There are increasing evidences suggesting bone marrow adiposity tissue (MAT) plays a critical role in affecting both bone quantity and quality. However, very limited studies that have investigated the association between the composition of MAT and bone mineral density (BMD). The goal of this study was to quantify MAT unsaturation profile of marrow samples from post-menopausal women using ex vivo high-resolution magic angle spinning (HRMAS) proton nuclear magnetic resonance (¹H NMR) spectroscopy, and to investigate the relationship between MAT composition and BMD. Bone marrow samples were obtained by iliac crest aspiration during surgical procedures from 24 postmenopausal women (65-89years) who had hip surgery due to bone fracture or arthroplasty. Marrow fat composition parameters, in particular, unsaturation level (UL), mono-unsaturation level (MUL) and saturation level (SL), were quantified using HRMAS ¹H NMR spectroscopy. The patients were classified into three groups based on the DXA BMD T-scores: controls, osteopenia and osteoporosis. Marrow fat composition was compared between these three groups as well as between subjects with and without factures using ANOCOVA, adjusted for age. Subjects with lower BMD (n=17) had significantly lower MUL (P=0.003) and UL (P=0.039), and significantly higher SL (P=0.039) compared to controls (n=7). When separating lower BMD into osteopenia (n=9) and osteoporosis (n=8) groups, subjects with osteopenia had significantly lower MUL (P=0.002) and UL (P=0.010), and significantly higher SL (P=0.010) compared to healthy controls. No significant difference was observed between subjects with osteopenia and osteoporosis. Using HRMAS ¹H NMR, significantly lower unsaturation and significantly higher saturation levels were observed in the marrow fat of subjects with lower BMD. HRMAS ¹H NMR was shown to be a powerful tool for identifying novel MR markers of marrow fat composition that are associated with bone quality and potentially fracture, and other bone pathologies and changes after treatment. A better understanding of the relationship between bone marrow composition and bone quality in humans may identify novel treatment targets, and provide guidance on novel interventions and therapeutic strategies for bone preservation.

Context

Bone marrow fat (BMF) and bone mineral density (BMD) by dual x-ray energy absorptiometry (DXA) are negatively correlated. However, little is known about the association of BMF with fracture or with separate trabecular and cortical bone compartments.

Objective

Our objective was to assess the relationships between vertebral BMF, BMD by quantitative computed tomography, and fracture in older adults.

Design, setting, and participants

We conducted a cross-sectional study in the Age Gene/Environment Susceptibility-Reykjavik cohort.

Main outcome measures

Outcomes measures included vertebral BMF (L1-L4) measured with magnetic resonance spectroscopy, quantitative computed tomography and DXA scans of the hip and spine, and DXA vertebral fracture assessments. Previous clinical fracture was determined from medical records.

Results

In 257 participants without recent bone-active medication use, mean age was 79 (SD 3.1) years. Mean BMF was 53.5% ± 8.1% in men and 55.0% ± 8.4% in women. Those with prevalent vertebral fracture (21 men, 32 women) had higher mean BMF in models adjusted for BMD. In separate models by sex, the difference was statistically significant only in men (57.3% vs 52.8%, P = 0.02). BMF was associated with lower trabecular volumetric BMD (vBMD) at the spine (-10.5% difference for each 1 SD increase in BMF, P < 0.01), total hip, and femoral neck, but not with cortical vBMD, in women. In men, BMF was marginally associated with trabecular spine vBMD (-6.1%, P = 0.05). Total hip and spine areal BMD (aBMD) were negatively correlated with BMF in women only.

Conclusion

Higher marrow fat correlated with lower trabecular, but not cortical, BMD in older women but not men. Higher marrow fat was associated with prevalent vertebral fracture in men, even after adjustment for BMD.

Background

Identifying factors that impair bone accrual during childhood is a critical step toward osteoporosis prevention. Exposure to per- and polyfluoroalkyl substances (PFASs) has been associated with lower bone mineral density, but data are limited, particularly in children.

