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The prevalence of hypertension increases with age and is the leading modifiable risk factor for cognitive impairment and dementia. At present, the neural mechanisms promoting hypertension across the lifespan are incompletely understood. Using the Sprague-Dawley (SD) rat as a model of normal aging, we hypothesized (1) blood brain barrier (BBB) disruption and neuroinflammation in the paraventricular nucleus (PVN) of the hypothalamus enhances sympathetic tone and contributes to age-dependent hypertension, (2) age-dependent hypertension is associated with cognitive impairment, and (3) lowering blood pressure in aged rats with established hypertension improves cognitive function. We found male, but not female, rats develop age-dependent hypertension with enhanced sympathetic tone, BBB disruption, and neuroinflammation in the PVN. Aged hypertensive male rats also showed impairments in recognition and spatial memory. Utilizing pharmacological interventions, blood pressure was lowered in male rats with established hypertension using either losartan (LOS) or hydrochlorothiazide. However, only losartan improved recognition memory. Further, LOS reduced BBB disruption, microglial activation, astrocyte reactivity, and proinflammatory cytokine expression in the PVN which we speculate contributes to a decrease in blood pressure. These data show SD rats develop age-dependent hypertension and cognitive impairment in a sex-dependent manner. However, not all antihypertensive agents improve cognitive function equally as only losartan, an angiotensin II type 1 receptor antagonist (AT1R) improved recognition memory. Thus, AT1R antagonists represent a potential therapeutic approach for treating cognitive decline in the aging population., Competing Interests: Declarations. Conflict of interests: The authors declare no competing interests., (© 2024. The Author(s).)

Aging is a non-modifiable understudied risk factor for hypertension. We hypothesized that sympathetically mediated activation of renal sodium reabsorption drives age-dependent hypertension and the salt sensitivity of blood pressure (BP). Using 3-, 8-, and 16-month-old male and female Sprague-Dawley rats as a model of normal aging, we assessed BP, indices of sympathetic tone, and the physiological responses to acute and chronic sodium challenge including sodium chloride cotransporter (NCC) regulation. The effects of renal nerve ablation and NCC antagonism were assessed in hypertensive male rats. We observed sex-dependent impaired renal sodium handling (24 h sodium balance (meq), male 3-month 0.36 ± 0.1 vs. 16-month 0.84 ± 0.2; sodium load excreted during 5% bodyweight isotonic saline volume expansion (%) male 3-month 77 ± 5 vs. 16-month 22 ± 8), hypertension (MAP (mmHg) male 3-month 123 ± 4 vs. 16-month 148 ± 6), and the salt sensitivity of BP in aged male, but not female, rats. Attenuated sympathoinhibitory afferent renal nerve (ARN) responses contributed to increased sympathetic tone and hypertension in male rats. Increased sympathetic tone contributes to renal sodium retention, in part through increased NCC activity via a dysfunctional with-no-lysine kinase-(WNK) STE20/SPS1-related proline/alanine-rich kinase signaling pathway, to drive hypertension and the salt sensitivity of BP in aged male rats. NCC antagonism and renal nerve ablation, which reduced WNK dysfunction and decreased NCC activity, attenuated age-dependent hypertension in male Sprague-Dawley rats. The contribution of an impaired sympathoinhibitory ARN reflex to sex- and age-dependent hypertension in an NCC-dependent manner, via an impaired WNK1/WNK4 dynamic, suggests this pathway as a mechanism-based target for the treatment of age-dependent hypertension., (© 2024. The Author(s).)

