Erythropoietin: elucidating new cellular targets that broaden therapeutic strategies

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.

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.

Hypoxia inducible factor-1 as a target for neurodegenerative diseases

Hypoxia inducible factor-1 (HIF-1) is a transcriptional factor responsible for cellular and tissue adaption to low oxygen tension. HIF-1, a heterodimer consisting of a constitutively expressed β subunit and an oxygen-regulated α subunit, regulates a series of genes that participate in angiogenesis, iron metabolism, glucose metabolism, and cell proliferation/survival. The activity of HIF-1 is controlled by post-translational modifications on different amino acid residues of its subunits, mainly the alpha subunit. Besides in ischemic stroke (see review [1]), emerging evidence has revealed that HIF-1 activity and expression of its down-stream genes, such as vascular endothelial growth factor and erythropoietin, are altered in a range of neurodegenerative diseases. At the same time, experimental and clinical evidence has demonstrated that regulating HIF-1 might ameliorate the cellular and tissue damage in the neurodegenerative diseases. These new findings suggest HIF-1 as a potential medicinal target for the neurodegenerative diseases. This review focuses on HIF-1α protein modifications and HIF-1's potential neuroprotective roles in Alzheimer's (AD), Parkinson's (PD), Huntington's diseases (HD), and amyotrophic lateral sclerosis (ALS).

Protective effect of systemic administration of erythropoietin on auditory brain stem response and compound action potential thresholds in an animal model of cochlear implantation

OBJECTIVES

An animal model of cochlear implantation has been developed, and the hearing threshold was evaluated after different surgical procedures. The effect of perioperative systemic administration of erythropoietin on the hearing loss induced by cochlear implantation was tested.

METHODS

Twenty-nine guinea pigs with normal hearing underwent implantation of a 254-microm-diameter array through a cochleostomy. The effects on hearing of cochleostomy and transient and long-term array implantation (21 days) were assessed by testing of the auditory brain stem responses and compound action potentials. Eleven implanted animals received intraperitoneal administration of erythropoietin. Selected computed tomographic scans and cochlear histologic studies were performed 1 month after implantation to confirm proper placement of the array. The erythropoietin concentration at the time of surgery was assessed in samples of perilymph, cerebrospinal fluid, and blood.

RESULTS

The cochleostomy and transient array insertion had no effect on hearing thresholds. Long-term array implantation induced a stable decrease of hearing threshold (30 dB), a decrease that was reduced by 12 dB in erythropoietin-treated animals. The erythropoietin-treated animals had better hearing preservation at higher frequencies. Fibrosis surrounding the array was seen in both groups.

CONCLUSIONS

The hearing loss observed was probably due to the presence of the array in the cochlea. The intraperitoneal injection of erythropoietin improved the hearing threshold shift induced by implantation.

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.

Treating anemia associated with chronic renal failure with erythropoiesis stimulators: recombinant human erythropoietin might be the best among the available choices

Chronic renal failure (CRF) is a widespread medical problem commonly accompanied by a hypoproliferative anemia ("renal anemia") due to erythropoietin deficiency. Anemia greatly contributes to reduced quality of life (Hr-QoL) and high morbidity and mortality in CRF patients. Recombinant human erythropoietin (rHu-Epo) was introduced to medical practice some 20years ago. It enables correction of anemia (hemoglobin levels, Hb) with dramatic immediate (Hr-QoL improvement) and long-term effects (reduced morbidity and mortality). Newer experimental data suggest that long-term benefits could be due not only to antianemic effect, but also to a direct organoprotective effect of (rHu)-Epo mediated through a receptor complex different from the "erythropoietic" erythropoietin receptor. During the last decade, two alternative treatments for renal anemia have been approved: darbepoetin and CERA. Both are direct agonists of the "erythropoietic" receptors and both were derived from rHu-Epo. Molecularly, they differ from rHu-Epo in that they are much larger molecules (darbepoetin is genetically modified rHu-Epo with a higher sugar content and CERA is pegylated rHu-Epo) with lower affinity for the erythropoietin receptor but with a longer circulating time. In terms of renal anemia correction, they are non-inferior to rHu-Epo and allow for less frequent dosing. They have never been compared to rHu-Epo regarding the long-term outcomes. It is hypothesized that regarding the long-term outcomes (morbidity, mortality), rHu-Epo might be superior to those larger molecules. The hypothesis is based on two types of observations. First, experimental data emphasize the role of small, erythropoietically less valuable rHu-Epo isoforms in its organoprotective effects. Second, clinical observations suggest that rHu-Epo enables for less variable Hb correction than the larger molecules, and pronounced within-subject Hb variability has been suggested as an independent predictor of poor long-term outcomes of renal anemia management.

Erythropoietin improves memory function with reducing endothelial dysfunction and amyloid-beta burden in Alzheimer's disease models

Neurovascular degeneration contributes to the pathogenesis of Alzheimer's disease (AD). Because erythropoietin (EPO) promotes endothelial regeneration, we investigated the therapeutic effects of EPO in animal models of AD. In aged Tg2576 mice, EPO receptors (EPORs) were expressed in the cortex and hippocampus. Tg2576 mice were treated with daily injection of EPO (5000 IU/kg/day) for 5 days. At 14 days, EPO improved contextual memory as measured by fear-conditioning test. EPO enhanced endothelial proliferation and the level of synaptophysin expression in the brain. EPO also increased capillary density, and decreased the level of the receptor for advanced glycation endproducts (RAGE) in the brain, while decreasing in the amount of amyloid plaque and amyloid-β (Aβ). In cultured human endothelial cells, EPO enhanced angiogenesis and suppressed the expression of the RAGE. These results show that EPO improves memory and ameliorates endothelial degeneration induced by Aβ in AD models. This pre-clinical evidence suggests that EPO may be useful for the treatment of AD.

