Early apoptotic vascular signaling is determined by Sirt1 through nuclear shuttling, forkhead trafficking, bad, and mitochondrial caspase activation

Neuroprotective effects of resveratrol on damages of mouse cortical neurons induced by β-amyloid through activation of SIRT1/Akt1 pathway

Resveratrol (3,5,4'-tihydroxy-trans-stilbene), a polyphenolic phytoalexin found in the skin and seeds of grapes, has been reported to possess a wide range of biological and pharmacological activities including antioxidant, anti-inflammatory, and antimutagenic effects. The present study intended to explore the neuroprotective effects of resveratrol against Aβ25-35 -induced neurotoxicity of cultured mouse cortical neurons and the possible mechanisms involved. For this purpose, mouse cortical neurons were cultured and exposed to 30 μM Aβ25-35 in the absence or presence of resveratrol (5, 10, and 25 μM). In addition, the potential contribution of the SIRT1/Akt1 neuroprotective pathway in resveratrol-mediated protection against Aβ25-35 -induced neurotoxicity was also investigated. The results showed that resveratrol dose-dependently increased cell viability and reduced the number of apoptotic cells as measured by 3-[4,5-dimethylthiazol-2-yl]-2, 5-diphenyltetrazolium bromide (MTT) assay, lactate dehydrogenase (LDH) activity assay, reactive oxygen species (ROS) activity assay, and Hoechst/PI double staining. Further study revealed that resveratrol through activation of SIRT1/Akt1 to avert apoptosis. These findings raise the possibility that resveratrol may be a potent therapeutic compound against the neurodegenerative diseases.

Mitochondrial response to oxidative and nitrosative stress in early stages of diabetes

Diabetes mellitus (DM) is associated with increased production of reactive oxygen and nitrogen species; consequently, an increase in lipid peroxidation and a decrease in antioxidants resulting in mitochondrial dysfunction. Using a rat model of DM induced by streptozotocin, we show the opposite: an increase in NO levels, S-nitrosylation, aconitase activity, and total glutathione and a decrease in lipid peroxidation at early stages of diabetes. These data imply that the decrease in lipid peroxidation is a vital early response to hyperglycemia to prevent escalation of ROS generation in mitochondria. These results also suggest a need for novel therapeutic targets to prevent the neurological consequences of diabetes.

Wnt1 inducible signaling pathway protein 1 (WISP1) targets PRAS40 to govern β-amyloid apoptotic injury of microglia

Given the present challenges to attain effective treatment for β-amyloid (Aβ) toxicity in neurodegenerative disorders such as Alzheimer's disease, development of novel cytoprotective pathways that can assist immune mediated therapies through the preservation of central nervous system microglia could offer significant promise. We show that the CCN4 protein, Wnt1 inducible signaling pathway protein 1 (WISP1), is initially up-regulated by Aβ and can modulate its endogenous expression for the protection of microglia during Aβ mediated apoptosis. WISP1 activates mTOR and phosphorylates p70S6K and 4EBP1 through the control of the regulatory mTOR component PRAS40. Loss of PRAS40 through gene reduction or inhibition by WISP1 is cytoprotective. WISP1 ultimately governs PRAS40 by sequestering PRAS40 intracellularly through post-translational phosphorylation and binding to protein 14-3-3. Our work identifies WISP1, mTOR signaling, and PRAS40 as targets for new strategies directed against Alzheimer's disease and related disorders.

Epsilon PKC increases brain mitochondrial SIRT1 protein levels via heat shock protein 90 following ischemic preconditioning in rats

Ischemic preconditioning is a neuroprotective mechanism whereby a sublethal ischemic exposure is protective against a subsequent lethal ischemic attack. We previously demonstrated that SIRT1, a nuclear localized stress-activated deacetylase, is vital for ischemic preconditioning neuroprotection. However, a recent study demonstrated that SIRT1 can also localize to the mitochondria. Mitochondrial localized SIRT1 may allow for a direct protection of mitochondria following ischemic preconditioning. The objective of this study was to determine whether ischemic preconditioning increases brain mitochondrial SIRT1 protein levels and to determine the role of PKCɛ and HSP90 in targeting SIRT1 to the mitochondria. Here we report that preconditioning rats, with 2 min of global cerebral ischemia, induces a delayed increase in non-synaptic mitochondrial SIRT1 protein levels which was not observed in synaptic mitochondria. This increase in mitochondrial SIRT1 protein was found to occur only in neuronal cells and was mediated by PKCε activation. Inhibition of HSP90, a protein chaperone involved in mitochondrial protein import, prevented preconditioning induced increases in mitochondrial SIRT1 and PKCε protein. Our work provides new insights into a possible direct role of SIRT1 in modulating mitochondrial function under both normal and stress conditions, and to a possible role of mitochondrial SIRT1 in activating preconditioning induced ischemic tolerance.

