Post-transcriptional regulation of placenta growth factor mRNA by hydrogen peroxide

The Worst Things in Life are Free: The Role of Free Heme in Sickle Cell Disease

Hemolysis is a pathological feature of several diseases of diverse etiology such as hereditary anemias, malaria, and sepsis. A major complication of hemolysis involves the release of large quantities of hemoglobin into the blood circulation and the subsequent generation of harmful metabolites like labile heme. Protective mechanisms like haptoglobin-hemoglobin and hemopexin-heme binding, and heme oxygenase-1 enzymatic degradation of heme limit the toxicity of the hemolysis-related molecules. The capacity of these protective systems is exceeded in hemolytic diseases, resulting in high residual levels of hemolysis products in the circulation, which pose a great oxidative and proinflammatory risk. Sickle cell disease (SCD) features a prominent hemolytic anemia which impacts the phenotypic variability and disease severity. Not only is circulating heme a potent oxidative molecule, but it can act as an erythrocytic danger-associated molecular pattern (eDAMP) molecule which contributes to a proinflammatory state, promoting sickle complications such as vaso-occlusion and acute lung injury. Exposure to extracellular heme in SCD can also augment the expression of placental growth factor (PlGF) and interleukin-6 (IL-6), with important consequences to enthothelin-1 (ET-1) secretion and pulmonary hypertension, and potentially the development of renal and cardiac dysfunction. This review focuses on heme-induced mechanisms that are implicated in disease pathways, mainly in SCD. A special emphasis is given to heme-induced PlGF and IL-6 related mechanisms and their role in SCD disease progression.

Low molecular weight heparin promotes transcription and release of placental growth factor from endothelial cells

Circulating levels of placental growth factor (PlGF) are significantly reduced in women who develop preeclampsia. Low molecular weight heparin (LMWH) has been shown to acutely elevate circulating PlGF levels in pregnant women at increased risk of preeclampsia. The objective of the current investigation was to determine the mechanisms by which LMWH mediates the extracellular release of PlGF from endothelial cells. Cultured human aortic endothelial cells (HAECs) and human umbilical vein endothelial cells (HUVECs) were exposed to LMWH; PlGF transcription, translation, mobilization, and secretion were then assessed. LMWH significantly increased the release of PlGF from both HAECs and HUVECs. LMWH treatment promoted a significant increase of PlGF-1 mRNA expression in HAECs, accompanied by the intracellular transport and release of PlGF into the conditioned media. LMWH-mediated release of PlGF from HAECs was not directly mediated by extracellular mobilization, synthesis, or stability of PlGF mRNA/protein. LMWH exposure promotes the release of PlGF from endothelial cells through the upregulation of PlGF-1 mRNA expression. Stimulation of circulating PlGF levels by LMWH may be an important mechanism by which LMWH could reduce the risk of preeclampsia or minimize disease severity.NEW & NOTEWORTHY There are few therapeutic options available for the prevention of preeclampsia, a serious hypertensive disorder of pregnancy. Women who subsequently develop preeclampsia exhibit significantly reduced circulating levels of the proangiogenic placental growth factor protein. Low molecular weight heparin (LMWH) has previously been investigated as a preventative therapy against the development of preeclampsia; however, its mechanism of action is not known. The current study determined that LMWH promotes the transcription and release of placental growth factor protein from endothelial cells, providing a mechanistic basis by which LMWH could reduce the risk of preeclampsia or minimize disease severity.

Placental growth factor levels in quadriceps muscle are reduced by a Western diet in association with advanced glycation end products

