The mineralocorticoid receptor contributes to barrier function of a model fish gill epithelium

Abstract

Cortisol-induced epithelial tightening of a primary cultured rainbow trout gill epithelium model occurs in association with reduced paracellular permeability and increased abundance of select barrier-forming TJ proteins. Corticosteroid receptor (CR) pharmacological blocker studies have suggested that to produce this tightening effect, cortisol acts on the mineralocorticoid receptor (MR) as well as glucocorticoid receptors (GRs). This study considered how cortisol influenced model gill epithelium permeability and TJ properties by transcriptional knockdown of the gene encoding MR (mr-KD) using double-stranded RNA. Following mr-KD a significant reduction in MR protein abundance was observed in the epithelium. The mr-KD epithelium demonstrated reduced transepithelial resistance (TER) and increased the paracellular flux of [3H] polyethylene glycol (MW 400 kDa, PEG-400). Concurrently, mRNA abundance of gr2 and 11βhsd increased, indicating a possible compensatory response to mr-KD. Transcript abundance of claudin (cldn) -6, -8d, 23a and -28b decreased while cldn-20a increased in mr-KD preparations. Cortisol-induced epithelial tightening was enhanced in mr-KD preparations, suggesting that alterations in CRs and TJ composition augmented model epithelium barrier function in response to lowered MR abundance. Cortisol treatment significantly increased the transcript and protein abundance of TJ proteins such as cldn/Cldn -8d, and -28b. However, in mr-KD preparations, Cldn-28b protein abundance did not significantly alter in response to cortisol treatment, while Cldn-8d significantly elevated. Data suggest that mr-KD compromises normal barrier function of a primary cultured rainbow trout gill epithelium both in the presence and absence of cortisol and that Cldn-28b protein abundance may be modulated by cortisol via the MR only.

11-Deoxycortisol controls hydromineral balance in the most basal osmoregulating vertebrate, sea lamprey (Petromyzon marinus)

“…A functional role for TJ complex proteins has more recently been elucidated in the sea lamprey [35][36][37][38] . Several studies have demonstrated putative corticosteroid control of TJ proteins in cultured teleost fish gill epithelia 24,39,40 , and it is possible that S may thus also control TJ complexing and paracellular permeability in the sea lamprey gill, in addition to its role in controlling active ion transport.…”

“…In anadromous salmonids, for instance, circulating concentrations of cortisol increase during the parr-smolt transformation (which includes development of SW tolerance) 16 , in vivo treatment with cortisol increases gill NKA activity and SW tolerance [17][18][19][20][21] , and the action of cortisol on affecting active ion transport in the gills of salmonids is mediated mainly through the GR rather than the MR 18,22,23 . In teleosts, although DOC signaling acting through the MR has a more minor role in osmoregulation, it has been implicated in partially regulating several osmoregulatory processes, including ion transport and paracellular permeability 14,24 .…”

Repeated hypoxic episodes allow hematological and physiological habituation in rainbow trout

“…Throughout the experiment, the density was constantly maintained at 6.80 ± 0.1 Kg/m 3 ( Figure 1 ). Following the hypoxia shock, the fish were transferred to a recovery tank with 7.2—8.1 mgO 2 /L, which was isolated from the system to avoid any possible circulating cortisol levels affecting the other fish, as a chemical detection by peripheral cortisol receptors that may affect fish response has been previously suggested ( Kolosov and Kelly, 2019 ). After the last hypoxia shock, the fish were transferred to a recovery tank where sampling took place.…”

Hematological and Physiological Responses under Repeated Acute Hypoxia in Rainbow Trout (<em>Onchorynchus mykiss</em>)

“…dissolved oxygen was continuously monitored to check that the levels were within the study range, and to avoid a decrease below 1,5 mgO2 /L. Following the hypoxia shock, fish were transferred to a recovery tank with 7.2 -8.1 mg O2/L which was isolated from the system to avoid any possible circulating cortisol levels affecting the other fish, as there is a possible chemical detection by peripheral cortisol receptors that may affect fish response [21] Sampling took place once the fish were in the recovery tank. By the time the sampling of the experimental group was finished, oxygen and water turnover recovered the optimal levels.…”