Erythropoietin activates mitochondrial biogenesis and couples red cell mass to mitochondrial mass in the heart

Inhibition the ubiquitination of ENaC and Na,K-ATPase with erythropoietin promotes alveolar fluid clearance in sepsis-induced acute respiratory distress syndrome

Sepsis-induced acute respiratory distress syndrome (ARDS) causes significant fatalities worldwide and lacks pharmacological intervention. Alveolar fluid clearance (AFC) plays a pivotal role in the remission of ARDS and is markedly impaired in the pathogenesis of ARDS. Here, we demonstrated that erythropoietin could effectively ameliorate lung injury manifestations and lethality, restore lung function and promote AFC in a rat model of lipopolysaccharide (LPS)-induced ARDS. Moreover, it was proven that EPO-induced restoration of AFC occurs through triggering the total protein expression of ENaC and Na,K-ATPase channels, enhancing their protein abundance in the membrane, and suppressing their ubiquitination for degeneration. Mechanistically, the data indicated the possible involvement of EPOR/JAK2/STAT3/SGK1/Nedd4-2 signaling in this process, and the pharmacological inhibition of the pathway markedly eliminated the stimulating effects of EPO on ENaC and Na,K-ATPase, and subsequently reversed the augmentation of AFC by EPO. Consistently, in vitro studies of alveolar epithelial cells paralleled with that EPO upregulated the expression of ENaC and Na,K-ATPase, and patch-clamp studies further demonstrated that EPO substantially strengthened sodium ion currents. Collectively, EPO could effectively promote AFC by improving ENaC and Na,K-ATPase protein expression and abundance in the membrane, dependent on inhibition of ENaC and Na,K-ATPase ubiquitination, and resulting in diminishing LPS-associated lung injuries.

Modulation of cAMP/cGMP signaling as prevention of congenital heart defects in Pde2A deficient embryos: a matter of oxidative stress

Phosphodiesterase 2A (Pde2A) is a dual-specific PDE that breaks down both cAMP and cGMP cyclic nucleotides. We recently highlighted a direct relationship between Pde2A impairment, a consequent increase of cAMP, and the appearance of mouse congenital heart defects (CHDs). Here we aimed to characterize the pathways involved in the development of CHDs and in their prevention by pharmacological approaches targeting cAMP and cGMP signaling. Transcriptome analysis revealed a modulation of more than 500 genes affecting biological processes involved in the immune system, cardiomyocyte development and contractility, angiogenesis, transcription, and oxidative stress in hearts from Pde2A-/- embryos. Metoprolol and H89 pharmacological administration prevented heart dilatation and hypertabeculation in Pde2A-/- embryos. Metoprolol was also able to partially impede heart septum defect and oxidative stress at tissue and molecular levels. Amelioration of cardiac defects was also observed by using the antioxidant NAC, indicating oxidative stress as one of the molecular mechanisms underpinning the CHDs. In addition, Sildenafil treatment recovered cardiac defects suggesting the requirement of cAMP/cGMP nucleotides balance for the correct heart development.

Myoglobin in Brown Adipose Tissue: A Multifaceted Player in Thermogenesis

Brown adipose tissue (BAT) plays an important role in energy homeostasis by generating heat from chemical energy via uncoupled oxidative phosphorylation. Besides its high mitochondrial content and its exclusive expression of the uncoupling protein 1, another key feature of BAT is the high expression of myoglobin (MB), a heme-containing protein that typically binds oxygen, thereby facilitating the diffusion of the gas from cell membranes to mitochondria of muscle cells. In addition, MB also modulates nitric oxide (NO•) pools and can bind C16 and C18 fatty acids, which indicates a role in lipid metabolism. Recent studies in humans and mice implicated MB present in BAT in the regulation of lipid droplet morphology and fatty acid shuttling and composition, as well as mitochondrial oxidative metabolism. These functions suggest that MB plays an essential role in BAT energy metabolism and thermogenesis. In this review, we will discuss in detail the possible physiological roles played by MB in BAT thermogenesis along with the potential underlying molecular mechanisms and focus on the question of how BAT-MB expression is regulated and, in turn, how this globin regulates mitochondrial, lipid, and NO• metabolism. Finally, we present potential MB-mediated approaches to augment energy metabolism, which ultimately could help tackle different metabolic disorders.

Cardiovascular safety of current and emerging drugs to treat anaemia in chronic kidney disease: a safety review

INTRODUCTION

Erythropoiesis-stimulating agents (ESAs) are the standard of treatment for anemia in chronic kidney disease. Hypoxia-inducible factor prolyl hydroxylase inhibitors (HIF-PHI) are small molecules that stimulate endogenous erythropoietin synthesis.

AREAS COVERED

The cardiovascular safety of ESAs and HIF-PHIs. We performed a PubMed search using several key words, including anemia, chronic kidney disease, safety, erythropoiesis stimulating agents, HIF-PH inhibitors.

EXPERT OPINION

ESAs are well-tolerated drugs with a long history of use; there are safety concerns, especially when targeting high hemoglobin levels. HIF-PHIs have comparable efficacy to ESAs in correcting anemia. Contrary to expectations, randomized phase 3 clinical trials have shown that overall HIF-PHIs were non-inferior to ESA or placebo with respect to the risk of cardiovascular endpoints. In addition, some phase 3 trials raised potential safety concerns regarding cardiovascular and thrombotic events, particularly in non-dialysis patients.Today, HIF-PHIs represent an additional treatment option for anemia in patients with chronic kidney disease. This has made the management of anemia in CKD more complex and heterogeneous. A better understanding of the mechanisms causing hypo-responsiveness to ESAs, combined with an individualized approach that balances ESAs, HIF-PHIs and iron doses, could increase the benefits while reducing the risks.

The Brain at High Altitude: From Molecular Signaling to Cognitive Performance

The brain requires over one-fifth of the total body oxygen demand for normal functioning. At high altitude (HA), the lower atmospheric oxygen pressure inevitably challenges the brain, affecting voluntary spatial attention, cognitive processing, and attention speed after short-term, long-term, or lifespan exposure. Molecular responses to HA are controlled mainly by hypoxia-inducible factors. This review aims to summarize the cellular, metabolic, and functional alterations in the brain at HA with a focus on the role of hypoxia-inducible factors in controlling the hypoxic ventilatory response, neuronal survival, metabolism, neurogenesis, synaptogenesis, and plasticity.

Erythropoietin receptor regulates tumor mitochondrial biogenesis through iNOS and pAKT

Erythropoietin receptor (EPOR) is widely expressed in healthy and malignant tissues. In certain malignancies, EPOR stimulates tumor growth. In healthy tissues, EPOR controls processes other than erythropoiesis, including mitochondrial metabolism. We hypothesized that EPOR also controls the mitochondrial metabolism in cancer cells. To test this hypothesis, we generated EPOR-knockdown cancer cells to grow tumor xenografts in mice and analyzed tumor cellular respiration via high-resolution respirometry. Furthermore, we analyzed cellular respiratory control, mitochondrial content, and regulators of mitochondrial biogenesis in vivo and in vitro in different cancer cell lines. Our results show that EPOR controls tumor growth and mitochondrial biogenesis in tumors by controlling the levels of both, pAKT and inducible NO synthase (iNOS). Furthermore, we observed that the expression of EPOR is associated with the expression of the mitochondrial marker VDAC1 in tissue arrays of lung cancer patients, suggesting that EPOR indeed helps to regulate mitochondrial biogenesis in tumors of cancer patients. Thus, our data imply that EPOR not only stimulates tumor growth but also regulates tumor metabolism and is a target for direct intervention against progression.

The multi-faced role of FUNDC1 in mitochondrial events and human diseases

Mitophagy plays a vital role in the selective elimination of dysfunctional and unwanted mitochondria. As a receptor of mitophagy, FUN14 domain containing 1 (FUNDC1) is attracting considerably critical attention. FUNDC1 is involved in the mitochondria fission, the clearance of unfolded protein, iron metabolism in mitochondria, and the crosstalk between mitochondria and endoplasmic reticulum besides mitophagy. Studies have demonstrated that FUNDC1 is associated with the progression of ischemic disease, cancer, and metabolic disease. In this review, we systematically examine the recent advancements in FUNDC1 and the implications of this protein in health and disease.

