Muscle derived stem cells are superior to other primary muscle derived Cells for use as a cellular vehicle for BMP4-based ex vivo gene therapy to heal full-thickness osteo-chondral defects.
Treatment of articular cartilage (AC) injuries remains a clinical challenge due to inability of cartilage to spontaneously heal. Tissue engineering based on cell-mediated gene therapy is a promising new approach to repair AC injuries due to the dual supplementation of chondrogenic progenitor cells and growth factors. Muscle tissue represents an abundant, accessible, and renewable source of adult stem cells, and several populations of osteochondral progenitor cells have been identified and isolated from muscle tissue. The purpose of this study was to assess the chondrogenic potential of bone morphogenetic protein 4 (BMP4)-gene modified subpopulations of muscle derived cells (MDCs) with the intention to identify the cell population that is optimal for muscle cell based gene therapy for AC repair.
Three populations of MDCs (fibroblasts, myoblasts, and muscle derived stem cells-MDSCs) were isolated from the hind-limb skeletal muscles of three 3-week-old C57/BL10J mice by using a modified pre-plate technique. Retroviral vectors encoding for BMP4 and GFP (retroBMP4-GFP) were used for the transduction of the subpopulations of the MDCs. After purifying for GFP positive cells, the proliferation capacity, cell survival rate under oxidative stress, and chondrogenic differentiation abilities of BMP4-transduced MDCs were determined in vitro. Their cartilage formation abilities were evaluated on a rat full-thickness osteo-chondral defect model.
All MDC subpopulations revealed over 80% transduction rate. Fibroblasts proliferated significantly slower than the myoblasts and MDSCs; the fibroblasts and MDSCs showed a superior rate of survival compared to the myoblasts under oxidative stress induced by H2O2; and the MDSCs showed significantly superior chondrogenic capabilities than PP1 and PP3 cells in terms of the expression of chondrogenic markers under chondrogenic induction. In vivo, macroscopic examination revealed that MDSCs were well integrated and had glossy-white appearance in the AC defect, while fibroblasts and myoblasts did not integrate well. Histologic evaluation revealed that regenerated tissue appeared fibrotic for the fibroblasts and myoblasts groups, whereas MDSCs groups showed regeneration of chondrocytic tissue. In vivo survival of MDCs at 4 weeks for the fibroblasts, myoblasts, and MDSCs groups was quantified at 21.13%, 55.57% and 89.37%, respectively. At 8 weeks, survival rates were 1.22%, 13.34%, and 52.9%, respectively.
MDSCs are superior to other primary MDCs for use as a cellular vehicle for BMP4-based ex vivo gene therapy to heal full-thickness osteo-chondral defects. The superiority of the MDSCs appears to be attributable to a combination of an increased rate of in vivo survival and superior chondrogenic differentiation capacity.
Establishing the superior MDC sets the foundation for future studies, in which MDSCs can be examine relative to the stem-cells derived from other tissue origins such as adipose and bone marrow to provide optimal translational treatment options.