Identification of risk loci for primary aldosteronism in genome-wide association studies

Primary aldosteronism affects up to 10% of hypertensive patients and is responsible for treatment resistance and increased cardiovascular risk. Here we perform a genome-wide association study in a discovery cohort of 562 cases and 950 controls and identify three main loci on chromosomes 1, 13 and X; associations on chromosome 1 and 13 are replicated in a second cohort and confirmed by a meta-analysis involving 1162 cases and 3296 controls. The association on chromosome 13 is specific to men and stronger in bilateral adrenal hyperplasia than aldosterone producing adenoma. Candidate genes located within the two loci, CASZ1 and RXFP2, are expressed in human and mouse adrenals in different cell clusters. Their overexpression in adrenocortical cells suppresses mineralocorticoid output under basal and stimulated conditions, without affecting cortisol biosynthesis. Our study identifies the first risk loci for primary aldosteronism and highlights new mechanisms for the development of aldosterone excess.

Detection of primary aldosteronism, the most common form of secondary arterial hypertension, is essential for targeted management and prevention of cardiovascular complications. Here, the authors identify genetic loci associated with primary aldosteronism, suggesting new mechanisms of disease.

FC074: Mineralocorticoid Receptor Drives Parietal Epithelial Cell Activation and Glomerular Injury During Crescentic Glomerulonephritis

BACKGROUND AND AIMS

We have recently demonstrated that targeting specific pathways in parietal epithelial cells (PEC) can markedly alleviate experimental extracapillary glomerular injury (1). Accumulating evidence has indicated the potential contributions of aldosterone and mineralocorticoid receptor (MR) to the pathophysiology of chronic kidney disease. MR is strongly expressed in endothelial cells, glomerular mesangial cells, podocytes and distal tubular cells. Previous studies have shown that administration of mineralocorticoid receptor antagonists, including spironolactone and eplerenone, has beneficial effects in various renal injury animal models, such as unilateral ureteral obstruction, ischemia-reperfusion, cyclosporine-induced nephrotoxicity and hypertensive renal injury. The role of the MR in extra capillary glomerulopathies is still elusive and mechanistically unclear.

METHOD

To investigate the cell-specific role of the MR in PEC in the course of crescentic glomerulonephritis, we generated chimeric mice specifically lacking MR (Pec Cre Nr3c2lox/lox) in PECs using an inducible Cre recombinase system. Crescentic glomerulonephritis (GN) was induced using the antiglomerular basement membrane nephrotoxic serum (NTS) model. In vivo, biological parameters (albuminuria, blood urea nitrogen—BUN), glomerular injury, as well as PEC activation (CD44, CD9 and fibronectin staining) were assessed.

RESULTS

At baseline, Pec Cre Nr3c2wt/wt and Pec Cre Nr3c2lox/lox mice displayed no kidney morphology and function differences. When challenged using the NTS model, Pec Cre Nr3c2lox/lox mice showed less albuminuria and preserved renal function as compared to Pec Cre Nr3c2 wt/wt counterparts. Crescents were also more numerous and organized in Pec Cre Nr3c2wt/wt mice.

Next, we examined whether pharmacological MR inhibition could alleviate the severity of crescentic GN. When Pec Cre Nr3c2wt/wt mice were orally given eplerenone for 14 days after the onset of the crescentic GN, they were significantly protected from renal injury and failure (decreased proteinuria, normal BUN and reduced number of crescent). Such global action was associated with less activation molecule CD44 on PECs. Thus, genetic disruption of MR in PEC as well as pharmacological inhibition using eplerenone reduced glomerular expression of CD44 and crescent formation.

Furthermore, kidney biopsies of individuals diagnosed with crescentic glomerulonephritis displayed increased expression of MR in PEC and crescents.

CONCLUSION

Altogether, these results indicate the critical role of MR in PEC activation during crescentic glomerulonephritis along with the recently discovered CD9/EGFR/PDGFR pathway. This further supports the idea that the PEC phenotype switch is not a bystander event but plays a targetable critical active pathogenic role in crescentic GN. MR modulation using eplerenone may be a new therapeutic option for the management of such severe disease.

