Leukemia cells remodel marrow adipocytes via TRPV4-dependent lipolysis

Relationship between adipocytes and hematological tumors in the bone marrow microenvironment: a literature review

Background and Objective

The bone marrow microenvironment is closely related to normal hematopoiesis and hematologic tumors. Adipocytes are an important part of the bone marrow microenvironment, in which they can release free fatty acids (FFAs) through lipolysis and secrete adipocytokines, etc., and participate in normal hematopoiesis, which is closely related to the occurrence and treatment of hematological tumors. In this review, we aim to discuss how bone marrow adipocytes (BMAs) can influence the proliferation, apoptosis, and chemotherapy resistance of cancer cells by reprogramming lipid metabolism and the secretion of various adipocytokines.

Methods

Studies from 2000 to July 2024 were reviewed from PubMed, Springer Link, and the Web of Science using the keywords bone marrow microenvironment, adipocytes, lipid metabolism, adipocytokines, hematological tumor, cancer, and their combinations. Unreliable articles such as those that are old and have a low impact factor are excluded, and there is no restriction on language.

Key Content and Findings

Adipocytes can regulate the proliferation and differentiation of hematopoietic stem cells (HSCs) by secreting inflammatory factors and adipocytokines to maintain hematopoietic homeostasis. Adipocytes can also stimulate and accelerate the occurrence and progression of hematological tumors by secreting adipocytokines and mediating the reprogramming of lipid metabolism. Moreover, abundant adipocytes in bone marrow can protect tumor cells by physically blocking and/or secreting cytokines, leading to chemotherapy resistance.

Conclusions

Therefore, the targeted inhibition of related lipid metabolism pathways and adipocytokines might be a potential therapeutic target for hematological tumors, which would be helpful to inhibit tumor growth and correct chemotherapy resistance.

Genetic analysis from multiple cohorts implies causality between 2200 druggable genes, telomere length, and leukemia

BACKGROUND

Clinical therapeutic targets for leukemia remain to be identified and the causality between leukemia and telomere length is unclear.

METHODS

This work employed cis expression quantitative trait locus (eQTL) for 2,200 druggable genes from the eQTLGen Consortium and genome-wide association studies (GWAS) summary data for telomere length in seven blood cell types from the UK Biobank, Netherlands Cohort as exposures. GWAS data for lymphoid leukemia (LL) and myeloid leukemia (ML) from FinnGen and Lee Lab were used as outcomes for discovery and replication cohorts, respectively. Robust Mendelian randomization (MR) findings were generated from seven MR models and a series of sensitivity analyses. Summary-data-based MR (SMR) analysis and transcriptome-wide association studies (TWAS) were further implemented to verify the association between identified druggable genes and leukemia. Single-cell type expression analysis was employed to identify the specific expression of leukemia casual genes on human bone marrow and peripheral blood immune cells. Multivariable MR analysis, linkage disequilibrium score regression (LDSC), and Bayesian colocalization analysis were performed to further validate the relationship between telomere length and leukemia. Mediation analysis was used to assess the effects of identified druggable genes affecting leukemia via telomere length. Phenome-wide MR (Phe-MR) analysis for assessing the effect of leukemia causal genes and telomere length on 1,403 disease phenotypes.

RESULTS

Combining the results of the meta-analysis for MR estimates from two cohorts, SMR and TWAS analysis, we identified five LL causal genes (TYMP, DSTYK, PPIF, GDF15, FAM20A) and three ML causal genes (LY75, ADA, ABCA2) as promising drug targets for leukemia. Univariable MR analysis showed genetically predicted higher leukocyte telomere length increased the risk of LL (odds ratio [OR] = 2.33, 95 % confidence interval [95 % CI] 1.70-3.18; P = 1.33E-07), and there was no heterogeneity and horizontal pleiotropy. Evidence from the meta-analysis of two cohorts strengthened this finding (OR = 1.88, 95 % CI 1.06-3.05; P = 0.01). Multivariable MR analysis showed the causality between leukocyte telomere length and LL without interference from the other six blood cell telomere length (OR = 2.72, 95 % CI 1.88-3.93; P = 1.23E-07). Evidence from LDSC supported the positive genetic correlation between leukocyte telomere length and LL (rg = 0.309, P = 0.0001). Colocalization analysis revealed that the causality from leukocyte telomere length on LL was driven by the genetic variant rs770526 in the TERT region. The mediation analysis via two-step MR showed that the causal effect from TYMP on LL was partly mediated by leukocyte telomere length, with a mediated proportion of 12 %.

