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theses

Excess consumption of saturated fat has shown to increase risk of colorectal cancer (CRC) development as well exacerbate inflammatory bowel disease (IBD) progression. In contrast, physical exercise has shown to significantly reduce the risk of CRC development and ameliorate symptoms of IBD. Although exercise has shown to exert profound anti-inflammatory effects in the colon, what is not well known are the exact mechanisms by which these health benefits are conferred. Of note are three primary processes that have been implicated in modulating intestinal inflammatory responses in the context of large bowel disorders. These include the production of intestinal mucus, the induction of the unfolded protein response (UPR) in the advent of endoplasmic reticulum (ER) stress, and the activation of inflammasomes which foster a microbe-host mutualism. The impact of dietary fat intake and physical activity on mucus thickness, the UPR and inflammasome activation where explored to elucidate putative mechanisms by which diet and exercise promote or disrupt intestinal homeostasis. In aim 1, we examined the extent to which 12 weeks of a 45% high-fat diet (HFD) contributes to colon inflammation and microbiota localization and whether voluntary wheel running could confer a therapeutic effect in 6-week-old male and female C57BL/6NTac mice. Voluntary wheel running attenuated HFD-induced colon inflammation in female mice only while no differences in microbiota localization were observed between treatment groups. In addition, sedentary male mice consuming a control low 10% fat diet demonstrated a greater degree of inflammation compared to their female counterparts. These findings demonstrate that 12 weeks of a 45% HFD is not sufficient to induce any structural changes to intestinal mucus but have shown that regular physical activity can ameliorate colon inflammation. In aim 2, we replicated aim 1 in a second cohort of 6-week-old male and female C57BL/6NTac mice using a 60% HFD in order to accelerate the occurrence of overt colon pathologies and to compare our findings from aim 1. In addition, we explored the effects of dietary fat and voluntary wheel running on colonic epithelial ER stress and the UPR. In contrast to aim 1, voluntary wheel running attenuated HFD-induced colon inflammation in both male and female mice. In agreement with aim 1, a similar increase in inflammation in sedentary male mice fed a control 10% fat diet was observed. Female mice demonstrated an inherent increase in colon IL-10 concentrations, an improved proliferative phenotype and an increase in goblet cell density compared to males. Voluntary wheel running contributed to a significantly improved proliferative phenotype compared to exercised mice. Sedentary and exercised male mice consuming a 60% HFD exhibited a unique compensatory response characterized by an increase in inner mucus layer thickness and mucin 2 production. While a 60% HFD modulated the gene expression of ER stress sensors activating transcription factor 6 (Atf6) and inositol-requiring kinase 1β (IRE1β) in female mice, a 60% HFD increased the phosphorylation of eukaryotic initiating factor-2α (eIF2α) in male mice which was attenuated by a control 10% fat diet and voluntary wheel running. Findings from this aim further corroborate the efficacy of exercise in contributing to colon health and suggests that females may possess an inherent resistance against the development of colon pathologies. In addition, we are the first to demonstrate that voluntary wheel running attenuates HFD-induced colonic epithelial ER stress in male mice. Utilizing the same cohort of animals from aim 2, aim 3 investigated the contribution of dietary fat and voluntary wheel running towards the transcription of inflammasome components and activation of caspase-1. Large increases in the gene expression of inflammasome components including the NOD-like receptor family pyrin domain containing (NLRP)3 and NLRP6 sensors, the adaptor PYD and CARD domain containing (Pycard), and caspase-1 where observed in sedentary female mice fed an HFD and in exercised female mice fed either diet relative to the sedentary control fed a 10% fat diet. This occurred in tandem with a non-significant increase in caspase-1 activation. In males, a non-significant and modest decrease in caspase-1 activation was observed, however. These findings illustrate putative sex differences in inflammasome activation in response to dietary fat and voluntary wheel running, but more rigorous analyses are required.

ETD_10587

Ph.D.

Includes bibliographical references

doi:10.7282/t3-wyq9-jq41

ETD doctoral

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