Colocalization of Wnt/β-Catenin and ACTH Signaling Pathways and Paracrine Regulation in Aldosterone-producing Adenoma

CONTEXT

Aldosterone-producing adenomas (APAs) are a common cause of primary aldosteronism (PA). Despite the discovery of somatic mutations in APA and the characterization of multiple factors regulating adrenal differentiation and function, the sequence of events leading to APA formation remains to be determined.

OBJECTIVE

We investigated the role of Wnt/β-catenin and adrenocorticotropin signaling, as well as elements of paracrine regulation of aldosterone biosynthesis in adrenals with APA and their relationship to intratumoral heterogeneity and mutational status.

METHODS

We analyzed the expression of aldosterone-synthase (CYP11B2), CYP17A1, β-catenin, melanocortin type 2 receptor (MC2R), phosphorlyated cAMP response element-binding protein (pCREB), tryptase, S100, CD34 by multiplex immunofluorescence, and immunohistochemistry-guided reverse transcription-quantitative polymerase chain reaction. Eleven adrenals with APA and 1 with micronodular hyperplasia from patients with PA were analyzed. Main outcome measures included localization of CYP11B2, CYP17A1, β-catenin, MC2R, pCREB, tryptase, S100, CD34 in APA and aldosterone-producing cell clusters (APCCs).

RESULTS

Immunofluorescence revealed abundant mast cells and a dense vascular network in APA, independent of mutational status. Within APA, mast cells were localized in areas expressing CYP11B2 and were rarely colocalized with nerve fibers, suggesting that their degranulation is not controlled by innervation. In these same areas, ß-catenin was activated, suggesting a zona glomerulosa cell identity. In heterogeneous APA with KCNJ5 mutations, MC2R and vascular endothelial growth factor A expression was higher in areas expressing CYP11B2. A similar pattern was observed in APCC, with high expression of CYP11B2, activated β-catenin, and numerous mast cells.

CONCLUSION

Our results suggest that aldosterone-producing structures in adrenals with APA share common molecular characteristics and cellular environment, despite different mutation status, suggesting common developmental mechanisms.

Modulation of Calcium Signaling by Chemogenetic Tools to Elucidate the Pathogenesis of Primary Aldosteronism

Primary aldosteronism (PA) is the most frequent form of secondary arterial hypertension. The identification of germline or somatic mutations in different genes coding for ion channels (KCNJ5, CACNA1D, CACNA1H and CLCN2) and ATPases (ATP1A1 and ATP2B3) defines PA as a channelopathy. These mutations promote increased intracellular calcium concentrations and activation of calcium signaling, the main trigger for aldosterone biosynthesis.

The aim of our study was to elucidate the mechanisms underlying the development of PA by modulating calcium signaling using chemogenetic tools.

We have generated two different adrenocortical H295R_S2 cell lines stably expressing different chimeric ion channels generated by fusing the mutated extracellular ligand binding domain of the α7 nicotinic acetylcholine receptor to the ion pore domain of large Cys-loop receptor ion channel family; these receptors constitute PSAM (Pharmacologically Selective Actuator Modules). The mutations introduced in the ligand-binding domain allow to use synthetic ligands, PSEM (Pharmacologically Selective Effector Molecules) to activate the PSAM. We used two different PSAM: the chimeric receptor α7-5HT3 or a mutated acetylcholine receptor nAchR, allowing respectively modulation of sodium or calcium entry into the cells in response to the specific PSEM: Varenicline for α7-5HT3 or Compound 9S for mutated nAChR. The cells lines were characterized in terms of intracellular calcium concentrations, cell proliferation, aldosterone production and steroidogenic gene expression.

