Hyperkyphosis is not dependent on bone mass and quality in the mouse model of Marfan syndrome.

Marfan syndrome (MFS) is an autosomal dominant disease affecting cardiovascular, ocular and skeletal systems. It is caused by mutations in the fibrillin-1 (FBN1) gene, leading to structural defects of connective tissue and increased activation of TGF-ß. Angiotensin II (ang-II) is involved in TGF-ß activity and in bone mass regulation. Inhibition of TGF-ß signaling by blockage of the ang-II receptor 1 (AT1R) via losartan administration leads to improvement of cardiovascular and pulmonary phenotypes, but has no effect on skeletal phenotype in the haploinsufficient mouse model of MFS mgR, suggesting a distinct mechanism of pathogenesis in the skeletal system. Here we characterized the skeletal phenotypes of the dominant-negative model for MFS mgΔlpn and tested the effect of inhibition of ang-II signaling in improving those phenotypes. As previously shown, heterozygous mice present hyperkyphosis, however we now show that only males also present osteopenia. Inhibition of ang-II production by ramipril minimized the kyphotic deformity, but had no effect on bone microstructure in male mutant animals. Histological analysis revealed increased thickness of the anterior longitudinal ligament (ALL) of the spine in mutant animals (25.8 ± 6.3 vs. 29.7 ± 7.7 µm), coupled with a reduction in type I (164.1 ± 8.7 vs. 139.0 ± 4.4) and increase in type III (86.5 ± 10.2 vs. 140.4 ± 5.6) collagen in the extracellular matrix of this ligament. In addition, we identified in the MFS mice alterations in the erector spinae muscles which presented thinner muscle fibers (1035.0 ± 420.6 vs. 655.6 ± 239.5 µm2) surrounded by increased area of connective tissue (58.17 ± 6.52 vs. 105.0 ± 44.54 µm2). Interestingly, these phenotypes were ameliorated by ramipril treatment. Our results reveal a sex-dependency of bone phenotype in MFS, where females do not present alterations in bone microstructure. More importantly, they indicate that hyperkyphosis is not a result of osteopenia in the MFS mouse model, and suggest that incompetent spine ligaments and muscles are responsible for the development of that phenotype.

Early versus late repair of rotator cuff tears in rats.

BACKGROUND: In the event of a traumatic rotator cuff tear, patients are routinely advised that early surgical intervention produces an optimal repair, despite a lack of direct evidence to support this recommendation. To address this knowledge gap, massive rotator cuff tears in rats were assessed by biomechanical and bone morphometric analyses after early or late repair. METHODS: Combined supraspinatus and infraspinatus tendon tears of the left shoulder were created in 21 adult Wistar rats, which were divided into 2 groups. The tendons of the injured shoulder in the animals in group I were surgically repaired 8 weeks after the injury. Under the same anesthesia, the same injury was created on the right shoulder, which was immediately repaired. The rats from group I were euthanized 8 weeks after the repairs. No repair was performed in the rats from group II, which were euthanized 8 weeks after the injury. Tissues from both groups were harvested and biomechanically tested for supraspinatus tendon and bone morphometry analysis of the humeral head. RESULTS: All biomechanical properties were significantly increased in the early repair group compared with the late repair group. No significant differences were observed in bone morphometry of the humeral head when early and late repair groups were compared. CONCLUSION: Early surgical repair of a massive rotator cuff tear leads to improved biomechanical properties of the tissue after healing. Proximal humerus bone morphometry was unaffected by surgical repair timing.

Lack of α2C-Adrenoceptor Results in Contrasting Phenotypes of Long Bones and Vertebra and Prevents the Thyrotoxicosis-Induced Osteopenia.

A series of studies have demonstrated that activation of the sympathetic nervous system (SNS) causes osteopenia via ß2-adrenoceptor (ß2-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, α2A-and α2C-AR (α2A/2C-AR-/-). These findings suggest that ß2-AR is not the single adrenoceptor involved in bone turnover regulation and show that α2-AR signaling may also mediate the SNS actions in the skeleton. In addition, we found that α2A/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 α2-AR signaling. In the present study, to further investigate these hypotheses and to discriminate the roles of α2-AR subtypes, we have evaluated the bone phenotype of mice with the single gene inactivation of α2C-AR subtype, which mRNA expression was previously shown to be down regulated by triiodothyronine (T3). A cohort of 30 day-old female α2CAR-/- 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 (µCT) analysis showed that α2C-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 α2C-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 α2C-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 α2C-AR-/- mice. Altogether, these findings suggest that α2C-AR subtype mediates the effects of the SNS in the bone in a skeletal site-dependent manner, and that thyrotoxicosis depends on α2C-AR signaling to promote bone loss, which sustains the hypothesis of a TH-SNS interaction to modulate bone remodeling and structure.

