Cerebral Microvasculature Research Articles

STAGE-DEPENDENT RESPONSES OF VASCULAR AND PARENCHYMAL CELLS IN THE HYPERTENSIVE RAT BRAIN

Objective: Long-term hypertension doubles all-cause dementia risk in aging by structural and functional alterations of the cerebral microvasculature and its surrounding tissue. However, therapeutical blood pressure lowering by itself is limited in its effectiveness depending on the progression of structural vessel remodeling, microvascular dysfunction and parenchymal tissue damage. Design and method: Therefore, the aim of this study was to investigate pathophysiological processes in different stages of hypertension. We explored acute, early- and late-chronic hypertension effects in the frontal brain of hypertensive rats, applying behavioral tests, histology, immunofluorescence, FACS and vascular/neural tissue RNA sequencing. Results: In response to initial increasing blood pressure and in absence of vascular pathology, microglia cells were found in close proximity to blood vessels and with morphological features of activation. Early chronic hypertensive animals showed frontal brain specific behavioral deficits, blood-brain-barrier leakage, leukocyte immigration, loss of glial reactivity and altered pathways related to cellular energy supply, protein synthesis and catabolism. In late chronic hypertension behavioral deficits and glial reactivity loss persisted. We also observed active angiogenesis, vascular fibroblast-related collagen aggregation and pathways related to decreased responsiveness to nutrients and increased metabolic demand. Additionally, we identified late-chronic vascular accumulation of insulin-like growth factor 1 (IGF1) binding proteins in brains of rats and humans with hypertensive cerebral small vessel disease, possibly attenuating protective IGF1 signaling in the cerebral microvasculature. Conclusions: Our results point towards stage-dependent reactions of vascular, glial, immune and neuronal cells in response to hypertension. Future studies have to verify, whether these mechanisms are valid in humans as well and whether they might be targeted to attenuate small vessel disease progression.

THE EFFECTS OF INDUCED BLOOD PRESSURE INCREASE AND DECREASE ON CEREBRAL SMALL VESSELS: THE HYPERINTENSE STUDY

Objective: Cerebral Small vessel disease (SVD) is a disorder of the cerebral microvessels and is the commonest vascular cause of stroke and dementia. Hypertension is the most established risk factor for SVD, but the pathophysiological mechanisms following hypertension that cause SVD remain poorly understood. We aim to examine the effects of changes in blood pressure on cerebral microvasculature in young- and middle-aged adults with hypertension to detect the earliest microvascular changes associated with SVD. Design and method: The Hyperintense study is an ongoing observational cohort study aiming to include 50 hypertensive adults (18–55 years). These patients temporarily discontinue antihypertensive medication for diagnostic purposes, often leading to a temporary increase in blood pressure. Data are collected before medication withdrawal (T = 0), once antihypertensives are withdrawn (T = 1), when patients have restarted medication and reached target blood pressure (T = 2) and 1 year later (T = 3). At each time-point, high-resolution 3T MRI scans are performed with conventional structural sequences and advanced techniques to assess various aspects of microvascular integrity, including integrity of the blood-brain barrier, microperfusion and microstructural integrity. Clinical data includes motor and cognitive examinations and blood sampling. Results: Between July-December 2021, 7 patients (86% male, mean age 47.4 ± 4.4 years) were enrolled. Baseline characteristics and SVD burden are shown in Table. In 3/4 participants who completed T = 1, systolic blood pressure increased after medication withdrawal (median increase systolic blood pressure: 13.7 [3.3 – 15.3] mmHg), demonstrating proof of principle of our approach. Conclusions: First data show increased blood pressure after medication withdrawal in most participants and demonstrate feasibility of our design. Analysis of the effect of blood pressure increase and decrease on MRI outcomes will improve understanding of the pathological mechanisms following hypertension that may lead to MRI markers of SVD. This knowledge can help identify new targets for treatment of SVD, aimed at preventing or limiting disease progression.

Liraglutide treatment attenuates inflammation markers in the cardiac, cerebral and renal microvasculature in streptozotocin-induced diabetic rats.

