February 2, 2011 by

Injured Liver Calls in Bone Marrow For Help?

Li et al. Cells Tissues Organs

It is known that administration of bone marrow cells into patients with liver failure has the ability to improve enzyme function and overall health http://www.youtube.com/watch?v=DdH6Mm4w98I. Additionally, numerous animal models have demonstrated that injection of various types of stem cells can result in regeneration of injured liver tissue. For example, Manuelpillai et al demonstrated that injection of human mesenchymal stem cells derived from the amnionic membrane into immune competent mice whose livers were damaged by carbon tetrachloride results in reduction in liver injury http://www.ncbi.nlm.nih.gov/pubmed/20447339. Even more interesting, administration of compounds that “instruct” bone marrow cells to enter circulation such as G-CSF, have been demonstrated to improve liver function and actually prevent mortality after liver injury http://www.ncbi.nlm.nih.gov/pubmed/20881764. This is relevant because G-CSF is a medication that is FDA approved and possesses a favorable safety profile.

One of the main scientific questions in the area of liver failure is whether the liver is actually “calling in” bone marrow stem cells to try to heal it after liver damage, or whether the therapeutic effects of stem cells in liver failure are an epiphenomena. In situations of cardiac damage after an acute myocardial infarction it has been demonstrated that the injured tissue causes upregulation of the protein SDF-1, which recruits bone marrow stem cells into the heart in order to promote healing. Whether similar mechanisms are at play in liver injury is not known. Part of the puzzle has to do with the fact that liver injury is a more chronic process than heart attacks and therefore recruitment of stem cells may be occurring at a much lower level. Alternatively, it is also known that chronic inflammatory processes actually suppress stem cell activity. So it may be that in chronic liver failure the stem cells are actually inhibited from possessing regenerative function.

This question was addressed in a recent study in which the gene expression profile of bone marrow cells was examined in animals with liver failure induced by administration of the hepatotoxin D-galactosamine to rats. To assess gene expression the Affymetrix GeneChip Rat Genome 230 2.0 Array was used, which quantifies gene expression of every gene in the rat genome. The scientists found that more than 87.7% of the genes/probe sets that were upregulated more than 2-fold in the bone marrow cells of rats with liver failure were also expressed by the liver cells, including 12 genes involved in liver development, early hepatocyte differentiation and hepatocyte metabolism. The concurrent upregulation of these genes was verified by the technique of reverse transcriptase polymerase chain reaction (RT-PCR).

The scientists also found that 940 genes were expressed in both the bone marrow cells of rats with liver failure and the hepatocytes of rats with liver failure but not in control cells. Specifically, many of the genes that were uprgulated in both the bone marrow and the liver seemed to be involved in regeneration of damaged tissue.

These data support the concept that the bone marrow stem cells can respond in similar ways to liver cells to injury. The hypothesis has been proposed by the authors that the bone marrow acts as a reservoir for the stem cells that are capable of regenerating liver. The mass amount of data in this publication is very interesting and requires detailed analysis to make sense of.

Filed Under: Adult Stem Cells, Liver, News, Stem Cell Research Tagged With: , , , ,
February 1, 2011 by

Scientists look to stem cells to mend broken hearts

Cardiac medicine has traditionally been associated with innovative procedures that sometimes where considered heretical to the present day dogma. For example, the first heart transplant, the use of the balloon catheter, the introduction of thrombolytics, all met substantial resistance from the “establishment” in their time. It appears that the next revolution in cardiac medicine is the use of stem cells. Aside from the obvious ethical and moral dilemmas surrounding embryonic tissues, the major controversy has been the belief that heart tissue does not repair itself after it has been lost. However, slowly but surely it appears that support behind the use of stem cells for heart conditions is gaining momentum.

One sign of this is the recent announcement that Britain’s leading heart charity, the British Heart Foundation (BHF), launched a 50 million pound ($80 million) research project into the potential of stem cells to regenerate heart tissue and “mend broken hearts”.