Drug Repositioning in Friedreich Ataxia

Friedreich ataxia is a rare neurodegenerative disorder caused by insufficient levels of the essential mitochondrial protein frataxin. It is a severely debilitating disease that significantly impacts the quality of life of affected patients and reduces their life expectancy, however, an adequate cure is not yet available for patients. Frataxin function, although not thoroughly elucidated, is associated with assembly of iron-sulfur cluster and iron metabolism, therefore insufficient frataxin levels lead to reduced activity of many mitochondrial enzymes involved in the electron transport chain, impaired mitochondrial metabolism, reduced ATP production and inefficient anti-oxidant response. As a consequence, neurons progressively die and patients progressively lose their ability to coordinate movement and perform daily activities. Therapeutic strategies aim at restoring sufficient frataxin levels or at correcting some of the downstream consequences of frataxin deficiency. However, the classical pathways of drug discovery are challenging, require a significant amount of resources and time to reach the final approval, and present a high failure rate. Drug repositioning represents a viable alternative to boost the identification of a therapy, particularly for rare diseases where resources are often limited. In this review we will describe recent efforts aimed at the identification of a therapy for Friedreich ataxia through drug repositioning, and discuss the limitation of such strategies.

Myoglobin, expressed in brown adipose tissue of mice, regulates the content and activity of mitochondria and lipid droplets

The identification of novel physiological regulators that stimulate energy expenditure through brown adipose tissue (BAT) activity in substrate catalysis is of utmost importance to understand and treat metabolic diseases. Myoglobin (MB), known to store or transport oxygen in heart and skeletal muscles, has recently been found to bind fatty acids with physiological constants in its oxygenated form (i.e., MBO2). Here, we investigated the in vivo effect of MB expression on BAT activity. In particular, we studied mitochondrial function and lipid metabolism as essential determinants of energy expenditure in this tissue. We show in a MB-null (MBko) mouse model that MB expression in BAT impacts on the activity of brown adipocytes in a twofold manner: i) by elevating mitochondrial density plus maximal respiration capacity, and through that, by stimulating BAT oxidative metabolism along with the organelles` uncoupled respiration; and ii) by influencing the free fatty acids pool towards a palmitate-enriched composition and shifting the lipid droplet (LD) equilibrium towards higher counts of smaller droplets. These metabolic changes were accompanied by the up-regulated expression of thermogenesis markers UCP1, CIDEA, CIDEC, PGC1-α and PPAR-α in the BAT of MB wildtype (MBwt) mice. Along with the emergence of the "browning" BAT morphology, MBwt mice exhibited a leaner phenotype when compared to MBko littermates at 20 weeks of age. Our data shed novel insights into MB's role in linking oxygen and lipid-based thermogenic metabolism. The findings suggest potential new strategies of targeting the MB pathway to treat metabolic disorders related to diminishing energy expenditure.

Acute erythropoietin injection increases muscle mitochondrial respiratory capacity in young men: a double-blinded randomized crossover trial

The aim was to investigate if acute recombinant human erythropoietin (rHuEPO) injection had an effect on mitochondrial function and if exercise would have an additive effect. Furthermore, to investigate if in vitro incubation with rHuEPO had an effect on muscle mitochondrial respiratory capacity. Eight healthy young men were recruited for this double-blinded randomized placebo-controlled crossover study. rHuEPO (400 IU/kg body wt) or saline injection was given intravenously, before an acute bout of exercise. Resting metabolic rate and fat oxidation were measured. Biopsies were obtained at baseline, 120 min after injection, and right after the acute exercise bout. Mitochondrial function (mitochondrial respiration and H₂O₂ emission) was measured in permeabilized skeletal muscle using high-resolution respirometry and fluorometry. Specific gene expression and enzyme activity were measured. Skeletal muscle mitochondrial respiratory capacity was measured with and without incubation with rHuEPO. Fat oxidation at rest increased after rHuEPO injection, but no difference was found in fat oxidation during exercise. Mitochondrial respiratory capacity was increased after rHuEPO injection when pyruvate was in the assay, which was not the case when saline was injected. No changes were seen in H₂O₂ emission after rHuEPO injection or acute exercise. Incubation of skeletal muscle fibers in vitro with rHuEPO increased mitochondrial respiratory capacity. Acute rHuEPO injection increased mitochondrial respiratory capacity when pyruvate was used in the assay. No statistical difference was found in H₂O₂ emission capacity, although a numerical increase was seen after rHuEPO injection. In vitro incubation of the skeletal muscle sample with rHuEPO increases mitochondrial respiratory capacity.NEW & NOTEWORTHY The effect of an acute rHuEPO injection on skeletal muscle mitochondrial function was investigated in young healthy male subjects. rHuEPO has an acute effect on skeletal muscle mitochondrial respiratory capacity in humans, where an increased mitochondrial respiratory capacity was seen. This could be the first step leading to increased mitochondrial biogenesis.

Erythropoietin promotes hippocampal mitochondrial function and enhances cognition in mice

Erythropoietin (EPO) improves neuronal mitochondrial function and cognition in adults after brain injury and in those afflicted by psychiatric disorders. However, the influence of EPO on mitochondria and cognition during development remains unexplored. We previously observed that EPO stimulates hippocampal-specific neuronal maturation and synaptogenesis early in postnatal development in mice. Here we show that EPO promotes mitochondrial respiration in developing postnatal hippocampus by increasing mitochondrial content and enhancing cellular respiratory potential. Ultrastructurally, mitochondria profiles and total vesicle content were greater in presynaptic axon terminals, suggesting that EPO enhances oxidative metabolism and synaptic transmission capabilities. Behavioural tests of hippocampus-dependent memory at early adulthood, showed that EPO improves spatial and short-term memory. Collectively, we identify a role for EPO in the murine postnatal hippocampus by promoting mitochondrial function throughout early postnatal development, which corresponds to enhanced cognition by early adulthood.

Robert Jacobs, Mostafa Aboouf, et al. examined the effect of erythropoietin (EPO) in hippocampal mitochondrial function and memory in two mouse models: one overexpressing EPO in the brain, and juvenile mice treated during three days with a high dose of intraperitoneal EPO. Their results suggest that erythropoietin in the neonatal brain may impact spatial memory by increasing mitochondrial content.

The erythropoietin receptor expressed in skeletal muscle is essential for mitochondrial biogenesis and physiological exercise

Erythropoietin (EPO) is a haematopoietic hormone that regulates erythropoiesis, but the EPO-receptor (EpoR) is also expressed in non-haematopoietic tissues. Stimulation of the EpoR in cardiac and skeletal muscle provides protection from various forms of pathological stress, but its relevance for normal muscle physiology remains unclear. We aimed to determine the contribution of the tissue-specific EpoR to exercise-induced remodelling of cardiac and skeletal muscle. Baseline phenotyping was performed on left ventricle and m. gastrocnemius of mice that only express the EpoR in haematopoietic tissues (EpoR-tKO). Subsequently, mice were caged in the presence or absence of a running wheel for 4 weeks and exercise performance, cardiac function and histological and molecular markers for physiological adaptation were assessed. While gross morphology of both muscles was normal in EpoR-tKO mice, mitochondrial content in skeletal muscle was decreased by 50%, associated with similar reductions in mitochondrial biogenesis, while mitophagy was unaltered. When subjected to exercise, EpoR-tKO mice ran slower and covered less distance than wild-type (WT) mice (5.5 ± 0.6 vs. 8.0 ± 0.4 km/day, p < 0.01). The impaired exercise performance was paralleled by reductions in myocyte growth and angiogenesis in both muscle types. Our findings indicate that the endogenous EPO-EpoR system controls mitochondrial biogenesis in skeletal muscle. The reductions in mitochondrial content were associated with reduced exercise capacity in response to voluntary exercise, supporting a critical role for the extra-haematopoietic EpoR in exercise performance.

The Effect of Increasing Donor Age on Myocardial Ischemic Tolerance in a Rodent Model of Donation After Circulatory Death

Hearts from older donors or procured via donation after circulatory death (DCD) can alleviate transplant waitlist; however, these hearts are particularly vulnerable to injury caused by warm ischemic times (WITs) inherent to DCD. This study investigates how the combination of increasing donor age and pharmacologic supplementation affects the ischemic tolerance and functional recovery of DCD hearts and how age impacts cardiac mitochondrial respiratory capacity and oxidative phosphorylation.