In peripheral artery disease (PAD), atherosclerotic occlusion chronically impairs limb blood flow. Arteriogenesis (collateral artery remodeling) is a vital adaptive response to PAD that protects tissue from ischemia. People with type II diabetes have a high risk of developing PAD and would benefit from arteriogenesis. However, arteriogenesis is suppressed in people with diabetes by a multifaceted mechanism which remains incompletely defined. Upregulation of placental growth factor (PLGF) is a key early step in arteriogenesis. Therefore, we hypothesized that metabolic dysfunction would impair PLGF expression in skeletal muscle. We tested this hypothesis in C57BL/6J and ApoE^-/- mice of both sexes fed a Western diet (WD) for 24 wk. We first assessed baseline levels of PLGF, vascular endothelial growth factor (VEGF-A), and VEGF receptor 1 (VEGFR1) protein in hindlimb skeletal muscle. Only PLGF was consistently decreased by the WD. We next investigated the effect of 24 wk of the WD on the response of PLGF, VEGF-A, VEGFR1, and monocyte chemoattractant protein-1 (MCP-1) to the physiological stimulus of vascular occlusion. Hindlimb ischemia was induced in mice by gradual femoral artery occlusion using an ameroid constrictor. Growth factor levels were measured 3-28 days postsurgery. In C57BL/6J mice, the WD decreased and delayed upregulation of PLGF and abolished upregulation of VEGF-A and VEGFR1 but had no effect on MCP-1. In ApoE^-/- mice fed either diet, all factors tested failed to respond to occlusion. Metabolic phenotyping of mice and in vitro studies suggest that an advanced glycation end product/TNFα-mediated mechanism could contribute to the effects observed in vivo.NEW & NOTEWORTHY In this study, we tested the effect of a Western diet on expression of the arteriogenic growth factor placental growth factor (PLGF) in mouse skeletal muscle. We provide the first demonstration that a Western diet interferes with both baseline expression and hindlimb ischemia-induced upregulation of PLGF. We further identify a potential role for advanced glycation end product/TNFα signaling as a negative regulator of PLGF. These studies provide insight into one possible mechanism by which type II diabetes may limit collateral growth.

PlGF and VEGF-A Regulate Growth of High-Risk MYCN-Single Copy Neuroblastoma Xenografts via Different Mechanisms

Neuroblastoma (NB) is the most common extracranial solid tumor of childhood and is a rapidly growing, highly-vascularized cancer. NBs frequently express angiogenic factors and high tumor angiogenesis has been associated with poor outcomes. Placental growth factor (PlGF) is an angiogenic protein belonging to the vascular endothelial growth factor (VEGF) family and is up-regulated mainly in pathologic conditions. Recently, PlGF was identified as a member of a gene expression signature characterizing highly malignant NB stem cells drawing attention as a potential therapeutic target in NB. In the present study, we sought to investigate the expression of PlGF in NB patients and the effect of PlGF inhibition on high-risk MYCN-non-amplified SK-N-AS NB xenografts. Human SK-N-AS cells, which are poorly differentiated and express PlGF and VEGF-A, were implanted subcutaneously in athymic nude mice. Treatment was done by intratumoral injection of replication-incompetent adenoviruses (Ad) expressing PlGF- or VEGF-specific short hairpin (sh)RNA, or soluble (s)VEGF receptor 2 (VEGFR2). The effect on tumor growth and angiogenesis was analyzed. High PlGF expression levels were observed in human advanced-stage NBs. Down-regulating PlGF significantly reduced NB growth in established NB xenografts by reducing cancer cell proliferation but did not suppress angiogenesis. In contrast, blocking VEGF by administration of Ad(sh)VEGF and Ad(s)VEGFR2 reduced tumor growth associated with decreased tumor vasculature. These findings suggest that PlGF and VEGF-A modulate MYCN-non-amplified NB tumors by different mechanisms and support a role for PlGF in NB biology.

Redox signaling in cardiovascular pathophysiology: A focus on hydrogen peroxide and vascular smooth muscle cells

Oxidative stress represents excessive intracellular levels of reactive oxygen species (ROS), which plays a major role in the pathogenesis of cardiovascular disease. Besides having a critical impact on the development and progression of vascular pathologies including atherosclerosis and diabetic vasculopathy, oxidative stress also regulates physiological signaling processes. As a cell permeable ROS generated by cellular metabolism involved in intracellular signaling, hydrogen peroxide (H₂O₂) exerts tremendous impact on cardiovascular pathophysiology. Under pathological conditions, increased oxidase activities and/or impaired antioxidant systems results in uncontrolled production of ROS. In a pro-oxidant environment, vascular smooth muscle cells (VSMC) undergo phenotypic changes which can lead to the development of vascular dysfunction such as vascular inflammation and calcification. Investigations are ongoing to elucidate the mechanisms for cardiovascular disorders induced by oxidative stress. This review mainly focuses on the role of H₂O₂ in regulating physiological and pathological signals in VSMC.

