Alpha-ketoglutarate ameliorates systemic sclerosis-associated fibrosis by restoring endothelial function.

Systemic sclerosis (SSc) is a devastating autoimmune disease characterized by multi-organ fibrosis with limited therapeutic options. Using targeted metabolomics, we first observed that levels of alpha-ketoglutarate (α-KG), a key TCA-cycle intermediate, were paradoxically elevated in bleomycin-induced fibrotic lungs and in TGF-β-stimulated fibroblasts, prompting us to test whether exogenous supplementation could augment this compensatory response. Using bleomycin-induced skin and lung fibrosis mouse models, we demonstrated that oral α-KG administration significantly attenuated dermal and pulmonary collagen deposition, reduced inflammatory infiltration, and improved survival. Although fibroblasts are conventionally regarded as the central effectors of fibrosis, integrated single-cell RNA sequencing and bulk transcriptomic deconvolution unexpectedly identified endothelial cells as the predominant cellular target of α-KG in fibrotic lungs. Consistently, α-KG restored endothelial cell proportions in vivo, rescued angiogenic function and preserved barrier integrity in association with upregulation of eNOS, and tight junction proteins in human umbilical vein endothelial cells (HUVECs) treated with bleomycin. Mechanistically, α-KG suppressed TGF-β/Smad activation and reversed bleomycin-induced metabolic repression, including restoration of fatty acid oxidation signatures and mitochondrial ultrastructure, accompanied by upregulation of the mitochondrial biogenesis regulator NRF1. Collectively, these findings reveal that α-KG exerts broad anti-fibrotic effects in SSc models by protecting endothelial function and inhibiting canonical pro-fibrotic signaling, highlighting its potential as a translatable metabolic therapeutic strategy for SSc.