CONCLUSION

Our study identified several druggable genes associated with leukemia risk and provided new insights into the etiology and drug development of leukemia. We also found that genetically predicted higher leukocyte telomere length increased LL risk and its potential mechanism of action.

Influences on the Hematopoietic Stem Cell Niche

Hematopoietic stem cells (HSCs) are supported by the bone marrow microenvironment to maintain normal production of blood cells. The niche may be considered an "ecosystem" that support the function of HSCs and other supportive cells. Alterations in the bone marrow niche are commonly observed in hematologic malignancies. Here, we review recent insights into the location and the molecular and cellular components of the bone marrow niche. Moreover, we discuss how the niche interacts with HSCs to drive the pathogenesis of hematopoietic malignancies. Overall, a better understanding of the influences on the HSC niche may drive therapeutic development targeting defective and aberrant hematopoiesis.

Molecular Deconvolution of Bone Marrow Adipose Tissue Interactions with Malignant Hematopoiesis: Potential for New Therapy Development

PURPOSE OF REVIEW

Along with a strong impact on skeletal integrity, bone marrow adipose tissue (BMAT) is an important modulator of the adult hematopoietic system. This review will summarize the current knowledge on the causal relationship between bone marrow (BM) adipogenesis and the development and progression of hematologic malignancies.

RECENT FINDINGS

BM adipocytes (BMAds) support a number of processes promoting oncogenesis, including the evolution of clonal hematopoiesis, malignant cell survival, proliferation, angiogenesis, and chemoresistance. In addition, leukemic cells manipulate surrounding BMAds by promoting lipolysis and release of free fatty acids, which are then utilized by leukemic cells via β-oxidation. Therefore, limiting BM adipogenesis, blocking BMAd-derived adipokines, or lipid metabolism obstruction have been considered as potential treatment options for hematological malignancies. Leukemic stem cells rely heavily on BMAds within the structural BM microenvironment for necessary signals which foster disease progression. Further development of 3D constructs resembling BMAT at different skeletal regions are critical to better understand these relationships in geometric space and may provide essential insight into the development of hematologic malignancies within the BM niche. In turn, these mechanisms provide promising potential as novel approaches to targeting the microenvironment with new therapeutic strategies.

Obesity, bone marrow adiposity, and leukemia: Time to act

Obesity has taken the face of a pandemic with less direct concern among the general population and scientific community. However, obesity is considered a low-grade systemic inflammation that impacts multiple organs. Chronic inflammation is also associated with different solid and blood cancers. In addition, emerging evidence demonstrates that individuals with obesity are at higher risk of developing blood cancers and have poorer clinical outcomes than individuals in a normal weight range. The bone marrow is critical for hematopoiesis, lymphopoiesis, and myelopoiesis. Therefore, it is vital to understand the mechanisms by which obesity-associated changes in BM adiposity impact leukemia development. BM adipocytes are critical to maintain homeostasis via different means, including immune regulation. However, obesity increases BM adiposity and creates a pro-inflammatory environment to upregulate clonal hematopoiesis and a leukemia-supportive environment. Obesity further alters lymphopoiesis and myelopoiesis via different mechanisms, which dysregulate myeloid and lymphoid immune cell functions mentioned in the text under different sequentially discussed sections. The altered immune cell function during obesity alters hematological malignancies and leukemia susceptibility. Therefore, obesity-induced altered BM adiposity, immune cell generation, and function impact an individual's predisposition and severity of leukemia, which should be considered a critical factor in leukemia patients.