Involvement of the FoxO3a pathway in the ischemia/reperfusion injury of cardiac microvascular endothelial cells

FoxO3a, a member of the forkhead transcription factors, has been demonstrated to be involved in myocardial ischemia/reperfusion (I/R) injury. Cardiac microvascular endothelial cells (CMECs) are some of the predominant cells damaged immediately after myocardial I/R injury. Despite the importance of injured CMECs in an ischemic heart, little is known about the involvement of FoxO3a in regulating CMECs injury. Thus, we used rat CMECs following simulated I/R to examine FoxO3a activation and signaling in relation to survival, the cell cycle and apoptosis in CMECs. We found that Akt negatively regulates activation of the FoxO3a pathway by phosphorylating FoxO3a in CMECs as demonstrated with an Akt inhibitor and activator. Upon I/R injury, the FoxO3a pathway was significantly activated in CMECs, which was accompanied by Akt deactivation. In parallel, the I/R of CMECs induced G1-phase arrest through p27(Kip1) up-regulation and significant activation of caspase-3. Accordingly, inhibition of the FoxO3a pathway by IGF-1, an Akt activator, could significantly block the I/R-enhanced activation of p27(Kip1) and caspase-3 in CMECs. Collectively, our results indicate that the FoxO3a pathway is involved in the I/R injury of CMECs at least in part through the regulation of cell cycle arrest and apoptosis, suggesting that the FoxO3a pathway may be a novel therapeutic target that protects against microvascular endothelial damage in ischemic hearts.

Tuberous sclerosis protein 2 (TSC2) modulates CCN4 cytoprotection during apoptotic amyloid toxicity in microglia

More than 110 million individuals will suffer from cognitive loss worldwide by the year 2050 with a majority of individuals presenting with Alzheimer's disease (AD). Yet, successful treatments for etiologies that involve β.-amyloid (Aβ.) toxicity in AD remain elusive and await novel avenues for drug development. Here we show that Wnt1 inducible signaling pathway protein 1 (WISP1/CCN4) controls the post-translational phosphorylation of Akt1, p70S6K, and AMP activated protein kinase (AMPK) to the extent that tuberous sclerosis complex 2 (TSC2) (Ser1387) phosphorylation, a target of AMPK, is decreased and TSC2 (Thr1462) phosphorylation, a target of Akt1, is increased. The ability of WISP1 to limit TSC2 activity allows WISP1 to increase the activity of p70S6K, since gene silencing of TSC2 further enhances WISP1 phosphorylation of p70S6K. However, a minimal level of TSC2 activity is necessary to modulate WISP1 cytoprotection that may require modulation of mTOR activity, since gene knockdown of TSC2 impairs the ability of WISP1 to protect microglia against apoptotic membrane phosphatidylserine (PS) exposure, nuclear DNA degradation, mitochondrial membrane depolarization, and cytochrome c release during Aβ. exposure.

WISP1 neuroprotection requires FoxO3a post-translational modulation with autoregulatory control of SIRT1

As a member of the secreted extracellular matrix associated proteins of the CCN family, Wnt1 inducible signaling pathway protein 1 (WISP1/CCN4) is garnering increased attention not only as a potent proliferative entity, but also as a robust cytoprotective agent during toxic insults. Here we demonstrate that WISP1 prevents forkhead transcription factor FoxO3a mediated caspase 1 and caspase 3 apoptotic cell death in primary neurons during oxidant stress. Phosphoinositide 3-kinase (PI 3-K) and protein kinase B (Akt1) are necessary for WISP1 to foster posttranslational phosphorylation of FoxO3a and sequester FoxO3a in the cytoplasm of neurons with protein 14-3-3. Through an autoregulatory loop, WISP1 also minimizes deacytelation of FoxO3a, prevents caspase 1 and 3 activation, and promotes an effective neuroprotective level of SIRT1 activity through SIRT1 nuclear trafficking and prevention of SIRT1 caspase degradation. Elucidation of the critical pathways of WISP1 that determine neuronal cell survival during oxidative stress may offer novel therapeutic avenues for neurodegenerative disorders.

Targeting disease through novel pathways of apoptosis and autophagy

INTRODUCTION

Apoptosis and autophagy impact cell death in multiple systems of the body. Development of new therapeutic strategies that target these processes must address their complex role during developmental cell growth as well as during the modulation of toxic cellular environments.

