Site-specific bone loss in senescence-accelerated mouse (SAMP6): a murine model for senile osteoporosis

Prevention of Osteoporosis in SAMP6 Mice by Rikkunshi-To: Japanese Kampo Medicine

Osteoporosis can increase the risk of fracture in elderly patients, and insufficient control affects quality of life. Rikkunshi-To (RKT) has been prescribed for elderly patients to improve gastrointestinal function. We postulated that RKT has preventive potential for the development of osteoporosis. Thus, we developed a simple method to evaluate osteoporosis using a continuous series of X-ray images of femurs in mice, and investigated the effects of RKT on the development of osteoporosis in these mice. Male senescence-accelerated mouse strain P6 (SAMP6) mice, a model of senile osteoporosis in humans, were fed diets with or without RKT (1%). We collected X-ray images of the whole body of each mouse weekly and measured the ratio of cortical thickness of the femur (C/F index). The C/F index in SAMP6 mice fed the normal diet was increased between 50 and 80 days old, but it was significantly decreased after 120 days old. On the other hand, the C/F index in SAMP6 mice fed the RKT diet was increased between 50 and 80 days old; however, it remained unchanged throughout the experimental period. We also confirmed that the C/F index in SAMP6 mice fed the RKT diet suddenly decreased on the replacement of the RKT diet with a normal diet, suggesting that we can collect data related to a series of continuous changes in bone mass, and that RKT is useful for the prevention of osteoporosis.

The novel small molecule E0924G dually regulates bone formation and bone resorption through activating the PPARδ signaling pathway to prevent bone loss in ovariectomized rats and senile mice

Osteoporosis is particularly prevalent among postmenopausal women and the elderly. In the present study, we investigated the effect of the novel small molecule E0924G (N-(4-methoxy-pyridine-2-yl)-5-methylfuran-2-formamide) on osteoporosis. E0924G significantly increased the protein expression levels of osteoprotegerin (OPG) and runt-related transcription factor 2 (RUNX2), and thus significantly promoted osteogenesis in MC3T3-E1 cells. E0924G also significantly decreased osteoclast differentiation and inhibited bone resorption and F-actin ring formation in receptor activator of NF-κB ligand (RANKL)-induced osteoclasts from RAW264.7 macrophages. Importantly, oral administration of E0924G in both ovariectomized (OVX) rats and SAMP6 senile mice significantly increased bone mineral density and decreased bone loss compared to OVX controls or SAMR1 mice. Further mechanistic studies showed that E0924G could bind to and then activate peroxisome proliferator-activated receptor delta (PPARδ), and the pro-osteoblast effect and the inhibition of osteoclast differentiation induced by E0924G were significantly abolished when PPARδ was knocked down or inhibited. In conclusion, these data strongly suggest that E0924G has the potential to prevent OVX-induced and age-related osteoporosis by dual regulation of bone formation and bone resorption through activation of the PPARδ signaling pathway.

A Senescence-Associated Secretory Phenotype of Bone Marrow Mesenchymal Stem Cells Inhibits the Viability of Breast Cancer Cells

Breast cancer, the most prevalent malignancy in women, often progresses to bone metastases, especially in older individuals. Dormancy, a critical aspect of bone-metastasized breast cancer cells (BCCs), enables them to evade treatment and recur. This dormant state is regulated by bone marrow mesenchymal stem cells (BMMSCs) through the secretion of various factors, including those associated with senescence. However, the specific mechanisms by which BMMSCs induce dormancy in BCCs remain unclear. To address this gap, a bone-specific senescence-accelerated murine model, SAMP6, was utilized to minimize confounding systemic age-related factors. Confirming senescence-accelerated osteoporosis, distinct BMMSC phenotypes were observed in SAMP6 mice compared to SAMR1 counterparts. Notably, SAMP6-BMMSCs exhibited premature senescence primarily due to telomerase activity loss and activation of the p21 signaling pathway. Furthermore, the effects of conditioned medium (CM) derived from SAMP6-BMMSCs versus SAMR1-BMMSCs on BCC proliferation were examined. Intriguingly, only CM from SAMP6-BMMSCs inhibited BCC proliferation by upregulating p21 expression in both MCF-7 and MDA-MB-231 cells. These findings suggest that the senescence-associated secretory phenotype (SASP) of BMMSCs suppresses BCC viability by inducing p21, a pivotal cell cycle inhibitor and tumor suppressor. This highlights a heightened susceptibility of BCCs to dormancy in a senescent microenvironment, potentially contributing to the increased incidence of breast cancer bone metastasis and recurrence observed with aging.

Mouse models of accelerated aging in musculoskeletal research for assessing frailty, sarcopenia, and osteoporosis - A review

Musculoskeletal aging encompasses the decline in bone and muscle function, leading to conditions such as frailty, osteoporosis, and sarcopenia. Unraveling the underlying molecular mechanisms and developing effective treatments are crucial for improving the quality of life for those affected. In this context, accelerated aging models offer valuable insights into these conditions by displaying the hallmarks of human aging. Herein, this review focuses on relevant mouse models of musculoskeletal aging with particular emphasis on frailty, osteoporosis, and sarcopenia. Among the discussed models, PolgA mice in particular exhibit hallmarks of musculoskeletal aging, presenting early-onset frailty, as well as reduced bone and muscle mass that closely resemble human musculoskeletal aging. Ultimately, findings from these models hold promise for advancing interventions targeted at age-related musculoskeletal disorders, effectively addressing the challenges posed by musculoskeletal aging and associated conditions in humans.

