A Bisubstrate Inhibitor of NNMT Suppresses Myofibroblast Reprogramming to Mitigate Skin Fibrosis

Systemic sclerosis (SSc) is characterized by fibroblast activation and fibrosis of the skin and multiple organs. Metabolic reprogramming is a critical determinant of fibroblast fate. Nicotinamide N-methyltransferase (NNMT), which links NAD⁺ metabolism with cellular methylation pathways, has emerged as a regulator of fibroblast activation. To investigate how NNMT modulates profibrotic fibroblast programming and skin fibrosis, the effects of the bisubstrate-like NNMT inhibitor II559 were examined in transforming growth factor-β (TGF-β)-stimulated foreskin, healthy, and SSc skin fibroblasts, and in bleomycin-induced skin fibrosis in mice. Fibrotic gene expression, extracellular matrix (ECM) production, metabolic intermediates, and H3K27-associated chromatin methylation was assessed. Treatment with II559 suppressed TGF-β-induced myofibroblast differentiation and reduced stimulation of profibrotic genes in healthy fibroblasts, and attenuated constitutive fibrotic gene expression and ECM secretion in SSc fibroblasts. Mechanistically, NNMT inhibition lowered 1-methylnicotinamide levels (1-MNA), restored methylation potential, and increased repressive H3K27me3 chromatin marks. In bleomycin-treated mice, NNMT inhibition reduced dermal thickening and collagen accumulation while preserving dermal white adipose tissue. These changes were accompanied by restoration of NAD homeostasis and methylation balance. These findings identify NNMT as a cell-autonomous regulator of metabolic and epigenetic reprogramming in fibroblasts and support pharmacologic NNMT inhibition as a potential therapeutic strategy for SSc skin fibrosis.