Defining the structural and functional properties of select agricultural fibers underlying their immunomodulatory actions

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The long-term goal of this program is to define the physiologically relevant microbe-mediated fermentation pathways for select fibers of interest, sourced from different common agricultural products and to uncover the biochemical mechanisms underlying fiber-associated immunomodulatory pathways in various environmental settings. Fibers are nondigestible carbohydrates that rely on fermentation by intestinal microorganisms (bacteria and fungi) for their decomposition into byproducts that can be utilized by human cells (e.g., short chain fatty acids). Our previous work showed specific dysbiotic microbial communities (altered microbe abundance/diversity), and more significantly, altered microbe functions (enzymes) were associated with reduced ß-fructan fibre fermentation. This altered fermentation was associated with reduced production of SCFA and increased immunomodulatory interactions of unfermented ß-fructans with leukocytes (macrophages, T cells, and neutrophils), particularly through Th17 cellular pathways. Our preliminary findings suggest that the structure of these fibers, which differs between fiber subtypes and the agricultural source from which they are isolated, plays a role in their fermentability and in leukocyte response processes, as the degree of polymerization (DP; length of the fiber) was associated with inflammasome (NLRP3:IL-1ß) activation; higher DP fibres increased cytokine secretion and expression of inflammasome genes (e.g., IL-1ß, IL-23). The short-term objectives of the proposed research are: (1) profile the structural features (e.g., phenolic content, degree polymerization) of dietary fibres (e.g., ß-glucans, galatooligosaccharides, inulins); fibres will be either purchased or extracted from agricultural food sources. Structural features will be correlated with the cellular pathways of leukocyte responses to each of the dietary fibre compounds, examined using mesoscale discovery and ELISA; (2) identify gut microenvironment factors (e.g., pH, metabolites) involved in regulating the functions (enzymes) of microbiota cultures that mediate their fibre fermentation activities; (3) reveal the role of specific microbial enzymes in mediating fibre fermentation processes; and (4) provide mechanistic insight into how fibre-microbe interactions impact leukocyte response (modulation of inflammasome pathways) using targeted microscopy and pathway analysis (qPCR, western blotting, ELISA). This program will advance our fundamental understanding of the role of dietary fibre physical properties in regulating interactions with leukocytes and fermentative microbes while providing multidisciplinary training opportunities for HQP in food chemistry, microbiology and immunology. Our work will aid to improve understanding of interactions that occur, between environmental factors (microenvironment and agricultural products) and leukocyte cell populations that reside in the intestinal mucosa, the physiological site of fibre fermentation.