Myeloperoxidase and Inflammation of the Adipose Tissue in Obesity. Adipokine Deregulation

SANDRA E. GOMEZ-MEJIBA; ZILI ZHAI; DARIO C. RAMIREZ

VENTURA, CA

Conferencia; Gordon Research Conference- Oxidative stress and diseases; 2011

MYELOPEROXIDASE AND OXIDATION OF ADIPOSE TISSUE IN OBESITY Sandra E. Gomez-Mejiba, Zili Zhai,  and Dario C. Ramirez Oxidative stress of the fat tissue is known to contribute to low-grade chronic systemic inflammation in obesity that leads to type-2 diabetes. Macrophages that infiltrate the adipose tissue are thought to be the leading cause of this oxidation; however, the agents, targets and mechanistic bases of the oxidation process that occurs in fat during obesity remain unclear. Adipocytes secrete both pro- (leptin) and anti-(adiponectin) inflammatory adipokines. In addition, macrophages that infiltrate lipid-rich and hypoxic tissue environments, and perhaps the fat tissue, express myeloperoxidase (MPO). In this study we sought to determine whether oxidation promoted by HOCl produced inside adipocytes by MPO causes fat tissue oxidation. We used a mouse model fed a low-fat (LFD, 10% calories from fat) or high-fat (HDF, 60% calories from fat) diet for 20 weeks. The visceral fat of HFD-fed animals showed extensive infiltration by macrophages that express MPO, located in crown-like structures in hypoxic areas (PIMO staining). Immuno-staining showed MPO inside the adipocytes, especially around the lipid droplets. Based on these findings we hypothesized that oxidation promoted by MPO inside adipocytes causes a switch in adipokine secretion towards inflammation, i.e., less adiponectin and more leptin. To test this hypothesis we used a human adipocyte cell line loaded with native or inactivated highly purified native human MPO and stressed the cell with a continuous flow of H2O2. In cells loaded with active MPO and stressed with H2O2, after 24 h we observed no changes in cell viability, but leptin secretion increased and adiponectin secretion was reduced. The fluorescent probe aminophenyl fluorescein (APF) showed that only native MPO produced HOCl inside adipocytes. This was prevented by the MPO inhibitor ABAH or resveratrol—a cell permeable scavenger of HOCl. HOCl produced inside the adipocyte produced oxidation and aggregation of adiponectin in the endoplasmic reticulum (ER) and caused ER stress. Intracellular production of HOCl also increased leptin secretion by adipocytes. Immuno-spin trapping with anti-DMPO of adipocytes loaded with MPO and treated with H2O2 and DMPO showed that adiponectin and prolyl hydroxylase-2 (PHD-2) were two of the major targets of oxidation in the adipocyte. Like resveratrol, the nitrone spin trap DMPO re-established the normal pattern of secretion of adipokines, prevented HIF-1? increase and ameliorated ER stress. The decreased secretion of adiponectin was related to increased retention of oxidized adiponectin in the ER, whereas increased leptin secretion might be due to increased HIF-1? stability, likely due to PHD-2 inhibition. These results highlight an important role of the synthesis and secretion of MPO by macrophages that infiltrate hypoxic sites in the adipose tissue during obesity and adipokine deregulation in adipocytes. Treatments aimed at preventing or stopping MPO oxidation inside adipocytes might offer new therapeutic avenues for preventing obese patients from becoming diabetics. Supported by NIEHS 5R00ES015415-04.