Methods

We studied 576 children in Project Viva, a Boston-area cohort of mother/child pairs recruited prenatally from 1999 to 2002. We quantified plasma concentrations of several PFASs and measured areal bone mineral density (aBMD) by dual-energy X-ray absorptiometry (DXA) in midchildhood. We used linear regression to examine associations between plasma concentrations of individual PFASs and aBMD z-score. We used weighted quantile sum (WQS) regression to examine the association of the PFAS mixture with aBMD z-score. All models were adjusted for maternal age, education, annual household income, census tract median household income, and child age, sex, race/ethnicity, dairy intake, physical activity, and year of blood draw.

Results

Children were [[Formula: see text]] [Formula: see text] of age. The highest PFAS plasma concentrations were of perfluorooctanesulfonic acid (PFOS) {median [interquartile range (IQR)]: 6.4 (5.6) ng/mL} and perfluorooctanoic acid (PFOA) [median (IQR): 4.4 (3.2) ng/mL]. Using linear regression, children with higher plasma concentrations of PFOA, PFOS, and perfluorodecanoate (PFDA) had lower aBMD z-scores [e.g., [Formula: see text]: [Formula: see text]; 95% confidence interval (CI): [Formula: see text], [Formula: see text] per doubling of PFOA]. The PFAS mixture was negatively associated with aBMD z-score ([Formula: see text]: [Formula: see text]; 95% CI: [Formula: see text], [Formula: see text] per IQR increment of the mixture index).

Conclusions

PFAS exposure may impair bone accrual in childhood and peak bone mass, an important determinant of lifelong skeletal health. https://doi.org/10.1289/EHP4918.

Context

Higher bone marrow fat (BMF)¹ is associated with osteoporosis and reduced hematopoiesis. Exogenous estradiol reduces BMF in older women, but effects of endogenous sex hormones are unknown.

Objective

To determine if endogenous sex hormones are associated with BMF in older men and women.

Design, setting and participants

Cross-sectional study in the Age Gene/Environment Susceptibility (AGES) Reykjavik cohort. Participants using medications that may affect BMF were excluded.

Main outcome measures

Vertebral BMF was measured with magnetic resonance spectroscopy. Estradiol, testosterone and sex hormone binding globulin were measured on archived serum. Linear regression models were adjusted for age, total percent body fat and visit window.

Results

Analyses included 244 men and 226 women, mean age 81.5 (SD 4.1) years. Mean BMF was 54.1% (SD 8.6) (men) and 54.7% (SD 8.1) (women). In adjusted models, per 1pg/ml increase in total estradiol, there was a statistically significant 0.26% decrease in BMF in men (95% CI: -0.41, -0.11) and a non-significant 0.20% decrease in women (95% CI: -0.55, 0.15), with no evidence of interaction by gender (p=0.88). Per 10ng/dl increase in total testosterone, there was a significant 0.10% decrease in BMF in men (95% CI: -0.17, -0.03) and a non-significant 0.13% (95% CI: -0.79, 0.53) decrease in women, with no evidence of interaction by gender (p=0.97).

Conclusion

Higher bone marrow fat is associated with lower total estradiol and testosterone levels in older men, with a similar but statistically non-significant association in older women. Sex hormone levels appear to play a role in the regulation of bone marrow fat in older adults.

Context

Higher bone marrow fat (BMF)¹ is associated with osteoporosis and reduced hematopoiesis. Exogenous estradiol reduces BMF in older women, but effects of endogenous sex hormones are unknown.

Objective

To determine if endogenous sex hormones are associated with BMF in older men and women.

Design, setting and participants

Cross-sectional study in the Age Gene/Environment Susceptibility (AGES) Reykjavik cohort. Participants using medications that may affect BMF were excluded.

Main outcome measures

Vertebral BMF was measured with magnetic resonance spectroscopy. Estradiol, testosterone and sex hormone binding globulin were measured on archived serum. Linear regression models were adjusted for age, total percent body fat and visit window.

Results

Analyses included 244 men and 226 women, mean age 81.5 (SD 4.1) years. Mean BMF was 54.1% (SD 8.6) (men) and 54.7% (SD 8.1) (women). In adjusted models, per 1pg/ml increase in total estradiol, there was a statistically significant 0.26% decrease in BMF in men (95% CI: -0.41, -0.11) and a non-significant 0.20% decrease in women (95% CI: -0.55, 0.15), with no evidence of interaction by gender (p=0.88). Per 10ng/dl increase in total testosterone, there was a significant 0.10% decrease in BMF in men (95% CI: -0.17, -0.03) and a non-significant 0.13% (95% CI: -0.79, 0.53) decrease in women, with no evidence of interaction by gender (p=0.97).

