[Effect of erythropoietin on proinflammatory factors of human monocytes and its mechanisms].

Erythropoietin (EPO) is the major means of treating anemia of chronic disease (ACD) through stimulating hematopoiesis, inhibiting hepcidin and decreasing proinflammatory factors. Recently, it has been found that monocytes are another source of hepcidin. EPO can reduce the hepcidin stimulated by IL-6 in monocytes, it is assumed that EPO can reduce hepcidin indirectly by reducing IL-6. However, the specific mechanism of EPO inhibiting the proinflammatory cytokines in monocytes is unclear now. This study was purposed to investigate the effect of EPO on monocyte proinflammatory factors and its molecular mechanism. IL-6 mRNA and TNF-α mRNA were detected by real time PCR, level of signaling molecule PARP-1 protein was detected by Western blot. THP-1 monocytes were stimulated by 1 µg/ml lipopolysaccharide (LPS) to observe the impact of EPO at different concentrations (0.5, 1, 2, 5, 10 U/ml) for different time (0, 3, 6, 12, 24 hours) on the expression of IL-6 mRNA, TNF-α mRNA and PARP-1 protein. 1 µg/ml or 5 µg/ml EPO receptor (EPOR) antibody and/or 3-aminobenzamide (3-AB, PARP-1 inhibitor) were added to observe the antagonistic effect on EPO and the impact on PARP-1. The results showed that LPS could stimulate the THP-1 cells. EPO could decrease the levels of IL-6 and TNF-α stimulated by LPS in a dose- and time-dependent manners. The most significant decrease in IL-6 mRNA expression was observed in 2 U/ml EPO for 6 hours. And down-regulation of TNF-α mRNA expression was pronounced at 10 U/ml EPO for 3 hours. IL-6 mRNA expression could be stimulated by LPS, PARP-1 protein was induced at the same time. EPO inhibited the expression of IL-6 mRNA, while PARP-1 protein also decreased. Down-regulation of IL-6 mRNA and PARP-1 protein level was pronounced at 2 U/ml EPO for 6 hours. 3AB is a direct inhibitor of PARP-1. Similar to 3AB, EPO receptor antibody could antagonize the decline of IL-6 induced by EPO. It is concluded that EPO can inhibit the expression of IL-6 and TNF-α in monocytes, and the inhibition of IL-6 expression may be associated with decrease of PARP level.