Bone marrow adipose tissue is an endocrine organ that contributes to increased circulating adiponectin during caloric restriction

Pathological roles of bone marrow adipocyte-derived monocyte chemotactic protein-1 in type 2 diabetic mice

Type 2 diabetes mellitus (T2DM) has become a prevalent public health concern, with beta-cell dysfunction involved in its pathogenesis. Bone marrow adipose tissue (BMAT) increases in both the quantity and area in individuals with T2DM along with heightened monocyte chemotactic protein-1 (MCP-1) secretion. This study aims to investigate the influence and underlying mechanisms of MCP-1 originating from bone marrow adipocytes (BMAs) on systemic glucose homeostasis in T2DM. Initially, a substantial decrease in the proliferation and glucose-stimulated insulin secretion (GSIS) of islet cells was observed. Moreover, a comparative analysis between the control (Ctrl) group and db/db mice revealed significant alterations in the gene expression profiles of whole bone marrow cells, with a noteworthy upregulation of Mcp-1. And the primary enriched pathways included chemokine signaling pathway and AGE-RAGE signaling pathway in diabetic complications. In addition, the level of MCP-1 was distinctly elevated in BMA-derived conditional media (CM), leading to a substantial inhibition of proliferation, GSIS and the protein level of phosphorylated Akt (p-Akt) in Min6 cells. After blocking MCP-1 pathway, we observed a restoration of p-Akt and the proliferation of islet cells, resulting in a marked improvement in disordered glucose homeostasis. In summary, there is an accumulation of BMAs in T2DM, which secrete excessive MCP-1, exacerbating the abnormal accumulation of BMAs in the bone marrow cavity through paracrine signaling. The upregulated MCP-1, in turn, worsens glucose metabolism disorder by inhibiting the proliferation and insulin secretion of islet cells through an endocrine pathway. Inhibiting MCP-1 signaling can partially restore the proliferation and insulin secretion of islet cells, ultimately ameliorating glucose metabolism disorder. It's worth noting that to delve deeper into the impact of MCP-1 derived from BMAs on islet cells and its potential mechanisms, it is imperative to develop genetically engineered mice with conditional Mcp-1 knockout from BMAs.

TET3 plays a critical role in white adipose development and diet-induced remodeling

Maintaining healthy adipose tissue is crucial for metabolic health, requiring a deeper understanding of adipocyte development and response to high-calorie diets. This study highlights the importance of TET3 during white adipose tissue (WAT) development and expansion. Selective depletion of Tet3 in adipose precursor cells (APCs) reduces adipogenesis, protects against diet-induced adipose expansion, and enhances whole-body metabolism. Transcriptomic analysis of wild-type and Tet3 knockout (KO) APCs unveiled TET3 target genes, including Pparg and several genes linked to the extracellular matrix, pivotal for adipogenesis and remodeling. DNA methylation profiling and functional studies underscore the importance of DNA demethylation in gene regulation. Remarkably, targeted DNA demethylation at the Pparg promoter restored its transcription. In conclusion, TET3 significantly governs adipogenesis and diet-induced adipose expansion by regulating key target genes in APCs.

The Impact of Interventional Weight Loss on Bone Marrow Adipose Tissue in People Living with Obesity and Its Connection to Bone Metabolism

This review focuses on providing physicians with insights into the complex relationship between bone marrow adipose tissue (BMAT) and bone health, in the context of weight loss through caloric restriction or metabolic and bariatric surgery (MBS), in people living with obesity (PwO). We summarize the complex relationship between BMAT and bone health, provide an overview of noninvasive imaging techniques to quantify human BMAT, and discuss clinical studies measuring BMAT in PwO before and after weight loss. The relationship between BMAT and bone is subject to variations based on factors such as age, sex, menopausal status, skeletal sites, nutritional status, and metabolic conditions. The Bone Marrow Adiposity Society (BMAS) recommends standardizing imaging protocols to increase comparability across studies and sites, they have identified both water-fat imaging (WFI) and spectroscopy (1H-MRS) as accepted standards for in vivo quantification of BMAT. Clinical studies measuring BMAT in PwO are limited and have shown contradictory results. However, BMAT tends to be higher in patients with the highest visceral adiposity, and inverse associations between BMAT and bone mineral density (BMD) have been consistently found in PwO. Furthermore, BMAT levels tend to decrease after caloric restriction-induced weight loss. Although weight loss was associated with overall fat loss, a reduction in BMAT did not always follow the changes in fat volume in other tissues. The effects of MBS on BMAT are not consistent among the studies, which is at least partly related to the differences in the study population, skeletal site, and duration of the follow-up. Overall, gastric bypass appears to decrease BMAT, particularly in patients with diabetes and postmenopausal women, whereas sleeve gastrectomy appears to increase BMAT. More research is necessary to evaluate changes in BMAT and its connection to bone metabolism, either in PwO or in cases of weight loss through caloric restriction or MBS, to better understand the role of BMAT in this context and determine the local or systemic factors involved.

Adipokines from adipose tissue and common variable immunodeficiency: Is there any association?

Adiponectin and leptin are adipokines, secreted by white adipose tissue (WAT), which play an important role in energy homeostasis. Some evidence has shown that adipokine-producing adipose cells present in the bone marrow (BM) appear to exert an influence on hematopoiesis and B cell development. Common variable immunodeficiency (CVID) is one of the most common inborn errors of immunity in humans. In CVID, numerical and/or functional defects of B cells and their precursors result in hypogammaglobulinemia, usually Immunoglobulin (Ig) A and IgG. Manifestations of CVID include immunodeficiency, autoimmunity, inflammation and lymphoproliferation, resulting in a wide range of phenotypes. How adipokines interact and influence the pathophysiology of CVID is still unclear. In this review, we seek to summarize the aspects known so far concerning the interface between adipokines, B cells and CVID. More research is needed to fully understand these interactions; this knowledge is a potential avenue for the discovery of useful biomarkers and may provide new therapeutic targets for the treatment of patients with CVID and related diseases.

Role of bone marrow adipocytes in bone metastasis development and progression: a systematic review

Purpose

Bone marrow adipocytes (BMAs) are the most plentiful cells in the bone marrow and function as an endocrine organ by producing fatty acids, cytokines, and adipokines. Consequently, BMAs can interact with tumor cells, influencing both tumor growth and the onset and progression of bone metastasis. This review aims to systematically evaluate the role of BMAs in the development and progression of bone metastasis.

Methods

A comprehensive search was conducted on PubMed, Web of Science, and Scopus electronic databases, following the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) statement standards, to identify studies published from March 2013 to June 2023. Two independent reviewers assessed and screened the literature, extracted the data, and evaluated the quality of the studies. The body of evidence was evaluated and graded using the ROBINS-I tool for non-randomized studies of interventions and the Systematic Review Centre for Laboratory Animal Experimentation (SYRCLE) tool for in vivo studies. The results were synthesized using descriptive methods.

Results

The search yielded a total of 463 studies, of which 17 studies were included in the final analysis, including 15 preclinical studies and two non-randomized clinical studies. Analysis of preclinical studies revealed that BMAs play a significant role in bone metastasis, particularly in prostate cancer followed by breast and malignant melanoma cancers. BMAs primarily influence cancer cells by inducing a glycolytic phenotype and releasing or upregulating soluble factors, chemokines, cytokines, adipokines, tumor-derived fatty acid-binding protein (FABP), and members of the nuclear receptor superfamily, such as chemokine (C-C motif) ligand 7 (CCL7), C-X-C Motif Chemokine Ligand (CXCL)1, CXCL2, interleukin (IL)-1β, IL-6, FABP4, and peroxisome proliferator-activated receptor γ (PPARγ). These factors also contribute to adipocyte lipolysis and regulate a pro-inflammatory phenotype in BMAs. However, the number of clinical studies is limited, and definitive conclusions cannot be drawn.

