Collagen IV was not induced by high D-glucose. L-805645 and pioglitazone suppressed collagen IV to 68.0 Ϯ 14.5 (P Ͻ 0.05) and 46.5 Ϯ 11.6% (P Ͻ 0.01) vs. high D-glucose, respectively. High D-glucose increased the nuclear binding of NF-B to 167 Ϯ 22.4% (P Ͻ 0.05), which was not modified with PPAR␥ agonists. In conclusion, PPAR␥ agonists exert antifibrotic effects in human PTC in high glucose by attenuating the increase in AP-1, TGF-1, and the downstream production of the extracellular matrix protein fibronectin. thiazolidinediones; diabetic nephropathy; proximal tubular cells DIABETES MELLITUS (DM) IS a major global health issue with up to one-third of patients suffering end-stage renal disease. The major burden of disease is derived from patients with type 2 DM (25), resulting in up to 50% of adult patients on dialysis in Westernized countries having diabetic nephropathy as their primary diagnosis.The interventions shown to prevent the onset or attenuate the progression of diabetic nephropathy include glycemic and blood pressure control (10, 32), specific interruption of the renin-angiotensin system with either angiotensin-converting enzyme inhibitors (30) or angiotensin II receptor blockers (6,20) and potentially lipid-lowering therapy (3, 9). Understanding the mechanisms underlying the development of diabetic nephropathy is essential in establishing novel therapeutic strategies for the prevention or arrest of progressive renal failure. The search for specific molecular targets is ongoing, and PPAR␥ agonists may show promise.PPAR␥ are members of the nuclear hormone receptor superfamily of ligand-activated transcription factors that have a central role in regulating insulin sensitivity, adipocyte differentiation, cell growth, and inflammation (13). Synthetic agonists of PPAR␥ like the thiazolidinediones (TZDs) are widely used as insulin-sensitizing agents in patients with type 2 DM.