Hypertension affects 1 in 2 U.S. adults and hypertension prevalence increases with aging. Both hypertension and aging can cause arterial remodeling. We investigated the hypothesis that aortic remodeling contributes to age-dependent hypertension in male Sprague Dawley (SD) rats. Compared to young 3-month-old rats 16-month-old male SD rats developed age-dependent hypertension that associated with increased sympathetic tone to the vasculature, elastin disarray and blood pressure variability. Our quantitative proteomic/phosphoproteomic workflow of the aorta identified 2366 proteins and 226 phosphoproteins, from which 58 proteins and 39 phosphoproteins were differentially expressed or phosphorylated respectively between young normotensive controls and aged hypertensive animals. Analysis of the proteome highlighted significant changes in the extracellular matrix, actin cytoskeleton and inflammatory pathways. Analysis of the differential phosphoproteome revealed significant differences in synapse and neuron projection and vascular smooth muscle cell (VSMC) function including actin remodeling and focal adhesions. STRING hypertension network analysis identified 13 differentially expressed and 10 differentially phosphorylated proteins associated with hypertension. Within the STRING analysis we observed 2 major areas of correlation of alterations in the aorta proteome with increased hypertension risk score - vascular inflammation and VSMC function. The majority of the identified phosphorylation sites (78.57%) in hypertension-relevant hyperphosphorylated proteins were located at serine residues. Collectively, we report that arterial remodeling in age-dependent hypertension is associated with an altered extracellular matrix and actin cytoskeleton and modulation of VSMC focal adhesion networks and neuron/synapse interactions.

Hypertension affects approximately one in two United States adults and sex plays an important role in the pathogenesis of hypertension. The Na + -Cl - cotransporter (NCC), regulated by a kinase network including with-no-lysine kinase (WNK)1 and WNK4, STE20/SPS1-related proline alanine-rich kinase (SPAK), and oxidative stress response 1 (OxSR1), is critical to Na + reabsorption and blood pressure regulation. Dietary salt differentially modulates NCC in salt-sensitive and salt-resistant rats, in part by modulation of WNK/SPAK/OxSR1 signaling. In this study, we tested the hypothesis that sex-dependent differences in NCC regulation contribute to the development of the salt sensitivity of blood pressure using male and female Sprague-Dawley (SD), Dahl salt-resistant (DSR), and Dahl salt-sensitive (DSS) rats. In normotensive salt-resistant SD and DSR rats, a high-salt diet evoked significant decreases in NCC activity, expression, and phosphorylation. In males, these changes were associated with no change in WNK1 expression, a decrease in WNK4 levels, and suppression of SPAK/OxSR1 expression and phosphorylation. In contrast, in females, there was decreased NCC activity associated with suppression of SPAK/OxSR1 expression and phosphorylation. In hypertensive DSS rats, the ability of females to suppress NCC (in opposition to males) via a SPAK/OxSR1 mechanism likely contributes to their lower magnitude of salt-sensitive hypertension. Collectively, our findings support the existence of sex differences in male versus female rats with NCC regulation during dietary salt intake involving suppression of WNK4 expression in male rats only and the involvement of SPAK/OxSR1 signaling in both males and females. NEW & NOTEWORTHY NCC regulation is sex dependent. In normotensive male and female Sprague-Dawley and Dahl salt-resistant rats, which exhibit dietary Na + -evoked NCC suppression, male rats exhibit decreased WNK4 expression and decreased SPAK and OxSR1 levels, whereas female rats only suppress SPAK and OxSR1. In hypertensive Dahl salt-sensitive rats, the ability of females to suppress NCC (in opposition to males) via a SPAK/OxSR1 mechanism likely contributes to their lower magnitude of salt-sensitive hypertension.

