Pathogenesis Of Age-related Bone Loss Research Articles

Metabolic shifts in ratio of ucOcn to cOcn toward bone resorption contribute to age-dependent bone loss in male mice.

The study of the senile osteoporosis in men still lags significantly behind that in women. The changes of protein molecule levels and their relationships with bone loss remain poorly understood. In the present study, we used C57BL/6J male mice at ages from 3 to 24 mo to delineate the mechanisms of aging effects on bone loss. We used the microcomputed tomography, mechanical testing, histomorphometry assays, and detection of serum levels of undercarboxylated osteocalcin (ucOcn) and carboxylated osteocalcin (cOcn) to assess bone mass changes and their relationships with the ratios of ucOcn-to-cOcn in mice from different age groups. The results showed that mouse trabecular bone mass reduced gradually with age, whereas cortical bone loss and mechanical property changes mostly occurred in advanced age. Our findings further demonstrated that the increase in osteoclast activity and the decrease in osteoblast function were significantly corelated with blood levels of ucOcn and cOcn, respectively. The dynamic metabolic changes of ucOcn to cOcn ratio were correlated with age-dependent bone loss in mice. In summary, metabolic shifts in the ratio of ucOcn to cOcn toward bone resorption from young adult to elderly mice contribute to the pathogenesis of age-related bone loss. Simultaneously monitoring blood ratios of ucOcn-to-cOcn may be useful to predict the status of bone mass in vivo.NEW & NOTEWORTHY To our knowledge, our finding in this study shows for the first time that metabolic shifts in ratio of ucOcn to cOcn toward bone resorption are markedly correlated with age-dependent bone loss in male mice. These findings for the effects of aging on bone loss will assist in studying the pathogenesis of human type II osteoporosis.

CD137 Regulates Bone Loss via the p53 Wnt/β-Catenin Signaling Pathways in Aged Mice.

Senile osteoporosis is a chronic skeletal disease, leading to increased bone brittleness and risk of fragile fractures. With the acceleration of population aging, osteoporosis has gradually become one of the most serious and prevalent problems worldwide. Bone formation is highly dependent on the proper osteogenic differentiation of bone marrow mesenchymal stem cells (BMSCs) in the bone marrow microenvironment, which is generated by the functional relationship among different cell types, including osteoblasts, adipogenic cells, and bone marrow stromal cells in the bone marrow. It is still not clear how osteoporosis is caused by its molecular mechanism. With aging, bone marrow is able to restrain osteogenesis. Discovering the underlying signals that oppose BMSC osteogenic differentiation from the bone marrow microenvironment and identifying the unusual changes in BMSCs with aging is important to elucidate possible mechanisms of senile osteoporosis. We used 3 gene expression profiles (GSE35956, GSE35957, and GSE35959) associated with osteoporosis. And a protein-protein interaction (PPI) network was also built to identify the promising gene CD137. After that, we performed in vivo experiments to verify its function and mechanism. In this experiment, we found that significant bone loss was observed in aged (18-month-old) mice compared with young (6-month-old) mice. The adipose tissue in bone marrow cavity from aged mice reached above 10 times more than young mice. Combining bioinformatics analysis and vivo experiments, we inferred that CD137 might be involved in the p53 and canonical Wnt/β-catenin signaling pathways and thereby influenced bone mass through regulation of marrow adipogenesis. Importantly, osteoporosis can be rescued by blocking CD137 signaling in vivo. Our research will contribute to our understanding not only of the pathogenesis of age-related bone loss but also to the identification of new targets for treating senile osteoporosis.

ASPH Regulates Osteogenic Differentiation and Cellular Senescence of BMSCs.

