Female protection from slow-pressor effects of angiotensin II involves prevention of ROS production independent of NMDA receptor trafficking in hypothalamic neurons expressing angiotensin 1A receptors

Estrogen receptor beta activity contributes to both tumor necrosis factor alpha expression in the hypothalamic paraventricular nucleus and the resistance to hypertension following angiotensin II in female mice

Sex differences in the sensitivity to hypertension and inflammatory processes are well characterized but insufficiently understood. In male mice, tumor necrosis factor alpha (TNFα) in the hypothalamic paraventricular nucleus (PVN) contributes to hypertension following slow-pressor angiotensin II (AngII) infusion. However, the role of PVN TNFα in the response to AngII in female mice is unknown. Using a combination of in situ hybridization, high-resolution electron microscopic immunohistochemistry, spatial-temporal gene silencing, and dihydroethidium microfluorography we investigated the influence of AngII on both blood pressure and PVN TNFα signaling in female mice. We found that chronic (14-day) infusion of AngII in female mice did not impact blood pressure, TNFα levels, the expression of the TNFα type 1 receptor (TNFR1), or the subcellular distribution of TNFR1 in the PVN. However, it was shown that blockade of estrogen receptor β (ERβ), a major hypothalamic estrogen receptor, was accompanied by both elevated PVN TNFα and hypertension following AngII. Further, AngII hypertension following ERβ blockade was attenuated by inhibiting PVN TNFα signaling by local TNFR1 silencing. It was also shown that ERβ blockade in isolated PVN-spinal cord projection neurons (i.e. sympathoexcitatory) heightened TNFα-induced production of NADPH oxidase (NOX2)-mediated reactive oxygen species, molecules that may play a key role in mediating the effect of TNFα in hypertension. These results indicate that ERβ contributes to the reduced sensitivity of female mice to hypothalamic inflammatory cytokine signaling and hypertension in response to AngII.

Angiotensin II differentially affects hippocampal glial inflammatory markers in young adult male and female mice

Hypertension is a risk factor for neurodegenerative disorders involving inflammation and inflammatory cytokine-producing brain cells (microglia and astrocytes) in the hippocampus and medial prefrontal cortex (mPFC). Here we investigated the effect of slow-pressor angiotensin II (AngII) on gliosis in the hippocampus and mPFC of young adult (2-mo-old) male and female mice. In males, AngII induced hypertension, and this resulted in an increase in the density of the astrocyte marker glial fibrillary acidic protein (GFAP) in the subgranular hilus and a decrease in the density of the microglial marker ionized calcium binding adapter molecule (Iba-1) in the CA1 region. Females infused with AngII did not show hypertension but, significantly, showed alterations in hippocampal glial activation. Compared with vehicle, AngII-infused female mice had an increased density of Iba-1 in the dentate gyrus and CA2/3a region. Like males, females infused with AngII exhibited decreased Iba-1 in the CA1 region. Neither male nor female mice showed differences in GFAP or Iba-1 in the mPFC following AngII infusion. These results demonstrate that the hippocampus is particularly vulnerable to AngII in young adulthood. Differences in gonadal hormones or the sensitivity to AngII hypertension may account for divergences in GFAP and Iba-1 in males and females.

Blocking FcγRIIB in Smooth Muscle Cells Reduces Hypertension

[Figure: see text].

Estrogen Receptor β Contributes to Both Hypertension and Hypothalamic Plasticity in a Mouse Model of Peri-Menopause

Hypertension susceptibility in women increases at the transition to menopause, termed perimenopause, a state characterized by erratic estrogen fluctuation and extended hormone cycles. Elucidating the role of estrogen signaling in the emergence of hypertension during perimenopause has been hindered by animal models that are confounded by abrupt estrogen cessation or effects of aging. In the present study, accelerated ovarian failure (AOF) in estrogen receptor β (ERβ) reporter mice was induced by 4-vinylcyclohexene diepoxide in young mice to model early-stage ovarian failure (peri-AOF) characteristic of peri-menopause. It was found that administering ERβ agonists suppressed elevated blood pressure in a model of neurogenic hypertension induced by angiotensin II (AngII) in peri-AOF, but not in age-matched male mice. It was also found that ERβ agonist administration in peri-AOF females, but not males, suppressed the heightened NMDAR signaling and reactive oxygen production in ERβ neurons in the hypothalamic paraventricular nucleus (PVN), a critical neural regulator of blood pressure. It was further shown that deleting ERβ in the PVN of gonadally intact females produced a phenotype marked by a sensitivity to AngII hypertension. These results suggest that ERβ signaling in the PVN plays an important role in blood pressure regulation in female mice and contributes to hypertension susceptibility in females at an early stage of ovarian failure comparable to human perimenopause.

