α2-3 Sialic acid binding and uptake by human monocyte-derived dendritic cells alters metabolism and cytokine release and initiates tolerizing T cell programming

Abstract

Dendritic cells (DCs) are key in the initiation of the adaptive T cell responses to tailor adequate immunity that corresponds to the type of pathogen encountered. Oppositely, DCs control the resolution phase of inflammation and are able to induce tolerance after receiving anti-inflammatory cytokines or upon encounter of self-associated molecular patterns, such as α2-3 linked sialic acid(α2-3sia). We here investigated whether α2-3sia, that bind immune inhibitory Siglec receptors, would alter signaling and reprogramming of LPS-stimulated human monocyte-derived DCs(moDCs). Transcriptomic analysis of moDCs stimulated with α2-3sia conjugated dendrimers revealed differentially expressed genes related to metabolic pathways, cytokines and T cell differentiation. An increase in genes involved in ATPase regulator activity, oxidoreductase activity and glycogen metabolic processes was detected. Metabolic extracellular flux analysis confirmed a more energetic moDC phenotype upon α2-3sia binding as evidenced by an increase in both glycolysis and mitochondrial oxidative phosphorylation. TH1 differentiation promoting genes IFNL and IL27, were significantly downregulated in the presence of α2-3sia. Functional assays confirmed that α2-3sia binding to moDCs induced phosphorylation of Siglec-9, reduced production of inflammatory cytokines IL-12 and IL-6, and increased IL-10. Surprisingly, α2-3sia-differentiated moDCs promoted FoxP3 +CD25 +/-CD127 - regulatory T cell differentiation and decreased FoxP3 -CD25 -CD127 - effector T cell proliferation. In conclusion, we demonstrate that α2-3sia binding to moDCs, phosphorylates Siglec-9, alters metabolic pathways, cytokine signaling and T cell differentiation processes in moDCs and promotes regulatory T cells. The sialic acid-Siglec axis on DCs is therefore, a novel target to induce tolerance and to explore for immunotherapeutic interventions aimed to restore inflammatory processes.

Inhibitory Siglec-sialic acid interactions in balancing immunological activation and tolerance during viral infections

“… 45 Consistently, the binding between Siglec-9 on the surface of lipopolysaccharides (LPS)-stimulated human monocyte-derived DCs and α2,3 sialic acid has multiple, tumor-supportive effects: it alters these cells’ metabolism, reduces their expression of inflammatory cytokines, induces their expression of anti-inflammatory cytokines, and induces T reg differentiation at the expense of effector T cell differentiation. 46 …”

Droplet‐Based Glycan and RNA Sequencing for Profiling the Distinct Cellular Glyco‐States in Single Cells

“…Our analysis uncovered the connections between glycan expressions and immune cell functions (Figures S17-S21, Supporting Information). Among the known associations, the p1 component had high weights for the Sia-binders (rACG, MAL, WGA), which were associated with gene sets involved in the differentiation of immune cells (from monocyte to DC) [26][27][28] (Figure S17, Supporting Information). The p2 component had a high weight for the Fuc-binders (TJAII, rAOL), which were associated with monocyte functions (Figure S17, Supporting Information).…”

N-Glycosylation and Inflammation; the Not-So-Sweet Relation

“…have recently demonstrated an alternative pathway for the induction of tolerance by DCs independent of their sialylation status, driven by the immunoregulatory sialic acid-siglec axis. Specifically, binding of α2-3-sialic acid to Siglec-9 expressed on the surface of DCs alters metabolic pathways and cytokine signaling and reprograms DCs to enhance regulatory T cell/T helper type 1 (Treg : Th1) ratio balance ( 142 ). Collectively, these data highlight the importance of glycan recognition by DCs in controlling both inflammation and its resolution.…”

“…Sialylation of antigens has been shown to cause a shift in the differentiation of effector T cells toward tolerogenic Treg through the sialic acid-siglec axis on DCs. This could open a new way to treat patients suffering from autoimmune diseases or allergies ( 142 , 185 ). Finally, another important glycosylation trait on T cells that is altered in chronic inflammation is fucosylation.…”