Regulation and Function of Adiponectin Oligomerization

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DESCRIPTION (provided by applicant): Adiponectin is an adipose tissue-derived hormone with anti-diabetic, anti-atherogenic, and anti-inflammatory functions. Circulating adiponectin exists as trimer, hexamer, and high molecular weight species which activate divergent signaling pathways and exert distinct biological functions on their target tissues. Adiponectin multimers are highly stable and do not interconvert from one species to another spontaneously. However, it is currently unknown how the biogenesis of the different adiponectin species is regulated in cells. To identify adiponectin interacting proteins involved in regulating adiponectin function, we screened a yeast two-hybrid cDNA library derived from human fetal brain, using adiponectin as bait. This screening led to the identification of a 25 kDa protein, previously named glutathione-S-transferase (GST)-kappa. GST-kappa contains two thioredoxin domains and the C-terminal thioredoxin domain shares high structural and sequence homology to bacterial disulfide-bond-A (DsbA) oxidoreductase, an enzyme involved in disulfide bond formation in the periplasm of Gram-negative bacteria. Our preliminary studies showed that GST-kappa and adiponectin are co-localized in distinct cellular organelle structures and GST-kappa interacts with adiponectin in vitro and in cells. In addition, we found that GST-kappa is highly expressed in adipose tissue and the expression of GST-kappa is reduced in obese mice and human subjects and by TNF1a-treatment, and is induced by troglitazone. Furthermore, we found that suppression of GST-kappa by RNAi markedly and specifically reduced adiponectin levels and secretion in differentiated 3T3-L1 adipocytes. Based on these novel findings, we hypothesize that GST-kappa may function as a protein disulfide isomerase and play an important role in regulating adiponectin multimerization and secretion. To further test this hypothesis, we will: 1) determine whether GST-kappa regulates adiponectin multimeric assembly and/or secretion in 3T3-L1 adipocytes; 2) elucidate the mechanism by which GST-kappa regulates adiponectin multimeric multimerization and/or secretion; and 3) generate adipose tissue-specific GST-kappa knockout mice to determine the physiological roles of GST-kappa in vivo. Results from these studies will not only shed light on our understanding of the mechanism regulating adiponectin multimerization and secretion, but will also provide valuable information on the design of new pharmacological interventions for metabolic diseases such as insulin resistance and type 2 diabetes. PUBLIC HEALTH RELEVANCE: Adiponectin is an adipose tissue-derived hormone with anti-diabetic and anti- inflammatory functions. Circulating adiponectin undergoes multimerization in cells and different oligomer isoforms exert distinct biological functions. The proposed study seeks to elucidate the biochemical and cellular mechanisms by which adiponectin multimerization is regulated, which will provide important information on the design of new pharmacological interventions for metabolic diseases such as insulin resistance and type 2 diabetes.