Conclusion

The preclinical studies reviewed indicate that BMAs may play a crucial role in bone metastasis in prostate, breast, and malignant melanoma cancers. Nevertheless, further preclinical and clinical studies are needed to better understand the complex role and relationship between BMAs and cancer cells in the bone microenvironment. Targeting BMAs in combination with standard treatments holds promise as a potential therapeutic strategy for bone metastasis.

Obesity as a risk factor for multiple myeloma: insight on the role of adipokines

Multiple myeloma (MM) is a hematologic disorder characterized by the accumulation of malignant plasma cells in the bone marrow. Genetic and environmental factors are contributed to the etiology of MM. Notably, studies have shown that obesity increases the risk of MM and worsens outcomes for MM patients. Adipokines play an important role in mediating the close association between MM and metabolic derangements. In this review, we summarize the epidemiologic studies to show that the risk of MM is increased in obese. Accumulating clinical evidence suggests that adipokines could display a correlation with MM. In vitro and in vivo studies have shown that adipokines are linked to MM, including roles in the biological behavior of MM cells, cancer-associated bone loss, the progression of MM, and drug resistance. Current and potential therapeutic strategies targeted to adipokines are discussed, proposing that adipokines can guide early patient diagnosis and treatment.

Bone marrow adiposity modulation after long duration spaceflight in astronauts

Space travel requires metabolic adaptations from multiple systems. While vital to bone and blood production, human bone marrow adipose (BMA) tissue modulation in space is unknown. Here we show significant downregulation of the lumbar vertebrae BMA in 14 astronauts, 41 days after landing from six months' missions on the International Space Station. Spectral analyses indicated depletion of marrow adipose reserves. We then demonstrate enhanced erythropoiesis temporally related to low BMA. Next, we demonstrated systemic and then, local lumbar vertebrae bone anabolism temporally related to low BMA. These support the hypothesis that BMA is a preferential local energy source supplying the hypermetabolic bone marrow postflight, leading to its downregulation. A late postflight upregulation abolished the lower BMA of female astronauts and BMA modulation amplitude was higher in younger astronauts. The study design in the extreme environment of space can limit these conclusions. BMA modulation in astronauts can help explain observations on Earth.

Orchiectomy sensitizes cortical bone in male mice to the harmful effects of kynurenine

Kynurenine (Kyn) is a tryptophan metabolite that increases with age and promotes musculoskeletal dysfunction. We previously found a sexually dimorphic pattern in how Kyn affects bone, with harmful effects more prevalent in females than males. This raises the possibility that male sex steroids might exert a protective effect that blunts the effects of Kyn in males. To test this, orchiectomy (ORX) or sham surgeries were performed on 6-month-old C57BL/6 mice, after which mice received Kyn (10 mg/kg) or vehicle via intraperitoneal injection, once daily, 5×/week, for four weeks. Bone histomorphometry, DXA, microCT, and serum marker analyses were performed after sacrifice. In vitro studies were performed to specifically test the effect of testosterone on activation of aryl hydrocarbon receptor (AhR)-mediated signaling by Kyn in mesenchymal-lineage cells. Kyn treatment reduced cortical bone mass in ORX- but not sham-operated mice. Trabecular bone was unaffected. Kyn's effects on cortical bone in ORX mice were attributed primarily to enhanced endosteal bone resorption activity. Bone marrow adipose tissue was increased in Kyn-treated ORX animals but was unchanged by Kyn in sham-operated mice. ORX surgery increased mRNA expression of the aryl hydrocarbon receptor (AhR) and its target gene Cyp1a1 in the bone, suggesting a priming and/or amplification of AhR signaling pathways. Mechanistic in vitro studies revealed that testosterone blunted Kyn-stimulated AhR transcriptional activity and Cyp1a1 expression in mesenchymal-linage cells. These data suggest a protective role for male sex steroids in blunting the harmful effects of Kyn in cortical bone. Therefore, testosterone may play an important role in regulating Kyn/AhR signaling in musculoskeletal tissues, suggesting crosstalk between male sex steroids and Kyn signaling may influence age-associated musculoskeletal frailty.

Modified activity-based anorexia paradigm dampens chronic food restriction-induced hyperadiponectinemia in adolescent female mice

Anorexia nervosa (AN) is a chronic, life-threatening disease with mental and physical components that include excessive weight loss, persistent food restriction, and altered body image. It is sometimes accompanied by hyperactivity, day-night reversal, and amenorrhea. No medications have been approved specific to the treatment of AN, partially due to its unclear etiopathogenesis. Because adiponectin is an appetite-regulating cytokine released by adipose tissue, we hypothesized that it could be useful as a specific biomarker that reflects the disease state of AN, so we developed a modified AN mouse model to test this hypothesis. Twenty-eight 3-week-old female C57BL/6J mice were randomly assigned to the following groups: 1) no intervention; 2) running wheel access; 3) food restriction (FR); and 4) activity-based anorexia (ABA) that included running wheel access plus FR. After a 10-day cage adaptation period, the mice of the FR and ABA groups were given 40% of their baseline food intake until 30% weight reduction (acute FR), then the body weight was maintained for 2.5 weeks (chronic FR). Running wheel activity and the incidence of the estrous cycle were assessed. Spontaneous food restriction and the plasma adiponectin level were evaluated at the end of the acute and chronic FR phases. An increase in running wheel activity was found in the light phase, and amenorrhea was found solely in the ABA group, which indicates that this is a good model of AN. This group showed a slight decrease in spontaneous food intake accompanied with an attenuated level of normally induced plasma adiponectin at the end of the chronic FR phase. These results indicate that the plasma adiponectin level may be a useful candidate biomarker for the status or stage of AN.

Adiponectin affects the migration ability of bone marrow-derived mesenchymal stem cells via the regulation of hypoxia inducible factor 1α

BACKGROUND

Bone marrow (BM) is progressively filled with adipocytes during aging process. Thus, BM adipocytes-derived adiponectin (APN) affects the function of bone marrow-derived mesenchymal stem cells (BMSCs). However, little is known about the effect of APN on migration ability of BMSCs cultured under hypoxic conditions, which is similar to the BM microenvironment.

RESULTS

We found that the population and migration ability of BMSCs from APN KO mice was higher than that of WT mice due to increased stability of hypoxia inducible factor 1α (HIF1α). Stem cell factor (SCF)-activated STAT3 stimulated the induction of HIF1α which further stimulated SCF production, indicating that the SCF/STAT3/HIF1α positive loop was highly activated in the absence of APN. It implies that APN negatively regulated this positive loop by stimulating HIF1α degradation via the inactivation of GSK3β. Furthermore, APN KO BMSCs were highly migratory toward EL-4 lymphoma, and the interaction between CD44 in BMSCs and hyaluronic acid (HA) from EL-4 enhanced the migration of BMSCs. On the other hand, the migrated BMSCs recruited CD8+ T cells into the EL-4 tumor tissue, resulting in the retardation of tumor growth. Additionally, gradually increased APN in BM on the aging process affects migration and related functions of BMSCs, thus aged APN KO mice showed more significant suppression of EL-4 growth than young APN KO mice due to higher migration and recruitment of CD8+ T cells.

CONCLUSION

APN deficiency enhances CD44-mediated migration ability of BMSCs in the hypoxic conditions by the SCF/STAT3/HIF1α positive loop and influences the migration ability of BMSCs for a longer time depending on the aging process. Video Abstract.

