PlGF gene knockdown in human retinal pigment epithelial cells

Retinopathy of prematurity: A review of pathophysiology and signaling pathways

Retinopathy of prematurity (ROP) is a vasoproliferative disorder of the retina and a leading cause of visual impairment and childhood blindness worldwide. The disease is characterized by an early stage of retinal microvascular degeneration, followed by neovascularization that can lead to subsequent retinal detachment and permanent visual loss. Several factors play a key role during the different pathological stages of the disease. Oxidative and nitrosative stress and inflammatory processes are important contributors to the early stage of ROP. Nitric oxide synthase and arginase play important roles in ischemia/reperfusion-induced neurovascular degeneration. Destructive neovascularization is driven by mediators of the hypoxia-inducible factor pathway, such as vascular endothelial growth factor and metabolic factors (succinate). The extracellular matrix is involved in hypoxia-induced retinal neovascularization. Vasorepulsive molecules (semaphorin 3A) intervene preventing the revascularization of the avascular zone. This review focuses on current concepts about signaling pathways and their mediators, involved in the pathogenesis of ROP, highlighting new potentially preventive and therapeutic modalities. A better understanding of the intricate molecular mechanisms underlying the pathogenesis of ROP should allow the development of more effective and targeted therapeutic agents to reduce aberrant vasoproliferation and facilitate physiological retinal vascular development.

Placental growth factor stabilizes VEGF receptor-2 protein in retinal pigment epithelial cells by downregulating glycogen synthase kinase 3 activity

Placental growth factor (PlGF) belongs to the vascular endothelial growth factor (VEGF) family of proteins that participate in angiogenesis and vasculogenesis. Anti-VEGF therapy has become the standard treatment for ocular angiogenic disorders in ophthalmological practice. However, there is emerging evidence that anti-VEGF treatment may increase the risk of atrophy of the retinal pigment epithelium (RPE), which is important for the homeostasis of retinal tissue. Whereas the cytoprotective role of VEGF family molecules, particularly that of VEGF A (VEGFA) through its receptor VEGF receptor-2 (VEGFR-2), has been recognized, the physiological role of PlGF in the retina is still unknown. In this study, we explored the role of PlGF in the RPE using PlGF-knockdown RPE cells generated by retrovirus-based PlGF-shRNA transduction. We show that VEGFA reduced apoptosis induced by serum starvation in RPE cells, whereas the antiapoptotic effect of VEGFA was abrogated by VEGFR-2 knockdown. Furthermore, PlGF knockdown increased serum starvation–induced cell apoptosis and unexpectedly reduced the protein level of VEGFR-2 in the RPE. The antiapoptotic effect of VEGFA was also diminished in PlGF-knockdown RPE cells. In addition, we found that glycogen synthase kinase 3 activity was involved in proteasomal degradation of VEGFR-2 in RPE cells and inactivated by PlGF via AKT phosphorylation. Overall, the present data demonstrate that PlGF is crucial for RPE cell viability and that PlGF supports VEGFA/VEGFR-2 signaling by stabilizing the VEGFR-2 protein levels through glycogen synthase kinase 3 inactivation.

PlGF silencing combined with PEDF overexpression: Modeling RPE secretion as potential therapy for retinal neovascularization

Ocular neovascularization is a defining feature of several blinding diseases. We have previously described the effectiveness of long-term pigment epithelium-derived factor (PEDF) expression in the retina of diabetic mice in ameliorating some diabetic retinopathy hallmarks. In this study, we aimed to investigate if the antiangiogenic potential of PEDF overexpression was enhanced in combination with placental growth factor (PlGF) silencing. Human RPE cells were transfected with a self-replicating episomal vector (pEPito) for PEDF overexpression and/or a siRNA targeting PlGF gene. Conditioned media from PEDF overexpression, from PlGF inhibition and from their combination thereof were used to culture human umbilical vein endothelial cells, and their proliferation rate, migration capacity, apoptosis and ability to form tube-like structures were analyzed in vitro. We here demonstrate that pEPito-driven PEDF overexpression in combination with PlGF silencing in RPE cells does not affect their viability and results in an enhanced antiangiogenic activity in vitro. We observed a significant decrease in the migration and proliferation of endothelial cells, and an increase in apoptosis induction as well as a significant inhibitory effect on tube formation. Our findings demonstrate that simultaneous PEDF overexpression and PlGF silencing strongly impairs angiogenesis compared with the single approaches, providing a rationale for combining these therapies as a new treatment for retinal neovascularization.