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.

Isotretinoin and FoxO1: A scientific hypothesis

Oral isotretinoin (13-cis retinoic acid) is the most effective drug in the treatment of acne and restores all major pathogenetic factors of acne vulgaris. isotretinoin is regarded as a prodrug which after isomerizisation to all-trans-retinoic acid (ATRA) induces apoptosis in cells cultured from human sebaceous glands, meibomian glands, neuroblastoma cells, hypothalamic cells, hippocampus cells, Dalton's lymphoma ascites cells, B16F-10 melanoma cells, and neuronal crest cells and others. By means of translational research this paper provides substantial indirect evidence for isotretinoin's mode of action by upregulation of forkhead box class O (FoxO) transcription factors. FoxOs play a pivotal role in the regulation of androgen receptor transactivation, insulin/insulin like growth factor-1 (IGF-1)-signaling, peroxisome proliferator-activated receptor-γ (PPArγ)- and liver X receptor-α (LXrα)-mediated lipogenesis, β-catenin signaling, cell proliferation, apoptosis, reactive oxygene homeostasis, innate and acquired immunity, stem cell homeostasis, as well as anti-cancer effects. An accumulating body of evidence suggests that the therapeutic, adverse, teratogenic and chemopreventive effecs of isotretinoin are all mediated by upregulation of FoxO-mediated gene transcription. These FoxO-driven transcriptional changes of the second response of retinoic acid receptor (RAR)-mediated signaling counterbalance gene expression of acne due to increased growth factor signaling with downregulated nuclear FoxO proteins. The proposed isotretinoin→ATRA→RAR→FoxO interaction offers intriguing new insights into the mode of isotretinoin action and explains most therapeutic, adverse and teratogenic effects of isotretinoin in the treatment of acne by a common mode of FoxO-mediated transcriptional regulation.

Non-erythropoietic erythropoietin derivatives protect from light-induced and genetic photoreceptor degeneration

Given the high genetic heterogeneity of inherited retinal degenerations (IRDs), a wide applicable treatment would be desirable to halt/slow progressive photoreceptor (PR) cell loss in a mutation-independent manner. In addition to its erythropoietic activity, erythropoietin (EPO) presents neurotrophic characteristics. We have previously shown that adeno-associated viral (AAV) vector-mediated systemic EPO delivery protects from PR degeneration. However, this is associated with an undesired hematocrit increase that could contribute to PR protection. Non-erythropoietic EPO derivatives (EPO-D) are available which allow us to dissect erythropoiesis's role in PR preservation and may be more versatile and safe than EPO as anti-apoptotic agents. We delivered in animal models of light-induced or genetic retinal degeneration either intramuscularly or subretinally AAV vectors encoding EPO or one of the three selected EPO-D: the mutant S100E, the helix A- and B-derived EPO-mimetic peptides. We observed that (i) systemic expression of S100E induces a significantly lower hematocrit increase than EPO and provides similar protection from PR degeneration, and (ii) intraocular expression of EPO-D protects PR from degeneration in the absence of significant hematocrit increase. On the basis of this, we conclude that erythropoiesis is not required for EPO-mediated PR protection. However, the lower efficacy observed when EPO or S100E is expressed intraocularly rather than systemically suggests that hormone systemic effects contribute to PR protection. Unlike S100E, EPO-mimetic peptides preserve PR only when given locally, suggesting that different EPO-D have a different potency or mode of action. In conclusion, our data show that subretinal delivery of AAV vectors encoding EPO-D protects from light-induced and genetic PR degeneration.

Erythropoietin: a hormone with multiple functions

Erythropoietin (EPO), the main hemopoietic hormone synthesized by the kidney as well as by the liver in fetal life, is implicated in mammalian erythropoiesis. Production and secretion of EPO and the expression of its receptor (EPO-R) are regulated by tissue oxygenation. EPO and EPO-R, expressed in several tissues, exert pleiotropic activities and have different effects on nonhemopoietic cells. EPO is a cytokine with antiapoptotic activity and plays a potential neuroprotective and cardioprotective role against ischemia. EPO is also involved in angiogenesis, neurogenesis, and the immune response. EPO can prevent metabolic alterations, neuronal and vascular degeneration, and inflammatory cell activation. Consequently, EPO may be of therapeutic use for a variety of disorders. Many tumors express EPO and/or EPO-R, but the action of EPO on tumor cells remains controversial. It has been suggested that EPO promotes the proliferation and survival of cancer cells expressing EPO-R. On the other hand, other reports have concluded that EPO-R plays no role in tumor progression. This review provides a detailed insight into the nonhemopoietic role of EPO and its mechanism(s) of action which may lead to a better understanding of its potential therapeutic value in diverse clinical settings.

