Polycythemia is associated with bone loss and reduced osteoblast activity in mice

Revisiting Circulating Extracellular Matrix Fragments as Disease Markers in Myelofibrosis and Related Neoplasms

Philadelphia chromosome-negative chronic myeloproliferative neoplasms (MPNs) arise due to acquired somatic driver mutations in stem cells and develop over 10-30 years from the earliest cancer stages (essential thrombocythemia, polycythemia vera) towards the advanced myelofibrosis stage with bone marrow failure. The JAK2V617F mutation is the most prevalent driver mutation. Chronic inflammation is considered to be a major pathogenetic player, both as a trigger of MPN development and as a driver of disease progression. Chronic inflammation in MPNs is characterized by persistent connective tissue remodeling, which leads to organ dysfunction and ultimately, organ failure, due to excessive accumulation of extracellular matrix (ECM). Considering that MPNs are acquired clonal stem cell diseases developing in an inflammatory microenvironment in which the hematopoietic cell populations are progressively replaced by stromal proliferation-"a wound that never heals"-we herein aim to provide a comprehensive review of previous promising research in the field of circulating ECM fragments in the diagnosis, treatment and monitoring of MPNs. We address the rationales and highlight new perspectives for the use of circulating ECM protein fragments as biologically plausible, noninvasive disease markers in the management of MPNs.

Hypoxia-Inducible Factors Signaling in Osteogenesis and Skeletal Repair

Sufficient oxygen is required to maintain normal cellular and physiological function, such as a creature’s development, breeding, and homeostasis. Lately, some researchers have reported that both pathological hypoxia and environmental hypoxia might affect bone health. Adaptation to hypoxia is a pivotal cellular event in normal cell development and differentiation and in pathological settings such as ischemia. As central mediators of homeostasis, hypoxia-inducible transcription factors (HIFs) can allow cells to survive in a low-oxygen environment and are essential for the regulation of osteogenesis and skeletal repair. From this perspective, we summarized the role of HIF-1 and HIF-2 in signaling pathways implicated in bone development and skeletal repair and outlined the molecular mechanism of regulation of downstream growth factors and protein molecules such as VEGF, EPO, and so on. All of these present an opportunity for developing therapies for bone regeneration.

Low bone mineral density and its related factors in adults with congenital heart disease in Vietnam: A cross‐sectional study

Background and Aims

Recent studies have highlighted the increased risk of low bone mineral density (BMD) in adults with cardiovascular disease. However, little is known about BMD in adults with congenital heart disease (CHD), particularly in developing countries. We hypothesized that factors related to BMD would lead to a high prevalence of low BMD in adults with CHD. This study aimed to determine the prevalence of low BMD and its related factors in Vietnamese adults with CHD.

Methods

We conducted a cross‐sectional study of 73 adults diagnosed with CHD in Vietnam. Low BMD was classified based on their site‐specific Z‐scores and T‐scores at the posteroanterior lumbar spine and left proximal femur. Logistic regression analyses were performed to evaluate factors related to low BMD.

Results

Low BMD was confirmed in one‐third of the adults with CHD. There were trends of more bone loss in certain parts of the body than in others, with the prevalence of low BMD at the sites of the lumbar vertebrae (L1‒L4) and left proximal femur (femoral neck, trochanteric femur, and intertrochanteric area) of 43.9%, 31.8%, 28.8%, 33.3%, 8.8%, 1.5%, and 6.1%, respectively. The prevalence of low BMD in the lumbar spine was significantly higher than that in the left proximal femur (34.3% vs. 2.9%, p < 0.001). Moreover, the prevalence of low BMD was significantly higher in adults with CHD than in those without polycythemia and vitamin D deficiency (55.6% vs. 20.9%, p = 0.001 and 46.2% vs. 19.4%, p = 0.002, respectively). A stratified multivariate logistic regression analysis revealed that low BMD was associated with polycythemia (odds ratio: 4.72; 95% confidence interval: 1.64–13.58, p = 0.004).

Conclusions

Low BMD is common among adults with CHD in Vietnam and related to polycythemia.

