Colon epithelial cell-specific Bmal1 deletion impairs bone formation in mice

The circadian clock system regulates multiple metabolic processes, including bone metabolism. Previous studies have demonstrated that both central and peripheral circadian signaling regulate skeletal growth and homeostasis. Disruption in central circadian rhythms has been associated with a decline in bone mineral density and the global and osteoblast-specific disruption of clock genes in bone tissue leads to lower bone mass. Gut physiology is highly sensitive to circadian disruption. Since the gut is also known to affect bone remodeling, we sought to test the hypothesis that circadian signaling disruption in colon epithelial cells affects bone. We therefore assessed structural, functional, and cellular properties of bone in 8 week old Ts4-Cre and Ts4-Cre;Bmal1fl/fl (cBmalKO) mice, where the clock gene Bmal1 is deleted in colon epithelial cells. Axial and appendicular trabecular bone volume was significantly lower in cBmalKO compared to Ts4-Cre 8-week old mice in a sex-dependent fashion, with male but not female mice showing the phenotype. Similarly, the whole bone mechanical properties were deteriorated in cBmalKO male mice. The tissue level mechanisms involved suppressed bone formation with normal resorption, as evidenced by serum markers and dynamic histomorphometry. Our studies demonstrate that colon epithelial cell-specific deletion of Bmal1 leads to trabecular and cortical bone loss in male mice.

Sexual dimorphism in the assessment of mineral apposition rate during osteoporosis

The objective of this study was to evaluate the daily maxillary and tibial bone mineral apposition rate of ovariectomized rats and orchiectomized rats through confocal laser microscopy. Twenty-four animals were divided into 4 groups (SHAMF, OVX, SHAMM and ORQ). Six rats were distributed to the SHAMF group (submitted to fictitious surgery); six rats to the OVX group (submitted to bilateral ovariectomy); six rats to the SHAMM group (submitted to fictitious surgery) and six rats to the ORQ group (submitted to bilateral orchiectomy). On the 60th day after the surgical procedures the animals received 20 mg/kg of calcein and after 24 days 20 mg/kg of alizarin red was administered. The euthanasia was performed 18 days after the last fluorochrome administration. The histological slides obtained were submitted to confocal microscopy analysis and then dynamic histomorphometry was performed to obtain the daily mineral apposition rate (MAR). In the tibias, the values of MAR were higher for the SHAMF group (P<0.05) (mean: 37.1μm² / day) compared to the ORQ group (mean: 7.16 μm²). In the jaws, the values were higher for the SHAMF group (P<0.05) (mean: 5.175μm² / day) compared to the SHAMM group (mean: 1.84 μm²), OVX (mean: 3.027 μm²) and ORQ group (mean: 1.56 μm²). It can be concluded that the female gender, regarding the characteristics of the maxillary and tibial bones, presented a daily mineral bone apposition rate higher than the male gender, mainly in the maxillary bone, presenting a statistically significant difference between all groups studied.

Longitudinal time-lapse in vivo micro-CT reveals differential patterns of peri-implant bone changes after subclinical bacterial infection in a rat model

Subclinical infection associated with orthopedic devices can be challenging to diagnose. The goal of this study was to evaluate longitudinal, microcomputed tomography (microCT) imaging in a rat model of subclinical orthopedic device-related infection caused by Staphylococcus epidermidis and four different Cutibacterium (previously Propionibacterium) acnes strains, and compare outcomes with non-inoculated and historical S. aureus-inoculated controls. Sterile screws or screws colonized with bacteria were placed in the tibia of 38 adult Wistar rats [n = 6 sterile screws; n = 6 S. epidermidis-colonized screws; n = 26 C. acnes-colonized screws (covering all three main subspecies)]. Regular microCT scans were taken over 28 days and processed for quantitative time-lapse imaging with dynamic histomorphometry. At euthanasia, tissues were processed for semiquantitative histopathology or quantitative bacteriology. All rats receiving sterile screws were culture-negative at euthanasia and displayed progressive bony encapsulation of the screw. All rats inoculated with S. epidermidis-colonized screws were culture-positive and displayed minor changes in peri-implant bone, characteristic of subclinical infection. Five of the 17 rats in the C. acnes inoculated group were culture positive at euthanasia and displayed bone changes at the interface of the screw and bone, but not deeper in the peri-implant bone. Dynamic histomorphometry revealed significant differences in osseointegration, bone remodeling and periosteal reactions between groups that were not measurable by visual observation of still microCT images. Our study illustrates the added value of merging 3D microCT data from subsequent timepoints and producing inherently richer 4D data for the detection and characterization of subclinical orthopedic infections, whilst also reducing animal use.

