Neuroimmunology of Cardiovascular Disease

PURPOSE OF REVIEW

Cardiovascular disease (CVD) is a leading cause of death and chronic disability worldwide. Yet, despite extensive intervention strategies the number of persons affected by CVD continues to rise. Thus, there is great interest in unveiling novel mechanisms that may lead to new treatments. Considering this dilemma, recent focus has turned to the neuroimmune mechanisms involved in CVD pathology leading to a deeper understanding of the brain's involvement in disease pathology. This review provides an overview of new and salient findings regarding the neuroimmune mechanisms that contribute to CVD.

RECENT FINDINGS

The brain contains neuroimmune niches comprised of glia in the parenchyma and immune cells at the brain's borders, and there is strong evidence that these neuroimmune niches are important in both health and disease. Mechanistic studies suggest that the activation of glia and immune cells in these niches modulates CVD progression in hypertension and heart failure and contributes to the inevitable end-organ damage to the brain. This review provides evidence supporting the role of neuroimmune niches in CVD progression. However, additional research is needed to understand the effects of prolonged neuroimmune activation on brain function.

BNIP3 as a new tool to promote healthy brain aging

The article "Neuronal induction of BNIP3-mediated mitophagy slows systemic aging in Drosophila" reveals BCL2-interacting protein 3 as a therapeutic target to counteract brain aging and prolong overall organismal health with age. In this spotlight, we consider the roles of BNIP3, a mitochondrial outer membrane protein, in the adult nervous system, including its induction of mitophagy and prevention of dysfunctional mitochondria in the aged brain. Implications for other tissue types to reduce the burden of aging are further considered.

Meningeal interleukin-17-producing T cells mediate cognitive impairment in a mouse model of salt-sensitive hypertension

Hypertension (HTN), a disease afflicting over one billion individuals worldwide, is a leading cause of cognitive impairment, the mechanisms of which remain poorly understood. In the present study, in a mouse model of HTN, we find that the neurovascular and cognitive dysfunction depends on interleukin (IL)-17, a cytokine elevated in individuals with HTN. However, neither circulating IL-17 nor brain angiotensin signaling can account for the dysfunction. Rather, IL-17 produced by T cells in the dura mater is the mediator released in the cerebrospinal fluid and activating IL-17 receptors on border-associated macrophages (BAMs). Accordingly, depleting BAMs, deleting IL-17 receptor A in brain macrophages or suppressing meningeal T cells rescues cognitive function without attenuating blood pressure elevation, circulating IL-17 or brain angiotensin signaling. Our data unveil a critical role of meningeal T cells and macrophage IL-17 signaling in the neurovascular and cognitive dysfunction in a mouse model of HTN.

Basic Mechanisms of Brain Injury and Cognitive Decline in Hypertension

Dementia affects almost 50 million adults worldwide, and remains a major cause of death and disability. Hypertension is a leading risk factor for dementia, including Alzheimer disease and Alzheimer disease-related dementias. Although this association is well-established, the mechanisms underlying hypertension-induced cognitive decline remain poorly understood. By exploring the mechanisms mediating the detrimental effects of hypertension on the brain, studies have aimed to provide therapeutic insights and strategies on how to protect the brain from the effects of blood pressure elevation. In this review, we focus on the basic mechanisms contributing to the cerebrovascular adaptions to elevated blood pressure and hypertension-induced microvascular injury. We also assess the cellular mechanisms of neurovascular unit dysfunction, focusing on the premise that cognitive impairment ensues when the dynamic metabolic demands of neurons are not met due to neurovascular uncoupling, and summarize cognitive deficits across various rodent models of hypertension as a resource for investigators. Despite significant advances in antihypertensive therapy, hypertension remains a critical risk factor for cognitive decline, and several questions remain about the development and progression of hypertension-induced cognitive impairment.

Hypertension, Neurovascular Dysfunction, and Cognitive Impairment

Hypertension affects a significant proportion of the adult and aging population and represents an important risk factor for vascular cognitive impairment and late-life dementia. Chronic high blood pressure continuously challenges the structural and functional integrity of the cerebral vasculature, leading to microvascular rarefaction and dysfunction, and neurovascular uncoupling that typically impairs cerebral blood supply. Hypertension disrupts blood-brain barrier integrity, promotes neuroinflammation, and may contribute to amyloid deposition and Alzheimer pathology. The mechanisms underlying these harmful effects are still a focus of investigation, but studies in animal models have provided significant molecular and cellular mechanistic insights. Remaining questions relate to whether adequate treatment of hypertension may prevent deterioration of cognitive function, the threshold for blood pressure treatment, and the most effective antihypertensive drugs. Recent advances in neurovascular biology, advanced brain imaging, and detection of subtle behavioral phenotypes have begun to provide insights into these critical issues. Importantly, a parallel analysis of these parameters in animal models and humans is feasible, making it possible to foster translational advancements. In this review, we provide a critical evaluation of the evidence available in experimental models and humans to examine the progress made and identify remaining gaps in knowledge.

Abstract 007: Hypertension-induced Neurovascular Dysfunction At Single-cell Resolution

Hypertension (HTN) disrupts vital neurovascular control mechanisms, thereby increasing the brain’s susceptibility to vascular insufficiency, white matter lesions, and cognitive impairment. Yet, the distinct vascular, neuronal, and glial cell types targeted by HTN, as well as the ensuing cellular network disruption driving the neurovascular and cognitive deficits remain undefined. Here we sought to uncover transcriptomic changes in neurons and vascular cells using unbiased, single-cell RNA sequencing on the neocortex of 10-week old C57BL/6 male mice with angiotensin II (AngII) HTN. Vehicle or AngII (600ng/kg/min s.c.) were administered for 3 days, when blood-brain barrier (BBB) permeability start to increase, or 42 days, when neurovascular and cognitive dysfunction are fully developed (n=3/group). We analyzed 39,451 single-cell transcriptomes comprising 26 cell types. Surprisingly, 3 days of AngII induced significantly greater transcriptional changes in venular ECs compared to arteriolar ECs (EdgeR; pval< 0.05, logFC> 2), supporting the notion that venular ECs are uniquely sensitive to the early effects of HTN (Hypertension 76:795, 2020). Gene ontology analysis of differentially expressed genes prominently implicated altered venular immune signaling, BBB dysfunction, and, notably, a secretory phenotype characteristic of senescence (pval <0.05). Moreover, unbiased ligand-receptor interaction analysis (CellChat) demonstrated that senescent venular ECs strongly communicate with oligodendrocyte precursors, and NPY-expressing interneurons, pointing to a previously unrecognized early disruption in the oligo-vascular niche, essential for maintaining white matter integrity, and neuronal network stability. Furthermore, at 42 days of AngII we observed an overrepresentation of aging and neurodegeneration-linked genes in oligos and NPY interneurons, relating to myelin disruption, synaptic dysfunction, and metabolic dysregulation. The data reveal a novel endothelial-oligo-interneuron crosstalk and transcriptomic alterations underlying the impact of HTN on the brain. Future studies will establish how these transcriptomic changes are linked to neurovascular dysfunction, white matter damage and cognitive impairment.

