Expansion of the replicative lifespan of human muscle cells by retroviral transduction of the catalytic telomerase subunit gene
Duchenne Muscular Dystrophy (DMD) is a genetic disorder which is caused by mutations in the dystrophin gene. One of the functions of this protein is to anchor the cell membrane to the sacrolemma. In DMD, the absence of this protein leads to muscle damage during contractions, resulting in continuous regeneration and repair of the muscle until the replicative ability of the muscle is exhausted. There have been many attempts to cure this disorder including the strategy of gene and cell therapy. Although these approaches have had some success in animal models there has been no improvement in human trials. At present the treatment of DMD consists of steroid therapy and supportive treatment. The aim of my work was to test the hypothesis that the transduction of telomerase in to muscle cells could produce a non transformed muscle cells with unlimited growth potential that could in principal, could serve as a target cell population for human dystrophin gene therapy. The expression of the catalytic subunit of telomerase (hTERT) has been successfully used to extend the lifespan of a number of different cell types without malignant transformation. However previous attempts to immortalise muscle cells in this manner had failed. Here I report the successful immortalisation of normal human skeletal muscle cells by retroviral infection of hTERT. The telomerase positive cells display an extended lifespan, with 4/5 clones exceeding 120 MPD. The clones show no feature of transformation in vitro, retain a stable diploid karyotype, have wild type unmethylated CDKN2A genes and do not express muscle specific markers desmin and spectrin. In vitro, they can repair and reconstitute muscle in immunosuppressed RAG-1 mice. These results suggest that telomerase expression can extend lifespan of human muscle cells and could aid attempts at gene therapy for muscle diseases.