Stimuli induced changes to mucus barrier properties and their implications to health

• Online Access: http://hdl.handle.net/2047/D20291376

Mucus is a complex gel that lines the gastrointestinal tract and is composed of mostly water, with 0.5-5% glycoproteins, and 1% proteins, lipids, and salts. Mucus selectively controls the diffusion of molecules, particulate matter, and microorganisms to the underlying epithelium. While the mucus layer plays an important role as the bodys first line of defense, the changes to this barrier due to physiological stimuli or disease are not fully understood. The overall aims of this work are to understand how the mucus barrier is impacted by: (1) exposure to exogenous agents (i.e. lipids and emulsifiers common in food), (2) developmental age (i.e. immature vs. mature) and disease (i.e. necrotizing enterocolitis (NEC)), and (3) bacterial by-products. By employing a robust multiple particle tracking technique along with biochemical analysis (i.e. protein assays, enzyme-linked immunosorbent assays) we can probe changes to the mucus barrier. We observed that emulsifiers common in processed foods altered mucus structure and reduced mucus thickness, which may contribute to the exposure of the epithelium to intestinal lumen contents and microbes, resulting in the progression of intestinal inflammation. In contrast, lipids significantly reduced particle diffusion in mucus, suggesting the potential to strengthen the mucus barrier with relatively safe, mild stimuli. Intestinal mucus of immature rats (5 day old pups) did not function as a significant barrier to the transport of microbes and particles, and had a lower mucin and protein concentration compared to mucus from mature rats (21 day old pups), which indicates that mucus barrier properties change with developmental age, and that a deficient mucus barrier may contribute to development of diseases associated with prematurity, such as NEC. Moreover, rat pups challenged with NEC stressors (i.e. cesarean section, hypoxia, formula feeding and microbial challenge) had reduced particle diffusion and microbe transport, indicating a less permeable mucus barrier in disease. Lastly, microbial by-products (e.g., endotoxins) from a human stool sample grown in medium containing pro-inflammatory factors was observed to induce mucus production and cytokine secretion from an in vitro cell culture to a greater extent compared to a regular microbe culture. Overall, this work provides support for the significance of multiple factors, including exogenous stimuli present in food, developmental age, and disease, in impacting mucosal barrier properties. The findings suggest that an altered mucus barrier may contribute to exposure of underlying tissues to microbes and intestinal lumen contents, potentially leading to inflammation and disease. Further, this project provides the basis for utilizing mild exogenous stimuli to alter the mucus barrier, for example to improve oral drug delivery, prevent microbe transport, and minimize or prevent intestinal inflammation.