ABHD4 regulates adipocyte differentiation in vitro but does not affect adipose tissue lipid metabolism in mice

Abstract

Alpha/beta hydrolase domain-containing protein 4 (ABHD4) catalyzes the deacylation of N-acyl phosphatidyl-ethanolamine (NAPE) and Lyso-NAPE to produce Glycerophospho-N-acyl ethanolamine (GP-NAE). Through a variety of metabolic enzymes, NAPE, Lyso-NAPE, and GP-NAE are ultimately converted into NAE, a group of bioactive lipids that control many physiological processes including inflammation, cognition, and food intake (i.e., oleoylethanolamide or OEA). In a diet-induced obese mouse model, adipose ABHD4 gene expression positively correlated with adiposity. However, it is unknown whether ABHD4 is a causal or a reactive gene to obesity. To fill this knowledge gap, we generated an ABHD4 knockout (KO) 3T3-L1 pre-adipocyte. During adipogenic stimulation, ABHD4 KO pre-adipocytes had increased adipogenesis and lipid accumulation, suggesting ABHD4 is responding to (a reactive gene), not contributing to (not a causal gene), adiposity and may serve as a mechanism for protecting against obesity. However, we did not observe any differences in adiposity and metabolic outcomes between adipocyte specific ABHD4 KO mice or whole body ABHD4 KO mice and their littermate control mice on chow or a high fat diet. This might be because we found that deletion of ABHD4 did not affect NAE such as OEA production, even though ABHD4 was highly expressed in adipose tissue and correlated with fasting adipose OEA levels and lipolysis. These data suggest that ABHD4 plays a role in adipocyte differentiation in vitro but not in adipose tissue lipid metabolism in mice despite nutrient overload, possibly due to compensation from other NAPE and NAE metabolic enzymes.