Extracellular conversion of adiponectin hexamers into trimers

Abstract

Adiponectin is an adipocyte-secreted hormone that exists as trimers, hexamers and larger species collectively referred to as HMW (high-molecular-weight) adiponectin. Whether hexamers or HMW adiponectin serve as precursors for trimers outside the circulation is currently unknown. Here, we demonstrate that adiponectin trimers can be generated from larger oligomers secreted from primary rat adipose cells or differentiated 3T3-L1 adipocytes. Purified hexameric, but not HMW, adiponectin converted into trimers in conditioned media separated from 3T3-L1 adipocytes or, more efficiently, when enclosed in the dialysis membrane in the presence of adipocytes. Several lines of evidence indicate that the conversion is mediated by an extracellular redox system. First, N-terminal epitope-tagged hexamers converted into trimers without proteolytic removal of the tag. Secondly, appearance of trimers was associated with conversion of disulfide-bonded dimers into monomers. Thirdly, thiol-reactive agents inhibited conversion into trimers. Consistent with a redox-based mechanism, purified hexamers reductively converted into trimers in defined glutathione redox buffer with reduction potential typically found in the extracellular environment while the HMW adiponectin remained stable. In addition, conversion of hexamers into trimers was enhanced by NADPH, but not by NADP+. Collectively, these data strongly suggest the presence of an extracellular redox system capable of converting adiponectin oligomers.

Regulation and Quality Control of Adiponectin Assembly by Endoplasmic Reticulum Chaperone ERp44

“…Previous studies (25,47) have reported that fully oxidized LMW adiponectin and MMW adiponectin fail to assemble into the HMW form, whereas reduced trimers could assemble into the HMW form through oxidative formation of disulfide bonds in vitro and in vivo (25,47,50). These observations indicate that the MMW form comprises oxidized trimers that are assembly-trapped.…”

A reciprocal inhibitory relationship between adiponectin and mammalian cytosolic thioredoxin

“…Mature monomeric adiponectin has a molecular weight of *26 kDa [9]. As human adiponectin circulates in plasma/ serum mainly as trimers (LMW, *78 kDa), hexamers (MMW, *156 kDa) and 12-18-mers (HMW, [300 kDa) isoforms [7], hTrx1 binding to different adiponectin isoforms was thus analyzed.…”

“…Adiponectin isoforms have differential actions [8]. Mature monomeric adiponectin has a molecular weight about 26 kDa [9]. The HMW and MMW isoforms of adiponectin are composed of disulfide bonded trimer [10].…”

Distinct Mechanisms for Globular Adiponectin That Integrate Vascular and Metabolic Actions of Insulin to Help Maintain Coordinated Cardiovascular and Glucose Homeostasis

“…20 Adiponectin exists as trimers, hexamers, and as higher molecular weight forms in the circulation. 28 Because of extremely high circulating levels of the hormone, some have proposed that altering the ratio of circulating adiponectin to higher molecular weight forms would be a more advantageous therapeutic approach than increasing its total levels. The disulfide bond A oxidoreductase-like protein promotes adiponectin multimerization, and overexpression of disulfide bond A oxidoreductase-like protein in mice shows beneficial effects on insulin resistance.…”

“…Methods to enhance proteolytic cleavage of full length adiponectin to gAd may serve as a potential therapeutic approach for enhancing adiponectin bioactivity. 28 Additional research on the role of adiponectin as a therapeutic agent may lead to the development of an additional safe intervention to help curtail the epidemic of metabolic and cardiovascular diseases.…”