengineering at the University of Illinois at Chicago, and its Director of the Islet and Pancreas Transplant Program and the Chief of the Division of Transplantation, said work described in today's Cell "will leave a dent in the history of diabetes. Doug Melton has put in a life-time of hard work in finding a way of generating human islet cells in vitro. He made it. This is a phenomenal accomplishment."
Melton, co-scientific director of the Harvard Stem Cell Institute, and the University's Department of Stem Cell and Regenerative Biology – both of which were created more than a decade after he began his quest – said that when he told his son and daughter they were surprisingly calm.
"I think like all kids, they always assumed that if I said I'd do this, I'd do it," he said with a self-deprecating grin.
Type 1 diabetes is an autoimmune metabolic condition in which the body kills off all the pancreatic beta cells that produce the insulin needed for glucose regulation in the body. Thus the final pre-clinical step in the development of a treatment involves protecting from immune system attack the approximately 150 million cells that would have to be transplanted into each patient being treated. Melton is collaborating on the development of an implantation device to protect the cells with Daniel G. Anderson, the Samuel A. Goldblith Professor of Applied Biology, Associate Professor in the Department of Chemical Engineering, the Institute of Medical Engineering and Science, and the Koch Institute at MIT.
Melton said that the device Anderson and his colleagues at MIT are currently testing has thus far protected beta cells implanted in mice from immune attack for many months.
"They are still producing insulin," Melton said.
Cell transplantation as a treatment for diabetes is still essentially experimental, uses cells from cadavers, requires the use of powerful immunosuppressive drugs, and has been available to only a very small number of patients.
MIT's Anderson said the new work by Melton's lab is "an incredibly important advance for diabetes. There is no question that ability to generate glucose-responsive, human beta cells through controlled differentiation of stem cells will accelerate the development of new therapeutics. In particular, this advance opens doors to an essentially limitless supply of tissue for diabetic patients awaiting cell therapy."
Richard A. Insel, M.D., chief scientific officer of the Juvenile Diabetes Research Foundation, a founder of Melton's work, said the "JDRF is thrilled with this advancement toward large scale production of mature, functional human beta cells by Dr. Melton and his team. This significant accomplishment has the potential to serve as a cell source for islet replacement in people with type 1 diabetes and may provide a resource for discovery of beta cell therapies that promote survival or regeneration of beta cells and development of screening biomarkers to monitor beta cell health and survival to guide therapeutic strategies for all stages of the disease."
Melton expressed gratitude to both the Juvenile Diabetes Research Foundation and the Helmsley Trust, saying "their support has been, and continues to be essential."
While diabetics can keep their glucose metabolism under general control by injecting insulin multiple times a day, that does not provide the kind of exquisite fine tuning necessary to properly control metabolism, and that lack of control leads to devastating complications from blindness to loss of limbs.
About 10 percent of the more than 26 million Americans living with type 2 diabetes are also dependent upon insulin injections, and would presumably be candidates for beta cell transplants, Melton said.
"There have been previous reports of other labs deriving beta cell types from stem cells, no other group has produced mature beta cells as suitable for use in patients," he said.
"The biggest hurdle has been to get to glucose sensing, insulin secreting beta cells, and that's what our group has done."
Source: Harvard University
Contact: B. D. Colen
Generation of Functional Human Pancreatic β Cells In Vitro
Felicia W. Pagliuca, Jeffrey R. Millman, Mads Gürtler, Michael Segel, Alana Van Dervort, Jennifer Hyoje Ryu, Quinn P. Peterson, Dale Greiner, Douglas A. Melton
Cell, 9 October 2014, Volume 159, Issue 2, p428–439
Tuesday, 7 October 2014
New Technique Allows Scientists to Find Rare Stem Cells within Bone Marrow
Tuesday, 07 October 2014
Deep within the bone marrow resides a type of cells known as mesenchymal stem cells (MSCs). These immature cells can differentiate into cells that produce bone, cartilage, fat, or muscle — a trait that scientists have tried to exploit for tissue repair.
MIT and SMART researchers have developed a
way to isolate mesenchymal stem cells based on
physical traits such as stiffness. Credit: Image
courtesy of the researchers.
Until now, there has been no good way to separate MSCs from bone marrow cells that have already begun to differentiate into other cell types, but share the same molecules on the cell surface. This may be one reason why research results vary among labs, and why stem-cell treatments now in clinical trials are not as effective as they could be, says Krystyn Van Vliet, an MIT associate professor of materials science and engineering and biological engineering and a senior author of the paper, which appears in the Proceedings of the National Academy of Sciences this week.
"Some of the cells that you're putting in and calling stem cells are producing a beneficial therapeutic outcome, but many of the cells that you're putting in are not," Van Vliet says.
"Our approach provides a way to purify or highly enrich for the stem cells in that population. You can now find the needles in the haystack and use them for human therapy."
