Paradoxical Effects of Microbial-Derived Butyrate: The Influences on Colonic Wnt/β-catenin Signaling and Cell Kinetics in In Vitro and In Vivo Models

Abstract

Abstract Objectives Butyrate is considered as an important mediator in the complex etiology of colorectal cancer (CRC) that integrates gut microbiota with dietary factors and genetic components. However, how microbial-derived butyrate mediates colonic tumorigenesis remains unclear, with contradictory results from only limited experimental studies. Methods In current studies, we examined the fecal concentration of butyrate in high and low fat-fed animals and its associations with Wnt-signaling and cell kinetics in the in vivo normal epithelial cells. We further examined the influence butyrate and its receptor gene, Free Fatty Acid Receptor 2 (FFAR2), on those molecular parameters in the in vitro Caco-2 cancer cells. Results Our results showed a diminished level of fecal butyrate concentration in the high fat-fed animals, and in parallel with it are the increased Wnt/β-catenin signaling, indicated by increased active β-catenin and Wnt-signaling downstream gene expressions (p < 0.05), and altered cell kinetics, manifested by increased Ki-67 and decreased apoptosis. Whereas the results from the Caco-2 cancer cells demonstrated that the addition of butyrate surprisingly increased Wnt-signaling (p < 0.05), but was associated with cell death (p < 0.05), and the knockdown of FFAR2 by siRNA reversed the effect of butyrate on Wnt/β-catenin signaling and cell death (p < 0.05). Conclusions These paradoxical results demonstrated that butyrate may have disparate effects on tumorigenesis, depending on whether it is exerting a direct effect on normal or tumor epithelial cells, and other genetic or environmental factors. This study provided critical evidence to inform the necessity to wisely apply butyrate for cancer protection and to avoid its potential cancer-promoting effect in other circumstances. Funding Sources This project was supported by the US Department of Agriculture Hatch funding (1,013,548).