SorCS2 is required for social memory and trafficking of the NMDA receptor

Social memory processing requires functional CA2 neurons, however the specific mechanisms that regulate their activity are poorly understood. Here, we document that SorCS2, a member of the family of the Vps10 family of sorting receptors, is highly expressed in pyramidal neurons of CA2, as well as ventral CA1, a circuit implicated in social memory. SorCS2 specifically localizes to the postsynaptic density and endosomes within dendritic spines of CA2 neurons. We have discovered that SorCS2 is a selective regulator of NMDA receptor surface trafficking in hippocampal neurons, without altering AMPA receptor trafficking. In addition, SorCS2 regulates dendritic spine density in CA2 neurons where SorCS2 expression is enriched, but not in dorsal CA1 neurons, which normally express very low levels of this protein. To specifically test the role of SorCS2 in behavior, we generated a novel SorCS2-deficient mouse, and identify a significant social memory deficit, with no change in sociability, olfaction, anxiety, or several hippocampal-dependent behaviors. Mutations in sorCS2 have been associated with bipolar disease, schizophrenia, and attention deficient-hyperactivity disorder, and abnormalities in social memory are core components of these neuropsychiatric conditions. Thus, our findings provide a new mechanism for social memory formation, through regulating synaptic receptor trafficking in pyramidal neurons by SorCS2.

Tumor Necrosis Factor α Receptor Type 1 Activation in the Hypothalamic Paraventricular Nucleus Contributes to Glutamate Signaling and Angiotensin II-Dependent Hypertension

There are significant neurogenic and inflammatory influences on blood pressure, yet the role played by each of these processes in the development of hypertension is unclear. Tumor necrosis factor α (TNFα) has emerged as a critical modulator of blood pressure and neural plasticity; however, the mechanism by which TNFα signaling contributes to the development of hypertension is uncertain. We present evidence that following angiotensin II (AngII) infusion the TNFα type 1 receptor (TNFR1) plays a key role in heightened glutamate signaling in the hypothalamic paraventricular nucleus (PVN), a key central coordinator of blood pressure control. Fourteen day administration of a slow-pressor dose of AngII in male mice was associated with transcriptional and post-transcriptional (increased plasma membrane affiliation) regulation of TNFR1 in the PVN. Further, TNFR1 was shown to be critical for elevated NMDA-mediated excitatory currents in sympathoexcitatory PVN neurons following AngII infusion. Finally, silencing PVN TNFR1 prevented the increase in systolic blood pressure induced by AngII. These findings indicate that TNFR1 modulates a cellular pathway involving an increase in NMDA-mediated currents in the PVN following AngII infusion, suggesting a mechanism whereby TNFR1 activation contributes to hypertension via heightened hypothalamic glutamate-dependent signaling.SIGNIFICANCE STATEMENT Inflammation is critical for the emergence of hypertension, yet the mechanisms by which inflammatory mediators contribute to this dysfunction are not clearly defined. We show that tumor necrosis factor α receptor 1 (TNFR1) in the paraventricular hypothalamic nucleus (PVN), a critical neuroregulator of cardiovascular function, plays an important role in the development of hypertension in mice. In the PVN, TNFR1 expression and plasma membrane localization are upregulated during hypertension induced by angiotensin II (AngII). Further, TNFR1 activation was essential for NMDA signaling and the heightening NMDA currents during hypertension. Finally, TNFR1 silencing in the PVN inhibits elevated blood pressure induced by AngII. These results point to a critical role for hypothalamic TNFR1 signaling in hypertension.

Sex and age influence gonadal steroid hormone receptor distributions relative to estrogen receptor β-containing neurons in the mouse hypothalamic paraventricular nucleus

Within the hypothalamic paraventricular nucleus (PVN), estrogen receptor (ER) β and other gonadal hormone receptors play a role in central cardiovascular processes. However, the influence of sex and age on the cellular and subcellular relationships of ERβ with ERα, G-protein ER (GPER1), as well as progestin and androgen receptors (PR and AR) in the PVN is uncertain. In young (2- to 3-month-old) females and males, ERβ-enhanced green fluorescent protein (EGFP) containing neurons were approximately four times greater than ERα-labeled and PR-labeled nuclei in the PVN. In subdivisions of the PVN, young females, compared to males, had: (1) more ERβ-EGFP neurons in neuroendocrine rostral regions; (2) fewer ERα-labeled nuclei in neuroendocrine and autonomic projecting medial subregions; and (3) more ERα-labeled nuclei in an autonomic projecting caudal region. In contrast, young males, compared to females, had approximately 20 times more AR-labeled nuclei, which often colocalized with ERβ-EGFP in neuroendocrine (approximately 70%) and autonomic (approximately 50%) projecting subregions. Ultrastructurally, in soma and dendrites, PVN ERβ-EGFP colocalized primarily with extranuclear AR (approximately 85% soma) and GPER1 (approximately 70% soma). Aged (12- to 24-month-old) males had more ERβ-EGFP neurons in a rostral neuroendocrine subregion compared to aged females and females with accelerated ovarian failure (AOF) and in a caudal autonomic subregion compared to post-AOF females. Late-aged (18- to 24-month-old) females compared to early-aged (12- to 14-month-old) females and AOF females had fewer AR-labeled nuclei in neuroendrocrine and autonomic projecting subregions. These findings indicate that gonadal steroids may directly and indirectly influence PVN neurons via nuclear and extranuclear gonadal hormone receptors in a sex-specific manner.

