Assessment of Bone Microstructure by Micro CT in C57BL/6J Mice for Sex-Specific Differentiation

Comparison of gene expression of bone regulators and bone microstructure in 20 weeks old female mice of two different strains (C57BL/6J and C3H/HeOuJ)

A huge number of inbred mouse strains with different bone properties have become available for musculoskeletal research. C57Bl/6J and C3H/HeOuJ mice show a significant difference in their bone characteristics. Nevertheless, there is a lack of knowledge on the molecular basis of these strain differences. The aim of this study is to determine the gene expression of selected regulators expressed in the bone marrow as well as bone microstructure of C57Bl/6J and C3H/HeOuJ mice. Bone properties were investigated in 20-week-old female C57Bl/6J and C3H/HeOuJ mice. Total RNA was extracted from the bone marrow of the tibia and gene expression of the following genes was determined by quantitative real-time PCR: SOST, DKK1, OPN, FGF23, RANKL, IL6, TNF, IL17a, and OPG. The femur and third lumbar vertebral body (L3) were investigated by μCT. Bone histomorphometric evaluations were performed in tartrate-resistant acid phosphatase/toluidine blue stained fourth lumbar vertebral bodies (L4). C57Bl/6J and C3H/HeOuJ mice showed significant differences in the gene expression of DKK1, FGF23, IL-6, TNF, and OPG. When compared with C57Bl/6J mice, C3H/HeOuJ mice had a stronger cortical and trabecular bone microstructure at the femur. In contrast, at L3 bone volume/total volume (BV/TV) and trabecular number were significantly higher in C57Bl/6J than in C3H/HeOuJ mice. Bone histomorphometry of L4 revealed significantly higher BV/TV, trabecular number, and thickness in C57Bl/6J mice. Furthermore, the number of osteoblasts and the number of osteoclasts/bone perimeter were higher in the C57Bl/6J mice. This study shows that C57Bl/6J and C3H/HeOuJ mice exhibit a differential expression of cytokines present in the bone marrow. Bone properties differ not only between both strains but also in relation to the investigated bone region.

Activation of osteoblast ferroptosis by risperidone accelerates bone loss in mice models of schizophrenia

BACKGROUND

Ferroptosis is an iron-dependent regulatory cell death, which plays an essential role in bone loss. This study investigated whether the mechanism of risperidone (RIS)-induced bone loss is related to ferroptosis.

METHODS

The schizophrenia mice were induced by administering MK-801. Subsequently, RIS were injected, or ferroptosis inhibitor Ferrostatin-1 (Fer-1) co-injected for 8 weeks. Bone loss of schizophrenia mice were assessed using microCT, H&E staining, ALP staining, ARS staining and WB, respectively. Ferroptosis of schizophrenia mice were detected by Iron Colorimetric Assay Kit and WB, respectively. In addition, ALP staining, ARS staining, and WB were performed to reveal the role of RIS in osteogenic differentiation of MC3T3-E1 and BMSCs cells.

RESULTS

RIS treatment facilitates bone loss in schizophrenia mice and inhibit osteogenic differentiation of MC3T3-E1 and BMSCs cells. Moreover, up-regulated ferroptosis was found in vivo and in vitro after RIS treatment. Interesting, the bone loss and inhibition of osteogenic differentiation induced by RIS in schizophrenia mice were reversed by ferroptosis inhibitor Fer-1.

CONCLUSION

Ferroptosis induced by RIS aggravates the bone loss of schizophrenia mice via inhibiting osteogenic differentiation.

Methyl-Beta-Cyclodextrin Restores Aberrant Bone Morphogenetic Protein 2-Signaling in Bone Marrow Stromal Cells Obtained from Aged C57BL/6 Mice

During aging, disruptions in various signaling pathways become more common. Some older patients will exhibit irregular bone morphogenetic protein (BMP) signaling, which can lead to osteoporosis (OP)-a debilitating bone disease resulting from an imbalance between osteoblasts and osteoclasts. In 2002, the Food and Drug Administration (FDA) approved recombinant human BMP-2 (rhBMP-2) for use in spinal fusion surgeries as it is required for bone formation. However, complications with rhBMP-2 arose and primary osteoblasts from OP patients often fail to respond to BMP-2. Although patient samples are available for study, previous medical histories can impact results. Consequently, the C57BL/6 mouse line serves as a valuable model for studying OP and aging. We find that BMP receptor type Ia (BMPRIa) is upregulated in the bone marrow stromal cells (BMSCs) of 15-month-old mice, consistent with prior data. Furthermore, conjugating BMP-2 with Quantum Dots (QDot®s) allows effective binding to BMPRIa, creating a fluorescent tag for BMP-2. Furthermore, after treating BMSCs with methyl-β-cyclodextrin (MβCD), a disruptor of cellular endocytosis, BMP signaling is restored in 15-month-old mice, as shown by von Kossa assays. MβCD has the potential to restore BMPRIa function, and the BMP signaling pathway offers a promising avenue for future OP therapies.

Risperidone accelerates bone loss in mice models of schizophrenia by inhibiting osteoblast autophagy

Background

Risperidone (RIS) is the first-line drug in the clinical treatment of schizophrenia, and long-term use may lead to bone loss and even osteoporosis. This study investigated whether the mechanism of RIS-induced bone loss is related to autophagy.