Prolonged Antibiotic Exposure during Adolescence Dysregulates Liver Metabolism and Promotes Adiposity in Mice

Antibiotic administration during early life has been shown to have lasting effects on the gut microbiota, which have been linked to sustained alterations in liver metabolism and adiposity. Recent investigations have discerned that the gut microbiota continues to develop toward an adult-like profile during adolescence. However, the impact of antibiotic exposure during adolescence on metabolism and adiposity is unclear. Herein, a retrospective analysis of Medicaid claims data was performed, which indicated that tetracycline class antibiotics are commonly prescribed for the systemic treatment of adolescent acne. The purpose of this was to discern the impact of a prolonged tetracycline antibiotic exposure during adolescence on the gut microbiota, liver metabolism, and adiposity. Male C57BL/6T specific pathogen-free mice were administered a tetracycline antibiotic during the pubertal/postpubertal adolescent growth phase. Groups were euthanized at different time points to assess immediate and sustained antibiotic treatment effects. Antibiotic exposure during adolescence caused lasting genera-level shifts in the intestinal bacteriome and persistent dysregulation of metabolic pathways in the liver. Dysregulated hepatic metabolism was linked to sustained disruption of the intestinal farnesoid X receptor-fibroblast growth factor 15 axis, a gut-liver endocrine axis that supports metabolic homeostasis. Antibiotic exposure during adolescence increased subcutaneous, visceral, and marrow adiposity, which intriguingly manifested following antibiotic therapy. This preclinical work highlights that prolonged antibiotic courses for the clinical treatment of adolescent acne may have unintended deleterious effects on liver metabolism and adiposity.

Reciprocal Effect of Environmental Stimuli to Regulate the Adipogenesis and Osteogenesis Fate Decision in Bone Marrow-Derived Mesenchymal Stem Cells (BM-MSCs)

Mesenchymal stem cells derived from bone marrow (BM-MSCs) can differentiate into adipocytes and osteoblasts. Various external stimuli, including environmental contaminants, heavy metals, dietary, and physical factors, are shown to influence the fate decision of BM-MSCs toward adipogenesis or osteogenesis. The balance of osteogenesis and adipogenesis is critical for the maintenance of bone homeostasis, and the interruption of BM-MSCs lineage commitment is associated with human health issues, such as fracture, osteoporosis, osteopenia, and osteonecrosis. This review focuses on how external stimuli shift the fate of BM-MSCs towards adipogenesis or osteogenesis. Future studies are needed to understand the impact of these external stimuli on bone health and elucidate the underlying mechanisms of BM-MSCs differentiation. This knowledge will inform efforts to prevent bone-related diseases and develop therapeutic approaches to treat bone disorders associated with various pathological conditions.

APN Expression in Serum and Corpus Luteum: Regulation of Luteal Steroidogenesis Is Possibly Dependent on the AdipoR2/AMPK Pathway in Goats

Adiponectin (APN) is an essential adipokine for a variety of reproductive processes. To investigate the role of APN in goat corpora lutea (CLs), CLs and sera from different luteal phases were collected for analysis. The results showed that the APN structure and content had no significant divergence in different luteal phases both in CLs and sera; however, high molecular weight APN was dominant in serum, while low molecular weight APN was more present in CLs. The luteal expression of both AdipoR1/2 and T-cadherin (T-Ca) increased on D11 and 17. APN and its receptors (AdipoR1/2 and T-Ca) were mainly expressed in goat luteal steroidogenic cells. The steroidogenesis and APN structure in pregnant CLs had a similar model as in the mid-cycle CLs. To further explore the effects and mechanisms of APN in CLs, steroidogenic cells from pregnant CLs were isolated to detect the AMPK-mediated pathway by the activation of APN (AdipoRon) and knockdown of APN receptors. The results revealed that P-AMPK in goat luteal cells increased after incubation with APN (1 μg/mL) or AdipoRon (25 μM) for 1 h, and progesterone (P4) and steroidogenic proteins levels (STAR/CYP11A1/HSD3B) decreased after 24 h. APN did not affect the steroidogenic protein expression when cells were pretreated with Compound C or SiAMPK. APN increased P-AMPK and reduced the CYP11A1 expression and P4 levels when cells were pretreated with SiAdipoR1 or SiT-Ca, while APN failed to affect P-AMPK, the CYP11A1 expression or the P4 levels when pretreated with SiAdipoR2. Therefore, the different structural forms of APN in CLs and sera may possess distinct functions; APN might regulate luteal steroidogenesis through AdipoR2 which is most likely dependent on AMPK.

Discoidin domain receptors; an ancient family of collagen receptors has major roles in bone development, regeneration and metabolism

The extracellular matrix (ECM) niche plays a critical role in determining cellular behavior during bone development including the differentiation and lineage allocation of skeletal progenitor cells to chondrocytes, osteoblasts, or marrow adipocytes. As the major ECM component in mineralized tissues, collagen has instructive as well as structural roles during bone development and is required for bone cell differentiation. Cells sense their extracellular environment using specific cell surface receptors. For many years, specific β1 integrins were considered the main collagen receptors in bone, but, more recently, the important role of a second, more primordial collagen receptor family, the discoidin domain receptors, has become apparent. This review will specifically focus on the roles of discoidin domain receptors in mineralized tissue development as well as related functions in abnormal bone formation, regeneration and metabolism.

Turning the spotlight on bone marrow adipocytes in haematological malignancy and non-malignant conditions

Whilst bone marrow adipocytes (BMAd) have long been appreciated by clinical haemato-pathologists, it is only relatively recently, in the face of emerging data, that the adipocytic niche has come under the watchful eye of biologists. There is now mounting evidence to suggest that BMAds are not just a simple structural entity of bone marrow microenvironments but a bona fide driver of physio- and pathophysiological processes relevant to multiple aspects of health and disease. Whilst the truly multifaceted nature of BMAds has only just begun to emerge, paradigms have shifted already for normal, malignant and non-malignant haemopoiesis incorporating a view of adipocyte regulation. Major efforts are ongoing, to delineate the routes by which BMAds participate in health and disease with a final aim of achieving clinical tractability. This review summarises the emerging role of BMAds across the spectrum of normal and pathological haematological conditions with a particular focus on its impact on cancer therapy.

Prospects of potential adipokines as therapeutic agents in obesity-linked atherogenic dyslipidemia and insulin resistance

BACKGROUND

In normal circumstances, AT secretes anti-inflammatory adipokines (AAKs) which regulates lipid metabolism, insulin sensitivity, vascular hemostasis, and angiogenesis. However, during obesity AT dysfunction occurs and leads to microvascular imbalance and secretes several pro-inflammatory adipokines (PAKs), thereby favoring atherogenic dyslipidemia and insulin resistance. Literature suggests decreased levels of circulating AAKs and increased levels of PAKs in obesity-linked disorders. Importantly, AAKs have been reported to play a vital role in obesity-linked metabolic disorders mainly insulin resistance, type-2 diabetes mellitus and coronary heart diseases. Interestingly, AAKs counteract the microvascular imbalance in AT and exert cardioprotection via several signaling pathways such as PI3-AKT/PKB pathway. Although literature reviews have presented a number of investigations detailing specific pathways involved in obesity-linked disorders, literature concerning AT dysfunction and AAKs remains sketchy. In view of the above, in the present contribution an effort has been made to provide an insight on the AT dysfunction and role of AAKs in modulating the obesity and obesity-linked atherogenesis and insulin resistance.

MAIN BODY

"Obesity-linked insulin resistance", "obesity-linked cardiometabolic disease", "anti-inflammatory adipokines", "pro-inflammatory adipokines", "adipose tissue dysfunction" and "obesity-linked microvascular dysfunction" are the keywords used for searching article. Google scholar, Google, Pubmed and Scopus were used as search engines for the articles.

CONCLUSIONS

This review offers an overview on the pathophysiology of obesity, management of obesity-linked disorders, and areas in need of attention such as novel therapeutic adipokines and their possible future perspectives as therapeutic agents.