AREAS COVERED

Novel signaling pathways involving Wnt1-inducible signaling pathway protein 1 (WISP1), phosphoinositide 3-kinase (PI3K), protein kinase B (Akt), β-catenin and mammalian target of rapamycin (mTOR) govern apoptotic and autophagic pathways during oxidant stress that affect the course of a broad spectrum of disease entities including Alzheimer's disease, Parkinson's disease, myocardial injury, skeletal system trauma, immune system dysfunction and cancer progression. Implications of potential biological and clinical outcome for these signaling pathways are presented.

EXPERT OPINION

The CCN family member WISP1 and its intimate relationship with canonical and non-canonical wingless signaling pathways of PI3K, Akt1, β-catenin and mTOR offer an exciting approach for governing the pathways of apoptosis and autophagy especially in clinical disorders that are currently without effective treatments. Future studies that can elucidate the intricate role of these cytoprotective pathways during apoptosis and autophagy can further the successful translation and development of these cellular targets into robust and safe clinical therapeutic strategies.

A Critical Kinase Cascade in Neurological Disorders: PI 3-K, Akt, and mTOR

Neurodegenerative disorders lead to disability and death in a significant proportion of the world's population. However, many disorders of the nervous system remain with limited effective treatments. Kinase pathways in the nervous system that involve phosphoinositide 3-kinase (PI 3-K), protein kinase B (Akt), and the mammalian target of rapamycin (mTOR) offer exciting prospects for the understanding of neurodegenerative pathways and the development of new avenues of treatment. PI 3-K, Akt, and mTOR pathways are vital cellular components that determine cell fate during acute and chronic disorders, such as Huntington's disease, Alzheimer's disease, Parkinson's disease, epilepsy, stroke, and trauma. Yet, the elaborate relationship among these kinases and the variable control of apoptosis and autophagy can lead to unanticipated biological and clinical outcomes. Crucial for the successful translation of PI 3-K, Akt, and mTOR into robust and safe clinical strategies will be the further elucidation of the complex roles that these kinase pathways hold in the nervous system.

Shedding new light on neurodegenerative diseases through the mammalian target of rapamycin

Neurodegenerative disorders affect a significant portion of the world's population leading to either disability or death for almost 30 million individuals worldwide. One novel therapeutic target that may offer promise for multiple disease entities that involve Alzheimer's disease, Parkinson's disease, epilepsy, trauma, stroke, and tumors of the nervous system is the mammalian target of rapamycin (mTOR). mTOR signaling is dependent upon the mTORC1 and mTORC2 complexes that are composed of mTOR and several regulatory proteins including the tuberous sclerosis complex (TSC1, hamartin/TSC2, tuberin). Through a number of integrated cell signaling pathways that involve those of mTORC1 and mTORC2 as well as more novel signaling tied to cytokines, Wnt, and forkhead, mTOR can foster stem cellular proliferation, tissue repair and longevity, and synaptic growth by modulating mechanisms that foster both apoptosis and autophagy. Yet, mTOR through its proliferative capacity may sometimes be detrimental to central nervous system recovery and even promote tumorigenesis. Further knowledge of mTOR and the critical pathways governed by this serine/threonine protein kinase can bring new light for neurodegeneration and other related diseases that currently require new and robust treatments.

Oxidant stress and signal transduction in the nervous system with the PI 3-K, Akt, and mTOR cascade

Oxidative stress impacts multiple systems of the body and can lead to some of the most devastating consequences in the nervous system especially during aging. Both acute and chronic neurodegenerative disorders such as diabetes mellitus, cerebral ischemia, trauma, Alzheimer’s disease, Parkinson’s disease, Huntington’s disease, and tuberous sclerosis through programmed cell death pathways of apoptosis and autophagy can be the result of oxidant stress. Novel therapeutic avenues that focus upon the phosphoinositide 3-kinase (PI 3-K), Akt (protein kinase B), and the mammalian target of rapamycin (mTOR) cascade and related pathways offer exciting prospects to address the onset and potential reversal of neurodegenerative disorders. Effective clinical translation of these pathways into robust therapeutic strategies requires intimate knowledge of the complexity of these pathways and the ability of this cascade to influence biological outcome that can vary among disorders of the nervous system.

Novel directions for diabetes mellitus drug discovery

INTRODUCTION

Diabetes mellitus impacts almost 200 million individuals worldwide and leads to debilitating complications. New avenues of drug discovery must target the underlying cellular processes of oxidative stress, apoptosis, autophagy, and inflammation that can mediate multi-system pathology during diabetes mellitus.

AREAS COVERED

The authors examine the novel directions for drug discovery that involve: the β-nicotinamide adenine dinucleotide (NAD(+)) precursor nicotinamide, the cytokine erythropoietin, the NAD(+)-dependent protein histone deacetylase SIRT1, the serine/threonine-protein kinase mammalian target of rapamycin (mTOR), and the wingless pathway. Furthermore, the authors present the implications for the targeting of these pathways that oversee gluconeogenic genes, insulin signaling and resistance, fatty acid beta-oxidation, inflammation, and cellular survival.

