Interactions among Peroxisome Proliferator Activated Receptor-γ, Insulin Signaling Pathways, and Steroidogenic Acute Regulatory Protein in Human Ovarian Cells

Abstract

Peroxisome proliferator activated receptor-gamma (PPAR-gamma) agonists thiazolidinediones (TZDs) are thought to ameliorate hyperandrogenism in polycystic ovary syndrome by reducing hyperinsulinemia. However, TZDs also exhibit direct effects in the human ovary. We examined interactions among PPAR-gamma, insulin signaling pathways, and steroidogenic acute regulatory (StAR) protein in human ovarian cells. Mixed human ovarian tissue culture that contained granulosa, theca, and stromal cells, and a culture of purified granulosa cells obtained during in vitro fertilization, were established as previously described. Cells were cultured in the presence or absence of insulin, with or without 25 or 50 microm rosiglitazone or pioglitazone. Expression of PPAR-gamma, insulin receptor, or insulin receptor substrate (IRS)-1 in both cell systems and of the StAR protein in granulosa cells was measured using immunoprecipitation and immunoblotting. Rosiglitazone stimulated expression of PPAR-gamma, insulin receptor alpha- and beta-subunits, and IRS-1 up to 168% (P < 0.05), 679% (P < 0.006), 290% (P < 0.037), and 323% (P < 0.01) of baseline, respectively. Pioglitazone stimulated expression of PPAR-gamma, insulin receptor alpha- and beta-subunits, and IRS-1 up to 222% (P < 0.01), 362% (P < 0.001), 402% (P < 0.029), and 492% (P < 0.03), respectively. Insulin alone stimulated expression of PPAR-gamma, alpha-subunit and beta-subunit of insulin receptor, and IRS-1 up to 174% (P < 0.001), 692% (P < 0.014), 275% (P < 0.024), and 431% (P < 0.01), respectively. In purified granulosa cell culture, rosiglitazone stimulated expression of StAR protein up to 540% (P < 0.007), and pioglitazone stimulated expression of StAR protein up to 670% (P < 0.007). Insulin alone stimulated expression of StAR protein up to 600% (P < 0.012). Insulin and TZDs independently stimulate expression of PPAR-gamma, insulin receptor, IRS-1, and StAR protein in human ovarian cells. Thus, PPAR-gamma, insulin receptor with its signaling pathways, and StAR protein constitute a novel human ovarian regulatory system with complex interactions among its components.