MP29-04 THE LOSS OF PTEN CONSEQUENT TO URETERAL OBSTRUCTION CONTRIBUTES TO RENAL FIBROSIS

Abstract

INTRODUCTION AND OBJECTIVES: Phosphate Tensin Homologue on Chromosome 10 (PTEN), the principle negative regulator of PI3K pathway, is a known tumor suppressor that is mutated or lost in many cancer types. Recent studies highlight the emerging role of tumor suppressor PTEN in organ fibrosis including lung and skin where loss of PTEN expression is linked to progression of fibrosis via promoting epithelial plasticity in the lung and induction of myofibroblasts in the skin. However, potential involvement of this molecule in obstructive uropathies is not defined. METHODS: Obstruction induced renal fibrosis was modeled in vivo by unilateral ureteral obstruction (UUO) in mice and in vitro by gene silencing and pharmacological inhibition of PTEN in HK-2 human renal tubular epithelial cells and NRK-49F rat renal fibroblasts. RESULTS: PTEN expression is dramatically decreased in the obstructed (ligated) kidney, while profibrotic TGF-b1/SMAD3 and p53 signal transduction is increased compared to contralateral control or sham kidney. PTEN silencing induced phenotypic modifications from typical cuboidal to an elongated fibroblast-like shape (4-fold increase) and a 40% decrease in the relative cell number compared to control shRNA expressing HK-2 cultures (p<0.01). Stable gene depletion of PTEN in HK-2 cells long term (3-5 days) resulted in increased expression of the profibrotic markers CTGF, PAI-1 and fibronectin compared to control shRNA expressing cultures. Loss of PTEN resulted in activation of SMAD2/3 transcription factor. SMAD3 knockdown or pharmacological inhibition of SMAD3 in PTEN depleted HK-2 cells reversed growth inhibition and suppressed PAI-1 induction, confirming a critical role of SMAD3 downstream of PTEN in orchestrating fibrotic responses. CONCLUSIONS: Unilateral ureteral obstruction induces loss of PTEN expression, resulting in the increased expression of profibrotic cytokines in renal tubular epithelial cells that is dependent on the SMAD3 signaling pathway. PTEN is a potential therapeutic target in the treatment of ureteral obstruction and renal fibrosis. This model paves the way for further clinical studies in humans.