Wednesday, 23 April 2014

Human Neural Stem Cells Survive Long-term when Transplanted into Primate Brain

Human Neural Stem Cells Survive Long-term when Transplanted into Primate Brain
Wednesday, 23 April 2014

A team of researchers in Korea who transplanted human neural stem cells (hNSCs) into the brains of nonhuman primates and assessed cell survival and differentiation after 22 and 24 months found that the hNSCs had differentiated into neurons at 24 months and did not cause tumours.

The study will be published in a future issue of Cell Transplantation but is currently freely available on-line.

The hNSCs were labelled with magnetic nanoparticles to enable them to be followed by magnetic resonance imaging (MRI). They did not use immunosuppressant’s. According to the researchers, their study is the first to evaluate and show the long-term survival and differentiation of hNSCs without the need for immunosuppression.

The researchers concluded that hNSCs could be of "great value" as a source for cell replacement and gene transfer for the treatment of Parkinson's disease, Huntington's disease, Alzheimer's disease, amyotrophic lateral sclerosis (ALS), spinal cord injury and stroke.

"Stroke is the fourth major cause of death in the US behind heart failure, cancer, and lower respiratory disease," said study co-author Dr. Seung U. Kim of University of British Columbia Hospital's department of neurology in Canada.

"While tissue plasminogen activator (tPA) treatment within three hours after a stroke has shown good outcomes, stem cell therapy has the potential to address the treatment needs of those stroke patients for whom tPA treatment was unavailable or did not help."

Dr. Kim and colleagues in Korea grafted magnetic particle-labelled hNSCs into the brains of laboratory primates and evaluated their performance to assess their survival and differentiation over 24 months. Of particular interest was determining their ability to differentiate into neurons and to determine whether the cells caused tumorigenesis.

"We injected hNSCs into the frontal lobe and the putamen of the monkey brain because they are included in the middle cerebral artery (MCA) territory, which is the main target in the development of the ischemic lesion in animal stroke models," commented Dr. Kim.

"Thus, research on survival and differentiation of hNSCs in the MCA territory should provide more meaningful information to cell transplantation in the MCA occlusion stroke model."

The researchers said that they chose NSCs for transplantation because the existence of multipotent NSCs "has been known in developing rodents and in the human brain with the properties of indefinite growth and multipotent potential to differentiate" into the three major CNS cell types – neurons, astrocytes and oligodendrocytes.

"The results of this study serve as a proof-of-principle and provide evidence that hNSCs transplanted into the non-human primate brain in the absence of immunosuppressant’s can survive and differentiate into neurons," wrote the researchers.

"The study also serves as a preliminary study in our planned preclinical studies of hNSC transplantation in non-human primate stroke models."

"The absence of tumours and differentiation of the transplanted cells into neurons in the absence of immunosuppression after transplantation into non-human primates provides hope that such a therapy could be applicable for use in humans." said Dr. Cesar V. Borlongan, Prof. of Neurosurgery and Director of the Center of Excellence for Aging & Brain Repair at the University of South Florida.

"This is an encouraging study towards the use of NSCs to treat neurodegenerative disorders".

Contact: Robert Miranda

Reference:
Long-term survival and differentiation of human neural stem cells in nonhuman primate brain with no immunosuppression 
Lee, S-R.; Lee, H. J.; Cha, S-H.; Jeong, K-J.; Lee, Y. J.; Jeon, C-Y.; Yi, K. S.; Lim, I.; Cho, Z-H.; Chang, K-T.; Kim, S. U.
Cell Transplant. Appeared or available online: January 29, 2014
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Monday, 21 April 2014

A Protein Required for Integrity of Induced Pluripotent Stem Cells

SIRT1 is necessary for telomere elongation and genome integrity during cell reprogramming
Monday, 21 April 2014

This image shows chromosome abnormalities in
reprogrammed cells in which SIRT1 protein has
been removed (in red). Credit: Centro Nacional
de Investigaciones Oncologicas. 
Cell reprogramming converts specialised cells such as nerve cells or skin cells towards an embryonic stem cell state. This reversal in the evolutionary development of cells also requires a reversal in the biology of telomeres, the structures that protect the ends of chromosomes; whilst under normal conditions telomeres shorten over time, during cell reprogramming they follow the opposite strategy and increase in length.