Endothelium-Macrophage Crosstalk Mediates Blood-Brain Barrier Dysfunction in Hypertension

Hypertension is a leading cause of stroke and dementia, effects attributed to disrupting delivery of blood flow to the brain. Hypertension also alters the blood-brain barrier (BBB), a critical component of brain health. Although endothelial cells are ultimately responsible for the BBB, the development and maintenance of the barrier properties depend on the interaction with other vascular-associated cells. However, it remains unclear if BBB disruption in hypertension requires cooperative interaction with other cells. Perivascular macrophages (PVM), innate immune cells closely associated with cerebral microvessels, have emerged as major contributors to neurovascular dysfunction. Using 2-photon microscopy in vivo and electron microscopy in a mouse model of Ang II (angiotensin II) hypertension, we found that the vascular segments most susceptible to increased BBB permeability are arterioles and venules >10 µm and not capillaries. Brain macrophage depletion with clodronate attenuates, but does not abolish, the increased BBB permeability in these arterioles where PVM are located. Deletion of AT1R (Ang II type-1 receptors) in PVM using bone marrow chimeras partially attenuated the BBB dysfunction through the free radical-producing enzyme Nox2. In contrast, downregulation of AT1R in cerebral endothelial cells using a viral gene transfer-based approach prevented the BBB disruption completely. The results indicate that while endothelial AT1R, mainly in arterioles and venules, initiate the BBB disruption in hypertension, PVM are required for the full expression of the dysfunction. The findings unveil a previously unappreciated contribution of resident brain macrophages to increased BBB permeability of hypertension and identify PVM as a putative therapeutic target in diseases associated with BBB dysfunction.

Eicosanoids and Oxidative Stress in Diabetic Retinopathy

Oxidative stress is an important factor to cause the pathogenesis of diabetic retinopathy (DR) because the retina has high vascularization and long-time light exposition. Cyclooxygenase (COX), lipoxygenase (LOX), and cytochrome P450 (CYP) enzymes can convert arachidonic acid (AA) into eicosanoids, which are important lipid mediators to regulate DR development. COX-derived metabolites appear to be significant factors causative to oxidative stress and retinal microvascular dysfunction. Several elegant studies have unraveled the importance of LOX-derived eicosanoids, including LTs and HETEs, to oxidative stress and retinal microvascular dysfunction. The role of CYP eicosanoids in DR is yet to be explored. There is clear evidence that CYP-derived epoxyeicosatrienoic acids (EETs) have detrimental effects on the retina. Our recent study showed that the renin-angiotensin system (RAS) activation augments retinal soluble epoxide hydrolase (sEH), a crucial enzyme degrading EETs. Our findings suggest that EETs blockade can enhance the ability of RAS blockade to prevent or mitigate microvascular damage in DR. This review will focus on the critical information related the function of these eicosanoids in the retina, the interaction between eicosanoids and reactive oxygen species (ROS), and the involvement of eicosanoids in DR. We also identify potential targets for the treatment of DR.

A novel interaction between soluble epoxide hydrolase and the AT1 receptor in retinal microvascular damage

Clinical studies have suggested that the renin-angiotensin system (RAS) may be a promising therapeutic target in treating diabetic retinopathy (DR). While AT1 receptor blockade decreased the incidence of DR in the DIRECT trial, it did not reduce the DR progression. Lack of understanding of the molecular mechanism of retinal microvascular damage induced by RAS is a critical barrier to the use of RAS blockade in preventing or treating DR. The purpose of this study is to investigate the interaction between soluble epoxide hydrolase (sEH) and the AT1 receptor in Angiotensin II (Ang II)- and diabetes-induced retinal microvascular damage. We demonstrate that Ang II increases retinal sEH levels, which is blunted by an AT1 blocker; administration of 11,12-epoxyeicosatrienoic acid (EET) exacerbates intravitreal Ang II-induced retinal albumin leakage; while sEH knockout (KO) and blockade reduce Ang II-induced retinal vascular remodeling, sEH KO causes retinal vascular leakage in Ang II-sEH KO mice; and sEH KO potentiates diabetes-induced retinal damage via promoting retinal vascular endothelial growth factor (VEGF) but reducing expression of tight junction proteins (ZO-1 and occludin). Our studies hold the promise of providing a new strategy, the use of combined EETs blockade with AT1 blocker, to prevent or reduce DR.