Conclusion

Higher bone marrow fat is associated with lower total estradiol and testosterone levels in older men, with a similar but statistically non-significant association in older women. Sex hormone levels appear to play a role in the regulation of bone marrow fat in older adults.

Bone marrow adiposity is associated with aging, osteoporosis, and reduced hematopoiesis, as well as anorexia nervosa, but little is known about the underlying mechanisms that affect marrow adiposity. Chronic kidney disease (CKD) may influence bone marrow adipose tissue (BMAT), possibly through loss of lean mass or higher circulating levels of sclerostin. To test these hypotheses, we investigated the cross-sectional association between estimated glomerular filtration rate (eGFR) as a measure of kidney function and ¹ H-MRS-based measurement of vertebral BMAT (L1 to L4) in 475 older adults from the Age Gene/Environment Susceptibility (AGES)-Reykjavik study. Mean BMAT was compared in those with eGFR >60 (n = 297) versus those with eGFR 45 to 60 (n = 120) or eGFR <45 (n = 58) using linear regression models. Participants had a mean age of 81.5 (SD 4.1) years, mean eGFR of 64.3 (SD 16.1) mL/min/1.734 cm² , mean BMAT of 54.5% (SD 8.5); 48.2% were women. In unadjusted and adjusted models (age, visit window, gender, diabetes and visceral adipose tissue), BMAT was higher in those with eGFR <45 (adjusted mean 58.5%; 95% CI, 56.2 to 60.7) compared with those with eGFR >60 (adjusted mean 53.8%; 95% CI, 52.8 to 54.8) (p = 0.0002). BMAT did not differ in those with eGFR 45 to 60 (adjusted mean 54.3%; 95% CI, 52.8 to 55.9) compared with those with eGFR >60 (p = 0.58). In a subgroup of participants with serum sclerostin available (n = 253), additional adjustment for sclerostin attenuated the difference in adjusted mean vertebral BMAT between those with eGFR <45 versus >60 from 3.7% (p = 0.04) to 2.4% (p = 0.20). CKD stage 3b or worse was associated with greater bone marrow adiposity; this association may be partially mediated by sclerostin. © 2018 American Society for Bone and Mineral Research.

Patient bone mineral density (BMD) predicts the likelihood of osteoporotic fracture. While substantial progress has been made toward elucidating the genetic determinants of BMD, our understanding of the factors involved remains incomplete. Here, using a systems genetics approach in the mouse, we predicted that bicaudal C homolog 1 (Bicc1), which encodes an RNA-binding protein, is responsible for a BMD quantitative trait locus (QTL) located on murine chromosome 10. Consistent with this prediction, mice heterozygous for a null allele of Bicc1 had low BMD. We used a coexpression network-based approach to determine how Bicc1 influences BMD. Based on this analysis, we inferred that Bicc1 was involved in osteoblast differentiation and that polycystic kidney disease 2 (Pkd2) was a downstream target of Bicc1. Knock down of Bicc1 and Pkd2 impaired osteoblastogenesis, and Bicc1 deficiency-dependent osteoblast defects were rescued by Pkd2 overexpression. Last, in 2 human BMD genome-wide association (GWAS) meta-analyses, we identified SNPs in BICC1 and PKD2 that were associated with BMD. These results, in both mice and humans, identify Bicc1 as a genetic determinant of osteoblastogenesis and BMD and suggest that it does so by regulating Pkd2 transcript levels.

Context

The conventional view that obesity is beneficial for bone strength has recently been challenged by studies that link obesity, particularly visceral obesity, to low bone mass and fractures. It is controversial whether effects of obesity on bone are mediated by increased bone resorption or decreased bone formation.

Objective

The objective of the study was to evaluate bone microarchitecture and remodeling in healthy premenopausal women of varying weights.

Design

We measured bone density and trunk fat by dual-energy x-ray absorptiometry in 40 women and by computed tomography in a subset. Bone microarchitecture, stiffness, remodeling, and marrow fat were assessed in labeled transiliac bone biopsies.