The TrkA agonist gambogic amide augments skeletal adaptation to mechanical loading through actions on sensory nerves and osteoblasts

ABSTRACTThe periosteal and endosteal surfaces of mature bone are densely innervated by sensory nerves expressing TrkA, the high-affinity receptor for nerve growth factor (NGF). In previous work, we demonstrated that administration of exogenous NGF significantly increased load-induced bone formation through the activation of Wnt signaling. However, the translational potential of NGF is limited by the induction of substantial mechanical and thermal hyperalgesia in mice and humans. Here, we tested the effect of gambogic amide (GA), a recently identified robust small molecule agonist for TrkA, on hyperalgesia and load-induced bone formation. Behavioral analysis was used to assess pain up to one week after axial forelimb compression. Contrary to our expectations, GA treatment was not associated with diminished use of the loaded forelimb or sensitivity to thermal stimulus. Furthermore, dynamic histomorphometry revealed a significant increase in relative periosteal bone formation rate as compared to vehicle treatment. Additionally, we found that GA treatment was associated with an increase in the number of osteoblasts per bone surface in loaded limbs as well as a significant upregulation of Wnt1, Wnt7b, and Ngf in loaded bones. To determine if these effects were exclusively mediated by NGF-TrkA signaling in sensory nerves, we cultured MC3T3-E1 cells for 7 or 14 days in osteogenic differentiation media containing NGF (50 ng/mL), GA (5, 50, or 500 nM), or vehicle (DMSO). After 7 days of culture, we observed increases in osteoblastic differentiation markers Runx2, Bglap2, and Sp7 in response to GA, whereas treatment with NGF was not different than vehicle. Only cells treated with the highest dose of GA (500 nM) had significantly impaired cell proliferation. In conclusion, our study indicates GA may be useful for augmenting skeletal adaptation to mechanical forces without inducing hyperalgesia through actions on both sensory nerves and osteoblasts.

Skeletal Toxicity of Coplanar Polychlorinated Biphenyl Congener 126 in the Rat Is Aryl Hydrocarbon Receptor Dependent

Epidemiological evidence links polychlorinated biphenyls (PCBs) to skeletal toxicity, however mechanisms whereby PCBs affect bone are poorly studied. In this study, coplanar PCB 126 (5 μmol/kg) or corn oil vehicle was administered to N = 5 and 6 male and female, wild type (WT) or AhR −/− rats via intraperitoneal injection. Animals were sacrificed after 4 weeks. Bone length was measured; bone morphology was assessed by microcomputed tomography and dynamic histomorphometry. Reduced bone length was the only genotype-specific effect and only observed in males (p &lt; .05). WT rats exposed to PCB 126 had reduced serum calcium, and smaller bones with reduced tibial length, cortical area, and medullary area relative to vehicle controls (p &lt; .05). Reduced bone formation rate observed in dynamic histomorphometry was consistent with inhibition of endosteal and periosteal bone growth. The effects of PCB 126 were abolished in AhR −/− rats. Gene expression in bone marrow and shaft were assessed by RNA sequencing. Approximately 75% of the PCB-regulated genes appeared AhR dependent with 89 genes significantly (p &lt; .05) regulated by both PCB 126 and knockout of the AhR gene. Novel targets significantly induced by PCB 126 included Indian hedgehog (Ihh) and connective tissue growth factor (Ctgf/Ccn2), which regulate chondrocyte proliferation and differentiation in the bone growth plate and cell-matrix interactions. These data suggest the toxic effects of PCB 126 on bone are mediated by AhR, which has direct effects on the growth plate and indirect actions related to endocrine disruption. These studies clarify important mechanisms underlying skeletal toxicity of dioxin-like PCBs and highlight potential therapeutic targets.