Central CYP1B1 (Cytochrome P450 1B1)-Estradiol Metabolite 2-Methoxyestradiol Protects From Hypertension and Neuroinflammation in Female Mice

Supplemental Digital Content is available in the text.

Previously, we showed that peripheral administration of 2-ME (2-methoxyestradiol), a CYP1B1 (cytochrome P450 1B1)-catechol-O-methyltransferase (COMT) generated metabolite of E2 (17β-Estradiol), protects against angiotensin II-induced hypertension in female mice. The demonstration that central E2 inhibits angiotensin II-induced hypertension, together with the expression of CYP1B1 in the brain, led us to hypothesize that E2-CYP1B1 generated metabolite 2-ME in the brain mediates its protective action against angiotensin II-induced hypertension in female mice. To test this hypothesis, we examined the effect of intracerebroventricularly (ICV) administered E2 in ovariectomized (OVX)-wild-type (Cyp1b1^+/+) and OVX-Cyp1b1^−/− mice on the action of systemic angiotensin II. ICV-E2 attenuated the angiotensin II-induced increase in mean arterial blood pressure, impairment of baroreflex sensitivity, and sympathetic activity in OVX-Cyp1b1^+/+ but not in ICV-injected short interfering (si)RNA-COMT or OVX-Cyp1b1^−/− mice. ICV-2-ME attenuated the angiotensin II-induced increase in blood pressure in OVX-Cyp1b1^−/− mice; this effect was inhibited by ICV-siRNA estrogen receptor-α (ERα) and G protein-coupled estrogen receptor 1 (GPER1). ICV-E2 in OVX-Cyp1b1^+/+ but not in OVX-Cyp1b1^−/− mice and 2-ME in the OVX-Cyp1b1^−/− inhibited angiotensin II-induced increase in reactive oxygen species production in the subfornical organ and paraventricular nucleus, activation of microglia and astrocyte, and neuroinflammation in paraventricular nucleus. Furthermore, central CYP1B1 gene disruption in Cyp1b1^+/+ mice by ICV-adenovirus-GFP (green fluorescence protein)-CYP1B1-short hairpin (sh)RNA elevated, while reconstitution by adenovirus-GFP-CYP1B1-DNA in the paraventricular nucleus but not in subfornical organ in Cyp1b1^−/− mice attenuated the angiotensin II-induced increase in systolic blood pressure. These data suggest that E2-CYP1B1-COMT generated metabolite 2-ME, most likely in the paraventricular nucleus via estrogen receptor-α and GPER1, protects against angiotensin II-induced hypertension and neuroinflammation in female mice.

Plasma Membrane Affiliated AMPA GluA1 in Estrogen Receptor β-containing Paraventricular Hypothalamic Neurons Increases Following Hypertension in a Mouse Model of Post-menopause

Sex and ovarian function contribute to hypertension susceptibility, however, the mechanisms are not well understood. Prior studies show that estrogens and neurogenic factors, including hypothalamic glutamatergic NMDA receptor plasticity, play significant roles in rodent hypertension. Here, we investigated the role of sex and ovarian failure on AMPA receptor plasticity in estrogen-sensitive paraventricular nucleus (PVN) neurons in naïve and angiotensin II (AngII) infused male and female mice and female mice at early and late stages of accelerated ovarian failure (AOF). High-resolution electron microscopy was used to assess the subcellular distribution of AMPA GluA1 in age-matched male and female estrogen receptor beta (ERβ) enhanced green fluorescent protein (EGFP) reporter mice as well as female ERβ-EGFP mice treated with 4-vinylcyclohexene diepoxide. In the absence of AngII, female mice at a late stage of AOF displayed higher levels of GluA1 on the plasma membrane, indicative of functional protein, in ERβ-expressing PVN dendrites when compared to male, naïve female and early stage AOF mice. Following slow-pressor AngII infusion, males, as well as early and late stage AOF females had elevated blood pressure. Significantly, only late stage-AOF female mice infused with AngII had an increase in GluA1 near the plasma membrane in dendrites of ERβ-expressing PVN neurons. In contrast, prior studies reported that plasmalemmal NMDA GluN1 increased in ERβ-expressing PVN dendrites in males and early, but not late stage AOF females. Together, these findings reveal that early and late stage AOF female mice display unique molecular signatures of long-lasting synaptic strength prior to, and following hypertension.

