Mammalian hosts and their intestinal microbiota have co-evolved over millennia. Although customarily described as commensal, the microbiota of the gut is now known to be crucial for the normal development of host immunity and for the homeostasis of the immune system. An imbalance in microbial colonization-dysbiosis-is associated with diverse inflammatory and autoimmune syndromes, such as the inflammatory bowel diseases of the lower gastrointestinal tract. During normal immunologic development and pathophysiological reactions to challenges, small molecules produced by commensal microbes, such as lipids, can play crucial roles in shaping the immune system and its responses. Bacteroides fragilis, a well-studied resident of the human lower gastrointestinal tract, exerts interesting immune-modulating biological effects in various autoimmune diseases. In germ-free mice, wild-type B. fragilis monocolonization suppresses gut natural killer T cell (NKT cell) numbers and protects the animals from NKT cell-mediated colitis, whereas a sphingolipid- knockout strain does not provide such protection. Primary results imply that unique sphingolipid mediators originated from B. fragilis can contribute to these protective mechanisms. The current proposal describes a 5-year plan of mentored research focusing on the unique sphingolipids produced by B. fragilis and other commensal Bacteroidales and assessing their ability to modulate host immunity and protect the host from excessive inflammation. This work addresses three specific aims: (1) Acquire a comprehensive sphingolipidomic map of commensal Bacteroidales and investigate biosynthesis pathways of immunoregulatory sphingolipids, (2) Chemically synthesize commensal glycosphingolipids and assess regulation of NKT cell activity and proliferation and (3) Investigate the NKT-regulatory functions of commensal glycosphingolipids during immune maturation and upon pathological challenge. In order to attaining these goals, the principal investigator will gain knowledge and experience in microbiology and immunology based on a broad understanding of analytical chemistry and lipid mediator immunology. Didactic and technical training, in conjunction with expert mentorship by Dr. Dennis Kasper (primary mentor) and a scientific advisory committee, will aid in the successful completion of the project, which represents a key step toward independence of the applicant.

Public Health Relevance

From the moment of birth, we share our environment with bacteria, many of which colonize the gut and guide the maturation of a healthy immune system. In this project, aided by highly sensitive analytical methods such as tandem mass spectrometry, I will determine the structure and understand biosynthetic pathways of commensal sphingolipids, chemically synthesize active molecules, administer them to germ-free mice, and assess how they protect the host from colitis. This information will be valuable in developing novel drugs active against a variety of infections and inflammatory diseases.

National Institute of Health (NIH)
National Institute of Diabetes and Digestive and Kidney Diseases (NIDDK)
Research Scientist Development Award - Research & Training (K01)
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Kidney, Urologic and Hematologic Diseases D Subcommittee (DDK)
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Saslowsky, David E
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Harvard Medical School
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