Hypoxia dysregulates the production of adiponectin and plasminogen activator inhibitor-1 independent of reactive oxygen species in adipocytes

https://doi.org/10.1016/j.bbrc.2006.01.004Get rights and content

Abstract

Low plasma levels of adiponectin (hypoadiponectinemia) and elevated circulating concentrations of plasminogen activator inhibitor (PAI)-1 are causally associated with obesity-related insulin resistance and cardiovascular disease. However, the mechanism that mediates the aberrant production of these two adipokines in obesity remains poorly understood. In this study, we investigated the effects of hypoxia and reactive oxygen species (ROS) on production of adiponectin and PAI-1 in 3T3-L1 adipocytes. Quantitative PCR and immunoassays showed that ambient hypoxia markedly suppressed adiponectin mRNA expression and its protein secretion, and increased PAI-1 production in mature adipocytes. Dimethyloxallyl glycine, a stabilizer of hypoxia-inducible factor 1α (HIF-1α), mimicked the hypoxia-mediated modulations of these two adipokines. Hypoxia caused a modest elevation of ROS in adipocytes. However, ablation of intracellular ROS by antioxidants failed to alleviate hypoxia-induced aberrant production of adiponectin and PAI-1. On the other hand, the antioxidants could reverse hydrogen peroxide (H2O2)-induced dysregulation of adiponectin and PAI-1 production. H2O2 treatment decreased the expression levels of peroxisome proliferator-activated receptor gamma (PPARγ) and CCAAT/enhancer binding protein (C/EBPα), but had no effect on HIF-1α, whereas hypoxia stabilized HIF-1α and decreased expression of C/EBPα, but not PPARγ. Taken together, these data suggest that hypoxia and ROS decrease adiponectin production and augment PAI-1 expression in adipocytes via distinct signaling pathways. These effects may contribute to hypoadiponectinemia and elevated PAI-1 levels in obesity, type 2 diabetes, and cardiovascular diseases.

Section snippets

Materials and methods

Reagents. Dimethyloxallyl glycine (DMOG) was purchased from Cayman Chemicals (Ann Arbor, Michigan, USA). N-Acetyl-l-cysteine (NAC), catalase, and hydrogen peroxide (H2O2) are the products of Sigma (St. Louis, MO, USA). The anti-actin antibody and the anti-HIF-1α monoclonal antibody were from Santa Cruz Biotechnology (Santa Cruz, CA, USA), and R&D Systems (Minneapolis, MN, USA), respectively. Trizol Reagent and Superscript first-strand cDNA synthesis system were purchased form Promega (Madison,

Ambient hypoxia markedly decreases adiponectin production, but increases PAI-1 expression in 3T3-L1 adipocytes

To examine the effects of hypoxia on the expression of adiponectin and PAI-1, fully differentiated 3T3-L1 adipocytes were cultured in 1% O2 atmosphere or in normoxia condition for different time periods. Methyl thiazole tetrazolium (MTT) assay revealed that treatment with hypoxia had no significant effect on cell viability (data not shown). Quantitative real-time PCR demonstrated that hypoxia significantly decreased the steady-state mRNA abundance of the adiponectin gene in a time-dependent

Discussion

Hypoadiponectinemia and elevated plasma levels of PAI-1 are the two important biochemical hallmarks in the pathogenesis of obesity-related disorders, especially type 2 diabetes and cardiovascular diseases [9], [10], [21]. Our present study demonstrated that hypoxia could markedly decrease the production of adiponectin and increase the expression of PAI in adipocytes, a major site for synthesizing these two adipokines. Accumulating evidence suggests that local hypoxia occurs in enlarged adipose

Acknowledgments

This work was supported by Hong Kong Research Council Grant HKU (7486/04M), and a research and conference grant from the University of Hong Kong (To A. Xu), Sun Chieh Yeh Heart Foundation, and the 973 program of China (2004CB720102).

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