Accelerated Ovarian Failure as a Unique Model to Study Peri-Menopause Influence on Alzheimer's Disease

Despite decades of extensive research efforts, efficacious therapies for Alzheimer's disease (AD) are lacking. The multi-factorial nature of AD neuropathology and symptomatology has taught us that a single therapeutic approach will most likely not fit all. Women constitute ~70% of the affected AD population, and pathology and rate of symptoms progression are 2-3 times higher in women than men. Epidemiological data suggest that menopausal estrogen loss may be causative of the more severe symptoms observed in AD women, however, results from clinical trials employing estrogen replacement therapy are inconsistent. AD pathological hallmarks-amyloid β (Aβ), neurofibrillary tangles (NFTs), and chronic gliosis-are laid down during a 20-year prodromal period before clinical symptoms appear, which coincides with the menopause transition (peri-menopause) in women (~45-54-years-old). Peri-menopause is marked by widely fluctuating estrogen levels resulting in periods of irregular hormone-receptor interactions. Recent studies showed that peri-menopausal women have increased indicators of AD phenotype (brain Aβ deposition and hypometabolism), and peri-menopausal women who used hormone replacement therapy (HRT) had a reduced AD risk. This suggests that neuroendocrine changes during peri-menopause may be a trigger that increases risk of AD in women. Studies on sex differences have been performed in several AD rodent models over the years. However, it has been challenging to study the menopause influence on AD due to lack of optimal models that mimic the human process. Recently, the rodent model of accelerated ovarian failure (AOF) was developed, which uniquely recapitulates human menopause, including a transitional peri-AOF period with irregular estrogen fluctuations and a post-AOF stage with low estrogen levels. This model has proven useful in hypertension and cognition studies with wild type animals. This review article will highlight the molecular mechanisms by which peri-menopause may influence the female brain vulnerability to AD and AD risk factors, such as hypertension and apolipoprotein E (APOE) genotype. Studies on these biological mechanisms together with the use of the AOF model have the potential to shed light on key molecular pathways underlying AD pathogenesis for the development of precision medicine approaches that take sex and hormonal status into account.

Angiotensin II Causes Neuronal Damage in Stretch-Injured Neurons: Protective Effects of Losartan, an Angiotensin T1 Receptor Blocker

Angiotensin II (Ang II) is a mediator of oxidative stress via activation/induction of reactive oxygen and nitrogen species-generating enzymes, NADPH oxidase (NOX) and inducible nitric oxide synthase (iNOS). We investigated the hypothesis that overproduction of Ang II during traumatic brain injury (TBI) induces the activation of the oxidative stress, which triggers neuroinflammation and cell apoptosis in a cell culture model of neuronal stretch injury. We first established that stretch injury causes a rapid increase in the level of Ang II, which causes the release of pro-inflammatory cytokines, IL-1β and TNF-α, via the induction of oxidative stress. Since angiotensin-converting enzyme (ACE) mediates the production of Ang II via the conversion of Ang I into Ang II, we analyzed the expression of ACE by western blotting. Further, we analyzed caspase-3-mediated apoptosis by TUNEL staining and annexin V western blotting. Angiotensin type I (AT₁) receptor antagonist losartan attenuated Ang II-induced oxidative stress and associated neuroinflammation and cell death in cultured neurons. Remarkably, we noticed that the expression of Ang II type 1 receptor (AngT₁R) upregulated in neuronal stretch injury; losartan mitigates this upregulation. Findings from this study significantly extend our understanding of the pathophysiology of TBI and may have significant implications for developing therapeutic strategies for TBI-associated brain dysfunctions.

Glutamatergic Regulation of Hypothalamic Presympathetic Neurons in Hypertension

Elevated sympathetic vasomotor tone emanating from the brain is a major mechanism involved in the development of hypertension. Increased glutamatergic excitatory input to presympathetic neurons in the paraventricular nucleus (PVN) of the hypothalamus leads to increased sympathetic outflow in various animal models of hypertension. Recent studies have revealed molecular and cellular mechanisms underlying enhanced glutamatergic synaptic input to PVN presympathetic neurons in hypertension. In this review article, we summarize recent findings on changes in inotropic and metabotropic glutamate receptors, at both presynaptic and postsynaptic sites, responsible for increased glutamatergic input to PVN presympathetic neurons in hypertension. Particular emphasis is placed on the role of protein kinases and phosphatases in the potentiated activity of synaptic NMDA receptors in the PVN in hypertension. New findings about glutamatergic synaptic plasticity in the PVN not only improve the understanding of molecular mechanisms involved in heightened activity of the sympathetic nervous system but also suggest new therapeutic targets for treating drug-resistant, neurogenic hypertension.

