Mechanisms involved in dual vasopressin/apelin neuron dysfunction during aging

The vascular footprint in cardiac homeostasis and hypertensive heart disease-A link between apelin receptor, vascular endothelial growth factor, and neuronal nitric oxide synthase

Recent studies have suggested a connection between disturbances of the apelin system and various cardiac pathologies, including hypertension, heart failure, and atherosclerosis. Vascular endothelial growth factor is crucial for cardiac homeostasis as a critical molecule in cardiac angiogenesis. Neuronal nitric oxide synthase is an essential enzyme producing nitric oxide, a key regulator of vascular tone. The present study aims to shed light upon the complex interactions between these three vital signaling molecules and examine their changes with the progression of hypertensive heart disease. We used two groups of spontaneously hypertensive rats and age-matched Wistar rats as controls. The expression of the apelin receptor, vascular endothelial growth factor, and neuronal nitric oxide synthase were assessed immunohistochemically. We used capillary density and cross-sectional area of the cardiomyocytes as quantitative parameters of cardiac hypertrophy. Immunoreactivity of the molecules was more potent in both ventricles of spontaneously hypertensive rats compared with age-matched controls. However, capillary density was lower in both ventricles of the two age groups of spontaneously hypertensive rats compared with controls, and the difference was statistically significant. In addition, the cross-sectional area of the cardiomyocytes was higher in both ventricles of the two age groups of spontaneously hypertensive rats compared with controls, and the difference was statistically significant. Our study suggests a potential link between the apelin receptor, vascular endothelial growth factor, and neuronal nitric oxide synthase in cardiac homeostasis and the hypertensive myocardium. Nevertheless, further research is required to better comprehend these interactions and their potential therapeutic implications.

Thirst: neuroendocrine regulation in mammals

Animals can sense their changing internal needs and then generate specific physiological and behavioural responses in order to restore homeostasis. Water-saline homeostasis derives from balances of water and sodium intake and output (drinking and diuresis, salt appetite and natriuresis), maintaining an appropriate composition and volume of extracellular fluid. Thirst is the sensation which drives to seek and consume water, regulated in the central nervous system by both neural and chemical signals. Water and electrolyte homeostasis depends on finely tuned physiological mechanisms, mainly susceptible to plasma Na+ concentration and osmotic pressure, but also to blood volume and arterial pressure. Increases of osmotic pressure as slight as 1-2% are enough to induce thirst ("homeostatic" or cellular), by activation of specialized osmoreceptors in the circumventricular organs, outside the blood-brain barrier. Presystemic anticipatory signals (by oropharyngeal or gastrointestinal receptors) inhibit thirst when fluids are ingested, or stimulate thirst associated with food intake. Hypovolemia, arterial hypotension, Angiotensin II stimulate thirst ("hypovolemic thirst", "extracellular dehydration"). Hypervolemia, hypertension, Atrial Natriuretic Peptide inhibit thirst. Circadian rhythms of thirst are also detectable, driven by suprachiasmatic nucleus in the hypothalamus. Such homeostasis and other fundamental physiological functions (cardiocircolatory, thermoregulation, food intake) are highly interdependent.

Several neuropeptides involved in parkinsonian neuroprotection modulate the firing properties of nigral dopaminergic neurons

Parkinson's disease is characterized by progressive degeneration of dopaminergic neurons in the substantia nigra pars compacta. The surviving nigral dopaminergic neurons display altered spontaneous firing activity in Parkinson's disease. The firing rate of nigral dopaminergic neurons decreases long before complete neuronal death and the appearance of parkinsonian symptoms. A mild stimulation could rescue dopaminergic neurons from death and in turn play neuroprotective effects. Several neuropeptides, including cholecystokinin (CCK), ghrelin, neurotensin, orexin, tachykinins and apelin, within the substantia nigra pars compacta play important roles in the modulation of spontaneous firing activity of dopaminergic neurons and therefore involve motor control and motor disorders. Here, we review neuropeptide-induced modulation of the firing properties of nigral dopaminergic neurons. This review may provide a background to guide further investigations into the involvement of neuropeptides in movement control by modulating firing activity of nigral dopaminergic neurons in Parkinson's disease.

