Synthesis of peptidoglycan saccharides and molecular probes to investigate innate immune signaling
Date
2019
Authors
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Publisher
University of Delaware
Abstract
The human body is teeming with trillions of commensal bacteria, known as the microbiome, that seemingly fly under the radar of our immune system. Nonetheless, when these organisms are misrecognized, a variety of illnesses, such as Crohn’s disease, are thought to arise. One important element of the bacterial cell responsible for this detection is peptidoglycan (PG), a polymer comprised of alternating carbohydrate units of N-acetylglucosamine (GlcNAc) and N-acetylmuramic acid (MurNAc) with an interconnecting peptide chain. Muramyl dipeptide (MDP), a small synthetic bacterial PG fragment, is known to activate human nucleotide-binding oligomerization domain-containing protein 2 (NOD2)-dependent NF¹̐±B innate immune response. Nonetheless, this small molecule does not accurately represent the diversity of bacterial PG fragments. Chemical variation can occur in the PG carbohydrate backbone and peptide side chain, further complicating the fragments and immune signaling patterns that are generated between commensal and pathogenic bacteria. Therefore, the identity of other “MDP-like” fragments, the mechanism by which these molecules are generated, as well as exactly how and when they interact with NOD2 or other receptors both in an innate and adaptive response remains elusive. In this thesis, new methodologies were developed to access a larger PG fragment library to probe the biological significance of the varying fragments through signaling and binding interactions. These fragments were then paired with assays to accurately survey the transcriptional response in bone marrow-derived macrophages (BMDMs). This research is incredibly valuable in better understanding how bacteria in the microbiome communicate by demonstrating how bacteria differential shed PG fragments to generate a specific and tuned immune response. These data are essential for the development of more effective and selective immunotherapies, as well as to finally decipher the host-PG interaction with the immune system.
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Keywords
Peptidoglycan, Saccharide, Molecular probe, Innate immune signaling