Role of erythropoietin in the angiogenic activity of bone marrow endothelial cells of MGUS and multiple myeloma patients

Uptake-Dependent and -Independent Effects of Fibroblasts-Derived Extracellular Vesicles on Bone Marrow Endothelial Cells from Patients with Multiple Myeloma: Therapeutic and Clinical Implications

Extracellular vesicles (EVs) have emerged as important players in cell-to-cell communication within the bone marrow (BM) of multiple myeloma (MM) patients, where they mediate several tumor-associated processes. Here, we investigate the contribution of fibroblasts-derived EVs (FBEVs) in supporting BM angiogenesis. We demonstrate that FBEVs' cargo contains several angiogenic cytokines (i.e., VEGF, HGF, and ANG-1) that promote an early over-angiogenic effect independent from EVs uptake. Interestingly, co-culture of endothelial cells from MM patients (MMECs) with FBEVs for 1 or 6 h activates the VEGF/VEGFR2, HGF/HGFR, and ANG-1/Tie2 axis, as well as the mTORC2 and Wnt/β-catenin pathways, suggesting that the early over-angiogenic effect is a cytokine-mediated process. FBEVs internalization occurs after longer exposure of MMECs to FBEVs (24 h) and induces a late over-angiogenic effect by increasing MMECs migration, chemotaxis, metalloproteases release, and capillarogenesis. FBEVs uptake activates mTORC1, MAPK, SRC, and STAT pathways that promote the release of pro-angiogenic cytokines, further supporting the pro-angiogenic milieu. Overall, our results demonstrate that FBEVs foster MM angiogenesis through dual time-related uptake-independent and uptake-dependent mechanisms that activate different intracellular pathways and transcriptional programs, providing the rationale for designing novel anti-angiogenic strategies.

STAT5 as a Key Protein of Erythropoietin Signalization

Erythropoietin (EPO) acts on multiple tissues through its receptor EPOR, a member of a cytokine class I receptor superfamily with pleiotropic effects. The interaction of EPO and EPOR triggers the activation of several signaling pathways that induce erythropoiesis, including JAK2/STAT5, PI3K/AKT, and MAPK. The canonical EPOR/JAK2/STAT5 pathway is a known regulator of differentiation, proliferation, and cell survival of erythroid progenitors. In addition, its role in the protection of other cells, including cancer cells, is under intense investigation. The involvement of EPOR/JAK2/STAT5 in other processes such as mRNA splicing, cytoskeleton reorganization, and cell metabolism has been recently described. The transcriptomics, proteomics, and epigenetic studies reviewed in this article provide a detailed understanding of EPO signalization. Advances in this area of research may be useful for improving the efficacy of EPO therapy in hematologic disorders, as well as in cancer treatment.

Thrombopoietin Promotes Angiogenesis and Disease Progression in Patients with Multiple Myeloma

Multiple myeloma (MM) progression closely depends on bone marrow (BM) angiogenesis. Several factors sustain angiogenesis, including cytokines, growth factors, and cell-to-cell interactions. Herein, BM thrombopoietin (TPO) was shown to support angiogenesis and disease progression in MM. Patients with MM at different progression phases had higher levels of BM and circulating TPO than monoclonal gammopathy of undetermined significance/smoldering MM patients, suggesting that TPO correlates with disease progression and prognosis. Endothelial cells from patients with monoclonal gammopathy of undetermined significance (MGECs) and endothelial cells from MM (MMECs) expressed TPO receptor, and the TPO treatment triggered their angiogenic capabilities in vitro. Indeed, TPO-treated MGECs and MMECs showed enhanced angiogenesis on Matrigel and spontaneous cell migration and chemotaxis by acting as a chemotactic agent. TPO also had an angiogenic activity in vivo in the chorioallantoic membrane assay system. Finally, TPO treatment increased the release of active matrix metalloproteinase (MMP)-9 and MMP-2 in MGECs and of MMP-2 in MMECs and affected the balance between angiogenic/antiangiogenic factors in the MM BM. Our results support the angiogenic activity of TPO, and suggest that it may have a critical role in promoting the angiogenic switch during MM progression. Accordingly, TPO may be envisaged as a new angiogenic and prognostic factor in patients with MM.