Ozone Improved Bone Dynamic of Female Rats Using Zoledronate

The aim of this study was to analyze the effect of ozone (OZN) therapy on the dynamics of bone tissue in ovariectomized rats treated with zoledronic acid (ZOL). Female Wistar rats aged 6 months (n = 110) were subjected to bilateral ovariectomy (OVX). At month 3 post-OVX, 10 animals were euthanized to characterize the bone tissue architecture using microtomography (micro-CT). The remaining animals were divided into two groups: ZOL group, administered with ZOL (100 μg/kg body weight); saline (SAL) group (0.45 mL of SAL solution), both for 28 days. At month 3 post-treatment, 10 animals from each group were euthanized to characterize the bone architecture using micro-CT. The remaining animals were divided into the following groups: ZOL (n = 20), ZOL + OZN (n = 20); SAL (n = 20), and SAL + OZN (n = 20). The animals in ZOL + OZN and SAL + OZN groups were intraperitoneally administered with OZN (0.7 mg/kg body weight) once every 2 days. On days 30 and 60, six animals from each group were euthanized for analysis and structural characterization of bones in the femoral head and spine. Some samples of the femoral neck were subjected to biomechanical tests, while some samples were analyzed under a laser confocal microscope. The other samples collected from the femoral neck and spine were analyzed for area of neoformed bone and used for performing inflammatory cell and osteocyte counts. Data were submitted to statistical analysis considering a significance level of p < 0.05. Bone volume percentage and osteocyte and inflammatory cell counts were upregulated in the femoral head region of the ZOL + OZN group. Biomechanical analysis of the femoral neck revealed that the modulus of elasticity was similar between the ZOL and ZOL + OZN groups but differed significantly between the SAL and SAL + OZN groups. The positive areas for calcein and alizarin in the ZOL and ZOL + OZN groups were higher than those in the SAL and SAL + OZN groups. This suggested a positive synergistic effect of OZN and ZOL on the maintenance of bone mass and restoration of bone tissue vitality in ovariectomized rats.

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.

Dolichos Lablab Linné Inhibits Bone Density Loss and Promotes Bone Union in Senile Osteoporosis through Osteogenesis

As populations continue to age, osteoporosis has emerged as an increasingly critical concern. Most advancements in osteoporosis treatment are predominantly directed toward addressing abnormal osteoclast activity associated with menopause, with limited progress in developing therapies that enhance osteoblast activity, particularly in the context of aging and fractures, and serious side effects associated with existing treatments have highlighted the necessity for natural-product-based treatments targeting senile osteoporosis and fractures. Dolichos lablab Linné (DL) is a natural product traditionally used for gastrointestinal disorders, and its potential role in addressing bone diseases has not been extensively studied. In this research, we investigated the anti-osteoporosis and bone-union-stimulating effects of DL using the SAMP6 model, a naturally aged mouse model. Additionally, we employed MC3T3-E1 cells to validate DL's osteoblast-promoting effect and to assess the involvement of core mechanisms such as the BMP-2/Smad and Wnt/β-catenin pathways. The experimental results revealed that DL promoted the formation of osteoblasts and calcified nodules by upregulating both the BMP-2/Smad and Wnt/β-catenin mechanisms. Based on its observed effects, DL demonstrated the potential to enhance bone mineral density in aged osteoporotic mice and promote bone union in fractured mice. These findings indicate the promising therapeutic potential of DL for the treatment of osteoporosis and bone-related conditions, thus warranting further investigation and potential clinical applications.

Inflammation and aging: signaling pathways and intervention therapies

Aging is characterized by systemic chronic inflammation, which is accompanied by cellular senescence, immunosenescence, organ dysfunction, and age-related diseases. Given the multidimensional complexity of aging, there is an urgent need for a systematic organization of inflammaging through dimensionality reduction. Factors secreted by senescent cells, known as the senescence-associated secretory phenotype (SASP), promote chronic inflammation and can induce senescence in normal cells. At the same time, chronic inflammation accelerates the senescence of immune cells, resulting in weakened immune function and an inability to clear senescent cells and inflammatory factors, which creates a vicious cycle of inflammation and senescence. Persistently elevated inflammation levels in organs such as the bone marrow, liver, and lungs cannot be eliminated in time, leading to organ damage and aging-related diseases. Therefore, inflammation has been recognized as an endogenous factor in aging, and the elimination of inflammation could be a potential strategy for anti-aging. Here we discuss inflammaging at the molecular, cellular, organ, and disease levels, and review current aging models, the implications of cutting-edge single cell technologies, as well as anti-aging strategies. Since preventing and alleviating aging-related diseases and improving the overall quality of life are the ultimate goals of aging research, our review highlights the critical features and potential mechanisms of inflammation and aging, along with the latest developments and future directions in aging research, providing a theoretical foundation for novel and practical anti-aging strategies.

MiR-21-5p regulates the dynamic of mitochondria network and rejuvenates the senile phenotype of bone marrow stromal cells (BMSCs) isolated from osteoporotic SAM/P6 mice

BACKGROUND

Progression of senile osteoporosis is associated with deteriorated regenerative potential of bone marrow-derived mesenchymal stem/stromal cells (BMSCs). According to the recent results, the senescent phenotype of osteoporotic cells strongly correlates with impaired regulation of mitochondria dynamics. Moreover, due to the ageing of population and growing osteoporosis incidence, more efficient methods concerning BMSCs rejuvenation are intensely investigated. Recently, miR-21-5p was reported to play a vital role in bone turnover, but its therapeutic mechanisms in progenitor cells delivered from senile osteoporotic patients remain unclear. Therefore, the goal of this paper was to investigate for the first time the regenerative potential of miR-21-5p in the process of mitochondrial network regulation and stemness restoration using the unique model of BMSCs isolated from senile osteoporotic SAM/P6 mice model.