Inhibition of Osteoblast Differentiation by JAK2V617F Megakaryocytes Derived From Male Mice With Primary Myelofibrosis

Past studies described interactions between normal megakaryocytes, the platelet precursors, and bone cell precursors in the bone marrow. This relationship has also been studied in context of various mutations associated with increased number of megakaryocytes. The current study is the first to examine the effects of megakaryocytes from transgenic mice carrying the most common mutation that causes primary myelofibrosis (PMF) in humans (JAK2^V617F) on bone cell differentiation. Organ level assessments of mice using micro-computed tomography showed decreased bone volume in JAK2^V617F males, compared to matching controls. Tissue level histology revealed increased deposition of osteoid (bone matrix prior mineralization) in these mutated mice, suggesting an effect on osteoblast differentiation. Mechanistic studies using a megakaryocyte-osteoblast co-culture system, showed that both wild type or JAK2^V617F megakaryocytes derived from male mice inhibited osteoblast differentiation, but JAK2^V617F cells exerted a more significant inhibitory effect. A mouse mRNA osteogenesis array showed increased expression of Noggin, Chordin, Alpha-2-HS-glycoprotein, Collagen type IV alpha 1 and Collagen type XIV alpha 1 (mostly known to inhibit bone differentiation), and decreased expression of alkaline phosphatase, Vascular cell adhesion molecule 1, Sclerostin, Distal-less homeobox 5 and Collagen type III alpha 1 (associated with osteogenesis) in JAK2^V617F megakaryocytes, compared to controls. This suggested that the mutation re-programs megakaryocytes to express a cluster of genes, which together could orchestrate greater suppression of osteogenesis in male mice. These findings provide mechanistic insight into the effect of JAK2^V617F mutation on bone, encouraging future examination of patients with this or other PMF-inducing mutations.

Molecular Mechanisms Involved in Hypoxia-Induced Alterations in Bone Remodeling

Bone is crucial for the support of muscles and the protection of vital organs, and as a reservoir of calcium and phosphorus. Bone is one of the most metabolically active tissues and is continuously renewed to adapt to the changes required for healthy functioning. To maintain normal cellular and physiological bone functions sufficient oxygen is required, as evidence has shown that hypoxia may influence bone health. In this scenario, this review aimed to analyze the molecular mechanisms involved in hypoxia-induced bone remodeling alterations and their possible clinical consequences. Hypoxia has been associated with reduced bone formation and reduced osteoblast matrix mineralization due to the hypoxia environment inhibiting osteoblast differentiation. A hypoxic environment is involved with increased osteoclastogenesis and increased bone resorptive capacity of the osteoclasts. Clinical studies, although with contradictory results, have shown that hypoxia can modify bone remodeling.

Hypobaric hypoxia deteriorates bone mass and strength in mice

Mountaineers at high altitude are at increased risk of acute mountain sickness as well as high altitude pulmonary and cerebral edema. A densitometric study in mountaineers has suggested that expeditions at high altitude decrease bone mineral density. Surprisingly, the in vivo skeletal effects of hypobaric hypoxia are largely unknown, and have not been studied using advanced contemporary methods to assess bone microstructure. Eighty-four 22-week-old female mice were divided into seven groups with 12 mice in each group: 1. Baseline; 2. Normobaric, 4 weeks; 3. Hypobaric hypoxia, 4 weeks; 4. Normobaric, 8 weeks; 5. Hypobaric hypoxia, 8 weeks; 6. Normobaric, 12 weeks; and 7. Hypobaric hypoxia, 12 weeks. Hypobaric hypoxia mice were housed in hypobaric chambers at an ambient pressure of 500 mbar (5500 m altitude), while normobaric mice were housed at sea level atmospheric pressure for 4, 8, or 12 weeks, respectively. Hypobaric hypoxia had a profound impact on femoral cortical bone and L4 trabecular bone, while the effect on femoral trabecular bone was less pronounced. Hypobaric hypoxia reduced the bone strength of the femoral mid-diaphysis and L4 at all time-points. At femoral cortical bone, hypobaric hypoxia reduced bone formation through fewer mineralizing surfaces and lower bone formation rate after 2 weeks. In addition, bone strength decreased, and C-terminal telopeptide of type I collagen (CTX-I) increased independently of the duration of exposure to simulated high altitude. At L4, hypobaric hypoxia resulted in a substantial reduction in bone volume fraction, trabecular thickness, and trabecular number after 4 weeks of exposure. Hypobaric hypoxia reduced bone strength and femoral bone mass, while femoral trabecular bone was much less affected, indicating the skeletal response to hypobaric hypoxia differ between cortical and trabecular bone. These findings provide initial preclinical support for future clinical studies in mountaineers to assess bone status and bone strength after exposure to prolonged high altitude exposure.

