Background: Primary Aldosteronism (PA) is the commonest curable cause of hypertension. Whole exome sequencing (WES) of an aldosterone producing adenoma from a 46-year-old man with resistant hypertension revealed a novel somatic mutation (Val380Asp) of the single transmembrane domain of Cell Adhesion Molecule-1 (CADM1). A Gly379Asp mutation was identified by WES of a PA patient in Munich. Both patients were cured of hypertension by adrenalectomy.
Method: Adrenocortical (H295R) cells were transduced with wild-type (WT) and mutant CADM1 to assess changes in aldosterone production. Previous studies showed CADM1 to regulate gap junctions (GJ) in islet cells. This was assessed in H295R cells by dye transfer. The effect of inhibiting GJs was also interrogated. Finally WT or mutant cells were co-transfected with CX-43 tagged by mApple or Venus fluorophores and mixed, allowing confocal visualisation of GJ formation between adjacent cells.
Results: Cells transduced with mutant CADM1 showed 3-6-fold increase in aldosterone secretion (P<0.0001) and 10-20-fold increase in CYP11B2 expression (P<0.0001). Transfer of calcein (a GJ-permeable dye) was reduced between mutant CADM1 cells, compared to untransfected or WT cells (P<0.001). Inhibition of CX-43 caused 2-fold increase in aldosterone secretion, 8-fold (<0.05) increase in CYP11B2 expression. Protein modelling suggested that mutations increased the angle of ectodomains to cell membrane, from 49° in WT, to 62° and 90° in Gly379Asp and Val380Asp respectively, increasing inter-cell distance from 21.2 nm to 24.7 and 27.9 nm. A role of CADM1 may be to bring opposing CX-43 hemichannels close enough to form GJ channels. Mixing of fluorescent-tagged CX-43 cells showed fewer intact GJ channels in CADM1-mutant cells.
Conclusion: Discovery of the CADM1 mutation reaffirms the importance of membrane proteins in aldosterone regulation, although CADM1s impact on cation traffic is indirect. The role of cell-adhesion in regulating GJs suggests a role for these in the regulation of aldosterone by oscillating Ca2+ currents.