METHODS

BMSCs were isolated from healthy BALB/c and osteoporotic SAM/P6 mice. We analysed the impact of miR-21-5p on the expression of crucial markers related to cells' viability, mitochondria reconstruction and autophagy progression. Further, we established the expression of markers vital for bone homeostasis, as well as defined the composition of extracellular matrix in osteogenic cultures. The regenerative potential of miR-21 in vivo was also investigated using a critical-size cranial defect model by computed microtomography and SEM-EDX imaging.

RESULTS

MiR-21 upregulation improved cells' viability and drove mitochondria dynamics in osteoporotic BMSCs evidenced by the intensification of fission processes. Simultaneously, miR-21 enhanced the osteogenic differentiation of BMSCs evidenced by increased expression of Runx-2 but downregulated Trap, as well as improved calcification of extracellular matrix. Importantly, the analyses using the critical-size cranial defect model indicated on a greater ratio of newly formed tissue after miR-21 application, as well as upregulated content of calcium and phosphorus within the defect site.

CONCLUSIONS

Our results demonstrate that miR-21-5p regulates the fission and fusion processes of mitochondria and facilitates the stemness restoration of senile osteoporotic BMSCs. At the same time, it enhances the expression of RUNX-2, while reduces TRAP accumulation in the cells with deteriorated phenotype. Therefore, miR-21-5p may bring a novel molecular strategy for senile osteoporosis diagnostics and treatment.

AAV-mediated expression of secreted and transmembrane αKlotho isoforms rescues relevant aging hallmarks in senescent SAMP8 mice

Senescence represents a stage in life associated with elevated incidence of morbidity and increased risk of mortality due to the accumulation of molecular alterations and tissue dysfunction, promoting a decrease in the organism's protective systems. Thus, aging presents molecular and biological hallmarks, which include chronic inflammation, epigenetic alterations, neuronal dysfunction, and worsening of physical status. In this context, we explored the AAV9-mediated expression of the two main isoforms of the aging-protective factor Klotho (KL) as a strategy to prevent these general age-related features using the senescence-accelerated mouse prone 8 (SAMP8) model. Both secreted and transmembrane KL isoforms improved cognitive performance, physical state parameters, and different molecular variables associated with aging. Epigenetic landscape was recovered for the analyzed global markers DNA methylation (5-mC), hydroxymethylation (5-hmC), and restoration occurred in the acetylation levels of H3 and H4. Gene expression of pro- and anti-inflammatory mediators in central nervous system such as TNF-α and IL-10, respectively, had improved levels, which were comparable to the senescence-accelerated-mouse resistant 1 (SAMR1) healthy control. Additionally, this improvement in neuroinflammation was supported by changes in the histological markers Iba1, GFAP, and SA β-gal. Furthermore, bone tissue structural variables, especially altered during senescence, recovered in SAMP8 mice to SAMR1 control values after treatment with both KL isoforms. This work presents evidence of the beneficial pleiotropic role of Klotho as an anti-aging therapy as well as new specific functions of the KL isoforms for the epigenetic regulation and aged bone structure alteration in an aging mouse model.

Obesity and Bone Health: A Complex Link

So far, the connections between obesity and skeleton have been extensively explored, but the results are inconsistent. Obesity is thought to affect bone health through a variety of mechanisms, including body weight, fat volume, bone formation/resorption, proinflammatory cytokines together with bone marrow microenvironment. In this review, we will mainly describe the effects of adipokines secreted by white adipose tissue on bone cells, as well as the interaction between brown adipose tissue, bone marrow adipose tissue, and bone metabolism. Meanwhile, this review also reviews the evidence for the effects of adipose tissue and its distribution on bone mass and bone-related diseases, along with the correlation between different populations with obesity and bone health. And we describe changes in bone metabolism in patients with anorexia nervosa or type 2 diabetes. In summary, all of these findings show that the response of skeleton to obesity is complex and depends on diversified factors, such as mechanical loading, obesity type, the location of adipose tissue, gender, age, bone sites, and secreted cytokines, and that these factors may exert a primary function in bone health.

Anti-osteoporotic effects of Salvia miltiorrhiza Bunge EtOH extract both in ovariectomized and naturally menopausal mouse models

ETHNOPHARMACOLOGICAL RELEVANCE

Salvia miltiorrhiza is a traditional oriental medicine widely used for preventing and treating disorders of the liver, menstrual, and blood circulation systems. Osteoporosis, loss of bone with age and/or estrogen deficiency, is an important causal factor of fracture. S. miltiorrhiza extract has been used to alleviate dysmenorrhea and painful osteoarthritis.

AIM OF THE STUDY

This study was performed to investigate the anti-osteoporosis activity of the Salvia miltiorrhiza ethanol extract (SME) in osteoporosis-prone conditions: ovariectomized (OVX) and naturally menopaused (NM) ICR mice.

MATERIALS AND METHODS

Anti-osteoporotic potentials of SME (50-200 mg/kg) were evaluated based on bone mineral density using microCT analysis, biochemical parameters, and changes in the gene expressions involved in bone resorption.

RESULTS

SME ameliorated the loss of trabecular bone both in OVX and NM mice. SME was effective in correcting aberrant levels of RANKL, osteocalcin, and BALP, which are critically involved in bone resorption. In addition, SME suppressed the expression of TRAF6 and NFATc1, which play a role in osteoclast differentiation.

