Functional characterization of two novel germline mutations of the KCNJ5 gene in hypertensive patients without primary aldosteronism but with ACTH-dependent aldosterone hypersecretion

Genetic screening of hypertensive patients with aldosterone hypersecretion under conditions of stress

PURPOSE

Although ACTH is considered a secondary regulator of aldosterone production, patients with apparent essential hypertension have been treated with mineralocorticoid receptor antagonists (MRAs). In this study, we aimed to identify potentially damaging variants that might be implicated in the phenotype of a well-characterized cohort of 21 hypertensive patients without PA but with stress-induced aldosterone hypersecretion. The patients' blood pressure was normalized though MRA administration.

METHODS

Genetic screening was performed through whole-exome sequencing (WES), and variants in PA-associated or in ion-channels of aldosterone-regulating genes were prioritized. Variants with population frequency < 0.01, predicted to alter protein structure and classified as likely pathogenic by in silico tools, were retained.

RESULTS

Qualifying variants were identified in nine of the 21 patients screened. Seven patients were carriers of six potentially damaging variants in six genes associated with PA (KCNK9, KCNK5, ATP13A3, SLC26A2, CACNA1H, and CACNA1D). A novel variant in the KCNK9 gene (p.V221M) is reported. Our analysis revealed two variants in two novel susceptibility genes for aldosterone hypersecretion, namely, KCNK16 (p.P255H) and CACNA2D3 (p.V557I).

CONCLUSION

WES revealed potentially damaging germline variants in genes participating in aldosterone synthesis/regulating pathways in 9/21 patients of our cohort. The variants identified might play a role in aldosterone hypersecretion under conditions of stress. The potential pathogenicity of these variants should be examined in future functional studies.

Update on the Genetics of Primary Aldosteronism and Aldosterone-Producing Adenomas

PURPOSE OF THE REVIEW

Primary aldosteronism (PA) is the leading cause of secondary hypertension, accounting for over 10% of patients with high blood pressure. It is characterized by autonomous production of aldosterone from the adrenal glands leading to low-renin levels. The two most common forms arise from bilateral adrenocortical hyperplasia (BAH) and aldosterone-producing adenoma (APA). We discuss recent discoveries in the genetics of PA.

RECENT FINDINGS

Most APAs harbor variants in the KCNJ5, CACNA1D, ATP1A1, ATP2B3, and CTNNB1 genes. With the exception of β-catenin (CTNNB1), all other causative genes encode ion channels; pathogenic variants found in PA lead to altered ion transportation, cell membrane depolarization, and consequently aldosterone overproduction. Some of these genes are found mutated in the germline state (CYP11B2, CLCN2, KCNJ5, CACNA1H, and CACNA1D), leading then to familial hyperaldosteronism, and often BAH rather than single APAs. Several genetic defects in the germline or somatic state have been identified in PA. Understanding how these molecular abnormalities lead to excess aldosterone contributes significantly to the elucidation of the pathophysiology of low-renin hypertension. It may also lead to new and more effective therapies for this disease acting at the molecular level.

Cushing Syndrome in a Pediatric Patient With a KCNJ5 Variant and Successful Treatment With Low-dose Ketoconazole

CONTEXT

Pathogenic variants in KCNJ5, encoding the GIRK4 (Kir3.4) potassium channel, have been implicated in the pathogenesis of familial hyperaldosteronism type-III (FH-III) and sporadic primary aldosteronism (PA). In addition to aldosterone, glucocorticoids are often found elevated in PA in association with KCNJ5 pathogenic variants, albeit at subclinical levels. However, to date no GIRK4 defects have been linked to Cushing syndrome (CS).

PATIENT

We present the case of a 10-year-old child who presented with CS at an early age due to bilateral adrenocortical hyperplasia (BAH). The patient was placed on low-dose ketoconazole (KZL), which controlled hypercortisolemia and CS-related signs. Discontinuation of KZL for even 6 weeks led to recurrent CS.

