Relations between histologic indices of bone formation: implications for the pathogenesis of spinal osteoporosis

Senescence of skeletal stem cells and their contribution to age-related bone loss

Human aging is linked to bone loss, resulting in bone fragility and an increased risk of fractures. This is primarily due to an age-related decline in the function of bone-forming osteoblastic cells and accelerated cellular senescence within the bone microenvironment. Here, we provide a detailed discussion of the hypothesis that age-related defective bone formation is caused by senescence of skeletal stem cells, as they are the main source of bone forming osteoblastic cells and influence the composition of bone microenvironment. Furthermore, this review discusses potential strategies to target cellular senescence as an emerging approach to treat age-related bone loss.

Osteoprogenitor recruitment and differentiation during intracortical bone remodeling of adolescent humans

BACKGROUND

Recruitment and proliferation of osteoprogenitors during the reversal-resorption phase, and their differentiation into mature bone-forming osteoblasts is crucial for initiation of bone formation during bone remodeling. This study investigates the osteoprogenitors' gradual recruitment, proliferation, and differentiation into bone-forming osteoblasts within intracortical remodeling events of healthy adolescent humans.

METHODS

The study was conducted on cortical bone specimens from 11 adolescent human controls - patients undergoing surgery due to coxa valga. The osteoprogenitor recruitment route and differentiation into osteoblasts were backtracked using immunostainings and in situ hybridizations with osteoblastic markers (CD271/NGFR, osterix/SP7, COL3A1 and COL1A1). The osteoblastic cell populations were defined based on the pore surfaces, and their proliferation index (Ki67), density and number/circumference were estimated in multiplex-immunofluorescence (Ki67, TRAcP, CD34) stained sections.

RESULTS

During the reversal-resorption phase, osteoclasts are intermixed with (COL3A1+NFGR+) osteoblastic reversal cells, which are considered to be osteoprogenitors of (COL1A1+SP7+) bone-forming osteoblasts. Initiation of bone formation requires a critical density of these osteoprogenitors (43 ± 9 cells/mm), which is reached though proliferation (4.4 ± 0.5 % proliferative) and even more so through recruitment of osteoprogenitors, but challenged by the ongoing expansion of the canal circumference. These osteoprogenitors most likely originate from osteoblastic bone lining cells and mainly lumen osteoprogenitors, which expand their population though proliferation (4.6 ± 0.3 %) and vascular recruitment. These lumen osteoprogenitors resemble canopy cells above trabecular remodeling sites, and like canopy cells they extend above bone-forming osteoblasts where they may rejuvenate the osteoblast population during bone formation.

CONCLUSION

Initiation of bone formation during intracortical remodeling requires a critical density of osteoprogenitors on eroded surfaces, which is reached though proliferation and recruitment of local osteoprogenitors: bone lining cells and lumen osteoprogenitors.

Lycopene Improves Bone Quality in SAMP6 Mice by Inhibiting Oxidative Stress, Cellular Senescence, and the SASP

SCOPE

Cellular senescence (CS) is closely related to tissue ageing including bone ageing. CS and the senescence-associated secretory phenotype (SASP) have emerged as critical pathogenesis elements of senile osteoporosis. This study aims to investigate the effect of lycopene on senile osteoporosis.

METHODS AND RESULTS

The senescence-accelerated mouse prone 6 (SAMP6) strain of mice is used as the senile osteoporosis model. Daily ingestion of lycopene for 8 weeks preserves the bone mass, density, strength, and microarchitecture in the SAMP6 mice. Moreover, these alterations are associated with a decrease in oxidative stress in the senile osteoporosis model. In addition, there is a reduction in osteoblast and osteocyte senescence and the SASP in the bone tissues of the SAMP6 mice. Lycopene improves bone health likely due to its antioxidant properties that may be linked with the regulation of CS and SASP in the SAMP6 mice.

CONCLUSION

These results suggest that lycopene may be beneficial for the management of senile osteoporosis by inhibiting oxidative stress, CS, and the SASP.

HYBID in osteoarthritis: Potential target for disease progression

HYBID is a new hyaluronan-degrading enzyme and exists in various cells of the human body. Recently, HYBID was found to over-express in the osteoarthritic chondrocytes and fibroblast-like synoviocytes. According to these researches, high level of HYBID is significantly correlated with cartilage degeneration in joints and hyaluronic acid degradation in synovial fluid. In addition, HYBID can affect inflammatory cytokine secretion, cartilage and synovium fibrosis, synovial hyperplasia via multiple signaling pathways, thereby exacerbating osteoarthritis. Based on the existing research of HYBID in osteoarthritis, HYBID can break the metabolic balance of HA in joints through the degradation ability independent of HYALs/CD44 system and furthermore affect cartilage structure and mechanotransduction of chondrocytes. In particular, in addition to HYBID itself being able to trigger some signaling pathways, we believe that low-molecular-weight hyaluronan produced by excess degradation can also stimulate some disease-promoting signaling pathways by replacing high-molecular-weight hyaluronan in joints. The specific role of HYBID in osteoarthritis is gradually revealed, and the discovery of HYBID raises the new way to treat osteoarthritis. In this review, the expression and basic functions of HYBID in joints were summarized, and reveal potential role of HYBID as a key target in treatment for osteoarthritis.

Aging and Bone Metabolism

Changes in bone architecture and metabolism with aging increase the likelihood of osteoporosis and fracture. Age-onset osteoporosis is multifactorial, with contributory extrinsic and intrinsic factors including certain medical problems, specific prescription drugs, estrogen loss, secondary hyperparathyroidism, microenvironmental and cellular alterations in bone tissue, and mechanical unloading or immobilization. At the histological level, there are changes in trabecular and cortical bone as well as marrow cellularity, lineage switching of mesenchymal stem cells to an adipogenic fate, inadequate transduction of signals during skeletal loading, and predisposition toward senescent cell accumulation with production of a senescence-associated secretory phenotype. Cumulatively, these changes result in bone remodeling abnormalities that over time cause net bone loss typically seen in older adults. Age-related osteoporosis is a geriatric syndrome due to the multiple etiologies that converge upon the skeleton to produce the ultimate phenotypic changes that manifest as bone fragility. Bone tissue is dynamic but with tendencies toward poor osteoblastic bone formation and relative osteoclastic bone resorption with aging. Interactions with other aging physiologic systems, such as muscle, may also confer detrimental effects on the aging skeleton. Conversely, individuals who maintain their BMD experience a lower risk of fractures, disability, and mortality, suggesting that this phenotype may be a marker of successful aging. © 2023 American Physiological Society. Compr Physiol 13:4355-4386, 2023.

Osteoporosis in hemophilia: what is its importance in clinical practice?

INTRODUCTION

The relationship between severe hemophilia and osteoporosis has been well established in the literature. However, although the importance of its prevention in order to reduce the risk of bone fractures has been reported, the importance of its treatment in clinical practice has not been well analyzed.

AREAS COVERED

In this paper a review of the available clinical and experimental information on osteoporosis in hemophilia has been performed, to better understand the relationship between hemophilia and osteoporosis. Prevention of osteoporosis in hemophilia should include primary hematological prophylaxis; a diet appropriate in calcium and vitamin D; a regular exercise program that includes aerobics, strength training and balance and flexibility activities; restriction of tobacco and alcohol use; and limitation of the duration of immobilization.

EXPERT OPINION

Prevention of osteoporosis in hemophilic patients is paramount. However, it is noteworthy that there is only one publication on the treatment of osteoporosis in patients with hemophilia. Until further research is done on this topic, the existing recommendations for non-hemophilic patients should be followed. They include the use of antiresorptives (estrogens, selective estrogen receptor modulators, bisphosphonates, denosumab) and anabolic agents (teriparatide, abaloparatide, romosozumab). Further studies on the management of osteoporosis in patients with hemophilia are required.

Salidroside protects against osteoporosis in ovariectomized rats by inhibiting oxidative stress and promoting osteogenesis via Nrf2 activation

BACKGROUND

Osteoporosis (OP) is characterized as low bone mass, bone microarchitecture breakdown and bone fragility. The increase of oxidative stress could lead to breakdown in the balance of bone formation and resorption which gives rise to OP. Nrf2 is a transcription factor which takes part in oxidative stress and recently was reported that it can regulate the occurrence of OP. Salidroside (SAL) with the efficacies of anti-oxidation, anti-aging and bone-protection is one of the active ingredients in Ligustri Lucidi Fructus, a traditional Chinese medicinal herb. Nevertheless, few studies have explored the potential mechanism of SAL preventing OP development from the perspective of oxidative stress intervention.

