Bone marrow changes in adolescent girls with anorexia nervosa

Bone-organ axes: bidirectional crosstalk

In addition to its recognized role in providing structural support, bone plays a crucial role in maintaining the functionality and balance of various organs by secreting specific cytokines (also known as osteokines). This reciprocal influence extends to these organs modulating bone homeostasis and development, although this aspect has yet to be systematically reviewed. This review aims to elucidate this bidirectional crosstalk, with a particular focus on the role of osteokines. Additionally, it presents a unique compilation of evidence highlighting the critical function of extracellular vesicles (EVs) within bone-organ axes for the first time. Moreover, it explores the implications of this crosstalk for designing and implementing bone-on-chips and assembloids, underscoring the importance of comprehending these interactions for advancing physiologically relevant in vitro models. Consequently, this review establishes a robust theoretical foundation for preventing, diagnosing, and treating diseases related to the bone-organ axis from the perspective of cytokines, EVs, hormones, and metabolites.

Age and BMI have different effects on subcutaneous, visceral, liver, bone marrow, and muscle adiposity, as measured by CT and MRI

OBJECTIVE

We analyzed quantitative computed tomography (CT) and chemical shift-encoded magnetic resonance imaging (MRI) data from a Chinese cohort to investigate the effects of BMI and aging on different adipose tissue (AT) depots.

METHODS

In 400 healthy, community-dwelling individuals aged 22 to 83 years, we used MRI to quantify proton density fat fraction (PDFF) of the lumbar spine (L2-L4) bone marrow AT (BMAT), the psoas major and erector spinae (ES) muscles, and the liver. Abdominal total AT, visceral AT (VAT), and subcutaneous AT (SAT) areas were measured at the L2-L3 level using quantitative CT. Partial correlation analysis was used to evaluate the relationship of each AT variable with age and BMI. Multiple linear regression analysis was performed in which each AT variable was evaluated in turn as a function of age and the other five independent AT measurements.

RESULTS

Of the 168 men, 29% had normal BMI (<24.0 kg/m2), 47% had overweight (24.0-27.9 kg/m2), and 24% had obesity (≥ 28.0 kg/m2). In the 232 women, the percentages were 46%, 32%, and 22%, respectively. Strong or very strong correlations with BMI were found for total AT, VAT, and SAT in both sexes. BMAT and ES PDFF was strongly correlated with age in women and moderately correlated in men. In both sexes, BMAT PDFF correlated only with age and not with any of the other AT depots. Psoas PDFF correlated only with ES PDFF and not with age or the other AT depots. Liver PDFF correlated with BMI and VAT and weakly with SAT in men. VAT and SAT correlated with age and each other in both sexes.

CONCLUSIONS

Age and BMI are both associated with adiposity, but their effects differ depending on the type of AT.

Bone Marrow Adipose Tissue

Bone marrow (BM) acts as a dynamic organ within the bone cavity, responsible for hematopoiesis, skeletal remodeling, and immune system control. Bone marrow adipose tissue (BMAT) was long simply considered a filler of space, but now it is known that it instead constitutes an essential element of the BM microenvironment that participates in homeostasis, influences bone health and bone remodeling, alters hematopoietic stem cell functions, contributes to the commitment of mesenchymal stem cells, provides effects to immune homeostasis and defense against infections, and participates in energy metabolism and inflammation. BMAT has emerged as a significant contributor to the development and progression of various diseases, shedding light on its complex relationship with health. Notably, BMAT has been implicated in metabolic disorders, hematological malignancies, and skeletal conditions. BMAT has been shown to support the proliferation of tumor cells in acute myeloid leukemia and niche adipocytes have been found to protect cancer cells against chemotherapy, contributing to treatment resistance. Moreover, BMAT's impact on bone density and remodeling can lead to conditions like osteoporosis, where high levels of BMAT are inversely correlated with bone mineral density, increasing the risk of fractures. BMAT has also been associated with diabetes, obesity, and anorexia nervosa, with varying effects on individuals depending on their weight and health status. Understanding the interaction between adipocytes and different diseases may lead to new therapeutic strategies.

Whitening of brown adipose tissue inhibits osteogenic differentiation via secretion of S100A8/A9

The mechanism by which brown adipose tissue (BAT) regulates bone metabolism is unclear. Here, we reveal that BAT secretes S100A8/A9, a previously unidentified BAT adipokine (batokine), to impair bone formation. Brown adipocytes-specific knockout of Rheb (RhebBAD KO), the upstream activator of mTOR, causes BAT malfunction to inhibit osteogenesis. Rheb depletion induces NF-κB dependent S100A8/A9 secretion from brown adipocytes, but not from macrophages. In wild-type mice, age-related Rheb downregulation in BAT is associated with enhanced S100A8/A9 secretion. Either batokines from RhebBAD KO mice, or recombinant S100A8/A9, inhibits osteoblast differentiation of mesenchymal stem cells in vitro by targeting toll-like receptor 4 on their surfaces. Conversely, S100A8/A9 neutralization not only rescues the osteogenesis repressed in the RhebBAD KO mice, but also alleviates age-related osteoporosis in wild-type mice. Collectively, our data revealed an unexpected BAT-bone crosstalk driven by Rheb-S100A8/A9, uncovering S100A8/A9 as a promising target for the treatment, and potentially, prevention of osteoporosis.

Quantitative MR Analysis of Changes in the Radius Bone Marrow in Osteoporosis

Purpose

This pilot study aimed to explore the feasibility of scanning the human distal radius bone marrow in vivo to detect osteoporosis-related changes using magnetic resonance and evaluate whether the radius may serve as an accessible probing site for osteoporosis. This may lead in the future to the use of affordable means such as low-field MRI scanners for the monitoring of disease progression.

Methods

A clinical trial was performed using a 3T MR scanner, including 26 women assigned into three study groups: healthy-premenopausal (n = 7; mean age 48.6 ± 3.5 years), healthy-postmenopausal (n = 10; mean age 54.5 ± 5.6 years), and osteoporotic-postmenopausal (n = 9; mean age 61.3 ± 5.6 years). Marrow fat composition was evaluated using T2 maps, a two-compartment model of T1, and a Dixon pulse sequence.

Results

The osteoporotic group exhibited higher fat content than the other two groups and lower T2 values than the healthy-premenopausal group.

Conclusions

Osteoporosis-related changes in the composition of the distal radius bone marrow may be detected in vivo using MRI protocols. The scanning protocols chosen here can later be repeated using low-field MRI scanners, thus offering the potential for early detection and treatment monitoring, using an accessible, affordable means that may be applied in small clinics. This trial is registered with MOH_2018-05-23_002247, NCT03742362.

Neuroendocrine adaptations to starvation

Famine and starvation have punctuated the evolutionary past of the human species. As such, we have developed hormonal responses to undernutrition that minimize energy expenditure on processes that are not critical for the survival of the individual, such as reproduction. In this review, we discuss neuroendocrine adaptations to starvation including hypogonadotropic hypogonadism, growth hormone resistance, hypercortisolemia, and the downregulation of the hypothalamic-pituitary-thyroid axis. We review the time-course of these adaptations by describing studies involving the short-term fasting of healthy individuals as well as studies describing the hormonal changes in states of chronic undernutrition, using individuals with anorexia nervosa as a model of chronic starvation. Lastly, we review representative clinical effects of chronic undernutrition.

New Insights into Calorie Restriction Induced Bone Loss

Caloric restriction (CR) is now a popular lifestyle choice due to its ability in experimental animals to improve lifespan, reduce body weight, and lessen oxidative stress. However, more and more emerging evidence suggests this treatment requires careful consideration because of its detrimental effects on the skeletal system. Experimental and clinical studies show that CR can suppress bone growth and raise the risk of fracture, but the specific mechanisms are poorly understood. Reduced mechanical loading has long been thought to be the primary cause of weight loss-induced bone loss from calorie restriction. Despite fat loss in peripheral depots with calorie restriction, bone marrow adipose tissue (BMAT) increases, and this may play a significant role in this pathological process. Here, we update recent advances in our understanding of the effects of CR on the skeleton, the possible pathogenic role of BMAT in CR-induced bone loss, and some strategies to mitigate any potential side effects on the skeletal system.