Osteogenesis and senescence of BMSCs play great roles in age-related bone loss. However, the causes of these dysfunctions remain unclear. In this study, we identified a differentially expressed ASPH gene in middle-aged and elderly aged groups which were obtained from GSE35955. Subsequent analysis in various databases, such as TCGA, GTEx, and CCLE, revealed that ASPH had positive correlations with several osteogenic markers. The depletion of mouse Asph suppressed the capacity of osteogenic differentiation in bone marrow mesenchymal stem cells (BMSCs). Notably, the expression of ASPH in vitro decreased during aging and senescence. The deficiency of Asph accelerated cellular senescence in BMSCs. Conversely, the overexpression of Asph enhanced the capacity of osteogenic differentiation and inhibited cellular senescence. Mechanistically, ASPH regulated Wnt signaling mediated by Gsk3β. Taken together, our data established that ASPH was potentially involved in the pathogenesis of age-related bone loss through regulating cellular senescence and osteogenic differentiation, which provides some new insights to treat age-related bone loss.

Vitamin D Deficiency and Its Influence on Bone Metabolism and Density in a Brazilian Population of Healthy Men

Vitamin D supplementation is universal for postmenopausal women, but not for elderly men, in whom osteoporosis is also commonly neglected. This study aimed to evaluate vitamin D deficiency and its association with secondary hyperparathyroidism, bone resorption, and bone density in Brazilian men. A total of 120 men, 20–93 years, were evaluated for serum calcium, phosphorus, creatinine, 25-hydroxyvitamin D (25(OH)D), parathyroid hormone, biochemical markers of bone resorption (carboxy-terminal telopeptide, carboxy-terminal peptide of type I collagen), and bone mineral density (dual-energy X-ray absorptiometry). Glomerular filtration rate (GFR) below 30 mL/min/1.73 m2, chronic diseases, and medications affecting bone were the exclusion criteria. No participant reported previous low-impact fractures. In the overall population, 25(OH)D levels were below 30 ng/mL in 46.7%, and below 20 ng/mL in 27.6%. Among the 93 patients 50 years and older, 28 had osteoporosis. In those 70 years and older, the prevalence of vitamin D deficiency (42.1%), secondary hyperparathyroidism (46.4%), high bone resorption (39.6%), decreased GFR (39.2%), and osteoporosis (41.4%) was significantly higher than in the younger subjects (p < 0.005 for all comparisons). Serum parathyroid hormone increased with aging and declining GFR, but was not significantly associated with 25(OH)D or bone mineral density. There was a clear contribution of vitamin D deficiency to increased bone resorption and osteoporosis. Binary logistic regression model considering age, 25(OH)D, and bone resorption identified age ≥70 years as the main determinant of osteoporosis. Our data demonstrate a high prevalence of vitamin D deficiency in a male population living in Rio de Janeiro, and emphasize its participation on the pathogenesis of age-related bone loss. (Vitamin D deficiency and osteoporosis are common in elderly Brazilian men.)

Fat and Bone Interactions

Fat and bone have a complicated relationship. Although obesity has been associated with low fracture risk, there is increasing evidence that some of the factors that are released by peripheral fat into the circulation may also have a deleterious effect on bone mass, thus, predisposing to fractures. More importantly, the local interaction between fat and bone within the bone marrow seems to play a significant role in the pathogenesis of age-related bone loss and osteoporosis. This "local interaction" occurs inside the bone marrow and is associated with the autocrine and paracrine release of fatty acids and adipokines, which affect the cells in their vicinity including the osteoblasts, reducing their function and survival. In this review, we explore the particularities of the fat and bone cell interactions within the bone marrow, their significance in the pathogenesis of osteoporosis, and the potential therapeutic applications that regulating marrow fat may have in the near future as a novel pharmacologic treatment for osteoporosis.