AKT/GSK-3β/β-catenin signaling pathway participates in erythropoietin-promoted glioma proliferation

PURPOSE

Although erythropoietin (EPO) has been proven to significantly promote the proliferation of cancer cells, the mechanism for promoting glioma proliferation is poorly understood. Here, we examined the functional role of the AKT/GSK-3β/β-catenin signaling pathway in the EPO-mediated proliferation of glioma.

METHODS

The distribution of EPO and Ki-67 among clinical samples with different WHO grades was plotted by Immunological Histological Chemistry analysis. U87 and U251 glioma cell lines were treated with short hairpin RNA targeting (shEPO), recombinant human erythropoietin (rhEPO) and/or AKT-specific inhibitor (MK-2206). The changes in phosphorylated AKT, nuclear β-catenin, cyclin D1 and p27kip1 expression were detected. Cell cycle distributions and glioma proliferation in vitro and in vivo were analyzed.

RESULTS

The expression level of EPO was significantly elevated with the increase of WHO grade and Ki67 in clinical glioma specimens. In vitro, knockdown of endogenous EPO in U87 and U251 cells effectively block the phosphorylation of AKT and GSK-3β and the expression of nuclear β-catenin. shEPO treatment also significantly decreased the expression of cyclin D1 and increased the expression of p27kip1. The cell cycle transition then slowed down and the proliferation of glioma cells or mouse xenograft tumors both decreased. Treatment of cells or tumors with extra rhEPO reversed the above biological effects mediated by shEPO. rhEPO-induced activation of the AKT/GSK-3β/β-catenin pathway and proliferation were abolished by MK-2206.

CONCLUSIONS

Our study identified the AKT/GSK-3β/β-catenin axis as a critical mediator of EPO-induced glioma proliferation and further provided a clinically significant dimension to the biology of EPO.

ADAM17-regulated CX3CL1 expression produced by bone marrow endothelial cells promotes spinal metastasis from hepatocellular carcinoma

Spinal metastasis occurs in 50-75% of bone metastases caused by hepatocellular carcinoma (HCC), and HCC-derived spinal metastasis can lead to a less favorable prognosis. Recently, several studies have demonstrated that C-X3-C motif chemokine ligand 1 (CX3CL1) is closely associated with cancer metastasis, and its secretion is modulated by a disintegrin and metalloproteinase 17 (ADAM17). Bone marrow endothelial cells (BMECs) are an essential component of bone marrow. However, little is known about the roles in and effects of BMECs on HCC spinal metastasis. The present study demonstrated that CX3CL1 and C-X-C motif chemokine receptor 3 (CXCR3) expression was upregulated in HCC spinal metastases, and that CX3CL1 promoted the migration and invasion of HCC cells to the spine. Western blot analysis revealed that the Src/protein tyrosine kinase 2 (PTK2) axis participated in CX3CL1-induced HCC cell invasion and migration. CX3CL1 also increased the expression of M2 macrophage markers in THP-1 monocytes. BMECs promoted the migration and invasion of Hep3B and MHCC97H cells by secreting soluble CX3CL1, whereas the neutralization of CX3CL1 inhibited this enhancement. CX3CL1 enhanced the activation of the phosphatidylinositol-4,5-bisphos-phate 3-kinase catalytic subunit alpha (PIK3CA)/AKT serine/threonine kinase 1 (AKT1) and Ras homolog family member A (RHOA)/Rho associated coiled-coil containing protein kinase 2 (ROCK2) signaling pathways through the Src/PTK2 signaling pathway. Furthermore, ADAM17 was activated by mitogen-activated protein kinase (MAPK) z14 in BMECs and significantly promoted the secretion of CX3CL1. HCC cells enhanced the recruitment and proliferation of BMECs. The overexpression of CX3CR1 facilitated the spinal metastasis of HCC in a mouse model in vivo. In addition, in vivo experiments revealed that BMECs promoted the growth of HCC in the spine. The present study demonstrated that CX3CL1 participates in HCC spinal metastasis, and that BMECs play an important role in the regulation of CX3CL1 in the spinal metastatic environment.

