Mito-xenophagic killing of bacteria is coordinated by a metabolic switch in dendritic cells

Nadine Radomski,Danny Kägebein,Elisabeth Liebler-Tenorio,Birke Andrea Tews,Axel Karger,Elke Rufer,Rebekka Einenkel,Michael R Knittler,Anne Müller,Annica Rebbig,Stefanie Nagel

doi:10.1038/s41598-017-04142-5

Abstract

Chlamydiae are bacterial pathogens that grow in vacuolar inclusions. Dendritic cells (DCs) disintegrate these compartments, thereby eliminating the microbes, through auto/xenophagy, which also promotes chlamydial antigen presentation via MHC I. Here, we show that TNF-α controls this pathway by driving cytosolic phospholipase (cPLA)2-mediated arachidonic acid (AA) production. AA then impairs mitochondrial function, which disturbs the development and integrity of these energy-dependent parasitic inclusions, while a simultaneous metabolic switch towards aerobic glycolysis promotes DC survival. Tubulin deacetylase/autophagy regulator HDAC6 associates with disintegrated inclusions, thereby further disrupting their subcellular localisation and stability. Bacterial remnants are decorated with defective mitochondria, mito-aggresomal structures, and components of the ubiquitin/autophagy machinery before they are degraded via mito-xenophagy. The mechanism depends on cytoprotective HSP25/27, the E3 ubiquitin ligase Parkin and HDAC6 and promotes chlamydial antigen generation for presentation on MHC I. We propose that this novel mito-xenophagic pathway linking innate and adaptive immunity is critical for effective DC-mediated anti-bacterial resistance.

Highlights

Chlamydiae are Gram-negative obligate intracellular bacteria that infect mainly epithelial mucosae, causing a broad spectrum of diseases in humans and animals[1]
We proposed that autophagy constitutes a critical pathway in the intracellular defence against chlamydia in infected dendritic cells (DCs)
Fig. S1D) revealed no detectable differences between infected and non-infected DCs before and after Beclin-1 and Atg[7] silencing. This suggests that the reduced CD8+ T cell stimulation by autophagy factor-silenced DCs is clearly not caused by defective surface expression of MHC I or coregulatory molecules, or disturbed TNF-α secretion required for functional DC maturation

Summary

Introduction

Chlamydiae are Gram-negative obligate intracellular bacteria that infect mainly epithelial mucosae, causing a broad spectrum of diseases in humans and animals[1]. Chlamydiae induce cell-mediated immune responses in humans and mice[3]. DCs are among the first professional antigen presenting cells (APCs) encountered by chlamydia[4], and cytotoxic CD8+ T cells, primed by infected DCs, likely play an important role in the effective anti-chlamydial immune response[3]. A membrane called phagophore engulfs cytosolic content and isolates it into a sealed double membrane-bound autophagosome. We previously established a mouse model for non-avian C. psittaci infection[6] and identified an autophagy-dependent immune defence pathway in DCs, in which chlamydial antigens are generated via autophagosomal degradation of cytosolically released microbes following host-mediated disruption of their inclusions[6]. We further identify a TNF-α/cPLA2/ AA axis involved in regulating this pathway and the components of the autophagy machinery responsible for executing this process

Methods

Results

Conclusion