Early Expression of CACNA2D1 in Satellite Cells Promotes Myogenicity and Repair of Dystrophic Muscle

The profound and progressive muscle degeneration of Duchenne Muscular Dystrophy (DMD) arises from a lack of the protein dystrophin. Muscle resident myogenic cells are activated upon injury to re-build damaged muscle. Replacement of muscle resident myogenic cells from dystrophic muscle with myogenic satellite cells that are capable of expressing dystrophin could potentially lead to the generation of a muscle that is not predisposed to progressive muscle damage characteristic of DMD. Previous trials of myoblast transfer show that these efforts are limited by the lack of capability of the donor cells to attach and migrate into host muscle. It has been demonstrated that the surface protein α2δ1 aids in the attachment and migration of satellite cell-like cells in vitro. We hypothesize that satellite cells that express α2δ1 will be more efficacious for use in satellite cell grafts into dystrophic muscle than cells without this surface protein. In these experiments, four populations of satellite cells are created based on the presence or absence of α2δ1 and CD34, a marker of primitive satellite cells. The separation of cells is performed by fluorescence activated cell sorting (FACS). We show that early expression of α2δ1 marks a population of satellite cells that elongate earlier than cells that do not express α2δ1, and that cells that express α2δ1 but not CD34 continue to elongate throughout the first week. Cells with α2δ1 express more myogenin than MyoD, consistent with a population of cells that are more advanced in the process of differentiation. We find that α2δ1 is expressed in over 50% of freshly isolated satellite cells. Next, we examine the differences in the ability of these cells to regenerate muscle in vivo. Satellite cells with and without α2δ1 are injected into the tibialis anterior of dystrophic mice. Muscles that are treated with cells that express α2δ1 are larger (p<0.05)), stronger (p<0.001), and contract and relax at a faster rate (p<0.001) than the contralateral muscle treated with vehicle only. Muscles that are treated with cells without α2δ1 exhibit a greater relaxation rate (p<0.002), but there are no differences in mass, force, or force generation rate of muscles treated with cells without α2δ1 compared to the contralateral muscle treated with vehicle only. Demonstration that cells with α2δ1 behave differently both in vitro and in vivo warrants further study of the mechanism of action. The demonstration of functional improvement upon treatment with cells that express α2δ1 is useful in the development of ideal cell population for graft into dystrophic muscles.