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Epithelial cells form highly organized polarized sheets with characteristic cell morphologies and tissue architecture. Cell–cell adhesion and intercellular communication are prerequisites of such cohesive sheets of cells, and cell connectivity is mediated through several junctional assemblies, namely desmosomes, adherens, tight and gap junctions. These cell–cell junctions form signalling hubs that not only mediate cell–cell adhesion but impact on multiple aspects of cell behaviour, helping to coordinate epithelial cell shape, polarity and function. This review will focus on the tight and adherens junctions, constituents of the apical junctional complex, and aims to provide a comprehensive overview of the complex signalling that underlies junction assembly, integrity and plasticity.

Histamine has been reported to decrease the ultrafiltration coefficient, which inversely correlates with glomerular permselectivity, however the mechanism(s) underling this effect have never been investigated. This study aimed to assess whether histamine could exert a direct detrimental effect on podocyte permeability and the possible involvement of two key proteins for the glomerular slit diaphragm (SD) integrity, zonula occludens-1 (ZO-1) and P-cadherin. The effect of histamine (100 pM–1000 nM) on coloured podocytes junctional integrity was evaluated functionally by a transwell assay of monolayer permeability and morphologically by electron microscopy. Histamine receptor (H 1-4 R) presence was evaluated at both mRNA (RT-PCR) and protein (immunofluorescence) levels. The K d and B max values for [ 3 H]mepyramine were determined by saturation binding analysis; IP 1 and cAMP production evoked by histamine were measured by TR-FRET. ZO-1, P-cadherin and vimentin expression was assessed by qRT-PCR and quantitative immunoblotting. Histamine elicited a time- and sigmoidal dose-dependent (maximum effect at 8 h, 10 nM) increase in podocyte paracellular permeability widening the paracellular spaces. Only H 1 R was predominantly localised to the podocyte membrane. Consistently, histamine elicited a sigmoidal dose-dependent increase in IP 1 , but not in cAMP. Histamine exposure evoked a concentration-dependent reduction in both ZO-1 and P-cadherin and a parallel induction of vimentin mRNA expression with a maximum effect after 6 h, and protein expression with a maximum effect after 8 h. These effects were prevented by the selective H 1 R antagonist chlorpheniramine. In conclusion, our data demonstrate that histamine, via the H 1 R, modifies SD morphological and functional integrity, in part, by decreasing the expression of ZO-1 and P-cadherin. [ABSTRACT FROM AUTHOR]