Hif-1α paralogs play a role in the hypoxic ventilatory response of larval and adult zebrafish (Danio rerio)

Abstract

Hypoxia-inducible factor (Hif) 1α, an extensively studied transcription factor, is involved in the regulation of many biological processes in hypoxia including the hypoxic ventilatory response. In zebrafish, there are two paralogs of Hif-1α (Hif-1A and Hif-1B), but little is known about the specific roles or potential sub-functionalization of the paralogs in response to hypoxia. Using knockout lines of Hif-1α paralogs, we examined their involvement in the hypoxic ventilatory response, measured as ventilation frequency (f V) in larval and adult zebrafish (Danio rerio). In wild-type zebrafish, f V increased across developmental time (4, 7, 10 and 15 days post-fertilization, dpf) in response to hypoxia (55 mmHg). In contrast, the Hif-1B knockout fish did not exhibit an increase in hypoxic f V at 4 dpf. Similar to wild-type, as larvae of all knockout lines developed, the magnitude of f V increased but to a lesser degree than in the wild-type larvae, until 15 dpf at which point there was no difference among the genotypes. In adult zebrafish, only in Hif-1B knockout fish was there an attenuation in f V during sustained exposure to 30 mmHg for 1 h but there was no effect when fish were exposed for a shorter duration to progressive hypoxia. The mechanism of action of Hif-1α, in part, may be through its downstream target, nitric oxide synthase, and its product, nitric oxide. Overall, the effect of each Hif-1α paralog on the hypoxic ventilatory response of zebrafish varies over development and is dependent on the type of hypoxic stress.

Evaluating the physiological significance of hypoxic hyperventilation in larval zebrafish (Danio rerio)

“…on f V because adult zebrafish increase f V , but not ventilation amplitude, during hypoxia and there is currently no reliable method for measuring ventilation amplitude in larval zebrafish. The results of the present study demonstrate that larval zebrafish are not only able to hyperventilate during hypoxia as early as 4 dpf, as has been previously reported (Jonz and Nurse, 2005;Mandic et al, 2019), but that they are also able to modify the magnitude and the duration of the HVR based on the level of hypoxia imposed and the developmental age. In 4 dpf and 7 dpf larvae exposed to mild hypoxia (60 mmHg), the increase in f V was transient, reducing to baseline levels after 5-10 min.…”

“…Thus, for each estimate associated with the fixed effect we determined whether the 95% HPDs included or excluded zero. For similar analysis, see Mandic et al (2019).…”

Loss of hypoxia-inducible factor 1α affects hypoxia tolerance in larval and adult zebrafish (Danio rerio)

“…The specific mechanism by which a loss of Hif-1α increases P crit is unknown. However, Hif-1α was previously shown to play a role in the hypoxic hyperventilatory response (HVR) in larval zebrafish [22]. A knockout of Hif-1α diminished the HVR [22] and by 7 dpf larvae hypoxic hyperventilation was shown to reduce P crit [28].…”

“…However, Hif-1α was previously shown to play a role in the hypoxic hyperventilatory response (HVR) in larval zebrafish [22]. A knockout of Hif-1α diminished the HVR [22] and by 7 dpf larvae hypoxic hyperventilation was shown to reduce P crit [28]. Hif-1α is also known to be a regulator of genes involved in angiogenesis [19] and a recent study demonstrated that Hif-1α plays an important role in macrophage-dependent angiogenesis in developing zebrafish larvae [20].…”

“…The evolutionary trajectory of the two paralogues of Hif-1α following duplication, mainly whether there has been sub-functionalization, neo-functionalization (paralogues acquire novel functions) or no change of function of either paralogue as compared to that of the ancestral gene, is unknown. However, some evidence points to differences in the effect of Hif-1α paralogues on the hypoxic control of breathing, suggesting divergence of function between the two paralogues [22]. As such, if the Hif-1α paralogues have diverged in function, we predicted that there would be a difference in the contribution of each paralogue to hypoxia tolerance and pre-conditioning to hypoxia.…”