Regulation of the phenylethanolamine N-methyltransferase gene in the adrenal gland of the spontaneous hypertensive rat

Adaptive remodeling of rat adrenomedullary stimulus-secretion coupling in a chronic hypertensive environment

Chronic elevated blood pressure impinges on the functioning of multiple organs and therefore harms body homeostasis. Elucidating the protective mechanisms whereby the organism copes with sustained or repetitive blood pressure rises is therefore a topical challenge. Here we address this issue in the adrenal medulla, the master neuroendocrine tissue involved in the secretion of catecholamines, influential hormones in blood pressure regulation. Combining electrophysiological techniques with catecholamine secretion assays on acute adrenal slices from spontaneously hypertensive rats, we show that chromaffin cell stimulus-secretion coupling is remodeled, resulting in a less efficient secretory function primarily upon sustained cholinergic challenges. The remodeling is supported by revamped both cellular and tissular mechanisms. This first includes a decrease in chromaffin cell excitability in response to sustained electrical stimulation. This hallmark was observed both experimentally and in a computational chromaffin cell model, and occurs with concomitant changes in voltage-gated ion channel expression. The cholinergic transmission at the splanchnic nerve-chromaffin cell synapses and the gap junctional communication between chromaffin cells are also weakened. As such, by disabling its competence to release catecholamines in response sustained stimulations, the hypertensive medulla has elaborated an adaptive shielding mechanism against damaging effects of redundant elevated catecholamine secretion and associated blood pressure.

Blood pressure reduction through brain delivery of nanoparticles loaded with plasmid DNA encoding angiotensin receptor shRNA

Elevated brain angiotensin II activity plays a key role in the development of neurogenic hypertension. While blood pressure (BP) control in neurogenic hypertension has been successfully demonstrated by regulating central angiotensin II activity, current techniques involving cerebrovascular injections of potential therapeutic agents are not suitable for clinical translation. To address this gap, we present the synthesis of dual-functionalized liposomes functionalized with targeting ligand and cell-penetrating peptide. Functionalized liposomes were synthesized using the thin film hydration technique and loaded with plasmid DNA encoding short hairpin RNA targeted toward angiotensin II receptors (PEAS), via the post-insertion method. The synthesized liposomes had a cationic surface charge, an average size of 150 nm, and effectively entrapped more than 89% of loaded PEAS. These liposomes loaded with PEAS demonstrated biocompatibility and efficient delivery to brain-derived cell lines, resulting in a remarkable reduction of more than 70% in receptor expression within 7 days. To assess the therapeutic potential, spontaneously hypertensive rats were administered intravenous injections of functionalized liposomes loaded with PEAS, and the changes in mean arterial pressure were monitored for 45 days. Remarkably, this treatment led to a significant (p < 0.001) decrease in BP of more than 30 mm Hg compared with saline-treated rats.

The abnormalities of adrenomedullary hormonal system in genetic hypertension: Their contribution to altered regulation of blood pressure

It is widely accepted that sympathetic nervous system plays a crucial role in the development of hypertension. On the other hand, the role of adrenal medulla (the adrenomedullary component of the sympathoadrenal system) in the development and maintenance of high blood pressure in man as well as in experimental models of hypertension is still controversial. Spontaneously hypertensive rats (SHR) are the most widely used animal model of human essential hypertension characterized by sympathetic hyperactivity. However, the persistence of moderately elevated blood pressure in SHR subjected to sympathectomy neonatally as well as the resistance of adult SHR to the treatment by sympatholytic drugs suggests that other factors (including enhanced activity of the adrenomedullary hormonal system) are involved in the pathogenesis of hypertension of SHR. This review describes abnormalities in adrenomedullary hormonal system of SHR rats starting with the hyperactivity of brain centers regulating sympathetic outflow, through the exaggerated activation of sympathoadrenal preganglionic neurons, to the local changes in chromaffin cells of adrenal medulla. All the above alterations might contribute to the enhanced release of epinephrine and/or norepinephrine from adrenal medulla. Special attention is paid to the alterations in the expression of genes involved in catecholamine biosynthesis, storage, release, reuptake, degradation and adrenergic receptors in chromaffin cells of SHR. The contribution of the adrenomedullary hormonal system to the development and maintenance of hypertension as well as its importance during stressful conditions is also discussed.

