The N-terminal domain of Chlamydia psittaci Pmp19G modulates macrophage autophagy by targeting the NOD1 receptor and the ATG16L1-RAB7 signaling pathway.

INTRODUCTION: Chlamydia psittaci (C. psittaci), a zoonotic intracellular Gram-negative bacterium, is responsible for human infections presenting as flu-like fever and community-acquired pneumonia. Previous studies have implicated polymorphic membrane (Pmp) G in tissue tropism and induction of immune responses. However, the mechanisms by which Pmp19G promotes C. psittaci infection and immune evasion-especially via macrophage subversion remain poorly understood.

METHODS AND RESULTS: This study demonstrates that both C. psittaci and recombinant C. psittaci-specific Pmp19G protein activated autophagy in macrophages. This activation was characterized by increased autophagosome formation, conversion of LC3-I to LC3-II, and accumulation of p62/SQSTM1, while lysosomal associated membrane protein 1 (LAMP1), a late autophagy biomarker, remained unaffected. Utilizing pull-down assays coupled with co-immunoprecipitation, we identified the NOD1 receptor as an interactor with the N-terminal domain of Pmp19G. Subsequent analysis confirmed activation of the NOD1-ATG16L1 signaling pathway. NOD1 knockout or knockdown significantly impaired Pmp19G-mediated autophagic flux. Furthermore, treatment with Pmp19G enhanced the recruitment of RAB7 during the late stages of autophagy.

DISCUSSION: Our findings indicate that Pmp19G regulates macrophage autophagy through distinct mechanisms in early and late phases: activation of the NOD1-ATG16L1 signaling pathway initiates early autophagy, while enhanced RAB7 recruitment inhibits autophagosome-lysosome fusion during late autophagy. Collectively, Pmp19G-involved manipulation of the autophagic process represents a critical strategy employed by C. psittaci to evade host immune defenses, leading bacterial survival and spread.