RNA silencing targeting PIN (protein inhibitor of neuronal nitric oxide synthase) attenuates the development of hypertension in young spontaneously hypertensive rats

Hypertension and renal disease programming: focus on the early postnatal period

The developmental origin of hypertension and renal disease is a concept highly supported by strong evidence coming from both human and animal studies. During development there are periods in which the organs are more vulnerable to stressors. Such periods of susceptibility are also called 'sensitive windows of exposure'. It was shown that as earlier an adverse event occurs; the greater are the consequences for health impairment. However, evidence show that the postnatal period is also quite important for hypertension and renal disease programming, especially in rodents because they complete nephrogenesis postnatally, and it is also important during preterm human birth. Considering that the developing kidney is vulnerable to early-life stressors, renal programming is a key element in the developmental programming of hypertension and renal disease. The purpose of this review is to highlight the great number of studies, most of them performed in animal models, showing the broad range of stressors involved in hypertension and renal disease programming, with a particular focus on the stressors that occur during the early postnatal period. These stressors mainly include undernutrition or specific nutritional deficits, chronic behavioral stress, exposure to environmental chemicals, and pharmacological treatments that affect some important factors involved in renal physiology. We also discuss the common molecular mechanisms that are activated by the mentioned stressors and that promote the appearance of these adult diseases, with a brief description on some reprogramming strategies, which is a relatively new and promising field to treat or to prevent these diseases.

The heart is lost without the hypothalamus

Neuroanatomic and functional studies show the paraventricular (PVN) of the hypothalamus to have a central role in the autonomic control that supports cardiovascular regulation. Direct and indirect projections from the PVN preautonomic neurons to the sympathetic preganglionic neurons in the spinal cord modulate sympathetic activity. The preautonomic neurons of the PVN adjust their level of activation in response to afferent signals arising from peripheral viscerosensory receptors relayed through the nucleus tractus solitarius. The prevailing sympathetic tone is a balance between excitatory and inhibitory influences that arises from the preautonomic PVN neurons. Under physiologic conditions, tonic sympathetic inhibition driven by a nitric oxide-γ-aminobutyric acid-mediated mechanism is dominant, but in pathologic situation such as heart failure there is a switch from inhibition to sympathoexcitation driven by glutamate and angiotensin II. Angiotensin II, reactive oxygen species, and hypoxia as a result of myocardial infarction/ischemia alter the tightly regulated posttranslational protein-protein interaction of CAPON (carboxy-terminal postsynaptic density protein ligand of neuronal nitric oxide synthase (NOS1)) and PIN (protein inhibitor of NOS1) signaling mechanism. Within the preautonomic neurons of the PVN, the disruption of CAPON and PIN signaling leads to a downregulation of NOS1 expression and reduced NO bioavailability. These data support the notion that CAPON-PIN dysregulation of NO bioavailability is a major contributor to the pathogenesis of sympathoexcitation in heart failure.

Central angiotensin II-Protein inhibitor of neuronal nitric oxide synthase (PIN) axis contribute to neurogenic hypertension

Activation of renin-angiotensin- system, nitric oxide (NO•) bioavailability and subsequent sympathoexcitation plays a pivotal role in the pathogenesis of many cardiovascular diseases, including hypertension. Previously we have shown increased protein expression of PIN (a protein inhibitor of nNOS: neuronal nitric oxide synthase, known to dissociate nNOS dimers into monomers) with concomitantly reduced levels of catalytically active dimers of nNOS in the PVN of rats with heart failure. To elucidate the molecular mechanism by which Angiotensin II (Ang II) increases PIN expression, we used Sprague-Dawley rats (250-300 g) subjected to intracerebroventricular infusion of Ang II (20 ng/min, 0.5 μl/h) or saline as vehicle (Veh) for 14 days through osmotic mini-pumps and NG108-15 hybrid neuronal cell line treated with Ang II as an in vitro model. Ang II infusion significantly increased baseline renal sympathetic nerve activity and mean arterial pressure. Ang II infusion increased the expression of PIN (1.24 ± 0.04* Ang II vs. 0.65 ± 0.07 Veh) with a concomitant 50% decrease in dimeric nNOS and PIN-Ub conjugates (0.73 ± 0.04* Ang II vs. 1.00 ± 0.03 Veh) in the PVN. Substrate-dependent ligase assay in cells transfected with pCMV-(HA-Ub)8 vector revealed a reduction of HA-Ub-PIN conjugates after Ang II and a proteasome inhibitor, Lactacystin (LC), treatment (4.5 ± 0.7* LC Ang II vs. 9.2 ± 2.5 LC). TUBE (Tandem Ubiquitin-Binding Entities) assay showed decrease PIN-Ub conjugates in Ang II-treated cells (0.82 ± 0.12* LC Ang II vs. 1.21 ± 0.06 LC) while AT₁R blocker, Losartan (Los) treatment diminished the Ang II-mediated stabilization of PIN (1.21 ± 0.07 LC Los vs. 1.16 ± 0.04* LC Ang II Los). Taken together, our studies suggest that increased central levels of Ang II contribute to the enhanced expression of PIN leading to reduced expression of the dimeric form of nNOS, thus diminishing the inhibitory action of NO• on pre-autonomic neurons in the PVN resulting in increased sympathetic outflow.

