Deficiency of CFB attenuates renal tubulointerstitial damage via inhibiting ceramide synthesis in diabetic kidney disease

Accumulating evidence suggests the pathogenic role of immunity and metabolism in diabetic kidney disease (DKD). Herein, we aimed to investigate the effect of complement factor B (CFB) on lipid metabolism in the development of DKD. We found that in patients with diabetic nephropathy (DN), the staining of Bb, CFB, C3a, C5a, and C5b-9 were significantly elevated in renal tubulointerstitium. Cfb knockout diabetic mice had significantly milder tubulointerstitial injury and less ceramide biosynthesis. The in vitro study demonstrated that cytokine secretion, endoplasmic reticulum stress, oxidative stress, and cell apoptosis were ameliorated in siCFB HK-2 cells under high glucose conditions. Exogenous ceramide supplementation attenuated the protective effect of CFB knockdown in HK-2 cells, while inhibiting ceramide synthases (CERS) with fumonisin B1 in CFB-overexpressing cells rescued the cell injury. CFB knockdown could downregulate the expression of NF-κB p65, which initiates the transcription of CERS3. Furthermore, C3 knockdown abolished CFB-mediated cytokine secretion, NF-κB signaling activation, and subsequently ceramide biosynthesis. Thus, CFB deficiency inhibited activation of the complement alternative pathway and attenuated kidney damage in DKD, especially tubulointerstitial injury, via inhibiting the NF-κB signaling pathway, further blocking the transcription of CERS, which regulates the biosynthesis of ceramide. CFB may be a promising therapeutic target of DKD. Comparative gene expression profiling analysis of RNA-seq data for Cfb knockout mice (STZ/HFD induced diabetic Cfb knockout mice and non-diabetic Cfb knockout mice) and its wide type control (diabetic mice and non-diabetic mice).