Sirtuin 1 Agonist Minimizes Injury and Improves the Immune Response Following Traumatic Shock

Optimisation of mitochondrial function as a novel target for resuscitation in haemorrhagic shock: a systematic review

INTRODUCTION

Traumatic injury is one of the leading causes of death worldwide, and despite significant improvements in patient care, survival in the most severely injured patients remains unchanged. There is a crucial need for innovative approaches to improve trauma patient outcomes; this is particularly pertinent in remote or austere environments with prolonged evacuation times to definitive care. Studies suggest that maintenance of cellular homeostasis is a critical component of optimal trauma patient management, and as the cell powerhouse, it is likely that mitochondria play a pivotal role. As a result, therapies that optimise mitochondrial function could be an important future target for the treatment of critically ill trauma patients.

METHODS

A systematic review of the literature was undertaken in accordance with the Preferred Reporting Items for Systematic Reviews and Meta-Analyses protocol to determine the potential role of mitochondria in traumatic injury and haemorrhagic shock (HS) and to identify current evidence for mitochondrial optimisation therapies in trauma. Articles were included if they assessed a mitochondrial targeted therapy in comparison to a control group, used a model of traumatic injury and HS and reported a method to assess mitochondrial function.

RESULTS

The search returned 918 articles with 37 relevant studies relating to mitochondrial optimisation identified. Included studies exploring a range of therapies with potential utility in traumatic injury and HS. Therapies were categorised into the key mitochondrial pathways impacted following traumatic injury and HS: ATP levels, cell death, oxidative stress and reactive oxygen species.

CONCLUSION

This systematic review provides an overview of the key cellular functions of the mitochondria following traumatic injury and HS and identifies why mitochondrial optimisation could be a viable and valuable target in optimising outcome in severely injured patients in the future.

SIRT2 suppresses expression of inflammatory factors via Hsp90-glucocorticoid receptor signalling

SIRT2 is a NAD⁺‐dependent deacetylase that deacetylates a diverse array of protein substrates and is involved in many cellular processes, including regulation of inflammation. However, its precise role in the inflammatory process has not completely been elucidated. Here, we identify heat‐shock protein 90α (Hsp90α) as novel substrate of SIRT2. Functional investigation suggests that Hsp90 is deacetylated by SIRT2, such that overexpression and knock‐down of SIRT2 altered the acetylation level of Hsp90. This subsequently resulted in disassociation of Hsp90 with glucocorticoid receptor (GR), and translocation of GR to the nucleus. This observation was further confirmed by glucocorticoid response element (GRE)‐driven reporter assay. Nuclear translocation of GR induced by SIRT2 overexpression repressed the expression of inflammatory cytokines, which were even more prominent under lipopolysaccharide (LPS) stimulation. Conversely, SIRT2 knock‐down resulted in the up‐regulation of cytokine expression. Mutation analysis indicated that deacetylation of Hsp90 at K294 is critical for SIRT2‐mediated regulation of cytokine expression. These data suggest that SIRT2 reduces the extent of LPS‐induced inflammation by suppressing the expression of inflammatory factors via SIRT2‐Hsp90‐GR axis.

Sirtuins: potential therapeutic targets for regulating acute inflammatory response?

Introduction: Sirtuins are highly conserved nicotinamide adenine dinucleotide (NAD+) sensors that are considered the guardians of homeostasis. Acute inflammation, which is intended to ward off pathogen invasion, is nature's highly conserved stress-associated and molecular-based survival mechanism for most life forms. Acute inflammatory responses deviate cells from the homeostasis to enable survival. It is not surprising perhaps, that these two must interact in the most dramatic way to preserve homeostasis and preserve life.Areas covered: In this review, we present an overview of sirtuin responses in acute life-threatening inflammatory conditions. We examine how the seven sirtuins (sirtuins 1-7) are responsible for modulating the acute inflammatory response in a context-dependent manner, thus presenting novel therapeutic targets. The database search includes Medline (since 1966) and PubMed (since 1996).Expert opinion: Sirtuins fine-tune the inflammatory response to acute infectious and noninfectious inflammatory stimuli. Modulating sirtuin activity leads to profound changes in inflammatory response. Sirtuin-activating and inhibiting agents are emerging as therapeutic agents to resolve inflammation and promote homeostasis in chronic inflammation. The use of sirtuin modulation in acute life-threatening inflammatory conditions has great potential.

