Marrow Adipocytes Research Articles

P-796 Single-cell transcriptomics unveils a role for leptin receptor in human endometrial mesenchymal stromal/stem cells

Abstract Study question What are the characteristics of leptin receptor (LepR) expressing cells within the endometrial mesenchymal stromal/stem cells (eMSCs) population? Summary answer LepR+ eMSCs display better stem-cell capacities as well as distinctively quiescent properties compared to eMSCs and LepR- eMSCs. What is known already Single-cell RNA sequencing (scRNA-seq) reveals that cultured eMSCs are heterogeneous. LepR is highly expressed in bone marrow MSCs, and LepR+ cells contribute towards the formation of fibroblast colony-forming units (CFU-F). Mouse LepR+ MSCs are quiescent and activate upon injuries to form osteoblasts and adipocytes in the bone marrow. In this study, we hypothesized that LepR+ cells play a critical role in the stem cell population in human endometrium. Study design, size, duration We performed scRNA-seq on magnetic bead selected eMSCs (CD140b+CD146+ cells). Functional stem cell assays such as clonogenicity and serial subcloning were performed on the different stromal subsets (eMSC, LepR- eMSC, and LepR+ eMSC) isolated by fluorescence-activated cell sorting (FACS) cultured endometrial stromal cells. The cell cycle analysis was evaluated by multicolor flow cytometry on freshly isolated endometrial stromal cells. Participants/materials, setting, methods The endometrial samples were collected from women aged 37–53 years with regular menstrual cycles undergoing hysterectomy. The expression and localization of LepR in human endometrium were determined by flow cytometry and immunohistochemistry, respectively. The in vitro colony-forming and self-renewal abilities were assessed on FACS sorted endometrial stromal populations. The cell cycle status of the stromal subsets was determined by flow cytometry and the quiescent property was determined by qPCR (RB1, RBL2, CDKN1A, CDKN1B, and E2F4). Main results and the role of chance Clustering analysis of the scRNA-seq data revealed 5 subpopulations (SP0-4) of cultured eMSCs. A high proportion (>90%) of the cells in SP3 and SP4 were at the G1 phase. The majority of the SP3 cells (92%) were located at the root of the cell trajectory and pseudo time inference analysis. The expression of LepR was highly specific in SP3 suggesting LepR eMSCs are potentially the origin progenitors.The expression of LepR in endometrial stromal cells was 2.61 ± 1.43%, and in eMSCs was 25.59 ± 19.04%. In vitro experiments demonstrated that LepR+ eMSCs exhibit better stem-cell properties, including clonogenic and self-renewal ability, than its negative counterparts. QPCR validation of cell-quiescence associated genes revealed higher expression of RB1, RBL2, and CDKN1B in the LepR+ eMSCs than eMSCs and LepR- eMSCs. In addition, multicolor flow analysis on freshly isolated endometrial cells revealed significantly higher proportion of LepR+ eMSCs are in the G0 phase of the cell cycle when compared to eMSCs and LepR- eMSCs. The above results indicate in vivo LepR+ eMSCs are relatively more quiescent. Limitations, reasons for caution The mechanism involved in maintaining or activating quiescent LepR+ eMSCs remains unknown. The role of LepR+ is likely to be different in human compared to mouse. We also lack an in vivo model for studying LepR+ eMSCs during endometrial repair. Wider implications of the findings Our findings extend the understanding of heterogeneous human endometrial mesenchymal stem cells and unveil a new role for LepR in endometrial regeneration. Trial registration number not applicatble

MiR-196b-5p Regulates Osteoblast and Osteoclast Differentiation and Bone Homeostasis by Targeting SEMA3A.

