Placental Growth Factor Protein Expression Research Articles

Total Versus Free Placental Growth Factor Levels in the Pathogenesis of Preeclampsia

Elevated circulating sFLT-1 (soluble fms-like tyrosine kinase) and low levels of its ligand, PlGF (placental growth factor), are key characteristics of preeclampsia. However, it is unclear if the low levels of plasma PlGF noted during preeclampsia are due to decreased placental production of PlGF or due to binding of PlGF by increased circulating sFLT-1. Here, we describe a biochemical procedure to dissociate PlGF-sFLT-1 complex ex vivo and when used in conjunction with an immunoassay platform, demonstrate a method to measure total and free PlGF in human blood samples. Using this method, we noted that plasma free PlGF levels were significantly lower in preeclampsia (N=22) than in nonhypertensive controls (N=24; mean, 314 versus 686 pg/mL, P<0.05), but total PlGF levels were not different (mean, 822 versus 800 pg/mL, P=0.49). In contrast, total sFLT-1 levels were significantly higher in preeclampsia than in nonhypertensive controls (mean, 16 957 versus 3029 pg/mL, P<0.01) and sFLT-1 levels correlated with bound PlGF levels (bound PlGF=total PlGF-free PlGF) in these samples (r2=0.68). We confirmed these findings in an independent cohort of subjects (N=49). Furthermore, we did not detect any difference in PlGF mRNA by quantitative polymerase chain reaction or in PlGF protein expression by immunohistochemistry in preeclamptic placentas when compared with nonhypertensive controls. In contrast, sFLT-1 mRNA and protein levels were upregulated in placentas from women with preeclampsia. Taken together with prior studies, our results provide evidence that decrease in circulating PlGF noted during preeclampsia is largely mediated by excess circulating sFLT-1.

Increased expression of placental growth factor in high-grade endometrial carcinoma

Placental growth factor (PlGF), a homolog of vascular endothelial growth factor (VEGF), exerts pleiotropic functions in cancer by affecting tumor cells as well as endothelial and inflammatory cells. Moreover, PlGF expression correlates with tumor stage, recurrence, metastasis and patient outcome in different types of cancer. Recently, administration of anti-PlGF therapy reduced tumor growth and metastasis in preclinical tumor models. In the present study, we evaluated the diagnostic and prognostic value of systemic and local expression of PlGF in primary endometrial carcinomas. PlGF levels in tumor lysates (n=128) and serum (n=88) of patients with primary endometrial cancer were determined using ELISA. PlGF mRNA expression in endometrial carcinoma tissues was quantified by quantitative qRT-PCR. Results were compared to endometrial cancer stage and grade. Systemic PlGF levels were not altered in patients with endometrial cancer (FIGO stage I-II-III) as compared to healthy controls. Only in FIGO stage IV patients, serum PlGF levels were slightly increased. Local PlGF mRNA and protein expression in endometrial tumors progressively increased with tumor grade. In endometrioid carcinomas, PlGF mRNA expression was significantly increased in endometrioid grade 3 tumors as compared to normal endometrial tissue. PlGF protein expression was significantly increased in endometrioid grade 2 and 3 carcinomas and in serous carcinomas as compared to normal endometrial tissue. Our study showed that systemic/serum PlGF levels cannot be used as a diagnostic or prognostic marker in endometrial cancer. However, the increased local expression of PlGF, primarily in high-grade carcinomas, underscores the possibility for preclinical assessment of anti-PlGF therapy in endometrial cancer.