CONCLUSIONS

SME suppressed the loss of trabecular bone via suppressing bone resorption and osteoclast differentiation both in OVX and NM mice. SME is likely to be developed as a therapeutic agent for osteoporosis.

Molecular changes to tendons after collagenase-induced acute tendon injury in a senescence-accelerated mouse model

BACKGROUND

Aging impairs tendon healing and is a potential risk factor for chronic tendinitis. During normal aging, tendons undergo structural and biomechanical degenerative changes, accompanied by a reduction in the number of tenocytes and changes to their properties. However, molecular changes in aged tendons under inflammatory conditions are not well understood. The present study analyzed the molecular changes in collagenase induced acute tendon injury using a senescence-accelerated mouse (SAM) model.

METHODS

SAMP6 mice were used as an aging animal model and SAMR1 mice were used as a control to represent a senescence-resistant inbred strain. All the mice used in the study were 40 weeks old. Collagenase I from Clostridium histolyticum (20 μL) was injected percutaneously to the tendon-bone junction of the Achilles tendon. Two weeks after treatment, the Achilles tendons were harvested and stained using Picrosirius Red to determine collagen expression. Real-time PCR was performed to analyze gene expression of IL-6, tenomodulin, type I and type II collagen, MMP-9, TIMP-1, and TIMP-2.

RESULTS

Collagenase injection resulted in significantly higher gene expression of IL-6 but significantly lower tenomodulin expression compared with the control in SAMP6 and SAMR1 mice. In SAMP6 mice, gene expression of type III collagen and MMP-9 was significantly higher in the collagenase-injected group compared with the control group. SAMP6 mice also showed lower expression of type I collagen, TIMP-1, and TIMP-2 in the collagenase-injected group compared with the control group. Picrosirius Red staining showed the highest expression of type III collagen in the collagenase-injected SAMP6 group compared with the other groups.

CONCLUSIONS

The collagenase-injected SAMP6 group showed higher expression of IL-6, MMP-9, and type III collagen and lower expression of type I collagen, TIMP-1, and TIMP-2, which are known to suppress metalloproteinases. The results indicate that aging may lead to dysfunction of the tendon healing process after acute tendon injury.

Morphological and molecular characterization of the senile osteoporosis in senescence-accelerated mouse prone 6 (SAMP6)

Although the understanding of the complex pathogenesis for osteoporosis is appreciable, the underlying mechanism is not yet fully elucidated. There is a great need to further characterize the available animal models in osteoporosis research. The senescence-accelerated mouse prone 6 (SAMP6) mice have been developed as the spontaneous experimental model for senile osteoporosis. Here, we provide a comprehensive overview of current research regarding the bone morphological and molecular alterations and the possible mechanisms involved in these changes. There were significant decrease in trabecular bone mass at the axial and appendicular skeletal sites, with no marked alterations of cortical bone. Decreased bone formation on the endosteal surface and trabecular bone, and increased bone marrow adiposity were observed in SAMP6 mice. The elevated expression level of proliferator activator gamma (PPARγ) in the bone marrow suggest that PPARγ might regulate osteoblastic bone formation negatively in SAMP6 mice. The expression level of secreted frizzled-related protein 4 (Sfrp4) was found to be higher in SAMP6 mice. Sfrp4 is considered to suppress osteoblastic proliferation mediated by inhibition of Wnt signaling pathway. These findings may help us to gain more insight into the potential mechanism of senile osteoporosis.

Cyperenoic acid suppresses osteoclast differentiation and delays bone loss in a senile osteoporosis mouse model by inhibiting non-canonical NF-κB pathway

Cyperenoic acid is a terpenoid isolated from the root of a medicinal plant Croton crassifolius with a wide range of biological activities. In this study, the effects of cyperenoic acid on osteoclast differentiation were investigated both in vitro and in vivo using receptor activator of nuclear factor-κB ligand (RANKL)-induced bone marrow-derived osteoclasts and senescence-accelerated mouse prone 6 (SAMP6). Cyperenoic acid significantly suppressed RANKL-induced osteoclast differentiation at the concentrations with no apparent cytotoxicity. The half maximum inhibitory concentration (IC₅₀) for osteoclast differentiation was 36.69 μM ± 1.02. Cyperenoic acid treatment evidently reduced the expression of two key transcription factors in osteoclast differentiation, NFATc1 and c-Fos. Detailed signaling analysis revealed that cyperenoic acid did not affect MAPK pathways and canonical NF-κB pathway but impaired activation of p100/p52 in the non-canonical NF-κB pathway upon RANKL stimulation. Moreover, the expression of osteoclast-related genes, nfatc1, ctsk, irf8, acp5 and cfos were disrupted by cyperenoic acid treatment. The bone resorption activity by cyperenoic acid-treated osteoclasts were impaired. In a senile osteoporosis mouse model SAMP6, mice fed on diet supplemented with cyperenoic acid showed delay in bone loss, compared to the control. Taken together, plant-derived cyperenoic acid shows great potential as therapeutic agent for osteoporosis.