“Scientifically, mending human hearts is an achievable goal and we really could make recovering from a heart attack as simple as getting over a broken leg,” said Professor Peter Weissberg, medical director at the BHF.

One example of research in this area being performed in England is the work of Professor Paul Riley of the Institute of Child Health at University College London (UCL) who has identified a natural protein, called thymosin beta 4, that plays a role in developing heart tissue. He said his researchers had already had some success in using this protein to “wake up” cells known as epicardial cells in mice with damaged hearts. “We hope to find similar molecules or drug-like compounds that might be able to stimulate these cells further,” he told reporters at the briefing.

Currently the most advanced type of stem cell therapy for the heart involves administration of the patient’s own bone marrow cells into the area of heart damage after a heart attack. This work, which was performed in England and internationally, seems to suggest that cardiac muscle may be preserved when cells from the bone marrow produce various growth factors that stimulate stem cells that are already existing in the heart.

Other methods of administering stem cells into the heart include direct injection into the heart muscle during bypass surgery. This is performed experimentally in patients with severe angina on the hope that the injected stem cells will provide support for formation of new blood vessels, called collaterals, which are anticipated to increase the blood flow to the heart and thereby reduce angina.

Currently embryonic or fetal derived stem cells have not been used for treatment of heart conditions in humans. Therefore, at least for now, ethical issues do not seem to be a major obstacle to advancement of stem cell medicine for hearts.

Filed Under: Adult Stem Cells, Bone Marrow, Heart Disease, News, Stem Cell Research Tagged With: , , , , ,
February 1, 2011 by

Limb Transplants Facilitated by Bone Marrow Stem Cells

Kuo et al. Plast Reconstr Surg. 2011 Feb;127(2):569-79.

Composite tissue allografts are usually transplants of anatomical structures that contain multiple types of tissues. We have seen numerous high-profile examples of human composite tissue allografts such as whole hands, faces, and arms. While advancement of surgical techniques have made such transplants a reality, immunologically-mediated rejection remains a formidable problem.

Mesenchymal stem cells are particularly interesting in terms of an “adjuvant” to transplant immune suppression for several reasons.

Firstly, mesenchymal stem cells are known to be immune modulatory. It is known that these cells suppress activation of dendritic cells (which are involved in stimulating immune responses). Mesenchymal stem cells also inhibit CD4 and CD8 T cell responses. This is beneficial in that the CD4 cell coordinates immune attacks and the CD8 T cell causes cytotoxicity of organs that are being rejected. Perhaps even more interestingly, mesenchymal stem cells are known to stimulate production of T regulatory cells. These are cells of the immune system that suppress other immune cells and are associated with prolongation of transplanted graft survival. At a molecular level how the mesenchymal stem cells modulate the immune system seems to involve several biological modulators. Mesenchymal stem cells express the enzyme indomlamine 2,3 deoxygenase, which metabolizes tryptophan. T cells are highly dependent on tryptophan for activation. Mesenchymal stem cells have been demonstrated to actively induce T cell death by localized starvation of tryptophan. Additionally, mesenchymal stem cells produce various immune suppressive cytokines such as Leukemia Inhibitory Factor (LIF), IL-10, TGF-b, and soluble HLA-G. One interesting method by which mesenchymal stem cells suppress the immune system is by expression of surface-bound immune cell killing molecules such as Fas ligand. Evidence supporting the immune suppressive effects of mesenchymal stem cells includes the ability of these cells to control pathological immunity such as graft versus host disease, multiple sclerosis, and Type 1 diabetes.

Secondly, mesenchymal stem cells are known to be angiogenic. This is the process of new blood vessel formation. Subsequent to organ transplantation it is essential that the transplanted organ receive a proper blood supply. While ligation of major blood vessels is performed during the transplantation surgery, proper integration of the donor and recipient blood vessels is an important factor in graft survival.

