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.