Primary Aldosteronism Takes (KCNJ)Five!
Maria-Christina Zennaro
Institut National de la Santé et de la Recherche Médicale, Unité Mixte de Recherche Scientifique-970, Paris Cardiovascular Research Center, Paris, France; Université Paris Descartes, Sorbonne Paris Cité; and Assistance Publique-Hôpitaux de Paris, Hôpital Européen Georges Pompidou, 75015 Paris, France
P rimary aldosteronism (PA) is the most common form of endocrine hypertension, due to autonomous aldo- sterone production from the adrenal cortex. Patients with PA typically present with hypertension, high plasma al- dosterone levels associated with low plasma renin activity, and varying degrees of hypokalemia and metabolic alka- losis (1). The prevalence of PA increases with the severity of hypertension and is currently estimated around 10% in referred patients and 4% in primary care (2, 3) but as high as 20% in patients with resistant hypertension (4, 5). The two main causes of PA are aldosterone-producing ade- noma (APA) and bilateral adrenal hyperplasia (BAH), also called idiopathic hyperaldosteronism. Efficient and timely screening for PA is of major importance, given the severe cardiovascular outcome of aldosterone excess that is in- dependent of blood pressure levels (6, 7). Yet, the patho- genic mechanisms leading to aldosterone hypersecretion and cell proliferation are largely unknown.
Recently, a few recurrent somatic mutations of the po- tassium inwardly-rectifying channel, subfamily J, member 5 (KCNJ5) gene, coding for the potassium channel Kir3.4, have been implicated as a cause of APA, whereas an in- herited mutation was identified in a family with a Men- delian form of early severe hypertension that features mas- sive adrenal hyperplasia and is referred to as familial hyperaldosteronism type 3 (FH3) (8, 9). These mutations all lie near or within the selectivity filter of the Kir3.4 channel; they result in a loss of channel selectivity, with increased sodium conductance leading to membrane depo- larization. These changes are presumed to be responsible for constitutive aldosterone secretion and cell proliferation by promoting opening of membrane voltage-dependent cal- cium channels that is followed by activation of the calcium
signaling pathway, the main trigger for aldosterone pro- duction in adrenal zona glomerulosa cells. In this issue of Endocrinology, Oki et al. (10) now formally establish a causal relationship between KCNJ5 mutations and hyperal- dosteronism. They demonstrate that the inherited KCNJ5 T158A mutation produces a marked stimulation in aldo- sterone biosynthesis that is dependent on membrane de- polarization followed by calcium influx into adrenal cor- tical carcinoma cells (10).
The paper by Oki et al. (10) indeed tackles a central issue that had not previously been addressed, i.e. the causal link between KCNJ5 mutations, membrane depo- larization, aldosterone overproduction, and cell prolifer- ation. By transiently infecting adrenocortical HAC15 cells with a lentivirus expressing wild-type KCNJ5 (potassium inwardly-rectifying channel, subfamily J, member 5) or mutated KCNJ5 T158A, the authors show that expression of channels harboring the T158A mutation potentiated basal aldosterone production, which was further stimu- lated by angiotensin II and the protein kinase A activator forskolin. Using different fluorescent dyes, they confirmed the enhanced sodium influx through the mutated Kir3.4 channel, leading to membrane depolarization and in- creased intracellular calcium concentrations. KCNJ5 T158A-transduced cells presented significantly increased expression of CYP11B2, the gene coding for aldosterone synthase, which ensures the last three enzymatic steps of aldosterone biosynthesis. Expression of CYP11B1, cod- ing for 11ß-hydroxylase, was also increased, as was basal and stimulated cortisol production. KCNJ5 T158A also induced significant production of 18-oxocortisol, a hybrid steroid largely produced in affected members of the orig- inal family with FH3 (11). CYP11B2 expression and al-
ISSN Print 0013-7227 ISSN Online 1945-7170 Printed in U.S.A. Copyright @ 2012 by The Endocrine Society
doi: 10.1210/en.2012-1146 Received February 7, 2012. Accepted February 13, 2012.
dosterone production were both inhibited by calcium channel antagonists and calmodulin inhibitors, confirm- ing the mechanistic link to activation of the calcium sig- naling pathway.