Methods

The schizophrenia mice were established with the administration of MK-801. Then, RIS were injected, or autophagy inducer rapamycin (RAPA) co-injected for 8 weeks. Cognitive performance was determined by the novel object recognition and Open field tests. Bone loss of schizophrenia mice were assessed using microCT, H&E staining, ALP staining, ARS staining and WB, respectively. Autophagy of schizophrenia mice were detected by immunofluorescence, transmission electron microscopy (TEM) and WB, respectively. In addition, osteogenic differentiation of MC3T3-E1 and BMSCs cells were assessed using H&E staining, ALP staining, ARS staining and WB, respectively.

Results

In the present study, we found that RIS treatment can promote bone loss in schizophrenia mice and inhibit osteogenic differentiation of MC3T3-E1 and BMSCs cells. Interesting, the number of autophagosome and autophagy-related protein expression were decreased after RIS treatment. However, the bone loss and inhibition of osteogenic differentiation induced by RIS in schizophrenia mice were reversed by autophagy inducer RAPA.

Conclusion

RIS significantly increased bone loss and inhibited osteogenic differentiation in schizophrenia mice; the underlying mechanism entails suppressing osteoblast autophagy.

Potential role of remimazolam in alleviating bone cancer pain in mice via modulation of translocator protein in spinal astrocytes

Bone cancer pain (BCP) is a complex clinical challenge, with current treatments often falling short of providing adequate relief. Remimazolam, a benzodiazepine receptor agonist recognized for its anxiolytic effects, has emerged as a potential agent in managing BCP. This study explores the analgesic properties of remimazolam and its interaction with the translocator protein (TSPO), previously known as the peripheral benzodiazepine receptor, in spinal astrocytes. In the context of BCP, previous research has indicated that TSPO expression in spinal astrocytes may serve a protective regulatory function in neuropathic pain models. Building on this, the BCP mice received various doses of remimazolam on the 15th day post-inoculation, and pain behavior was assessed over time. The results showed that BCP induced an upregulation of TSPO and astrocyte activation in the spinal dorsal horn, alongside increased extracellular signal-regulated kinase (ERK) signaling and inflammatory cytokine expression. Remimazolam administration resulted in a dose-dependent reduction of pain behaviors, which corresponded with a decrease in both ERK pathway activation and inflammatory factor expression. This suggests that remimazolam's analgesic effects are mediated through its action as a TSPO agonist, leading to the attenuation of neuroinflammation and pain signaling pathways. Importantly, the analgesic effects of remimazolam were reversed by the TSPO antagonist PK11195, underscoring the pivotal role of TSPO in the drug's mechanism of action. This reversal also reinstated the heightened levels of ERK activity and inflammatory mediators, further confirming the involvement of TSPO in the modulation of these pain-related processes. These findings open new avenues for the therapeutic management of bone cancer pain, positioning remimazolam as a promising candidate for further investigation and development.

Compromised femoral and lumbovertebral bone in the Dp(16)1Yey Down syndrome mouse model

Down syndrome (DS), affecting ∼1 in 800 live births, is caused by the triplication of human chromosome 21 (Hsa21). Individuals with DS have skeletal features including craniofacial abnormalities and decreased bone mineral density (BMD). Lowered BMD can lead to increased fracture risk, with common fracture points at the femoral neck and lumbar spine. While the femur has been studied in DS mouse models, there is little research done on the vertebrae despite evidence that humans with DS have affected vertebrae. Additionally, it is important to establish when skeletal deficits occur to find times of potential intervention. The Dp(16)1Yey DS mouse model has all genes triplicated on mouse chromosome 16 orthologous to Hsa21 and displayed deficits in long bone, including trabecular and cortical deficits in male but not female mice, at 12 weeks. We hypothesized that the long bone and lumbovertebral microarchitecture would exhibit sexually dimorphic deficits in Dp(16)1Yey mice compared to control mice and long bone strength would be diminished in Dp(16)1Yey mice at 6 weeks. The trabecular region of the 4th lumbar (L4) vertebra and the trabecular and cortical regions of the femur were analyzed via micro-computed tomography and 3-point bending in 6-week-old male and female Dp(16)1Yey and control mice. Trabecular and cortical deficits were observed in femurs from male Dp(16)1Yey mice, and cortical deficits were seen in femurs of male and female Dp(16)1Yey mice. Male Dp(16)1Yey femurs had more deficits in bone strength at whole bone and tissue-estimate level properties, but female Dp(16)1Yey mice were also affected. Additionally, the L4 of male and female Dp(16)1Yey mice show trabecular deficits, which have not been previously reported in a DS mouse model. Our results indicate that skeletal deficits associated with DS occur early in skeletal development, are dependent on skeletal compartment and site, are sex dependent, and potential interventions should likely begin early in skeletal development of DS mouse models.

Semi-Automated MicroCT Analysis of Bone Anatomy and Mineralization in Mouse Models

The skeletal system mirrors several processes in the vertebrate body that impact developmental malfunctions, hormonal disbalance, malfunction of calcium metabolism and turn over, and inflammation processes such as arthrosis. X-ray micro computed tomography is a useful tool for 3D in situ evaluation of the skeletal system in a time-related manner, but results depend highly on resolution. Here, we provide the methodological background for a graduated evaluation from whole-body analysis of skeletal morphology and mineralization to high-resolution analysis of femoral and vertebral microstructure. We combine an expert-based evaluation with a machine-learning-based computational approach, including pre-setup analytical task lists. © 2024 Wiley Periodicals LLC. Basic Protocol 1: In vivo microCT scanning and skeletal analysis in mice Basic Protocol 2: Ex vivo high-resolution microCT scanning and microstructural analysis of the femur and L4 vertebra.