Aldosterone-induced changes in endothelial function

Meng, Yao (2022): Aldosterone-induced changes in endothelial function: the epoxyeicosatrienoic acid pathway in aldosterone excess and receptor transactivation by co-stimulation with gluco- and mineralocorticoids. Dissertation, LMU München: Medizinische Fakultät

Abstract

Patients with primary aldosteronism (PA) are characterized by an excess of cardiovascular morbidities independent of the degree of associated arterial hypertension. These comorbidities share the same etiology as the sequelae of atherosclerosis of which endothelial dysfunction is considered to be the initiating step. Endothelial cells feature a variety of pathways to relax vas-cular smooth muscle and maintain a healthy vascular homeostasis, one of the pathways being the epoxyeicosatrienoic acid (EET) pathway as a component of the endothelium-derived hy-perpolarizing factor (EDHF) family. At present, little is known about whether primary aldosteron-ism affects EET release from endothelial cells. Knowledge about the EET pathway functional integrity could translate to therapeutic applications targeting EET breakdown to ultimately target the cardiovascular comorbidities observed in PA. Endothelial mineralocorticoid receptors are exposed not only to aldosterone but also to circulat-ing glucocorticoids at much higher concentrations. 11-β-HSD (hydroxysteroid dehydrogenase) type 2 protects mineralocorticoid receptors from glucocorticoids in a cell-type specific manner. Significant knowledge gaps still exist with regard to the role of this glucocorticoid inactivation system in endothelial cells and its role in mineralocorticoid excess. The aims of this project were (A) to investigate a potential impairment of endothelium-derived vasoactive EETs in a context of aldosterone-induced endothelial dysfunction and (B) to deter-mine the existence and the degree of endothelial gluco- and mineralocorticoid receptor transac-tivation. It could be shown that endothelial cells exposed to aldosterone excess retain their original ex-pression levels of enzymes critical for the synthesis and degradation of EETs. On the other hand, aldosterone increased expression levels of a mesenchymal marker gene and impaired calcium response to stimulation by acetylcholine, thereby underpinning the biological activity of the steroid concentrations which were used. Despite these broad changes in endothelial physi-ology, stimulated secretion of EETs into the endothelial supernatant was unchanged in condi-tions of aldosterone excess, arguing for an undisturbed endothelial EET pathway in primary aldosteronism. Because of the seemingly unimpaired EET synthesis, inhibition of EET break-down may therefore be a reasonable therapeutic option in treating vascular disease in primary aldosteronism. With respect to aim (B), qPCR revealed negligible expression levels of both 11-β-HSD type 1 or 11-β-HSD type 2. These data could be corroborated functionally by measurements of cortisone and cortisol in the supernatants. Aldosterone at various concentrations did not modulate the expression or activity of both 11-β-HSD enzymes. Traditional markers of transcriptional activity of mineralocorticoid and glucocorticoid receptors turned out to be not useful for endothelial cells, since they could not be shown to be affected by stimulation with cortisol and aldosterone. A semiquantitative, immunofluorescence-based nuclear localization assay of steroid receptors as global readout of activity was established. This assay revealed that aldosterone antagonized nuclear translocation of glucocorticoid receptors in a mineralocorticoid receptor-dependent manner. This novel finding suggests that under certain circumstances mineralocorticoids might antagonize glucocorticoids and highlights the complex interaction between both corticosteroids. Future studies will apply the developed assay to tissues derived from patients harboring single and combined excessive secretion of gluco- and mineralocorticoids to further investigate steroid interactions in endothelial cells following in vivo exposure.

• Dokumententyp: Dissertationen (Dissertation, LMU München)
• Themengebiete: 600 Technik, Medizin, angewandte Wissenschaften ; 600 Technik, Medizin, angewandte Wissenschaften > 610 Medizin und Gesundheit
• Fakultäten: Medizinische Fakultät
• Sprache der Hochschulschrift: Englisch
• Datum der mündlichen Prüfung: 24. November 2022
• 1. Bericht­erstatter:in: Reinecke, Martin