Reduced Basal Nitric Oxide Production Induces Precancerous Mammary Lesions via ERBB2 and TGFβ

One third of newly diagnosed breast cancers in the US are early-stage lesions. The etiological understanding and treatment of these lesions have become major clinical challenges. Because breast cancer risk factors are often linked to aberrant nitric oxide (NO) production, we hypothesized that abnormal NO levels might contribute to the formation of early-stage breast lesions. We recently reported that the basal level of NO in the normal breast epithelia plays crucial roles in tissue homeostasis, whereas its reduction contributes to the malignant phenotype of cancer cells. Here, we show that the basal level of NO in breast cells plummets during cancer progression due to reduction of the NO synthase cofactor, BH₄, under oxidative stress. Importantly, pharmacological deprivation of NO in prepubertal to pubertal animals stiffens the extracellular matrix and induces precancerous lesions in the mammary tissues. These lesions overexpress a fibrogenic cytokine, TGFβ, and an oncogene, ERBB2, accompanied by the occurrence of senescence and stem cell-like phenotype. Consistently, normalization of NO levels in precancerous and cancerous breast cells downmodulates TGFβ and ERBB2 and ameliorates their proliferative phenotype. This study sheds new light on the etiological basis of precancerous breast lesions and their potential prevention by manipulating the basal NO level.

Regulation of Nitric Oxide Production in the Developmental Programming of Hypertension and Kidney Disease

Development of the kidney can be altered in response to adverse environments leading to renal programming and increased vulnerability to the development of hypertension and kidney disease in adulthood. By contrast, reprogramming is a strategy shifting therapeutic intervention from adulthood to early life to reverse the programming processes. Nitric oxide (NO) is a key mediator of renal physiology and blood pressure regulation. NO deficiency is a common mechanism underlying renal programming, while early-life NO-targeting interventions may serve as reprogramming strategies to prevent the development of hypertension and kidney disease. This review will first summarize the regulation of NO in the kidney. We also address human and animal data supporting the link between NO system and developmental programming of hypertension and kidney disease. This will be followed by the links between NO deficiency and the common mechanisms of renal programming, including the oxidative stress, renin–angiotensin system, nutrient-sensing signals, and sex differences. Recent data from animal studies have suggested that interventions targeting the NO pathway could be reprogramming strategies to prevent the development of hypertension and kidney disease. Further clinical studies are required to bridge the gap between animal models and clinical trials in order to develop ideal NO-targeting reprogramming strategies and to be able to have a lifelong impact, with profound savings in the global burden of hypertension and kidney disease.

Post-translational regulation of neuronal nitric oxide synthase: implications for sympathoexcitatory states

INTRODUCTION

Nitric oxide (NO) synthesized via neuronal nitric oxide synthase (nNOS) plays a significant role in regulation/modulation of autonomic control of circulation. Various pathological states are associated with diminished nNOS expression and blunted autonomic effects of NO in the central nervous system (CNS) including heart failure, hypertension, diabetes mellitus, chronic renal failure etc. Therefore, elucidation of the molecular mechanism/s involved in dysregulation of nNOS is essential to understand the pathogenesis of increased sympathoexcitation in these diseased states. Areas covered: nNOS is a highly regulated enzyme, being regulated at transcriptional and posttranslational levels via protein-protein interactions and modifications viz. phosphorylation, ubiquitination, and sumoylation. The enzyme activity of nNOS also depends on the optimal concentration of substrate, cofactors and association with regulatory proteins. This review focuses on the posttranslational regulation of nNOS in the context of normal and diseased states within the CNS. Expert opinion: Gaining insight into the mechanism/s involved in the regulation of nNOS would provide novel strategies for manipulating nNOS directed therapeutic modalities in the future, including catalytically active dimer stabilization and protein-protein interactions with intracellular protein effectors. Ultimately, this is expected to provide tools to improve autonomic dysregulation in various diseases such as heart failure, hypertension, and diabetes.

