Loss of Proximal Tubular Krüppel-Like Factor 15 in Kidney Injury Is Detrimental Through Suppression of Fatty Acid Oxidation

Background: Loss of fatty acid oxidation in the proximal tubule (PT) is a critical mediator of acute kidney injury (AKI) and eventual fibrosis. The transcription factor PPARα is a key regulator of fatty acid oxidation (FAO); however, Ppara knockout mice do not have kidney injury at baseline, suggesting that other important regulators remain to be described. Krüppel-like factor 15 is expressed in PT, downregulated in AKI, and with PPARα, regulates FAO in cardiomyocytes. Our aim was to investigate the role of PT KLF15 in AKI and fibrosis. Methods: PT-specific Klf15 knockdown (Klf15PTKO) mice were generated by breeding Klf15fl/fl and Pepck-Cre mice. Kidney injury was induced using the PT-specific DNA damaging agent aristolochic acid I (AAI) or by ischemia-reperfusion (IR). Blood was collected for serum biochemistry, and kidneys harvested for histological and immunofluorescence analyses. Chromatin immunoprecipitation (ChIP) studies were undertaken to detect binding of KLF15 to FAO gene promoters. Primary PT cells were harvested from Klf15fl/fl mice and Klf15 knocked out by infection with adenovirus-Cre (control = adenovirus-GFP), followed by qRT-PCR analysis and live cell metabolic assays using a Seahorse bioanalyzer. Gene expression and eGFR data for human CKD patients in Nephroseq were utilized for correlation analyses. Results: PT KLF15 expression was downregulated in response to injury in control mice. Klf15PTKO mice subjected to AKI using AAI or IR had significantly worse injury than Klf15fl/fl mice, as assessed by higher serum creatinine and urea nitrogen levels, exacerbated histopathological features, more extensive loss of mature PT brush borders, and increased fibrosis in AAI-treated mice. ChIP studies showed binding of KLF15 to the promoters of genes encoding key FAO enzymes CPT1A and ACAA2. Knockdown of Klf15 in primary PT cells resulted in decreased expression of Ppara, Cpt1a and Acaa2. Live cell metabolic assays demonstrated that loss of Klf15 compromised PT cellular metabolism, particularly the ability to utilize palmitate in FAO. KLF15 expression positively correlated with eGFR and PPARA expression in human kidney biopsies with CKD. Conclusions: PT KLF15 is a key regulator of FAO, and loss of KLF15 in kidney injury is detrimental through compromised FAO. Funding: NIDDK Support, Veterans Affairs Support