miR-196b-5p plays a role in various malignancies. We have recently reported its function in regulating adipogenesis. However, it remains to be clarified whether and how miR-196b-5p affects bone cells and bone homeostasis. In this study, in vitro functional experiments showed an inhibitory effect of miR-196b-5p on osteoblast differentiation. Mechanistic explorations revealed that miR-196b-5p directly targeted semaphorin 3a (Sema3a) and inhibited Wnt/β-catenin signaling. SEMA3A attenuated the impaired osteogenesis induced by miR-196b-5p. Osteoblast-specific miR-196b transgenic mice showed significant reduction of bone mass. Trabecular osteoblasts were reduced and bone formation was suppressed, whereas osteoclasts, marrow adipocytes, and serum levels of bone resorption markers were increased in the transgenic mice. The osteoblastic progenitor cells from the transgenic mice had decreased SEMA3A levels and exhibited retarded osteogenic differentiation, whereas those marrow osteoclastic progenitors exhibited enhanced osteoclastogenic differentiation. miR-196b-5p and SEMA3A oppositely regulated the expression of receptor activator of nuclear factor-κB ligand and osteoprotegerin. The calvarial osteoblastic cells expressing the transgene promoted osteoclastogenesis, whereas the osteoblasts overexpressing Sema3a inhibited it. Finally, in vivo transfection of miR-196b-5p inhibitor to the marrow reduced ovariectomy-induced bone loss in mice. Our study has identified that miR-196b-5p plays a key role in osteoblast and osteoclast differentiation and regulates bone homeostasis. Inhibition of miR-196b-5p may be beneficial for amelioration of osteoporosis. © 2023 American Society for Bone and Mineral Research (ASBMR).

Single-Cell RNA-Sequencing Reveals the Skeletal Cellular Dynamics in Bone Repair and Osteoporosis.

The bone is an important organ that performs various functions, and the bone marrow inside the skeleton is composed of a complex intermix of hematopoietic, vascular, and skeletal cells. Current single-cell RNA sequencing (scRNA-seq) technology has revealed heterogeneity and sketchy differential hierarchy of skeletal cells. Skeletal stem and progenitor cells (SSPCs) are located upstream of the hierarchy and differentiate into chondrocytes, osteoblasts, osteocytes, and bone marrow adipocytes. In the bone marrow, multiple types of bone marrow stromal cells (BMSCs), which have the potential of SSPCs, are spatiotemporally located in distinct areas, and SSPCs' potential shift of BMSCs may occur with the advancement of age. These BMSCs contribute to bone regeneration and bone diseases, such as osteoporosis. In vivo lineage-tracing technologies show that various types of skeletal lineage cells concomitantly gather and contribute to bone regeneration. In contrast, these cells differentiate into adipocytes with aging, leading to senile osteoporosis. scRNA-seq analysis has revealed that alteration in the cell-type composition is a major cause of tissue aging. In this review, we discuss the cellular dynamics of skeletal cell populations in bone homeostasis, regeneration, and osteoporosis.

Isoflavones and probiotics effect on bone calcium and bone cells in rats

Isoflavones and probiotics have shown the therapeutic potential to alter calcium absorption and bone cell metabolism. This study sought to ascertain the effect of isoflavones and probiotics on calcium status and bone health in healthy female rats. Forty-eight adult female Wistar rats were grouped and fed: a standard diet (control); and standard diets with tempeh; soy; daidzein and genistein; Lactobacillus acidophilus; and a combination of daidzein, genistein, and L. acidophilus. The biochemical serum parameters, such as alanine transaminase, aspartate transaminase, glucose, and triacylglycerol concentrations, were measured, and calcium contents in tissues were determined. After staining the bone with hematoxylin and eosin, the number of osteoblasts, osteocytes, and the percentage of bone marrow adipocytes were counted. Compared with the control group, the soy group showed a significantly lower triacylglycerol concentration. The L. acidophilus group considerably increased the calcium content in the femoral bone. The daidzein and genistein, L. acidophilus, and a combination of daidzein, genistein, and L. acidophilus groups showed significantly lower calcium contents in the heart and kidneys. The daidzein and genistein group significantly enhanced the number of osteoblasts and osteocytes. A substantial inverse correlation was observed between calcium contents in kidneys and osteoblasts. In conclusion, the combination of daidzein, genistein, and L. acidophilus may improve bone calcium concentrations and bone cells. However, no synergistic effect between isoflavones and probiotics was detected in this study.