BackgroundDiabetes mellitus (DM) induces cardiac and cerebral microvascular dysfunction via increased glycation, oxidative stress and endothelial activation. Liraglutide, a glucagon‐like peptide‐1 analogue, inhibited NOX2 and adhesion molecules in isolated endothelial cells. Here, we have studied how Liraglutide affects advanced glycation, NOX expression and inflammation of the cardiac, cerebral and renal microvasculature in diabetic rats.MethodsDM was induced in Sprague–Dawley rats (n = 15) via intraperitoneal streptozotocin (STZ) injection (60 mg/kg bodyweight). Ten control rats remained nondiabetic. From day 9 post‐STZ injection, Liraglutide (200 μg/kg bodyweight; n = 7) or vehicle (n = 8) was injected subcutaneously daily until termination on day 29. The advanced glycation endproduct N‐ε‐(carboxymethyl)lysine (CML), NOX2, NOX4, ICAM‐1 and VCAM‐1 were subsequently immunohistochemically analysed and quantified to compare Liraglutide treatment with placebo.ResultsIn the heart, Liraglutide treatment significantly reduced the DM‐increased scores/cm2 for CML in both ventricles (from 253 ± 53 to 72 ± 12; p = .003) and atria (343 ± 29 to 122 ± 8; p = .0001) and for NOX2, ICAM‐1 and VCAM‐1, but not for NOX4. Also in the cerebrum and cerebellum of the brain, Liraglutide significantly reduced the scores/cm2 for CML (to 60 ± 7 (p = .0005) and 47 ± 13 (p = .02), respectively), and for NOX2 and NOX4. In the kidney, the DM‐induced expression of ICAM‐1 and VCAM‐1 was decreased in the blood vessels and glomeruli by Liraglutide treatment. Liraglutide did not affect blood glucose levels or bodyweight.ConclusionsOur study implies that Liraglutide protects the cardiac, cerebral and renal microvasculature against diabetes‐induced dysfunction, independent of lowering blood glucose in a type 1 diabetes rat model.

Sphingolipids Imbalanced in Brain Microvessel of Predisposed Reduced Uterine Perfusion Mice

Preeclampsia (PE), a hypertension disorder, is one of the most serious complications that can occur during pregnancy. It affects at least 2‐8% of pregnancies, causing up to 76,000 maternal deaths and 500,000 infant fatalities. PE negatively impacts the vasculature of multiple body systems and has significant neurovascular implications including reversible cerebral vasoconstriction syndrome and ischemic stroke. Although PE resolves after delivery, long term cerebrovascular effects remain. Women who have experienced PE are estimated to have an 80% increased risk of future stroke. Although the consequences of PE are extensive and prevalent, its full etiology is not yet known. It is suspected that cerebrovascular dysfunction plays a significant role in these critical ramifications of PE. Interestingly, the ceramide and sphingosine‐1‐phosphate (S1P) pathway is known to regulate many of the systems that are altered in PE. Specifically, ceramide and S1P are involved in regulation of blood pressure, vascular tone, and vessel permeability in addition to other cell and tissue processes. Because of the significant involvement of ceramide, S1P, and their signaling constituents in endothelial cell and vascular integrity, variations within this pathway may explain the link between PE and cerebrovascular disease. We hypothesize that the ceramide and S1P signaling pathway is linked to dysfunctional brain vasculature in mice that had a PE‐induced pregnancy. This study aims to prove the ceramide and S1P signaling pathway is altered in the cerebral microvasculature of PE murine models. C57BL female mice underwent reduced uterine perfusion pressure (RUPP) surgery at 10 weeks old to simulate PE or sham surgery. Brain microvessels (BMVs) were isolated from these mice dams nine months following delivery. Two step reverse transcription qPCR was performed to assess the mRNA expression of the various ceramide and S1P signaling components. It was found that RUPP mice BMVs express significantly less sphingosine kinase 1 (SphK1) in comparison to sham BMVs. RUPP mice BMVs also demonstrated significantly increased sphingosine‐1‐phosphate lyase 1 (Sgpl1) and phospholipid phosphatase 1 (Plpp1). RUPP mice BMVs exhibited decreased expression of ceramide kinase and sphingosine kinase 2 (Sphk2) as well. SphK1 and Sphk2 are key enzymes in producing S1P, an active signaling lipid responsible for maintaining the blood brain barrier, cerebrovascular integrity, and angiogenesis. Sgpl1 is responsible for the degradation of S1P into its inactive form, therefore contributing to endothelial apoptosis and diminished vessel integrity. Plpp1 catalyzes the production of pro‐apoptotic ceramide and was discovered to promote the metabolism of S1P. Ceramide kinase is a crucial enzyme in producing anti‐apoptotic ceramide‐1‐phosphate. These discrepancies in ceramide and S1P signaling pathway expression may contribute to impaired cerebrovascular health, providing insight into the increased incidence of stroke with PE.

