Altered Tumor Necrosis Factor-α (TNF-α) Processing in Adipocytes and Increased Expression of Transmembrane TNF-α in Obesity

Abstract

Tumor necrosis factor-α (TNF-α) is synthesized as a 26-kDa transmembrane protein (mTNF-α), which may present on the cell surface or be processed to release the 17-kDa soluble form (sTNF-α). Because regulation of this ectodomain shedding might be critical in the generation of systemic versus local cytokine responses, we examined the rate of mTNF-α processing in adipocytes and its regulation in obesity. Here, we demonstrate that the 26-kDa mTNF-α is present in adipose tissue and that its production is significantly increased in different rodent obesity models as well as in obese humans. There was no apparent deficiency in the level of the major TNF-α converting enzyme in adipose tissue to account for the excess amount of mTNF-α produced in obesity. However, experiments in cultured fat cells stably expressing TNF-α demonstrated a significantly decreased rate of TNF-α cleavage in differentiated adipocytes compared with preadipocytes. Thus, a decreased processing rate of mTNF-α in mature adipocytes combined with an increase in TNF-α production may be a potential mechanism resulting in elevated membrane-associated TNF-α in adipose tissue in obesity.