Peroxisome Proliferator-Activated Receptor (PPAR)γ Can Inhibit Chronic Renal Allograft Damage

Chronic inflammation and fibrosis are the leading causes of chronic allograft failure. The nuclear receptor peroxisome proliferator-activated receptor (PPAR)γ is a transcription factor known to have antidiabetogenic and immune effects, and PPARγ forms obligate heterodimers with the retinoid X receptor (RXR). We have reported that a retinoic acid (RAR)/RXR-agonist can potently influence the course of renal chronic allograft dysfunction. In this study, in a Fischer to Lewis rat renal transplantation model, administration of the PPARγ-agonist, rosiglitazone, independent of dose (3 or 30 mg/kgBW/day), lowered serum creatinine, albuminuria, and chronic allograft damage with a chronic vascular damage score as follows: 35.0 ± 5.8 (controls) vs. 8.1 ± 2.4 (low dose-Rosi; P < 0.05); chronic tubulointerstitial damage score: 13.6 ± 1.8 (controls) vs. 2.6 ± 0.4 (low dose-Rosi; P < 0.01). The deposition of extracellular matrix proteins (collagen, fibronectin, decorin) was strikingly lower. The expression of transforming growth factor-β1 was inhibited, whereas that of bone morphogenic protein-7 (BMP-7) was increased. Intragraft mononuclear cells and activated fibroblast numbers were reduced by 50%. In addition, the migratory and proliferative activity of these cells was significantly inhibited in vitro. PPARγ activation diminished the number of cells expressing the proinflammatory and fibrogenic proteoglycan biglycan. In macrophages its secretion was blocked by rosiglitazone in a predominantly PPARγ-dependent manner. The combination of PPARγ- and RAR/RXR-agonists resulted in additive effects in the inhibition of fibrosis. In summary, PPARγ activation was potently immunosuppressive and antifibrotic in kidney allografts, and these effects were enhanced by a RAR/RXR-agonist