Cortisol Regulates Acid Secretion of H+-ATPase-rich Ionocytes in Zebrafish (Danio rerio) Embryos

Abstract

Systemic acid-base regulation is vital for physiological processes in vertebrates. Freshwater (FW) fish live in an inconstant environment, and thus frequently face ambient acid stress. FW fish have to efficiently modulate their acid secretion processes for body fluid acid-base homeostasis during ambient acid challenge; hormonal control plays an important role in such physiological regulation. The hormone cortisol was previously proposed to be associated with acid base regulation in FW fish; however, the underlying mechanism has not been fully described. In the present study, mRNA expression of acid-secreting related transporters and cyp11b (encoding an enzyme involved in cortisol synthesis) in zebrafish embryos was stimulated by treatment with acidic FW (AFW, pH 4.0) for 3 d. Exogenous cortisol treatment (20 mg/L, 3 d) resulted in upregulated expression of transporters related to acid secretion and increased acid secretion function at the organism level in zebrafish embryos. Moreover, cortisol treatment also significantly increased the acid secretion capacity of H+-ATPase-rich cells (HRCs) at the cellular level. In loss-of-function experiments, microinjection of glucocorticoid receptor (GR) morpholino (MO) suppressed the expression of acid-secreting related transporters, and decreased acid secretion function at both the organism and cellular levels; on the other hand, mineralocorticoid receptor (MR) MO did not induce any effects. Such evidence supports the hypothesized role of cortisol in fish acid-base regulation, and provides new insights into the roles of cortisol; cortisol-GR signaling stimulates zebrafish acid secretion function through transcriptional/translational regulation of the transporters and upregulation of acid secretion capacity in each acid-secreting ionocyte.

Neuroendocrine control of ionic balance in zebrafish

“…Similar to some other freshwater species, exposure of zebrafish to cortisol stimulates the uptake of both Na + and Ca 2+ (Kumai et al, 2012a;Lin et al, 2016;Lin et al, 2011), and the secretion of H + (Lin et al, 2015). Using in situ hybridization or immunohistochemistry, the glucocorticoid receptor (GR) was found to be expressed in NaRCs (Cruz et al, 2013), HRCs (Kumai et al, 2012a) and NCCCs (Lin et al, 2016) in zebrafish.…”

“…Using in situ hybridization or immunohistochemistry, the glucocorticoid receptor (GR) was found to be expressed in NaRCs (Cruz et al, 2013), HRCs (Kumai et al, 2012a) and NCCCs (Lin et al, 2016) in zebrafish. Exposure to cortisol was also shown to increase mRNA expression of genes that are involved in ion uptake or H + secretion, including ecac, ncc, nhe3b, atp6v1a, ae1b, ca2-like a, and ca15a (Lin et al, 2015;Lin et al, 2011).…”

A novel function of calcitonin gene-related peptide in body fluid Cl−homeostasis

“…Isotocin, prolactin, and cortisol enhance the expression of ncc2b via the upregulation of cell differentiation in zebrafish [14,44]. It remains to be established how these hormones work together to regulate the function of NCC2b and other Cl 2 transporters in the context of body fluid Cl 2 homeostasis in different vertebrate species.…”

The Control of Calcium Metabolism in Zebrafish (Danio rerio)

“…According to studies of cell experiments, cortisol is able to stimulate the transcription activity of reporter construct with the teleost glucocorticoid receptor (GR) and mineralcorticoid receptor (MR) [45,46,47,48]. Nevertheless, in vivo study indicated that cortisol regulates body fluid ion homeostasis via GR rather than MR in zebrafish [33,49,50,51,52]. …”