A genome-wide screen in macrophages identifies PTEN as required for myeloid restriction ofListeria monocytogenesinfection

Abstract

AbstractListeria monocytogenes(Lm) is an intracellular foodborne pathogen which causes the severe disease listeriosis in immunocompromised individuals. Macrophages play a dual role duringLminfection by both promoting dissemination ofLmfrom the gastrointestinal tract and limiting bacterial growth upon immune activation. Despite the relevance of macrophages toLminfection, the mechanisms underlying phagocytosis ofLmby macrophages are not well understood. To identify host factors important forLminfection of macrophages, we performed an unbiased CRISPR/Cas9 screen which revealed pathways that are specific to phagocytosis ofLmand those that are required for internalization of bacteria generally. Specifically, we discovered the tumor suppressor PTEN promotes macrophage phagocytosis ofLmandL. ivanovii, but not other Gram-positive bacteria. Additionally, we found that PTEN enhances phagocytosis ofLmvia its lipid phosphatase activity by promoting adherence to macrophages. Using conditional knockout mice lackingPtenin myeloid cells, we show that PTEN-dependent phagocytosis is important for host protection during oralLminfection. Overall, this study provides a comprehensive identification of macrophage factors involved in regulatingLmuptake and characterizes the function of one factor, PTEN, duringLminfectionin vitroandin vivo. Importantly, these results demonstrate a role for opsonin-independent phagocytosis inLmpathogenesis and suggest that macrophages play a primarily protective role during foodborne listeriosis.Author SummaryListeria monocytogenes(Lm) is a bacterial pathogen that causes the foodborne illness listeriosis primarily in immunocompromised, elderly, and pregnant individuals. Listeriosis is one of the deadliest bacterial infections known, with a mortality rate of ~30% even when treated with antibiotics. The high mortality rate of listeriosis is due to inefficient restriction ofLmby the immune system, and subsequent spread of bacteria beyond the gastrointestinal tract to internal organs such as the liver and brain. Macrophages are important for immune clearance ofLmbut are also hypothesized to promote dissemination of intracellularLm; thus, studies ofLm-macrophage interactions are critical for understanding the balance between bacterial growth and restriction by these phagocytes. We performed a forward genetic screen in macrophages and discovered that the tumor suppressor PTEN promotes phagocytosis ofLmby enhancing adherence to macrophages. These results demonstrate a novel function of macrophage PTEN, which canonically acts as a repressor of phagocytosis. In addition, we found that PTEN protects mice from severe disease and lowers bacterial burdens following oral inoculation ofLm. Our results demonstrate for the first time that macrophage phagocytosis is an important immune defense against invasiveLmduring the foodborne route of infection.