NNMT Safeguards Vascular Aging by Modulating an Endothelial LMNA-HSP Stress-Response Axis

BACKGROUND: NNMT (nicotinamide N-methyltransferase) is a pivotal metabolic-epigenetic integrator that regulates cellular methylation balance. Although its expression and function exhibit profound, context-dependent heterogeneity in metabolic diseases and cancer, its role within the vascular system, particularly in aging endothelial cells, remains elusive. METHODS: We examined NNMT expression in a small, pathological, male-only cohort of older versus younger plaque-adjacent human carotid intimal donors, primary mouse aortic endothelial cells, and senescent human umbilical vein endothelial cells. Using endothelial-targeted adeno-associated virus–Tie systems, we assessed the effects of NNMT restoration and knockdown on vasodilation and arterial stiffness in aged mice. Mechanistic insights were obtained through exploratory multiomics integration. RESULTS: We established that NNMT expression exhibits an exploratory inverse association in a small, pathological, male-only cohort of older versus younger plaque-adjacent human carotid intimal donors, a pattern mirrored by declines observed in primary mouse aortic endothelial cells and senescent human umbilical vein endothelial cells. Functional assays demonstrated that NNMT restoration improves vasodilation and arterial stiffness in aged mice, whereas knockdown exacerbates these deficits. Mechanistically, exploratory multiomics integration, including Cleavage Under Targets and Tagmentation and transcriptomic analyses, suggests that NNMT-associated reduction in histone H3 lysine 27 trimethylation occupancy at the LMNA (lamin A/C) promoter correlates with its transcriptional maintenance, a process influenced by S-adenosylmethionine supplementation. Downstream, we identified that NNMT-induced LMNA stabilization operates in concert with HSF1 (heat shock transcription factor 1) activation and nuclear translocation, a process accompanied by enhanced binding to HSP90 and HSP70 promoters to drive their transcription. Furthermore, we demonstrated that the vascular protective effects of the natural compound Heterophyllin B are mediated, at least in part, by NNMT, as these benefits were partially attenuated after endothelial NNMT knockdown in vivo. CONCLUSIONS: We identify a protective, age-dependent role for NNMT in vascular endothelium. Our findings reveal that NNMT maintains endothelial homeostasis through coordinated regulation of nuclear LMNA and the downstream HSP (heat shock protein) stress response, highlighting the therapeutic potential of this pathway for addressing age-related endothelial dysfunction.