Myeloproliferative Disorders and its Effect on Bone Homeostasis: The Role of Megakaryocytes

Myeloproliferative Neoplasms (MPNs) are a heterogeneous group of chronic hematological diseases that arise from the clonal expansion of abnormal hematopoietic stem cells, of which Polycythemia Vera (PV), Essential Thrombocythemia (ET), and Primary Myelofibrosis (PMF) have been extensively reviewed in context of clonal expansion, fibrosis and other phenotypes. Here, we review current knowledge on the influence of different forms of MPN on bone health. Studies implicated various degrees of effect of different forms of MPN on bone density, and on osteoblast proliferation and differentiation, using murine models and human data. The majority of studies show that bone volume is generally increased in PMF patients, whereas it is slightly decreased or not altered in ET and PV patients, although possible differences between male and female phenotypes were not fully explored in most MPN forms. Osteosclerosis seen in PMF patients is a serious complication that can lead to bone marrow failure, and the loss of bone reported in some ET and PV patients can lead to osteoporotic fractures. Some MPN forms are associated with increased number of megakaryocytes (MKs), and several of the MK-associated factors in MPN are known to affect bone development. Here, we review known mechanisms involved in these processes, with focus on the role of MKs and secreted factors. Understanding MPN-associated changes in bone health could improve early intervention and treatment of this side effect of the pathology.

Murine Modeling of Myeloproliferative Neoplasms

Myeloproliferative neoplasms, such as polycythemia vera, essential thrombocythemia, and primary myelofibrosis, are bone marrow disorders that result in the overproduction of mature clonal myeloid elements. Identification of recurrent genetic mutations has been described and aid in diagnosis and prognostic determination. Mouse models of these mutations have confirmed the biologic significance of these mutations in myeloproliferative neoplasm disease biology and provided greater insights on the pathways that are dysregulated with each mutation. The models are useful tools that have led to preclinical testing and provided data as validation for future myeloproliferative neoplasm clinical trials.

Erythropoietin in bone homeostasis-Implications for efficacious anemia therapy

Bone homeostasis and hematopoiesis are irrevocably linked in the hypoxic environment of the bone marrow. Erythropoietin (Epo) regulates erythropoiesis by binding to its receptor, Epor, on erythroid progenitor cells. The continuous process of bone remodeling is achieved by the finely balanced activity of osteoblasts in bone synthesis and osteoclasts in bone resorption. Both osteoblasts and osteoclasts express functional Epors, but the underlying mechanism of Epo‐Epor signaling in bone homeostasis is incompletely understood. Two recent publications have provided new insights into the contribution of endogenous Epo to bone homeostasis. Suresh et al examined Epo‐Epor signaling in osteoblasts in bone formation in mice and Deshet‐Unger et al investigated osteoclastogenesis arising from transdifferentiation of B cells. Both groups also studied bone loss in mice caused by exogenous human recombinant EPO‐stimulated erythropoiesis. They found that either deletion of Epor in osteoblasts or conditional knockdown of Epor in B cells attenuates EPO‐driven bone loss. These findings have direct clinical implications because patients on long‐term treatment for anemia may have an increased risk of bone fractures. Phase 3 trials of small molecule inhibitors of the PHD enzymes (hypoxia inducible factor‐prolyl hydroxylase inhibitors [HIF‐PHIs]), such as Roxadustat, have shown improved iron metabolism and increased circulating Epo levels in a titratable manner, avoiding the supraphysiologic increases that often accompany intravenous EPO therapy. The new evidence presented by Suresh and Deshet‐Unger and their colleagues on the effects of EPO‐stimulated erythropoiesis on bone homeostasis seems likely to stimulate discussion on the relative merits and safety of EPO and HIF‐PHIs.

