Macrophages are functionally plastic and can thus play different roles in various microenvironments. Testis is an immune privileged organ, and testicular macrophages (TMs) show special immunosuppressive phenotype and low response to various inflammatory stimuli. However, the underlying mechanism to maintain the immunosuppressive function of TMs remains unclear. S100A9, a small molecular Ca2+ binding protein, is associated with the immunosuppressive function of macrophages. However, no related research is available about S100A9 in mouse testis. In the present study, we explored the role of S100A9 in TMs. We found that S100A9 was expressed in TMs from postnatal to adulthood and contributed to maintaining the immunosuppressive phenotype of TMs, which is associated with the activation of PI3K/Akt pathway. S100A9 treatment promotes the polarization of bone marrow-derived macrophages from M0 to M2 in vitro. S100A9 was significantly increased in TMs following UPEC-infection and elevated S100A9 contributed to maintain the M2 polarization of TMs. Treatment with S100A9 and PI3K inhibitor decreased the proportion of M2-type TMs in control and UPEC-infected mouse. Our findings reveal a crucial role of S100A9 in maintaining the immunosuppressive function of TMs through the activation of PI3K/Akt pathway, and provide a reference for further understanding the mechanism of immunosuppressive function of TMs.

Sphingosylphosphorylcholine (SPC) is a bioactive sphingolipid metabolite that can enhance wound healing. In an effort to find downstream effectors of SPC, we performed microarray analysis and found that the expression of the gene for connective tissue growth factor (CTGF) was significantly affected in human skin fibroblasts cultured in vitro. Northern blot analysis showed that SPC markedly induced CTGF mRNA expression in a dose-and time-dependent manner. Consistent with this result, Western blot analysis also showed that SPC significantly induced the CTGF production. Pretreatment with cycloheximide did not prevent the CTGF induction by SPC, indicating that SPC stimulates CTGF mRNA expression without the increased synthesis of a regulatory protein. Inhibition by pretreatment with Y27632, but not by PD98059 (a mitogen-activated protein kinase 1/2 inhibitor) and LY294002 (a phosphatidylinositol 3-kinase inhibitor), indicated that r-kinase pathway was involved in SPC-induced CTGF expression. Together, these results reveal the potential importance of CTGF induction as a downstream event in SPC-induced cellular responses.