Treadmill running exercise prevents senile osteoporosis and upregulates the Wnt signaling pathway in SAMP6 mice

This study examined the effects of different exercise intensities and durations on bone mineral density (BMD) and bone strength in senescence-accelerated mouse prone 6 (SAMP6) and determined the involvement of the Wnt signaling pathway in exercise-induced osteogenesis. Three-month-old male SAMP6 mice were randomly assigned to different speeds of treadmill running exercise representing low, medium and high intensity, with the duration of five and nine weeks, respectively. We showed that medium-intensity exercise had positive effects on skeletal health, including BMD and bone strength, and the efficacy was higher than that of low-intensity exercise. Interestingly, high-intensity exercise can maintain or even increase bone strength, despite its negative effects on bone mass. Nine weeks of exercise was superior to 5 weeks of exercise, particularly for low-intensity exercise. Furthermore, these effects of exercise-induced osteogenesis are accompanied by activation of the Wnt signaling pathway. Taken together, these results suggest that the positive effects of exercise on osteoporosis prevention are intensity and duration-dependent, and may involve the regulation of Wnt signaling pathways.

Resveratrol as anti-aging therapy for age-related bone loss

INTRODUCTION

Previous studies have indicated that resveratrol, a natural phytoestrogen, can act as an anti-aging therapy to resist age-related changes of several body tissues. However, the anti-aging effects of resveratrol on bone have been poorly investigated in this natural aging population. Accordingly, this study was design to evaluate the effects of resveratrol on bone mass and biomechanical properties in old rat femora.

METHODS

Twenty 22-month-old male Wistar rats were divided into two randomly assigned groups (n=10). The first group was treated for 10 weeks with resveratrol (10 mg/kg per day) and the second group was left untreated (control). Rat femora were collected. Bone mass and bone microestructure were investigated by microcomputed tomography and histomorphometry. Biomechanical properties were determined by a three-point bending test. Plasma levels of CTX (carboxy-terminal telopeptide of type I collagen) and osteocalcin were also determined. Statistical analyses were performed by a Student two-tailed unpaired t-test. In all experiments, a value of p<0.05 was considered significant.

RESULTS

Microcomputed tomography analyses demonstrated that resveratrol-treated rats had significant higher bone volume, bone trabecular number, and cortical thickness and lower spacing between trabeculae in comparison to the control group. Histomorphometric analyses confirmed the increase of bone volume in resveratrol-treated rats compared to controls. Resveratrol-treated rats had significant higher bone flexural modulus, stiffness, and ultimate load compared to control group. Treatment was not associated with changes in plasma CTX or osteocalcin.

CONCLUSION

These findings demonstrate that resveratrol increases bone microstructure and bone mechanical properties in old male rats, suggesting that resveratrol might be used as anti-aging therapy to resist age-induced bone loss.

Tooth loss early in life accelerates age-related bone deterioration in mice

Both osteoporosis and tooth loss are health concerns that affect many older people. Osteoporosis is a common skeletal disease of the elderly, characterized by low bone mass and microstructural deterioration of bone tissue. Chronic mild stress is a risk factor for osteoporosis. Many studies showed that tooth loss induced neurological alterations through activation of a stress hormone, corticosterone, in mice. In this study, we tested the hypothesis that tooth loss early in life may accelerate age-related bone deterioration using a mouse model. Male senescence-accelerated mouse strain P8 (SAMP8) mice were randomly divided into control and toothless groups. Removal of the upper molar teeth was performed at one month of age. Bone response was evaluated at 2, 5 and 9 months of age. Tooth loss early in life caused a significant increase in circulating corticosterone level with age. Osteoblast bone formation was suppressed and osteoclast bone resorption was activated in the toothless mice. Trabecular bone volume fraction of the vertebra and femur was decreased in the toothless mice with age. The bone quality was reduced in the toothless mice at 5 and 9 months of age, compared with the age-matched control mice. These findings indicate that tooth loss early in life impairs the dynamic homeostasis of the bone formation and bone resorption, leading to reduced bone strength with age. Long-term tooth loss may have a cumulative detrimental effect on bone health. It is important to take appropriate measures to treat tooth loss in older people for preventing and/or treating senile osteoporosis.

Genetic manipulation of the ghrelin signaling system in male mice reveals bone compartment specificity of acylated and unacylated ghrelin in the regulation of bone remodeling

Ghrelin receptor-deficient (Ghsr-/-) mice that lack acylated ghrelin (AG) signaling retain a metabolic response to unacylated ghrelin (UAG). Recently, we showed that Ghsr-deficiency affects bone metabolism. The aim of this study was to further establish the impact of AG and UAG on bone metabolism. We compared bone metabolism in Ghsr-/- (lacking only AG signaling) and ghrelin-deficient (Ghrl-/-; both AG and UAG deficient) male mice. Ghrl-/- mice had lower cortical bone mass, whereas Ghsr-/- mice had lower trabecular bone mass. This demonstrates bone compartment-specific effects of AG and a role for UAG in bone metabolism. Also, Ghrl-/- but not Ghsr-/- mice had increased bone formation rate and increased osteogenic stem cell numbers in their bone marrow. In ex vivo bone marrow cultures both AG and UAG inhibited osteoblast differentiation. This indicated that bone resorption must be increased in these mice. Accordingly, osteoclastogenesis rate was faster in bone marrow cultures from Ghsr-/- and Ghrl-/- mice, and osteoclast formation was inhibited by AG signaling and partially suppressed by UAG. In osteoblast cultures, AG markedly induced osteoprotegerin gene expression and both peptides reduced RANKL/osteoprotegerin ratio. These data describe unique cell-type specific effects of AG and UAG within a single tissue, supporting a tight and complex control of bone formation and resorption as well as a link between nutrition and bone metabolism. The balance between AG and UAG actions in the bone marrow may lead to bone compartmental-specific effects.

