Galectin-8 Senses Phagosomal Damage and Recruits Selective Autophagy Adapter TAX1BP1 To Control Mycobacterium tuberculosis Infection in Macrophages

Mycobacterium tuberculosis (Mtb) causes one of the deadliest infectious diseases worldwide. Upon infection, Mtb is phagocytosed by macrophages and uses its virulence-associated ESX-1 secretion system to modulate the host cell. We showed previously that the ESX-1 secretion system perturbs the Mtb-containing phagosome, and a population (∼30%) of intracellular Mtb is tagged with ubiquitin and targeted to selective autophagy. However, our understanding of how macrophages sense and respond to damaged Mtb-containing phagosomes remains incomplete. Here, we demonstrate that several cytosolic glycan-binding proteins called galectins recognize Mtb-containing phagosomes; in macrophage cell lines and in primary macrophages, galectin-3, -8, and -9 are all recruited to the same Mtb population that colocalizes with selective autophagy markers (ubiquitin, p62, and LC3). To test whether galectins are required for controlling Mtb replication in macrophages, we generated CRISPR/Cas9 knockouts and found that galectin-8 −/− and galectin-3/8/9 −/− macrophages were similarly defective in targeting Mtb to selective autophagy and controlling replication. This suggests galectin-8 plays a unique role in anti-Mtb autophagy. In investigating galectin-8's role, we identified a novel and specific interaction between galectin-8 and the selective autophagy adapter TAX1BP1 and found that this galectin-8/TAX1BP1 interaction was necessary for macrophages to efficiently target Mtb to selective autophagy. Remarkably, overexpressing galectin-8 increased targeting of Mtb to autophagy and limited Mtb replication. Taken together, these data demonstrate that while several galectins are capable of recognizing damaged Mtb-containing phagosomes, galectin-8 plays a privileged role in recruiting downstream autophagy machinery and may represent a promising target for host-directed tuberculosis therapies.