Reverse Effect of Mammalian Hypocalcemic Cortisol in Fish: Cortisol Stimulates Ca2+ Uptake via Glucocorticoid Receptor-Mediated Vitamin D3 Metabolism

Abstract

Cortisol was reported to downregulate body-fluid Ca2+ levels in mammals but was proposed to show hypercalcemic effects in teleostean fish. Fish, unlike terrestrial vertebrates, obtain Ca2+ from the environment mainly via the gills and skin rather than by dietary means, and have to regulate the Ca2+ uptake functions to cope with fluctuating Ca2+ levels in aquatic environments. Cortisol was previously found to regulate Ca2+ uptake in fish; however, the molecular mechanism behind this is largely unclear. Zebrafish were used as a model to explore this issue. Acclimation to low-Ca2+ fresh water stimulated Ca2+ influx and expression of epithelial calcium channel (ecac), 11β-hydroxylase and the glucocorticoid receptor (gr). Exogenous cortisol increased Ca2+ influx and the expressions of ecac and hydroxysteroid 11-beta dehydrogenase 2 (hsd11b2), but downregulated 11β-hydroxylase and the gr with no effects on other Ca2+ transporters or the mineralocorticoid receptor (mr). Morpholino knockdown of the GR, but not the MR, was found to impair zebrafish Ca2+ uptake function by inhibiting the ecac expression. To further explore the regulatory mechanism of cortisol in Ca2+ uptake, the involvement of vitamin D3 was analyzed. Cortisol stimulated expressions of vitamin D-25hydroxylase (cyp27a1), cyp27a1 like (cyp27a1l), 1α-OHase (cyp27b1) at 3 dpf through GR, the first time to demonstrate the relationship between cortisol and vitamin D3 in fish. In conclusion, cortisol stimulates ecac expression to enhance Ca2+ uptake functions, and this control pathway is suggested to be mediated by the GR. Lastly, cortisol also could mediate vitamin D3 signaling to stimulate Ca2+ uptake in zebrafish.

Cortisol regulates epithelial permeability and sodium losses in zebrafish exposed to acidic water

“…The final concentration of DMSO vehicle in the exposure water was %0.1% and had no observable effects on zebrafish survival, behaviour or the absorption of a paracellular permeability marker PEG-4000 (detailed below). Concentrations of 0-50 mM cortisol were used based on previous studies (Lin et al 2011, Kumai et al 2012. Because a significant reduction in PEG-4000 absorption was observed at 10 mM cortisol (see Results section), this concentration was used for all subsequent experiments except where mentioned otherwise.…”

β-Adrenergic regulation of Na+uptake by larval zebrafishDanio rerioin acidic and ion-poor environments

“…Cortisol, though initially identified as a "seawater (SW)" acclimation hormone, is now recognized to play an important role in regulating ion balance in FW fish. For example, Lin et al (22) and Kumai et al (19) reported that waterborne exposure to cortisol significantly increased Ca 2ϩ and Na ϩ uptake by zebrafish larvae, and a similar stimulation of ion uptake following cortisol treatment was also reported for rainbow trout (11,21). In addition, application of cortisol to a cell culture derived from rainbow trout gill led to a significant reduction in paracellular permeability, presumably serving to reduce the passive loss of ions to the environment (4).…”

“…Immediately after the addition of pharmacological agents, the rate of Na ϩ uptake was measured using 22 Na. For the measurement, 0.25 Ci…”

“…Numerous HR cells (e.g., 22) and an extensive network of nerves (e.g., 17) were detected on the yolk sack of 4-dpf larvae (Fig. 6A).…”

Hydrogen sulfide promotes calcium uptake in larval zebrafish

“…The Ca 2ϩ -transporting ionocytes are Na ϩ -K ϩ -ATPase-rich cells (NaRCs), which express epithelial Ca 2ϩ channels (ECaC) at the apical membrane, and plasma membrane Ca 2ϩ -ATPase (PMCA) and Na ϩ /Ca 2ϩ exchanger (NCX) at the basolateral membrane (7). It has been documented that acclimation to low-Ca 2ϩ water increases the capacity for Ca 2ϩ uptake in zebrafish (14,19,29). Various mechanisms for chronic modulation of Ca 2ϩ uptake have been identified, primarily involving regulated expression of ECaC (7).…”