Inhibition of calcium uptake during hypoxia in developing zebrafish, Danio rerio, is mediated by hypoxia-inducible factor

Abstract

The present study investigated the potential role of hypoxia-inducible factor (HIF) in calcium homeostasis in developing zebrafish (Danio rerio). It was demonstrated that zebrafish raised in hypoxic water (30 mmHg; control, 155 mmHg P O2 ) until 4 days post-fertilization exhibited a substantial reduction in whole-body Ca 2+ levels and Ca 2+ uptake. Ca 2+ uptake in hypoxia-treated fish did not return to prehypoxia (control) levels within 2 h of transfer back to normoxic water. Results from real-time PCR showed that hypoxia decreased the whole-body mRNA expression levels of the epithelial Ca 2+ channel (ecac), but not plasma membrane Ca 2+ -ATPase ( pmca2) or Na + / Ca 2+ -exchanger (ncx1b). Whole-mount in situ hybridization revealed that the number of ecac-expressing ionocytes was reduced in fish raised in hypoxic water. These findings suggested that hypoxic treatment suppressed the expression of ecac, thereby reducing Ca 2+ influx. To further evaluate the potential mechanisms for the effects of hypoxia on Ca 2+ regulation, a functional gene knockdown approach was employed to prevent the expression of HIF-1αb during hypoxic treatment. Consistent with a role for HIF-1αb in regulating Ca 2+ balance during hypoxia, the results demonstrated that the reduction of Ca 2+ uptake associated with hypoxic exposure was not observed in fish experiencing HIF-1αb knockdown. Additionally, the effects of hypoxia on reducing the number of ecac-expressing ionocytes was less pronounced in HIF-1αb-deficient fish. Overall, the current study revealed that hypoxic exposure inhibited Ca 2+ uptake in developing zebrafish, probably owing to HIF-1αb-mediated suppression of ecac expression.

Hypoxia-inducible transcription factors in fish: expression, function and interconnection with the circadian clock

“…Morpholino experiments and analysis of Hif-1αB-deficient zebrafish embryos confirmed that ECAC expression was under the control of Hif-1αB ( Fig. 4), which was not the case for expression of the plasma membrane Ca 2+ -ATPase (PMCA) and the sodium-dependent Ca 2+ transporter (NXC1b) (Kwong et al, 2016).…”

“…In addition to Na + and Cl − , freshwater fish also take up Ca 2+ from the environmental water. Hypoxia impairs Ca 2+ uptake in developing zebrafish embryos, and Ca 2+ uptake has been shown to remain low even after reoxygenation (Kwong et al, 2016). The decrease in Ca 2+ uptake was shown to be caused by a decrease in the expression level of an epithelial Ca 2+ channel (ECAC).…”

Interação do cálcio e nitrito na água: sobrevivência, crescimento, parí­¢metros hematológicos e metabólicos em jundiá

“…Hypoxia inhibited Ca 2+ uptake in zebrafish, Danio rerio (KWONG et al, 2016), and consequently the exposure of silver catfish to high Ca 2+ levels may facilitate the maintenance of plasma Ca 2+ levels and partially reduce the effect of tissue hypoxia (higher muscle lactate levels) provoked by high NO 2 -levels. The high Ca 2+ level alone was sufficient to reduce hepatic carbohydrate and protein levels of silver catfish in the present study.…”