In Research
Subscribe to this blog
Find out when new entries are posted the instant they are published on Action Duchenne via RSS.
Disclaimer
The Action Duchenne website aims to offer a unique forum for sharing information and ideas in the search for a cure and better medical care for Duchenne and Becker and will at all times attempt to ensure postings are accurate, scientifically peer reviewed and not offensive to individuals. Action Duchenne, however, cannot take responsibility for personal opinions, information and the content of links to other websites. It is essential that you always contact your clinician or GP before taking any course of medication, therapy or supplement.
Recent Publications on Stem Cell research
1. Delay of the onset of symptoms or alleviate some of the symptoms.
2. Alleviate the condition such that a reasonably normal life can be led by the DMD-sufferers.
3. Totally cure or at least virtually totally cure DMD.
Previously I discussed Exon-Skipping, in section 2. This review will deal with aspects of recent stem cell research with the hope to obtain a cure as envisioned in heading 3.
The object of stem cell research, with respect to DMD, is to attempt to place cells containing the corrected dystrophin gene into all the affected muscles and thereby have fully operational muscles instead.
In principle stem cells carrying the dystrophin gene would be used to replace the dystrophic muscle.
The papers under discussion.
The first paper to be discussed takes us back just over a year, being published in November 2006 (1). In their study they used the Golden Retriever model of DMD. These animals have a single mutation in intron 6, which results in the complete absence of dystrophin. Muscle degeneration sets in rapidly in these dogs, which die at about one year of age. Mesangioblasts were isolated from both wild-type and dystrophic dogs and maintained in culture. Such cells taken originally from dystrophic dogs were transduced with lentiviruses, which had been engineered to express the human microdystrophin gene. The results, which are well-illustrated, show that it was possible to transplant mesangioblasts into dystrophic dogs, which resulted in, extensive reconstitution of muscle fibres expressing dystrophin with concomitant preservation of physical movement of the dogs. Donor wild-type mesangioblasts appeared more efficient than the autologous genetically corrected cells. They explain this by suggesting that the microdystrophin may only provide a modest functional rescue compared to the complete dystrophin provided by the wild-type cells. This study shows clearly the two possible approaches how stem cells might cure DMD. Either related cells with a wild-type gene are presented to the patient or cells derived from the patient himself are genetically modified to produce dystrophin and then re-introduced into the patient. The main problem in using foreign wild-type cells is their possible if not probable immune rejection, even if they are taken from a close relative. To overcome this experiments were done with mdx mice attempting to systemically insert into foetal mice in the uterus such cells and thereby overcome the immune response (2). Unfortunately while they did establish themselves the total production of dystrophin was only 0.5-1.0%. Even if useful amounts of dystrophin could be produced this technique could only be applied to babies diagnosed before birth.
Thus to use the body’s own stem cells, genetically modified to produce dystrophin would clearly seem the better bet. Here the problems to be overcome are how to introduce the gene into such cells. As the development of such a technique would have many uses apart from treating DMD, much work has been done on this. An example is a recent study in which HUVECs (Human Umbilical Vein Endothelial Cells) were successfully modified by means of introducing into them the gene for VEGF165 , a cytokine (hormone-like substance), using an adenoviral vector carrying the gene for VEGF165 (3).
Assuming the genetically modified myoblasts are available and have been successfully transported to the muscle cells, it is important for them to start differentiating into muscle cells. These cells carry a master gene (MyoD), which produces a master transcription factor that plays an essential role in the muscle stem cell differentiation. In a recent study (4) it was shown that myoblasts from which the MyoD gene had been suppressed were better at preserving their stem cell characteristics, including resistance to apoptosis (programmed cell death), expression of stem cell genes, and ability to contribute to satellite cells after transplantation. These authors suggest that suppression of the MyoD gene in such cells would be beneficial in using such cell therapeutically for muscular dystrophy patients.
