New advances in endocrine hypertension: from genes to biomarkers

Hypertension (HT) is a major cardiovascular risk factor that affects 10% to 40% of the general population in an age-dependent manner. Detection of secondary forms of HT is particularly important because it allows the targeted management of the underlying disease. Among hypertensive patients, the prevalence of endocrine HT reaches up to 10%. Adrenal diseases are the most frequent cause of endocrine HT and are associated with excess production of mineralocorticoids (mainly primary aldosteronism), glucocorticoids (Cushing syndrome), and catecholamines (pheochromocytoma). In addition, a few rare diseases directly affecting the action of mineralocorticoids and glucocorticoids in the kidney also lead to endocrine HT. Over the past years, genomic and genetic studies have allowed improving our knowledge on the molecular mechanisms of endocrine HT. Those discoveries have opened new opportunities to transfer knowledge to clinical practice for better diagnosis and specific treatment of affected subjects. In this review, we describe the physiology of adrenal hormone biosynthesis and action, the clinical and biochemical characteristics of different forms of endocrine HT, and their underlying genetic defects. We discuss the impact of these discoveries on diagnosis and management of patients, as well as new perspectives related to the use of new biomarkers for improved patient care.

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.

Deletion of a conserved Gata2 enhancer impairs haemogenic endothelium programming and adult Zebrafish haematopoiesis

Gata2 is a key transcription factor required to generate Haematopoietic Stem and Progenitor Cells (HSPCs) from haemogenic endothelium (HE); misexpression of Gata2 leads to haematopoietic disorders. Here we deleted a conserved enhancer (i4 enhancer) driving pan-endothelial expression of the zebrafish gata2a and showed that Gata2a is required for HE programming by regulating expression of runx1 and of the second Gata2 orthologue, gata2b. By 5 days, homozygous gata2aΔi4/Δi4 larvae showed normal numbers of HSPCs, a recovery mediated by Notch signalling driving gata2b and runx1 expression in HE. However, gata2aΔi4/Δi4 adults showed oedema, susceptibility to infections and marrow hypo-cellularity, consistent with bone marrow failure found in GATA2 deficiency syndromes. Thus, gata2a expression driven by the i4 enhancer is required for correct HE programming in embryos and maintenance of steady-state haematopoietic stem cell output in the adult. These enhancer mutants will be useful in exploring further the pathophysiology of GATA2-related deficiencies in vivo.