Expression and Function of Leptin Receptor Isoforms in Myeloid Leukemia and Myelodysplastic Syndromes: Proliferative and Anti-Apoptotic Activities

Unveiling novel insights in acute myeloid leukemia through single-cell RNA sequencing

Acute myeloid leukemia (AML) is a complex and heterogeneous group of aggressive hematopoietic stem cell disease. The presence of diverse and functionally distinct populations of leukemia cells within the same patient's bone marrow or blood poses a significant challenge in diagnosing and treating AML. A substantial proportion of AML patients demonstrate resistance to induction chemotherapy and a grim prognosis upon relapse. The rapid advance in next generation sequencing technologies, such as single-cell RNA-sequencing (scRNA-seq), has revolutionized our understanding of AML pathogenesis by enabling high-resolution interrogation of the cellular heterogeneity in the AML ecosystem, and their transcriptional signatures at a single-cell level. New studies have successfully characterized the inextricably intertwined interactions among AML cells, immune cells and bone marrow microenvironment and their contributions to the AML development, therapeutic resistance and relapse. These findings have deepened and broadened our understanding the complexity and heterogeneity of AML, which are difficult to detect with bulk RNA-seq. This review encapsulates the burgeoning body of knowledge generated through scRNA-seq, providing the novel insights and discoveries it has unveiled in AML biology. Furthermore, we discuss the potential implications of scRNA-seq in therapeutic opportunities, focusing on immunotherapy. Finally, we highlight the current limitations and future direction of scRNA-seq in the field.

The role of adiposity, adipokines and polymorphisms of leptin and adiponectin in myelodysplastic syndromes

The aim of the present study was to investigate the relationship between leptin and adiponectin gene polymorphisms, circulating levels of leptin and adiponectin, adiposity and clinical markers in patients with myelodysplastic syndrome (MDS). This cross-sectional study was conducted with 102 adults and elderly MDS patients and 102 age- and sex-matched controls. Clinical characteristics, co-morbidities, anthropometric data, laboratory evaluation and genetic analysis (polymorphisms -2548G > A/rs7799039 of the LEP gene and +276G > T/rs1501299 of the ADIPOQ gene) were investigated. Serum leptin was higher and adiponectin lower in MDS when compared with controls. There was a significant positive correlation between serum leptin levels and BMI (r = 0·264, P = 0·025), waist circumference (r = 0·235, P = 0·047), body fat percentage (BF %) (r = 0·373, P = 0·001) and the fat mass index (FMI) (r = 0·371, P < 0·001). A lower mean adiponectin was found among patients with high BF %, higher visceral adiposity index and metabolic syndrome. A significant association was found between the AA genotype (mutant) of the LEP polymorphism rs7799039 and male sex and blast excess (≥ 5 %). In addition, a significant association was observed between the TT genotype (mutant) of the ADIPOQ rs1501299 polymorphism and Fe overload. These results demonstrate the importance of a comprehensive and systematic evaluation in patients with MDS in order to identify and control negative factors not related to the disease at an early stage.

Obesity and Leukemia: Biological Mechanisms, Perspectives, and Challenges

PURPOSE OF REVIEW

To examine the epidemiological data on obesity and leukemia; evaluate the effect of obesity on leukemia outcomes in childhood acute lymphoblastic leukemia (ALL) survivors; assess the potential mechanisms through which obesity may increase the risk of leukemia; and provide the effects of obesity management on leukemia. Preventive (diet, physical exercise, obesity pharmacotherapy, bariatric surgery) measures, repurposing drugs, candidate therapeutic agents targeting oncogenic pathways of obesity and insulin resistance in leukemia as well as challenges of the COVID-19 pandemic are also discussed.

RECENT FINDINGS

Obesity has been implicated in the development of 13 cancers, such as breast, endometrial, colon, renal, esophageal cancers, and multiple myeloma. Leukemia is estimated to account for approximately 2.5% and 3.1% of all new cancer incidence and mortality, respectively, while it represents the most frequent cancer in children younger than 5 years. Current evidence indicates that obesity may have an impact on the risk of leukemia. Increased birthweight may be associated with the development of childhood leukemia. Obesity is also associated with worse outcomes and increased mortality in leukemic patients. However, there are several limitations and challenges in meta-analyses and epidemiological studies. In addition, weight gain may occur in a substantial number of childhood ALL survivors while the majority of studies have documented an increased risk of relapse and mortality among patients with childhood ALL and obesity. The main pathophysiological pathways linking obesity to leukemia include bone marrow adipose tissue; hormones such as insulin and the insulin-like growth factor system as well as sex hormones; pro-inflammatory cytokines, such as IL-6 and TNF-α; adipocytokines, such as adiponectin, leptin, resistin, and visfatin; dyslipidemia and lipid signaling; chronic low-grade inflammation and oxidative stress; and other emerging mechanisms. Obesity represents a risk factor for leukemia, being among the only known risk factors that could be prevented or modified through weight loss, healthy diet, and physical exercise. Pharmacological interventions, repurposing drugs used for cardiometabolic comorbidities, and bariatric surgery may be recommended for leukemia and obesity-related cancer prevention.

LEP promoter methylation in the initiation and progression of clonal cytopenia of undetermined significance and myelodysplastic syndrome

BACKGROUND

Idiopathic non-clonal cytopenia (ICUS) and clonal cytopenia (CCUS) are common in the elderly population. While these entities have similar clinical presentations with peripheral blood cytopenia and less than 10% bone marrow dysplasia, their malignant potential is different and the biological relationship between these disorders and myeloid neoplasms such as myelodysplastic syndrome (MDS) is not fully understood. Aberrant DNA methylation has previously been described to play a vital role in MDS and acute myeloid leukemia (AML) pathogenesis. In addition, obesity confers a poorer prognosis in MDS with inferior overall survival and a higher rate of AML transformation. In this study, we measured DNA methylation of the promoter for the obesity-regulated gene LEP, encoding leptin, in hematopoietic cells from ICUS, CCUS and MDS patients and healthy controls. We investigated whether LEP promoter methylation is an early event in the development of myeloid neoplasms and whether it is associated with clinical outcome.