Bone marrow adipocyte: Origin, biology and relationship with hematological malignancy

Bone marrow adipose tissue (BMAT) has been histologically recognized for decades. In this study, we performed a bibliometric analysis to quantitatively analyze the clusters of keywords of BMAT and hematopoiesis to better understand BMAT and hematopoiesis. Starting with conclusive keywords, our results demonstrated that BMAds is distinct from extramedullary adipose tissues and maintains a routine but dynamic accumulation throughout an individual's life. Various pathophysiological factors take part in dysregulation of the adipose-osteogenic balance throughout life. Bone marrow adipocytes (BMAds) are also contradictorily involved in normal hematopoiesis, and positively participate in the occurrence and progression of hematologic malignancies, exerting a chemoprotective role in tumor treatment. Mechanically, metabolic reprogramming and abnormal secretory profile of BMAds and tumor cells play a critical role in the chemotherapy resistance. Overall, we hope that this work will provide new ideas for relevant future research on BMAds.

TRPV4 enhances the synthesis of fatty acids to drive the progression of ovarian cancer through the calcium-mTORC1/SREBP1 signaling pathway

Transient receptor potential vanilloid 4 (TRPV4) is a nonselective cation channel activated by various stimuli, such as heat. A recent study reported that high expression of TRPV4 predicted a poor prognosis in ovarian cancer patients. This study demonstrated that TRPV4 was highly expressed in ovarian cancer and had the ability to promote proliferation and migration. Through RNA-seq and related experiments, we confirmed that the oncogenic pathway of TRPV4 in ovarian cancer may be related to the fatty acid synthesis. By correlation analysis and RNA-seq, we demonstrated that SREBP1 and mTORC1 were inseparably related to that. Therefore, we used inhibitors to perform experiments. Calcium fluorescent probe experiments suggest that the change of calcium content in ovarian cancer cells was related to the downstream mTORC1 signaling pathway and fatty acid synthesis. These results confirmed that TRPV4 affected the fatty acid synthesis through the calcium-mTOR/SREBP1 signaling pathway, thereby promoting ovarian cancer progression.

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.

DEX-Induced SREBF1 Promotes BMSCs Differentiation into Adipocytes to Attract and Protect Residual T-Cell Acute Lymphoblastic Leukemia Cells After Chemotherapy

T-cell acute lymphoblastic leukemia (T-ALL) is an aggressive malignant blood disorder with a high rate of relapse. Patients relapse as a result of minimal residual disease (MRD), which originates from residual T-ALL cells in the bone marrow microenvironment (BMM). In the present study, it is observed that adipocytes increase dramatically in the BMM of T-ALL patients after exposure to chemotherapeutic drugs. Then, it is proved that adipocytes attract T-ALL cells by releasing CXCL13 and support leukemia cell survival by activating the Notch1 signaling pathway via DLL1 and Notch1 binding. Furthermore, it is verified that dexamethasone (DEX) induces adipogenic differentiation by enhancing the expression of SREBF1 in bone marrow mesenchymal stromal cells (BMSCs), and an SREBF1 inhibitor significantly decreases the adipogenic potential of BMSCs and the subsequent ability of adipocytes to support T-ALL cells in vitro and in vivo. These findings confirm that the differentiation of BMSCs to adipocytes induced by DEX contributes to MRD in T-ALL and provides an auxiliary clinical treatment to reduce the recurrence rate.

The role of bone marrow adipocytes in cancer progression: the impact of obesity

Bone marrow adipose tissues (BMATs) and their main cellular component, bone marrow adipocytes (BMAds), are found within the bone marrow (BM), which is a niche for the development of hematological malignancies as well as bone metastasis from solid tumors such as breast and prostate cancers. In humans, BMAds are present within the hematopoietic or "red" BMAT and in the "yellow" BMAT where they are more densely packed. BMAds are emerging as new actors in tumor progression; however, there are many outstanding questions regarding their precise role. In this review, we summarized our current knowledge regarding the development, distribution, and regulation by external stimuli of the BMATs in mice and humans and addressed how obesity could affect these traits. We then discussed the specific metabolic phenotype of BMAds that appear to be different from "classical" white adipocytes, since they are devoid of lipolytic function. According to this characterization, we presented how tumor cells affect the in vitro and in vivo phenotype of BMAds and the signals emanating from BMAds that are susceptible to modulate tumor behavior with a specific emphasis on their metabolic crosstalk with cancer cells. Finally, we discussed how obesity could affect this crosstalk. Deciphering the role of BMAds in tumor progression would certainly lead to the identification of new targets in oncology in the near future.

