Increased Expression of Pigment Epithelium-derived Factor in Tubulo-interstitial Fibrosis
Regression of peritubular capillaries is an important mechanism underlying the progression of tubulo-interstitial fibrosis. Vascular endothelial growth factor-A (VEGF) promotes endothelial cell survival while pigment epithelium-derived factor (PEDF) opposes the actions of VEGF, in part by down-regulating the apoptosis inhibitor, FLICE-inhibitory protein (c-FLIP). We studied the expression of PEDF, c-FLIP and VEGF in a murine model of tubulo-interstitial fibrosis.
Methods: Unilateral ureteric obstruction was performed by surgical ligation of the left ureter in male C57BL/6 mice. mRNA for PEDF, c-FLIP and VEGF isoforms was quantified in kidneys by real-time RT-PCR at 3, 7 and 14 days. Western blotting and ELISA were performed on kidney homogenates. Left kidneys (L) were compared to right (R) for each animal by paired t-test.
Results: PEDF mRNA was upregulated 7-fold at 7 days and greater than 20-fold at 14 days (L vs. R; p=0.01 and p=0.007 at 7 and 14 days respectively). c-FLIP mRNA was increased 3-fold in L kidneys at 7 days but was not different from R at 14 days. VEGF protein levels in left kidneys were reduced at both 3 (L vs. R, 0.68±0.15 vs. 2.13±0.38; p=0.015) and 7 days (L vs. R, 0.50±0.11 vs. 1.32±0.16; p=0.007). Western blot for PEDF confirmed up-regulation in left kidneys beyond 3 days.
Conclusions: This is the first study to show increased PEDF in renal fibrosis. This, combined with reduced VEGF, may predispose to endothelial cell apoptosis, tissue hypoxia and worsening fibrosis. PEDF may be a potential therapeutic target for delaying progression of fibrosis.