Genomic Approaches to Understanding Primary Aldosteronism

Presentation Number: SAT-54
Date of Presentation: June 15th, 2013

Namita Hattangady*1, Fumitoshi Satoh2, Ryo Morimoto2, Hironobu Sasano2, Yasuhiro Nakamura2, Franco Mantero3, Maria Verena Cicala3, Raffaele Pezzani3, Beatrice Rubin3, Hirotaka Shibata4, Isao Kurihara5, Richard J. Auchus1, Tobias Else1, Thomas J Giordano1 and William E Rainey1
1University of Michigan, Ann Arbor, MI, 2Tohoku University Hospital, Sendai, Japan, 3University of Padova, Padova, Italy, 4Keio University, School of Medicine, Tokyo, Japan, 5School of Medicine, Keio University, Tokyo, Japan

Abstract

Introduction: Primary aldosteronism (PA) causes almost 8% of hypertension and is often caused by adrenal aldosterone-producing adenomas (APA).  Recently, somatic mutations in the KCNJ5 potassium channel were shown to cause dysregulation of aldosterone production in APA. The objective of our study was to compare the transcriptomes of normal adrenals (NA) and APA with/without KCNJ5 mutations, and to determine the prevalence of KCNJ5 mutations in an expanded cohort of NA and APA.

Methods: RNA was isolated from 111 APA and 28 NA tissue samples. Sanger sequencing was performed on cDNA to categorize APA as harboring wild type (WT) or mutant KCNJ5 for prevalence studies. Further, RNA from 61 APA (33 KCNJ5 mutants, 28 WT APA) and 28 NA was analyzed using Illumina microarray. Statistical analyses included unpaired T test (p≤0.001; all APA vs. NA) and One Way ANOVA (p≤0.001; WT APA vs. KCNJ5 mutant APA vs. NA) and included genes up-regulated by ≥1.5-fold.

Results: KCNJ5 mutations had an overall prevalence of 44 % in APA, with a higher prevalence in women (59 %) than men (27 %). Microarray comparison of all APA samples with NA revealed a significant increase in the expression of 294 transcripts. Comparison of NA separately with KCNJ5 mutant and WT tumors revealed a larger number of differentially expressed transcripts in mutant tumors (344 vs. 147 genes, respectively). Furthermore, comparison KCNJ5 mutant and WT APA indicated 63 differentially expressed genes. In all these analyses, CYP11B2 (aldosterone synthase) appeared as the top-most upregulated gene in APA (5-fold in WT and 15-fold in KCNJ5 mutant APA vs. NA; 3-fold in KCNJ5 mutant vs. WT APA). KCNJ5 expression was higher 2-fold in all APA (as compared to NA), and also 2-fold higher in KCNJ5 mutant vs. WT APA. Other interesting genes upregulated in both KCNJ5 mutant and WT APA include selective G protein coupled receptors including MC2R, GPRC5C and HTR4, as well as genes normally expressed in the adrenal glomerulosa including PCP4, PLD5 and HOPX.

Conclusion: Our results indicate considerable overlap between the transcriptome changes in WT and KCNJ5 mutant APA, suggesting similar downstream genetic alternations in the formation of APA and/or the dysregulation of aldosterone secretion. However, the findings also suggest that KCNJ5 mutant APA have increased capacity to produce aldosterone when compared to WT APA. Functional analyses of candidate genes could increase understanding of the molecular mechanisms of PA.

 

Nothing to Disclose: NH, FS, RM, HS, YN, FM, MVC, RP, BR, HS, IK, RJA, TE, TJG, WER