Finding a New Prognostic Biomarker for Metastatic Colorectal Cancer

See Article on Page 315-320 For detecting new biomarkers in colorectal cancer, whether they are prognostic or predictive, we should understand the mechanism of the metastatic process at the gene expression level. This article presents a new prognostic biomarker, 'placental growth factor (PlGF)' to the clinical field. PlGF, which is a member of the vascular endothelial growth factor (VEGF) family in conjunction with VEGF-A and VEGF-B, is a ligand for VEGF receptor-1, which is expressed on endothelial cells, monocytes/macrophages, and some tumor cells. PlGF was isolated in 1991 from the placenta and was found only in very low levels under physiological conditions, but it was up-regulated in pathological circumstances such as wound healing, ischemia and tumor growth [1]. PlGF up-regulation has been found in human meningiomas, hemangioblastomas, melanomas, and cervical squamous cell carcinomas and is associated with angiogenesis in renal cell carcinomas. On the contrary, PlGF is down-regulated in thyroid carcinomas, germ cell tumors and cervical adenocarcinomas. Chen et al. [2] reported that PlGF was significantly up-regulated in gastric cancer tissue and was significantly correlated with microvessel density-evaluated angiogenesis and tumor stage. In this research, the authors found that the PlGF protein expression level in colorectal cancer tissue was significantly correlated with microvessel density, overall patient survival, and clinicopathological factors such as lymph-node metastasis, tumor stage, and lymphovascular invasion. According to the authors, PlGF seems to be an independent surrogate prognostic factor for colorectal cancer progression. However, for these results to be adopted in the clinical filed, it is very important that a large-sample-size study be brought conducted in a validation setting. The findings of this research finding suggest that PlGF may constitute a novel approach to colorectal cancer treatment. Several agents against PlGF have already developed or are currently under development. Among these agents, two novel agents against PlGF will be briefly discussed. Firstly, aflibercept (ZALTRAP) is a recombinant fusion protein that acts as a soluble receptor that binds to VEGF-A, VEGF-B and PIGF. In April 2011, Van Cutsem et al. [3] reported that aflibercept improved the primary endpoint of overall survival in the Velour phase III clinical trial for second-line treatment for metastatic colorectal cancer. Secondly, the humanized anti-PlGF mAb (TB-403) is directed against PlGF. A trial with TB-403 has only completed its first phase. Antitumor activity has been demonstrated with TB-403 in human tumor xenograft models of renal cell carcinomas and hepatocellular carcinomas. The mechanism of action for TB-403 is currently under investigation; preclinical studies suggest its effects may include blocking tumor angiogenesis and primary tumor growth, as well as inhibition of metastasis. In addition, PIGF inhibition may complement and potentiate the antitumor effects of VEGF inhibition, in part by inhibiting macrophage recruitment [4].

VEGFR‐2‐mediated increased proliferation and survival in response to oxygen and glucose deprivation in PlGF knockout astrocytes

In hypoxic/ischemic conditions, astrocytes are involved in neuroprotection and angiogenesis. Vascular endothelial growth factor (VEGF) induces angiogenesis and exhibits neuroprotective and neurotrophic properties. However, the role of placental growth factor (PlGF), a VEGF homolog, in these processes is unclear. Therefore, proliferation and survival studies were performed on PlGF knockout (PlGF-/-) and wild-type (PlGF+/+) mouse astrocytes. A significant increase in cell proliferation and survival to oxygen and glucose deprivation (OGD) was observed in PlGF-/- compared to PlGF+/+ astrocytes. Interestingly, no PlGF protein expression was detected in PlGF+/+ astrocytes and no changes in VEGF protein levels were observed between the two genotypes. Real-time PCR and immunocytochemistry showed over-expression of VEGF receptor-2 (VEGFR-2) in PlGF-/- compared with PlGF+/+ astrocytes. Confocal microscopy revealed nuclear, membrane, and cytoplasmic localization of VEGFR-2. In vivo over-expression of VEGFR-2 mRNA was also detected in PlGF-/- compared with PlGF+/+ astrocytes. Stimulation with VEGF165 resulted in increased proliferation in PlGF-/- compared with PlGF+/+ astrocytes. This effect was blocked by the VEGFR-2 antagonist, VEGF165b. The enhanced proliferation of PlGF-/- astrocytes correlated with increased phospho-extracellular-signal-regulated kinase-1/2 levels, while the resistance to OGD was independent of the phosphatidylinositol 3'-kinase/Akt pathway. These results suggest that VEGFR-2 mediates the enhanced proliferative/OGD resistant phenotype observed in PlGF-/- astrocytes.

Hyperbaric oxygen induces placental growth factor expression in bone marrow-derived mesenchymal stem cells

The bone marrow is home to mesenchymal stem cells (MSCs) that are able to differentiate into many different cell types. The effect of hyperbaric oxygen (HBO) on MSCs is poorly understood. Placental growth factor (PlGF) is an attractive therapeutic agent for stimulating revascularization of ischemic tissue. HBO has been shown to improve diabetic wound healing by increase circulating stem cells. We hypothesized that HBO induces PlGF expression in bone marrow-derived MSCs. The MSCs were obtained from adult human bone marrow and expanded in vitro. The purity and characteristics of MSCs were identified by flow cytometry and immunophenotyping. HBO at 2.5 ATA (atmosphere absolute) significantly increased PlGF protein and mRNA expression. The induction of PlGF protein by HBO was significantly blocked by the addition of N-acetylcysteine, while wortmannin, PD98059, SP600125 and SB203580 had no effect on PlGF protein expression. However, the specific inhibitor of nitric oxide synthase, L-NAME did not alter the PlGF protein expression induced by HBO. HBO significantly increased the reactive oxygen species production and pretreatment with N-acetylcysteine significantly blocked the induction of reactive oxygen species by HBO. HBO significantly increased the migration and tube formation of MSCs and pretreatment with N-acetylcysteine and PlGF siRNA significantly blocked the induction of migration and tube formation by HBO. In conclusion, HBO induced the expression of PlGF in human bone marrow-derived MSCs at least through the oxidative stress-related pathways, which may play an important role in HBO-induced vasculogenesis.