The tight junction protein claudin-b regulates epithelial permeability and sodium handling in larval zebrafish,Danio rerio

Abstract

Kwong RWM, Perry SF. The tight junction protein claudin-b regulates epithelial permeability and sodium handling in larval zebrafish, Danio rerio. Am J Physiol Regul Integr Comp Physiol 304: R504 -R513, 2013. First published January 13, 2013 doi:10.1152/ajpregu.00385.2012.-The functional role of the tight junction protein claudin-b in larval zebrafish (Danio rerio) was investigated. We showed that claudin-b protein is expressed at epithelial cell-cell contacts on the skin. Translational gene knockdown of claudin-b protein expression caused developmental defects, including edema in the pericardial cavity and yolk sac. Claudin-b morphants exhibited an increase in epithelial permeability to the paracellular marker polyethylene glycol (PEG-4000) and fluorescein isothiocyanate-dextran (FD-4). Accumulation of FD-4 was confined mainly to the yolk sac and pericardial cavity in the claudin-b morphants, suggesting these regions became particularly leaky in the absence of claudin-b expression. Additionally, Na ϩ efflux was substantially increased in the claudin-b morphants, which contributed to a significant reduction in whole-body Na ϩ levels. These results indicate that claudin-b normally acts as a paracellular barrier to Na ϩ . Nevertheless, the elevated loss of Na ϩ in the morphants was compensated by an increase in Na ϩ uptake. Notably, we observed that the increased Na ϩ uptake in the morphants was attenuated in the presence of the selective Na ϩ /Cl Ϫ -cotransporter (NCC) inhibitor metolazone, or during exposure to Cl Ϫ -free water. These results suggested that the increased Na ϩ uptake in the morphants was, at least in part, mediated by NCC. Furthermore, treatment with an H ϩ -ATPase inhibitor bafilomycin A1 was found to reduce Na ϩ uptake in the morphants, suggesting that H ϩ -ATPase activity was essential to provide a driving force for Na ϩ uptake. Overall, the results suggest that claudin-b plays an important role in regulating epithelial permeability and Na ϩ handling in zebrafish.claudin-b; epithelial permeability; sodium; tight junction proteins; zebrafish TIGHT JUNCTIONS (TJS) ARE important components regulating the paracellular movement of solutes and water in vertebrates. TJs are composed of four major transmembrane proteins: occludin, claudins, tricellulins, and junctional adhesion molecule. However, claudins are thought to be the major determinant of the epithelial barrier functions (35). To date, more than 20 claudin isoforms have been identified in mammals (16), as well as in teleost fish (9,24,27,32), and the expression of these claudin isoforms appears to be cell-and tissue-specific. Studies using mammalian cell models have shown that the various claudin isoforms exhibit marked differences in their permeability characteristics, presumably establishing unique properties for different epithelia and endothelia (34,37). It has also been demonstrated that some claudin isoforms can form ion-specific seals or pores to regulate the paracellular movement of ions (1,20). The ion selectivity of claudins is sug...

Dietary phenylalanine-improved intestinal barrier health in young grass carp (Ctenopharyngodon idella) is associated with increased immune status and regulated gene expression of cytokines, tight junction proteins, antioxidant enzymes and related signalling molecules

“…It has been reported that claudin b and claudin 15 regulate paracellular Na þ movement [70,77]. In zebrafish (Danio rerio), claudin b is predominantly expressed in forebrain, olfactory vesicles, neuromasts and skin [78], but claudin 15 is highly expressed throughout the intestine and plays a role in the development of a normal intestinal lumen [79]. In our study, optimal Phe supplementation up-regulated the gene expression of claudin 15a in the grass carp intestine.…”

Intestinal immune function, antioxidant status and tight junction proteins mRNA expression in young grass carp ( Ctenopharyngodon idella ) fed riboflavin deficient diet

“…In zebrafish (Danio rerio), Claudin-b acts as a paracellular barrier to Na þ and the decreased expression of Claudin-b could lead Na þ loss [74]. Moreover, Na þ , K þ -ATPase could transport Na þ out of cells [74]. Our lab previous study found that riboflavin deficiency could decrease Na þ , K þ -ATPase activity in the intestine of Jian carp [5].…”

“…It was reported that the homeostasis of Na þ in the intestinal epithelial cells was an important guarantee for its function [73]. In zebrafish (Danio rerio), Claudin-b acts as a paracellular barrier to Na þ and the decreased expression of Claudin-b could lead Na þ loss [74]. Moreover, Na þ , K þ -ATPase could transport Na þ out of cells [74].…”

“…Thus, riboflavin deficiency decreased Claudin-b mRNA level in the intestine may be an adaptation to the intestinal function. In zebrafish, apart from Na þ , K þ -ATPase and Claudin-b, electroneutral Na þ /H þ exchange, Na þ /Cl À cotransport and H þ -ATPase could also regulate Na þ movement [74]. Therefore, the gills of fish maintain the Na þ homeostasis may not through Claudin-b.…”

Dietary riboflavin deficiency decreases immunity and antioxidant capacity, and changes tight junction proteins and related signaling molecules mRNA expression in the gills of young grass carp (Ctenopharyngodon idella)

“…Therefore, we next investigated the effects of riboflavin on TJ complex and antioxidant system in the gills of fish. acted as barrier-forming TJ proteins in fish [22,23,73], whereas Claudin-12 and Claudin-15 acted as pore-forming TJ proteins in mice [74]. Moreover, studies showed that decreased Claudin-b, -3, Occludin and ZO-1 mRNA levels in fish [23], and up-regulated Claudin-12 and Claudin-15 gene expression in mice [75,76] impaired TJ barrier function.…”