Metabolism of cholecalciferol in land snails

Vitamin D3/VDR inhibits inflammation through NF-κB pathway accompanied by resisting apoptosis and inducing autophagy in abalone Haliotis discus hannai

Vitamin D3 is believed to be a contributing factor to innate immunity. Vitamin D receptor (VDR) has a positive effect on inhibiting nuclear factor κB (NF-κB)-mediated inflammation. The underlying molecular mechanisms remain unclear, particularly in mollusks. Consequently, this study will investigate the process of vitamin D3/VDR regulating NF-κB pathway and further explore their functions on inflammation, autophagy, and apoptosis in abalone Haliotis discus hannai. Results showed that knockdown of VDR by using siRNA and dsRNA of VDR in vitro and in vivo led to more intense response of NF-κB signaling to lipopolysaccharide and higher level of apoptosis and autophagy. In addition, 1,25(OH)2D3 stimulation after VDR silencing could partially alleviate apoptosis and induce autophagy. Overexpression of VDR restricted the K48-polyubiquitin chain-dependent inhibitor of κB (IκB) ubiquitination and apoptosis-associated speck-like protein containing CARD (ASC) oligomerization. Besides, VDR silencing resulted in increase of ASC speck formation. In further mechanistic studies, we showed that VDR can directly bind to IκB and IKK1 in vitro and in vivo. In the feeding trial, H&E staining, TUNEL, and electron microscope results showed that vitamin D3 deficiency (0 IU/kg) could recruit more basophilic cells and increase more TUNEL-positive apoptotic cells and lipid droplets (LDs) than vitamin D3 supplement (1000 IU/kg and 5000 IU/kg). In summary, abalone VDR plays a negative regulator role in NF-κB-mediated inflammation via interacting with IκB and inhibiting ubiquitin-dependent degradation of IκB. Vitamin D3 in combination with VDR is essential to establish a delicate balance between autophagy and apoptosis in response to inflammation.

Characterization and spatiotemporal expression of orchestin, a gene encoding an ecdysone-inducible protein from a crustacean organic matrix

We report the characterization of a new gene encoding an acidic protein named Orchestin. This protein is a component of the organic matrix of calcium storage structures (calcareous concretions) elaborated during the moulting cycles of the terrestrial crustacean Orchestia cavimana. The deduced molecular mass of Orchestin is estimated to be 12.4 kDa and the pI to be 4.4, whereas the native protein extracted from the calcium deposits migrates as a 23 kDa band on SDS/PAGE. This discrepancy is probably due to the richness of this protein in acidic amino acids (approx. 30%). The protein obtained by expressing the Orchestin cDNA in Escherichia coli presents an electrophoretic mobility of 25 kDa. Antibodies raised against the recombinant protein recognize the 23 kDa native protein exclusively among the organic-matrix components. Spatiotemporal analysis of the expression of the orchestin gene shows that it is expressed only in the storage organ cells when the concretions are elaborated during the premoult period and also, to a smaller extent, during the postmoult period. The translation products are expressed in accordance with the transcript expression during both the premoult and postmoult periods. Study of the hormonal stimulation of orchestin reveals that 20-hydroxyecdysone induces this gene as a secondary-response or late-response gene.

Calcium cells from snails: response to vitamin D metabolites

Calcium is one of the most important substances affecting the life of molluscs, and vitamin D was shown to be an essential nutrient for land snails. In an attempt to elucidate the role that vitamin D plays in calcium metabolism of land snails, we have developed a procedure for the isolation of specialized calcium cells from digestive gland of land snails, and were able to culture these cells. The effect of vitamin D metabolites on the intracellular exchangeable calcium and alkaline phosphatase activity was studied. The metabolites tested were 25-hydroxycholecalciferol (25(OH)D3), 24,25-dihydroxycholecalciferol (24,25(OH)2D3), 1,25-dihydroxycholecalciferol (1,25(OH)2D3), and the molluscan metabolite E. 25(OH)D3 was found to be the most active sterol in elevating intracellular exchangeable calcium and the activity of alkaline phosphatase, and the molluscan metabolite E was found to be the most potent sterol in the suppression of alkaline phosphatase activity. 1,25(OH)2D3 was shown to suppress both activities at high concentrations, and 24,25(OH)2D3 increased the intracellular exchangeable calcium only at high concentrations. Thus, 25(OH)D3 which is regarded as a storage form of vitamin D and devoid of biological activity, seems to be biologically active in invertebrates.

Variations of vitamin D-like reactivity in the crustacean Orchestia cavimana during the molt cycle

An investigation into vitamin D-like molecules has been performed on whole extracts of the terrestrial amphipod Orchestia cavimana, using a sensitive nonequilibrium assay employing 1,25-(OH)2 D receptor from calf thymus. Relatively large amounts of these secosteroid-like molecules were observed and they varied in concentration according to the stages of the molt cycle. The amplitude of these variations reaches a ratio of about 40 from the minimum in premolt to the intermolt sharp peak.

Calcium binding protein in squid brain: biochemical similarity to the 28,000-Mr vitamin D-dependent calcium binding protein (calbindin-D28k)

A calcium binding protein that is biochemically similar to vertebrate 28,000-Mr vitamin D-dependent calcium binding protein (calbindin-D28k) has been purified from squid brain. Squid brain calbindin was found to have an isoelectric point of 5.0, was heat stable up to 60 degrees C, and showed increased electrophoretic mobility in the presence of chelator. Amino acid analysis revealed a high content of glutamic and aspartic acids and a low level of methionine, histidine, and tyrosine, a finding similar but not identical to the composition of vertebrate calbindin-D28k. The molecular weight of the squid protein, determined by Ferguson plot analysis of data obtained from sodium dodecyl sulfate-gel electrophoresis, was calculated to be 25,700, as compared with 27,800 for rat renal calbindin. Immunocytochemical analysis demonstrated immunoreactive protein in a selected population of neurons and fibers in several areas of the molluscan nervous system. This study represents the first purification from an invertebrate of a calcium binding protein that is biochemically similar to vitamin D-dependent calcium binding protein. These results demonstrate that calbindin, although not identical in vertebrates and cephalopods, may be phylogenetically conserved in structure. The restricted distribution of immunoreactive calbindin in both the cephalopod and mammalian brain suggests that the function of neuronal calbindin may also be conserved in evolution.