Erythropoietin Regulates Transcription and YY1 Dynamics in a Pre-established Chromatin Architecture

The three-dimensional architecture of the genome plays an essential role in establishing and maintaining cell identity. However, the magnitude and temporal kinetics of changes in chromatin structure that arise during cell differentiation remain poorly understood. Here, we leverage a murine model of erythropoiesis to study the relationship between chromatin conformation, the epigenome, and transcription in erythroid cells. We discover that acute transcriptional responses induced by erythropoietin (EPO), the hormone necessary for erythroid differentiation, occur within an invariant chromatin topology. Within this pre-established landscape, Yin Yang 1 (YY1) occupancy dynamically redistributes to sites in proximity of EPO-regulated genes. Using HiChIP, we identify chromatin contacts mediated by H3K27ac and YY1 that are enriched for enhancer-promoter interactions of EPO-responsive genes. Taken together, these data are consistent with an emerging model that rapid, signal-dependent transcription occurs in the context of a pre-established chromatin architecture.

•

EPO induces rapid RNA Pol II response at a key subset of genes

•

YY1 is redistributed in the genome following 1 h EPO stimulation

•

CTCF and YY1 bind different locations pre and post 1 h EPO stimulation

•

E-P loops mediated by H3K27ac are largely invariant in response to EPO

Role of ketogenic starvation sensors in mediating the renal protective effects of SGLT2 inhibitors in type 2 diabetes

Sodium-glucose cotransporter 2 (SGLT2) inhibitors ameliorate the progression of diabetic chronic kidney disease, but the mechanisms underlying this nephroprotective effect have not been fully elucidated. These drugs induce a fasting-like transcriptional paradigm, which includes activation of sirtuin-1 (SIRT1) and its downstream effectors, peroxisome proliferator-activated receptor γ coactivator 1α (PGC-1α) and fibroblast growth factor 21 (FGF21). This triad of enzymes and transcription factors serve as master regulators of nutrient and cellular homeostasis, and each acts to enhance gluconeogenesis, fatty acid oxidation and ketogenesis, the hallmarks of treatment with SGLT2 inhibitors. At the same time, SIRT1/PGC-1α/FGF21 signaling also promotes autophagy, a lysosome-dependent degradative pathway that cleanses the cytosol of dysfunctional organelles. This action alleviates cellular stress, ameliorates inflammation, and is strikingly nephroprotective. Interestingly, type 2 diabetes is characterized by both a deficiency of SIRT1/PGC-1α signaling and an impairment of autophagic flux, thus explaining the high levels of oxidative stress in the diabetic kidney. SIRT1 gene polymorphisms have been linked with an increased risk of diabetic nephropathy in several epidemiological studies. Importantly, there is an inverse relationship between the activity of SGLT2 and signaling through the SIRT1/PGC-1α/FGF21 pathway, and SGLT2 inhibition leads to activation of these ketogenic nutrient deprivation sensors. Therefore, activation of SIRT1/PGC-1α/FGF21 may explain the effect of SGLT2 inhibitors not only to promote ketogenesis, but also to preserve renal function in type 2 diabetes.

Dual Switch Mechanism of Erythropoietin as an Antiapoptotic and Pro-Angiogenic Determinant in the Retina

Constant or intense light degenerates the retina and retinal pigment epithelial cells. Light generates reactive oxygen species and nitric oxide leading to initial reactions of retinal degeneration. Apoptosis is the primary mechanism of abnormal death of photoreceptors, retinal ganglion cells, or retinal pigment epithelium (RPE) in degenerative retinal diseases, including diabetic retinopathy and age-related macular degeneration. The current study evaluated the function of erythropoietin (EPO) on angiogenesis and apoptosis in the retina and RPE under oxidative stress. We determined the pro-angiogenic and antiapoptotic mechanism of EPO under stress conditions using a conditional EPO knockdown model using siRNA, EPO addition, proteomics, immunocytochemistry, and bioinformatic analysis. Our studies verified that EPO protected retinal cells from light-, hypoxia-, hyperoxia-, and hydrogen peroxide-induced apoptosis through caspase inhibition, whereas up-regulated angiogenic reactions through vascular endothelial growth factor (VEGF) and angiotensin pathway. We demonstrated that the EPO expression in the retina and subsequent serine/threonine/tyrosine kinase phosphorylations might be linked to oxidative stress response tightly to determining angiogenesis and apoptosis. Neuroprotective roles of EPO may involve the balance between antiapoptotic and pro-angiogenic signaling molecules, including BCL-xL, c-FOS, caspase-3, nitric oxide, angiotensin, and VEGF receptor. Our data indicate a new therapeutic application of EPO toward retinal degeneration based on the dual roles in apoptosis and angiogenesis at the molecular level under oxidative stress.

Alpha-lipoic acid protects against pressure overload-induced heart failure via ALDH2-dependent Nrf1-FUNDC1 signaling

Alpha-lipoic acid (α-LA), a well-known antioxidant, was proved to active ALDH2 in nitrate tolerance and diabetic animal model. However, the therapeutic advantage of α-LA for heart failure and related signaling pathway have not been explored. This study was designed to examine the role of α-LA–ALDH2 in heart failure injury and mitochondrial damage. ALDH2 knockout (ALDH2^−/−) mice and primary neonatal rat cardiomyocytes (NRCMs) were subjected to assessment of myocardial function and mitochondrial autophagy. Our data demonstrated α-LA significantly reduced the degree of TAC-induced LV hypertrophy and dysfunction in wild-type mice, not in ALDH2^−/− mice. In molecular level, α-LA significantly restored ALDH2 activity and expression as well as increased the expression of a novel mitophagy receptor protein FUNDC1 in wild-type TAC mice. Besides, we confirmed that ALDH2 which was activated by α-LA governed the activation of Nrf1–FUNDC1 cascade. Our data suggest that α-LA played a positive role in protecting the heart against adverse effects of chronic pressure overload.

Erythropoietin Alleviates Burn-induced Muscle Wasting

Background: Burn injury induces long-term skeletal muscle pathology. We hypothesized EPO could attenuate burn-induced muscle fiber atrophy. Methods: Rats were allocated into four groups: a sham burn group, an untreated burn group subjected to third degree hind paw burn, and two burn groups treated with weekly or daily EPO for four weeks. Gastrocnemius muscle was analyzed at four weeks post-burn. Results: EPO attenuated the reduction of mean myofiber cross-sectional area post-burn and the level of the protective effect was no significant difference between two EPO-treated groups (p=0.784). Furthermore, EPO decreased the expression of atrophy-related ubiquitin ligase, atrogin-1, which was up-regulated in response to burn. Compared to untreated burn rats, those receiving weekly or daily EPO groups had less cell apoptosis by TUNEL assay. EPO decreased the expression of cleaved caspase 3 (key factor in the caspase-dependent pathway) and apoptosis-inducing factor (implicated in the caspase-independent pathway) after burn. Furthermore, EPO alleviated connective tissue overproduction following burn via transforming growth factor beta 1-Smad2/3 pathway. Daily EPO group caused significant erythrocytosis compared with untreated burn group but not weekly EPO group. Conclusion: EPO therapy attenuated skeletal muscle apoptosis and fibrosis at four weeks post-burn. Weekly EPO may be a safe and effective option in muscle wasting post-burn.