Is bone transplantation the gold standard for repair of alveolar bone defects?

New strategies to fulfill craniofacial bone defects have gained attention in recent years due to the morbidity of autologous bone graft harvesting. We aimed to evaluate the in vivo efficacy of bone tissue engineering strategy using mesenchymal stem cells associated with two matrices (bovine bone mineral and α-tricalcium phosphate), compared to an autologous bone transfer. A total of 28 adult, male, non-immunosuppressed Wistar rats underwent a critical-sized osseous defect of 5 mm diameter in the alveolar region. Animals were divided into five groups. Group 1 (n = 7) defects were repaired with autogenous bone grafts; Group 2 (n = 5) defects were repaired with bovine bone mineral free of cells; Group 3 (n = 5) defects were repaired with bovine bone mineral loaded with mesenchymal stem cells; Group 4 (n = 5) defects were repaired with α-tricalcium phosphate free of cells; and Group 5 (n = 6) defects were repaired with α-tricalcium phosphate loaded with mesenchymal stem cells. Groups 2-5 were compared to Group 1, the reference group. Healing response was evaluated by histomorphometry and computerized tomography. Histomorphometrically, Group 1 showed 60.27% ± 16.13% of bone in the defect. Groups 2 and 3 showed 23.02% ± 8.6% (p = 0.01) and 38.35% ± 19.59% (p = 0.06) of bone in the defect, respectively. Groups 4 and 5 showed 51.48% ± 11.7% (p = 0.30) and 61.80% ± 2.14% (p = 0.88) of bone in the defect, respectively. Animals whose bone defects were repaired with α-tricalcium phosphate and mesenchymal stem cells presented the highest bone volume filling the defects; both were not statistically different from autogenous bone.

A TRbeta-selective agonist confers resistance to diet-induced obesity.

Thyroid hormone receptor beta (TRbeta also listed as THRB on the MGI Database)-selective agonists activate brown adipose tissue (BAT) thermogenesis, while only minimally affecting cardiac activity or lean body mass. Here, we tested the hypothesis that daily administration of the TRbeta agonist GC-24 prevents the metabolic alterations associated with a hypercaloric diet. Rats were placed on a high-fat diet and after a month exhibited increased body weight (BW) and adiposity, fasting hyperglycemia and glucose intolerance, increased plasma levels of triglycerides, cholesterol, nonesterified fatty acids and interleukin-6. While GC-24 administration to these animals did not affect food ingestion or modified the progression of BW gain, it did increase energy expenditure, eliminating the increase in adiposity without causing cardiac hypertrophy. Fasting hyperglycemia remained unchanged, but treatment with GC-24 improved glucose tolerance by increasing insulin sensitivity, and also normalized plasma triglyceride levels. Plasma cholesterol levels were only partially normalized and liver cholesterol content remained high in the GC-24-treated animals. Gene expression in liver, skeletal muscle, and white adipose tissue was only minimally affected by treatment with GC-24, with the main target being BAT. In conclusion, during high-fat feeding treatment with the TRbeta-selective agonist, GC-24 only partially improves metabolic control probably as a result of accelerating the resting metabolic rate.

Isoflavone-supplemented soy yoghurt associated with resistive physical exercise increase bone mineral density of ovariectomized rats.

OBJECTIVE: To determine the effects produced by the ingestion of a fermented soy product (soy yoghurt), supplemented with isoflavones and associated with a resistive exercise program, on the bone metabolism of mature ovariectomized (Ovx) and sham-ovariectomized (sham-Ovx) rats. METHODS: A total of 56 rats were used. They were divided into 2 sedentary control groups, the Ovx control group (C-Ovx) and the sham-Ovx control group (C-Sovx), each with 7 sedentary animals, and 2 treated groups, Ovx and sham-Ovx, with 21 animals each. These two treated groups were subdivided into three subgroups of seven animals each, which received the following treatments: consuming the soy yoghurt+sedentary, only subjected to resistive exercise, and consuming the soy yoghurt+resistive exercise. Both the program of resistive exercise and the consumption of soy yoghurt (at 3 mL/(kg body weight day)) continued for 12 weeks. The soy yoghurt was supplemented with isoflavones at 50mg/100g of product. The animals were sacrificed and their right-side femurs and tibias removed and assessed for bone mineral density (BMD). The alkaline phosphatase activity (AP) was determined in the blood serum. RESULTS: There was a significant increase in both femur and tibia BMD values and in serum alkaline phosphatase activity in all the treated subgroups, compared with the control groups (p<0.05). CONCLUSION: The ingestion of the soy yoghurt supplemented with isoflavones was capable of preventing a loss of bone mass in Ovx rats and of increasing bone mass in sham rats, whilst the resistive exercise program was effective in augmenting the bone mass in sham and Ovx rats.