RESULTS

We found that blood cells of patients with ICUS, CCUS and MDS all have a significantly hypermethylated LEP promoter compared to healthy controls and that LEP hypermethylation is associated with anemia, increased bone marrow blast percentage, and lower plasma leptin levels. MDS patients with a high LEP promoter methylation have a higher risk of progression, shorter progression-free survival, and inferior overall survival. Furthermore, LEP promoter methylation was an independent risk factor for the progression of MDS in a multivariate Cox regression analysis.

CONCLUSION

In conclusion, hypermethylation of the LEP promoter is an early and frequent event in myeloid neoplasms and is associated with a worse prognosis.

Whole-Genome DNA Methylation Sequencing Reveals Epigenetic Changes in Myelodysplastic Syndromes

Epigenetic dysregulation of cancer-associated genes has been identified to contribute to the pathogenesis of myelodysplastic syndromes (MDS). However, few studies have elucidated the whole-genome DNA methylation in the initiation pathogenesis of MDS. Reduced representation bisulfite sequencing was performed in five de novo MDS patients and four controls to investigate epigenetic alterations in MDS pathogenesis. The mean global methylation in five MDS patients showed no significant difference compared with the four controls. In depth, a total of 1,459 differentially methylated fragments, including 759 hypermethylated and 700 hypomethylated fragments, were identified between MDS patients and controls. Targeted bisulfite sequencing further identified that hypermethylation of DLEU7, FOXR1, LEP, and PANX2 were frequent events in an additional cohort of MDS patients. Subsequently, LEP hypermethylation was confirmed by real-time quantitative methylation-specific PCR in an expanded cohort of larger MDS patients. In clinics, LEP hypermethylation tended to be associated with lower bone marrow blasts and was significantly correlated with U2AF1 mutation. Survival analysis indicated that LEP hypermethylation was associated with a markedly longer survival time but was not an independent prognostic biomarker in MDS patients. Functional studies revealed pro-proliferative and anti-apoptotic effects of leptin in the MDS cell line SKM-1, and it was significantly associated with cell growth and death as well as the Toll-like receptor and NF-kappa B signaling pathways. Collectively, our findings demonstrated that whole-genome DNA methylation analysis identified novel epigenetic alterations such as DLEU7, FOXR1, LEP, and PANX2 methylations as frequent events in MDS. Moreover, LEP might play a role in MDS pathogenesis, and LEP hypermethylation was associated with longer survival but not as an independent prognostic biomarker in MDS.

Management of Hematologic Malignancies in the Era of COVID-19 Pandemic: Pathogenetic Mechanisms, Impact of Obesity, Perspectives, and Challenges

The COVID-19 pandemic brought about an unprecedented societal and healthcare system crisis, considerably affecting healthcare workers and patients, particularly those with chronic diseases. Patients with hematologic malignancies faced a variety of challenges, pertinent to the nature of an underlying hematologic disorder itself as well as its therapy as a risk factor for severe SARS-CoV-2 infection, suboptimal vaccine efficacy and the need for uninterrupted medical observation and continued therapy. Obesity constitutes another factor which was acknowledged since the early days of the pandemic that predisposed people to severe COVID-19, and shares a likely causal link with the pathogenesis of a broad spectrum of hematologic cancers. We review here the epidemiologic and pathogenetic features that obesity and hematologic malignancies share, as well as potential mutual pathophysiological links predisposing people to a more severe SARS-CoV-2 course. Additionally, we attempt to present the existing evidence on the multi-faceted crucial challenges that had to be overcome in this diverse patient group and discuss further unresolved questions and future challenges for the management of hematologic malignancies in the era of COVID-19.

The Head-to-Toe Hormone: Leptin as an Extensive Modulator of Physiologic Systems

Leptin is a well-known hunger-sensing peptide hormone. The role of leptin in weight gain and metabolic homeostasis has been explored for the past two decades. In this review, we have tried to shed light upon the impact of leptin signaling on health and diseases. At low or moderate levels, this peptide hormone supports physiological roles, but at chronically higher doses exhibits detrimental effects on various systems. The untoward effects we observe with chronically higher levels of leptin are due to their receptor-mediated effect or due to leptin resistance and are not well studied. This review will help us in understanding the non-anorexic roles of leptin, including their contribution to the metabolism of various systems and inflammation. We will be able to get an alternative perspective regarding the physiological and pathological roles of this mysterious peptide hormone.

The Bone Marrow Microenvironment in B-Cell Development and Malignancy

B lymphopoiesis is characterized by progressive loss of multipotent potential in hematopoietic stem cells, followed by commitment to differentiate into B cells, which mediate the humoral response of the adaptive immune system. This process is tightly regulated by spatially distinct bone marrow niches where cells, including mesenchymal stem and progenitor cells, endothelial cells, osteoblasts, osteoclasts, and adipocytes, interact with B-cell progenitors to direct their proliferation and differentiation. Recently, the B-cell niche has been implicated in initiating and facilitating B-cell precursor acute lymphoblastic leukemia. Leukemic cells are also capable of remodeling the B-cell niche to promote their growth and survival and evade treatment. Here, we discuss the major cellular components of bone marrow niches for B lymphopoiesis and the role of the malignant B-cell niche in disease development, treatment resistance and relapse. Further understanding of the crosstalk between leukemic cells and bone marrow niche cells will enable development of additional therapeutic strategies that target the niches in order to hinder leukemia progression.