Erythropoietin and caffeine exert similar protective impact against neonatal intermittent hypoxia: Apnea of prematurity and sex dimorphism

Apnea of prematurity (AoP) is associated with severe and repeated episodes of arterial oxygen desaturation (intermittent hypoxia - IH), which in turn increases the number of apneas. So far, there is no data addressing whether IH leads to sex-specific respiratory consequences, neither if drugs targeting AoP are more effective in males or females. We used rat pups for investigating whether IH-mediated increase of apneas is sex-specific. We also tested whether caffeine (treatment of choice of AoP), erythropoietin (Epo - a neuroprotective factor and potent respiratory stimulant), and combination of both (caffeine+Epo) prevent the IH-mediated formation of apneas in a sex-dependent manner. Newborn rats exposed to IH (21% - 10% FIO₂-8 h a day - 10 cycles per hour) during postnatal days (P) 3-10 were used in this work. Animals were administered drug vehicle, Epo, caffeine and Epo + caffeine (daily from P3 to P10) gavage. At P10 the frequency of apneas at rest (as an index of respiratory dysfunction induced by IH), and respiratory parameters were measured by plethysmography. Our results showed that IH significantly increases the number of apneas in male but not in female rat pups. Moreover, caffeine and Epo in males similarly prevented the increase of apneas induced by IH, and the administration of both drugs together did not provide a cumulative beneficial effect. No impact of drugs was evidenced in females. Apart from apneas, IH increased the normoxic basal ventilation (ventilation at rest) of male animals, and treatments did not prevent such alteration. Besides, no IH- nor treatment-mediated modulation of basal ventilation was found in the basal ventilation of female animals. Analysis of the activity of pro- and antioxidative molecules revealed that IH induces oxidative stress in the brainstem of male and female animals and that all tested treatments similarly prevented such oxidative imbalance in pups of both sexes. We concluded that neonatal IH and the treatments tested to prevent its respiratory consequences are sex-specific. The mechanics associated with such prevention are directly linked with the prevention of oxidative stress and the maturation of the brain. These findings are relevant to understanding better the AoP disorder and for proposing Epo as a new therapeutical tool.

Regulation of Mitochondrial Biogenesis as a Way for Active Longevity: Interaction Between the Nrf2 and PGC-1α Signaling Pathways

Aging is a general degenerative process related to deterioration of cell functions in the entire organism. Mitochondria, which play a key role in energy homeostasis and metabolism of reactive oxygen species (ROS), require lifetime control and constant renewal. This explains recently peaked interest in the processes of mitochondrial biogenesis and mitophagy. The principal event of mitochondrial metabolism is regulation of mitochondrial DNA (mtDNA) transcription and translation, which is a complex coordinated process that involves at least two systems of transcription factors. It is commonly believed that its major regulatory proteins are PGC-1α and PGC-1β, which act as key factors connecting several regulator cascades involved in the control of mitochondrial metabolism. In recent years, the number of publications on the essential role of Nrf2/ARE signaling in the regulation of mitochondrial biogenesis has grown exponentially. Nrf2 is induced by various xenobiotics and oxidants that oxidize some Nrf2 negative regulators. Thus, ROS, in particular H₂O₂, were found to be strong Nrf2 activators. At present, there are two major concepts of mitochondrial biogenesis. Some authors suggest direct involvement of Nrf2 in the regulation of this process. Others believe that Nrf2 regulates expression of the antioxidant genes, while the major and only regulator of mitochondrial biogenesis is PGC-1α. Several studies have demonstrated the existence of the regulatory loop involving both PGC-1α and Nrf2. In this review, we summarized recent data on the Nrf2 role in mitochondrial biogenesis and its interaction with PGC-1α in the context of extending longevity.

Erythropoietin and Friedreich Ataxia: Time for a Reappraisal?

Friedreich ataxia (FRDA) is a rare neurological disorder due to deficiency of the mitochondrial protein frataxin. Frataxin deficiency results in impaired mitochondrial function and iron deposition in affected tissues. Erythropoietin (EPO) is a cytokine which was mostly known as a key regulator of erythropoiesis until cumulative evidence showed additional neurotrophic and neuroprotective properties. These features offered the rationale for advancement of EPO in clinical trials in different neurological disorders in the past years, including FRDA. Several mechanisms of action of EPO may be beneficial in FRDA. First of all, EPO exposure results in frataxin upregulation in vitro and in vivo. By promoting erythropoiesis, EPO influences iron metabolism and induces shifts in iron pool which may ameliorate conditions of free iron excess and iron accumulation. Furthermore, EPO signaling is crucial for mitochondrial gene activation and mitochondrial biogenesis. Up to date nine clinical trials investigated the effects of EPO and derivatives in FRDA. The majority of these studies had a proof-of-concept design. Considering the natural history of FRDA, all of them were too short in duration and not powered for clinical changes. However, these studies addressed significant issues in the treatment with EPO, such as (1) the challenge of the dose finding, (2) stability of frataxin up-regulation, (3) continuous versus intermittent stimulation with EPO/regimen, or (4) tissue changes after EPO exposure in humans in vivo (muscle biopsy, brain imaging). Despite several clinical trials in the past, no treatment is available for the treatment of FRDA. Current lines of research focus on gene therapy, frataxin replacement strategies and on regulation of key metabolic checkpoints such as NrF2. Due to potential crosstalk with all these mechanisms, interventions on the EPO pathway still represent a valuable research field. The recent development of small EPO mimetics which maintain cytoprotective properties without erythropoietic action may open a new era in EPO research for the treatment of FRDA.

A common pattern of DNase I footprinting throughout the human mtDNA unveils clues for a chromatin-like organization

Human mitochondrial DNA (mtDNA) is believed to lack chromatin and histones. Instead, it is coated solely by the transcription factor TFAM. We asked whether mtDNA packaging is more regulated than once thought. To address this, we analyzed DNase-seq experiments in 324 human cell types and found, for the first time, a pattern of 29 mtDNA Genomic footprinting (mt-DGF) sites shared by ∼90% of the samples. Their syntenic conservation in mouse DNase-seq experiments reflect selective constraints. Colocalization with known mtDNA regulatory elements, with G-quadruplex structures, in TFAM-poor sites (in HeLa cells) and with transcription pausing sites, suggest a functional regulatory role for such mt-DGFs. Altered mt-DGF pattern in interleukin 3-treated CD34⁺ cells, certain tissue differences, and significant prevalence change in fetal versus nonfetal samples, offer first clues to their physiological importance. Taken together, human mtDNA has a conserved protein-DNA organization, which is likely involved in mtDNA regulation.

Effects of erythropoietin abuse on exercise performance

The present review provides a comprehensive overview on the erythropoietic and non-erythropoietic effects of rHuEpo on human sport performance, paying attention to quantifying numerically how rHuEpo affects exercise performance and describing physiological changes regarding the most important exercise variables. Much attention has been paid to treatment schedules, in particular, to assess the effects of microdoses of rHuEpo and the prolonged effects on sport performance following withdrawal. Moreover, the review takes into account non-erythropoietic ergogenic effects of rHuEpo, including cognitive benefits of rHuEpo. A significant increase in both Vo2max and maximal cycling power was evidenced in studies taken into account for this review. rHuEpo, administered at clinical dosage, may have significant effects on haematological values, maximal and submaximal physiological variables, whereas few reports show positive effects on exercise perfomance. However, the influence of micro-dose rHuEpo on endurance performance in athletes is still unclear and further studies are warranted.

Erythropoietin attenuates motor neuron programmed cell death in a burn animal model

Burn-induced neuromuscular dysfunction may contribute to long-term morbidity; therefore, it is imperative to develop novel treatments. The present study investigated whether erythropoietin (EPO) administration attenuates burn-induced motor neuron apoptosis and neuroinflammatory response. To validate our hypothesis, a third-degree hind paw burn rat model was developed by bringing the paw into contact with a metal surface at 75°C for 10 s. A total of 24 male Sprague–Dawley rats were randomly assigned to four groups: Group A, sham-control; Group B, burn-induced; Group C, burn + single EPO dose (5000 IU/kg i.p. at D0); and Group D, burn + daily EPO dosage (3000 IU/kg/day i.p. at D0–D6). Two treatment regimens were used to evaluate single versus multiple doses treatment effects. Before sacrifice, blood samples were collected for hematological parameter examination. The histological analyses of microglia activation, iNOS, and COX-2 in the spinal cord ventral horn were performed at week 1 post-burn. In addition, we examined autophagy changes by biomarkers of LC3B and ATG5. The expression of BCL-2, BAX, cleaved caspase-3, phospho-AKT, and mTOR was assessed simultaneously through Western blotting. EPO administration after burn injury attenuated neuroinflammation through various mechanisms, including the reduction of microglia activity as well as iNOS and COX-2 expression in the spinal cord ventral horn. In addition, the expression of phospho-AKT, mTOR and apoptotic indicators, such as BAX, BCL-2, and cleaved caspase-3, was modulated. Furthermore, the activity of burn-induced autophagy in the spinal cord ventral horn characterized by the expression of autophagic biomarkers, LC3B and ATG5, was reduced after EPO administration. The present results indicate that EPO inhibits the AKT-mTOR pathway to attenuate burn-induced motor neuron programmed cell death and microglia activation. EPO can modulate neuroinflammation and programmed cell death and may be a therapeutic candidate for neuroprotection.