Pathogenesis of Age-Related Bone Loss in Humans

Although data from rodent systems are extremely useful in providing insights into possible mechanisms of age-related bone loss, concepts evolving from animal models need to ultimately be tested in humans. This review provides an update on mechanisms of age-related bone loss in humans based on the author's knowledge of the field and focused literature reviews. Novel imaging, experimental models, biomarkers, and analytic techniques applied directly to human studies are providing new insights into the patterns of bone mass acquisition and loss as well as the role of sex steroids, in particular estrogen, on bone metabolism and bone loss with aging in women and men. These studies have identified the onset of trabecular bone loss at multiple sites that begins in young adulthood and remains unexplained, at least based on current paradigms of the mechanisms of bone loss. In addition, estrogen appears to be a major regulator of bone metabolism not only in women but also in men. Studies assessing mechanisms of estrogen action on bone in humans have identified effects of estrogen on RANKL expression by several different cell types in the bone microenvironment, a role for TNF-α and IL-1β in mediating effects of estrogen deficiency on bone, and possible regulation of the Wnt inhibitor, sclerostin, by estrogen. There have been considerable advances in our understanding of age-related bone loss in humans. However, there are also significant gaps in knowledge, particularly in defining cell autonomous changes in bone in human studies to test or validate concepts emerging from studies in rodents. Decision Editor: Luigi Ferrucci, MD, PhD.

Role of the nuclear envelope in the pathogenesis of age-related bone loss and osteoporosis

The nuclear envelope is the most important border in the eukaryotic cell. The role of the nuclear envelope in cell differentiation and function is determined by a constant interaction between the elements of the nuclear envelope and the transcriptional regulators involved in signal transcription pathways. Among those components of the nuclear envelope, there is a growing evidence that changes in the expression of A-type lamins, which are essential components of the nuclear lamina, are associated with age-related changes in bone affecting the capacity of differentiation of mesenchymal stem cells into osteoblasts, favoring adipogenesis and affecting the function and survival of the osteocytes. Overall, as A-type lamins are considered as the 'guardians of the soma', these proteins are also essential for the integrity and quality of the bone and pivotal for the longevity of the musculoskeletal system.

Decreased oxidative stress and greater bone anabolism in the aged, when compared to the young, murine skeleton with parathyroid hormone administration

Because of recent insights into the pathogenesis of age-related bone loss, we investigated whether intermittent parathyroid hormone (PTH) administration antagonizes the molecular mechanisms of the adverse effects of aging on bone. Parathyroid hormone produced a greater increase in vertebral trabecular bone mineral density and bone volume as well as a greater expansion of the endocortical bone surface in the femur of 26- when compared to 6 -month-old female C57BL/6 mice. Moreover, PTH increased trabecular connectivity in vertebrae, and the toughness of both vertebrae and femora in old, but not young, mice. Parathyroid hormone also increased the rate of bone formation and reduced osteoblast apoptosis to a greater extent in the old mice. Most strikingly, PTH reduced reactive oxygen species, p66(Shc) phosphorylation, and expression of the lipoxygenase Alox15, and it increased glutathione and stimulated Wnt signaling in bone of old mice. Parathyroid hormone also antagonized the effects of oxidative stress on p66(Shc) phosphorylation, Forkhead Box O transcriptional activity, osteoblast apoptosis, and Wnt signaling in vitro. In contrast, administration of the antioxidants N-acetyl cysteine or pegylated catalase reduced osteoblast progenitors and attenuated proliferation and Wnt signaling. These results suggest that PTH has a greater bone anabolic efficacy in old age because in addition to its other positive actions on bone formation, it antagonizes the age-associated increase in oxidative stress and its adverse effects on the birth and survival of osteoblasts. On the other hand, ordinary antioxidants cannot restore bone mass in old age because they slow remodeling and attenuate osteoblastogenesis by interfering with Wnt signaling.

Winning the battle against childhood physical inactivity

pathogenesis of age-related bone loss show that most bone loss with age is cortical, not trabecular, and is the result of intracortical remodelling on the surfaces of the myriads of haversian canals traversing the cortex. These excavated canals increase in number, size and coalesce, particularly in the cortex adjacent to the marrow space leaving a layer of chaotically connected cortical remnants that look like trabeculae. Half of the total bone loss that occurs during ageing is produced during the process of formation of cortical remnants; indeed, the ratio of the thickness of the layer of cortical remnants to the thickness of the entire cortical mass (proportion compact remnants; PCR) appears to be a more reliable indicator of age-related bone loss than the cortical thickness. The calculation of porosity in the compactappearing cortex without including porosity produced by cortical remnants underestimates the true age related increase in porosity by three-fold. Moreover, the true decline with age is underestimated fourfold when cortical remnants are erroneously included in the trabecular compartments as is commonly done in standard bone structure analyses. Thus, overlooking intracortical porosity producing cortical remnants has resulted in a significant underestimation of agerelated cortical decay and loss.Contrary to prevailing notions, most bone loss is cortical, occurs by intracortical remodelling, causes most structural decay, and occurs after 60 years of age, not in the decade after menopause. Intracortical remodelling is a neglected target for preventing and reversing bone fragility in old age.