To close, a summary of a recent review of on the use of stem cells’ therapeutic potential in muscle diseases, will be presented (5). The authors state that while the muscle satellite cells are the principal muscle stem cells, recent studies have demonstrated that there are other stem cell sources, which on activation can participate in muscle regeneration. These may well have a potential for the treatment of muscular dystrophies. Under normal circumstances the turnover of muscle cells in adults is relatively low, however, after disease or injury regeneration it is rapid and very efficient. Activated satellite cells can produce many muscle cells. It has been estimated that a few satellite cells can regenerate over 100 myofibres, while also maintaining the level of satellite cells.
In the case of DMD, a therapeutic stem cell population, must treat the damaged necrotic muscle fibres as well as produce cells containing sufficient dystrophin to either prevent necrosis from recurring or even more advantageously, to replace the damaged muscle fibres with new dystrophin-containing fibres. They must also be able to replenish themselves with functional stem cells, which act to maintain the new situation.
In their discussion on mode of delivery of such stem cells, they consider systemic delivery superior to intramuscular injection and report that intra-arterial injection is superior to intravenous injection, because this provides widespread distribution through the muscle capillary network. They note that so far only one successful study on delivering intra-arterially muscle precursor cells (MPCs) has been reported and this was in rats. Grafting cells into irradiated mdx mice was a very efficient way of providing effective regenerating satellite cells.
Using synthetic ‘patch’ scaffolds to transplant MPCs especially to such difficult tissues as diaphragm and heart, has shown that the cells maintain their viability for extended periods of time, while also being able to migrate out and populate the surrounding tissue.
They then discuss other possible stem cells and of these muscle-derived stem cells (MDSCs) were initially considered as potential therapeutic agents, especially as they have many valuable properties including being easily expanded in the laboratory, they show a high potential to differentiate and are able to migrate through the vascular system. Unfortunately, there was no improvement when dystrophic mouse muscle was treated with them, thus not making MDSCs suitable candidates to treat DMD.
Another cell type, known as muscle side cells transduced with microdystrophin, when injected into the femoral artery of mdx mice, can engraft into the dystrophic muscle and produce dystrophin but of insufficient amount to be of therapeutic value.
After discussing a number of other studies on various cell types, which have not yet reached the level of the ones discussed above, the authors conclude that: “Encouraging findings suggest that during muscle regeneration many stem cells could be enrolled in the repair process”. They consider that “the satellite cell remains the first protagonist in muscle regeneration”, but that a significant amount of work still needs to be done to achieve a successful therapeutic approach.
References
1. Sampaolesi, M., Blot, S., D’Antona, G., Granger, N., Tonlorenzi, R., Innocenzi, A., Mognol, P., Thibaud, J.-L., Galvez, B.G., Barthélémy, I., Perani, L., Mantero, S., Guttinger, M., Pansarasa, O., Rinaldi, C., Cusella de Angelis, M.G., Torrenre, Y., Bordignon, C., Bottinelli, R. Cossu, G. (2006) Mesagioblast stem cells ameliorate muscle function in dystophic dogs. Nature. 444(7119):574-579.
2. Chan, J., Waddington, S.N., O'Donoghue, K., Kurata, H., Guillot, P.V., Gotherstrom, C., Themis, M., Morgan, J.E. & Fisk, N.M. (2007) Widespread distribution and muscle differentiation of human fetal mesenchymal cells after intrauterine transplantation in dystrophic mdx mouse. Stem Cells 25(4):875-884.
3. Rufaihah, A.J., Haider, H.K., Heng, B.C., Ye, L., Toh, W.S., Tian, X.F., Lu, K., Sim, E.K.W. & Cao, T. (2007) Directing endothelial differentiation of human embryonic stem cells via transduction with an adenoviral vector expressing the VEGF165 gene. Journal of Gene Medicine. 9(6):452-461.
4. Asakura, A., Hirai, H., Kablar, B., Morita, S., Ishibashi, J., Piras, B.A., Christ, A.J., Verma, M., Vineretsky, K.A. & Rudnicki, M.A. (2007) Increased survival of muscle stem cells lacking the MyoD gene after transplantation into regenerating skeletal muscle. Proceedings of the National Academy of Sciences of the United States of America. 104(42):16552-16557.
5. Boldrin, L. & Morgan, J.E. (2007) Activating muscle stem cells: therapeutic potential in muscle diseases. Current Opinion in Neurology. 20(5):577-582.
Karl A. Bettelheim