Thirdly, mesenchymal stem cells have the ability to repair injured organs. There is a substantial amount of injury that occurs as a result of the organ procurement, transportation , and implantation procedure. This injury is termed ischemia/reperfusion injury. The extent of ischemia reperfusion injury contributes more to graft long term survival as compared even to MHC mismatches. As a result of the injury chemoattractants are generated that cause homing of stem cells into the injured organ. It is possible that these stem cells actually contribute to healing and perhaps regeneration of the injured organ.

In the publication discussed, the authors used a porcine model of hind limb transplantation. Four groups of pigs were used:

Group 1: Four untreated recipients

Group 2: Three recipients that received mesenchymal stem cells alone

Group 3: Five recipients that received cyclosporine alone

Group 4: Three recipients that received cyclosporine, irradiation, and mesenchymal stem cells

It was found that treatment with mesenchymal stem cells along with irradiation and cyclosporine A resulted in significant increases in allograft survival as compared with other groups (>120 days; p = 0.018).

Flow cytometric analysis revealed a significant increase in the percentage of CD4/CD25 and CD4/FoxP3 T cells in both the blood and graft in the mesenchymal stem cell/irradiation/cyclosporine A group.

These preliminary data suggest that addition of mesenchymal stem cells to the combination of cyclosporine and irradiation resulted in significant allograft survival. Unfortunately in Group 3 they did not add irradiation so it is impossible to know whether the graft survival was caused by the irradiation or by the mesenchymal stem cells.

Previous collaborations between Thomas Ichim of Medistem and Hao Wang’s group from University of Western Ontario, Canada suggests that a radioresistant element in free bone transplants contributes to prolonged allograft survival. It may be possible that the radioresistant cells were mesenchymal stem cells in nature. This is an area in which future studies are definitely warranted.

Filed Under: Adult Stem Cells, Bone Marrow, News, Stem Cell Research Tagged With: , , , ,
January 31, 2011 by

New Cell That Keeps Stem Cells in the Bone Marrow

Chow et al. J Exp Med.

When a bone marrow transplant is performed, the bone marrow cells of the donor are injected intravenously into the recipient and somehow find their way back into the bone marrow of the recipient. The mechanism known to be responsible for this has always been cited as being SDF-1 (also called CXCL12) produced by bone marrow “stromal” cells. This mechanism is of fundamental importance to stem cell therapists for two reasons:

Firstly, stem cells are known to be recruited by injured tissue, which produces SDF-1. This has been explained as one of the mechanisms by which both cardiac and brain infarcts cause recruitment of endogenous and exogenous stem cells to the area of injury.

Secondly, by temporarily interrupting the production of SDF-1 or recognition of SDF-1 by CXCR-4, drugs such as Mozibil have been developed which are used in the mobilization of stem cells for patients who mobilize poorly in response to G-CSF.

In a paper that we view as groundbreaking, scientists found that one of the key cells in the bone marrow that produces SDF-1 is the CD169 positive macrophage. The scientists examined three populations of BM mononuclear phagocytes that include Gr-1(hi) monocytes (MOs), Gr-1(lo) MOs, and macrophages (MΦ) based on differential expression of Gr-1, CD115, F4/80, and CD169. Using MO and MΦ conditional depletion models, we found that reductions in BM mononuclear phagocytes led to reduced production of SDF-1 by the bone marrow.

They also found that depletion of CD169(+) MΦ, which spares BM MOs, was sufficient to induce stem cell mobilization. This depletion also enhanced mobilization induced by a CXCR4 antagonist or granulocyte colony-stimulating factor.

Thus it appears that specific macrophage subsets play specific roles in the bone marrow stem cell system. It may be possible to use these macrophages as therapeutic agents to cause recruitment of stem cells into injured organs.

