30 YEARS OF THE MINERALOCORTICOID RECEPTOR: The scientific impact of cloning the mineralocorticoid receptor: 30 years on

The role of the mineralocorticoid receptor in immune cells in in cardiovascular disease

Chronic low-grade inflammation and immune cell activation are important mechanisms in the pathophysiology of cardiovascular disease (CVD). Therefore, targeted immunosuppression is a promising novel therapy to lower cardiovascular risk. In this review, we identify the mineralocorticoid receptor (MR) on immune cells as a potential target to modulate inflammation. The MR is present in almost all cells of the cardiovascular system, including immune cells. Activation of the MR in innate and adaptive immune cells induces inflammation which can contribute to CVD, by inducing endothelial dysfunction and hypertension. Moreover, it accelerates atherosclerotic plaque formation and destabilization and impairs tissue regeneration after ischemic events. Identifying the molecular targets for these non-renal actions of the MR provide promising novel cardiovascular drug targets for mineralocorticoid receptor antagonists (MRAs), which are currently mainly applied in hypertension and heart failure.

Progesterone: An enigmatic ligand for the mineralocorticoid receptor

The progesterone receptor (PR) mediates progesterone regulation of female reproductive physiology, as well as gene transcription in non-reproductive tissues, such as brain, bone, lung and vasculature, in both women and men. An unusual property of progesterone is its high affinity for the mineralocorticoid receptor (MR), which regulates electrolyte transport in the kidney in humans and other terrestrial vertebrates. In humans, rats, alligators and frogs, progesterone antagonizes activation of the MR by aldosterone, the physiological mineralocorticoid in terrestrial vertebrates. In contrast, in elephant shark, ray-finned fishes and chickens, progesterone activates the MR. Interestingly, cartilaginous fishes and ray-finned fishes do not synthesize aldosterone, raising the question of which steroid(s) activate the MR in cartilaginous fishes and ray-finned fishes. The simpler synthesis of progesterone, compared to cortisol and other corticosteroids, makes progesterone a candidate physiological activator of the MR in elephant sharks and ray-finned fishes. Elephant shark and ray-finned fish MRs are expressed in diverse tissues, including heart, brain and lung, as well as, ovary and testis, two reproductive tissues that are targets for progesterone, which together suggests a multi-faceted physiological role for progesterone activation of the MR in elephant shark and ray-finned fish. The functional consequences of progesterone as an antagonist of some terrestrial vertebrate MRs and as an agonist of fish and chicken MRs are not fully understood. The physiological activities of progesterone through binding to vertebrate MRs merits further investigation.

Transcriptional activation of elephant shark mineralocorticoid receptor by corticosteroids, progesterone, and spironolactone

The mineralocorticoid receptor (MR) is a nuclear receptor and part of a large and diverse family of transcription factors that also includes receptors for glucocorticoids, progesterone, androgens, and estrogens. The corticosteroid aldosterone is the physiological activator of the MR in humans and other terrestrial vertebrates; however, its activator is not known in cartilaginous fish, the oldest group of extant jawed vertebrates. Here, we analyzed the ability of corticosteroids and progesterone to activate the full-length MR from the elephant shark (Callorhinchus milii). On the basis of their measured activities, aldosterone, cortisol, 11-deoxycorticosterone, corticosterone, 11-deoxcortisol, progesterone, and 19-norprogesterone are potential physiological mineralocorticoids. However, aldosterone, the physiological mineralocorticoid in humans and other terrestrial vertebrates, is not found in cartilaginous or ray-finned fish. Although progesterone activates MRs in ray-finned fish, progesterone does not activate MRs in humans, amphibians, or alligator, suggesting that during the transition to terrestrial vertebrates, progesterone lost the ability to activate the MR. Both elephant shark MR and human MR are expressed in the brain, heart, ovary, testis, and other nonepithelial tissues, suggesting that MR expression in diverse tissues evolved in the common ancestor of jawed vertebrates. Our data suggest that 19-norprogesterone– and progesterone-activated MR may have unappreciated functions in reproductive physiology.