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Updated: Jul 29, 2025
Author Spotlight: An Economic and Efficient Method for Quantitative Evaluation of Bone Microarchitecture in a Murine Osteoporosis Model
Published on: September 8, 2023
Germ-Free C57BL/6 Mice Have Increased Bone Mass and Altered Matrix Properties but Not Decreased Bone Fracture
Ghazal Vahidi1, Maya Moody2, Hope D Welhaven2
1Department of Mechanical & Industrial Engineering, Montana State University, Bozeman, Montana, USA.
Abstract:
The gut microbiome impacts bone mass, which implies a disruption to bone homeostasis. However, it is not yet clear how the gut microbiome affects the regulation of bone mass and bone quality. We hypothesized that germ-free (GF) mice have increased bone mass and decreased bone toughness compared with conventionally housed mice. We tested this hypothesis using adult (20- to 21-week-old) C57BL/6J GF and conventionally raised female and male mice (n = 6-10/group). Trabecular microarchitecture and cortical geometry were measured from micro-CT of the femur distal metaphysis and cortical midshaft. Whole-femur strength and estimated material properties were measured using three-point bending and notched fracture toughness. Bone matrix properties were measured for the cortical femur by quantitative back-scattered electron imaging and nanoindentation, and, for the humerus, by Raman spectroscopy and fluorescent advanced glycation end product (fAGE) assay. Shifts in cortical tissue metabolism were measured from the contralateral humerus. GF mice had reduced bone resorption, increased trabecular bone microarchitecture, increased tissue strength and decreased whole-bone strength that was not explained by differences in bone size, increased tissue mineralization and fAGEs, and altered collagen structure that did not decrease fracture toughness. We observed several sex differences in GF mice, most notably for bone tissue metabolism. Male GF mice had a greater signature of amino acid metabolism, and female GF mice had a greater signature of lipid metabolism, exceeding the metabolic sex differences of the conventional mice. Together, these data demonstrate that the GF state in C57BL/6J mice alters bone mass and matrix properties but does not decrease bone fracture resistance. © 2023 The Authors. Journal of Bone and Mineral Research published by Wiley Periodicals LLC on behalf of American Society for Bone and Mineral Research (ASBMR).
Insights
Germ-free mice exhibit altered bone mass and matrix properties, with increased bone microarchitecture and tissue strength but no reduction in fracture resistance. Sex differences in bone metabolism were more pronounced in germ-free mice.
Area of Science:
- Microbiome research
- Bone biology
- Metabolic studies
Background:
- The gut microbiome influences bone homeostasis, but its precise role in regulating bone mass and quality remains unclear.
- Germ-free (GF) models offer a unique opportunity to study microbiome-bone interactions by eliminating microbial influence.
Purpose of the Study:
- To investigate the impact of a germ-free state on bone mass, microarchitecture, material properties, and fracture resistance in mice.
- To explore potential sex-specific differences in bone responses to the absence of a gut microbiome.
Main Methods:
- Comparison of adult female and male C57BL/6J germ-free and conventionally housed mice.
- Micro-computed tomography (micro-CT) for bone microarchitecture and cortical geometry assessment.
- Mechanical testing (three-point bending, notched fracture toughness) and advanced material property analysis (quantitative back-scattered electron imaging, nanoindentation, Raman spectroscopy, fAGE assay).
Main Results:
- Germ-free mice showed reduced bone resorption, enhanced trabecular bone microarchitecture, and increased bone tissue strength.
- Despite increased mineralization and altered collagen structure, fracture toughness was not diminished in germ-free mice.
- Significant sex differences in bone tissue metabolism were observed, with male GF mice showing greater amino acid metabolism and female GF mice exhibiting greater lipid metabolism.
Conclusions:
- The germ-free state significantly alters bone mass and matrix properties in C57BL/6J mice.
- Absence of the gut microbiome does not compromise bone fracture resistance.
- Germ-free conditions exacerbate existing sex differences in bone metabolism.