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.

Abstract 050: Essential Role of Cerebral Endothelial AT1 Receptors in the Blood-Brain Barrier Disruption Induced by Angiotensin-II Hypertension

The blood-brain barrier (BBB) controls the molecular exchange between blood and brain and is critical for maintaining brain health. Although hypertension (HTN) is well known to disrupt the BBB, the underlying cellular bases and the susceptible cerebrovascular segments(s) remain unclear. Here, we addressed these open questions in male mice in which HTN was induced by angiotensin II (Ang II; 600ng/kg/min s.c.; n=9-14/group) for 14 days. HTN increased BBB permeability to 3000 MW FITC-dextran, measured spectrophotometrically in brain extracts (30 ± 1 vs 18 ± 0.5 ng/g in controls; p<0.01). In vivo 2-photon microscopy revealed that dextran leaks out more from microvessels >10ϒm (+38%; p<0.05) than cerebral capillaries (+7%; p>0.05). Electron microscopy showed that HTN induces tight junction remodeling (length -25%; complexity: -11%), and increases endothelial transcytosis (capillaries 1.9 and arterioles 3.5 folds; p<0.05), which is consistent with the downregulation of tight junction proteins (occludin: -17%; claudin-5: -30%) and of the transcytosis inhibitor Msfd2a (-43%). Since AT1 receptors (AT1R) on brain perivascular macrophages (PVM) mediate the deleterious cerebrovascular effects of Ang II HTN (JCI 126:4674), we tested if PVM also mediate the BBB dysfunction. However, PVM depletion (icv clodronate) or deletion of AT1R on PVM (bone marrow chimeras), attenuated the BBB dysfunction only partially (-60% and -49%, respectively; p<0.05), whereas AT1R-/- mice harboring AT1R+ PVM were completely protected (19 ± 1 ng/g; p>0.05 vs control), pointing to a key role of endothelial AT1R. Consistent with this prediction, cerebral endothelial AT1R deletion using a cerebral endothelial specific AAV-BR1-iCre in AT1R floxed mice prevented the BBB disruption completely (21 ± 1 ng/g; p>0.05 vs control). We conclude that AT1 signaling in cerebral endothelial cells initiates the BBB opening induced by Ang II HTN by increasing both paracellular and vesicular transport mainly in arterioles and venules, and that AT1 signaling in PVM, presumably from circulating Ang II crossing the BBB, amplifies the dysfunction. Such increase in BBB permeability to circulating agents may contribute to the cerebrovascular and cognitive dysfunction associated with HTN.

Elevated bone marrow sympathetic drive precedes systemic inflammation in angiotensin II hypertension

Increased sympathetic nervous system activity is a hallmark of hypertension (HTN), and it is implicated in altered immune system responses in its pathophysiology. However, the precise mechanisms of neural-immune interaction in HTN remain elusive. We have previously shown an association between elevated sympathetic drive to the bone marrow (BM) and activated BM immune cells in rodent models of HTN. Moreover, microglial-dependent neuroinflammation is also seen in rodent models of HTN. However, the cause-effect relationship between central and systemic inflammatory responses and the sympathetic drive remains unknown. These observations led us to hypothesize that increase in the femoral BM sympathetic nerve activity (fSNA) initiates a cascade of events leading to increase in blood pressure (BP). Here, we investigated the temporal relationship between the BM sympathetic drive, activation of the central and peripheral immune system, and increase in BP in the events leading to established HTN. The present study demonstrates that central infusion of angiotensin II (ANG II) induces early microglial activation in the paraventricular nucleus of hypothalamus, which preceded increase in the fSNA. In turn, activation of fSNA correlated with the timing of increased production and release of CD4⁺.IL17⁺ T cells and other proinflammatory cells into circulation and elevation in BP, whereas infiltration of CD4⁺ cells to the paraventricular nucleus marked establishment of ANG II HTN. This study identifies cellular and molecular mechanisms involved in neural-immune interactions in early and established stages of rodent ANG II HTN. NEW & NOTEWORTHY Early microglia activation in paraventricular nucleus precedes sympathetic activation of the bone marrow. This leads to increased bone marrow immune cells and their release into circulation and an increase in blood pressure. Infiltration of CD4+ T cells into paraventricular nucleus paraventricular nucleus marks late hypertension.

Hypertension, dietary salt and cognitive impairment

Dementia is growing at an alarming rate worldwide. Although Alzheimer disease is the leading cause, over 50% of individuals diagnosed with Alzheimer disease have vascular lesions at autopsy. There has been an increasing appreciation of the pathogenic role of vascular risk factors in cognitive impairment caused by neurodegeneration. Midlife hypertension is a leading risk factor for late-life dementia. Hypertension alters cerebrovascular structure, impairs the major factors regulating the cerebral microcirculation, and promotes Alzheimer pathology. Experimental studies have identified brain perivascular macrophages as the major free radical source mediating neurovascular dysfunction of hypertension. Recent evidence indicates that high dietary salt may also induce cognitive impairment. Contrary to previous belief, the effect is not necessarily associated with hypertension and is mediated by a deficit in endothelial nitric oxide. Collectively, the evidence suggests a remarkable cellular diversity of the impact of vascular risk factors on the cerebral vasculature and cognition. Whereas long-term longitudinal epidemiological studies are needed to resolve the temporal relationships between vascular risk factors and cognitive dysfunction, single-cell molecular studies of the vasculature in animal models will provide a fuller mechanistic understanding. This knowledge is critical for developing new preventive, diagnostic, and therapeutic approaches for these devastating diseases of the mind.