Stem cell transplantation improves aging-related diseases

Aging is a complex process of damage accumulation, and has been viewed as experimentally and medically intractable. The number of patients with age-associated diseases such as type 2 diabetes mellitus (T2DM), osteoporosis, Alzheimer's disease (AD), Parkinson's disease, atherosclerosis, and cancer has increased recently. Aging-related diseases are related to a deficiency of the immune system, which results from an aged thymus and bone marrow cells. Intra bone marrow-bone marrow transplantation (IBM-BMT) is a useful method to treat intractable diseases. This review summarizes findings that IBM-BMT can improve and treat aging-related diseases, including T2DM, osteoporosis and AD, in animal models.

Chewing ameliorates chronic mild stress-induced bone loss in senescence-accelerated mouse (SAMP8), a murine model of senile osteoporosis

Chronic mild stress is a risk factor for osteoporosis and chewing inhibits the stress response. We examined the effect of chewing on chronic stress-induced bone loss and bone microstructural deterioration in mice. The senescence-accelerated mouse strain P8 (SAMP8) was randomly divided into control, stress, and stress with chewing groups of fifteen animals each. Mice in the stress and stress with chewing groups were placed in a ventilated restraint tube for 60minutes, twice a day for 4weeks. The restrained mice were simultaneously subjected daily to one of the following stressors: water immersion, physical shaking and flashing lights. Mice in the stress with chewing group were allowed to chew a wooden stick during the experimental period. After the experiment, the bone response was evaluated using quantitative micro computed tomography, bone histomorphometry, and biochemical markers. Exposure of SAMP8 mice to chronic stress resulted in significant increase of the blood corticosterone and noradrenaline levels, and adrenal weight. The bone resorption was activated and the bone formation was suppressed. Trabecular bone volume and trabecular number were decreased in both the vertebra and distal femur of the stress group. Chewing under chronic stress prevented the increase in the blood corticosterone and noradrenaline levels, attenuated the reduced bone formation and increased bone resorption, improved the trabecular bone loss and bone microstructural deterioration induced by chronic mild stress. These findings indicate that chewing can ameliorate chronic stress-induced bone loss in SAMP8 mice. Thus, chewing may represent a useful method preventing and/or treating chronic stress-related osteoporosis.

Aberrant bone density in aging mice lacking the adenosine transporter ENT1

Adenosine is known to regulate bone production and resorption in humans and mice. Type 1 equilibrative nucleoside transporter (ENT1) is responsible for the majority of adenosine transport across the plasma membrane and is ubiquitously expressed in both humans and mice. However, the contribution of ENT1-mediated adenosine levels has not been studied in bone remodeling. With the recent identification of the importance of adenosine signaling in bone homeostasis, it is essential to understand the role of ENT1 to develop novel therapeutic compounds for bone disorders. Here we examined the effect of ENT1 deletion on bone density using X-ray, dual energy X-ray absorptiometry and micro-computerized tomography analysis. Our results show that bone density and bone mineral density is reduced in the lower thoracic and lumbar spine as well as the femur of old ENT1 null mice (>7 months) compared to wild-type littermates. Furthermore, we found increased mRNA expression of tartrate-resistant acid phosphatase (TRAP), an osteoclast marker, in isolated long bones from 10 month old ENT1 null mice compared to wild-type mice. In addition, aged ENT1 null mice displayed severe deficit in motor coordination and locomotor activity, which might be attributed to dysregulated bone density. Overall, our study suggests that ENT1-regulated adenosine signaling plays an essential role in lumbar spine and femur bone density.

Resveratrol supplementation preserves long bone mass, microstructure, and strength in hindlimb-suspended old male rats

Resveratrol has gained popularity as an "anti-aging" compound due to its antioxidant and anti-inflammatory properties. Few studies have investigated the role of resveratrol supplementation in the prevention of age-related bone loss and skeletal disuse despite increased inactivity and age-related bone loss in the elderly. The objective of the study was to investigate the effect of resveratrol supplementation on disuse and age-related bone loss. Old (age 33 months) Fischer 344 × Brown Norway male rats were provided either trans-resveratrol (12.5 mg/kg bw/day) or deionized distilled water by oral gavage for 21 days. Rats were hindlimb-suspended (HLS) or kept ambulatory (AMB) for 14 days. Both femora and tibiae were collected. Bone mass was measured by dual-energy X-ray absorptiometry and bone microstructure was determined by micro-computed tomography. HLS of old male rats accelerated loss of bone mineral content, decreased trabecular bone volume per unit of total volume, and increased trabecular separation. Resveratrol supplementation ameliorated bone demineralization and loss of bone microarchitecture in HLS old male rats. The peak force measured by the three-point bending test was reduced (P = 0.007) in HLS/control compared to AMB/control rats. Resveratrol supplementation ameliorated HLS-induced loss of femur strength. Plasma osteocalcin and alkaline phosphatase was higher (P < 0.04) and C-reactive protein was lower (P = 0.04) in old male rats given resveratrol. The bone protective effects of resveratrol appeared to be mediated through increased osteoblast bone formation, possibly due to reduced inflammation. Based on the results, resveratrol supplementation appeared to provide a feasible dietary therapy for preserving the skeletal system during disuse and age-related bone loss.

