#4966 CELLULAR PRION PROTEIN ACTIVATES THE TBK1-IRF3 SIGNALING PATHWAY TO AGGRAVATE RENAL FIBROSIS
Authors: Long Tantan , MA Yuanyuan , Zhou Miaomiao , MA Jingyi , Zhu Fengxin , Nie Jing 
Published: June 2023

Abstract

Background and Aims
Chronic kidney disease (CKD) is an irreversible degenerative disease characterized by gradual loss of renal function, contributing to high morbidity and mortality as well as heavy economic cost to society. Clinically, there are few available strategies to slow CKD progression. Because the uremic phenotypes include many features of aging, CKD is considered as a premature aging syndrome. Neurodegenerative diseases, such as Alzheimer's disease, and Parkinson's disease are extensively studied aging-related diseases, in which cytotoxic proteins misfolding and aggregation in neural cells is the main characteristic. The misfolding and aggregation of the prion protein is tightly linked to the development of prion diseases. Interestingly, a remarkable elevation of cellular prion protein (PrPC) in the urine and plasma of CKD patients was reported. However, the role of PrPC in the pathogenesis of kidney diseases remains largely unknown. The aim of the current study is to investigate the role of PrPC in renal fibrosis.

Methods
Immunohistochemistry staining was conducted to evaluate the expression of PrPC in renal biopsies from CKD patients. Enzyme linked immunosorbent assay (ELISA) was performed to detect urinary PrPC of CKD patients. Animal model of renal fibrosis was induced by unilateral ureteral occlusion (UUO). Western blot, real time PCR and immunofluorescence staining were performed to evaluate the expression and distribution of PrPC. Proximal tubule specific Prnp knockout mice (PEPCK-Prnp-KO) was constructed to explore the pathogenic role of PrPC in renal fibrosis. Primary proximal tubular epithelial cells (PTCs) overexpressed PrPC were collected for RNA-seq analysis. TBK1 inhibitor amlexanox, and IRF3 siRNA were used to block TBK1-IRF3 pathway in rat tubular epithelial cells (NRK-52E), respectively. Amlexanox was administered orally to UUO mice. H&E, Masson and Sirius red staining were used to estimate renal pathology.

Results
The protein expression levels of PrPC both in renal biopsies and urine from CKD patients were elevated and significantly correlated with the severity of interstitial fibrosis and the decline of eGFR. PrPC proteins were significantly increased, and aggregated in proximal renal tubules in fibrotic renal tissues induced by UUO. Compared with wild-type littermates, PEPCK-Prnp-KO mice showed reduced extracellular matrix accumulation and interstitial inflammation at day 7 after UUO. PrPC provokes profibrotic response of renal tubular cells via the TBK1-IRF3 pathway. TBK1 inhibitor amlexanox or silencing endogenous IRF3 significantly inhibited PrPC-induced profibrogenic phenotypic transformation in NRK-52 cells. Amlexanox attenuated interstitial fibrosis induced by UUO.

Conclusion
Our experimental results indicate that PrPC-TBK1-IRF3 pathway plays a detrimental role in profibrogenic transformation of renal tubular cells and thus contributes to interstitial fibrosis. Blocking TBK1 activation is a plausible strategy for therapeutic intervention of chronic kidney disorders.