A theoretical model for flow regulation in the cerebral cortex: role of penetrating arterioles

Activation of a region of the brain results in a local increase in blood flow, a process known as neurovascular coupling (NVC). Here, a theoretical model of blood flow regulation in the cerebral cortex is utilized to investigate the potential role of penetrating arterioles as the primary mechanism for local control of blood flow. Penetrating arterioles connect pial arterioles with the capillary meshwork deeper in the cortex and have a typical length of approximately 600 μm. This is about one‐sixth of the length of corresponding small arterioles in skeletal muscle. The question arises whether these relatively short arterioles can achieve the range of flow modulation observed in the cerebral cortex. A previously developed compartmental model for flow regulation in skeletal muscle was modified to represent the structure of cerebral microvasculature. A compartment consisting of penetrating arterioles with a reference diameter of 14.8 μm and a length of 600 μm is assumed to provide active control of blood flow. Smooth muscle tone in these arterioles is assumed to depend on a combination of signals representing myogenic, shear‐dependent, and metabolic responses. The metabolic response is represented by a change in endothelial cell membrane potential, propagated upstream along arterioles by conducted responses. Sensitivity of diameter to membrane potential was determined based on experimental data. According to the model, a hyperpolarization of 40 mV can result in an increase in local blood flow by approximately 70%. Since increases in local blood flow of 50% with activation have been observed, these results imply that vasoconstriction and vasodilation by penetrating arterioles can provide typical levels of blood flow control seen in neurovascular coupling.

Post‐menopausal Cerebral Microvascular Alterations in a Mouse Model of Alzheimer’s Disease

Cognitive decline, as seen in Alzheimer’s disease (AD), is a growing public health concern and is linked to decreased cerebral blood flow, particularly in women after menopause. Impaired cerebrovascular function precedes the onset of AD, possibly due to reduced endothelial function in parenchymal arterioles, the bottlenecks of the cerebral microcirculation, although exact mechanisms by menopause remain elusive. The goal of this study was to determine whether menopause impairs endothelial function in parenchymal arterioles of wild‐type (WT) and 5x‐FAD mouse model of AD. Menopause was induced by the 4‐vinylcyclohexene diepoxide (VCD) model, which induces gradual ovarian failure. Cerebral parenchymal arterioles were isolated and studied by pressure myography. Data are means ± SEM. In WT mice, menopause caused a significant increase in myogenic tone (myogenic tone: 24.73 ± 1.2 vs. 34 ± 2.6%, vehicle vs VCD, n = 5 / 8; p<0.05), as well as a small but significant reduction in resting lumen diameter (32.68 ± 1.3 vs. 28.40 ± 2.1 µm, vehicle vs VCD, n = 5 / 8; p<0.05). We then tested endothelial function, focusing on K+ channels, namely small and intermediate Ca2+‐activated K+ channels (SKCa / IKCa) and inwardly rectifying K+ channels (KIR2). Menopause did not affect arteriolar dilation to a cumulative concentration‐response curve of the SKCa/ IKCa activator NS‐309 (at 1 µM, vasodilation: 23.49 ± 11.5 vs. 17.80 ± 1.7%, vehicle vs VCD, n = 3 / 6). Similarly, KIR2 function was unchanged (vasodilation: 16.06 ± 6.6 vs. 16.21 ± 2.9%, vehicle vs VCD, n = 4 / 8). In the 5x‐FAD mice, menopause did not affect myogenic tone (myogenic tone: 23.49 ± 2.2 vs. 28 3.2%, vehicle vs VCD, n = 10 / 7), although there was a significant decrease in resting lumen diameter (39.16 ± 2.6 vs. 27.79 ± 2.0 µm, vehicle vs VCD, n = 10 / 7 p<0.05). Arterioles from menopausal 5x‐FAD mice showed a significantly blunted response to NS‐309 (at 1 µM, vasodilation: 14.96 ± 2.9 vs. 9.42 ± 1.4%, vehicle vs VCD, n = 7 / 4, p<0.05), without differences in KIR2‐induced dilation (vasodilation: 16.02 ± 1.3 vs. 13.69 ± 2.3%, vehicle vs VCD n = 9 / 6). In conclusion, we found that in WT mice, menopause leads to changes in myogenic tone without affecting K+‐dependent dilation. However, in 5x‐FAD mice, menopause impairs endothelial SKCa/IKCa channels independent of KIR2 function or myogenic tone. These findings identify new targets modulated by menopause in the cerebral microvasculature of WT and AD mice, which may contribute to cognitive dysfunction.