RESULTS

Screening for known genes causing cortisol-producing BAHs (PRKAR1A, PRKACA, PRKACB, PDE11A, PDE8B, ARMC5) failed to identify any gene defects. Whole-exome sequencing showed a novel KCNJ5 pathogenic variant (c.506T>C, p.L169S) inherited from her father. In vitro studies showed that the p.L169S variant affects conductance of the Kir3.4 channel without affecting its expression or membrane localization. Although there were no effects on steroidogenesis in vitro, there were modest changes in protein kinase A activity. In silico analysis of the mutant channel proposed mechanisms for the altered conductance.

CONCLUSION

We present a pediatric patient with CS due to BAH and a germline defect in KCNJ5. Molecular investigations of this KCNJ5 variant failed to show a definite cause of her CS. However, this KCNJ5 variant differed in its function from KCNJ5 defects leading to PA. We speculate that GIRK4 (Kir3.4) may play a role in early human adrenocortical development and zonation and participate in the pathogenesis of pediatric BAH.

Unravelling the Genetic Basis of Primary Aldosteronism

Primary aldosteronism (PA), a condition characterized by autonomous aldosterone hypersecretion, constitutes the most common cause of secondary hypertension. Over the last decade, major breakthroughs have been made in the field of genetics underpinning PA. The advent and wide application of Next Generation Sequencing (NGS) technology led to the identification of several somatic and germline mutations associated with sporadic and familial forms of PA. Somatic mutations in ion-channel genes that participate in aldosterone biosynthesis, including KCNJ5, CACNA1D, ATP1A1, and ATP2B3, have been implicated in the development of aldosterone-producing adenomas (APAs). On the other hand, germline variants in CLCN2, KCNJ5, CACNA1H, and CACNA1D genes have been implicated in the pathogenesis of the familial forms of PA, FH-II, FH-III, and F-IV, as well as PA associated with seizures and neurological abnormalities. However, recent studies have shown that the prevalence of PA is higher than previously thought, indicating the need for an improvement of our diagnostic tools. Further research is required to recognize mild forms of PA and to investigate the underlying molecular mechanisms.

Hereditary causes of primary aldosteronism and other disorders of apparent excess mineralocorticoid activity

Secondary hypertension is a common condition with a broad differential diagnosis. Identification of the true cause of hypertension can be critical for guiding appropriate management. Here, we review hereditary conditions underlying the most common cause of secondary hypertension, primary aldosteronism, as well as other disorders impacting various levels of mineralocorticoid action. Recently, several pathogenic variants of ion channels have been described as etiologies of familial aldosteronism. Defects in steroid hormone synthesis cause hypertension in 11β-hydroxylase deficiency and 17α-hydroxylase deficiency, two types of congenital adrenal hyperplasia. Inappropriate activation of mineralocorticoid receptors underlies the syndrome of apparent mineralocorticoid excess and constitutive activation of the mineralocorticoid receptor. Finally, Liddle syndrome and pseudohypoaldosteronism type 2 are disorders impacting the function of renal sodium channels, the endpoint of mineralocorticoid action. We discuss the pathophysiology, clinical presentation, diagnosis and management of these low renin hypertension states that ultimately result in apparent excess mineralocorticoid activity.

Drugena: A Fully Automated Immunoinformatics Platform for the Design of Antibody-Drug Conjugates Against Neurodegenerative Diseases

Antibodies are proteins that are the first line of defense in the adaptive immune response of vertebrates. Thereby, they are involved in a multitude of biochemical mechanisms and clinical manifestations with significant medical interest, such as autoimmunity, the regulation of infection, and cancer. An emerging field in antibody science that is of huge medicinal interest is the development of novel antibody-interacting drugs. Such entities are the antibody-drug conjugates (ADCs), which are a new type of targeted therapy, which consist of an antibody linked to a payload drug. Overall, the underlying principle of ADCs is the discerning delivery of a drug to a target, hoping to increase the potency of the original drug. Drugena suite is a pioneering platform that employs state-of-the-art computational biology methods in the fight against neurodegenerative diseases using ADCs. Drugena encompasses an up-to-date structural database of specialized antibodies for neurological disorders and the NCI database with over 96 million entities for the in silico development of ADCs. The pipeline of the Drugena suite has been divided into several steps and modules that are closely related with a synergistic fashion under a user-friendly graphical user interface.

