RasGRP4 Exacerbates Diabetic Kidney Fibrosis via Aloxe3-Mediated Oxidative Stress and Scar-Associated Macrophage Activation.

Renal fibrosis is an irreversible pathological feature of diabetic kidney disease (DKD), and targeting macrophage phenotype is a promising strategy to prolong it. Ras guanine nucleotide-releasing protein 4 (RasGRP4) is a signaling protein involved in immune regulation. This study aimed to investigate how RasGRP4 contributes to kidney fibrosis by regulating scar-associated macrophages (SAM). Kidney biopsy tissues and peripheral blood mononuclear cells (PBMCs) were collected from diabetic patients. Findings indicated that RasGRP4-expressing macrophages infiltrated the kidneys more extensively, and RasGRP4 levels in PBMCs rose with the progression of proteinuria. The DKD model was constructed using RasGRP4 knockout mice to assess the impact of RasGRP4 on renal interstitial fibrosis. Transcriptomic sequencing of PBMCs revealed that RasGRP4 reduced the expression of the downstream gene Arachidonate lipoxygenase 3 (Aloxe3), which colocalized with RasGRP4 in macrophages. Aloxe3 was found to enhance oxidative stress, promoting the infiltration of Trem2SPP1SAM and the release of fibrotic mediators. In vitro experiments showed that silencing RasGRP4 or Aloxe3 in macrophages downregulated oxidative stress and fibrosis markers associated with SAM. This study is the first to identify RasGRP4 as a key mediator in diabetic kidney fibrosis, acting through Aloxe3-mediated oxidative stress and facilitating SAM activation, thus offering new therapeutic insights for DKD.