PURPOSE

This study aimed to investigate the pharmacological effect and molecular mechanisms of SAL on OP.

STUDY DESIGNS AND METHODS

A tert-butyl hydroperoxide (t-BHP)-induced oxidative stress model was applied for investigating the effects of SAL in vitro, and an ovariectomized (OVX) model was used for in vivo study on the effect of SAL for OP. Related pharmacodynamic actions and molecular mechanisms of SAL were explored in both rat osteoblasts (ROBs) and OVX rats. Network biology and cell metabolomics were performed for further investigating the correlation and association among potential biomarkers, targets and pathways.

RESULTS

SAL reduced levels of ROS and lipid peroxidation (LPO), increased activities of antioxidant enzymes like GPx and SOD, and enhanced osteogenic differentiation in t-BHP-induced ROBs and OVX rats. Mechanistic studies showed SAL prevented OP development and reduced oxidative damage in ROBs and OVX rats through up-regulating Nrf2 expression and facilitating its nuclear translocation. The joint analysis of network biology and cell metabolomics revealed that galactose metabolism and fatty acid metabolism could be the major influenced pathways following treatment with SAL.

CONCLUSION

SAL could protect against OP by inhibiting oxidative stress, promoting osteogenesis through the up-regulation of Nrf2 and intervening galactose metabolism and fatty acid metabolism. Our study implied that SAL may be a potential drug to treat OP.

Promotion of osteogenesis by Sweroside via BMP2-involved signaling in postmenopausal osteoporosis

Phlomis umbrosa has been traditionally used for bone diseases in traditional Korean Medicine. Sweroside (SOS), marker compounds of P. umbrosa, has been known to promote osteoblast differentiation. In this study, ameliorative effects of SOS on osteoporosis and potential target pathway were investigated. Ovariectomized mice were administered three doses of SOS three times a week for 4 weeks after inducing osteoporosis. Bone mineral content (BMC) and bone mineral density (BMD) were analyzed by dual energy X-ray absorptiometry. A human osteosarcoma cell line (SaOS-2) was differentiated to clarify the promoting effects of SOS on osteoblast differentiation and bone formation. Osteoblastic bone-forming markers were evaluated in lumbar vertebrae (LV) and mineralized SaOS-2 cells. SOS markedly elevated BMC and BMD levels and attenuated the bone marrow adipocytes in the femoral shaft. SOS increased the formation of bone matrix in SaOS-2 cells. Bone morphogenetic protein-2 (BMP2) and runt-related transcription factor 2 (CBFA1) in LV and SaOS-2 cells were up-regulated by SOS. SOS increased alkaline phosphatase (ALPL), osteopontin (SPP1), and bone sialoprotein-1 (BSPH1). In conclusion, SOS induced the formation of mineralized bone matrix by regulating BMP2/CBFA1-mediated molecules. Therefore, SOS could be a therapeutic compound of treatment for osteoporosis by producing the new bone matrix.

A Novel Mouse Model for SNP in Steroid Receptor Co-Activator-1 Reveals Role in Bone Density and Breast Cancer Metastasis

The steroid receptor coactivator-1 (SRC-1) is a nuclear receptor co-activator, known to play key roles in both estrogen response in bone and in breast cancer metastases. We previously demonstrated that the P1272S single nucleotide polymorphism (SNP; P1272S; rs1804645) in SRC-1 decreases the activity of estrogen receptor in the presence of selective estrogen receptor modulators (SERMs) and that it is associated with a decrease in bone mineral density (BMD) after tamoxifen therapy, suggesting it may disrupt the agonist action of tamoxifen. Given such dual roles of SRC-1 in the bone microenvironment and in tumor cell-intrinsic phenotypes, we hypothesized that SRC-1 and a naturally occurring genetic variant, P1272S, may promote breast cancer bone metastases. We developed a syngeneic, knock-in mouse model to study if the SRC-1 SNP is critical for normal bone homeostasis and bone metastasis. Our data surprisingly reveal that the homozygous SRC-1 SNP knock-in increases tamoxifen-induced bone protection after ovariectomy. The presence of the SRC-1 SNP in mammary glands resulted in decreased expression levels of SRC-1 and reduced tumor burden after orthotopic injection of breast cancer cells not bearing the SRC-1 SNP, but increased metastases to the lungs in our syngeneic mouse model. Interestingly, the P1272S SNP identified in a small, exploratory cohort of bone metastases from breast cancer patients was significantly associated with earlier development of bone metastasis. This study demonstrates the importance of the P1272S SNP in both the effect of SERMs on BMD and the development of tumor in the bone.

Zanthoxylum piperitum alleviates the bone loss in osteoporosis via inhibition of RANKL-induced c-fos/NFATc1/NF-κB pathway

BACKGROUND

The fruit of Zanthoxylum piperitum (ZP) is an herbal medicine as well as a spice agent in Asia to treat carminative, stomachic, anthelmintic and degenerative diseases. Z. piperitum was reported to have anti-oxidant, anti-inflammatory, anti-osteoarthritic and osteosarcoma proliferation-control effects.

PURPOSE AND STUDY DESIGN

This study was conducted to determine the anti-osteoporotic effects and mechanisms of action of ZP.

METHODS

Female ICR mice underwent ovariectomies (OVX) and were orally administered ZP at 1, 10 and 100 mg/kg for 6 weeks. The femoral and tibial bones were assessed by dual-energy X-ray absorptiometry and histology to analyze the bone mineral density (BMD) and the number of osteoclasts. Raw 264.7 cells were stimulated by 100 ng/ml receptor activator of nuclear factor-κB ligand (RANKL) for 7 days in the presence of ZP. RANKL-induced signaling molecules were analyzed in osteoclasts.

RESULTS

The levels of femoral and tibial BMD were significantly increased by ZP administration. Serum biomarkers such as osteocalcin, calcium, alkaline phosphatase and bone-specific alkaline phosphatase concentrations were markedly recovered to normal levels in ZP-treated osteoporotic mice. In addition, the number of osteoclasts in the head, trochanter and body of the femur was obviously decreased in the ZP treatment groups. Moreover, ZP treated-cells showed a reduction in the number of TRAP-positive multinuclear cells in RANKL-stimulated Raw 264.7 cells. ZP decreased the RANKL-activated NFATc1 and c-fos, transcription factors of osteoclast formation. The nuclear translocation of NF-κB and phosphorylation of ERK42/44 were inhibited by the ZP treatment in RANKL-induced osteoclasts.

CONCLUSION

Collectively, ZP exerts its inhibitory effect against bone resorption by regulating RANKL-mediated c-fos/NFATc1/NF-κB in osteoclast. ZP may prove to be a therapeutic agent for osteoporosis.

Re-thinking the bone remodeling cycle mechanism and the origin of bone loss

Proper bone remodeling necessarily requires that osteoblasts reconstruct the bone that osteoclasts have resorbed. However, the cellular events connecting resorption to reconstruction have remained poorly known. The consequence is a fragmentary understanding of the remodeling cycle where only the resorption and formation steps are taken into account. New tools have recently made possible to elucidate how resorption shifts to formation, thereby allowing to comprehend the remodeling cycle as a whole. This new knowledge is reviewed herein. It shows how teams of osteoclasts and osteoblast lineage cells are progressively established and how they are subjected therein to reciprocal interactions. Contrary to the common view, osteoclasts and osteoprogenitors are intermingled on the eroded surfaces. The analysis of the resorption and cell population dynamics shows that osteoprogenitor cell expansion and resorption proceed as an integrated mechanism; that a threshold cell density of osteoprogenitors on the eroded surface is mandatory for onset of bone formation; that the cell initiating osteoprogenitor cell expansion is the osteoclast; and that the osteoclast therefore triggers putative osteoprogenitor reservoirs positioned at proximity of the eroded bone surface (bone lining cells, canopy cells, pericytes). The interplay between magnitude of resorption and rate of cell expansion governs how soon bone reconstruction is initiated and may determine uncoupling and permanent bone loss if a threshold cell density is not reached. The clinical perspectives opened by these findings are discussed.

Molecular Basis of Bone Aging

A decline in bone mass leading to an increased fracture risk is a common feature of age-related bone changes. The mechanisms underlying bone senescence are very complex and implicate systemic and local factors and are the result of the combination of several changes occurring at the cellular, tissue and structural levels; they include alterations of bone cell differentiation and activity, oxidative stress, genetic damage and the altered responses of bone cells to various biological signals and to mechanical loading. The molecular mechanisms responsible for these changes remain greatly unclear and many data derived from in vitro or animal studies appear to be conflicting and heterogeneous, probably due to the different experimental approaches; nevertheless, understanding the main physio-pathological processes that cause bone senescence is essential for the development of new potential therapeutic options for treating age-related bone loss. This article reviews the current knowledge concerning the molecular mechanisms underlying the pathogenesis of age-related bone changes.

