Injured proximal tubule-driven paracrine signaling promotes lipid-associated macrophage expansion and chondroitin sulfate biosynthesis via PPARG/TCF12 in diabetic kidney disease.

BACKGROUND

Diabetic kidney disease (DKD) is a leading cause of end-stage renal disease, yet its immune-mediated pathogenesis remains incompletely understood. Lipid-associated macrophages (LAMs) have emerged as key mediators of metabolic tissue injury, but their role in DKD and the upstream signals governing their transcriptional programs are undefined.

METHODS

We performed integrative single-cell transcriptomic analysis of 133,303 kidney cells (GSE211785), incorporating pseudotime trajectory analysis, SCENIC regulon inference, and CellChat/NicheNet intercellular communication modeling. Key findings were validated in an independent bulk RNA-seq cohort (GSE142025, n = 36) and in vitro by stimulating CD14+ monocyte-derived macrophages with conditioned medium from iPT-like HK-2 cells, followed by siRNA knockdown of PPARG, TCF12, and ANXA2.

RESULTS

LAMs were markedly expanded in DKD kidneys (~6.2-fold; 13.1% vs. 2.1% in controls) across both SC-RNA-seq and SN-RNA-seq platforms. SCENIC identified PPARG and TCF12 as dominant LAM-enriched transcription factor regulons, with downstream target genes converging on chondroitin sulfate (CS) biosynthesis via CHST11 and CSGALNACT1. CellChat revealed that iPT exhibited the highest incoming interaction strength toward LAM among all analyzed cell populations in DKD. NicheNet prioritized 11 candidate iPT-derived ligands preferentially targeting PPARG and TCF12, nine of which were independently elevated in advanced diabetic nephropathy. In vitro, iPT conditioned medium upregulated PPARG, TCF12, CHST11, CSGALNACT1, and intracellular CS in macrophages. siRNA knockdown of ANXA2 in HK-2 cells significantly attenuated CM-induced PPARG and TCF12 upregulation in macrophages, identifying ANXA2 as a key paracrine mediator.

CONCLUSIONS

We define a novel iPT-to-LAM paracrine axis in DKD wherein tubular injury signals drive macrophage transcriptional reprogramming through PPARG and TCF12, culminating in aberrant CS biosynthesis. These findings implicate LAM-associated glycosaminoglycan remodeling as a previously unrecognized mechanism in DKD pathogenesis and identify PPARG/TCF12 as candidate therapeutic targets.