Project description:Cellular senescence is a stable cell growth arrest that is implicated in tissue aging and cancer. Senescent cells are characterized by an upregulation of proinflammatory and immunosuppressive cytokines and chemokines, which is termed as senescence-associated secretory phenotype (SASP). NAD+ metabolism plays a critical role in both tissue aging and cancer. However, the role of NAD+ metabolism in regulating the SASP is not well understood. Here we show that nicotinamide phosphoribosyltransferase (NAMPT), the rate-limiting enzyme of the NAD+ salvage pathway, governs the strengths of proinflammatory SASP during senescence. In contrast to downregulation of NAMPT during replicative senescence, NAMPT is upregulated during oncogene-induced senescence. NAMPT selectively regulates proinflammatory, but not immunosuppressive, SASP. NAMPT is regulated by HMGA1 through a distal enhancer element during senescence. HMGA1/NAMPT/NAD+ signaling axis promotes proinflammatory SASP through enhancing glycolysis and mitochondria respiration. Mechanistically, HMGA1/NAMPT promotes proinflammatory SASP through NAD+-mediated suppression of AMPK kinase, which suppresses p53-mediated inhibition of p38MAPK to enhance NFb activity. SASP regulation by NAD+ metabolism is independent of senescence-associated cell growth arrest. An increase in NAD+ levels is sufficient to convert SASP from low to high levels during replicative senescence. Together, we conclude that NAD+ metabolism governs the strengths of proinflammatory SASP. Given the tumor promoting effects of proinflammatory SASP, our results suggest that anti-ageing dietary NAD+ augmentation should be administered with precision.
Project description:Cellular senescence is a stable growth arrest that is implicated in tissue ageing and cancer. Senescent cells are characterized by an upregulation of proinflammatory cytokines, which is termed the senescence-associated secretory phenotype (SASP). NAD+ metabolism influences both tissue ageing and cancer. However, the role of NAD+ metabolism in regulating the SASP is poorly understood. Here, we show that nicotinamide phosphoribosyltransferase (NAMPT), the rate-limiting enzyme of the NAD+ salvage pathway, governs the proinflammatory SASP independent of senescence-associated growth arrest. NAMPT expression is regulated by high mobility group A (HMGA) proteins during senescence. The HMGA-NAMPT-NAD+ signalling axis promotes the proinflammatory SASP by enhancing glycolysis and mitochondrial respiration. HMGA proteins and NAMPT promote the proinflammatory SASP through NAD+-mediated suppression of AMPK kinase, which suppresses the p53-mediated inhibition of p38 MAPK to enhance NF-κB activity. We conclude that NAD+ metabolism governs the proinflammatory SASP. Given the tumour-promoting effects of the proinflammatory SASP, our results suggest that anti-ageing dietary NAD+ augmentation should be administered with precision.
Project description:Alzheimer's disease (AD) is a severe neurodegenerative disorder. Clinical trials to identify agents to treat AD have failed, and its underlying molecular pathology and etiology remain elusive. Neuroinflammation is thought to play a key role in the progression of AD. Emerging evidence has identified lower Nicotinamide adenine dinucleotide (NAD+) levels as a major factor in neurodegeneration, especially in AD. NAD+ is an important metabolite in all human cells, as it is at the convergence of many central processes in cellular and mitochondrial maintenance, including DNA repair and mitophagy (the degradation of damaged mitochondria). Our previous work found that treatment of 3xTgAD mice with an NAD+ precursor, nicotinamide riboside (NR), can improve key AD features including tau phosphorylation and learning deficits in mice. Here we used the APP/PS1 AD mouse model to interrogate the effect of NR on neuroinflammation. Microarray analysis revealed major changes in pathways and genes associated with inflammation and the APP/PS1 mice had lower NAD+ levels than WT mice. Thus, seven months old mice were treated with NR for five months and their NAD+/NADH ratio increased. Brain neuroinflammation decreased as determined by decreased activation of astrocytes and microglia, decreased pro-inflammatory cytokines and chemokines in the brains of the APP/PS1 mice. NR decreased neuroinflammation by lowering the NLRP3 inflammasome and NF-κB pathways. NR also attenuated DNA damage and apoptosis in the AD mouse brains. NR dramatically decreased senescence in the hippocampus and cortex of AD mice, relative to controls. Recent studies suggest that cyclic GMP-AMP synthase (cGAS) and stimulator of interferon genes (STING) activation are associated with DNA damage and senescence. cGAS-STING was activated in AD mice and decreases after NR treatment. Suggesting that NR can diminish neuroinflammation and senescence through the cGAS-STING pathway. NR treatment also greatly improved cognition and synaptic function in the APP/PS1 mice. We propose that the cGAS-STING pathway should be evaluated as a potential novel therapeutic target in AD.
Project description:During the progression of type 1 diabetes (T1D), β-cells are exposed to significant stress and therefore require adaptive responses to survive. The adaptive mechanisms that can preserve β-cell function and survival in the face of autoimmunity remain unclear. Here we show that deletion of the unfolded protein response genes, Atf6α or Ire1α, in β-cells of NOD mice prior to insulitis generates a p21-driven early senescence phenotype and altered β-cell secretome that significantly enhances leukemia inhibitory factor-mediated recruitment of M2 macrophages to the islets. Consequently, M2 macrophages promote anti-inflammatory responses and immune surveillance that cause resolution of islet inflammation, removal of terminally senesced β-cells, reduction of β-cell apoptosis, and prevention of T1D. We further demonstrate that p21-mediated early senescence signature is conserved in residual β-cells of T1D patients. Our findings reveal a previously unrecognized link between β-cell UPR and senescence that, if leveraged, may represent a novel therapeutic strategy for T1D.
Project description:Senescence phenotypes and mitochondrial dysfunction are implicated in aging and neurodegeneration, and in the premature aging disease, including A-T. Loss of mitochondrial function can drive age-related decline in the brain, but little is known about whether improving mitochondrial homeostasis alleviates senescence phenotypes. Here we demonstrate impaired mitochondrial function and increased senescence growth arrest with senescence-associated secretory phenotype (SASP) in A-T patient fibroblasts, and in ATM-deficient cells and mice. We find that boosting intracellular NAD+ levels with nicotinamide riboside (NR) reduces senescence, suppresses neuroinflammation, and improves motor function in Atm-/- mice. We further show that the senescence responses are mediated by stimulator of interferon genes (STING), which is activated by cytoplasmic mtDNA and that NR prevents senescence and neuroinflammation through stimulation of mitophagy. Our findings suggest a pivotal role for mitochondrial dysfunction induced senescence in A-T pathogenesis, and that enhancing mitophagy is a potential therapeutic intervention.
Project description:Senescence phenotypes and mitochondrial dysfunction are implicated in aging and neurodegeneration, and in the premature aging disease, including A-T. Loss of mitochondrial function can drive age-related decline in the brain, but little is known about whether improving mitochondrial homeostasis alleviates senescence phenotypes. Here we demonstrate impaired mitochondrial function and increased senescence growth arrest with senescence-associated secretory phenotype (SASP) in A-T patient fibroblasts, and in ATM-deficient cells and mice. We find that boosting intracellular NAD+ levels with nicotinamide riboside (NR) reduces senescence, suppresses neuroinflammation, and improves motor function in Atm-/- mice. We further show that the senescence responses are mediated by stimulator of interferon genes (STING), which is activated by cytoplasmic mtDNA and that NR prevents senescence and neuroinflammation through stimulation of mitophagy. Our findings suggest a pivotal role for mitochondrial dysfunction induced senescence in A-T pathogenesis, and that enhancing mitophagy is a potential therapeutic intervention.