Oxidative Stress Mediates the Fetal Programming of Hypertension by Glucocorticoids

The field of cardiovascular fetal programming has emphasized the importance of the uterine environment on postnatal cardiovascular health. Studies have linked increased fetal glucocorticoid exposure, either from exogenous sources (such as dexamethasone (Dex) injections), or from maternal stress, to the development of adult cardiovascular pathologies. Although the mechanisms are not fully understood, alterations in gene expression driven by altered oxidative stress and epigenetic pathways are implicated in glucocorticoid-mediated cardiovascular programming. Antioxidants, such as the naturally occurring polyphenol epigallocatechin gallate (EGCG), or the superoxide dismutase (SOD) 4-hydroxy-TEMPO (TEMPOL), have shown promise in the prevention of cardiovascular dysfunction and programming. This study investigated maternal antioxidant administration with EGCG or TEMPOL and their ability to attenuate the fetal programming of hypertension via Dex injections in WKY rats. Results from this study indicate that, while Dex-programming increased blood pressure in male and female adult offspring, administration of EGCG or TEMPOL via maternal drinking water attenuated Dex-programmed increases in blood pressure, as well as changes in adrenal mRNA and protein levels of catecholamine biosynthetic enzymes phenylalanine hydroxylase (PAH), tyrosine hydroxylase (TH), dopamine beta hydroxylase (DBH), and phenylethanolamine N-methyltransferase (PNMT), in a sex-specific manner. Furthermore, programmed male offspring displayed reduced antioxidant glutathione peroxidase 1 (Gpx1) expression, increased superoxide dismutase 1 (SOD1) and catalase (CAT) expression, and increased pro-oxidant NADPH oxidase activator 1 (Noxa1) expression in the adrenal glands. In addition, prenatal Dex exposure alters expression of epigenetic regulators histone deacetylase (HDAC) 1, 5, 6, 7, 11, in male and HDAC7 in female offspring. These results suggest that glucocorticoids may mediate the fetal programming of hypertension via alteration of epigenetic machinery and oxidative stress pathways.

HIF1α is a direct regulator of steroidogenesis in the adrenal gland

Endogenous steroid hormones, especially glucocorticoids and mineralocorticoids, derive from the adrenal cortex, and drastic or sustained changes in their circulatory levels affect multiple organ systems. Although hypoxia signaling in steroidogenesis has been suggested, knowledge on the true impact of the HIFs (Hypoxia-Inducible Factors) in the adrenocortical cells of vertebrates is scant. By creating a unique set of transgenic mouse lines, we reveal a prominent role for HIF1α in the synthesis of virtually all steroids in vivo. Specifically, mice deficient in HIF1α in adrenocortical cells displayed enhanced levels of enzymes responsible for steroidogenesis and a cognate increase in circulatory steroid levels. These changes resulted in cytokine alterations and changes in the profile of circulatory mature hematopoietic cells. Conversely, HIF1α overexpression resulted in the opposite phenotype of insufficient steroid production due to impaired transcription of necessary enzymes. Based on these results, we propose HIF1α to be a vital regulator of steroidogenesis as its modulation in adrenocortical cells dramatically impacts hormone synthesis with systemic consequences. In addition, these mice can have potential clinical significances as they may serve as essential tools to understand the pathophysiology of hormone modulations in a number of diseases associated with metabolic syndrome, auto-immunity or even cancer.