Antibody Clustering Using a Machine Learning Pipeline that Fuses Genetic, Structural, and Physicochemical Properties

Antibody V domain clustering is of paramount importance to a repertoire of immunology-related areas. Although several approaches have been proposed for antibody clustering, still no consensus has been reached. Numerous attempts use information from genes, protein sequences, 3D structures, and 3D surfaces in an effort to elucidate unknown action mechanisms directly related to their function and to either link them directly to diseases or drive the discovery of new medicines, such as antibody drug conjugates (ADC). Herein, we describe a new V domain antibody clustering method based on the comparison of the interaction sites between each antibody and its antigen. A more specific clustering analysis of the antibody's V domain was provided using deep learning and data mining techniques. The multidimensional information was extracted from the structural resolved antibodies when they were captured to interact with other proteins. The available 3D structures of protein antigen-antibody (Ag-Ab) interfaces contain information about how antibody V domains recognize antigens as well as about which amino acids are involved in the recognition. As such, the antibody surface holds information about antigens' folding that reside with the Ab-Ag interface residues and how they interact. In order to gain insight into the nature of such interactions, we propose a new simple philosophy to transform the conserved framework (fragment regions, complementarity-determining regions) of antibody V domain in a binary form using structural features of antibody-antigen interactions, toward identifying new antibody signatures in V domain binding activity. Finally, an advanced three-level hybrid classification scheme has been set for clustering antibodies in subgroups, which can combine the information from the protein sequences, the three-dimensional structures, and specific "key patterns" of recognized interactions. The clusters provide multilevel information about antibodies and antibody-antigen complexes.

Structural Study of the DNA: Clock/Bmal1 Complex Provides Insights for the Role of Cortisol, hGR, and HPA Axis in Stress Management and Sleep Disorders

Herein, we deploy an in silico pipeline of structural bioinformatics, thermodynamics, and molecular dynamics to investigate the role of cortisol in circadian rhythms, biorhythms, stress response, and even sleep disorders. Our study shows that high concentrations of cortisol intercalate in the minor groove of DNA. This phenomenon widens the adjacent major grooves and provides the Clock/Bmal1 complex with more space to dock and interact with DNA. Then, the strong charges of cortisol pull the alpha helices of the Clock/Bmal1 complex and bend it inward, thus establishing stronger interactions and prolonged signaling. Our results indicate that elevated cortisol levels play an important role in stress, inflammation, and sleep disorders as a result of prolonged and stronger dsDNA - Clock/Bmal1 interactions.

Olive Oil Polyphenols in Neurodegenerative Pathologies

Neurodegenerative diseases lead to the death of nerve cells in the brain or the spinal cord. A wide range of diseases are included within the group of neurodegenerative disorders, with the most common ones being dementia, Alzheimer's, and Parkinson's diseases. Millions of older people are suffering from such pathologies. The global increase of life expectancy unavoidably leads to a consequent increase in the number of people who will be at some degree affected by neurodegenerative-related diseases. At this moment, there is no effective therapy or treatment that can reverse the loss of neurons. A growing number of studies highlight the value of the consumption of medical foods, and in particular olive oil, as one of the most important components of the Mediterranean diet. A diet based on extra virgin olive oil seems to contribute toward the lowering of risk of age-related pathologies due to high phenol concentration. The link of a polyphenol found in extra virgin olive oil, namely, tyrosol, with the protein tyrosinase, associated to Parkinson's disease is underlined as a paradigm of affiliation between polyphenols and neurodegenerative disorders.

