Introduction

Aldosterone plays a key role in controlling blood pressure values by maintaining salt, water, and body fluid homeostasis. It exerts genomic effects that are mediated by activation of the mineralocorticoid receptor (MR) and ‘rapid’ or ‘non genomic’ effects that involve additional receptors as the G-protein coupled estrogen receptor (GPER). Excessive production of aldosterone generates an inflammatory state that is associated with cardiovascular and metabolic diseases that can be promoted by the involvement of innate and adaptive immunity.  However, it is unknown if cells of the innate and adaptive immunity are endowed with aldosterone receptor(s) and are implicated in the inflammatory action of aldosterone.

 Aims

Therefore, we sought for aldosterone receptors on human T lymphocytes and investigate whether aldosterone affects T cells activation.

Method

The expression of MR and GPER on human T cells was tested by measuring mRNA copy number by droplet digital PCR and immunoblotting from 7 healthy donors (HD). Peripheral blood mononuclear cells (PBMCs) from HD were exposed to different concentrations of aldosterone (from 10^-10 M to 10^-8 M) with or without MR antagonist (canrenone) and GPER antagonist (G36) under chronic and acute stimulation. We evaluated the effect of aldosterone CD8⁺ T cells by measuring IFNÉ£ release with flow cytometry. We also sought for the expression of the cortisol inactivating enzyme 11β-Hydroxysteroid Dehydrogenase Type 2 (11bHSD2) in CD4⁺ and CD8⁺ lymphocytes.

Results

We detected the MR and GPER both at mRNA and protein level in CD8⁺ and CD4⁺ T cells. MR mRNA copy number (CD4⁺= 3061 ± 4037 copies/50 ng of mRNA and CD8⁺= 3379 ± 3112 copies/50 ng of mRNA) was at least 40-fold high that of the GPER (CD4⁺= 65 ± 71.7 copies/50 ng of mRNA and CD8⁺=86.4 ± 68.9 copies/50 ng of mRNA). At the protein level, the rank expression was GPER>MR in both CD4⁺ and CD8⁺ lymphocytes. Aldosterone significantly increased IFNÉ£ release in CD8⁺ T-cell both under chronic and acute stimulation. Chronic exposure to aldosterone increased IFNÉ£ production in a dose-dependent manner in CD8⁺ T cells by acting via the MR, as it was prevented by canrenone (p < 0.0001), while the rapid aldosterone action was slight reduced by G36 and mimicked by G1. However, we found only a bare expression of mRNA for 11bHSD2 in CD4+ (4.2±8.3 copies/50ng mRNA) and CD8+ (3.6±6.3 copies/50ng mRNA) lymphocytes of HD subjects. Therefore, as the physiological concentration of cortisol in plasma is 10² -10³ fold higher then aldosterone, it could be that some effect elicited in vitro by aldosterone are in fact driven by cortisol.

Conclusions

In conclusion we found compelling evidence for the presence of MR and GPER receptors in human T lymphocytes and suggested that aldosterone and cortisol affect IFNÉ£ release in human CD8⁺ lymphocytes.