Filed Under: Adult Stem Cells, Bone Marrow, News Tagged With: , , ,
January 4, 2011 by

Male-Pattern Baldness Found Rooted in Stem Cells

Amanda Chan, MyHealthNewsDaily Staff Writer

A new discovery regarding the presence of stem cells in males with androgenetic alopecia (male-pattern baldness) has led to hope that the disease may be treatable. It was previously believed that people who suffered from baldness also had a depleted number of hair follicle stem cells, meaning that new hair growth would not be possible. However, this new discovery has shown that the number of stem cells present in bald areas and non-bald areas is equal; the difference is a depleted number of hair follicle progenitor cells.

The implication for this discovery are if scientists are able to coax the present stem cells into developing into hair follicle progenitor cells, they would be able to regrow hair. The only FDA approved baldness treatments; Rogaine and Propecia do not have the ability to regrow cells. Propecia works by inhibiting testosterone’s effect on hair follicles, disrupting its ability to decrease the size of hair follicles.

http://www.livescience.com/health/male-pattern-baldness-stem-cells-110104.html

Filed Under: Adult Stem Cells, News, Stem Cell Research Tagged With: , , , , ,
January 1, 2011 by

Study Shows Patient’s Own Stem Cells Help Stroke Recovery: 16 Treated Patients Improve in Comparison to 36 Controls

