Elevated MTORC1 signaling and impaired autophagy.

A-type lamins, generated from the LMNA gene by differential splicing, are type V intermediate filament proteins that polymerize to form part of the nuclear lamina, and are of considerable medical interest because missense mutations in LMNA give rise to a wide range of dystrophic and progeroid syndromes. Among these are dilated cardiomyopathy and two forms of muscular dystrophy (limb-girdle and Emery-Dreifuss), which are modeled in lmna (-/-) mice and mice engineered to express human disease mutations. Our recent study demonstrates that cardiac and skeletal muscle pathology in lmna (-/-) mice can be attributed to elevated MTORC1 signaling leading to impairment of autophagic flux. An accompanying paper from another laboratory shows similar impairments in mice engineered to express the LMNA H222P associated with dilated cardiomyopathy in humans and also in left ventricular tissue from human subjects. MTORC1 inhibition with rapalogs restores autophagic flux and improves cardiac function in both mouse models, and extends survival in the lmna (-/-) mice. These findings elaborate a potential treatment option for dilated cardiomyopathy and muscular dystrophy associated with LMNA mutation and supplement growing evidence linking impaired autophagy to human disease.