Pre-Transplant Serum Leptin Levels and Relapse of Acute Myeloid Leukemia after Allogeneic Transplantation

Weight loss and metabolic activity influence outcome after allogeneic stem cell transplantation (alloSCT). This study evaluates pre-conditioning Leptin, a peptide hormone involved in metabolism and immune homeostasis, as a prognostic factor for survival, relapse and non-relapse mortality (NRM) following alloSCT. Leptin serum levels prior to conditioning were determined in a cohort of patients transplanted for various hematologic malignancies (n = 524) and correlated retrospectively with clinical outcome. Findings related to patients with acute leukemia (AL) from this sample were validated in an independent cohort. Low pre-conditioning serum Leptin was an independent prognostic marker for increased risk of relapse (but not of NRM and overall mortality) following alloSCT for AL of intermediate and advanced stage (beyond first complete remission). Multivariate analysis revealed a hazard ratio (HR) for relapse of 0.75 per log2 increase (0.59–0.96, p = 0.020). This effect was similar in an independent validation cohort. Pre-conditioning serum Leptin was validated as a prognostic marker for early relapse by fitting the multivariate Cox model to the validation data. Pre-conditioning serum Leptin levels may serve as an independent prognostic marker for relapse following alloSCT in intermediate and advanced stage AL patients. Prospective studies are required to prove whether serum Leptin could be used for guiding nutritional intervention in patients with AL undergoing alloSCT.

CCN2 (Cellular Communication Network factor 2) in the bone marrow microenvironment, normal and malignant hematopoiesis

CCN2, formerly termed Connective Tissue Growth Factor, is a protein belonging to the Cellular Communication Network (CCN)-family of secreted extracellular matrix-associated proteins. As a matricellular protein it is mainly considered to be active as a modifier of signaling activity of several different signaling pathways and as an orchestrator of their cross-talk. Furthermore, CCN2 and its fragments have been implicated in the regulation of a multitude of biological processes, including cell proliferation, differentiation, adhesion, migration, cell survival, apoptosis and the production of extracellular matrix products, as well as in more complex processes such as embryonic development, angiogenesis, chondrogenesis, osteogenesis, fibrosis, mechanotransduction and inflammation. Its function is complex and context dependent, depending on cell type, state of differentiation and microenvironmental context. CCN2 plays a role in many diseases, especially those associated with fibrosis, but has also been implicated in many different forms of cancer. In the bone marrow (BM), CCN2 is highly expressed in mesenchymal stem/stromal cells (MSCs). CCN2 is important for MSC function, supporting its proliferation, migration and differentiation. In addition, stromal CCN2 supports the maintenance and longtime survival of hematopoietic stem cells, and in the presence of interleukin 7, stimulates the differentiation of pro-B lymphocytes into pre-B lymphocytes. Overexpression of CCN2 is seen in the majority of B-acute lymphoblastic leukemias, especially in certain cytogenetic subgroups associated with poor outcome. In acute myeloid leukemia, CCN2 expression is increased in MSCs, which has been associated with leukemic engraftment in vivo. In this review, the complex function of CCN2 in the BM microenvironment and in normal as well as malignant hematopoiesis is discussed. In addition, an overview is given of data on the remaining CCN family members regarding normal and malignant hematopoiesis, having many similarities and some differences in their function.

Increased body mass index is a risk factor for acute promyelocytic leukemia

Introduction

Obesity has become increasingly prevalent worldwide and is a risk factor for many malignancies. We studied the correlation between body mass index (BMI) and the incidence of acute promyelocytic leukemia (APL), non-APL acute myeloid leukemia (AML), acute lymphoblastic leukemia (ALL), and control hospitalized patients without leukemia in the same community.

Methods

Multi-center, retrospective analysis of 71,196 patients: APL (n=200), AML (n=437), ALL (n=103), non-leukemia hospitalized (n=70,456) admitted to University of Maryland and Johns Hopkins Cancer Centers, and University of Maryland Medical Center.

Results

Patients with APL had a significantly higher unadjusted mean and median BMI (32.5 kg/m2 and 30.3 kg/m2) than those with AML (28.3 kg/m2 and 27.1 kg/m2), ALL (29.3 kg/m2 and 27.7 kg/m2), and others (29.3 kg/m2 and 27.7 kg/m2) (p<0.001). Log-transformed BMI multivariable models demonstrated that APL patients had a significantly higher adjusted mean BMI by 3.7 kg/m2 (p<0.001) or approximately 10% (p<0.01) compared to the other groups, when controlled for sex, race, and age.

Conclusions

This study confirms that when controlled for sex, age, and race there is an independent association of higher BMI among patients with APL compared to patients with ALL, AML, and hospitalized individuals without leukemia in the same community.

Leptin receptor, a surface marker for a subset of highly engrafting long-term functional hematopoietic stem cells

The hematopoietic system is sustained by a rare population of hematopoietic stem cells (HSCs), which emerge during early embryonic development and then reside in the hypoxic niche of the adult bone marrow microenvironment. Although leptin receptor (Lepr)-expressing stromal cells are well-studied as critical regulators of murine hematopoiesis, the biological implications of Lepr expression on HSCs remain largely unexplored. We hypothesized that Lepr⁺HSCs are functionally different from other HSCs. Using in vitro and in vivo experimental approaches, we demonstrated that Lepr further differentiates SLAM HSCs into two distinct populations; Lepr⁺HSCs engrafted better than Lepr^-HSCs in primary transplant. Compared to Lepr^-LSK cells, Lepr⁺LSK cells were highly enriched for extensively repopulating and self-renewing HSCs. Molecularly, Lepr⁺HSCs were characterized by a pro-inflammatory transcriptomic profile enriched for Type-I Interferon and Interferon-gamma (IFN-γ) response pathways, which are known to be critical for the emergence of HSCs in the embryo. We conclude that although Lepr⁺HSCs represent a minor subset of HSCs, they are highly engrafting cells that possess embryonic-like transcriptomic characteristics, and that Lepr can serve as a reliable marker for functional long-term HSCs, which may have potential clinical applicability.

