Osteoporosis: pathogenesis, diagnosis, prevention and management

Deubiquitinase USP17 Regulates Osteoblast Differentiation by Increasing Osterix Protein Stability

Deubiquitinases (DUBs) are essential for bone remodeling by regulating the differentiation of osteoblast and osteoclast. USP17 encodes for a deubiquitinating enzyme, specifically known as ubiquitin-specific protease 17, which plays a critical role in regulating protein stability and cellular signaling pathways. However, the role of USP17 during osteoblast differentiation has not been elusive. In this study, we initially investigated whether USP17 could regulate the differentiation of osteoblasts. Moreover, USP17 overexpression experiments were conducted to assess the impact on osteoblast differentiation induced by bone morphogenetic protein 4 (BMP4). The positive effect was confirmed through alkaline phosphatase (ALP) expression and activity studies since ALP is a representative marker of osteoblast differentiation. To confirm this effect, Usp17 knockdown was performed, and its impact on BMP4-induced osteoblast differentiation was examined. As expected, knockdown of Usp17 led to the suppression of both ALP expression and activity. Mechanistically, it was observed that USP17 interacted with Osterix (Osx), which is a key transcription factor involved in osteoblast differentiation. Furthermore, overexpression of USP17 led to an increase in Osx protein levels. Thus, to investigate whether this effect was due to the intrinsic function of USP17 in deubiquitination, protein stabilization experiments and ubiquitination analysis were conducted. An increase in Osx protein levels was attributed to an enhancement in protein stabilization via USP17-mediated deubiquitination. In conclusion, USP17 participates in the deubiquitination of Osx, contributing to its protein stabilization, and ultimately promoting the differentiation of osteoblasts.

Identification of key variants correlated with susceptibility of primary osteoporosis in the Chinese Han group

BACKGROUND

Primary osteoporosis is a systemic skeletal disease characterized by reduced bone mass and vulnerability to fractures. The genetics of osteoporosis in the Chinese population remain unclear, which hinders the prevention and treatment of osteoporosis in China. This study aimed to explore the susceptibility genes and the roles played by their variants in osteoporosis.

METHODS

Blood samples were collected from 45 osteoporosis patients and 30 healthy individuals, and genome-wide association study was performed on array data. The expression levels of the candidate gene in different genotypes were further determined by using quantitative real-time PCR. Moreover, the differentiation capacity of bone marrow mesenchymal stem cells under different genotypes from osteoporosis patients was investigated.

RESULTS

The most significant variant rs1891632 located in the upstream (918 bp) region of CRB2, which could down-regulate the expression levels of CRB2 in genotype-tissue expression database and played an essential role in the regulation of osteoblastic and osteoclastic differentiation during skeletal development. Another significant variant rs1061657 located within the 3'UTR region of TBX3 gene. We found that the mRNA levels of TBX3 decreased in the bMSCs of old osteoporosis patients. Interestingly, osteoblast differentiation capacity and TBX3 mRNA levels were similar between the young healthy individuals carrying derived and ancestral allele of rs1061657, whereas the differentiation capacity and TBX3 mRNA levels dramatically declined in elderly patients with osteoporosis.

CONCLUSIONS

The variant rs1061657 might affect the osteogenesis of bMSCs in an age-dependent manner and that TBX3 may be a key susceptibility gene for primary osteoporosis. In conclusion, CRB2 and TBX3 may influence the development of osteoporosis; additionally, rs1891632 and rs1061657, as the key variants first reported to be associated with primary osteoporosis, may potentially contribute to predicting the risk of osteoporosis (especially for older individuals) and may serve as therapeutic targets.

Can gait kinetic data predict femoral bone mineral density in elderly men and women aged 50 years and older?

This retrospective study was conducted to investigate the correlation between kinetic gait parameters and femoral bone mineral density (BMD) in elderly subjects aged 50 years and older that could walk independently. Four hundred and twenty-six subjects (158 men and 258 women; mean age 68.7 years, standard deviation (SD) 7.9 years) were included in the study. BMDs (g/cm²) of the femoral neck, trochanter, shaft, and total proximal femur were collected. Kinetic data including maximum hip power and hip power-time integral was obtained from a three-dimensional gait analysis with self-selected walking speed. Correlation between BMDs of proximal femur and gait kinetic data was analyzed. Multiple regression analysis was also performed to identify factors significantly associated with BMD. Correlation between BMD and hip kinetic data was not prominent in elderly men. In women, BMD was significantly correlated with hip kinetic data. Hip power-time integral showed greater correlation with BMD than maximum hip power during gait in elderly women. Age (p < 0.001), weight (p = 0.007) and hip power-time integral (p = 0.008) were significant factors associated with femoral neck BMD, and these factors explained 25.4% of femoral neck BMD. In conclusion, the association between the mechanical load and BMD in the different sexes provokes future research into these issues. The effects of various types of exercises on BMD should be investigated more precisely using a gait analysis tool.

