Role of long-chain acyl-CoA synthetase 4 in formation of polyunsaturated lipid species in hepatic stellate cells

Hepatic stellate cell (HSC) activation is a critical step in the development of chronic liver disease. We previously observed that the levels of triacylglycerol (TAG) species containing long polyunsaturated fatty acids (PUFAs) are increased in in vitro activated HSCs. Here we investigated the cause and consequences of the rise in PUFA-TAGs by profiling enzymes involved in PUFA incorporation. We report that acyl CoA synthetase (ACSL) type 4, which has a preference for PUFAs, is the only upregulated ACSL family member in activated HSCs. Inhibition of the activity of ACSL4 by siRNA-mediated knockdown or addition of rosiglitazone specifically inhibited the incorporation of deuterated arachidonic acid (AA-d8) into TAG in HSCs. In agreement with this, ACSL4 was found to be partially localized around lipid droplets (LDs) in HSCs. Inhibition of ACSL4 also prevented the large increase in PUFA-TAGs in HSCs upon activation and to a lesser extent the increase of arachidonate-containing phosphatidylcholine species. Inhibition of ACSL4 by rosiglitazone was associated with an inhibition of HSC activation and prostaglandin secretion. Our combined data show that upregulation of ACSL4 is responsible for the increase in PUFA-TAG species during activation of HSCs, which may serve to protect cells against a shortage of PUFAs required for eicosanoid secretion.