Whole transcriptome analysis of adrenal glands from prenatal glucocorticoid programmed hypertensive rodents

Prenatal glucocorticoid exposure is associated with the development of hypertension in adults. We have previously demonstrated that antenatal dexamethosone (DEX) administration in Wistar-Kyoto dams results in offspring with increased blood pressure coupled with elevated plasma epinephrine levels. In order to elucidate the molecular mechanisms responsible for prenatal DEX-mediated programming of hypertension, a whole-transcriptome analysis was performed on DEX programmed WKY male adrenal glands using the Rat Gene 2.0 microarray. Differential gene expression (DEG) analysis of DEX-exposed offspring compared with saline-treated controls revealed 142 significant DEGs (109 upregulated and 33 downregulated genes). DEG pathway enrichment analysis demonstrated that genes involved in circadian rhythm signaling were most robustly dysregulated. RT-qPCR analysis confirmed the increased expression of circadian genes Bmal1 and Npas2, while Per2, Per3, Cry2 and Bhlhe41 were significantly downregulated. In contrast, gene expression profiling of Spontaneously Hypertensive (SHR) rats, a genetic model of hypertension, demonstrated decreased expression of Bmal1 and Npas2, while Per1, Per2, Per3, Cry1, Cry2, Bhlhe41 and Csnk1D were all upregulated compared to naïve WKY controls. Taken together, this study establishes that glucocorticoid programmed adrenals have impaired circadian signaling and that changes in adrenal circadian rhythm may be an underlying molecular mechanism responsible for the development of hypertension.

The Role of DNMT and HDACs in the Fetal Programming of Hypertension by Glucocorticoids

The causes of hypertension are complex and involve both genetic and environmental factors. Environment changes during fetal development have been linked to adult diseases including hypertension. Studies show that timed in utero exposure to the synthetic glucocorticoid (GC) dexamethasone (Dex) results in the development of hypertension in adult rats. Evidence suggests that in utero stress can alter patterns of gene expression, possibly a result of alterations in the topology of the genome by epigenetic markers such as DNA methyltransferases (DNMTs) and histone deacetylases (HDACs). The objective of this study was to determine the effects of epigenetic regulators in the fetal programming and the development of adult hypertension. Specifically, this research examined the effects of the HDAC inhibitor valproic acid (VPA) and the DNMT inhibitor 5-aza-2′-deoxycytidine (5aza2DC) on blood pressure (BP) and gene expression in prenatal Dex-programmed rats. Data suggest that both VPA and 5aza2DC attenuated the Dex-mediated development of hypertension and restored BP to control levels. Epigenetic DNMT inhibition (DNMTi) or HDAC inhibition (HDACi) also successfully attenuated elevations in the majority of altered catecholamine (CA) enzyme expression, phenylethanolamine N-methyltransferase (PNMT) protein, and elevated epinephrine (Epi) levels in males. Although females responded to HDACi similar to males, DNMTi drove increased glucocorticoid receptor (GR) and PNMT expression and elevations in circulating Epi in females despite showing normotensive BP.

Fetal programming of adrenal PNMT and hypertension by glucocorticoids in WKY rats is dose and sex-dependent

Biochemical changes in utero may alter normal fetal development, resulting in disease later in life, a phenomenon known as fetal programming. Recent epidemiological studies link fetal programming to negative health outcomes, such as low birth weight and hypertension in adulthood. Here, we used a WKY rat model and studied the molecular changes triggered by prenatal glucocorticoid (GC) exposure on the development of hypertension, and on the regulation of phenylethanolamine N-methyl transferase (PNMT), the enzyme responsible for biosynthesis of epinephrine, and a candidate gene linked to hypertension. Clinically, high doses of the synthetic GC dexamethasone (DEX) are used to treat infant respiratory distress syndrome. Elevated maternal GCs have been correlated with fetal programming of hypertension. The aim of this study was to determine if lower doses of DEX would not lead to detrimental fetal programming effects such as hypertension. Our data suggests that prenatal stress programs for increased expression of PNMT and altered regulation of PNMT in males and females. Importantly, we identified that DEX mediated programming was more apparent in the male rats, and the lower dose 10μg/kg/day of DEX did not lead to changes in blood pressure (BP) in female rats suggesting that this dose is below the threshold for programming of hypertension. Furthermore, sex-specific differences were observed in regards to programming mechanisms that may account for hypertension in males.

