Background/Purpose: Systemic sclerosis (SSc) is characterized by progressive fibrosis driven by sustained fibroblast activation and senescence. Nicotinamide N-methyltransferase (NNMT), a SAM-dependent enzyme, is upregulated in SSc and contributes to both NAD⁺ depletion and methylation imbalance. This study evaluates the therapeutic impact of a novel bisubstrate NNMT inhibitor, II559, in modulating fibroblast activation and reversing metabolic-epigenetic dysfunction in SSc.

Methods: We utilized TGF-β1 to induce fibroblast activation in healthy dermal fibroblasts and evaluated basal activity in primary SSc fibroblasts. Cells were treated with 30 µM II559 for 48–72 hours. Gene and protein expression of fibrosis markers (COL1A1, α-SMA, Fibronectin), senescence markers (p16, p21), and inflammatory cytokines (IL-6, IL-8) were assessed by qPCR, Western blot, and immunofluorescence. Epigenetic status was evaluated using H3K27me3 staining. 1MNA levels were measured to assess NNMT enzymatic activity. In vivo, a bleomycin-induced mouse model of dermal fibrosis was treated with II559 (10 mg/kg, intraperitoneally) for 28 days. Hydroxyproline, NAD⁺, SAM, and SAH levels were quantified in skin tissues.

Results: TGF-β1 increased NNMT, fibrotic markers, inflammatory cytokines (Fig 1A,2A,2C), and reduced H3K27me3 (Fig 2C) in healthy fibroblasts; all were reversed by II559. In SSc fibroblasts, II559 downregulated p16/p21 (Fig 1B) and ECM proteins (Fig 1A), and restored repressive H3K27me3 marks. 1MNA levels were elevated with TGF-β1 and suppressed with II559 (Fig 2B, 3B), confirming target engagement. In vivo, II559 reduced skin fibrosis, hydroxyproline content, and restored NAD⁺ and SAM without altering SAH levels (Fig 3A), suggesting recovery of redox and methylation potential.

Conclusion: NNMT acts as a metabolic-epigenetic driver of fibrosis in SSc. II559 reverses fibroblast activation by restoring NAD⁺ and histone methylation balance, suppressing pro-fibrotic and inflammatory pathways. These findings support NNMT inhibition as a promising therapeutic strategy in SSc and justify further investigation through transcriptomic and chromatin accessibility profiling.

« Back to ACR Convergence 2025

ACR Meeting Abstracts - https://acrabstracts.org/abstract/inhibition-of-nicotinamide-n-methyltransferase-reverses-fibroblast-activation-via-epigenetic-and-metabolic-remodeling-in-systemic-sclerosis/