Oxylipin-PPARγ-initiated adipocyte senescence propagates secondary senescence in the bone marrow

The chronic use of glucocorticoids decreases bone mass and quality and increases bone-marrow adiposity, but the underlying mechanisms remain unclear. Here, we show that bone-marrow adipocyte (BMAd) lineage cells in adult mice undergo rapid cellular senescence upon glucocorticoid treatment. The senescent BMAds acquire a senescence-associated secretory phenotype, which spreads senescence in bone and bone marrow. Mechanistically, glucocorticoids increase the synthesis of oxylipins, such as 15d-PGJ2, for peroxisome proliferator-activated receptor gamma (PPARγ) activation. PPARγ stimulates the expression of key senescence genes and also promotes oxylipin synthesis in BMAds, forming a positive feedback loop. Transplanting senescent BMAds into the bone marrow of healthy mice is sufficient to induce the secondary spread of senescent cells and bone-loss phenotypes, whereas transplanting BMAds harboring a p16INK4a deletion did not show such effects. Thus, glucocorticoid treatment induces a lipid metabolic circuit that robustly triggers the senescence of BMAd lineage cells that, in turn, act as the mediators of glucocorticoid-induced bone deterioration.

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.

Adipose tissue and hematopoiesis: Friend or foe?

AIM

Hematopoietic stem cells are the origin of all hematopoietic cells. They have the self-renewal ability and can differentiate into various blood cells. In physiological state, most of the hematopoietic stem cells are dormant, and only a few cells proliferate to maintain hematopoietic homeostasis.

METHODS

This precise steady-state maintenance is regulated by complex mechanisms. Bone marrow adipocytes make up half of all cells in the bone marrow cavity, a feature that has attracted the attention of researchers from multiple fields. The adipocyte density within marrow increases during aging and obesity.

RESULTS

Recent studies have shown that bone marrow adipocytes play important roles in regulating hematopoiesis, but the effects of bone marrow adipocytes on hematopoiesis are often conflicting. Bone marrow adipocytes, participating in the formation of bone marrow hematopoietic microenvironment, influence hematopoiesis positively or negatively. In addition, other adipose tissue, especially white adipose tissue, also regulates hematopoiesis.

CONCLUSION

In this review, we describe the role of adipose tissue in hematological malignancies, which may be useful for understanding hematopoiesis and the pathogenesis of related diseases.

Vertebrae but not femur marrow fat transiently decreases in response to body weight loss in an 18-month randomized control trial

BACKGROUND

Increased levels of bone marrow adipose tissue (BMAT) are negatively associated with skeletal health and hematopoiesis. BMAT is known to increase with age; however, the effect of long-term weight loss on BMAT is still unknown.

OBJECTIVE

In this study, we examined BMAT response to lifestyle-induced weight loss in 138 participants (mean age 48 y; mean body mass index 31 kg/m²), who participated in the CENTRAL-MRI trial.

METHODS

Participants were randomized for dietary intervention of low-fat or low-carb, with or without physical activity. Magnetic resonance imaging (MRI) was used to quantify BMAT and other fat depots at baseline, six and eighteen months of intervention. Blood biomarkers were also measured at the same time points.

RESULTS

At baseline, the L3 vertebrae BMAT is positively associated with age, HDL cholesterol, HbA1c and adiponectin; but not with other fat depots or other metabolic markers tested. Following six months of dietary intervention, the L3 BMAT declined by an average of 3.1 %, followed by a return to baseline after eighteen months (p < 0.001 and p = 0.189 compared to baseline, respectively). The decrease of BMAT during the first six months was associated with a decrease in waist circumference, cholesterol, proximal-femur BMAT, and superficial subcutaneous adipose tissue (SAT), as well as with younger age. Nevertheless, BMAT changes did not correlate with changes in other fat depots.

CONCLUSIONS

We conclude that physiological weight loss can transiently reduce BMAT in adults, and this effect is more prominent in younger adults. Our findings suggest that BMAT storage and dynamics are largely independent of other fat depots or cardio-metabolic risk markers, highlighting its unique functions.

MiR-422a promotes adipogenesis via MeCP2 downregulation in human bone marrow mesenchymal stem cells

Methyl-CpG binding protein 2 (MeCP2) is a ubiquitous transcriptional regulator. The study of this protein has been mainly focused on the central nervous system because alterations of its expression are associated with neurological disorders such as Rett syndrome. However, young patients with Rett syndrome also suffer from osteoporosis, suggesting a role of MeCP2 in the differentiation of human bone marrow mesenchymal stromal cells (hBMSCs), the precursors of osteoblasts and adipocytes. Here, we report an in vitro downregulation of MeCP2 in hBMSCs undergoing adipogenic differentiation (AD) and in adipocytes of human and rat bone marrow tissue samples. This modulation does not depend on MeCP2 DNA methylation nor on mRNA levels but on differentially expressed miRNAs during AD. MiRNA profiling revealed that miR-422a and miR-483-5p are upregulated in hBMSC-derived adipocytes compared to their precursors. MiR-483-5p, but not miR-422a, is also up-regulated in hBMSC-derived osteoblasts, suggesting a specific role of the latter in the adipogenic process. Experimental modulation of intracellular levels of miR-422a and miR-483-5p affected MeCP2 expression through direct interaction with its 3' UTR elements, and the adipogenic process. Accordingly, the knockdown of MeCP2 in hBMSCs through MeCP2-targeting shRNA lentiviral vectors increased the levels of adipogenesis-related genes. Finally, since adipocytes released a higher amount of miR-422a in culture medium compared to hBMSCs we analyzed the levels of circulating miR-422a in patients with osteoporosis-a condition characterized by increased marrow adiposity-demonstrating that its levels are negatively correlated with T- and Z-scores. Overall, our findings suggest that miR-422a has a role in hBMSC adipogenesis by downregulating MeCP2 and its circulating levels are associated with bone mass loss in primary osteoporosis.

The role of WNT10B in physiology and disease: A 10-year update

WNT10B, a member of the WNT family of secreted glycoproteins, activates the WNT/β-catenin signaling cascade to control proliferation, stemness, pluripotency, and cell fate decisions. WNT10B plays roles in many tissues, including bone, adipocytes, skin, hair, muscle, placenta, and the immune system. Aberrant WNT10B signaling leads to several diseases, such as osteoporosis, obesity, split-hand/foot malformation (SHFM), fibrosis, dental anomalies, and cancer. We reviewed WNT10B a decade ago, and here we provide a comprehensive update to the field. Novel research on WNT10B has expanded to many more tissues and diseases. WNT10B polymorphisms and mutations correlate with many phenotypes, including bone mineral density, obesity, pig litter size, dog elbow dysplasia, and cow body size. In addition, the field has focused on the regulation of WNT10B using upstream mediators, such as microRNAs (miRNAs) and long non-coding RNAs (lncRNAs). We also discussed the therapeutic implications of WNT10B regulation. In summary, research conducted during 2012-2022 revealed several new, diverse functions in the role of WNT10B in physiology and disease.

Update on the Role of Glucocorticoid Signaling in Osteoblasts and Bone Marrow Adipocytes During Aging

PURPOSE OF REVIEW

Bone marrow adipose tissue (BMAT) in the skeleton likely plays a variety of physiological and pathophysiological roles that are not yet fully understood. In elucidating the complex relationship between bone and BMAT, glucocorticoids (GCs) are positioned to play a key role, as they have been implicated in the differentiation of bone marrow mesenchymal stem cells (BMSCs) between osteogenic and adipogenic lineages. The purpose of this review is to illuminate aspects of both endogenous and exogenous GC signaling, including the influence of GC receptors, in mechanisms of bone aging including relationships to BMAT.

RECENT FINDINGS

Harmful effects of GCs on bone mass involve several cellular pathways and events that can include BMSC differentiation bias toward adipogenesis and the influence of mature BMAT on bone remodeling through crosstalk. Interestingly, BMAT involvement remains poorly explored in GC-induced osteoporosis and warrants further investigation. This review provides an update on the current understanding of the role of glucocorticoids in the biology of osteoblasts and bone marrow adipocytes (BMAds).