Although these results confirm the pathogenic role of the KCNJ5 T158A mutation in promoting aldosterone overproduction, the same does not hold true for its effects on cell proliferation. Indeed, KCNJ5 T158A had an in- hibitory effect (~30% reduction) on HAC15 cell prolif- eration, in stably infected cells, an effect that was not due to increased apoptosis and was unrelated to calcium sig- naling. Interestingly, a similar negative effect of KCNJ5 mutations on cell proliferation was recently described for two other mutants. The KCNJ5 G151R mutation is one of the recurrent somatic mutations found in APA and has recently been described as inherited mutation in two fam- ilies with early onset, severe progressive hyperaldosteron- ism and adrenal cortex hyperplasia, requiring bilateral ad- renalectomy in childhood to control blood pressure (12). Despite this adrenal phenotype, in vitro studies demon- strated that the G151R mutation significantly reduced cell survival when transfected into human embryonic kidney 293T cells. A second mutation affecting the same amino acid, G151E, was recently described in a family diagnosed with non-glucocorticoid-remediable familial hyperaldo- steronism (13). This mutation was associated with a much milder phenotype of the two affected family members, compared with classical FH3, with blood pressure levels and hypokalemia easily corrected by medical therapy. Re- markably, the adrenals appeared normal by computed to- mography scanning, and hybrid steroids were produced at a rate comparable to that of other patients with sporadic PA. Again, the KCNJ5 G151E mutant channel was sim-
ilarly permeable for sodium and potassium, resulting in depolarization of the plasma membrane and a continuous sodium influx (13). The KCNJ5 G151E mutation was re- ported in two additional families with early-onset hyper- aldosteronism of unknown cause (12). These subjects also had easily controlled hypertension and no evidence of ad- renal hyperplasia. Remarkably enough, in this study, KCNJ5 G151E channels produced a much larger sodium conductance compared with KCNJ5 G151R, resulting in rapid sodium-dependent cell lethality (12). Although G151E carriers do not present adrenal cortex hyperplasia, indicating that the mutation may limit adrenocortical cell proliferation yet promoting aldosterone overproduction, it is difficult to conceive how the G151R mutation, which also leads to reduced cell survival in the same study, in- duces BAH when inherited and APA formation when oc- curring somatically. Based on these studies and the work by Oki et al. (10), it remains therefore unclear whether and how KCNJ5 mutations are responsible for increased cell proliferation. Alternatively, the observed effects raise the possibility that KCNJ5 mutations are responsible for al- dosterone hypersecretion, whereas increased cell prolifer- ation is triggered by other, yet to be identified, mecha- nisms. Consistent with this hypothesis is the observation that inactivation of several relevant adrenal potassium channels in mice leads to increased aldosterone produc- tion, but not to adrenal cortex hyperplasia or APA for- mation (Table 1).
Somatic KCNJ5 mutations have been demonstrated to be present in a large proportion of patients with APA, with an estimated prevalence in unselected patients of approx- imately 34% (14) and even higher frequencies described depending on the sample size, the screening procedures for
| TABLE 1. Mouse models inactivated for potassium channels featuring adrenal aldosterone hypersecretion | |||||
|---|---|---|---|---|---|
| Inactivated channel (gene) | A phenotype | Adrenal cortex expression | Hyperplasia/ APA | Gender difference described | Refs. |
| MaxiK (KCNMA1/KCNMB1) | KCNMA1 KO: hyperaldosteronism, hypokalemia, normal renin levels; KCNMB1 KO: hyperaldosteronism linked to renal K retention and hyperkalemia | KCNMA1: ZGZF, ZR KCNMB1: adrenal gland | No | No | 17, 18 |
| TASK1 (KCNK3) | Glucocorticoid-remediable hyperaldosteronism, decreased plasma renin, hypokalemia | ZG, ZF, ZR | No | Females only | 19 |
| TASK1/TASK3 (KCNK3/KCNK9) | Hyperaldosteronism, reduced plasma renin | TASK3: ZG | No | No | 20 |
| KvLQT1/ISK (KCNQ1/KCNE1) | Hyperaldosteronism in KCNE1 KO mice, normal renin, fecal sodium and potassium loss | ZG (KCNQ1, KCNE1) | No | No | 21 |
KO, Knockout; MaxiK, large-conductance, voltage- and Ca2-dependent potassium channel; TASK, TWIK-related acid sensitive potassium channel; KvLQT1/IsK, voltage-dependent potassium channel responsible for slowly activating delayed potassium current lks; ZG, zona glomerulosa; ZF, zona fasciculata; ZR, zona reticularis.