Effects of Obesity on Overall Survival of Adults With Acute Myeloid Leukemia

BACKGROUND

The role of obesity in prognosis of acute myeloid leukemia (AML) is debatable. Our retrospective study aimed to determine the effect of obesity on overall survival (OS) in AML.

PATIENTS AND METHODS

AML patients diagnosed at University of Nebraska Medical Center were divided into 3 groups according to body mass index (BMI): normal (18.5-25 kg/m2) or underweight (< 18.5 kg/m2); overweight (25-30 kg/m2); and obese (≥ 30 kg/m2). Chi-square test, Kruskal-Wallis test, and ANOVA were used to examine the association of BMI with baseline characteristics. Mann-Whitney test was used for pairwise comparisons of hematopoietic cell transplantation (HCT) comorbidity index. Bonferroni correction was used to adjust P values. OS, defined as time from diagnosis to death from any cause, was determined by the Kaplan-Meier method; comparisons of survival curves were done using log-rank test. Cox regression analysis was performed to detect the effect of BMI on OS.

RESULTS

Of 314 patients, 38% were obese, 68% received intensive chemotherapy, and 30% underwent HCT. Patient characteristics for all BMI groups were similar except greater HCT comorbidity index in obese patients. Actual body weight was used to calculate the chemotherapy dose in 92% of obese patients. The rates of receipt of HCT in normal, overweight, and obese groups were 33%, 32%, and 25%, respectively (P = .6). One-year OS values for normal/underweight, overweight, and obese groups was 42%, 45%, and 39%, respectively (P = .31). On multivariate analysis, obesity was associated with worse OS compared to normal-weight (hazard ratio = 0.6; 95% confidence interval, 0.4-0.9; P = .03) but not overweight patients.

CONCLUSION

Obesity confers worse prognosis in AML. Differences in OS were not the result of differences in chemotherapy dose or receipt of HCT.

Serum Levels of Leptin in Multiple Myeloma Patients and Its Relation to Angiogenic and Inflammatory Cytokines

Background

Leptin, apart from the regulation of food intake, has been implicated in hematopoiesis, the immune response and angiogenesis. Leptin has been found to be decreased in various hematological malignancies. In the present study leptin was measured in multiple myeloma (MM) patients before and after treatment and correlated with other angiogenic molecules and markers of disease activity.

Methods

Serum leptin, vascular endothelial growth factor (VEGF), basic fibroblast growth factor (b-FGF), interleukin-1 beta (IL-1β), beta 2 microglobulin (β2M) and C-reactive protein (CRP) were measured in 62 newly diagnosed MM patients, 22 of whom obtaining disease stabilization after treatment. The same parameters were measured in 20 healthy controls. Disease stage was defined according to the Durie-Salmon criteria.

Results

Leptin, VEGF, b-FGF, IL-1β, and β2M were significantly higher in newly diagnosed MM patients than in controls (p<0.05). VEGF, b-FGF, IL-1β, β2M, CRP but not leptin increased with advancing stage of disease (p<0.01). All parameters decreased significantly following treatment (p<0.001). Although IL-1β correlated positively with VEGF, β2M, b-FGF and CRP, leptin did not correlate with any of the measured parameters.

Conclusion

Leptin serum levels do not reflect disease severity in MM. However, there seems to be a decrease in leptin following treatment, which may be associated with an alteration in the metabolic state or the chemokine milieu.

Leptin Receptor-Deficient MMTV-TGF-α/Leprdb Leprdb Female Mice Do Not Develop Oncogene-Induced Mammary Tumors

Being overweight is a risk factor for postmenopausal breast cancer and is associated with an increased incidence and shortened latency of spontaneous and chemically Induced mammary tumors in rodents. However, leptin-deficient obese Lepob Lepob female mice have reduced incidences of spontaneous and oncogene-induced mammary tumors. Of interest, leptin enhances the proliferation of human breast cancer cell lines in which leptin receptors are expressed, which suggests that leptin signaling plays a role in tumor development. We evaluated oncogene-induced mammary tumor development in obese MMTV-TGF-α/Leprdb Leprdb mice that exhibit a defect in OB-Rb, which is considered to be the major signaling isoform of the leptin receptor. Lepr and MMTV-TGF-α mice were crossed, and the offspring were genotyped for oncogene expression and the determination of Lepr status. Lean MMTV-TGF-α/Lepr+ Lepr+ (homozygous) and MMTV-TGF-α/Lepr+ Leprdb (heterozygous) mice and obese MMTV-TGF-α/Leprdb Leprdb mice were monitored until age 104 weeks. Body weights of MMTV-TGF-α/Leprdb Leprdb mice were significantly heavier than those of the lean groups. No mammary tumors were detected in MMTV-TGF-α/LeprdbLeprdb mice, whereas the incidence of mammary tumors in MMTV-TGF-α/Lepr+ Lepr+ and MMTV-TGF-α/Lepr+ Leprdb mice was 69% and 82%, respectively. Examination of mammary tissue whole mounts indicated an absence of duct formation and branching for MMTV-TGF-α/Leprdb Leprdb mice. Both age at mammary tumor detection and tumor burden (tumors/mouse and tumor weights) were similar for the lean genotypes. Serum leptin levels of MMTV-TGF-α/Leprdb Leprdb mice were 12-20-fold higher than levels of lean mice. Thus, despite elevated serum leptin levels, leptin receptor-deficient MMTV-TGF-α/Leprdb Leprdb mice do not develop mammary tumors. This study provides additional evidence that leptin and its cognate receptor may be involved in mammary tumorigenesis.