MR Imaging of the Developing Pediatric Marrow: An Overview of Pearls and Pitfalls

The dynamic and developing pediatric skeleton is a well-elucidated process that occurs in a stepwise faction. Normal development has been reliably tracked and described with Magnetic Resonance (MR) imaging. The recognition of the normal patterns of skeletal development is essential, as normal development may mimic pathology and vice versa. The authors review normal skeleton maturation and the corollary imaging findings while highlighting common marrow imaging pitfalls and pathology.

Metformin increases bone marrow adipose tissue by promoting mesenchymal stromal cells apoptosis

Bone marrow adipose tissue (MAT) has the potential to exert both local and systemic effects on metabolic homeostasis. As a first-line drug used to treat type 2 diabetes mellitus, metformin has conflicting effects on MAT and bone marrow mesenchymal stem cell (BM-MSC) differentiation. Through a series of experiments in vivo and in vitro, we found that except improving the glucose and lipid metabolism disorder in ob/ob mice, 200 mg/kg metformin increased MAT in mice tibia, and prompted osteogenic genes (RunX2, OPN, OCN) and lipogenic genes (Ppar-γ, Cebpα, Scd1) expression in mice bone marrow. However, metformin promoted osteogenesis and inhibited lipogenesis of MSC in vitro, which is inconsistent with the results in vivo. Given MAT being considered the "filler" of the space after the apoptosis of bone marrow stroma, the effect of metformin on MSC apoptosis was examined. We discovered that metformin induces MSC apoptosis in vivo and in vitro. Therefore, we speculated that the increased MAT in mice tibia may be attributed to the filling of adipose tissue after apoptosis of bone marrow stromal cells induced by metformin. The increased MAT may be involved in the regulation of metformin on glucose, lipid, and bone metabolism in diabetic mice, providing a new way to understand the metabolic regulation of metformin. While increased MAT-associated insulin resistance and metabolic disorders may account for the poorer clinical benefits in patients with intensive glucose control.

Bone marrow adipose tissue is associated with fracture history in anorexia nervosa

Although bone mineral density (BMD) is decreased and fracture risk increased in anorexia nervosa, BMD does not predict fracture history in this disorder. We assessed BMD, bone microarchitecture, and bone marrow adipose tissue (BMAT) in women with anorexia nervosa and found that only BMAT was associated with fracture history.

INTRODUCTION

Anorexia nervosa (AN) is a psychiatric disorder characterized by low body weight, low BMD, and increased risk of fracture. Although BMD is reduced and fracture risk elevated, BMD as assessed by DXA does not distinguish between individuals with versus those without prior history of fracture in AN. Despite having decreased peripheral adipose tissue stores, individuals with AN have enhanced bone marrow adipose tissue (BMAT), which is inversely associated with BMD. Whether increased BMAT is associated with fracture in AN is not known.

METHODS

We conducted a cross-sectional study in 62 premenopausal women, including 34 with AN and 28 normal-weight women of similar age. Fracture history was collected during patient interviews and BMD measured by DXA, BMAT by 1H-MRS, and parameters of bone microarchitecture by HR-pQCT.

RESULTS

Sixteen women (47.1%) with AN reported prior history of fracture compared to 11 normal-weight women (39.3%, p = 0.54). In the entire group and also the subset of women with AN, there were no significant differences in BMD or parameters of bone microarchitecture in women with prior fracture versus those without. In contrast, women with AN with prior fracture had greater BMAT at the spine and femur compared to those without (p = 0.01 for both).

CONCLUSION

In contrast to BMD and parameters of bone microarchitecture, BMAT is able to distinguish between women with AN with prior fracture compared to those without. Prospective studies will be necessary to understand BMAT's potential pathophysiologic role in the increased fracture risk in AN.

Changes in Bone Marrow Adipose Tissue in Transgender and Gender Non-Conforming Youth Undergoing Pubertal Suppression: A Pilot Study

Pubertal suppression with gonadotropin-releasing hormone (GnRH) agonists in transgender and gender non-conforming (TGNC) youth may affect acquisition of peak bone mass. Bone marrow adipose tissue (BMAT) has an inverse relationship with bone mineral density (BMD). To evaluate the effect of pubertal suppression on BMAT, in this pilot study we prospectively studied TGNC youth undergoing pubertal suppression and cisgender control participants with similar pubertal status over a 12-month period. BMD was measured by dual-energy X-ray absorptiometry and peripheral quantitative computed tomography. Magnetic Resonance T1 relaxometry (T1-R) and spectroscopy (MRS) were performed to quantify BMAT at the distal femur. We compared the change in BMD, T1-R values, and MRS lipid indices between the two groups. Six TGNC (two assigned female and four assigned male at birth) and three female control participants (mean age 10.9 and 11.7 years, respectively) were enrolled. The mean lumbar spine BMD Z-score declined by 0.29 in the TGNC group, but increased by 0.48 in controls (between-group difference 0.77, 95% CI: 0.05, 1.45). Similar findings were observed with the change in trabecular volumetric BMD at the 3% tibia site (-4.1% in TGNC, +3.2% in controls, between-group difference 7.3%, 95% CI: 0.5%-14%). Distal femur T1 values declined (indicative of increased BMAT) by 7.9% in the TGNC group, but increased by 2.1% in controls (between-group difference 10%, 95% CI: -12.7%, 32.6%). Marrow lipid fraction by MRS increased by 8.4% in the TGNC group, but declined by 0.1% in controls (between-group difference 8.5%, 95% CI: -50.2%, 33.0%). In conclusion, we observed lower bone mass acquisition and greater increases in BMAT indices by MRI and MRS in TGNC youth after 12 months of GnRH agonists compared with control participants. Early changes in BMAT may underlie an alteration in bone mass acquisition with pubertal suppression, including alterations in mesenchymal stem cells within marrow.

Bone density and bone marrow composition in transgender girls prior to pubertal blockade: A case series

PURPOSE

To determine bone mineral density (BMD) of transgender girls before pubertal blockade, and correlate with lifestyle and clinical variables.

METHODS

Six transfemale peri-pubertal girls had knee magnetic resonance imaging (MRI) with T1-weighted images and single-voxel proton magnetic resonance spectroscopy (MRS). BMD measurements were obtained via dual-energy X-ray absorptiometry. Questionnaires about physical activity, diet, and the Eating Attitudes Test (EAT-26) were completed. The T2 relaxation rate of water (R2 = 1/T2 in s -1) was correlated with scores on surveys.

RESULTS

Three participants (50 %) had a low bone mineral density for age based on total body less head Z-score less than -2; two participants (33 %) had a low BMD for age at lumbar spine. All had EAT-26 scores below threshold for clinical concern. All participants self-reported regular exercise. Bone marrow MR variables (T1, fat fraction, unsaturation index and R2 of water) were not correlated with DXA measures.

CONCLUSIONS

Participants had low BMD on beginning pubertal blockade. Clinicians should consider monitoring BMD among youth AMAB, a group at potential risk for poor bone health.

