Regulation of APC development, immune response, and autoimmunity by Bach1/HO-1 pathway in mice.

APCs are essential for innate and adaptive immunity as well as self-immune tolerance. Here, we show that the Cap'n'collar member Bach1 regulates the generation of APCs, specifically macrophages and dendritic cells, in mice. The impaired APC development in Bach1(-/-) mice was accompanied by defects in downstream T-cell responses and partial protection from experimental autoimmune encephalomyelitis. Genomewide analyses identified a panel of Bach1 target genes and ablation of the direct Bach1 target gene HO-1 exacerbated the impaired APC development observed in Bach1(-/-) mice. This was attributed to the impaired ability of HO-1(-/-)Bach1(-/-) double mutants to produce upstream APC progenitor cells, including common myeloid progenitor (CMP)-Flk2(+). By contrast, we observed an increase in hematopoietic stem-progenitor cells (HSPCs) in these mice, suggesting a developmental block in the progression of HSPCs to CMP-Flk2(+) and subsequently APCs.

Sirtuin1 Targeting Reverses Innate and Adaptive Immune Tolerance in Septic Mice.

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 TGFß 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.

Pyruvate dehydrogenase complex stimulation promotes immunometabolic homeostasis and sepsis survival.

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.

Sirtuin-2 Regulates Sepsis Inflammation in ob/ob Mice.

OBJECTIVE: Obesity 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. METHODS: Sepsis 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. RESULTS: We 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. CONCLUSION: SIRT-2 regulates microvascular inflammation in obese mice with sepsis and may provide a novel treatment target for obesity with sepsis.

Correction: Sirtuin-2 Regulates Sepsis Inflammation in ob/ob Mice.

[This corrects the article DOI: 10.1371/journal.pone.0160431.].