Regulation of dynein-mediated autophagosomes trafficking by ASM in CASMCs

Acid sphingomyelinase (ASM; gene symbol Smpd1) has been shown to play a crucial role in autophagy maturation by controlling lysosomal fusion with autophagosomes in coronary arterial smooth muscle cells (CASMCs). However, the underlying molecular mechanism by which ASM controls autophagolysosomal fusion remains unknown. In primary cultured CASMCs, lysosomal Ca²⁺ induced by 7-ketocholesterol (7-Ket, an atherogenic stimulus and autophagy inducer) was markedly attenuated by ASM deficiency or TRPML1 gene silencing suggesting that ASM signaling is required for TRPML1 channel activity and subsequent lysosomal Ca²⁺ release. In these CASMCs, ASM deficiency or TRPML1 gene silencing markedly inhibited 7-Ket-induced dynein activation. In addition, 7-Ket-induced autophagosome trafficking, an event associated with lysosomal Ca²⁺ release and dynein activity, was significantly inhibited in ASM-deficient (Smpd1^-/-) CASMCs compared to that in Smpd1^+/+ CASMCs. Finally, overexpression of TRPML1 proteins restored 7-Ket-induced lysosomal Ca²⁺ release and autophagosome trafficking in Smpd1^-/- CASMCs. Collectively, these results suggest that ASM plays a critical role in regulating lysosomal TRPML1-Ca²⁺ signaling and subsequent dynein-mediated autophagosome trafficking, which leads its role in controlling autophagy maturation in CASMCs under atherogenic stimulation.