Abstract 025: Cellular Mechanisms of Blood-Brain Barrier Disruption in Ang II-Induced Hypertension

The blood-brain barrier (BBB) is critically important for brain health by regulating molecular exchanges between blood and brain. Hypertension (HTN) induces breakdown of the BBB which may contribute to its deleterious effect on the brain, but the cellular bases of the BBB opening remain to be established. We used a model of angiotensin II (AngII) HTN (600ng/kg/min x 2 weeks; n>5/group) to investigate the mechanisms of the BBB opening. BBB permeability was assessed spectrophotometrically in C57BL/6J mice using 3000 MW FITC-dextran as a tracer. HTN increased BBB permeability in Ang II HTN (29.8 ± 0.9 vs 18.1 ± 0.5 ng/g in control, p<0.01), an effect partially ameliorated by the angiotensin type 1 receptor (AT1R) antagonist losartan in the drinking water (22.9 ± 0.6 ng/g) but not by hydralazine + hydrochlorothiazide (27.4 ± 0.7 ng/g), suggesting involvement of AT1R and not elevated blood pressure. Next, we sought to identify the mechanisms of the breakdown of the BBB in HTN. First, we used electron microscopy to examine the ultrastructure of endothelial tight junctions (TJ) and assess vesicular transport, key components of the BBB. HTN reduced the length (-25%) and complexity (-11%) of TJ, and increased the number of endothelial vesicles (2.22 vs 1.42 vesicles/endothelial area, p<0.05). The TJ remodeling was associated with a reduction in occludin (-17%, p<0.01) and claudin-5 (-30%, p<0.05) mRNA in microvascular preparations. Additionally, the expression of Mfsd2a, a lipid transporter that also suppresses vesicular transcytosis, was markedly attenuated (-43%, p<0.01). Taken together, these data suggest a strong effect of Ang II on cerebral endothelial cells to induce BBB opening. Since perivascular macrophages (PVM) mediate cerebral endothelial dysfunction in HTN (J Clin Invest 2016;126:4674), we tested their involvement in the BBB opening. PVM depletion with icv clodronate or deletion of AT1 receptors in PVM partially attenuated the BBB opening in Ang II HTN (p<0.05). Thus, we conclude that AT1R in cerebral endothelial cells and PVM mediate the BBB opening by targeting both paracellular and vesicular transport. Such increase in BBB permeability to circulating agents may contribute to the cerebrovascular and cognitive dysfunction associated with HTN.

Abstract TMP94: Dietary Salt Impairs Cognitive Function Through Suppression of Endothelial Nitric Oxide Synthesis and Hippocampal BDNF Signaling

High sodium diet (HSD) is a risk factor for stroke and dementia independent of hypertension, but it remains unclear if dietary salt impairs cognition. To address this question, we fed HSD (8% NaCl) or normal diet (ND; 0.5% NaCl) to males C57BL/6 mice for 12 weeks (n=10/group) and assessed cognitive function. At a novel object recognition task (non-spatial memory) HSD mice failed to identify a new object from a familiar one (ND: 72.4±2%, HSD: 56.4±2%, p<0.05). At the Barnes maze test, HSD mice took longer to locate the escape hole (ND: 26±5sec, HSD: 64±12sec, p<0.05), suggesting impaired spatial memory. Nesting behavior, akin to activities of daily living in humans, was also impaired (ND: 4.6±0.1, HSD: 4.1±0.1, Deacon scale, p<0.05). Since HSD alters endothelial function (Compr Physiol, 6:215, 2015) and endothelial nitric oxide (NO) plays a role in cognition (J Neurosc, 26:11513, 2006), we assessed NO production in isolated brain microvessels using DAF-FM as a marker. In HSD mice, NO levels were markedly reduced (ND: 0.33±0.04, HSD: 0.19±0.02 RFU/μm2, p<0.05) and the NO increase produced by the endothelium-dependent agonist acetylcholine (ACh) was suppressed (ND, Veh: 0.33±0.04, ACh: 0.54±0.05 RFU, p<0.05; HSD, Veh: 0.19±0.02, ACh: 0.25±0.05 RFU/μm2, p>0.05). Endothelial NO participates in synaptic plasticity by contributing to maintain normal levels of the neurotrophic factor BDNF (Eur J Neurosc, 44:2226, 2016). Hippocampal BDNF levels were reduced in HSD mice (-52±3%, p<0.05). Consistent with attenuated BDNF signaling, we also observed reductions in the phosphorylation of the BDNF receptor TrkB (-31±0.1%), and of related signaling molecules (ERK1/2: -36±1%; CREB: -45±1%; p<0.05). Arc, a protein involved in memory formation and dependent on BDNF, was also reduced (-41±1%; p<0.05). The data suggest that HSD-induced endothelial dysfunction leads to reduced NO, which, in turn, suppresses hippocampal BDNF and attendant signaling pathways, resulting in impaired synaptic plasticity and cognitive deficits. The finding that dietary salt has a profound impact of on cognition highlights the harmful effects of endothelial dysfunction on brain health and supports public health efforts to curb salt intake especially in individuals at high vascular risk.

Dietary salt promotes neurovascular and cognitive dysfunction through a gut-initiated TH17 response

A diet rich in salt is linked to an increased risk of cerebrovascular diseases and dementia, but it remains unclear how dietary salt harms the brain. We report that, in mice, excess dietary salt suppresses resting cerebral blood flow and endothelial function, leading to cognitive impairment. The effect depends on expansion of TH17 cells in the small intestine, resulting in a marked increase in plasma interleukin-17 (IL-17). Circulating IL-17, in turn, promotes endothelial dysfunction and cognitive impairment by the Rho kinase-dependent inhibitory phosphorylation of endothelial nitric oxide synthase and reduced nitric oxide production in cerebral endothelial cells. The findings reveal a new gut-brain axis linking dietary habits to cognitive impairment through a gut-initiated adaptive immune response compromising brain function via circulating IL-17. Thus, the TH17 cell-IL-17 pathway is a putative target to counter the deleterious brain effects induced by dietary salt and other diseases associated with TH17 polarization.

