Abstract LB-213: Thrombospondin-1 regulates intestinal microbiota and bile acid metabolism in a murine model of colorectal cancer
Authors: Soto-Pantoja David R. , Sipes John M. , Westwood Brian , Morris Nicole , Emenaker Nancy J. , Roberts David D. 
Published: July 2017

Abstract
Colon cancer is major public health concern with over 50,000 deaths annually in the US. Environmental and genetic factors influence colon cancer progression, and expression of thrombospondin-1 (TSP1) inversely correlates with colon cancer aggressiveness. TSP1 is a matricellular protein that regulates vascular physiology and tissue responses to stress. We previously demonstrated that deleting the TSP1 (Thbs1) gene in ApcMin/+ mice results in systemic metabolic changes as assessed in liver tissue, increased tumorigenesis, and lower survival of mice fed a low fat diet. We now show that TSP1 induces changes in intestinal microbiota that may cause shifts in secondary bile acid metabolism that influence colon carcinogenesis. Mice were maintained and bred at least two generations on a low fat western diet to equalize dietary effects on their epigenetic context and microbiomes. Mice were pair-fed a low fat or a 21% high-fat western diet beginning at weaning. Mouse fecal matter was collected 8 weeks after dietary exposures and subjected to 16S sequencing for bacterial population identification. Lactobacillaceae, Lachnopiraceae, Ruminococcacea, Verrucomicrobiaceae families were present in all groups. The family Verrucomicrobiaceae and its genus Akkemensi represented a high proportion of the bacterial population. The relative levels of Akkemensia were elevated in low fat fed mice in mice ApcMin/+ and Thbs1−/−:ApcMin/+ when compared to WT counterparts. Interestingly Akkenmensia abundance was reduced in ApcMin/+ mice fed a high-fat diet when compared to other groups. The relative population of the genus Ruminococcus was reduced in Thbs1−/− mice as well as in Thbs1−/−:ApcMin/+ mice fed low and high fat diets, suggesting that these population shifts are driven by genotype. Because intestinal bacteria can alter metabolism, particularly of bile acids, we collected large intestine tissue from mice and subjected it to metabolomics analysis. Our data showed primary and secondary bile metabolism were regulated by the absence of TSP1 in mice fed a high fat diet when compared to WT. High 6-beta-hydroxylithocholate levels were associated with onset of carcinogenesis since it was elevated in ApcMin/+ and Thbs1−/−:ApcMin/+ mice but not in WT or Thbs1−/−. 6-oxolithocholate, hyocholate and hyodeoxycholate were elevated only in ApcMin/+ mice fed a high fat diet but not in Thbs1−/−:ApcMin/+, suggesting that these metabolites contribute to the shift in survival and carcinogenesis observed between low and high fat diets. On the other hand levels of taurohyodeoxycholic acid, 3-dehydrocholate, 7-ketodeoxycholate were elevated in Thbs1−/−:ApcMin/+ and Thbs1−/− mice but not in ApcMin/+, indicating that changes in these metabolites are driven by the loss of Thbs1 and may pre-dispose mice to increased carcinogenesis when fed a high fat diet. Taken together our data shows an unexpected role of TSP1 in regulation of microbiota and bile acid metabolism and reveals potential targets for prevention and treatment of colorectal cancer.
Citation Format: David R. Soto-Pantoja, John M. Sipes, Brian Westwood, Nicole Morris, Nancy J. Emenaker, David D. Roberts. Thrombospondin-1 regulates intestinal microbiota and bile acid metabolism in a murine model of colorectal cancer [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2017; 2017 Apr 1-5; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2017;77(13 Suppl):Abstract nr LB-213. doi:10.1158/1538-7445.AM2017-LB-213