Bone marrow adipocytes alteration in an in vitro model of Gaucher Disease

Gaucher disease (GD) is caused by biallelic pathogenic variants in GBA1 gene that encodes the lysosomal enzyme glucocerebrosidase. Up to now, specific treatment for GD cannot completely reverse bone complications. Bone is composed of different cell types; including osteoblasts, osteocytes and osteoclasts. Osteoblasts are present on bone surfaces and are derived from local mesenchymal stem cells (MSCs). Depending on environment conditions, MSCs could differentiate into osteoblasts and adipocytes. Mature adipocytes-secreted adipokines and free fatty acids affect both osteoblasts and osteoclasts formation/activity and therefore mediate skeletal homeostasis. The aim of this study was to evaluate possible alterations in GD adipocyte (GD Ad) that could contribute to bone complications. MSCs were grown in adipogenic media in order to evaluate expression of differentiation markers as PPAR-γ. PPAR-γ was observed into the nucleus of GD Ad, indicating that these cells are properly stimulated. However, these cells accumulate lesser lipid droplets (LDs) than Control Ad. In order to study lipid droplet metabolism, we evaluated the lipolysis of these structures by the measurement of free glycerol in culture supernatant. Our results indicated that GD Ad had an alteration in this process, evidenced by an increase in glycerol release. We have also evaluated two enzymes involved in LDs synthesis: fatty acid synthase (FASN) and stearoyl-coenzyme A desaturase 1 (SCD1). The transcription of these genes was decreased in GD Ad, suggesting a dysfunction in the synthesis of LDs. In conclusion, our results show an alteration in LDs metabolism of GD Ad, independent of adipocyte differentiation process. This alteration would be caused by an increase in lipolysis in early stages of differentiation and also by a reduction of lipid synthesis, which could contribute with the skeletal imbalance in GD.

Bone Marrow Adipocytes Contribute to Tumor Microenvironment-Driven Chemoresistance via Sequestration of Doxorubicin.

Chemoresistance is a significant problem in the effective treatment of bone metastasis. Adipocytes are a major stromal cell type in the bone marrow and may play a crucial role in developing microenvironment-driven chemoresistance. However, detailed investigation remains challenging due to the anatomical inaccessibility and intrinsic tissue complexity of the bone marrow microenvironment. In this study, we developed 2D and 3D in vitro models of bone marrow adipocytes to examine the mechanisms underlying adipocyte-induced chemoresistance. We first established a protocol for the rapid and robust differentiation of human bone marrow stromal cells (hBMSCs) into mature adipocytes in 2D tissue culture plastic using rosiglitazone (10 μM), a PPARγ agonist. Next, we created a 3D adipocyte culture model by inducing aggregation of hBMSCs and adipogenesis to create adipocyte spheroids in porous hydrogel scaffolds that mimic bone marrow sinusoids. Simulated chemotherapy treatment with doxorubicin (2.5 μM) demonstrated that mature adipocytes sequester doxorubicin in lipid droplets, resulting in reduced cytotoxicity. Lastly, we performed direct coculture of human multiple myeloma cells (MM1.S) with the established 3D adipocyte model in the presence of doxorubicin. This resulted in significantly accelerated multiple myeloma proliferation following doxorubicin treatment. Our findings suggest that the sequestration of hydrophobic chemotherapeutics by mature adipocytes represents a potent mechanism of bone marrow microenvironment-driven chemoresistance.

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.

Targeting adipocyte ESRRA rebalances bone and marrow adipocyte homeostasis through opposite regulation of LEPTIN and SPP1

Searchable abstracts of presentations at key conferences in endocrinology ISSN 1470-3947 (print) | ISSN 1479-6848 (online)

Glucocorticoid-induced bone loss linked with marrow adipocyte senescence.

Glucocorticoid-induced bone loss linked with marrow adipocyte senescence.

The role and mechanism of tumor necrosis factor-alpha in alcohol-induced bone loss.

It is well known that alcohol can cause bone loss and that bone mineral density has an inverse relationship with bone marrow adipocyte (BMA). However, little is known about the mechanisms that link alcohol and bone loss, and existing studies lack data on BMA in alcohol-induced bone loss. Here, wild-type (WT) and tumor necrosis factor-alpha knockout (TNF-α KO) mice were used to examine the effects of alcohol on bone metabolism. The effects of alcohol on bone metabolism were demonstrated in vivo by feeding WT and TNF-α KO mice with alcohol. The osteogenesis and adipogenesis of primary bone marrow stromal cells (BMSCs) derived from WT and TNF-α KO mice under alcohol intervention were compared in vitro. Tissue staining, cell staining, micro-CT, and quantitative RT-PCR were used to explore the potential mechanism. Alcohol induced trabecular bone loss, increased BMA, and promoted the mRNA expression of Adipoq, Fabp4, visfatin， Pparg, TNF-α, IL-1β, and IL-6 in BMA in WT mice, but not in TNF-α KO mice. In addition, alcohol promoted BMSC adipogenesis and inhibited BMSC osteogenesis, while TNF-α knockout could restrain this situation. Our study demonstrated that alcohol may reduce bone mass by disrupting the balance of osteogenesis and adipogenesis in bone marrow, and TNF-α plays an important role in this process.

Local senolysis in aged mice only partially replicates the benefits of systemic senolysis.