EXPERT OPINION

Nicotinamide, erythropoietin, and the downstream pathways of SIRT1, mTOR, forkhead transcription factors, and wingless signaling offer exciting prospects for novel directions of drug discovery for the treatment of metabolic disorders. Future investigations must dissect the complex relationship and fine modulation of these pathways for the successful translation of robust reparative and regenerative strategies against diabetes mellitus and the complications of this disorder.

PRAS40 is an integral regulatory component of erythropoietin mTOR signaling and cytoprotection

Emerging strategies that center upon the mammalian target of rapamycin (mTOR) signaling for neurodegenerative disorders may bring effective treatment for a number of difficult disease entities. Here we show that erythropoietin (EPO), a novel agent for nervous system disorders, prevents apoptotic SH-SY5Y cell injury in an oxidative stress model of oxygen-glucose deprivation through phosphatidylinositol-3-kinase (PI 3-K)/protein kinase B (Akt) dependent activation of mTOR signaling and phosphorylation of the downstream pathways of p70 ribosomal S6 kinase (p70S6K), eukaryotic initiation factor 4E-binding protein 1 (4EBP1), and proline rich Akt substrate 40 kDa (PRAS40). PRAS40 is an important regulatory component either alone or in conjunction with EPO signal transduction that can determine cell survival through apoptotic caspase 3 activation. EPO and the PI 3-K/Akt pathways control cell survival and mTOR activity through the inhibitory post-translational phosphorylation of PRAS40 that leads to subcellular binding of PRAS40 to the cytoplasmic docking protein 14-3-3. However, modulation and phosphorylation of PRAS40 is independent of other protective pathways of EPO that involve extracellular signal related kinase (ERK 1/2) and signal transducer and activator of transcription (STAT5). Our studies highlight EPO and PRAS40 signaling in the mTOR pathway as potential therapeutic strategies for development against degenerative disorders that lead to cell demise.

WISP1 (CCN4) autoregulates its expression and nuclear trafficking of β-catenin during oxidant stress with limited effects upon neuronal autophagy

Wnt1 inducible signaling pathway protein 1 (WISP1/CCN4) is a CCN family member more broadly identified with development and tumorigenesis. However, recent studies have shed new light and enthusiasm on WISP1 as a novel target directed against toxic cell degeneration. Here we show WISP1 prevents apoptotic degeneration in primary neurons during oxidant stress through the activation of protein kinase B (Akt1), the post-translational maintenance of β-catenin integrity that is consistent with inhibition of glycogen synthase kinase-3β (GSK-3β), and the subcellular trafficking of β- catenin to foster its translocation to the nucleus. Interestingly, WISP1 autoregulates its expression through the promotion of β-catenin activity and may employ β-catenin to have a limited control over autophagy, but neuronal injury during oxidant stress as a result of autophagy appears portioned to a small population of neurons without significant impact upon overall cell survival. New strategies that target WISP1, its autoregulation, and the pathways responsible for neuronal cell injury may bring forth new insight for the treatment of neurodegenerative disorders.

Erythropoietin: new directions for the nervous system

New treatment strategies with erythropoietin (EPO) offer exciting opportunities to prevent the onset and progression of neurodegenerative disorders that currently lack effective therapy and can progress to devastating disability in patients. EPO and its receptor are present in multiple systems of the body and can impact disease progression in the nervous, vascular, and immune systems that ultimately affect disorders such as Alzheimer's disease, Parkinson's disease, retinal injury, stroke, and demyelinating disease. EPO relies upon wingless signaling with Wnt1 and an intimate relationship with the pathways of phosphoinositide 3-kinase (PI 3-K), protein kinase B (Akt), and mammalian target of rapamycin (mTOR). Modulation of these pathways by EPO can govern the apoptotic cascade to control β-catenin, glycogen synthase kinase-3β, mitochondrial permeability, cytochrome c release, and caspase activation. Yet, EPO and each of these downstream pathways require precise biological modulation to avert complications associated with the vascular system, tumorigenesis, and progression of nervous system disorders. Further understanding of the intimate and complex relationship of EPO and the signaling pathways of Wnt, PI 3-K, Akt, and mTOR are critical for the effective clinical translation of these cell pathways into robust treatments for neurodegenerative disorders.