Inflammatory Signaling in Hypertension: Regulation of Adrenal Catecholamine Biosynthesis

The immune system is increasingly recognized for its role in the genesis and progression of hypertension. The adrenal gland is a major site that coordinates the stress response via the hypothalamic-pituitary-adrenal axis and the sympathetic-adrenal system. Catecholamines released from the adrenal medulla function in the neuro-hormonal regulation of blood pressure and have a well-established link to hypertension. The immune system has an active role in the progression of hypertension and cytokines are powerful modulators of adrenal cell function. Adrenal medullary cells integrate neural, hormonal, and immune signals. Changes in adrenal cytokines during the progression of hypertension may promote blood pressure elevation by influencing catecholamine biosynthesis. This review highlights the potential interactions of cytokine signaling networks with those of catecholamine biosynthesis within the adrenal, and discusses the role of cytokines in the coordination of blood pressure regulation and the stress response.

Comparative Analysis of Renin-Angiotensin System (RAS)-Related Gene Expression Between Hypertensive and Normotensive Rats

BACKGROUND The renal renin-angiotensin system (RAS) is physiologically important for blood pressure regulation. Altered regulation of RAS-related genes has been observed in an animal model of hypertension (spontaneously hypertensive rats - SHRs). The current understanding of certain RAS-related gene expression differences between Wistar-Kyoto rats (WKYs) and SHRs is either limited or has not been compared. The purpose of this study was to compare the regulation of key RAS-related genes in the kidneys of adult WKYs and SHRs. MATERIAL AND METHODS Coronal sections were dissected through the hilus of kidneys from 16-week-old male WKYs and SHRs. RT-PCR analysis was performed for Ace, Ace2, Agt, Agtr1a, Agtr1b, Agtr2, Atp6ap2 (PRR), Mas1, Ren, Rnls, and Slc12a3 (NCC). RESULTS Increased mRNA expression was observed for Ace, Ace2, Agt, Agtr1a, Agtr1b, and Atp6ap2 in SHRs compared to WKYs. Mas1, Ren, Slc12a3, and Rnls showed no difference in expression between animal types. CONCLUSIONS This study shows that the upregulation of several key RAS-related genes in the kidney may account for the increased blood pressure of adult SHRs.

Phenylethanolamine N-methyltransferase gene expression in adrenergic neurons of spontaneously hypertensive rats

Epinephrine is synthesised by the catecholamine biosynthetic enzyme, phenylethanolamine N-methyltransferase (PNMT), primarily in chromaffin cells of the adrenal medulla and secondarily in brainstem adrenergic neurons of the medulla oblongata. Epinephrine is an important neurotransmitter/neurohormone involved in cardiovascular regulation; however, overproduction is detrimental with negative outcomes such as cellular damage, cardiovascular dysfunction, and hypertension. Genetic mapping studies have linked elevated expression of PNMT to hypertension. Adrenergic neurons are responsible for blood pressure regulation and are the only PNMT containing neurons in the brainstem. The purpose of the current study was to determine whether elevated blood pressure found in adult spontaneously hypertensive rats (SHR) is associated with altered regulation of the PNMT gene in catecholaminergic neurons. C1, C2, and C3 adrenergic regions of 16 week old Wistar Kyoto (WKY) and SHR rats were excised using micropunch microdissection for mRNA expression analyses. Results from the current study confirm high PNMT mRNA expression in all three brainstem adrenergic regions (C1: 2.96-fold; C2: 2.17-fold; C3 1.20-fold) of the SHR compared to normotensive WKY rats. Furthermore, the immediate early gene transcription factor (Egr-1) mRNA was elevated in the C1 (1.84-fold), C2 (8.57-fold) and C3 (2.41-fold) regions in the brainstem of the SHR. Low mRNA expression for transcription factors Sp1 and GR was observed, while no change was observed for AP-2. The findings presented propose that alterations in the PNMT gene regulation in the brainstem contribute to enhanced PNMT production and epinephrine synthesis in the SHR, a genetic model of hypertension.

