Table 1.
Literature review of the effects of germ-free (GF) status on hindlimb bone quality. Arrows directions are in reference to the effect of GF versus conventionally raised mice.
| Study | Mouse model |
Bone measurement |
Key findings | |
|---|---|---|---|---|
| Sjögren et al., “The gut microbiota regulates bone mass in mice”, JBMR, 2012.(19) | Female C57BL/6J 7-9 weeks old |
pQCT, microCT, histomorphometry | Proximal tibia metaphysis | at 7 weeks: |
| vBMD | ↑ 3.2% | |||
| Femur diaphysis | at 9 weeks: | |||
| Ct. Area | ↑ 8.9% | |||
| Distal femur metaphysis | at 7 weeks | |||
| BV/TV | ↑ 39.7% | |||
| Tb.N | ↑ 36.% | |||
| Tb.Sp | ↓ 29.2% | |||
| Tb.Th | ≈ | |||
| Distal femur metaphysis | at 9 weeks | |||
| MAR | ≈ | |||
| M.S/Tb.S | ↑ 17.0% | |||
| N.Oc/BS | ↓ 11.0% | |||
| TRAP+ Oc.N (> 5 nuclei) | ↓ 57.8% (at 8 weeks) | |||
| Schwarzer et al., “Lactobacillus plantarum strain maintains growth of infant mice during chronic undernutrition”, Science, 2016.(69) | Male BALB/c 7 weeks old |
MicroCT | Femur length | ↓ 3.09% |
| Femur diaphysis | ||||
| Ct.Th | ↓ ~9.6% | |||
| Ct.Ar./Tt.Ar | ↓ ~4.7% | |||
| Ct.BMD | ≈ | |||
| Distal femur metaphysis | ||||
| BV/TV | ↓ ~24.6% | |||
| Li et al., “Sex steroid deficiency–associated bone loss is microbiota dependent and prevented by probiotics”, JCI, 2016.(10) | Female C57BL/6J 20 weeks old |
MicroCT | Femur metaphysis | |
| BV/TV | ↑ ~25% | |||
| Tb.N | ↑ ~30% | |||
| Tb.Sp | ↓ ~24% | |||
| Tb.Th | ≈ | |||
| Femur diaphysis | ||||
| Ct.Vol | ↑ ~6% | |||
| Ct.Th | ↑ ~10% | |||
| Li et al., “Parathyroid hormone–dependent bone formation requires butyrate production by intestinal microbiota”, JCI, 2020.(20) | Female C57BL/6 12 weeks old |
MicroCT, histomorphometry | Femur metaphysis | |
| BV/TV | ≈ | |||
| Tb.Th, Tb.N and Tb.Sp | ≈ | |||
| Femur diaphysis | ||||
| Ct.Ar | ≈ | |||
| Ct.Th | ↑ ~12% | |||
| MAR | ≈ | |||
| BFR/BS | ≈ | |||
| N.Oc/BS | ≈ | |||
| N.Ob/BS | ≈ | |||
| Ohlsson et al., “Regulation of bone mass by the gut microbiota is dependent on NOD1 and NOD2 signaling”, Cell. Immun., 2017.(21) | Female C57BL/6J 9-10 weeks old |
MicroCT | Femur diaphysis | |
| Ct.Th | ↑ ~4.9% | |||
| Hahn et al., “The microbiome mediates subchondral bone loss and metabolomic changes after acute joint trauma”, Osteoarth. Cartil, 2021.(22) | Female & male (pooled data) C57BL/6 21 weeks old |
MicroCT | Femur epiphysis | |
| BV/TV | ↑ 23% | |||
| Tb.Th | ↑ 11% | |||
| Tb.N and Tb.Sp | ≈ | |||
| Novince et al. “Commensal Gut Microbiota Immunomodulatory Actions in Bone Marrow and Liver have Catabolic Effects on Skeletal Homeostasis in Health”, Scientific Report, 2017.(26) | Male C57BL/6 11-12 weeks old |
MicroCT, histomorphometry, cell cultures | GF vs SPF mice: | |
| Proximal tibia metaphysis | ||||
| BV/TV | ↑~19% | |||
| Tb.N | ↑~22% | |||
| Tb.Th and Tb.Sp | ≈ | |||
| Distal femur | ||||
| Trab. B.Ar/T.Ar | ↑~33% | |||
| MAR | ↑~166% | |||
| BFR | ↑~218% | |||
| N.Oc/B.Pm | ≈ | |||
| Oc.Ar/Oc | ↓~58% | |||
| Oc.Pm/B.Pm | ↓~51 | |||
| Bone marrow cultures from femur and tibia | ||||
| Ob. Differentiation Potential (Runx2, SP7, Col12a) | ↑ |
|||
| Ob. Mineralization | ↑~29% | |||
| Yan et al. “Gut microbiota induce IGF-1 and promote bone formation and growth”, PNAS, 2016.(27) | Female & male CB6F1 13 weeks old &10 months old |
MicroCT, histomorphometry, cell cultures |
GF vs colonized with SPF microbiota for 1 month: (females) | |
| Femur metaphysis | ||||
| BV/TV | ↑~29% | |||
| MAR | ↓ ~20% | |||
| BFR/BS | ↓ ~34% | |||
| Epiphyseal bone Runx2 | ↓ | |||
| GF vs colonized with SPF microbiota for 8 months: (females & males) | ||||
| Femur length | F↓~2%, M↓~3% | |||
| Femur metaphysis | ||||
| BV/TV | F≈, M≈ | |||
| Ct. Porosity | F≈, M≈ | |||
| Ct. Th | F≈, M≈ | |||
| Ec. Ar | F≈, M↓~20% | |||
| Ps. Ar | F≈, M↓~13% | |||
Abbreviations: vBMD, volumetric bone mineral density; Ct.Ar cortical area; BV/TV, trabecular bone volume; Tb.N, trabecular number; Tb.Sp, trabecular spacing; Tb.Th, trabecular thickness; MAR, mineral apposition rate; N.Oc/BS, number of osteoclasts per mm bone surface; TRAP+ Oc.N , number of TRAP+ osteoclasts; Ct.Th, cortical thickness; Ct.Vol, cortical volume; Ct.Ar/Tt.Ar, cortical area to total cross-sectional area; BFR/BS, trabecular bone formation rate per mm bone surface; N.Ob/BS, number of osteoblasts per mm bone surface. SPF mice, specific pathogen free mice; F, female; M, male; Ec , endocortical; Ps, periosteal.