Neuropeptide apelin presented in the dopaminergic neurons modulates the neuronal excitability in the substantia nigra pars compacta

The dopaminergic neurons in the substantia nigra pars compacta are characterized by autonomous pacemaking activity. The spontaneous firing activity of nigral dopaminergic neurons plays an important role in physiological function and is essential for their survival. Importantly, the spontaneous firing activity may also be involved in the preferential vulnerability of the nigral dopaminergic neurons in Parkinson's disease (PD). The neuropeptide apelin was reported to exert neuroprotective effects in neurodegenerative diseases, including PD. And it was noticed that apelin modulates neuronal activity in some brain regions. The present study investigated the electrophysiological and behavioral effects of apelin in the substantia nigra. Double-labeling immunofluorescence showed that apelin was present in nigral dopaminergic neurons and that these neurons expressed apelin receptor APJ. Further single unit in vivo electrophysiological recordings revealed that endogenous apelin tonically increased the firing rate of nigral dopaminergic neurons in both normal and parkinsonian animals. Exogenous apelin-13 exerted excitatory effects on the majority of nigral dopaminergic neurons, yet reduced excitability in a subset of neurons. In addition, nigral application of apelin-13 increased motor activity in normal rats and blocking endogenous apelin reduced motor activity. Considering the involvement of the spontaneous firing activity of nigral dopaminergic neurons in the development of PD and the possibility that apelin acts in an autocrine manner on apelin receptors expressed by nigral dopaminergic neurons, the modulation of the spontaneous firing activity of nigral dopaminergic neurons by apelin may serve as a neuroprotective factor in PD.

Beta-Sitosterol Facilitates GLUT4 Vesicle Fusion on the Plasma Membrane via the Activation of Rab/IRAP/Munc 18 Signaling Pathways in Diabetic Gastrocnemius Muscle of Adult Male Rats

Nutritional overload in the form of high-fat and nonglycolysis sugar intake contributes towards the accelerated creation of reactive oxygen species (ROS), hyperglycemia, and dyslipidemia. Glucose absorption and its subsequent oxidation processes in fat and muscle tissues alter as a consequence of these modifications. Insulin resistance (IR) caused glucose transporter 4 (GLUT4) translocation to encounter a challenge that manifested itself as changes in glycolytic pathways and insulin signaling. We previously found that beta (β)-sitosterol reduces IR in fat tissue via IRS-1/PI3K/Akt facilitated signaling due to its hypolipidemic and hypoglycemic activity. The intention of this research was to see whether the phytosterol β-sitosterol can aid in the translocation of GLUT4 in rats fed on high-fat diet (HFD) and sucrose by promoting Rab/IRAP/Munc 18 signaling molecules. The rats were labeled into four groups, namely control rats, HFD and sucrose-induced diabetic control rats, HFD and sucrose-induced diabetic rats given oral dose of 20 mg/kg body wt./day of β-sitosterol treatment for 30 days, and HFD and sucrose-induced diabetic animals given oral administration of 50 mg/kg body wt./day metformin for 30 days. Diabetic rats administered with β-sitosterol and normalized the titers of blood glucose, serum insulin, serum testosterone, and the status of insulin tolerance and oral glucose tolerance. In comparison with the control group, β-sitosterol effectively regulated both glycolytic and gluconeogenesis enzymes. Furthermore, qRT-PCR analysis of the mRNA levels of key regulatory genes such as SNAP23, VAMP-2, syntaxin-4, IRAP, vimentin, and SPARC revealed that β-sitosterol significantly regulated the mRNA levels of the above genes in diabetic gastrocnemius muscle. Protein expression analysis of Rab10, IRAP, vimentin, and GLUT4 demonstrated that β-sitosterol had a positive effect on these proteins, resulting in effective GLUT4 translocation in skeletal muscle. According to the findings, β-sitosterol reduced HFD and sucrose-induced IR and augmented GLUT4 translocation in gastrocnemius muscle through insulin signaling modulation via Rab/IRAP/Munc 18 and glucose metabolic enzymes. The present work is the first of its kind to show that β-sitosterol facilitates GLUT4 vesicle fusion on the plasma membrane via Rab/IRAP/Munc 18 signaling molecules in gastrocnemius muscle.