Bone marrow adiposity in pediatric Crohn's disease

Patients with Crohn's disease often have low bone mineral density and an increased risk of osteoporosis. Although decreased bone formation can be seen at diagnosis, the underlying pathophysiology of suboptimal bone accrual remains poorly understood. We sought to evaluate a novel mechanism affecting osteogenesis in patients with Crohn's disease. In this case series, we evaluated bone marrow composition at the distal femur and proximal tibia of the left knee measured via magnetic resonance (MR) spectroscopy and relaxometry in five adolescents with the diagnosis of Crohn's disease. The subjects were enrolled prospectively between 2011 and 2013 at Boston Children's Hospital. Additional clinical information, including DXA scans to evaluate bone mineral density and body composition, and Crohn's disease history, such as glucocorticoid use and disease duration, were assessed. Healthy adolescents have persistent hematopoietic marrow with only 40 to 50 % fat in the long bone metaphyses. The current participants with Crohn's disease had increased marrow adiposity, with a mean fat fraction of 67.8 %. There appeared to be a trend towards higher fat fraction with shorter disease duration, while participants with the longest disease duration had the lowest fat fraction. Participants also had decreased bone density, increased fat mass, and lower lean mass, as assessed by DXA and compared to pediatric reference data. Our MRI results demonstrate increased marrow adiposity in children with Crohn's disease, especially early in the course of the disease. DXA may better demonstrate longer-term effects on bone. Additional studies are needed to evaluate bone marrow composition in these patients and to elucidate further the inverse relationship between marrow adipocytes and osteogenesis, as well as the relationship between bone marrow adiposity and body composition.

An integrative bioinformatics approach to decipher adipocyte-induced transdifferentiation of osteoblast

In human, bone loss is associated with increased marrow adipose tissue and recent data suggest that medullary adipocytes could play a role in osteoporosis by acting on neighboring bone-forming osteoblasts. Supporting this hypothesis, we previously showed, in a coculture model based on human bone marrow stromal cells, that factors secreted by adipocytes induced the conversion of osteoblasts towards an adipocyte-like phenotype. In this work, we employed an original integrative bioinformatics approach connecting proteomic and transcriptomic data from adipocytes and osteoblasts, respectively, to investigate the mechanisms underlying their crosstalk. Our analysis identified a total of 271 predicted physical interactions between adipocyte-secreted proteins and osteoblast membrane protein coding genes and proposed three pathways for their potential contribution to osteoblast transdifferentiation, the PI3K-AKT, the JAK2-STAT3 and the SMAD pathways. Our findings demonstrated the effectiveness of our integrative omics strategy to decipher cell-cell communication events.

Skeletal Aging

Aging represents the single greatest risk factor for chronic diseases, including osteoporosis, a skeletal fragility syndrome that increases fracture risk. Optimizing bone strength throughout life reduces fracture risk. Factors critical for bone strength include nutrition, physical activity, and vitamin D status, whereas unhealthy lifestyles, illnesses, and certain medications (eg, glucocorticoids) are detrimental. Hormonal status is another important determinant of skeletal health, with sex steroid concentrations, particularly estrogen, having major effects on bone remodeling. Aging exacerbates bone loss in both sexes and results in imbalanced bone resorption relative to formation; it is associated with increased marrow adiposity, osteoblast/osteocyte apoptosis, and accumulation of senescent cells. The mechanisms underlying skeletal aging are as diverse as the factors that determine the strength (and thus fragility) of bone. This review updates our current understanding of the epidemiology, pathophysiology, and treatment of osteoporosis and provides an overview of the underlying hallmark mechanisms that drive skeletal aging.

Update on the Effects of Energy Metabolism in Bone Marrow Mesenchymal Stem Cells Differentiation

Background

As common progenitor cells of osteoblasts and adipocytes, bone marrow mesenchymal (stromal) stem cells (BMSCs) play key roles in bone homeostasis, tissue regeneration, and global energy homeostasis; however, the intrinsic mechanism of BMSC differentiation is not well understood. Plasticity in energy metabolism allows BMSCs to match the divergent demands of osteo-adipogenic differentiation. Targeting BMSC metabolic pathways may provide a novel therapeutic perspective for BMSC differentiation unbalance related diseases.

Scope of review

This review covers the recent studies of glucose, fatty acids, and amino acids metabolism fuel the BMSC differentiation. We also discuss recent findings about energy metabolism in BMSC differentiation.

Major conclusions

Glucose, fatty acids, and amino acids metabolism provide energy to fuel BMSC differentiation. Moreover, some well-known regulators including environmental stress, hormone drugs, and biological and pathological factors may also influence BMSC differentiation by altering metabolism. This offers insight to the significance of metabolism on BMSC fate determination and provides the possibility of treating diseases related to BMSC differentiation, such as obesity and osteoporosis, from a metabolic perspective.

Severity Level and Duration of Energy Deficit in Mice Affect Bone Phenotype and Bone Marrow Stromal Cell Differentiation Capacity

Anorexia nervosa is known to induce changes in bone parameters and an increase in bone marrow adiposity (BMA) that depend on the duration and seriousness of the disease. Previous studies have found that bone loss is associated with BMA accumulation. Sirtuin of type 1 (Sirt1), a histone deacetylase that is partly regulated by energy balance, was shown to have pro-osteoblastogenic and anti-adipogenic effects. To study the effects of the severity and duration of energy deficits related to bone loss, a mouse model of separation-based anorexia (SBA) was established. We recently demonstrated that moderate body weight loss (18%) 8-week SBA protocol in mice resulted in an increase in BMA, bone loss, and a significant reduction in Sirt1 expression in bone marrow stromal cells (BMSCs) extracted from SBA mice. We hypothesised that Sirt1 deficit in BMSCs is associated with bone and BMA alterations and could potentially depend on the severity of weight loss and the length of SBA protocol. We studied bone parameters, BMA, BMSC differentiation capacity, and Sirt1 expression after induction of 4 different levels of body weight loss (0%,12%,18%,24%), after 4 or 10 weeks of the SBA protocol. Our results demonstrated that 10 week SBA protocols associated with body weight loss (12%, 18%, 24%) induced a significant decrease in bone parameters without any increase in BMA. BMSCs extracted from 12% and 18% SBA groups showed a significant decrease in Sirt1 mRNA levels before and after co-differentiation. For these two groups, decrease in Sirt1 was associated with a significant increase in the mRNA level of adipogenic markers and a reduction of osteoblastogenesis. Inducing an 18% body weight loss, we tested a short SBA protocol (4-week). We demonstrated that a 4-week SBA protocol caused a significant decrease in Tb.Th only, without change in other bone parameters, BMA, Sirt1 expression, or differentiation capacity of BMSCs. In conclusion, this study showed, for the first time, that the duration and severity of energy deficits are critical for changes in bone parameters, BMSC differentiation, and Sirt1 expression. Furthermore, we showed that in this context, Sirt1 expression could impact BMSC differentiation with further effects on bone phenotype.

Adipocyte-Cancer Cell Interactions in the Bone Microenvironment

When compared to adipocytes in other anatomical sites, the interaction of bone marrow resident adipocytes with the other cells in their microenvironment is less well understood. Bone marrow adipocytes originate from a resident, self-renewing population of multipotent bone marrow stromal cells which can also give rise to other lineages such as osteoblasts. The differentiation fate of these mesenchymal progenitors can be influenced to favour adipogenesis by several factors, including the administration of thiazolidinediones and increased age. Experimental data suggests that increases in bone marrow adipose tissue volume may make bone both more attractive to metastasis and conducive to cancer cell growth. Bone marrow adipocytes are known to secrete a variety of lipids, cytokines and bioactive signaling molecules known as adipokines, which have been implicated as mediators of the interaction between adipocytes and cancer cells. Recent studies have provided new insight into the impact of bone marrow adipose tissue volume expansion in regard to supporting and exacerbating the effects of bone metastasis from solid tumors, focusing on prostate, breast and lung cancer and blood cancers, focusing on multiple myeloma. In this mini-review, recent research developments pertaining to the role of factors which increase bone marrow adipose tissue volume, as well as the role of adipocyte secreted factors, in the progression of bone metastatic prostate and breast cancer are assessed. In particular, recent findings regarding the complex cross-talk between adipocytes and metastatic cells of both lung and prostate cancer are highlighted.

