Trem-2 modulation of gut microbiota is blunted during hepatotoxic injury and uncoupled from liver repair responses
The involvement of gut microbiota in liver disease has been addressed in the context of the "leaky gut hypothesis" postulating that dysbiosis allow microbial components to elicit liver inflammatory responses and hepatic tissue damage. Conversely, commensal gut microbiota acting on innate immune receptors protect against hepatotoxic insults. Given that mice deficient for the triggering receptor expressed on myeloid cells-2 (Trem-2) show increased vulnerability to experimental drug-induced hepatic damage we explored the possibility that Trem-2 is a modulator of gut microbiota composition. We found that microbiota composition in untreated Trem-2 KO mice differs from the wild-type showing overall decrease in microbiota diversity and increased representation of Verrucomicrobia. Interestingly, induction of liver damage with hepatotoxic drugs blunted this microbiota diversity difference and altered phyla composition with increased representation of Verrucomicrobia during acute hepatic injury and Proteobacteria during chronic challenge. Furthermore, co-housing experiments that homogenized microbiota diversity showed that the increased liver tissue vulnerability to hepatotoxic insults in Trem-2 KO mice was not dependent on microbiota composition. This work uncouples Trem-2 dependent alterations in gut commensal microbiota from Trem-2 pro-recovery effects in the damaged liver tissue. These findings support the possibility that unlinked actions of innate immune receptors contribute to disease association with microbiota alterations, particularly with the Verrucomicrobia phylum. ImportanceTrem-2 is a mammalian innate immunity receptor involved in development and resolution of tissue damage, namely in the brain and in the liver. Nevertheless, it is not known whether gut microbiota is contributing to these Trem-2 mediated phenotypes. We found that Trem-2 KO mice spontaneously display different gut microbiota composition as compared to wild-type mice, namely with increased abundance of the phylum Verrucomicrobia. Notably these differences do not impact the control of Trem-2 on liver tissue vulnerability to hepatotoxic insults. This work uncouples Trem-2 modulation of gut microbiota and the role of Trem-2 on responses to liver damage. This work brings new insights on role of innate immune receptors on the association of organic and systemic diseases with gut microbiota.