Cells expressing α7-5HT3 treated for 24h with increasing concentrations of Varenicline (10^–9 to 10^-5M) showed increased intracellular calcium concentrations and an increase in expression of steroidogenic genes such as StAR CYP17A1, CYP21A2 and CYP11B2. Cell proliferation was not affected. Calcium entry into cells expressing the mutated nAChR receptor treated for 24h with increasing concentrations of Compound 9S (10^–9 to 10^-5M) induced an increase in expression of steroidogenic genes such as StAR, CYP21A2 and HSD3B2, but not CYP11B2. Similarly to the results obtained in cells expressing α7-5HT3, cell proliferation was unaffected in response to Compound 9S.

These cell lines, in which we can modulate the intracellular calcium concentration « on demand », are a useful tool for a better understanding of the alterations of intracellular ion balance and calcium signaling in the pathophysiology of PA.

Interaction Between Wnt/β-catenin and ACTH Signaling Pathways and Paracrine Regulation in Aldosterone Producing Adenoma

Primary aldosteronism (PA) is the most frequent form of secondary arterial hypertension and is caused in the majority of cases by an aldosterone producing adenoma (APA) or bilateral adrenal hyperplasia. Different somatic mutations have been identified in APA and in other aldosterone producing structures, which can be distinct within the same adrenal, suggesting multiple mechanisms underlying APA development. Also, APA show important cellular and molecular heterogeneity which may be due to interaction of different signaling pathways involved in adrenal cortex cell differentiation and function. The aim of this study was to investigate the role of Wnt/β-catenin and ACTH signaling as well as elements of paracrine regulation of aldosterone biosynthesis and vascularization in the development of APA and aldosterone producing cell clusters (APCC) and their relationship with intratumoral heterogeneity and mutational status. We performed immunohistochemistry and multiplex immunofluorescence (CYP11B2, CYP17A1, β-catenin, MC2R, pCREB, Tryptase, S100, CD34) multispectral image analysis on 11 adrenals with APA and one with micronodular hyperplasia from patients with PA. CYP11B2 (aldosterone synthase) IHC guided RT-qPCR was performed on RNA extracted from formalin-fixed paraffin-embedded tissues in 7 adrenals. Multiplex immunofluorescence revealed high abundance of tryptase positive mast cells and a dense vascular component in APA, which were independent of the mutational status. Within APA, mast cells were mainly localized in zones expressing CYP11B2, but not in areas expressing CYP17A1, and were rarely colocalized with nerve fibers, suggesting that their activity is not controlled by innervation. In cells expressing aldosterone synthase, β-catenin was activated, i.e. shows nuclear and/or cytoplasmic staining, features suggestive of a zona glomerulosa cell identity; MC2R was found at the cell membrane. Expression of MC2R mRNA was observed at different levels in APA, similar to expression of MRAP and VEGFA; MRAP2 was not detected. Within heterogeneous APA carrying KCNJ5 mutations, both MC2R and VEGFA expression was higher in areas expressing CYP11B2. Remarkably, this pattern was maintained in APCC, where cells show high CYP11B2 expression, together with activated β-catenin, independently of the mutation status. In addition, a high number of mast cells was detected around APCC, with a reorganization of the capillaries around the CYP11B2 positive cells. Our results suggest that aldosterone producing structures in adrenals with APA share common molecular characteristics and cellular environment, despite different mutation status. Mast cells appear to be closely associated with cells expressing aldosterone synthase, both in APA and APCC, and their role in regulating aldosterone biosynthesis in the context of somatic mutations in PA remains to be established.

Genetic, Cellular, and Molecular Heterogeneity in Adrenals With Aldosterone-Producing Adenoma

Supplemental Digital Content is available in the text.