Fluid shear stress upregulates placental growth factor in the vessel wall via NADPH oxidase 4

Placental growth factor (PLGF), a potent stimulator of arteriogenesis, is upregulated during outward arterial remodeling. Increased fluid shear stress (FSS) is a key physiological stimulus for arteriogenesis. However, the role of FSS in regulating PLGF expression is unknown. To test the hypothesis that FSS regulates PLGF expression in vascular cells and to identify the signaling pathways involved, human coronary artery endothelial cells (HCAEC) and human coronary artery smooth muscle cells were cultured on either side of porous Transwell inserts. HCAEC were then exposed to pulsatile FSS of 0.07 Pa ("normal," mimicking flow through quiescent collaterals), 1.24 Pa ("high," mimicking increased flow in remodeling collaterals), or 0.00 Pa ("static") for 2 h. High FSS increased secreted PLGF protein ∼1.4-fold compared with static control (n = 5, P < 0.01), while normal FSS had no significant effect on PLGF. Similarly, high flow stimulated PLGF mRNA expression nearly twofold in isolated mouse mesenteric arterioles. PLGF knockdown using siRNA revealed that HCAEC were the primary source of PLGF in cocultures (n = 5, P < 0.01). Both H2O2 and nitric oxide production were increased by FSS compared with static control (n = 5, P < 0.05). N(G)-nitro-l-arginine methyl ester (100 μM) had no significant effect on the FSS-induced increase in PLGF. In contrast, both catalase (500 U/ml) and diphenyleneiodonium (5 μM) attenuated the effects of FSS on PLGF protein in cocultures. Diphenyleneiodonium also blocked the effect of high flow to upregulate PLGF mRNA in isolated arterioles. Further studies identified NADPH oxidase 4 as a source of reactive oxygen species for this pathway. We conclude that FSS regulates PLGF expression via NADPH oxidase 4 and reactive oxygen species signaling.

Basal and apical regulation of VEGF-A and placenta growth factor in the RPE/choroid and primary RPE

PURPOSE

Members of the vascular endothelial growth factor (VEGF) family are strongly involved in pathological processes in the retina, such as age-related macular degeneration and diabetic retinopathy. Cells of the retinal pigment epithelium (RPE) constitutively secrete VEGF-A, and the secretion of placental growth factor (PlGF) has also been described. RPE cells are strongly polarized cells with different secretome at the apical and basal side. In this study, we evaluated the basal and apical regulation of VEGF-A and PlGF secretion in RPE/choroid explants and primary RPE cells.

METHODS

RPE/choroid tissue explants were prepared from porcine eyes and cultivated in modified Ussing chambers, separating apical (RPE) and basal (choroid) supernatant. Primary RPE cells were also prepared from porcine eyes and cultivated on Transwell plates. Explants and cells were treated with inhibitors for VEGFR-2 (SU1498), p38 (SB203580), and the transcription factors nuclear factor-kappa B (NF-κB) and SP-1 (mithramycin), respectively. VEGF-A and PlGF content was evaluated with enzyme-linked immunosorbent assay (ELISA). In addition, western blots were performed.

RESULTS

In the RPE/choroid, VEGF-A can initially be found on the apical and basal sides with significantly more pronounced secretion on the basal side. VEGF-A secretion is differentially regulated on the apical and basal sides, with the inhibition of SP-1 and NF-κB showing strong effects apically and basally after 24 h and 48 h, the inhibition of p38 displaying its effect mainly on the basal side with some effect apically after 48 h, and the inhibition of VEGFR-2 reducing the secretion of VEGF only on the apical side at 24 h and 48 h. In the RPE cell culture, similar effects were found, with inhibition of NF-κB or SP-1 displaying a strong decrease in VEGF-A on both sides, and p38 inhibition displaying only an inhibitory effect on the basal side. In contrast, an apical effect of VEGFR-2 inhibition was not found. However, the western blot experiments exhibited a significant decrease in the VEGF-A protein under SU1498 treatment. In the RPE/choroid organ cultures, PlGF was initially found mainly on the basal site with only minute amounts of PlGF found apically. NF-κB and SP-1 were strongly involved in PlGF regulation apically and basally, while VEGFR2 and to a lesser degree p38 displayed some regulation at the basal site. In the primary RPE cell culture, PlGF was not found on the apical or basal side.

