Endocrine Abstracts

Objective: Aldosterone-producing adenomas (APA) are a major cause of primary aldosteronism. Somatic mutations explain the excess aldosterone production in the majority of patients with APA with mutations in KCNJ5 encoding a potassium channel the most prevalent in most reported populations. Mechanisms driving cell proliferation are largely undefined.

Design and method: Quantitative transcriptome analysis using RNA-seq was used to identify differentially expressed genes between macro-APAs (n = 9, diameter ≥ 30 mm) and micro-APAs (n = 12, diameter ≤10 mm). Validation of RNA-seq data by TaqMan real-time PCR was performed for 14 genes in a broader cohort of APAs (NMD, no mutation detected, n = 28; KCNJ5-mutated, n = 43).

Results: Hierarchical cluster analysis of the 500 genes with largest coefficient of variation indicated sample clustering based on genotype (KCNJ5 or NMD) and APA diameter. Differential expression of 155 and 348 genes was found between micro- and macro-APAs with KCNJ5 mutations and NMD, respectively. Among the top 5 overrepresented Gene Ontology terms (biological process), cell death was exclusively enriched in NMD micro- vs NMD macro-APAs. The expression levels of 10 genes were validated with a potential function related to cell growth. Expression of BEX1 (a reported tumour suppressor) was 2.8-fold down regulated in macro-APAs relative to micro-APAs (P < 0.001), and a linear negative correlation of BEX1 expression with APA diameter was observed in NMD APAs (r = −0.501, P = 0.007). A human adrenocortical cell line with stable expression of BEX1 was established and showed that BEX1 induced a reduction in cell viability (difference P < 0.01 from control cells) and an increase in aldosterone production (2.9-fold increase, difference P < 0.0001 from control cells).

Conclusions: PA display distinct transcriptome profiles according to adenoma diameter and we show a potential dual function for BEX1 in APA pathophysiology in adrenocortical cell growth and aldosterone production.