Recent advances in research on nitrergic nerve-mediated vasodilatation

Cerebral vascular resistance and blood flow were widely considered to be regulated solely by tonic innervation of vasoconstrictor adrenergic nerves. However, pieces of evidence suggesting that parasympathetic nitrergic nerve activation elicits vasodilatation in dog and monkey cerebral arteries were found in 1990. Nitric oxide (NO) as a neurotransmitter liberated from parasympathetic postganglionic neurons decreases cerebral vascular tone and resistance and increases cerebral blood flow, which overcome vasoconstrictor responses to norepinephrine liberated from adrenergic nerves. Functional roles of nitrergic vasodilator nerves are found also in peripheral vasculature, including pulmonary, renal, mesenteric, hepatic, ocular, uterine, nasal, skeletal muscle, and cutaneous arteries and veins; however, adrenergic nerve-induced vasoconstriction is evidently greater than nitrergic vasodilatation in these vasculatures. In coronary arteries, neurogenic NO-mediated vasodilatation is not clearly noted; however, vasodilatation is induced by norepinephrine released from adrenergic nerves that activates β1-adrenoceptors. Impaired actions of NO liberated from the endothelium and nitrergic neurons are suggested to participate in cerebral hypoperfusion, leading to brain dysfunction, like that in Alzheimer's disease. Nitrergic neural dysfunction participates in impaired circulation in peripheral organs and tissues and also in systemic blood pressure increase. NO and vasodilator peptides, as sensory neuromediators, are involved in neurogenic vasodilatation in the skin. Functioning of nitrergic vasodilator nerves is evidenced not only in a variety of mammals, including humans and monkeys, but also in non-mammals. The present review article includes recent advances in research on the functional importance of nitrergic nerves concerning the control of cerebral blood flow, as well as other regions, and vascular resistance. Although information is still insufficient, the nitrergic nerve histology and function in vasculatures of non-mammals are also summarized.

Role of Nitric Oxide Synthase Uncoupling at Rostral Ventrolateral Medulla in Redox-Sensitive Hypertension Associated With Metabolic Syndrome

Metabolic syndrome (MetS), which is rapidly becoming prevalent worldwide, is long known to be associated with hypertension and recently with oxidative stress. Of note is that oxidative stress in the rostral ventrolateral medulla (RVLM), where sympathetic premotor neurons reside, contributes to sympathoexcitation and hypertension. This study sought to identify the source of tissue oxidative stress in RVLM and their roles in neural mechanism of hypertension associated with MetS. Adult normotensive rats subjected to a high-fructose diet for 8 weeks developed metabolic traits of MetS, alongside increases in sympathetic vasomotor activity and blood pressure. In RVLM of these MetS rats, the tissue level of reactive oxygen species was increased, nitric oxide (NO) was decreased, and mitochondrial electron transport capacity was reduced. Whereas the protein expression of neuronal NO synthase (nNOS) or protein inhibitor of nNOS was increased, the ratio of nNOS dimer/monomer was significantly decreased. Oral intake of pioglitazone or intracisternal infusion of tempol or coenzyme Q 10 significantly abrogated all those molecular events in high-fructose diet–fed rats and ameliorated sympathoexcitation and hypertension. Gene silencing of protein inhibitor of nNOS mRNA in RVLM using lentivirus carrying small hairpin RNA inhibited protein inhibitor of nNOS expression, increased the ratio of nNOS dimer/monomer, restored NO content, and alleviated oxidative stress in RVLM of high-fructose diet–fed rats, alongside significantly reduced sympathoexcitation and hypertension. These results suggest that redox-sensitive and protein inhibitor of nNOS–mediated nNOS uncoupling is engaged in a vicious cycle that sustains the production of reactive oxygen species in RVLM, resulting in sympathoexcitation and hypertension associated with MetS.

Restoration of asymmetric dimethylarginine-nitric oxide balance to prevent the development of hypertension

Despite the use of extensive antihypertensive therapy in patients with hypertension, little attention has been paid to early identification and intervention of individuals at risk for developing hypertension. The imbalance between nitric oxide (NO) and reactive oxygen species (ROS) resulting in oxidative stress has been implicated in the pathophysiology of hypertension. NO deficiency can precede the development of hypertension. Asymmetric dimethylarginine (ADMA) can inhibit nitric oxide synthase (NOS) and regulate local NO/ROS balance. Emerging evidence supports the hypothesis that ADMA-induced NO–ROS imbalance is involved in the development and progression of hypertension. Thus, this review summarizes recent experimental approaches to restore ADMA–NO balance in order to prevent the development of hypertension. Since hypertension might originate in early life, we also discuss the putative role of the ADMA–NO pathway in programmed hypertension. Better understanding of manipulations of the ADMA–NO pathway prior to hypertension in favor of NO will pave the way for the development of more effective medicine for the treatment prehypertension and programmed hypertension. However, more studies are needed to confirm the clinical benefit of these interventions.