DHPR α1S subunit controls skeletal muscle mass and morphogenesis
Résumé
The α1S subunit has a dual function in skeletal muscle: it forms the L-type Ca2+ channel in T-tubules and is the voltage sensor of excitation-contraction coupling at the level of triads. It has been proposed that L-type Ca2+ channels might also be voltage-gated sensors linked to transcriptional activity controlling differentiation. By using the U7-exon skipping strategy, we have achieved long-lasting downregulation of α1S in adult skeletal muscle. Treated muscles underwent massive atrophy while still displaying significant amounts of α1S in the tubular system and being not paralysed. This atrophy implicated the autophagy pathway, which was triggered by neuronal nitric oxide synthase redistribution, activation of FoxO3A, upregulation of autophagy-related genes and autophagosome formation. Subcellular investigations showed that this atrophy was correlated with the disappearance of a minor fraction of α1S located throughout the sarcolemma. Our results reveal for the first time that this sarcolemmal fraction could have a role in a signalling pathway determining muscle anabolic or catabolic state and might act as a molecular sensor of muscle activity.