Abstract 104: Cerebrovascular and Cognitive Dysfunction in DOCA-Salt Hypertension is Mediated by Perivascular Macrophages

Hypertension (HTN) and high-salt diets are important risk factors for stroke and dementia. DOCA-salt is a recognized model of HTN driven by sodium retention and brain renin-angiotensin system (RAS) activation. However, it is unknown whether essential mechanisms regulating the cerebral circulation are altered in DOCA-salt mice, and, if so, whether these alterations are associated with cognitive impairment. To this end, C57BL/6 mice were implanted with 50mg DOCA pellets SQ and received 0.9% NaCl drinking water for 3 weeks. Cerebral blood flow (CBF) was measured in the somatosensory cortex by laser-Doppler flowmetry through a cranial window. DOCA-salt increased systolic blood pressure (BP; 148±3 vs 112±3 mmHg in controls; p<0.01), and attenuated the CBF increase induced by whisker stimulation (WS; 16.0±1.1 vs 22.4±0.6 %; p<0.01) or by cortical application of acetylcholine (ACh; 13.5±0.9 vs 22.8±1.1 %; p<0.01), without affecting the response to the smooth muscle relaxant adenosine. Cerebrovascular dysfunction was associated with cognitive impairment as assessed by Novel Object Recognition and Barnes Maze tasks (p<0.01). Perivascular macrophages (PVM) express AT1R and Nox2, and, as such, may be a key source of radicals mediating the cerebrovascular effects of brain RAS overactivity. To test this hypothesis, brain PVM were depleted by icv administration of clodronate (CLO) liposomes. BP was not affected by CLO in either control or DOCA mice (p>0.05). PVM depletion improved novel object exploration (p<0.01) and time spent in the target quadrant of Barnes Maze (p<0.05), while also restoring the CBF responses to both WS (DOCA-CLO 19.6±0.9%; p<0.05) and ACh (DOCA-CLO 20.0±1.7%; p<0.05). Next, we tested whether reactive oxygen species (ROS) are involved in the cerebrovascular dysfunction. We observed a 45% upregulation in gp91 mRNA in cerebral vessels from DOCA mice, which was prevented by PVM depletion (p<0.05). Application of the ROS scavenger MnTBAP rescued CBF responses to both WS (20.3±0.9%; p<0.05) and ACh (19.0±0.8%; p<0.05) in DOCA-salt HTN. We conclude that PVM play a previously unrecognized role in the cerebrovascular and cognitive dysfunction of DOCA-salt HTN and may represent a new therapeutic target to alleviate the neurocognitive effects of HTN.

A Single Angiotensin II Hypertensive Stimulus Is Associated with Prolonged Neuronal and Immune System Activation in Wistar-Kyoto Rats

Activation of autonomic neural pathways by chronic hypertensive stimuli plays a significant role in pathogenesis of hypertension. Here, we proposed that even a single acute hypertensive stimulus will activate neural and immune pathways that may be important in initiation of memory imprinting seen in chronic hypertension. We investigated the effects of acute angiotensin II (Ang II) administration on blood pressure, neural activation in cardioregulatory brain regions, and central and systemic immune responses, at 1 and 24 h post-injection. Administration of a single bolus intra-peritoneal (I.P.) injection of Ang II (36 μg/kg) resulted in a transient increase in the mean arterial pressure (MAP) (by 22 ± 4 mmHg vs saline), which returned to baseline within 1 h. However, in contrast to MAP, neuronal activity, as measured by manganese-enhanced magnetic resonance (MEMRI), remained elevated in several cardioregulatory brain regions over 24 h. The increase was predominant in autonomic regions, such as the subfornical organ (SFO; ~20%), paraventricular nucleus of the hypothalamus (PVN; ~20%) and rostral ventrolateral medulla (RVLM; ~900%), among others. Similarly, systemic and central immune responses, as evidenced by circulating levels of CD4⁺/IL17⁺ T cells, and increased IL17 levels and activation of microglia in the PVN, respectively, remained elevated at 24 h following Ang II challenge. Elevated Fos expression in the PVN was also present at 24 h (by 73 ± 11%) following Ang II compared to control saline injections, confirming persistent activation of PVN. Thus, even a single Ang II hypertensive stimulus will initiate changes in neuronal and immune cells that play a role in the developing hypertensive phenotype.

Perivascular macrophages mediate the neurovascular and cognitive dysfunction associated with hypertension

Hypertension is a leading risk factor for dementia, but the mechanisms underlying its damaging effects on the brain are poorly understood. Due to a lack of energy reserves, the brain relies on continuous delivery of blood flow to its active regions in accordance with their dynamic metabolic needs. Hypertension disrupts these vital regulatory mechanisms, leading to the neuronal dysfunction and damage underlying cognitive impairment. Elucidating the cellular bases of these impairments is essential for developing new therapies. Perivascular macrophages (PVMs) represent a distinct population of resident brain macrophages that serves key homeostatic roles but also has the potential to generate large amounts of reactive oxygen species (ROS). Here, we report that PVMs are critical in driving the alterations in neurovascular regulation and attendant cognitive impairment in mouse models of hypertension. This effect was mediated by an increase in blood-brain barrier permeability that allowed angiotensin II to enter the perivascular space and activate angiotensin type 1 receptors in PVMs, leading to production of ROS through the superoxide-producing enzyme NOX2. These findings unveil a pathogenic role of PVMs in the neurovascular and cognitive dysfunction associated with hypertension and identify these cells as a putative therapeutic target for diseases associated with cerebrovascular oxidative stress.

Hypertension-linked mechanical changes of rat gut

Hypertension is the most prevalent risk factor for cardiovascular disease caused by a persistent increase in arterial blood pressure that has lasting effects on the mechanical properties of affected tissues like myocardium and blood vessels. Our group recently discovered that gut dysbiosis is linked to hypertension in several animal models and humans; however, whether hypertension influences the gut's mechanical properties remains unknown. In this study, we evaluated the hypothesis that hypertension increases fibrosis and thus mechanical properties of the gut. A custom indentation system was used to test colon samples from Wistar Kyoto (WKY) normotensive rats and Spontaneously Hypertensive Rats (SHR). Using force-displacement data, we derived an steady-state modulus metric to quantify mechanical properties of gastrointestinal tissue. We observed that SHR proximal colon has a mean steady-state modulus almost 3 times greater than WKY control rat colon (5.11±1.58kPa and 18.17±11.45kPa, respectively). These increases were associated with increase in vascular smooth muscle cells layer and collagen deposition in the intestinal wall in the SHR.