Time Course of Changes in the Neurovascular Unit after Hypoxic-Ischemic Injury in Neonatal Rats.

Exposure to hypoxic-ischemic (HI) insults in newborns can predispose them to severe neurological sequela. The mechanisms underlying HI-related brain injury have not been completely elucidated. The neurovascular unit (NVU) is a composite of structures that protect the brain from the influx of detrimental molecules. Changes in the NVU after HI are important because they could reveal endogenous neuroprotective pathways in the cerebral microvasculature. Furthermore, the time course of changes in the NVU after exposure to HI in the newborn remains to be determined. In this study, we examined the effects of severe HI on the time course of changes in the NVU in neonatal rats. Brains were collected from rats exposed to right carotid artery ligation and 2 h of hypoxia on postnatal day 7 with recovery for 6 or 48 h after exposure to sham treatment (Sham) or HI. The right HI and left hypoxic alone sides of the brains were examined by quantitative immunohistochemistry for vascular density (laminin), pericyte vascular coverage (PDGFRβ), astrocyte vascular coverage (GFAP), and claudin-5 expression in the microvasculature of the cerebral cortex, white matter, and hippocampus. HI-related brain injury in neonatal rats was associated with increases in vascular density in the cortex and hippocampus 48 h after HI as well as neurovascular remodeling, including loss of pericyte coverage in the cortex and increases in claudin-5 in the hippocampus 6 h after HI. Astrocyte coverage was not affected by HI injury. The time course of the responses in the different components of the NVU varied after exposure to HI. There were also differential regional responses in the elements of the NVU in response to HI and hypoxia alone.

Multiscale modelling of brain tissue oxygen and glucose dynamics in tortuous capillary during ischaemia-reperfusion

Brain ischaemia causes reduction of cerebral blood flow, which interrupts the transport of oxygen and glucose to brain tissue. These transport inefficiencies have also been associated with the complex cerebral microvasculature. In this study, the importance of cerebral capillary complexity and tissue interstitial porosity in oxygen and glucose transport and metabolism during brain tissue ischaemia is investigated using an asymptotic expansion homogenization method. Applying this technique produces new macroscale governing equations with associated microscale cell problems. Solving the latter on the brain tissue microstructural geometry will obtain parametric tensors, namely the conductivities of the capillary, K and interstitial space, E; and the diffusivities of a substrate in the capillary, DM,c, and in interstitial space, DM,t. From the microscale simulations, increasing the capillary tortuosity resulted in a decrement of K and DM,c, but no significant changes in E and DM,t. Meanwhile, increasing the capillary radius resulted in the decrease of all parameters except K. Then, the parametric tensors obtained are used to solve the macroscale governing equations on a one-dimensional brain model under ischaemia-reperfusion conditions. From the macroscale simulations, changing the capillary tortuosity affects the uptake and metabolism of oxygen and glucose during brain ischaemia-reperfusion. In addition, in more tortuous capillaries, oxygen and glucose are utilized rapidly at tissues proximal to the capillary during the reperfusion process, leaving only a small amount of these substrates for distal tissues. This could be associated with severe stroke outcome. It is thus proposed that the capillary tortuosity of a patient could potentially be used as an additional indicator in determining the severity of ischaemic stroke.

Association between retinal vascular measures and brain white matter lesions in schizophrenia.

Recent studies have examined retinal vascular abnormalities in schizophrenia as retinal vascular imaging is a non-invasive proxy to cerebral microvasculature. However, relation between retinal vascular abnormalities and brain structure is not well examined in schizophrenia. Hence in this study, for the first time, we examined the relationship between retinal vascular measures and brain white matter lesions in schizophrenia. We examined brain white matter lesions as they are considered a predictive marker for future adverse cerebrovascular event. We acquired retinal vascular images of both eyes using a non-mydriatic camera and calculated retinal vascular diameter, tortuosity, trajectory and fractal dimension using validated methods. All patients underwent Magnetic Resonance Imaging of bran and we computed white matter hypo-intensities using Freesurfer software. We performed a linear regression analysis to examine the relationship between white matter hypo-intensities and retinal vascular measures controlling for age, sex, fasting blood sugar, creatinine, whole-brain volume, and antipsychotic dose. The regression model was significant in Schizophrenia patients (R=0.983;R2=0.966;-F=10.849;p=0.008) but not in healthy volunteers (R=0.828;R2=0.686;F=0.182; p=0.963). Among the retinal vascular measures, arterial tortuosity (β=0.963;p-0.002), tortuosity (β=-1.002;p=0.001) and fractal dimension (β=-0.688;p=0.014) were significant predictors of white matter lesions. The current study's findings support the conclusion that retinal vascular fractal dimension and tortuosity are associated with changes in cerebral white matter and may be considered proxy markers for cerebral microvasculature in schizophrenia. Considering the relationship between white matter lesions and stroke, these observations could have important clinical implications to screen schizophrenia patients for risk of adverse cerebrovascular event.

