The role of Ndfip1 in macrophage-mediated bacterial clearance

Abstract

Abstract Macrophages are essential components of the innate immune response to bacteria. While these cells must mount an inflammatory response to harmful pathogens, they require tight regulation to prevent host damage. One way in which macrophages attenuate inflammatory signaling cascades is through ubiquitination. This post-translational modification can target a protein substrate for downstream signaling or for degradation. E3 ubiquitin ligases are required to facilitate the formation of these chains. Nedd4-family interacting protein 1 (Ndfip1) activates multiple E3 ubiquitin ligases, including Itch, which is crucial for attenuating cytokine production by T cells, and Nedd 4-2, which is required for iron regulation by neurons. While Itch has been shown to limit macrophage activity, it is unclear how Ndfip1 functions in macrophages, and how it affects macrophage antibacterial responses. We generated mice lacking Ndfip1 in myeloid cells (Ndfip1fl/fl LysM Cre). Unlike mice lacking Ndfip1 in T cells, these mice have no evidence of inflammation at baseline. Upon i.n. infection with Klebsiella pneumoniae, Ndfip1 fl/fl LysM Cre mice show reduced bacterial loads three days post infection, despite normal innate cell recruitment. This result could be recapitulated when mice were infected intraperitoneally. Peritoneal macrophages lacking Ndfip1 have unchanged cytokine responses when stimulated with K. pneumonia, suggesting Ndfip1 attenuates macrophage activity through a mechanism other than limiting cytokine production. This project may reveal new mechanisms used by myeloid cells in eliminating bacteria, providing insight into the regulatory mechanisms that prevent excess inflammation.