STATEMENT OF SIGNIFICANCE

Mechanical characterization of biological materials can provide insight into health and disease of tissue. Recent investigations into a variety of cardiovascular pathologies show coincident changes in the microbiome and pathology of the gut. In this study, we sought to quantify changes in the gut in hypertension through mechanical characterization. Our methods and simple models for characterization, adapted from Hertz indentation models, prove useful to identify a meaningful steady-state modulus metric for small and irregular tissues from laboratory animals. Our data, for the first time, establish a stiffening of the gut wall in Spontaneously Hypertensive Rats. This observation suggests significant structural and functional changes in the gut correlate with hypertension, and future experiments are warranted to explore the specific causal relationship between dysbiosis, fibrosis, and stiffening in the gut during the development and maintenance of hypertension.

Hypertension-Linked Pathophysiological Alterations in the Gut

RATIONALE

Sympathetic nervous system control of inflammation plays a central role in hypertension. The gut receives significant sympathetic innervation, is densely populated with a diverse microbial ecosystem, and contains immune cells that greatly impact overall inflammatory homeostasis. Despite this uniqueness, little is known about the involvement of the gut in hypertension.

OBJECTIVE

Test the hypothesis that increased sympathetic drive to the gut is associated with increased gut wall permeability, increased inflammatory status, and microbial dysbiosis and that these gut pathological changes are linked to hypertension.

METHODS AND RESULTS

Gut epithelial integrity and wall pathology were examined in spontaneously hypertensive rat and chronic angiotensin II infusion rat models. The increase in blood pressure in spontaneously hypertensive rat was associated with gut pathology that included increased intestinal permeability and decreased tight junction proteins. These changes in gut pathology in hypertension were associated with alterations in microbial communities relevant in blood pressure control. We also observed enhanced gut-neuronal communication in hypertension originating from paraventricular nucleus of the hypothalamus and presenting as increased sympathetic drive to the gut. Finally, angiotensin-converting enzyme inhibition (captopril) normalized blood pressure and was associated with reversal of gut pathology.

CONCLUSIONS

A dysfunctional sympathetic-gut communication is associated with gut pathology, dysbiosis, and inflammation and plays a key role in hypertension. Thus, targeting of gut microbiota by innovative probiotics, antibiotics, and fecal transplant, in combination with the current pharmacotherapy, may be a novel strategy for hypertension treatment.

Brain-Gut-Bone Marrow Axis: Implications for Hypertension and Related Therapeutics

Hypertension is the most prevalent modifiable risk factor for cardiovascular disease and disorders directly influencing cardiovascular disease morbidity and mortality, such as diabetes mellitus, chronic kidney disease, obstructive sleep apnea, etc. Despite aggressive attempts to influence lifestyle modifications and advances in pharmacotherapeutics, a large percentage of patients still do not achieve recommended blood pressure control worldwide. Thus, we think that mechanism-based novel strategies should be considered to significantly improve control and management of hypertension. The overall objective of this review is to summarize implications of peripheral- and neuroinflammation as well as the autonomic nervous system-bone marrow communication in hematopoietic cell homeostasis and their impact on hypertension pathophysiology. In addition, we discuss the novel and emerging field of intestinal microbiota and roles of gut permeability and dysbiosis in cardiovascular disease and hypertension. Finally, we propose a brain-gut-bone marrow triangular interaction hypothesis and discuss its potential in the development of novel therapies for hypertension.

Abstract P610: Hypertension Is Associated With Profound Pathological Changes In The Gut

Background and objective: Our previous studies have shown that gut microbial dysbiosis is linked to hypertension (HTN) in both animal models and patients with high blood pressure (BP) ( Hypertension 2015; 65:1331-40 ). The intestinal epithelial layer serves as a barrier against pathogens and is altered in paracellular permeability with bowel diseases. Accordingly, our objective in the present study was to test the hypothesis that HTN-linked gut dysbiosis is associated with changes in gut wall pathophysiology.

Methods and Results: Two rat models of were used: pre-hypertensive juvenile SHR (MAP 97 ± 5 mmHg) and adult SHR (MAP 160 ± 3 mmHg) with corresponding control WKY rats and chronic Angiotensin II (Ang II) infusion rat model of HTN (saline MAP 95 ± 2 mmHg vs. Ang II 150 ± 3 mmHg). A fluorescein isothiocyanate conjugated (FITC) dextran feeding protocol and a custom indentation system were used for permeability and stiffness assessments, respectively. Segments of small intestine were used for histology. We observed no significant differences in gut permeability and stiffness in pre-hypertensive juvenile SHR vs WKY controls. However, a 2-fold difference in gut permeability was observed in adult SHR (SHR 3514±563.4 vs WKY 1777±427.8, RFU, p<0.05). In addition, a 10-fold difference in gut wall stiffness (effective modulus) in adult SHR was observed (SHR 53.3±32.2 vs WKY 5.3±1.6, kPA, p<0.05). Histology revealed that adult SHR had 20% stunted villi length (SHR 580±54 vs WKY 718±6, μm, p<0.05) and a 60% increase in fibrotic area (SHR 13.8±1.3 vs WKY 8.5±0.8, p<0.05). Similar differences in gut permeability, elastic modulus, villi length and fibrotic area were observed in the Ang II HTN rat model. In contrast, pre-hypertensive, juvenile SHR did not show these differences.

Conclusions: These observations, for the first time, demonstrate that increased BP is associated with profound gut pathology. They suggest that gut wall integrity likely plays a critical role in regulation of BP hemostasis and host microbiota communications with blood vessels.

Abstract 027: Intestinal Permeability and Dysbiosis are Linked to Hypertension

Introduction: Emerging evidence implicates the involvement of intestinal microbiota in overall physiological homeostasis. Altered microbial composition is associated with metabolic, cardiovascular, and neurological diseases. However, the role of intestinal microbiota in blood pressure control and hypertension (HTN) remains unexplored. The present study was designed to evaluate the hypothesis that both intestinal dysbiosis and altered intestinal function are critical pathophysiological events in HTN.

Methods: 16S ribosomal DNA from fecal samples from SHR and chronic angiotensin II (Ang II, 200ng/kg/min) rat models was utilized to compare gut microbial communities between normotensive and hypertensive animals. Gut permeability was assessed by accumulation of FITC-dextran (44mg/100g BW) in the plasma 4 hours following oral feeding. Ex vivo atomic force microscopy was used to determine small intestine and colon stiffness (a measure of permeability). Tight junction gene expression was quantified by qPCR.