Therapeutic Opportunities and Delivery Strategies for Brain Revascularization in Stroke, Neurodegeneration, and Aging

Central nervous system (CNS) diseases, especially acute ischemic events and neurodegenerative disorders, constitute a public health problem with no effective treatments to allow a persistent solution. Failed therapies targeting neuronal recovery have revealed the multifactorial and intricate pathophysiology underlying such CNS disorders as ischemic stroke, Alzheimeŕs disease, amyotrophic lateral sclerosis, vascular Parkisonism, vascular dementia, and aging, in which cerebral microvasculature impairment seems to play a key role. In fact, a reduction in vessel density and cerebral blood flow occurs in these scenarios, contributing to neuronal dysfunction and leading to loss of cognitive function. In this review, we provide an overview of healthy brain microvasculature structure and function in health and the effect of the aforementioned cerebral CNS diseases. We discuss the emerging new therapeutic opportunities, and their delivery approaches, aimed at recovering brain vascularization in this context. SIGNIFICANCE STATEMENT: The lack of effective treatments, mainly focused on neuron recovery, has prompted the search of other therapies to treat cerebral central nervous system diseases. The disruption and degeneration of cerebral microvasculature has been evidenced in neurodegenerative diseases, stroke, and aging, constituting a potential target for restoring vascularization, neuronal functioning, and cognitive capacities by the development of therapeutic pro-angiogenic strategies.

Isolation and characterization of peritoneal microvascular pericytes.

As a potential source of myofibroblasts, pericytes may play a role in human peritoneal fibrosis. The culture of primary vascular pericytes in animals has previously been reported, most of which are derived from cerebral and retinal microvasculature. Here, in the field of peritoneal dialysis, we describe a method to isolate and characterize mouse peritoneal microvascular pericytes. The mesenteric tissues of five mice were collected and digested by type II collagenase and type I DNase. After cell attachment, the culture fluid was replaced with pericyte‐conditioned medium. Pericytes with high purity (99.0%) could be isolated by enzymatic disaggregation combined with conditional culture and magnetic activated cell sorting. The primary cells were triangular or polygonal with protrusions, and confluent cell culture could be established in 3 days. The primary pericytes were positive for platelet‐derived growth factor receptor‐β, α‐smooth muscle actin, neuron‐glial antigen 2, and CD13. Moreover, they promoted formation of endothelial tubes, and pericyte–myofibroblast transition occurred after treatment with transforming growth factor‐β1. In summary, we describe here a reproducible isolation protocol for primary peritoneal pericytes, which may be a powerful tool for in vitro peritoneal fibrosis studies.

Carotid Artery Stiffness: Imaging Techniques and Impact on Cerebrovascular Disease

Arterial stiffness is an important measure of vascular aging and atherosclerosis. Though it is measured in many well-known epidemiologic cohort studies, arterial stiffness is often overlooked in routine clinical practice for a number of reasons including difficulties in measurement, variations in definition, and uncertainties surrounding treatment. Central arterial stiffness, a surrogate for aortic stiffness, is the most commonly measured marker of arterial stiffness. In addition to central stiffness, there are also a number of ultrasound based techniques to measure local vascular stiffness, including carotid stiffness. There is evidence that both local carotid stiffness and central arterial stiffness measures are associated with multiple cerebrovascular processes, including stroke and cognitive dysfunction. Mechanistic explanations supporting this association include increased flow load experienced by the cerebral microvasculature leading to cerebral parenchymal damage. In this article, we review definitions of carotid artery stiffness measures and pathophysiologic mechanisms underpinning its association with plaque development and downstream cerebral pathology. We will review the evidence surrounding the association of carotid stiffness measures with downstream manifestations including stroke, cerebral small vessel disease detected on brain MR such as white matter hyperintensities and covert brain infarctions, brain atrophy, and cognitive dysfunction. With consistent definitions, measurement methods, and further scientific support, carotid stiffness may have potential as an imaging-based risk factor for stroke and cognitive decline.