The Effect of Caloric Restriction with and without n-3 PUFA Supplementation on Bone Turnover Markers in Blood of Subjects with Abdominal Obesity: A Randomized Placebo-Controlled Trial

Weight loss contributes to an increased risk of hip fracture, especially in postmenopausal women. Omega-3 polyunsaturated fatty acid (n-3 PUFA) supplementation could diminish the adverse effect of weight loss on bone health. The aim of this randomized, placebo-controlled, double-blind parallel trial was to investigate the effect of caloric restriction and n-3 PUFA supplement intake on osteogenic markers (carboxylated osteocalcin (Gla-OC); procollagen I N-terminal propeptide (PINP)), as well as a bone resorption marker (C-terminal telopeptide of type I collagen (CTX-I)) in a serum of 64 middle aged individuals (BMI 25-40 kg/m²) with abdominal obesity. Bone remodeling, metabolic and inflammatory parameters and adipokines were determined before and after 3 months of an isocaloric diet (2300-2400 kcal/day) or a low-calorie diet (1200 kcal/day for women and 1500 kcal/day for men) along with n-3 PUFA (1.8 g/day) or placebo capsules. CTX-I and adiponectin concentrations were increased following 7% weight loss independently of supplement use. Changes in CTX-I were positively associated with changes in adiponectin level (rho = 0.25, p = 0.043). Thus, an increase in serum adiponectin caused by body weight loss could adversely affect bone health. N-3 PUFAs were without effect.

Bone Health in Pediatric Patients with IBD: What Is New?

PURPOSE OF THE REVIEW

Patients with inflammatory bowel disease (IBD) have increased bone fragility, demonstrated by increased fracture risk, and often have low bone density and altered bone geometry, but the underlying pathophysiology remains poorly understood.

RECENT FINDINGS

Children and adolescents with IBD appear to have decreased bone formation, at diagnosis, which frequently improves with treatment of their underlying IBD. There is a growing body of evidence regarding how the immune system interacts with bone metabolism. There are likely multi-factorial etiologies that contribute to suboptimal bone accrual and subsequent lack of peak bone mass attainment in growing patients with IBD. There appears to be differential effects dependent upon IBD sub-type and bone compartment. Pediatric patients with IBD require recognition of several risk factors that may adversely impact their bone accrual. Future studies are necessary to further delineate the effects of IBD on pediatric bone health.

The Impact of Sedentary Lifestyle, High-fat Diet, Tobacco Smoke, and Alcohol Intake on the Hematopoietic Stem Cell Niches

Hematopoietic stem and progenitor cells maintain hematopoiesis throughout life by generating all major blood cell lineages through the process of self-renewal and differentiation. In adult mammals, hematopoietic stem cells (HSCs) primarily reside in the bone marrow (BM) at special microenvironments called “niches.” Niches are thought to extrinsically orchestrate the HSC fate including their quiescence and proliferation. Insight into the HSC niches mainly comes from studies in mice using surface marker identification and imaging to visualize HSC localization and association with niche cells. The advantage of mouse models is the possibility to study the 3-dimensional BM architecture and cell interactions in an intact traceable system. However, this may not be directly translational to human BM. Sedentary lifestyle, unhealthy diet, excessive alcohol intake, and smoking are all known risk factors for various diseases including hematological disorders and cancer, but how do lifestyle factors impact hematopoiesis and the associated niches? Here, we review current knowledge about the HSC niches and how unhealthy lifestyle may affect it. In addition, we summarize epidemiological data concerning the influence of lifestyle factors on hematological disorders and malignancies.

The dynamics of human bone marrow adipose tissue in response to feeding and fasting

BACKGROUND

Adipocytes were long considered inert components of the bone marrow niche, but mouse and human models suggest bone marrow adipose tissue (BMAT) is dynamic and responsive to hormonal and nutrient cues.

METHODS

In this study of healthy volunteers, we investigated how BMAT responds to acute nutrient changes, including analyses of endocrine determinants and paracrine factors from marrow aspirates. Study participants underwent a 10-day high-calorie protocol, followed by a 10-day fast.

RESULTS

We demonstrate (a) vertebral BMAT increased significantly during high-calorie feeding and fasting, suggesting BMAT may have different functions in states of caloric excess compared with caloric deprivation; (b) ghrelin, which decreased in response to high-calorie feeding and fasting, was inversely associated with changes in BMAT; and (c) in response to high-calorie feeding, resistin levels in the marrow sera, but not the circulation, rose significantly. In addition, TNF-α expression in marrow adipocytes increased with high-calorie feeding and decreased upon fasting.

CONCLUSION

High-calorie feeding, but not fasting, induces an immune response in bone marrow similar to what has been reported in peripheral adipose tissue. Understanding the immunomodulatory regulators in the marrow may provide further insight into the homeostatic function of this unique adipose tissue depot.

FUNDING

NIH grant R24 DK084970, Harvard Catalyst/The Harvard Clinical and Translational Science Center (National Center for Advancing Translational Sciences, NIH, award UL 1TR002541), and NIH grants P30 DK040561 and U19 AG060917S1.

Chronic stress and adipose tissue in the anorexic state: endocrine and epigenetic mechanisms

Although adipose tissue metabolism in obesity has been widely studied, there is limited research on the anorexic state, where the endocrine system is disrupted by reduced adipose tissue mass and there are depot-specific changes in adipocyte type and function. Stress exposure at different stages of life can alter the balance between energy intake and expenditure and thereby contribute to the pathogenesis of anorexia nervosa. This review integrates information from human clinical trials to describe endocrine, genetic and epigenetic aspects of adipose tissue physiology in the anorexic condition. Changes in the hypothalamus-pituitary-thyroid, -adrenal, and -gonadal axes and their relationships to appetite regulation and adipocyte function are discussed. Because of the role of stress in triggering or magnifying anorexia, and the dynamic but also persistent nature of environmentally-induced epigenetic modifications, epigenetics is likely the link between stress and long-term changes in the endocrine system that disrupt homoeostatic food intake and adipose tissue metabolism. Herein, we focus on the adipocyte and changes in its function, including alterations reinforced by endocrine disturbance and dysfunctional adipokine regulation. This information is critical because of the poor understanding of anorexic pathophysiology, due to the lack of suitable research models, and the complexity of genetic and environmental interactions.

Human Bone Marrow Adipose Tissue is a Metabolically Active and Insulin-Sensitive Distinct Fat Depot

CONTEXT

Bone marrow (BM) in adult long bones is rich in adipose tissue, but the functions of BM adipocytes are largely unknown. We set out to elucidate the metabolic and molecular characteristics of BM adipose tissue (BMAT) in humans.

OBJECTIVE

Our aim was to determine if BMAT is an insulin-sensitive tissue, and whether the insulin sensitivity is altered in obesity or type 2 diabetes (T2DM).

DESIGN

This was a cross-sectional and longitudinal study.

SETTING

The study was conducted in a clinical research center.

PATIENTS OR OTHER PARTICIPANTS

Bone marrow adipose tissue glucose uptake (GU) was assessed in 23 morbidly obese subjects (9 with T2DM) and 9 healthy controls with normal body weight. In addition, GU was assessed in another 11 controls during cold exposure. Bone marrow adipose tissue samples for molecular analyses were collected from non-DM patients undergoing knee arthroplasty.

INTERVENTION(S)

Obese subjects were assessed before and 6 months after bariatric surgery and controls at 1 time point.

MAIN OUTCOME MEASURE

We used positron emission tomography imaging with 2-[18F]fluoro-2-deoxy-D-glucose tracer to characterize GU in femoral and vertebral BMAT. Bone marrow adipose tissue molecular profile was assessed using quantitative RT-PCR.

RESULTS

Insulin enhances GU in human BMAT. Femoral BMAT insulin sensitivity was impaired in obese patients with T2DM compared to controls, but it improved after bariatric surgery. Furthermore, gene expression analysis revealed that BMAT was distinct from brown and white adipose tissue.

CONCLUSIONS

Bone marrow adipose tissue is a metabolically active, insulin-sensitive and molecularly distinct fat depot that may play a role in whole body energy metabolism.