Mitochondrial dynamics, mitophagy and biogenesis in neonatal hypoxic-ischaemic brain injury

Hypoxic-ischaemic encephalopathy, resulting from asphyxia during birth, affects 2-3 in every 1000 term infants and depending on severity, brings about life-changing neurological consequences or death. This hypoxic-ischaemia (HI) results in a delayed neural energy failure during which the majority of brain injury occurs. Currently, there are limited treatment options and additional therapies are urgently required. Mitochondrial dysfunction acts as a focal point in injury development in the immature brain. Not only do mitochondria become permeabilised, but recent findings implicate perturbations in mitochondrial dynamics (fission, fusion), mitophagy and biogenesis. Mitoprotective therapies may therefore offer a new avenue of intervention for babies who suffer lifelong disabilities due to birth asphyxia.

Phosphorylation of signal transducer and activator of transcription 3 induced by hyperglycemia is different with that induced by lipopolysaccharide or erythropoietin via receptor‑coupled signaling in cardiac cells

The signal transducer and activator of transcription 3 (STAT3) is known to be involved in hypertrophy and fibrosis in cardiac dysfunction. The activation of STAT3 via the phosphorylation of STAT3 is required for the production of functional activity. It has been established that lipopolysaccharide (LPS)‑induced phosphorylation of STAT3 in cardiomyocytes primarily occurs through a direct receptor‑mediated action. This effect is demonstrated to be produced rapidly. STAT3 in cardiac fibrosis of diabetes is induced by high glucose through promotion of the STAT3‑associated signaling pathway. However, the time schedule for STAT3 activation between LPS and high glucose appears to be different. Therefore, the difference in STAT3 activation between LPS and hyperglycemia in cardiomyocytes requires elucidation. The present study investigated the phosphorylation of STAT3 induced by LPS and hyperglycemia in the rat cardiac cell line H9c2. Additionally, phosphorylation of STAT3 induced by erythropoietin (EPO) via receptor activation was compared. Then, the downstream signals for fibrosis, including the connective tissue growth factor (CTGF) and matrix metalloproteinase (MMP)‑9, were determined using western blotting, while the mRNA levels were quantified. LPS induced a rapid elevation of STAT3 phosphorylation in H9c2 cells within 30 min, similar to that produced by EPO. However, LPS or EPO failed to modify the mRNA level of STAT3, and/or the downstream signals for fibrosis. High glucose increased STAT3 phosphorylation to be stable after a long period of incubation. Glucose incubation for 24 h may augment the STAT3 expression in a dose‑dependent manner. Consequently, fibrosis‑associated signals, including CTGF and MMP‑9 protein, were raised in parallel. In the presence of tiron, an antioxidant, these changes by hyperglycemia were markedly reduced, demonstrating the mediation of oxidative stress. Therefore, LPS‑ or EPO‑induced STAT3 phosphorylation is different compared with that caused by high glucose in H9c2 cells. Sustained activation of STAT3 by hyperglycemia may promote the expression of fibrosis‑associated signals, including CTGF and MMP‑9, in H9c2 cells. Therefore, regarding the cardiac dysfunctions associated with diabetes and/or hyperglycemia, the identification of nuclear STAT3 may be more reliable compared with the assay of phosphorylated STAT3 in cardiac cells.

Erythropoietin Increases Myelination in Oligodendrocytes: Gene Expression Profiling Reveals Early Induction of Genes Involved in Lipid Transport and Metabolism

Several studies have shown that erythropoietin (EPO) has neuroprotective or neuroreparative actions on diseases of the nervous system and that improves oligodendrocyte (OL) differentiation and myelination in vivo and in vitro. This study aims at investigating the early molecular mechanisms for the pro-myelinating action of EPO at the gene expression level. For this purpose, we used a differentiating OL precursor cell line, rat central glia-4 cells. Cells were differentiated or not, and then treated with EPO for 1 or 20 h. RNA was extracted and changes in the gene expression profile were assessed using microarray analysis. Experiments were performed in biological replicates of n = 4. Differentiation alone changed the expression of 11% of transcripts (2,663 out of 24,272), representing 2,436 genes, half of which were upregulated and half downregulated. At 20 h of treatment, EPO significantly affected the expression of 99 genes that were already regulated by differentiation and of 150 genes that were not influenced by differentiation alone. Analysis of the transcripts most upregulated by EPO identified several genes involved in lipid transport (e.g., Cd36) and lipid metabolism (Ppargc1a/Pgc1alpha, Lpin1, Pnlip, Lpin2, Ppard, Plin2) along with Igf1 and Igf2, growth factors known for their pro-myelinating action. All these genes were only induced by EPO and not by differentiation alone, except for Pnlip which was highly induced by differentiation and augmented by EPO. Results were validated by quantitative PCR. These findings suggest that EPO might increase remyelination by inducing insulin-like growth factors and increasing lipid metabolism.

Mitochondrial Biogenesis in Response to Chromium (VI) Toxicity in Human Liver Cells

Hexavalent chromium (Cr(VI)) is a ubiquitous environmental pollutant, which poses a threat to human public health. Recent studies have shown that mitochondrial biogenesis can be activated by inflammatory and oxidative stress. However, whether mitochondrial biogenesis is involved in Cr(VI)-induced hepatotoxicity is unclear. Here, we demonstrated the induction of inflammatory response and oxidative stress, as indicated by upregulation of inflammatory factors and reactive oxygen species (ROS). Subsequently, we demonstrated that mitochondrial biogenesis, comprising the mitochondrial DNA copy number and mitochondrial mass, was significantly increased in HepG2 cells exposed to low concentrations of Cr(VI). Expression of genes related to mitochondrial function complex I and complex V was upregulated at low concentrations of Cr(VI). mRNA levels of antioxidant enzymes, including superoxide dismutase 1 and 2 (SOD1 and SOD2, respectively), kech like ECH associate protein 1 (KEAP1) and nuclear respiratory factor 2 (NRF-2), were also upregulated. Consistent with the above results, mRNA and protein levels of key transcriptional regulators of mitochondrial biogenesis such as the peroxisome-proliferator-activated receptor γ coactivator-1α (PGC-1α), NRF-1 and mitochondrial transcription factor A (TFAM) were increased by low concentrations of Cr(VI) in HepG2 cells. Moreover, we found that PGC-1α and NRF-1 tended to translocate into the nucleus. The expression of genes potentially involved in mitochondrial biogenesis pathways, including mRNA level of silent information regulator-1 (SIRT1), forkhead box class-O (FOXO1), threonine kinase 1 (AKT1), and cAMP response element-binding protein (CREB1), was also upregulated. In contrast, mitochondrial biogenesis was inhibited and the expression of its regulatory factors and antioxidants was downregulated at high and cytotoxic concentrations of Cr(VI) in HepG2 cells. It is believed that pretreatment with α-tocopherol could be acting against the mitochondrial biogenesis imbalance induced by Cr(VI). In conclusion, our study suggests that the homeostasis of mitochondrial biogenesis may be an important cellular compensatory mechanism against Cr(VI)-induced toxicity and a promising detoxification target.

Mitochondria, Bioenergetics and Excitotoxicity: New Therapeutic Targets in Perinatal Brain Injury

Injury to the fragile immature brain is implicated in the manifestation of long-term neurological disorders, including childhood disability such as cerebral palsy, learning disability and behavioral disorders. Advancements in perinatal practice and improved care mean the majority of infants suffering from perinatal brain injury will survive, with many subtle clinical symptoms going undiagnosed until later in life. Hypoxic-ischemia is the dominant cause of perinatal brain injury, and constitutes a significant socioeconomic burden to both developed and developing countries. Therapeutic hypothermia is the sole validated clinical intervention to perinatal asphyxia; however it is not always neuroprotective and its utility is limited to developed countries. There is an urgent need to better understand the molecular pathways underlying hypoxic-ischemic injury to identify new therapeutic targets in such a small but critical therapeutic window. Mitochondria are highly implicated following ischemic injury due to their roles as the powerhouse and main energy generators of the cell, as well as cell death processes. While the link between impaired mitochondrial bioenergetics and secondary energy failure following loss of high-energy phosphates is well established after hypoxia-ischemia (HI), there is emerging evidence that the roles of mitochondria in disease extend far beyond this. Indeed, mitochondrial turnover, including processes such as mitochondrial biogenesis, fusion, fission and mitophagy, affect recovery of neurons after injury and mitochondria are involved in the regulation of the innate immune response to inflammation. This review article will explore these mitochondrial pathways, and finally will summarize past and current efforts in targeting these pathways after hypoxic-ischemic injury, as a means of identifying new avenues for clinical intervention.

