BACKGROUND: Long-term high-fat diet (HFD) consumption is associated with the development of metabolic cardiomyopathy and contributes to accelerated cardiac aging. Nicotinamide mononucleotide (NMN), a key NADprecursor, has shown promise in ameliorating age-related cardiac decline, but its mechanisms are not fully understood. +
METHODS: 14-month-old male C57BL/6J mice were divided into three groups: normal-diet (ND) group, high-fat diet (HFD) group and HFD+NMN group. NMN was added to their drinking water at a dose of 400 mg/kg for 7 months. Cardiac tissues were collected and analyzed using hematoxylin and eosin (H&E) and Masson's trichrome staining, Western blotting, Quantitative Real-Time PCR, and immunohistochemistry. In vitro, H9c2 cardiomyocytes were exposed to palmitic acid (PA) to establish a lipotoxicity model, and the effects of NMN on cell viability and autophagy flux were assessed via MTT assay and mRFP-GFP-LC3 adenoviral transfection.
RESULTS: Compared to HFD group, NMN treatment significantly reduced the heart index, ameliorated myocardial fibrosis, and decreased the expression levels of senescence-associated secretory phenotype (SASP) markers (Serpine1, MMP3, CXCL-1, CXCL-10, P16; P<0.05), as well as senescence markers (P21 and β-gal; P<0.01), pro-inflammatory cytokines (IL-1β and TNF-α; P<0.05) and apoptotic indicators (Bax/Bcl-2 ratio, cleaved caspase-3; P<0.01). Conversely, NMN treatment upregulated the levels of anti-inflammatory factor IL-10 (P<0.01) in the cardiac tissue. Furthermore, NMN treatment increased protein levels of Sirt3, PINK1 and Parkin (P<0.01), and enhanced autophagy-lysosomal markers including LC3-II/LC3-I ratio and TFEB (P<0.05), alongside decreased p62 level (P<0.01) in cardiac tissue. In H9c2 cardiomyocytes, NMN treatment significantly attenuated PA-induced cytotoxicity (P<0.01) and enhanced PA-induced the impaired autophagy flux. Notably, these protective effects were abolished by co-treatment with 3-TYP, a selective Sirt3 inhibitor.
CONCLUSION: NMN alleviates HFD-induced myocardial damage of aging mice by activating the Sirt3/PINK1/Parkin signaling pathway, enhancing autophagy-lysosomal function. These findings indicate that NMN is a promising therapeutic candidate for the treatment of metabolic cardiomyopathy.
