Galectin-8 senses phagosomal damage and recruits selective autophagy adapter TAX1BP1 to control Mycobacterium tuberculosis infection in macrophages
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ABSTRACTMycobacterium tuberculosis (Mtb) infects a quarter of the world and causes the deadliest infectious disease worldwide. Upon infection, Mtb is phagocytosed by macrophages and uses its virulence-associated ESX-1 secretion system to modulate the host cell and establish a replicative niche. We have previously shown the ESX-1 secretion system permeabilizes the Mtb-containing phagosome and that a population (~30%) of intracellular Mtb are recognized within the cytosol, tagged with ubiquitin, and targeted to the selective autophagy pathway. Despite the importance of selective autophagy in controlling infection, the mechanisms through which macrophages sense and respond to damaged Mtb-containing phagosomes remains unclear. Here, we demonstrate that several cytosolic glycan-binding proteins, known as galectins, recognize Mtb-containing phagosomes. We found that galectins-3, -8, and -9 are all recruited to the same Mtb population that colocalizes with selective autophagy markers like ubiquitin, p62, and LC3, which indicates Mtb damages its phagosomal membrane such that cytosolic host sensors can recognize danger signals in the lumen. To determine which galectins are required for controlling Mtb replication in macrophages, we generated CRISPR/Cas9 knockout macrophages lacking individual or multiple galectins and found that galectin-8-/- and galectin-3/8/9-/- knockout macrophages were similarly defective in targeting Mtb to selective autophagy and controlling replication, suggesting galectin-8 plays a privileged role in anti-Mtb autophagy. In investigating this specificity, we identified a novel and specific interaction between galectin-8 and TAX1BP1, one of several autophagy adaptors that bridges cargo and LC3 during the course of autophagosome formation, and this galectin-8/TAX1BP1 interaction was necessary to efficiently target Mtb to selective autophagy. Remarkably, overexpressing individual galectins increased targeting of Mtb to antibacterial autophagy and limited Mtb replication. Taken together, these data imply that galectins recognize damaged Mtb-containing phagosomes, recruit downstream autophagy machinery, and may represent promising targets for host-directed therapeutics to treat Mtb.
