Pro-mutagenic effects of the gut microbiota in a Lynch syndrome mouse model

Abstract

The gut microbiota strongly impacts the development of sporadic colorectal cancer (CRC), but it is largely unknown how the microbiota affects the pathogenesis of mismatch-repair-deficient CRC in the context of Lynch syndrome. In a mouse model for Lynch syndrome, we found a nearly complete loss of intestinal tumor development when animals were transferred from a conventional “open” animal facility to specific-pathogen-free (SPF) conditions. Using 16S sequencing we detected large changes in microbiota composition between the two facilities. Transcriptomic analyses of tumor-free intestinal tissues showed signs of strong intestinal inflammation in conventional mice. Whole exome sequencing of tumors developing in Msh2-Lynch mice revealed a much lower mutational load in the single SPF tumor than in tumors developing in conventional mice, suggesting reduced epithelial proliferation in SPF mice. Fecal microbiota transplantations with conventional feces altered the immune landscape and gut homeostasis, illustrated by increased gut length and elevated epithelial proliferation and migration. This was associated with drastic changes in microbiota composition, in particular increased relative abundances of different mucus-degrading taxa such as Desulfovibrio and Akkermansia , and increased bacterial-epithelial contact. Strikingly, transplantation of conventional microbiota increased microsatellite instability in untransformed intestinal epithelium of Msh2-Lynch mice, indicating that the composition of the microbiota influences the rate of mutagenesis in MSH2-deficient crypts.

Unexpected moves: a conformational change in MutSα enables high-affinity DNA mismatch binding

“…Msh2 V63E/V63E mice were only slightly more tumor-prone than WT mice, and showed drastically prolonged tumor-free survival as compared to Msh2 − / − mice, which all developed lymphomas within 4 months of age (Figure 1F and Supplementary Table S1 ) ( 25 ). Unfortunately, we could not study intestinal tumorigenesis in Msh2-Lynch and V63E-Lynch mice because the microbiota in our animal facility was unfavorable for intestinal tumor development ( 47 ). Instead, we investigated whether Msh2 V63E/V63E mice were susceptible to TMZ-induced lymphomagenesis.…”

“…Additionally, (low levels of) methylating agents in the form of dietary components, bacterial metabolites or cigarette smoke may enhance cancer risk in patients with a single germline MSH2 V63E mutation ( 54 , 55 ). Unfortunately, we were not able to study this possibility as the microbiota composition in our current mouse facility did not support intestinal tumorigenesis ( 47 ).…”

Gut microbiome composition in Lynch syndrome with and without history of colorectal neoplasia and non-Lynch controls

“…This nding may explain the lack of any protective effect observed in LS carriers randomized to resistant starch despite increasing their levels of butyrate concentration in the CAPP2 randomized control trial in contrast to the protective effect observed in sporadic CRC [31]. Another MSH2 knockout mouse model exposed to conventional microbiome exhibited increased epithelial turnover rates, increased rate of spontaneous mutations in MSH2 de cient crypts and increased microsatellite instability compared to speci c pathogen free (SPF mice) [32]. The authors hypothesized that bacterial presence in MMR de cient crypts drives epithelial turnover and subsequent mutations in DNA.…”

Genetic heterogeneity of colorectal cancer and the microbiome

“…It is believed that with an increase in the number of intestinal bacteria, hypersecretion of cytokines contributes to bacterial invasion into the dense layer of mucus. Bacterial invasion into the mucus layer and interaction with the epithelium may cause early stages of cellular transformation with a deficiency in DNA MMR as a consequence of increased epithelial proliferation[ 77 ].…”

“…Transfer of Msh2-Lynch mice from a normal room to a specific SPF room resulted in an almost complete loss of the intestinal tumor phenotype and increased survival of the experimental animals. SPF mice showed a decrease or absence of Lactobacillus and Epsilonproteobacteria taxa in the feces[ 77 ]. In addition, transplantation of cryopreserved conventional feces into SPF mice did not restore the tumor phenotype but increased the rate of epithelial renewal and accelerated the development of microsatellite instability (MSI).…”