Resolvin D5: A lipid mediator with a therapeutic effect on hepatic steatosis through SIRT6/autophagy

Resolvin D5 (RD5), a lipid mediator derived from DHA via 5-lipoxygenase signaling, has been shown to resolve inflammation in various disease models. This study aimed to investigate the role of RD5 in the development of hepatic steatosis in individuals with obesity and explore the detailed mechanisms involved. Protein expression was evaluated via Western blot analysis, whereas hepatic lipid deposition was examined via Oil Red O staining and triglyceride quantification. Autophagosomes were detected via MDC staining. Our findings indicated that RD5 treatment normalized lipogenic lipid accumulation, fatty acid uptake, oxidation, apoptosis, and endoplasmic reticulum (ER) stress in palmitate-treated primary hepatocytes. As a cytoprotective signaling pathway, RD5 treatment increased the expression of SIRT6 and autophagy markers, such as those involved in LC3 conversion and p62 degradation. The beneficial effects of RD5 on hepatic lipid metabolism, apoptosis, and ER stress were negated by SIRT6 small interfering RNA or 3-methyladenine, an inhibitor of autophagy. Furthermore, RD5 administration decreased hepatic steatosis, apoptosis, and ER stress in the livers of high-fat diet (HFD)-fed mice. In line with the in vitro results, RD5 treatment elevated SIRT6 and autophagy levels in the livers of HFD-fed mice. These novel findings suggest that RD5 improves hepatic lipid metabolism, apoptosis and ER stress through SIRT6/autophagy signaling, thereby attenuating hepatic steatosis. RD5 may have therapeutic potential for treating nonalcoholic fatty liver disease with minimal side effects.