Deficiency of T-type Ca2+ channels Cav3.1 and Cav3.2 has no effect on angiotensin II-induced hypertension but differential effect on plasma aldosterone in mice

Smooth muscle-specific deletion of cellular communication network factor 2 causes severe aorta malformation and atherosclerosis

AIMS

Cellular communication network factor 2 (CCN2) is a matricellular protein implicated in fibrotic diseases, with ongoing clinical trials evaluating anti-CCN2-based therapies. By uncovering CCN2 as abundantly expressed in non-diseased artery tissue, this study aimed to investigate the hypothesis that CCN2 plays a pivotal role in maintaining smooth muscle cell (SMC) phenotype and protection against atherosclerosis.

METHODS AND RESULTS

Global- and SMC-specific Ccn2 knockout mouse models were employed to demonstrate that Ccn2 deficiency leads to SMC de-differentiation, medial thickening, and aorta elongation under normolipidaemic conditions. Inducing hyperlipidaemia in both models resulted in severe aorta malformation and a 17-fold increase in atherosclerosis formation. Lipid-rich lesions developed at sites of the vasculature typically protected from atherosclerosis development by laminar blood flow, covering 90% of aortas and extending to other vessels, including coronary arteries. Evaluation at earlier time points revealed medial lipid accumulation as a lesion-initiating event. Fluorescently labelled LDL injection followed by confocal microscopy showed increased LDL retention in the medial layer of Ccn2 knockout aortas, likely attributed to marked proteoglycan enrichment of the medial extracellular matrix. Analyses leveraging data from the Athero-Express study cohort indicated the relevance of CCN2 in established human lesions, as CCN2 correlated with SMC marker transcripts across 654 transcriptomically profiled carotid plaques. These findings were substantiated through in situ hybridization showing CCN2 expression predominantly in the fibrous cap.

CONCLUSION

This study identifies CCN2 as a major constituent of the normal artery wall, critical in regulating SMC differentiation and aorta integrity and possessing a protective role against atherosclerosis development. These findings underscore the need for further investigation into the potential effects of anti-CCN2-based therapies on the vasculature.

T- and L-Type Calcium Channels Maintain Calcium Oscillations in the Murine Zona Glomerulosa

BACKGROUND

The zona glomerulosa of the adrenal gland is responsible for the synthesis and release of the mineralocorticoid aldosterone. This steroid hormone regulates salt reabsorption in the kidney and blood pressure. The most important stimuli of aldosterone synthesis are the serum concentrations of angiotensin II and potassium. In response to these stimuli, voltage and intracellular calcium levels in the zona glomerulosa oscillate, providing the signal for aldosterone synthesis. It was proposed that the voltage-gated T-type calcium channel CaV3.2 is necessary for the generation of these oscillations. However, Cacna1h knock-out mice have normal plasma aldosterone levels, suggesting additional calcium entry pathways.

METHODS

We used a combination of calcium imaging, patch clamp, and RNA sequencing to investigate calcium influx pathways in the murine zona glomerulosa.

RESULTS

Cacna1h-/- glomerulosa cells still showed calcium oscillations with similar concentrations as wild-type mice. No calcium channels or transporters were upregulated to compensate for the loss of CaV3.2. The calcium oscillations observed were instead dependent on L-type voltage-gated calcium channels. Furthermore, we found that L-type channels can also partially compensate for an acute inhibition of CaV3.2 in wild-type mice. Only inhibition of both T- and L-type calcium channels abolished the increase of intracellular calcium caused by angiotensin II in wild-type.

CONCLUSIONS

Our study demonstrates that T-type calcium channels are not strictly required to maintain glomerulosa calcium oscillations and aldosterone production. Pharmacological inhibition of T-type channels alone will likely not significantly impact aldosterone production in the long term.