Osteoporosis and Bone Marrow Adipose Tissue

PURPOSE OF REVIEW

This review focuses on the recent findings regarding bone marrow adipose tissue (BMAT) concerning bone health. We summarize the variations in BMAT in relation to age, sex, and skeletal sites, and provide an update on noninvasive imaging techniques to quantify human BMAT. Next, we discuss the role of BMAT in patients with osteoporosis and interventions that affect BMAT.

RECENT FINDINGS

There are wide individual variations with region-specific fluctuation and age- and gender-specific differences in BMAT content and composition. The Bone Marrow Adiposity Society (BMAS) recommendations aim to standardize imaging protocols to increase comparability across studies and sites. Water-fat imaging (WFI) seems an accurate and efficient alternative for spectroscopy (¹H-MRS). Most studies indicate that greater BMAT is associated with lower bone mineral density (BMD) and a higher prevalence of vertebral fractures. The proton density fat fraction (PDFF) and changes in lipid composition have been associated with an increased risk of fractures independently of BMD. Therefore, PDFF and lipid composition could potentially be future imaging biomarkers for assessing fracture risk. Evidence of the inhibitory effect of osteoporosis treatments on BMAT is still limited to a few randomized controlled trials. Moreover, results from the FRAME biopsy sub-study highlight contradictory findings on the effect of the sclerostin antibody romosozumab on BMAT. Further understanding of the role(s) of BMAT will provide insight into the pathogenesis of osteoporosis and may lead to targeted preventive and therapeutic strategies.

Bone circuitry and interorgan skeletal crosstalk

The past decade has seen significant advances in our understanding of skeletal homeostasis and the mechanisms that mediate the loss of bone integrity in disease. Recent breakthroughs have arisen mainly from identifying disease-causing mutations and modeling human bone disease in rodents, in essence, highlighting the integrative nature of skeletal physiology. It has become increasingly clear that bone cells, osteoblasts, osteoclasts, and osteocytes, communicate and regulate the fate of each other through RANK/RANKL/OPG, liver X receptors (LXRs), EphirinB2-EphB4 signaling, sphingolipids, and other membrane-associated proteins, such as semaphorins. Mounting evidence also showed that critical developmental pathways, namely, bone morphogenetic protein (BMP), NOTCH, and WNT, interact each other and play an important role in postnatal bone remodeling. The skeleton communicates not only with closely situated organs, such as bone marrow, muscle, and fat, but also with remote vital organs, such as the kidney, liver, and brain. The metabolic effect of bone-derived osteocalcin highlights a possible role of skeleton in energy homeostasis. Furthermore, studies using genetically modified rodent models disrupting the reciprocal relationship with tropic pituitary hormone and effector hormone have unraveled an independent role of pituitary hormone in skeletal remodeling beyond the role of regulating target endocrine glands. The cytokine-mediated skeletal actions and the evidence of local production of certain pituitary hormones by bone marrow-derived cells displays a unique endocrine-immune-skeletal connection. Here, we discuss recently elucidated mechanisms controlling the remodeling of bone, communication of bone cells with cells of other lineages, crosstalk between bone and vital organs, as well as opportunities for treating diseases of the skeleton.

Development and characterization of three cell culture systems to investigate the relationship between primary bone marrow adipocytes and myeloma cells

The unique properties of the bone marrow (BM) allow for migration and proliferation of multiple myeloma (MM) cells while also providing the perfect environment for development of quiescent, drug-resistant MM cell clones. BM adipocytes (BMAds) have recently been identified as important contributors to systemic adipokine levels, bone strength, hematopoiesis, and progression of metastatic and primary BM cancers, such as MM. Recent studies in myeloma suggest that BMAds can be reprogrammed by tumor cells to contribute to myeloma-induced bone disease, and, reciprocally, BMAds support MM cells in vitro. Importantly, most data investigating BMAds have been generated using adipocytes generated by differentiating BM-derived mesenchymal stromal cells (BMSCs) into adipocytes in vitro using adipogenic media, due to the extreme technical challenges associated with isolating and culturing primary adipocytes. However, if studies could be performed with primary adipocytes, then they likely will recapitulate in vivo biology better than BMSC-derived adipocytes, as the differentiation process is artificial and differs from in vivo differentiation, and progenitor cell(s) of the primary BMAd (pBMAds) may not be the same as the BMSCs precursors used for adipogenic differentiation in vitro. Therefore, we developed and refined three methods for culturing pBMAds: two-dimensional (2D) coverslips, 2D transwells, and three-dimensional (3D) silk scaffolds, all of which can be cultured alone or with MM cells to investigate bidirectional tumor-host signaling. To develop an in vitro model with a tissue-like structure to mimic the BM microenvironment, we developed the first 3D, tissue engineered model utilizing pBMAds derived from human BM. We found that pBMAds, which are extremely fragile, can be isolated and stably cultured in 2D for 10 days and in 3D for up to 4 week in vitro. To investigate the relationship between pBMAds and myeloma, MM cells can be added to investigate physical relationships through confocal imaging and soluble signaling molecules via mass spectrometry. In summary, we developed three in vitro cell culture systems to study pBMAds and myeloma cells, which could be adapted to investigate many diseases and biological processes involving the BM, including other bone-homing tumor types.

Resistance to energy metabolism - targeted therapy of AML cells residual in the bone marrow microenvironment

In response to the changing availability of nutrients and oxygen in the bone marrow microenvironment, acute myeloid leukemia (AML) cells continuously adjust their metabolic state. To meet the biochemical demands of their increased proliferation, AML cells strongly depend on mitochondrial oxidative phosphorylation (OXPHOS). Recent data indicate that a subset of AML cells remains quiescent and survives through metabolic activation of fatty acid oxidation (FAO), which causes uncoupling of mitochondrial OXPHOS and facilitates chemoresistance. For targeting these metabolic vulnerabilities of AML cells, inhibitors of OXPHOS and FAO have been developed and investigated for their therapeutic potential. Recent experimental and clinical evidence has revealed that drug-resistant AML cells and leukemic stem cells rewire metabolic pathways through interaction with BM stromal cells, enabling them to acquire resistance against OXPHOS and FAO inhibitors. These acquired resistance mechanisms compensate for the metabolic targeting by inhibitors. Several chemotherapy/targeted therapy regimens in combination with OXPHOS and FAO inhibitors are under development to target these compensatory pathways.

Risk Factors Associated with Bone Marrow Adiposity Deposition in Postmenopausal Women in the CASH China Study

Purpose

To investigated the factors that influence BMAC.

Patients and Methods

Quantitative computed tomography (QCT) and magnetic resonance imaging (MRI) were applied to measure abdominal fat areas, liver fat content, erector muscle fat content, and BMAC of the L2-4 vertebrae. Sex hormone, adipokine, and inflammatory factor levels were measured on the same day.

Results

Although age, erector muscle fat content, estradiol, testosterone, and adiponectin/leptin levels showed correlations with BMAC in the correlation analysis, the equations obtained from the whole population by multivariate analysis were unclear. Patients were stratified according to BMAC quartiles, and differences were found in vBMD, age, estradiol, testosterone, and erector muscle fat content among the four quartiles. Logistic analyses confirmed that age, estradiol/testosterone ratio, and TNF-α had independent effects on BMAC in all quartiles. In addition, height was related to higher BMAC quartiles, and glucose was related to lower BMAC quartiles.

Conclusion

Compared to other body fats, BMAC is a unique fat depot. Age, estradiol/testosterone ratio, and TNF-α are all key influencing factors related to BMAC in postmenopausal women. Furthermore, height and glucose levels were related to BMAC in the higher and lower BMAC quartiles, respectively.