Apelin-13 protects against memory impairment and neuronal loss, Induced by Scopolamine in male rats

The present study aimed to evaluate the effects of Apelin-13 on scopolamine-induced memory impairment in rats. Forty male rats were divided into five groups of eight. The control group received no intervention; the scopolamine group underwent stereotaxic surgery and received 3 mg/kg intraperitoneal scopolamine. The treatment groups additionally received 1.25, 2.5 and 5 µg apelin-13 in right lateral ventricles for 7 days. All rats (except the control group) were tested for the passive avoidance reaction, 24 h after the last drug injection. For histological analysis, hippocampal sections were stained with cresyl violet; synaptogenesis biochemical markers were determined by immunoblotting. Apelin-13 alleviated scopolamine-induced passive avoidance memory impairment and neuronal loss in the rats' hippocampus (P<0.001). The reduction observed in mean concentrations of hippocampal synaptic proteins (including neurexin1, neuroligin, and postsynaptic density protein 95) in scopolamine-treated animals was attenuated by apelin-13 treatment. The results demonstrated that apelin-13 can protect against passive avoidance memory deficiency, and neuronal loss, induced by scopolamine in male rats. Further experimental and clinical studies are required to confirm its therapeutic potential in neurodegenerative diseases.

Impact of the apelin/APJ axis in the pathogenesis of Parkinson's disease with therapeutic potential

The pathogenesis of Parkinson's disease (PD) remains elusive. There is still no available disease-modifying strategy against PD, whose management is mainly symptomatic. A growing amount of preclinical evidence shows that a complex interplay between autophagy dysregulation, mitochondrial impairment, endoplasmic reticulum stress, oxidative stress, and excessive neuroinflammation underlies PD pathogenesis. Identifying key molecules linking these pathological cellular processes may substantially aid in our deeper understanding of PD pathophysiology and the development of novel effective therapeutic approaches. Emerging preclinical evidence indicates that apelin, an endogenous neuropeptide acting as a ligand of the orphan G protein-coupled receptor APJ, may play a key neuroprotective role in PD pathogenesis, via inhibition of apoptosis and dopaminergic neuronal loss, autophagy enhancement, antioxidant effects, endoplasmic reticulum stress suppression, as well as prevention of synaptic dysregulation in the striatum, excessive neuroinflammation, and glutamate-induced excitotoxicity. Underlying signaling pathways involve phosphoinositide 3-kinase (PI3K)/Akt/mammalian target of rapamycin, extracellular signal-regulated kinase 1/2, and inositol requiring kinase 1α/XBP1/C/EBP homologous protein. Herein, we discuss the role of apelin/APJ axis and associated molecular mechanisms on the pathogenesis of PD in vitro and in vivo and provide evidence for its challenging therapeutic potential.

Circulating plasma factors involved in rejuvenation

Aging is defined as a time-dependent functional decline that occurs in many physiological systems. This decline is the primary risk factor for prominent human pathologies such as cancer, metabolic disorders, cardiovascular disorders, and neurodegenerative diseases. Aging and age-related diseases have multiple causes. Parabiosis experiments, in which the circulatory systems of young and old mice were surgically joined, revealed that young plasma counteracts aging and rejuvenates organs in old mice, suggesting the existence of rejuvenating factors that become less abundant with aging. Diverse approaches have identified a large number of plasma proteins whose levels differ significantly between young and old mice, as well as numerous rejuvenating factors that reverse aged-related impairments in multiple tissues. These observations suggest that increasing the levels of key rejuvenating factors could promote restorative biological processes or inhibit pathological degeneration. Inspired by such findings, several companies have begun selling “young blood transfusions,” and others have tested young plasma as a treatment for Alzheimer’s disease. Here, we summarize the current findings regarding rejuvenating factors.