selecting patients for adrenalectomy, and genetic back- ground (15, 16). However, although germinal KCNJ5 mutations are responsible for inherited forms of familial hyperaldosteronism, they are not similarly causative for sporadic BAH (14). Even though unilateral adrenalec- tomy represents the treatment of choice for PA in special- ized departments, the fact that only 30% of operated pa- tients are cured and that a subset of patients don’t even go into surgery because of the multitiered process for subtype identification, sets medical treatment as an attractive ther- apeutic option even in lateralized forms of PA. Kir3.4 po- tassium channels may thus represent interesting new drug targets for a subset of APA not eligible for surgery. Cell as well as animal models expressing mutant Kir3.4 channels may provide valuable tools to address the functional con- sequences of KCNJ5 mutations, allowing us to further dissect the mechanistic determinants of aldosterone over- production and increased cell proliferation in PA.
Acknowledgments
Address all correspondence and requests for reprints to: Maria-Christina Zennaro, M.D., Ph.D., Institut National de la Santé et de la Recherche Médicale Unité 970, Paris Car- diovascular Research Center, 56 rue Leblanc, 75015 Paris, France. E-mail: maria-christina.zennaro@inserm.fr.
Disclosure Summary: The author has nothing to disclose.
References
1. Funder JW, Carey RM, Fardella C, Gomez-Sanchez CE, Mantero F, Stowasser M, Young Jr WF, Montori VM 2008 Case detection, diagnosis, and treatment of patients with primary aldosteronism: an Endocrine Society clinical practice guideline. J Clin Endocrinol Metab 93:3266-3281
2. Hannemann A, Wallaschofski H 1 December 2011 Prevalence of primary aldosteronism in patient’s cohorts and in population-based studies: a review of the current literature. Horm Metab Res 10.1055/ s-0031-1295438
3. Plouin PF, Amar L, Chatellier G 2004 Trends in the prevalence of primary aldosteronism, aldosterone-producing adenomas, and sur- gically correctable aldosterone-dependent hypertension. Nephrol Dial Transplant 19:774-777
4. Douma S, Petidis K, Doumas M, Papaefthimiou P, Triantafyllou A, Kartali N, Papadopoulos N, Vogiatzis K, Zamboulis C 2008 Prev- alence of primary hyperaldosteronism in resistant hypertension: a retrospective observational study. Lancet 371:1921-1926
5. Calhoun DA, Nishizaka MK, Zaman MA, Thakkar RB, Weissmann P 2002 Hyperaldosteronism among black and white subjects with resistant hypertension. Hypertension 40:892-896
6. Rossi GP, Sechi LA, Giacchetti G, Ronconi V, Strazzullo P, Funder JW 2008 Primary aldosteronism: cardiovascular, renal and meta- bolic implications. Trends Endocrinol Metab 19:88-90
7. Milliez P, Girerd X, Plouin PF, Blacher J, Safar ME, Mourad JJ 2005 Evidence for an increased rate of cardiovascular events in patients with primary aldosteronism. J Am Coll Cardiol 45:1243-1248
8. Choi M, Scholl UI, Yue P, Björklund P, Zhao B, Nelson-Williams C,
Ji W, Cho Y, Patel A, Men CJ, Lolis E, Wisgerhof MV, Geller DS, Mane S, Hellman P, Westin G, Åkerström G, Wang W, Carling T, Lifton RP 2011 K+ channel mutations in adrenal aldosterone-producing adeno- mas and hereditary hypertension. Science 331:768-772
9. Mulatero P 2008 A new form of hereditary primary aldosteronism: familial hyperaldosteronism type III. J Clin Endocrinol Metab 93: 2972-2974
