Pioglitazone Inhibits Periprostatic White Adipose Tissue Inflammation in Obese Mice

Obesity is associated with an increased incidence of high-grade prostate cancer and poor prognosis for prostate cancer patients. Recently, we showed that obesity-related periprostatic white adipose tissue (WAT) inflammation, characterized by crown-like structures (CLS) consisting of dead or dying adipocytes surrounded by macrophages, was associated with high-grade prostate cancer. It is possible, therefore, that agents that suppress periprostatic WAT inflammation will alter the development or progression of prostate cancer. Pioglitazone, a ligand of PPARγ, is used to treat diabetes and possesses anti-inflammatory properties. Here, our main objectives were to determine whether pioglitazone inhibited obesity-related periprostatic WAT inflammation in mice and then to elucidate the underlying mechanism. Treatment with pioglitazone reduced the density of CLS in periprostatic fat and suppressed levels of TNFα, TGFβ, and the chemokine monocyte chemoattractant protein-1 (MCP-1). Importantly, the ability of pioglitazone to suppress periprostatic WAT inflammation was abrogated in MCP-1 knockout mice. Pioglitazone caused dose-dependent induction of both adiponectin, an anti-inflammatory adipokine, and its receptor AdipoR2 in cultured 3T3-L1 cells and in periprostatic WAT of obese mice. Pioglitazone blocked TNFα-mediated induction of MCP-1 in 3T3-L1 cells, an effect that was attenuated when either adiponectin or AdipoR2 were silenced. Taken together, pioglitazone-mediated induction of adiponectin suppressed the elevation in MCP-1 levels, thereby attenuating obesity-related periprostatic WAT inflammation. These findings strengthen the rationale for future efforts to determine whether targeting the PPARγ-adiponectin-MCP-1 axis will decrease periprostatic adipose inflammation and thereby reduce the risk of high-grade prostate cancer or improve outcomes for men with prostate cancer. Cancer Prev Res; 11(4); 215-26. ©2017 AACR.