Protein Deimination Signatures in Plasma and Plasma-EVs and Protein Deimination in the Brain Vasculature in a Rat Model of Pre-Motor Parkinson's Disease

The identification of biomarkers for early diagnosis of Parkinson’s disease (PD) is of pivotal importance for improving approaches for clinical intervention. The use of translatable animal models of pre-motor PD therefore offers optimal opportunities for novel biomarker discovery in vivo. Peptidylarginine deiminases (PADs) are a family of calcium-activated enzymes that contribute to protein misfolding through post-translational deimination of arginine to citrulline. Furthermore, PADs are an active regulator of extracellular vesicle (EV) release. Both protein deimination and extracellular vesicles (EVs) are gaining increased attention in relation to neurodegenerative diseases, including in PD, while roles in pre-motor PD have yet to be investigated. The current study aimed at identifying protein candidates of deimination in plasma and plasma-EVs in a rat model of pre-motor PD, to assess putative contributions of such post-translational changes in the early stages of disease. EV-cargo was further assessed for deiminated proteins as well as three key micro-RNAs known to contribute to inflammation and hypoxia (miR21, miR155, and miR210) and also associated with PD. Overall, there was a significant increase in circulating plasma EVs in the PD model compared with sham animals and inflammatory and hypoxia related microRNAs were significantly increased in plasma-EVs of the pre-motor PD model. A significantly higher number of protein candidates were deiminated in the pre-motor PD model plasma and plasma-EVs, compared with those in the sham animals. KEGG (Kyoto encyclopedia of genes and genomes) pathways identified for deiminated proteins in the pre-motor PD model were linked to “Alzheimer’s disease”, “PD”, “Huntington’s disease”, “prion diseases”, as well as for “oxidative phosphorylation”, “thermogenesis”, “metabolic pathways”, “Staphylococcus aureus infection”, gap junction, “platelet activation”, “apelin signalling”, “retrograde endocannabinoid signalling”, “systemic lupus erythematosus”, and “non-alcoholic fatty liver disease”. Furthermore, PD brains showed significantly increased staining for total deiminated proteins in the brain vasculature in cortex and hippocampus, as well as increased immunodetection of deiminated histone H3 in dentate gyrus and cortex. Our findings identify EVs and post-translational protein deimination as novel biomarkers in early pre-motor stages of PD.

Apelin Promotes ECM Synthesis by Enhancing Autophagy Flux via TFEB in Human Degenerative NP Cells under Oxidative Stress

Background

Apelin alleviates oxidative stress which contributes to the development of aging. IVDD is a disease closely correlated to aging and oxidative stress which is known to be harmful to NP cells' matrix synthesis. The purpose of the present study was to investigate the role and underlying mechanism of Apelin in NP cells' matrix degradation under oxidative stress.

Methods

First, the mRNA and protein expressions of Apelin were checked by RT-PCR and Western blot in NP from normal and degenerative IVD to explore the relationship between Apelin and IVDD preliminarily. Then, H₂O₂ was used to mimic oxidative stress of NP cells. After treated with Apelin 13 and CQ, the GAG content was assessed by DMMB and the mRNA/protein expressions of NP matrix macromolecules (Collagen II and Aggrecan) and autophagy-related markers (LC3 and p62) were assessed by RT-PCR/Western blot. Finally, TFEB was knocked down by esiRNA-TFEB transfection and the nucleoprotein expression of TFEB and autophagy-related markers (LC3 and p62) were assessed by Western blot to discuss whether TFEB is involved in Apelin regulating autophagy flux in NP cells under oxidative stress.