Romosozumab: a novel bone anabolic treatment option for osteoporosis?

Research into the drug romosozumab began with the investigation of patients with excess bone formation. The understanding of the wingless-type mouse mammary tumor virus integration site (Wnt) signaling pathway in bone metabolism identified the negative regulator of bone mass sclerostin as a potential target for the treatment of osteoporosis. Preclinical studies confirmed this idea because they showed that sclerostin antibodies have the potential to increase bone formation. Biochemical analyses of clinical studies showed a significant increase in bone formation markers, which then slowly decreased within a year. This was accompanied by a particularly initially pronounced decrease in bone resorption. This dual mechanism of action led to an increase in bone mineral density and a significant reduction in fracture risk. Clinical vertebral fractures decreased by between 28 and 36%, nonvertebral fractures shown in a post hoc analysis by 42%. Romosozumab is administered once a month in the form of two injections. At the puncture site, reactions occur in about 5%. The most significant side effects are cardiovascular. In phase III studies, the number of serious cardiovascular complications was not significantly, albeit numerically, higher than in the control group. In Japan, South Korea, Canada, Australia, and the USA, osteoporosis patients at a high risk of fracture may already be treated with romosozumab (Evenity). Approval in the European Union was granted by 2019-12-12.

Biomarkers of Osteoporosis: An Update

Background:

Osteoporosis, characterized by compromised bone quality and strength is associated with bone fragility and fracture risk. Biomarkers are crucial for the diagnosis or prognosis of a disease as well as elucidating the mechanism of drug action and improve decision making.

Objective:

An exhaustive description of traditional markers including bone mineral density, vitamin D, alkaline phosphatase, along with potential markers such as microarchitectural determination, trabecular bone score, osteocalcin, etc. is provided in the current piece of work. This review provides insight into novel pathways such as the Wnt signaling pathway, neuro-osseous control, adipogenic hormonal imbalance, gut-bone axis, genetic markers and the role of inflammation that has been recently implicated in osteoporosis.

Methods:

We extensively reviewed articles from the following databases: PubMed, Medline and Science direct. The primary search was conducted using a combination of the following keywords: osteoporosis, bone, biomarkers, bone turnover markers, diagnosis, density, architecture, genetics, inflammation.

Conclusion:

Early diagnosis and intervention delay the development of disease and improve treatment outcome. Therefore, probing for novel biomarkers that are able to recognize people at high risk for developing osteoporosis is an effective way to improve the quality of life of patients and to understand the pathomechanism of the disease in a better way.

Anabolic effects of vitamin D and magnesium in aging bone

Decreased bone mass and an increased risk of bone fractures become more common with age. This condition is often associated with osteoporosis and is caused by an imbalance of bone resorption and new bone formation. Lifestyle factors that affect the risk of osteoporosis include alcohol, diet, hormones, physical activity, and smoking. Calcium and vitamin D are particularly important for the age-related loss of bone density and skeletal muscle mass, but other minerals, such as magnesium, also have an important role. Here, we summarize how optimal magnesium and vitamin D balance improve health outcomes in the elderly, the role of magnesium and vitamin D on bone formation, and the implications of widespread deficiency of these factors in the United States and worldwide, particularly in the elderly population.

Elimination of senescent osteoclast progenitors has no effect on the age-associated loss of bone mass in mice

Both an increase in osteoclast and a decrease in osteoblast numbers contribute to skeletal aging. Markers of cellular senescence, including expression of the cyclin inhibitor p16, increase with aging in several bone cell populations. The elimination of p16-expressing cells in old mice, using the INK-ATTAC transgene, increases bone mass indicating that senescent cells contribute to skeletal aging. However, the identity of the senescent cells and the extent to which ablation of p16-expressing cells may prevent skeletal aging remain unknown. Using mice expressing the p16-3MR transgene, we examined whether elimination of p16-expressing cells between 12 and 24 months of age could preserve bone mass; and whether elimination of these cells from 20 to 26 months of age could restore bone mass. The activation of the p16-3MR transgene by ganciclovir (GCV) greatly diminished p16 levels in the brain, liver, and osteoclast progenitors from the bone marrow. The age-related increase in osteoclastogenic potential of myeloid cells was also abrogated by GCV. However, GCV did not alter p16 levels in osteocytes-the most abundant cell type in bone-and had no effect on the skeletal aging of p16-3MR mice. These findings indicate that the p16-3MR transgene does not eliminate senescent osteocytes but it does eliminate senescent osteoclast progenitors and senescent cells in other tissues, as described previously. Elimination of senescent osteoclast progenitors, in and of itself, has no effect on the age-related loss of bone mass. Hence, other senescent cell types, such as osteocytes, must be the seminal culprits.

Molecular-Based Treatment Strategies for Osteoporosis: A Literature Review

Osteoporosis is an unavoidable public health problem in an aging or aged society. Anti-resorptive agents (calcitonin, estrogen, and selective estrogen-receptor modulators, bisphosphonates, anti-receptor activator of nuclear factor κB ligand antibody along with calcium and vitamin D supplementations) and anabolic agents (parathyroid hormone and related peptide analogs, sclerostin inhibitors) have major roles in current treatment regimens and are used alone or in combination based on the pathological condition. Recent advancements in the molecular understanding of bone metabolism and in bioengineering will open the door to future treatment paradigms for osteoporosis, including antibody agents, stem cells, and gene therapies. This review provides an overview of the molecular mechanisms, clinical evidence, and potential adverse effects of drugs that are currently used or under development for the treatment of osteoporosis to aid clinicians in deciding how to select the best treatment option.

KIAA1199 is a secreted molecule that enhances osteoblastic stem cell migration and recruitment

Factors mediating mobilization of osteoblastic stem and progenitor cells from their bone marrow niche to be recruited to bone formation sites during bone remodeling are poorly known. We have studied secreted factors present in the bone marrow microenvironment and identified KIAA1199 (also known as CEMIP, cell migration inducing hyaluronan binding protein) in human bone biopsies as highly expressed in osteoprogenitor reversal cells (Rv.C) recruited to the eroded surfaces (ES), which are the future bone formation sites. In vitro, KIAA1199 did not affect the proliferation of human osteoblastic stem cells (also known as human bone marrow skeletal or stromal stem cells, hMSCs); but it enhanced cell migration as determined by scratch assay and trans-well migration assay. KIAA1199 deficient hMSCs (KIAA1199down) exhibited significant changes in cell size, cell length, ratio of cell width to length and cell roundness, together with reduction of polymerization actin (F-actin) and changes in phos-CFL1 (cofflin1), phos-LIMK1 (LIM domain kinase 1) and DSTN (destrin), key factors regulating actin cytoskeletal dynamics and cell motility. Moreover, KIAA1199down hMSC exhibited impaired Wnt signaling in TCF-reporter assay and decreased expression of Wnt target genes and these effects were rescued by KIAA1199 treatment. Finally, KIAA1199 regulated the activation of P38 kinase and its associated changes in Wnt-signaling. Thus, KIAA1199 is a mobilizing factor that interacts with P38 and Wnt signaling, and induces changes in actin cytoskeleton, as a mechanism mediating recruitment of hMSC to bone formation sites.

Pathophysiology of the Risk Factors Associated with Osteoporosis and their Correlation to the T-score Value in Patients with Osteopenia and Osteoporosis in the United Arab Emirates

Introduction:

Osteoporosis is a growing major health problem with medical, social, and economic burden. The pathogenesis of osteoporosis involves excessive bone resorption by osteoclasts and decreased new bone formation by osteoblasts. Early diagnosis is the key to minimize the impact of osteoporosis on patients. Dual-energy X-ray absorptiometry at the hip or spine is the main standard test for measuring bone mineral density, and according to the World Health Organization, the T-score value of –2.5 or less determines osteoporosis.

Aim:

In this work, we aimed to study the risk factors associated with osteoporosis among a population sample of osteoporotic and controls in the United Arab Emirates (UAE) and relate them to the T-score value.

Material and Methods:

Two hundred male and female participants were recruited in the study. A questionnaire was used and data were correlated with the T-score value of the participants.