Multiple myeloma cells induce lipolysis in adipocytes and uptake fatty acids through fatty acid transporter proteins

Adipocytes occupy 70% of the cellular volume within the bone marrow (BM) wherein multiple myeloma (MM) originates and resides. However, the nature of the interaction between MM cells and adipocytes remains unclear. Cancer-associated adipocytes support tumor cells through various mechanisms, including metabolic reprogramming of cancer cells. We hypothesized that metabolic interactions mediate the dependence of MM cells on BM adipocytes. Here we show that BM aspirates from precursor states of MM, including monoclonal gammopathy of undetermined significance and smoldering MM, exhibit significant upregulation of adipogenic commitment compared with healthy donors. In vitro coculture assays revealed an adipocyte-induced increase in MM cell proliferation in monoclonal gammopathy of undetermined significance/smoldering MM compared with newly diagnosed MM. Using murine MM cell/BM adipocyte coculture assays, we describe MM-induced lipolysis in adipocytes via activation of the lipolysis pathway. Upregulation of fatty acid transporters 1 and 4 on MM cells mediated the uptake of secreted free fatty acids (FFAs) by adjacent MM cells. The effect of FFAs on MM cells was dose dependent and revealed increased proliferation at lower concentrations vs induction of lipotoxicity at higher concentrations. Lipotoxicity occurred via the ferroptosis pathway. Exogenous treatment with arachidonic acid, a very-long-chain FFA, in a murine plasmacytoma model displayed a reduction in tumor burden. Taken together, our data reveal a novel pathway involving MM cell-induced lipolysis in BM adipocytes and suggest prevention of FFA uptake by MM cells as a potential target for myeloma therapeutics.

Role of TRPV4 Channel in Human White Adipocytes Metabolic Activity

BACKGROUND

Intracellular calcium (Ca2+) homeostasis plays an essential role in adipocyte metabolism and its alteration is associated with obesity and related disorders. Transient receptor potential vanilloid 4 (TRPV4) channels are an important Ca2+ pathway in adipocytes and their activity is regulated by metabolic mediators such as insulin. In this study, we evaluated the role of TRPV4 channels in metabolic activity and adipokine secretion in human white adipocytes.

METHODS

Human white adipocytes were freshly cultured and the effects of the activation and inhibition of TRPV4 channels on lipolysis, glucose uptake, lactate production, and leptin and adiponectin secretion were evaluated.

RESULTS

Under basal and isoproterenol-stimulated conditions, TRPV4 activation by GSK1016709A decreased lipolysis whereas HC067047, an antagonist, increased lipolysis. The activation of TRPV4 resulted in increased glucose uptake and lactate production under both basal conditions and insulin-stimulated conditions; in contrast HC067047 decreased both parameters. Leptin production was increased, and adiponectin production was diminished by TRPV4 activation and its inhibition had the opposite effect.

CONCLUSION

Our results suggested that TRPV4 channels are metabolic mediators involved in proadipogenic processes and glucose metabolism in adipocyte biology. TRPV4 channels could be a potential pharmacological target to treat metabolic disorders.