Novel avenues of drug discovery and biomarkers for diabetes mellitus

Globally, developed nations spend a significant amount of their resources on health care initiatives that poorly translate into increased population life expectancy. As an example, the United States devotes 16% of its gross domestic product to health care, the highest level in the world, but falls behind other nations that enjoy greater individual life expectancy. These observations point to the need for pioneering avenues of drug discovery to increase life span with controlled costs. In particular, innovative drug development for metabolic disorders such as diabetes mellitus becomes increasingly critical given that the number of diabetic people will increase exponentially over the next 20 years. This article discusses the elucidation and targeting of novel cellular pathways that are intimately tied to oxidative stress in diabetes mellitus for new treatment strategies. Pathways that involve wingless, β-nicotinamide adenine dinucleotide (NAD(+)) precursors, and cytokines govern complex biological pathways that determine both cell survival and longevity during diabetes mellitus and its complications. Furthermore, the role of these entities as biomarkers for disease can further enhance their utility irrespective of their treatment potential. Greater understanding of the intricacies of these unique cellular mechanisms will shape future drug discovery for diabetes mellitus to provide focused clinical care with limited or absent long-term complications.

Therapeutic promise and principles: metabotropic glutamate receptors

For a number of disease entities, oxidative stress becomes a significant factor in the etiology and progression of cell dysfunction and injury. Therapeutic strategies that can identify novel signal transduction pathways to ameliorate the toxic effects of oxidative stress may lead to new avenues of treatment for a spectrum of disorders that include diabetes, Alzheimer's disease, Parkinson's disease and immune system dysfunction. In this respect, metabotropic glutamate receptors (mGluRs) may offer exciting prospects for several disorders since these receptors can limit or prevent apoptotic cell injury as well as impact upon cellular development and function. Yet the role of mGluRs is complex in nature and may require specific mGluR modulation for a particular disease entity to maximize clinical efficacy and limit potential disability. Here we discuss the potential clinical translation of mGluRs and highlight the role of novel signal transduction pathways in the metabotropic glutamate system that may be vital for the clinical utility of mGluRs.

A fork in the path: Developing therapeutic inroads with FoxO proteins

Advances in clinical care for disorders involving any system of the body necessitates novel therapeutic strategies that can focus upon the modulation of cellular proliferation, metabolism, inflammation and longevity. In this respect, members of the mammalian forkhead transcription factors of the O class (FoxOs) that include FoxO1, FoxO3, FoxO4 and FoxO6 are increasingly being recognized as exciting prospects for multiple disorders. These transcription factors govern development, proliferation, survival and longevity during multiple cellular environments that can involve oxidative stress. Furthermore, these transcription factors are closely integrated with several novel signal transduction pathways, such as erythropoietin and Wnt proteins, that may influence the ability of FoxOs to act as a “double-edge sword” to sometimes promote cell survival, but at other times lead to cell injury. Here we discuss the fascinating but complex role of FoxOs during cellular injury and oxidative stress, progenitor cell development, fertility, angiogenesis, cardiovascular function, cellular metabolism and diabetes, cell longevity, immune surveillance and cancer.

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.

Wnt1 neuroprotection translates into improved neurological function during oxidant stress and cerebral ischemia through AKT1 and mitochondrial apoptotic pathways

Although essential for the development of the nervous system, Wnt1 also has been associated with neurodegenerative disease and cognitive loss during periods of oxidative stress. Here we show that endogenous expression of Wnt1 is suppressed during oxidative stress in both in vitro and in vivo experimental models. Loss of endogenous Wnt1 signaling directly correlates with neuronal demise and increased functional deficit, illustrating that endogenous neuronal Wnt1 offers a vital level of intrinsic cellular protection against oxidative stress. Furthermore, transient overexpression of Wnt1 or application of exogenous Wnt1 recombinant protein is necessary to preserve neurological function and rescue neurons from apoptotic membrane phosphatidylserine externalization and genomic DNA degradation, since blockade of Wnt1 signaling with a Wnt1 antibody or dickkopf related protein 1 abrogates neuronal protection by Wnt1. Wnt1 ultimately relies upon the activation of Akt1, the modulation of mitochondrial membrane permeability, and the release of cytochrome c to control the apoptotic cascade, since inhibition of Wnt1 signaling, the phosphatidylinositol 3-kinase pathway, or Akt1 activity abrogates the ability of Wnt1 to block these apoptotic components. Our work identifies Wnt1 and its downstream signaling as cellular targets with high clinical potential for novel treatment strategies for multiple disorders precipitated by oxidative stress.

Perinatal hypoxic-ischemic encephalopathy

Perinatal hypoxic-ischemic encephalopathy (HIE) is an important cause of brain injury in the newborn and can result in long-term devastating consequences. Perinatal hypoxia is a vital cause of long-term neurologic complications varying from mild behavioural deficits to severe seizure, mental retardation, and/or cerebral palsy in the newborn. In the mammalian developing brain, ongoing research into pathophysiological mechanism of neuronal injury and therapeutic strategy after perinatal hypoxia is still limited. With the advent of promising therapy of hypothermia in HIE, this paper reviews the pathophysiology of HIE and the future potential neuroprotective strategies for clinical potential for hypoxia sufferers.

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.