Distribution and chemical composition of estrogen receptor β neurons in the paraventricular nucleus of the female and male mouse hypothalamus

Activation of estrogen receptor beta (ERβ)-expressing neurons regulates the mammalian stress response via the hypothalamic-pituitary-adrenal (HPA) axis. These neurons densely populate the paraventricular nucleus of the hypothalamus (PVN). Recent research has revealed striking differences between rat and mouse PVN cytochemistry, but careful exploration of PVN ERβ neurons in mice has been hindered by a lack of specific ERβ antisera. Therefore, we used male and female transgenic mice expressing EGFP under the control of the mouse ERβ promoter (ERβ-EGFP) to examine the chemical architecture of PVN ERβ cells. Using immunohistochemistry, we found that 90% of ERβ-immunoreactivity (-ir) colocalized with EGFP. Cellular colocalization of EGFP with neuropeptides, transcription modulators, and neuronal tracers was examined throughout the PVN. ERβ-EGFP cells expressed oxytocin more abundantly in the rostral (71 ± 3%) than caudal (33 ± 8%) PVN. Arginine vasopressin colocalized with EGFP more often in females (18 ± 3%) than males (4 ± 1%). Moreover, estrogen receptor α-ir colocalized with ERβ-EGFP at low levels (15 ± 3%). Using a corticotropin releasing hormone-cre driver X tdTomato reporter mouse, we found a moderate colocalization with ERβ-ir (48 ± 16%) in the middle PVN. Peripheral injection of fluorogold revealed that the rostral PVN ERβ-EGFP cells are neuroendocrine neurons whereas non-neuroendocrine (presumably pre-autonomic) ERβ-EGFP neurons predominated in the posterior PVN. These data demonstrate chemoarchitectural differences in ERβ neurons of the mouse PVN that are different from that previously described for the rat, thus, elucidating potential neuronal pathways involved in the regulation of the HPA axis in mice.

SorCS2-mediated NR2A trafficking regulates motor deficits in Huntington's disease

Motor dysfunction is a prominent and disabling feature of Huntington's disease (HD), but the molecular mechanisms that dictate its onset and progression are unknown. The N-methyl-D-aspartate receptor 2A (NR2A) subunit regulates motor skill development and synaptic plasticity in medium spiny neurons (MSNs) of the striatum, cells that are most severely impacted by HD. Here, we document reduced NR2A receptor subunits on the dendritic membranes and at the synapses of MSNs in zQ175 mice that model HD. We identify that SorCS2, a vacuolar protein sorting 10 protein-domain (VPS10P-domain) receptor, interacts with VPS35, a core component of retromer, thereby regulating surface trafficking of NR2A in MSNs. In the zQ175 striatum, SorCS2 is markedly decreased in an age- and allele-dependent manner. Notably, SorCS2 selectively interacts with mutant huntingtin (mtHTT), but not WT huntingtin (wtHTT), and is mislocalized to perinuclear clusters in striatal neurons of human HD patients and zQ175 mice. Genetic deficiency of SorCS2 accelerates the onset and exacerbates the motor coordination deficit of zQ175 mice. Together, our results identify SorCS2 as an interacting protein of mtHTT and demonstrate that impaired SorCS2-mediated NR2A subunit trafficking to dendritic surface of MSNs is, to our knowledge, a novel mechanism contributing to motor coordination deficits of HD.

Understanding the broad influence of sex hormones and sex differences in the brain

Sex hormones act throughout the entire brain of both males and females via both genomic and nongenomic receptors. Sex hormones can act through many cellular and molecular processes that alter structure and function of neural systems and influence behavior as well as providing neuroprotection. Within neurons, sex hormone receptors are found in nuclei and are also located near membranes, where they are associated with presynaptic terminals, mitochondria, spine apparatus, and postsynaptic densities. Sex hormone receptors also are found in glial cells. Hormonal regulation of a variety of signaling pathways as well as direct and indirect effects on gene expression induce spine synapses, up- or downregulate and alter the distribution of neurotransmitter receptors, and regulate neuropeptide expression and cholinergic and GABAergic activity as well as calcium sequestration and oxidative stress. Many neural and behavioral functions are affected, including mood, cognitive function, blood pressure regulation, motor coordination, pain, and opioid sensitivity. Subtle sex differences exist for many of these functions that are developmentally programmed by hormones and by not yet precisely defined genetic factors, including the mitochondrial genome. These sex differences and responses to sex hormones in brain regions, which influence functions not previously regarded as subject to such differences, indicate that we are entering a new era of our ability to understand and appreciate the diversity of gender-related behaviors and brain functions. © 2016 Wiley Periodicals, Inc.

