Presentation Authors: Erin Salter*, Jiaqi Tang, Paul Higgins, Rohan Samarakoon, Albany, NY
Introduction: Despite success of surgical intervention in relieving ureteral obstruction, a fraction of patients develop resultant renal fibrosis and end stage kidney disease. Hippo pathway is a major regulator of organ size, with Yes associated protein (YAP) and its paralog, Transcriptional coactivator with PDZ-binding motif (TAZ), as its major nuclear effectors. We recently demonstrated that TAZ upregulation consequent to obstructive renal injury contributes to progressive fibrosis. The mechanistic contribution of YAP, however, was not investigated. Here, we test the hypothesis that YAP renal induction in obstructive uropathy promotes fibrotic epithelial dysfunction and assess Verteporfin as a potential anti-fibrotic agent.
Methods: We utilized a mouse model of unilateral ureteral obstruction (UUO) to investigate YAP involvement in obstructive nephropathy. Human kidney tubular epithelial cells (HK-2) were stably transduced with either control vector (CMV-Control) or YAP1 (CMV-YAP) expression contracts, driven by CMV promoter via lentiviral transduction. Phenotypic alterations, fibrotic marker expression and growth properties of these transgenic cells were assessed by microscopy, western blot analysis and flow cytometry. Pharmacologic inhibition of YAP/TAZ is also investigated as a therapeutically relevant anti-fibrotic approach.
Results: YAP expression was elevated in tubulointerstitial regions of UUO kidneys compared to contralateral controls, correlating with fibrosis. HK-2 cells with stable YAP1 expression, mimicking epithelial YAP upregulation during kidney obstruction, underwent epithelial dedifferentiation, marked by loss of epithelial marker E-Cadherin and acquisition of mesenchymal properties including vimentin upregulation. CMV-Control HK-2 cells retained epithelial characteristics including cuboidal appearance and E-Cadherin expression. YAP overexpressing cells assumed fibrogenic properties, evident by increased fibronectin, Collagen-1 expression; underwent G2/M cell cycle arrest; and promoted p21 upregulation compared to control cells. Blockade of YAP/TAZ activation with a clinically relevant drug, verteporfin attenuated the fibrotic reprogramming induced by YAP upregulation.
Conclusions: YAP upregulation promotes epithelial plasticity and growth inhibition, contributing to dysfunctional renal epithelium and fibrotic maladaptive repair. Verteporfin could be a novel and plausible strategy to reduce prevalence of obstructive uropathy via pharmacologic and molecular targeting of YAP upregulation.
Source of Funding: National Institute of Health, Capital District Medical Research Institute