The benefits of adipocyte metabolism in bone health and regeneration

Patients suffering from musculoskeletal diseases must cope with a diminished quality of life and an increased burden on medical expenses. The interaction of immune cells and mesenchymal stromal cells during bone regeneration is one of the key requirements for the restoration of skeletal integrity. While stromal cells of the osteo-chondral lineage support bone regeneration, an excessive accumulation of cells of the adipogenic lineage is thought to promote low-grade inflammation and impair bone regeneration. Increasing evidence indicates that pro-inflammatory signaling from adipocytes is responsible for various chronic musculoskeletal diseases. This review aims to summarize the features of bone marrow adipocytes by phenotype, function, secretory features, metabolic properties and their impact on bone formation. In detail, the master regulator of adipogenesis and prominent diabetes drug target, peroxisome proliferator-activated receptor γ (PPARG), will be debated as a potential therapeutic approach to enhance bone regeneration. We will explore the possibilities of using clinically established PPARG agonists, the thiazolidinediones (TZDs), as a treatment strategy to guide the induction of a pro-regenerative, metabolically active bone marrow adipose tissue. The impact of this PPARG induced bone marrow adipose tissue type on providing the necessary metabolites to sustain osteogenic-as well as beneficial immune cells during bone fracture healing will be highlighted.

Lipocalin 2 - mutation screen and serum levels in patients with anorexia nervosa or obesity and in lean individuals

CONTEXT

The bone-derived adipokine lipocalin-2 is relevant for body weight regulation by stimulating the leptin-melanocortin pathway.

OBJECTIVE

We aimed to (i) detect variants in the lipocalin-2 gene (LCN2) which are relevant for body weight regulation and/or anorexia nervosa (AN); (ii) describe and characterize the impact of LCN2 and MC4R variants on circulating lipocalin-2 level.

METHODS

Sanger sequencing of the coding region of LCN2 in 284 children and adolescents with severe obesity or 287 patients with anorexia nervosa. In-silico analyses to evaluate functional implications of detected LCN2 variants. TaqMan assays for rare non-synonymous variants (NSVs) in additional independent study groups. Serum levels of lipocalin-2 were measured by ELISA in 35 females with NSVs in either LCN2 or MC4R, and 33 matched controls without NSVs in the two genes.

RESULTS

Fourteen LCN2-variants (five NSVs) were detected. LCN2-p.Leu6Pro and p.Gly9Val located in the highly conserved signal peptide region may induce functional consequences. The secondary structure change of lipocalin-2 due to LCN2-p.Val89Ile may decrease solubility and results in a low lipocalin-2 level in a heterozygotes carrier (female recovered from AN). Lean individuals had lower lipocalin-2 levels compared to patients with obesity (p = 0.033).

CONCLUSION

Lipocalin-2 levels are positively associated with body mass index (BMI). Single LCN2-variants might have a profound effect on lipocalin-2 levels.

Bone Marrow Stromal Stem Cell Fate Decision: A Potential Mechanism For Bone Marrow Adipose Increase with Aging-related Osteoporosis

OBJECTIVE

Osteoporosis is a systemic bone disease that seriously threatens the health and quality of life in middle-aged and older adults. In this review, we describe the relationship between bone marrow adipose tissue and aging osteoporosis and mainly focus on bone marrow mesenchymal stem cell osteogenic-adipose differentiation fate with aging along with the relevant mechanisms responsible for these changes.

METHODS

We summarized recent advances in regulating the bone marrow mesenchymal stem cell differentiation due to aging in this review.

RESULTS

Aging-related bone mass loss is accompanied by expanding bone marrow adipose because of an imbalance of bone marrow mesenchymal stem cell differentiation, resulting in adipogenesis. Ectopic adipocytes in the bone marrow increase with age and are a key factor responsible for the aging-related bone mass decrease. Transcription factors and classical regulating pathways are involved in this process during aging.

CONCLUSION

As the global aging population increases, not only older women but also older men face a great fracture risk. Therefore, finding molecular mechanisms controlling the stimulating adipogenesis in BMSC during aging is important for providing the new cue for prevention and therapeutics for aging-related bone loss. Furthermore, upon physical examination of older people, except for the bone mineral density and bone turnover biochemical marker, the bone marrow adipose measurement should be taken into account when assessing the fracture risk and treatment plan that will be beneficial in clinical practice.

Symptomatic bone marrow metastases in breast cancer: A retrospective cohort study

Objective

Breast cancer symptomatic bone marrow metastasis (BMM) is rare and has a poor prognosis. Chemotherapy is usually the primary treatment, but it has limited efficacy, resulting in dose reduction and a decrease in quality of life due to the adverse effects of the agent. Other than chemotherapy, there are no other treatment studies for BMM. This study aimed to explore the clinicopathological characteristics of BMM patients with breast cancer, the prognosis using different treatment modalities, and the risk factors that affect the prognosis.

Methods

This retrospective study included patients diagnosed with breast cancer BMM from January 2018 to January 2022 in the Cancer Center of the First Hospital of Jilin University. The analysis focused on the characteristics of the patients, the treatment regimen, and the prognosis.

Results

Of 733 patients with advanced breast cancer, 33 patients were identified with BMM. All patients showed a hemoglobin decrease, and 25 (75.75%) presented with a fever of unknown origin. As for the metastasis breast cancer subtype, 25 (75.75%) were hormone receptor (HR) positive/human epidermal growth factor receptor 2 (HER2) negative, three (9.09%) had HER2 overexpression, and five (15.15%) were triple negative. The BMM patients had a median progression-free survival (PFS) of 7 months (1-21 months) and a median overall survival (OS) of 18 months (2-108 months). Among 25 HR⁺/HER2^- BMM patients treated with different modalities, the median OS of the endocrine therapy (ET) group was 23 months, compared with 5 months in the chemotherapy group. Cox proportional hazards models suggested that higher Eastern Cooperative Oncology Group (ECOG) scores and old age were associated with shorter survival.

Conclusion

When breast cancer patients present with anemia and fever of unknown origin, BMM should be considered. For HR⁺/HER2^- patients with good physical status and can receive active treatment, CDK4/6 inhibitors combined with ET can be used to control disease progression, improve quality of life, and prolong survival.

Gene therapy restores adipose tissue and metabolic health in a pre-clinical mouse model of lipodystrophy

Congenital generalized lipodystrophy type 2 is a serious multisystem disorder with limited treatment options. It is caused by mutations affecting the BSCL2 gene, which encodes the protein seipin. Patients with congenital generalized lipodystrophy type 2 lack both metabolic and mechanical adipose tissue and develop severe metabolic complications including hepatic steatosis, lipoatrophic diabetes, and cardiovascular disease. Gene therapies are becoming viable treatments, helping to alleviate inherited and acquired human disorders. We aimed to determine whether gene therapy could offer an effective form of medical intervention for lipodystrophy. We examined whether systemic adeno-associated virus delivery of human BSCL2 could reverse metabolic disease in seipin knockout mice, where white adipose tissue is absent. We reveal that adeno-associated virus gene therapy targets adipose progenitor cells in vivo and substantially restores white adipose tissue development in adult seipin knockout mice. This resulted in both rapid and prolonged beneficial effects to metabolic health in this pre-clinical mouse model of congenital generalized lipodystrophy type 2. Hyperglycemia was normalized within 2 weeks post-treatment together with normalization of severe insulin resistance. We propose that gene therapy offers great potential as a therapeutic strategy to correct multiple metabolic complications in patients with congenital lipodystrophy.

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.

Associations between bone mineral density, body composition and amenorrhoea in females with eating disorders: a systematic review and meta-analysis

BACKGROUND

Lower bone mineral density (BMD) increases the risk of osteoporosis in individuals with eating disorders (EDs), particularly women with anorexia nervosa (AN), making them susceptible to pain and fractures throughout adulthood. In AN, low weight, hypothalamic amenorrhoea, and longer illness duration are established risk factors for low BMD, and in people with other EDs a history of AN seems to be an important risk factor for low BMD.

