Muscle-derived stem cells: Implications for effective myoblast transfer therapy

Myogenic precursor cells in craniofacial muscles

Craniofacial skeletal muscles (CskM), including the masticatory (MM), extraocular (EOM) and laryngeal muscles (LM), have a number of properties that set them apart from the majority of skeletal muscles (SkM). They have embryological origins that are distinct from musculature elsewhere in the body, they express a number of immature myosin heavy chain isoforms and maintain increased and distinct expression of a number of myogenic growth factors and their receptors from other adult SkMs. Furthermore, it has recently been demonstrated that unlike limb SkM, normal adult EOM and LM retain a population of activated satellite cells, the regenerative cell in adult SkM. In order to maintain this proliferative pool throughout life, CSkM may contain more satellite cells and/or more multipotent precursor cells that may be more resistant to apoptosis than those found in limb muscle. A further exciting question is whether this potentially more active muscle precursor cell population could be utilized not only for SkM repair, but be harnessed for repair or reconstruction of other tissues, such as nervous tissue or bone. This is a highly attractive speculation as the innate regenerative capacity of craniofacial muscles would ensure the donor tissue would not have compromised future function.

Autologous Transplantation of Muscle Precursor Cells Modified with a Lentivirus for Muscular Dystrophy: Human Cells and Primate Models

Duchenne muscular dystrophy (DMD) is characterized by the absence of dystrophin. We tested the ability of lentiviral vectors to deliver a transgene into myogenic cells before their transplantation. Enhanced green fluorescent protein (eGFP) transgene was efficiently transferred into cells and eGFP-positive fibers were generated following transplantation. An eGFP-micro-dystrophin transgene under the control of a cytomegalovirus promoter was then transferred with the same viral vector but caused some toxicity to the mono-nucleated cells. We then used instead a muscle creatine kinase promoter. Dystrophin expression was observed in the muscle fibers after the transplantation of such genetically modified cells into mdx and severe combined immunodeficient mice. Micro-dystrophin expression was also observed in monkey muscles a month after allogenic or autologous transplantation of genetically modified myoblasts. Therapeutic exon skipping was induced by infecting myoblasts of a DMD patient, deleted for dystrophin exons 49 and 50, with a lentivirus expressing a U7 small nuclear RNA containing antisense sequences against exon 51. The modification led to correct exon skipping and to the expression of a quasi-dystrophin in vitro and in vivo. These results demonstrate the feasibility of lentiviral-based ex vivo gene therapy for DMD.

Treating muscular dystrophy with stem cells?

There is currently no effective treatment for the devastating muscle-wasting disease Duchenne muscular dystrophy (DMD). Cossu and colleagues report in a recent Nature paper that transplantation of mesoangioblast stem cells may hold promise for treating DMD. Further studies are required to fully evaluate the clinical potential of these blood-vessel-associated stem cells.