Impact of PepT1 deletion on microbiota composition and colitis requires multiple generations

Emilie Viennois,Junsik Sung,Chunhua Yang,Andrew T Gewirtz,Benoit Chassaing,Adani Pujada,Didier Merlin

doi:10.1038/s41522-020-0137-y

Abstract

Numerous studies of knockout mice find impacts on microbiota composition that influence host phenotype. However, such differences can vanish when KO mice are compared directly to WT littermates, suggesting these differences do not reflect the genetic deletion per se but microbiota composition drifting over generations. Hence, our hypothesis that absence of di/tri-peptide transporter PepT1 altered microbiota composition resulting in resistance to colitis compelled scrutiny. In this study, we used PepT1−/− and WT founder mice bred separately for multiple generations. Such mice were then bred to each other to generate F1 PepT1−/− and WT littermates, which were then bred within their genotype to generate F2, F3, and F4, offspring. Here we report that founder PepT1−/− mice were, relative to their WT counterparts, resistant to DSS colitis. Such resistance was associated with alterations in gut microbiota, which, when transplanted to germfree mice, was sufficient to transfer resistance to colitis. Such differences were not observed when comparing F1 PepT1−/− to F1 WT littermates but rather, returned gradually over subsequent generations such that, relative to their F4 WT controls, F4 PepT1−/− displayed microbiota composition and colitis-resistant phenotype nearly identical to the founder PepT1−/− mice. Our findings indicate a role for PepT1 in influencing microbiota composition and, consequently, proneness to colitis and cancer. Overall, our study indicates that littermate-controlled experiments can be insufficient for assessing microbiota-dependent phenotypes and prevent a full comprehension of genotype-driven phenomena. Rather, impact of a single genetic alteration on microbiota and host phenotype may take generations to manifest.

Highlights

Peptide transporter 1 (PepT1), encoded by the SLC15A1 gene, is an apical proton-coupled oligopeptide transporter that mediates the uptake of a wide range of dietary and bacterial di- or tripeptide substrates into intestinal epithelial cells[1]
While PepT1 expression is normally restricted to the small intestine, our studies in mice show that overexpression of human PepT1 in the colon exacerbates experimental colitis, whereas a PepT1 deficiency (PepT1−/− mice) is sufficient to protect against dextran sulfate sodium (DSS)induced colitis and colitis-associated cancer (CAC)[5,6]
Data are presented as the mean ± standard error of the mean (SEM)

Summary

Introduction

Peptide transporter 1 (PepT1), encoded by the SLC15A1 gene, is an apical proton-coupled oligopeptide transporter that mediates the uptake of a wide range of dietary and bacterial di- or tripeptide substrates into intestinal epithelial cells[1]. While microbiota composition is generally viewed as an environmental factor, recent studies have demonstrated that host genetics influence the gut microbiome[11,12]. In this context, we sought to investigate the role played by the microbiota in the protective phenotype against intestinal inflammation observed in PepT1−/− mice. F1 generation PepT1−/− mice showed no greater resistance to DSS-induced colitis than their WT littermates; the protective effect of a PepT1 deficiency was progressively restored in the descendants of littermates (F2-F4). The gradual restoration of the protective phenotype correlated with progressive changes in the microbiota across generations Together, these findings demonstrate the potential of PepT1 genotype to shape microbiota and impact colitis susceptibility. Our findings show that exclusive use of littermate comparison can mask genotype-driven phenotypes that take more than one generation to establish

Methods

Results

Conclusion