Erythropoietin's Beta Common Receptor Mediates Neuroprotection in Spinal Cord Neurons

Erythropoietin enhances iron bioavailability in HepG2 cells by downregulating hepcidin through mTOR, C/EBPα and HIF-1α

The regulation of iron (Fe) levels is essential to maintain an adequate supply for erythropoiesis, among other processes, and to avoid possible toxicity. The liver-produced peptide hepcidin is regarded as the main regulator of Fe absorption in enterocytes and release from hepatocytes and macrophages, as it impairs Fe export through ferroportin. The glycoprotein erythropoietin (Epo) drives erythroid progenitor survival and differentiation in the bone marrow, and has been linked to the mobilization of Fe reserves necessary for hemoglobin production. Herein we show that Epo inhibits hepcidin expression directly in the HepG2 hepatic cell line, thus leading to a decrease in intracellular Fe levels. Such inhibition was dependent on the Epo receptor-associated kinase JAK2, as well as on the PI3K/AKT/mTOR pathway, which regulates nutrient homeostasis. Epo was also found to decrease binding of the C/EBP-α transcription factor to the hepcidin promoter, which could be attributed to an increased expression of its inhibitor CHOP. Epo did not only hinder the stimulating effect of C/EBP-α on hepcidin transcription, but also favored hepcidin inhibition by HIF-1α, by increasing is nuclear translocation as well as its protein levels. Moreover, in assays with the inhibitor genistein, this transcription factor was found necessary for Epo-induced hepcidin suppression. Our findings support the involvement of the PI3K/AKT/mTOR pathway in the regulation of Fe levels by Epo, and highlight the contrasting roles of the C/EBP-α and HIF-1α transcription factors as downstream effectors of the cytokine in this process.

Second-generation non-hematopoietic erythropoietin-derived peptide for neuroprotection

Erythropoietin (EPO) is a well-known erythropoietic cytokine having a tissue-protective effect in various tissues against hypoxic stress, including the brain. Thus, its recombinants may function as neuroprotective compounds. However, despite considerable neuroprotective effects, the EPO-based therapeutic approach has side effects, including hyper-erythropoietic and tumorigenic effects. Therefore, some modified forms and derivatives of EPO have been proposed to minimize the side effects. In this study, we generated divergently modified new peptide analogs derived from helix C of EPO, with several amino acid replacements that interact with erythropoietin receptors (EPORs). This modification resulted in unique binding potency to EPOR. Unlike recombinant EPO, among the peptides, ML1-h3 exhibited a potent neuroprotective effect against oxidative stress without additional induction of cell-proliferation, owing to a differential activating mode of EPOR signaling. Furthermore, it inhibited neuronal death and brain injury under hypoxic stress in vitro and in an in vivo ischemic brain injury model. Therefore, the divergent modification of EPO-derivatives for affinity to EPOR could provide a basis for a more advanced and optimal neuroprotective strategy.

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Short peptides derived from helix C of EPO have a neuroprotective effect.

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Divergent modification of EPO-derived peptides has a differential affinity to EPOR.

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ML1 and its analogs have differential cell protective and proliferative effects.

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ML1-h3 protects neurons by suppressing in vitro oxidative stress.

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ML1-h3 mitigates brain injury in the in vivo mouse ischemic model without hematopoietic effect.

Whether erythropoietin can be a neuroprotective agent against premature brain injury: cellular mechanisms and clinical efficacy

Preterm infants are at high risk of brain injury. With more understanding of the preterm brain injury's pathogenesis, neuroscientists are looking for more effective methods to prevent and treat it, among which erythropoietin (Epo) is considered as a prime candidate. This review tries to clarify the possible mechanisms of Epo in preterm neuroprotection and summarize updated evidence considering Epo as a pharmacological neuroprotective strategy in animal models and clinical trials. To date, various animal models have validated that Epo is an anti-apoptotic, anti-inflammatory, anti-oxidant, anti-excitotoxic, neurogenetic, erythropoietic, angiogenetic, and neurotrophic agent, thus preventing preterm brain injury. However, although the scientific rationale and preclinical data for Epo's neuroprotective effect are promising, when translated to bedside, the results vary in different studies, especially in its long-term efficacy. Based on existing evidence, it is still too early to recommend Epo as the standard treatment for preterm brain injury.

Mutant erythropoietin enhances white matter repair via the JAK2/STAT3 and C/EBPβ pathway in middle-aged mice following cerebral ischemia and reperfusion

Previous studies have indicated that EPO maintains the M2 microglia phenotype that contributes to white matter repair after ischemic stroke in young mice (2 months old). However, the underlying mechanisms that regulate microglial polarization are poorly defined. This study investigated the neuroprotective effects of nonerythropoietic mutant EPO (MEPO) on white matter and the underlying mechanism in middle-aged (9-month-old) male mice following cerebral ischemia. Middle-aged male C57 BL/6 mice were treated with MEPO (5000 IU/kg) or vehicle after middle cerebral artery occlusion (MCAO) and reperfusion. The specific inhibitor AG490 was used to block the JAK2/STAT3 pathway. Neurological function was assessed by beam walking and adhesive removal tests. Immunofluorescence staining and western blotting were used to assess the severity of white matter injury, phenotypic changes in the microglia and the expression of the signaling molecules. MEPO significantly improved neurobehavioral outcomes, alleviated brain tissue loss, and ameliorated white matter injury after MCAO compared with the vehicle group. Moreover, MEPO promoted oligodendrogenesis by shifting microglia toward M2 polarization by promoting JAK2/STAT3 activation and inhibiting the expression of C/EBPβ at 14 days after cerebral ischemia-reperfusion. However, the MEPO's effect on microglial M2 polarization and oligodendrogenesis was largely suppressed by AG490 treatment. Collectively, these data indicate that MEPO treatment improves white matter integrity after cerebral ischemia, which may be partly explained by MEPO facilitating microglia toward the beneficial M2 phenotype to promote oligodendrogenesis via JAK2/STAT3 and the C/EBPβ signaling pathway. This study provides novel insight into MEPO treatment for ischemic stroke.