Wnt1, FoxO3a, and NF-kappaB oversee microglial integrity and activation during oxidant stress

Elucidating the underlying mechanisms that govern microglial activation and survival is essential for the development of new treatment strategies for neurodegenerative disorders, since microglia serve not only as guardian sentries of the nervous system, but also play a significant role in determining neuronal and vascular cell fate. Here we show that endogenous and exogenous Wnt1 in inflammatory microglial cells is necessary for the prevention of apoptotic early membrane phosphatidylserine exposure and later DNA degradation, since blockade of Wnt1 signaling abrogates cell survival during oxidative stress. Wnt1 prevents apoptotic demise through the post-translational phosphorylation and maintenance of FoxO3a in the cytoplasm to inhibit an apoptotic cascade that relies upon the loss of mitochondrial membrane permeability, cytochrome c release, Bad phosphorylation, and activation of caspase 3 and caspase 1 as demonstrated by complimentary gene knockdown studies of FoxO3a. Furthermore, subcellular trafficking and gene knockdown studies of NF-kappaB p65 illustrate that microglial cell survival determined by Wnt1 during oxidative stress requires NF-kappaB p65. Our work highlights Wnt1 and the control of novel downstream transcriptional pathways as critical components for the oversight of nervous system microglial cells.

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

Complications of diabetes mellitus (DM) weigh heavily upon the endothelium that ultimately affect multiple organ systems. These concerns call for innovative treatment strategies that employ molecular pathways responsible for cell survival and longevity. Here we show in a clinically relevant model of DM with elevated D-glucose that endothelial cell (EC) SIRT1 is vital for the prevention of early membrane apoptotic phosphatidylserine externalization and subsequent DNA degradation supported by studies with modulation of SIRT1 activity and gene knockdown of SIRT1. Furthermore, during elevated D-glucose exposure, we show that SIRT1 is sequestered in the cytoplasm of ECs, but specific activation of SIRT1 shuttles the protein to the nucleus to allow for cytoprotection. The ability of SIRT1 to avert apoptosis employs the activation of protein kinase B (Akt1), the post-translational phosphorylation of the forkhead member FoxO3a, the blocked trafficking of FoxO3a to the nucleus, and the inhibition of FoxO3a to initiate a "pro-apoptotic" program as shown by complimentary gene knockdown studies of FoxO3a. Vascular apoptotic oversight by SIRT1 extends to the direct modulation of mitochondrial membrane permeability, cytochrome c release, Bad activation, and caspase 1 and 3 activation, since inhibition of SIRT1 activity and gene knockdown of SIRT1 significantly accentuate cascade progression while SIRT1 activation abrogates these apoptotic elements. Our work identifies vascular SIRT1 and its control over early apoptotic membrane signaling, Akt1 activation, post-translational modification and trafficking of FoxO3a, mitochondrial permeability, Bad activation, and rapid caspase induction as new avenues for the treatment of vascular complications during DM.

Diabetes mellitus: channeling care through cellular discovery

Diabetes mellitus (DM) impacts a significant portion of the world's population and care for this disorder places an economic burden on the gross domestic product for any particular country. Furthermore, both Type 1 and Type 2 DM are becoming increasingly prevalent and there is increased incidence of impaired glucose tolerance in the young. The complications of DM are protean and can involve multiple systems throughout the body that are susceptible to the detrimental effects of oxidative stress and apoptotic cell injury. For these reasons, innovative strategies are necessary for the implementation of new treatments for DM that are generated through the further understanding of cellular pathways that govern the pathological consequences of DM. In particular, both the precursor for the coenzyme beta-nicotinamide adenine dinucleotide (NAD(+)), nicotinamide, and the growth factor erythropoietin offer novel platforms for drug discovery that involve cellular metabolic homeostasis and inflammatory cell control. Interestingly, these agents and their tightly associated pathways that consist of cell cycle regulation, protein kinase B, forkhead transcription factors, and Wnt signaling also function in a broader sense as biomarkers for disease onset and progression.

FOXO3a governs early and late apoptotic endothelial programs during elevated glucose through mitochondrial and caspase signaling

Mechanisms that preserve endothelial cell (EC) integrity remain elusive, but are critical for new strategies directed against endocrine disorders such as diabetes mellitus (DM). Here we demonstrate in primary cerebral ECs with a clinically relevant model of elevated d-glucose that Akt1 and the post-translational modification and subcellular trafficking of the forkhead transcription factor FoxO3a are critical for early apoptotic membrane signaling and subsequent degradation of nuclear DNA. FoxO3a also directly governs apoptotic mitochondrial signal transduction pathways, since gene knockdown of FoxO3a prevents mitochondrial membrane depolarization as well as the release of cytochrome c. Control of this apoptotic cascade extends to the rapid and progressive activation of caspases. The presence of FoxO3a is necessary for cleaved (active) caspase 1 and 3 expression, since loss of FoxO3a abrogates the induction of caspase activity. Our work identifies Akt1, FoxO3a and closely aligned pathways as key therapeutic targets during impaired glucose tolerance and DM.

FoxO3a governs early microglial proliferation and employs mitochondrial depolarization with caspase 3, 8, and 9 cleavage during oxidant induced apoptosis