Effects of Erythropoietin in White Adipose Tissue and Bone Microenvironment

Erythropoietin (EPO) is expressed primarily in fetal liver and adult kidney to stimulate red blood cell production. Erythropoietin receptor expression is not restricted to erythroid progenitor cells, and non-erythroid EPO activity includes immune response and bone remodeling. In bone fracture models, EPO administration promotes bone formation and accelerates bone healing. In contrast, in healthy adult mice, exogenous EPO-stimulated erythropoiesis has been concomitant with bone loss, particularly at high EPO, that may be accompanied by increased osteoclast activation. Other EPO-associated responses include reduced inflammation and loss of fat mass with high-fat diet feeding, especially in male mice. While EPO exhibited a sex-dimorphic response in regulation of fat mass and inflammation in obese mice, EPO-stimulated erythropoiesis as well as EPO-associated bone loss was comparable in males and females. EPO administration in young mice and in obese mice resulted in bone loss without increasing osteoclasts, suggesting an osteoclast-independent mechanism, while loss of endogenous EPO decreased bone development and maintenance. Ossicle formation of bone marrow stromal cell transplants showed that EPO directly regulates the balance between osteogenesis and adipogenesis. Therefore, during development, endogenous EPO contributes to normal bone development and in maintaining the balance between osteogenesis and adipogenesis in bone marrow stromal cells, while EPO treatment in mice increased erythropoiesis, promoted bone loss, decreased bone marrow adipogenesis, and increased osteoclast activity. These observations in mouse models suggest that the most prevalent use of EPO to treat anemia associated with chronic kidney disease may compromise bone health and increase fracture risk, especially at a high dose.

Highly increased risk of fracture in patients with myeloproliferative neoplasm

The risk for hip and vertebral fracture was determined in 10,752 patients diagnosed with myeloproliferative neoplasms (MPN) in Sweden 1995-2015. The mean follow-up time were 6.34 years. Five percent developed hip fracture and 1.3% a vertebral fracture. There was a significant increased risk for fracture among the MPN patients compared with the Swedish population. The ratio of observed (obs) and expected (exp) number of hip fracture in all MPN patients, polycythemia vera (PV), essential thrombocythemia and MPN undetermined (MPNu) was 1.20 (95% confidence interval (CI): 1.10-1.31), 1.37 (95% CI: 1.19-1.58), 1.02 (95% CI: 0.87-1.19), and 1.28 (95% CI: 1.07-1.52), respectively. Corresponding figures for vertebral fractures were 1.94 (95% CI: 1.64-2.29), 2.09 (95% CI: 1.56-2.75), 1.50 (95% CI: 1.06-2.07) and 2.47 (95% CI: 1.77-3.35), respectively. Patients with MPN had an increased risk of hip and vertebral fracture, especially patients with PV and MPNu in comparison with the entire Swedish population.

"Take My Bone Away?" Hypoxia and bone: A narrative review

To maintain normal cellular and physiological function, sufficient oxygen is required. Recently, evidence has suggested that hypoxia, either pathological or environmental, may influence bone health. It appears that bone cells are distinctly responsive to hypoxic stimuli; for better or worse, this is still yet to be elucidated. Hypoxia has been shown to offer potentially therapeutic effects for bone by inducing an osteogenic-angiogenic response, although, others have noted excessive osteoclastic bone resorption instead. Much evidence suggests that the hypoxic-inducible pathway is integral in mediating the changes in bone metabolism. Furthermore, many factors associated with hypoxia including changes in energy metabolism, acid-base balance and the increased generation of reactive oxygen species, are known to influence bone metabolism. This review aims to examine some of the putative mechanisms responsible for hypoxic-induced alterations of bone metabolism, with regard to osteoclasts and osteoblasts, both positive and negative.

Erythropoietin receptor in B cells plays a role in bone remodeling in mice

Erythropoietin (EPO) is a key regulator of erythropoiesis. However, EPO receptors (EPO-Rs) are also expressed on non-erythroid cell types, including myeloid and bone cells. Immune cells also participate in bone homeostasis. B cells produce receptor activator of nuclear factor kappa-Β ligand (RANKL) and osteoprotegerin (OPG), two pivotal regulators of bone metabolism. Here we explored the ability of B cells to transdifferentiate into functional osteoclasts and examined the role of EPO in this process in a murine model.