HCV co-infection is related to acute ischemic severity and outcome

Background and aimHCV infection is associated with increased risk of ischemic cerebral stroke. HCV stroked patients are younger with a lower burden of classical risk factors and higher levels of systemic inflammation. The present study aimed to discover the association between HCV infection functional outcome of stroke.Patients and methodsThe present prospective study included 60 patients with acute ischemic stroke. All patients were subjected to careful history taking and through clinical and neurological examination. Stroke severity at presentation was assessed using National Institute of Health Stroke Scale (NIHSS). Quantitative HCV RNA test was used to diagnose HCV infection. The prognosis of the studied patients was 3 months after treatment using modified Rankin scale (mRS) for neurologic disability.ResultsThe present study was conducted on 60 patients with ischemic stroke. They comprised 13 patients (21.7%) with HCV and 47 patients without. Stroke patients with HCV had significantly higher frequency of carotid artery stenosis, higher NIHSS (17.9 ± 6.9 versus 9.9 ± 5.3, p < 0.001) and higher frequency of severe stroke (46.1% versus 4.3%, p = 0.001) when compared with patients without HCV. Logistic regression analysis identified patients’ sex, NIHSS and HCV as significant predictors of outcome in univariate analysis. However, in multivariate analysis, only NIHSS proved to be significant.ConclusionsThe present study suggests a significant link between chronic HCV infection and ischemic stroke severity and poor outcome. This is probably related to the pathogenic effects of the chronic inflammatory state induced by HCV infection on the cerebral microvasculature.

Impact of Stellate Ganglion Block in the Management of Cerebral Vasospasm: A Prospective Interventional Study.

Stellate ganglion block (SGB) causes blockage of sympathetic nerve activity, which may lead to intracerebral vessel dilatation and relieve cerebral vasospasm in patients of aneurysmal subarachnoid hemorrhage (aSAH). The aim of this study was to evaluate the efficacy and safety of SGB to relieve cerebral vasospasm on clinicoradiological parameters. We prospectively included 20 patients with clinical and angiographic evidence of vasospasm post aneurysmal clipping. Cerebral blood flow velocity and Lindegaard ratio were assessed using transcranial Doppler (TCD). Location of vasospasm, vessel diameter, vasospasm severity, parenchymal filling time, and venous sinus filling time were assessed on digital subtraction angiography (DSA). Patients received ultrasound-guided SGB with 10 mL of 0.5% bupivacaine on the ipsilateral side of the vasospasm. After 30 minutes, the neurological status, TCD, and DSA parameters were reevaluated. After SGB, there was statistically significant reduction in the middle cerebral artery (MCA) peak systolic velocity (P = 0.005), mean flow velocity (P = 0.025), and Lindegaard ratio (P = 0.022) on TCD. We observed significant dilatation in the mean vessel diameter measured at the mid-M1 segment of MCA (P = 0.003) and mid-A1 segment of ACA (P = 0.002) on DSA. The mean parenchymal filling time and mean venous sinus filling time decreased nonsignificantly after SGB (P = 0.163/0.104). Neurological improvement was observed in five (25%) patients. SGB has positive clinicoradiological influence in the management of cerebral vasospasm of large vessels. However, its effect on cerebral microvasculature is limited and needs a larger database for further analysis.

Neuroinflammation as a mechanism linking hypertension with the increased risk of Alzheimer’s disease