CaV3.1 channels facilitate calcium wave generation and myogenic tone development in mouse mesenteric arteries

The arterial myogenic response to intraluminal pressure elicits constriction to maintain tissue perfusion. Smooth muscle [Ca2+] is a key determinant of constriction, tied to L-type (CaV1.2) Ca2+ channels. While important, other Ca2+ channels, particularly T-type could contribute to pressure regulation within defined voltage ranges. This study examined the role of one T-type Ca2+ channel (CaV3.1) using C57BL/6 wild type and CaV3.1-/- mice. Patch-clamp electrophysiology, pressure myography, blood pressure and Ca2+ imaging defined the CaV3.1-/- phenotype relative to C57BL/6. CaV3.1-/- mice had absent CaV3.1 expression and whole-cell current, coinciding with lower blood pressure and reduced mesenteric artery myogenic tone, particularly at lower pressures (20-60 mmHg) where membrane potential is hyperpolarized. This reduction coincided with diminished Ca2+ wave generation, asynchronous events of Ca2+ release from the sarcoplasmic reticulum, insensitive to L-type Ca2+ channel blockade (Nifedipine, 0.3 µM). Proximity ligation assay (PLA) confirmed IP3R1/CaV3.1 close physical association. IP3R blockade (2-APB, 50 µM or xestospongin C, 3 µM) in nifedipine-treated C57BL/6 arteries rendered a CaV3.1-/- contractile phenotype. Findings indicate that Ca2+ influx through CaV3.1 contributes to myogenic tone at hyperpolarized voltages through Ca2+-induced Ca2+ release tied to the sarcoplasmic reticulum. This study helps establish CaV3.1 as a potential therapeutic target to control blood pressure.

CaV3.2 (CACNA1H) in Primary Aldosteronism

Aldosterone is a steroid hormone produced in the zona glomerulosa (ZG) of the adrenal cortex. The most prominent function of aldosterone is the control of electrolyte homeostasis and blood pressure via the kidneys. The primary factors regulating aldosterone synthesis are the serum concentrations of angiotensin II and potassium. The T-type voltage-gated calcium channel Ca_V3.2 (encoded by CACNA1H) is an important component of electrical as well as intracellular calcium oscillations, which govern aldosterone production in the ZG. Excessive aldosterone production that is (partially) uncoupled from physiological stimuli leads to primary aldosteronism, the most common cause of secondary hypertension. Germline gain-of-function mutations in CACNA1H were identified in familial hyperaldosteronism, whereas somatic mutations are a rare cause of aldosterone-producing adenomas. In this review, we summarize these findings, put them in perspective, and highlight missing knowledge.

Genetics of Primary Aldosteronism

Primary aldosteronism is considered the commonest cause of secondary hypertension. In affected individuals, aldosterone is produced in an at least partially autonomous fashion in adrenal lesions (adenomas, [micro]nodules or diffuse hyperplasia). Over the past decade, next-generation sequencing studies have led to the insight that primary aldosteronism is largely a genetic disorder. Sporadic cases are due to somatic mutations, mostly in ion channels and pumps, and rare cases of familial hyperaldosteronism are caused by germline mutations in an overlapping set of genes. More than 90% of aldosterone-producing adenomas carry somatic mutations in K⁺ channel Kir3.4 (KCNJ5), Ca²⁺ channel Ca_V1.3 (CACNA1D), alpha-1 subunit of the Na⁺/K⁺ ATPase (ATP1A1), plasma membrane Ca²⁺ transporting ATPase 3 (ATP2B3), Ca²⁺ channel Ca_V3.2 (CACNA1H), Cl⁻ channel ClC-2 (CLCN2), β-catenin (CTNNB1), and/or G-protein subunits alpha q/11 (GNAQ/11). Mutations in some of these genes have also been identified in aldosterone-producing (micro)nodules, suggesting a disease continuum from a single cell, acquiring a somatic mutation, via a nodule to adenoma formation, and from a healthy state to subclinical to overt primary aldosteronism. Individual glands can have multiple such lesions, and they can occur on both glands in bilateral disease. Familial hyperaldosteronism, typically with early onset, is caused by germline mutations in steroid 11-beta hydroxylase/ aldosterone synthase (CYP11B1/2), CLCN2, KCNJ5, CACNA1H, and CACNA1D.