Erythropoietin activates SIRT1 to protect human cardiomyocytes against doxorubicin-induced mitochondrial dysfunction and toxicity

The hormone erythropoietin (EPO) has been demonstrated to protect against chemotherapy drug doxorubicin (DOX)-induced cardiotoxicity, but the underlying mechanism remains obscure. We hypothesized that silent mating type information regulation 2 homolog 1 (SIRT1), an NAD⁺-dependent protein deacetylase that activates peroxisome proliferator-activated receptor gamma coactivator 1-alpha (PGC-1α), plays a crucial role in regulating mitochondrial function and mediating the beneficial effect of EPO. Our study in human cardiomyocyte AC16 cells showed that DOX-induced cytotoxicity and mitochondrial dysfunction, as manifested by decreased mitochondrial DNA (mtDNA) copy number, mitochondrial membrane potential, and increased mitochondrial superoxide accumulation, can be mitigated by EPO pretreatment. EPO was found to upregulate SIRT1 activity and protein expression to reverse DOX-induced acetylation of PGC-1α and suppression of a suite of PGC-1α-activated genes involved in mitochondrial function and biogenesis, such as nuclear respiratory factor-1 (NRF1), mitochondrial transcription factor A (TFAM), citrate synthase (CS), superoxide dismutase 2 (SOD2), cytochrome c oxidase IV (COXIV), and voltage-dependent anion channel (VDAC). Silencing of SIRT1 via small RNA interference sensitized AC16 cells to DOX-induced cytotoxicity and reduction in mtDNA copy number. Although with SIRT1 silenced, EPO could reverse to some extent DOX-induced mitochondrial superoxide accumulation, loss of mitochondrial membrane potential and ATP depletion, it failed to normalize protein expression of PGC-1α and its downstream genes. Taken together, our results indicated that EPO may activate SIRT1 to enhance mitochondrial function and protect against DOX-induced cardiotoxicity.

Exercise capacity and cardiac hemodynamic response in female ApoE/LDLR(-/-) mice: a paradox of preserved V'O2max and exercise capacity despite coronary atherosclerosis

We assessed exercise performance, coronary blood flow and cardiac reserve of female ApoE/LDLR^−/− mice with advanced atherosclerosis compared with age-matched, wild-type C57BL6/J mice. Exercise capacity was assessed as whole body maximal oxygen consumption (V’O_2max), maximum running velocity (v_max) and maximum distance (DIST_max) during treadmill exercise. Cardiac systolic and diastolic function in basal conditions and in response to dobutamine (mimicking exercise-induced cardiac stress) were assessed by Magnetic Resonance Imaging (MRI) in vivo. Function of coronary circulation was assessed in isolated perfused hearts. In female ApoE/LDLR^−/− mice V’O_2max, v_max and DIST_max were not impaired as compared with C57BL6/J mice. Cardiac function at rest and systolic and diastolic cardiac reserve were also preserved in female ApoE/LDLR^−/− mice as evidenced by preserved fractional area change and similar fall in systolic and end diastolic area after dobutamine. Moreover, endothelium-dependent responses of coronary circulation induced by bradykinin (Bk) and acetylcholine (ACh) were preserved, while endothelium-independent responses induced by NO-donors were augmented in female ApoE/LDLR^−/− mice. Basal COX-2-dependent production of 6-keto-PGF_1α was increased. Concluding, we suggest that robust compensatory mechanisms in coronary circulation involving PGI₂- and NO-pathways may efficiently counterbalance coronary atherosclerosis-induced impairment in V’O_2max and exercise capacity.

Erythropoietin and the use of a transgenic model of erythropoietin-deficient mice

Despite its well-known role in red blood cell production, it is now accepted that erythropoietin (Epo) has other physiological functions. Epo and its receptors are expressed in many tissues, such as the brain and heart. The presence of Epo/Epo receptors in these organs suggests other roles than those usually assigned to this protein. Thus, the aim of this review is to describe the effects of Epo deficiency on adaptation to normoxic and hypoxic environments and to suggest a key role of Epo on main physiological adaptive functions. Our original model of Epo-deficient (Epo-TAg^h) mice allowed us to improve our knowledge of the possible role of Epo in O₂ homeostasis. The use of anemic transgenic mice revealed Epo as a crucial component of adaptation to hypoxia. Epo-TAg^h mice survive well in hypoxic conditions despite low hematocrit. Furthermore, Epo plays a key role in neural control of ventilatory acclimatization and response to hypoxia, in deformability of red blood cells, in cerebral and cardiac angiogenesis, and in neuro- and cardioprotection.

Mitochondrial Quality Control as a Therapeutic Target

In addition to oxidative phosphorylation (OXPHOS), mitochondria perform other functions such as heme biosynthesis and oxygen sensing and mediate calcium homeostasis, cell growth, and cell death. They participate in cell communication and regulation of inflammation and are important considerations in aging, drug toxicity, and pathogenesis. The cell's capacity to maintain its mitochondria involves intramitochondrial processes, such as heme and protein turnover, and those involving entire organelles, such as fusion, fission, selective mitochondrial macroautophagy (mitophagy), and mitochondrial biogenesis. The integration of these processes exemplifies mitochondrial quality control (QC), which is also important in cellular disorders ranging from primary mitochondrial genetic diseases to those that involve mitochondria secondarily, such as neurodegenerative, cardiovascular, inflammatory, and metabolic syndromes. Consequently, mitochondrial biology represents a potentially useful, but relatively unexploited area of therapeutic innovation. In patients with genetic OXPHOS disorders, the largest group of inborn errors of metabolism, effective therapies, apart from symptomatic and nutritional measures, are largely lacking. Moreover, the genetic and biochemical heterogeneity of these states is remarkably similar to those of certain acquired diseases characterized by metabolic and oxidative stress and displaying wide variability. This biologic variability reflects cell-specific and repair processes that complicate rational pharmacological approaches to both primary and secondary mitochondrial disorders. However, emerging concepts of mitochondrial turnover and dynamics along with new mitochondrial disease models are providing opportunities to develop and evaluate mitochondrial QC-based therapies. The goals of such therapies extend beyond amelioration of energy insufficiency and tissue loss and entail cell repair, cell replacement, and the prevention of fibrosis. This review summarizes current concepts of mitochondria as disease elements and outlines novel strategies to address mitochondrial dysfunction through the stimulation of mitochondrial biogenesis and quality control.

Redox mechanisms of cardiomyocyte mitochondrial protection

Oxidative and nitrosative stress are primary contributors to the loss of myocardial tissue in insults ranging from ischemia/reperfusion injury from coronary artery disease and heart transplantation to sepsis-induced myocardial dysfunction and drug-induced myocardial damage. This cell damage caused by oxidative and nitrosative stress leads to mitochondrial protein, DNA, and lipid modifications, which inhibits energy production and contractile function, potentially leading to cell necrosis and/or apoptosis. However, cardiomyocytes have evolved an elegant set of redox-sensitive mechanisms that respond to and contain oxidative and nitrosative damage. These responses include the rapid induction of antioxidant enzymes, mitochondrial DNA repair mechanisms, selective mitochondrial autophagy (mitophagy), and mitochondrial biogenesis. Coordinated cytoplasmic to nuclear cell-signaling and mitochondrial transcriptional responses to the presence of elevated cytoplasmic oxidant production, e.g., H₂O₂, allows nuclear translocation of the Nfe2l2 transcription factor and up-regulation of downstream cytoprotective genes such as heme oxygenase-1 which generates physiologic signals, such as CO that up-regulates Nfe212 gene transcription. Simultaneously, a number of other DNA binding transcription factors are expressed and/or activated under redox control, such as Nuclear Respiratory Factor-1 (NRF-1), and lead to the induction of genes involved in both intracellular and mitochondria-specific repair mechanisms. The same insults, particularly those related to vascular stress and inflammation also produce elevated levels of nitric oxide, which also has mitochondrial protein thiol-protective functions and induces mitochondrial biogenesis through cyclic GMP-dependent and perhaps other pathways. This brief review provides an overview of these pathways and interconnected cardiac repair mechanisms.