Leukemia stem cell-bone marrow microenvironment interplay in acute myeloid leukemia development

Despite the advances in intensive chemotherapy regimens and targeted therapies, overall survival (OS) of acute myeloid leukemia (AML) remains unfavorable due to inevitable chemotherapy resistance and high relapse rate, which mainly caused by the persistence existence of leukemia stem cells (LSCs). Bone marrow microenvironment (BMM), the home of hematopoiesis, has been considered to play a crucial role in both hematopoiesis and leukemogenesis. When interrupted by the AML cells, a malignant BMM formed and thus provided a refuge for LSCs and protecting them from the cytotoxic effects of chemotherapy. In this review, we summarized the alterations in the bidirectional interplay between hematopoietic cells and BMM in the normal/AML hematopoietic environment, and pointed out the key role of these alterations in pathogenesis and chemotherapy resistance of AML. Finally, we focused on the current potential BMM-targeted strategies together with future prospects and challenges. Accordingly, while further research is necessary to elucidate the underlying mechanisms behind LSC–BMM interaction, targeting the interaction is perceived as a potential therapeutic strategy to eradicate LSCs and ultimately improve the outcome of AML.

Bone marrow adiposity and the hematopoietic niche: A historical perspective of reciprocity, heterogeneity, and lineage commitment

PURPOSE

Here we review the current knowledge on bone marrow adipocytes (BMAds) as active contributors to the regulation of the hematopoietic niche, and as potentially pivotal players in the progression of hematological malignancies. We highlight the hierarchical and functional heterogeneity of the adipocyte lineage within the bone marrow, and how potentially different contexts dictate their interactions with hematopoietic populations.

RECENT FINDINGS

Growing evidence associates the adipocyte lineage with important functions in hematopoietic regulation within the BM niche. Initially proposed to serve as negative regulators of the hematopoietic microenvironment, studies have also demonstrated that BMAds positively influence the survival and maintenance of hematopoietic stem cells (HSCs). These seemingly incongruous findings may at least be partially explained by stage-specificity across the adipocytic differentiation axis and by BMAds subtypes, suggesting that the heterogeneity of these populations allows for differential context-based interactions. One such distinction relies on the location of adipocytes. Constitutive bone marrow adipose tissue (cBMAT) historically associates to the "yellow" marrow containing so-called "stable" BMAs larger in size, less responsive to stimuli, and linked to HSC quiescence. On the other hand, regulated bone marrow adipose tissue (rBMAT)-associated adipocytes, also referred to as "labile" are smaller, more responsive to hematopoietic demand and strategically situated in hematopoietically active regions of the skeleton. Here we propose a model where the effect of distinct BM stromal cell populations (BMSC) in hematopoiesis is structured along the BMSC-BMAd differentiation axis, and where the effects on HSC maintenance versus hematopoietic proliferation are segregated. In doing so, it is possible to explain how recently identified, adipocyte-primed leptin receptor-expressing, CXCL12-high adventitial reticular cells (AdipoCARs) and marrow adipose lineage precursor cells (MALPs) best support active hematopoietic cell proliferation, while adipose progenitor cells (APCs) and maturing BMAd gradually lose the capacity to support active hematopoiesis, favoring HSC quiescence. Implicated soluble mediators include MCP-1, PAI-1, NRP1, possibly DPP4 and limiting availability of CXCL12 and SCF. How remodeling occurs within the BMSC-BMAd differentiation axis is yet to be elucidated and will likely unravel a three-way regulation of the hematopoietic, bone, and adipocytic compartments orchestrated by vascular elements. The interaction of malignant hematopoietic cells with BMAds is precisely contributing to unravel specific mechanisms of remodeling.

SUMMARY

BMAds are important operative components of the hematopoietic microenvironment. Their heterogeneity directs their ability to exert a range of regulatory capacities in a manner dependent on their hierarchical, spatial, and biological context. This complexity highlights the importance of (i) developing experimental tools and nomenclature adapted to address stage-specificity and heterogeneity across the BMSC-BMAd differentiation axis when reporting effects in hematopoiesis, (ii) interpreting gene reporter studies within this framework, and (iii) quantifying changes in all three compartments (hematopoiesis, adiposity and bone) when addressing interdependency.