Erythropoietin and its derivatives: from tissue protection to immune regulation

Erythropoietin (EPO) is an evolutionarily conserved hormone well documented for its erythropoietic role via binding the homodimeric EPO receptor (EPOR)₂. In past decades, evidence has proved that EPO acts far beyond erythropoiesis. By binding the tissue-protective receptor (TPR), EPO suppresses proinflammatory cytokines, protects cells from apoptosis and promotes wound healing. Very recently, new data revealed that TPR is widely expressed on a variety of immune cells, and EPO could directly modulate their activation, differentiation and function. Notably, nonerythropoietic EPO derivatives, which mimic the structure of helix B within EPO, specifically bind TPR and show great potency in tissue protection and immune regulation. These small peptides prevent the cardiovascular side effects of EPO and are promising as clinical drugs. This review briefly introduces the receptors and tissue-protective effects of EPO and its derivatives and highlights their immunomodulatory functions and application prospects.

Erythropoietin Signaling in the Microenvironment of Tumors and Healthy Tissues

Erythropoietin (EPO), the primary cytokine of erythropoiesis, stimulates both proliferation and differentiation of erythroid progenitors and their maturation to red blood cells. Basal EPO levels maintain the optimum levels of circulating red blood cells. However, during hypoxia, EPO secretion and its expression is elevated drastically in renal interstitial fibroblasts, thereby increasing the number of erythroid progenitors and accelerating their differentiation to mature erythrocytes. A tight regulation of this pathway is therefore of paramount importance. The biological response to EPO is commenced through the involvement of its cognate receptor, EPOR. The receptor-ligand complex results in homodimerization and conformational changes, which trigger downstream signaling events and cause activation or inactivation of critical transcription factors that promote erythroid expansion. In recent years, recombinant human EPO (rEPO) has been widely used as a therapeutic tool to treat a number of anemias induced by infection, and chemotherapy for various cancers. However, several studies have uncovered a tumor promoting ability of EPO in man, which likely occurs through EPOR or alternative receptor(s). On the other hand, some studies have demonstrated a strong anticancer activity of EPO, although the mechanism still remains unclear. A thorough investigation of EPOR signaling could yield enhanced understanding of the pathobiology for a variety of disorders, as well as the potential novel therapeutic strategies. In this chapter, in addition to the clinical relevance of EPO/EPOR signaling, we review its anticancer efficacy within various tumor microenvironments.

Aquaporin-1 plays a key role in erythropoietin-induced endothelial cell migration

Water influx through aquaporin-1 (AQP-1) has been linked to the ability of different cell types to migrate, and therefore plays an important part in processes like metastasis and angiogenesis. Since the erythroid growth factor erythropoietin (Epo) is now recognized as an angiogenesis promoter, we investigated the participation of AQP-1 as a downstream effector of this cytokine in the migration of endothelial cells. Inhibition of AQP-1 with either mercury ions (Hg²⁺) or a specific siRNA led to an impaired migration of EA.hy926 endothelial cells exposed to Epo (wound-healing assays). Epo also induced the expression of AQP-1 at mRNA and protein levels, an effect which was dependent on the influx of extracellular calcium through L-type calcium channels as well as TRPC3 channels. The relationship between Epo and AQP-1 was further confirmed at shorter exposure times, as the cytokine was unable to trigger calcium influxes in cells where AQP-1 had previously been knocked down. Moreover, Epo promoted changes in the subcellular localization of AQP-1 as well as rearrangements in the actin cytoskeleton, which are consistent with a migratory phenotype. Worthy of note, carbamylated erythropoietin (cEpo), the non-erythropoietic and non-promigratory derivative of Epo, was incapable of AQP-1 modulation. The therapeutical implications of aquaporin targeting in angiogenesis-related diseases highlight the importance of the present results in the context of the relationship between AQP-1 and Epo.

Hematopoietic growth factors and tumor angiogenesis

Angiogenesis is regulated by numerous "classic" factors such as vascular endothelial growth factor (VEGF) and many other endogenous "non-classic"peptides, including erythropoietin (Epo), and granulocyte-/granulocyte macrophage colony stimulating factor (G-/GM-CSF). The latter play an important regulatory role in angiogenesis, especially under pathological conditions and constitute a crosslink between angiogenesis and hematopoiesis. This article reviews studies on the ability of hematopoietic cytokines to affect several endothelial cell functions in tumor angiogenesis. These findings in all these studies support the hypothesis formulated at the beginning of this century that a common ancestral cell, the hemangioblast, gives rise to cells of both the endothelial and the hematopoietic lineages.