PURPOSE

To conduct a systematic review and meta-analysis of BMD in individuals with EDs, including AN, bulimia nervosa (BN), binge-eating disorder (BED) and other specified feeding or eating disorders (OSFED) compared to healthy controls (HC).

METHODS

Following PRISMA guidelines, electronic databases were reviewed and supplemented with a literature search until 2/2022 of publications measuring BMD (dual-energy X-ray absorptiometry or dual photon absorptiometry) in females with any current ED diagnosis and a HC group. Primary outcomes were spine, hip, femur and total body BMD. Explanatory variables were fat mass, lean mass and ED clinical characteristics (age, illness duration, body mass index (BMI), amenorrhoea occurrence and duration, and oral contraceptives use).

RESULTS

Forty-three studies were identified (N = 4163 women, mean age 23.4 years, min: 14.0, max: 37.4). No study with individuals with BED met the inclusion criteria. BMD in individuals with AN (total body, spine, hip, and femur), with BN (total body and spine) and with OSFED (spine) was lower than in HC. Meta-regression analyses of women with any ED (AN, BN or OSFED) (N = 2058) showed low BMI, low fat mass, low lean mass and being amenorrhoeic significantly associated with lower total body and spine BMD. In AN, only low fat mass was significantly associated with low total body BMD.

CONCLUSION

Predictors of low BMD were low BMI, low fat mass, low lean mass and amenorrhoea, but not age or illness duration. In people with EDs, body composition measurement and menstrual status, in addition to BMI, are likely to provide a more accurate assessment of individual risk to low BMD and osteoporosis.

Metformin can mitigate skeletal dysplasia caused by Pck2 deficiency

As an important enzyme for gluconeogenesis, mitochondrial phosphoenolpyruvate carboxykinase (PCK2) has further complex functions beyond regulation of glucose metabolism. Here, we report that conditional knockout of Pck2 in osteoblasts results in a pathological phenotype manifested as craniofacial malformation, long bone loss, and marrow adipocyte accumulation. Ablation of Pck2 alters the metabolic pathways of developing bone, particularly fatty acid metabolism. However, metformin treatment can mitigate skeletal dysplasia of embryonic and postnatal heterozygous knockout mice, at least partly via the AMPK signaling pathway. Collectively, these data illustrate that PCK2 is pivotal for bone development and metabolic homeostasis, and suggest that regulation of metformin-mediated signaling could provide a novel and practical strategy for treating metabolic skeletal dysfunction.

Constitutive bone marrow adipocytes suppress local bone formation

BM adipocytes (BMAd) are a unique cell population derived from BM mesenchymal progenitors and marrow adipogenic lineage precursors. Although they have long been considered to be a space filler within bone cavities, recent studies have revealed important physiological roles in hematopoiesis and bone metabolism. To date, the approaches used to study BMAd function have been confounded by contributions by nonmarrow adipocytes or by BM stromal cells. To address this gap in the field, we have developed a BMAd-specific Cre mouse model to deplete BMAds by expression of diphtheria toxin A (DTA) or by deletion of peroxisome proliferator-activated receptor gamma (Pparg). We found that DTA-induced loss of BMAds results in decreased hematopoietic stem and progenitor cell numbers and increased bone mass in BMAd-enriched locations, including the distal tibiae and caudal vertebrae. Elevated bone mass appears to be secondary to enhanced endosteal bone formation, suggesting a local effect caused by depletion of BMAd. Augmented bone formation with BMAd depletion protects mice from bone loss induced by caloric restriction or ovariectomy, and it facilitates the bone-healing process after fracture. Finally, ablation of Pparg also reduces BMAd numbers and largely recapitulates high-bone mass phenotypes observed with DTA-induced BMAd depletion.

Adipose tissue-to-breast cancer crosstalk: Comprehensive insights

The review focuses on mechanistic evidence for the link between obesity and breast cancer. According to the IARC study, there is sufficient evidence that obesity is closely related to a variety of cancers. Among them, breast cancer is particularly disturbed by adipose tissue due to the unique histological structure of the breast. The review introduces the relationship between obesity and breast cancer from two aspects, including factors that promote tumorigenesis or metastasis. We summarize alterations in adipokines and metabolic pathways that contribute to breast cancer development. Breast cancer metastasis is closely related to obesity-induced pro-inflammatory microenvironment, adipose stem cells, and miRNAs. Based on the mechanism by which obesity causes breast cancer, we list possible therapeutic directions, including reducing the risk of breast cancer and inhibiting the progression of breast cancer. We also discussed the risk of autologous breast remodeling and fat transplantation. Finally, the causes of the obesity paradox and the function of enhancing immunity are discussed. Evaluating the balance between obesity-induced inflammation and enhanced immunity warrants further study.

White adipose tissue-derived factors and prostate cancer progression: mechanisms and targets for interventions

Obesity represents an important risk factor for prostate cancer, driving more aggressive disease, chemoresistance, and increased mortality. White adipose tissue (WAT) overgrowth in obesity is central to the mechanisms that lead to these clinical observations. Adipose stromal cells (ASCs), the progenitors to mature adipocytes and other cell types in WAT, play a vital role in driving PCa aggressiveness. ASCs produce numerous factors, especially chemokines, including the chemokine CXCL12, which is involved in driving EMT and chemoresistance in PCa. A greater understanding of the impact of WAT in obesity-induced progression of PCa and the underlying mechanisms has begun to provide opportunities for developing interventional strategies for preventing or offsetting these critical events. These include weight loss regimens, therapeutic targeting of ASCs, use of calorie restriction mimetic compounds, and combinations of compounds as well as specific receptor targeting strategies.

The potential molecular implications of adiponectin in the evolution of SARS-CoV-2: Inbuilt tendency

Adiponectin (APN) is an adipokine concerned in the regulation of glucose metabolism, insulin sensitivity and fatty acid oxidation. APN plays a critical role in viral infections by regulating the immune response through its anti-inflammatory/pro-inflammatory axis. Reduction of APN may augment the severity of viral infections because APN inhibits immune cells’ response via suppression of inflammatory signaling pathways and stimulation of adenosine monophosphate protein kinase (AMPK). Moreover, APN inhibits the stimulation of nuclear factor kappa B (NF-κB) and regulates the release of pro-inflammatory cytokines, such as tumor necrosis factor alpha (TNF-α) and interleukins (IL-18, IL-6). In COVID-19, abnormalities of the fatty tissue due to oxidative stress (OS) and hyperinflammation may inhibit the production and release of APN. APN has lung-protective effect and can prevent SARS-CoV-2-induced acute lung injury (ALI) through the amelioration of endoplasmic reticulum (ER) stress, endothelial dysfunction (ED) and stimulation of peroxisome proliferator-activated receptor-alpha (PPAR-α). It has been established that there is a potential correlation between inflammatory signal transduction pathways and APN that contributes to the development of SARS-CoV-2 infections. Deregulation of these molecular pathways affects the expression of APN and vice versa. In addition, the reduction of APN effect in SARS-CoV-2 infection could be a potential cause of the exacerbation of pro-inflammatory effects which are associated with the disease severity. In this context, exploratory, developmental, and extensive prospective studies are necessary.

Sex Differences in Adiposity and Cardiovascular Diseases

Body fat distribution is a well-established predictor of adverse medical outcomes, independent of overall adiposity. Studying body fat distribution sheds insights into the causes of obesity and provides valuable information about the development of various comorbidities. Compared to total adiposity, body fat distribution is more closely associated with risks of cardiovascular diseases. The present review specifically focuses on the sexual dimorphism in body fat distribution, the biological clues, as well as the genetic traits that are distinct from overall obesity. Understanding the sex determinations on body fat distribution and adiposity will aid in the improvement of the prevention and treatment of cardiovascular diseases (CVD).

