The vitamin D receptor and its ligand 1α,25-dihydroxyvitamin D3 in Atlantic salmon (Salmo salar)

Abstract

Seaward migration of Salmo salar is preceded by preparatory physiological adaptations (parr-smolt transformation) to allow for a switch from freshwater (FW) to seawater (SW), which also means a switch in ambient calcium from hypocalcic (!1 mM Ca 2C ) to the plasma (w1 . 25 mM Ca 2C ) and to strongly hypercalcic (8-12 mM Ca 2C ). Uptake, storage (skeleton, scales) and excretion of calcium need careful regulation. In fish, the vitamin D endocrine system plays a rather enigmatic role in calcium physiology. Here, we give direct evidence for calcitriol involvement in SW migration. We report the full sequence of the nuclear vitamin D receptor (sVDR0) and two alternatively spliced variants resulting from intron retention (sVDR1 and sVDR2). In FW parr, SW adapting smolts, and in SW adults, plasma concentrations of 25(OH)D 3 and 24,25(OH) 2 D 3 did not change significantly. Plasma calcitriol concentrations were lowest in FW parr, doubled during smoltification and remained elevated in SWadults. Increased calcitriol coincided with a twofold decrease in sVDR mRNA levels in gill, intestine, and kidney of FW smolts and SW adults, when compared with parr. Clearly, there was a negative feedback and dynamic response of the vitamin D endocrine system during parr-smolt transformation. The onset of these dynamic changes in FW parr warrants a further search for the endocrines that initiate these changes. We speculate that the vitamin D system plays a crucial role in calcium and phosphorus handling in Atlantic salmon.

Vitamin D: calcium and bone homeostasis during evolution

“…Enzymes capable of metabolizing vitamin D into more polar metabolites already emerged early in the evolution of life as shown in plants, snails and crustacean (see above) but it is unknown whether this involves P450/CYP proteins. Several bacteria express CYP enzymes capable to produce 1,25(OH) 2 D 3 with high efficacy but the relation of these CYP107 54 There are several P450 enzymes with highly selective activity for vitamin D metabolism such as CYP2R1 (25-hydroxylation of vitamin D), CYP27B1 (1a-hydroxylation of 25OHD) and CYP24A1 (24R-hydroxylation of 25OHD) but the evolutionary origin of these CYP genes in chordates and early vertebrates is not well defined. Zebrafish, however, clearly express CYP27B1 and CYP24A1.…”

The effects of concurrent supplementation of dietary phytase, citric acid and vitamin D3 on growth and mineral utilization in juvenile yellow catfish Pelteobagrus fulvidraco

“…Excessive intake of vitamin D 3 depressed the growth rate of channel catfish (Andrews et al, 1980) and rainbow trout (O. mykiss) (Vielma et al, 1998). The vitamin D endocrine system plays a crucial role in calcium and phosphorus handling during parr-smolt transformation in Atlantic salmon (Salmo salar) (Lock et al, 2007). However, Rao and Raghuramulu (1999) reported that vitamin D 3 probably played no role in Ca or P metabolism in tilapia (Oreochromis spp.).…”

“…In fish, vitamin D is reported to be involved in normal growth, development, bone mineralization, and Ca and P homeostasis (Lock et al, 2007). There is evidence that supplementation of diets with vitamin D is an effective method in increasing phytate hydrolysis in broiler chickens (Mitchell and Edwards, 1996).…”

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

“…In fish, vitamin D 3 had been demonstrated to elevate serum Ca 2+ level [20], [21] .Vitamin D 3 was also proposed to be associated with Ca 2+ transport in the gills based on the vitamin D 3 deficiency-induced impairment of growth and mineralization in the fish skeleton [22], [23]. Indeed, changes in the plasma levels of 1,25 (OH) 2 D 3 or mRNA expression of gill/kidney VDR have been observed in salmon undergoing smoltification and migrating from freshwater (low Ca 2+ concentrations) to seawater (high Ca 2+ concentrations), suggesting that synthesis of the sterol and its receptor might be regulated depending upon ambient Ca 2+ concentrations [23]. In mammals, glucocorticoid has been well documented to affect vitamin D 3 metabolism although the actions varied depending on species [24]–[29].…”