Pericytes, integral components of adult hematopoietic stem cell niches

The interest in perivascular cells as a niche for adult hematopoietic stem cells (HSCs) is significantly growing. In the adult bone marrow (BM), perivascular cells and HSCs cohabit. Among perivascular cells, pericytes are precursors of mesenchymal stem/stromal cells (MSCs) that are capable of differentiating into osteoblasts, adipocytes and chondrocytes. In situ, pericytes are recognised by their localisation to the abluminal side of the blood vessel wall and closely associated with endothelial cells, in combination with the expression of markers such as CD146, neural glial 2 (NG2), platelet derived growth factor receptor β (PDGFRβ), α-smooth muscle actin (α-SMA), nestin (Nes) and/or leptin receptor (LepR). However, not all pericytes share a common phenotype: different immunophenotypes can be associated with distinct mesenchymal features, including hematopoietic support. In adult BM, arteriolar and sinusoidal pericytes control HSC behaviour, maintenance, quiescence and trafficking through paracrine effects. Different groups identified and characterized hematopoietic supportive pericyte subpopulations using various markers and mouse models. In this review, we summarize recent work performed by others to understand the role of the perivascular niche in the biology of HSCs in adults, as well as their importance in the development of therapies.

miRNA-mRNA integrative analysis in primary myelofibrosis CD34+ cells: role of miR-155/JARID2 axis in abnormal megakaryopoiesis

Primary myelofibrosis (PMF) is a myeloproliferative neoplasm characterized by megakaryocyte (MK) hyperplasia, bone marrow fibrosis, and abnormal stem cell trafficking. PMF may be associated with somatic mutations in JAK2, MPL, or CALR. Previous studies have shown that abnormal MKs play a central role in the pathophysiology of PMF. In this work, we studied both gene and microRNA (miRNA) expression profiles in CD34(+) cells from PMF patients. We identified several biomarkers and putative molecular targets such as FGR, LCN2, and OLFM4. By means of miRNA-gene expression integrative analysis, we found different regulatory networks involved in the dysregulation of transcriptional control and chromatin remodeling. In particular, we identified a network gathering several miRNAs with oncogenic potential (eg, miR-155-5p) and targeted genes whose abnormal function has been previously associated with myeloid neoplasms, including JARID2, NR4A3, CDC42, and HMGB3. Because the validation of miRNA-target interactions unveiled JARID2/miR-155-5p as the strongest relationship in the network, we studied the function of this axis in normal and PMF CD34(+) cells. We showed that JARID2 downregulation mediated by miR-155-5p overexpression leads to increased in vitro formation of CD41(+) MK precursors. These findings suggest that overexpression of miR-155-5p and the resulting downregulation of JARID2 may contribute to MK hyperplasia in PMF.

Connective tissue growth factor regulates adipocyte differentiation of mesenchymal stromal cells and facilitates leukemia bone marrow engraftment

Mesenchymal stromal cells (MSCs) are a major component of the leukemia bone marrow (BM) microenvironment. Connective tissue growth factor (CTGF) is highly expressed in MSCs, but its role in the BM stroma is unknown. Therefore, we knocked down (KD) CTGF expression in human BM-derived MSCs by CTGF short hairpin RNA. CTGF KD MSCs exhibited fivefold lower proliferation compared with control MSCs and had markedly fewer S-phase cells. CTGF KD MSCs differentiated into adipocytes at a sixfold higher rate than controls in vitro and in vivo. To study the effect of CTGF on engraftment of leukemia cells into BM, an in vivo model of humanized extramedullary BM (EXM-BM) was developed in NOD/SCID/IL-2rg(null) mice. Transplanted Nalm-6 or Molm-13 human leukemia cells engrafted at a threefold higher rate in adipocyte-rich CTGF KD MSC-derived EXM-BM than in control EXM-BM. Leptin was found to be highly expressed in CTGF KD EXM-BM and in BM samples of patients with acute myeloid and acute lymphoblastic leukemia, whereas it was not expressed in normal controls. Given the established role of the leptin receptor in leukemia cells, the data suggest an important role of CTGF in MSC differentiation into adipocytes and of leptin in homing and progression of leukemia.

A high-fat diet increases interleukin-3 and granulocyte colony-stimulating factor production by bone marrow cells and triggers bone marrow hyperplasia and neutrophilia in wistar rats

It is well established that the excessive consumption of a high-fat diet (HFD) results in overweight, obesity and an increase in leptin concentrations, which triggers a chronic inflammatory condition that is associated with a high white blood cell count. Two-month-old male Wistar rats were fed a control (CON) diet or an HFD for 12 weeks. After this period, hemogram, myelogram and biochemical parameters were evaluated along with the cell cycle and the percentage of CD34+ cells in the bone marrow as well as cell proliferation and differentiation assays and the production of stem cell factor, interleukin 3 (IL-3), granulocyte colony-stimulating factor (G-CSF) and granulocyte macrophage colony-stimulating factor (GM-CSF). The HFD animals exhibited leukocytosis and neutrophilia with increased C-reactive protein, leptin, cholesterol and triglyceride concentrations. In the HFD group, the bone marrow revealed myeloid hyperplasia, especially of the granulocytic compartment with a higher percentage of CD34+ cells and a higher percentage of cells in the G2/S/M cell cycle phases. In addition, the HFD bone marrow cells had a higher capacity to proliferate and differentiate into granulocytic cells in an in vitro system and a higher capacity to produce IL-3 and G-CSF. These data led us to infer that the HFD induces leukocytosis and neutrophilia suggesting alterations in hematopoiesis system modulation.