Lee et al Stem Cells 28:1099
Stroke is caused by blocked circulation to parts of the brain usually as a result of a blood clot. Outcomes of stroke are generally proportional to the length of time the circulation was blocked and to the amount of brain tissue injury and death. Although the introduction of “clot busters” has improved outcomes in these patients, substantially morbidity and mortality still occurs. Numerous pharmaceutical approaches have been attempted in the treatment of stroke, both from the perspective of inhibiting tissue damage, and more recently trying to stimulate regeneration of injured brain tissue. To date clinical progress in this area has been relatively insignificant. In fact, in the pharmaceutical industry the condition of stroke has been referred to as a “graveyard for biotechs”.
One potentially promising treatment for stroke would be to augment the body’s own repair processes through activation of stem cells that are either pre-existing in the body, or through administration of stem cells either directly into the damaged brain tissue or areas associated with the damaged brain tissue. Rationale for this includes observations that stem cells from the bone marrow called endothelial progenitor cells are known to enter circulation in patients with stroke. A study from Dunac et al in France demonstrated that patients who have a higher degree of stem cells in circulation after a stroke have a better neurological outcome in comparison to patients who have lower numbers of circulating stem cells. In rats which are given a stroke experimental by ligation of one of the arteries that feeds the brain, called the middle cerebral artery, administration of human or rat stem cells reduces the size of brain damage, as well as causes regeneration of new neurons. Additionally, animal studies have demonstrated that administration of stem cells causes improved behavior as compared to animals receiving control cells or saline.
One reason why there exists a belief in the field that bone marrow derived cells may be capable of generating new neurons is that in female recipients of bone marrow transplant nerve cells have been found that express the Y-chromosome (Weimann et al. Contribution of transplanted bone marrow cells to purkinje neurons in human adult brains Proc Natl Acad Sci USA 100:2088).
In a recent paper (Lee et al. A long-term follow-up study of intravenous autologous mesenchymal stem cell transplantation in patients with ischemic stroke. Stem Cells 28:1099) a group from Korea reported what to date is the largest clinical trial of stem cells in stroke. The investigators used mesenchymal stem cells generated from the bone marrow of the stroke patients. These cells are believed to be capable of generating new neurons, as well as producing growth factors that stimulate the brain to heal itself. Mesenchymal stem cells are currently used in clinical trials in the US and internationally for treatment of graft versus host disease, heart failure, and critical limb ischemia (an advanced form of peripheral artery disease that causes 100-200,000 amputations per year). Advantages of mesenchymal stem cells include: a) ability to be expanded in tissue culture; b) Well-known safety profile; and c) Ability to use between individuals without need for matching.
In the study discussed, the investigators selected 52 patients with a defined type of stroke (non-lacunar infarction within the middle cerebral artery territory). Patients were selected 7 days after the stroke in order to have a standardized level of dysfunction. It was previously published that before 7 days the patient may have a sudden increase or decrease in neurological function, but after 7 days post-stroke the neurological function remains stable.
The investigators extracted 5 ml of bone marrow from 16 patients and expanded the mesenchymal stem cells over a 4 week period. The mesenchymal stem cells were defined as cells expressing the markers CD105 (SH-2) and SH-4. Cells were grown as adherent cells in media containing fetal calf serum. The 16 patients received two administrations of 50 million cells intravenously spread apart by a week.
Patients were followed for an average of 117 weeks, with some patients followed as long as 5-years after the stroke. There was a statistically significant difference in overall survival in the patients that received the mesenchymal stem cells as compared to controls. Specifically, 4 of the 16 patients who received the mesenchymal stem cells passed away during the follow-up period as compared to 21 of the 36 control patients.
In studies of embryonic or fetal stem cells, one of the major concerns is development of tumors. This stems from the fact that administration of embryonic stem cells into immune deficient animals causes tumors called teratomas, and in humans there is at least one documented case of a brain tumor developing in a patient who received fetal derived stem cells. Of the patients administered mesenchymal stem cells, no tumors were detected. This is important because this study has one of the longest follow up periods.
Functional improvements as quantified by the modified Rankin Score were noted in patients receiving stem cells, whereas controls overall suffered a decline in function. Specifically, function was assessed at a median of 3.5 years in the control group and 3.2 years in the mesenchymal stem cell treated group. Function was assessed by doctors where were “blinded” to which patient received stem cells and which patient was in the control group. In the control group 13 of 26 patients had a negative rank, which indicates an improved functional outcome for each patient, whereas 21 patients had a positive rank, which means worse outcome. In contrast, in the treatment group 11 of the 16 patients had a negative rank. The difference between groups reached statistical significance.
In 9 patients of the group that received stem cells, a correlation was studied between the cytokine SDF-1 and functional outcome. Functional outcome was determined both by the modified Rankin score as well as by the Barthel index. A positive correlation was found between levels of SDF-1 at the time of MSC treatment and functional outcome in the patients studied. This protein is known to be involved in recruiting stem cells to the site of injury. Given that in this study the stem cells were administered intravenously and not locally (eg by sterotactic injection), it would be logical that a correlation exist between chemotactic signaling and improved outcome. Currently there are companies such as Juvantis, that are administering plasmids expressing SDF-1 in order to induce homing of endogenous stem cells into cardiac infarcts. It is interesting that the same priniciple may be valid in situations of ischemic stroke. To date no studies have been performed clinically using co-administration of stem cells and SDF-1, however, myoblasts transfected with SDF-1 have been used in a clinical trial in Jordan by the company BioHeart for treatment of heart failure.
One other interesting finding of the study besides lack of ectopic tissue or tumor formation is that no adverse effects were associated with using stem cells grown in fetal calf serum. There has been concern in the literature, particularly the academic literature, that fetal calf serum may induce autoimmunity or sensitization upon second MSC administration. This did not appear to be the case.

Filed Under: Adult Stem Cells, Bone Marrow, News, Stem Cell Research, Stroke Tagged With: , , , , ,
December 31, 2010 by

Differences between Stem Cells from the Placenta and Bone Marrow

Fazekasova et al. Mesenchymal stem cells were historically isolated from the bone marrow as an adherent stem cell population capable of “orthodox” differentiation, meaning that they have ability to become bone, cartilage, and fat. Further research revealed that these cells are also capable of “non-orthodox” differentiation, that is, becoming neurons, hepatocytes, insulin producing cells, and lung cells. Given the high number of growth factors secreted by mesenchymal stem cells, numerous companies have sought to develop therapeutic products from mesenchymal stem cells. For example, Osiris Therapeutics has been developing bone marrow mesenchymal stem cells as a treatment for Graft Versus Host Disease. Athersys has been using bone marrow derived mesenchymal-like cells for treatment of heart disease, and Mesoblast has been using these cells for treatment of bone injury.

