Endogenous activation of peroxisome proliferator-activated receptor-a in proximal tubule cells in counteracting phosphate toxicity

Increased dietary phosphate consumption intensifies renal phosphate burden. Several mechanisms for phosphate-induced renal tubulointerstitial fibrosis have been reported. Considering the dual nature of phosphate as both a potential renal toxin and an essential nutrient for the body, kidneys may possess inherent protective mechanisms against phosphate overload, rather than succumbing solely to injury. However, there is limited understanding of such mechanisms. To identify these mechanisms, we conducted single-cell RNA sequencing (scRNA-seq) analysis of the kidneys of control and dietary phosphate-loaded (Phos) mice at a time point when the Phos group had not yet developed tubulointerstitial fibrosis. scRNA-seq analysis identified the highest number of differentially expressed genes in the clusters belonging to proximal tubular epithelial cells (PTECs). Based on these differentially expressed genes, in silico analyses suggested that the Phos group activated peroxisome proliferator-activated receptor-a (PPAR-a) and fatty acid b-oxidation (FAO) in the PTECs. This activation was further substantiated through various experiments, including the use of an FAO activity visualization probe. Compared with wild-type mice, Ppara knockout mice exhibited exacerbated tubulointerstitial fibrosis in response to phosphate overload. Experiments conducted with cultured PTECs demonstrated that activation of the PPAR-a/FAO pathway leads to improved cellular viability under high-phosphate conditions. The Phos group mice showed a decreased serum concentration of free fatty acids, which are endogenous PPAR-a agonists. Instead, experiments using cultured PTECs revealed that phosphate directly activates the PPAR-a/FAO pathway. These findings indicate that noncanonical metabolic reprogramming via endogenous activation of the PPAR-a/FAO pathway in PTECs is essential to counteract phosphate toxicity. NEW & NOTEWORTHY This study revealed the activation of peroxisome proliferator-activated receptor-a and fatty acid b-oxidation in proximal tubular epithelial cells as an endogenous mechanism to protect the kidney from phosphate toxicity. These findings highlight noncanonical metabolic reprogramming as a potential target for suppressing phosphate toxicity in the kidneys.