Bidirectional crosstalk between Hypoxia-Inducible Factor and glucocorticoid signalling in zebrafish larvae

Abstract

<jats:title>Abstract</jats:title><jats:p>In the last decades <jats:italic>in vitro</jats:italic> studies highlighted the potential for crosstalk between Hypoxia-Inducible Factor-(HIF) and glucocorticoid-(GC) signalling pathways. However, how this interplay precisely occurs <jats:italic>in vivo</jats:italic> is still debated. Here, we use zebrafish larvae (<jats:italic>Danio rerio</jats:italic>) to elucidate how and to what degree hypoxic signalling affects the endogenous glucocorticoid pathway and <jats:italic>vice versa, in vivo</jats:italic>. Firstly, our results demonstrate that in the presence of upregulated HIF signalling, both glucocorticoid receptor (Gr) responsiveness and endogenous cortisol levels are repressed in 5 days post fertilisation larvae. In addition, despite HIF activity being low at normoxia, our data show that it already impedes both glucocorticoid activity and levels. Secondly, we further analysed the <jats:italic>in vivo</jats:italic> contribution of glucocorticoids to HIF activity. Interestingly, our results show that both glucocorticoid receptor (GR) and mineralocorticoid receptor (MR) play a key role in enhancing it. Finally, we found indications that glucocorticoids promote HIF signalling via multiple routes. Cumulatively, our findings allowed us to suggest a model for how this crosstalk occurs <jats:italic>in vivo</jats:italic>.</jats:p><jats:sec><jats:title>Author summary</jats:title><jats:p>Hypoxia is a common pathophysiological condition to which cells must rapidly respond in order to prevent metabolic shutdown and subsequent death. This is achieved via the activity of Hypoxia-Inducible Factors (HIFs), which are key oxygen sensors that mediate the ability of the cell to cope with decreased oxygen levels.</jats:p><jats:p>Although it aims to restore tissue oxygenation and perfusion, it can sometimes be maladaptive and contributes to a variety of pathological conditions including inflammation, tissue ischemia, stroke and growth of solid tumours. In this regard, synthetic glucocorticoids which are analogous to naturally occurring steroid hormones, have been used for decades as anti-inflammatory drugs for treating pathological conditions which are linked to hypoxia (i.e. asthma, rheumatoid arthritis, ischemic injury). Indeed, previous <jats:italic>in vitro</jats:italic> studies highlighted the presence of a crosstalk between HIF and glucocorticoids. However, how this interplay precisely occurs in an organism and what the molecular mechanism is behind it are questions that still remain unanswered. Here, we provide a thorough <jats:italic>in vivo</jats:italic> genetic analysis, which allowed us to propose a logical model of interaction between glucocorticoid and HIF signalling. In addition, our results are important because they suggest a new route to downregulate HIF for clinical purposes.</jats:p></jats:sec>

HIF1α is an essential regulator of steroidogenesis in the adrenal gland

“…Undoubtedly, such models would help us to better understand the crosstalk between HPPs and adrenal steroid metabolism, while simultaneously serving as an essential tool to study the pathophysiology of multiple conditions associated with dramatically altered steroid hormone levels (2). Ablation of HIF1α revealed an important role for this transcription factor in steroidogenesis, which concurs with results from previous studies (20,50). However, our findings that HIF1α deletion results in the upregulation of mRNA of a vast majority of steroid-related enzymes is counterintuitive to the nature of this transcription factor (12, 51), and therefore we believe this effect is most likely indirect with potential involvement of one or more transcriptional repressors (13,52,53).…”

“…Studies on the role of HIFs in the regulation of steroidogenesis in vitro are few, apart from those in zebra fish larvae that describe differential regulation of the enzymes involved in the steroid pathway (7,18,20). However, to the best of our knowledge, there are no mouse models to study the role of HPPs in adrenal cortical cells.…”

“…Previous in vitro studies and reports on HIF1α alterations in zebrafish larvae have suggested negative regulation of StAR, the mitochondrial cholesterol transporter (7,17,20). However, data on the effects of HPP alterations in adrenal cortex of mice is scant at best.…”

“…Recent in vitro and zebrafish studies have revealed a continuous cross talk between HIF and steroidogenesis pathways, along with potential interference in the production of aldosterone and glucocorticoids (17)(18)(19)(20). There is also evidence suggesting a role for the hypoxia pathway in modulating glucocorticoid/glucocorticoid receptor (GR) signaling (21,22).…”

A unique neurogenomic state emerges after aggressive confrontations in males of the fishBetta splendens

“…Similarly, GRE motifs have a vital role in the cellular response to stress (64). A recent study showed that glucocorticoids promote HIF activity via multiple routes including glucocorticoid receptors (65). Collectively, it seems that both winners and losers were tolerant of oxygen deficiency and stress based on the enrichment of HRE and GRE transcription factor−binding motifs among the DEGs that were expressed in the brains of these fish.…”