A new generation of companies has been focusing other mesenchymal-like cells derived from other tissues. For example, Medistem Inc has identified endometrial regenerative cells (ERC), a type of mesenchymal-like stem cell that is found in the endometrium and appears to have higher ability to produce growth factors that stimulate new blood vessel production as compared to other sources of mesenchymal stem cells. General Biotechnology LLC has been developing tooth derived mesenchymal stem cells for treatment of neurological disorders. Celgene has been using placental-derived mesenchymal stem cells for treatment of critical limb ischemia, a disorder associated with poor circulation of the legs.

Given that there appear to be various sources of mesenchymal stem cells, an important question is how do these cells compare when they are used in experiments side by side. In a paper published this month, placental derived and bone marrow derived mesenchymal stem cells were compared. The scientists found that higher numbers of mesenchymal stem cells could be isolated from the placenta as compared to the bone marrow. Interestingly, placental mesenchymal stem cells were found to be comprised of both fetal and maternal origin.

One of the critical features of mesenchymal stem cells is that they are able to be used without need for matching with the recipient. This is because mesenchymal stem cells are historically known to be “immune privileged”. One of the experiments that the scientists did was to examine whether there is a difference between the bone marrow and placentally derived mesenchymal stem cells in terms of immunogenicity.

Placentally derived mesenchymal stem cells expressed lower levels of the immune stimulatory molecule HLA class I and higher levels of the immune suppressive molecules PDL-1 and CD1a, compared to bone marrow derived mesenchymal stem cells. However, when both cell types were treated with interferon gamma, the placentally derived mesenchymal became much more immune stimulatory as compared to the bone marrow cells. Furthermore it appeared that direct incubation with T cells resulted in higher T cell stimulation with the placental mesenchymal stem cells as compared to the bone marrow cells. Thus from these data it appears that bone marrow derived mesenchymal stem cells are more immune privileged as compare to placental derived cells.

Filed Under: Adult Stem Cells, Bone Marrow, Endometrial Stem Cells, News, Stem Cell Research Tagged With: , , , , , ,
December 29, 2010 by

Enhancing Efficacy of Bone Marrow Transplant

Huang et al. Blood. [Epub ahead of print]

Bone marrow transplantation has cured many patients of hematological diseases such as leukemias and lymphomas. Additionally, bone marrow transplantation is becoming used more and more in treatment of autoimmune diseases such as type 1 diabetes and multiple sclerosis. Unfortunately, there are still numerous limitations to this procedure. One of the biggest ones is that occurrence of graft versus host disease, in which the transplanted stem cells produce immune cells that attack the recipient. The other major problem is graft failure, in which the transplanted stem cells do not “take”.

The group of Dr. Ildstad from the University of Louisville has been working on enhancing bone marrow transplantation by co-administration of other cells called “facilitator cells.” In a recent publication (Huang et al. CD8{alpha}+ plasmacytoid precursor DC induce antigen-specific regulatory T cells that enhance HSC engraftment in vivo. Blood. 2010 Dec 29) it was shown that a type of dendritic cell, called the plasmacytoid dendritic cell, is capable of promoting bone marrow transplant efficacy through stimulation of T regulatory cells.

The scientists demonstrated that after bone marrow transplant from mismatched donors, there are immune suppressive cells, called T regulatory cells, that develop under specific conditions that stop the new (donor derived) immune system cells from attacking the recipient. When a mismatched bone marrow transplant is performed together with plasmacytoid dendritic cells, these cells “instruct” the donor immune system to generate T regulatory cells, which prevent graft versus host disease.

Implications of this research may be profound in areas outside of bone marrow transplantation for leukemias. In solid organ transplants, patients are required to take life-long immune suppressants to prevent the transplanted organ from being rejected. If donor bone marrow transplantation is performed with the donor organ, then the body does not reject the organ. Unfortunately this is not possible because bone marrow transplantation has a high risk of graft versus host disease. If the discovery of Dr. Ilstad’s group can be translated to humans, it may be possible to induce “immunological tolerance”, which is a state of immune un-responsiveness to the transplanted organ, while maintaining a functioning immune system towards pathogens and bacteria.

