Influence of aging and hemorrhage injury on Sirt1 expression: possible role of myc-Sirt1 regulation in mitochondrial function

Juvenile Plasma Factors Improve Organ Function and Survival following Injury by Promoting Antioxidant Response

Studies have shown that factors in the blood of young organisms can rejuvenate the old ones. Studies using heterochronic parabiosis models further reinforced the hypothesis that juvenile factors can rejuvenate aged systems. We sought to determine the effect of juvenile plasma-derived factors on the outcome following hemorrhagic shock injury in aged mice. We discovered that pre-pubertal (young) mice subjected to hemorrhagic shock survived for a prolonged period, in the absence of fluid resuscitation, compared to mature or aged mice. To further understand the mechanism of maturational dependence of injury resolution, extracellular vesicles isolated from the plasma of young mice were administered to aged mice subjected to hemorrhagic shock. The extracellular vesicle treatment prolonged life in the aged mice. The treatment resulted in reduced oxidative stress in the liver and in the circulation, along with an enhanced expression of the nuclear factor erythroid factor 2-related factor 2 (Nrf2) and its target genes, and a reduction in the expression of the transcription factor BTB and CNC homology 1 (Bach1). We propose that plasma factors in the juvenile mice have a reparative effect in the aged mice in injury resolution by modulating the Nrf2/Bach1 axis in the antioxidant response pathway.

Regulation of NAD+ metabolism in aging and disease

More than a century after discovering NAD⁺, information is still evolving on the role of this molecule in health and diseases. The biological functions of NAD⁺ and NAD⁺ precursors encompass pathways in cellular energetics, inflammation, metabolism, and cell survival. Several metabolic and neurological diseases exhibit reduced tissue NAD⁺ levels. Significantly reduced levels of NAD⁺ are also associated with aging, and enhancing NAD⁺ levels improved healthspan and lifespan in animal models. Recent studies suggest a causal link between senescence, age-associated reduction in tissue NAD⁺ and enzymatic degradation of NAD⁺. Furthermore, the discovery of transporters and receptors involved in NAD⁺ precursor (nicotinic acid, or niacin, nicotinamide, and nicotinamide riboside) metabolism allowed for a better understanding of their role in cellular homeostasis including signaling functions that are independent of their functions in redox reactions. We also review studies that demonstrate that the functional effect of niacin is partially due to the activation of its cell surface receptor, GPR109a. Based on the recent progress in understanding the mechanism and function of NAD⁺ and NAD⁺ precursors in cell metabolism, new strategies are evolving to exploit these molecules' pharmacological potential in the maintenance of metabolic balance.

Melatonin Promotes in vitro Development of Vitrified-Warmed Mouse GV Oocytes, Potentially by Modulating Phosphorylation of Drp1

Previous studies have shown that melatonin can mitigate cryopreservation-induced mitochondrial dysfunction in oocytes; however, the underlying molecular mechanism remains unclear. The objective of the present study was to investigate whether melatonin can improve the mitochondrial function during in vitro maturation of vitrified-warmed mouse germinal vesicle (GV) oocytes by modulating phosphorylation of dynamin related protein 1 (Drp1). Vitrification/warming procedures resulted in the following: (1) After cryopreservation of mouse GV oocytes, the phosphorylation level of Drp1 at Ser616 (p-Drp1 Ser616) in metaphase II (MII) oocytes was increased (P < 0.05). Furthermore, the rates of in vitro maturation, cleavage and blastocyst formation after parthenogenetic activation were decreased (P < 0.05). (2) In MII oocytes, the expression levels of translocase of the mitochondrial outer membrane 20 (TOMM20), mitochondrial membrane potential (MMP), adenosine triphosphate (ATP) content, and mRNA levels of mitochondrial biogenesis-related genes (Sirt1, Pgc-1α, Tfam) were all decreased (P < 0.05), and (3) Reactive oxygen species (ROS) level, early apoptosis level, Cytochrome C release and mRNA levels of pro-apoptotic related genes (Bax, Caspase9, Caspase3) in MII oocytes were all increased (P < 0.05). The results of this study further revealed that negative impacts of GV oocyte cryopreservation were mitigated by supplementation of warming and in vitro maturation media with 10⁻⁷mol /L melatonin or 2 x 10⁻⁵mol/L Mdivi-1 (Drp1 inhibitor). Therefore, we concluded that 10⁻⁷mol/L melatonin improved mitochondrial function, reduced oxidative stress and inhibited apoptosis by regulating phosphorylation of Drp1, thereby enhancing in vitro development of vitrified-warmed mouse GV oocytes.