Results:

Results showed a positive correlation between the T-score value of the patients with osteoporosis and their calcium intake, exercise duration, and the age at menopause of female patients, whereas a negative correlation was evident between the T-score value and both caffeine and nicotine consumption. Results also revealed that patients with osteoporosis have significantly low body mass index, low calcium intake, and shorter duration of exposure to the sun than the control group.

Conclusion:

In conclusion, more intervention should be directed toward changing the modifiable risk factors in patients with osteoporosis and more studies should be directed toward osteoporosis in the UAE.

Bone health and evaluation of bone mineral density in patients with premature ovarian insufficiency

Oestrogens exert an influence on skeletal homeostasis during growth and adulthood. Regulation of osteoclasts and osteoblasts generation and apoptosis and prolongation of the lifespan of osteocytes are some of their actions on bone metabolism. Premature ovarian insufficiency (POI) and associated loss of oestrogen action on osteoclasts leads to trabecular perforation and loss of connectivity. Lack of oestrogens acting on osteoblast progenitors also causes a decrease in critical bone mass. Postmenopausal hypoestrogenism is associated with an increase in the number of lymphocyte B-cells expressing nuclear factor κB ligand (RANKL) in the bone marrow and elevated expression of RANKL by B-cells. Increased concentration of RANKL stimulates activation of osteoclasts and leads to oestrogen deficiency-associated bone loss. It has been proven that women with POI have decreased bone mineral density (BMD) measured in lumbar spine and femoral neck. The loss of bone mass associated with oestrogen deficiency is greater in trabecular than in cortical bone, thus women with POI have a significant decrease in BMD, particularly in the lumbar spine vertebrae. Smoking cessation, weight-bearing, and muscle-strengthening exercises on most days of the week, avoidance of excessive alcohol intake, and adequate supplementation of calcium and vitamin D are the main lifestyle rules necessary to avoid decline in BMD. The most important component of decreased BMD treatment in POI patients is systemic hormonal replacement therapy (HRT). HRT should provide hormonal balance and should mimic normal ovarian function as much as possible.

Bone marrow stromal cells from low-turnover osteoporotic mouse model are less sensitive to the osteogenic effects of fluvastatin

This study aimed to investigate the effects of fluvastatin on the differentiation of bone marrow stromal cells (BMSCs) into osteoblasts in senescence-accelerated mouse prone 6 (SAMP6) compared with that in the normal senescence-accelerated-resistant mouse (SAMR1) model. SAMP strains arose spontaneously from the AKR/J background and display shortened life span and an array of signs of accelerated aging, compared with control SAMR strains. The dose effects of fluvastatin were also evaluated. BMSCs were cultured with/without fluvastatin (0 μM, 0.1 μM, 0.5 μM, and 1.0 μM). WST-1-based colorimetry was performed to evaluate cell proliferation. To evaluate cell differentiation, gene expression levels of bmp2 and runx2 were determined by quantitative reverse transcription polymerase chain reaction (qRT-PCR), and protein expression levels were determined using enzyme-linked immunosorbent assay (BMP2) and immunofluorescence staining (BMP2 and Runx2). Alkaline phosphatase (ALP) activity assay and histochemical detection were determined; the effect of noggin, a BMP-specific antagonist, was examined using ALP histochemical detection. To assess for mature osteogenic marker, gene expression levels of bglap2 were determined by qRT-PCR and mineralization was determined by alizarin red staining. RhoA activity was also examined by Western blotting. In SAMP6, BMP2, Runx2 and Bglap2 mRNA and protein expressions were significantly increased by fluvastatin, and ALP activity was increased by BMP2 action. RhoA activity was also inhibited by fluvastatin. The concentration of fluvastatin sufficient to increase BMP2 and Runx2 expression and ALP activity was 0.5 μM in SAMP6 and 0.1 μM in SAMR1. In conclusion, the present study revealed that fluvastatin promoted BMSC differentiation into osteoblasts by RhoA-BMP2 pathway in SAMP6. BMSCs of SAMP6 are less sensitive to the osteogenic effects of fluvastatin than SAMR1.

Increased bone resorption in hemophilia

In patients with hemophilia, osteoporosis is frequently observed for which the etiology remains unclear. The aim of this paper is to review the available experimental evidence indicating the presence of this disorder in patients with hemophilia, explore the potential mechanisms which may lead to reduced bone mineral density (BMD) and speculate on useful interventions to circumvent it. A narrative review of the English literature up to April 2018 was performed. The available evidence demonstrates an increased rate of bone resorption and an excess of osteoporosis among patients with hemophilia. FVIII and FIX may act through at least two pathways: promoting bone formation by a thrombin-mediated mitogenic effect on osteoblasts and by cytokine-mediated osteoclast activity. Another potential indirect mechanism mediated through the RANK-RANKL pathway has been suggested but remains controversial. The role of confounders such as lack of activity and immobility must be considered.

The Quest for Osteoporosis Mechanisms and Rational Therapies: How Far We've Come, How Much Further We Need to Go

During the last 40 years, understanding of bone biology and the pathogenesis of osteoporosis, the most common and impactful bone disease of old age, has improved dramatically thanks to basic and clinical research advances, genetic insights from humans and rodents, and newer imaging technologies. Culprits of osteoporosis are no longer a matter of speculation based on in vitro observations. Instead, they can be identified and dissected at the cellular and molecular level using genetic approaches; and their effect on distinct bone envelopes and anatomic regions can be functionally assessed in vivo. The landscape of pharmacotherapies for osteoporosis has also changed profoundly with the emergence of several potent antiresorptive drugs as well as anabolic agents, displacing estrogen replacement as the treatment of choice. In spite of these major positive developments, the optimal duration of the available therapies and their long-term safety remain matters of conjecture and some concern. Moreover, antiresorptive therapies are used indiscriminately for patients of all ages on the assumption that suppressing remodeling is always beneficial for bone, but rebound remodeling upon their discontinuation suggests otherwise. In this invited perspective, I highlight the latest state of knowledge of bone-intrinsic and extrinsic mechanisms responsible for the development of osteoporosis in both sexes; differences between the mechanisms responsible for the effects of aging and estrogen deficiency; and the role of old osteocytes in the development of cortical porosity. In addition, I highlight advances toward the goal of developing drugs for several degenerative diseases of old age at once, including osteoporosis, by targeting shared mechanisms of aging. © 2018 American Society for Bone and Mineral Research.

Perimenopausal bone histomorphometry before and after menopause

Investigators and clinicians have had few normal bone histomorphometry data available to compare with those found in diseased patients, or in the results of treatments. The Goals and Objectives of this work are two-fold: 1. to present static and dynamic bone histomorphometry data from transilial bone biopsies performed on 76 healthy, premenopausal women. 2. To present paired static and dynamic bone histomorphometry data from bone biopsies on a subset (N=51 pairs) of these same healthy women whose biopsies were repeated 12months after their last menses. Statistical comparisons between the pre- and postmenopausal data are presented. These data will shrink this important gap, both for clinicians and investigators. We enrolled 76 healthy, premenopausal women over age 46, performed transilial bone biopsies after tetracycline labeling, and during a period of 9.5years, we re-biopsied 51 of them who passed through menopause and remained healthy the entire time. We also obtained serum biochemical measurements, and serial DXA exams during the period of observation. The dynamic bone histomorphometry demonstrated a doubling of bone remodeling, and increases in serum bone markers at the time of the second biopsy. Lumbar spine bone density also declined, and there were significant correlations between serum markers and histomorphometry variables. The data demonstrate that healthy menopause results in an important increase in bone remodeling, and a loss of bone density. We do not fully understand the mechanisms of these transmenopausal changes, but the data provide some clues that are helpful.

Use of bone turnover markers in postmenopausal osteoporosis

Bone turnover comprises two processes: the removal of old bone (resorption) and the laying down of new bone (formation). N-terminal propeptide of type I procollagen (PINP) and C-telopeptide of type I collagen (CTX-I) are markers of bone formation and resorption, respectively, that are recommended for clinical use. Bone turnover markers can be measured on several occasions in one individual with good precision. However, these markers are subject to several sources of variability, including feeding (resorption decreases) and recent fracture (all markers increase for several months). Bone turnover markers are not used for diagnosis of osteoporosis and do not improve prediction of bone loss or fracture within an individual. In untreated women, very high bone turnover marker concentrations suggest secondary causes of high bone turnover (eg, bone metastases or multiple myeloma). In people with osteoporosis, bone turnover markers might be useful to assess the response to anabolic and antiresorptive therapies, to assess compliance to therapy, or to indicate possible secondary osteoporosis. Much remains to be learnt about how bone turnover markers can be used to monitor the effect of stopping bisphosphonate therapy (eg, to identify a threshold above which restarting therapy should be considered). More studies are needed to investigate the use of bone turnover markers for assessment of the bone safety of new medications.

