Molecular Genetics and Microbiology
First Thesis Advisor
Stuart M. Levitz, MD
Carrier Proteins, Inflammasomes, Chitin, Chitosan, Interleukin-1beta
Dissertations, UMMS; Carrier Proteins; Inflammasomes; Chitin; Chitosan; Interleukin-1beta
Chitin is an abundant polysaccharide found in fungal cell walls, crustacean shells, and insect exoskeletons. The immunological properties of both chitin and its deacetylated derivative chitosan are of relevance due to frequent natural exposure and their increasing use in translational applications. Depending on the preparation studied and the endpoint measured, these compounds have been reported to induce allergic responses, inflammatory responses, or no response at all. Highly purified chitosan and chitin were prepared and the capacity of these glycans to stimulate the release of the inflammasomeassociated cytokine IL-1β was examined. Chitosan was shown to be a potent inflammasome activator in mouse bone marrow macrophages, macrophages polarized towards a M1 or M2 phenotype, dendritic cells, peritoneal cells, and human PBMCs. Acetylation of the chitosan to chitin resulted in a near total loss of IL-1β activity in all cell types tested. The size of the chitosan particles played an important role, with small particles eliciting the greatest activity. An inverse relationship between size and stimulatory activity was demonstrated using chitosan passed through size exclusion filters as well as with chitosan-coated beads of defined size. Partial digestion of chitosan with pepsin resulted in a larger fraction of small phagocytosable particles and more potent inflammasome activity. Inhibition of phagocytosis with cytochalasin D abolished the IL- 1β stimulatory activity of chitosan, offering an explanation for why the largest particles were nearly devoid of activity. Thus, the deacetylated polysaccharide chitosan potently activates the NLRP3 inflammasome in a phagocytosis-dependent manner. The reason for chitin’s inability to elicit IL-1β is unknown, but it does not appear to be due to active inhibition of the inflammasome and while chitin appears to be more readily digested by macrophage cell lysates, it does not occur at a rate which would likely impact inflammasome activation. There are three proposed mechanisms for NLRP3 inflammasome activation: K+ efflux, ROS, and lysosomal destabilization. The contributions of these mechanisms were tested and it was revealed that each of these pathways participated in optimal NLRP3 inflammasome activation by chitosan. Finally, the laminin receptor was evaluated as a potential chitin receptor. These studies provide insight into the activating properties of chitin and chitosan and highlight the importance of matching particle size and degree of acetylation to the level of activity desired for translational applications.
Bueter, CL. Disparate Activation of the Inflammasome by Chitin and Chitosan: A Dissertation. (2013). University of Massachusetts Medical School. GSBS Dissertations and Theses. Paper 687. DOI: 10.13028/M2W02Z. http://escholarship.umassmed.edu/gsbs_diss/687
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