Results: We observed a significant decrease in microbial richness (20%), diversity (12%), and evenness (10%) in SHR vs WKY. This was associated with an increased Firmicutes (F)/Bacteroidetes (B) ratio (4±1 vs 24±5), a hallmark of gut dysbiosis. Additionally, we observed a 95% increase in plasma FITC-dextran in SHRs (1777±428 vs 3514±563 ng/ml, p<0.05), which correlated with decreased mRNA of several tight junction genes throughout the intestine, including Ocln , Tjp1 , and Cldn4 . In addition, we found increased stiffness of both small intestine and colonic tissue, as evidenced by increased elastic modulus in SHR (small intestine: 21.2±3 vs 53.7±8 kPa, colon: 15.7±2 vs 53.4±14 kPa, p<0.05). Similar decreased microbial richness and increased F/B ratio (~2 fold) were observed in the Ang II rat model at 4 weeks. Plasma FITC-dextran began to rise by day 14 (SBP=160 mmHg), and reached maximal increase of 65% by day 21 (SBP=185 mmHg). Furthermore, colon wall stiffness was significantly increased by day 21 of Ang II infusion.

Conclusions: These observations show that increased gut permeability/leakiness and dysbiosis is associated with HTN. They are the first to demonstrate a profound intestinal pathophysiology and microbial dysbiosis in HTN.

Abstract P057: Is Hypertension a Disease of the Bone Marrow?

Decades of evidence have implicated involvement of inflammation in the development and establishment of hypertension (HTN); however, the central mechanisms remain elusive. We propose a hypothesis that dysfunctional bone marrow (BM) activity is critical in HTN, in view of the fact that BM is the predominant source of inflammatory and angiogenic cells. We provide the following evidence in support of this hypothesis: (1) BM from animal models of HTN is proinflammatory. Ablation of the spontaneously hypertensive rat (SHR) BM, and reconstitution with BM from the normotensive Wistar Kyoto (WKY), results in significant reduction in mean arterial pressure (MAP), as well as the decrease in proinflammatory and increase in angiogenic cells in the chimeric SHR; (2) Oral minocycline treatment attenuates MAP, restores autonomic balance, and decreases inflammation in both the SHR and Ang II rat HTN models; (3) Sympathetic nerve activity (SNA) and norepinephrine levels in the BM of the SHR and Ang II rat HTN models are elevated compared to normotensive rats; (4) C57-AdrB1.B2 knock-out (KO) chimera, generated by reconstitution of irradiated C57BL/6J mice with the BM cells of the adrenergic receptor beta 1/2 KO mice (Adrb1tm1Bkk Adrb2tm1Bkk/J), exhibits reduced peripheral inflammatory cell counts. Furthermore, transcriptomics analysis of the BM cells from these chimeric mice revealed significant changes in 67 signaling pathways, thirty-five of which were directly related to modulation of different immune system responses (P<0.01). Most notable were changes in the pathways involved in activation and migration of monocytes and T lymphocytes. These observations demonstrate that BM plays a critical role in regulation of the inflammatory status, and support our hypothesis that dysfunctional BM activity may be an important aspect in the development and establishment of HTN. AHA14SDG18300010.

Involvement of bone marrow cells and neuroinflammation in hypertension

RATIONALE

Microglial activation in autonomic brain regions is a hallmark of neuroinflammation in neurogenic hypertension. Despite evidence that an impaired sympathetic nerve activity supplying the bone marrow (BM) increases inflammatory cells and decreases angiogenic cells, little is known about the reciprocal impact of BM-derived inflammatory cells on neuroinflammation in hypertension.

OBJECTIVE

To test the hypothesis that proinflammatory BM cells from hypertensive animals contribute to neuroinflammation and hypertension via a brain-BM interaction.

METHODS AND RESULTS

After BM ablation in spontaneously hypertensive rats, and reconstitution with normotensive Wistar Kyoto rat BM, the resultant chimeric spontaneously hypertensive rats displayed significant reduction in mean arterial pressure associated with attenuation of both central and peripheral inflammation. In contrast, an elevated mean arterial pressure along with increased central and peripheral inflammation was observed in chimeric Wistar-Kyoto rats reconstituted with spontaneously hypertensive rat BM. Oral treatment with minocycline, an inhibitor of microglial activation, attenuated hypertension in both the spontaneously hypertensive rats and the chronic angiotensin II-infused rats. This was accompanied by decreased sympathetic drive and inflammation. Furthermore, in chronic angiotensin II-infused rats, minocycline prevented extravasation of BM-derived cells to the hypothalamic paraventricular nucleus, presumably via a mechanism of decreased C-C chemokine ligand 2 levels in the cerebrospinal fluid.

CONCLUSIONS

The BM contributes to hypertension by increasing peripheral inflammatory cells and their extravasation into the brain. Minocycline is an effective therapy to modify neurogenic components of hypertension. These observations support the hypothesis that BM-derived cells are involved in neuroinflammation, and targeting them may be an innovative strategy for neurogenic resistant hypertension therapy.

Gut dysbiosis is linked to hypertension

Emerging evidence suggests that gut microbiota is critical in the maintenance of physiological homeostasis. This study was designed to test the hypothesis that dysbiosis in gut microbiota is associated with hypertension because genetic, environmental, and dietary factors profoundly influence both gut microbiota and blood pressure. Bacterial DNA from fecal samples of 2 rat models of hypertension and a small cohort of patients was used for bacterial genomic analysis. We observed a significant decrease in microbial richness, diversity, and evenness in the spontaneously hypertensive rat, in addition to an increased Firmicutes/Bacteroidetes ratio. These changes were accompanied by decreases in acetate- and butyrate-producing bacteria. In addition, the microbiota of a small cohort of human hypertensive patients was found to follow a similar dysbiotic pattern, as it was less rich and diverse than that of control subjects. Similar changes in gut microbiota were observed in the chronic angiotensin II infusion rat model, most notably decreased microbial richness and an increased Firmicutes/Bacteroidetes ratio. In this model, we evaluated the efficacy of oral minocycline in restoring gut microbiota. In addition to attenuating high blood pressure, minocycline was able to rebalance the dysbiotic hypertension gut microbiota by reducing the Firmicutes/Bacteroidetes ratio. These observations demonstrate that high blood pressure is associated with gut microbiota dysbiosis, both in animal and human hypertension. They suggest that dietary intervention to correct gut microbiota could be an innovative nutritional therapeutic strategy for hypertension.