The Importance of the Selection of Appropriate Reference Genes for Gene Expression Profiling in Adrenal Medulla or Sympathetic Ganglia of Spontaneously Hypertensive Rat

Catecholaminergic system plays an important role in hypertension development. The available results on mRNA expression of catecholaminergic system genes in spontaneously hypertensive rats (SHR) are often contradictory. One of the possible causes might be the use of various reference genes as internal controls. In the present study, we searched for suitable reference genes in adrenal medulla or sympathetic ganglia of SHR and Wistar-Kyoto (WKY) rats, which would enable reliable comparison of mRNA expression between these two strains. The mRNA expression was measured by quantitative real-time PCR in adrenal medulla and superior cervical ganglia of 4-week-old or 24-week-old SHR and WKY rats. We evaluated 12 reference genes by three software tools (Normfinder, BestKeeper, geNorm) and compared them for the standardization of mRNA expression. Combination of reference genes Hprt1 and Ywhaz in adrenal medulla and Gapdh and 18S in sympathetic ganglia were chosen as the best ones. 18S was found as applicable reference gene in both tissues. We found many alterations in expression of catecholaminergic system genes in adrenal medulla and sympathetic ganglia of SHR. The usage of the most or the least stable reference gene as internal control changed results moderately in sympathetic ganglia but seriously in adrenal medulla. For example, tyrosine hydroxylase (Th) gene was underexpressed in adrenal medulla of adult SHR using the appropriate reference gene but unchanged after the standardization to the least stable reference gene. Our results indicate the importance of appropriate internal control. The suitability of reference genes should be checked again in the case of change in experimental conditions.

Prenatal glucocorticoid exposure programs adrenal PNMT expression and adult hypertension

Prenatal exposure to glucocorticoids (GCs) programs for hypertension later in life. The aim of the current study was to examine the impact of prenatal GC exposure on the postnatal regulation of the gene encoding for phenylethanolamine N-methyltransferase (PNMT), the enzyme involved in the biosynthesis of the catecholamine, epinephrine. PNMT has been linked to hypertension and is elevated in animal models of hypertension. Male offspring of Wistar-Kyoto dams treated with dexamethasone (DEX) developed elevated systolic, diastolic and mean arterial blood pressure compared to saline-treated controls. Plasma epinephrine levels were also elevated in adult rats exposed to DEX in utero. RT-PCR analysis revealed adrenal PNMT mRNA was higher in DEX exposed adult rats. This was associated with increased mRNA levels of transcriptional regulators of the PNMT gene: Egr-1, AP-2, and GR. Western blot analyses showed increased expression of PNMT protein, along with increased Egr-1 and GR in adult rats exposed to DEX in utero. Furthermore, gel mobility shift assays showed increased binding of Egr-1 and GR to DNA. These results suggest that increased PNMT gene expression via altered transcriptional activity is a possible mechanism by which prenatal exposure to elevated levels of GCs may program for hypertension later in life.

Cardiac phenylethanolamine N-methyltransferase: localization and regulation of gene expression in the spontaneously hypertensive rat

Phenylethanolamine N-methyltransferase (PNMT) is the terminal enzyme in the catecholamine biosynthetic pathway responsible for adrenaline biosynthesis. Adrenaline is involved in the sympathetic control of blood pressure; it augments cardiac function by increasing stroke volume and cardiac output. Genetic mapping studies have linked the PNMT gene to hypertension. This study examined the expression of cardiac PNMT and changes in its transcriptional regulators in the spontaneously hypertensive (SHR) and wild type Wistar-Kyoto (WKY) rats. SHR exhibit elevated levels of corticosterone, and lower levels of the cytokine IL-1β, revealing systemic differences between SHR and WKY. PNMT mRNA was significantly increased in all chambers of the heart in the SHR, with the greatest increase in the right atrium. Transcriptional regulators of the PNMT promoter show elevated expression of Egr-1, Sp1, AP-2, and GR mRNA in all chambers of the SHR heart, while protein levels of Sp1, Egr-1, and GR were elevated only in the right atrium. Interestingly, only AP-2 protein-DNA binding was increased, suggesting it may be a key regulator of cardiac PNMT in SHR. This study provides the first insights into the molecular mechanisms involved in the dysregulation of cardiac PNMT in a genetic model of hypertension.