Beneficial effects of phytoestrogens and their metabolites produced by intestinal microflora on bone health

Phytoestrogens are a class of bioactive compounds derived from plants and exert various estrogenic and antiestrogenic effects. Estrogen deficiency osteoporosis has become a serious problem in elderly women. The use of ovariectomized (OVX) rat or mice models to simulate the postmenopausal condition is well established. This review aimed to clarify the sources, biochemistry, absorption, metabolism, and mode of action of phytoestrogens on bone health in intervention studies. In vitro, phytoestrogens promote protein synthesis, osteoprotegerin/receptor activation of nuclear factor-kappa B ligand ratio, and mineralization by osteoblast-like cells (MC3T3-E1). In the OVX murine model, administration of phytoestrogens can inhibit differentiation and activation of osteoclasts, expression of tartrate-resistant acid phosphatase, and secretion of pyridinoline compound. Phytoestrogens also enhance bone formation and increase bone mineral density and levels of alkaline phosphatase, osteocalcin, osteopontin, and α1(I) collagen. Results of mechanistic studies have indicated that phytoestrogens suppress the rate of bone resorption and enhance the rate of bone formation.

Single nucleotide polymorphisms in sFRP4 are associated with bone and body composition related parameters in Danish but not in Belgian men

The senescence accelerated mouse P6 (SAMP6) has a low bone mass and has previously shown to be a good model for senile osteoporosis in humans. In addition to a reduced bone mass, SAMP6 mice are obese and have hyperlipidemia. Using positional cloning and expression studies, an increased expression of sfrp4 was found in these mice. SFRP4 is a modulator of the Wnt signalling pathway. This pathway has been previously shown to be involved in regulating bone mass. Additional evidence that sFRP4 has an influence on BMD was delivered by linkage and association studies mostly performed in Asian populations. Based on these data we decided to perform an association study between common variants in sFRP4, BMD, hip geometry parameters and body composition parameters in a population consisting of 1383 Danish men (783 aged 20-29 years; 600 aged 60-74 years). Afterwards we tried to replicate the significant results in a population of 994 Belgian men. In the Danish population we found 6 SNPs associated with BMD at the hip and/or femoral neck. Furthermore, all 6 SNPs were associated with several hip geometry parameters. The homozygous presence of the minor allele resulted for all SNPs (except rs4720265) in a decrease in bone density and bone strength. Finally, we observed in the Danish population age specific associations with height and fat mass. In the Belgian population we tried to replicate the results of three SNPs with BMD and body composition parameters. Unfortunately, we were not able to replicate the results found in the Danish cohort but we found one SNP (rs2598116) associated with height. In conclusion, genetic variation in sFRP4 has an influence on hip fracture risk, percentage body fat and height in a Danish male population. However, we were unable to replicate these results in an independent Belgian population.

Combined treatment with a traditional Chinese medicine, Hachimi-jio-gan (Ba-Wei-Di-Huang-Wan) and alendronate improves bone microstructure in ovariectomized rats

ETHNOPHARMACOLOGICAL RELEVANCE

Hachimi-jio-gan is one of the most common recipes in traditional Chinese, Japanese and Korean medicines and has been used for preventing and treating various diseases associated with aging, including osteoporosis.

AIM OF THE STUDY

The present study was performed to examine the combined effects of a traditional Chinese medicine, Hachimi-jio-gan (HJG) and antiresorptive agent, alendronate (ALN) on ovariectomy-induced bone loss in rats.

MATERIALS AND METHODS

Six-month-old female Sprague-Dawley rats were underwent ovariectomy (OVX) or sham operation. Eight weeks later, the OVX rats were treated either with HJG or ALN alone or in combination of both. The skeletal response was evaluated using micro-computed tomography (micro-CT), image analysis software, and biochemical markers.

RESULTS

This study demonstrated that treatment with HJG or ALN alone increased trabecular bone volume and bone mineral density (BMD), and partially improved bone microstructure of the proximal tibia and vertebra in OVX rats. Treatment with ALN to OVX rats resulted in significant reduction in both bone resorption and bone formation. Treatment with HJG to OVX rats inhibited bone resorption, with no marked effects on bone formation. Combined treatment of HJG and ALN significantly improved trabecular bone mass and bone microstructure, compared with either agent alone.

CONCLUSIONS

We conclude that the combined treatment with HJG and ALN has beneficial effects on trabecular bone mass, improving the structural properties of both tibia and vertebra in OVX rats.

Dysregulated in vitro hematopoiesis, radiosensitivity, proliferation, and osteoblastogenesis with marrow from SAMP6 mice

The senescence accelerated-prone mouse variant 6 (SAMP6) shows normal growth followed by rapid aging, development of osteopenia, and shortened lifespan, compared with control R1 mice. Because oxidative stress is a fundamental mechanism of tissue aging, we tested whether cellular parameters that are associated with oxidative stress are impaired with marrow from SAMP6 mice. We compared in vitro hematopoiesis, irradiation sensitivity, proliferative potential, and osteoblastogenesis with marrow cells from SAMP6 and R1 mice. Marrow cells from SAMP6 mice showed shortened in vitro hematopoiesis; their stromal cells showed greater radiation sensitivity and decreased proliferation. Consistent with those properties, there was constitutive upregulation of transforming growth factor-β(1), an inhibitor of hematopoiesis, and of cell cycle inhibitory genes, p16(INK4A) and p19(ARF). Paradoxically, there was constitutive expression of osteoblast genes in stromal cells from SAMP6 mice, but in vitro matrix mineralization was impaired. These studies and data included in other reports indicate that impaired proliferation of osteoblast progenitors in SAMP6 marrow may be a major factor contributing to accelerated loss of bone mass. In sum, marrow from SAMP6 mice had diminished capacity for long-term hematopoiesis, increased radiosensitivity, and reduced proliferative capacity.

