Defective autophagosome trafficking contributes to impaired autophagic flux in coronary arterial myocytes lacking CD38 gene

Abstract

Autophagic flux is an important process during autophagy maturation in smooth muscle cells. However, the molecular mechanisms underlying autophagic flux in these cells are largely unknown. Here, we revealed a previously undefined role of CD38, an enzyme that metabolizes NADP(+) into NAADP, in the regulation of autophagic flux in coronary arterial myocytes (CAMs). In vivo CD38 gene knockout mice (CD38(-/-)) fed the high-fat Western diet showed increased accumulation of autophagosomes in coronary arterial media compared with that in wild-type (CD38(+/+)) mice, suggesting that CD38 gene deletion results in a defective autophagic process in CAMs of coronary arteries. In primary cultured CAMs, CD38 gene deletion markedly enhanced 7-ketocholesterol (7-Ket, an atherogenic stimulus and autophagy inducer)-induced accumulation of autophagosomes and increased expression of an autophagic marker, LC3B. However, no difference in autophagosome formation was observed between CD38(+/+) and CD38(-/-) CAMs when autophagic flux was blocked, which indicates that CD38 regulates autophagic flux rather than induction of autophagosome formation. Further, 7-Ket-induced formation of autophagolysosomes was markedly attenuated in CD38(-/-) CAMs compared with CD38(+/+) CAMs. Mechanistically, CD38 gene deletion markedly inhibited 7-Ket-induced dynein activation and autophagosome trafficking, which were associated with attenuated lysosomal Ca(2+) release. Importantly, coronary arterial smooth muscle from CD38(-/-) mice fed the Western diet exhibited phenotypic changes towards a more dedifferentiated state with abnormal extracellular matrix metabolism. Taken together, these results suggest that CD38 plays a critical role in autophagosome trafficking and fusion with lysosomes, thus controlling autophagic flux in CAMs under atherogenic stimulation.