Prevention of β-amyloid degeneration of microglia by erythropoietin depends on Wnt1, the PI 3-K/mTOR pathway, Bad, and Bcl-xL

Central nervous system microglia promote neuronal regeneration and sequester toxic β-amyloid (Aβ) deposition during Alzheimer's disease. We show that the cytokine erythropoietin (EPO) decreases the toxic effect of Aβ on microgliain vitro. EPO up-regulates the cysteine-rich glycosylated wingless protein Wnt1 and activates the PI 3-K/Akt1/mTOR/ p70S6K pathway. This in turn increases phosphorylation and cytosol trafficking of Bad, reduces the Bad/Bcl-x_L complex and increases the Bcl-x_L/Bax complex, thus preventing caspase 1 and caspase 3 activation and apoptosis. Our data may foster development of novel strategies to use cytoprotectants such as EPO for Alzheimer's disease and other degenerative disorders.

Mammalian target of rapamycin signaling in diabetic cardiovascular disease

Diabetes mellitus currently affects more than 170 million individuals worldwide and is expected to afflict another 200 million individuals in the next 30 years. Complications of diabetes as a result of oxidant stress affect multiple systems throughout the body, but involvement of the cardiovascular system may be one of the most severe in light of the impact upon cardiac and vascular function that can result in rapid morbidity and mortality for individuals. Given these concerns, the signaling pathways of the mammalian target of rapamycin (mTOR) offer exciting prospects for the development of novel therapies for the cardiovascular complications of diabetes. In the cardiovascular and metabolic systems, mTOR and its multi-protein complexes of TORC1 and TORC2 regulate insulin release and signaling, endothelial cell survival and growth, cardiomyocyte proliferation, resistance to β-cell injury, and cell longevity. Yet, mTOR can, at times, alter insulin signaling and lead to insulin resistance in the cardiovascular system during diabetes mellitus. It is therefore vital to understand the complex relationship mTOR and its downstream pathways hold during metabolic disease in order to develop novel strategies for the complications of diabetes mellitus in the cardiovascular system.

75-kd sirtuin 1 blocks tumor necrosis factor α-mediated apoptosis in human osteoarthritic chondrocytes

OBJECTIVE

Sirtuin 1 (SirT1) has been implicated in the regulation of human cartilage homeostasis and chondrocyte survival. Exposing human osteoarthritic (OA) chondrocytes to tumor necrosis factor α (TNFα) generates a stable and enzymatically inactive 75-kd form of SirT1 (75SirT1) via cathepsin B-mediated cleavage. Because 75SirT1 is resistant to further degradation, we hypothesized that it has a distinct role in OA, and the present study was undertaken to identify this role.

METHODS

The presence of cathepsin B and 75SirT in OA and normal human chondrocytes was analyzed. Confocal imaging of SirT1 was used to monitor its subcellular trafficking following TNFα stimulation. Coimmunofluorescence staining for cathepsin B, mitochondrial cytochrome oxidase subunit IV, and lysosome-associated membrane protein 1 together with SirT1 was performed. Human chondrocytes were tested for apoptosis by fluorescence-activated cell sorter analysis and immunoblotting for caspases 3 and 8. Human chondrocyte mitochondrial extracts were obtained and analyzed for 75SirT1-cytochrome c association.

RESULTS

Confocal imaging and immunoblot analyses following TNFα challenge of human chondrocytes demonstrated that 75SirT1 was exported to the cytoplasm and colocalized with the mitochondrial membrane. Consistent with this, immunoprecipitation and immunoblot analyses revealed that 75SirT1 is enriched in mitochondrial extracts and associates with cytochrome c following TNFα stimulation. Preventing nuclear export of 75SirT1 or reducing levels of full-length SirT1 and 75SirT1 augmented chondrocyte apoptosis in the presence of TNFα. Levels of cathepsin B and 75SirT1 were elevated in OA versus normal chondrocytes. Additional analyses showed that human chondrocytes exposed to OA-derived synovial fluid generated the 75SirT1 fragment.

CONCLUSION

These data suggest that 75SirT1 promotes chondrocyte survival following exposure to proinflammatory cytokines.

Wnt1 inducible signaling pathway protein 1 (WISP1) blocks neurodegeneration through phosphoinositide 3 kinase/Akt1 and apoptotic mitochondrial signaling involving Bad, Bax, Bim, and Bcl-xL

