Abstract B024: Deconvolution by scRNAseq, scATACseq and functional genomics of impact of a relevant high risk diet on stem cells and homeostasis
Authors: Choi Jiahn , Zhang Xusheng , Li Wenge , Houston Michele , Peregrina Karina , Dubin Robert , Ye Kenny , Augenlicht Leonard H. 
Published: December 2022

Abstract
Dietary patterns are major determinants of sporadic colon cancer incidence, the vast majority of the disease. NWD1 is a unique purified rodent diet that establishes mouse exposure to key nutrients recapitulating levels linked to higher risk in human, and is the only mouse model that develops sporadic intestinal and colon tumors, reflecting the etiology, incidence, frequency and lag with developmental age of the human disease. NWD1 fed mice reflect human metabolic syndrome with chronic inflammation, exhibit elevated Wnt signaling throughout the small and large intestinal mucosa and altered lineage marker expression, but Lgr5hi cells are suppressed in their lineage tracing, accumulation of mutations, and efficiency in tumor initiation. Alternate cells are mobilized to maintain the mucosa with increased efficiency to cause tumors. Deconvolving impact of NWD1 using scRNAseq, scATACseq and functional genomics provided novel insight into mechanisms elevating risk for sporadic tumors. NWD1 extensively, rapidly, and reversibly reprogrammed Lgr5hi stem cells, down-regulating Ppargc1a expression that altered mitochondrial structure and function and suppressed Oxphos and the TCA cycle. Ppargc1a genetic knockout in Lgr5hi cells recapitulated the dietary effects, and NWD1 or Ppargc1a inactivation repressed developmental maturation of Lgr5hi cell progeny as cells progressed through progenitor cell compartments. In compensation, mobilized Bmi1+, Ascl2hi cells maintained and adapted the mucosa. In parallel, NWD1 altered Ppargc1a chromatin structure in stem cells, and also for genes adapting enterocytes to the diet, independently confirming NWD1 epigenetic reprogramming of stem and differentiated cells. Importantly, pathways of antigen processing and presentation were elevated, especially in mature enterocytes, a pathogenic mechanism causing human chronic low-level pro-tumorigenic inflammation in IBD, also present in NWD1 fed mice. Fundamental conclusions: 1) plasticity of cells to function as stem cells mediates physiological adaptation of the mucosa. Thus, the human mucosa is in constant flux in response to its environment, supporting historic concepts of homeostasis by Claude Bernard and Walter Cannon as a continual process of tissue adaptation to its environment, not a single optimized state. 2) our data and the literature suggest that failure to recapitulate key human nutritional exposures contributes to why human stem cells reach crypt clonality in 6 years, 50-fold longer than the 6 weeks in the mouse. Thus, better modeling of human nutritional exposures in the mouse more accurately reflects human mechanisms of homeostasis and pathogenesis. 3) Complexity of cell reprogramming reported for the earliest premalignant human colon tumors is already present in the mucosa at nutritional risk for tumor development. 4) Oncogenic mutations provide a competitive advantage to intestinal stem cells in tumorigenesis, but the competition takes place on a playing field sculpted by the nutritional environment, a major determinant of who wins.
Citation Format: Jiahn Choi, Xusheng Zhang, Wenge Li, Michele Houston, Karina Peregrina, Robert Dubin, Kenny Ye, Leonard H. Augenlicht. Deconvolution by scRNAseq, scATACseq and functional genomics of impact of a relevant high risk diet on stem cells and homeostasis [abstract]. In: Proceedings of the AACR Special Conference on Colorectal Cancer; 2022 Oct 1-4; Portland, OR. Philadelphia (PA): AACR; Cancer Res 2022;82(23 Suppl_1):Abstract nr B024.