inactivation, but not obesity, synergizes with deficiency to drive intestinal stem cell-derived tumorigenesis.

Obesity is a major risk factor for colorectal cancer and can accelerate Lgr5+ intestinal stem cell (ISC)-derived tumorigenesis after the inactivation of However, whether non-canonical pathways involving PI3K-Akt signaling in ISCs can lead to tumor formation, and if this can be further exacerbated by obesity is unknown. Despite the synergy between and inactivation in epithelial cells on intestinal tumor formation, their combined role in Lgr5+-ISCs, which are the most rapidly dividing ISC population in the intestine, is unknown. Lgr5+-GFP mice were provided low-fat diet (LFD) or high-fat diet (HFD) for 8 months, and the transcriptome was evaluated in Lgr5+-ISCs. For tumor studies, Lgr5+-GFP and Lgr5+-GFP- mice were tamoxifen treated to inactivate in ISCs and provided LFD or HFD until 14-15 months of age. Finally, various combinations of Lgr5+-ISC-specific, and -deleted mice were generated and evaluated for histopathology and survival. HFD did not overtly alter Akt signaling in ISCs, but did increase other metabolic pathways. deficiency, but not HFD, increased BrdU-positive cells in the small intestine ( < 0.05). However, combining and deficiency synergistically increased proliferative markers, tumor pathology and mortality, in a dose-dependent fashion ( < 0.05). In summary, we show that HFD alone fails to drive Akt signaling in ISCs and that deficiency is dispensable as a tumor suppressor in Lgr5+-ISCs. However, combining and deficiency in ISCs synergistically increases proliferation, tumor formation and mortality. Thus, aberrant Wnt/β-catenin, rather than PI3K-Akt signaling, is requisite for obesity to drive Lgr5+ ISC-derived tumorigenesis.