Wnt1 inducible signaling pathway protein 1 (WISP1) is a member of the CCN family of proteins that determine cell growth, cell differentiation, immune system activation, and cell survival in tissues ranging from the cardiovascular-pulmonary system to the reproductive system. Yet, little is known of the role of WISP1 as a neuroprotective entity in the nervous system. Here we demonstrate that WISP1 is present in primary hippocampal neurons during oxidant stress with oxygen-glucose deprivation (OGD). WISP1 expression is significantly enhanced during OGD exposure by the cysteine-rich glycosylated protein Wnt1. Similar to the neuroprotective capabilities known for Wnt1 and its signaling pathways, WISP1 averts neuronal cell injury and apoptotic degeneration during oxidative stress exposure. WISP1 requires activation of phosphoinositide 3-kinase (PI 3-K) and Akt1 pathways to promote neuronal cell survival, since blockade of these pathways abrogates cellular protection. Furthermore, WISP1 through PI 3-K and Akt1 phosphorylates Bad and GSK-3β, minimizes expression of the Bim/Bax complex while increasing the expression of Bclx(L)/Bax complex, and prevents mitochondrial membrane permeability, cytochrome c release, and caspase 3 activation in the presence of oxidant stress. These studies provide novel considerations for the development of WISP1 as an effective and robust therapeutic target not only for neurodegenerative disorders, but also for disease entities throughout the body.

Targeting cardiovascular disease with novel SIRT1 pathways

Sirtuin (the mammalian homolog of silent information regulation 2 of yeast Saccharomyces cerevisiae) 1 (SIRT1), a NAD-dependent histone deacetylase, has emerged as a critical regulator in response to oxidative stress. Through antagonism of oxidative stress-induced cell injury and through the maintenance of metabolic homeostasis in the body, SIRT1 can block vascular system injury. SIRT1 targets multiple cellular proteins, such as peroxisome proliferator-activated receptor-γ and its coactivator-1α, forkhead transcriptional factors, AMP-activated protein kinase, NF-κB and protein tyrosine phosphatase to modulate intricate cellular pathways of multiple diseases. In the cardiovascular system, activation of SIRT1 can not only protect against oxidative stress at the cellular level, but can also offer increased survival at the systemic level to limit coronary heart disease and cerebrovascular disease. Future knowledge regarding SIRT1 and its novel pathways will open new directions for the treatment of cardiovascular disease as well as offer the potential to limit disability from several related disorders.

High expression of the longevity gene product SIRT1 and apoptosis induction by sirtinol in adult T-cell leukemia cells

Adult T-cell leukemia-lymphoma (ATL) is an aggressive peripheral T-cell neoplasm that develops after long-term infection with human T-cell leukemia virus (HTLV-1). SIRT1, a nicotinamide adenine dinucleotide(+)-dependent histone/protein deacetylase, plays a crucial role in various physiological processes, such as aging, metabolism, neurogenesis and apoptosis, owing to its ability to deacetylate numerous substrates, such as histone and NF-κB, which is implicated as an exacerbation factor in ATL. Here, we assessed how SIRT1 is regulated in primary ATL cells and leukemic cell lines. SIRT1 expression in ATL patients was significantly higher than that in healthy controls, especially in the acute type. Sirtinol, a SIRT1 inhibitor, induced significant growth inhibition or apoptosis in cells from ATL patients and leukemic cell lines, especially HTLV-1-related cell lines. Sirtinol-induced apoptosis was mediated by activation of the caspase family and degradation of SIRT1 in the nucleus. Furthermore, SIRT1 knockdown by SIRT1-specific small interfering RNA caused apoptosis via activation of caspase-3 and PARP in MT-2 cells, HTLV-1-related cell line. These results suggest that SIRT1 is a crucial antiapoptotic molecule in ATL cells and that SIRT1 inhibitors may be useful therapeutic agents for leukemia, especially in patients with ATL.

EPO relies upon novel signaling of Wnt1 that requires Akt1, FoxO3a, GSK-3β, and β-catenin to foster vascular integrity during experimental diabetes

Multiple complications can ensue in the cardiovascular, renal, and nervous systems during diabetes mellitus (DM). Given that endothelial cells (ECs) are susceptible targets to elevated serum D-glucose, identification of novel cellular mechanisms that can protect ECs may foster the development of unique strategies for the prevention and treatment of DM complications. Erythropoietin (EPO) represents one of these novel strategies but the dependence of EPO upon Wnt1 and its downstream signaling in a clinically relevant model of DM with elevated D-glucose has not been elucidated. Here we show that EPO can not only maintain the integrity of EC membranes, but also prevent apoptotic nuclear DNA degradation and the externalization of membrane phosphatidylserine (PS) residues during elevated D-glucose over a 48-hour period. EPO modulates the expression of Wnt1 and utilizes Wnt1 to confer EC protection during elevated D-glucose exposure, since application of a Wnt1 neutralizing antibody, treatment with the Wnt1 antagonist DKK-1, or gene silencing of Wnt1 with Wnt1 siRNA transfection abrogates the protective capability of EPO. EPO through a novel Wnt1 dependent mechanism controls the post-translational phosphorylation of the "pro-apoptotic" forkhead member FoxO3a and blocks the trafficking of FoxO3a to the cell nucleus to prevent apoptotic demise. EPO also employs the activation of protein kinase B (Akt1) to foster phosphorylation of GSK-3β that appears required for EPO vascular protection. Through this inhibition of GSK-3β, EPO maintains β-catenin activity, allows the translocation of β-catenin from the EC cytoplasm to the nucleus through a Wnt1 pathway, and requires β-catenin for protection against elevated D-glucose since gene silencing of β-catenin eliminates the ability of EPO as well as Wnt1 to increase EC survival. Subsequently, we show that EPO requires modulation of both Wnt1 and FoxO3a to oversee mitochondrial membrane depolarization, cytochrome c release, and caspase activation during elevated D-glucose. Our studies identify critical elements of the protective cascade for EPO that rely upon modulation of Wnt1, Akt1, FoxO3a, GSK-3β, β-catenin, and mitochondrial apoptotic pathways for the development of new strategies against DM vascular complications.

