M. tuberculosis infection of human iPSC-derived macrophages reveals complex membrane dynamics during xenophagy evasion

Xenophagy is an important cellular defence mechanism against cytosol-invading pathogens, such as Mycobacterium tuberculosis (Mtb). Activation of xenophagy in macrophages targets Mtb to autophagosomes; however, how Mtb is targeted to autophagosomes in human macrophages at a high spatial and temporal resolution is unknown. Here, we use human induced pluripotent stem cell-derived macrophages (iPSDMs) to study the human macrophage response to Mtb infection and the role of the ESX-1 type VII secretion system. Using RNA-seq, we identify ESX-1-dependent transcriptional responses in iPSDMs after infection with Mtb. This analysis revealed differential inflammatory responses and dysregulated pathways such as eukaryotic initiation factor 2 (eIF2) signalling and protein ubiquitylation. Moreover, live-cell imaging revealed that Mtb infection in human macrophages induces dynamic ESX-1-dependent, LC3B-positive tubulovesicular autophagosomes (LC3-TVS). Through a correlative live-cell and focused ion beam scanning electron microscopy (FIB SEM) approach, we show that upon phagosomal rupture, Mtb induces the formation of LC3-TVS, from which the bacterium is able to escape to reside in the cytosol. Thus, iPSDMs represent a valuable model for studying spatiotemporal dynamics of human macrophage-Mtb interactions, and Mtb is able to evade capture by autophagic compartments. This article has an associated First Person interview with the first author of the paper.

Automated summary

Xenophagy is an important defense mechanism in macrophages against pathogens like Mycobacterium tuberculosis, and the ESX-1 secretion system plays a critical role in inducing autophagosome formation and facilitating the escape of bacteria into the cytosol during infection. The study utilized human induced pluripotent stem cell-derived macrophages to investigate the spatiotemporal dynamics of the interaction between human macrophages and Mtb, revealing specific transcriptional responses and pathways dysregulated by Mtb infection.