Possible involvement of gap junctions in the barrier function of tight junctions of brain and lung endothelial cells

Abstract

Gap-junction plaques are often observed with tight-junction strands of vascular endothelial cells but the molecular interaction and functional relationships between these two junctions remain obscure. We herein show that gap-junction proteins connexin40 (Cx40) and Cx43 are colocalized and coprecipitated with tight-junction molecules occludin, claudin-5, and ZO-1 in porcine blood-brain barrier (BBB) endothelial cells. Gap junction blockers 18beta-glycyrrhetinic acid (18beta-GA) and oleamide (OA) did not influence expression of Cx40, Cx43, occludin, claudin-5, junctional adhesion molecule (JAM)-A, JAM-B, JAM-C, or ZO-1, or their subcellular localization in the porcine BBB endothelial cells. In contrast, these gap-junction blocking agents inhibited the barrier function of tight junctions in cells, determined by measurement of transendothelial electrical resistance and paracellular flux of mannitol and inulin. 18beta-GA also significantly reduced the barrier property in rat lung endothelial (RLE) cells expressing doxycycline-induced claudin-1, but did not change the interaction between Cx43 and either claudin-1 or ZO-1, nor their expression levels or subcellular distribution. These findings suggest that Cx40- and/or Cx43-based gap junctions might be required to maintain the endothelial barrier function without altering the expression and localization of the tight-junction components analyzed.

The tight junction protein CAR regulates cardiac conduction and cell–cell communication

“…Proteins of the adherens junction and the desmosome aff ect conduction, heart ( 6 ). On a molecular level, the functional interaction of gap and tight junction is supported by coprecipitation and colocalization of Cx40 and Cx43 with tight junction molecules occludin, claudin-5, and ZO-1 in endothelial cells ( 25 ). The increased dye coupling does not lead to altered electrical properties of the atrium or ventricle in the CAR KO.…”

The protein phosphatase 2A regulatory subunit Ppp2r2a is required for Connexin‐43 dephosphorlyation during epidermal barrier acquisition

“…Gap junctions also play an important role in epithelial barrier function. Connexin 43 (Cx43) co-localises and co-immunoprecipitates with the tight junction proteins Zonula occludins-1 (Zo-1) and Occludin (11). Mice with a C-terminal truncation of the Cx43 gene, lacking the region where Zo-1 interaction occurs (12) die perinatally due to regionally restricted epidermal barrier defects and excessive transepidermal water loss.…”

Role of connexins in metastatic breast cancer and melanoma brain colonization

“…Glial cells play a key role in the maintenance of the blood-brain barrier by facilitating strong GJ-mediated adhesive interactions with the endothelium and by regulating heterocellular ion and small molecule transport activities (Simard et al, 2003;Balabanov and Dore-Duffy, 1998;Nagasawa et al, 2006;Haefliger et al, 2004). Similarly, metastatic tumors cells, which express connexins, may adhere to and propagate along the connexin-rich vasculature by forming heterotypic GJs with the endothelium and/or glia.…”