DNA damage and senescence in osteoprogenitors expressing Osx1 may cause their decrease with age

Age-related bone loss in mice results from a decrease in bone formation and an increase in cortical bone resorption. The former is accounted by a decrease in the number of postmitotic osteoblasts which synthesize the bone matrix and is thought to be the consequence of age-dependent changes in mesenchymal osteoblast progenitors. However, there are no specific markers for these progenitors, and conclusions rely on results from in vitro cultures of mixed cell populations. Moreover, the culprits of such changes remain unknown. Here, we have used Osx1-Cre;TdRFP mice in which osteoprogenitors express the TdRFP fluorescent protein. We report that the number of TdRFP-Osx1 cells, freshly isolated from the bone marrow, declines by more than 50% between 6 and 24 months of age in both female and male mice. Moreover, TdRFP-Osx1 cells from old mice exhibited markers of DNA damage and senescence, such as γH2AX foci, G1 cell cycle arrest, phosphorylation of p53, increased p21CIP1 levels, as well as increased levels of GATA4 and activation of NF-κB - two major stimulators of the senescence-associated secretory phenotype (SASP). Bone marrow stromal cells from old mice also exhibited elevated expression of SASP genes, including several pro-osteoclastogenic cytokines, and increased capacity to support osteoclast formation. These changes were greatly attenuated by the senolytic drug ABT263. Together, these findings suggest that the decline in bone mass with age is the result of intrinsic defects in osteoprogenitor cells, leading to decreased osteoblast numbers and increased support of osteoclast formation.

Coupling of Bone Resorption and Formation in Real Time: New Knowledge Gained From Human Haversian BMUs

It is well known that bone remodeling starts with a resorption event and ends with bone formation. However, what happens in between and how resorption and formation are coupled remains mostly unknown. Remodeling is achieved by so-called basic multicellular units (BMUs), which are local teams of osteoclasts, osteoblasts, and reversal cells recently proven identical with osteoprogenitors. Their organization within a BMU cannot be appropriately analyzed in common histology. The originality of the present study is to capture the events ranging from initiation of resorption to onset of formation as a functional continuum. It was based on the position of specific cell markers in longitudinal sections of Haversian BMUs generating new canals through human long bones. It showed that initial resorption at the tip of the canal is followed by a period where newly recruited reversal/osteoprogenitor cells and osteoclasts alternate, thus revealing the existence of a mixed "reversal-resorption" phase. Three-dimensional reconstructions obtained from serial sections indicated that initial resorption is mainly involved in elongating the canal and the additional resorption events in widening it. Canal diameter measurements show that the latter contribute the most to overall resorption. Of note, the density of osteoprogenitors continuously grew along the "reversal/resorption" surface, reaching at least 39 cells/mm on initiation of bone formation. This value was independent of the length of the reversal/resorption surface. These observations strongly suggest that bone formation is initiated only above a threshold cell density, that the length of the reversal/resorption period depends on how fast osteoprogenitor recruitment reaches this threshold, and thus that the slower the rate of osteoprogenitor recruitment, the more bone is degraded. They lead to a model where the newly recognized reversal/resorption phase plays a central role in the mechanism linking osteoprogenitor recruitment and the resorption-formation switch. © 2017 American Society for Bone and Mineral Research.

The Effects of Aging and Sex Steroid Deficiency on the Murine Skeleton Are Independent and Mechanistically Distinct

Old age and sex steroid deficiency are the two most critical factors for the development of osteoporosis. It remains unknown, however, whether the molecular culprits of the two conditions are similar or distinct. We show herein that at 19.5 months of age-a time by which the age-dependent decline of cortical and cancellous bone mass and cortical porosity were fully manifested in C57BL/6J mice-these animals remained functionally estrogen sufficient. Transgenic mice with conditional expression of mitochondria-targeted catalase-a potent H2 O2 inactivating enzyme-in cells of the myeloid lineage (mitoCAT;LysM-Cre mice) were protected from the loss of cortical, but not cancellous, bone caused by gonadectomy in either sex. Consistent with these findings, in vitro studies with ERα-deficient Prx1+ cells and gonadectomized young adult mice showed that in both sexes decreased ERα signaling in Prx1+ cells leads to an increase in SDF1, a.k.a. CXCL12, an osteoclastogenic cytokine whose effects were abrogated in macrophages from mitoCAT;LysM-Cre mice. In contrast to sex steroid deficiency, the adverse effects of aging on either cortical or cancellous bone were unaffected in mitoCAT;LysM-Cre mice. On the other hand, attenuation of H2 O2 generation in cells of the mesenchymal lineage targeted by Prx1-Cre partially prevented the loss of cortical bone caused by old age. Our results suggest the effects of sex steroid deficiency and aging on the murine skeleton are independent and result from distinct mechanisms. In the former, the prevailing mechanism of the cortical bone loss in both sexes is increased osteoclastogenesis caused by estrogen deficiency; this is likely driven, at least in part, by mesenchymal/stromal cell-derived SDF1. Decreased osteoblastogenesis, owing in part to increased H2 O2, combined with increased osteoclastogenesis caused by aging mechanisms independent of estrogen deficiency, are the prevailing mechanisms of the loss of cortical bone with old age. © 2016 American Society for Bone and Mineral Research.

Estrogens and Androgens in Skeletal Physiology and Pathophysiology

Estrogens and androgens influence the growth and maintenance of the mammalian skeleton and are responsible for its sexual dimorphism. Estrogen deficiency at menopause or loss of both estrogens and androgens in elderly men contribute to the development of osteoporosis, one of the most common and impactful metabolic diseases of old age. In the last 20 years, basic and clinical research advances, genetic insights from humans and rodents, and newer imaging technologies have changed considerably the landscape of our understanding of bone biology as well as the relationship between sex steroids and the physiology and pathophysiology of bone metabolism. Together with the appreciation of the side effects of estrogen-related therapies on breast cancer and cardiovascular diseases, these advances have also drastically altered the treatment of osteoporosis. In this article, we provide a comprehensive review of the molecular and cellular mechanisms of action of estrogens and androgens on bone, their influences on skeletal homeostasis during growth and adulthood, the pathogenetic mechanisms of the adverse effects of their deficiency on the female and male skeleton, as well as the role of natural and synthetic estrogenic or androgenic compounds in the pharmacotherapy of osteoporosis. We highlight latest advances on the crosstalk between hormonal and mechanical signals, the relevance of the antioxidant properties of estrogens and androgens, the difference of their cellular targets in different bone envelopes, the role of estrogen deficiency in male osteoporosis, and the contribution of estrogen or androgen deficiency to the monomorphic effects of aging on skeletal involution.

Activation of Wnt Signaling by Mechanical Loading Is Impaired in the Bone of Old Mice

Aging diminishes bone formation engendered by mechanical loads, but the mechanism for this impairment remains unclear. Because Wnt signaling is required for optimal loading-induced bone formation, we hypothesized that aging impairs the load-induced activation of Wnt signaling. We analyzed dynamic histomorphometry of 5-month-old, 12-month-old, and 22-month-old C57Bl/6JN mice subjected to multiple days of tibial compression and corroborated an age-related decline in the periosteal loading response on day 5. Similarly, 1 day of loading increased periosteal and endocortical bone formation in young-adult (5-month-old) mice, but old (22-month-old) mice were unresponsive. These findings corroborated mRNA expression of genes related to bone formation and the Wnt pathway in tibias after loading. Multiple bouts (3 to 5 days) of loading upregulated bone formation-related genes, e.g., Osx and Col1a1, but older mice were significantly less responsive. Expression of Wnt negative regulators, Sost and Dkk1, was suppressed with a single day of loading in all mice, but suppression was sustained only in young-adult mice. Moreover, multiple days of loading repeatedly suppressed Sost and Dkk1 in young-adult, but not in old tibias. The age-dependent response to loading was further assessed by osteocyte staining for Sclerostin and LacZ in tibia of TOPGAL mice. After 1 day of loading, fewer osteocytes were Sclerostin-positive and, corroboratively, more osteocytes were LacZ-positive (Wnt active) in both 5-month-old and 12-month-old mice. However, although these changes were sustained after multiple days of loading in 5-month-old mice, they were not sustained in 12-month-old mice. Last, Wnt1 and Wnt7b were the most load-responsive of the 19 Wnt ligands. However, 4 hours after a single bout of loading, although their expression was upregulated threefold to 10-fold in young-adult mice, it was not altered in old mice. In conclusion, the reduced bone formation response of aged mice to loading may be due to failure to sustain Wnt activity with repeated loading. © 2016 American Society for Bone and Mineral Research.

