Background: Switching from the acute early initiation to late adaptation response after TLR4 stimulation depends on SirT1. Results: Switching from glucose to fatty acid oxidation between initiation and adaptation responses requires SirT6 and SirT1. Conclusion: Bioenergy integrates metabolism and acute inflammation. Significance: Understanding bioenergy shifts during inflammation may enable development of new therapies.

Gene-selective epigenetic reprogramming and shifts in cellular bioenergetics develop when Toll-like receptors (TLR) recognize and respond to systemic life-threatening infections. Using a human monocyte cell model of endotoxin tolerance and human leukocytes from acute systemic inflammation with sepsis, we report that energy sensor sirtuin 1 (SIRT1) coordinates the epigenetic and bioenergy shifts. After TLR4 signaling, SIRT1 rapidly accumulated at the promoters of TNF-␣ and IL-1␤, but not IB␣; SIRT1 promoter binding was dependent on its co-factor, NAD ؉ . During this initial process, SIRT1 deacetylated RelA/ p65 lysine 310 and nucleosomal histone H4 lysine 16 to promote termination of NFB-dependent transcription. SIRT1 then remained promoter bound and recruited de novo induced RelB, which directed assembly of the mature transcription repressor complex that generates endotoxin tolerance. SIRT1 also promoted de novo expression of RelB. During sustained endotoxin tolerance, nicotinamide phosphoribosyltransferase (Nampt), the rate-limiting enzyme for endogenous production of NAD ؉ , and SIRT1 expression increased. The elevation of SIRT1 required protein stabilization and enhanced translation. To support the coordination of bioenergetics in human sepsis, we observed elevated NAD ؉ levels concomitant with SIRT1 and RelB accumulation at the TNF-␣ promoter of endotoxin tolerant sepsis blood leukocytes. We conclude that TLR4 stimulation and human sepsis activate pathways that couple NAD ؉ and its sensor SIRT1 with epigenetic reprogramming.Two cellular processes predictably accompany TLR-mediated acute systemic inflammation caused by sepsis, a highly destructive and often lethal process. The first process occurs when epigenetic alterations reprogram distinct functional sets of genes to both activate and repress transcription of hundreds of genes (1, 2); this transcriptome reprogramming generates the phenomenon known as endotoxin tolerance (3). Endotoxin tolerance requires TLR 3 receptor signaling of NFB master regulator, which first induces and then represses rapid response and potentially autotoxic proinflammatory TNF-␣ and IL-1␤. To control the initial recognition and response phases induced by TLR, gene-specific reprogramming selectively modifies chromatin structure and shifts nucleosomes on responsive euchromatin to form silent heterochromatin at acute proinflammatory genes; in contrast, genes encoding anti-inflammatory and antimicrobial mediators maintain responsive euchromatin (4, 5). This gene set-selective reprogramming generates a clinically relevant phenotypic transition from the hyperinflammatory to the hypoinflammatory endotoxin tolerant state, which may last hours, days, or weeks, depending on the strength of the initial TLR response (4, 5). The physiologic importance of endotoxin tolerance is still incompletely understood, but likely reflects an attempt to recover homeostasis (3).Others and we (6 -9) reported how temporal transitions in epigenetic programming alter the course of acute inflammation. NFB master ...

Sirtuins (SIRT), first discovered in yeast as NAD+ dependent epigenetic and metabolic regulators, have comparable activities in human physiology and disease. Mounting evidence supports that the seven-member mammalian sirtuin family (SIRT1–7) guard homeostasis by sensing bioenergy needs and responding by making alterations in the cell nutrients. Sirtuins play a critical role in restoring homeostasis during stress responses. Inflammation is designed to “defend and mend” against the invading organisms. Emerging evidence supports that metabolism and bioenergy reprogramming direct the sequential course of inflammation; failure of homeostasis retrieval results in many chronic and acute inflammatory diseases. Anabolic glycolysis quickly induced (compared to oxidative phosphorylation) for ROS and ATP generation is needed for immune activation to “defend” against invading microorganisms. Lipolysis/fatty acid oxidation, essential for cellular protection/hibernation and cell survival in order to “mend,” leads to immune repression. Acute/chronic inflammations are linked to altered glycolysis and fatty acid oxidation, at least in part, by NAD+ dependent function of sirtuins. Therapeutically targeting sirtuins may provide a new class of inflammation and immune regulators. This review discusses how sirtuins integrate metabolism, bioenergetics, and immunity during inflammation and how sirtuin-directed treatment improves outcome in chronic inflammatory diseases and in the extreme stress response of sepsis.

