Hypoxia Shapes Autophagy in LPS-Activated Dendritic Cells.

Sara Monaci,Cristina Ulivieri,Daniela Rossi,Silvano Sozzani,Fabio Carraro,Gaia Giuntini,Giuseppe Marotta,Carlo Aldinucci,Irene Filippi,Antonella Naldini

doi:10.3389/fimmu.2020.573646

Sara Monaci, Cristina Ulivieri + Show 8 more

Open Access

https://doi.org/10.3389/fimmu.2020.573646

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Abstract

During their lifespan, dendritic cells (DCs) are exposed to different pO2 levels that affect their differentiation and functions. Autophagy is one of the adaptive responses to hypoxia with important implications for cell survival. While the autophagic machinery in DCs was shown to impact signaling of TLRs, its regulation by the MD-2/TLR4 ligand LPS is still unclear. The aim of this study was to evaluate whether LPS can induce autophagy in DCs exposed to either aerobic or hypoxic conditions. Using human monocyte-derived DCs and the combination of immunofluorescence confocal analysis, measure of mitochondrial membrane potential, Western blotting, and RT-qPCR, we showed that the ability of LPS to modulate autophagy was strictly dependent upon pO2 levels. Indeed, LPS inhibited autophagy in aerobic conditions whereas the autophagic process was induced in a hypoxic environment. Under hypoxia, LPS treatment caused a significant increase of functional lysosomes, LC3B and Atg protein upregulation, and reduction of SQSTM1/p62 protein levels. This selective regulation was accompanied by activation of signalling pathways and expression of cytokines typically associated with DC survival. Bafilomycin A1 and chloroquine, which are recognized as autophagic inhibitors, confirmed the induction of autophagy by LPS under hypoxia and its impact on DC survival. In conclusion, our results show that autophagy represents one of the mechanisms by which the activation of the MD-2/TLR4 ligand LPS promotes DC survival under hypoxic conditions.

Highlights

Tissue hypoxia occurs in many physiological and pathological conditions, including lymphoid organs, inflammation, and cancer [1, 2]
In this paper we described for the first time how hypoxia may affect Dendritic cells (DCs) autophagy, with particular regard to DC final maturation induced by the MD-2/TLR4 ligand LPS [50]
In the same study, when hypoxic DCs were maturated with LPS, we did not observe an increase in cell death, while hypoxia inducible factors (HIFs)-1a accumulation and BNIP3 expression were still significantly upregulated

Summary

Introduction

Tissue hypoxia occurs in many physiological and pathological conditions, including lymphoid organs, inflammation, and cancer [1, 2]. Hypoxia and Dendritic Cell Autophagy hypoxic areas, represented by immunological niches [5]. Dendritic cells (DCs) are the most effective antigen presenting cells and, based on their differentiation and maturation states, they can be represented as immature and mature [6]. Immature DCs circulate through tissues and lymphoid organs, while mature DCs are deputed to initiate the innate and adaptive immune response [7]. Many of the adaptive responses to hypoxia are mediated by a family of transcription factors known as hypoxia inducible factors (HIFs) [13] and include modulation of glycolytic metabolism, cell survival and migration, pro-angiogenic cytokines, and pro- and anti-apoptotic molecules [14, 15]. Autophagy is a complex self-degradative process that involves several key steps [19]

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