Genetic and Acquired Lysosomal Disorders Drive Susceptibility to Tuberculosis by Compromising Macrophage Migration

A zebrafish forward genetic screen for determinants of susceptibility to Mycobacterium marinum identified a hypersusceptible mutant deficient in the lysosomal hydrolase Cathepsin L that manifests the hallmarks of human lysosomal storage diseases. In uninfected mutants, macrophages progressively accumulate undigested material in their lysosomes, leading to impaired migration and the accumulation of unengulfed cell debris. During mycobacterial infection, these vacuolated macrophages cannot migrate to phagocytose infected macrophages undergoing apoptosis in the tuberculous granuloma. Consequently, unengulfed apoptotic macrophages undergo secondary necrosis causing granuloma breakdown and increased mycobacterial growth. Macrophage lysosomal accumulations similarly impair migration to newly infecting mycobacteria. We find that important aspects of this phenotype are recapitulated in human smokers, who are at increased risk for tuberculosis. A majority of alveolar macrophages from smokers exhibit lysosomal accumulations and do not migrate to Mycobacterium tuberculosis. This incapacitation of highly microbicidal first-responding macrophages may contribute to smokers' susceptibility to tuberculosis. Overall design: A forward genetic screen for zebrafish larvae that are hypersusceptible to Mycobacterium marinum infection identified a mutation in the transcription factor snapc1b at 13: 37996163 (T->C). Individuals of wild type (T/T) and mutant (C/C) were genotyped and pooled respectively for RNA isolation and transcriptome analysis.

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Berg RD, Levitte S, O'Sullivan MP, O'Leary SM, Cambier CJ, Cameron J, Takaki KK, Moens CB, Tobin DM, Keane J, Ramakrishnan L