Segmental variations in trabecular bone density and microstructure of the spine in senescence-accelerated mouse (SAMP6): a murine model for senile osteoporosis

The senescence-accelerated mouse strain P6 (SAMP6) is a model of senile osteoporosis, which possesses many features of senile osteoporosis in humans. So far, little is known about the systemic bone microstructural changes that occur at the cervical, thoracic, and lumbar vertebrae. In this study, we therefore investigated segmental variations of vertebral trabecular bone mineral density (BMD) and three-dimensional microstructure in SAMP6 and the normal control mouse (SAMR1) at 12 months of age using quantitative micro computed tomography (micro-CT) and image analysis software. The vertebral height and vertebral cross-sectional area (CSA) increased, while vertebral trabecular BMD and trabecular bone volume fraction (BV/TV) decreased from the cervical to lumbar spine both in SAMR1 and SAMP6. As compared with SAMR1, the thoracic vertebral CSA had a tendency to be low and the lumbar vertebral CSA was significantly declined in SAMP6. The vertebral trabecular BMD, BV/TV, trabecular thickness (Tb.Th), and trabecular number (Tb.N) significantly decreased in cervical, thoracic and lumbar spine of SAMP6. Trabecular bone pattern factor (TBPf) was higher at the lumbar spine and the structure model index (SMI) of the lower thoracic and lumbar spine was higher in SAMP6. These results indicate that vertebral trabecular bone microstructures are remarkably heterogeneous throughout the spine in both SAMR1 and SAMP6. The decrease of vertebral trabecular bone density in SAMP6 advanced faster caudally than cranially within the spine, similar phenomena were observed in humans. These findings highlight the relevance of SAMP6 for studies of vertebral fragility associated with senile osteoporosis.

Effect of bioactive compounds in lactobacilli-fermented soy skim milk on femoral bone microstructure of aging mice

BACKGROUND

Soy skim milks fermented with lactobacilli contain various phytochemicals such as isoflavones and peptides. We used lactobacilli-fermented soy skim milk as a nutritional supplement for 6 weeks to investigate its anti-osteoporosis effect in 13-month-old female BALB/c aging mice. Freeze-dried powder of soy skim milk fermented by Lactobacillus paracasei subsp. paracasei NTU 101 (NTU 101F) and L. plantarum NTU 102 (NTU 102F) were used in this study.

RESULTS

The trabecular bone volumes in mice fed NTU 101F and NTU 102F increased by a factor of 3.48 and 2.16 compared with control values, respectively. The network density and thickness of distal metaphyseal trabecular bone in mice fed with NTU 101F and NTU 102F milks were significantly denser than that of control mice; moreover, the NTU 101F group had the largest resting area ratio and smallest resorbing area compared with other groups. The beneficial effect may due to isoflavones as well as higher amounts of polysaccharide and peptide in NTU 101F milk.

CONCLUSION

The results suggest that dietary supplement with fermented soy skim milk can attenuate aging-induced bone loss in BALB/c mice and possibly lower the risk of osteopenia or osteoporosis in aging.

Rodent models of aging bone: an update

With an increase in the average life span especially in the Western hemisphere, there is renewed interest in treating maladies of old age including osteoporosis. Age-related bone loss and resultant osteoporosis substantially increase risk of fractures and morbidity in the geriatric population leading to both a decline in the quality of life for the elderly as well as a substantial burden on the health care system. Herein, we review recent research in murine and rodent models looking at how both extrinsic and intrinsic factors such as hormones, biochemicals, neuromodulators, inflammatory cytokines, oxidative stress, nutrition, and exercise influence the skeleton with age. Recent studies on the relationship between bone and fat in the marrow, and the fate of the marrow mesenchymal stromal cell population, which can give rise to either bone-forming osteoblasts or fat-forming adipocytic cells as a function of age, have also been highlighted. An appreciable range of studies using aging murine as well as cellular models are discussed, as these studies have broadened our understanding of the pathways and players in the aging bone. Impactful information regarding aging and the bone may then allow the application of better pharmacologic as well as nonpharmacologic regimens to alleviate bone loss due to aging.

Obesity-mediated inflammatory microenvironment stimulates osteoclastogenesis and bone loss in mice

Clinical evidence indicates that fat is inversely proportional to bone mass in elderly obese women. However, it remains unclear whether obesity accelerates bone loss. In this report we present evidence that increased visceral fat leads to inflammation and subsequent bone loss in 12-month-old C57BL/6J mice that were fed 10% corn oil (CO)-based diet and a control lab chow (LC) for 6 months. As expected from our previous work, CO-fed mice demonstrated increased visceral fat and enhanced total body fat mass compared to LC. The adipocyte-specific PPARγ and bone marrow (BM) adiposity were increased in CO-fed mice. In correlation with those modifications, inflammatory cytokines (IL-1β, IL-6, TNF-α) were significantly elevated in CO-fed mice compared to LC-fed mice. This inflammatory BM microenvironment resulted in increased superoxide production in osteoclasts and undifferentiated BM cells. In CO-fed mice, the increased number of osteoclasts per trabecular bone length and the increased osteoclastogenesis assessed ex-vivo suggest that CO diet induces bone resorption. Additionally, the up-regulation of osteoclast-specific cathepsin k and RANKL expression and down-regulation of osteoblast-specific RUNX2/Cbfa1 supports this bone resorption in CO-fed mice. Also, CO-fed mice exhibited lower trabecular bone volume in the distal femoral metaphysis and had reduced OPG expression. Collectively, our results suggest that increased bone resorption in mice fed a CO-enriched diet is possibly due to increased inflammation mediated by the accumulation of adipocytes in the BM microenvironment. This inflammation may consequently increase osteoclastogenesis, while reducing osteoblast development in CO-fed mice.