Lead authors of the paper are W.C. Lee, a former graduate student at the National University of Singapore and SMART, and Hui Shi, a former SMART postdoc. Other authors are Jongyoon Han, an MIT professor of electrical engineering and biological engineering, SMART researchers Zhiyong Poon, L.M. Nyan, and Tanwi Kaushik, and National University of Singapore faculty members G.V. Shivashankar, J.K.Y. Chan, and C.T. Lim.
MSCs make up only a small percentage of cells in the bone marrow. Other immature cells found there include osteogenic cells, which have already begun the developmental path toward becoming cartilage- or bone-producing cells. Currently, researchers try to isolate MSCs based on protein markers found on the cell surfaces. However, these markers are not specific to MSCs and can also yield other types of immature cells that are more differentiated.
"Conventional cell-surface markers are frequently used to isolate different types of stem cells from the human bone marrow, but they lack sufficient 'resolution' to distinguish between subpopulations of mesenchymal stromal cells with distinct functions," Lee says.
The researchers set out to find biophysical markers for multipotency — the ability to become many different cell types. They first suspected that cell size might be a factor, because foetal bone marrow stem cells, which tend to have a higher percentage of MSCs, are usually small in diameter.
To test this hypothesis, the researchers used a device Han had previously developed to capture circulating tumour cells based on their size. They isolated bone marrow cells based on size and found that while none of the larger cells were multipotent, not all of the smaller cells were multipotent, so size alone cannot be used to distinguish MSCs.
After measuring several other physical traits, the researchers found two that could be combined with size to completely distinguish MSCs from other stem cells: stiffness of the cell, and the degree of fluctuation in the cell's nuclear membrane.
"You don't need more than these three, but you also can't use fewer than these three," Van Vliet says.
"We now have a triplet of characteristics that identifies populations of cells that are going to be multipotent versus populations of cells that are only going to be able to become bone or cartilage cells."
These features appear to correspond to what is already known about stem cells, Van Vliet says. Compared with cells that have already committed to their final fate, immature cells have genetic material that moves around inside the nucleus, producing more fluctuations of the nuclear cell membrane. Stem cells also have a less rigid cytoskeletal structure than those of highly differentiated cells, at least when adhered to materials such as glass, making those attached cells seem less stiff.
The researchers then tested the regenerative abilities of the isolated MSCs in mice. They found that these cells could help repair both muscle and bone injuries, while cells identified as osteogenic stromal cells were able to repair bone but not muscle.
"We have provided the first demonstration that subpopulations of mesenchymal stromal cells can be identified and highly enriched for bone growth and muscle repair," Lee says.
"We envision that this approach would also be important in the selection and purification of bone marrow-derived stem cells for tissue repair in human patients suffering from a range of tissue-degenerative diseases."
The team is now working on high-speed methods for separating MSCs. Creating more pure populations of such cells should lead to more effective stem-cell treatments for tissue injuries, Van Vliet says.
"Instead of putting in 30 percent of the cells that you want, and 70 percent filler, you're putting in 100 percent of the cells that you want," she explains.
"That should lead to more reliable patient outcomes, because you're not going to have this variability from batch to batch, or patient to patient, in how many of each cell population are present."
Van Vliet and Poon also hope to begin a clinical trial of the osteogenic cells isolated in this study, which could prove useful for treating bone injuries.
Contact: Sarah McDonnell
Neurons react to the transmission activity of exosomes on three fundamental levels
Tuesday, 07 October 2014
The JGU researchers were able to show that
exosomes are absorbed by the nerve cells and
thus help protect these against stress. Credit:
Institute of Molecular Cell Biology.
Neurons (blue) which have absorbed exosomes
(green) have increased levels of the enzyme
catalase (red), which helps protect them against
peroxides. Credit: Institute of Molecular Cell
"As we have now discovered in cell cultures, exosomes seem to have a whole range of functions," explained Dr. Eva-Maria Krämer-Albers. By means of their transmission activity, the small bubbles that are the vesicles not only promote electrical activity in the nerve cells, but also influence them on the biochemical and gene regulatory level.
Cultivated neurons on a multielectrode array
chip: the electrodes register the electrical
impulses of the neurons. Credit: Institute of
Physiology, Mainz University Medical Center.
"The extent of activities of the exosomes is impressive," added Krämer-Albers. The researchers hope that the understanding of these processes will contribute to the development of new strategies for the treatment of neuronal diseases. Their next aim is to uncover how vesicles actually function in the brains of living organisms.
Contact: Dr. Eva-Maria Krämer-Albers
Multifaceted effects of oligodendroglial exosomes on neurons: impact on neuronal firing rate, signal transduction and gene regulation
Dominik Fröhlich, Wen Ping Kuo, Carsten Frühbeis, Jyh-Jang Sun, Christoph M. Zehendner, Heiko J. Luhmann, Sheena Pinto, Joern Toedling, Jacqueline Trotter and Eva-Maria Krämer-Albers
Philosophical Transactions of the Royal Society B, 18 August 2014 DOI: 10.1098/rstb.2013.0510