Loss of polarity by CDC42 depletion and oncogenic Kras activation in the intestine lead to a necrotizing enterocolitis (NEC)-like disease
Cdc42 is a key regulator of cell polarity that modulates cytoskeletal dynamics, morphology, and directional movement and plays a important role in maintaining epithelial integrity. Loss of Cdc42 in the small intestine causes disrupted polarity, hyperplasia, and mislocalization and expansion of transit-amplifying (TA) cells at the expense of intestinal stem cells (ISCs). KRAS, on the other hand, is essential for intestinal cell proliferation and differentiation, and oncogenic KRAS mutations can lead to disrupted epithelial homeostasis and contribute to gastrointestinal transformation. A human cancer database analysis suggests that loss of polarity mutations and oncogenic KRAS mutations are mutually exclusive in colon cancer patients. We found that intestinal epithelium-specific deletion of Cdc42 combined with oncogenic Kras expression in inducible Villin-CreER mice causes severe defects in the small intestine leading to lethality. Mice with Cdc42 deletion and oncogenic Kras expression in the intestinal epithelium exhibited reduced weight, disrupted villous mucosal structure, altered tight junction protein expression, reduced proliferation, loss of ISCs, inflammation, and enterocyte necrosis. These defects resemble Necrotizing Enterocolitis (NEC), a severe gastrointestinal disorder affecting preterm infants characterized by inflammation and necrosis of the small intestine epithelial cells. Single cell RNAseq analyses revealed that Cdc42 loss combined with oncogenic Kras expression resulted in disrupted intestinal polarity machinery with altered hippo signaling, exacerbated inflammation highlighted with elevated IL1 expression, and necroptosis. Targeted inhibition of necroptosis, IL-1 receptor, or YAP signaling rescues NEC-like defects. Additionally, ISCs-specific deletion of Cdc42 and oncogenic Kras expression induced by an intestinal stem cell driver, Omlf4-CreER, led to similar NEC-like defects in the mouse intestinal epithelium. These findings present a mechanism involving YAP-IL1-necroptosis signaling by combined disruption of polarity and oncogenic cues such as Kras in intestine function and provide insights into the effects of hyperactivation of these pathways in disrupting intestinal epithelia. Overall design: intestinal epithelium-specific deletion of Cdc42 combined with oncogenic Kras expression in inducible Villin-CreER mice to generate CDC42KO/Kras sample, while WT, CDC42 KO, and Kras are used as control. After harvesting using described methods (Barker et al., 2007), villi/crypts were resuspended in mixed medium comprised of 30% 10x TrypLE and 70% Advanced DMEM/F12 , incubated at 37 degree for 30-45 min. Mixing and passaging through a glass pipette was preformed every 10 min and suspensions were monitored with a microscope. After disruption of the cell aggregates, cells were filtered through a 40 um filter and then pelleted by centrifugation (5 min at 300–400g), washed once with Advanced DMEM/F12, and resuspended in the same medium for 10x genomics sc-RNA seq.