Claudin 28b and F-actin are involved in rainbow trout gill pavement cell tight junction remodeling under osmotic stress

Abstract

SUMMARYPermeability of rainbow trout gill pavement cells cultured on permeable supports (single seeded inserts) changes upon exposure to freshwater or treatment with cortisol. The molecular components of this change are largely unknown, but tight junctions that regulate the paracellular pathway are prime candidates in this adaptational process. Using differential display polymerase chain reaction we found a set of 17 differentially regulated genes in trout pavement cells that had been exposed to freshwater apically for 24h. Five genes were related to the cell-cell contact. One of these genes was isolated and identified as encoding claudin 28b, an integral component of the tight junction. Immunohistochemical reactivity to claudin 28b protein was concentrated in a circumferential ring colocalized to the cortical F-actin ring. To study the contribution of this isoform to changes in transepithelial resistance and Phenol Red diffusion under apical hypo-or hyperosmotic exposure we quantified the fluorescence signal of this claudin isoform in immunohistochemical stainings together with the fluorescence of phalloidin-probed F-actin. Upon hypoosmotic stress claudin 28b fluorescence and epithelial tightness remained stable. Under hyperosmotic stress, the presence of claudin 28b at the junction significantly decreased, and epithelial tightness was severely reduced. Cortical F-actin fluorescence increased upon hypo-osmotic stress, whereas hyperosmotic stress led to a separation of cortical F-actin rings and the number of apical crypt-like pores increased. Addition of cortisol to the basolateral medium attenuated cortical F-actin separation and pore formation during hyperosmotic stress and reduced claudin 28b in junctions except after recovery of cells from exposure to freshwater. Our results showed that short-term salinity stress response in cultured trout gill cells was dependent on a dynamic remodeling of tight junctions, which involves claudin 28b and the supporting F-actin ring.

Claudins in teleost fishes

“…Because changes in environmental conditions can be extremely varied, and diverse species of teleost fish cope with environmental change quite differently, the importance of cldns in the gill has already been addressed in a range of teleost species. These include broadly used model organisms such as zebrafish 53 and Tetraodon, 51 , 52 , 54 - 56 as well as other models such as Tetraodon biocellatus, 57 Salmo salar , 58 , 59 Oncorhynchus mykiss , 21 , 60 , 61 Fundulus heteroclitus , 62 Carassius auratus 21 , 23 and Paralichthys lethostigma 63 . When taking into account the aforementioned species and others, the number of cldns reported in gill tissue of teleost fishes is at least 44 (for review see ref.…”

A role for tricellulin in the regulation of gill epithelium permeability

“…In this regard, the bulk of work conducted thus far has focused on members of the claudin superfamily (e.g., Refs. 1,2,4,7,16,17,29,37,38,44,49,53,56). However, a number of studies have also revealed the potential importance of occludin (a member of the TAMP subfamily) in teleost fish gills (5,6,7,8,9,10,11,12,29).…”

Effects of Osmolality on Paracellular Transport in MDCK II Cells

“…In 1983, Madara reported that apical hyperosmolality increases transepithelial electrical resistance (TER) and decreases cation selectivity concomitantly with an increase of TJ strands in guinea pig jejunum [5]. After that, however, there have not been many reports that studied the effects of osmolality on the paracellular transport [26–33]. In addition, most of these reports showed that apical osmotic changes decreased TER but did not measure charge selectivity; therefore, the reduction in the barrier in these reports might result simply from disruption of cell-cell contacts.…”