Pathogenic Effects of Mineralocorticoid Pathway Activation in Retinal Pigment Epithelium

Abstract

Glucocorticoids are amongst the most used drugs to treat retinal diseases of various origins. Yet, the transcriptional regulations induced by glucocorticoid receptor (GR) and mineralocorticoid receptor (MR) activation in retinal pigment epithelium cells (RPE) that form the outer blood–retina barrier are unknown. Levels of endogenous corticoids, ligands for MR and GR, were measured in human ocular media. Human RPE cells derived from induced pluripotent stem cells (iRPE) were used to analyze the pan-transcriptional regulations induced by aldosterone—an MR-specific agonist, or cortisol or cortisol + RU486—a GR antagonist. The retinal phenotype of transgenic mice that overexpress the human MR (P1.hMR) was analyzed. In the human eye, the main ligand for GR and MR is cortisol. The iRPE cells express functional GR and MR. The subset of genes regulated by aldosterone and by cortisol + RU-486, and not by cortisol alone, mimics an imbalance toward MR activation. They are involved in extracellular matrix remodeling (CNN1, MGP, AMTN), epithelial–mesenchymal transition, RPE cell proliferation and migration (ITGB3, PLAUR and FOSL1) and immune balance (TNFSF18 and PTX3). The P1.hMR mice showed choroidal vasodilation, focal alteration of the RPE/choroid interface and migration of RPE cells together with RPE barrier function alteration, similar to human retinal diseases within the pachychoroid spectrum. RPE is a corticosteroid-sensitive epithelium. MR pathway activation in the RPE regulates genes involved in barrier function, extracellular matrix, neural regulation and epithelial differentiation, which could contribute to retinal pathology.

Letter to the Editor From Behar-Cohen et al.: “The Cortisol Response of Male and Female Choroidal Endothelial Cells: Implications for Central Serous Chorioretinopathy”

“…The MR immunohistochemistry images shown in this paper supports that MR might have been degraded since the MR signal in the retina is extremely low, without any signal in ganglion cells, in retinal endothelial cells and very scarce signal in few cells the inner retina, which is very different with what has been found by several other authors (2-4). There is no MR signal in the nuclei of any cells in the choroid and no MR signal in the nuclei of retinal pigment epithelial cells either, which is very different from previous results obtained on fresh tissues and cells (5,6). More importantly, the positive MR control do not show any signal in the nuclei, which could indicate methodological issues.…”

“…The authors claim that there is no animal model that recapitulate human pachychoroid phenotype but they omitted to cite the P1hMR mouse model (mouse that overexpresses human MR) (6) and the NAS (nephrectomy aldosterone salt) models ( 7) that show all features of human eyes with pachychoroid.…”

Mineralocorticoid pathway in retinal health and diseases

“…In our experiments, we never detected any aldosterone in the retina nor in the ocular media from rodents and humans, using either radioimmunoassay or highly sensitive MS techniques (Canonica et al, 2019; Zhao et al, 2021). Previous results also indicated that the human retinal pigment epithelium cell line, ARPE19, could produce and secrete cortisol (Zmijewski et al, 2007), but using native human retinal pigment epithelium cells and human retinal pigment epithelium cells derived from induced pluripotent stem (iPS) cells, we have not been able to reproduce this result nor to show that retinal pigment epithelium could produce either cortisol or aldosterone (Canonica et al, 2021).…”

“…We recently described the retinal phenotype of these mice (provided by Marc Lombes, Damien Le Menuet and Say Viengchareun). Interestingly, enlarged choroidal vessels, choroidal excavations, disorganization of the Bruch membrane and pigments in retinal pigment epithelium cells, focal retinal pigment epithelium proliferation and elongation of photoreceptor outer segments (Canonica et al, 2021) (Figure 3d) resemble human pachychoroid pigment epitheliopathy (Figure 3e).…”

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

“…In RPE/ choroid complex, we quantified the expression of genes shown to be upregulated by aldosterone or MR pathway activation in human RPE cells derives from iPS such as Plaur encoding the urokinase plasminogen activator receptor (uPAR) and Fosl1 encoding the FOS like 1 AP-1 transcription factor subunit protein, Ptx3 encoding pentraxin 3 and Omg that encodes the oligodendrocyte myelin glycoprotein and that was down-regulated by aldosterone or Cortisol+ RU486 [65]. We also tested genes showed to be upregulated in the RPE/choroid complex after intravitreal injection of aldosterone such as Ngal encoding lipocalin 2 and Mmp9 and the Shroom Family Member 2 Shroom2, that is implicated in amiloride-sensitive sodium channel activity [66].…”