Transient Receptor Potential Melastatin 2 Regulates Phagosome Maturation and Is Required for Bacterial Clearance in Escherichia coli Sepsis.

Background: Transient receptor potential melastatin 2 is a Ca-permeable cation channel abundantly expressed in macrophages. Trpm2 mice showed exacerbated infection and mortality during polymicrobial sepsis, which is associated with inefficient bacterial killing in macrophages. However, the mechanism of transient receptor potential melastatin 2 regulating bacterial killing remains unknown.

Methods: Trpm2 mice were intraperitoneally injected with Escherichia coli. The survival rate (n = 21) and bacterial burden (n = 5) were assessed. The processes of phagosome maturation and phagosome-lysosome fusion in peritoneal macrophages were extensively studied. The impact of increasing intracellular Ca concentration on bacterial clearance in macrophages (n = 3) and on survival rate of Trpm2 mice infected with E. coli (n = 21) was investigated.

Results: Trpm2 mice exhibited increased mortality (85% vs. 54%; P < 0.01) and aggravated bacterial burden during E. coli sepsis. Trpm2 peritoneal macrophages infected with E. coli showed dampened recruitment of lysosomal-associated membrane protein 1 and impaired phagosome maturation evidenced by a decrease in the accumulation of early endosome antigen 1, whereas a normal acquisition of Ras-related protein in brain 5. Increasing the cytosolic Ca concentration in Trpm2 peritoneal macrophages via ionomycin treatment facilitated early endosome antigen 1 recruitment to Ras-related protein in brain 5 and phagosomal localization of lysosomal-associated membrane protein 1 and consequently enhanced bactericidal activity. Adoptive transfer of ionomycin-treated Trpm2 peritoneal macrophages improved bacterial clearance and survival (67% vs. 29%; P < 0.01) in Trpm2 mice challenged with E. coli.

Conclusions: Transient receptor potential melastatin 2 plays a critical role in host defense against invading bacteria via promoting phagosome maturation through facilitation of early endosome antigen 1 recruitment.