Dysregulation of cellular energetics in Gulf War Illness

Gulf War Illness (GWI) is estimated to have affected about one third of the Veterans who participated in the first Persian Gulf War. The symptoms of GWI include chronic neurologic impairments, chronic fatigue syndrome, as well as fibromyalgia and immune system disorders, collectively referred to as chronic multi-symptom illness. Thirty years after the war, we still do not have an effective treatment for GWI. It is necessary to understand the molecular basis of the symptoms of GWI in order to develop appropriate therapeutic strategies. Cellular energetics are critical to the maintenance of cellular homeostasis, a process that is highly dependent on intact mitochondrial function and there is significant evidence from both human studies and animal models that mitochondrial impairments may lead to GWI symptoms. The available clinical and pre-clinical data suggest that agents that improve mitochondrial function have the potential to restore cellular energetics and treat GWI. To date, the experiments conducted in animal models of GWI have mainly focused on neurobehavioral aspects of the illness. Additional studies to address the fundamental biological processes that trigger the dysregulation of cellular energetics in GWI are warranted to better understand the underlying pathology and to develop new treatment methods. This review highlights studies related to mitochondrial dysfunction observed in both GW veterans and in animal models of GWI.

An Assay Using Localized Surface Plasmon Resonance and Gold Nanorods Functionalized with Aptamers to Sense the Cytochrome-c Released from Apoptotic Cancer Cells for Anti-Cancer Drug Effect Determination

To determine the degree of cancer cell killing after treatment with chemotherapeutic drugs, we have developed a sensitive platform using localized surface plasmon resonance (LSPR) and aptamers to detect the extracellular cytochrome-c (cyto-c), a mitochondrial protein released from cancer cells for the induction of apoptosis after treatment, to evaluate the effectiveness of cancer therapy. In this assay, a short single-stranded 76-mer DNA aptamer with a unique DNA sequence, which binds towards the cyto-c like an antibody with a high binding affinity and specificity, was conjugated to gold nanorods (AuNR) for LSPR sensing. Practically, cyto-c was first grabbed by a capturing antibody functionalized on the surface of micro-magnetic particles (MMPs). Subsequently, the AuNR-conjugated aptamer was added to form a complex sandwich structure with cyto-c (i.e., (MMP-Ab)-(cyto-c)-(AuNR-aptamer)) after washing away the non-target impurities, such as serum residues and intracellular contents, in a microfluidic chip. The sandwich complex led to formation of AuNR aggregates, which changed the LSPR signals in relation to the amount of cyto-c. With the LSPR signal enhancement effects from the AuNRs, the detection limit of cyto-c, sparked in human serum or culture medium, was found to be 0.1 ng/mL in our platform and the whole sensing process could be completed within two hours. Moreover, we have applied this assay to monitor the apoptosis in leukemia cancer cells induced by a potential anti-cancer agent phenylarsine oxide.

Epigenetic Regulatory Mechanisms Induced by Resveratrol

Resveratrol (RVT) is one of the main natural compounds studied worldwide due to its potential therapeutic use in the treatment of many diseases, including cancer, diabetes, cardiovascular diseases, neurodegenerative diseases and metabolic disorders. Nevertheless, the mechanism of action of RVT in all of these conditions is not completely understood, as it can modify not only biochemical pathways but also epigenetic mechanisms. In this paper, we analyze the biological activities exhibited by RVT with a focus on the epigenetic mechanisms, especially those related to DNA methyltransferase (DNMT), histone deacetylase (HDAC) and lysine-specific demethylase-1 (LSD1).