Abstract 082: Oral Minocycline Reduces Blood Pressure and Restores Autonomic Balance in Chronic Ang II-Infusion Rat Model of Hypertension

Introduction: We have established that microglial activation and dysfunctional autonomic nervous system (ANS) are associated with Ang II hypertension (HTN). The objective of this study was to test the hypothesis that oral delivery of minocycline (Mino), an anti-inflammatory antibiotic that crosses the blood brain barrier, would impact PVN microglia activation, improve autonomic function, and reverse HTN.

Methods: SD rats irradiated and reconstituted with donor eGFP bone marrow (BM) cells were infused with saline or 200ng/kg/min Ang II S.C. for 7 wks. Additionally, rats received vehicle or Mino (50 mg/kg) by oral gavage. MAP was measured weekly by telemetry (n=3/group) and tailcuff (n=9/group). Spectral analysis of telemetry BP signal was performed for ZT12-13 at 3 wks to reveal autonomic balance.

Results: Ang II increased MAP vs control (178±9 mmHg vs 104±2 mmHg; p<0.05), while a reduction was achieved by Mino (121±7 mmHg; p<0.05). Cardiac spontaneous baroreflex gain, measured by ΔsBRG(PI), was dampened in Ang II treated rats vs control (-0.51±0.09 ms/mmHg vs 0.21±0.23 ms/mmHg; p<0.05). This effect was attenuated by Mino treatment (-0.08±0.08 ms/mmHg; p<0.05). Vasomotor sympathetic tone (ΔLF[SBP]) and vasovagal balance (ΔLF[SBP]:HF[PI]) were increased in Ang II rats (1.0 ±0.48 mmHg2; 0.12±0.06 mmHg2/ms2, respectively; p<0.05), and were reversed by Mino (-0.83±0.45 mmHg2; -0.11±0.05 mmHg2/ms2, respectively; p<0.05). In contrast, no significant changes were observed in cardiac parasympathetic drive (ΔHF[PI]) and cardiac sympathetic tone (ΔLF[PI]:HF[PI]). Immunohistochemical analysis revealed 5.7 fold increase (p<0.05) in GFP+/Iba1+ cells in PVN of Ang II group vs control, indicating an increase in BM-derived microglia/macrophages. Treatment with Mino was associated with a 32% decrease in these cells. Blood CD4+8+ cells, indicative of peripheral inflammation, increased by ~29% in the Ang II group, and decreased in the Ang II/Mino group by 31% (p<0.05).

Conclusions: These observations demonstrate that oral Mino treatment inhibits microglia activation, attenuates autonomic dysfuction and peripheral inflammation that arrests the progression of HTN. This suggests that Mino might be an effective therapeutic agent to target neurogenic HTN.

Altered inflammatory response is associated with an impaired autonomic input to the bone marrow in the spontaneously hypertensive rat

Autonomic nervous system dysfunction, exaggerated inflammation, and impaired vascular repair are all hallmarks of hypertension. Considering that bone marrow (BM) is a major source of the inflammatory cells (ICs) and endothelial progenitor cells (EPCs), we hypothesized that impaired BM-autonomic nervous system interaction contributes to dysfunctional BM activity in hypertension. In the spontaneously hypertensive rat (SHR), we observed a >30% increase in BM and blood ICs (CD4.8(+)) and a >50% decrease in EPCs (CD90(+).CD4.5.8(-)) when compared with the normotensive Wistar-Kyoto rat. Increased tyrosine hydroxylase (70%) and norepinephrine (160%) and decreased choline acetyl transferase (30%) and acetylcholine esterase (55%) indicated imbalanced autonomic nervous system in SHR BM. In Wistar-Kyoto rat, night time-associated elevation in sympathetic nerve activity (50%) and BM norepinephrine (41%) was associated with increased ICs (50%) and decreased EPCs (350%) although BM sympathetic denervation decreased ICs (25%) and increased EPCs (40%). In contrast, these effects were blunted in SHR, possibly because of chronic downregulation of BM adrenergic receptor α2a (by 50%-80%) and β2 (30%-45%). Application of norepinephrine resulted in increased BM IC activation/release, which was prevented by preadministration of acetylcholine. Electrophysiological recordings of femoral sympathetic nerve activity showed a more robust femoral sympathetic nerve activity in SHR when compared with Wistar-Kyoto rat, peaking earlier in the respiratory cycle, indicative of increased sympathetic tone. Finally, manganese-enhanced MRI demonstrated that presympathetic neuronal activation in SHR was associated with an accelerated retrograde transport of the green fluorescent protein-labeled pseudorabies virus from the BM. These observations demonstrate that a dysfunctional BM autonomic nervous system is associated with imbalanced EPCs and ICs in hypertension.

Abstract 181: Brain Angiotensin II Elevates Bone Marrow Sympathetic Drive

Introduction: Bone marrow (BM)-derived endothelial progenitor cells (EPCs) contribute to the repair of vasculature, whereas the inflammatory cells (ICs) contribute to the vascular damage. Recently, dysfunctional brain-BM communication has been associated with an impaired BM activity, reflecting a decrease in EPCs and increase in ICs. We hypothesized that an overactive brain RAS leads to elevated sympathetic drive to the BM, which precedes the increase in blood pressure (BP), initiates the EPC/IC imbalance, and contributes to the development of vascular pathophysiology.

Methods: Sprague-Dawley (SD) rats were infused with 15ng/kg/min Ang II ICV for 7 days. Following this, indirect BP measurements were taken, and the in situ decerebrated artificially-perfused preparation (DAPR) was used to compare thoracic (tSNA) and femoral BM sympathetic nerve activity (fSNA) between control and Ang II rats. In order to characterize tSNA and fSNA, we monitored the effects of elevated CO 2 (9%) on the phrenic nerve activity (PNA), tSNA and fSNA. PNA-triggered averaging of integrated tSNA and fSNA signals was performed across 100 phrenic cycles, allowing for quantification of averaged tSNA and fSNA during discrete phases of the respiratory cycle: inspiration (I), post-inspiration (P-I), mid-expiration (M-E) and late expiration (L-E). Thus, the peak levels of tSNA and fSNA during each respiratory phase could be compared across preparations.

