Epidermis-Type Lipoxygenase 3 Regulates Adipocyte Differentiation and Peroxisome Proliferator-Activated Receptor γ Activity

Abstract

The nuclear receptor peroxisome proliferator-activated receptor ␥ (PPAR␥) is essential for adipogenesis. Although several fatty acids and their derivatives are known to bind and activate PPAR␥, the nature of the endogenous ligand(s) promoting the early stages of adipocyte differentiation has remained enigmatic. Previously, we showed that lipoxygenase (LOX) activity is involved in activation of PPAR␥ during the early stages of adipocyte differentiation. Of the seven known murine LOXs, only the unconventional LOX epidermis-type lipoxygenase 3 (eLOX3) is expressed in 3T3-L1 preadipocytes. Here, we show that forced expression of eLOX3 or addition of eLOX3 products stimulated adipogenesis under conditions that normally require an exogenous PPAR␥ ligand for differentiation. Hepoxilins, a group of oxidized arachidonic acid derivatives produced by eLOX3, bound to and activated PPAR␥. Production of hepoxilins was increased transiently during the initial stages of adipogenesis. Furthermore, small interfering RNA-mediated or retroviral short hairpin RNA-mediated knockdown of eLOX3 expression abolished differentiation of 3T3-L1 preadipocytes. Finally, we demonstrate that xanthine oxidoreductase (XOR) and eLOX3 synergistically enhanced PPAR␥-mediated transactivation. Collectively, our results indicate that hepoxilins produced by the concerted action of XOR and eLOX3 may function as PPAR␥ activators capable of promoting the early PPAR␥-dependent steps in the conversion of preadipocytes into adipocytes.

PPARγ ligand production is tightly linked to clonal expansion during initiation of adipocyte differentiation

“…eLOX3 converts the peroxidized lipids into hepoxilin-like products that function as endogenous PPAR ␥ agonists during adipose conversion ( 35 ). The dependency on eLOX3 in PPAR ␥ ligand production is consistent with the observation that a lipoxygenase inhibitor, baicalein, decreases PPAR ␥ ligand generation ( 8 ).…”

“…The generation of hepoxilins during adipogenesis is likely to rely on a reactive oxygen species (ROS)-mediated conversion of arachidonic acid or structurally similar PUFAs into substrates for the unconventional lipoxygenase, epidermal type-3 lipoxygenase (eLOX3) ( 35 ). The source of these PUFAs was, however, not determined.…”

Effects of arachidonic acid on the concentration of hydroxyeicosatetraenoic acids in culture media of mesenchymal stromal cells differentiating into adipocytes or osteoblasts

“…Thus, adipogenesis is inhibited in such cells when they are treated with the nordihydroguaiaretic acid (NDGA) and baicalein (BC) lipoxygenase inhibitors during the first four days of differentiation induction (Madsen et al 2003). More recently, it has been demonstrated that hepoxilins, which are produced by the eLOX2 lipoxygenase activity, activate PPARc and adipogenesis in the 3T3-L1 cells (Hallenborg et al 2010). Additionally, other compounds produced by lipoxygenases, such as the leukotriene B4 (LTB4), which is generated by the 5-LOX enzyme, are an adipogenesis inhibitor via binding to its receptor (BLT) (Hirata et al 2012).…”

The PPAR-RXR Transcriptional Complex in the Vasculature

“…27,29 PPAR␥ regulates expression of multiple genes involved in redox balance 24,161,162 ; certain oxidizing enzymes may also activate PPAR␥ and promote adipogenesis. 163,164 Endothelial PPAR␥ is involved in blood pressure regulation, including the possibility that certain angiotensin receptor blockers may activate PPAR␥. 20,165 PPAR␦ limits endothelial inflammation, is activated by COX2 metabolism of endocannabinoids, and may play a part in reducing endothelial glucose uptake.…”