Effect And Mechanism Of Activin A And LPS On Activation Of Mouse Peritoneal Macrophages

Activin A, a number of the transforming growth factor-β (TGF-β) superfamilyof cytokines, is an inhibitor of lipopolysaccharide (LPS)-activated macrophages,which is also known as restrictin-P. Our previous studies confirm that LPS canstimulate macrophages to produce high levels of activin A, which can inhibit theactivation of macrophages caused by LPS in turn. Nevertheless, the mechanism thatactivin A inhibit the LPS-activated macrophages is not fully understood. The mainpurpose of this study is to investigate the effect and mechanism of activin A and LPSon activation of mouse peritoneal macrophages in vitro and in vivo.1. Effect of activin A and LPS on activation of cultured mouse peritonealmacrophages in vitroIn this research, we first detected the secretion and phagocytic function ofmacrophages. The results showed that LPS significantly promoted the secretion ofIL-1β, IL-10, TNF-α and NO of cultured mouse peritoneal macrophages in vitro;Activin A could promote the secretion of IL-10and NO but had little effect on thesecretion of IL-1β and TNF-α of macrophages. However, activin A could inhibitLPS-activated mouse peritoneal macrophages secreting IL-1β, IL-10, TNF-α and NO.Both activin A and LPS could promote the phagocytic activity of mouse peritonealmacrophages, while activin A could inhibit the phagocytic activity of LPS-activatedmouse peritoneal macrophages as well.In order to investigate the regulation mechanism of activin A activatingmacrophage function, we did further research on the Toll-like receptor2,4(TLR2,TLR4) and CD14expression on cultured mouse peritoneal macrophages in vitro.Results indicated that LPS observably increased TLR2, TLR4and CD14expressionon macrophages in vitro, and activin A had no obvious effect on TLR2, TLR4andCD14expression, but could significantly reduce the expression of TLR4onLPS-activated mouse peritoneal macrophages, with no apparent inhibitory effect onTLR2or CD14expression. 2. Effect of activin A and LPS on activation of mouse peritoneal macrophagesin vivoWhen the body comes into contact with foreign antigens, the macrophages willbe activated and these occur in vivo. Therefore, in order to define whether activin Aand LPS have the similar regulation effect and mechanism on macrophages in vivo,we continued to detect the corresponding indicators of activated macrophages invivo models. The data showed that LPS could markedly increase IL-10, TNF-α andNO levels in mouse peritoneal fluid while activin A had no obvious effect on TNF-αlevel. Yet activin A could significantly inhibit LPS-induced IL-10, TNF-α and NOproduction. Similar to the in vitro results, activin A and LPS could promote thephagocytic activity of mouse peritoneal macrophages in vivo, and activin A couldalso inhibit the phagocytic activity of LPS-activated peritoneal macrophage.Likewise, through the analysis of TLR2, TLR4and CD14expression onmacrophages surface, we found that LPS could significantly up-regulate TLR2,TLR4and CD14expression, while activin A significantly reduced TLR4expressionon LPS-activated mouse peritoneal macrophage, with no apparent inhibitory effecton TLR2or CD14expression.In conclusion, activin A can stimulate macrophage activation directly in bothvivo and vitro, but the cytokines secreted by activin A-activated macrophages aredifferent from those by LPS-activated macrophages, which may be related todifferent types of activated macrophages. On the other hand, activin A can inhibitLPS-activated macrophages function in both vitro and vivo, and also, can inhibit theexpression of TLR4on LPS-activated macrophages. This indicates that activin Amay deregulate LPS-activated macrophage function through LPS-TLR4pathway.The above studies suggest that activin A may increase the body’s defense capabilitiesby promoting macrophage phagocytosis in the early inflammatory response andprevent tissue damage by inhibiting the excessive activation of macrophages in thelate inflammatory response. Activin A plays a significant role in the macrophage-involved inflammation regulation.