Complement C5a induces renal injury in diabetic kidney disease via mitochondrial reprogramming

Background and aims: The sequelae of diabetes mellitus include microvascular complications such as diabetic kidney disease (DKD), which involves glucose-mediated renal injury that is associated with a disruption in mitochondrial metabolic agility, inflammation and fibrosis. We explored the role of a potent mediator of inflammation, complement component C5a in the pathogenesis of DKD in clinical and experimental diabetes. Materials and methods: Complement C5a was determined by ELISA in plasma from patients with diabetes with and without renin angiotensin system (RAS) inhibitors. C5a and its receptor (C5aR1) were determined in several rodent models of diabetes (Ins2-Akita, db/db and streptozotocin (STZ)-induced diabetic rats). STZ-induced diabetic C57BL/6 mice were treated with the highly selective C5aR1 antagonist, PMX-53 (2mg/kg/ day) in drinking water for 24 weeks (n=10). C5aR1 deficient mice (C5ar1-/-) and their wild type littermates were rendered diabetic with STZ and followed for 24 weeks (n=10). Kidney injury was assessed by urinary albumin excretion and glomerulosclerosis (GSI). Immunohistochemistry for Collagen IV and FoxP3+ regulatory T cells was performed. Transcriptomics of renal cortex was performed by RNAsequencing using the Illumina platform and pathway analyses using Gene Set Enrichment Analysis. Lipidomics on renal cortices was determined. Results: We found marked systemic C5a activation in patients with diabetes which was not targetable with classical clinical therapies (RAS blockade) (183±20 vs 209±17ng/ml, p<0.05). C5a and its receptor (C5aR1) were upregulated early in the disease process and prior to kidney injury in several diverse rodent models of diabetes. Diabetic C5ar1-/- mice showed protection against renal injury with decreased albumin excretion (154.8±30.9 vs 59.7±7.2μg/24hr, p<0.001). Treatment of diabetic mice with PMX-53 led to a reduction in proteinuria (83.2±18.3 vs 30.1±9.5μg/24hr, p<0.05), inhibition of glomerular injury (2.8±0.1 vs 2.3 ±0.2, p<0.05) and fibrosis (11.8±1 vs 8.0±0.5%, p<0.05), and resolution of inflammation via activation of FoxP3+ regulatory T cells (0.15±0.03 vs 1.03±0.40 cells/field, p<0.05). Transcriptomic profiling of kidney revealed diabetes-induced downregulation of mitochondrial fatty acid metabolism. The top differential gene downregulated in the diabetic kidney was acyl-CoA dehydrogenase 10 (Acad-10), which participates in the beta-oxidation of fatty acids in mitochondria. Blockade of C5aR signalling in diabetic mice restored Acad-10 expression (0.45±0.11 vs 0.94 ±0.07 fold change, p<0.01). Interrogation of the lipidomics signature revealed abnormal cardiolipin remodelling in the diabetic kidney, a cardinal sign of disrupted mitochondrial architecture and bioenergetics. PMX53 normalized cardiolipin remodelling. Conclusion: This study provides evidence for a pivotal role of the C5a/ C5aR1 axis in propagating renal injury in the development of DKD via mitochondrial reprogramming. Supported by: JDRF Disclosure: M.T. Coughlan: Grants; JDRF Innovative Grant