Mycobacterium\nLacI-type Transcription Regulator Rv3575c\nAffects Host Innate Immunity by Regulating Bacterial <i>mce4</i> Operon-Mediated Cholesterol Transport

Mycobacterium tuberculosis has evolved\na highly specialized system to snatch essential nutrients from its\nhost, among which host-derived cholesterol has been established as\none main carbon source for M. tuberculosis to survive within granulomas. The uptake, catabolism, and utilization\nof cholesterol are important for M. tuberculosis to sustain within the host largely via remodeling of the bacterial\ncell walls. However, the regulatory mechanism of cholesterol uptake\nand its impact on bacterium fate within infected hosts remain elusive.\nHere, we found that M. tuberculosis LacI-type transcription regulator Rv3575c negatively regulates its <i>mce4</i> family gene transcription. Overexpression of <i>Rv3575c</i> impaired the utilization of cholesterol as the sole\ncarbon source by Mycobacterium smegmatis, activating the host’s innate immune response and triggering\ncell pyroptosis. The M. smegmatis homologue\nof <i>Rv3575c MSMEG6044</i> knockout showed enhanced hydrophobicity\nand permeability of the cell wall and resistance to ethambutol, suppressed\nthe host innate immune response to M. smegmatis, and promoted the survival of M. smegmatis in macrophages and infected mouse lungs, leading to reduced transcriptional\nlevels of TNFα and IL-6. In summary, these data indicate a role\nof <i>Rv3575c</i> in the pathogenesis of mycobacteria and\nreveal the key function of <i>Rv3575c</i> in cholesterol\ntransport in mycobacteria.