Filed Under: Adult Stem Cells, Bone Marrow, News, Stem Cell Research Tagged With: , , , ,
December 29, 2010 by

Increasing Efficacy of Stem Cell Therapy for Spinal Cord Injury

Jin et al. Spine (Phila Pa 1976).

Clinical trials of stem cells for treatment of spinal cord injury are currently being conducted in the United States and abroad. For example, the Covington Louisiana company TCA Cellular Therapy LLC is recruiting 10 patients with spinal cord injury to receive intrathecal infusion (lumbar puncture) of autologous, ex vivo expanded bone marrow-derived mesenchymal stem cells. Completed clinical trials have demonstrated some rationale that stem cells may be useful. For example, Kumar et al. (Autologous bone marrow derived mononuclear cell therapy for spinal cord injury: A phase I/II clinical safety and primary efficacy data. Exp Clin Transplant. 2009 Dec;7(4):241-8) reported on 297 spinal cord injury patients that were treated with their own bone marrow cells injected intrathecal. 33% of the patients reported an objective improvement.

As with other clinical trials of stem cell therapy, it appears that in the area of spinal cord injury there still remains room for improvement. We at Cellmedicine have reported a stunning improvement in a spinal cord injury patient by using a combination of CD34 and mesenchymal stem cells, which was recently published http://www.intarchmed.com/content/pdf/1755-7682-3-30.pdf. Unfortunately this was only one patient and more studies are required.

In an attempt to improve efficacy of stem cell therapy for spinal cord injury, a group from the Department of Neurosurgery, Spine and Spinal Cord Institute, at the Yonsei University College of Medicine, Seoul, Republic of Korea, has created an artificial method of increasing growth factor production from stem cells of the nervous system called neural progenitor cells. Previous studies have shown that neural progenitor cells are capable of treating several models of spinal cord injury, however their effects appear to be transient. Vascular endothelial growth factor (VEGF) is a protein that increases blood vessel production in tissues and has been previously demonstrated to stimulate integration of nervous system cells after spinal cord injury. Since increasing VEGF production could hypothetically increase efficacy of neural stem cells, a series of experiments were performed in order to generate modified neural stem cells which have enhanced VEGF production.

It is known that insertion of a gene into a cell can cause the cell to produce the protein made by the gene. So theoretically all the researchers had to do is to transfect (insert) the VEGF gene into the neural stem cells and the neural stem cells would be more effective. The problem with this is that too much VEGF can have negative effects. A more attractive approach would be to program the progenitor cells in such a manner so that they produce VEGF only when it is necessary. During spinal cord injury, the area of damage is associated with reduced oxygen, a condition called hypoxia. Ideally one would want to engineer the stem cells in a manner so that they produce VEGF only during times of hypoxia. One way of doing this is to control the expression the gene by using an inducible promoter.

Promoters are pieces of DNA that control expression of genes that are in front of them. Some promoters always turn on gene expression (these are called constitutive promoters), others turn on expression only under specific conditions (these are called inducible promoters. The promoter that turns on erythropoietin is an inducible promoter. Erythropoietin is made by the kidney and stimulates production of red blood cells. Its expression is turned on under conditions of lack of oxygen. This is why people who live in high altitudes have higher expression of erythropoietin. The scientists in the current publication developed a genetically engineered neural stem cell that contains the VEGF gene under control of the erythropoietin promoter. What this means is that the cells will be producing VEGF only under conditions of hypoxia. In order to selectively detect the areas of hypoxia, the scientists also developed stem cells that have the luciferase gene in front of the erythropoietin promoter. Luciferase is a protein that generates light and allows for easy detection in vitro and in vivo of the hypoxic cells.

