BEX1 Is Differentially Expressed in Aldosterone-Producing Adenomas and Protects Human Adrenocortical Cells From Ferroptosis

Abstract

Aldosterone-producing adenomas (APAs) are a major cause of primary aldosteronism. Somatic mutations in ion channels and transporters drive the aldosterone overproduction in the majority of APAs with mutations in the KCNJ5 G protein-coupled potassium channel predominating in most reported populations. Our objective was to gain insight into biological mechanisms of APA tumorigenesis by comparing transcriptomes of APAs of distinct sizes by mRNA sequencing analysis (9 APAs with adenoma diameter ≥30 mm versus 12 APAs ≤10 mm). Genes with significantly altered expression levels between these 2 groups were identified in APAs with no mutation detected (348 genes) and with a KCNJ5 mutation (155 genes). We validated the differential expression of 10 genes with a known function related to cell death and proliferation in an expanded sample set of 71 APAs by real-time quantitative polymerase chain reaction (58 macro-APAs, diameter ≥10 mm; 13 micro-APAs, diameter <10 mm). We focused on BEX1 that was upregulated in micro-APAs relative to macro-APAs (2.76-fold, P <0.001) and compared with paired adrenal cortex (3.85-fold, P <0.05), and showed a linear negative correlation with APA diameter in the no mutation detected group (r=−0.501, P =0.007). Compared with control cells, stable expression of BEX1 in human adrenocortical cells did not alter cell cycle progression or sensitivity to apoptosis but conferred protection from ferroptosis ( P <0.01), a form of regulated cell death, measured by flow cytometry. Taken together, these findings demonstrate that BEX1 promotes cell survival in adrenal cells by mediating the inhibition of ferroptosis and suggest a function for BEX1 in the pathogenesis of APAs.

Primary Aldosteronism: Metabolic Reprogramming and the Pathogenesis of Aldosterone-Producing Adenomas

“…It has been reported that adrenocortical cells are sensitive to ferroptosis-triggering agents, such as RSL3, which can inhibit GPX4 activity [17,45]. Indeed, our data showed elevated GPX4 expression in APAs compared with adjacent zona glomerulosa.…”

“…Furthermore, we demonstrated a functional link between lipid biology and ferroptosis. This is relevant because adrenocortical cells have previously been shown to be highly sensitive to cell death by ferroptosis due to the inhibition of glutathione biosynthesis (Figure 2A) [17,44,45]. Of note, the ferroptosis suppressor gene coding for glutamate-cysteine ligase catalytic subunit (GCLC) and the gene coding for stearoyl-CoA desaturase (SCD) are highly expressed in APAs compared with adjacent zona glomerulosa (Figure 2C).…”

“…The role of somatic mutations in constitutive aldosterone production is well defined, but many other mechanisms may modulate aldosterone production from APAs [10][11][12][13][14][15]. Regulated forms of cell death, including apoptosis [16] and ferroptosis [17], have also been implicated in the pathogenesis of APAs.…”

Transcriptomics, Epigenetics, and Metabolomics of Primary Aldosteronism

“…In particular, both micro-APAs and APAs present higher BEX1 expression with CACNA1D, ATP1A1 or non-KCNJ5 mutations. This gene is involved in ferroptosis, and it is hypothesized that increasing APA size leads to reduction of the need for anti-ferroptotic mechanisms [ 25 , 82 ].…”

Primary aldosteronism: Pathophysiological mechanisms of cell death and proliferation

“…To detect mechanisms of APA tumorigenesis, Yang et al. ( 73 ) compared APA transcriptomes of highly diverse sizes (9 macro APAs with adenoma diameter ≥30 mm versus 12 micro APAs ≤10 mm). Over-representation analysis of the transcriptome dataset from Yang et al.…”