Aging alters bone-fat reciprocity by shifting in vivo mesenchymal precursor cell fate towards an adipogenic lineage

Bone marrow derived mesenchymal progenitor cells (MPCs) play an important role in bone homeostasis. Age-related changes occur in bone resulting in a decrease in bone density and a relative increase in adipocity. Although in vitro studies suggest the existence of an age-related lineage switch between osteogenic and adipogenic fates, stem cell and microenvironmental contributions to this process have not been elucidated in vivo. In order to study the effects of MPC and microenvironmental aging on functional engraftment and lineage switching, transplantation studies were performed under non-myeloablative conditions in old recipients, with donor MPCs derived from young and old green fluorescent protein (GFP) transgenic mice. Robust engraftment by young MPCs or their progeny was observed in the marrow, bone-lining region and in the matrix of young recipients; however, significantly lower engraftment was seen at the same sites in old recipients transplanted with old MPCs. Differentiation of transplanted MPCs strongly favored adipogenesis over osteogenesis in old recipients irrespective of MPC donor age, suggesting that microenvironmental alterations that occur with in vivo aging are predominately responsible for MPC lineage switching. These data indicate that aging alters bone-fat reciprocity and differentiation of mesenchymal progenitors towards an adipogenic fate.

Odanacatib Restores Trabecular Bone of Skeletally Mature Female Rabbits With Osteopenia but Induces Brittleness of Cortical Bone: A Comparative Study of the Investigational Drug With PTH, Estrogen, and Alendronate

Cathepsin K (CK), a lysosomal cysteine protease, is highly expressed in mature osteoclasts and degrades type 1 collagen. Odanacatib (ODN) is a selective and reversible CK inhibitor that inhibits bone loss in preclinical and clinical studies. Although an antiresorptive, ODN does not suppress bone formation, which led us to hypothesize that ODN may display restorative effect on the osteopenic bones. In a curative study, skeletally mature New Zealand rabbits were ovarectomized (OVX) and after induction of bone loss were given a steady-state exposure of ODN (9 mM/d) for 14 weeks. Sham-operated and OVX rabbits treated with alendronate (ALD), 17b-estradiol (E2), or parathyroid hormone (PTH) served as various controls. Efficacy was evaluated by assessing bone mineral density (BMD), bone microarchitecture (using micro-computed tomography), fluorescent labeling of bone, and biomechanical strength. Skeletal Ca/P ratio was measured by scanning electron microscopy (SEM) with X-ray microanalysis, crystallinity by X-ray diffraction, and bone mineral density distribution (tissue mineralization) by backscattered SEM. Between the sham and ODN-treated osteopenic groups, lumbar and femur metaphyseal BMD, Ca/P ratio, trabecular microstructure and geometric indices, vertebral compressive strength, trabecular lining cells, cortical parameters (femoral area and thickness and periosteal deposition), and serum P1NP were largely comparable. Skeletal improvements in ALD-treated or E2-treated groups fell significantly short of the sham/ODN/PTH group. However, the ODN group displayed reduced ductility and enhanced brittleness of central femur, which might have been contributed by higher crytallinity and tissue mineralization. Rabbit bone marrow stromal cells expressed CK and when treated with ODN displayed increased formation of mineralized nodules and decreased apoptosis in serum-deficient medium compared with control. In vivo, ODN did not suppress remodeling but inhibited osteoclast activity more than ALD. Taken together, we show that ODN reverses BMD, skeletal architecture, and compressive strength in osteopenic rabbits; however, it increases crystallinity and tissue mineralization, thus leading to increased cortical bone brittleness.

Advanced Oxidation Protein Products as a Novel Marker of Oxidative Stress in Postmenopausal Osteoporosis

BACKGROUND

Advanced oxidation protein products (AOPPs) are acknowledged as a novel marker of oxidation-mediated protein damage. This study aimed to investigate the plasma levels of AOPPs in postmenopausal osteoporotic women, and to determine the relationship between AOPPs accumulation and lumbar bone mineral destiny (BMD) or bone turnover markers.

MATERIAL AND METHODS

Lumbar BMD was measured by dual-energy X-ray absorptiometry. Plasma AOPPs levels as a marker of protein oxidation damage and malondialdehyde (MDA) levels as a marker of lipid peroxidation were measured by spectrophotometry. The concentrations of 2 specific markers of bone turnover, bone-specific alkaline phosphatase (BALP) and tartrate-resistant acid phosphatase5b, (TRACP 5b) were quantified using ELISA kits.

RESULTS

We recruited 60 postmenopausal women meeting osteoporosis (OP) diagnostic criteria of World Health Organization (WHO) and 60 postmenopausal women without OP. Plasma levels of AOPPs (P<0.001), BALP (P<0.001) and TRACP 5b (P<0.001) were statistically significantly increased in the postmenopausal osteoporotic women compared with controls, but there was no statistically significant difference in MDA (P=0.124) between the 2 groups. Plasma AOPPs levels were negatively correlated with lumbar BMD and positively correlated with bone turnover markers both in postmenopausal osteoporotic women and in all subjects. However, plasma MDA levels were not correlated with lumbar BMD or bone turnover markers.

CONCLUSIONS

In postmenopausal osteoporotic women elevated AOPPs is associated with reduced BMD and increased bone turnover markers. Because AOPPs is stable and easy to detect it may be used as a simple plasma marker to predict the severity of postmenopausal OP.

MAGED1 is a negative regulator of bone remodeling in mice

Melanoma antigen family D1 (MAGED1), an important adaptor protein, has been shown to ubiquitously express and play critical roles in many aspects of cellular events and physiological functions. However, its role in bone remodeling remains unknown. We, therefore, analyzed the bone phenotype of Maged1-deficient mice. Maged1-deficient mice displayed a significant osteoporotic phenotype with a marked decrease in bone density and deterioration of trabecular architecture. Histomorphometric analysis demonstrated an increased mineral apposition rate as well as increased osteoclast number and surface in Maged1 knockout mice. At the cellular level, Maged1-deficient osteoblasts exhibited an increased proliferation rate and accelerated differentiation. MAGED1 deficiency also caused a promotion in osteoclastogenesis, and that was attributed to the cell autonomous acceleration of differentiation in osteoclasts and an increased receptor activator of NF-κB ligand/osteoprotegerin ratio, a major index of osteoclastogenesis, in osteoblasts. Thus, we identified MAGED1 as a novel regulator of osteoblastogenesis, osteoclastogenesis, and bone remodeling in a mouse model.

Determination of a critical size calvarial defect in senile osteoporotic mice model based on in vivo micro-computed tomography and histological evaluation

PURPOSE

To evaluate differences in the spontaneous healing capacity of senescence-prone inbred strains (SAMP6) and senescence-resistant inbred strains (SAMR1) and determine the critical defect size in a mouse model of senescence-accelerated osteoporosis.

METHODS

Unilateral full-thickness calvarial defects 2 or 4mm in diameter were made in 6-month-old male SAMP6 and SAMR1. Defects were evaluated in vivo by micro-CT at day 0 and 6 and 12 weeks postoperatively. Calvarial specimens were harvested at 12 weeks for hematoxylin and eosin staining, Masson's trichrome staining, and tartrate-resistant-acid-phosphatase (TRAP) staining.

RESULTS

Less new bone was observed in defects in SAMP6 compared to SAMR1 at 12 weeks postsurgery, with <5% healing in SAMP6 for both 2- and 4-mm defects compared to >5% healing in 2-mm defects in SAMRI (P<0.05). Histological analysis revealed dense connective tissue but little bone healing in 2- and 4-mm defects in SAMP6 and 4-mm defects in SAMR1. New bone was observed at the periphery of the 2-mm defects in SAMR1. Masson's trichrome staining also supported these findings. No obvious TRAP-positive cells were observed at the defect margins, but SAMP6 exhibited greater osteoclast numbers and surface areas in the diploë of contralateral bone compared to smaller osteoblast numbers and surface areas at the defect sites in SAMR1.

CONCLUSIONS

Defects of 2mm or larger in the cranium was critical-size or nonhealing defects in both SAMP6 and SAMR1. The differential findings on micro-CT and histomorphometry for the calvarial defect sites between SAMP6 and SAMR1 may imply different regenerative abilities of intramembranous ossification in these two strains.

