A ubiquitin-proteasome inhibitor bortezomib suppresses the expression of CYP11B2, a key enzyme of aldosterone synthesis

Increased adrenal steroidogenesis and suppressed corticosteroid responsiveness in critical COVID-19

BACKGROUND

The effect of coronavirus disease 2019 (COVID-19) on adrenal endocrine metabolism in critically ill patients remains unclear. This study aimed to investigate the alterations in adrenal steroidogenic activity, elucidate underlying mechanisms, provide in situ histopathological evidence, and examine the clinical implications.

METHODS

The comparative analyses of the adrenal cortices from 24 patients with fatal COVID-19 and 20 matched controls were performed, excluding patients previously treated with glucocorticoids. SARS-CoV-2 and its receptors were identified and pathological alterations were examined. Furthermore, histological examinations, immunohistochemical staining and ultrastructural analyses were performed to assess corticosteroid biosynthesis. The zona glomerulosa (ZG) and zona fasciculata (ZF) were then dissected for proteomic analyses. The biological processes that affected steroidogenesis were analyzed by integrating histological, proteomic, and clinical data. Finally, the immunoreactivity and responsive genes of mineralocorticoid and glucocorticoid receptors in essential tissues were quantitatively measured to evaluate corticosteroid responsiveness.

FINDINGS

The demographic characteristics of COVID-19 patients were comparable with those of controls. SARS-CoV-2-like particles were identified in the adrenocortical cells of three patients; however, these particles did not affect cellular morphology or steroid synthesis compared with SARS-CoV-2-negative specimens. Although the adrenals exhibited focal necrosis, vacuolization, microthrombi, and inflammation, widespread degeneration was not evident. Notably, corticosteroid biosynthesis was significantly enhanced in both the ZG and ZF of COVID-19 patients. The increase in the inflammatory response and cellular differentiation in the adrenal cortices of patients with critical COVID-19 was positively correlated with heightened steroidogenic activity. Additionally, the appearance of more dual-ZG/ZF identity cells in COVID-19 adrenals was in accordance with the increased steroidogenic function. However, activated mineralocorticoid and glucocorticoid receptors and their responsive genes in vital tissues were markedly reduced in patients with critical COVID-19.

INTERPRETATION

Critical COVID-19 was characterized by potentiated adrenal steroidogenesis, associated with increased inflammation, enhanced differentiation and elevated dual-ZG/ZF identity cells, alongside suppressed corticosteroid responsiveness. These alterations implied the reduced effectiveness of conventional corticosteroid therapy and underscored the need for evaluation of the adrenal axis and corticosteroid sensitivity.

Role of Environmental Toxicants in the Development of Hypertensive and Cardiovascular Diseases

The incidence of hypertension with diabetes mellitus (DM) as a co-morbid condition is on the rise worldwide. In 2000, an estimated 972 million adults had hypertension, which is predicted to grow to 1.56 billion by 2025. Hypertension often leads to diabetes mellitus that strongly puts the patients at an increased risk of cardiovascular, kidney, and/or atherosclerotic diseases. Hypertension has been identified as a major risk factor for the development of diabetes; patients with hypertension are at two-to-three-fold higher risk of developing diabetes than patients with normal blood pressure (BP). Causes for the increase in hypertension and diabetes are not well understood, environmental factors (e.g., exposure to environmental toxicants like heavy metals, organic solvents, pesticides, alcohol, and urban lifestyle) have been postulated as one of the reasons contributing to hypertension and cardiovascular diseases (CVD). The mechanism of action(s) of these toxicants in developing hypertension and CVDs is not well defined. Research studies have linked hypertension with the chronic consumption of alcohol and exposure to metals like lead, mercury, and arsenic have also been linked to hypertension and CVD. Workers chronically exposed to styrene have a higher incidence of CVD. Recent studies have demonstrated that exposure to particulate matter (PM) in diesel exhaust and urban air contributes to increased CVD and mortality. In this review, we have imparted the role of environmental toxicants such as heavy metals, organic pollutants, PM, alcohol, and some drugs in hypertension and CVD along with possible mechanisms and limitations in extrapolating animal data to humans.

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Rising incidence of hypertension may be linked to chronic exposure with environmental toxicants.

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Urban lifestyle and alcohol intake may be responsible for increased incidence of hypertension among urbanites.

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Exposure with organic solvent, heavy metals and pesticides could also be contributing to the rise in blood pressure.

