Lysosomal two-pore channel subtype 2 (TPC2) regulates skeletal muscle autophagic signaling [Signal Transduction]

December 5th, 2014 by Lin, P.-H., Duann, P., Komazaki, S., Park, K. H., Li, H., Sun, M., Sermersheim, M., Gumpper, K., Parrington, J., Galione, A., Evans, A. M., Zhu, M. X., Ma, J.

Postnatal skeletal muscle mass is regulated by the balance between anabolic protein synthesis and catabolic protein degradation, and muscle atrophy occurs when protein homeostasis is disrupted. Autophagy has emerged as critical in clearing dysfunctional organelles and thus in regulating protein turnover. Here we show that endolysosomal TPC2 contributes to autophagy signaling and protein homeostasis in skeletal muscle. Muscles derived from Tpcn2-/- mice exhibit an atrophic phenotype with exacerbated autophagy under starvation. Compared to wild types, animals lacking TPC2 demonstrated an enhanced autophagy flux characterized by increased accumulation of autophagosomes upon combined stress induction by starvation and colchicine treatment. In addition, deletion of TPC2 in muscle caused aberrant lysosomal pH homeostasis and reduced lysosomal protease activity. Association between mammalian target of rapamycin (mTOR) and TPC2 was detected in skeletal muscle, which allows for appropriate adjustments to cellular metabolic states and subsequent execution of autophagy. TPC2 therefore impacts mTOR reactivation during the process of autophagy and contributes to maintenance of muscle homeostasis.