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Occlusal disharmony-induced stress causes osteopenia of the lumbar vertebrae and long bones in mice.

ABSTRACT: Excessive exposure to glucocorticoids causes osteoporosis in children and adults. Occlusal disharmony is known to induce an increase in serum corticosteroid levels in murine models, but the influence of occlusal disharmony-induced stress on the bone mass during the growth period has not yet been clarified. The purpose of this study was to investigate whether occlusal disharmony-induced stress decreases bone mass. Five-week-old C57BL/6J male mice were used. A 0.5-mm increase in the vertical height of occlusion was used to induce occlusal disharmony for a period of 7 days. Serum corticosterone levels were significantly higher on post-induction day 7, with radiological evidence of osteopenia of the third lumbar vertebra and long bones of the hind limbs. Osteopenia was associated with a reduction of the mechanical properties of the tibia and femur, with significant suppression of bone formation parameters and an increase in bone resorption parameters, as evaluated by bone histomorphometric analysis of the tibial/femur metaphysis. Our findings at the level of bones were supported by our assessment of serum markers of systemic metabolism. Therefore, occlusal disharmony-induced stress may lead to osteopenia and reduce the mechanical strength of bone through an increase in serum glucocorticoid levels in mice.

SUBMITTER: Shimizu Y

PROVIDER: S-EPMC5760568 | biostudies-literature | 2018 Jan

REPOSITORIES: biostudies-literature

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Occlusal disharmony-induced stress causes osteopenia of the lumbar vertebrae and long bones in mice.

Shimizu Yasuhiro Y Khan Masud M Kato Genki G Aoki Kazuhiro K Ono Takashi T

Scientific reports 20180109 1

Excessive exposure to glucocorticoids causes osteoporosis in children and adults. Occlusal disharmony is known to induce an increase in serum corticosteroid levels in murine models, but the influence of occlusal disharmony-induced stress on the bone mass during the growth period has not yet been clarified. The purpose of this study was to investigate whether occlusal disharmony-induced stress decreases bone mass. Five-week-old C57BL/6J male mice were used. A 0.5-mm increase in the vertical heigh ...[more]

PMID: 29317698

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Project description:A series of studies have demonstrated that activation of the sympathetic nervous system (SNS) causes osteopenia via ?2-adrenoceptor (?2-AR) signaling. However, in a recent study, we found an unexpected and generalized phenotype of high bone mass in female mice with chronic sympathetic hyperactivity, due to double gene inactivation of adrenoceptors that negatively regulate norepinephrine release, ?2A-and ?2C-AR (?2A/2C-AR-/-). These findings suggest that ?2-AR is not the single adrenoceptor involved in bone turnover regulation and show that ?2-AR signaling may also mediate the SNS actions in the skeleton. In addition, we found that ?2A/2C-AR-/- animals are resistant to the thyrotoxicosis-induced osteopenia, suggesting that thyroid hormone (TH), when in supraphysiological levels, interacts with the SNS to control bone mass and structure, and that this interaction may also involve ?2-AR signaling. In the present study, to further investigate these hypotheses and to discriminate the roles of ?2-AR subtypes, we have evaluated the bone phenotype of mice with the single gene inactivation of ?2C-AR subtype, which mRNA expression was previously shown to be down regulated by triiodothyronine (T3). A cohort of 30 day-old female ?2CAR-/- mice and their wild-type (WT) controls were treated with a supraphysiological dose of T3 for 30 or 90 days, which induced a thyrotoxic state in both mouse lineages. The micro-computed tomographic (?CT) analysis showed that ?2C-AR-/- mice present lower trabecular bone volume (BV/TV) and number (Tb.N), and increased trabecular separation (Tb.Sp) in the femur compared with WT mice; which was accompanied by decreased bone strength (determined by the three-point bending test) in the femur and tibia. The opposite was observed in the vertebra, where ?2C-AR-/- mice show increased BV/TV, Tb.N and trabecular thickness (Tb.Th), and decreased Tb.Sp, compared with WT animals. In spite of the contrasting bone phenotypes of the femur and L5, thyrotoxicosis negatively regulated most of the micro architectural features of the trabecular bone in both skeletal sites of WT, but not of ?2C-AR-/- mice. T3 treatment also decreased biomechanical properties (maximum load and ultimate load) in the femur and tibia of WT, but not of knockout mice. The mRNA expression of osteocalcin, a marker of mature osteoblasts, and tartrate-resistant acid phosphatase, which is expressed by osteoclasts and is involved in collagen degradation, was increased by T3 treatment only in WT, and not in ?2C-AR-/- mice. Altogether, these findings suggest that ?2C-AR subtype mediates the effects of the SNS in the bone in a skeletal site-dependent manner, and that thyrotoxicosis depends on ?2C-AR signaling to promote bone loss, which sustains the hypothesis of a TH-SNS interaction to modulate bone remodeling and structure.

Project description:BackgroundOur recent studies demonstrate that the focal adhesion protein Kindlin-2 exerts crucial functions in the mesenchymal stem cells, mature osteoblasts and osteocytes in control of early skeletal development and bone homeostasis in mice. However, whether Kindlin-2 plays a role in osteoprogenitors remains unclear.Materials and methodsMice lacking Kindlin-2 expression in osterix (Osx)-expressing cells (i.e., osteoprogenitors) were generated. Micro-computerized tomography (μCT) analyses, histology, bone histomorphometry and immunohistochemistry were performed to determine the effects of Kindlin-2 deletion on skeletal development and bone mass accrual and homeostasis. Bone marrow stromal cells (BMSCs) from mutant mice (Kindlin-2 fl/fl ; Osx Cre ) and control littermates were isolated and determined for their osteoblastic differentiation capacity.ResultsKindlin-2 was highly expressed in osteoprogenitors during endochondral ossification. Deleting Kindlin-2 expression in osteoprogenitors impaired both intramembranous and endochondral ossifications. Mutant mice displayed multiple severe skeletal abnormalities, including unmineralized fontanel, limb shortening and growth retardation. Deletion of Kindlin-2 in osteoprogenitors impaired the growth plate development and largely delayed formation of the secondary ossification center in the long bones. Furthermore, adult mutant mice displayed a severe low-turnover osteopenia with a dramatic decrease in bone formation which exceeded that in bone resorption. Primary BMSCs isolated from mutant mice exhibited decreased osteoblastic differentiation capacity.ConclusionsOur study demonstrates an essential role of Kinlind-2 expression in osteoprogenitors in regulating skeletogenesis and bone mass accrual and homeostasis in mice.The translational potential of this articleThis study reveals that Kindlin-2 through its expression in osteoprogenitor cells controls chondrogenesis and bone mass. We may define a novel therapeutic target for treatment of skeletal diseases, such as chondrodysplasia and osteoporosis.

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Occlusal disharmony-induced stress causes osteopenia of the lumbar vertebrae and long bones in mice.

Publications

Occlusal disharmony-induced stress causes osteopenia of the lumbar vertebrae and long bones in mice.

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