Cytokines concentrations in aqueous humor of eyes with uveal melanoma

Uveal melanoma (UM) is the major intraocular malignancy in adults, of which the molecular biology is still unknown. Therefore, this study was designed to determine the aqueous concentrations of angiogenic, inflammatory, and chemotactic cytokines in eyes with UM.Aqueous humor samples were collected from 38 patients with UM and 22 patients undergoing cataract surgery. Interleukin 6, 8 (IL-6, IL-8, respectively), interferon-inducible protein-10 (IP-10), placental growth factor1 (PIGF1), regulated on activation, normal T Cell expressed and secreted (RANTES), monocyte chemoattractant protein-1 (MCP-1), nerve growth factor-beta (NGF-β), epidermal growth factor (EGF), basic fibroblast growth factor (bFGF), and vascular endothelia growth factor A (VEGF-A) were assessed by multiplex bead assay.In the study group, significantly higher concentrations of IL-6 (P = .006), IL-8 (P = .018), IP-10 (P = .004), RANTES (P = .008), MCP-1 (P = .02), NGF-β (P = .013), EGF (P < .001), PIGF1 (P = .01), bFGF (P = .016), and VEGF (P = .017) were measured, when compared with the control group.Several angiogenic, inflammatory, and chemotactic cytokines are highly expressed in the aqueous humor of the UM eyes, which provides new insights into the pathophysiology of UM and could be potential targets for treatment.

Influences of placental growth factor on mouse retinal vascular development

BACKGROUND

Placental growth factor (PGF) is important for wound-healing and vascular collaterogenesis. PGF deficiency is associated with preeclampsia, a hypertensive disease of human pregnancy. Offspring born to preeclamptic mothers display cognitive impairments and brain vascular and neurostructural deviations. Low PGF production during development may contribute to alterations in offspring cerebrovascular beds. Retina is a readily accessible part of the central nervous system with a well-described pattern of vascular development in mice. Impacts of PGF deficiency were addressed during mouse retinal vascularization.

RESULTS

Retinal vessels were compared between Pgf^-/- and congenic C57BL/6 (B6) mice. PGF deficiency altered neonatal retinal vascularization patterns. Some anatomic alterations persisted into adulthood, particularly in males. Greater arterial wall collagen IV expression was found in adult Pgf^-/- females. Pregnancy (studied in adult females at gestational days 11.5 or 18.5) induced subtle changes upon the mother's retinal vasculature but these pregnancy-induced changes did not differ between genotypes. Significant sex-related differences occurred between adult male and female B6 although sexually dimorphic retinal vascular differences were absent in B6 neonates.

CONCLUSIONS

Overall, PGF has a role in retinal vascular angiogenesis and vessel organization during development but does not affect retinal vessel adaptations in adult females during pregnancy. Developmental Dynamics 246:700-712, 2017. © 2017 Wiley Periodicals, Inc.

Retinal pigment epithelium-secretome: A diabetic retinopathy perspective

Diabetic retinopathy is a major complication of diabetes mellitus that can lead to retinal vascular abnormalities and visual impairment. While retinal endothelial pathology is well studied, retinal pigment epithelium (RPE) layer modifications and the patho-physiological regulations are not widely understood. The RPE is a highly specialized pigmented layer regulating not only physiological functions such as transport of nutrients, ions, absorption of light, phagocytosis of photoreceptor membranes, but also secretion of a number of cytokines, chemokines, angiogenic and anti-angiogenic factors. The RPE secretome, though crucial in health and disease, remains elusive in diabetic retinopathy. A knowledge of these secreted factors would help explain and correlate the clinical phase of the disease aiding in improved disease management. A comprehensive knowledge of the secreted factors of the RPE is a potential tool for understanding the differential treatment regime of early diabetic retinopathy, diabetic proliferative retinopathy and diabetic macular edema. In this review, we have delineated the importance of factors secreted by the retinal pigment epithelium and its regulation in the pathogenesis of diabetic retinopathy.