Trimming the fat: obesity and hematopoietic cell transplantation

Obesity, increasing worldwide, is common in patients undergoing hematopoietic cell transplantation (HCT). This complex physiological state may alter the outcome of cancer therapies by many mechanisms including direct effects on pathogenesis, host responses to disease and altered pharmacology of chemotherapy. Obesity has been associated with multiple adverse health outcomes. Reports of obese patients undergoing HCT are challenging to interpret because of the heterogeneity of obesity definitions, underlying diseases, graft sources and chemotherapy regimens employed. Compared with normal-weight patients, it appears that obese patients undergoing allogeneic HCT have a higher risk of non-relapse mortality and inferior survival whereas those receiving autologous HCT appear to have equivalent outcomes. These findings are also difficult to interpret because there is no consistent standard for calculating chemotherapy dose in this group and future studies on specific regimens in this population are urgently needed. Patients who have undergone bariatric surgery may be at risk for unexpected events because of impaired nutritional state and altered pharmacokinetics of oral drugs. We recommend that future studies utilize more consistent and biologically relevant definitions of obesity and that the pharmacokinetics and pharmacodynamics of specific conditioning regimens be studied. Until more evidence is available, a rationale is presented for dosing based on adjusted body weight. Moreover, recommendations are provided to guide future research efforts based on more definitive measurements of body fat and its distribution available through modern quantitative imaging techniques using dual energy X-ray absorptiometry or magnetic resonance imaging scanning.

Prevention of fasting-mediated bone marrow atrophy by leptin administration

Leptin is an adipokine that regulates body weight. In the current study, we demonstrate that continuous injection of leptin prevents the lymphocyte reduction observed in fasted mice, especially the immature B cell populations in the bone marrow. Although leptin administration reduced apoptotic cells in the bone marrow of fasted mice, it did not prevent glucocorticoid-mediated apoptosis in vitro. Bone marrow atrophy has also been shown in the leptin receptor-deficient db/db mice. In order to investigate the mechanisms underlying these processes, we transplanted bone marrow cells from db/db or control (+m/+m) mice into C.B-17/lcr-scid/scid mice. We found that the spleen and bone marrow B cell populations were completely reconstituted when db/db and +m/+m cells were transplanted into scid mice. Our findings suggest that direct interactions between leptin and bone marrow cells are not essential for the development of B cells in a metabologically normal environment.

Obesity and the risk for a hematological malignancy: leukemia, lymphoma, or myeloma

Studies on obesity and the risk for hematological malignancies are reviewed. The paper includes a discussion of the metabolic effects of obesity and their possible role in linking increased body fat to neoplasia.

The aggregate of epidemiological studies indicates a significantly elevated risk for cancer in people with a high body mass index (BMI); a “dose–response” effect exists with increasing risk as BMI increases from the normal to overweight to obese categories. Successful sustained weight loss decreases future risk. The relationship of being overweight to the risk for leukemia in the aggregate has been supported in several large cohort studies and two meta-analyses of cohort and case–control studies. One meta-analysis found an elevated risk for each of the four major subtypes of leukemia. A significant association between the risk for non-Hodgkin's lymphoma and elevated BMI was supported by a meta-analysis of 13 cohort and nine case–control studies. The risk for diffuse large B-cell lymphoma may be especially significant. A high BMI increases the risk for myeloma, as judged by a meta-analysis of 11 cohort and four case–control studies. The biological relationship of obesity to the risk for cancer (biological plausibility) is unresolved. The two major causal final pathways could be “inductive” or “selective.” The metabolic, endocrinologic, immunologic, and inflammatory-like changes resulting from obesity may increase the cell mutation rate, dysregulate gene function, disturb DNA repair, or induce epigenetic changes, favoring the induction of neoplastic transformation (inductive). Alternatively, obesity may create an environment in which pre-existing clones that are dormant are permitted (selected) to emerge.

Effect of Obesity on Breast Cancer Development

In recent years, obesity has been identified as a risk factor for the development of breast cancer in postmenopausal women, and it has been associated with a poor outcome. Many factors appear to be important in the mechanism of this increased risk, including estrogen, estrogen receptors, and the adipokines leptin and adiponectin. Estrogen, a potent mitogen for mammary cells, has long been implicated in the development of mammary tumors. Because adipose-associated aromatase activity increases the conversion of androgen to estrogen, mammary adipose tissue is thought to be an important source of local estrogen production. Leptin, which increases in the circulation in proportion to body fat stores, has been demonstrated in vitro to promote breast cancer cell growth. Animal models have also identified leptin as an important factor for the development of mammary tumors. In contrast to leptin, serum adiponectin concentrations are inversely related to body fat stores, and the addition of adiponectin to human breast cancer cells reduces cell proliferation and enhances apoptosis. This review explores the relationship between these factors and the development of mammary cancer in humans and mouse models.

Serial plasma concentrations of adiponectin, leptin, and resistin during therapy in children with acute lymphoblastic leukemia

PURPOSE

To investigate adipocytokine secretion, at diagnosis and during chemotherapy in children with the acute lymphoblastic leukemia (ALL).

PATIENTS AND METHODS

Serial measurements (6/patient) of the anti-inflammatory cytokine adiponectin and the proinflammatory adipocytokines leptin and resistin were performed at diagnosis and in nearly the entire period of therapy (up to 21 months), in 9 patients with ALL aged 2 to 7 years (median 4.3 y). Body mass index and leukemic burden were estimated at the same time points and correlated with adipocytokine levels. Nine healthy children matched for age, sex, and body mass index were used as controls.

RESULTS

At diagnosis, mean adiponectin levels were low (P<0.001) and mean leptin and resistin levels were high, compared with controls (P<0.001). During maintenance phase, adiponectin increased significantly (P=0.024), whereas leptin and resistin decreased (P=0.018 and P=0.020, respectively), compared with baseline values. However, adiponectin, despite its progressive increase, remained at lower levels toward the end of the maintenance phase, compared with controls, (P<0.001). Delta (final-baseline) mean adiponectin was negatively correlated with leukemic burden (P=0.019), whereas delta mean leptin and resistin were positively correlated with it (P=0.011 and P=0.031, respectively).