Sirtuin 1 deficiency decreases bone mass and increases bone marrow adiposity in a mouse model of chronic energy deficiency

Sirtuin of type 1 (Sirt1), a class III HDAC, is known to be involved in the regulation of differentiation of skeletal stem cells (SSCs) into osteoblasts and adipocytes. In caloric restriction, it has been shown that the expression and activity of Sirt1 is a tissue-dependent regulation. However, at present, no study has focused on the link between Sirt1, bone marrow adiposity (BMA) and osteoporosis related to anorexia nervosa (AN). Thus, the aims of this work were to (i) determine BMA and bone changes in a mouse model replicating the phenotypes of AN (separation-based anorexia model (SBA)); (ii) determine the expression of Sirt1 in bone marrow stromal cells (BMSCs) extracted from these mice and identify their differentiation capacities; (iii) study the effects of pharmacological activation and inhibition of Sirt1 on the osteoblastogenesis and adipogenesis of these cells and (iiii) delineate the molecular mechanism by which Sirt1 could regulate osteogenesis in an SBA model. Our results demonstrated that SBA protocol induces an increase in BMA and alteration of bone architecture. In addition, BMSCs from restricted mice present a down-regulation of Sirt1 which is accompanied by an increase in adipogenesis at expense of osteogenesis. After a 10-day organotypic culture, tibias from SBA mice displayed low levels of Sirt1 mRNA which are restored by resveratrol treatment. Interestingly, this recovery of Sirt1 levels also returned the BMA, BV/TV and Tb.Th in cultured tibias from SBA mice to normal levels. In contrast of down-regulation of Sirt1 expression induced by sirtinol treatment, stimulation of Sirt1 expression by resveratrol lead to a decrease in adipogenesis and increase in osteogenesis. Finally, to investigate the molecular mechanisms by which Sirt1 could regulate osteogenesis in the SBA model, the acetylation levels of Runx2 and Foxo1 transcription factors were determined. Our data show that this chronic energy deficiency in female mice causes a decrease in BMSC activity, resulting in critical changes to Runx2 and Foxo1 acetylation levels and thus to their activity. Altogether, these data suggest that Sirt1 could be considered as a potential therapeutic target in osteoporosis related to AN.

Spinal 'flip-flop' effect in anorexia nervosa: A case report

Anorexia nervosa is a psychiatric eating disorder related to malnutrition and consequent altered metabolism. A 48-year-old female with a history of anorexia in the last 2 years referred to our hospital with spinal pain. She underwent spinal X-ray and magnetic resonance imaging (MRI) showing multiple vertebral collapses in dorsal and lumbar spine with inversion of normal bone marrow and soft tissue signal in T1-weighted and STIR images. We describe this case of spinal 'flip-flop' phenomenon, underlining how what seems a technical failure is actually a specific imaging pattern related to the clinical context.

Transdermal Estrogen in Women With Anorexia Nervosa: An Exploratory Pilot Study

Anorexia nervosa (AN) is a psychiatric disorder characterized by self‐induced starvation, low body weight, and elevated levels of bone marrow adipose tissue (BMAT). BMAT is negatively associated with BMD in AN and more than 85% of women with AN have low bone mass and an increased risk of fracture. Although a majority of women with AN are amenorrheic, which is associated with low BMD, oral contraceptive pills, containing supraphysiologic doses of estrogen, are not effective in increasing bone mass. We performed a 6‐month, open‐label study of transdermal estradiol (0.045 mg/day) + levonorgestrel (0.015 mg/day) in 11 women with AN (mean age ± SEM: 37.2 ± 2.3 years) to investigate the effects of transdermal, physiologic doses of estrogen on BMD and BMAT in women with AN. We measured change in BMD by DXA, change in BMAT at the spine/hip by ¹H‐magnetic resonance spectroscopy, and change in C‐terminal collagen cross‐links (CTX), P1NP, osteocalcin, IGF‐1, and sclerostin after 3 and 6 months of transdermal estrogen. Lumbar spine (2.0% ± 0.8%; p = 0.033) and lateral spine (3.2% ± 1.1%; p = 0.015) BMD increased after 6 months of transdermal estrogen. Lumbar spine BMAT decreased significantly after 3 months (−13.9 ± 6.0%; p = 0.046). Increases in lateral spine BMD were associated with decreases in CTX (p = 0.047). In conclusion, short‐term treatment with transdermal, physiologic estrogen increases spine BMD in women with AN. Future studies are needed to assess the long‐term efficacy of this treatment. © 2019 The Authors. JBMR Plus published by Wiley Periodicals, Inc. on behalf of American Society for Bone and Mineral Research.

Marrow Fat-Secreted Factors as Biomarkers for Osteoporosis

PURPOSE OF REVIEW

The age-related accumulation of bone marrow adipose tissue (BMAT) negatively impacts bone metabolism and hematopoiesis. This review provides an overview about BMAT-secreted factors as biomarkers for BMAT accumulation and osteoporosis risk.

RECENT FINDINGS

The adipokines leptin and adiponectin are regulators of BMAT. It remains to be clarified if locally produced adipokines substantially contribute to their peripheral serum levels and if they influence bone metabolism beyond that of extraosseous adipokine production. Existing data also suggests that BMAT disturbs bone metabolism primarily through palmitate-mediated toxic effects on osteoblasts and osteocytes, including dysregulated autophagy and apoptosis. BMAT-secreted factors are important modulators of bone metabolism. However, the majority of our understanding about MAT-secreted factors and their paracrine and endocrine effects is derived from in vitro studies and animal experiments. Therefore, more research is needed before BMAT-secreted biomarkers can be applied in medical practice.

Factors influencing bone loss in anorexia nervosa: assessment and therapeutic options

Decreased mineral density is one of the major complications of anorexia nervosa. The phenomenon is even more pronounced when the disease occurs during adolescence and when the duration of amenorrhoea is long. The mechanisms underlying bone loss in anorexia are complex. Oestrogen deficiency has long been considered as the main factor, but cannot explain the phenomenon on its own. The essential role of nutrition-related factors—especially leptin and adiponectin—has been reported in recent studies. Therapeutic strategies to mitigate bone involvement in anorexia are still a matter for debate. Although resumption of menses and weight recovery appear to be essential, they are not always accompanied by a total reversal of bone loss. There are no studies in the literature demonstrating that oestrogen treatment is effective, and the best results seem to have been obtained with agents that induce bone formation—such as IGF-1—especially when associated with oestrogen. As such, bone management in anorexia remains difficult, hence, the importance of early detection and multidisciplinary follow-up.

Marrow Adipocytes: Origin, Structure, and Function

The skeleton harbors an array of lineage cells that have an essential role in whole body homeostasis. Adipocytes start the colonization of marrow space early in postnatal life, expanding progressively and influencing other components of the bone marrow through paracrine signaling. In this unique, closed, and hypoxic environment close to the endosteal surface and adjacent to the microvascular space the marrow adipocyte can store or provide energy, secrete adipokines, and target neighboring bone cells. Adipocyte progenitors can also migrate from the bone marrow to populate white adipose tissue, a process that accelerates during weight gain. The marrow adipocyte also has an endocrine role in whole body homeostasis through its varied secretome that targets distant adipose depots, skeletal muscle, and the nervous system. Further insights into the biology of this unique and versatile cell will undoubtedly lead to novel therapeutic approaches to metabolic and age-related disorders such as osteoporosis and diabetes mellitus.

Marrow adipose tissue gradient is preserved through high protein diet and bed rest. A randomized crossover study

Context

Marrow adipose tissue (MAT) has a peripheral to central distribution in adults, higher in peripheral bones. Similarly, the spine has a caudal to cephalad MAT distribution, higher in lumbar vertebras. Diet and the level of physical activities are known modulators of MAT with significant impact on bone; however, whether these can modulate the MAT gradient is unknown.

Objective

To measure the effect of high protein diet and bed rest interventions on the lumbar MAT gradient.

