Glutamate is the chemotaxis-inducing factor in placental extracts

Human placental extracts are known to help wound healing. Rapid migration of neutrophils to the wound site is a prerequisite to the wound healing process. Gel filtration analysis of heat-treated placental extract gave the initial cue to the small nature of the migration promoting factor of the extract. HPLC analysis of the extract revealed glutamate to be the predominant free amino acid. Our studies show that glutamate at an optimum concentration of 8 μM induced phenotypic neutrophil chemotaxis, as seen in the time lapse- and transwell assays. Glutamate was also found to induce chemokinesis of the neutrophil, though the stimulation of chemotaxis was more pronounced. The glutamate induced chemotaxis was accompanied by polarization of the actin cytoskeleton, and by polymerization of F-actin. These data indicate that glutamate has a strong chemotactic functionality in the neutrophil, which could be of interest both therapeutically and in further investigation of the molecular basis of chemotaxis.     

Erratum to: Glutamate functions in stomatal closure in Arabidopsis and fava bean

Journal of Plant Research -     

Calcitonin gene-related peptide (CALCA) is a proangiogenic growth factor in the human placental development

Recent studies have shown that homozygous knockout of gene for calcitonin gene-related peptide (CALCA) receptor component, calcitonin receptor-like receptor (CALCRL), led to extreme hydrops fetalis and embryonic death, underlining the critical role of CALCA in embryonic development and fetal growth. The present study was designed to determine the cellular localization of CALCA and its receptor components, CALCRL and receptor activity modifying protein 1 (RAMP1), at the human implantation site during early pregnancy; to assess whether CALCA regulates in vitro angiogenesis of human endothelial cells; and to examine whether CALCA can improve angiogenic imbalance in preeclamptic placental explants. Our studies demonstrated that both protein and mRNA for CALCA were expressed by the villous and extravillous trophoblasts and decidual cells in the first-trimester villous tissues. CALCA receptor components, CALCRL and RAMP1, were expressed by both villous and extravillous trophoblast cells, as well as vascular endothelial cells. CALCA induced both endothelial proliferation and migration in a dose- and time-dependent manner, and it promoted capillarylike tube formation of human umbilical vein endothelial cells (HUVECs) on Matrigel. CALCA-induced angiogenesis of human endothelial cells was completely blocked by CALCA antagonist CALCA(8-37). Further, conditioned medium from preeclamptic placental explants significantly inhibited HUVEC capillarylike tube formation compared with gestational age-matched controls, and conditioned medium from preeclamptic placental explants incubated with CALCA significantly improved capillarylike tube formation. We conclude that CALCA induces in vitro angiogenesis by stimulating endothelial cell proliferation, migration, and capillarylike tube formation; thus, CALCA at the human implantation site may constitute a potential autocrine or paracrine mechanism that could modify placental angiogenesis and neovascularization.     

Adrenomedullin-induced dilation of human placental arteries is modulated by an endothelium-derived constricting factor

Adrenomedullin is synthesized and secreted by fetoplacental tissues. Given that the placenta lacks autonomic innervation, we proposed that adrenomedullin acts locally to control blood flow in the placental vasculature through a balance of dilatory and constrictive pathways. Placental stem villous arteries (200 microm) from normotensive human pregnancies were dissected and mounted on a wire myograph. The vessels were preconstricted with the thromboxane A(2) mimetic U46619 (EC(80) concentration), and exposed to cumulative concentrations of adrenomedullin (1 x 10(-9) to 3 x 10(-7) mol/L). Adrenomedullin caused concentration-dependent vasorelaxation which, in endothelium-intact vessels, was attenuated in the presence of the nitric oxide synthase inhibitor L-NMMA. This suggested that the vasodilation was mediated, at least in part, through nitric oxide. However, removal of the endothelium did not similarly alter the response. Nor did L-NMMA have any effect in endothelium-denuded vessels. We hypothesized that adrenomedullin must induce release of both endothelium-derived relaxing (nitric oxide) and constricting factors. When we blocked the two major pathways through which adrenomedullin is known to induce vasodilation, by incubating the vessels with L-NMMA (nitric oxide synthase inhibitor) and Rp-cAMPS (cAMP-dependent protein kinase inhibitor), adrenomedullin induced concentration-dependent vasoconstriction. This was not mediated through endothelin, since addition of the non-specific endothelin receptor antagonist PD142893 failed to alter the response to adrenomedullin. We conclude that, in addition to increasing endothelial nitric oxide biosynthesis in placental stem villous arteries, adrenomedullin induces release of an endothelium-derived constricting factor.     