Microglia of the central nervous system have a dual role in the ability to influence the survival of neighboring cells. During inflammatory cell activation, microglia can lead to the disposal of toxic cellular products and permit tissue regeneration, but microglia also may lead to cellular destruction with phagocytic removal. For these reasons, it is essential to elucidate not only the underlying pathways that control microglial activation and proliferation, but also the factors that determine microglial survival. In this regard, we investigated in the EOC 2 microglial cell line with an oxygen-glucose deprivation (OGD) injury model of oxidative stress the role of the "O" class forkhead transcription factor FoxO3a that in some scenarios is closely linked to immune system function. We demonstrate that FoxO3a is a necessary element in the control of early and late apoptotic injury programs that involve membrane phosphatidylserine externalization and nuclear DNA degradation, since transient knockdown of FoxO3a in microglia preserves cellular survival 24 hours following OGD exposure. However, prior to the onset of apoptotic injury, FoxO3a facilitates the activation and proliferation of microglia as early as 3 hours following OGD exposure that occurs in conjunction with the trafficking of the unphosphorylated and active post-translational form of FoxO3a from the cytoplasm to the cell nucleus. FoxO3a also can modulate apoptotic mitochondrial signal transduction pathways in microglia, since transient knockdown of FoxO3a prevents mitochondrial membrane depolarization as well as the release of cytochrome c during OGD. Control of this apoptotic cascade also extends to progressive caspase activation as early as 1 hour following OGD exposure. The presence of FoxO3a is necessary for the expression of cleaved (active) caspase 3, 8, and 9, since loss of FoxO3a abrogates the induction of caspase activity. Interestingly, elimination of FoxO3a reduced caspase 9 activity to a lesser extent than that noted with caspase 3 and 8 activities, suggesting that FoxO3a in relation to caspase 9 may be more reliant upon other signal transduction pathways potentially independent from caspase 3 and 8.

Oxidative stress: Biomarkers and novel therapeutic pathways

Oxidative stress significantly impacts multiple cellular pathways that can lead to the initiation and progression of varied disorders throughout the body. It therefore becomes imperative to elucidate the components and function of novel therapeutic strategies against oxidative stress to further clinical diagnosis and care. In particular, both the growth factor and cytokine erythropoietin (EPO) and members of the mammalian forkhead transcription factors of the O class (FoxOs) may offer the greatest promise for new treatment regimens since these agents and the cellular pathways they oversee cover a range of critical functions that directly influence progenitor cell development, cell survival and degeneration, metabolism, immune function, and cancer cell invasion. Furthermore, both EPO and FoxOs function not only as therapeutic targets, but also as biomarkers of disease onset and progression, since their cellular pathways are closely linked and overlap with several unique signal transduction pathways. However, biological outcome with EPO and FoxOs may sometimes be both unexpected and undesirable that can raise caution for these agents and warrant further investigations. Here we present the exciting as well as complicated role EPO and FoxOs possess to uncover the benefits as well as the risks of these agents for cell biology and clinical care in processes that range from stem cell development to uncontrolled cellular proliferation.

Wnt1 neuroprotection translates into improved neurological function during oxidant stress and cerebral ischemia through AKT1 and mitochondrial apoptotic pathways

Although essential for the development of the nervous system, Wnt1 also has been associated with neurodegenerative disease and cognitive loss during periods of oxidative stress. Here we show that endogenous expression of Wnt1 is suppressed during oxidative stress in both in vitro and in vivo experimental models. Loss of endogenous Wnt1 signaling directly correlates with neuronal demise and increased functional deficit, illustrating that endogenous neuronal Wnt1 offers a vital level of intrinsic cellular protection against oxidative stress. Furthermore, transient overexpression of Wnt1 or application of exogenous Wnt1 recombinant protein is necessary to preserve neurological function and rescue neurons from apoptotic membrane phosphatidylserine externalization and genomic DNA degradation, since blockade of Wnt1 signaling with a Wnt1 antibody or dickkopf related protein 1 abrogates neuronal protection by Wnt1. Wnt1 ultimately relies upon the activation of Akt1, the modulation of mitochondrial membrane permeability, and the release of cytochrome c to control the apoptotic cascade, since inhibition of Wnt1 signaling, the phosphatidylinositol 3-kinase pathway, or Akt1 activity abrogates the ability of Wnt1 to block these apoptotic components. Our work identifies Wnt1 and its downstream signaling as cellular targets with high clinical potential for novel treatment strategies for multiple disorders precipitated by oxidative stress.

New strategies for Alzheimer's disease and cognitive impairment

Approximately five million people suffer with Alzheimer's disease (AD) and more than twenty-four million people are diagnosed with AD, pre-senile dementia, and other disorders of cognitive loss worldwide. Furthermore, the annual cost per patient with AD can approach $200,000 with an annual population aggregate cost of $100 billion. Yet, complete therapeutic prevention or reversal of neurovascular injury during AD and cognitive loss is not achievable despite the current understanding of the cellular pathways that modulate nervous system injury during these disorders. As a result, identification of novel therapeutic targets for the treatment of neurovascular injury would be extremely beneficial to reduce or eliminate disability from diseases that lead to cognitive loss or impairment. Here we describe the capacity of intrinsic cellular mechanisms for the novel pathways of erythropoietin and forkhead transcription factors that may offer not only new strategies for disorders such as AD and cognitive loss, but also function as biomarkers for disease onset and progression.

Erythropoietin, forkhead proteins, and oxidative injury: biomarkers and biology

Oxidative stress significantly impacts multiple cellular pathways that can lead to the initiation and progression of varied disorders throughout the body. It therefore becomes imperative to elucidate the components and function of novel therapeutic strategies against oxidative stress to further clinical diagnosis and care. In particular, both the growth factor and cytokine erythropoietin (EPO), and members of the mammalian forkhead transcription factors of the O class (FoxOs), may offer the greatest promise for new treatment regimens, since these agents and the cellular pathways they oversee cover a range of critical functions that directly influence progenitor cell development, cell survival and degeneration, metabolism, immune function, and cancer cell invasion. Furthermore, both EPO and FoxOs function not only as therapeutic targets, but also as biomarkers of disease onset and progression, since their cellular pathways are closely linked and overlap with several unique signal transduction pathways. Yet, EPO and FoxOs may sometimes have unexpected and undesirable effects that can raise caution for these agents and warrant further investigations. Here we present the exciting as well as the complex role that EPO and FoxOs possess to uncover the benefits as well as the risks of these agents for cell biology and clinical care in processes that range from stem cell development to uncontrolled cellular proliferation.

