Hepatic transcriptome response to glucocorticoid receptor activation in rainbow trout

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.