M-C ZENNARO and others Novel mechanisms of primary 224:2 R63–R77 Review aldosteronism An update on novel mechanisms of primary aldosteronism Correspondence 1,2,3 1,2 1,2,3 Maria-Christina Zennaro , Sheerazed Boulkroun and Fabio Fernandes-Rosa should be addressed to M-C Zennaro 1INSERM, UMRS_970, Paris Cardiovascular Research Center – PARCC, 56, rue Leblanc, 75015 Paris, France Email 2University Paris Descartes, Sorbonne Paris Cite´ , Paris, France maria-christina.zennaro@ 3Assistance Publique-Hoˆ pitaux de Paris, Hoˆ pital Europe´ en Georges Pompidou, Service de Ge´ ne´ tique, Paris, France inserm.fr Abstract Primary aldosteronism (PA) is the most common and curable form of secondary Key Words hypertension. It is caused in the majority of cases by either unilateral aldosterone " primary aldosteronism overproduction due to an aldosterone-producing adenoma (APA) or by bilateral adrenal " aldosterone producing hyperplasia. Recent advances in genome technology have allowed researchers to unravel adenoma part of the genetic abnormalities underlying the development of APA and familial " bilateral adrenal hyperplasia hyperaldosteronism. Recurrent somatic mutations in genes coding for ion channels (KCNJ5 " potassium channels and CACNA1D) and ATPases (ATP1A1 and ATP2B3) regulating intracellular ionic homeostasis " calcium channels and cell membrane potential have been identified in APA. Similar germline mutations of " ATPase KCNJ5 were identified in a severe familial form of PA, familial hyperaldosteronism type 3 " phenotypic variability (FH3), whereas de novo germline CACNA1D mutations were found in two cases of " genotype-phenotype correlation hyperaldosteronism associated with a complex neurological disorder. These results have " genetic susceptibility allowed a pathophysiological model of APA development to be established. This model Journal of Endocrinology " somatic mutations involves modifications in intracellular ionic homeostasis and membrane potential, " endocrine tumor accounting for w50% of all tumors, associated with specific gender differences and severity of PA. In this review, we describe the different genetic abnormalities associated with PA and discuss the mechanisms whereby they lead to increased aldosterone production and cell proliferation. We also address some of the foreseeable consequences that genetic knowledge may contribute to improve diagnosis and patient care. Journal of Endocrinology (2015) 224, R63–R77 Introduction Primary aldosteronism (PA) is the most common and study, involving 459 patients with PA and 1290 controls curable form of secondary arterial hypertension, with an with essential hypertension, individually matched for estimated prevalence of w10% in referred patients and 4% sex, age, and office systolic blood pressure, showed an in primary care (Hannemann & Wallaschofski 2012), but increased prevalence of left ventricular hypertrophy, as high as 20% in patients with resistant hypertension coronary artery disease, nonfatal myocardial infarction, (Calhoun et al. 2002, Douma et al. 2008). Increased heart failure, and atrial fibrillation (Savard et al. 2013). aldosterone levels in PA are associated with increased The excess cardiovascular morbidity is related to blood cardiovascular risk compared with essential hypertension pressure-independent cardiac remodeling (Rossi et al. (Mulatero et al. 2013, Savard et al. 2013). Comparison of 1997) and myocardial fibrosis (Freel et al. 2012), with left cardiovascular events in a large controlled cross-sectional ventricular changes being reversible in the long-term with http://joe.endocrinology-journals.org Ñ 2015 Society for Endocrinology Published by Bioscientifica Ltd. DOI: 10.1530/JOE-14-0597 Printed in Great Britain Downloaded from Bioscientifica.com at 09/27/2021 06:02:53PM via free access Review M-C ZENNARO and others Novel mechanisms of primary 224:2 R64 aldosteronism surgical or medical treatment of PA (Rossi et al. 2013). highlighted by the discovery of genetic alterations Vascular remodeling associated with aldosterone excess affecting proteins involved in the regulation of ZG cell and duration of hypertension predict the outcome of membrane potential and ionic homeostasis in familial adrenalectomy in patients with PA, emphasizing the and sporadic forms of PA. importance of early diagnosis of unilateral forms of the disease (Rossi et al. 2008). Somatic mutations in APA PA results from autonomous aldosterone production from the adrenal cortex. It is caused in the majority of Availability of high throughput next-generation seq- cases by a unilateral aldosterone-producing adenoma uencing technologies has allowed for comparison of (APA) or bilateral adrenal hyperplasia (BAH) and is often whole-exome genetic alterations between germline DNA accompanied