Variations in mass transfer to single endothelial cells.

Mass transfer between flowing blood and arterial mural cells (including vascular endothelial cells) may play an important role in atherogenesis. Endothelial cells are known to have an apical surface topography that is not flat, and hence mass transfer patterns to individual endothelial cells are likely affected by the local cellular topography. The purpose of this paper is to investigate the relationship between vascular endothelial cell surface topography and cellular level mass transfer. Confluent porcine endothelial monolayers were cultured under both shear and static conditions and atomic force microscopy was used to measure endothelial cell topography. Using finite element methods and the measured cell topography, flow and concentration fields were calculated for a typical, small, blood-borne solute. A relative Sherwood number was defined as the difference between the computed Sherwood number and that predicted by the Leveque solution for mass transfer over a flat surface: this eliminates the effects of axial location on mass transfer efficiency. The average intracellular relative Sherwood number range was found to be dependent on cell height and not dependent on cell elongation due to shear stress in culture. The mass flux to individual cells reached a maximum at the highest point on the endothelial cell surface, typically corresponding to the nucleus of the cell. Therefore, for small receptor-mediated solutes, increased solute uptake efficiency can be achieved by concentrating receptors near the nucleus. The main conclusion of the work is that although the rate of mass transfer varies greatly over an individual cell, the average mass transfer rate to a cell is close to that predicted for a flat cell. In comparison to other hemodynamic factors, the topography of endothelial cells therefore seems to have little effect on mass transfer rates and is likely physiologically insignificant.

Relative reduction of endothelial nitric-oxide synthase expression and transcription in atherosclerosis-prone regions of the mouse aorta and in an in vitro model of disturbed flow.

Atherosclerosis develops in distinct regions of the arterial tree. Defining patterns and mechanisms of endothelial cell gene expression in different regions of normal arteries is key to understanding the initial molecular events in atherogenesis. In this study, we demonstrated that the expression of endothelial nitric-oxide synthase (eNOS), an atheroprotective gene, and its phosphorylation on Ser(1177), a marker of activity, were lower in regions of the normal mouse aorta that are predisposed to atherosclerosis. The same expression pattern was observed in mouse strains that are both susceptible and resistant to atherosclerosis, and the topography of eNOS expression was inverse to p65, the main nuclear factor-kappaB subunit. Modeling of disturbed and uniform laminar flow in vitro reproduced the expression patterns of eNOS and p65 that were found in vivo. Heterogeneous nuclear RNA expression and RNA polymerase II chromosome immunoprecipitation studies demonstrated that regulation of transcription contributed to increased eNOS expression in response to shear stress. In vivo, the transcription of eNOS was reduced in regions of the mouse aorta predisposed to atherosclerosis, as defined by reporter gene expression in eNOS promoter-beta-galactosidase reporter transgenic mice. These data suggest that disturbed hemodynamic patterns found at arterial branches and curvatures uniquely modulate endothelial cell gene expression by regulating transcription, potentially explaining why these regions preferentially develop atherosclerosis when risk factors such as hypercholesterolemia are introduced.

Leukocyte recruitment to atherosclerotic lesions.

Atherosclerosis is a complex disease process in which monocytes and lymphocytes are recruited from the blood into the arterial intima. Mouse models of atherosclerosis have been developed, carefully characterized and used to elucidate molecular mechanisms of atherosclerotic lesion formation. Deficiency of various chemokines, chemokine receptors and leukocyte adhesion molecules that are known to participate in mononuclear leukocyte emigration, such as monocyte chemoattractant protein-1 and its receptor chemokine (CC motif) receptor 2, CX3C chemokine receptor 1 and vascular cell adhesion molecule 1, results in decreased formation of atherosclerotic lesions. In these studies, analysis was usually limited to assessment of lesion size, cellular composition and histological features. An assumption is often made that leukocyte recruitment is diminished if a reduction in lesions is found in chemokine- or adhesion molecule-deficient animals. However, direct quantification of leukocyte recruitment to atherosclerotic lesions is lacking and there is a need for practical recruitment assays that have the potential to provide precise and novel insights. For example, insights may be gained to distinguish the contribution of chemokines, chemokine receptors and adhesion molecules to the recruitment, survival or proliferation of different leukocyte types in atherosclerotic lesions.

Prenatal stress alters seizure thresholds and the development of kindled seizures in infant and adult rats.

Stressful events during gestation and in the neonatal period have important effects on the later physical and mental health of the offspring. The present study tested the hypothesis that pre- and/or postnatal stress would affect seizure susceptibility in infant and adult rats, using the hippocampal kindling model. Prenatal stress consisted of daily restraint of the dam under bright light (for 45 min, 3 x / day) during either early gestation or mid/late gestation. Pups were compared to pups born to unstressed dams. Postnatal stress (administered on Days 4 and 5 after birth) consisted of either separation from the dam and placement in the bedding of a strange male for 1 h or injection of dexamethasone. Pups were compared to nonstressed siblings of the same litter. Both early and mid/late-gestation prenatal stress significantly lowered the after-discharge threshold (ADT) in infant, 14-day-old rat offspring, as compared to nonstressed control offspring. This effect on ADT was lost by adulthood. Mid/late-gestation stress increased the rate of kindled seizure development in infant rats and in their adult male, but not female, siblings. Postnatal stress had no significant effect on ADT or kindling rate. These findings indicate that prenatal stress, particularly during the latter half of pregnancy, may play an important role in increasing seizure vulnerability in the unborn offspring. These effects are more pronounced in infancy, but can also extend to adulthood.