Nutritional status dictates the rate and mode of intestinal epithelial stem cell proliferation through an AMPK dependent mechanism

Obesity is the leading cause of preventable chronic disease, such as diabetes, heart disease and cancer. The most significant factor driving obesity and the development of these secondary disorders is diet. There is significant evidence that the amount of food one eats induces adaptational growth and functional changes of several tissues, including bone, skin, adipose, liver and intestinal tissue. Understanding how the amount of food induces these changes may reveal mechanisms by which we can manipulate to reverse the negative impact of obesity on tissue size and function. One tissue significantly impacted by obesity is the intestinal epithelium. It is known that the amount of food, and not the type of diet, drives changes in tissue size by increasing the number of epithelial cells, villi height and crypt depth. Because increases in tissue size are under the control of stem cells located within the tissue, I investigated if and how the amount of food may drive increases in the rate and mode (asymmetric vs. symmetric) of stem proliferation. In vivo, 48 male C57/B6 mice were used. Mice were fed varying amounts of chow diet and were separated into 4 groups; 1) ab libitum (adlib) fed 2) fifty-percent (50%) of their average consumption 3) fasted or 4) fasted-refed. Mice were sacrificed and the small intestine was excised and immunohistochemically processed to determine the rate of stem cell proliferation and the mode of division. The results revealed that adlib fed animals showed a higher % of symmetrically dividing cells compared with the 50% and fasted animals. An increase in symmetric division results in an increase in the pool of stem cells and expansion of the tissue size. In order to investigate the mechanism driving nutrient-driven changes in the mode of stem cell division, in vitro analysis of intestinal epithelial organoids (primary isolated intestinal epithelial crypts allowed to grow into fully functional tissue) were used. In vivo analysis was mimicked by varying the amount of glucose (no, low or high) and measuring the mode of division. In addition, the effect of activating or inhibiting a metabolic pathway known to be involved in obesity and growth, LKB1-AMPK, on the mode of division was tested. Consistent with our in vivo results, high glucose conditions greatly increased the % of symmetrically dividing cells compared with low glucose conditions. Inhibiting LKB1-AMPK blocks the normal switch to asymmetric division under low nutrient conditions and activation induces a greater asymmetric division even under high glucose conditions. Taken together, these data suggest that nutrient availability determines the mode of stem cell division through an LKB1-AMPK dependent mechanism to drive an increase in tissue and may be mechanism by which abnormal tissue function occurs