Milk kefir therapy improves the skeletal response to resistance exercise in rats submitted to glucocorticoid-induced osteoporosis

Glucocorticoid-induced osteoporosis (GIO) has emerged as a challenge after long-term glucocorticoids (GCs) administration. Exercise has been an important non-pharmacological option, while medications modulate bone remodeling despite adverse effects. In this way, milk Kefir (MK) therapy stands out as a safe alternative to improve bone metabolism. Our study aimed to investigate the effect of MK associated to resistance exercise on bone loss in rats with GIO. For this, sixty male Wistar rats were divided into 2 groups: normal (N) and subjected to GIO, which was subdivided into 4 groups: control (C), milk kefir therapy (K), Exercise (Ex), and Exercise+K (ExK). GIO was induced by dexamethasone (7 mg/kg - i.m.; 1×/wk, 5 wk). MK was administered daily (1×/day; 0.7 ml/animal) and the climb exercise with load was performed 3×/wk; both for 16 wk. Femur was collected for assessment of bone microarchitecture, quality and metabolism. GIO markedly reduced trabecular bone volume density (BV/TV) (-35 %), trabecular thickness (Tb.Th) (-33 %), mineral content of femur (-26 %) as well as bone collagen content (-56 %). Bone strength and its biomechanical properties given by flexural strength (-81 %), fracture load (-80 %), and the number of osteocytes (-84 %) were lowered after GIO. GCs reduced osteoblast number and function while increased osteoclast number, altering bone remodeling (p < 0.05). On the other hand, ExK significantly improved bone microarchitecture and quality, marked by fractal dimension increase (+38 %), cortical volume (+34 %), BV/TV (+34 %), Tb.Th (+33 %), mineral content and collagen maturity, while reduced the space between trabecula (-34 %). The Ex and ExK increased the number of osteocytes (p < 0.05) and they were able to reverse the lower osteoblast number. Both treatments used alone significantly enhanced bone biomechanical properties, but the ExK showed a more significant improvement. ExK ameliorated bone strength and biomechanics (p < 0.05) and stimulated bone formation and modulated bone remodeling (p < 0.05). MK and exercise administered isolated or in association increased the percentage of collagen bone filling after GIO (p < 0.05), but only ExK improved collagen maturity. Our results showed that MK associated to resistance exercise enhanced bone microarchitecture, quality and metabolism, being therefore an interesting tool to improve skeletal response during GIO.

EXTENSIVE EXPERTISE IN ENDOCRINOLOGY: My quarter century quest to understand the paradox of marrow adiposity

Understanding the development and regulation of marrow adiposity, as well as its impact on skeletal remodeling has been a major challenge for our field and during my career as well. The story behind this unique phenotype and its relationship to bone turnover is highlighted in my own quest to defining the physiology and pathophysiology of marrow adipocytes.

Bone marrow adiposity in diabetes and clinical interventions

PURPOSE OF REVIEW

This study aims to review bone marrow adipose tissue (BMAT) changes in people with diabetes, contributing factors, and interventions.

RECENT FINDINGS

In type 1 diabetes (T1D), BMAT levels are similar to healthy controls, although few studies have been performed. In type 2 diabetes (T2D), both BMAT content and composition appear altered, and recent bone histomorphometry data suggests increased BMAT is both through adipocyte hyperplasia and hypertrophy. Position emission tomography scanning suggests BMAT is a major source of basal glucose uptake. BMAT is responsive to metabolic interventions.

SUMMARY

BMAT is a unique fat depot that is influenced by metabolic factors and proposed to negatively affect the skeleton. BMAT alterations are more consistently seen in T2D compared to T1D. Interventions such as thiazolidinedione treatment may increase BMAT, whereas metformin treatment, weight loss, and exercise may decrease BMAT. Further understanding of the role of BMAT will provide insight into the pathogenesis of diabetic bone disease and could lead to targeted preventive and therapeutic strategies.

Obesity and COVID-19: What are the Consequences?

Obesity is an increasing health problem all over the world. In combination with the current COVID-19 pandemic, this has turned into a massive challenge as individuals with overweight and obesity at all ages show a significant increase in their risk of getting severe COVID-19. Around 20% of all patients that were hospitalized for COVID-19 suffered from obesity alone, whereas obesity in combination with other metabolic comorbidities, such as type 2 diabetes and hypertension, account for up to 60% of all hospitalizations in relation to COVID-19. Therefore, it is of immense importance to put the spotlight on the high incidence of obesity present already in childhood both by changing the individual minds and by encouraging politicians and the whole society to commence preventive interventions for achieving a better nutrition for all social classes all over the world. In the current review, we aim to explain the different pathways and mechanisms that are responsible for the increased risk of severe COVID-19 in people with overweight and obesity. Furthermore, we discuss how the pandemic has led to weight gains in many people during lockdown. At the end, we discuss the importance of preventing such an interface between a non-communicable disease like obesity and a communicable disease like COVID-19 in the future.

Calorie restriction has no effect on bone marrow tumour burden in a Vk*MYC transplant model of multiple myeloma

Multiple myeloma (MM) is an incurable haematological malignancy, caused by the uncontrolled proliferation of plasma cells within the bone marrow (BM). Obesity is a known risk factor for MM, however, few studies have investigated the potential of dietary intervention to prevent MM progression. Calorie restriction (CR) is associated with many health benefits including reduced cancer incidence and progression. To investigate if CR could reduce MM progression, dietary regimes [30% CR, normal chow diet (NCD), or high fat diet (HFD)] were initiated in C57BL/6J mice. Diet-induced changes were assessed, followed by inoculation of mice with Vk*MYC MM cells (Vk14451-GFP) at 16 weeks of age. Tumour progression was monitored by serum paraprotein, and at endpoint, BM and splenic tumour burden was analysed by flow cytometry. 30% CR promoted weight loss, improved glucose tolerance, increased BM adiposity and elevated serum adiponectin compared to NCD-fed mice. Despite these metabolic changes, CR had no significant effect on serum paraprotein levels. Furthermore, endpoint analysis found that dietary changes were insufficient to affect BM tumour burden, however, HFD resulted in an average two-fold increase in splenic tumour burden. Overall, these findings suggest diet-induced BM changes may not be key drivers of MM progression in the Vk14451-GFP transplant model of myeloma.

Acute Myeloid Leukaemia Drives Metabolic Changes in the Bone Marrow Niche

Acute myeloid leukaemia (AML) is a highly proliferative cancer characterised by infiltration of immature haematopoietic cells in the bone marrow (BM). AML predominantly affects older people and outcomes, particularly in this difficult to treat population remain poor, in part due to inadequate response to therapy, and treatment toxicity. Normal haematopoiesis is supported by numerous support cells within the BM microenvironment or niche, including adipocytes, stromal cells and endothelial cells. In steady state haematopoiesis, haematopoietic stem cells (HSCs) primarily acquire ATP through glycolysis. However, during stress-responses HSCs rapidly transition to oxidative phosphorylation, enabled by mitochondrial plasticity. Historically it was thought that cancer cells preferentially used glycolysis for ATP production, however recently it has become evident that many cancers, including AML primarily use the TCA cycle and oxidative phosphorylation for rapid proliferation. AML cells hijack the stress-response pathways of their non-malignant counterparts, utilising mitochondrial changes to drive expansion. In addition, amino acids are also utilised by leukaemic stem cells to aid their metabolic output. Together, these processes allow AML cells to maximise their ATP production, using multiple metabolites and fuelling rapid cell turnover which is a hallmark of the disease. This review of AML derived changes in the BM niche, which enable enhanced metabolism, will consider the important pathways and discuss future challenges with a view to understanding how AML cells are able to hijack metabolic pathways and how we may elucidate new targets for potential therapies.