New Insights in Anti-Angiogenesis in Multiple Myeloma

Angiogenesis is a constant hallmark of multiple myeloma (MM) progression and involves direct production of angiogenic cytokines by plasma cells and their induction within the bone marrow microenvironment. This article summarizes the more recent literature data concerning the employment of anti-angiogenic therapeutic agents actually used in preclinical models and clinical settings for the treatment of multiple myeloma.

[Erythropoietin accelerates the proliferation of glioma cells via activating Akt pathway]

OBJECTIVE

To determine whether erythropoietin (EPO) promotes rapid proliferation of glioma through Akt pathway.

METHODS

We detected the expression of EPO in human glioma tissues using immunohistochemistry. A nude mouse model bearing human glioma U87 cell xenograft was established and given intraperitoneal injection of EPO or saline every other day, and the tumor growth was observed. In the in vitro experiment, U87 cells were treated with PBS (control), EPO, or EPO with Akt inhibitor, and the expression of p-Akt and cyclin D1 was detected using Western blotting; the cell proliferation rate was determined using cell counting kit-8 and clone formation assay, and the cell cycle changes were analyzed with flow cytometry.

RESULTS

Compared with low-grade glioma tissues, high-grade glioma tissues exhibited a significantly increased EPO expression (P=0.0002). In the tumor-bearing mice, EPO treatment significantly increased the expression of EPO (P=0.0006) and p-Akt (P=0.0003) in the tumor and obviously increased the tumor volume (P<0.0001) and weight (P=0.0003). In U87 cells cultured in vitro, EPO treatment obviously accelerated the cell proliferation (P=0.020 on day 3 and 0.028 on day 5), promoted clone formation (P=0.0010), and increased proliferation index (P=0.0028); EPO significantly enhanced the protein expression of p-Akt (P=0.0020) and cyclin D1 (P=0.0022). The application of Akt inhibitor significantly suppressed the effect of EPO in enhancing cyclin D1 and p-Akt expression (both P<0.0001) and promoting cell proliferation.

CONCLUSION

EPO can significantly accelerate the proliferation of glioma through Akt pathway.

[Erythropoietin accelerates the proliferation of glioma cells via activating Akt pathway]

OBJECTIVE

To determine whether erythropoietin (EPO) promotes rapid proliferation of glioma through Akt pathway.

METHODS

We detected the expression of EPO in human glioma tissues using immunohistochemistry. A nude mouse model bearing human glioma U87 cell xenograft was established and given intraperitoneal injection of EPO or saline every other day, and the tumor growth was observed. In the in vitro experiment, U87 cells were treated with PBS (control), EPO, or EPO with Akt inhibitor, and the expression of p-Akt and cyclin D1 was detected using Western blotting; the cell proliferation rate was determined using cell counting kit-8 and clone formation assay, and the cell cycle changes were analyzed with flow cytometry.

RESULTS

Compared with low-grade glioma tissues, high-grade glioma tissues exhibited a significantly increased EPO expression (P=0.0002). In the tumor-bearing mice, EPO treatment significantly increased the expression of EPO (P=0.0006) and p-Akt (P=0.0003) in the tumor and obviously increased the tumor volume (P<0.0001) and weight (P=0.0003). In U87 cells cultured in vitro, EPO treatment obviously accelerated the cell proliferation (P=0.020 on day 3 and 0.028 on day 5), promoted clone formation (P=0.0010), and increased proliferation index (P=0.0028); EPO significantly enhanced the protein expression of p-Akt (P=0.0020) and cyclin D1 (P=0.0022). The application of Akt inhibitor significantly suppressed the effect of EPO in enhancing cyclin D1 and p-Akt expression (both P<0.0001) and promoting cell proliferation.

CONCLUSION

EPO can significantly accelerate the proliferation of glioma through Akt pathway.

