The TRPM4 channel controls monocyte and macrophage, but not neutrophil, function for survival in sepsis

A favorable outcome following acute bacterial infection depends on the ability of phagocytic cells to be recruited and properly activated within injured tissues. Calcium (Ca²⁺) is a ubiquitous second messenger implicated in the functions of many cells, but the mechanisms involved in the regulation of Ca²⁺ mobilization in hematopoietic cells are largely unknown. The monovalent cation channel transient receptor potential melastatin (TRPM) 4 is involved in the control of Ca²⁺ signaling in some hematopoietic cell types, but the role of this channel in phagocytes and its relevance in the control of inflammation remain unexplored. In this study, we report that the ablation of the Trpm4 gene dramatically increased mouse mortality in a model of sepsis induced by cecal ligation and puncture. The lack of the TRPM4 channel affected macrophage population within bacteria-infected peritoneal cavities and increased the systemic level of Ly6C⁺ monocytes and proinflammatory cytokine production. Impaired Ca²⁺ mobilization in Trpm4^-/- macrophages downregulated the AKT signaling pathway and the subsequent phagocytic activity, resulting in bacterial overgrowth and translocation to the bloodstream. In contrast, no alteration in the distribution, function, or Ca²⁺mobilization of Trpm4 ^-/- neutrophils was observed, indicating that the mechanism controlling Ca²⁺ signaling differs among phagocytes. Our results thus show that the tight control of Ca²⁺ influx by the TRPM4 channel is critical for the proper functioning of monocytes/macrophages and the efficiency of the subsequent response to infection.