Alzheimer’s disease, the most common type of dementia among older adults, currently cannot be prevented or effectively treated. Only a very small percentage of Alzheimer’s disease cases have an established genetic cause. The majority of Alzheimer’s disease cases lack a clear causative event, but several modifiable factors have been associated with an increased risk of this disease. Persistent midlife hypertension is one such risk factor, which can be effectively controlled through changes in diet, lifestyle, and antihypertensive drugs. Identifying molecular mechanisms linking modifiable risk factors with the increased risk of Alzheimer’s disease could enhance our understanding of this disease and lead to identification of novel targets and therapeutic approaches for effective treatments. Glial cell-driven neuroinflammation is one of the key pathological features of Alzheimer’s disease. In this review, we illustrate that neuroinflammation could also be one of the possible mechanisms linking hypertension and Alzheimer’s disease. Animal studies have demonstrated that chronically elevated blood pressure leads to adverse glial activation and increased brain inflammatory mediators. We highlight damage to cerebral microvasculature and locally activated renin-angiotensin system as the key pathogenetic mechanisms linking hypertension to neuroinflammation and the accompanying neurodegeneration. The role of tumor necrosis factor-α and interleukin-1β as pro-inflammatory signaling molecules providing this link is discussed. We also summarize the available experimental data indicating that neuroinflammatory changes and glial activation can be reversed by several different classes of antihypertensive medicines. These studies suggest antihypertensives could be beneficial in Alzheimer’s disease not only due to their ability to control the blood pressure, but also due to their anti-neuroinflammatory effects. Confirmation of these observations in human subjects is required and recent advances in the brain imaging techniques allowing visualization of both microglia and astrocyte activation will be essential for this research.

Effect of Pericytes on Cerebral Microvasculature at Different Time Points of Stroke

Pericyte, as an important component of the blood-brain barrier, has received increasing attention in the study of cerebrovascular diseases. However, the mechanism of pericytes after the occurrence of cerebral ischemia is controversial. On the one hand, the expression of pericytes increases after cerebral ischemia, constricting the blood vessels to restrict blood supply and aggravating the damage caused by ischemia; on the other hand, pericytes participate in capillary angiogenesis in the ischemic area, which facilitates the repair of the ischemic injury area. The multifunctionality of pericytes is an important reason for this phenomenon, but the different time points of observation for the outcome indicators in each study are also an important factor that leads to the controversy of pericytes. Based on the review of a large database of original studies, the authors' team summarized the effects of pericytes on cerebral microvasculature at different time points after stroke, searched the possible markers, and explored possible therapeutic.

Putative Concussion Biomarkers Identified in Adolescent Male Athletes Using Targeted Plasma Proteomics.

Sport concussions can be difficult to diagnose and if missed, they can expose athletes to greater injury risk and long-lasting neurological disabilities. Discovery of objective biomarkers to aid concussion diagnosis is critical to protecting athlete brain health. To this end, we performed targeted proteomics on plasma obtained from adolescent athletes suffering a sports concussion. A total of 11 concussed male athletes were enrolled at our academic Sport Medicine Concussion Clinic, as well as 24 sex-, age- and activity-matched healthy control subjects. Clinical evaluation was performed and blood was drawn within 72 h of injury. Proximity extension assays were performed for 1,472 plasma proteins; a total of six proteins were considered significantly different between cohorts (P < 0.01; five proteins decreased and one protein increased). Receiver operating characteristic curves on the six individual protein biomarkers identified had areas-under-the-curves (AUCs) for concussion diagnosis ≥0.78; antioxidant 1 copper chaperone (ATOX1; AUC 0.81, P = 0.003), secreted protein acidic and rich in cysteine (SPARC; AUC 0.81, P = 0.004), cluster of differentiation 34 (CD34; AUC 0.79, P = 0.006), polyglutamine binding protein 1 (PQBP1; AUC 0.78, P = 0.008), insulin-like growth factor-binding protein-like 1 (IGFBPL1; AUC 0.78, P = 0.008) and cytosolic 5'-nucleotidase 3A (NT5C3A; AUC 0.78, P = 0.009). Combining three of the protein biomarkers (ATOX1, SPARC and NT5C3A), produced an AUC of 0.98 for concussion diagnoses (P < 0.001; 95% CI: 0.95, 1.00). Despite a paucity of studies on these three identified proteins, the available evidence points to their roles in modulating tissue inflammation and regulating integrity of the cerebral microvasculature. Taken together, our exploratory data suggest that three or less novel proteins, which are amenable to a point-of-care immunoassay, may be future candidate biomarkers for screening adolescent sport concussion. Validation with protein assays is required in larger cohorts.