Activation of sirtuin 1/3 improves vascular hyporeactivity in severe hemorrhagic shock by alleviation of mitochondrial damage

Vascular hyporeactivity is one of the major causes responsible for refractory hypotension and associated mortality in severe hemorrhagic shock. Mitochondrial permeability transition (mPT) pore opening in arteriolar smooth muscle cells (ASMCs) is involved in the pathogenesis of vascular hyporeactivity. However, the molecular mechanism underlying mitochondrial injury in ASMCs during hemorrhagic shock is not well understood. Here we produced an in vivo model of severe hemorrhagic shock in adult Wistar rats. We found that sirtuin (SIRT)1/3 protein levels and deacetylase activities were decreased in ASMCs following severe shock. Immunofluorescence staining confirmed reduced levels of SIRT1 in the nucleus and SIRT3 in the mitochondria, respectively. Acetylation of cyclophilin D (CyPD), a component of mPT pore, was increased. SIRT1 activators suppressed mPT pore opening and ameliorated mitochondrial injury in ASMCs after severe shock. Furthermore, administration of SIRT1 activators improved vasoreactivity in rats under severe shock. Our data suggest that epigenetic mechanisms, namely histone post-translational modifications, are involved in regulation of mPT by SIRT1/SIRT3- mediated deacetylation of CyPD. SIRT1/3 is a promising therapeutic target for the treatment of severe hemorrhagic shock.

Mitochondrial function in hypoxic ischemic injury and influence of aging

Mitochondria are a major target in hypoxic/ischemic injury. Mitochondrial impairment increases with age leading to dysregulation of molecular pathways linked to mitochondria. The perturbation of mitochondrial homeostasis and cellular energetics worsens outcome following hypoxic-ischemic insults in elderly individuals. In response to acute injury conditions, cellular machinery relies on rapid adaptations by modulating posttranslational modifications. Therefore, post-translational regulation of molecular mediators such as hypoxia-inducible factor 1α (HIF-1α), peroxisome proliferator-activated receptor γ coactivator α (PGC-1α), c-MYC, SIRT1 and AMPK play a critical role in the control of the glycolytic-mitochondrial energy axis in response to hypoxic-ischemic conditions. The deficiency of oxygen and nutrients leads to decreased energetic reliance on mitochondria, promoting glycolysis. The combination of pseudohypoxia, declining autophagy, and dysregulation of stress responses with aging adds to impaired host response to hypoxic-ischemic injury. Furthermore, intermitochondrial signal propagation and tissue wide oscillations in mitochondrial metabolism in response to oxidative stress are emerging as vital to cellular energetics. Recently reported intercellular transport of mitochondria through tunneling nanotubes also play a role in the response to and treatments for ischemic injury. In this review we attempt to provide an overview of some of the molecular mechanisms and potential therapies involved in the alteration of cellular energetics with aging and injury with a neurobiological perspective.

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

Survival from traumatic injury requires a coordinated and controlled inflammatory and immune response. Mitochondrial and metabolic responses to stress have been shown to play a role in these inflammatory and immune responses. We hypothesized that increases in mitochondrial biogenesis via a sirtuin 1 agonist would decrease tissue injury and partially ameliorate the immunosuppression seen following trauma. C57Bl/6 mice were subjected to a multiple trauma model. Mice were pretreated with either 100 mg/kg per day of the sirtuin 1 agonist, Srt1720, via oral gavage for 2 days prior to trauma and extended until the day the animals were killed, or they were pretreated with peroxisome proliferator-activated receptor γ coactivator 1α (PGC1α) siRNA via hydrodynamic tail vein injection 48 h prior to trauma. Markers for mitochondrial function and biogenesis were measured in addition to splenocyte proliferative capacity and bacterial clearance. Srt1720 was noted to improve mitochondrial biogenesis, mitochondrial function, and complex IV activity following traumatic injury (P < 0.05), whereas knockdown of PGC1α resulted in exacerbation of mitochondrial dysfunction (P < 0.05). These changes in mitochondrial function were associated with altered severity of hepatic injury with significant reductions in serum alanine aminotransferase levels seen in mice treated with srt1720. Splenocyte proliferative capacity and intraperitoneal bacterial clearance were evaluated as markers for overall immune function following trauma-hemorrhage. Treatment with Srt1720 minimized the trauma-induced decreases in splenocyte proliferation (P < 0.05), whereas treatment with PGC1α siRNA led to diminished bacterial clearance. The PGC1α signaling pathway is an important regulator of mitochondrial function and biogenesis, which can potentially be harnessed to protect against hepatic injury and minimize the immunosuppression that is seen following trauma-hemorrhage.