A study published today in the journal Stem Cell Reports, from the Cell Publishing Group, reveals that the SIRT1 protein is needed to lengthen and maintain telomeres during cell reprogramming. SIRT1 also guarantees the integrity of the genome of stem cells that come out of the cell reprogramming process; these cells are known as iPS cells (induced Pluripotent Stem cells).

The study has been carried out by the Spanish National Cancer Research Centre's Telomeres and Telomerase Group, in collaboration with the CNIO's Transgenic Mice Core Unit.

Since the Japanese scientist Shinya Yamanaka first obtained iPS cells from adult tissue in 2006, regenerative medicine has become one of the most exciting and rapidly developing fields in biomedicine. There is a very ambitious aim, given the ability to differentiate iPS cells into any type of cell; this would allow for the regeneration of organs damaged by diseases such as Alzheimer, diabetes or cardiovascular diseases.

The nature of iPS cells however is causing intense debate. The latest research shows that chromosome aberrations and DNA damage can accumulate in these cells.

"The problem is that we don't know if these cells are really safe", says MarĂ­a Luigia De Bonis, a postdoctoral researcher of the Telomeres and Telomerase Group who has done a large part of the work.

In 2009, the same CNIO laboratory discovered that telomeres increase in length during cell reprogramming (Marion et al., Cell Stem Cell, 2009); this increase is important as it allows stem cells to acquire the immortality that characterises them.

One year later, it was demonstrated that the levels of SIRT1 — a protein belonging to the sirtuin family and that is involved in the maintenance of telomeres, genomic stability and DNA damage response — are increased in embryonic stem cells. The question CNIO researchers asked was: is SIRT1 involved in cell reprogramming?

Safer Stem Cells
Employing mouse models and cell cultures as research tools in which SIRT1 had been removed, the team has discovered that this protein is necessary for reprogramming to occur correctly and safely.

"We observed cell reprogramming in the absence of SIRT1, but over time the produced iPS cells lengthen telomeres less efficiently and suffer from chromosome aberrations and DNA damage," says De Bonis.

"SIRT1 helps iPS cells to remain healthy," she concludes.

The authors describe how this protective effect on iPS cells is, in part, mediated by the cMYC regulator. SIRT1 slows the degradation of cMYC, which results in an increase in telomerase (the enzyme that increases telomere length) in cells.

The study sheds light on how cell reprogramming guarantees the healthy functioning of stem cells. This knowledge will help to overcome barriers that come out of the use of iPS cells so they may be used in regenerative medicine.

Contact: Nuria Noriega

Reference:
SIRT1 Is Necessary for Proficient Telomere Elongation and Genomic Stability of Induced Pluripotent Stem Cells
Maria Luigia De Bonis, Sagrario Ortega, Maria A. Blasco
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Thursday, 3 April 2014

Study Helps Unravel the Tangled Origin of ALS

Study Helps Unravel the Tangled Origin of ALS
Thursday, 03 April 2014

By studying nerve cells that originated in patients with a severe neurological disease, a University of Wisconsin-Madison researcher has pinpointed an error in protein formation that could be the root of amyotrophic lateral sclerosis.

In this microscope photo of motor neurons created
in the laboratory of Su-Chun Zhang at the University
of Wisconsin-Madison, green marks the nucleus, and
red marks the nerve fibres. Zhang and co-workers at
the Waisman Center have identified a mis-regulation
of protein in the nucleus as the likely first step in the
pathology of ALS, a fatal neurological disorder that
blocks nerve signals to the muscles, and later causes
motor neurons to die. Credit: Hong Chen and
Su-Chun Zhang, Waisman Center, University of
Wisconsin-Madison.
Also called Lou Gehrig's disease, ALS causes paralysis and death. According to the ALS Association, as many as 30,000 Americans are living with ALS.

After a genetic mutation was discovered in a small group of ALS patients, scientists transferred that gene to animals and began to search for drugs that might treat those animals. But that approach has yet to work, says Su-Chun Zhang, a neuroscientist at the Waisman Center at UW-Madison, who is senior author of the new report, published April 3 in the journal Cell Stem Cell.