Results

Body mass index (BMI) ranged from 20.1 to 39.2 kg/m(2). Dual-energy x-ray absorptiometry-trunk fat was directly associated with BMI (r = 0.78, P < .001) and visceral fat by computed tomography (r = 0.79, P < .001). Compared with women in the lowest tertile of trunk fat, those in the highest tertile had inferior bone quality: lower trabecular bone volume (20.4 ± 5.8 vs 29.1 ± 6.1%; P = .001) and stiffness (433 ± 264 vs 782 ± 349 MPa; P = .01) and higher cortical porosity (8.8 ± 3.5 vs 6.3 ± 2.4%; P = .049). Bone formation rate (0.004 ± 0.002 vs 0.011 ± 0.008 mm(2)/mm · year; P = .006) was 64% lower in the highest tertile. Trunk fat was inversely associated with trabecular bone volume (r = -0.50; P < .01) and bone formation rate (r = -0.50; P < .001). The relationship between trunk fat and bone volume remained significant after controlling for age and BMI.

Conclusions

At the tissue level, premenopausal women with more central adiposity had inferior bone quality and stiffness and markedly lower bone formation. Given the rising levels of obesity, these observations require further investigation.

Context

Osteocyte activity is crucial to the maintenance of bone quality. Sclerostin, an osteocyte product, inhibits bone formation, yet higher circulating sclerostin is associated with higher bone density. Bone marrow fat (MF) is associated with osteoporosis, but little is known about the relationship between osteocyte activity and MF.

Objective

Our objective was to assess the relationships between circulating sclerostin, vertebral MF, volumetric bone mineral density (vBMD), and other fat depots in older adults.

Design, setting, and participants

We conducted a cross-sectional study in the Age Gene/Environment Susceptibility-Reykjavik cohort.

Main outcome measures

Outcome measures included vertebral MF (L1-L4) measured with magnetic resonance spectroscopy and vBMD (spine and hip) and abdominal fat measured with quantitative computed tomography.

Results

After excluding subjects with bone-active medication use (n = 50), inadequate serum (n = 2), or inadequate magnetic resonance spectroscopy (n = 1), analyses included 115 men and 134 women (mean age 79 y, mean body mass index 27.7 kg/m(2)). In men, but not women, vertebral MF was greater in those with higher serum sclerostin levels. MF was 52.2 % in the lowest tertile of serum sclerostin and 56.3% in the highest tertile in men (P for trend <.01) in models adjusted for age, body mass index, and diabetes. Sclerostin was positively associated with cortical and trabecular total hip vBMD, weight in men and women, and total fat mass in men but was not associated with total lean mass or abdominal fat depots.

Conclusion

Circulating sclerostin levels are associated with higher vertebral marrow fat in men, suggesting a relationship between osteocyte function and marrow adipogenesis.

Background

CRISPR-Cas9 gene-editing technology has facilitated the generation of knockout mice, providing an alternative to cumbersome and time-consuming traditional embryonic stem cell-based methods. An earlier study reported up to 16% efficiency in generating conditional knockout (cKO or floxed) alleles by microinjection of 2 single guide RNAs (sgRNA) and 2 single-stranded oligonucleotides as donors (referred herein as "two-donor floxing" method).

Results

We re-evaluate the two-donor method from a consortium of 20 laboratories across the world. The dataset constitutes 56 genetic loci, 17,887 zygotes, and 1718 live-born mice, of which only 15 (0.87%) mice contain cKO alleles. We subject the dataset to statistical analyses and a machine learning algorithm, which reveals that none of the factors analyzed was predictive for the success of this method. We test some of the newer methods that use one-donor DNA on 18 loci for which the two-donor approach failed to produce cKO alleles. We find that the one-donor methods are 10- to 20-fold more efficient than the two-donor approach.

Conclusion

We propose that the two-donor method lacks efficiency because it relies on two simultaneous recombination events in cis, an outcome that is dwarfed by pervasive accompanying undesired editing events. The methods that use one-donor DNA are fairly efficient as they rely on only one recombination event, and the probability of correct insertion of the donor cassette without unanticipated mutational events is much higher. Therefore, one-donor methods offer higher efficiencies for the routine generation of cKO animal models.