Chronic Systemic Dexamethasone Regulates the Mineralocorticoid/Glucocorticoid Pathways Balance in Rat Ocular Tissues

Abstract

Central serous chorioretinopathy (CSCR) is a retinal disease affecting the retinal pigment epithelium (RPE) and the choroid. This is a recognized side-effect of glucocorticoids (GCs), administered through nasal, articular, oral and dermal routes. However, CSCR does not occur after intraocular GCs administration, suggesting that a hypothalamic-pituitary-adrenal axis (HPA) brake could play a role in the mechanistic link between CSCR and GS. The aim of this study was to explore this hypothesis. To induce HPA brake, Lewis rats received a systemic injection of dexamethasone daily for five days. Control rats received saline injections. Baseline levels of corticosterone were measured by Elisa at baseline and at 5 days in the serum and the ocular media and dexamethasone levels were measured at 5 days in the serum and ocular media. The expression of genes encoding glucocorticoid receptor (GR), mineralocorticoid receptors (MR), and the 11 beta hydroxysteroid dehydrogenase (HSD) enzymes 1 and 2 were quantified in the neural retina and in RPE/ choroid. The expression of MR target genes was quantified in the retina (Scnn1A (encoding ENac-α, Kir4.1 and Aqp4) and in the RPE/choroid (Shroom 2, Ngal, Mmp9 and Omg, Ptx3, Plaur and Fosl-1). Only 10% of the corticosterone serum concentration was measured in the ocular media. Corticosterone levels in the serum and in the ocular media dropped after 5 days of dexamethasone systemic treatment, reflecting HPA axis brake. Whilst both GR and MR were downregulated in the retina without MR/GR imbalance, in the RPE/choroid, both MR/GR and 11β-hsd2/11β-hsd1 ratio increased, indicating MR pathway activation. MR-target genes were upregulated in the RPE/ choroid but not in the retina. The psychological stress induced by the repeated injection of saline also induced HPA axis brake with a trend towards MR pathway activation in RPE/ choroid. HPA axis brake causes an imbalance of corticoid receptors expression in the RPE/choroid towards overactivation of MR pathway, which could favor the occurrence of CSCR.

Keywords: central serous chorioretinopathy; glucocorticoid; mineralocorticoid; retina.

Figure 1

Corticosterone and dexamethasone levels in the rat serum and ocular media. Corticosterone in the serum (A) and ocular media (B) at baseline (n = 7) and after 5 days of daily injection of dexamethasone (D5) (n = 16) or saline (n = 5). Spearman correlation between corticosterone ocular and serum levels (r = 0.76, p = 0.0001) (C). Dexamethasone serum (n = 14) and ocular media (n = 7) after 5 days of daily injection of dexamethasone (D). Spearman correlation between dexamethasone ocular and serum levels (r = −0.28, p = 0.55) (E), ** p < 0.001, *** p < 0.0001, ns non significant.

Figure 2

Corticoid receptors and hydroxysteroid dehydrogenase gene expression in the retina and RPE/choroid. (A) neural retina: Nr3c1, encoding GR, Nr3c2 encoding MR and 11β-hsd1 and 2 expression at baseline (n = 7), after 5 days of daily injection of dexamethasone (n = 16), or saline (n = 6); (B) RPE/choroid: Nr3c1, encoding GR, Nr3c2 encoding MR and 11β-hsd1(HSD1) and 2 (HSD2) expression at baseline (n = 7), after 5 days of daily injection of dexamethasone (n = 16), or saline (n = 6), * p < 0.05, ** p < 0.01, *** p < 0.001, **** p < 0.0001.

Figure 3

Corticoid receptors and hydroxysteroid dehydrogenase gene expression in the iris/ciliary body. Nr3c1, encoding GR, Nr3c2 encoding MR and 11β-hsd1 and 2 expression at baseline (n = 7), after 5 days of daily injection of dexamethasone (n = 16), or saline (n = 6), * p < 0.05, ** p < 0.01.

Figure 4

Regulation of MR-induced genes in the neural retina. Scnn1A encoding ENac-α Kir4.1 and Aqp4 expression at baseline (n = 7), after 5 days of daily injection of dexamethasone (n = 16), or saline (n = 6), * p < 0.05, *** p < 0.001.

Figure 5

Regulation of MR-induced genes in the RPE/choroid. Expression of Shroom 2, Ngal, Mmp9 and Omg, Ptx3, Plaur and Fosl-1 in the RPE/choroid of rats at baseline (n = 7), after 5 days of daily injection of dexamethasone (n = 16) or saline (n = 6), * p < 0.05, ** p < 0.01.

Figure 6

Schematic representation of the ocular consequences of HPA axis brake on ocular GR/MR pathways [34,49,61].

Figure 7

Schematic representation of the experiments. Serum was extracted from blood samples, intraocular fluids include aqueous humour and vitreous from each eye. Ocular tissue dissection separated the iris-ciliary body complex, the neural retina, the retinal pigment epithelium (RPE)-choroid complex or each eye separately.