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

Abstract

The coordination of the hypoxic response is attributed, in part, to hypoxia-inducible factor 1α (Hif-1α), a regulator of hypoxia-induced transcription. After the teleost-specific genome duplication, most teleost fishes lost the duplicate copy of Hif-1α, except species in the cyprinid lineage that retained both paralogues of Hif-1α (Hif1aa and Hif1ab). Little is known about the contribution of Hif-1α, and specifically of each paralogue, to hypoxia tolerance. Here, we examined hypoxia tolerance in wild-type (Hif1aa +/+ ab +/+ ) and Hif-1α knockout lines (Hif1aa −/− ; Hif1ab −/− ; Hif1aa −/− ab −/− ) of zebrafish ( Danio rerio ). Critical O 2 tension ( P crit ; the partial pressure of oxygen (PO 2 ) at which O 2 consumption can no longer be maintained) and time to loss of equilibrium (LOE), two indices of hypoxia tolerance, were assessed in larvae and adults. Knockout of both paralogues significantly increased P crit (decreased hypoxia tolerance) in larval fish. Prior exposure of larvae to hypoxia decreased P crit in wild-type fish, an effect mediated by the Hif1aa paralogue. In adults, individuals with a knockout of either paralogue exhibited significantly decreased time to LOE but no difference in P crit . Together, these results demonstrate that in zebrafish, tolerance to hypoxia and improved hypoxia tolerance after pre-exposure to hypoxia (pre-conditioning) are mediated, at least in part, by Hif-1α.

Hypoxia inducible factor-1 α knockout does not impair acute thermal tolerance or heat hardening in zebrafish

“…In a subset of individuals, we replicated the recent result of Mandic et al [31] in demonstrating that Hif-1α knockout reduces hypoxia tolerance (figure 2). Hif-1α −/− fish rapidly succumbed once PO 2 fell below 15 mmHg (figure 2a) and the time to loss of equilibrium was significantly (t 10 = 5.48, p < 0.001) shorter than in wild types (figure 2b).…”

“…Oxygen partial pressure (PO 2 ) was recorded at 1 Hz with a Firesting optical sensor (PyroScience GmbH, Aachen, Germany) connected to a personal computer. Water PO 2 was rapidly reduced from 153 mm Hg (normoxia) to less than 14 mmHg after approximately 15 min and less than 12 mmHg after 20 min, thereafter plateauing between 12 and 10.5 mmHg, the target range for loss of equilibrium [31]. The fish were removed when they lost equilibrium for at least 3 s and the time from the start of hypoxia induction was recorded.…”

“…No analogous studies have been performed in fish, but are critical to establish a mechanistic link between Hif-1a expression and thermal tolerance. Recently, it was demonstrated that Hif-1α −/− zebrafish (Danio rerio) exhibit vastly reduced whole-animal hypoxia tolerance based on a reduced time to loss of equilibrium during acute hypoxia [31]. If oxygen tolerance underlies thermal tolerance [14,17], we hypothesized that the hypoxia-sensitive Hif-1α −/− line would exhibit reduced thermal tolerance.…”

Hypoxia-Inducible Factor (HIF) in Ischemic Stroke and Neurodegenerative Disease

“…Similar effects were obtained in zebrafish (Danio rerio), where pre-exposure of larvae to hypoxia increased hypoxia tolerance in adult fish ( Mandic et al, 2020 ). Mandic et al (2020) also demonstrated that in zebrafish, such improved hypoxia tolerance after pre-conditioning as well as general tolerance to hypoxia are mediated by HIF-1.…”

Hif‐1α is not required for the development of cardiac adrenergic control in zebrafish (Danio rerio)

“…Because exposure to hypoxia during early development has been shown to increase sympathetic nerve innervation in mammals and birds (Rook et al, 2014; Rouwet et al, 2002), for our studies of sympathetic nerve innervation (immunohistochemistry), some larvae were raised from 0 to 7 days postfertilisation (dpf) in flow through mesh‐bottomed containers that were flushed with pre‐equilibrated normoxic (O 2 partial pressure [PO 2 ]: 153 mmHg; 20.4 kPa) or hypoxic (PO2: 45 mmHg; 6.0 kPa) system water at 28.5°C. This level of hypoxia (45 mmHg) was selected as it induces a peak hypoxic ventilatory response in zebrafish larvae (Mandic et al, 2020) but is above the P crit (oxygen partial pressure at which aerobic metabolism begins to decline) in both genotypes (wild‐type and hif‐1α −/− ), (Mandic et al, 2020) meaning that they would presumably not need to resort to anaerobic metabolism. These fish were then raised to adulthood (3.5 months postfertilisation) under standard (normoxic) rearing conditions.…”