NLRX1 Facilitates Histoplasma capsulatum-Induced LC3-Associated Phagocytosis for Cytokine Production in Macrophages

Abstract

LC3-associated phagocytosis (LAP) is an emerging non-canonical autophagy process that bridges signaling from pattern-recognition receptors (PRRs) to autophagic machinery. LAP formation results in incorporation of lipidated LC3 into phagosomal membrane (termed LAPosome). Increasing evidence reveals that LAP functions as an innate defense mechanism against fungal pathogens. However, the molecular mechanism involved and the consequence of LAP in regulating anti-fungal immune response remain largely unexplored. Here we show that Histoplasma capsulatum is taken into LAPosome upon phagocytosis by macrophages. Interaction of H. capsulatum with Dectin-1 activates Syk and triggers subsequent NADPH oxidase-mediated reactive oxygen species (ROS) response that is involved in LAP induction. Inhibiting LAP induction by silencing LC3α/β or treatment with ROS inhibitor impairs the activation of MAPKs-AP-1 pathway, thereby reduces macrophage proinflammatory cytokine response to H. capsulatum. Additionally, we unravel the importance of NLRX1 in fungus-induced LAP. NLRX1 facilitates LAP by interacting with TUFM which associates with autophagic proteins ATG5-ATG12 for LAPosome formation. Macrophages from Nlrx1−/− mice or TUFM-silenced cells exhibit reduced LAP induction and LAP-mediated MAPKs-AP-1 activation for cytokine response to H. capsulatum. Furthermore, inhibiting ROS production in Nlrx1−/− macrophages almost completely abolishes H. capsulatum-induced LC3 conversion, indicating that both Dectin-1/Syk/ROS-dependent pathway and NLRX1-TUFM complex-dependent pathway collaboratively contribute to LAP induction. Our findings reveal new pathways underlying LAP induction by H. capsulatum for macrophage cytokine response.

HPV16 drives cancer immune escape via NLRX1-mediated degradation of STING

“…We first characterized the role of NLRX1 in promoting autophagy in response to RNA virus infection (33). This autophagy-promoting function was later found to be also a central mechanism regulating bacteria-and fungi-host interactions (54,55). Now we show that the NLRX1-centered autophagy-promoting molecular complex keeps dsDNA virus-induced immune activation in check by increasing the turnover of autophagosome cargos that include STING.…”

NLRX1 is a key regulator of immune signaling during invasive pulmonary aspergillosis

“…Nlrx1 (NOD9) is a critical regulator of immune signaling, metabolism, autophagy, and cell death in response to viruses, bacteria, eukaryotes, cancer, autoimmunity, and tumors [15][16][17][18][19][20][21][22][23]. Nlrx1 functions as a negative regulator of innate immunity towards a number of DNA viruses and HIV-1 through endogenous binding to the DNA-Sensing adaptor STING.…”

“…Nlrx1 has been shown to directly bind to a number of pathogen and danger associated molecular patterns via its C-terminal three helix bundle resulting in enhanced immune signaling and inflammation [25,26]. Furthermore, Nlrx1 plays an important role in the killing of Histoplasma capsulatum through LC3-associated phagocytosis (LAP) via TUFM/ ATG5-ATG12 interactions [23]. A N-terminus targeting sequence has the ability to translocate NLRX1 to the mitochondria where it has been shown to also interact with ubiquinol-cytochrome c reductase core protein II (UQCRC2), a component of mitochondrial complex III [27].…”

Crosstalk Between Autophagy and Hypoxia-Inducible Factor-1α in Antifungal Immunity

“…Regarding Histoplasma capsulatum, the implication of LC3-associated phagocytosis (LAP) is still unclear as regulation of the autophagic host response is independent of Rubicon, a key regulator of LAP [ 53 ]. Upon infection, yeasts are ingested by innate immune cells.…”