Endothelial mineralocorticoid receptor ablation confers protection towards endothelial dysfunction in experimental diabetes in mice

AIM

With diabetes comes a significant risk of macrovascular and microvascular complications. Circulating aldosterone levels increase in patients with diabetes. Aldosterone can directly affect vascular function via activation of the mineralocorticoid receptor (MR). We hypothesized that aldosterone via endothelial MR impairs endothelial function in a murine model of experimental diabetes.

METHOD

Endothelial cell-specific mineralocorticoid receptor knockout MR^flox/flox ; Tie2-Cre mice (ECMR-KO) and wild-type FVB littermates were subjected to an experimental type-1 diabetic model by low dose streptozotocin injections (55mg/kg/day) for five consecutive days. After 10 weeks of diabetes, second-order mesenteric resistance arteries were perfused ex vivo to evaluate vessel contractility and endothelial function. The effect of ex vivo incubation with aldosterone with and without the antagonist, spironolactone was determined.

RESULTS

Diabetic ECMR-KO and wild-type mice had similar, elevated, plasma aldosterone concentration while only diabetic wild-type mice displayed elevated urine albumin excretion and cardiac and kidney hypertrophy at 10 weeks. There were no differences in contraction (Emax and EC₅₀ ) to thromboxane receptor agonist (U46619) and elevated K⁺ between groups. Wild-type diabetic mice showed impaired acetylcholine (ACh)-dependent relaxation, while diabetic ECMR-KO mice had intact ACh-mediated relaxation. Aldosterone incubation ex vivo impaired ACh mediated relaxation and rendered responses similar to diabetic WT arteries. Direct, ex vivo aldosterone effects were absent in ECMR-KO animals. Ex vivo inhibitory effects of aldosterone on endothelial relaxation in arteries from WT were abolished by spironolactone.

CONCLUSION

These findings show that endothelial cell mineralocorticoid receptor activation accounts for diabetes-induced systemic endothelial dysfunction in experimental diabetes and may explain the cardiovascular protection by MR antagonists in diabetes.

Calcium channel blocker in patients with chronic kidney disease

BACKGROUND

Chronic kidney disease (CKD) is involved in a progressive deterioration in renal function over the years and is now a global public health problem. Currently, reducing the number of patients progressing to end-stage renal failure is urgently necessary. Hypertension and CKD interact with each other, and good control of blood pressure (BP) can improve CKD patients' prognosis. With the current global trend for more strict BP control, the importance of BP management and the need for medication to achieve this strict goal are increasing. Calcium channel blockers (CCBs), which target voltage-dependent calcium channels, are frequently used in combination with renin-angiotensin-aldosterone system inhibitors for CKD patients because of their strong BP-lowering properties and relatively few adverse side effects. Calcium channels have several subtypes, including L, N, T, P/Q, and R, and three types of CCBs, L-type CCBs, L-/T-type CCBs, and L-/N-type CCBs, that are available. Nowadays, the new functions and effects of the CCBs are being elucidated.

CONCLUSION

We should use different types of CCBs properly depending on their pharmacological effects, such as the strength of antihypertensive effects and the organ protection effects, taking into account the pathophysiology of the patients. In this article, the role and the use of CCBs in CKD patients are reviewed.

The mineralocorticoid receptor leads to increased expression of EGFR and T-type calcium channels that support HL-1 cell hypertrophy