The vitamin nicotinamide: translating nutrition into clinical care

Nicotinamide, the amide form of vitamin B(3) (niacin), is changed to its mononucleotide compound with the enzyme nicotinic acide/nicotinamide adenylyltransferase, and participates in the cellular energy metabolism that directly impacts normal physiology. However, nicotinamide also influences oxidative stress and modulates multiple pathways tied to both cellular survival and death. During disorders that include immune system dysfunction, diabetes, and aging-related diseases, nicotinamide is a robust cytoprotectant that blocks cellular inflammatory cell activation, early apoptotic phosphatidylserine exposure, and late nuclear DNA degradation. Nicotinamide relies upon unique cellular pathways that involve forkhead transcription factors, sirtuins, protein kinase B (Akt), Bad, caspases, and poly (ADP-ribose) polymerase that may offer a fine line with determining cellular longevity, cell survival, and unwanted cancer progression. If one is cognizant of the these considerations, it becomes evident that nicotinamide holds great potential for multiple disease entities, but the development of new therapeutic strategies rests heavily upon the elucidation of the novel cellular pathways that nicotinamide closely governs.

A "FOXO" in sight: targeting Foxo proteins from conception to cancer

The successful treatment for multiple disease entities can rest heavily upon the ability to elucidate the intricate relationships that govern cellular proliferation, metabolism, survival, and inflammation. Here we discuss the therapeutic potential of the mammalian forkhead transcription factors predominantly in the O class, FoxO1, FoxO3, FoxO4, and FoxO6, which play a significant role during normal cellular function as well as during progressive disease. These transcription factors are integrated with several signal transduction pathways, such as Wnt proteins, that can regulate a broad array of cellular process that include stem cell proliferation, aging, and malignancy. FoxO transcription factors are attractive considerations for strategies directed against human cancer in light of their pro-apoptotic effects and ability to lead to cell cycle arrest. Yet, FoxO proteins can be associated with infertility, cellular degeneration, and unchecked cellular proliferation. As our knowledge continues to develop for this novel family of proteins, potential clinical applications for the FoxO family should heighten our ability to limit disease progression without clinical compromise.

The forkhead transcription factor FOXO3a controls microglial inflammatory activation and eventual apoptotic injury through caspase 3

Memory loss and cognitive failure are increasingly being identified as potential risks with the recognized increase in life expectancy of the general population. As a result, the development of novel therapeutic strategies for disorders such as Alzheimer's disease have garnered increased attention. The etiologies that can lead to Alzheimer's disease are extremely varied, but a number of therapeutic options are directed against amyloid-beta peptide and inflammatory cell regulation to prevent or halt progressive cognitive loss. In particular, inflammatory microglial cells may have disparate functions that in some scenarios lead to disability through the removal of functional neurovascular cells and in other circumstances foster tissue repair. Given the significance microglial cells hold for neurodegenerative disorders, we therefore examined the function that amyloid (Abeta(1-42)) has upon the microglial cell line EOC 2 and identified a novel role for the forkhead transcription factor FoxO3a and caspase 3. Here we show that Abeta(1-42) leads to progressive injury and apoptotic cell loss in microglial cells that involves both early phosphatidylserine (PS) externalization and late genomic DNA fragmentation over a 24 hour course. Prior to these injury programs, Abeta(1-42) results in the activation and proliferation of microglia as demonstrated by increased proliferating cell nuclear antigen (PCNA) expression and bromodeoxyuridine (BrdU) uptake. Both apoptotic injury as well as the prior activation and proliferation of microglial cells relies upon the presence of FoxO3a, since specific gene silencing of FoxO3a promotes microglial cell protection and prevents the early activation and proliferation of these cells. Furthermore, Abeta(1-42) exposure maintained FoxO3a in an unphosphorylated "active" state and facilitated the cellular trafficking of FoxO3a from the cytoplasm to the cell nucleus to potentially lead to "pro-apoptotic" programs by this transcription factor. One apoptotic program in particular appears to involve the activation of caspase 3, since loss of FoxO3a through gene silencing prevents the induction of caspase 3 activity by Abeta(1-42).

Optimal neuroprotection by erythropoietin requires elevated expression of its receptor in neurons

Erythropoietin receptor (EpoR) binding mediates neuroprotection by endogenous Epo or by exogenous recombinant human (rh)Epo. The level of EpoR gene expression may determine tissue responsiveness to Epo. Thus, harnessing the neuroprotective power of Epo requires an understanding of the Epo-EpoR system and its regulation. We tested the hypothesis that neuronal expression of EpoR is required to achieve optimal neuroprotection by Epo. The ventral limbic region (VLR) in the rat brain was used because we determined that its neurons express minimal EpoR under basal conditions, and they are highly sensitive to excitotoxic damage, such as occurs with pilocarpine-induced status epilepticus (Pilo-SE). We report that (i) EpoR expression is significantly elevated in nearly all VLR neurons when rats are subjected to 3 moderate hypoxic exposures, with each separated by a 4-day interval; (ii) synergistic induction of EpoR expression is achieved in the dorsal hippocampus and neocortex by the combination of hypoxia and exposure to an enriched environment, with minimal increased expression by either treatment alone; and (iii) rhEpo administered after Pilo-SE cannot rescue neurons in the VLR, unless neuronal induction of EpoR is elicited by hypoxia before Pilo-SE. This study thus demonstrates using environmental manipulations in normal rodents, the strict requirement for induction of EpoR expression in brain neurons to achieve optimal neuroprotection. Our results indicate that regulation of EpoR gene expression may facilitate the neuroprotective potential of rhEpo.