CONCLUSIONS

Low-plasma adiponectin and high leptin and resistin level are present at the ALL diagnosis. Adipocytokines alterations are progressively restored during therapy.

The warburg effect in leukemia-stroma cocultures is mediated by mitochondrial uncoupling associated with uncoupling protein 2 activation

In 1956, Otto Warburg proposed that the origin of cancer cells was closely linked to a permanent respiratory defect that bypassed the Pasteur effect (i.e., the inhibition of anaerobic fermentation by oxygen). Since then, permanent defects in oxygen consumption that could explain the dependence of cancer cells on aerobic glycolysis have not been identified. Here, we show that under normoxic conditions exposure of leukemia cells to bone marrow-derived mesenchymal stromal cells (MSC) promotes accumulation of lactate in the culture medium and reduces mitochondrial membrane potential (DeltaPsiM) in both cell types. Notably, the consumption of glucose was not altered in cocultures, suggesting that the accumulation of lactate was the result of reduced pyruvate metabolism. Interestingly, the decrease in DeltaPsiM was mediated by mitochondrial uncoupling in leukemia cells and was accompanied by increased expression of uncoupling protein 2 (UCP2). HL60 cells fail to increase UCP2 expression, are not uncoupled after coculture, and do not exhibit increased aerobic glycolysis, whereas small interfering RNA-mediated suppression of UCP2 in OCI-AML3 cells reversed mitochondrial uncoupling and aerobic glycolysis elicited by MSC. Taken together, these data suggest that microenvironment activation of highly conserved mammalian UCPs may facilitate the Warburg effect in the absence of permanent respiratory impairment.

Molecular signature of CD34+ hematopoietic stem and progenitor cells of patients with CML in chronic phase

In this study, we provide a molecular signature of highly enriched CD34+ cells from bone marrow of untreated patients with chronic myelogenous leukemia (CML) in chronic phase in comparison with normal CD34+ cells using microarrays covering 8746 genes. Expression data reflected several BCR-ABL-induced effects in primary CML progenitors, such as transcriptional activation of the classical mitogen-activated protein kinase pathway and the phosphoinositide-3 kinase/AKT pathway as well as downregulation of the proapoptotic gene IRF8. Moreover, novel transcriptional changes in comparison with normal CD34+ cells were identified. These include upregulation of genes involved in the transforming growth factorbeta pathway, fetal hemoglobin genes, leptin receptor, sorcin, tissue inhibitor of metalloproteinase 1, the neuroepithelial cell transforming gene 1 and downregulation of selenoprotein P. Additionally, genes associated with early hematopoietic stem cells (HSC) and leukemogenesis such as HoxA9 and MEIS1 were transcriptionally activated. Differential expression of differentiation-associated genes suggested an altered composition of the CD34+ cell population in CML. This was confirmed by subset analyses of chronic phase CML CD34+ cells showing an increase of the proportion of megakaryocyte-erythroid progenitors, whereas the proportion of HSC and granulocyte-macrophage progenitors was decreased in CML. In conclusion, our results give novel insights into the biology of CML and could provide the basis for identification of new therapeutic targets.

Susceptibility to Induced and Spontaneous Carcinogenesis Is Increased in Fatless A-ZIP/F-1 but not in Obese ob/ob Mice

Obesity is typically associated with increased tumor susceptibility, whereas caloric restriction, a regimen resulting in leanness, inhibits carcinogenesis. The link between adiposity and malignancies suggests that adipose tissue may influence carcinogenesis. An adipose tissue hormone, leptin, could be procarcinogenic because it stimulates proliferation in various tissues and tumor cell lines. Leptin may contribute to the correlation between adiposity and malignancies as its levels are usually increased in obese subjects and reduced by caloric restriction. We hypothesized that leptin deficiency, despite obesity, would inhibit carcinogenesis in leptin-null ob/ob mice and tested this hypothesis in two models: (a) two-stage skin carcinogenesis initiated by 7,12-dimethylbenz(a)anthracene and promoted by phorbol 12-myristate 13-acetate (PMA) and (b) p53 deficiency. Contrary to a typical association between obesity and enhanced carcinogenesis, obese ob/ob mice developed induced skin papillomas and spontaneous p53-deficient malignancies, mostly lymphomas, similarly to their lean littermates. Surprisingly, lipodystrophic (ZIP) mice that had very little both adipose tissue and leptin were highly susceptible to carcinogenesis. Hyperphagia, hyperinsulinemia, and hyperglycemia are unlikely to have contributed significantly to the enhancement of carcinogenesis in ZIP mice because similarly hyperphagic, hyperinsulinemic, and hyperglycemic ob/ob mice had normal susceptibility to carcinogenesis. Our data suggest that, in contrast to a well-known correlation between obesity and cancer, the direct effect of adipose tissue may rather be protective.

Leptin and leptin receptor polymorphisms are associated with increased risk and poor prognosis of breast carcinoma

BACKGROUND

Leptin (LEP) has been consistently associated with angiogenesis and tumor growth. Leptin exerts its physiological action through its specific receptor (LEPR). We have investigated whether genetic variations in LEP and LEPR have implications for susceptibility to and prognosis in breast carcinoma.

METHODS

We used the polymerase chain reaction and restriction enzyme digestion to characterize the variation of the LEP and LEPR genes in 308 unrelated Tunisian patients with breast carcinoma and 222 healthy control subjects. Associations of the clinicopathologic parameters and these genetic markers with the rates of the breast carcinoma-specific overall survival (OVS) and the disease free survival (DFS) were assessed using univariate and multivariate analyses.