Design participants intervention

In a prospective randomized crossover trial, 10 healthy men participated in 2 consecutive campaigns of 21days head-down-tilt-bed-rest (HDTBR). They received either whey protein and potassium bicarbonate-supplemented or control diet separated by a 4-month washout period.

Main outcome measures

Ten serial MRI measures of lumbar vertebral fat fraction (VFF) were performed at baseline, 10days and 20days of HDTBR and 3 and 28days after HDTBR of each bed rest campaign.

Results

The mean L5-L1 VFF difference of 4.2 ± 1.2 percentage point higher at L5 (p = 0.008) constituted a caudal to cephalad lumbar MAT gradient. High protein diet did not alter the lumbar VFF differences during both HDTBR campaigns (all time points p > 0.05). Similarly, 2 campaigns of 21days of HDTBR did not change the lumbar VFF differences (all time points p > 0.05).

Conclusions

This pilot study established that the lumbar vertebral MAT gradient was not altered by a high protein nor by 2 × 21days bed rest interventions. These findings demonstrated that this lack of mechanical stimulus was not an important modulator of the lumbar MAT gradient. The highly preserved MAT gradient needs to be measured in more situations of health and disease and may potentially serve to detect pathological situations.

Impact of Adrenal Hormone Supplementation on Bone Geometry in Growing Teens With Anorexia Nervosa

PURPOSE

Adolescents with anorexia nervosa (AN) have decreased dehydroepiandrosterone (DHEA) and estrogen concentrations that may contribute to skeletal deficits. We sought to determine whether DHEA + estrogen replacement (ERT) prevented bone loss in young adolescents with AN.

METHODS

We recruited females with AN (n = 70, ages 11-18 years) into a 12-month, randomized, double-blind placebo-controlled trial. Participants were randomized to oral micronized DHEA 50 mg + 20 mcg ethinyl estradiol/.1 mg levonorgestrel daily (n = 35) or placebo (n = 35). Outcomes included serial measures of bone mineral density (BMD) by dual-energy X-ray absorptiometry (total body, hip, spine) and peripheral quantitative computed tomography (pQCT; tibia). Magnetic resonance imaging of T1-weighted images of the left knee determined physeal status (open/closed).

RESULTS

Sixty-two subjects completed the trial. Physeal closure status was the strongest predictor of aBMD changes. Among girls with open physes, those who received DHEA + ERT showed a decline in BMD Z-scores compared with those receiving placebo, whereas there was no effect in those with at least one closed physis. Treatment did not affect any pQCT measures, regardless of physeal closure status.

CONCLUSIONS

Combined DHEA + ERT did not significantly improve dual-energy X-ray absorptiometry or pQCT BMD measurements in young adolescent girls with AN, in contrast to an earlier trial showing benefit in older adolescents and young women. In girls with open physes, the mean change in the placebo arm was greater than that of the DHEA + ERT group. We conclude that DHEA + ERT is ineffective for preserving bone health in growing young adolescents with AN at the dose and route of administration described in this report.

Bone Marrow Adiposity: Basic and Clinical Implications

The presence of adipocytes in mammalian bone marrow (BM) has been recognized histologically for decades, yet, until recently, these cells have received little attention from the research community. Advancements in mouse transgenics and imaging methods, particularly in the last 10 years, have permitted more detailed examinations of marrow adipocytes than ever before and yielded data that show these cells are critical regulators of the BM microenvironment and whole-body metabolism. Indeed, marrow adipocytes are anatomically and functionally separate from brown, beige, and classic white adipocytes. Thus, areas of BM space populated by adipocytes can be considered distinct fat depots and are collectively referred to as marrow adipose tissue (MAT) in this review. In the proceeding text, we focus on the developmental origin and physiologic functions of MAT. We also discuss the signals that cause the accumulation and loss of marrow adipocytes and the ability of these cells to regulate other cell lineages in the BM. Last, we consider roles for MAT in human physiology and disease.

A case-control pilot study of stress fracture in adolescent girls: the discriminative ability of two imaging technologies to classify at-risk athletes

Since stress fractures are common among adolescent athletes, it is important to identify bone assessment tools that accurately identify risk. We investigated the discriminative ability of two imaging technologies to classify at-risk athletes. Findings suggested that peripheral quantitative computed tomography (pQCT) has the ability to distinguish differences in bone structure in injured vs. uninjured limbs.

INTRODUCTION

Given the high stress fracture (SFX) prevalence among adolescent girls, an understanding of the most informative assessment tools to identify SFX risks are required. We investigated the discriminative ability of pQCT vs. dual-energy X-ray absorptiometry (DXA) to classify athletes with or without SFX.

METHODS

Twelve adolescent athletes diagnosed with a lower-extremity SFX were compared with 12 matched controls. DXA measured areal bone mineral density (aBMD) and content of the total body, and lumbar spine. Bilateral tibiae were assessed with pQCT. At the metaphysis (3%), total density (ToD), trabecular density (TrD), trabecular area (TrA), and estimated bone strength in compression (BSIc), and at the diaphysis (38% and 66%), total bone area (ToA), cortical density (CoD), cortical area (CoA), estimated bone strength in torsion (SSIp), and peri- and endocortical and muscle area (MuA) were obtained. Cortical bone mass/density around the center of mass and marrow density (estimate of adiposity) were calculated using ImageJ software. General estimated equations adjusting for multiple comparisons (Holm-Bonferroni method) were used to compare means between (1) injured limb of the case athletes vs. uninjured limb of the control athletes and (2) uninjured limb of the case athletes vs. uninjured limbs of the controls and injured vs. uninjured limb of case athletes with a SFX.

RESULTS

aBMD and content showed no significant differences between cases and controls. When comparing the injured vs. uninjured leg in the case athletes by pQCT at the 3% tibia, unadjusted TrD, total density, and BSIc were significantly lower (p < 0.05) in the injured vs. uninjured leg. Marrow density at the 66% site was 1% (p < 0.05) lower in the injured vs. uninjured leg.

CONCLUSIONS

These preliminary data in athletes with SFX suggest that pQCT has the ability to distinguish differences in bone structure in injured vs. uninjured limbs. No discriminative bone parameter classifications were identified between adolescent athletes with or without SFX.

Low bone mineral density in anorexia nervosa: Treatments and challenges

Anorexia nervosa, a psychiatric disease predominantly affecting women, is characterized by self- induced starvation and a resultant low-weight state. During starvation, a number of hormonal adaptations - including hypothalamic amenorrhea and growth hormone resistance - allow for decreased energy expenditure during periods of decreased nutrient intake, but these very same adaptations also contribute to the medical complications associated with chronic starvation, including low bone mass. Almost 90% of women with anorexia nervosa have bone mineral density (BMD) values more than one-standard deviation below the mean of healthy women at peak bone mineral density and this disease is associated with a significantly increased risk of fracture. Although multiple therapies have been studied for the treatment of low bone mass in anorexia nervosa, there are currently no approved therapies and few promising long-term therapeutic options. This review will outline the mediators of low bone mass in anorexia nervosa, discuss therapies that have been studied for the treatment of low BMD in this disorder, and highlight the important challenges that remain, including the differences in bone modeling in adolescents with anorexia nervosa as compared to adults, necessitating that potential therapies be tested in these two populations separately, and the paucity of long-term therapeutic strategies for treating bone loss in this disorder.

Changes in marrow adipose tissue with short-term changes in weight in premenopausal women with anorexia nervosa

OBJECTIVE

In anorexia nervosa, a psychiatric disease characterized by self-induced starvation and a model of chronic undernutrition, levels of subcutaneous (SAT) and visceral (VAT) adipose tissue are low, whereas marrow adipose tissue (MAT) levels are elevated compared to normal-weight women. The reason for this paradoxical elevation of an adipose tissue depot in starvation is not known. We sought to understand changes in MAT in response to subacute changes in weight and to compare these changes with those of other fat depots and body composition parameters.