Clearance of senescent cells (SnCs) can prevent several age-related pathologies, including bone loss. However, the local versus systemic roles of SnCs in mediating tissue dysfunction remain unclear. Thus, we developed a mouse model (p16-LOX-ATTAC) that allowed for inducible SnC elimination (senolysis) in a cell-specific manner and compared the effects of local versus systemic senolysis during aging using bone as a prototype tissue. Specific removal of Sn osteocytes prevented age-related bone loss at the spine, but not the femur, by improving bone formation without affecting osteoclasts or marrow adipocytes. By contrast, systemic senolysis prevented bone loss at the spine and femur and not only improved bone formation, but also reduced osteoclast and marrow adipocyte numbers. Transplantation of SnCs into the peritoneal cavity of young mice caused bone loss and also induced senescence in distant host osteocytes. Collectively, our findings provide proof-of-concept evidence that local senolysis has health benefits in the context of aging, but, importantly, that local senolysis only partially replicates the benefits of systemic senolysis. Furthermore, we establish that SnCs, through their senescence-associated secretory phenotype (SASP), lead to senescence in distant cells. Therefore, our study indicates that optimizing senolytic drugs may require systemic instead of local SnC targeting to extend healthy aging.

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.

Senescence of bone marrow fat cells: A new clue for glucocorticoid-induced bone deterioration

Glucocorticoid (GC)-induced osteoporosis is the most common secondary cause of osteoporosis, resulting in fractures and significant morbidity. In this issue of Cell Metabolism, Liu etal. reveal that in response to GCs, bone marrow adipocytes (BMAds) undergo rapid cellular senescence, triggering secondary senescence in bone marrow and causing bone deterioration.

Antibodies to sclerostin or G-CSF receptor partially eliminate bone or marrow adipocyte loss, respectively, following vertical sleeve gastrectomy.

Vertical sleeve gastrectomy (VSG), the most utilized bariatric procedure in clinical practice, greatly reduces body weight and improves a variety of metabolic disorders. However, one of its long-term complications is bone loss and increased risk of fracture. Elevated circulating sclerostin (SOST) and granulocyte-colony stimulating factor (G-CSF) concentrations have been considered as potential contributors to VSG-associated bone loss. To test these possibilities, we administrated antibodies to SOST or G-CSF receptor and investigated alterations to bone and marrow niche following VSG. Neutralizing either SOST or G-CSF receptor did not alter beneficial effects of VSG on adiposity and hepatic steatosis, and anti-SOST treatment provided a further improvement to glucose tolerance. SOST antibodies partially reduced trabecular and cortical bone loss following VSG by increasing bone formation, whereas G-CSF receptor antibodies had no effects on bone mass. The expansion in myeloid cellularity and reductions in bone marrow adiposity seen with VSG were partially eliminated by treatment with Anti-G-CSF receptor. Taken together, these experiments demonstrate that antibodies to SOST or G-CSF receptor may act through independent mechanisms to partially block effects of VSG on bone loss or marrow niche cells, respectively.

Bone marrow adipocytes induce cancer-associated fibroblasts and immune evasion, enhancing invasion and drug resistance.

Bone metastasis occurs frequently occurred in cancer patients. Conventional therapies have limited therapeutic outcomes, and thus, exploring the mechanisms of cancer progression in the bone metastasis is important to develop new effective therapies. In the bone microenvironment, adipocytes are the major stromal cells that interact with cancer cells during the bone metastasis. However, the comprehensive functions of bone marrow adipocytes in cancer progression are not yet fully understood. To address this, we investigated the role of bone marrow adipocytes on cancer cells, by focusing on an invasive front which reflects the direct effects of stromal cells on cancer. In comprehensive histopathological and genetic analysis using bone metastasis specimens, we examined invasive fronts in bone metastasis and compared invasive fronts with adipocyte-rich bone marrow (adipo-BM) to those with hematopoietic cell-rich bone marrow (hemato-BM) as a normal counterpart of adipocytes. We found morphological complexity of invasive front with adipo-BM was significantly higher than that with hemato-BM. Based on immunohistochemistry, the invasive front with adipo-BM comparatively had significantly increased cancer-associated fibroblasts (CAFs) marker-positive area and lower density of CD8 positive lymphocytes compared to that with hemato-BM. RNA-seq analysis of primary and bone metastasis cancer reveals that bone metastasized cancer cells acquired drug resistance related gene expression phenotypes. Clearly, these findings indicate that bone marrow adipocytes provide favorable tumor microenvironment for cancer invasion and therapeutic resistance of bone metastasized cancers via CAF induction and immune evasion, providing a potential target for the treatment of bone metastasis.