Differential expression of cytokines in subcutaneous and marrow fat of aging C57BL/6J mice

Increasing marrow adipogenesis plays a causative role in the pathogenesis of age-related bone loss that could be associated with high cytokine production. In this study, we characterized the age-related changes in cytokine expression by bone marrow (BM) adipocytes as compared with subcutaneous (SC) fat. BM and SC adipocytes were isolated from young (4 months) and old (24 months) male C57BL/6J. Total proteins were extracted and proteomic analysis of 96 cytokines was performed using a cytokine antibody array. Proteins showing a significant change were grouped according with their known function in bone. We found a significant age-induced difference in the expression of 53 cytokines. As compared with SC adipocytes, aging BM adipocytes showed a more pro-adipogenic, anti-osteoblastogenic and pro-apoptotic phenotype. These data suggest that, with aging, BM adipocytes become significantly more toxic than SC adipocytes. These cytokines, if secreted, could play a role in the pathogenesis of age-related bone loss by affecting other cells within the marrow milieu.

Endocrine regulation of bone turnover in men

Causes of age-related bone loss have been extensively investigated in postmenopausal women. In contrast, osteoporosis in men has only recently received more attention, and studies have been performed to elucidate the pathogenesis of age-related bone loss in men. It is estimated that about one-third of all osteoporotic fractures occur in men 1,2 and that the residual lifetime fracture risk in a man aged 60 years may be as high as 30%. 3 These fractures result in significant morbidity, mortality and healthcare costs. 4,5

IGF-I and testosterone levels as predictors of bone mineral density in healthy, community-dwelling men.

Age-related decline in IGF-I and gonadal hormones have been postulated to play an important role in the pathogenesis of age-related bone loss in men. In this cross-sectional study, the relation between serum IGF-I and gonadal hormones with bone mineral density (BMD) was examined in community-dwelling men. Serum IGF-I, testosterone and BMD were examined in 61 community-dwelling men over the age of 27, who were randomly selected from the Calgary cohort of 1000 subjects in the Canadian Multicentre Osteoporosis Study. In the present study, IGF-I, serum testosterone, SHBG, free androgen index (FAI), parathyroid hormone (PTH), 25-hydroxy-vitamin D [25(OH)D] and other markers of bone turnover were measured. BMD was measured at the spine and hip (HOLOGIC 4500). Simple linear regression was used to assess the linear relation between IGF-I, testosterone, BMD and other biochemical markers of bone metabolism and potential confounding variables and subsequent multivariate regression models were constructed separately for each BMD measurement to assess the importance of IGF-I and testosterone in the presence of potential confounding variables. Serum IGF-I, FAI and SHBG significantly decreased as a function of age, whereas serum levels of PTH increased. Only 25(OH)D, total testosterone and FAI were positively associated with serum IGF-I after adjusting for age and BMI. Multiple linear regression models revealed that IGF-I was a significant predictor of BMD at the total hip, femoral neck and femoral trochanter neck (P < or = 0.001). In contrast, the FAI was a significant predictor of BMD at the lumbar spine and wards area (P < or = 0.011), and SHBG was a significant predictor at the total hip and femoral trochanter (P < or = 0.045). These data support the hypothesis that the age-related decline in bone mass in men is associated with declining levels of IGF-I and testosterone.

Predictors of bone mineral density in aging healthy men varies by skeletal site.