Erythropoietin receptor expression is concordant with erythropoietin but not with common beta chain expression in the rat brain throughout the life span

Brain effects of erythropoietin (Epo) are proposed to involve a heteromeric receptor comprising the classical Epo receptor (Epo-R) and the common beta chain (betac). However, data documenting the pattern of betac gene expression in the healthy brain, in comparison with that of the Epo-R gene, are still lacking. The present study is the first to investigate at the same time betac, Epo-R, and Epo gene expression within different rat brain areas throughout the life span, from neonatal to elderly stages, using quantitative RT-PCR for transcripts. Corresponding proteins were localized by using immunohistochemistry. We demonstrate that the betac transcript level does not correlate with that of Epo-R or Epo, whereas the Epo-R transcript level strongly correlates with that of Epo throughout the life span in all brain structures analyzed. Both Epo and Epo-R were detected primarily in neurons. In the hippocampus, the greatest Epo-R mRNA levels were measured during the early postnatal period and in middle-aged rats, associated with an intense neuronal immunolabeling. Conversely, betac protein was barely detectable in the brain at all ages, even in neurons expressing high levels of Epo-R. Finally, betac transcript could not be detected in PC12 cells, even after nerve growth factor-induced neuritogenesis, which is a condition that dramatically enhances Epo-R transcript level. Altogether, our data suggest that most neurons are likely to express high levels of Epo-R but low, if not null, levels of betac. Given that Epo protects extended populations of neurons after injury, a yet-to-be-identified receptor heterocomplex including Epo-R may exist in the large population of brain neurons that does not express betac.

Protective effects of erythropoietin on ischemia/reperfusion injury of rat ovary

OBJECTIVES

To evaluate the effects of erythropoietin (EPO) as an antioxidant and tissue protective agent and study the biochemical and histopathological changes in experimental ischemia and ischemia/reperfusion (I/R) injury in rat ovaries.

STUDY DESIGN

36 Adult female rats were used. The experimental groups were designed as Group 1: sham operation; Group 2: bilateral ovarian ischemia; and Group 3: 3 h period of ischemia followed by 3 h reperfusion. Group 4 rats were administered a 5000 IU dose of EPO, before 0.5 h of ischemia, and then bilateral ovarian ischemia was applied. After a 3 h period of ischemia, the bilateral ovaries were removed. In Group 5, a 3 h period of bilateral ovarian ischemia was applied. 2.5 h after the induction of ischemia, the rats were administered the same dose of EPO. At the end of a 3 h period of ischemia, 3h reperfusion was continued after the ovaries were removed. Group 6 underwent a sham operation after administration of 5000 IU/kg of EPO. After the experiments, superoxide dismutase (SOD), inducible nitric oxide synthase (iNOS), and myeloperoxidase (MPO) activity were determined, and histopathological changes were examined in all rat ovarian tissue.

RESULTS

Ischemia and ischemia/reperfusion increased the iNOS and MPO activity while decreasing the SOD activity significantly in comparison to the sham group. The 5000 IU/kg of EPO before ischemia and I/R reversed the trend in iNOS and MPO activities. The levels of SOD were decreased by the ischemia and I/R. The administration of EPO before ischemia and I/R treatments also reversed the trend in the SOD levels. In the ischemia/reperfusion plus EPO groups, though we observed minimal vascular dilation in the ovary stroma and some degenerative cell clusters, most of cellular structures did not show any pathological changes.

CONCLUSIONS

Administration of EPO is effective in reversing tissue damage induced by ischemia and/or ischemia/reperfusion in ovaries.

Enhanced tolerance against early and late apoptotic oxidative stress in mammalian neurons through nicotinamidase and sirtuin mediated pathways

Focus upon therapeutic strategies that intersect between pathways that govern cellular metabolism and cellular survival may offer the greatest impact for the treatment of a number of neurodegenerative and metabolic disorders, such as diabetes mellitus. In this regard, we investigated the role of a Drosophila nicotinamidase (DN) in mammalian SH-SY5Y neuronal cells during oxidative stress. We demonstrate that during free radical exposure to nitric oxide generators DN neuronal expression significantly increased cell survival and blocked cellular membrane injury. Furthermore, DN neuronal expression prevented both apoptotic late DNA degradation and early phosphatidylserine exposure that may serve to modulate inflammatory cell activation in vivo. Nicotinamidase activity that limited nicotinamide cellular concentrations appeared to be necessary for DN neuroprotection, since application of progressive nicotinamide concentrations could abrogate the benefits of DN expression during oxidative stress. Pathways that involved sirtuin activation and SIRT1 were suggested to be vital, at least in part, for DN to confer protection through a series of studies. First, application of resveratrol increased cell survival during oxidative stress either alone or in conjunction with the expression of DN to a similar degree, suggesting that DN may rely upon SIRT1 activation to foster neuronal protection. Second, the overexpression of either SIRT1 or DN in neurons prevented apoptotic injury specifically in neurons expressing these proteins during oxidative stress, advancing the premise that DN and SIRT1 may employ similar pathways for neuronal protection. Third, inhibition of sirtuin activity with sirtinol was detrimental to neuronal survival during oxidative stress and prevented neuronal protection during overexpression of DN or SIRT1, further supporting that SIRT1 activity may be necessary for DN neuroprotection during oxidative stress. Implementation of further work to elucidate the cellular mechanisms that govern nicotinamidase activity in mammalian cells may offer novel avenues for the treatment of disorders tied to oxidative stress and cellular metabolic dysfunction.