Results

Our data first confirmed that the mRNA and protein expressions of Apelin were decreased with IVDD. Furthermore, Apelin increased GAG content of NP cells and mRNA/protein expressions of NP matrix macromolecules (Collagen II and Aggrecan) and promoted autophagic flux (LC3II/I increased and p62 decreased) under oxidative stress. Finally, after transfected with esiRNA-TFEB, Apelin cannot promote autophagic flux any more in human degenerative NP cells.

Conclusion

Our data indicated that Apelin promotes ECM synthesis by enhancing autophagy flux via TFEB in human degenerative NP cells under oxidative stress. This viewpoint may provide a new therapeutic idea for IVDD.

Cerebral transcriptome analysis reveals age-dependent progression of neuroinflammation in P301S mutant tau transgenic male mice

Aggregation of the microtubule-associated protein, tau, can lead to neurofibrillary tangle formation in neurons and glia which is the hallmark of tauopathy. The cellular damage induced by the formation of neurofibrillary tangles leads to neuroinflammation and consecutive neuronal death. However, detailed observation of transcriptomic changes under tauopathy together with the comparison of age-dependent progression of neuroinflammatory gene expressions mediated by tau overexpression is required. Employing RNA sequencing on PS19 transgenic mice that overexpress human mutant tau harboring the P301S mutation, we have examined the effects of age-dependent tau overexpression on transcriptomic changes of immune and inflammatory responses in the cerebral cortex. Compared to age-matched wild type control, P301S transgenic mice exhibit significant transcriptomic alterations. We have observed age-dependent neuroinflammatory gene expression changes in both wild type and P301S transgenic mice where tau overexpression further promoted the expression of neuroinflammatory genes in 10-month old P301S transgenic mice. Moreover, functional gene network analyses (gene ontology and pathway enrichment) and prospective target protein interactions predicted the potential involvement of multiple immune and inflammatory pathways that may contribute to tau-mediated neuronal pathology. Our current study on P301S transgenic mice model revealed for the first time, the differences of gene expression patterns in both early and late stage of tau pathology in cerebral cortex. Our analyses also revealed that tau overexpression alone induces multiple inflammatory and immune transcriptomic changes and may provide a roadmap to elucidate the targets of anti-inflammatory therapeutic strategy focused on tau pathology and related neurodegenerative diseases.

Osmoregulation Performance and Kidney Transplant Outcome

BACKGROUND

Kidney transplant recipients have an impaired ability to dilute urine but seldom develop baseline hyponatremia before ESRD. Although hyponatremia is a risk factor for adverse events in CKD and in kidney transplant recipients, it remains unclear whether subtler alterations in osmoregulation performance are associated with outcome.

METHODS

We studied a single-center prospective cohort of 1258 kidney transplant recipients who underwent a water-loading test 3 months after transplant to determine osmoregulation performance. Measured GFR (mGFR) was performed at the same visit. A group of 164 healthy candidates for kidney donation served as controls. We further evaluated the association of osmoregulation performance with transplantation outcomes and subsequent kidney function.

RESULTS

Unlike controls, most kidney transplant recipients failed to maintain plasma sodium during water loading (plasma sodium slope of -0.6±0.4 mmol/L per hour in transplant recipients versus -0.12±0.3 mmol/L per hour in controls; P<0.001). Steeper plasma sodium reduction during the test independently associated with the composite outcome of all-cause mortality and allograft loss (hazard ratio [HR], 1.73 per 1 mmol/L per hour decrease in plasma sodium; 95% confidence interval [95% CI], 1.23 to 2.45; P=0.002) and allograft loss alone (HR, 2.04 per 1 mmol/L per hour decrease in plasma sodium; 95% CI, 1.19 to 3.51; P=0.01). The association remained significant in a prespecified sensitivity analysis excluding patients with hyperglycemia. In addition, a steeper plasma sodium slope 3 months after transplantation independently correlated with lower mGFR at 12 months (β=1.93; 95% CI, 0.46 to 3.41; P=0.01).

