Deletion of Tfam in Prx1-Cre expressing limb mesenchyme results in spontaneous bone fractures

J Bone Miner Metab. 2022 Sep;40(5):839-852. doi: 10.1007/s00774-022-01354-2. Epub 2022 Aug 10.


Introduction: Osteoblasts require substantial amounts of energy to synthesize the bone matrix and coordinate skeleton mineralization. This study analyzed the effects of mitochondrial dysfunction on bone formation, nano-organization of collagen and apatite, and the resultant mechanical function in mouse limbs.

Materials and methods: Limb mesenchyme-specific Tfam knockout (Tfamf/f;Prx1-Cre: Tfam-cKO) mice were analyzed morphologically and histologically, and gene expressions in the limb bones were assessed by in situ hybridization, qPCR, and RNA sequencing (RNA-seq). Moreover, we analyzed the mitochondrial function of osteoblasts in Tfam-cKO mice using mitochondrial membrane potential assay and transmission electron microscopy (TEM). We investigated the pathogenesis of spontaneous bone fractures using immunohistochemical analysis, TEM, birefringence analyzer, microbeam X-ray diffractometer and nanoindentation.

Results: Forelimbs in Tfam-cKO mice were significantly shortened from birth, and spontaneous fractures occurred after birth, resulting in severe limb deformities. Histological and RNA-seq analyses showed that bone hypoplasia with a decrease in matrix mineralization was apparent, and the expression of type I collagen and osteocalcin was decreased in osteoblasts of Tfam-cKO mice, although Runx2 expression was unchanged. Decreased type I collagen deposition and mineralization in the matrix of limb bones in Tfam-cKO mice were associated with marked mitochondrial dysfunction. Tfam-cKO mice bone showed a significantly lower Young's modulus and hardness due to poor apatite orientation which is resulted from decreased osteocalcin expression.

Conclusion: Mice with limb mesenchyme-specific Tfam deletions exhibited spontaneous limb bone fractures, resulting in severe limb deformities. Bone fragility was caused by poor apatite orientation owing to impaired osteoblast differentiation and maturation.

Keywords: Apatite orientation; Mitochondrial dysfunction; Osteoblast differentiation; Spontaneous bone fracture; Type I collagen.

MeSH terms

  • Animals
  • Apatites
  • Collagen Type I / metabolism
  • DNA-Binding Proteins / metabolism
  • Fractures, Spontaneous* / metabolism
  • High Mobility Group Proteins / metabolism
  • Integrases
  • Mesoderm / metabolism
  • Mice
  • Mice, Knockout
  • Osteoblasts / metabolism
  • Osteocalcin / metabolism


  • Apatites
  • Collagen Type I
  • DNA-Binding Proteins
  • High Mobility Group Proteins
  • Tfam protein, mouse
  • Osteocalcin
  • Cre recombinase
  • Integrases