Methods: We have combined specifically-designed experimental mouse models and in vitro based osteoclastogenesis assays, as well as PCR analysis of gene expression.

Results: (i) EPO treatment in vivo increased RANKL expression in bone marrow (BM) B cells, suggesting a paracrine effect on osteoclastogenesis; (ii) B cell-derived osteoclastogenesis occured in vivo and in vitro, as demonstrated by B cell lineage tracing in murine models; (iii) B-cell-derived osteoclastogenesis in vitro was restricted to Pro-B cells expressing CD115/CSF1-R and is enhanced by EPO; (iv) EPO treatment increased the number of B-cell-derived preosteoclasts (β3⁺CD115⁺), suggesting a physiological rationale for B cell derived osteoclastogenesis; (v) finally, mice with conditional EPO-R knockdown in the B cell lineage (cKD) displayed a higher cortical and trabecular bone mass. Moreover, cKD displayed attenuated EPO-driven trabecular bone loss, an effect that was observed despite the fact that cKD mice attained higher hemoglobin levels following EPO treatment.

Conclusions: Our work highlights B cells as an important extra-erythropoietic target of EPO-EPO-R signaling and suggests their involvement in the regulation of bone homeostasis and possibly in EPO-stimulated erythropoietic response. Importantly, we present here for the first time, histological evidence for B cell-derived osteoclastogenesis in vivo.

High Plasma Erythropoietin Predicts Incident Fractures in Elderly Men with Normal Renal Function: The MrOS Sweden Cohort

Preclinical studies on the role of erythropoietin (EPO) in bone metabolism are contradictory. Regeneration models indicate an anabolic effect on bone healing, whereas models on physiologic bone remodeling indicate a catabolic effect on bone mass. No human studies on EPO and fracture risk are available. It is known that fibroblast growth factor 23 (FGF23) affects bone mineralization and that serum concentration of FGF23 is higher in men with decreased estimated glomerular filtration rate (eGFR). Recently, a direct association between EPO and FGF23 has been shown. We have explored the potential association between EPO and bone mineral density (BMD), fracture risk, and FGF23 in humans. Plasma levels of EPO were analyzed in 999 men (aged 69 to 81 years), participating in the Gothenburg part of the population-based Osteoporotic Fractures in Men (MrOS) study, MrOS Sweden. The mean ± SD EPO was 11.5 ± 9.0 IU/L. Results were stratified by eGFR 60 mL/min. For men with eGFR ≥60 mL/min (n = 728), EPO was associated with age (r = 0.13, p < 0.001), total hip BMD (r = 0.14, p < 0.001), intact (i)FGF23 (r = 0.11, p = 0.004), and osteocalcin (r = -0.09, p = 0.022). The association between total hip BMD and EPO was independent of age, body mass index (BMI), iFGF23, and hemoglobin (beta = 0.019, p < 0.001). During the 10-year follow-up, 164 men had an X-ray-verified fracture, including 117 major osteoporotic fractures (MOF), 39 hip fractures, and 64 vertebral fractures. High EPO was associated with higher risk for incident fractures (hazard ratio [HR] = 1.43 per tertile EPO, 95% confidence interval [CI] 1.35-1.63), MOF (HR = 1.40 per tertile EPO, 95% CI 1.08-1.82), and vertebral fractures (HR = 1.42 per tertile EPO, 95% CI 1.00-2.01) in a fully adjusted Cox regression model. In men with eGFR<60 mL/min, no association was found between EPO and BMD or fracture risk. We here demonstrate that high levels of EPO are associated with increased fracture risk and increased BMD in elderly men with normal renal function. © 2019 American Society for Bone and Mineral Research.

Separate and combined effects of hypobaric hypoxia and hindlimb suspension on skeletal homeostasis and hematopoiesis in mice

Purpose

Bone marrow response to an organismal stress is made by orchestrating the interplay between hematopoietic stem/progenitor cells (HSPCs) and mesenchymal stromal cells (MSCs). Neither the cellular nor the molecular factors that regulate this process are fully understood, especially since this mechanism probably varies depending on the type of stress. Herein, we explored the differentiation and fate of MSCs and HSPCs in mice challenged with a hematopoietic stress or a mechanical stress applied separately or in combination.

