Fecal microbiota transplantation in mice improves bone material properties through altered mineral quality

Disruptions of the composition of the gut microbiome are linked to impaired bone tissue strength. Fecal microbiota transplantation (FMT) is an established clinical therapy that can restore a healthy gut microbiome and reduce systemic inflammation. However, whether FMT from a healthy donor could rescue bone fragility is unknown. As induced inflammation causes mineralization defects, we hypothesize that manipulations of the gut microbiota alter bone fracture resilience through changes in mineral quality. Here, we altered the compositions of the gut microbiome in mice via antibiotics (ampicillin and neomycin) and FMT. Mice were allocated to 5 groups (M/F, N = 13-18/group): Unaltered, Continuous (dosed 4-24 wk), Initial (dosed 4-16 wk), Reconstituted (dosed 4-16 wk with subsequent FMT from age- and sex-matched mice with unaltered gut microbiota), and Delayed (dosed 16-24 wk). Fracture toughness testing and Raman spectroscopy were conducted on the femora. The maximum toughness was greater in the Reconstituted group (for females, p < .05 compared to Continuous, Unaltered, and Delayed groups; for males, p < .05 compared to groups with antibiotic dosing). The Reconstituted group showed lower type-B carbonate substitution in the bone mineral (all p < .01 for both sexes), and lower mineral-to-matrix ratio (all p < .01 for males, for females, p < .01 compared to Unaltered, Initial, and Delayed groups). In females, mineral crystallinity was higher in the Reconstituted group than those dosed with antibiotics (all p < .05). Serum inflammation marker TNF-α was positively correlated with type-B carbonate substitutions (ρ = 0.66), mineral-to-matrix ratio (ρ = 0.71), and carboxymethyl-lysine (CML) in bone matrix (ρ = 0.43). Enhanced bone maximum fracture toughness was associated with reduced type-B carbonate substitution (r = -0.45), decreased mineral-to-matrix ratio (r = -0.40), increased mineral crystallinity (r = 0.33), and lower levels of bone CML (r = -0.49, all p < .01). These results suggest that the introduction of more beneficial gut microbiota can increase fracture resistance by modifying mineral composition and quality, likely through the reduction of systemic inflammation.