The mechanisms that sense alterations in total body sodium content to facilitate sodium homeostasis in response to an acute sodium challenge that does not increase blood pressure have not been fully elucidated. We hypothesized that the renal sympathetic nerves are critical to mediate natriuresis via α 1 - or β-adrenoceptors signal transduction pathways to maintain sodium balance in the face of acute increases in total body sodium content that do not activate the pressure-natriuresis mechanism. To address this hypothesis, we used acute bilateral renal denervation (RDNX), an anteroventral third ventricle (AV3V) lesion and α 1 - or β-antagonism during an acute 1M NaCl sodium challenge in conscious male Sprague Dawley rats. An acute 1M NaCl infusion did not alter blood pressure and evoked profound natriuresis and sympathoinhibition. Acute bilateral RDNX attenuated the natriuretic and sympathoinhibitory responses evoked by a 1M NaCl infusion [peak natriuresis (μeq/min) sham 14.5 ± 1.3 vs. acute RDNX: 9.2 ± 1.4, p < 0.05; plasma NE (nmol/L) sham control: 44 ± 4 vs. sham 1M NaCl infusion 11 ± 2, p < 0.05; acute RDNX control: 42 ± 6 vs. acute RDNX 1M NaCl infusion 25 ± 3, p < 0.05]. In contrast, an AV3V lesion did not impact the cardiovascular, renal excretory or sympathoinhibitory responses to an acute 1M NaCl infusion. Acute i.v. α 1 -adrenoceptor antagonism with terazosin evoked a significant drop in baseline blood pressure and significantly attenuated the natriuretic response to a 1M NaCl load [peak natriuresis (μeq/min) saline 17.2 ± 1.4 vs. i.v. terazosin 7.8 ± 2.5, p < 0.05]. In contrast, acute β-adrenoceptor antagonism with i.v. propranolol infusion did not impact the cardiovascular or renal excretory responses to an acute 1M NaCl infusion. Critically, the natriuretic response to an acute 1M NaCl infusion was significantly blunted in rats receiving a s.c. infusion of the α 1 -adrenoceptor antagonist terazosin at a dose that did not lower baseline blood pressure [peak natriuresis (μeq/min) sc saline: 18 ± 1 vs. sc terazosin 7 ± 2, p < 0.05]. Additionally, a s.c. infusion of the α 1 -adrenoceptor antagonist terazosin further attenuated the natriuretic response to a 1M NaCl infusion in acutely RDNX animals. Collectively these data indicate a specific role of a blood pressure-independent renal sympathetic nerve-dependent α 1 -adrenoceptor-mediated pathway in the natriuretic and sympathoinhibitory responses evoked by acute increases in total body sodium., Competing Interests: The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest., (Copyright © 2022 Frame, Nist, Kim, Kuwabara and Wainford.)

We have previously reported that brain Gαi 2 subunit proteins are required to maintain sodium homeostasis and are endogenously upregulated in the hypothalamic paraventricular nucleus (PVN) in response to increased dietary salt intake to maintain a salt resistant phenotype in rats. However, the origin of the signal that drives the endogenous activation and up-regulation of PVN Gαi 2 subunit protein signal transduction pathways is unknown. By central oligodeoxynucleotide (ODN) administration we show that the pressor responses to central acute administration and central infusion of sodium chloride occur independently of brain Gαi 2 protein pathways. In response to an acute volume expansion, we demonstrate, via the use of selective afferent renal denervation (ADNX) and anteroventral third ventricle (AV3V) lesions, that the sensory afferent renal nerves, but not the sodium sensitive AV3V region, are mechanistically involved in Gαi 2 protein mediated natriuresis to an acute volume expansion [peak natriuresis (μeq/min) sham AV3V: 43 ± 4 vs. AV3V 45 ± 4 vs. AV3V + Gαi 2 ODN 25 ± 4, p < 0.05; sham ADNX: 43 ± 4 vs. ADNX 23 ± 6, AV3V + Gαi 2 ODN 25 ± 3, p < 0.05]. Furthermore, in response to chronically elevated dietary sodium intake, endogenous up-regulation of PVN specific Gαi 2 proteins does not involve the AV3V region and is mediated by the sensory afferent renal nerves to counter the development of the salt sensitivity of blood pressure (MAP [mmHg] 4% NaCl; Sham ADNX 124 ± 4 vs. ADNX 145 ± 4, p < 0.05; Sham AV3V 125 ± 4 vs. AV3V 121 ± 5). Additionally, the development of the salt sensitivity of blood pressure following central ODN-mediated Gαi 2 protein down-regulation occurs independently of the actions of the brain angiotensin II type 1 receptor. Collectively, our data suggest that in response to alterations in whole body sodium the peripheral sensory afferent renal nerves, but not the central AV3V sodium sensitive region, evoke the up-regulation and activation of PVN Gαi 2 protein gated pathways to maintain a salt resistant phenotype. As such, both the sensory afferent renal nerves and PVN Gαi 2 protein gated pathways, represent potential targets for the treatment of the salt sensitivity of blood pressure., Competing Interests: The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest., (Copyright © 2021 Moreira, Nist, Carmichael, Kuwabara and Wainford.)

