Site-specific characteristics of bone and progenitor cells in control and ovariectomized rats

Menopause-Associated Changes in Mandibular Bone Microarchitecture Are Site-Specific

BACKGROUND

There are conflicting reports on the effects of decreased estrogen levels on mandibular bone microarchitecture. Whether these effects are consistent throughout the mandible is unclear and may have important implications for treatment planning.

PURPOSE

The goal of this study was to evaluate trabecular and cortical bone microstructure in the mandibular condyle and the mandibular basal bone and compare these sites between premenopausal and postmenopausal women.

STUDY DESIGN, SETTING, SAMPLE

Participants were recruited for a cross-sectional cohort study at Columbia University Irving Medical Center. Each participant had cone-beam computed tomography taken of their mandibular condyles and the basal bone. Exclusion criteria for the population included a) current chemotherapy or immunotherapy; b) history of bisphosphonate or other osteoporosis therapy; and c) currently pregnant, nursing, or on hormonal birth control.

INDEPENDENT VARIABLE

The predictor variables are menopausal status (before or after menopause) and mandibular region of interest (condyle/basal bone).

MAIN OUTCOME VARIABLE

Parameters of interest included the following indicators of bone quality: trabecular bone volume fraction, trabecular thickness, trabecular number, trabecular separation, cortical bone volume fraction, cortical thickness, and cortical porosity.

COVARIATES

Covariates included demographic variables such as age, estrogen levels, and ethnicity.

ANALYSES

Quantitative microstructure analyses were conducted on cone-beam computed tomography images, and differences between groups for continuous measures (including age) were assessed with an unpaired t-test, and demographic variables were assessed by χ2. Statistical significance was recorded at P < .05.

RESULTS

The premenopausal and postmenopausal groups each had 31 participants, with the following average age: premenopausal = 43.9 ± 6.9 versus postmenopausal = 57.5 ± 7.6 years old; P < .001, and estrogen levels: premenopausal = 91.77 ± 80.13 pg/ml versus postmenopausal = 41.44 ± 61.62 pg/ml; P < .01). Postmenopausal women had significantly greater condylar trabecular separation (0.61 ± 0.18 vs 0.47 ± 0.11 mm; P < .001) and lower trabecular number (1.03 ± 0.18 vs 1.21 ± 0.19 mm-1; P < .001) compared to premenopausal women. There were no significant differences in the basal bone microarchitectural parameters between the menopausal groups.

CONCLUSION AND RELEVANCE

Menopause is associated with mandibular condylar trabecular bone loss but has minimal effects on the mandibular basal bone. This may have important ramifications for treatment planning in advanced-age individuals.

The detection of Gper1 as an important gene promoting jawbone regeneration in the context of estrogen deficiency

Numerous studies have demonstrated that estrogen deficiency inhibit the proliferation and differentiation of pre-osteoblasts in skeleton by affecting osteogenic signaling, lead to decreased bone mass and impaired regeneration. To explore the mechanisms maintaining bone regeneration under estrogen deficiency, we randomly selected 1102 clinical cases, in which female patients aged between 18 and 75 have underwent tooth extraction in Stomatological Hospital of Tongji University, there is little difference in the healing effect of extraction defects, suggesting that to some extent, the regeneration of jawbone is insensitive to the decreased estrogen level. To illuminate the mechanisms promoting jawbone regeneration under estrogen deficiency, a tooth extraction defect model was established in the maxilla of female rats who underwent ovariectomy (OVX) or sham surgery, and jawbone marrow stromal cells (BMSCs) were isolated for single-cell sequencing. Further quantitative PCR, RNA interference, alizarin red staining, immunohistochemistry and western blotting experiments demonstrated that in the context of ovariectomy, maxillary defects promoted G protein-coupled estrogen receptor 1 (Gper1) expression, stimulate downstream cAMP/PKA/pCREB signaling, and facilitate cell proliferation, and thus provided sufficient progenitors for osteogenesis and enhanced the regeneration capacity of the jawbone. Correspondingly, the heterozygous deletion of the Gper1 gene attenuated the phosphorylation of CREB, led to decreased cell proliferation, and impaired the restoration of maxillary defects. This study demonstrates the importance of Gper1 in maintaining jawbone regeneration, especially in the context of estrogen deficiency.