Role of the UPR-glycosylation axis in activation of plasmacytoid dendritic cells

• Main Author: Ustymenko, Bárbara
• Publication Date: 2023
• Format: Master thesis
• Language: eng
• Source: Repositórios Científicos de Acesso Aberto de Portugal (RCAAP)
• Download full: http://hdl.handle.net/10773/41161
• topic: Plasmacytoid dendritic cells; Unfolded protein response; PERK; Glycosylation; Autoimmunity

Plasmacytoid dendritic cells (pDCs) play a crucial role in mediating the immune response against viral infections. Still, pDCs activity is also associated with several autoimmune diseases, such as Systemic Lupus Erythematosus (SLE), Systemic Sclerosis (SSc) or psoriasis, mostly due to their capacity to produce large amounts of type I interferon (IFN-I). Therefore, these cells display a large endoplasmic reticulum (ER) and Golgi. And in fact, pDCs unfolded protein response (UPR) is an important checkpoint for the synthesis and secretion of pro-inflammatory cytokines. Moreover, N-glycosylation influences and is influenced by the efficiency of cellular proteostasis. However, the interaction between UPR pathways and glycosylation remains underexplored. Alterations in Protein kinase R-like endoplasmic reticulum kinase (PERK) activity, a UPR sensor, and glycosylation pathways have been identified in autoimmune diseases where pDCs are dysregulated. Thus, this project aims to unravel the dynamics between the PERK axis and glycosylation in pDCs function. For that, we used CAL-1 cells, a pDC cell line, and PERK knockout (KO) CAL-1 cells as our cell models. The cells were activated with CL307, a Toll-like receptor 7 (TLR7) agonist. We found that upon PERK abrogation, CAL-1 cells response to TLR7 activation was significantly reduced. Despite that, no significant changes were observed in TLR7 expression or some proteins from the TLR7 signalling cascade. Flow cytometry analysis showed that CAL-1 cell surface is abundant in complex tri/tetra-antennary and sialylated glycans, typically found in higher organisms including humans. Moreover, there was a tendency for an increase in the expression of these glycan structures upon cellular stimulation with CL307. Interestingly, PERK abrogation promoted an upregulation in sialic acid expression, correlated with increased levels of β-galactoside α-2,6-sialyltransferase 1 (ST6GAL 1) mRNA detected in these cells. This increased sialylation might selectively contribute to changes in the activity of some proteins, including TLR7. With this project, we began by uncovering a complex interplay between UPR and glycosylation in pDCs function. Future studies must clarify how this crosstalk is regulated in pDCs and how it contributes to their activity in the context of autoimmune diseases.