Regulation of inflammatory cytokines for spinal cord injury recovery

Spinal cord injury (SCI) is one of the most destructive traumatic diseases in human beings. The balance of inflammation in the microenvironment is crucial to the repair process of spinal cord injury. Inflammatory cytokines are direct mediators of local lesion inflammation and affect the prognosis of spinal cord injury to varying degrees. In spinal cord injury models, some inflammatory cytokines are beneficial for spinal cord repair, while others are harmful. A large number of animal studies have shown that local targeted administration can effectively regulate the secretion and delivery of inflammatory cytokines and promote the repair of spinal cord injury. In addition, many clinical studies have shown that drugs can promote the repair of spinal cord injury by regulating the content of inflammatory cytokines. However, topical administration affects only a small portion of inflammatory cytokines. In addition, different individuals have different inflammatory cytokine profiles during spinal cord injury. Therefore, future research should aim to develop a personalized local delivery therapeutic cocktail strategy to effectively and accurately regulate inflammation and obtain substantial functional recovery from spinal cord injury.

Plasma Erythropoietin, IL-17A, and IFNγ as Potential Biomarkers of Motor Function Recovery in a Canine Model of Spinal Cord Injury

Traumatic spinal cord injury (SCI) is a devastating neurological disease for which an accurate, cost-effective prediction of motor function recovery is in pressing need. A plethora of neurochemical changes involved in the pathophysiological process of SCI may serve as a new source of biomarkers for patient outcomes. Five dogs were included in this study. We characterized the plasma cytokine profiles in acute phase (0, 1, and 3 days after SCI) and subacute phase (7, 14, and 21 days after SCI) with microarray analysis. The motor function recovery following SCI was monitored by Olby scores. The expression level of differentially expressed proteins (DEPs) was measured with enzyme-linked immunosorbent assay (ELISA). Then, correlations with the Olby scores and receiver operating characteristic curve (ROC) analysis were performed. We identified 12 DEPs including 10 pro-inflammatory and 2 anti-inflammatory cytokines during the 21-day study period. Among those, the expression levels of erythropoietin (EPO), IL-17A, and IFNγ significantly correlated with the Olby scores with R² values of 0.870, 0.740, and 0.616, respectively. The results of the ROC analysis suggested that plasma EPO, IL-17A, and IFNγ exhibited a significant predictive power with an area under the curve (AUC) of 0.656, 0.848, and 0.800 for EPO, IL-17A, and IFNγ, respectively. Our results provide a longitudinal description of the changes in plasma cytokine expression in the acute and subacute stages of canine SCI. These data reveal novel panels of inflammation-related cytokines which have the potential to be evaluated as biomarkers for predicting motor function prognosis after SCI.

Erythropoietin and its derivatives: from tissue protection to immune regulation

Erythropoietin (EPO) is an evolutionarily conserved hormone well documented for its erythropoietic role via binding the homodimeric EPO receptor (EPOR)₂. In past decades, evidence has proved that EPO acts far beyond erythropoiesis. By binding the tissue-protective receptor (TPR), EPO suppresses proinflammatory cytokines, protects cells from apoptosis and promotes wound healing. Very recently, new data revealed that TPR is widely expressed on a variety of immune cells, and EPO could directly modulate their activation, differentiation and function. Notably, nonerythropoietic EPO derivatives, which mimic the structure of helix B within EPO, specifically bind TPR and show great potency in tissue protection and immune regulation. These small peptides prevent the cardiovascular side effects of EPO and are promising as clinical drugs. This review briefly introduces the receptors and tissue-protective effects of EPO and its derivatives and highlights their immunomodulatory functions and application prospects.

Alternative Erythropoietin Receptors in the Nervous System

In addition to its regulatory function in the formation of red blood cells (erythropoiesis) in vertebrates, Erythropoietin (Epo) contributes to beneficial functions in a variety of non-hematopoietic tissues including the nervous system. Epo protects cells from apoptosis, reduces inflammatory responses and supports re-establishment of compromised functions by stimulating proliferation, migration and differentiation to compensate for lost or injured cells. Similar neuroprotective and regenerative functions of Epo have been described in the nervous systems of both vertebrates and invertebrates, indicating that tissue-protective Epo-like signaling has evolved prior to its erythropoietic function in the vertebrate lineage. Epo mediates its erythropoietic function through a homodimeric Epo receptor (EpoR) that is also widely expressed in the nervous system. However, identification of neuroprotective but non-erythropoietic Epo splice variants and Epo derivatives indicated the existence of other types of Epo receptors. In this review, we summarize evidence for potential Epo receptors that might mediate Epo's tissue-protective function in non-hematopoietic tissue, with focus on the nervous system. In particular, besides EpoR, we discuss three other potential neuroprotective Epo receptors: (1) a heteroreceptor consisting of EpoR and common beta receptor (βcR), (2) the Ephrin (Eph) B4 receptor and (3) the human orphan cytokine receptor-like factor 3 (CRLF3).