CONCLUSIONS

Reduced osmoregulation performance occurs frequently in kidney transplant recipients and is an independent predictor of renal outcome.

Apelin-13 attenuates motor impairments and prevents the changes in synaptic plasticity-related molecules in the striatum of Parkinsonism rats

The striatum plays a critical role in motor control and also learning and memory of motor skills. It has been reported that striatal synaptic components are significantly decreased in dopaminergic-denervated striatum. In this study the effects of apelin-13 were investigated on motor disorders and striatal synaptosomal expression of PSD-95, neurexin1, neuroligin, metabotropic glutamate receptor (mGlu R1) and dopaminergic receptors (DR1 and DR2) in rat parkinsonism experimental model. 6-hydroxydopamine (6-OHDA) was injected into the substantia nigra. Apelin-13 (1, 2 and 3 μg/rat) was administered into the substantia nigra one week after the 6-OHDA injection. Accelerating rotarod, beam-balance, beam-walking and bar tests were performed one month after the apelin injection. Immunohistochemistry staining of dopaminergic neurons was performed. The levels of synaptic proteins were determined by immunoblotting. 6-OHDA-treated animals showed a significant impairment in motor-skill tasks and a dramatically change in the expression levels of mentioned proteins. Apelin-13 (3 μg/rat) significantly attenuates the motor impairments and prevents the changes in striatal synaptic elements in 6-OHDA-treated animals. In addition, it could rescue the dopaminergic neurons of the substantia nigra. The data will potentially extend the possible benefic aspect of apelin in neurodegenerative disorders.

Apelin/APJ system: A novel promising target for anti-aging intervention

Apelin, an endogenous ligand for the G protein-coupled receptor APJ, is widely expressed in various organs. Recent research has indicated that the Apelin/APJ system plays an important role in aging. Apelin and APJ receptor expression are down-regulated with increasing age. In murine models, Apelin and APJ knockouts exhibit accelerated senescence whereas Apelin-restoration results in enhanced vigor and rejuvenated behavioral and circadian phenotypes. Furthermore, aged Apelin knockout mice develop progressive impairment of cardiac contractility associated with systolic dysfunction. Apelin is crucial to maintain cardiac contractility in aging. Moreover, the Apelin/APJ system appears to be involved in regulation of renin-angiotensin-aldosterone system (RAAS), apoptosis, inflammation and oxidative stress which promotes aging. Likewise, the Apelin/APJ system regulates autophagy, stem cells and the sirtuin family thus contributing to anti-aging. In this review, we describe the relationship between Apelin/APJ system and aging. We elaborate on the role of the Apelin/APJ system in aging stimulators, aging inhibitors and age-related diseases such as obesity, diabetes and cardiovascular disease. We conclude that Apelin/APJ system might become a novel promising therapeutic target for anti-aging.

Downregulation of the Apelinergic Axis Accelerates Aging, whereas Its Systemic Restoration Improves the Mammalian Healthspan

Aging drives the occurrence of numerous diseases, including cardiovascular disease (CVD). Recent studies indicate that blood from young mice reduces age-associated pathologies. However, the "anti-aging" factors in juvenile circulation remain poorly identified. Here, we characterize the role of the apelinergic axis in mammalian aging and identify apelin as an anti-aging factor. The expression of apelin (apln) and its receptor (aplnr) exhibits an age-dependent decline in multiple organs. Reduced apln signaling perturbs organismal homeostasis; mice harboring genetic deficiency of aplnr or apln exhibit enhanced cardiovascular, renal, and reproductive aging. Genetic or pharmacological abrogation of apln signaling also induces cellular senescence mediated, in part, by the activation of senescence-promoting transcription factors. Conversely, restoration of apln in 15-month-old wild-type mice reduces cardiac hypertrophy and exercise-induced hypertensive response. Additionally, apln-restored mice exhibit enhanced vigor and rejuvenated behavioral and circadian phenotypes. Hence, a declining apelinergic axis promotes aging, whereas its restoration extends the murine healthspan.