Factors contributing to the pathogenesis of osteoporosis in women are well defined. However, changes in bone mineral metabolism in aging men and the role of various factors in the pathogenesis of age-related bone loss in men are less well understood. To further clarify these changes, serum and urine biochemical parameters, and lumbar spine, hip, and total body bone mineral density (BMD) were evaluated in a small sample of 45 healthy men aged 20-80 years, and multiple regression models were developed to predict age-related bone loss. Serum calcium, phosphate, albumin, creatinine clearance, osteocalcin, C-terminal propeptide of type I procollagen, log-free androgen index, dehydroepiandrosterone sulfate (DHEA-S), and androstenedione decreased with age, and serum sex hormone binding globulin and urine total and free pyridinoline increased with age. Femoral neck BMD decreased with age, but remained stable at the other sites measured. Multiple regression analysis indicated that serum phosphate, DHEA-S, and intact parathyroid hormone (PTH) predicted lumbar spine BMD. Age, serum phosphate, and PTH predicted femoral neck BMD. Urine-free deoxypyridinoline alone predicted femoral greater trochanter BMD. Weight, serum creatinine, and urine-free deoxypyridinoline predicted total body BMD. We conclude that predictor variables of bone density vary by skeletal site in healthy men. Alterations in adrenal androgens, phosphate, and PTH may be important in the pathogenesis of bone loss with aging in men.

Combination Treatment with Estrogen and Calcitriol in the Prevention of Age-Related Bone Loss

Estrogen deficiency and declining calcium absorption due to reduced calcitriol levels or intestinal resistance to calcitriol, are important factors in the pathogenesis of age-related bone loss. The main objective of this study was to examine the effect of estrogen and 1,25-dihydroxyvitamin D therapy given individually or in combination on bone loss in elderly women. Four hundred eighty-nine elderly women with normal bone density for their age, aged 65–77 yr, were entered into a randomized double blind, placebo-controlled trial. Women were randomized to one of four groups: conjugated estrogens (0.625 mg, daily) to women without a uterus (estrogen replacement therapy) plus medroxyprogesterone acetate (2.5 mg, daily) to women with a uterus (hormone replacement therapy), calcitriol (0.25μg twice daily), a combination of hormone replacement therapy/estrogen replacement therapy plus calcitriol, or placebos for 3 yr. The primary outcome was the change in bone mineral density of the femoral neck and spine. In the intent to treat analysis, hormone therapy (hormone replacement therapy/estrogen replacement therapy) produced a mean (±1 sd) increase in bone mineral density of 2.98% (±5.45%) at the femoral neck (P < 0.0001) and 4.36% (±6.42%) at the spine (P < 0.0001). There were parallel increases in total hip and trochanter bone mineral density. Calcitriol increased bone mineral density 0.10% (± 4.27%) at the femoral neck (P = 0.57) and 1.65% (± 4.83%) at the spine (P < 0.0124). The combination of hormone replacement therapy/estrogen replacement therapy+ calcitriol increased bone mineral density 3.80% (±4.95%) at the femoral neck (P < 0.001), 4.91% (±6.0%) at the spine (P < 0.0001), and parallel changes at the total hip and trochanter. All three treatment groups differed significantly from placebo at the spine and for the hormone replacement therapy/estrogen replacement therapy groups at the femoral neck, spine, total hip and trochanter. There were no significant differences between combination therapy and hormone replacement therapy/estrogen replacement therapy alone on bone mineral density at any site in the intent to treat analysis. In a secondary analysis of the effect in women who were adherent to treatment, calcitriol had a more significant effect on spine (P = 0.003) and total hip (P = 0.004). The increase in bone mineral density in the adherent groups of women was always higher compared with the intent to treat groups. Combination therapy compared with hormone replacement therapy/estrogen replacement therapy alone produced a significantly greater response in trochanter (P = 0.007) and total hip bone mineral density (P = 0.0017). In summary, hormone replacement therapy/estrogen replacement therapy alone and in combination with calcitriol therapy was highly effective in reducing bone resorption and increasing bone mineral density at the hip and other clinically relevant sites in a group of elderly women, with normal bone density for their age. Calcitriol was effective in increasing spine bone mineral density. In the adherent women, combination therapy with hormone replacement therapy/estrogen replacement therapy and calcitriol increased bone mineral density significantly more in the total hip and trochanter than did hormone replacement therapy/estrogen replacement therapy alone.

