Single-cell NAD(H) levels predict clonal lymphocyte expansion dynamics.

Adaptive immunity requires the expansion of high-affinity lymphocytes from a heterogeneous pool. Whereas current models explain this through signal transduction, we hypothesized that antigen affinity tunes discrete metabolic pathways to license clonal lymphocyte dynamics. Here, we identify nicotinamide adenine dinucleotide (NAD) biosynthesis as a biochemical hub for the T cell receptor affinity-dependent metabolome. Through this central anabolic role, we found that NAD biosynthesis governs a quiescence exit checkpoint, thereby pacing proliferation. Normalizing cellular NAD(H) likewise normalizes proliferation across affinities, and enhancing NAD biosynthesis permits the expansion of lower affinity clones. Furthermore, single-cell differences in NAD(H) could predict division potential for both T and B cells, before the first division, unmixing proliferative heterogeneity. We believe that this supports a broader paradigm in which complex signaling networks converge on metabolic pathways to control single-cell behavior.

Sirtuin 1 aggravates hypertrophic heart failure caused by pressure overload via shifting energy metabolism.

Sirtuin1 (SIRT1) is involved in regulating substrate metabolism in the cardiovascular system. Metabolic homeostasis plays a critical role in hypertrophic heart failure. We hypothesize that cardiac SIRT1 can modulate substrate metabolism during pressure overload-induced heart failure. The inducible cardiomyocyte Sirt1 knockout (icSirt1-/-) and its wild type littermates (Sirt1f/f) C57BL/6J mice were subjected to transverse aortic constriction (TAC) surgery to induce pressure overload. The pressure overload induces upregulation of cardiac SIRT1 in Sirt1f/f but not icSirt1-/- mice. The cardiac contractile dysfunctions caused by TAC-induced pressure overload occurred in Sirt1f/f but not in icSirt1-/- mice. Intriguingly, Sirt1f/f heart showed a drastic reduction in systolic contractility and electric signals during post-TAC surgery, whereas icSirt1-/- heart demonstrated significant resistance to pathological stress by TAC-induced pressure overload as evidenced by no significant changes in systolic contractile functions and electric properties. The targeted proteomics showed that the pressure overload triggered downregulation of the SIRT1-associated IDH2 (isocitrate dehydrogenase 2) that resulted in increased oxidative stress in mitochondria. Moreover, metabolic alterations were observed in Sirt1f/f but not in icSirt1-/- heart in response to TAC-induced pressure overload. Thus, SIRT1 interferes with metabolic homeostasis through mitochondrial IDH2 during pressure overload. Inhibition of SIRT1 activity benefits cardiac functions under pressure overload-related pathological conditions.

Activated Protein C Strengthens Cardiac Tolerance to Ischemic Insults in Aging.

BACKGROUND: APC (activated protein C) is a plasma serine protease with anticoagulant and anti-inflammatory activities. EPCR (Endothelial protein C receptor) is associated with APC's activity and mediates its downstream signaling events. APC exerts cardioprotective effects during ischemia and reperfusion (I/R). This study aims to characterize the role of the APC-EPCR axis in ischemic insults in aging. METHODS: Young (3-4 months) and aged (24-26 months) wild-type C57BL/6J mice, as well as EPCR point mutation (EPCRR84A/R84A) knockin C57BL/6J mice incapable of interaction with APC and its wild type of littermate C57BL/6J mice, were subjected to I/R. Wild-type APC, signaling-selective APC-2Cys, or anticoagulant-selective APC-E170A were administrated before reperfusion. RESULTS: The results demonstrated that cardiac I/R reduces APC activity, and the APC activity was impaired in the aged versus young hearts possibly attributable to the declined EPCR level with aging. Serum EPCR measurement showed that I/R triggered the shedding of membrane EPCR into circulation, while administration of APC attenuated the I/R-induced EPCR shedding in both young and aged hearts. Subsequent echocardiography showed that APC and APC-2Cys but not APC-E170A ameliorated cardiac dysfunction during I/R in both young and aged mice. Importantly, APC elevated the resistance of the aged heart to ischemic insults through stabilizing EPCR. However, all these cardioprotective effects of APC were blunted in the EPCRR84A/R84A mice versus its wild-type littermates. The ex vivo working heart and metabolomics results demonstrated that AMPK (AMP-activated protein kinase) mediates acute adaptive response while AKT (protein kinase B) is involved in chronic metabolic programming in the hearts with APC treatment. CONCLUSIONS: I/R stress causes shedding of the membrane EPCR in the heart, and administration of APC prevents I/R-induced cardiac EPCR shedding that is critical for limiting cardiac damage in aging.