In vitro studies of composite bone filler based on poly(propylene fumarate) and biphasic α-tricalcium phosphate/hydroxyapatite ceramic powder

While many different filler materials have been applied in vertebral augmentation procedures, none is perfect in all biomechanical and biological characteristics. To minimize possible shortages, we synthesized a new biodegradable, injectable, and premixed composite made from poly(propylene fumarate) (PPF) and biphasic α-tricalcium phosphate (α-TCP)/hydroxyapatite (HAP) ceramics powder and evaluated the material properties of the compound in vitro. We mixed the PPF cross-linked by N-vinyl pyrrolidinone and biphasic α-TCP/HAP powder in different ratios with benzoyl peroxide as an initiator. The setting time and temperature were recorded, although they could be manipulated by modulating the concentrations of hydroquinone and N,N-dimethyl-p-toluidine. Degradation, cytocompatibility, mechanical properties, and radiopacity were analyzed after the composites were cured by a cylindrical shape. We also compared the study materials with poly(methyl methacrylate) (PMMA) and PPF with pure HAP particles. Results showed that lower temperature during curing process (38-44°C), sufficient initial mechanical compressive fracture strength (61.1±3.7MPa), and gradual degradation were observed in the newly developed bone filler. Radiopacity in Hounsfield units was similar to PMMA as determined by computed tomography scan. Both pH value variation and cytotoxicity were within biological tolerable limits based on the biocompatibility tests. Mixtures with 70% α-TCP/HAP powder were superior to other groups. This study indicated that a composite of PPF and biphasic α-TCP/HAP powder is a promising, premixed, injectable biodegradable filler and that a mixture containing 70% α-TCP/HAP exhibits the best properties.

Long-term safety and efficacy of raloxifene in the prevention and treatment of postmenopausal osteoporosis: an update

The integrity of bone tissue and its remodeling that occurs throughout life requires a coordinated activity of osteoblasts and osteoclasts. The decreased estrogen circulating level during postmenopausal transition, with a prevalence of osteoclastic activity over osteoblastic activity, represents the main cause of bone loss and osteoporosis. Osteoporosis is a chronic disease requiring long-term therapy and it is important to evaluate the efficacy and safety of treatments over several years, as the fear of health risks is a common reason for discontinuing therapy. Raloxifene is a selective estrogen receptor modulator (SERM) leading to estrogen-agonist effects in some tissues and estrogen-antagonist effects in others. Raloxifene is effective to prevent and treat postmenopausal vertebral osteoporosis, with reduction of spine fractures and, in post-hoc analyses, non-spine fractures in high-risk subjects. Moreover, raloxifene reduces the risk of invasive breast cancer and improves the levels of serum lipoprotein but with an increased risk of venous thromboembolism and fatal stroke, without significant change in the incidence of coronary events. For these reasons the overall risk-benefit profile is favorable. Therefore, when considering the use of raloxifene in a postmenopausal woman, we should take into account the osteoporosis-related individual risk and weigh the potential benefits, skeletal and extra-skeletal, against the health risks.

Short-term immobilization-induced cancellous bone loss is limited to regions undergoing high turnover and/or modeling in mature rats

Estrogen and calcium deficiencies increase both bone resorption and formation, whereas immobilization mainly decreases bone formation. How these functionally different risk factors for bone loss interact in cancellous bone undergoing modeling or remodeling activity is not well understood. Mature (6-month-old) female rats were subjected to sham operation (sham), ovariectomy (ovx), dietary calcium deficiency (LoCa, 0.1% Ca), and sciatic and femoral denervation (IM), ovx+IM, or LoCa+IM for 4 weeks. The primary spongiosa, the region of active modeling within 1 mm of the growth plate, in ovx, LoCa, and IM groups showed a decrease in cancellous bone volume, trabecular number, and connectivity when compared to sham controls. Groups combining two risk factors exhibited additive changes when compared with single risk factor groups. In the secondary spongiosa, an area with little modeling activity, ovx and LoCa groups, as expected, lost bone. In contrast with the primary spongiosa, IM alone did not induce bone loss in the secondary spongiosa, and the groups with a combination of IM and ovx or IM and LoCa showed a greater bone loss than either ovx or LoCa alone. Ovx and LoCa groups showed increases in both bone formation rate and eroded surface in the secondary spongiosa, while IM groups showed a decrease in bone formation rate. Combining IM with either ovx or LoCa resulted in increased eroded surface. The effects on cortical bone were assessed at the tibio-fibular junction. A trend toward decreased percentage of cortical bone area and an increase in marrow cavity area were observed in the combined deficiency groups only. These changes were the result of a statistically significant increase in endosteal eroded surface in IM+ovx and IM+LoCa groups. Our results demonstrate that immobilization-induced bone loss is restricted to the primary spongiosa where most modeling events occur. However, the inhibitory effect of IM on bone formation in the secondary spongiosa is unmasked in remodeling sites when a high turnover state is provided by either estrogen or dietary calcium deficiency. These results suggest that the presence of a risk factor, such as immobilization, which in the short-term causes inhibition of bone formation, does not predispose the skeleton to rapid cancellous bone loss except when accompanied by modeling or high turnover.