C3aR Antagonist Alleviates C3a Induced Tubular Profibrotic Phenotype Transition via Restoring PPARα/CPT-1α Mediated Mitochondrial Fatty Acid Oxidation in Renin-Dependent Hypertension

Background: Renin-dependent hypertension with tubulointerstitial injury remains a problem with high prevalence in the clinic. However, whether and how renin participates in tubulointerstitial injury remains incompletely understood. New evidence suggests that renin cleaves C3 into C3a and C3b. In the present study, we aimed to explore the role of renin-mediated C3a/C3a receptor (C3aR) signaling in renin-dependent hypertension-induced kidney injury and illustrate the detailed mechanisms.

Methods: C3a concentration changes in serum from healthy volunteers incubated with recombinant renin were detected by ELISA. C3aR expression in human tubular epithelial cells was evaluated in renal biopsy sections from malignant arteriolonephrosclerosis and benign arteriolonephrosclerosis patients. C3aR changes in human kidney 2 (HK2) cells were detected after the cells were treated with human serum, renin and aliskiren. The C3a analogue and C3aR antagonist SB290157 were used to stimulate HK2 cells to explore the downstream signaling of C3a/C3aR activation. For in vivo studies, two-kidney, one-clipped (2K1C) hypertensive rat model was established to simulate renin-dependent hypertension conditions. C3a and C3aR expression was detected in the clipped kidneys. SB290157 was injected intraperitoneally to block C3a/C3aR signaling in 2K1C rats.

Results: The results showed that renin cleaved C3 into C3a and activated C3a/C3aR signaling in tubular epithelial cells (TECs) from both humans and rats. In vitro results demonstrated that C3a/C3aR activation impaired peroxisome proliferator-activated receptor alpha (PPARα)/carnitine palmitoyltransterase-1alpha (CPT-1α)-mediated mitochondrial fatty acid oxidation (Mito FAO) in HK2 cells and induced HK2 cell transition to a profibrotic phenotype, which was inhibited by treatment with the C3aR antagonist SB290157. In vivo results showed that renin mRNA levels, C3a concentrations, C3aR levels and tubulointerstitial fibrosis increased concurrently in the clipped kidney cortex of 2K1C rats. Treatment with the C3aR antagonist SB290157 significantly mitigated the effect of renin induction of C3aR expression and alleviated renin-dependent hypertension-induced tubulointerstitial fibrosis by improving PPARα/CPT-1α-mediated Mito FAO in TECs, as well as inhibiting tubular profibrotic phenotype transition.

Conclusions: Our results prove that renin activates C3a/C3aR signaling to promote renal tubulointerstitial fibrosis by impairing PPARα/CPT-1α-mediated tubular Mito FAO. SB290157 confers a potential therapeutic approach for renin-dependent hypertension-induced kidney injury.