Transient Receptor Potential (TRP) Channels in Haematological Malignancies: An Update

Transient receptor potential (TRP) channels are improving their importance in different cancers, becoming suitable as promising candidates for precision medicine. Their important contribution in calcium trafficking inside and outside cells is coming to light from many papers published so far. Encouraging results on the correlation between TRP and overall survival (OS) and progression-free survival (PFS) in cancer patients are available, and there are as many promising data from in vitro studies. For what concerns haematological malignancy, the role of TRPs is still not elucidated, and data regarding TRP channel expression have demonstrated great variability throughout blood cancer so far. Thus, the aim of this review is to highlight the most recent findings on TRP channels in leukaemia and lymphoma, demonstrating their important contribution in the perspective of personalised therapies.

Myeloma-bone marrow adipocyte axis in tumour survival and treatment response

Multiple myeloma is an incurable cancer of the bone marrow that is dependent on its microenvironment, including bone marrow adipocytes (BMAds). Here, we discuss our findings that the reciprocal interaction of myeloma cells and BMAds, leads to myeloma cell survival and induces metabolic dysfunction and senescence-associated secretory phenotype in BMAds.

Hematopoietic Stem Cell Niche During Homeostasis, Malignancy, and Bone Marrow Transplantation

Self-renewal and multidirectional differentiation of hematopoietic stem cells (HSCs) are strictly regulated by numerous cellular components and cytokines in the bone marrow (BM) microenvironment. Several cell types that regulate HSC niche have been identified, including both non-hematopoietic cells and HSC-derived cells. Specific changes in the niche composition can result in hematological malignancies. Furthermore, processes such as homing, proliferation, and differentiation of HSCs are strongly controlled by the BM niche and have been reported to be related to the success of hematopoietic stem cell transplantation (HSCT). Single-cell sequencing and in vivo imaging are powerful techniques to study BM microenvironment in hematological malignancies and after HSCT. In this review, we discuss how different components of the BM niche, particularly non-hematopoietic and hematopoietic cells, regulate normal hematopoiesis, and changes in the BM niche in leukemia and after HSCT. We believe that this comprehensive review will provide clues for further research on improving HSCT efficiency and exploring potential therapeutic targets for leukemia.

Bone Marrow Adipocytes: A Link between Obesity and Bone Cancer

Cancers that grow in the bone marrow are for most patients scary, painful, and incurable. These cancers are especially hard to treat due to the supportive microenvironment provided by the bone marrow niche in which they reside. New therapies designed to target tumor cells have extended the life expectancy for these patients, but better therapies are needed and new ideas for how to target these cancers are crucial. This need has led researchers to interrogate whether bone marrow adipocytes (BMAds), which increase in number and size during aging and in obesity, contribute to cancer initiation or progression within the bone marrow. Across the globe, the consensus in the field is a unified "yes". However, how to target these adipocytes or the factors they produce and how BMAds interact with different tumor cells are open research questions. Herein, we review this research field, with the goal of accelerating research in the network of laboratories working in this area and attracting bright scientists with new perspectives and ideas to the field in order to bring about better therapies for patients with bone cancers.

Calcium and TRPV4 promote metastasis by regulating cytoskeleton through the RhoA/ROCK1 pathway in endometrial cancer

Transient receptor potential vanilloid 4 (TRPV4) is a calcium-permeable cation channel that has been associated with several types of cancer. However, its biological significance, as well as its related mechanism in endometrial cancer (EC) still remains elusive. In this study, we examined the function of calcium in EC, with a specific focus on TRPV4 and its downstream pathway. We reported here on the findings that a high level of serum ionized calcium was significantly correlated with advanced EC progression, and among all the calcium channels, TRPV4 played an essential role, with high levels of TRPV4 expression associated with cancer progression both in vitro and in vivo. Proteomic and bioinformatics analysis revealed that TRPV4 was involved in cytoskeleton regulation and Rho protein pathway, which regulated EC cell migration. Mechanistic investigation demonstrated that TRPV4 and calcium influx acted on the cytoskeleton via the RhoA/ROCK1 pathway, ending with LIMK/cofilin activation, which had an impact on F-actin and paxillin (PXN) levels. Overall, our findings indicated that ionized serum calcium level was significantly associated with poor outcomes and calcium channel TRPV4 should be targeted to improve therapeutic and preventive strategies in EC.