Polydatin protects hepatocytes against mitochondrial injury in acute severe hemorrhagic shock via SIRT1-SOD2 pathway

OBJECTIVE

The aim of the study was to determine whether hepatocyte mitochondrial injury instigates severe shock and to explore effective therapy.

METHODS

Wistar rats were randomly divided into five groups: Control (sham) group, shock + normal saline, shock + cyclosporine A, shock + resveratrol (Res) and shock + polydatin (PD) group. Mitochondrial morphology and function in hepatocytes following treatment were determined.

RESULTS

Hepatocytes following severe shock exhibited mitochondrial dysfunction characterized with opening of mitochondrial permeability transition pores, mitochondrial swelling, decreased mitochondrial membrane potential (ΔΨm) and reduced ATP levels. Moreover, severe shock induced oxidative stress with increased lipid peroxidation and reactive oxygen species, decreased SOD2 (Superoxide Dismutase 2) and GSH/GSSG, which resulted in increased lysosomal membrane permeabilization and hepatocyte mitochondrial injury. Additionally, Res and PD restored decreased deacetylase sirtuin1 activity and protein expression in liver tissue following severe shock, suppressed oxidative stress-induced lysosomal unstability and mitochondrial injury by increasing the protein expression of SOD2, and thereby contributed to the prevention of hepatocyte mitochondria dysfunction and liver injury.

CONCLUSIONS

PD effectively preserved hepatocytes from mitochondrial injury via SIRT1-SOD2 pathway and may be a new approach to treatment of irreversible shock.

Polydatin Alleviates Small Intestine Injury during Hemorrhagic Shock as a SIRT1 Activator

Objective. To evaluate the role of SIRT1 in small intestine damage following severe hemorrhagic shock and to investigate whether polydatin (PD) can activate SIRT1 in shock treatment. Research Design and Methods. The severe hemorrhagic shock model was reproduced in Sprague Dawley rats. Main Outcome Measures. Two hours after drug administration, half of the rats were assessed for survival time evaluation and the remainder were used for small intestinal tissue sample collection. Results. Bleeding and swelling appeared in the small intestine with epithelial apoptosis and gut barrier disturbance during hemorrhagic shock. SIRT1 activity and PGC-1α protein expression of the small intestine were decreased, which led to an increase in acetylated SOD2 and decreases in the expression and activity of SOD2, resulting in severe oxidative stress. The decreased SIRT1 activity and expression were partially restored in the PD administration group, which showed reduced intestine injury and longer survival time. Notably, the effect of PD was abolished after the addition of Ex527, a selective inhibitor of SIRT1. Conclusions. The results collectively suggest a role for the SIRT1-PGC-1α-SOD2 axis in small intestine injury following severe hemorrhagic shock and that PD is an effective SIRT1 activator for the shock treatment.

Hemorrhagic shock-induced cerebral bioenergetic imbalance is corrected by pharmacologic treatment with EF24 in a rat model

Maintenance of cerebral viability and function is an important goal of critical care in victims of injury due to ischemia and hypovolemia. As part of the multiple organ dysfunction syndrome, the brain function after trauma is influenced by the systemic inflammatory response. We investigated the effect of EF24, an anti-inflammatory bis-chalcone, on cerebral bioenergetics in a rat model of 45% hemorrhagic shock. The rats were treated with EF24 (0.4 mg/kg) or EF24 with an artificial oxygen carrier liposome-encapsulated hemoglobin (LEH). The volume of LEH administered was equal to the shed blood. The brain was collected after 6 h of shock for biochemical assays. EF24 treatment showed significant recovery of ATP, phosphocreatine, and NAD/NADH ratio. It also increased citrate synthase activity and cytochrome c oxidase subunit IV expression which were reduced in shock brain. Furthermore, it reduced the shock-induced accumulation of pyruvate and pyruvate dehydrogenase kinase-1 expression, suggesting that EF24 treatment improves cerebral energetics by restoring perturbed pyruvate metabolism in the mitochondria. These effects of EF24 were associated with reduced poly(ADP-ribose) polymerase cleavage and a significant improvement in the levels of nerve growth factor and brain-derived neurotrophic factor in shock brain. Co-administration of LEH with EF24 was only marginally more effective as compared to the treatment with EF24 alone. These results show that EF24 treatment sets up a pro-survival phenotype in shock by resurrecting cerebral bioenergetics. Since EF24 was effective in the absence of accompanying fluid resuscitation, it has potential utility as a pre-hospital pharmacotherapy in shock due to accidental blood loss.