SAT-392 The Role of β-arrestin2 in Bone Catabolic Response to Hyperparathyroidism In Vivo

Primary hyperparathyroidism (PHPT) is an endocrine disorder characterized by elevated parathyroid hormone (PTH) levels and hypercalcemia caused by the overactive parathyroid glands, resulting in negative impacts on the skeleton including bone loss and increased bone fragility1. PTH binds and activates parathyroid hormone type 1 receptor (PTH1R) which primary couples to Gαs, stimulating the downstream effectors that mediate bone remodeling processes2. PTH1R activity is regulated by arrestins, specially β-arrestin2 (β-arr2), through signal termination and receptor internalization2. Previously, we have seen anabolic effects of hyperparathyroidism (cPTH) on trabecular bone in mice overexpressing Gαs3. We hypothesized that increased Gαs protein levels in osteoblasts outcompete β-arr binding to PTH1R, leading to reduced signal termination and increased bone formation. To test this hypothesis, we are testing if the deletion of β-arr2 will also result in an anabolic response to cPTH in this study. The response of β-arr2 knockout (KO) mice to cPTH have yet to be documented. The hypothesis of this study is that β-arr2 KO mice treated with cPTH will exhibit anabolic effects on the trabecular bone. Nine-week-old wild-type (WT) C57BL/6 and β-arr2 KO mice were treated for 14 days with either rPTH1-34 (80ng/g/day) or saline (PBS) using micro-osmotic pumps to simulate hyperparathyroidism. There are 8 groups (n=10 per group) including both sexes, 2 genotypes (WT and KO), and 2 treatment groups (PTH and PBS). Two 30 mg/kg doses of 0.6% calcein green were administered subcutaneously to mice at 7 and 2 days prior to euthanasia to label bones. Decalcified tibiae were embedded in paraffin for histological analysis. Undecalcified tibiae were embedded in plastic for dynamic histomorphometry. Micro-computed tomography (μCT) was used to access bone microarchitecture of femurs and vertebrae followed by biomechanical testing of bone strength. The μCT data of distal femurs show that cPTH treatment increased bone volume in female KO mice (6.864 ± 2.318 vs 4.690 ± 1.555 %; P= 0.0328; n=9 per group) and maintained bone in male KO mice (13.37 ± 2.860 vs 13.38 ± 3.135; P= 0.9968, n= 10) compared to control. Histological analysis show higher osteoclastic activity in both sexes and genotypes when treated with cPTH, suggesting that the anabolic response may be at the level of osteoblasts and osteocytes. These promising results support our hypothesis that arrestin-mediated PTH receptor downregulation plays an importance role in bone weakness associated with hyperparathyroidism. These studies are important for understanding the clinical phenotype of PHPT patients and suggest that inhibition of β-arr2 in PHPT could be a path for drug therapy. References: (1) Mosekilde L. Clin Endocrinol 2008;69:1-9. (2) Ferrari SL et al., J Biol Chem 1999; 274:29968–29975 (3) Zhang L. PhD thesis University of Toronto, 2018.

Histological, Histomorphometrical, and Biomechanical Studies of Bone-Implanted Medical Devices: Hard Resin Embedding

The growing incidence of degenerative musculoskeletal disorders as well as lifestyle changes has led to an increase in the surgical procedures involving implanted medical devices in orthopedics. When studying implant/tissue interface in hard materials (i.e., metals or dense plastics) and/or in large bone segments, the hard plastic embedding of the intact undecalcified tissue envelope with the implant in situ is needed. The aim of this work is to describe the advances and the possibilities of high-temperature methyl methacrylate (MMA) embedding for the histological, histomorphometrical, and biomechanical assessment of bone-implanted medical devices. Unlike routine techniques, undecalcified bone processing histology, using high-temperature MMA, requires a complex and precise sample processing methodology and the availability of sophisticated equipment and software for both sample preparation and analyses. MMA embedding permits the evaluation of biological responses to the presence of implanted medical devices without implant removal, allowing simultaneous qualitative and quantitative histological evaluation, both static and dynamic histomorphometry, and biomechanical analyses not possible with tissue decalcification. MMA embedding, despite being a demanding procedure, is still preferred to other kinds of resin-based embedding because of its peculiar characteristics, which allow the study of samples of big dimensions also implanted with hard materials without reducing the sample or removing the material. Dynamic measurements are allowed together with biomechanical investigations at the bone-biomaterial interface, obtaining a comprehensive and precise evaluation of the safety and effectiveness of medical devices for orthopedic regenerative, reconstructive, and reparative surgery.