The human placental anti-aggregating factor is neither prostacyclin, nor a prostacyclin metabolite

Using PGH₂ as substrate, we have previously demonstrated that human placenta synthetizes mainly PGE₂, TxB₂ and PGD₂(1,2). Other reports have shown that placental tissue generates a substance which inhibits ADP-induced platelet aggregation and which was supposed to be PGI₂ (3). The present study indicates that the stability of that substance is different from the stability of prostacyclin (released by umbilical artery pieces). By GC-MS and multiple ion-monitoring, we have shown the presence of 6 keto-PGF_1α (the stable metabolite of PGI₂) in the umbilical artery incubation medium, while no trace of 6-keto-PGF_1α could be found in the placental medium. No conversion of AA to 6-keto-PGF_1α by placental microsomes was observed, even in the presence of antioxidants. The placenta possesses, in addition to the known 15-OH-PGDH and Δ-13 reductase activities, a weak 9 OH pGDH which is specific for PGF_2α (and not PGI₂ nor 6-keto-PGF_1α). GC-MS analysis is showed that the expected metabolites of PGI₂ through those three enzymes were not found in the placental medium, indicating that neither PGI₂ synthesis nor metabolism could be demonstrated in the placenta.     

Glutamate is not a messenger in insulin secretion

Experiments do not support a recent claim that glutamate formed from the amination of citric acid cycle-derived alpha-ketoglutarate is a messenger in glucose-induced insulin secretion (Maechler, P., and Wollheim, C. (1999) Nature 402, 685-689). Glucose, leucine, succinic acid methyl ester, and alpha-ketoisocaproic acid all markedly stimulate insulin release but do not increase glutamate levels in pancreatic islets. Increasing the intracellular glutamate levels to 10-fold higher than basal levels by adding glutamine to islets does not stimulate insulin release. When leucine, in addition to glutamine, is applied to islets, insulin release is almost as high as with glucose alone. This is consistent with the known ability of leucine to allosterically activate glutamate deamination by glutamate dehydrogenase, which can supply alpha-ketoglutarate to the citric acid cycle. Experiments with mitochondria from pancreatic islets suggest that flux through the glutamate dehydrogenase reaction is quiescent during glucose-induced insulin secretion. These experiments support the traditional idea that when insulin release is associated with flux through glutamate dehydrogenase, the flux is in the direction of alpha-ketoglutarate.     

Relationship between placental vascular endothelial growth factor expression and placental/endometrial vascularity in the pig

We investigated the temporal association between placental vascular endothelial growth factor (VEGF), a potent stimulator of angiogenesis and vascular permeability, and changes in placental/endometrial vascularity on selected days throughout gestation in the pig. Placental and endometrial tissues were collected from sows on Days 25 (n = 4), 36 (n =6), 44 (n = 6), 70 (n =5), 90 (n =5 ), and 112 (n = 7) of gestation. Cross sections of the placental/endometrial interface of each conceptus were used to estimate the number of blood vessels per unit area via image analysis and the intensity of VEGF staining via immunohistochemistry. Placental tissues were also collected on these days to evaluate VEGF mRNA expression. Placental VEGF mRNA expression and the numbers of blood vessels per unit area of placental and adjacent endometrial tissue were low and decreasing from Day 25 to Day 44, before increasing (P < 0.05) markedly and progressively through Day 112. These data are consistent with the marked increase in VEGF immunostaining in the chorionic and uterine luminal epithelium from early to late gestation. Further, these increases in placental VEGF mRNA were positively correlated with fetal weight (r = 0.73; P < 0.0001) and placental efficiency (fetal weight/placental weight ratio; r = 0.66, P < 0.0001). These data are consistent with a role for VEGF in increasing the number of blood vessels at the placental endometrial interface, resulting in an increased capacity for nutrient transfer from the maternal to the fetal compartment.     

Erratum to: Herbal decoctosome is a novel form of medicine

Science China Life Sciences - Following the published article, we noticed an error duplication in Figure 5G “control” and “PGY-6” that was introduced during the revised...