SIRT1: new avenues of discovery for disorders of oxidative stress

INTRODUCTION

The sirtuin SIRT1 is expressed throughout the body, has broad biological effects and can significantly affect both cellular survival and longevity during acute and long-term injuries, which involve both oxidative stress and cell metabolism.

AREAS COVERED

SIRT1 has an intricate role in the pathology, progression, and treatment of several disease entities, including neurodegenerative disorders such as Alzheimer's disease and Parkinson's disease, tumorigenesis, cardiovascular disease with myocardial injury and atherosclerosis, metabolic disease, and aging-related disease. New areas of study in these disciplines, with discussion of the cellular biology, are highlighted.

EXPERT OPINION

Novel signaling pathways for SIRT1, which can be targeted to enhance cellular protection and potentially extend lifespan, continue to emerge. Investigations that can further determine the intracellular signaling, trafficking and post-translational modifications that occur with SIRT1 in a variety of cell systems and environments will allow us to further translate this knowledge into effective therapeutic strategies that will be applicable to multiple systems of the body.

Erythropoietin employs cell longevity pathways of SIRT1 to foster endothelial vascular integrity during oxidant stress

Given the cytoprotective ability of erythropoietin (EPO) in cerebral microvascular endothelial cells (ECs) and the invaluable role of ECs in the central nervous system, it is imperative to elucidate the cellular pathways for EPO to protect ECs against brain injury. Here we illustrate that EPO relies upon the modulation of SIRT1 (silent mating type information regulator 2 homolog 1) in cerebral microvascular ECs to foster cytoprotection during oxygen-glucose deprivation (OGD). SIRT1 activation which results in the inhibition of apoptotic early membrane phosphatidylserine (PS) externalization and subsequent DNA degradation during OGD becomes a necessary component for EPO protection in ECs, since inhibition of SIRT1 activity or diminishing its expression by gene silencing abrogates cell survival supported by EPO during OGD. Furthermore, EPO promotes the subcellular trafficking of SIRT1 to the nucleus which is necessary for EPO to foster vascular protection. EPO through SIRT1 averts apoptosis through activation of protein kinase B (Akt1) and the phosphorylation and cytoplasmic retention of the forkhead transcription factor FoxO3a. SIRT1 through EPO activation also utilizes mitochondrial pathways to prevent mitochondrial depolarization, cytochrome c release, and Bad, caspase 1, and caspase 3 activation. Our work identifies novel pathways for EPO in the vascular system that can govern the activity of SIRT1 to prevent apoptotic injury through Akt1, FoxO3a phosphorylation and trafficking, mitochondrial membrane permeability, Bad activation, and caspase 1 and 3 activities in ECs during oxidant stress.

Erythropoietin and Wnt1 govern pathways of mTOR, Apaf-1, and XIAP in inflammatory microglia

Inflammatory microglia modulate a host of cellular processes in the central nervous system that include neuronal survival, metabolic fluxes, foreign body exclusion, and cellular regeneration. Elucidation of the pathways that oversee microglial survival and integrity may offer new avenues for the treatment of neurodegenerative disorders. Here we demonstrate that erythropoietin (EPO), an emerging strategy for immune system modulation, prevents microglial early and late apoptotic injury during oxidant stress through Wnt1, a cysteine-rich glycosylated protein that modulates cellular development and survival. Loss of Wnt1 through blockade of Wnt1 signaling or through the gene silencing of Wnt1 eliminates the protective capacity of EPO. Furthermore, endogenous Wnt1 in microglia is vital to preserve microglial survival since loss of Wnt1 alone increases microglial injury during oxidative stress. Cellular protection by EPO and Wnt1 intersects at the level of protein kinase B (Akt1), the mammalian target of rapamycin (mTOR), and p70S6K, which are necessary to foster cytoprotection for microglia. Downstream from these pathways, EPO and Wnt1 control "anti-apoptotic" pathways of microglia through the modulation of mitochondrial membrane permeability, the release of cytochrome c, and the expression of apoptotic protease activating factor-1 (Apaf-1) and X-linked inhibitor of apoptosis protein (XIAP). These studies offer new insights for the development of innovative therapeutic strategies for neurodegenerative disorders that focus upon inflammatory microglia and novel signal transduction pathways.