Apelin-13 ameliorates cognitive impairments in 6-hydroxydopamine-induced substantia nigra lesion in rats

Although Parkinson's disease (PD) is well known with its motor deficits, the patients often suffer from cognitive dysfunction. Apelin, as the endogenous ligand of the APJ receptor, is found in several brain regions such as substantia nigra and mesolimbic pathway. However, the role of apelin in cognition and cognitive disorders has not been fully clarified. In this study the effects of apelin-13 were investigated on cognitive disorders in rat Parkinsonism experimental model. 6-hydroxydopamine (6-OHDA) was administrated into the substantia nigra. Apelin-13 (1, 2 and 3μg/rat) was administered into the substantia nigra one week after the 6-OHDA injection. Morris water maze (MWM), object location and novel object recognition tests were performed one month after the apelin injection. 6-OHDA-treated animals showed a significant impairment in cognitive functions which was revealed by the increased in the escape latency and traveled distance in MWM test and decreased in the exploration index in novel object recognition and object location tasks. Apelin-13 (3μg/rat) significantly attenuates the mentioned cognitive impairments in 6-OHDA-treated animals. In conclusion, the data support the pro-cognitive property of apelin-13 in 6-OHDA-induced cognitive deficit and provided a new pharmacological aspect of the neuropeptide apelin.

Role of the Vasopressin/Apelin Balance and Potential Use of Metabolically Stable Apelin Analogs in Water Metabolism Disorders

Apelin, a (neuro)vasoactive peptide, plays a prominent role in controlling body fluid homeostasis and cardiovascular functions. In animal models, experimental data demonstrate that intracerebroventricular injection of apelin into lactating rats inhibits the phasic electrical activity of arginine vasopressin (AVP) neurons, reduces plasma AVP levels, and increases aqueous diuresis. In the kidney, apelin increases diuresis by increasing the renal microcirculation and by counteracting the antidiuretic effect of AVP at the tubular level. Moreover, after water deprivation or salt loading, in humans and in rodents, AVP and apelin are conversely regulated to facilitate systemic AVP release and to avoid additional water loss from the kidney. Furthermore, apelin and vasopressin secretion are significantly altered in various water metabolism disorders including hyponatremia and polyuria-polydipsia syndrome. Since the in vivo half-life of apelin is in the minute range, metabolically stable apelin analogs were developed. The efficacy of these lead compounds for decreasing AVP release and increasing both renal blood flow and diuresis, make them promising candidates for the treatment of water retention and/or hyponatremic disorders.

A Direct Neurokinin B Projection from the Arcuate Nucleus Regulates Magnocellular Vasopressin Cells of the Supraoptic Nucleus

Central administration of neurokinin B (NKB) agonists stimulates immediate early gene expression in the hypothalamus and increases the secretion of vasopressin from the posterior pituitary through a mechanism that depends on the activation of neurokinin receptor 3 receptors (NK3R). The present study reports that, in the rat, immunoreactivity for NK3R is expressed in magnocellular vasopressin and oxytocin neurones in the supraoptic nucleus (SON) and paraventricular nucleus (PVN) of the hypothalamus, and that NKB immunoreactivity is expressed in fibres in close juxtaposition with vasopressin neurones at both of these sites. Retrograde tracing in the rat shows that some NKB-expressing neurones in the arcuate nucleus project to the SON and, in mice, using an anterograde tracing approach, it is found that kisspeptin-expressing neurones of the arcuate nucleus, which are known to co-express NKB, project to the SON and PVN. Finally, i.c.v. injection of the NK3R agonist senktide is shown to potently increase the electrical activity of vasopressin neurones in the SON in vivo with no significant effect detected on oxytocin neurones. The results suggest that NKB-containing neurones in the arcuate nucleus regulate the secretion of vasopressin from magnocellular neurones in rodents, and the possible significance of this is discussed.

