Hepatic transcriptome response to glucocorticoid receptor activation in rainbow trout

Abstract

Cortisol, the principal corticosteroid in teleosts, is thought to play a key role in the metabolic adjustments critical for regaining homeostasis. However, the target tissue molecular mechanisms involved in this adaptive response to corticosteroid stimulation are still unclear. Cortisol signaling is mediated predominantly by the glucocorticoid receptor (GR), and previous studies have shown that RU486 (a GR antagonist) offsets corticosteroid signaling in teleosts. To elucidate the molecular basis of GR-mediated metabolic readjustments, we exposed primary culture of trout hepatocytes in vitro to cortisol (to mimic stressed levels seen in fish), RU486, or a combination of both for 24 h. The gene expression was analyzed using a low-density custom-made rainbow trout cDNA array enriched with endocrine-, metabolic-, and stress-related genes. The microarray results for select genes were further validated using quantitative real-time PCR. Cortisol treatment significantly increased glucose production in hepatocytes, and this response was blocked by RU486, confirming GR-mediated corticosteroid signaling. Cortisol also elevated GR transcript levels, and this response was abolished by RU486, whereas both cortisol and RU486, either alone or in combination, reduced GR protein content in trout hepatocytes. Cortisol treatment significantly modulated the expression of several genes known to be involved in intermediary metabolism, cellular stress response, reproduction, and xenobiotic metabolism. Most of these cortisol-mediated transcript changes were abolished in the presence of RU486, suggesting a key role for GR-specific signaling in this adaptive response. Taken together, our results suggest a key role for genomic cortisol signaling in the liver molecular reprogramming that is critical for coping with stress in fish.RU486; cortisol; fish; Oncorhynchus mykiss; salmonid; cDNA microarray; stress response; intermediary metabolism CORTISOL, THE PRINCIPAL GLUCOCORTICOID in teleosts, is secreted by the interrenal tissues (analogous to the adrenal cortex) dispersed in the head kidney region. This steroid is involved in a diverse array of functions, including growth and metabolism, osmoregulation, immune function, and reproduction (31, 63). A well-studied role for cortisol involves tissue-specific metabolic reprogramming to cope with the increased energy demands associated with stress, but the associated molecular responses are far from clear. It is well established that cortisol actions are mediated via the glucocorticoid receptor (GR) belonging to the nuclear receptor family of ligand-bound transcription factors (46, 59).From a comparative standpoint, unlike mammals, teleosts appear to have multiple isoforms of GR (7,18,46), although the physiological role for each isoform is unknown. Also, some of the cortisol effects may be mediated via mineralocorticoid receptor (MR) activation; recently, an MR-specific ligand was identified in trout (46,56). In addition to genomic signaling mediated by GR and MR, recent studies also point to a no...

Chronic cortisol and the regulation of food intake and the endocrine growth axis in rainbow trout

“…The cortisolmediated changes in HSI, CF, as well as in liver and muscle glycogen and lipid content, also demonstrate that the catabolic effects of cortisol in this study had a much larger impact on the energy reserves of the liver than on those of white muscle. In the liver, numerous fish studies have shown that cortisol increases gluconeogenic capacity (Mommsen et al 1999, Aluru & Vijayan 2007, Momoda et al 2007) and the increases in plasma glucose levels associated with the Cort-II treatment during the dosing period support these findings. The marked reductions in liver glycogen content also suggest that glycogenolysis may have contributed to the cortisol-induced increase in plasma glucose levels.…”

Environmental stress-related gene expression and blood physiological responses in olive flounder (Paralichthys olivaceus) exposed to osmotic and thermal stress

“…Wap65 was not detected, whereas HSP70 expression was significantly increased in cortisoltreated hepatocytes (Figure 4). In rainbow trout hepatocytes treated with cortisol, HSP90 mRNA expression was increased (Aluru and Vijayan 2007). Basu et al (2003) found that HSP70 mRNA expression was significantly increased in rainbow trout fed cortisol.…”

The regulatory role of glucocorticoid and mineralocorticoid receptors in pulsatile urea excretion of the gulf toadfish,Opsanus beta

“…Each of these treatments should have similar effects if indeed cortisol is exerting its effects through GRs. Both compounds have been used successfully in a number of piscine studies (Bennett and Rhodes, 1986;Vijayan and Leatherland, 1992;Bernier and Peter, 2001;Milligan, 2003;Aluru and Vijayan, 2007;Killerich et al, 2007a). Although metyrapone treatment has been shown previously to elicit small urea pulses , this drug has been used successfully in toadfish to prevent the acute stress-dependent increase in cortisol following crowding .…”