Zhang has been using a different approach — studying diseased human cells in lab dishes. Those cells, called motor neurons, direct muscles to contract and are the site of failure in ALS.

About 10 years ago, Zhang was the first in the world to grow motor neurons from human embryonic stem cells. More recently, he updated that approach by transforming skin cells into iPS (induced pluripotent stem) cells that were transformed, in turn, into motor neurons.

IPS cells can be used as "disease models," as they carry many of the same traits as their donor. Zhang says the iPS approach offers a key advantage over the genetic approach, which "can only study the results of a known disease-causing gene. With iPS, you can take a cell from any patient, and grow up motor neurons that have ALS. That offers a new way to look at the basic disease pathology."

In the new report, Zhang, Waisman scientist Hong Chen, and colleagues have pointed a finger at proteins that build a transport structure inside the motor neurons. Called neurofilament, this structure moves chemicals and cellular subunits to the far reaches of the nerve cell. The cargo needing movement includes neurotransmitters, which signal the muscles, and mitochondria, which process energy.

Motor neurons that control foot muscles are about three feet long, so neurotransmitters must be moved a yard from their origin in the cell body to the location where they can signal the muscles, Zhang says. A patient lacking this connection becomes paralyzed; tellingly, the first sign of ALS is often paralysis in the feet and legs.

Scientists have known for some time that in ALS, "tangles" along the nerve's projections, formed of misshapen protein, block the passage along the nerve fibres, eventually causing the nerve fibre to malfunction and die. The core of the new discovery is the source of these tangles: a shortage of one of the three proteins in the neurofilament.

The neurofilament combines structural and functional roles, Zhang says.

"Like the studs, joists and rafters of a house, the neurofilament is the backbone of the cell, but it's constantly changing. These proteins need to be shipped from the cell body, where they are produced, to the most distant part, and then be shipped back for recycling. If the proteins cannot form correctly and be transported easily, they form tangles that cause a cascade of problems."

Finding neurofilament tangles in an autopsy of an ALS patient "will not tell you how they happen, when or why they happen," Zhang says. But with millions of cells — all carrying the human disease — to work with, Zhang's research group discovered the source of the tangles in the protein subunits that compose the neurofilaments.

"Our discovery here is that the disease ALS is caused by mis-regulation of one step in the production of the neurofilament," he says.

Beyond ALS, Zhang says "very similar tangles" appear in Alzheimer's and Parkinson's diseases.

"We got really excited at the idea that when you study ALS, you may be looking at the root of many neurodegenerative disorders."

While working with motor neurons sourced in stem cells from patients, Zhang says he and his colleagues saw "quite an amazing thing.”

“The motor neurons we reprogrammed from patient skin cells were relatively young, and we found that the mis-regulation happens very early, which means it is the most likely cause of this disease. Nobody knew this before, but we think if you can target this early step in pathology, you can potentially rescue the nerve cell."

In the experiment just reported, Zhang found a way to rescue the neural cells living in his lab dishes. When his group "edited" the gene that directs formation of the deficient protein, "suddenly the cells looked normal," Zhang says.

Already, he reports, scientists at the Small Molecule Screening and Synthesis Facility at UW-Madison are looking for a way to rescue diseased motor neurons. These neurons are made by the millions from stem cells using techniques that Zhang has perfected over the years.

Zhang says "libraries" of candidate drugs, each containing a thousand or more compounds, are being tested.

"This is exciting. We can put this into action right away. The basic research is now starting to pay off. With a disease like this, there is no time to waste."

Contact: Su-Chun Zhang

Reference:
Modeling ALS with iPSCs Reveals that Mutant SOD1 Misregulates Neurofilament Balance in Motor Neurons
Hong Chen, Kun Qian, Zhongwei Du, Jingyuan Cao, Andrew Petersen, Huisheng Liu, Lisle W. Blackbourn, CindyTzu-Ling Huang, Anthony Errigo,Yingnan Yin, Jianfeng Lu, Melvin Ayala, Su-Chun Zhang
Cell Stem Cell, April 3 2014, DOI: http://dx.doi.org/10.1016/j.stem.2014.02.004
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