Dissecting the Contribution of Vascular Alterations and Aging to Alzheimer's Disease

Alzheimer's disease (AD) is a neurodegenerative disease characterized by cognitive decline that afflicts as many as 45 % of individuals who survive past the age of 85. AD has been associated with neurovascular dysfunction and brain accumulation of amyloid-β peptide, as well as tau phosphorylation and neurodegeneration, but the pathogenesis of the disease is still somewhat unclear. According to the amyloid cascade hypothesis of AD, accumulation of amyloid-β peptide (Aβ) aggregates initiates a sequence of events leading to neuronal injury and loss, and dementia. Alternatively, the vascular hypothesis of AD incorporates the vascular contribution to the disease, stating that a primary insult to brain microcirculation (e.g., stroke) not only contributes to amyloidopathy but initiates a non-amyloidogenic pathway of vascular-mediated neuronal dysfunction and injury, which involves blood-brain barrier compromise, with increased permeability of blood vessels, leakage of blood-borne components into the brain, and, consequently, neurotoxicity. Vascular dysfunction also includes a diminished brain capillary flow, causing multiple focal ischemic or hypoxic microinjuries, diminished amyloid-β clearance, and formation of neurotoxic oligomers, which lead to neuronal dysfunction. Here we present and discuss relevant findings on the contribution of vascular alterations during aging to AD, with the hope that a better understanding of the players in the "orchestra" of neurodegeneration will be useful in developing therapies to modulate the "symphony".

Aquaporins, vasopressin, and aging: current perspectives

Functioning of the hypothalamic-neurohypophyseal-vasopressin axis is altered in aging, and the pathway may represent a plausible target to slow the process of aging. Arginine vasopressin, a nine-amino acid peptide that is secreted from the posterior pituitary in response to high plasma osmolality and hypotension, is central in this pathway. Vasopressin has important roles in circulatory and water homoeostasis mediated by vasopressin receptor subtypes V1a (vascular), V1b (pituitary), and V2 (vascular, renal). A dysfunction in this pathway as a result of aging can result in multiple abnormalities in several physiological systems. In addition, vasopressin plasma concentration is significantly higher in males than in females and vasopressin-mediated effects on renal and vascular targets are more pronounced in males than in females. These findings may be caused by sex differences in vasopressin secretion and action, making men more susceptible than females to diseases like hypertension, cardiovascular and chronic kidney diseases, and urolithiasis. Recently the availability of new, potent, orally active vasopressin receptor antagonists, the vaptans, has strongly increased the interest on vasopressin and its receptors as a new target for prevention of age-related diseases associated with its receptor-altered signaling. This review summarizes the recent literature in the field of vasopressin signaling in age-dependent abnormalities in kidney, cardiovascular function, and bone function.

Modulation of pain in pediatric sickle cell disease: understanding the balance between endothelin mediated vasoconstriction and apelin mediated vasodilation

Children with sickle cell disease (SCD) have painful vaso-occlusive episodes (VOEs), which often reoccur across the individual's lifespan. Vaso-constrictive and vaso-dilatory molecules have been hypothesized to play a role in VOEs. Endothelin-1 (ET-1) is a potent vasoconstrictor that is released during VOEs and is correlated with pain history. Apelin is a vaso-dilatory peptide that also has a modulatory role in pain processing. We hypothesize that the ratio between vaso-dilatory and vaso-constrictive tone in children with SCD may be a marker of pain sensitization and vaso-occlusion. Plasma endothelin and apelin levels were measured in 47 children with SCD. Procedural pain and baseline pain were assessed via child- and caregiver-reports and observational distress. Pain history was assessed using retrospective chart review. Plasma apelin was related to age, with decreased levels in older children. The ratio between apelin and ET-1 was negatively correlated to observational baseline pain. The ratio between apelin and Big ET was negatively correlated to caregiver ratings of baseline pain and positively correlated to history of VOEs, which is possibly due to hydroxyurea treatment. These results suggest that an imbalance in the apelin and endothelin systems may contribute to an increasing number of VOEs and baseline pain in children with SCD.