The blockade of lipophagy pathway is necessary for docosahexaenoic acid to regulate lipid droplet turnover in hepatic stellate cells

Abstract

Hepatic stellate cell (HSC) activation is treated as a dominator segment in hepatic fibrosis, which is accompanied by significant loss of lipid droplets (LDs). However, the regulatory network of LD disappearance is still unclear. It has been reported that lipophagy activation contributed to LD loss by upregulating RAB25 expression. In the present study, we sought to determine the regulation of docosahexaenoic acid (DHA) on LD disappearance, and to further examine potential molecular mechanisms. Interestingly, DHA treatment completely impaired LD disappearance during HSC activation. Moreover, treatment with DHA evidently promoted LD regeneration in activated HSCs that displayed matrix-producing myofibroblasts. Attractively, DHA-induced LD regeneration was coupled with the inhibition of lipophagy signaling. DHA treatment increased autophagosome generation and autophagic flux, but inhibited the target recognition of lipophagy for LDs by inhibiting RAB25 expression. Importantly, up-regulation of RAB25 expression, using RAB25 plasmid, completely blocked DHA-induced LD regeneration in activated HSCs. Noteworthy, treatment of DHA prominently alleviated murine liver fibrosis by reversing HSC lipocyte phenotype. HSC-specific overexpression of RAB25 impaired DHA-induced LD regeneration of activated HSCs, and in turn abolished anti-hepatic fibrosis effect of DHA in murine liver fibrosis. Overall, these results showed that DHA induced LD regeneration by inhibiting lipophagy signaling in activated HSCs, and also identified RAB25 dependent lipophagy as an important target for the prevention of hepatic fibrosis.

Keywords: Docosahexaenoic acid; Hepatic stellate cell; Lipid droplet; Lipophagy; RAB25.