PlGF Knockdown Decreases Tumorigenicity and Stemness Properties of Spheroid Body Cells Derived from Gastric Cancer Cells

Placental growth factor (PlGF) a member of the vascular endothelial growth factor family regulates some cell processes such as survival, growth of vascular endothelial cells, invasiveness, and also involves in pathological angiogenesis and metastasis in most cancers. Cancer stem cells are believed to be the main reason for the tumor relapse and resistance to therapy. These cells have various characteristics as same as normal tissue-specific adult stem cells including self-renewability and potent to differentiate into various cell types. However, the function of PlGF in gastric cancer stem cells is not well understood. We have investigated the effect of PlGF knockdown on the tumorigenicity and stem cell properties of spheroid body cells derived from two human gastric cancer cell lines. In this study, we isolated spheroid body cells which have stemness properties from MKN-45 and AGS without using growth factors. Validation of spheroid body cells was confirmed by various methods. Then the effects of PlGF knockdown were investigated on in vitro tumorigenicity, differentiation, migration, angiogenesis, and transcription levels of stemness markers of spheroid body cells. Our findings indicated that isolation of spheroid body cells from MKN-45 and AGS cells without using growth factors is an easy and inexpensive method to isolate cancer stem cells and knockdown of PlGF in spheroid body cells reduced in vitro tumorigenicity and stemness properties of spheroid body cells such as Self-renewal ability, colony forming, migratory, and MMPs activities and decreased ability to differentiation and angiogenesis. J. Cell. Biochem. 118: 851-859, 2017. © 2016 Wiley Periodicals, Inc.

A novel model of retinopathy of prematurity in normobaric hyperoxic conditions

AIM

To examine changes in retinal vasculature after treatment with different oxygen concentrations from common retinopathy of prematurity (ROP) models and to determine a novel and practical ROP model.

METHODS

A sample of 14 newborn Sprague-Dawley rats was used. The study group (n=7) was exposed to 95% oxygen for 4h per day followed by normoxic laboratory conditions for 20h. This cycle was repeated for 14d. The control group (n=7) was subjected to normobaric normoxic conditions. On postnatal day 14 (P14), the two groups were placed in room air for 7d. On P21, the two groups were examined using indirect ophthalmoscopy. All eyes were enucleated for immunofluorescence (IF) staining of the vasculature of retinas and analysis of vascular endothelial growth factor (VEGF), hypoxia inducible factor-1 alpha (HIF-1α), placental growth factor (PLGF) in vitreous humor, and then the rats were sacrificed by decapitation. All procedures were repeated using another litter of 14 pups.

RESULTS

In the study group and under normobaric hyperoxic conditions, retinal neovascularization and peripheral avascular retina were determined in 85% of the rats through indirect ophthalmoscopic examination. Also IF staining of retina of the study group showed retarded peripheral vascular growth. The difference between the two groups for VEGF, HIF-1α and PLGF concentrations of vitreous humor was statistically significant (P=0.003, 0.007, 0.027 respectively).

CONCLUSION

Fluctuating oxygen concentrations are primarily responsible for retinal neovascularization. Our new ROP model is practical and applicable for all retinal neovascularization studies, considering the laboratory procedures.

Osmotic induction of placental growth factor in retinal pigment epithelial cells in vitro: contribution of NFAT5 activity

One risk factor of neovascular age-related macular degeneration is systemic hypertension; hypertension is mainly caused by extracellular hyperosmolarity after consumption of dietary salt. In retinal pigment epithelial (RPE) cells, high extracellular osmolarity induces vascular endothelial growth factor (VEGF)-A (Hollborn et al. in Mol Vis 21:360-377, 2015). The aim of the present study was to determine whether extracellular hyperosmolarity and chemical hypoxia trigger the expression of further VEGF family members including placental growth factor (PlGF) in human RPE cells. Hyperosmotic media were made up by addition of 100 mM NaCl or sucrose. Chemical hypoxia was induced by CoCl2. Gene expression was quantified by real-time RT-PCR, and secretion of PlGF-2 was investigated with ELISA. Nuclear factor of activated T cell 5 (NFAT5) was depleted using siRNA. Extracellular hyperosmolarity triggered expression of VEGF-A, VEGF-D, and PlGF genes, and secretion of PlGF-2. Hypoosmolarity decreased PlGF gene expression. Hypoxia induced expression of VEGF-A, VEGF-B, VEGF-D, and PlGF genes. Extracellular hyperosmolarity and hypoxia produced additive PlGF gene expression. Both hyperosmolarity and hypoxia induced expression of KDR and FLT-4 receptor genes, while hyperosmolarity caused neuropilin-2 and hypoxia neuropilin-1 gene expression. The hyperosmotic, but not the hypoxic, PlGF gene expression was in part mediated by NFAT5. The expression of PlGF in RPE cells depends on the extracellular osmolarity. The data suggest that high consumption of dietary salt may exacerbate the angiogenic response of RPE cells in the hypoxic retina via transcriptional activation of various VEGF family member genes.