Molecular Mechanisms of Functional Adrenocortical Adenoma and Carcinoma: Genetic Characterization and Intracellular Signaling Pathway

The adrenal cortex produces steroid hormones as adrenocortical hormones in the body, secreting mineralocorticoids, glucocorticoids, and adrenal androgens, which are all considered essential for life. Adrenocortical tumors harbor divergent hormonal activity, frequently with steroid excess, and disrupt homeostasis of the body. Aldosterone-producing adenomas (APAs) cause primary aldosteronism (PA), and cortisol-producing adenomas (CPAs) are the primary cause of Cushing’s syndrome. In addition, adrenocortical carcinoma (ACC) is a highly malignant cancer harboring poor prognosis. Various genetic abnormalities have been reported, which are associated with possible pathogenesis by the alteration of intracellular signaling and activation of transcription factors. In particular, somatic mutations in APAs have been detected in genes encoding membrane proteins, especially ion channels, resulting in hypersecretion of aldosterone due to activation of intracellular calcium signaling. In addition, somatic mutations have been detected in those encoding cAMP-PKA signaling-related factors, resulting in hypersecretion of cortisol due to its driven status in CPAs. In ACC, mutations in tumor suppressor genes and Wnt-β-catenin signaling-related factors have been implicated in its pathogenesis. In this article, we review recent findings on the genetic characteristics and regulation of intracellular signaling and transcription factors in individual tumors.

The establishment of a novel high-throughput screening system using RNA-guided genome editing to identify chemicals that suppress aldosterone synthase expression

Aldosterone is synthesized in the adrenal by the aldosterone synthase CYP11B2. Although the control of CYP11B2 expression is important to maintain the mineral homeostasis, its overexpression induced by the depolarization-induced calcium (Ca2+) signaling activation has been reported to increase the synthesis of aldosterone in primary aldosteronism (PA). The drug against PA focused on the suppression of CYP11B2 expression has not yet been developed, since the molecular mechanism of CYP11B2 transcriptional regulation activated via Ca2+ signaling remains unclear. To address the issue, we attempted to reveal the mechanism of the transcriptional regulation of CYP11B2 using chemical screening. We generated a cell line by inserting Nanoluc gene as a reporter into CYP11B2 locus in H295R adrenocortical cells using the CRSPR/Cas9 system, and established the high-throughput screening system using the cell line. We then identified 9 compounds that inhibited the CYP11B2 expression induced by potassium-mediated depolarization from the validated compound library (3399 compounds). Particularly, tacrolimus, an inhibitor of phosphatase calcineurin, strongly suppressed the CYP11B2 expression even at 10 nM. These results suggest that the system is effective in identifying drugs that suppress the depolarization-induced CYP11B2 expression. Our screening system may therefore be a useful tool for the development of novel medicines against PA.

[Innovation of novel anti-hypertensive drug(s) that inhibit adrenal aldosterone synthase gene (CYP11B2) expression]

In Japan, hypertensive patients are speculated to be 40 million, and 30 million among them are poor controlled. Moreover, 20% of them are estimated as "resistant hypertension" those are above their target blood pressure even in the simultaneous use of three different classes anti-hypertensive drugs. Recently, aldosterone is recognized as one of the main causes of the etiology of "resistant hypertension." Therefore, it is important to discover novel drugs that inhibit the synthesis and secretion of aldosterone. We recently generated a stable H295R cell line expressing aldosterone synthase gene (CYP11B2) promoter (-1521~+2)/luciferase cDNA chimeric reporter construct. We thereafter established a high-throughput screening (HTS) system for the discovery of novel anti-hypertensive drugs that inhibit angiotensin II-induced CYP11B2 expression using the cell line. After confirmation of its validation (Z' score > 0.5), we performed HTS using Core Library (9,600 chemical compounds) and Validated Compound Library (1,979 chemical compounds) obtained from Drug Discovery Initiative (The University of Tokyo), and Tohoku University Chemical Library (5,562 chemical compounds), respectively. We obtained several hit compounds from each library, and focused on one compound (bortezomib) obtained from Validated Compound Library. The compound did not affect cell viability by WST-1 assay, and was demonstrated to lower blood pressure of Tsukuba Hypertensive Mice, significantly. The compound may therefore be a potential candidate of novel anti-hypertensive drugs in the future.

Endogenous Purification of NR4A2 (Nurr1) Identified Poly(ADP-Ribose) Polymerase 1 as a Prime Coregulator in Human Adrenocortical H295R Cells

Aldosterone is synthesized in zona glomerulosa of adrenal cortex in response to angiotensin II. This stimulation transcriptionally induces expression of a series of steroidogenic genes such as HSD3B and CYP11B2 via NR4A (nuclear receptor subfamily 4 group A) nuclear receptors and ATF (activating transcription factor) family transcription factors. Nurr1 belongs to the NR4A family and is regarded as an orphan nuclear receptor. The physiological significance of Nurr1 in aldosterone production in adrenal cortex has been well studied. However, coregulators supporting the Nurr1 function still remain elusive. In this study, we performed RIME (rapid immunoprecipitation mass spectrometry of endogenous proteins), a recently developed endogenous coregulator purification method, in human adrenocortical H295R cells and identified PARP1 as one of the top Nurr1-interacting proteins. Nurr1-PARP1 interaction was verified by co-immunoprecipitation. In addition, both siRNA knockdown of PARP1 and treatment of AG14361, a specific PARP1 inhibitor suppressed the angiotensin II-mediated target gene induction in H295R cells. Furthermore, PARP1 inhibitor also suppressed the aldosterone secretion in response to the angiotensin II. Together, these results suggest PARP1 is a prime coregulator for Nurr1.