Changes in quantitative bone histomorphometry in aging healthy men.

Changes in bone mineral metabolism with aging in healthy men and the roles of various factors in the pathogenesis of age-related changes in quantitative bone histomorphometry in men are poorly defined. To clarify these changes and factors, serum and urinary biochemical parameters and iliac crest bone biopsies were evaluated in 43 healthy men, aged 20-80 yr. The static histomorphometric parameters, cancellous bone volume and osteoblast-osteoid interface, decreased by 40.0% and 19.2%, respectively, between 20-80 yr of age. The dynamic histomorphometric parameters, double and single labeled osteoid, also decreased by 18.6% and 18.0%, respectively, over this period. None of the other static or dynamic histomorphometric parameters changed with age in this population sample of healthy men. Univariate analysis of static bone histomorphometric parameters and biochemical parameters revealed significant correlations between osteoid surface and intact PTH (r = 0.37; P = 0.015); osteoclast surface and serum total testosterone (r = 0.36; P = 0.016), estradiol (r = 0.40; P = 0.009), and FSH (r = 0.49; P = 0.001); osteoblast-osteoid interface and serum phosphate (r = 0.31; P = 0.046); and cortical thickness and serum total calcium (r = 0.38; P = 0.013). Univariate analysis of dynamic bone histomorphometric parameters and biochemical parameters revealed correlations between mineral apposition rate and serum total testosterone (r = 0.32; P = 0.037); total volume-referent bone formation rate and serum osteocalcin (r = 0.43; P = 0.004), total testosterone (r = 0.47; P = 0.001), estradiol (r = 0.35; P = 0.023), and dehydroepinadrosterone sulfate (r = 0.31; P = 0.045); and mean wall thickness and serum total calcium (r = 0.36; P = 0.019) and creatinine clearance (r = 0.42; P = 010). Mineralization lag time and serum phosphate (r = -0.39; P = 0.012) and urinary total pyridinoline (r = 0.36; P = 0.023), and mean wall thickness and urinary total pyridinoline (r = -0.38; P = 0.013), were inversely correlated. Multiple regression analysis using all-subset analysis comparing cancellous bone volume to serum and urinary biochemical parameters in these men indicated that the log free androgen index and body weight best predicted the age-related decline in iliac crest cancellous bone volume (r2 = 0.19; P = 0.015). Multiple regression analysis by the same method, comparing bone density at different skeletal sites to bone histomorphometric parameters, indicated that lumbar spine bone mineral density (BMD) was best predicted by cancellous bone volume and mineral apposition rate (r2 = 0.31; P = 0.001), femoral neck BMD by cancellous bone volume and osteoid surface (r2 = 0.19; P = 0.020), femoral greater trochanter BMD by cortical thickness and single labeled osteoid surface (r2 = 0.13; P = 0.060), and total body BMD by cancellous bone volume and surface-based bone formation rate (r2 = 0.31; P = 0.001). In summary, cancellous bone volume, osteoblast-osteoid interface, and double and single labeled osteoid decreased with age in this sample of healthy men. The lack of detectable change in bone density at some skeletal sites in these men may be due to the small sample size or other confounding factors. Multivariate analysis suggests that different combinations of histomorphometric parameters predict bone density at different skeletal sites, and that cancellous bone volume predicts bone density at the lumbar spine, femoral neck, and total body, but not at the femoral greater trochanter. We conclude that alterations in several biochemical parameters are important in the pathogenesis of age-related bone loss in healthy men.

The effect of age on bone collagen turnover as assessed by pyridinium crosslinks and procollagen I C-terminal peptide

Bone collagen turnover increases with age up to the ninth decade in women. This increase in bone turnover may result from secondary hyperparathyroidism and it could play a role in the pathogenesis of age-related bone loss.