Astrocytes protect neurons from Aβ1-42 peptide-induced neurotoxicity increasing TFAM and PGC-1 and decreasing PPAR-γ and SIRT-1

One of the earliest neuropathological events in Alzheimer's disease is accumulation of astrocytes at sites of Aβ1-42 depositions. Our results indicate that Aβ1-42 toxic peptide increases lipid peroxidation, apoptosis and cell death in neurons but not in astrocytes in primary culture. Aβ1-42-induced deleterious neuronal effects are not present when neurons and astrocytes are mixed cultured. Stimulation of astrocytes with toxic Aβ1-42 peptide increased p-65 and decreased IκB resulting in inflammatory process. In astrocytes Aβ1-42 decreases protein expressions of sirtuin 1 (SIRT-1) and peroxisome proliferator-activated receptor γ (PPAR-γ) and over-expresses peroxisome proliferator-activated receptor γ coactivator 1 (PGC-1) and mitochondrial transcription factor A (TFAM), protecting mitochondria against Aβ1-42-induced damage and promoting mitochondrial biogenesis. In summary our data suggest that astrocytes may have a key role in protecting neurons, increasing neural viability and mitochondrial biogenesis, acquiring better oxidative stress protection and perhaps modulating inflammatory processes against Aβ1-42 toxic peptide. This might be a sign of a complex epigenetic process in Alzheimer's disease development.

The roles of FoxOs in modulation of aging by calorie restriction

FoxO activity and modifications, such as its phosphorylation, acetylation, and methylation, may help drive the expression of genes involved in combating oxidative stress by causing the epigenetic modifications, and thus, preserve cellular function during aging and age-related diseases, such as diabetes, cancer, and Alzheimer disease. Insulin signaling has been postulated to influence the aging process by increasing resistance to oxidative stress, and slowing the accumulation of oxidative damage. Some antioxidative effects are mediated by a conserved family of forkhead box transcription factors (FoxOs), which in the absence of insulin signaling freely bind to promoters of antioxidant enzymes, superoxide dismutase, and catalase. On the other hand, calorie restriction (CR) extends the lifespans of several species via the insulin pathway, and extends longevity and healthspan in diverse species via a conserved mechanism. CR enhances adaptive stress responses at the cellular and organism levels and extends lifespan in a FoxO-independent manner. Thus, increased modification of FoxO is modulated via the hyperinsulinemia-induced PI3K/Akt pathway during aging, and CR reverses this process. Accordingly, FoxO plays an important role in maintenance of metabolic homeostasis and removal of oxidative stress in the aging process and in the effect of CR on lifespan.

The essential role of FoxO6 phosphorylation in aging and calorie restriction

Changes in the activities of FoxOs caused by phosphorylation, acetylation, or ubiquitination induce expressional changes in the genes involved in the modulation of oxidative stress by modifying histones and chromatins and can substantially alter cellular functions during aging and age-related diseases. However, the precise role that FoxO6, a novel member of the FoxO class of transcription factors, plays in the aging kidney has not been determined. The purpose of this study was to determine the role played by FoxO6 in the maintenance of redox homeostasis in HEK293T cells and aged kidney tissues isolated from ad libitum (AL)-fed and 40 % calorie restriction (CR) rats. The results obtained from AL-fed rats showed that diminished FoxO6 activity during aging was caused by FoxO6 phosphorylation, which disabled its transcriptional activity. In contrast, CR rats were found to have significantly higher FoxO6 activities and maintained redox balance. To determine the molecular mechanism responsible for FoxO6 modification by age-related oxidative stress, we examined H2O2-treated HEK293T cells in which FoxO6 was inactivated by phosphorylation and found that H2O2-induced oxidative stress promoted FoxO6 phosphorylation via PI3K/Akt signaling. The results of this study show that the protective role of FoxO6 in the aging process may in part be related to its ability to attenuate oxidative stress by upregulating catalase expression, as shown in CR. This delineation of the role of FoxO6 expands understanding of the pathological and physiological mechanisms of aging.

