Dynamic Changes in Colonic Structure and Protein Expression Suggest Regulatory Mechanisms of Colonic Barrier Function in Torpor–Arousal Cycles of the Daurian Ground Squirrel

Background: Both pathological conditions and hibernation can affect the barrier function of small intestine mucosa. However, the effect of hibernation on the barrier function of colonic mucosa remains unclear. Methods: We investigated morphological changes in colonic mucosa, the concentrations of specific proteins and molecules, and the enzymatic activity of diamine oxidase (DAO), in serum and colonic tissue; the expression of tight junction proteins and mucin, and the changes in inflammatory, farnesoid X receptor (FXR)–small heterodimer partner (SHP), and apoptosis-related molecules that could play a role in gut permeability changes in Daurian ground squirrels in summer active (SA), late torpor (LT), and interbout arousal (IBA) periods. Results: The results show that hibernation reduced the thickness of the colonic mucosa and the depth of the crypt, decreased the number of goblet cells (GCs), and damaged the structure of some microvilli. The concentrations of proteins and molecules, and the enzymatic activity of DAO, were all increased in the serum and colon, and the localization of tight junction proteins and mucin in the colonic mucosa were altered (compensatory response). Although the ground squirrels ate during the interbout arousal period, the changes remained similar to the response to torpor. Inflammation, apoptosis–anti-apoptosis, and FXR–SHP signaling may be involved in the possible changes in intestinal gut permeability during the torpor–arousal cycle in Daurian ground squirrels. In addition, periodic interbout arousal may play an inflammation-correcting role during the long hibernation season of Daurian ground squirrels.