An update on adrenal endocrinology: significant discoveries in the last 10 years and where the field is heading in the next decade

The last 10 years have produced an amazing number of significant discoveries in the field of adrenal endocrinology. The development of the adrenal gland was linked to specific molecules. Cortisol-producing lesions were associated mostly with defects of the cyclic AMP (cAMP) signaling pathway, whereas aldosterone-producing lesions were found to be the result of defects in aldosterone biosynthesis or the potassium channel KCNJ5 and related molecules. Macronodular adrenal hyperplasia was linked to ARMC5 defects and new genes were found to be involved in adrenocortical cancer (ACC). The succinate dehydrogenase (SDH) enzyme was proven to be the most important molecular pathway involved in pheochromocytomas, along with several other genes. Adrenomedullary tumors are now largely molecularly elucidated. Unfortunately, most of these important discoveries have yet to produce new therapeutic tools for our patients with adrenal diseases: ACC in its advanced stages remains largely an untreatable disorder and malignant pheochromocytomas are equally hard to treat. Thus, the challenge for the next 10 years is to translate the important discoveries of the previous decade into substantial advances in the treatment of adrenal disorders and tumors.

Of channels and pumps: different ways to boost the aldosterone?

The mineralocorticoid aldosterone is a major factor controlling the salt and water balance and thereby also the arterial blood pressure. Accordingly, primary aldosteronism (PA) characterized by an inappropriately high aldosterone secretion is the most common form of secondary hypertension. The physiological stimulation of aldosterone synthesis in adrenocortical glomerulosa cells by angiotensin II and an increased plasma K⁺ concentration depends on a membrane depolarization and an increase in the cytosolic Ca²⁺ activity. Recurrent gain-of-function mutations of ion channels and transporters have been identified in a majority of cases of aldosterone-producing adenomas and in familial forms of PA. In this review, the physiological role of these genes in the regulation of aldosterone synthesis and the altered function of the mutant proteins as well are described. The specific changes of the membrane potential and the cellular ion homoeostasis in adrenal cells expressing the different mutants are compared, and their impact on autonomous aldosterone production and proliferation is discussed.

Genetic screening in arterial hypertension

Studies involving adoptive families and twins have demonstrated the genetic basis of hypertension and shown that genetic factors account for about 40% of the variance in blood pressure among individuals. Arterial hypertension is genetically complex: multiple genes influence the blood pressure phenotype through allelic effects from single genes and gene-gene interactions. Moreover, environmental factors also modify the blood pressure phenotype. This complexity explains why the identification of the underlying genes has not been as successful in hypertension as in other diseases (such as type 1 and type 2 diabetes mellitus). The identification of the genetic determinants of hypertension has been most successful in endocrine forms of hypertension, which have well-defined phenotypes that permit a precise patient stratification into homogeneous cohorts. A promising area for the application of genetic testing to personalized medicine is the prediction of responses and adverse reactions to antihypertensive drugs. The identification of genetic markers of drug response will enable the design of randomized controlled trials in much smaller series of patients than is currently possible, decreasing the costs and times from drug design to clinical use and ultimately providing patients and doctors with a larger number of tools to combat hypertension, the most important risk factor for cardiovascular disease. This Review focuses on the rapidly developing field of genetic testing in patients with arterial hypertension.

Familial hyperaldosteronism type III

Primary aldosteronism is the most common form of endocrine hypertension. This disorder comprises both sporadic and familial forms. Four familial forms of primary aldosteronism (FH-I to FH-IV) have been described. FH-III is caused by germline mutations in KCNJ5, encoding the potassium channel Kir3.4 (also called GIRK4). These mutations alter the selectivity filter of the channel and lead to abnormal ion currents with loss of potassium selectivity, sodium influx and consequent increased intracellular calcium that causes excessive aldosterone biosynthesis. To date, eleven families have been reported, carrying six different mutations. Although the clinical features are variable, FH-III patients often display severe hyperaldosteronism with an early onset, associated with hypokalemia and diabetes insipidus-like symptoms. In most cases FH-III patients are resistant to pharmacological therapy and require bilateral adrenalectomy to control symptoms. In the present manuscript, we review the genetics and pathological basis of FH-III, the diagnostic work-up, clinical features and therapeutic management. Finally, we will describe a new case of FH-III of an Italian patient carrying a Gly151Arg mutation.