CONCLUSIONS

VEGF-A and PlGF were constitutively secreted and regulated by the RPE/choroid complex, with PlGF secreted mainly by the choroid. Although the transcription factors NF-κB and SP-1 were involved in apical and basal regulation of both growth factors, VEGFR-2 displayed a strong polarity, with regulation of apical VEGF-A and basal PlGF secretion.

Expression of leukemia inhibitory factor in Müller glia cells is regulated by a redox-dependent mRNA stability mechanism

Background

Photoreceptor degeneration is a main hallmark of many blinding diseases making protection of photoreceptors crucial to prevent vision loss. Thus, regulation of endogenous neuroprotective factors may be key for cell survival and attenuation of disease progression. Important neuroprotective factors in the retina include H₂O₂ generated by injured photoreceptors, and leukemia inhibitory factor (LIF) expressed in Müller glia cells in response to photoreceptor damage.

Results

We present evidence that H₂O₂ connects to the LIF response by inducing stabilization of Lif transcripts in Müller cells. This process was independent of active gene transcription and p38 MAPK, but relied on AU-rich elements (AREs), which we identified within the highly conserved Lif 3′UTR. Affinity purification combined with quantitative mass spectrometry identified several proteins that bound to these AREs. Among those, interleukin enhancer binding factor 3 (ILF3) was confirmed to participate in the redox-dependent Lif mRNA stabilization. Additionally we show that KH-type splicing regulatory protein (KHSRP) was crucial for maintaining basal Lif expression levels in non-stressed Müller cells.

Conclusions

Our results suggest that H₂O₂-induced redox signaling increases Lif transcript levels through ILF3 mediated mRNA stabilization. Generation of H₂O₂ by injured photoreceptors may thus enhance stability of Lif mRNA and therefore augment neuroprotective LIF signaling during degenerative conditions in vivo.

Electronic supplementary material

The online version of this article (doi:10.1186/s12915-015-0137-1) contains supplementary material, which is available to authorized users.

Placenta growth factor and vascular endothelial growth factor a have differential, cell-type specific patterns of expression in vascular cells

OBJECTIVE

PLGF, a VEGF-A related protein, mediates collateral enlargement via monocytes but plays little role in capillary proliferation. In contrast, VEGF-A mediates both collateral enlargement and capillary proliferation. PLGF has been less thoroughly studied than VEGF-A, and questions remain regarding its regulation and function. Therefore, our goal was to characterize the expression of PLGF by vascular cells. We hypothesized that vascular SMC would express more PLGF than EC, since VEGF-A is primarily expressed by non-EC.

METHODS

We compared PLGF and VEGF-A across eight EC and SMC lines, then knocked down PLGF and evaluated cell function. We also assessed the effect of hypoxia on PLGF expression and promoter activity.

RESULTS

PLGF was most highly expressed in EC, whereas VEGF-A was most highly expressed in SMC. PLGF knockdown did not affect EC number, migration, or tube formation, but reduced monocyte migration toward EC. Monocyte migration was rescued by exogenous PLGF. Hypoxia increased PLGF protein without activating PLGF gene transcription.

CONCLUSIONS

PLGF and VEGF-A have distinct patterns of expression in vascular cells. EC derived PLGF may function primarily in communication between EC and circulating cells. Hypoxia increases EC PLGF expression posttranscriptionally.

