The metabolic basis of renal fibrosisrole of micrRNAas and insight from genetic models targeting lipid metabolism

Resumen

Chronic kidney disease (CKD) involves the progressive deterioration of kidney function and affects around 10% of the worldwide population. Chronic injury of renal epithelial cells conveys a persistent inflammatory and profibrogenic response, which ultimately results in tubulointerstitial fibrosis and a progressive loss of renal function. Mitochondrial dysfunction and defective fatty acid oxidation (FAO), which compromise the main source of energy for the renal tubular epithelial cell (RTEC), have been proposed to be fundamental contributors to the development and progression of kidney fibrosis. To determine if a functional gain in FAO could protect the kidney from fibrosis, we generated a conditional transgenic mouse model with specific overexpression of the fatty acid shuttling enzyme carnitine palmitoyl-transferase 1 A (CPT1A) in RTECs. This was achieved by crossing mice expressing the rtTA transactivator under the paxillin-8 promoter with the newly generated TRE/CPT1A mice. CPT1A expression was upregulated by 10-fold after doxycycline induction and showed the expected mitochondrial localization. This was reflected in an increased rate of palmitate oxidation and ATP production. Studies in Cpt1a knock-in mice subjected to the experimental models of renal fibrosis, unilateral ureteral obstruction (UUO), folic acid nephropathy (FAN) or adenine-induced renal failure (ADN) exhibited decreased expression of fibrotic markers compared with wild type animals (WT). In the FAN model, CPT1A overexpression reduced the abundance of the pro-inflammatory M1 subpopulation. This FAO gain-of-function partially prevented the decrease in FAO rate 3 days after UUO, FAN and ADN models but not in kidneys after 7 days of UUO. Furthermore, both primary renal tubule epithelial cells isolated from transgenic mice and HKC-8 cells transduced with adenoviral particles for CPT1A were protected from TGF-β-induced dedifferentiation. These cells exhibited higher levels of FAO-associated oxygen consumption rate (OCR) and decreased glucose utilization. Tissue from kidneys corresponding to mice overexpressing CPT1A also presented a reduced proportion of damaged epithelial cells in the UUO and FAN models. These results support that overexpression of CPT1A has a protective impact on the outcome of kidney fibrosis, most likely due to the enhancement of FAO in RTECs. MicroRNAs (miRNAs), which regulate gene expression post-transcriptionally, have been reported to control renal fibrogenesis. To identify miRNAs involved in the metabolic derangement of renal fibrosis, we performed a miRNA array screen in the renal fibrosis mouse model of unilateral ureteral obstruction (UUO). MiR-150-5p, miR-495-3p and miR-33-5p were selected for their link to human pathology, their role in mitochondrial metabolism and their targeting of CPT1A. Studies in miR-33a-deficient mice (KO) subjected to UUO and FAN showed decreased kidney fibrosis and lipid accumulation compared with wild type animals. MiR-33 analogs reduced FAO-related OCR while miR-33 antagonists increased it in HKC-8 cells. MiR-495-3p and miR-150-5p were upregulated both in the UUO and FAN models. These miRNAs synergized with TGF-β regarding their profibrotic effects and reduced FAO-associated OCR in the human epithelial renal cell line HKC-8. These data support that miR-150, miR-495 and miR-33 can be exploited as targets to prevent the metabolic impairment leading to renal fibrosis. Overall, this work proposes that strategies directed towards restoring FAO may prove useful for the prevention or treatment of kidney fibrosis.