Activating mitochondrial function and haemoglobin expression with EH-201, an inducer of erythropoietin in neuronal cells, reverses memory impairment

BACKGROUND AND PURPOSE

Memory impairment can be progressive in neurodegenerative diseases, and physiological ageing or brain injury, mitochondrial dysfunction and oxidative stress are critical components of these issues. An early clinical study has demonstrated cognitive improvement during erythropoietin treatment in patients with chronic renal failure. As erythropoietin cannot freely cross the blood-brain barrier, we tested EH-201 (2,3,5,4'-tetrahydroxystilbene-2-O-β-d-glucoside, also known as TSG), a low MW inducer of erythropoietin, for its therapeutic effects on memory impairment in models of neurodegenerative diseases, physiological ageing or brain injury.

EXPERIMENTAL APPROACH

The effects of EH-201 were investigated in astrocytes and PC12 neuronal-like cells. In vivo, we used sleep-deprived (SD) mice as a stress model, amyloid-β (Aβ)-injected mice as a physiological ageing model and kainic acid (KA)-injected mice as a brain damage model to assess the therapeutic effects of EH-201.

KEY RESULTS

EH-201 induced expression of erythropoietin, PPAR-γ coactivator 1α (PGC-1α) and haemoglobin in astrocytes and PC12 neuronal-like cells. In vivo, EH-201 treatment restored memory impairment, as assessed by the passive avoidance test, in SD, Aβ and KA mouse models. In the hippocampus of mice given EH-201 in their diet, levels of erythropoietin, PGC-1α and haemoglobin were increased

CONCLUSIONS AND IMPLICATIONS

The induction of endogenous erythropoietin in neuronal cells by inducers such as EH-201 might be a therapeutic strategy for memory impairment in neurodegenerative disease, physiological ageing or traumatic brain injury.

Emerging EPO and EPO receptor regulators and signal transducers

As essential mediators of red cell production, erythropoietin (EPO) and its cell surface receptor (EPO receptor [EPOR]) have been intensely studied. Early investigations defined basic mechanisms for hypoxia-inducible factor induction of EPO expression, and within erythroid progenitors EPOR engagement of canonical Janus kinase 2/signal transducer and activator of transcription 5 (JAK2/STAT5), rat sarcoma/mitogen-activated protein kinase/extracellular signal-regulated kinase (RAS/MEK/ERK), and phosphatidylinositol 3-kinase (PI3K) pathways. Contemporary genetic, bioinformatic, and proteomic approaches continue to uncover new clinically relevant modulators of EPO and EPOR expression, and EPO's biological effects. This Spotlight review highlights such factors and their emerging roles during erythropoiesis and anemia.

Activation of mitochondrial function and Hb expression in non-haematopoietic cells by an EPO inducer ameliorates ischaemic diseases in mice

BACKGROUND AND PURPOSE

Many organs suffer from ischaemic injuries that reduce their ability to generate sufficient energy, which is required for functional maintenance and repair. Erythropoietin (EPO) ameliorates ischaemic injuries by pleiotropic effects. The aim of this study was to investigate the effect and mechanism of a small molecule EH-201, and found it as a potent EPO inducer and its effect in non-haematopoietic cells for therapeutic potential in ischemic disorders.

EXPERIMENTAL APPROACH

Mice kidney slices, primary hepatocytes, primary cardiomyocytes and C2C12 myoblasts were treated with EH-201. The effects of this treatment on EPO, Hb expression and mitochondrial biogenesis were analysed. In vivo, doxorubicin-induced cardiomyopathic mice were treated with EH-201. The mice were subjected to an endurance test, electrocardiography and echocardiography, and a histological examination of the isolated hearts was performed. EH-201 was also administered to cisplatin-induced nephropathic mice.

KEY RESULTS

In non-haematopoietic cells, EH-201 was potent at inducing EPO. EH-201 also stimulated mitochondrial biogenesis and enhanced the expression of Hb by a mechanism dependent on EPO-mediated signalling. In mechanistic studies, using EPO and EPO receptor-neutralizing antibodies, we confirmed that EH-201 enhances EPO-EPOR autocrine activity. EH-201 robustly increased the endurance performance activity of healthy and cardiomyopathic mice during hypoxic stress, enhanced myocardial mitochondrial biogenesis and Hb expression, and also improved cardiac function. EH-201 ameliorated anaemia and renal dysfunction in nephropathic mice.

CONCLUSIONS AND IMPLICATIONS

The enhancement and recovery of cellular functions through the stimulation of mitochondrial activity and Hb production in non-haematopoietic cells by an inducer of endogenous EPO has potential as a therapeutic strategy for ischaemic diseases.

Erythropoietin, a novel versatile player regulating energy metabolism beyond the erythroid system

Erythropoietin (EPO), the required cytokine for promoting the proliferation and differentiation of erythroid cells to stimulate erythropoiesis, has been reported to act as a pleiotropic cytokine beyond hematopoietic system. The various activities of EPO are determined by the widespread distribution of its cell surface EPO receptor (EpoR) in multiple tissues including endothelial, neural, myoblasts, adipocytes and other cell types. EPO activity has been linked to angiogenesis, neuroprotection, cardioprotection, stress protection, anti-inflammation and especially the energy metabolism regulation that is recently revealed. The investigations of EPO activity in animals and the expression analysis of EpoR provide more insights on the potential of EPO in regulating energy metabolism and homeostasis. The findings of crosstalk between EPO and some important energy sensors and the regulation of EPO in the cellular respiration and mitochondrial function further provide molecular mechanisms for EPO activity in metabolic activity regulation. In this review, we will summarize the roles of EPO in energy metabolism regulation and the activity of EPO in tissues that are tightly associated with energy metabolism. We will also discuss the effects of EPO in regulating oxidative metabolism and mitochondrial function, the interactions between EPO and important energy regulation factors, and the protective role of EPO from stresses that are related to metabolism, providing a brief overview of previously less appreciated EPO biological function in energy metabolism and homeostasis.

AMPK is involved in mediation of erythropoietin influence on metabolic activity and reactive oxygen species production in white adipocytes

Erythropoietin, discovered for its indispensable role during erythropoiesis, has been used in therapy for selected red blood cell disorders in erythropoietin-deficient patients. The biological activities of erythropoietin have been found in animal models to extend to non-erythroid tissues due to the expression of erythropoietin receptor. We previously demonstrated that erythropoietin promotes metabolic activity and white adipocytes browning to increase mitochondrial function and energy expenditure via peroxisome proliferator-activated receptor alpha and Sirtuin1. Here we report that AMP-activated protein kinase was activated by erythropoietin possibly via Ca(2+)/calmodulin-dependent protein kinase kinase in adipocytes as well as in white adipose tissue from diet induced obese mice. Erythropoietin increased cellular nicotinamide adenine dinucleotide via increased AMP-activated protein kinase activity, possibly leading to Sirtuin1 activation. AMP-activated protein kinase knock down reduced erythropoietin mediated increase in cellular oxidative function including the increased oxygen consumption rate, fatty acid utilization and induction of key metabolic genes. Under hypoxia, adipocytes were found to generate more reactive oxygen species, and erythropoietin reduced the reactive oxygen species and increased antioxidant gene expression, suggesting that erythropoietin may provide protection from oxidative stress in adipocytes. Erythropoietin also reversed increased nicotinamide adenine dinucleotide by hypoxia via increased AMP-activated protein kinase. Additionally, AMP-activated protein kinase is found to be involved in erythropoietin stimulated increase in oxygen consumption rate, fatty acid oxidation and mitochondrial gene expression. AMP-activated protein kinase knock down impaired erythropoietin stimulated increases in antioxidant gene expression. Collectively, our findings identify the AMP-activated protein kinase involvement in erythropoietin signaling in regulating adipocyte cellular redox status and metabolic activity.