Bone Marrow Adipose Tissue: Regulation of Osteoblastic Niche, Hematopoiesis and Hematological Malignancies.

Bone marrow adipose tissue (BMAT) creates a specific microniche within multifunctional bone marrow (BM) ecosystem which imposes changes in surrounding cells and at systemic level. Moreover, BMAT contributes to spatial and temporal separation and metabolic compartmentalization of BM, thus regulating BM homeostasis and diseases. Recent findings have identified novel progenitor subsets of bone marrow adipocytes (BMAd)s recruited during the BM adipogenesis within different skeletal and hematopoietic stem cell niches. Potential of certain mesenchymal BM cells to differentiate into both osteogenic and adipogenic lineages, contributes to the complex interplay of BMAT with endosteal (osteoblastic) niche compartments as an important cellular player in bone tissue homeostasis. Targeting and ablation of BMAT cells at certain states might be an optional and promising strategy for improvement of bone health. Additionally, recent findings demonstrated spatial distribution of BMAds related to hematopoietic cells and pointed out important functional roles in the vital processes such as long-term hematopoiesis. BM adipogenesis appears to be an emergency phenomenon that follows the production of hematopoietic stem and progenitor cell niche factors, thus regulating physiological, stressed, and malignant hematopoiesis. Lipolytic and secretory activity of BMAds can influence survival and proliferation of hematopoietic cells at different maturation stages. Due to their different lipid status, constitutive and regulated BMAds are important determinants of normal and malignant hematopoietic cells. Further elucidation of cellular and molecular players involved in BMAT expansion and crosstalk with malignant cells is of paramount importance for conceiving the new therapies for improvement of BM health.

Adipose tissue and hematopoiesis: Friend or foe?

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. 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. 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. 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.

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.

Chidamide suppresses adipogenic differentiation of bone marrow derived mesenchymal stem cells via increasing REEP2 expression

Increased propensity of bone marrow-derived mesenchymal stem cells (BM-MSCs) toward adipogenic differentiation at the expense of osteogenesis has been implicated in obesity, diabetes, and age-related osteoporosis as well as various hematopoietic disorders. Defining small molecules with role in rectifying the adipo-osteogenic differentiation imbalance is of great significance. Here, we unexpectedly found that Chidamide, a selective histone deacetylases inhibitor, exhibited remarkably suppressive effect on the invitro induced adipogenic differentiation of BM-MSCs. Multifaceted alterations in the spectrum of gene expression were observed in Chidamide-managed BM-MSCs during adipogenic induction. Finally, we focused on REEP2, which presented decreased expression in BM-MSCs-mediated adipogenesis and was restored by Chidamide treatment. REEP2 was subsequently demonstrated as a negative regulator of adipogenic differentiation of BM-MSCs and mediated the suppressive effect of Chidamide on adipocyte development. Our findings provide the theoretical and experimental foundation for the clinical application of Chidamide for disorders associated with excessive marrow adipocytes.

Bone marrow Adipoq-lineage progenitors are a major cellular source of M-CSF that dominates bone marrow macrophage development, osteoclastogenesis, and bone mass.

M-CSF is a critical growth factor for myeloid lineage cells, including monocytes, macrophages, and osteoclasts. Tissue-resident macrophages in most organs rely on local M-CSF. However, it is unclear what specific cells in the bone marrow produce M-CSF to maintain myeloid homeostasis. Here, we found that Adipoq-lineage progenitors but not mature adipocytes in bone marrow or in peripheral adipose tissue, are a major cellular source of M-CSF, with these Adipoq-lineage progenitors producing M-CSF at levels much higher than those produced by osteoblast lineage cells. The Adipoq-lineage progenitors with high CSF1 expression also exist in human bone marrow. Deficiency of M-CSF in bone marrow Adipoq-lineage progenitors drastically reduces the generation of bone marrow macrophages and osteoclasts, leading to severe osteopetrosis in mice. Furthermore, the osteoporosis in ovariectomized mice can be significantly alleviated by the absence of M-CSF in bone marrow Adipoq-lineage progenitors. Our findings identify bone marrow Adipoq-lineage progenitors as a major cellular source of M-CSF in bone marrow and reveal their crucial contribution to bone marrow macrophage development, osteoclastogenesis, bone homeostasis, and pathological bone loss.