Pathways for ischemic cytoprotection: role of sirtuins in caloric restriction, resveratrol, and ischemic preconditioning

Caloric restriction (CR), resveratrol, and ischemic preconditioning (IPC) have been shown to promote protection against ischemic injury in the heart and brain, as well as in other tissues. The activity of sirtuins, which are enzymes that modulate diverse biologic processes, seems to be vital in the ability of these therapeutic modalities to prevent against cellular dysfunction and death. The protective mechanisms of the yeast Sir2 and the mammalian homolog sirtuin 1 have been extensively studied, but the involvement of other sirtuins in ischemic protection is not yet clear. We examine the roles of mammalian sirtuins in modulating protective pathways against oxidative stress, energy depletion, excitotoxicity, inflammation, DNA damage, and apoptosis. Although many of these sirtuins have not been directly implicated in ischemic protection, they may have unique roles in enhancing function and preventing against stress-mediated cellular damage and death. This review will include in-depth analyses of the roles of CR, resveratrol, and IPC in activating sirtuins and in mediating protection against ischemic damage in the heart and brain.

Translating cell survival and cell longevity into treatment strategies with SIRT1

The sirtuin SIRT1, a class III NAD(+)-dependent protein histone deacetylase, is present throughout the body that involves cells of the central nervous system, immune system, cardiovascular system, and the musculoskeletal system. SIRT1 has broad biological effects that affect cellular metabolism as well as cellular survival and longevity that can impact both acute and chronic disease processes that involve neurodegenerative disease, diabetes mellitus, cardiovascular disease, and cancer. Given the intricate relationship SIRT1 holds with a host of signal transduction pathways ranging from transcription factors, such as forkhead, to cytokines and growth factors, such as erythropoietin, it becomes critical to elucidate the cellular pathways of SIRT1 to safely and effectively develop and translate novel avenues of treatment for multiple disease entities.

SIRT1 and AMPK in regulating mammalian senescence: a critical review and a working model

Ageing in mammals remains an unsolved mystery. Anti-ageing is a recurring topic in the history of scientific research. Lifespan extension evoked by Sir2 protein in lower organisms has attracted a large amount of interests in the last decade. This review summarizes recent evidence supporting the role of a Sir2 mammalian homologue, SIRT1 (Silent information regulator T1), in regulating ageing and cellular senescence. The various signaling networks responsible for the anti-ageing and anti-senescence activity of SIRT1 have been discussed. In particular, a counter-balancing model involving the cross-talks between SIRT1 and AMP-activated protein kinase (AMPK), another stress and energy sensor, is suggested for controlling the senescence program in mammalian cells.

Mammalian target of rapamycin: hitting the bull's-eye for neurological disorders

The mammalian target of rapamycin (mTOR) and its associated cell signaling pathways have garnered significant attention for their roles in cell biology and oncology. Interestingly,the explosion of information in this field has linked mTOR to neurological diseases with promising initial studies. mTOR, a 289 kDa serine/threonine protein kinase, plays an important role in cell growth and proliferation and is activated through phosphorylation in response to growth factors, mitogens and hormones. Growth factors, amino acids, cellular nutrients and oxygen deficiency can downregulate mTOR activity. The function of mTOR signaling is mediated primarily through two mTOR complexes: mTORC1 and mTORC2. mTORC1 initiates cap-dependent protein translation, a rate-limiting step of protein synthesis, through the phosphorylation of the targets eukaryotic initiation factor 4E-binding protein 1 (4EBP1) and p70 ribosomal S6 kinase (p70S6K). In contrast, mTORC2 regulates development of the cytoskeleton and also controls cell survival. Although closely tied to tumorigenesis, mTOR and the downstream signaling pathways are significantly involved in the central nervous system (CNS) with synaptic plasticity, memory retention, neuroendocrine regulation associated with food intake and puberty and modulation of neuronal repair following injury. The signaling pathways of mTOR also are believed to be a significant component in a number of neurological diseases, such as Alzheimer disease, Parkinson disease and Huntington disease, tuberous sclerosis, neurofibromatosis, fragile X syndrome, epilepsy, traumatic brain injury and ischemic stroke. Here we describe the role of mTOR in the CNS and illustrate the potential for new strategies directed against neurological disorders.