by hypokalemia. Aldosterone production and DNA extracted from APA (somatic DNA). Recurrent from the zona glomerulosa (ZG) of the adrenal cortex is somatic mutations in genes coding for ion channels tightly controlled in an exquisite regulatory loop to (KCNJ5 (Choi et al. 2011) and CACNA1D (Azizan et al. maintain sodium and electrolyte homeostasis in the 2013, Scholl et al.2013)) and ATPases (ATP1A1 and kidney. The main intracellular mechanism involved is ATP2B3 (Beuschlein et al. 2013)) regulating intracellular calcium signaling, which is induced by both angiotensin II ionic homeostasis and cell membrane potential have been (AngII) and potassium, the major regulators of aldosterone identified (Fig. 1). No germline mutations are found in biosynthesis (Spat & Hunyady 2004). Increased calcium patients harboring somatic mutations in APA (although a signaling affects many of the steps involved in aldosterone few germline mutations in KCNJ5 were recently described biosynthesis, including increased cholesterol availability in patients with BAH (Murthy et al. 2014), see below). and influx into the mitochondria, as well as stimulation KCNJ5 encodes the G protein-activated inward rectifier of the expression of CYP11B2, coding for the enzyme potassium channel GIRK4 (alternative protein name aldosterone synthase (AS), catalyzing the final steps of KIR3.4). All KCNJ5 mutations identified so far in APA, as aldosterone biosynthesis (Guagliardo et al. 2012a). AngII well as different germline mutations identified in familial acts through the AngII type 1 receptor (AT1R) to stimulate hyperaldosteronism type III (FH3) (see below), are located C inositol trisphosphate-dependent Ca2 release from the in exon 2; the most frequent of them are p.Gly151Arg C endoplasmic reticulum. In addition, both AngII and K and p.Leu168Arg, but less frequent ones located nearby act by depolarizing the ZG cell membrane potential, have also been described (for an extensive list of identified Journal of Endocrinology leading to opening of voltage-gated calcium channels. mutations, see Gomez-Sanchez (2014) and Monticone Indeed, ZG cells have an intrinsic capacity to behave as et al. (2014)). All these mutations are located near or electrical oscillators. In the ZG, the main ionic conduc- within the selectivity filter of GIRK4, which allows C tance is that of K , due to the expression of different types selective passage of potassium ions through the channel C of K channels. Thus, the cell membrane potential closely pore, and affect the ion selectivity of the channel. C follows the equilibrium potential of K over a large range Increased sodium conductance leads to sodium influx C of extracellular K concentrations. Potassium channels into the cell with chronic cell membrane depolarization thus play an important role in the pathogenesis of PA followed by opening of voltage-dependent calcium as they are central regulators of the ZG cell membrane channels and activation of calcium signaling and aldos- potential, functioning as an extracellular potassium terone production. Transfection of different mutant C sensor. The concentration gradient of K between the channels into adrenocortical cells leads to increased intracellular and extracellular space that is required for CYP11B2 transcription and aldosterone production, as the establishment of the membrane potential is generated well as increased expression of two of the transcriptional C C by the activity of the Na ,K-ATPase. Elevation of regulators of CYP11B2, NURR1 (encoded by NR4A2) and C extracellular K concentration, decrease in intracellular NOR1 (encoded by NR4A3)(Monticone et al. 2012, Oki C C C K concentration, inhibition of the Na ,K -ATPase, or et al. 2012a). More recently, whole-exome sequencing in potassium channels all lead to cell membrane depolariz- APA has identified recurrent somatic mutations in C ation, allowing opening of voltage-dependent Ca2 two members of the P-type ATPase gene family, namely C C channels. The importance of the maintenance of the ATP1A1 encoding the a1 subunit of the Na ,K -ATPase strongly negative resting membrane potential (K80 mV) and ATP2B3, coding for the plasma membrane calcium- and intracellular calcium concentrations of ZG cells for transporting ATPase 3 (PMCA3) (Beuschlein et al. 2013), physiological aldosterone production has recently been as well as mutations in the CACNA1D gene, coding for http://joe.endocrinology-journals.org Ñ 2015 Society for Endocrinology Published by Bioscientifica Ltd. DOI: 10.1530/JOE-14-0597 Printed in Great Britain Downloaded from Bioscientifica.com at 09/27/2021 06:02:53PM via free access Review M-C ZENNARO and others Novel mechanisms of primary 224:2 R65 aldosteronism a A Na+,K+-ATPase the 1 subunit of the Cav1.3 calcium channel (calcium