Mycobacterial virulence factor CpsA activates type I IFN signaling in macrophages via cGAS-mediated cytosolic DNA sensing

Type I IFN production is known to mediate tuberculosis pathogenesis. While sensing the host mitochondrial and nuclear DNA in the cytosol has been identified as a key host innate mechanism responsible for the cytokine expression, bacterial factors that initiate this process are incompletely understood. CpsA, a secreted protein of Mycobacterium marinum (Mm) and Mycobacterium tuberculosis (Mtb), plays a key role in maintaining bacterial cell wall integrity and inhibiting host cell phagocytosis. Here, we demonstrated that CpsA is essential for infection-induced pathology and type I IFN production. CpsA deficiency impaired type I IFN expression and secretion in the infected mouse macrophages in vitro as well as zebrafish and mice in vivo. Noteably, the CpsA-induced type I IFN production was diminished in Cgas knockout macrophages, and the levels of TBK1 and IRF3 phosphorylation were significantly decreased in macrophages infected with CpsA-deficient bacterial strain, suggesting cGAS-TBK1-IRF3 pathway is involved in CpsA-induced type I IFN production. Moreover, we further show that the bacterial DNA released into the cytosol was comparable between macrophages infected with wild-type and CpsA-deficient strains, whereas mitochondrial and nuclear DNA decreased greatly in macrophages infected with the mutant strain. The decreased cytosolic DNA was correlated with the impaired phagosomal membrane rupture. Together, our results uncovered a novel role of mycobacterial CpsA in type I IFN production and provide a new molecular basis for mycobacterial infection induced pathology