The N-glycosyltransferase ST6GAL1 plays a key role in M2 macrophage anti-inflammatory functions

Abstract Macrophages are effector cells of the innate immune system, and play distinct roles depending on their polarization state. Glycosylation is a ubiquitous post translational modification made to proteins that plays a large role in protein biophysical properties and function. Through computational analysis of a publicly available macrophage transcriptome data set, we demonstrated that glycosylation changes dramatically across different macrophage polarizations. Specifically, we identified the gene coding for the glycosyltransferase ST6GAL1, which terminally sialylates protein glycans, as significantly differentially expressed across macrophage polarities. ST6GAL1 was downregulated in macrophages polarized by M1 polarizing signals TNFa and TNFa+IFNg and upregulated by M2 polarizing signals IL-4 and IL-13. We hypothesized that changes in terminal sialic acid frequency during glycosylation play a role in M2 macrophage immunosuppressive actions. An analysis of SIGLEC signaling pathways revealed that increasing ST6GAL1 expression was concordant with increasing CD52 expression, a ligand for SIGLEC10. SIGLEC proteins contain an immunoreceptor tyrosine-based inhibitory motif (ITIM) which inhibits immune action upon activation. SIGLEC10 expression increased in both M1 and M2 polarized macrophages, suggesting a possible mode of immunosuppression regulated by ST6GAL1. The increased frequency of terminally sialylated glycans and CD52 on M2 surfaces may increase the frequency with which M2 macrophages bind to and activate SIGLEC proteins on other immune cells. To test this hypothesis, we will knockout and amplify M2 macrophage ST6GAL1 expression to determine its influence on M2 immunosuppressive capacity.