Aldosterone-producing adenoma (APA) cause primary aldosteronism—the most frequent form of secondary hypertension. Somatic mutations in genes coding for ion channels and ATPases are found in APA and in aldosterone-producing cell clusters. We investigated the genetic, cellular, and molecular heterogeneity of different aldosterone-producing structures in adrenals with APA, to get insight into the mechanisms driving their development and to investigate their clinical and biochemical correlates. Genetic analysis of APA, aldosterone-producing cell clusters, and secondary nodules was performed in adrenal tissues from 49 patients by next-generation sequencing following CYP11B2 immunohistochemistry. Results were correlated with clinical and biochemical characteristics of patients, steroid profiles, and histological features of the tumor and adjacent adrenal cortex. Somatic mutations were identified in 93.75% of APAs. Adenoma carrying KCNJ5 mutations had more clear cells and cells expressing CYP11B1, and fewer cells expressing CYP11B2 or activated β-catenin, compared with other mutational groups. 18-hydroxycortisol and 18-oxocortisol were higher in patients carrying KCNJ5 mutations and correlated with histological features of adenoma; however, mutational status could not be predicted using steroid profiling. Heterogeneous CYP11B2 expression in KCNJ5-mutated adenoma was not associated with genetic heterogeneity. Different mutations were identified in secondary nodules expressing aldosterone synthase and in independent aldosterone-producing cell clusters from adrenals with adenoma; known KCNJ5 mutations were identified in 5 aldosterone-producing cell clusters. Genetic heterogeneity in different aldosterone-producing structures in the same adrenal suggests complex mechanisms underlying APA development.

Different Somatic Mutations in Multinodular Adrenals With Aldosterone-Producing Adenoma

Primary aldosteronism is the most common form of secondary hypertension. Somatic mutations in KCNJ5, ATP1A1, ATP2B3, and CACNA1D are found in aldosterone-producing adenoma. In addition, adrenals with aldosterone-producing adenomas show cortical remodeling and frequently multiple secondary nodules. Our aim was to investigate whether different aldosterone-producing nodules from the same adrenal share the same mutational status. Aldosterone synthase expression was assessed in multinodular adrenals from 27 patients. DNA of 37 aldosterone-producing secondary nodules was extracted from formalin-fixed paraffin-embedded tissues and genotyped for KCNJ5, ATP1A1, ATP2B3, and CACNA1D mutations. Among 17 adrenals with a somatic mutation in the principal nodule, 4 showed the same mutation in a secondary nodule, whereas 10 had no mutation in any of the known genes. In 1 adrenal harboring the KCNJ5 p.Gly151Arg mutation in the principal nodule, the same mutation was present in 2 secondary nodules, but no mutation was found in a third nodule. Finally, in 2 adrenals with a CACNA1D mutation in the principal nodule, a KCNJ5 mutation was identified in the secondary nodule. Among 10 adrenals without mutations in the principal nodule, 1 carried a KCNJ5 mutation in the secondary nodule. No mutations were detected in 7 aldosterone-producing cell clusters from 6 adrenals. No association was observed between the presence of mutations in secondary nodules and clinical parameters. In conclusion, different mutations are found in different aldosterone-producing nodules from the same adrenal, suggesting that somatic mutations are independent events triggered by mechanisms that remain to be identified.

The Warburg effect is genetically determined in inherited pheochromocytomas

The Warburg effect describes how cancer cells down-regulate their aerobic respiration and preferentially use glycolysis to generate energy. To evaluate the link between hypoxia and Warburg effect, we studied mitochondrial electron transport, angiogenesis and glycolysis in pheochromocytomas induced by germ-line mutations in VHL, RET, NF1 and SDH genes. SDH and VHL gene mutations have been shown to lead to the activation of hypoxic response, even in normoxic conditions, a process now referred to as pseudohypoxia. We observed a decrease in electron transport protein expression and activity, associated with increased angiogenesis in SDH- and VHL-related, pseudohypoxic tumors, while stimulation of glycolysis was solely observed in VHL tumors. Moreover, microarray analyses revealed that expression of genes involved in these metabolic pathways is an efficient tool for classification of pheochromocytomas in accordance with the predisposition gene mutated. Our data suggest an unexpected association between pseudohypoxia and loss of p53, which leads to a distinct Warburg effect in VHL-related pheochromocytomas.