Results: We observed no differences in the BPs of control (95±5 mm Hg) and Ang II rats (96±2 mm Hg). Electrophysiology revealed a characteristic PNA pattern, and peak activity of tSNA and fSNA during the P-I phase, typical of the respiratory-sympathetic coupling. Exposure to 9% CO 2 elevated both the tSNA and fSNA in the control and Ang II rats. However, a 75% increase in the tSNA peak firing, and a 20% increase in the fSNA peak firing were observed in the Ang II rats when compared to the control.

Conclusion: These observations demonstrate, for the first time, that elevated brain Ang II, at sub-pressor conditions, results in an increased sympathetic drive to the BM. This may initiate early impaired BM activity, reflecting in an imbalance in BM EPCs and ICs, which may contribute to the development of hypertension-related pathophysiology.

Abstract 606: Reconstitution Of Bone Marrow With WKY Cells Lowers Central/Peripheral Inflammation And Blood Pressure In The SHR

Introduction: Bone marrow (BM) is a crucial meeting point for the sympathetic innervation and hematopoietic/stem cells, including the inflammatory cells (ICs). However, the role of the BM in hypertension is not well defined. We recently demonstrated that a dysfunctional brain-bone marrow communication in rat models of neurogenic hypertension may be associated with impaired BM activity, characterized by elevated levels of ICs in the blood and BM when compared to the normotensive controls. Therefore, we hypothesized that BM of the spontaneously hypertensive rat (SHR) is pro-inflammatory, and that it contributes to hypertension in this rat model.

Methods: 6-week old female SHR rats underwent BM ablation via a lethal dose of gamma ray irradiation (950 Rads), followed by reconstitution with whole BM mononuclear cells (MNCs, 10E6 cells per rat), derived from the BM of either SHR or WKY male rats (naïve SHR n=7; SHR-SHR n=11; SHR-WKY n=9). Following a three-month recovery period, BM reconstitution was confirmed by Y-chromosome FISH in blood MNCs. Blood pressure was measured by tail-cuff plethysmography. Blood was collected for isolation of MNCs, and quantification of T-cells (CD4/CD8 + ) was carried out by flow cytometry. Brains were collected and immunohistochemistry was performed using the microglial specific marker Iba1. Microglial activation was quantified by number of microglia per 40,000um 2 in the paraventricular nucleus (PVN) of the hypothalamus.

Results: We observed no significant difference in the mean arterial pressures (MAP) between the naïve SHR (MAP= 134 ± 5 mmHg) and the SHR-SHR groups (MAP = 137 ± 5 mmHg). However, the SHR-WKY group showed an approximate 10% decrease in MAP, to 119 ± 4 mmHg (p<0.05). This was accompanied by a 30% decrease in the circulating T-cell levels, and a 20% decrease in activated microglial cells in the PVN of the SHR-WKY when compared to the SHR-SHR group (p<0.05).

Conclusions: These data suggest that the pro-inflammatory properties of the SHR BM contribute to hypertension by increasing both the peripheral and central inflammatory status in the SHR. These observations support the role of the BM in hypertension, especially in affecting the inflammatory status, which is a hallmark of hypertension in the SHR.

Dysfunctional brain-bone marrow communication: a paradigm shift in the pathophysiology of hypertension

It is widely accepted that the pathophysiology of hypertension involves autonomic nervous system dysfunction, as well as a multitude of immune responses. However, the close interplay of these systems in the development and establishment of high blood pressure and its associated pathophysiology remains elusive and is the subject of extensive investigation. It has been proposed that an imbalance of the neuro-immune systems is a result of an enhancement of the "proinflammatory sympathetic" arm in conjunction with dampening of the "anti-inflammatory parasympathetic" arm of the autonomic nervous system. In addition to the neuronal modulation of the immune system, it is proposed that key inflammatory responses are relayed back to the central nervous system and alter the neuronal communication to the periphery. The overall objective of this review is to critically discuss recent advances in the understanding of autonomic immune modulation, and propose a unifying hypothesis underlying the mechanisms leading to the development and maintenance of hypertension, with particular emphasis on the bone marrow, as it is a crucial meeting point for neural, immune, and vascular networks.

Abstract 81: Activation of Microglia in the PVN Precedes Increase in Blood Pressure in Chronic Angiotensin II Infusion Rat Model of Hypertension

Introduction: Hypertension is the most important risk factor for cardiovascular disease. Dysregulation of the autonomic nervous system (ANS) with increased sympathetic stimulation is a hallmark of neurogenic hypertension, and has been shown to precede the rise in the blood pressure. We have previously shown that chronic Angiotensin II (Ang II) infusion increases blood pressure by activation of the microglia in the cardioregulatory brain regions, such as the paraventricular nucleus of the hypothalamus (PVN). Here, we studied the activation of microglia following 3- and 7-day Ang II infusion as a marker of neuroinflammation. We hypothesize that activation of the microglia in the PVN is a possible precursor to the ANS dysfunction and the blood pressure increase in Ang II-dependent hypertension.

Methods: An osmotic minipump delivering either saline or 200ng/kg/min Ang II S.C. was implanted in 9-week old adult male Sprague-Dawley rats randomly assigned to control (saline), or 3-day or 7-day Ang II infusion (n=4) . Blood pressures were measured using radiotelemetry. CD11b immunoblotting of the PVN was used to assess the activated microglia in the PVN. Additionally, Iba1 immunohistochemistry of the PVN was used to image and quantify the increase in total size and number of activated microglia.

Results: Despite no significant change in the blood pressure, we found a 1.40 fold increase in the CD11b protein quantity, and a 12% increase in microglia size at 3-days of Ang II infusion compared to control. At 7-days of Ang II infusion, we observed a 4.93 fold increase in the CD11b protein quantity, a 33% increase in microglia size, and a 29% higher number of microglia, which was accompanied by ∼ 25mmHg elevation in the blood pressure compared to control.

Conclusion: These data suggests that microglia in the PVN become activated in as early as 3-days following Ang II infusion, before the blood pressure changes occur. Therefore, activation of microglia precedes the increase in blood pressure. This implicates the microglia in the dysregulation of the ANS in Ang II hypertension.