Objective—In our previous studies that examined in vivo activities of oncostatin M (OM) in upregulation of hepatic LDL receptor (LDLR) expression, we observed reductions of LDL-cholesterol and triglyceride (TG) levels in OM-treated hyperlipidemic hamsters. Interestingly, the OM effect of lowering plasma TG was more pronounced than LDL-cholesterol reduction, suggesting additional LDLR-independent actions. Here, we investigated mechanisms underlying the direct TG-lowering effect of OM.

Methods and Results—We demonstrate that OM activates transcription of long-chain acyl-coenzymeA (CoA) synthetase isoforms 3 and 5 (ACSL3, ACSL5) in HepG2 cells through the extracellular signal-regulated kinase (ERK) signaling pathway. Increased acyl-CoA synthetase activities in OM-stimulated HepG2 cells and in livers of OM-treated hamsters are associated with decreased TG accumulation and increased fatty acid -oxidation. We further show that overexpression of ACSL3 or ACSL5 alone in the absence of OM led to fatty acid partitioning into -oxidation. Importantly, we demonstrate that transfection of siRNAs targeted to ACSL3 and ACSL5 abrogated the enhancing effect of OM on fatty acid oxidation in HepG2 cells.

Conclusions—These new findings identify ACSL3 and ACSL5 as OM-regulated genes that function in fatty acid metabolism and suggest a novel cellular mechanism by which OM directly lowers the plasma TG in hyperlipidemic animals through stimulating the transcription of ACSL specific isoforms in the liver.