Key module genes in proximal tubular cells drive microenvironmental chronic inflammation and fibrosis in diabetic kidney disease: A single-cell transcriptomic study.

Diabetic kidney disease (DKD) is one of the most severe microvascular complications of diabetes, with proximal tubular (PT) epithelial cells playing a pivotal role in its progression, yet the underlying dynamic molecular mechanisms remain unclear. In this study, single-cell transcriptomic dataset GSE183276 and bulk RNA-seq dataset GSE30122 were integrated to systematically analyze the heterogeneity and functional alterations of PT epithelial cells in DKD. PT epithelial cells were classified into three subpopulations: PT-Homeostatic, PT-Transitional and PT-Stressed. In DKD, the PT-Homeostatic subpopulation decreased markedly, whereas PT-Transitional and PT-Stressed subpopulations increased significantly. Functional enrichment analyses revealed that PT-Homeostatic cells mainly participated in amino acid and fatty acid metabolism; PT-Transitional cells were enriched in wound repair, Wnt signaling and oxidative stress response; PT-Stressed cells were associated with fibroblast proliferation, anti-apoptosis and chemotaxis regulation. Pseudotime analysis indicated that PTECs gradually shift from a homeostatic to a stressed phenotype during DKD progression. Eight core downregulated genes were further screened, among which HPGD and G6PC were specifically highly expressed in PT-Homeostatic cells and significantly downregulated in DKD. In vitro experiments demonstrated that high glucose repressed transcription factor RXRA expression to further reduce G6PC transcription. RXRA overexpression restored G6PC levels, inhibited pro-inflammatory and fibrotic markers, and upregulated E-cadherin, while G6PC knockdown reversed these protective effects. Collectively, this study uncovered the dynamic phenotypic transition of PTECs in DKD and identified the RXRA-G6PC axis as a potential therapeutic target.