Rhu-Epo down-regulates pro-tumorigenic activity of cancer-associated fibroblasts in multiple myeloma

We have previously demonstrated that recombinant human erythropoietin (rHuEpo) is involved in the regulation of the angiogenic response in multiple myeloma (MM) through a direct effect on macrophages and endothelial cells isolated from the bone marrow of patients with MM. The aim of the present study was designed to determine the effects of rHuEpo on cancer-associated fibroblasts (CAFs) from monoclonal gammopathy of undetermined significance (MGUS) and MM patients by means of in vitro and in vivo assays. rHuEpo treatment reduces the expression of mRNA levels of fibroblast activation markers, namely alpha smooth actin (αSMA) and fibroblast activation protein (FAP) in MGUS and MM CAFs, and of pro-inflammatory and pro-angiogenic cytokines, including interleukin (IL)-6 and IL-8, vascular endothelial growth factor-A (VEGF-A), fibroblast growth factor-2 (FGF-2), and hepatocyte growth factor (HGF) in MM CAFs. Moreover, rHuEpo inhibits the proliferative activity of MM CAFs and increased the apoptosis of MGUS and MM CAFs. Overall, these data suggest that rHu-Epo down-regulates CAFs pro-tumorigenic activity. Moreover, these results are not suggestive for a pro-angiogenic activity of rHuEpo on CAFs. In fact, rHuEpo pre-treatment induces a low angiogenic response in vivo in the chorioallantoic membrane (CAM) assay of MGUS and MM CAFs conditioned medium, not comparable to that of a well-known angiogenic cytokine, VEGF-A, tested in the same assay.

Tissue-specific endothelial cells: a promising approach for augmentation of soft tissue repair in orthopedics

Biologics are playing an increasingly significant role in the practice of modern medicine and surgery in general and orthopedics in particular. Cell-based approaches are among the most important and widely used modalities in orthopedic biologics, with mesenchymal stem cells and other multi/pluripotent cells undergoing evaluation in numerous preclinical and clinical studies. On the other hand, fully differentiated endothelial cells (ECs) have been found to perform critical roles in homeostasis of visceral tissues through production of an adaptive panel of so-called "angiocrine factors." This newly discovered function of ECs renders them excellent candidates for novel approaches in cell-based biologics. Here, we present a review of the role of ECs and angiocrine factors in some visceral tissues, followed by an overview of current cell-based approaches and a discussion of the potential applications of ECs in soft tissue repair.

Associations between erythropoietin polymorphisms and risk of diabetic microvascular complications

We conducted a meta-analysis to evaluate the relationship between erythropoietin (EPO) polymorphisms and diabetic microvascular complications. We searched the PubMed, Embase, Cochrane library, Web of Science, Wanfang, and Chinese National Knowledge Infrastructure databases for appropriate studies. Odds ratios (ORs) with 95% confidence intervals (CIs) were calculated to evaluate the associations. Ultimately, eight studies consisting of 2,861 cases and 2,136 controls were identified and included in our meta-analysis. Results with our genotype model indicated an association between rs1617640 polymorphisms and diabetic microvascular complications (TT vs. GG: OR = 1.544, 95% CI = 1.089–2.189, P = 0.015). No clear associations between the rs1617640 and rs507392 polymorphisms and diabetic retinopathy were observed. By contrast, rs551238 polymorphisms were associated with increased diabetic retinopathy risk (allele model: OR = 0.774, 95% CI = 0.658–0.911, P = 0.002; genotype model: AC vs. CC: OR = 0.598, 95% CI = 0.402–0.890, P = 0.011; dominant model: OR = 0.561, 95% CI = 0.385–0.817, P = 0.003; recessive model: OR = 0.791, 95% CI = 0.643–0.973, P = 0.026). These results indicate that EPO polymorphisms are a risk factor for diabetic microvascular complications.

Erythropoietin and Its Angiogenic Activity

Erythropoietin (EPO) is the main hematopoietic hormone acting on progenitor red blood cells via stimulation of cell growth, differentiation, and anti-apoptosis. However, its receptor (EPOR) is also expressed in various non-hematopoietic tissues, including endothelium. EPO is a pleiotropic growth factor that exhibits growth stimulation and cell/tissue protection on numerous cells and tissues. In this article we review the angiogenesis potential of EPO on endothelial cells in heart, brain, and leg ischemia, as well as its role in retinopathy protection and tumor promotion. Furthermore, the effect of EPO on bone marrow and adipose tissue is also discussed.