EPO

Official Full Name

erythropoietin

Organism

Homo sapiens

GeneID

2056

Background

This gene encodes a secreted, glycosylated cytokine composed of four alpha helical bundles. The encoded protein is mainly synthesized in the kidney, secreted into the blood plasma, and binds to the erythropoietin receptor to promote red blood cell production, or erythropoiesis, in the bone marrow. Expression of this gene is upregulated under hypoxic conditions, in turn leading to increased erythropoiesis and enhanced oxygen-carrying capacity of the blood. Expression of this gene has also been observed in brain and in the eye, and elevated expression levels have been observed in diabetic retinopathy and ocular hypertension. Recombinant forms of the encoded protein exhibit neuroprotective activity against a variety of potential brain injuries, as well as antiapoptotic functions in several tissue types, and have been used in the treatment of anemia and to enhance the efficacy of cancer therapies. [provided by RefSeq, Aug 2017]

Synonyms

EP; DBAL; ECYT5; MVCD2;

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Detailed Information

EPO (erythropoietin), one of the members of the hematopoietic factor superfamily, is a sialic acid-containing acidic glycoprotein. EPO consists of two parts, protein and sugar, with a sugar content of 40%. EPO contains four glycosylation sites, which are located in Asn24, Asn38, Asn83, and Ser126. The first three are N glycosylation sites, and the fourth is O glycosylation site. Two pairs of disulfide bonds are formed between the 7th and 161th, 29th and 33th cysteines in the EPO molecule, and four stable α-helix structures are formed by the disulfide bond.

Under the hypoxic condition, EPO promotes the production of red blood cells (RBC). In the hypothalamus, EPO-Rs expressed in neurons producing POMC regulate food intake and energy expenditure. In white adipose tissue, EPO reduces inflammation, normalizes insulin sensitivity and reduces glucose intolerance. In the pancreas, EPO exerts anti-apoptotic, anti-inflammatory, proliferative and angiogenic effects on beta cells.

EPO Figure 1. Erythroid and nonerythroid effects of EPO. (Woo, et al. 2014)

Mechanism of Action of EPO

The lack of oxygen in the body is an important factor in stimulating the secretion of EPO. EPO is secreted in the body and binds to the erythroid progenitor receptor (EPOR) on the surface of erythroid progenitor cells and young red blood cells in the bone marrow, and then regulates erythroid proliferation and differentiation, increase red blood cell count and hemoglobin content, stabilize erythrocyte membrane, improve erythrocyte membrane antioxidant enzyme function, and correct anemia through JAK/STAT and Ras/ MAPK kinases. Existing studies have shown that EPO and EPOR are not only found on the surface of young red blood cells, but also in different non-erythropoiesis tissues, such as nerve cells, epithelial cells, myocardium, smooth muscle cells, and tumor cells.

EPO Protects the Heart

It was found that EPO can significantly reduce the area of myocardial infarction in rats and reduce the apoptosis of cardiomyocytes. The mechanism may be related to up-regulation of p-Akt protein expression and activation of Akt anti-apoptotic signaling pathway. It has also been reported that EPO can significantly reduce the myocardial ischemia and infarct size of rats with ischemia-reperfusion injury, reduce myocardial cell apoptosis, and have obvious protective effect on myocardial ischemia-reperfusion injury. The mechanism may be related to down-regulation of Caspase-3 protein expression.

Myocardial fibrosis is an important pathological process in the development of cardiovascular disease to a certain stage. It is the main reason for the continuous development of ventricular remodeling and its difficulty in reversal. The mechanism of its occurrence remains unclear. It was found that EPO inhibited TGF-β-induced proliferation, transformation and collagen synthesis of rat cardiac fibroblasts and promoted collagen degradation. The study found that EPO inhibits the conversion of AngII-induced neonatal rat cardiac fibroblast phenotype into cardiac fibroblasts, reduces myocardial fibrosis, and reduces the expression of mRNA and protein of related signaling molecules. Therefore, it is speculated that EPO inhibits myocardial fibrosis and reduces ventricular remodeling through the TGF-β1-TAK1-p38MAPK signaling pathway. These studies suggest that EPO has potential therapeutic value for a variety of cardiovascular diseases.

EPO and Tumor

EPO is expressed in some glioma cells and vascular endothelial cells, which is related to the pathological grade of tumors. The expression of EPO in highly malignant tumor cells is significantly higher than that in low-grade malignant tumor cells. According to the histological and biological characteristics of tumor cells, WHO classifies gliomas into 4 grades. As the grade increases, the heterogeneity of tumor cells increases, showing active proliferation and infiltration growth, indicating EPO is related to the biological behavior of glioma to a certain extent, predicting the prognosis of the patient. Prognostic studies have shown that EPO is expressed in gliomas and participates in the proliferation and development of tumors. Therefore, studies on inhibition of glioma EPO can be carried out. Signal transduction pathways in which EPO interacts with EPO-R may also have therapeutic targets that can be manipulated.

Studies have shown that the serum EPO level of cancer anemia is significantly higher than that of the anemia-free group and the control group, indicating that the serum EPO of the cancer anemia group is at a high level, but the patient is still in an anemia state. Studies have shown that EPO is more effective in patients with serum EPO < 100Iu /mL, and EPO is less effective in patients with serum EPO > 100Iu /mL. Therefore, patients with cancerous anemia can be treated with EPO, and the determination of serum EPO concentration before treatment can better predict the therapeutic effect and guide clinical treatment.

The osteosarcoma primary cell line responds to EPO treatment, but has a very low effect on proliferation, indicating weak anti-apoptotic activity or EPOR reactivity in the experimental environment. Based on the different biological behaviors of cat and canine osteosarcoma and the expression of EPOR mRNA, Meyer et al. concluded that the paracrine/autocrine mechanism and species-specific growth promotion or inhibition of EPO can be imagined. Given the increasing focus on the role of EPO in cancer and the recent discovery of EPO on osteoblasts or osteoclasts, Meyer et al. proposed a useful comparative model to study the role of EPO in cancer.

References:

Woo, M., & Hawkins, M. (2014). Beyond erythropoiesis: emerging metabolic roles of erythropoietin. Diabetes, 63(7), 2229-31.
Sfacteria, A. (2015). Insights into erythropoietin in veterinary oncology: the other side of the coin. Veterinary Journal, 206(3), 247-248.
Meyer, F. R. L., Steinborn, R., Grausgruber, H., Wolfesberger, B., & Walter, I. (2015). Expression of platelet-derived growth factor bb, erythropoietin and erythropoietin receptor in canine and feline osteosarcoma. Veterinary Journal, 206(1), 67-74.
Guo, L., Luo, T., Fang, Y., Yang, L., Wang, L., & Liu, J., et al. (2014). Effects of erythropoietin on osteoblast proliferation and function. Clinical & Experimental Medicine, 14(1), 69-76.
Hiram-Bab., S. Hiram-Bab, T. Liron, N. Deshet-Unger, et al. (2015) Erythropoietin directly stimulates osteoclast precursors and induces bone loss. The FASEB Journal, 29, pp. 1890-1900.

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