Redistribution of NMDA Receptors in Estrogen-Receptor-β-Containing Paraventricular Hypothalamic Neurons following Slow-Pressor Angiotensin II Hypertension in Female Mice with Accelerated Ovarian Failure

Hypertension in male and aging female rodents is associated with glutamate-dependent plasticity in the hypothalamus, but existing models have failed to capture distinct transitional menopausal phases that could have a significant impact on the synaptic plasticity and emergent hypertension. In rodents, accelerated ovarian failure (AOF) induced by systemic injection of 4-vinylcyclohexane diepoxide mimics the estrogen fluctuations seen in human menopause including the perimenopause transition (peri-AOF) and postmenopause (post-AOF). Thus, we used the mouse AOF model to determine the impact of slow-pressor angiotensin II (AngII) administration on blood pressure and on the subcellular distribution of obligatory N-methyl-D-aspartate (NMDA) receptor GluN1 subunits in the paraventricular hypothalamic nucleus (PVN), a key estrogen-responsive cardiovascular regulatory area. Estrogen-sensitive neuronal profiles were identified in mice expressing enhanced green fluorescent protein under the promoter for estrogen receptor (ER) β, a major ER in the PVN. Slow-pressor AngII increased arterial blood pressure in mice at peri- and post-AOF time points. In control oil-injected (nonhypertensive) mice, AngII decreased the total number of GluN1 in ERβ-containing PVN dendrites. In contrast, AngII resulted in a reapportionment of GluN1 from the cytoplasm to the plasma membrane of ERβ-containing PVN dendrites in peri-AOF mice. Moreover, in post-AOF mice, AngII increased total GluN1, dendritic size and radical production in ERβ-containing neurons. These results indicate that unique patterns of hypothalamic glutamate receptor plasticity and dendritic structure accompany the elevated blood pressure in peri- and post-AOF time points. Our findings suggest the possibility that distinct neurobiological processes are associated with the increased blood pressure during perimenopausal and postmenopausal periods.

Alterations in the subcellular distribution of NADPH oxidase p47(phox) in hypothalamic paraventricular neurons following slow-pressor angiotensin II hypertension in female mice with accelerated ovarian failure

At younger ages, women have a lower risk for hypertension than men, but this sexual dimorphism declines with the onset of menopause. These differences are paralleled in rodents following "slow-pressor" angiotensin II (AngII) administration: young male and aged female mice, but not young females, develop hypertension. There is also an established sexual dimorphism both in the cardiovascular response to the neurohypophyseal hormone arginine vasopressin (AVP) and in the expression of oxidative stress. We examined the relationship between AngII-mediated hypertension and the cellular distribution of the superoxide generating NADPH oxidase (NOX) in AVP-expressing hypothalamic paraventricular nucleus (PVN) neurons in "menopausal" female mice. Dual-labeling immunoelectron microscopy was used to determine whether the subcellular distribution of the organizer/adapter NOX p47(phox) subunit is altered in PVN dendrites following AngII administered (14 days) during the "postmenopausal" stage of accelerated ovarian failure (AOF) in young female mice treated with 4-vinylcyclohexene diepoxide. Slow-pressor AngII elevated blood pressure in AOF females and induced a significant increase in near plasmalemmal p47(phox) and a decrease in cytoplasmic p47(phox) in PVN AVP dendrites. These changes are the opposite of those observed in AngII-induced hypertensive male mice (Coleman et al. [2013] J. Neurosci. 33:4308-4316) and may be ascribed in part to baseline differences between young females and males in the near plasmalemmal p47(phox) on AVP dendrites seen in the present study. These findings highlight fundamental differences in the neural substrates of oxidative stress in the PVN associated with AngII hypertension in postmenopausal females compared with males. J. Comp. Neurol. 524:2251-2265, 2016. © 2015 Wiley Periodicals, Inc.

Sex, the brain and hypertension: brain oestrogen receptors and high blood pressure risk factors

Hypertension is a major contributor to worldwide morbidity and mortality rates related to cardiovascular disease. There are important sex differences in the onset and rate of hypertension in humans. Compared with age-matched men, premenopausal women are less likely to develop hypertension. However, after age 60, the incidence of hypertension increases in women and even surpasses that seen in older men. It is thought that changes in levels of circulating ovarian hormones as women age may be involved in the increase in hypertension in older women. One of the key mechanisms involved in the development of hypertension in both men and women is an increase in sympathetic nerve activity (SNA). Brain regions important for the regulation of SNA, such as the subfornical organ, the paraventricular nucleus and the rostral ventral lateral medulla, also express specific subtypes of oestrogen receptors. Each of these brain regions has also been implicated in mechanisms underlying risk factors for hypertension such as obesity, stress and inflammation. The present review brings together evidence that links actions of oestrogen at these receptors to modulate some of the common brain mechanisms involved in the ability of hypertensive risk factors to increase SNA and blood pressure. Understanding the mechanisms by which oestrogen acts at key sites in the brain for the regulation of SNA is important for the development of novel, sex-specific therapies for treating hypertension.

