Live Cell Imaging
Muscle derived stem cells (MDSCs) for skeletal muscle repair:
One disease for which stem cell therapy holds promise is Duchenne muscular dystrophy (DMD). DMD is a muscle disease characterized by severe and progressive muscle weakness due to the lack of dystrophin protein expression at the sarcolemma of muscle fibers. Onset occurs early in childhood (between 2 and 6 years of age), and survival beyond 30 years of age is rare. The lack of dystrophin in the muscle disrupts the structural connection between the cytoskeleton and the extracellular matrix, resulting in muscle fiber necrosis and weakness. Effective treatment of DMD will require replacing the missing dystrophin protein. Because of the natural tendency of muscle progenitor cells to fuse with existing or newly forming muscle fiber cells, cell transplantation-based approaches to DMD treatment are very promising. Indeed, research has shown that allogeneic muscle progenitor cells (such as myoblasts) can fuse with host cells after transplantation into injured or diseased tissue in which the host cells are undergoing regeneration (e.g., in dystrophic tissue). Although the transplantation of normal myoblasts into dystrophin-deficient muscle can restore dystrophin expression, the use of less-committed stem cells can improve the efficiency of this approach. Specifically, the use of mouse muscle-derived stem cells (mMDSCs), which have unique properties, has enhanced the success of cell transplantation in mdx mice, which model DMD.
We have recently observed a high degree of variability in the ability of different populations of MDSCs to regenerate skeletal muscle. While investigating MDSC population heterogeneity and characteristics that define efficient in vivo skeletal muscle regeneration, we have found that cell sex, a rarely considered variable, has a significant effect on in vivo outcome. Compared with transplantation of male MDSCs (M-MDSCs), transplantation of female MDSCs (F-MDSCs) leads to significantly more regeneration of the diseased skeletal muscle of mdx mice, which model Duchenne muscular dystrophy. We are currently investigating the mechanism of sex-related differences in skeletal muscle regeneration.
The role of vascular endothelial growth factor (VEGF):
Regenerative therapies for skeletal muscle injuries and disorders need to consider the re-vascularization of the tissue as well as myofiber regeneration. The use of the angiogenic factor, vascular endothelial growth factor (VEGF), in gene therapy or VEGF-expressing cells in cell therapy has shown promise in a number of studies which demonstrate a role for VEGF in skin, bone, liver, and cardiac and skeletal muscle tissue regeneration. The glycoprotein VEGF is a known mitogen for vascular endothelial cells. It has been shown that VEGF can promote both myogenesis and vascularization in a number of skeletal muscle injuries; however, the role of VEGF in the myofiber regeneration of dystrophic muscle has not been investigated. In these projects we investigate the possibility that over-expression of VEGF by MDSCs may lead to an additional improvement in skeletal muscle regeneration in the muscular dystrophy model. To address these questions, we are using an ex vivo gene therapy approach based on muscle-derived stem cells (MDSCs) that have been genetically engineered to express either human VEGF165, or the VEGF antagonist soluble Flt1 (sFlt1).