Mukherjee, Shreyartha

Myocardial infarction (MI) remains a leading cause of mortality worldwide, yet effective cardioprotective strategies remain limited in clinical settings. Vascular endothelial growth factor B (VEGFB) has emerged as a promising therapeutic candidate in MI, but the role of its co-receptor, Neuropilin-1 (NRP1), in cardiomyocyte (CM) survival under ischemic stress remains poorly understood. Here, we investigated VEGFB-NRP1 signaling using an in vivo zebrafish model of cardiac injury as well as in vitro hypoxia models in CMs. We demonstrated that VEGFB overexpression conferred protection against ischemic injury and enhanced cardiac regeneration in the zebrafish heart. Mechanistically, we showed that VEGFB treatment enhances CM viability through reducing reactive oxygen species (ROS), ferroptosis activation, and preserving mitochondrial integrity. We also demonstrated that NRP1 knockdown in the CMs abolished the VEGFB-mediated protective effects, indicating the significant role of NRP1 signaling in VEGFB-induced cardioprotective effects in MI. Lastly, using transcriptome analysis, we confirmed that VEGFB induces anti-apoptotic and anti-ferroptosis gene programs in CMs in response to hypoxic stress. Collectively, our findings provide mechanistic insight into cell death activation pathways, including ferroptosis, in response to ischemic stress and further validate the therapeutic potential of VEGFB in promoting CM survival in ischemic heart disease.

ABSTRACT Nicotinamide adenine dinucleotide (NAD) is a key coenzyme involved in energy metabolism, DNA repair, and cellular signaling. While the effects of acute NAD depletion have been better characterized, the consequences of chronic NAD deficiency remain unclear. Here, we investigated the impact of chronic NAD depletion in cultured cells by removing the availability of nicotinamide (NAM), a key precursor for NAD synthesis, from the culture media. In NIH3T3 fibroblasts, NAM depletion caused a dramatic drop in intracellular NAD levels within 2 days. Remarkably, the cells remained viable even after 7–14 days of NAM depletion, despite NAD + levels falling to less than 10% of control conditions. This chronic NAD depletion led to distinct metabolic alterations. Mitochondrial basal respiration remained unchanged, but cells exhibited reduced spare respiratory and maximal capacities, along with significantly impaired glycolysis. Notably, NAD depletion triggered an interferon‐dependent inflammatory response, resembling viral infections. This was driven by cytosolic leakage of mitochondrial DNA (mtDNA) through voltage‐dependent anion channel 1 (VDAC1), which activated the cGAS‐STING signaling pathway. Inhibition of VDAC oligomerization with VBIT‐4, STING signaling with H‐151, or mtDNA depletion blocked the upregulation of interferon genes induced by NAM depletion. Similar interferon responses triggered by NAD depletion were observed in IMR90 human fibroblasts and HS5 stromal cells. Our findings reveal a novel link between chronic NAD deficiency, VDAC‐mediated mtDNA release to the cytoplasm, and the activation of the inflammatory response, providing new insight into how NAD decline affects cellular metabolic and inflammatory processes.