Biomedical subjects

C H Graham

Publications and source records attributed to C H Graham.

76 records · Page 5Linked to original sources

PubMedDate not supplied

Effect of transforming growth factor-beta on the plasminogen activator system in cultured first trimester human cytotrophoblasts.

Plasminogen activators (PAs) play an important role in facilitating trophoblast invasion of the uterus and in the maintenance of blood fluidity within the placental intervillous spaces. We previously found that transforming growth factor-beta (TGF-beta), produced mainly by the decidua, inhibits first trimester trophoblast invasiveness at least partly via induction of tissue inhibitor of metalloproteinases-1 production and secretion by the trophoblasts. The present study examined whether TGF-beta 1 affects PA and plasminogen activator inhibitor-1 (PAI-1) production by cultured human cytotrophoblasts. Immortalized first trimester human cytotrophoblasts (HTR-8/SVneo) were cultured in the absence or presence of TGF-beta 1 (0-10 ng/ml) for 24 h, after which the levels of urokinase-type PA (uPA), PAI-1 and uPA activity in the serum-free conditioned media were determined by enzyme-linked immunosorbent assay (ELISA), protein zymography, and a chromogenic uPA activity assay. Cellular PAI-1 mRNA levels were also determined in cultures following a 24-h incubation with a single dose (5 ng/ml) of TGF-beta 1. Presence of TGF-beta 1 at 1 ng/ml resulted in a greater than 12-fold reduction in the levels of total uPA as determined by ELISA. Furthermore, released uPA activity levels in similar cultures incubated with 5 ng/ml of TGF-beta 1 were reduced to 35 per cent of control values. In contrast, cultures incubated with as little as 0.1 ng/ml TGF-beta exhibited a 63 per cent increase in the levels of secreted PAI-1 protein. Similarly, both the 2.2- and 3.0-kb PAI-1 cellular mRNA species were elevated in trophoblast cells incubated with 5 ng/ml TGF-beta 1 when compared with control cells. Thus, it appears that the reduced uPA activity observed in the cultures incubated with TGF-beta 1 is due to reduced secretion of uPA and increased PAI-1 production and secretion. These results suggest that TGF-beta may also exert its anti-invasive effect by down-regulating trophoblast-derived PA activity. Through its effects on the PA system, TGF-beta may also play an indirect role in the regulation of uteroplacental blood flow.

Blotting, Northern↗

PubMedDate not supplied

Adriana and Luisa Castellucci award lecture 1999: role of oxygen in the regulation of trophoblast gene expression and invasion.

Changes in oxygen levels characterize normal and pathological human placentation. For example, relatively low Po(2)values are present around the blastocyst during implantation and in the placenta of the first trimester of pregnancy, a time of maximal trophoblast invasion. Our studies have revealed that low oxygen levels stimulate the in vitro invasiveness of cultured first trimester trophoblasts. This increased invasive ability is linked to elevated expression of some components of the plasminogen activator system and requires the participation of a putative haem protein. As gestation proceeds beyond the first trimester, and the extent of trophoblast invasion decreases, placental oxygen levels rise with a corresponding increase in blood flow. However, during certain pathological conditions, such as pre-eclampsia/intrauterine growth restriction, impaired remodelling of the uterine spiral arterioles leads to vessels with reduced diameters and localized regions of placental ischaemia/hypoxia. Placental hypoxia in the second half of gestation, as a consequence of reduced uteroplacental blood flow, may result in aberrant expression of genes that contribute to the pathophysiology of pre-eclampsia. Some of these genes encode certain cytokines and vasoactive molecules. We have also identified other genes whose expression is regulated by oxygen. Expression of one of them is induced in trophoblast and other cell types cultured under low oxygen levels and the product of the gene is a 43-kDa protein which we have termed PROXY-1. Compared to placental tissues and membranes isolated from uncomplicated pregnancies, PROXY-1 expression is elevated in tissues from pre-eclamptic pregnancies such as chorionic villi of peri-infarct regions, basal plate and membrane decidua, as well as chorion. Overall, these observations suggest that oxygen levels play an important role in placentation and in the pathophysiology of certain complications of pregnancy.

Adult↗

PubMedDate not supplied

Carbon monoxide decreases perfusion pressure in isolated human placenta.

Carbon monoxide (CO) is one of the metabolites formed via heme oxidation catalysed by the enzyme heme oxygenase (HO). Endogenous formation of CO, mediated by HO, has been noted in both placental and umbilical vessels. In blood vessels from different mammalian sources, it has been proposed that the vasodilator effect of CO is mediated via stimulation of soluble guanylyl cyclase (sGC) and consequent increased cGMP formation. The purpose of the present study was to determine the effect of exogenous CO on placental cotyledon perfusion pressure and to determine the role of sGC in the CO-induced decrease of perfusion pressure using the in vitro human placental perfusion preparation. A thromboxane A2 mimetic (U46619) was added to the foetal perfusion medium to constrict the placental blood vessels. Carbon monoxide was added to the foetal perfusion medium in increasing concentrations to determine its effect on placental perfusion pressure. Carbon monoxide produced a concentration-dependent decrease in placental perfusion pressure. The addition of ODQ, a sGC inhibitor, attenuated the CO-induced decrease in placental perfusion pressure, while addition of YC-1, an activator of sGC, augmented the CO-induced decrease in placental perfusion pressure. The data indicate that CO causes vasorelaxation of placental resistance blood vessels, in large part, via activation of sGC.

15-Hydroxy-11 alpha,9 alpha-(epoxymethano)prosta-5↗

PubMedDate not supplied

Mechanisms of placental invasion of the uterus and their control.

Trophoblast cells of the placenta in many species have acquired mechanisms to invade the uterus, inclusive of its blood vessels, to establish efficient fetomaternal exchange of molecules. This invasion is strictly controlled both spatially and temporally and, in humans, usually continues until midgestation. Key mechanisms underlying various steps in trophoblast invasion are: (i) the attachment to the basement membrane, most likely by binding to laminin; (ii) the detachment from the basement membrane matrix, a process requiring the presence of complex-type oligosaccharides on the cell surface; and (iii) the breakdown of basement membrane components, mediated by secretion of metalloproteases (such as type IV collagenases) and serine proteases (plasminogen activator). Activation of trophoblast-derived metalloproteases appears to be plasmin dependent. Trophoblast invasiveness in situ is controlled by the microenvironment, owing to local production of anti-invasive factors by the decidual tissue of the uterus. One of these factors is TIMP (tissue inhibitor of metalloproteases), which neutralizes metalloproteases in an equimolar ratio. Another is TGF-beta (transforming growth factor-beta), which has a dual effect: it induces TIMP-1 secretion by the trophoblast and decidual cells and promotes differentiation of invasive trophoblast cells into multinucleated giant cells, which are presumably noninvasive. Thus, TGF-beta provides the key control of trophoblast invasiveness in situ. This control is lost in certain choriocarcinomas. In contrast to the response shown by the normal trophoblast, JAR and JEG-3 choriocarcinoma cell invasiveness does not seem to be inhibited by TGF-beta. In fact, in preliminary studies, JAR cells responded to TGF-beta by increased invasiveness.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