Survival and Clinicopathological Significance of SIRT1 Expression in Cancers: A Meta-Analysis

Background: Silent information regulator 2 homolog 1 (SIRT1) is an evolutionarily conserved enzymes with nicotinamide adenine dinucleotide (NAD)⁺-dependent deacetylase activity. SIRT1 is involved in a large variety of cellular processes, such as genomic stability, energy metabolism, senescence, gene transcription, and oxidative stress. SIRT1 has long been recognized as both a tumor promoter and tumor suppressor. Its prognostic role in cancers remains controversial. Methods: A meta-analysis of 13,138 subjects in 63 articles from PubMed, EMBASE, and Cochrane Library was performed to evaluate survival and clinicopathological significance of SIRT1 expression in various cancers. Results: The pooled results of meta-analysis showed that elevated expression of SIRT1 implies a poor overall survival (OS) of cancer patients [Hazard Ratio (HR) = 1.566, 95% CI: 1.293-1.895, P < 0.0001], disease free survival (DFS) (HR = 1.631, 95% CI: 1.250-2.130, P = 0.0003), event free survival (EFS) (HR = 2.534, 95% CI: 1.602-4.009, P = 0.0001), and progress-free survival (PFS) (HR = 3.325 95% CI: 2.762-4.003, P < 0.0001). Elevated SIRT1 level was associated with tumor stage [Relative Risk (RR) = 1.299, 95% CI: 1.114-1.514, P = 0.0008], lymph node metastasis (RR = 1.172, 95% CI: 1.010-1.360, P = 0.0363), and distant metastasis (RR = 1.562, 95% CI: 1.022-2.387, P = 0.0392). Meta-regression and subgroup analysis revealed that ethnic background has influence on the role of SIRT1 expression in predicting survival and clinicopathological characteristics of cancers. Overexpression of SIRT1 predicted a worse OS and higher TNM stage and lymphatic metastasis in Asian population especially in China. Conclusion: Our data suggested that elevated expression of SIRT1 predicted a poor OS, DFS, EFS, PFS, but not for recurrence-free survival (RFS) and cancer-specific survival (CCS). SIRT1 overexpression was associated with higher tumor stage, lymph node metastasis, and distant metastasis. SIRT1-mediated molecular events and biological processes could be an underlying mechanism for metastasis and SIRT1 is a therapeutic target for inhibiting metastasis, leading to good prognosis.

Heme Oxygenase-2 Localizes to Mitochondria and Regulates Hypoxic Responses in Hepatocytes

Hypoxia occurs as a part of multiple disease states, including hemorrhagic shock. Adaptive responses occur within the cell to limit the consequences of hypoxia. This includes changes in mitochondrial respiration, stress-induced cell signaling, and gene expression that is regulated by hypoxia inducible factor-1α (HIF-1α). Heme oxygenase-2 (HO-2) has been shown to be involved in oxygen sensing in several cell types. The purpose of these experiments was to test the hypothesis that HO-2 is a critical regulator of mitochondrial oxygen consumption and reactive oxygen species (ROS) production to influence hypoxia-adaptive responses such as HIF-1α protein levels and JNK signaling. Methods and Results. In vitro studies were performed in primary mouse hepatocytes. HO-2, but not HO-1, was expressed in mitochondria at baseline. Decreased oxygen consumption and increased mitochondrial ROS production in response to hypoxia were dependent upon HO-2 expression. HO-2 expression regulated HIF-1α and JNK signaling in a mitochondrial ROS-dependent manner. Furthermore, knockdown of HO-2 led to increased organ damage, systemic inflammation, tissue hypoxia, and shock in a murine model of hemorrhage and resuscitation. Conclusion. HO-2 signaling plays a role in hypoxic signaling and hemorrhagic shock. This pathway may be able to be harnessed for therapeutic effects.