RESULTS

A significantly increased risk of breast carcinoma was associated with heterozygous LEP (-2548) GA (OR = 1.45; P = 0.04) and homozygous LEP (-2548) AA (OR = 3.17; P = 0.001) variants. A highly significant association was found between the heterozygous LEPR 223QR genotype (OR = 1.68; P = 0.007) or homozygous LEPR 223RR genotype (OR = 2.26; P = 0.001) and breast carcinoma. Moreover, the presence of the LEP (-2548) A allele showed a significant association with decreased disease-free survival in breast carcinoma patients, and the presence of the LEPR 223R allele showed a significant association with decreased overall survival.

CONCLUSION

Our results indicated that the polymorphisms in LEP and LEPR genes are associated with increased breast cancer risk as well as disease progress, supporting our hypothesis for leptin involvement in cancer pathogenesis.

High Serum Leptin in Patients with Chronic Graft-Versus-Host Disease after Hematopoietic Stem Cell Transplantation

BACKGROUND

Increased serum leptin has been described after various organ transplants, with a mechanism that is still unclear.

METHODS

We measured serum leptin in 60 patients before and after allogeneic (allo) or autologous (auto) stem cell transplant (SCT) and in 60 healthy controls, matched for age and body mass index (BMI).

RESULTS

Serum leptin was higher in patients after SCT than before and in controls. Leptin production was higher after allo- than after auto-SCT; the presence of chronic graft-versus-host disease (cGVHD) was associated with the highest values. The physiological correlation with BMI was lost in the allogeneic setting, indicating a strong influence of factors other than the nutritional status on circulating leptin. No relationship was found between serum leptin levels and time from transplant, age, cortisol, C-reactive protein, and T-lymphocyte CD4-to-CD8 ratio. Among the cytokines secreted by type-1/type-2 T-helper lymphocytes, only serum interferon-gamma significantly correlated with serum leptin levels. Anti-leptin blocking antibodies partially inhibited T-cell activation in mixed lymphocyte reaction, suggesting a link between leptin and T-lymphocyte activation in the allo-SCT setting.

CONCLUSION

Taken together, these findings suggest that increased serum leptin concentrations may contribute to T-cell activation during development of cGVHD.

Leptin induces apoptosis via ERK/cPLA2/cytochrome c pathway in human bone marrow stromal cells

Leptin, the Ob gene product, has emerged recently as a key regulator of bone mass. However, the mechanism mediating leptin effect remains controversial. Because the action of leptin is dependent on its receptors, we analyzed their expression in osteoblast-lineage primary human bone marrow stromal cells (hBMSC). Both the short and long forms of leptin receptors were detected in hBMSC. Leptin significantly decreased the viability of hBMSC. This cytotoxic effect was prevented by Z-Val-Ala-Asp-fluoromethylketone, a pan-caspase inhibitor, implicating that leptin-induced hBMSC death was caspase-dependent. Further investigation demonstrated that leptin activated caspase-3 and caspase-9, but not caspase-8, and increased the cleavage of poly-(ADP-ribose) polymerase and cytochrome c release into cytosol. Leptin activated ERK, but not p38 and JNK, and up-regulated cPLA2 activity; the latter was abolished by pre-treatment of cells with the MEK inhibitor (PD98059 or U0126) or cPLA2 inhibitor (AACOCF3). PD98059, U0126, and AACOCF3 also diminished the leptin-induced cytochrome c release into cytosol, cell death, and caspase-3 activation. These data indicated that leptin induced hBMSC apoptosis via ERK/cPLA2/cytochrome c pathway with activation of caspase-9 and caspase-3, and cleavage of poly(ADP-ribose) polymerase. To our knowledge, this is the first study demonstrating the direct detrimental effect of leptin on bone cells.

Leptin accelerates autoimmune diabetes in female NOD mice

We have recently shown that leptin, the product of the obese gene, can directly influence T-cell function. In the work presented here, we explored the role of leptin in the development of spontaneous autoimmunity in the nonobese diabetic (NOD) mouse, an animal model for the study of human insulin-dependent diabetes mellitus (type 1 diabetes). We found that expression of serum leptin increased soon before the onset of hyperglycemia and diabetes in susceptible females. A pathogenetic role of leptin was assessed by administering recombinant leptin to young female and male NOD mice. Intraperitoneal injections of leptin accelerated autoimmune destruction of insulin-producing beta-cells and significantly increased interferon-gamma production in peripheral T-cells. These findings indicate that leptin can favor proinflammatory cell responses and directly influence development of autoimmune disease mediated by Th1 responses.

Leptin inhibits stress-induced apoptosis of T lymphocytes

Leptin, which is secreted by adipocytes, the placenta and the stomach, not only controls appetite through leptin receptors in the hypothalamus but also regulates cell-mediated immunity. In this study we have demonstrated that continuous injection of leptin prevents the reduction in lymphocyte numbers normally observed in fasted and steroid-injected mice. Consistent with leptin-induced protection, we observed up-regulation of the bcl-xL gene as a result of signal transduction via leptin receptors on lymphocytes. We suggest that leptin might contribute to the recovery of immune suppression in malnourished mice by inhibiting lymphocyte apoptosis.

Molecular classification of cancer: class discovery and class prediction by gene expression monitoring

Although cancer classification has improved over the past 30 years, there has been no general approach for identifying new cancer classes (class discovery) or for assigning tumors to known classes (class prediction). Here, a generic approach to cancer classification based on gene expression monitoring by DNA microarrays is described and applied to human acute leukemias as a test case. A class discovery procedure automatically discovered the distinction between acute myeloid leukemia (AML) and acute lymphoblastic leukemia (ALL) without previous knowledge of these classes. An automatically derived class predictor was able to determine the class of new leukemia cases. The results demonstrate the feasibility of cancer classification based solely on gene expression monitoring and suggest a general strategy for discovering and predicting cancer classes for other types of cancer, independent of previous biological knowledge.