DESIGN AND METHODS

We conducted a 12-month longitudinal study including 46 premenopausal women (n = 26 with anorexia nervosa and n = 20 normal-weight controls) with a mean (s.e.m.) age of 28.2 ± 0.8 years. We measured MAT, SAT, VAT and bone mineral density (BMD) at baseline and after 12 months.

RESULTS

At baseline, SAT (P < 0.0001), VAT (P < 0.02) and BMD of the spine and hip (P ≤ 0.0002) were significantly lower and vertebral and metaphyseal MAT (P ≤ 0.001) significantly higher in anorexia nervosa compared to controls. Weight gain over 12 months was associated with increases not only in SAT and VAT, but also epiphyseal MAT (P < 0.03). Changes in epiphyseal MAT were positively associated with changes in BMD (P < 0.03).

CONCLUSIONS

In contrast to the steady state, in which MAT levels are higher in anorexia nervosa and MAT and BMD are inversely associated, short-term weight gain is associated with increases in both MAT and BMD. These longitudinal data demonstrate the dynamic nature of this fat depot and provide further evidence of its possible role in mineral metabolism.

Fat-bone interaction within the bone marrow milieu: Impact on hematopoiesis and systemic energy metabolism

The relationship between fat, bone and systemic metabolism is a growing area of scientific interest. Marrow adipose tissue is a well-recognized component of the bone marrow milieu and is metabolically distinct from current established subtypes of adipose tissue. Despite recent advances, the functional significance of marrow adipose tissue is still not clearly delineated. Bone and fat cells share a common mesenchymal stem cell (MSC) within the bone marrow, and hormones and transcription factors such as growth hormone, leptin, and peroxisomal proliferator-activated receptor γ influence MSC differentiation into osteoblasts or adipocytes. MSC osteogenic potential is more vulnerable than adipogenic potential to radiation and chemotherapy, and this confers a risk for an abnormal fat-bone axis in survivors following cancer therapy and bone marrow transplantation. This review provides a summary of data from animal and human studies describing the relationship between marrow adipose tissue and hematopoiesis, bone mineral density, bone strength, and metabolic function. The significance of marrow adiposity in other metabolic disorders such as osteoporosis, diabetes mellitus, and estrogen and growth hormone deficiency are also discussed. We conclude that marrow adipose tissue is an active endocrine organ with important metabolic functions contributing to bone energy maintenance, osteogenesis, bone remodeling, and hematopoiesis. Future studies on the metabolic role of marrow adipose tissue may provide the critical insight necessary for selecting targeted therapeutic interventions to improve altered hematopoiesis and augment skeletal remodeling in cancer survivors.

Reliability of measuring the fat content of the lumbar vertebral marrow and paraspinal muscles using MRI mDIXON-Quant sequence

PURPOSE

We aimed to assess the reliability of measuring the fat content of the lumbar vertebral marrow and the paraspinal muscles using magnetic resonance imaging (MRI) mDIXON-Quant sequence.

METHODS

Thirty-one healthy volunteers were included. All participants underwent liver mDIXON-Quant imaging on a 3.0 T Philips MRI scanner by observer A. Within two weeks, observer B repeated the scan. After the examination, each observer independently measured the fat content of the third lumbar vertebra (L3), and the psoas (PS), erector spinae (ES), and multifidus (MF) muscles on central L3 axial images. After two weeks, each observer repeated the same measurements. They were blinded to their previous results. Reliability was estimated by evaluating the repeatability and reproducibility.

RESULTS

The repeatability of the fat content measurements of L3, PS, ES, and MF was high. The intraclass correlation coefficients of the fat content of L3, PS, ES, and MF were 0.997, 0.984, 0.997, and 0.995 for observer A and 0.948, 0.974, 0.963, and 0.995 for observer B, respectively. The reproducibility of the measurement of the fat content of L3, PS, ES, and MF was high, and the interclass correlation coefficients were 0.984, 0.981, 0.977, and 0.998, respectively.

CONCLUSION

Using mDIXON-Quant imaging to measure the fat content of the lumbar vertebral marrow and paraspinal muscles shows high reliability and is suitable for use in clinical practice.

Injuries of the adolescent girl athlete: a review of imaging findings

With the rising participation of girls in sports at both the recreational and elite levels, there has also been increased awareness of injuries common in this athlete population. Anatomic differences between boys and girls cause girl athletes to be predisposed to certain injuries. Certain behavioral patterns, such as eating disorders, also cause problems specific to girl athletes that may result in injury. Imaging plays a large role in diagnosis and ongoing management, but there has been only scant literature dedicated to the specific topic of imaging in girl athletes. The purpose of this article is to review the imaging findings and recommendations for injuries and other conditions affecting the adolescent girl athlete. This article first provides an overview of the key anatomic differences between boys and girls, including both static and dynamic factors, as well as non-anatomic differences, such as hormonal factors, and discusses how these differences contribute to the injury patterns that are seen more typically in girls. The article then reviews the imaging findings in injuries that are commonly seen in girl athletes. There is also a discussion of the "female athlete triad," which consists of osteoporosis, disordered eating, and amenorrhea, and the role of imaging in this condition.

The Unique Metabolic Characteristics of Bone Marrow Adipose Tissue

Bone marrow adipose tissue (MAT) is distinct from white adipose tissue (WAT) or brown adipose tissue (BAT) for its location, feature and function. As a largely ignored adipose depot, it is situated in bone marrow space and resided with bone tissue side-by-side. MAT is considered not only as a regulator of bone metabolism through paracrine, but also as a functionally particular adipose tissue that may contribute to global metabolism. Adipokines, inflammatory factors and other molecules derived from bone marrow adipocytes may exert systematic effects. In this review, we summary the evidence from several aspects including development, distribution, histological features and phenotype to elaborate the basic characteristics of MAT. We discuss the association between bone metabolism and MAT, and highlight our current understanding of this special adipose tissue. We further demonstrate the probable relationship between MAT and energy metabolism, as well as glucose metabolism. On the basis of preliminary results from animal model and clinical studies, we propose that MAT has its unique secretory and metabolic function, although there is no in-depth study at present.

The paradox of marrow adipose tissue in anorexia nervosa

Anorexia nervosa (AN) is a psychiatric disorder characterized by inappropriate nutrient intake resulting in low body weight. Multiple hormonal adaptations facilitate decreased energy expenditure in this state of caloric deprivation including non-thyroidal illness syndrome, growth hormone resistance, and hypogonadotropic hypogonadism. Although these hormonal adaptations confer a survival advantage during periods of negative energy balance, they contribute to the long-term medical complications associated with AN, the most common of which is significant bone loss and an increased risk of fracture. In recent years, marrow adipose tissue (MAT) has emerged as an important potential determinant of the low bone mass state characteristic of AN. Unlike subcutaneous and visceral adipose tissue depots which are low in AN, MAT levels are paradoxically elevated and are inversely associated with BMD. In this review, we discuss what is known about MAT in AN and the proposed hormonal determinants of this adipose tissue depot.

Effects of Anorexia Nervosa on Bone Metabolism

Anorexia nervosa is a psychiatric disease characterized by a low-weight state due to self-induced starvation. This disorder, which predominantly affects women, is associated with hormonal adaptations that minimize energy expenditure in the setting of low nutrient intake. These adaptations include GH resistance, functional hypothalamic amenorrhea, and nonthyroidal illness syndrome. Although these adaptations may be beneficial to short-term survival, they contribute to the significant and often persistent morbidity associated with this disorder, including bone loss, which affects >85% of women. We review the hormonal adaptions to undernutrition, review hormonal treatments that have been studied for both the underlying disorder as well as for the associated decreased bone mass, and discuss the important challenges that remain, including the lack of long-term treatments for bone loss in this chronic disorder and the fact that despite recovery, many individuals who experience bone loss as adolescents have chronic deficits and an increased risk of fracture in adulthood.

