Growth factor receptors, phospholipases, phospholipid kinases and actin reorganization

Upon binding to their ligand, several growth factor receptors that contain a tyrosine kinase within their cytoplasmic domain [receptor tyrosine kinases (RTKs)] induce a substantial reorganization of the actin cytoskeleton. This change in actin superstructure is necessary to produce multiple motile responses within the target cells. RTKs catalyse the clustering of effector proteins within functional units underneath the plasma membrane. Upon reaching a critical mass, RTK-effector units send out signals through the metabolism of membrane phospholipids and other second messenger molecules that regulate the interaction of actin with its satellite regulatory molecules. Several actin binding proteins interact transiently with small clusters of membrane inositol phospholipids in vitro (4 to 5 phospholipid molecules per actin binding protein). Such transient complex formation can either down-regulate or up-regulate the interaction of regulatory proteins with actin. The phospholipids involved in the surface catalytic control of the actin cytoskeleton are metabolically very active and abundant in cells, and are therefore poised to mediate reactions linking signal transduction molecules to the reorganization of the actin cytoskeleton upon cell activation

17β-Estradiol Inhibits Apoptosis of Endothelial Cells

Endothelial cells provide an antithrombotic and anti-inflammatory barrier for the normal vessel wall. Dysfunction of endothelial cells has been shown to promote atherosclerosis, and normalization of previously dysfunctional endothelial cells can inhibit the genesis of atheroma. In normal arteries, endothelial cells are remarkably quiescent. Acceleration of the turnover rate of endothelial cells can lead to their dysfunction. Apoptosis is a physiological process that contributes to vessel homeostasis, by eliminating damaged cells from the vessel wall. However, increased endothelial cell turnover mediated through accelerated apoptosis may alter the function of the endothelium and therefore, promote atherosclerosis. Apoptotic endothelial cells can be detected on the luminal surface of atherosclerotic coronary vessels, but not in normal vessels. This finding links endothelial cell apoptosis and the process of atherosclerosis, although a causative role for apoptosis in this process remains hypothetical. Estrogen metabolites have been shown to be among the most potent anti-atherogenic agents available to date for post-menopausal women. The mechanism of estrogen's protective effect is currently incompletely characterized. Here we show that 17β-estradiol, a key estrogen metabolite, inhibits apoptosis in cultured endothelial cells. Our data support the hypothesis that 17β-estradiol's anti-apoptotic effect may be mediated via improved endothelial cell interaction with the substratum, increased tyrosine phosphorylation of pp125 focal adhesion kinase, and a subsequent reduction in programmed cell death of endothelial cells. Inhibition of apoptosis by estrogens may account for some of the anti-atherogenic properties of these compounds

Progress toward the development of a point-of-care photonic crystal ammonia sensor

We have developed an ammonia-sensitive material by coupling the Berthelot reaction to our polymerized crystalline colloidal array (PCCA) technology. The material consists of a periodic array of highly charged colloidal particles (110 nm diameter) embedded in a poly(hydroxyethyl acrylate) hydrogel. The particles have a lattice spacing such that they Bragg-diffract visible light. In the Berthelot reaction, ammonia, hypochlorite, and phenol react to produce the dye molecule indophenol blue in an aqueous solution. We use this reaction in our sensor by covalently attaching 3-aminophenol to the hydrogel backbone, which forms cross-links through the Berthelot mechanism. Ammonia reacts with hypochlorite, forming monochloramine, which then reacts with a pendant aminophenol to form a benzoquinone chlorimine. The benzoquinone chlorimine reacts with another pendant aminophenol to form a cross-link. The creation of new cross-links causes the hydrogel to shrink, which reduces the lattice spacing of the embedded colloidal array. This volume change results in a blue-shift in the diffracted light proportional to the concentration of NH3 in the sample. We demonstrate that the NH3 photonic crystal sensing material is capable of quantitative determination of concentrations in the physiological range (50-350 μmol NH3 L-1) in human blood serum