| Adipose tissue |
MSCs, cultured in specific media formulations, can be induced to form muscle cells. MSCs also display similar potential when introduced in vivo, into injured mouse muscle (135–140). When FLK-1+ MSCs, derived from human adipose tissue, were injected i.m. into a mouse model of muscular dystrophy, a decrease in serum CK was noted, as well as an increase in sarcolemmal dystrophin expression. Of note, no rejection was reported despite the fact that the cells were derived from human tissue (141). Similar experiments were performed earlier (142) which also suggested that MSCs derived from human adipose tissue display immune privilege. |
| Amniotic fluid |
Several investigators (143–146) have used amniotic fluid-derived MSCs for regenerative medicine and cellular therapeutics. Following routine amniocentesis, samples are processed to yield MSCs, which proliferate quickly and have multilineage potential. The ease of collection and the therapeutic applicability of these cells holds clinical promise. |
| Amniotic membranes |
The use of the amniotic membrane in surgery has a long history (147). Various groups (77, 148) have described methods for successful isolation of human amniotic membrane-derived MSCs. The expression of surface markers from cells derived from amniotic membranes likely changes over time similar to the changes observed in amniotic fluid-derived stem cells (149, 150). However, if amniotic membranes are used to obtain MSCs at a given time point, (at term, for example) it is likely that some surface markers are the same as MSCs derived from bone marrow and other tissues. Our group is currently investigating amniotic membrane-derived MSCs in a pre-clinical model of DMD. |
| Bone marrow |
The best defined source of MSCs is the bone marrow, and marrow-derived MSCs are capable of forming muscle cells (151). Bone marrow-derived MSCs are capable of more than 70 population doublings (152) and retain multilineage potential even when expanded in vitro (153). Muscle cells formed from bone marrow-derived MSC have been observed without the use of demethylation reagents (154). Detailed reviews of bone marrow-derived MSCs are available elsewhere (155, 156). |
| Ear |
Ear punches, which are a part of a routine marking procedure of live mice, were shown to contain MSCs with the ability to form muscle cells in vitro (157). Use of these cells in DMD research has not been reported. |
| Fetal blood |
Rapid progress in imaging and thin-guage fetoscopy has allowed the collection of fetal blood. For example, Chan et al (158) collected first trimester fetal blood by ultrasound-guided cardiac aspiration, and exposed cultured MSCs to various media formulations including 5-azacytidine, conditioned media, dexamethasone and hydrocortisone. They observed either massive cell death or a lack of muscle marker expression using these myogenic induction methods. However, when galectin-1 was added to the media, they observed multinucleated myotubes positive for desmin staining. Interestingly, when the human fetal blood-derived MSCs were injected into immunodeficient mouse muscular dystrophy muscles, no spectrin-positive nor desmin-positive cell clusters were observed unless there was galectin-1 pretreatment. Later work by the same laboratory showed that intrauterine transplantation of human fetal blood-derived MSCs into immunocompetent mdx mice lead to widespread engraftment, although the levels of engraftment were low (159). |
| Skeletal muscle blood vessels |
Perivascular stem cells (pericytes) can be isolated from skeletal muscle biopsies from both healthy individuals and DMD patients (160). Because MSCs are found throughout the body, it is thought that MSCs are derived from perivascular stem cells associated with blood vessels. Regardless of the donor population, pericytes have an anatomical niche distinct from satellite cells. Satellite cells reside inside the basal lamina of muscle cells, while pericytes are located underneath the basal lamina of small vessels. Intra-arterial delivery of a type of perivascular stem cell, known as a meso-angioblast, was shown to ameliorate severe muscle pathology observed in the dystrophin-deficient GRMD dog (21). This exciting discovery may represent one of the most significant breakthroughs in DMD cell-based research yet reported. |
| Synovial membranes |
Early work determined that MSCs can be isolated from human synovial membranes, and that these cells were expandable while maintaining pluripotency in culture (161). Human synovial membrane MSCs (hSM-MSCs) injected into skeletal muscle of nude mice or immunosuppressed muscular dystrophy mice, the injected cells engrafted into the satellite cell niche (160). Additionally, hSM-MSC homed to cardiotoxin-injured muscle when injected into blood vessels. When administered intramuscularly to immunosuppressed muscular dystrophy mice, transplanted cells restored human dystrophin expression, and reduced the amount of immature muscle fibers. Finally, hSM-MSC partially rescued expression of mechano growth factor (MGF) in the muscular dystrophy mouse, providing some explanation for the amelioration of dystrophic muscle pathology. |