Methods

Mice were subjected to 4 days of hypobaric hypoxia (hematopoietic challenge) and/or 7 days of hindlimb suspension (stromal challenge) and then sacrificed for blood and bone collection. Using hematological measurements, colony-forming unit assays, bone histomorphometry and array-based multiplex ELISA analysis, we evaluated challenge influences on both MSC and HSPC mobilization, differentiation (osteoblasts, osteoclasts, and mature blood cells) and fate.

Results

We found that hypoxia leads to HSPC mobilization and that an imbalance between bone formation and bone resorption accounts for this mobilization. Whilst suspension is also associated with an imbalance between bone formation and bone resorption, it does not induce HSPC mobilization. Then, we revealed cellular interactions by combining hematopoietic and stromal challenges together in mice. We showed that the hypoxia-driven HSPC mobilization is moderated by suspension. Moreover, when applied in a hypoxic environment, suspension offsets bone imbalance. We identified stroma cell-derived factors MIP-1α, HGF and SDF-1 as potent molecular key players sustaining interactions between hindlimb suspension and hypobaric hypoxia.

Conclusion

Taken together, our data highlight the benefit of combining different types of stress to better understand the interplay between MSCs and HSPCs.

Erythrocytosis and fatigue fractures associated with hepatoblastoma in a 3-year-old gelding

Hepatoblastoma was diagnosed in a 3-year-old Thoroughbred gelding presented with forelimb lameness with bilateral fatigue fractures of the proximal third metacarpal bones. An abdominal mass was detected on ultrasound examination of the abdomen. Absolute erythrocytosis was diagnosed after clinical and haematological evaluation. The fractured metacarpal bones were surgically removed but complications after surgery were fatal. The liver mass was diagnosed as a hepatoblastoma based on histology and immunochemical staining. The combination of hepatoblastoma and fatigue fractures has not been described previously in horses. A potential link between the hepatic and orthopaedic pathologies is hypothesised.

Erythropoiesis, EPO, macrophages, and bone

The regulation of erythropoiesis in the bone marrow microenvironment is a carefully orchestrated process that is dependent upon both systemic and local cues. Systemic erythropoietin (EPO) production by renal interstitial cells plays a critical role in maintaining erythropoietic homeostasis. In addition, there is increasing clinical and preclinical data linking changes in EPO and erythropoiesis to altered skeletal homeostasis, suggesting a functional relationship between the regulation of erythropoiesis and bone homeostasis. As key local components of the bone marrow microenvironment and erythropoietic niche, macrophage subsets play important roles in both processes. In this review, we summarize our current understanding of the cellular and molecular mechanisms that may facilitate the coordinated regulation of erythropoiesis and bone homeostasis.

Context-Dependent Skeletal Effects of Erythropoietin

Erythropoietin (Epo) is the main hormone that regulates the production of red blood cells (hematopoiesis), by stimulating their progenitors. Beyond this vital function, several emerging roles have been noted for Epo in other tissues, including neurons, heart, and retina. The skeletal system is also affected by Epo; however, its actions on bone are, as yet, controversial. Here, we review the seemingly contradicting evidence regarding Epo effects on bone remodeling. We also discuss the evidence pointing to a direct vs indirect effect of Epo on the osteoblastic and osteoclastic cell lineages. The current controversy may derive from a context-dependent mode of function of Epo, namely, opposite skeletal actions during bone regeneration and steady-state bone remodeling. Differences in conclusions deriving from the published in vitro studies may thus relate to the different experimental conditions. Taken together, the current state-of-the-art indicates definite Epo effects on bone cells and points to the complexity of the mode of function.

Bone mineral density and microarchitecture in patients with essential thrombocythemia and polycythemia vera

In this cross-sectional study of 45 patients with myeloproliferative neoplasms, we found no evidence of secondary osteoporosis.

INTRODUCTION

Patients with essential thrombocythemia (ET) and polycythaemia vera (PV) are at increased risk of fractures but the underlying mechanisms have not been settled. We conducted a study to assess bone mineral density, microarchitecture, estimated bone strength and global bone turnover in 45 patients with ET or PV.