NMDA Receptor Plasticity in the Hypothalamic Paraventricular Nucleus Contributes to the Elevated Blood Pressure Produced by Angiotensin II

Hypertension induced by angiotensin II (Ang II) is associated with glutamate-dependent dysregulation of the hypothalamic paraventricular nucleus (PVN). Many forms of glutamate-dependent plasticity are mediated by NMDA receptor GluN1 subunit expression and the distribution of functional receptor to the plasma membrane of dendrites. Here, we use a combined ultrastructural and functional analysis to examine the relationship between PVN NMDA receptors and the blood pressure increase induced by chronic infusion of a low dose of Ang II. We report that the increase in blood pressure produced by a 2 week administration of a subpressor dose of Ang II results in an elevation in plasma membrane GluN1 in dendrites of PVN neurons in adult male mice. The functional implications of these observations are further demonstrated by the finding that GluN1 deletion in PVN neurons attenuated the Ang II-induced increases in blood pressure. These results indicate that NMDA receptor plasticity in PVN neurons significantly contributes to the elevated blood pressure mediated by Ang II.

Angiotensin type 1a receptors on corticotropin-releasing factor neurons contribute to the expression of conditioned fear

Although generally associated with cardiovascular regulation, angiotensin II receptor type 1a (AT1a R) blockade in mouse models and humans has also been associated with enhanced fear extinction and decreased post-traumatic stress disorder (PTSD) symptom severity, respectively. The mechanisms mediating these effects remain unknown, but may involve alterations in the activities of corticotropin-releasing factor (CRF)-expressing cells, which are known to be involved in fear regulation. To test the hypothesis that AT1a R signaling in CRFergic neurons is involved in conditioned fear expression, we generated and characterized a conditional knockout mouse strain with a deletion of the AT1a R gene from its CRF-releasing cells (CRF-AT1a R((-/-)) ). These mice exhibit normal baseline heart rate, blood pressure, anxiety and locomotion, and freeze at normal levels during acquisition of auditory fear conditioning. However, CRF-AT1a R((-/-)) mice exhibit less freezing than wild-type mice during tests of conditioned fear expression-an effect that may be caused by a decrease in the consolidation of fear memory. These results suggest that central AT1a R activity in CRF-expressing cells plays a role in the expression of conditioned fear, and identify CRFergic cells as a population on which AT1 R antagonists may act to modulate fear extinction.

Sex differences in NMDA GluN1 plasticity in rostral ventrolateral medulla neurons containing corticotropin-releasing factor type 1 receptor following slow-pressor angiotensin II hypertension

There are profound, yet incompletely understood, sex differences in the neurogenic regulation of blood pressure. Both corticotropin signaling and glutamate receptor plasticity, which differ between males and females, are known to play important roles in the neural regulation of blood pressure. However, the relationship between hypertension and glutamate plasticity in corticotropin-releasing factor (CRF)-receptive neurons in brain cardiovascular regulatory areas, including the rostral ventrolateral medulla (RVLM) and paraventricular nucleus of the hypothalamus (PVN), is not understood. In the present study, we used dual-label immuno-electron microscopy to analyze sex differences in slow-pressor angiotensin II (AngII) hypertension with respect to the subcellular distribution of the obligatory NMDA glutamate receptor subunit 1 (GluN1) subunit of the N-methyl-D-aspartate receptor (NMDAR) in the RVLM and PVN. Studies were conducted in mice expressing the enhanced green fluorescence protein (EGFP) under the control of the CRF type 1 receptor (CRF1) promoter (i.e., CRF1-EGFP reporter mice). By light microscopy, GluN1-immunoreactivity (ir) was found in CRF1-EGFP neurons of the RVLM and PVN. Moreover, in both regions tyrosine hydroxylase (TH) was found in CRF1-EGFP neurons. In response to AngII, male mice showed an elevation in blood pressure that was associated with an increase in the proportion of GluN1 on presumably functional areas of the plasma membrane (PM) in CRF1-EGFP dendritic profiles in the RVLM. In female mice, AngII was neither associated with an increase in blood pressure nor an increase in PM GluN1 in the RVLM. Unlike the RVLM, AngII-mediated hypertension had no effect on GluN1 localization in CRF1-EGFP dendrites in the PVN of either male or female mice. These studies provide an anatomical mechanism for sex-differences in the convergent modulation of RVLM catecholaminergic neurons by CRF and glutamate. Moreover, these results suggest that sexual dimorphism in AngII-induced hypertension is reflected by NMDA receptor trafficking in presumptive sympathoexcitatory neurons in the RVLM.