PlGF knockdown inhibited tumor survival and migration in gastric cancer cell via PI3K/Akt and p38MAPK pathways

The molecular signalling of placental growth factor (PlGF), a member of the vascular endothelial growth factor family, was not uncovered in human adenocarcinoma gastric cell line (AGS). The purpose of this study was to examine the inhibitory effects of PlGF knockdown on cell proliferation, apoptosis and migration through p38 mitogen-activated protein kinase (p38MAPK) and PI3K pathways in human adenocarcinoma gastric cell line (AGS). To study PlGF knockdown effect, AGS cells were treated with 40 pmol of small interfering RNA (siRNA) related to PlGF gene and also a scrambled siRNA as control. Trypan Blue and Anexin V staining of AGS cells treated with PlGF-specific siRNA showed induction of apoptosis. Wound healing assay and zymography indicated that cellular migration and matrix metalloproteinases activities were reduced in response to PlGF knockdown. Phosphorylation of Akt and p38MAPK was reduced in AGS cells treated with PlGF-specific siRNA. PlGF knockdown decreased transcripts of PI3K, Akt, p38MAPK, PCNA, Caspase-3, OCT3/OCT4 and CD44, but elevated p53 and SOX2 transcripts. Our results indicated that PlGF knockdown decreased migration and induced apoptosis through PI3K/Akt1 and p38MAPK signal transduction in AGS cells.

The pathophysiology of retinopathy of prematurity: an update of previous and recent knowledge

Retinopathy of prematurity (ROP) is a disease that can cause blindness in very low birthweight infants. The incidence of ROP is closely correlated with the weight and the gestational age at birth. Despite current therapies, ROP continues to be a highly debilitating disease. Our advancing knowledge of the pathogenesis of ROP has encouraged investigations into new antivasculogenic therapies. The purpose of this article is to review the findings on the pathophysiological mechanisms that contribute to the transition between the first and second phases of ROP and to investigate new potential therapies. Oxygen has been well characterized for the key role that it plays in retinal neoangiogenesis. Low or high levels of pO2 regulate the normal or abnormal production of hypoxia-inducible factor 1 and vascular endothelial growth factors (VEGF), which are the predominant regulators of retinal angiogenesis. Although low oxygen saturation appears to reduce the risk of severe ROP when carefully controlled within the first few weeks of life, the optimal level of saturation still remains uncertain. IGF-1 and Epo are fundamentally required during both phases of ROP, as alterations in their protein levels can modulate disease progression. Therefore, rhIGF-1 and rhEpo were tested for their abilities to prevent the loss of vasculature during the first phase of ROP, whereas anti-VEGF drugs were tested during the second phase. At present, previous hypotheses concerning ROP should be amended with new pathogenetic theories. Studies on the role of genetic components, nitric oxide, adenosine, apelin and β-adrenergic receptor have revealed new possibilities for the treatment of ROP. The genetic hypothesis that single-nucleotide polymorphisms within the β-ARs play an active role in the pathogenesis of ROP suggests the concept of disease prevention using β-blockers. In conclusion, all factors that can mediate the progression from the avascular to the proliferative phase might have significant implications for the further understanding and treatment of ROP.

PlGF: a multitasking cytokine with disease-restricted activity

Placental growth factor (PlGF) is a member of the vascular endothelial growth factor (VEGF) family that also comprises VEGF-A (VEGF), VEGF-B, VEGF-C, and VEGF-D. Unlike VEGF, PlGF is dispensable for development and health but has diverse nonredundant roles in tissue ischemia, malignancy, inflammation, and multiple other diseases. Genetic and pharmacological gain-of-function and loss-of-function studies have identified molecular mechanisms of this multitasking cytokine and characterized the therapeutic potential of delivering or blocking PlGF for various disorders.