Genetic Variation in the Patterns of Skeletal Progenitor Cell Differentiation and Progression During Endochondral Bone Formation Affects the Rate of Fracture Healing

Abstract

These studies examined how genetic differences that regulate architectural and bone material properties would be expressed during fracture healing and determine whether any of these features would affect rates of healing as defined by regain of strength. Controlled fractures were generated in three inbred strains of mice: A/J, C57Bl/6J (B6), and C3H/HeJ (C3H). Both the A/J and B6 strains showed faster healing than the C3H strain based on regains in strength and stiffness. Strain-specific architectural features such as moment of inertia, cross-sectional area, and cortical thickness were all recapitulated during the development of the callus tissues. None of these traits were directly relatable to rates of fracture healing. However, rates of healing were related to variations in the temporal patterns of chondrogenic and osteogenic lineage development. The B6 strain expressed the highest percentage of cartilage gene products and had the longest period of chondrocyte maturation and hypertrophy. The slowest healing strain (C3H) had the shortest period of chondrogenic development and earliest initiation of osteogenic development. Although the A/J strain showed an almost identical pattern of chondrogenic development as the C3H strain, A/J initiated osteogenic development several days later than C3H during fracture healing. Long bone growth plates at 28 days after birth showed similar strain-specific variation in cartilage tissue development as seen in fracture healing. Thus, the B6 strain had the largest growth plate heights, cell numbers per column, and the largest cell size, whereas the C3H columns were the shortest, had the smallest number of cells per column, and showed the smallest cell sizes. These results show that (1) different strains of mice express variations of skeletal stem cell lineage differentiation and (2) that these variations affect the rate of fracture healing.

A2B Adenosine Receptor Promotes Mesenchymal Stem Cell Differentiation to Osteoblasts and Bone Formation in Vivo

“…In addition, tissue from the fracture callus was dissected and analyzed by qRT-PCR. As reported earlier for this injury model, a significant up-regulation of Osterix and Runx2 should be observed, both during early periods of MSC differentiation at day 3 postfracture and later starting on day 7 postfracture when mineralized cartilage resorption and primary bone formation are initiated (35). A2BAR KO mice tend to show decreased expression of Runx2 and Osterix at 3 days postfracture and show significantly decreased expression at 7 days postfracture, as compared with WT (Fig.…”

Lysyl Oxidase-like-2 (LOXL2) Is a Major Isoform in Chondrocytes and Is Critically Required for Differentiation

“…Fracture Model-Unilateral fractures were produced in the right femur of 8 -10-week-old male mice as previously described (17). The location and quality of fractures was assessed by x-ray analysis while animals were still anesthetized after surgery.…”

“…Fracture configurations that were comminuted or were not localized to the mid-diaphyseal region were excluded from the study. Days 10 and 14 time points during fracture healing were chosen for the histological studies because the B6 mouse strain has a corresponding peak period of cartilage formation and hypertrophic chondrocyte differentiation (17). For molecular biological studies of fracture healing, mRNA was extracted from callus tissues on day 0 (no fracture) and at intervals up to day 21 of healing.…”

Mouse Strain Dependent and Independent Effects of Type 1 Diabetic Bone Pathology

“…Similar analyses performed on C57BL/6 and 129/Sv mice identified Bmd20 on chromosome 6 and Bmd22 on Chromosome 1 as contributing to both total body and vertebral BMD levels [21]. Genetic variation in such areas could impact skeletal stem cell lineage differentiation [22], inflammation, metabolism, and hormone levels that ultimately regulate osteoblast and osteoclast activities.…”