Hydrostatic pressure incubation affects barrier properties of mammary epithelial cell monolayers, in vitro

Circulating Ouabain Modulates Expression of Claudins in Rat Intestine and Cerebral Blood Vessels

The ability of exogenous low ouabain concentrations to affect claudin expression and therefore epithelial barrier properties was demonstrated previously in cultured cell studies. We hypothesized that chronic elevation of circulating ouabain in vivo can affect the expression of claudins and tight junction permeability in different tissues. We tested this hypothesis in rats intraperitoneally injected with ouabain (1 μg/kg) for 4 days. Rat jejunum, colon and brain frontal lobes, which are variable in the expressed claudins and tight junction permeability, were examined. Moreover, the porcine jejunum cell line IPEC-J2 was studied. In IPEC-J2-cells, ouabain (10 nM, 19 days of incubation) stimulated epithelial barrier formation, increased transepithelial resistance and the level of cSrc-kinase activation by phosphorylation, accompanied with an increased expression of claudin-1, -5 and down-regulation of claudin-12; the expression of claudin-3, -4, -8 and tricellulin was not changed. In the jejunum, chronic ouabain increased the expression of claudin-1, -3 and -5 without an effect on claudin-2 and -4 expression. In the colon, only down-regulation of claudin-3 was observed. Chronic ouabain protected the intestine transepithelial resistance against functional injury induced by lipopolysaccharide treatment or by modeled acute microgravity; this regulation was most pronounced in the jejunum. Claudin-1 was also up-regulated in cerebral blood vessels. This was associated with reduction of claudin-3 expression while the expression of claudin-5 and occludin was not affected. Altogether, our results confirm that circulating ouabain can functionally and tissue-specifically affect barrier properties of epithelial and endothelial tissues via Na,K-ATPase-mediated modulation of claudins expression.

Regulation of Epithelial Cell Functions by the Osmolality and Hydrostatic Pressure Gradients: A Possible Role of the Tight Junction as a Sensor

Epithelia act as a barrier to the external environment. The extracellular environment constantly changes, and the epithelia are required to regulate their function in accordance with the changes in the environment. It has been reported that a difference of the environment between the apical and basal sides of epithelia such as osmolality and hydrostatic pressure affects various epithelial functions including transepithelial transport, cytoskeleton, and cell proliferation. In this paper, we review the regulation of epithelial functions by the gradients of osmolality and hydrostatic pressure. We also examine the significance of this regulation in pathological conditions especially focusing on the role of the hydrostatic pressure gradient in the pathogenesis of carcinomas. Furthermore, we discuss the mechanism by which epithelia sense the osmotic and hydrostatic pressure gradients and the possible role of the tight junction as a sensor of the extracellular environment to regulate epithelial functions.

Mechanical stimuli enhance simultaneous differentiation into oesophageal cell lineages in a double-layered tubular scaffold

The tissue-engineered oesophagus serves as an alternative and promising therapeutic approach for long-gap oesophageal replacement. This study proposes an advanced in vitro culture platform focused on construction of the oesophagus by combining an electrospun double-layered tubular scaffold, stem cells, biochemical reagents, and biomechanical factors. Human mesenchymal stem cells were seeded onto the inner and outer surfaces of the scaffold. Mechanical stimuli were applied with a hollow organ bioreactor along with different biochemical reagents inside and outside of the scaffold. Electrospun fibres in a tubular scaffold were found to be randomly and circumferentially oriented for the inner and outer surfaces, respectively. Amongst the two types of mechanical stimuli, the intermittent shear flow that can simultaneously cause circumferential stretching due to hydrostatic pressure, and shear stress caused by flow on the inner surface, was found to be more effective for simultaneous differentiation into epithelial and muscle lineage than steady shear flow. Under these conditions, the expression of epithelial markers on the inner surface was significantly observed, although it was minimal on the outer surface. Muscle differentiation showed the opposite expression pattern. Meanwhile, the mechanical tests showed that the strength of the scaffold was improved after incubation for 14 days. We have developed a potential platform for tissue-engineered oesophagus construction. Specifically, simultaneous differentiation into epithelial and muscle lineages can be achieved by utilizing the double-layered scaffold and appropriate mechanical stimulation.