Vascular hyperpermeability and aging

Vascular hyperpermeability, the excessive leakage of fluid and proteins from blood vessels to the interstitial space, commonly occurs in traumatic and ischemic injuries. This hyperpermeability causes tissue vasogenic edema, which often leads to multiple organ failure resulting in patient death. Vascular hyperpermeability occurs most readily in small blood vessels as their more delicate physical constitution makes them an easy target for barrier dysfunction. A single layer of endothelial cells, linked to one another by cell adhesion molecules, covers the interior surface of each blood vessel. The cell adhesion molecules play a key role in maintaining barrier functions like the regulation of permeability. Aging is a major risk factor for microvascular dysfunction and hyperpermeability. Apart from age-related remodeling of the vascular wall, endothelial barrier integrity and function declines with the advancement of age. Studies that address the physiological and molecular basis of vascular permeability regulation in aging are currently very limited. There have been many cellular and molecular mechanisms proposed to explain aging-related endothelial dysfunction but their true relationship to barrier dysfunction and hyperpermeability is not clearly known. Among the several mechanisms that promote vascular dysfunction and hyperpermeability, the following are considered major contributors: oxidative stress, inflammation, and the activation of apoptotic signaling pathways. In this review we highlighted (a) the physiological, cellular and molecular changes that occur in the vascular system as a product of aging; (b) the potential mechanisms by which aging leads to barrier dysfunction and vascular hyperpermeability in the peripheral and the blood-brain barrier; (c) the mechanisms by which the age-related increases in oxidative stress, inflammatory markers and apoptotic signaling etc. cause endothelial dysfunction and their relationship to hyperpermeability; and (d) the relationship between aging, vascular permeability and traumatic injuries.

Aging and injury: alterations in cellular energetics and organ function

Aging is characterized by increased oxidative stress, heightened inflammatory response, accelerated cellular senescence and progressive organ dysfunction. The homeostatic imbalance with aging significantly alters cellular responses to injury. Though it is unclear whether cellular energetic imbalance is a cause or effect of the aging process, preservation of mitochondrial function has been reported to be important in organ function restoration following severe injury. Unintentional injuries are ranked among the top 10 causes of death in adults of both sexes, 65 years and older. Aging associated decline in mitochondrial function has been shown to enhance the vulnerability of heart, lung, liver and kidney to ischemia/reperfusion injury. Studies have identified alterations in the level or activity of factors such as SIRT1, PGC-1α, HIF-1α and c-MYC involved in key regulatory processes in the maintenance of mitochondrial structural integrity, biogenesis and function. Studies using experimental models of hemorrhagic injury and burn have demonstrated significant influence of aging in metabolic regulation and organ function. Understanding the age-associated molecular mechanisms regulating mitochondrial dysfunction following injury is important towards identifying novel targets and therapeutic strategies to improve the outcome after injury in the elderly.

Resveratrol restores sirtuin 1 (SIRT1) activity and pyruvate dehydrogenase kinase 1 (PDK1) expression after hemorrhagic injury in a rat model

Severe hemorrhage leads to decreased blood flow to tissues resulting in decreased oxygen and nutrient availability affecting mitochondrial function. A mitoscriptome profiling study demonstrated alteration in several genes related to mitochondria, consistent with the mitochondrial functional decline observed after trauma hemorrhage (T-H). Our experiments led to the identification of sirtuin 1 (SIRT1) as a potential target in T-H. Administration of resveratrol (a naturally occurring polyphenol and activator of SIRT1) after T-H improved left ventricular function and tissue ATP levels. Our hypothesis was that mitochondrial function after T-H depends on SIRT1 activity. In this study, we evaluated the activity of SIRT1, a mitochondrial functional modulator, and the mitochondrial-glycolytic balance after T-H. We determined the changes in protein levels of pyruvate dehydrogenase kinase (PDK)-1 and nuclear c-Myc, peroxisome proliferator-activated receptor-γ coactivator (PGC)-1α and NF-E2-related factor (NRF)2 after T-H and after treatment with resveratrol or a combination of sirtinol (a SIRT1 inhibitor) and resveratrol. We have also tested the activity of mitochondrial complex 1. SIRT1 enzyme activity was significantly decreased after T-H, whereas resveratrol treatment restored the activity. We found elevated PDK1 and c-Myc levels and decreased PGC-1α, NRF2 and mitochondrial complex I activity after T-H. The reduced SIRT1 activity after T-H may be related to declining mitochondrial function, since resveratrol was able to reinstate SIRT1 activity and mitochondrial function. The elevated level of PDK1 (an inhibitor of pyruvate dehydrogenase complex) after T-H indicates a possible shift in cellular energetics from mitochondria to glycolysis. In conclusion, SIRT1 modulation alters left ventricular function after T-H through regulation of cellular energetics.

