O03 In vivo gene therapy for striated muscle laminopathy

LMNA mutations induce a group of disorders called laminopathies, mainly affecting striated muscles. In the case of LMNA-related Congenital Muscular Dystrophy (L-CMD), it is the most severe form of striated muscle laminopathy with cardiomyopathy. We previously reported the phenotype of KI- LmnadelK32 mouse model mimicking a human LMNA mutation. This mouse model developed L-CMD phenotype at the homozygous state and isolated dilated cardiomyopathy at the heterozygous state. Taking the advantage of our mouse model, we have previously shown that the pathomechanism of the diseases involves both the expression of toxic mutant lamin A/C and lamin A/C decreased expression. Based on these pathophysiological observations, we aim at assessing a therapeutic approach that both reduces the expression of the mutant protein and restores the normal lamin A/C level. We produced AAV2/9 vectors containing human mature lamin A under control of a CMV promoter, either alone, or in combination with shRNA specifically targeting p.K32del Lmna mRNA or WT and mutated allele under a H1 promoter. Systemic administration in homozygous new-born mice resulted in a significant increase of their maximal survival after treatment, and important increase of lamin A/C protein level, reaching or overpassing lamin A/C level observed in wild type hearts. By contrast, despite an increased expression of human lamin A mRNA and protein in heterozygous mouse hearts, we did not observe any improvement in terms of survival or cardiac function after treatment. The absence of therapeutic benefit at long term is neither due to a loss of AAV genome particle nor to a loss of its expression with time. Rather, it is due to the absence of mouse Lmna mRNA knock-down and side effect in the liver strongly targeted by AAV2/9. Further development of our gene therapy will include new design, new promoters and AAV capsids to increase mouse Lmna mRNA knock-down and tissue specificity.