Gal-1 is a multifunctional lectin involved in the modulation of immune responses. Using animal models of autoimmunity and chronic inflammation Gal-1 has been shown to have anti- as well as pro-inflammatory properties. Here, a model of rat experimental autoimmune orchitis (EAO) was used to investigate the role of Gal-1 in chronic testicular inflammation. EAO is characterized by leukocytic infiltration in the interstitium, spermatogenic damage and elevated production of inflammatory mediators like TNFa and MCP-1. In normal rat testis Gal-1 is predominantly expressed in Sertoli and germ cells. In extracts from inflamed testes a significant downregulation of Gal-1 mRNA and protein expression was observed. In contrast, relative expression of Gal-1 mRNA normalized to SOX9, a Sertoli cell marker, was not significantly changed. This suggests that downregulation of Gal-1 in the EAO testis is the consequence of germ cell loss. In order to investigate an influence of Gal-1 on the immune properties of Sertoli cells, primary cells were isolated and challenged with the pro-inflammatory cytokine TNFa. Subsequently, Gal-1 expression was found to be upregulated. However, binding of the lectin SNA to Sertoli cells was increased as shown by flow cytometry. SNA is recognizing terminal a-2-6-sialic acid residues that block binding of Gal-1. In contrast, binding of L-PHA, that is recognizing ß-1-6-branching of complex N-glycans, was downregulated in TNFa challenged Sertoli cells. These findings suggest that under inflammatory conditions the glycan composition on the Sertoli cell plasma membrane becomes less favorable for Gal-1 binding so that excessive immune reactions elicited by concerted action of TNFa and Gal-1 in sterile testicular inflammations may be dampened.Gal-1 and TNFa synergistically increased expression of pro-inflammatory mediators such as MCP1, IL-1a, and IL-6 when applied to primary Sertoli cells. These effects were abrogated when Gal-1 binding was blocked by preincubation with the galactose containing disaccharide lactose. Combined stimulation of Sertoli cells with Gal-1 and TNFa lead to enhanced phosphorylation of MAP kinases p38 and JNK as compared to TNFa alone, whereas Gal-1 alone did not activate MAPK signaling. In addition, treatment of Sertoli cells with p38 and JNK inhibitors abrogated Gal-1 and TNFa induced expression of IL-1a, TNFa, IL-6 and MCP-1 mRNAs. These data show that Gal-1 enhances the pro-inflammatory activity of TNFa on Sertoli cells via stimulation of MAPK signaling.