Mitochondrial dysfunction in rat splenocytes following hemorrhagic shock

The regulation of mitochondrial function is critical in cellular homeostasis following hemorrhagic shock. Hemorrhagic shock results in fluid loss and reduced availability of oxygen and nutrients to tissues. The spleen is a secondary lymphoid organ playing a key role in 'filtering the blood' and in the innate and adaptive immune responses. To understand the molecular basis of hemorrhagic shock, we investigated the changes in splenocyte mitochondrial respiration, and concomitant immune and metabolic alterations. The hemorrhagic injury (HI) in our rat model was induced by bleeding 60% of the total blood volume followed by resuscitation with Ringers lactate. Another group of animals was subjected to hemorrhage, but did not receive fluid resuscitation. Oxygen consumption rate of splenocytes were determined using a Seahorse analyzer. We found a significantly reduced oxygen consumption rate in splenocytes following HI compared to sham operated rats. The mitochondrial stress test revealed a decreased basal oxygen consumption rate, ATP production, maximal respiration and spare respiratory capacity. The mitochondrial membrane potential, and citrate synthase activity, were also reduced in the splenocytes following HI. Hypoxic response in the splenocyte was confirmed by increased gene expression of Hif1α. Elevated level of mitochondrial stress protein, hsp60 and induction of high mobility group box1 protein (HMGB1) were observed in splenocytes following HI. An increased inflammatory response was demonstrated by significantly increased expression of IL-6, IFN-β, Mip-1α, IL-10 and NFκbp65. In summary, we conclude that splenocyte oxidative phosphorylation and metabolism were severely compromised following HI.

SIRTUIN 1 ACTIVATOR SRT1720 PROTECTS AGAINST ORGAN INJURY INDUCED BY INTESTINAL ISCHEMIA-REPERFUSION

Intestinal ischemia-reperfusion (I/R) occurs in various clinical situations and causes local and remote organ injury, especially in the lungs, leading to significant morbidity and mortality. The maintenance of mitochondrial biogenesis is essential for cell survival and is regulated in part by sirtuin 1 (SIRT1), an energy-sensing enzyme. We hypothesized that SIRT1 activation with SRT1720 would reduce local and remote organ injury after intestinal I/R. Intestinal I/R was induced by the occlusion of the superior mesenteric artery of adult male C57BL/6 mice for 45 min, followed by reperfusion for 4 h. SRT1720 or vehicle was injected intravenously at the time of reperfusion. Blood, small intestine, and lung tissues were collected for analysis. The SRT1720 treatment of I/R mice resulted in a 57% increase in protein levels of succinate dehydrogenase, an index of mitochondrial mass, and a 120% increase in messenger RNA levels of mitochondrial transcription factor A, a marker for mitochondrial biogenesis. The microscopic architecture and apoptosis of the gut tissue was improved in the SRT1720-treated I/R mice. SRT1720 decreased intestinal messenger RNA levels of tumor necrosis factor-α by 60% and inducible nitric oxide synthase to baseline after I/R. Systemic inflammation, as determined by serum interleukin-6, was reduced in treated mice. Lung injury, as measured by histological architecture and myeloperoxidase activity, and lung apoptosis were also improved after the SRT1720 treatment. SRT1720 preserved mitochondrial biogenesis and mass, leading to inhibition of inflammation and oxidative stress, thereby protecting against intestinal I/R-induced injury. Thus, the SIRT1-mediated pathway is a promising target for the treatment of intestinal I/R injury.