Fractures in geriatric mice show decreased callus expansion and bone volume

BACKGROUND

Poor fracture healing in geriatric populations is a significant source of morbidity, mortality, and cost to individuals and society; however, a fundamental biologic understanding of age-dependent healing remains elusive. The development of an aged-based fracture model system would allow for a mechanistic understanding that could guide future biologic treatments.

QUESTIONS/PURPOSES

Using a small animal model of long-bone fracture healing based on chronologic age, we asked how aging affected (1) the amount, density, and proportion of bone formed during healing; (2) the amount of cartilage produced and the progression to bone during healing; (3) the callus structure and timing of the fracture healing; and (4) the behavior of progenitor cells relative to the observed deficiencies of geriatric fracture healing.

METHODS

Transverse, traumatic tibial diaphyseal fractures were created in 5-month-old (n=104; young adult) and 25-month-old (n=107; which we defined as geriatric, and are approximately equivalent to 70-85 year-old humans) C57BL/6 mice. Fracture calluses were harvested at seven times from 0 to 40 days postfracture for micro-CT analysis (total volume, bone volume, bone volume fraction, connectivity density, structure model index, trabecular number, trabecular thickness, trabecular spacing, total mineral content, bone mineral content, tissue mineral density, bone mineral density, degree of anisotropy, and polar moment of inertia), histomorphometry (total callus area, cartilage area, percent of cartilage, hypertrophic cartilage area, percent of hypertrophic cartilage area, bone and osteoid area, percent of bone and osteoid area), and gene expression quantification (fold change).

RESULTS

The geriatric mice produced a less robust healing response characterized by a pronounced decrease in callus amount (mean total volume at 20 days postfracture, 30.08±11.53 mm3 versus 43.19±18.39 mm3; p=0.009), density (mean bone mineral density at 20 days postfracture, 171.14±64.20 mg hydroxyapatite [HA]/cm3 versus 210.79±37.60 mg HA/cm3; p=0.016), and less total cartilage (mean cartilage area at 10 days postfracture, 101,279±46,755 square pixels versus 302,167±137,806 square pixels; p=0.013) and bone content (mean bone volume at 20 days postfracture, 11.68±3.18 mm3 versus 22.34±10.59 mm3; p<0.001) compared with the young adult mice. However, the amount of cartilage and bone relative to the total callus size was similar between the adult and geriatric mice (mean bone volume fraction at 25 days postfracture, 0.48±0.10 versus 0.50±0.13; p=0.793), and the relative expression of chondrogenic (mean fold change in SOX9 at 10 days postfracture, 135+25 versus 90±52; p=0.221) and osteogenic genes (mean fold change in osterix at 20 days postfracture, 22.2±5.3 versus 18.7±5.2; p=0.324) was similar. Analysis of mesenchymal cell proliferation in the geriatric mice relative to adult mice showed a decrease in proliferation (mean percent of undifferentiated mesenchymal cells staining proliferating cell nuclear antigen [PCNA] positive at 10 days postfracture, 25%±6.8% versus 42%±14.5%; p=0.047).

CONCLUSIONS

Our findings suggest that the molecular program of fracture healing is intact in geriatric mice, as it is in geriatric humans, but callus expansion is reduced in magnitude.

CLINICAL RELEVANCE

Our study showed altered healing capacity in a relevant animal model of geriatric fracture healing. The understanding that callus expansion and bone volume are decreased with aging can help guide the development of targeted therapeutics for these difficult to heal fractures.

Identification of differentiation-stage specific markers that define the ex vivo osteoblastic phenotype

The phenotype of osteoblastic (OB) cells in culture is currently defined using a limited number of markers of low sensitivity and specificity. For the clinical use of human skeletal (stromal, mesenchymal) stem cells (hMSC) in therapy, there is also a need to identify a set of gene markers that predict in vivo bone forming capacity. Thus, we used RNA sequencing to examine changes in expression for a set of skeletally-related genes across 8 time points between 0 and 12days of ex vivo OB differentiation of hMSC. We identified 123 genes showing significant temporal expression change. Hierarchical clustering and Pearson's correlation generated 4 groups of genes: early stage differentiation genes (peak expression: 0-24h, n=28) which were enriched for extracellular matrix organisation, e.g. COL1A1, LOX, and SERPINH1; middle stage differentiating genes (peak expression days: 3 and 6, n=20) which were enriched for extracellular matrix/skeletal system development e.g. BMP4, CYP24A1, and TGFBR2; and late stage differentiation genes (peak expression days: 9 and 12, n=27) which were enriched for bone development/osteoblast differentiation, e.g. BMP2 and IGF2. In addition, we identified 13 genes with bimodal temporal expression (2 peaks of expression: days 0 and 12) including VEGFA, PDGFA and FGF2. We examined the specificity of the 123 genes' expression in skeletal tissues and thus propose a set of ex vivo differentiation-stage-specific markers (n=21). In an independent analysis, we identified a subset of genes (n=20, e.g. ELN, COL11A1, BMP4) to predict the bone forming capacity of hMSC and another set (n=20, e.g. IGF2, TGFB2, SMAD3) associated with the ex vivo phenotype of hMSC obtained from osteoporotic patients.

The role of estrogen and androgen receptors in bone health and disease

Mouse models with cell-specific deletion of the estrogen receptor (ER) α, the androgen receptor (AR) or the receptor activator of nuclear factor κB ligand (RANKL), as well as cascade-selective estrogenic compounds have provided novel insights into the function and signalling of ERα and AR. The studies reveal that the effects of estrogens on trabecular versus cortical bone mass are mediated by direct effects on osteoclasts and osteoblasts, respectively. The protection of cortical bone mass by estrogens is mediated via ERα, using a non-nucleus-initiated mechanism. By contrast, the AR of mature osteoblasts is indispensable for the maintenance of trabecular bone mass in male mammals, but not required for the anabolic effects of androgens on cortical bone. Most unexpectedly, and independently of estrogens, ERα in osteoblast progenitors stimulates Wnt signalling and periosteal bone accrual in response to mechanical strain. RANKL expression in B lymphocytes, but not T lymphocytes, contributes to the loss of trabecular bone caused by estrogen deficiency. In this Review, we summarize this evidence and discuss its implications for understanding the regulation of trabecular and cortical bone mass; the integration of hormonal and mechanical signals; the relative importance of estrogens versus androgens in the male skeleton; and, finally, the pathogenesis and treatment of osteoporosis.

Basic biology of skeletal aging: role of stress response pathways

Although a decline in bone formation and loss of bone mass are common features of human aging, the molecular mechanisms mediating these effects have remained unclear. Evidence from pharmacological and genetic studies in mice has provided support for a deleterious effect of oxidative stress in bone and has strengthened the idea that an increase in reactive oxygen species (ROS) with advancing age represents a pathophysiological mechanism underlying age-related bone loss. Mesenchymal stem cells and osteocytes are long-lived cells and, therefore, are more susceptible than other types of bone cells to the molecular changes caused by aging, including increased levels of ROS and decreased autophagy. However, short-lived cells like osteoblast progenitors and mature osteoblasts and osteoclasts are also affected by the altered aged environment characterized by lower levels of sex steroids, increased endogenous glucocorticoids, and higher oxidized lipids. This article reviews current knowledge on the effects of the aging process on bone, with particular emphasis on the role of ROS and autophagy in cells of the osteoblast lineage in mice.

Diabetes mellitus and corticotherapy as risk factors for alendronate-related osteonecrosis of the jaws: a study in Wistar rats

BACKGROUND

The purpose of this study was to investigate the influence of diabetes and corticotherapy on the development of osteonecrosis of the jaws associated with sodium alendronate.

METHODS

Rats were allocated into 4 groups of 11 animals each, representing different treatments: (1) alendronate; (2) alendronate and corticotherapy; (3) alendronate and diabetes; and (4) control. Tooth extractions were performed in all animals, and histological analysis was performed by hematoxylin and eosin staining and immunohistochemistry using anti-bone morphogenetic protein (BMP)-4 and anti-matrix metalloproteinase (MMP)-13 antibodies.

RESULTS

On hematoxylin and eosin analysis, proportions of inflammatory infiltrate, microbial colonies, and osteonecrosis were significantly greater in the diabetes group. BMP-4 expression in connective tissue was higher in the corticosteroid group than the alendronate group. There were no significant differences between the other groups. MMP-13 expression did not differ between the groups analyzed.

CONCLUSION

Diabetes but not corticotherapy is associated with jaw osteonecrosis in rats undergoing alendronate therapy and subjected to tooth extractions.

