Erythropoietin Is An Endogenous Protective Molecule In EAN

Inflammation is a protective reaction of the body which plays an important role indefensing and removing the pathogenic factors in vitro and in vivo. However,uncontrolled inflammatory response can also lead to the tissue injuries. Inflammatory injuryparticipates in various pathophysiological processes. On the other hand, inflammation caninduce endogenous feedback mechanisms to control and limit inflammation at a reasonablelevel. Therefore it is of great theoretical and practical significance to research theendogenous feedback mechanisms in inflammation so as to achieve more understandingand better treatment for inflammation.EPO is a glycoprotein cytokine synthesized and secreted by the kidney, and it is themost important hematopoietic stimulating hormone in the body. The function of EPO isreceptor-dependent. The EPO receptor or EPOR is expressed on cell surface ofhematopoietic progenitors, and the hematopoietic role of the EPO is mediated by EPORhomodimers. Recent studies have shown that the EPOR in not only expressed in thehematopoietic system, but also in many non-hematopoietic systems, for example in thenervous system. This finding suggests that in addition to the hematopoietic function, EPOmay have other biological activities. Actually, it has been discovered that EPO has a directcytoprotective effect in vitro and in vivo. Unlike the hematopoietic function, cytoprotectioneffect of EPO is mediated by a heterodimer com posed of EPOR and common β chain.More interestingly, EPOR is also found on the inflammatory cells such as macrophages andlymphocytes. This finding indicated EPO might have inflammation regulatoury activity andis an endogenous inflammation regulatory molecule.In our study an animal model of EAN was used. EAN inflammation is primarilymediated by CD4~+T cells and the disease is characterised by a single-phase andspontaneous recovery. Many endogenous protective mechanisms are involved in thespontaneous regression. This important feature allows us to study the potential endogenous protective mechanisms in EAN inflammation. In addition, inflammatory cells involved inEAN is relatively clear including lymphocytes, macrophages and Schwann cells, and itprovides a great convenience for us to study the inflammation componets of EAN.Here, the role of EPO in inflammation was studied in EAN. We studied the expressionof endogenous EPO in EAN inflammatory tissues. Then we researched the impacts of EPOon inflammatory cells in vitro. Finally, EAN rats were treated by EPO administration andthe therapeutic mechanisms was analysised.In the first part, EAN was induced by active immunization in Lewis rats. EndogenousEPO expression in peripheral nerves and lymph nodes was detected by Real-time PCR andimmunohistochemical assay. We found that endogenous EPO is significantly increased inEAN. This result indicats that endogenous EPO is induced in EAN.In the second part, the effects of EPO was analysed in vitro in macrophages, Schwanncells and lymphocytes. We found that in Schwann cells, EPO promoted cell proliferationand myelin secretion while reduced TNF-α and iNOS expression. In macrophages, EPOpromoted phagocytosis of macrophages and inhibited TNF-α and iNOS expression. Inlymphocytes, proliferation was inhibited by EPO. These results showed the cytoprotectiveand inflammation regulatory activities of EPO in vitro.In the third part, EPO was used in treating EAN rats and results showed EPO cansignificantly shortened the duration of EAN and reduced neuromotor dysfunction. EPOprotected nerve from demyelination, reduced inflammatory cell infiltration andpro-inflammation cytokine. FACS analysis showed that EPO significantly reduced the CD4~+T cells proportion in spleen PBMC and favoured Treg cells. PCR analysis of lymph nodeshowed that EPO reduced T-bet/ROR-γt but increased Foxp3expression. These resultssuggest that EPO potents a strong tissue-protective and inflammation-regulatory function invivo.In summary, our study showed that exprssion of endogenous EPO was increased inEAN and that EPO is an endogenous protective cytokine in EAN.