METHODS

Patients were evaluated in a cross-sectional study with dual energy X-ray absorptiometry (DXA) at the hip and spine; high-resolution peripheral quantitative computed tomography (HR-pQCT) at the distal radius and distal tibia; and biochemical markers of bone turnover including pro-collagen type 1 N-terminal pro-peptide, osteocalcin, C-terminal cross-linking telopeptide of type 1 collagen and bone-specific alkaline phosphatase. Also, 45 healthy comparisons, matched on age, height and weight with each patient were included as control subjects.

RESULTS

Patients and comparisons had almost identical BMDs: 0.96 (IQR: 0.85-1.07) g/cm² and 0.96 g/cm² (IQR: 0.86-1.05 g/cm²), respectively. As well all microarchitecture and estimated bone strength measures were highly similar in the two groups. Levels of bone turnover markers were within reference values in patients.

CONCLUSION

These results reveal no evidence of secondary osteoporosis among patients with ET or PV. The mechanism behind the increased fracture risk in ET or PV patients remains unknown.

Erythropoietin treatment in murine multiple myeloma: immune gain and bone loss

Multiple myeloma (MM) is a plasma cell malignancy, characterized by osteolytic lesions and monoclonal immunoglobulins. The anemia, accompanying the disease is often treated with recombinant human EPO. Diverse non-erythropoietic effects of EPO have led us to question its combined action on the immune system and bone in the 5T33MM mouse model. EPO administration to MM mice attenuated disease progression as demonstrated by a decrease in serum MM IgG2b, splenic CD138 expressing cells, IL-6 and RORγτ transcripts in bone marrow (BM). IFN-γ transcript levels and macrophages (F4/80⁺CD11b⁺) in the BM both increased ~1.5 fold in the EPO-treated MM mice. In-vitro, EPO stimulated phagocytosis of 5T33MM cells (+30%) by BM-derived macrophages. In contrast, high-resolution microCT analysis of distal femurs revealed EPO-associated bone loss in both healthy and 5T33MM mice. EPO significantly increased expression of the osteoclastogenic nuclear factor-kappa B ligand (RANKL) in healthy mice, but not in MM mice, likely due to antagonizing effects on MM progression. Thus, in MM, EPO may act as a double-edged-sword stimulating immune response, while accelerating bone resorption, possibly via direct action on BM macrophages. This study supports a prudent approach of treating anemia in MM patients, aiming to maintain EPO-associated anti-MM effects, while considering bone damage.

Lack of hepcidin ameliorates anemia and improves growth in an adenine-induced mouse model of chronic kidney disease

Growth delay is common in children with chronic kidney disease (CKD), often associated with poor quality of life. The role of anemia in uremic growth delay is poorly understood. Here we describe an induction of uremic growth retardation by a 0.2% adenine diet in wild-type (WT) and hepcidin gene (Hamp) knockout (KO) mice, compared with their respective littermates fed a regular diet. Experiments were started at weaning (3 wk). After 8 wk, blood was collected and mice were euthanized. Adenine-fed WT mice developed CKD (blood urea nitrogen 82.8 ± 11.6 mg/dl and creatinine 0.57 ± 0.07 mg/dl) and were 2.1 cm shorter compared with WT controls. WT adenine-fed mice were anemic and had low serum iron, elevated Hamp, and elevated IL6 and TNF-α. WT adenine-fed mice had advanced mineral bone disease (serum phosphorus 16.9 ± 3.1 mg/dl and FGF23 204.0 ± 115.0 ng/ml) with loss of cortical and trabecular bone volume seen on microcomputed tomography. Hamp disruption rescued the anemia phenotype resulting in improved growth rate in mice with CKD, thus providing direct experimental evidence of the relationship between Hamp pathway and growth impairment in CKD. Hamp disruption ameliorated CKD-induced growth hormone-insulin-like growth factor 1 axis derangements and growth plate alterations. Disruption of Hamp did not mitigate the development of uremia, inflammation, and mineral and bone disease in this model. Taken together, these results indicate that an adenine diet can be successfully used to study growth in mice with CKD. Hepcidin appears to be related to pathways of growth retardation in CKD suggesting that investigation of hepcidin-lowering therapies in juvenile CKD is warranted.