10. Oki K, Plonczynski MW, Lam ML, Gomez-Sanchez EP, Gomez- Sanchez CE 2012 Potassium channel mutant KCNJ5 T158A ex- pression in HAC-15 cells increases aldosterone synthesis. Endocri- nology 153:1774-1782
11. Geller DS, Zhang J, Wisgerhof MV, Shackleton C, Kashgarian M, Lifton RP 2008 A novel form of human Mendelian hypertension featuring nonglucocorticoid-remediable aldosteronism. J Clin En- docrinol Metab 93:3117-3123
12. Scholl UI, Nelson-Williams C, Yue P, Grekin R, Wyatt RJ, Dillon MJ, Couch R, Hammer LK, Harley FL, Farhi A, Wang WH, Lifton RP 2012 Hypertension with or without adrenal hyperplasia due to different inherited mutations in the potassium channel KCNJ5. Proc Natl Acad Sci USA 109:2533-2538
13. Mulatero P, Tauber P, Zennaro MC, Monticone S, Lang K, Beusch- lein F, Fischer E, Tizzani D, Pallauf A, Viola A, Amar L, Williams TA, Strom TM, Graf E, Bandulik S, Penton D, Plouin PF, Warth R, Allolio B, Jeunemaitre X, Veglio F, Reincke M 2012 KCNJ5 mu- tations in European families with nonglucocorticoid remediable fa- milial hyperaldosteronism. Hypertension 59:235-240
14. Boulkroun S, Beuschlein F, Rossi GP, Golib-Dzib JF, Fischer E, Amar L, Mulatero P, Samson-Couterie B, Hahner S, Quinkler M, Fallo F, Letizia C, Allolio B, Ceolotto G, Cicala MV, Lang K, Le- febvre H, Lenzini L, Maniero C, Monticone S, Perrocheau M, Pilon C, Plouin PF, Rayes N, Seccia TM, Veglio F, Williams TA, Zinnamosca L, Mantero F, Benecke A, Jeunemaitre X, Reincke M, Zennaro MC 2012 Prevalence, clinical, and molecular correlates of KCNJ5 muta- tions in primary aldosteronism. Hypertension 59:592-598
15. Azizan EA, Murthy M, Stowasser M, Gordon R, Kowalski B, Xu S, Brown MJ, O’Shaughnessy KM 2012 Somatic mutations affecting the selectivity filter of KCNJ5 are frequent in 2 large unselected collections of adrenal aldosteronomas. Hypertension 59:587-591
16. Taguchi R, Yamada M, Nakajima Y, Satoh T, Hashimoto K, Shi- busawa N, Ozawa A, Okada S, Rokutanda N, Takata D, Koibuchi Y, Horiguchi J, Oyama T, Takeyoshi I, Mori M 25 January 2012 Expression and mutations of KCNJ5 mRNA in Japanese patients with aldosterone-producing adenomas. J Clin Endocrinol Metab 10.1210/jc.2011-2885
17. Sausbier M, Arntz C, Bucurenciu I, Zhao H, Zhou XB, Sausbier U, Feil S, Kamm S, Essin K, Sailer CA, Abdullah U, Krippeit-Drews P, Feil R, Hofmann F, Knaus HG, Kenyon C, Shipston MJ, Storm JF, Neuhuber W, Korth M, Schubert R, Gollasch M, Ruth P 2005 Elevated blood pressure linked to primary hyperaldosteronism and impaired vasodilation in BK channel-deficient mice. Circulation 112:60-68
18. Grimm PR, Irsik DL, Settles DC, Holtzclaw JD, Sansom SC 2009 Hypertension of Kcnmb1-/- is linked to deficient K secretion and aldosteronism. Proc Natl Acad Sci USA 106:11800-11805
19. Heitzmann D, Derand R, Jungbauer S, Bandulik S, Sterner C, Schweda F, El Wakil A, Lalli E, Guy N, Mengual R, Reichold M, Tegtmeier I, Bendahhou S, Gomez-Sanchez CE, Aller MI, Wisden W, Weber A, Lesage F, Warth R, Barhanin J 2008 Invalidation of TASK1 potassium channels disrupts adrenal gland zonation and mineralocorticoid homeostasis. EMBO J 27:179-187
20. Davies LA, Hu C, Guagliardo NA, Sen N, Chen X, Talley EM, Carey RM, Bayliss DA, Barrett PQ 2008 TASK channel deletion in mice causes primary hyperaldosteronism. Proc Natl Acad Sci USA 105: 2203-2208
21. Arrighi I, Bloch-Faure M, Grahammer F, Bleich M, Warth R, Men- gual R, Drici MD, Barhanin J, Meneton P 2001 Altered potassium balance and aldosterone secretion in a mouse model of human con- genital long QT syndrome. Proc Natl Acad Sci USA 98:8792-8797