ObjectiveObesity increases morbidity and resource utilization in sepsis patients. Sepsis transitions from early/hyper-inflammatory to late/hypo-inflammatory phase. Majority of sepsis-mortality occurs during the late sepsis; no therapies exist to treat late sepsis. In lean mice, we have shown that sirtuins (SIRTs) modulate this transition. Here, we investigated the role of sirtuins, especially the adipose-tissue abundant SIRT-2 on transition from early to late sepsis in obese with sepsis.MethodsSepsis was induced using cecal ligation and puncture (CLP) in ob/ob mice. We measured microvascular inflammation in response to lipopolysaccharide/normal saline re-stimulation as a “second-hit” (marker of immune function) at different time points to track phases of sepsis in ob/ob mice. We determined SIRT-2 expression during different phases of sepsis. We studied the effect of SIRT-2 inhibition during the hypo-inflammatory phase on immune function and 7-day survival. We used a RAW264.7 (RAW) cell model of sepsis for mechanistic studies. We confirmed key findings in diet induced obese (DIO) mice with sepsis.ResultsWe observed that the ob/ob-septic mice showed an enhanced early inflammation and a persistent and prolonged hypo-inflammatory phase when compared to WT mice. Unlike WT mice that showed increased SIRT1 expression, we found that SIRT2 levels were increased in ob/ob mice during hypo-inflammation. SIRT-2 inhibition in ob/ob mice during the hypo-inflammatory phase of sepsis reversed the repressed microvascular inflammation in vivo via activation of endothelial cells and circulating leukocytes and significantly improved survival. We confirmed the key finding of the role of SIRT2 during hypo-inflammatory phase of sepsis in this project in DIO-sepsis mice. Mechanistically, in the sepsis cell model, SIRT-2 expression modulated inflammatory response by deacetylation of NFκBp65.ConclusionSIRT-2 regulates microvascular inflammation in obese mice with sepsis and may provide a novel treatment target for obesity with sepsis.

Limited understanding of the mechanisms responsible for life-threatening organ and immune failure hampers scientists' ability to design sepsis treatments. Pyruvate dehydrogenase kinase 1 (PDK1) is persistently expressed in immune-tolerant monocytes of septic mice and humans and deactivates mitochondrial pyruvate dehydrogenase complex (PDC), the gate-keeping enzyme for glucose oxidation. Here, we show that targeting PDK with its prototypic inhibitor dichloroacetate (DCA) reactivates PDC; increases mitochondrial oxidative bioenergetics in isolated hepatocytes and splenocytes; promotes vascular, immune, and organ homeostasis; accelerates bacterial clearance; and increases survival. These results indicate that the PDC/PDK axis is a druggable mitochondrial target for promoting immunometabolic and organ homeostasis during sepsis.

IntroductionAbnormal development of APCs can result in immunodeficiency and autoimmune disease. APCs, which include macrophages, B cells, and dendritic cells (DCs), and are critical for mediating adaptive immunity to foreign antigens as well as inducing tolerance to self-antigens. At steady state, macrophages are generated from monocytes, and classic DCs are derived from their precursor (pre-cDCs) and common DC progenitors (CDPs). [1][2][3][4][5][6] These cells are all generated from upstream macrophage-DC precursor (MDP) cells, 7-9 which are themselves derived from less lineage-restricted common myeloid progenitors (CMPs). 1 The entire populations of hematopoietic cells originate from pluripotent HSCs in the BM (see Figure 7A). Despite recent advances, the cellular factors that regulate the progression of HSCs to the development of APCs remain largely uncharacterized.Cap 'n' collar (CNC) proteins are evolutionarily conserved factors that are known to be essential for the resolution of oxidative stress. 10 In Caenorhabditis elegans, the CNC protein SKN-1 regulates longevity. 11,12 In mammals, there are 6 members within the CNC family (p45, Nrf1, Nrf2, Nrf3, Bach1, and Bach2) that heterodimerize with small Maf proteins (MafK, MafG, and MafF) to direct either gene induction or repression. 13 For instance, although the co-occupancy of p45 and MafK at genome elements activates transcription, binding of a Bach1 and MafK heterodimer to these elements results in gene repression. 14 Many different CNC and Maf heterodimers are formed, 15 causing the biology of CNC and Maf members to be complex. Although Nrf1 Ϫ/Ϫ mice are anemic and have embryonic or postnatal lethality, 16 ablation of p45 in mice leads to defective platelet production. 17 Although deletion of Bach2 in mice caused impaired antibody class switching, 18 disruption of Nrf2 resulted in a neurodegenerative disorder and autoimmune disease. [19][20][21] Deciphering the physiologic role of some of the CNC/Maf proteins has also proven to be challenging because of the potential functional redundancy among them. 22,23 The CNC/Maf network has been associated with a myriad of human disorders, including those of the skin, respiratory system, and hematopoietic system. 10,15,24 Thus, drug therapy involving the CNC pathway is actively being studied in humans for cancer chemoprevention, inflammatory diseases, and autoimmune diseases (for review, see Sykiotis and Bohmann 10 ). For example, the fumaric acid ester dimethylfumarate, which exerts neuroprotection by inducing Nrf2 expression, is currently in a phase 3 clinical trial as an orally active effective treatment of human multiple sclerosis with limited side effects. 25,26 Thus, deciphering the functions of the individual CNC subunits will not only be crucial to unraveling the overlapping and unique functions of these proteins but also provide insights to the potential of targeting CNC proteins for therapy against relevant diseases. In particular, the CNC member Bach1 is up-regulated in fetal Down syndrome (DS) brain. ...

Resistance and tolerance to infection are two universal fitness and survival strategies used by inflammation and immunity in organisms and cells to guard homeostasis. During sepsis, however, both strategies fail, and animal and human victims often die from combined innate and adaptive immune suppression with persistent bacterial and viral infections. NAD+-sensing nuclear sirtuin1 (SIRT1) epigenetically guards immune and metabolic homeostasis during sepsis. Pharmacologically inhibiting SIRT1 deacetylase activity in septic mice reverses monocyte immune tolerance, clears infection, rebalances glycolysis and glucose oxidation, resolves organ dysfunction, and prevents most septic deaths. Whether SIRT1 inhibition during sepsis treatment concomitantly reverses innate and T cell antigen-specific immune tolerance is unknown. Here, we show that treating septic mice with a SIRT1 selective inhibitor concordantly reverses immune tolerance splenic dendritic and antigen-specific tolerance of splenic CD4+ and CD8+ T cells. SIRT1 inhibition also increases the ratio of IL12 p40+ and TNFα proinflammatory/immune to IL10 and TGFβ anti-inflammatory/immune cytokines and decreases the ratio of CD4+ TReg repressor to CD4+ activator T cells. These findings support the unifying concept that nuclear NAD+ sensor SIRT1 broadly coordinates innate and adaptive immune reprogramming during sepsis and is a druggable immunometabolic enhancement target.

Bar graphs are missing from Fig 3A of the published article. Please see the correct Fig 3 here.