Vasorelaxant and antihypertensive effects of formononetin through endothelium-dependent and -independent mechanisms

AIM

To investigate the mechanisms underlying the vasorelaxant effect of formononetin, an O-methylated isoflavone, in isolated arteries, and its antihypertensive activity in vivo.

METHODS

Arterial rings of superior mesenteric arteries, renal arteries, cerebral basilar arteries, coronary arteries and abdominal aortas were prepared from SD rats. Isometric tension of the arterial rings was recorded using a myograph system. Arterial pressure was measured using tail-cuff method in spontaneously hypertensive rats.

RESULTS

Formononetin (1-300 μmol/L) elicited relaxation in arteries of the five regions that were pre-contracted by KCl (60 mmol/L), U46619 (1 μmol/L) or phenylephrine (10 μmol/L). The formononetin-induced relaxation was reduced by removal of endothelium or by pretreatment with L-NAME (100 μmol/L). Under conditions of endothelium denudation, formononetin (10, 30, and 100 μmol/L) inhibited the contraction induced by KCl and that induced by CaCl(2) in Ca(2+)-free depolarized medium. In the absence of extracellular Ca(2+), formononetin (10, 30, and 100 μmol/L) depressed the constriction caused by phenylephrine (10 μmol/L), but did not inhibit the tonic contraction in response to the addition of CaCl(2) (2 mmol/L). The contraction caused by caffeine (30 mmol/L) was not inhibited by formononetin (100 μmol/L). Formononetin (10 and 100 μmol/L) reduced the change rate of Ca(2+)-fluorescence intensity in response to KCl (50 mmol/L). In spontaneously hypertensive rats, formononetin (5, 10, and 20 mg/kg) slowly lowered the systolic, diastolic and mean arterial pressure.

CONCLUSION

Formononetin causes vasodilatation via two pathways: (1) endothelium-independent pathway, probably due to inhibition of voltage-dependent Ca(2+) channels and intracellular Ca(2+) release; and (2) endothelium-dependent pathway by releasing NO. Both the pathways may contribute to its antihypertensive effect.

Systematic polymorphism discovery after genome-wide identification of potential susceptibility loci in a hereditary rodent model of human hypertension

Genetic strategies such as linkage analysis and quantitative trait locus (QTL) mapping have identified a multitude of loci implicated in the pathogenesis of hypertension in the spontaneously hypertensive rat (SHR). While several candidate genetic regions have been identified in the SHR and its control, the Wistar-Kyoto rat (WKY), systematic follow-up of candidate identification with polymorphism discovery has not been widespread. In the current report, we develop a data-mining strategy to identify candidate genes for hypertension in the SHR, and then sequence each gene in the SHR and WKY strains. We integrate blood pressure QTL data, microarray data and data-mining methods. First, we determined the set of genes differentially expressed in SHR and WKY adrenal glands. Next, the chromosomal position of all differentially expressed genes was compared with peak marker position of all reported SHR blood pressure QTLs. We also identified the set of differentially expressed genes with the most extreme fold-change. Finally, the QTL positional candidates and the genes with extreme differential expression were proposed as candidate genes if they had biologically plausible roles in hypertensive pathology. We identified seven candidate genes that merit resequencing (catechol-O-methyltransferase [Comt], chromogranin A [Chga], dopamine beta-hydroxylase [Dbh], electron transferring flavoprotein dehydrogenase [Etfdh], endothelin receptor type B [Ednrb], neuropeptide Y [Npy] and phenylethanolamine-N-methyltransferase [Pnmt]), and then discovered polymorphism in four of these seven candidate genes. Chga is proposed as the strongest candidate for additional functional investigation. Our method for candidate gene identification is portable and can be applied to microarray data from any tissue, in any disease model with a QTL database.