Investigation Of The Mechanism Of Heat Stress-induced Damage And Repair In Pig And Rat Small Intestinal Mucosa

With the presence of global warming, heat stress is becoming a key stressor influencing animal health and growth, especially during the summer months. The intestinal mucosa of the pig presents an extensive surface area providing direct contact between the pig and a large assortment of nutrients, microbes and exogenous toxins. The intestinal epithelium should permit the exchange of nutrients between the gut lumen and the systemic circulation, while at the same time preventing penetration of pathogenic organisms and toxic compounds. Thus, the integrity of the pig gastrointestinal tract epithelium ensures its barrier function and the absorption of nutrients; however, when animals become exposed to environmental temperatures greater than their thermoneutral temperature, their peripheral blood flow is increased to dissipate internal body heat, thereby resulting in a significant reduction in blood flow to the small intestine. During this time, the epithelial tissue of the small intestine can experience ischemic and hypoxic conditions, resulting in tissue damage, which, in turn, can lead to low-production performance and increased risk of morbidity and mortality. The intestinal epithelium has very rapid turnover rates as mature differentiated epithelial cells are shed into the lumen and are continuously replaced by the progeny of stem cells, so the damaged epithelial cells are continually and rapidly replaced by new cells, crucial for maintaining sufficient intestinal function. Thus, in the present study we used heat stress model of pig, rat and rat IEC-6 cells to investigate the mechanism of heat stress-induced damage and repair in small intestinal mucosa, which includes the following studies:1. Effect of heat stress on morphology and gene expression profiles in pig and rat small intestine, and complete the bioinformatics analysis of the different expression genes..2. Effect of heat stress on growth factor gene expression and ERK1/2 phosphorylation levels in rat small intestine.3. Effect of heat strss on cell morphology, cell viability, apoptosis, growth factor expression and ERK1/2 phosphorylation levels in rat IEC-6 cells.4. Effect of ERK1/2 signaling on cell morphology damage and apoptosis, and the growth factor gene expression in rat IEC-6 cells during heat stress.5. Correlation analysis of the three heat stress models.RESULTS:1. Heat stress reduced the growth rate of pig, caused damage to pig intestinal mucosa which was more serious in duodenum and jejunum on 3th day after heat teatment.2. Heat stress changed the gene expression profiles in pig small intestine.93 genes were found to be significantly up-regulated, while 110 were significantly down-regulated (T< 0.01, Fold chang> 2) in 20,000 knowned genes of pig. 3. Bioinformatics analysis of the different expression genes shows pathways of Linoleic acid metabolism, MAPK signaling pathway, Metabolism of xenobiotics by cytochrome P450 and Arachidonic acid metabolism may play a critical role in heat stress.4. Heat stress caused damage to rat small intestinal mucosa, and changed its gene expression profiles. Basica pig and rat microarray results,10 differentially expressed growth factors (Fgfr3, Tgif, Pdgfa, Vegfa, Gdf15, Ok138, Gdf9, Alb, Egfr, and Ctgf) and ERK1/2 signaling pathway were chosed for following studys. Western-blot results showed that ERK1/2 phosphorylation levels in rats' jejunum were significantly increased after heat treatment.5. When IEC-6 cells was in heat stress, U0126 (a specific inhibitor of ERK1/2) was added to, more serious cell damage and apoptosis were found (more than 80% of early apoptosis,10% in late apoptosis). Growth factor genes expression also was changed significantly.6. There changes in gene expression and ERK1/2 phosphorylation among pig, rat and IEC-6 cells heat stress models were similar.CONCLUSIONS:1. Heat stress caused serious damage to pig and rat small intestinal mucosa.2. Heat stress changes the gene expression profiles of pig and rat jejunum, bioinformatics analysis showed that growth factor genes and several signaling pathway were involved in the damage and repair process.3. Growth factor gene and ERK1/2 signaling pathway play a critical role in the damage and repair process by regulating epithelial cell growth, proliferation, differentiation and migration. Moreover, ERKl/2 signaling can regulat growth factor genes expression during heat stress.4. There was a good correlation among the three heat stress models.