Suppression of autophagy in osteocytes mimics skeletal aging

Bone mass declines with age but the mechanisms responsible remain unclear. Here we demonstrate that deletion of a conditional allele for Atg7, a gene essential for autophagy, from osteocytes caused low bone mass in 6-month-old male and female mice. Cancellous bone volume and cortical thickness were decreased, and cortical porosity increased, in conditional knock-out mice compared with control littermates. These changes were associated with low osteoclast number, osteoblast number, bone formation rate, and wall width in the cancellous bone of conditional knock-out mice. In addition, oxidative stress was higher in the bones of conditional knock-out mice as measured by reactive oxygen species levels in the bone marrow and by p66(shc) phosphorylation in L6 vertebra. Each of these changes has been previously demonstrated in the bones of old versus young adult mice. Thus, these results demonstrate that suppression of autophagy in osteocytes mimics, in many aspects, the impact of aging on the skeleton and suggest that a decline in autophagy with age may contribute to the low bone mass associated with aging.

Low molecular weight hydroxyethyl chitosan-prednisolone conjugate for renal targeting therapy: synthesis, characterization and in vivo studies

To further evaluate the potential renal targeting profile of low molecular weight hydroxyethyl chitosan (LMWHC) we developed before, prednisolone (Pre) was conjugated with LMWHC by EDC/NHS chemistry to improve the therapeutic effect of glucocorticoids in vivo. The conjugate was denoted as LMWHC-Pre. The prednisolone content of the conjugate was determined by reversed-phase high-performance liquid chromatography (HPLC) with Kromasil C18 column. The results showed that the average coupling degree of prednisolone to LMWHC was 76.7±3.2 μg·mg^-1. The stability and physicochemical characterization of LMWHC-Pre under various conditions were also investigated. To study the fate of LMWHC-Pre after intravenous (i.v.) administration, fluorescein isothiocyanate (FITC) was coupled to the conjugate to explore the renal targeting efficacy. The in vivo results showed that significant amount of the conjugate was accumulated into the kidneys while negligible signal could be detected when the mixture of FITC-LMWHC and prednisolone was co-administered. The preliminary pharmacodynamics study of LMWHC-Pre showed that the conjugate could effectively alleviate the nephrotic syndrome of rats induced by minimal change nephrosis (MCN) model. Toxicity study also revealed that there was little glucocorticoid-induced osteoporosis by LMWHC-Pre upon 20 days of treatment. From this study, LMWHC-Pre may be employed as an effective potential drug candidate for the treatment of chronic renal disease.

Differential responsiveness to 17β-estradiol of mesenchymal stem cells from postmenopausal women between osteoporosis and osteoarthritis

Differential osteogenic potential and responsiveness to 17β-estradiol (E2) of mesenchymal stem cells (MSCs) were found between postmenopausal women with osteoporosis (OP) and osteoarthritis (OA). These results suggest differential biological mechanisms of estrogen deficiency in regulation of bone remodeling between OP and OA.

INTRODUCTION

OP and OA are two common disorders in postmenopausal women. The inverse relationship has been suggested between OP and OA, but their mechanisms that relate to estrogen deficiency are not fully understood. The aim of this study was to compare the differential responsiveness to E2 of MSCs from osteoporotic versus osteoarthritic donors.

METHODS

Twenty postmenopausal patients, ten with osteoporotic hip fractures and ten with hip osteoarthritis, were included into this study. MSCs were derived from cancellous bones of femoral heads from OA and OP donors and cultured in osteogenic and adipogenic medium with or without E2 added. The alkaline phosphatase (ALP) activity, calcium content, calcified nodules, lipid droplets, messenger RNA (mRNA) expression of ALP, osteocalcin (OC), collagen 1α (COL1α), peroxisome proliferators-activated receptor γ2 (PPARγ2) and lipoprotein lipase (LPL) were measured and compared between two groups with OP and OA.

RESULTS

In osteogenic medium, ALP activity, calcium content and mRNA expression of OC and COL1α in MSCs from OA were significantly higher than those from OP group. In adipogenic condition, there was no significant difference in lipid droplets formation and mRNA expression of PPARγ2 and LPL between OP and OA groups. With E2 added in osteogenic medium, ALP activity, calcium content and OC mRNA were significantly higher in OP group than in OA group, whereas E2 had no significant effect on lipid droplet formation and mRNA expression of PPARγ2 and LPL.

CONCLUSION

Differential osteogenic potential and responsiveness to E2 of MSCs were found between postmenopausal women with OP and OA. These results may provide information for clinical application of MSCs in the differential setting of estrogen deficiency.

Fracture risk in the femoral hip region: A finite element analysis supported experimental approach

The decrease of bone mineral density (BMD) is a multifactorial bone pathology, commonly referred to as osteoporosis. The subsequent decline of the bone's micro-structural characteristics renders the human skeletal system, and especially the hip, susceptible to fragility fractures. This study represents a systematic attempt to correlate BMD spectrums to the mechanical strength characteristics of the femoral neck and determine a fracture risk indicator based on non-invasive imaging techniques. The BMD of 30 patients' femurs was measured in vivo by Dual-energy X-ray absorptiometry (DXA). As these patients were subjected to total hip replacement, the mechanical strength properties of their femurs' were determined ex-vivo using uniaxial compression experiments. FEA simulations facilitated the correlation of the DXA measurements to the apparent fracture risk, indicating critical strain values during complex loading scenarios.

Keratocan is expressed by osteoblasts and can modulate osteogenic differentiation

Keratocan is an extracellular matrix protein that belongs to the small leucine-rich proteoglycan family that also includes lumican, biglycan, decorin, mimecan, and fibromodulin. Members of this family are known to play a role in regulating cellular processes such as proliferation and modulation of osteoprogenitor lineage differentiation. The aims of this study were to evaluate the expression pattern of the keratocan within the osteoprogenitor lineage and to assess its role in regulating osteoblast maturation and function. Results from gene expression analyses of cells at different maturation stages within the osteoblast lineage indicate that keratocan is differentially expressed by osteoblasts and shows little or no expression by osteocytes. During primary osteoblast cultures, high keratocan mRNA expression was observed on day 14, whereas lower expression was detected at days 7 and 21. To assess the effects of keratocan on osteoprogenitor cell differentiation, we evaluated primary calvarial cell cultures from keratocan-deficient mice. The mineralization of calvarial osteoblast cultures derived from keratocan null (Kera-/-) mice was lower than in wild-type osteoblast cultures. Furthermore, analysis of RNA derived from Kera-/- calvarial cell cultures showed a reduction in the mature osteoblast differentiation markers, that is, bone sialoprotein and osteocalcin. In addition, we have evaluated the bone formation in keratocan-deficient mice. Histomorphometric analysis indicated that homozygous knockout mice have significantly decreased rates of bone formation and mineral apposition. Taken together, our results demonstrate the expression of keratocan by osteoblast lineage cells and its ability to modulate osteoblast function.

Telomerase-deficient mice exhibit bone loss owing to defects in osteoblasts and increased osteoclastogenesis by inflammatory microenvironment

Telomere shortening owing to telomerase deficiency leads to accelerated senescence of human skeletal (mesenchymal) stem cells (MSCs) in vitro, whereas overexpression leads to telomere elongation, extended life span, and enhanced bone formation. To study the role of telomere shortening in vivo, we studied the phenotype of telomerase-deficient mice (Terc(-/-)). Terc(-/-) mice exhibited accelerated age-related bone loss starting at 3 months of age and during 12 months of follow-up revealed by dual-energy X-ray absorptiometric (DXA) scanning and by micro-computed tomography (µCT). Bone histomorphometry revealed decreased mineralized surface and bone-formation rate as well as increased osteoclast number and size in Terc(-/-) mice. Also, serum total deoxypyridinoline (tDPD) was increased in Terc(-/-) mice. MSCs and osteoprogenitors isolated from Terc(-/-) mice exhibited intrinsic defects with reduced proliferating cell number and impaired osteogenic differentiation capacity. In addition, the Terc(-/-) -MSC cultures accumulated a larger proportion of senescent β-galactosidase(+) cells and cells exhibiting DNA damage. Microarray analysis of Terc(-/-) bone revealed significant overexpression of a large number of proinflammatory genes involved in osteoclast (OC) differentiation. Consistently, serum obtained from Terc(-/-) mice enhanced OC formation of wild-type bone marrow cultures. Our data demonstrate two mechanisms for age-related bone loss caused by telomerase deficiency: intrinsic osteoblastic defects and creation of a proinflammatory osteoclast-activating microenvironment. Thus telomerization of MSCs may provide a novel approach for abolishing age-related bone loss.