Erythropoietin action in stress response, tissue maintenance and metabolism

Erythropoietin (EPO) regulation of red blood cell production and its induction at reduced oxygen tension provides for the important erythropoietic response to ischemic stress. The cloning and production of recombinant human EPO has led to its clinical use in patients with anemia for two and half decades and has facilitated studies of EPO action. Reports of animal and cell models of ischemic stress in vitro and injury suggest potential EPO benefit beyond red blood cell production including vascular endothelial response to increase nitric oxide production, which facilitates oxygen delivery to brain, heart and other non-hematopoietic tissues. This review discusses these and other reports of EPO action beyond red blood cell production, including EPO response affecting metabolism and obesity in animal models. Observations of EPO activity in cell and animal model systems, including mice with tissue specific deletion of EPO receptor (EpoR), suggest the potential for EPO response in metabolism and disease.

Erythropoietin enhances mitochondrial biogenesis in cardiomyocytes exposed to chronic hypoxia through Akt/eNOS signalling pathway

Adaptation of cardiomyocytes to chronic hypoxia in cyanotic patients remains unclear. Mitochondrial biogenesis is enhanced in myocardium from cyanotic patients, which is possibly an adaptive response. Erythropoietin (EPO) in blood and its receptor (EPOR) on cardiomyocytes are upregulated by chronic hypoxia, suggesting that EPO-EPOR interaction is increased, which is inferred to positively regulate mitochondrial biogenesis through protein kinase B (Akt)/endothelial nitric oxide synthase (eNOS) signalling pathway. H9c2 cardiomyocytes were exposed to hypoxia (1% O(2)) for 1 week and treated with different doses of recombinant human erythropoietin (rhEPO). Mitochondrial number, mitochondrial DNA (mtDNA) copy number and peroxisome proliferator activated receptor gamma coactivator alpha (PGC-1α) mRNA expression increased in a dose-dependent manner induced by rhEPO. Akt and eNOS were significantly phosphorylated by rhEPO. Both blocking Akt with Wortmannin and silencing eNOS expression with shRNA plasmid decreased the mtDNA copy number and PGC-1α mRNA expression induced by rhEPO. Blocking Akt was associated with the decreased phosphorylation of Akt and eNOS. RNA interference led to a reduction in the total and phosphorylated proteins of eNOS. Thus EPO enhances mitochondrial biogenesis in cardiomyocytes exposed to chronic hypoxia, at least partly through Akt/eNOS signalling, which might be an adaptive mechanism of cardiomyocytes associated with the increased EPO-EPOR interaction in patients with cyanotic congenital heart disease (CCHD).

Erythropoietin and the heart: physiological effects and the therapeutic perspective

Erythropoietin (Epo) has been thought to act exclusively on erythroid progenitor cells. The identification of Epo receptor (EpoR) in non-haematopoietic cells and tissues including neurons, astrocytes, microglia, immune cells, cancer cell lines, endothelial cells, bone marrow stromal cells, as well as cells of myocardium, reproductive system, gastrointestinal tract, kidney, pancreas and skeletal muscle indicates that Epo has pleiotropic actions. Epo shows signals through protein kinases, anti-apoptotic proteins and transcription factors. In light of interest of administering recombinant human erythropoietin (rhEpo) and its analogues for limiting infarct size and left ventricular (LV) remodelling after acute myocardial infarction (AMI) in humans, the foremost studies utilising rhEpo are reviewed. The putative mechanisms involved in Epo-induced cardioprotection are related to the antiapoptotic, anti-inflammatory and angiogenic effects of Epo. Thus, cardioprotective potentials of rhEpo are reviewed in this article by focusing on clinical applicability. An overview of non-haematopoietic Epo analogues, which are a reliable alternative to the classic EpoR agonists and may prevent undesired side effects, is also provided.

Modulation of intestinal folate absorption by erythropoietin in vitro

Besides the direct stimulation of erythropoiesis, erythropoietin (EPO) therapy in renal anemia may also play a regulatory role in maintaining the homeostasis of hematopoietic nutrients. It has been reported that EPO can stimulate intestinal iron absorption. However, the involvement of EPO in intestinal folate absorption remains elusive. The objective of this study was to investigate the effect of EPO on intestinal transport of folate in vitro and to elucidate the possible mechanism(s) involved in this regulation. Transport assays of folic acid were performed in Caco-2 monolayers treated with EPO. The effect of EPO on the expression of transporters involved in the folate absorption was investigated. The possible involvement of three main EPO signaling pathways, the janus protein tyrosine kinase 2 (JAK-2) pathway, extracellular signal regulated kinases (ERK) pathway, and phosphatidylinositol 3 kinase/Akt (PI3K/Akt) pathway, in the transporter regulation was explored. The absorptive flux (apical to basolateral) of folic acid was enhanced by EPO treatment in a dose-dependent manner, which was companied with the significant up-regulation of reduced folate carrier (RFC) and apical proton coupled folate transporter (PCFT). The efflux (basolaterial to apical) of folic acid was enhanced only by the high dose of EPO treatment, which was associated with the significant up-regulation of apical multidrug resistance-associated protein 2 (MRP2). The expression levels of all of these transporters were up-regulated by EPO treatment in a dose- and time-dependent manner. Transporter expression in response to blocking EPO induced activation of JAK-2, ERK, and PI3K/Akt was changed to a different extent. As a conclusion, intestinal folate absorption was enhanced by EPO treatment in vitro. Our findings provided direct evidence to establish the correlation between EPO and folate homeostasis.

PPARα and Sirt1 mediate erythropoietin action in increasing metabolic activity and browning of white adipocytes to protect against obesity and metabolic disorders

Erythropoietin (EPO) has shown beneficial effects in the regulation of obesity and metabolic syndrome; however, the detailed mechanism is still largely unknown. Here, we created mice with adipocyte-specific deletion of EPO receptor. These mice exhibited obesity and decreased glucose tolerance and insulin sensitivity, especially when fed a high-fat diet. Moreover, EPO increased oxidative metabolism, fatty acid oxidation, and key metabolic genes in adipocytes and in white adipose tissue from diet-induced obese wild-type mice. Increased metabolic activity by EPO is associated with induction of brown fat-like features in white adipocytes, as demonstrated by increases in brown fat gene expression, mitochondrial content, and uncoupled respiration. Peroxisome proliferator-activated receptor (PPAR)α was found to mediate EPO activity because a PPARα antagonist impaired EPO-mediated induction of brown fat-like gene expression and uncoupled respiration. PPARα also cooperates with Sirt1 activated by EPO through modulating the NAD+ level to regulate metabolic activity. PPARα targets, including PPARγ coactivator 1α, uncoupling protein 1, and carnitine palmitoyltransferase 1α, were increased by EPO but impaired by Sirt1 knockdown. Sirt1 knockdown also attenuated adipose response to EPO. Collectively, EPO, as a novel regulator of adipose energy homeostasis via these metabolism coregulators, provides a potential therapeutic strategy to protect against obesity and metabolic disorders.

Whole body metabolic effects of prolonged endurance training in combination with erythropoietin treatment in humans: a randomized placebo controlled trial

Erythropoietin (Epo) administration improves aerobic exercise capacity and insulin sensitivity in renal patients and also increases resting energy expenditure (REE). Similar effects are observed in response to endurance training. The aim was to compare the effects of endurance training with erythropoiesis-stimulating agent (ESA) treatment in healthy humans. Thirty-six healthy untrained men were randomized to 10 wk of either: 1) placebo (n = 9), 2) ESA (n = 9), 3) endurance training (n = 10), or 4) ESA and endurance training (n = 8). In a single-blinded design, ESA/placebo was injected one time weekly. Training consisted of biking for 1 h at 65% of wattmax three times per week. Measurements performed before and after the intervention were as follows: body composition, maximal oxygen uptake, insulin sensitivity, REE, and palmitate turnover. Uncoupling protein 2 (UCP2) mRNA levels were assessed in skeletal muscle. Fat mass decreased after training (P = 0.003), whereas ESA induced a small but significant increase in intrahepatic fat (P = 0.025). Serum free fatty acid (FFA) levels and palmitate turnover decreased significantly in response to training, whereas the opposite pattern was found after ESA. REE corrected for lean body mass increased in response to ESA and training, and muscle UCP2 mRNA levels increased after ESA (P = 0.035). Insulin sensitivity increased only after training (P = 0.011).

IN CONCLUSION

1) insulin sensitivity is not improved after ESA treatment despite improved exercise capacity, 2) the calorigenic effects of ESA may be related to increased UCP2 gene expression in skeletal muscle, and 3) training and ESA exert opposite effects on lipolysis under basal conditions, increased FFA levels and liver fat fraction was observed after ESA treatment.