FoxO proteins: cunning concepts and considerations for the cardiovascular system

Dysfunction in the cardiovascular system can lead to the progression of a number of disease entities that can involve cancer, diabetes, cardiac ischaemia, neurodegeneration and immune system dysfunction. In order for new therapeutic avenues to overcome some of the limitations of present clinical treatments for these disorders, future investigations must focus upon novel cellular processes that control cellular development, proliferation, metabolism and inflammation. In this respect, members of the mammalian forkhead transcription factors of the O class (FoxOs) have increasingly become recognized as important and exciting targets for disorders of the cardiovascular system. In the present review, we describe the role of these transcription factors in the cardiovascular system during processes that involve angiogenesis, cardiovascular development, hypertension, cellular metabolism, oxidative stress, stem cell proliferation, immune system regulation and cancer. Current knowledge of FoxO protein function combined with future studies should continue to lay the foundation for the successful translation of these transcription factors into novel and robust clinical therapies.

The "O" class: crafting clinical care with FoxO transcription factors

Forkhead Transcription Factors: Vital Elements in Biology and Medicine provides a unique platform for the presentation of novel work and new insights into the vital role that forkhead transcription factors play in both cellular physiology as well as clinical medicine. Internationally recognized investigators provide their insights and perspectives for a number of forkhead genes and proteins that may have the greatest impact for the development of new strategies for a broad array of disorders that can involve aging, cancer, cardiac function, neurovascular integrity, fertility, stem cell differentiation, cellular metabolism, and immune system regulation. Yet, the work clearly sets a precedent for the necessity to understand the cellular and molecular function of forkhead proteins since this family of transcription factors can limit as well as foster disease progression depending upon the cellular environment. With this in mind, our concluding chapter for Forkhead Transcription Factors: Vital Elements in Biology andMedicine offers to highlight both the diversity and complexity of the forkhead transcription family by focusing upon the mammalian forkhead transcription factors of the O class (FoxOs) that include FoxO1, FoxO3, FoxO4, and FoxO6. FoxO proteins are increasingly considered to represent unique cellular targets that can control numerous processes such as angiogenesis, cardiovascular development, vascular tone, oxidative stress, stem cell proliferation, fertility, and immune surveillance. Furthermore, FoxO transcription factors are exciting considerations for disorders such as cancer in light of their pro-apoptotic and inhibitory cell cycle effects as well as diabetes mellitus given the close association FoxOs hold with cellular metabolism. In addition, these transcription factors are closely integrated with several novel signal transduction pathways, such as erythropoietin and Wnt proteins, that may influence the ability of FoxOs to lead to cell survival or cell injury. Further understanding of both the function and intricate nature of the forkhead transcription factor family, and in particular the FoxO proteins, should allow selective regulation of cellular development or cellular demise for the generation of successful future clinical strategies and patient well-being.

Clever cancer strategies with FoxO transcription factors

Given that cancer and related disorders affect a wide spectrum of the world's population, and in most cases are progressive in nature, it is essential that future care must overcome the present limitations of existing therapies in the absence of toxic side effects. Mammalian forkhead transcription factors of the O class (FoxOs) may fill this niche since these proteins are increasingly considered to represent unique cellular targets directed against human cancer in light of their pro-apoptotic effects and ability to lead to cell cycle arrest. Yet, FoxOs also can significantly affect normal cell survival and longevity, requiring new treatments for neoplastic growth to modulate novel pathways that integrate cell proliferation, metabolism, inflammation and survival. In this respect, members of the FoxO family are extremely compelling to consider since these transcription factors have emerged as versatile proteins that can control angiogenesis, stem cell proliferation, cell adhesion and autoimmune disease. Further elucidation of FoxO protein function during neoplastic growth should continue to lay the foundation for the successful translation of these transcription factors into novel and robust clinical therapies for cancer.

Erythropoietin and oxidative stress

Unmitigated oxidative stress can lead to diminished cellular longevity, accelerated aging, and accumulated toxic effects for an organism. Current investigations further suggest the significant disadvantages that can occur with cellular oxidative stress that can lead to clinical disability in a number of disorders, such as myocardial infarction, dementia, stroke, and diabetes. New therapeutic strategies are therefore sought that can be directed toward ameliorating the toxic effects of oxidative stress. Here we discuss the exciting potential of the growth factor and cytokine erythropoietin for the treatment of diseases such as cardiac ischemia, vascular injury, neurodegeneration, and diabetes through the modulation of cellular oxidative stress. Erythropoietin controls a variety of signal transduction pathways during oxidative stress that can involve Janus-tyrosine kinase 2, protein kinase B, signal transducer and activator of transcription pathways, Wnt proteins, mammalian forkhead transcription factors, caspases, and nuclear factor kappaB. Yet, the biological effects of erythropoietin may not always be beneficial and may be poor tolerated in a number of clinical scenarios, necessitating further basic and clinical investigations that emphasize the elucidation of the signal transduction pathways controlled by erythropoietin to direct both successful and safe clinical care.