Stromal NNMT links metabolic and epigenetic drivers of fibrosis in systemic sclerosis

Summary: Abstract Body: Background: Fibroblasts in systemic sclerosis (SSc) show striking cellular metabolic and epigenetic changes. Enzymes mediating fibroblast activation and senescence require NAD. NAD bioavailability is regulated by nicotinamide N-methyl transferase (NNMT), which converts nicotinamide (NAM) to 1-MNAM, thereby disrupting the NAD salvage pathway and methylation donors. Since NNMT is a hub gene in SSc, and its product 1-MNAM is elevated in SSc patients, here we sought to characterize the pathogenic role of NNMT. Methods: Expression and regulation of NNMT was measured in SSc skin biopsies and explanted fibroblasts. Its pathogenic role was examined using genetic and pharmacological loss -of-function experiments in isolated human fibroblasts, 3D systems and in animal models. Results: NNMT was significantly elevated in SSc skin biopsies and localized to COL8A1+ fibroblasts. In vitro, NNMT expression and activity were stimulated by TGF-ß, and constitutively up-regulated in SSc fibroblasts. Inhibiting NNMT with a novel small molecule mitigated cellular senescence, oxidative stress and fibrotic phenotypes in healthy and SSc fibroblasts, while boosting NAD levels and H3K4 methylation. Treatment with NNMT inhibitor prevented and reversed bleomycin-induced skin fibrosis in C57/BL6 mice. NNMT-null mice showed elevated NAD and altered fibrosis. Conclusions: Upregulation of the inducible metabolic enzyme NNMT in stromal cells has a previously unrecognized role in pathological fibrosis. Thus, targeting NNMT with selective inhibitors represents an entirely novel therapeutic approach for SSc and other fibrotic diseases. Kamal Saba², Bo Shi¹, Hassan Draz², John Keyorkgy², Christiana Kapetaneas², Priyanka Verma², Matija Bajzelj², Brendon Baker², Ernst Lengyel³, Nicholas Lukacs², Kristine E. Konopka², Pei-Suen Tsou², Dinesh Khanna², Poulami Dey², Johann E. Gudjonsson², Eduardo Chini⁴, M. Asif Amin², John Varga² 1. Northwestern University, Evanston, IL, United States. 2. University of Michigan, Ann Arbor, MI, United States. 3. The University of Chicago Division of the Biological Sciences, Chicago, IL, United States. 4. Mayo Foundation for Medical Education and Research, Rochester, MN, United States. Translational Studies: Cell and Molecular Biology