The EGF receptor (EGFR) has been extensively studied in tumor biology and recently a role in cardiovascular pathophysiology was suggested. The mineralocorticoid receptor (MR) is an important effector of the renin-angiotensin-aldosterone-system and elicits pathophysiological effects in the cardiovascular system; however, the underlying molecular mechanisms are unclear. Our aim was to investigate the importance of EGFR for MR-mediated cardiovascular pathophysiology because MR is known to induce EGFR expression. We identified a SNP within the EGFR promoter that modulates MR-induced EGFR expression. In RNA-sequencing and qPCR experiments in heart tissue of EGFR KO and WT mice, changes in EGFR abundance led to differential expression of cardiac ion channels, especially of the T-type calcium channel CACNA1H. Accordingly, CACNA1H expression was increased in WT mice after in vivo MR activation by aldosterone but not in respective EGFR KO mice. Aldosterone- and EGF-responsiveness of CACNA1H expression was confirmed in HL-1 cells by Western blot and by measuring peak current density of T-type calcium channels. Aldosterone-induced CACNA1H protein expression could be abrogated by the EGFR inhibitor AG1478. Furthermore, inhibition of T-type calcium channels with mibefradil or ML218 reduced diameter, volume and BNP levels in HL-1 cells. In conclusion the MR regulates EGFR and CACNA1H expression, which has an effect on HL-1 cell diameter, and the extent of this regulation seems to depend on the SNP-216 (G/T) genotype. This suggests that the EGFR may be an intermediate for MR-mediated cardiovascular changes and that SNP analysis can help identify subgroups of patients that will benefit most from MR antagonists.

Enhanced Ca2+ signaling, mild primary aldosteronism, and hypertension in a familial hyperaldosteronism mouse model (Cacna1h M1560V/+ )

Primary aldosteronism (increased production of the adrenal steroid hormone aldosterone) is the most common cause of secondary hypertension. We here generated a mouse model of familial hyperaldosteronism type IV with a heterozygous gain-of-function mutation in a calcium channel gene (Cacna1h^M1560V/+). Cacna1h^M1560V/+ mice have about twofold elevated aldosterone:renin ratios (a screening parameter for primary aldosteronism) and elevated blood pressure, with an overall mild phenotype. Elevated adrenal aldosterone synthase expression in Cacna1h^M1560V/+ mice is associated with increased intracellular calcium concentrations in glomerulosa cells. This model allows for the ex vivo analysis of calcium signaling in aldosterone-producing glomerulosa cells of the adrenal gland. Cacna1h^−/− mice have normal aldosterone synthase expression, with implications for the evaluation of CACNA1H as a therapeutic target.

Gain-of-function mutations in the CACNA1H gene (encoding the T-type calcium channel Ca_V3.2) cause autosomal-dominant familial hyperaldosteronism type IV (FH-IV) and early-onset hypertension in humans. We used CRISPR/Cas9 to generate Cacna1h^M1560V/+ knockin mice as a model of the most common FH-IV mutation, along with corresponding knockout mice (Cacna1h^−/−). Adrenal morphology of both Cacna1h^M1560V/+ and Cacna1h^−/− mice was normal. Cacna1h^M1560V/+ mice had elevated aldosterone:renin ratios (a screening parameter for primary aldosteronism). Their adrenal Cyp11b2 (aldosterone synthase) expression was increased and remained elevated on a high-salt diet (relative autonomy, characteristic of primary aldosteronism), but plasma aldosterone was only elevated in male animals. The systolic blood pressure of Cacna1h^M1560V/+ mice was 8 mmHg higher than in wild-type littermates and remained elevated on a high-salt diet. Cacna1h^−/− mice had elevated renal Ren1 (renin-1) expression but normal adrenal Cyp11b2 levels, suggesting that in the absence of Ca_V3.2, stimulation of the renin-angiotensin system activates alternative calcium entry pathways to maintain normal aldosterone production. On a cellular level, Cacna1h^M1560V/+ adrenal slices showed increased baseline and peak intracellular calcium concentrations in the zona glomerulosa compared to controls, but the frequency of calcium spikes did not rise. We conclude that FH-IV, on a molecular level, is caused by elevated intracellular Ca²⁺ concentrations as a signal for aldosterone production in adrenal glomerulosa cells. We demonstrate that a germline Cacna1h gain-of-function mutation is sufficient to cause mild primary aldosteronism, whereas loss of Ca_V3.2 channel function can be compensated for in a chronic setting.