Hypoxia-Inducible Factor in Ringed Seal (Phoca hispida) Tissues

Abstract

Tissue hypoxia and ischemia-reperfusion pose a dangerous situation for oxidative stress. However, diving mammals and birds show pronounced resistance to oxidative injury under such conditions, which are a consequence of selective vasoconstriction during a dive. As the function of Hypoxia-Inducible Factor-1alpha (HIF-1alpha) in protection against and adaptation to hypoxia has been recognized in terrestrial animals, we have investigated the genomics and expression of this protein in ringed seal (Phoca hispida) in order to determine if it may play a protective role in this diving mammal. PCR studies using primers based on sequences from mouse HIF-1alpha exons 3, 4, 5, 6, 9, 10, 11, 12 and 15 showed that DNA from seal lung generated PCR products similar to those from mouse DNA. These studies have established that a putative HIF-1alpha gene exists in the seal genome that appears to have a similar but not identical sequence to the mouse gene. Seal lung and skeletal muscle tissues showed the highest relative levels of HIF-1alpha protein expression, with heart muscle showing significantly lower levels, and levels of HIF-1beta protein expression paralleled this situation. Analysis of oxidized cellular protein levels indicated that seal lung and heart muscle had the lowest levels of oxidized proteins. Thus, as seal lung tissue had the highest level of HIF-1alpha protein expression and the second lowest level of protein oxidation, this suggests that HIF-1alpha expression may have an important protective effect in this tissue in diving mammals. Our results support the hypothesis that HIF-1alpha expression is dependent on both tissue-specific energy requirements and adequate metabolic supply-to-demand ratio. Combined, the evidence available suggests that diving mammals have an overall anticipatory response to avoid the ill effects of dive-associated ischemia-reperfusion which may involve the HIF-1 system.

Prolonged fasting does not increase oxidative damage or inflammation in postweaned northern elephant seal pups

“…It has been suggested that diving seals possess an enhanced antioxidant system that contributes to the protection against ROS produced in response to recurrent episodes of dive-induced ischemia/reperfusion (Elsner et al, 1998;HermesLima and Zenteno-Savín, 2002;Zenteno-Savín et al, 2002;Johnson et al, 2004;Johnson et al, 2005). Higher activities of the antioxidant enzymes SOD, catalase, GPx, glutathione S-transferase and glutathione disulfide reductase, as well as higher GSH content, have been found in seal tissues than in tissues of terrestrial mammals (Vázquez-Medina et al, 2006;Vázquez-Medina et al, 2007).…”

Apnea stimulates the adaptive response to oxidative stress in elephant seal pups

“…The role of HIF-1 as a physiological mediator of the protective effects of ischemic preconditioning has been extensively demonstrated (Bergeron et al, 2000;Grimm et al, 2005;Semenza, 2000b). The observed increases in HIF-1 nuclear content after repetitive breath-holds suggest that rest-and voluntary submersion-associated apneas also contribute to the preconditioning of the seal's muscle by activating the HIF-1-mediated adaptive response to hypoxia (Johnson et al, 2004;Johnson et al, 2005;Zenteno-Savín et al, 2002). The observed increase in Mb further supports the latter idea as Mb is upregulated in response to hypoxia in mammalian tissues and cells (Kanatous and Mammen, 2010), and without physical activity in vertebrates adapted to dive such as penguins and seals (Noren et al, 2005).…”

“…Plasma, tissues and RBCs of seals possess higher basal activities of several antioxidant enzymes and higher glutathione (GSH) levels than those of terrestrial mammals (Murphy and Hochachka, 1981 . Furthermore, hypoxia-inducible factor 1 (HIF-1), a key transcriptional regulator of the adaptive response to hypoxia, and NF-E2-related factor 2 (Nrf2), which controls the adaptive response to oxidative stress by upregulating antioxidant genes in response to increased oxidant production, have also been implicated in seal's protection against apnea-induced hypoxemia and ischemia/reperfusion (Johnson et al, 2004;Johnson et al, 2005;Vázquez-Medina et al, 2011b). No in vivo studies, however, have been conducted to elucidate the cellular and molecular responses that protect seals against apnea-induced hypoxemia and ischemia/reperfusion.…”

Subcellular Energetics and Metabolism: A Cross-Species Framework

“…136 Such behavior may be mediated by HIF-1, as its expression has been identified in seals and is associated with lower levels of protein oxidation. 137,138 Neuroglobin, a recently discovered protein located in the central nervous system, 139 may play a role in attenuating ROS damage in diving animals, although its exact function in controversial. 134,140 …”