Clinically relevant doses of vitamin A decrease cortical bone mass in mice

Excess vitamin A has been associated with decreased cortical bone thickness and increased fracture risk. While most studies in rodents have employed high dosages of vitamin A for short periods of time, we investigated the bone phenotype in mice after longer exposure to more clinically relevant doses. For 1, 4 and 10 weeks, mice were fed a control diet (4.5 µg retinyl acetate/g chow), a diet modeled from the human upper tolerable limit (UTL; 20 µg retinyl acetate/g chow) and a diet three times UTL (supplemented; 60 µg retinyl acetate/g chow). Time-dependent decreases in periosteal circumference and bone mineral content were noted with the supplemented dose. These reductions in cortical bone resulted in a significant time-dependent decrease of predicted strength and a non-significant trend toward reduced bone strength as analyzed by three-point bending. Trabecular bone in tibiae and vertebrae remained unaffected when vitamin A was increased in the diet. Dynamic histomorphometry demonstrated that bone formation was substantially decreased after 1 week of treatment at the periosteal site with the supplemental dose. Increasing amount of vitamin A decreased endocortical circumference, resulting in decreased marrow area, a response associated with enhanced endocortical bone formation. In the presence of bisphosphonate, vitamin A had no effect on cortical bone, suggesting that osteoclasts are important, even if effects on bone resorption were not detected by osteoclast counting, genes in cortical bone or analysis of serum TRAP5b and CTX. In conclusion, our results indicate that even clinically relevant doses of vitamin A have a negative impact on the amount of cortical bone.

Enhanced angiogenesis and increased bone turnover characterize bone marrow lesions in osteoarthritis at the base of the thumb

ObjectivesLittle is known about tissue changes underlying bone marrow lesions (BMLs) in non-weight-bearing joints with osteoarthritis (OA). Our aim was to characterize BMLs in OA of the hand using dynamic histomorphometry. We therefore quantified bone turnover and angiogenesis in subchondral bone at the base of the thumb, and compared the findings with control bone from hip OA.MethodsPatients with OA at the base of the thumb, or the hip, underwent preoperative MRI to assess BMLs, and tetracycline labelling to determine bone turnover. Three groups were compared: trapezium bones removed by trapeziectomy from patients with thumb base OA (n = 20); femoral heads with (n = 24); and those without (n = 9) BMLs obtained from patients with hip OA who underwent total hip arthroplasty.ResultsAll trapezium bones demonstrated MRI-defined BMLs. Compared with femoral heads without BMLs, the trapezia demonstrated significantly higher bone turnover (mean sd 0.2 (0.1) versus 0.01 (0.01) µm3/µm2/day), mineralizing surface (18.5% (13.1) versus 1.4% (1.3)) and vascularity (5.2% (1.1) versus 1.2% (0.6)). Femoral heads with BMLs exhibited higher bone turnover (0.3 (0.2) versus 0.2 (0.1) µm3/µm2/day), a higher mineralization rate (26.6% (10.6) versus 18.6% (11.9)) and greater trabecular thickness (301.3 µm (108) versus 163.6 µm (24.8)) than the trapezia.ConclusionBone turnover and angiogenesis were enhanced in BMLs of both the thumb base and hip OA, of which the latter exhibited the highest bone turnover. Thus, the increase in bone turnover in weight-bearing joints like the hip may be more pronounced than less mechanically loaded osteoarthritic joints demonstrating BMLs. The histological changes observed may explain the water signal from BMLs on MRI. Cite this article: M. Shabestari, N. J. Kise, M. A. Landin, S. Sesseng, J. C. Hellund, J. E. Reseland, E. F. Eriksen, I. K. Haugen. Enhanced angiogenesis and increased bone turnover characterize bone marrow lesions in osteoarthritis at the base of the thumb. Bone Joint Res 2018;7:406–413. DOI: 10.1302/2046-3758.76.BJR-2017-0083.R3.