Increased sympathoexcitation and renal sodium retention during high salt intake are hallmarks of the salt sensitivity of blood pressure. The mechanism(s) by which excessive sympathetic nervous system release of norepinephrine influences renal sodium reabsorption is unclear. However, studies demonstrate that norepinephrine can stimulate the activity of the NCC (sodium chloride cotransporter) and promote the development of SSH (salt-sensitive hypertension). The adrenergic signaling pathways governing NCC activity remain a significant source of controversy with opposing studies suggesting a central role of upstream α 1 - and β-adrenoceptors in the canonical regulatory pathway involving WNKs (with-no-lysine kinases), SPAK (STE20/SPS1-related proline alanine-rich kinase), and OxSR1 (oxidative stress response 1). In our previous study, α 1 -adrenoceptor antagonism in norepinephrine-infused male Sprague-Dawley rats prevented the development of norepinephrine-evoked SSH in part by suppressing NCC activity and expression. In these studies, we used selective adrenoceptor antagonism in male Dahl salt-sensitive rats to test the hypothesis that norepinephrine-mediated activation of the NCC in Dahl SSH occurs via an α 1 -adrenoceptor dependent pathway. A high-salt diet evoked significant increases in NCC activity, expression, and phosphorylation in Dahl salt-sensitive rats that developed SSH. Increases were associated with a dysfunctional WNK1/4 dynamic and a failure to suppress SPAK/OxSR1 activity. α 1 -adrenoceptor antagonism initiated before high-salt intake or following the establishment of SSH attenuated blood pressure in part by suppressing NCC activity, expression, and phosphorylation. Collectively, our findings support the existence of a norepinephrine-activated α 1 -adrenoceptor gated pathway that relies on WNK/SPAK/OxSR1 signaling to regulate NCC activity in SSH.

New Findings: • What is the central question of this study? We hypothesized that central inflammatory processes that involve activation of microglia and astrocytes contribute to the development of Gαi 2 protein-dependent, salt-sensitive hypertension. • What is the main finding and its importance? The main finding is that PVN-specific inflammatory processes, driven by microglial activation, appear to be linked to the development of Gαi 2 protein-dependent, salt-sensitive hypertension in Sprague-Dawley rats. This finding might reveal new mechanistic targets in the treatment of hypertension., Abstract: The central mechanisms underlying salt-sensitive hypertension, a significant public health issue, remain to be established. Researchers in our laboratory have reported that hypothalamic paraventricular nucleus (PVN) Gαi 2 proteins mediate the sympathoinhibitory and normotensive responses to high sodium intake in salt-resistant rats. Given the recent evidence of central inflammation in animal models of hypertension, we hypothesized that PVN inflammation contributes to Gαi 2 protein-dependent, salt-sensitive hypertension. Male Sprague-Dawley rats received chronic intracerebroventricular infusions of a targeted Gαi 2 or control scrambled oligodeoxynucleotide (ODN) and were maintained for 7 days on a normal-salt (NS; 0.6% NaCl) or high-salt (HS; 4% NaCl) diet; in subgroups on HS, intracerebroventricular minocycline (microglial inhibitor) was co-infused with ODNs. Radiotelemetry was used in subgroups of rats to measure mean arterial pressure (MAP) chronically. In a separate group of rats, plasma noradrenaline, plasma renin activity, urinary angiotensinogen and mRNA levels of the PVN pro-inflammatory cytokines TNFα, IL-1β and IL-6 and the anti-inflammatory cytokine IL-10 were assessed. In additional groups, immunohistochemistry was performed for markers of PVN and subfornical organ microglial activation and cytokine levels and PVN astrocyte activation. High salt intake evoked salt-sensitive hypertension, increased plasma noradrenaline, PVN pro-inflammatory cytokine mRNA upregulation, anti-inflammatory cytokine mRNA downregulation and PVN-specific microglial activation in rats receiving a targeted Gαi 2 but not scrambled ODN. Minocycline co-infusion significantly attenuated the increase in MAP and abolished the increase in plasma noradrenaline and inflammation in Gαi 2 ODN-infused animals on HS. Our data suggest that central Gαi 2 protein prevents microglial-mediated PVN inflammation and the development of salt-sensitive hypertension., (© 2019 The Authors. Experimental Physiology published by John Wiley & Sons Ltd on behalf of The Physiological Society.)