Mechanism-based sepsis treatments are unavailable, and their incidence is rising worldwide. Deaths occur during the early acute phase of hyperinflammation or subsequent postacute hypoinflammatory phase with sustained organ failure. The acute sepsis phase shifts rapidly, and multiple attempts to treat early excessive inflammation have uniformly failed. We reported in a sepsis cell model and human sepsis blood leukocytes that nuclear NAD+ sensor SIRT1 deacetylase remodels chromatin at specific gene sets to switch the acute-phase proinflammatory response to hypoinflammatory. Importantly, SIRT1 chromatin reprogramming is reversible, suggesting that inhibition of SIRT1 might reverse postacute-phase hypoinflammation. We tested this concept in septic mice, using the highly specific SIRT1 inhibitor EX-527, a small molecule that closes the NAD+ binding site of SIRT1. Strikingly, when administered 24 h after sepsis, all treated animals survived, whereas only 40% of untreated mice survived. EX-527 treatment reversed the inability of leukocytes to adhere at the small intestine MVI, reversed in vivo endotoxin tolerance, increased leukocyte accumulation in peritoneum, and improved peritoneal bacterial clearance. Mechanistically, the SIRT1 inhibitor restored repressed endothelial E-selectin and ICAM-1 expression and PSGL-1 expression on the neutrophils. Systemic benefits of EX-527 treatment included stabilized blood pressure, improved microvascular blood flow, and a shift toward proimmune macrophages in spleen and bone marrow. Our findings reveal that modifying the SIRT1 NAD+ axis may provide a novel way to treat sepsis in its hypoinflammatory phase.

Background: Nuclear SIRT1 and SIRT6 switch monocyte energy sources from glycolysis to fatty acid oxidation during sepsis adaptation. Results: Sequential actions of nuclear SIRT1 and RELB differentially induce SIRT3 expression and increase mitochondrial biogenesis during sepsis adaptation. Conclusion: SIRT1 and RELB link nuclear and mitochondrial alterations in bioenergetics during sepsis. Significance: Communication between nuclear and mitochondrial functions may influence sepsis outcomes.

These findings suggest that the increased morbidity to sepsis in obesity may result from exaggerated microvascular inflammatory and thrombogenic responses that include the activation of endothelial cells with subsequent expression of adhesion molecules, such as P-selectin.

We review the emerging concept that changes in cellular bioenergetics concomitantly reprogram inflammatory and metabolic responses. The molecular pathways of this integrative process modify innate and adaptive immune reactions associated with inflammation, as well as influencing the physiology of adjacent tissue and organs. The initiating proinflammatory phase of inflammation is anabolic and requires glucose as the primary fuel, whereas the opposing adaptation phase is catabolic and requires fatty acid oxidation. The fuel switch to fatty acid oxidation depends on the sensing of AMP and NAD(+) by AMPK and the SirT family of deacetylases (e.g., SirT1, -6, and -3), respectively, which couple inflammation and metabolism by chromatin and protein reprogramming. The AMP-AMPK/NAD(+)-SirT axis proceeds sequentially during acute systemic inflammation associated with sepsis but ceases during chronic inflammation associated with diabetes, obesity, and atherosclerosis. Rebalancing bioenergetics resolves inflammation. Manipulating cellular bioenergetics is identifying new ways to treat inflammatory and immune diseases.

Expression of the inflammatory cytokine TNF is tightly controlled. During endotoxin tolerance, transcription of TNF mRNA is repressed, although not entirely eliminated. Production of TNF cytokine, however, is further controlled by post-transcriptional regulation. In this study, we detail a mechanism of post-transcriptional repression of TNF mRNA by GAPDH binding to the TNF 3’UTR. Using RNA immunoprecipitation, we demonstrate that GAPDH-TNF mRNA binding increases when THP-1 monocytes are in a low glycolysis state, and that this binding can be reversed by knocking down GAPDH expression or by increasing glycolysis. We show that reducing glycolysis decreases TNF mRNA association with polysomes. We demonstrate that GAPDH-TNF mRNA binding results in post-transcriptional repression of TNF and that the TNF mRNA 3’UTR is sufficient for repression. Finally, after exploring this model in THP-1 cells, we demonstrate this mechanism affects TNF expression in primary human monocytes and macrophages. We conclude that GAPDH-TNF mRNA binding regulates expression of TNF based on cellular metabolic state. We believe this mechanism has potentially significant implications for treatment of various immunometabolic conditions, including immune paralysis during septic shock.