Polynucleotide phosphorylase protects against renal tubular injury via blocking mt-dsRNA-PKR-eIF2α axis

Renal tubular atrophy is a hallmark of chronic kidney disease. The cause of tubular atrophy, however, remains elusive. Here we report that reduction of renal tubular cell polynucleotide phosphorylase (PNPT1) causes renal tubular translation arrest and atrophy. Analysis of tubular atrophic tissues from renal dysfunction patients and male mice with ischemia-reperfusion injuries (IRI) or unilateral ureteral obstruction (UUO) treatment shows that renal tubular PNPT1 is markedly downregulated under atrophic conditions. PNPT1 reduction leads to leakage of mitochondrial double-stranded RNA (mt-dsRNA) into the cytoplasm where it activates protein kinase R (PKR), followed by phosphorylation of eukaryotic initiation factor 2α (eIF2α) and protein translational termination. Increasing renal PNPT1 expression or inhibiting PKR activity largely rescues IRI- or UUO-induced mouse renal tubular injury. Moreover, tubular-specific PNPT1-knockout mice display Fanconi syndrome-like phenotypes with impaired reabsorption and significant renal tubular injury. Our results reveal that PNPT1 protects renal tubules by blocking the mt-dsRNA-PKR-eIF2α axis.