t-AUCB, a Pharmacological Inhibitor of Soluble Epoxide Hydrolase, Promotes Brown Adipogenesis:
Role of PPAR alpha and PPAR gamma

Brown adipose tissue (BAT) has recently emerged as a novel target for obesity treatment and prevention. In contrast to the lipid storing function of white adipocytes, brown adipocytes are responsible for dissipating energy as heat, a process involving uncoupling protein 1 (UCP1). Soluble epoxide hydrolase (sEH) is a cytosolic enzyme that converts epoxy fatty acids (EpFAs) into less active diols. By stabilizing endogenous EpFAs, potent small molecule sEH inhibitors have been shown to be beneficial for many diseases. Several recent studies have reported that sEH inhibitors can improve diet-induced metabolic disorders, possibly by upregulating UCP1 expression. In the current study, we sought to investigate the mechanisms by which the sEH inhibition affects brown adipocytes using trans-4-[4-(3-adamantan-1-yl-ureido)-cyclohexyloxy]-benzoic acid (t-AUCB). The effects of t-AUCB on murine brown adipocyte differentiation were evaluated by lipid accumulation and expression of brown adipocyte marker genes. PPARα[alpha] and PPARγ[gamma] activation by t-AUCB was measured by their respective transactivation assays. The roles of PPARs were further studied by pharmacological antagonism and knockdown experiments. Finally, the mechanisms of t-AUCB were explored in BAT derived sEH wildtype (WT) and knockout (KO) stromal cells. We report that sEH expression was increased during murine brown adipocyte differentiation. t-AUCB dose-dependently promoted brown adipocyte differentiation. Moreover, we demonstrate that t-AUCB activated PPARα[alpha], but not PPARγ[gamma]. t-AUCB-induced upregulation of thermogenic genes Ucp1, Pgc-1a, and Cidea and the general differentiation marker Fabp4 was significantly attenuated by the antagonist of PPARα[alpha], GW6471 and specific knockdown of Pparα. In contrast, upregulation was only partially attenuated by the antagonist of PPARγ[gamma], GW9662, and specific knockdown of Pparg. We also show that t-AUCB activation of PPARα[alpha] occurs regardless of sEH presence. Our findings suggest that PPARα[alpha], more so than PPARγ[gamma], plays an important role in t-AUCB’s effects on brown adipogenesis and that these effects may be independent of sEH.