Date of Award

1-1-2018

Embargo Period

1-1-2022

Document Type

Thesis

Degree Name

Master of Biomedical Science

Department

Microbiology and Immunology

College

College of Graduate Studies

First Advisor

Chad Novince

Second Advisor

Bei Liu

Third Advisor

Caroline Westwater

Fourth Advisor

Chenthamarakshan Vasu

Abstract

Problem: The role of individual commensal microbes within the commensal gut microbiota on regulating osteoimmune effects in the growing/developing skeleton is currently unidentified. Discerning a specific commensal gut microbe’s impact on osteoimmune processes is important because this knowledge could be employed to optimize skeletal growth in adolescents. Approach: To investigate this, two specific pathogen free murine models were used because of their one reported microbial difference: murine pathogen free (MPF) mice are colonized by segmented filamentous bacteria (SFB) vs. excluded flora (EF) mice, which are void of SFB. The mice were sacrificed at 9 weeks to investigate SFB’s effects on the adolescent skeleton. Micro-CT and histomorphometry were used to investigate tibia bone architecture, osteoclast, and growth plate differences. Nanostring and qRT-PCR were used to investigate gene expression levels of osteoblast, osteoclast, and inflammatory immune response genes. Flow cytometry was used to assess the frequencies of T and B-cells in the mesenteric lymph nodes (mLNs), spleen, and marrow. Results: Bone mineral density, bone volume per tissue volume, and trabecular number were all decreased in MPF vs. EF mice proximal tibia. The number of osteoclasts per bone perimeter and the osteoclast master regulator Nfatc1 expression were increased in MPF vs. EF mice. Pattern recognition receptor related genes for the TLR4 signaling response were increased in MPF vs. EF marrow. There was no difference in the helper T-cell frequencies in the marrow. Conclusion: The results suggest alterations of gut commensal microbiota, even a single gut microbe, SFB, within health models for the gut commensal microbiota, can lead to decreased trabecular bone area per tissue area, bone volume per tissue volume, bone mineral density, and trabecular number as well as increased osteoclast number per bone perimeter. A healthy microbial composition with SFB can have similar implications in osteoclastogenesis, causing decreases in trabecular parameters as seen in SPF / Conventionalized vs. germfree studies caused by immunomodulation.

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