Peroxisome proliferator-activated receptor-gamma agonist is protective in podocyte injury-associated sclerosis

We have previously observed increased expression of peroxisome proliferator-activated receptor gamma (PPARgamma) in podocytes in both rat and human sclerotic conditions. The aim of the present study was to investigate whether activation of PPARgamma can attenuate podocyte injury-associated glomerulosclerosis in vivo. Puromycin aminonucleoside nephropathy was induced in Sprague-Dawley rats. The animals then either received no further treatment (control group (CONT)); or the PPARgamma agonist, pioglitazone (Pio) starting at week 0 (P0); or Pio starting at week 6 (P6), with sacrifice at week 12. At week 12, urinary protein excretion and systolic blood pressure were similar in the three groups. Glomerular filtration rate and glomerulosclerosis were decreased in CONT and P0 at week 12, but preserved in P6 rats. PPARgamma expression in CONT at 12 weeks was increased in podocytes and in mesangial WT-1 cells in segmentally sclerotic glomeruli, with less Wilms' tumor 1 (WT-1) staining. In P6 rats, mesangial WT-1 staining was lessened, but podocyte staining was strongly accentuated. Delayed treatment with Pio partially restored podocyte staining and tended to decrease the ratio of proliferating cell nuclear antigen-positive to apoptotic cells in glomeruli. Both treatment groups showed significantly reduced infiltrating glomerular macrophages and plasminogen activator inhibitor-1 mRNA expression in cortex, with no change in transforming growth factor-beta1 and tissue inhibitor of metalloproteinase-1 mRNA. Pio also decreased renal cortical angiopoietin-like protein 4 expression to almost 20% of CONT group, associated with increased vascular endothelial-derived growth factor expression in glomeruli. We conclude that treatment with PPARgamma agonist has protective effects on progression of glomerulosclerosis.