Cytoskeleton Rearrangement Decreases Mitochondrial Fatty Acid Oxidation in Renal Tubular Epithelial Cells Contributing to Renal Fibrogenesis

Abstract

Purpose: The epithelial-mesenchymal transition (EMT) plays an important role in renal fibrosis. Defective fatty acid oxidation (FAO) is the metabolic hallmark in injured tubular epithelial cells (TECs) contributing to renal fibrogenesis. Dysregulated cytoskeleton is believed to be an important element of renal injury and its function has been linked to cell metabolism, but little is known about the influence of the cytoskeleton on FAO in TECs. Herein, we aimed to investigate the protective effects and molecular mechanisms of pharmacological stabilization of the cytoskeleton against unilateral ureteric obstruction (UUO) -induced renal tubulointerstitial fibrosis.

Materials and methods: TGF-β1-treated primary tubular epithelial cells (PTECs) and UUO mice served as renal interstitial fibrosis (RIF) models, with or without pharmacological cytoskeleton stabilization by Bis-T-23 (TargetMol, T30479; 20 mg/kg/day intraperitoneally in vivo; 5 μM in vitro). Biomarkers, HE staining, PAS staining, Masson staining, Sirius red staining, and TUNEL assay were used to assess kidney function and apoptosis. Real-time quantitative PCR (qPCR), Western blotting and immunohistochemistry (IHC) were performed to measure mRNA and protein expression levels respectively. PTECs viability was assessed by CCK-8 assay. Bulk mRNA sequencing was used for transcriptomic analysis of cellular metabolism. FITC-phalloidin fluorescence staining was used to detect the cytoskeleton. Fluorescent co-staining was used to detect the interactions between lipid droplets (LDs) and mitochondria.

Results: Pharmacological stabilization of the cytoskeleton alleviated tubulointerstitial injury, functional changes and TEC damage in UUO mouse models. Stabilization of cytoskeleton restored FAO and enhanced FAO-associated respiration impaired by UUO injury. Here, we demonstrate that cytoskeleton rearrangement is a critical regulator of mitochondrial FAO in TECs both in vitro and in vivo. We further show that this cytoskeleton-dependent regulation of FAO occurs through altered interactions between LDs and mitochondria.

Conclusion: These findings indicate that cytoskeleton stabilization is required to maintain TECs metabolism and that therapeutic manipulation of cytoskeleton remodeling could protect the kidney from fibrogenesis conditions.