Resveratrol improves cardiac contractility following trauma-hemorrhage by modulating Sirt1

Mitochondria play a critical role in metabolic homeostasis of a cell. Our recent studies, based on the reported interrelationship between c-Myc and Sirt1 (mammalian orthologue of yeast sir2 [silent information regulator 2]) expression and their role in mitochondrial biogenesis and function, demonstrated a significant downregulation of Sirt1 protein expression and an upregulation of c-Myc following trauma-hemorrhage (T-H). Activators of Sirt1 are known to improve mitochondrial function and the naturally occurring polyphenol resveratrol (RSV) has been shown to significantly increase Sirt1 activity by increasing its affinity to both NAD+ and the acetylated substrate. In this study we tested the salutary effect of RSV following T-H and its influence on Sirt1 expression. Rats were subjected to T-H or sham operation. RSV (8 mg/kg body weight, intravenously) or vehicle was administered 10 min after the onset of resuscitation, and the rats were killed 2 h following resuscitation. Sirtinol, a Sirt1 inhibitor, was administered 5 min prior to RSV administration. Cardiac contractility (±dP/dt) was measured and heart tissue was tested for Sirt1, Pgc-1α, c-Myc, cytosolic cytochrome C expression and ATP level. Left ventricular function, after T-H, was improved (P < 0.05) following RSV treatment, with significantly elevated expression of Sirt1 (P < 0.05) and Pgc-1α (P < 0.05), and decreased c-Myc (P < 0.05). We also observed significantly higher cardiac ATP content, declined cytosolic cytochrome C and decreased plasma tumor necrosis factor-α in the T-H-RSV group. The salutary effect due to RSV was abolished by sirtinol, indicating a Sirt1-mediated effect. We conclude that RSV may be a useful adjunct to resuscitation fluid following T-H.

Involvement of SIRT1 in hypoxic down-regulation of c-Myc and β-catenin and hypoxic preconditioning effect of polyphenols

SIRT1 has been found to function as a Class III deacetylase that affects the acetylation status of histones and other important cellular nonhistone proteins involved in various cellular pathways including stress responses and apoptosis. In this study, we investigated the role of SIRT1 signaling in the hypoxic down-regulations of c-Myc and β-catenin and hypoxic preconditioning effect of the red wine polyphenols such as piceatannol, myricetin, quercetin and resveratrol. We found that the expression of SIRT1 was significantly increased in hypoxia-exposed or hypoxic preconditioned HepG2 cells, which was closely associated with the up-regulation of HIF-1α and down-regulation of c-Myc and β-catenin expression via deacetylation of these proteins. In addition, blockade of SIRT1 activation using siRNA or amurensin G, a new potent SIRT1 inhibitor, abolished hypoxia-induced HIF-1α expression but increased c-Myc and β-catenin expression. SIRT1 was also found to stabilize HIF-1α protein and destabilize c-Myc, β-catenin and PHD2 under hypoxia. We also found that myricetin, quercetin, piceatannol and resveratrol up-regulated HIF-1α and down-regulated c-Myc, PHD2 and β-catenin expressions via SIRT1 activation, in a manner that mimics hypoxic preconditioning. This study provides new insights of the molecular mechanisms of hypoxic preconditioning and suggests that polyphenolic SIRT1 activators could be used to mimic hypoxic/ischemic preconditioning.