Dynamic proteomic profiles of in vivo- and in vitro-produced mouse postimplantation extraembryonic tissues and placentas

As the interface between the mother and the developing fetus, the placenta is believed to play an important role in assisted reproductive technology (ART)-induced aberrant intrauterine and postnatal development. However, the mechanisms underlying aberrant placentation remain unclear, especially during extraembryonic tissue development and early stages of placental formation. Using a mouse model, this investigation provides the first comparative proteomic analysis of in vivo (IVO) and in vitro-produced (IVP) extraembryonic tissues and placentas after IVO fertilization and development, or in vitro fertilization and culture, respectively. We identified 165 and 178 differentially expressed proteins (DEPs) between IVO and IVP extraembryonic tissues and placentas on Embryonic Day 7.5 (E7.5) and E10.5, respectively. Many DEPs were functionally associated with genetic information processing, such as impaired de novo DNA methylation, as well as posttranscriptional, translational and posttranslational dysregulation. These novel findings were further confirmed by global hypomethylation, and a lower level of correlation was found between the transcriptome and proteome in the IVP groups. In addition, numerous DEPs were involved in energy and amino acid metabolism, cytoskeleton organization and transport, and vasculogenesis and angiogenesis. These disturbed processes and pathways are likely to be associated with embryonic intrauterine growth restriction, an enlarged placenta, and impaired labyrinth morphogenesis. This study provides a direct and comprehensive reference for the further exploration of the placental mechanisms that underlie ART-induced developmental aberrations.

Nox2 and p47(phox) modulate compensatory growth of primary collateral arteries

The role of NADPH oxidase (Nox) in both the promotion and impairment of compensatory collateral growth remains controversial because the specific Nox and reactive oxygen species involved are unclear. The aim of this study was to identify the primary Nox and reactive oxygen species associated with early stage compensatory collateral growth in young, healthy animals. Ligation of the feed arteries that form primary collateral pathways in rat mesentery and mouse hindlimb was used to assess the role of Nox during collateral growth. Changes in mesenteric collateral artery Nox mRNA expression determined by real-time PCR at 1, 3, and 7 days relative to same-animal control arteries suggested a role for Nox subunits Nox2 and p47(phox). Administration of apocynin or Nox2ds-tat suppressed collateral growth in both rat and mouse models, suggesting the Nox2/p47(phox) interaction was involved. Functional significance of p47(phox) expression was assessed by evaluation of collateral growth in rats administered p47(phox) small interfering RNA and in p47(phox-/-) mice. Diameter measurements of collateral mesenteric and gracilis arteries at 7 and 14 days, respectively, indicated no significant collateral growth compared with control rats or C57BL/6 mice. Chronic polyethylene glycol-conjugated catalase administration significantly suppressed collateral development in rats and mice, implying a requirement for H2O2. Taken together, these results suggest that Nox2, modulated at least in part by p47(phox), mediates early stage compensatory collateral development via a process dependent upon peroxide generation. These results have important implications for the use of antioxidants and the development of therapies for peripheral arterial disease.

Reactive oxygen species, vascular Noxs, and hypertension: focus on translational and clinical research

SIGNIFICANCE

Reactive oxygen species (ROS) are signaling molecules that are important in physiological processes, including host defense, aging, and cellular homeostasis. Increased ROS bioavailability and altered redox signaling (oxidative stress) have been implicated in the onset and/or progression of chronic diseases, including hypertension.

RECENT ADVANCES

Although oxidative stress may not be the only cause of hypertension, it amplifies blood pressure elevation in the presence of other pro-hypertensive factors, such as salt loading, activation of the renin-angiotensin-aldosterone system, and sympathetic hyperactivity, at least in experimental models. A major source for ROS in the cardiovascular-renal system is a family of nicotinamide adenine dinucleotide phosphate oxidases (Noxs), including the prototypic Nox2-based Nox, and Nox family members: Nox1, Nox4, and Nox5.

CRITICAL ISSUES

Although extensive experimental data support a role for increased ROS levels and altered redox signaling in the pathogenesis of hypertension, the role in clinical hypertension is unclear, as a direct causative role of ROS in blood pressure elevation has yet to be demonstrated in humans. Nevertheless, what is becoming increasingly evident is that abnormal ROS regulation and aberrant signaling through redox-sensitive pathways are important in the pathophysiological processes which is associated with vascular injury and target-organ damage in hypertension.

FUTURE DIRECTIONS

There is a paucity of clinical information related to the mechanisms of oxidative stress and blood pressure elevation, and a few assays accurately measure ROS directly in patients. Such further ROS research is needed in humans and in the development of adequately validated analytical methods to accurately assess oxidative stress in the clinic.