The scientists found that the stem cells administered during hypoxia generated significantly higher concentrations of VEGF, which was associated with the promoter being turned on, as assessed by luciferase expression. Furthermore, rats receiving the VEGF expressing stem cells possessed a significantly lower amount of nerve damage and higher ability to recuperate after spinal cord injury.

These data suggest that it is feasible to combine inducible promoters with stem cells in order to augment various activities of the stem cells. This concept could be applied to numerous settings. For example, mesenchymal stem cells are known to selectively migrate to areas of inflammation. In the setting of cancer, mesenchymal stem cells could be transfected with genes that are encoding toxic substances. This way chemotherapy could be targeted only to cancer cells and therefore have a better safety profile.

Gene therapy has failed to a large extent because of lack of ability to control where the genes are administered. It may be possible that advancements in stem cell technologies will allow for a rebirth of gene therapy in that the stem cells may be used to deliver genes only to the tissues where they are needed.

Filed Under: Adult Stem Cells, News, Spinal Cord Injury, Stem Cell Research Tagged With: , , , , , ,
December 3, 2010 by

How Inflammation Suppresses Stem Cell Function

Wang et al. PLoS One;5(12):e14206.

Low grade inflammation is well known to correlate with development of numerous disease conditions such as heart failure, kidney failure, and diabetes. It is generally accepted that oxidative stress caused by inflammation is one of the means by which disease evolution occurs. Inflammatory conditions usually generate oxygen free radicals that damage cells and cause the cells of the body to lose function. Importance of reducing inflammation in terms of preventing diseases, such as heart disease, is seen by the beneficial effects of antiinflammatories such as aspirin.

A recent paper (Wang et al. TLR4 Inhibits Mesenchymal Stem Cell (MSC) STAT3 Activation and Thereby Exerts Deleterious Effects on MSC-Mediated Cardioprotection. PLoS One. 2010 Dec 3;5(12):e14206.) suggests that inflammation may actually inhibit the activity of stem cells, and through suppressing the body’s repair processes, causes various diseases to appear.

The mesenchymal stem cell is a type of stem cell found in the bone marrow, fat, heart, and other tissues, that is activated in response to injury and acts to heal damaged tissues. Particularly in the case of heart attacks, it has been demonstrated that administration of bone marrow mesenchymal stem cells causes accelerated healing both in humans and animals. The therapeutic effects of mesenchymal stem cells seem to be mediated by production of growth factors, as well as proteins that support creation of new blood vessels, a process called angiogenesis. Currently several companies are currently developing mesenchymal stem cell based drug candidates including Osiris Therapeutics, Athersys Inc, Mesoblast, and Medistem.

Given the fact that these cells are not a “laboratory experiment” but have actually been used in more than a 1000 patients, understanding conditions that affect their activity, as well as means of making them more effective is important. Inflammatory mediators are believed to influence activity of mesenchymal stem cells, since the protein toll like receptor 4 (TLR4), which recognizes tissue inflammation is found in high concentrations on mesenchymal stem cells. TLR-4 was originally found on cells of the “innate” immune system as a molecule that recognizes “danger signals”.

In order to determine the function of TLR4 on bone marrow mesenchymal stem cells, scientists at Indiana University used mice that have been genetically engineered not to have expression of this protein. Bone marrow mesenchymal stem cells from the mice lacking TLR-4 were demonstrated to function in a similar manner to normal mesenchymal stem cells in the test tube. However when these mesenchymal stem cells were administered to mice after a heart attack, the cells were capable of generating a highly significant improvement in heart function as compared to normal mesenchymal stem cells. The scientists concluded that inflammatory signals “instruct” mesenchymal stem cells to produce less therapeutic factors than they normally would.

These data are very interesting since other reports have suggested that inflammatory mediators actually stimulate mesenchymal stem cells to produce higher amounts of anti-inflammatory factors such as interleukin-10. One of the reasons for the discrepancy may be that inflammation in the context of a heart attack may be different than the inflammatory signals used by other studies.

Filed Under: Adult Stem Cells, News, Stem Cell Research Tagged With: , , , , ,
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