Novel leptin receptor signaling mutants identify location and sex-dependent modulation of bone density, adiposity, and growth

Leptin, a hormone primarily produced by adipocytes, contributes to the regulation of bone health by modulating bone density, growth and adiposity. Upon leptin binding, multiple sites of the long form of the leptin receptor (LepRb) are phosphorylated to trigger activation of downstream signaling pathways. To address the role of LepRb-signaling pathways in bone health, we compared the effects of three LepRb mutations on bone density, adiposity, and growth in male and female mice. The ∆65 mutation, which lacks the known tyrosine phosphorylation sites, caused obesity and the most dramatic bone phenotype marked by excessive bone adiposity, osteoporosis, and decreased growth, consistent with the phenotype of db/db and ob/ob mice that fully lack leptin receptor signaling. Mutation of LepRb Tyr ₁₁₃₈ , which results in an inability to recruit and phosphorylate signal transducer and activator of transcription 3, also caused obesity, but bone loss and adiposity were more dominant in male mice and no growth defect was observed. In contrast, mutation of LepRb Tyr ₉₈₅ , which blocks SHP2/SOCS3 recruitment to LepRb and contributes to leptin hypersensitivity, promoted increased femur bone density only in male mice, while marrow adiposity and bone growth were not affected. Additional analyses of vertebral trabecular bone volume indicate that only the Tyr ₁₁₃₈ mutant mice exhibit bone loss in vertebrae. Together, our findings suggest that the phosphorylation status of specific sites of the LepRb contribute to the sex- and location-dependent bone responses to leptin. Unraveling the mechanisms by which leptin responses are sex- and location-dependent can contribute to the development of uniquely targeted osteoporosis therapies.

Update on bone density measurements and their interpretation in children and adolescents

Following the increased awareness about the central role of the pediatric age in building bone for life, clinicians face more than ever the necessity of assessing bone health in pediatric subjects at risk for early bone mass derangements or in healthy children, in order to optimize their bone mass accrual and prevent osteoporosis. Although the diagnosis of osteoporosis is not made solely upon bone mineral density measurements during growth, such determination can be very useful in the follow-up of pediatric patients with primary and secondary osteoporosis. The ideal instrument would give information on the mineral content and density of the bone, and on its architecture. It should be able to perform the measurements on the skeletal sites where fractures are more frequent, and it should be minimally invasive, accurate, precise and rapid. Unfortunately, none of the techniques currently utilized fulfills all requirements. In the present review, we focus on the pediatric use of dual-energy X-ray absorptiometry (DXA), quantitative computed tomography (QCT), peripheral QCT (pQCT), and magnetic resonance imaging (MRI), highlighting advantages and limits for their use and providing indications for bone densitometry interpretation and of vertebral fractures diagnosis in pediatric subjects.

Magnetic resonance imaging and spectroscopy evidence of efficacy for adrenal and gonadal hormone replacement therapy in anorexia nervosa

PURPOSE

Dehydroepiandrosterone (DHEA)+estrogen/progestin therapy for adolescent girls with anorexia nervosa (AN) has the potential to arrest bone loss. The primary aim of this study was to test the effects of DHEA+estrogen/progestin therapy in adolescent girls with AN on bone marrow in the distal femur using magnetic resonance imaging (MRI) and spectroscopy.

METHODS

Seventy adolescent girls with AN were enrolled in a double blind, randomized, placebo-controlled trial at two urban hospital-based programs.

INTERVENTION

Seventy-six girls were randomly assigned to receive 12months of either oral micronized DHEA or placebo. DHEA was administered with conjugated equine estrogens (0.3mg daily) for 3months, then an oral contraceptive (20μg ethinyl estradiol/ 0.1mg levonorgestrel) for 9months. The primary outcome measure was bone marrow fat by MRI and magnetic resonance spectroscopy (MRS).

RESULTS

T2 of the water resonance dropped significantly less in the active vs. placebo group over 12months at both the medial and lateral distal femur (p=0.02). Body mass index (BMI) was a significant effect modifier for T1 and for T2 of unsaturated (T2_unsat) and saturated fat (T2_sat) in the lateral distal femur. Positive effects of the treatment of DHEA+estrogen/progestin were seen primarily for girls above a BMI of about 18kg/m².

CONCLUSIONS

These findings suggest treatment with oral DHEA+estrogen/progestin arrests the age- and disease-related changes in marrow fat composition in the lateral distal femur reported previously in this population.

Adipokines and bone status in a cohort of anorexic patients

INTRODUCTION

Bone loss in anorexia nervosa (AN) is multifactorial; its mechanisms are not yet clearly understood and may vary depending on disease duration and severity. To determine to what extent adipokines may be involved in the bone alterations found in anorexic patients, we evaluated plasma levels for leptin, adiponectin and Pref-1 against other clinical and biological parameters in a population of anorexic patients split according to weight and bone status.

METHODS

Plasma concentrations of leptin, total adiponectin, high molecular weight (HMW) adiponectin, and Pref-1 were measured. The ratio of HMW adiponectin to total adiponectin - HMW (percentage) - was calculated. We divided our population into 5 groups with different phenotypes characterizing the severity of the disease and/or the severity of bone involvement: 1 - Normal BMD and body mass index (BMI): recovery from AN; 2 - Osteopenia (-2<Z-score<-1) and BMI>17kg/m²; 3 - Osteopenia and BMI≤17kg/m²; 4 - Osteoporosis (Z-score≤-2) and BMI>17kg/m²; 5 - Osteoporosis and BMI≤17kg/m².

RESULTS

The study involved 80 anorexia nervosa patients. Mean BMI was 16.8±2.4kg/m². No significant difference was found in total and HMW adiponectin plasma concentrations between the 5 groups. HMW (percentage) was significantly higher in group 5 compared to group 1. Leptin was significantly lower in groups 3 and 5 compared to the other groups. For the whole group femoral neck and hip BMD correlated negatively with total adiponectin and HMW adiponectin. No correlation was found between BMD (whatever the site) and plasma leptin. Multivariate analysis revealed that 2 factors - leptin and BMI - explained 10% of the variance in spine BMD. For femoral neck BMD, the 2 explanatory factors were BMI and total adiponectin which explained 14% of the variance in BMD. For total hip BMD, 27% of the variance in BMD was explained by 3 factors: leptin, BMI, and total adiponectin.

CONCLUSION

Bone status in anorexia nervosa is mainly determined by BMI, leptin and adiponectin.

Heterogeneity of adipose tissue in development and metabolic function

Adipose tissue is a central metabolic organ. Unlike other organs, adipose tissue is compartmentalized into individual depots and distributed throughout the body. These different adipose depots show major functional differences and risk associations for developing metabolic syndrome. Recent advances in lineage tracing demonstrate that individual adipose depots are composed of adipocytes that are derived from distinct precursor populations, giving rise to different populations of energy-storing white adipocytes. Moreover, distinct lineages of energy-dissipating brown and beige adipocytes exist in discrete depots or within white adipose tissue depots. In this Review, we discuss developmental and functional heterogeneity, as well as sexual dimorphism, between and within individual adipose tissue depots. We highlight current data relating to the differences between subcutaneous and visceral white adipose tissue in the development of metabolic dysfunction, with special emphasis on adipose tissue expansion and remodeling of the extracellular matrix. Moreover, we provide a detailed overview of adipose tissue development as well as the consensus and controversies relating to adult adipocyte precursor populations.

Adult stem cells in psychiatric disorders - New discoveries in peripheral blood

The new area of research in psychiatric disorders is concerned with abnormal regeneration processes. The role of brain neurogenesis has been studied for decades. New discoveries, concerned with the pluripotency of VSEL cells and the role of factors involved in stem cell trafficking in peripheral blood create hope that it will be possible to develop a better understanding of the processes of neuroregeneration/neurodegeneration. There is an ongoing research investigating concentrations of: sphingosine -1-phosphate, SDF-1, elements of complement cascade, and stem cells in peripheral blood, including their possible connection to psychiatric disorders. Collected data, suggesting an abnormal course of regeneration processes in psychiatric disorders, raises hope of finding new potential markers of psychosis and anxiety disorders.