Pharmacological inhibition of carbonic anhydrases ameliorates cognitive dysfunction, rescuing Aβ‐induced neurovascular pathology in vivo

Cerebrovascular dysfunction (CVD) is an early feature of Alzheimer's disease (AD), contributing to the pathology progression, and suggesting a strict association between CVD and neurodegeneration. The majority of AD cases present cerebral amyloid angiopathy (CAA), neuropathological feature characterized by abnormal vasculotropic deposition of amyloid beta, mainly Aβ40. Severe CAA is also induced by familial Aβ variants, such as the Dutch-Q22. Our previous in vitro studies demonstrated that brain vascular amyloidosis elicits mitochondrial dysregulation and caspase-mediated apoptosis, in cells composing the neurovascular unit, including neurons, endothelial, glial and smooth muscle cells. Additionally, we showed that acetazolamide (ATZ) and methazolamide (MTZ), FDA-approved carbonic anhydrase inhibitors (CAIs) which cross the blood-brain barrier (BBB), hamper these detrimental processes. Carbonic anhydrases (CAs) represent a family of metalloenzymes catalyzing the reversible hydration of carbon dioxide, and their inhibition improves cerebral blood flow, vasoreactivity and neuronal excitability, pointing to CAs as CVD targets in AD.We employed Tg-SwDI mice (expressing human amyloid precursor protein, APP, carrying the Swedish, Dutch and Iowa mutations), which develop fibrillar amyloid burden, primarily in the cerebral microvasculature, starting at 6 months. We fed the animals (from 8 to 16 months of age) a CAI-diet, following which we performed behavioral analysis, and harvested the brains for both biochemical and immunohistochemical examination.Compared to untreated Tg mice, ATZ- and MTZ-fed animals showed reduced cognitive impairment, along with decreased vascular Aβ overload and astrogliosis, main pathological hallmarks of the disease. Tg animals exhibited Aβ deposition in endothelial and glial cells, leading to cell-specific caspase-3 activation. Interestingly, CAI-diet reduced endothelial and astrocytic Aβ deposits, and Aβ-induced caspase activation. Interestingly, the augmented expression of cerebral TREM2 and CD68 in CAI-treated mice suggests an attenuated inflammatory response, concomitantly with a boost of the cerebral clearance and active Aβ removal from brain microglia/macrophages, respectively, which may underlie the observed Aβ reduction. Furthermore, preliminary data suggest that both ATZ and MTZ promote microglial endocytosis, possibly facilitating Aβ degradation.CAIs provide neuroprotection, fostering neurovascular and glial physiological functions and clearance mechanisms, and attenuating CVD.

Presenilin1 FAD mutants impair ischemia-induced brain neovascularization and neuronal survival decreasing γ-secretase processing of ephrinB2 and ephrinB2-mediated angiogenic functions.

Cerebral microvasculature abnormalities are implicated in Alzheimer's disease (AD) neuropathology. Ischemic lesions causing neuronal damage are often found in AD brains. The brain responds to ischemia by stimulating tissue neovascularization via sprouting angiogenesis, impairment of this function renders the brain vulnerable to the insult. It has been hypothesized that decreased angiogenesis in AD leads to insufficient blood flow and neuronal dysfunction in affected areas. The EphB4/ephrinB2 (efnB2) ligand-receptor system regulates brain angiogenesis in response to ischemia. To study the EphB4-induced angiogenic functions of primary cortical endothelial cells (pCEC) we used the in vitro angiogenesis assays: sprouting on beads and tube formation. To analyze the VE-cadherin angiogenic complexes in pCEC and brain extracts we used co-immunoprecipitations, western blotting and spPLA. For the in vivo experiments we used kcnockin mice (KI) expressing PS1 FAD mutants and MCAO, MRI and immunohistochemistry of brain sections. The behavioral tests were: Novel object recognition, Ymaze, Open field and Rotarod test. PS1/γ-secretase regulate EphB4-induced sprouting, tube formation and VE-cadherin angiogenic complexes in pCEC and these functions including processing of efnB2 by γ-secretase are decreased by PS1 FAD mutants. Ischemia stimulates formation of these angiogenic complexes in the brain and this function is attenuated by PS1 FAD mutants together with ischemia-induced neovascularization and cerebral blood flow while neuronal death and cognitive decline are increased. We finally found that a small peptide, which derives from the product of cleavage of efnB2 by γ-secretase rescues angiogenic functions of PS1 FAD ECs. Together, our data support the hypothesis that PS1 FAD mutants inhibit ischemia-induced angiogenic functions of ECs by decreasing the γ-secretase processing of efnB2 and impairing the EphB4/efnB2 signaling, thus decreasing neovascularization in the brain and leading to increased vulnerability to the insult, cognitive decline and neuronal death. Furthermore, our data reveal a novel brain angiogenic mechanism targeted by PS1 FAD mutants and a potential therapeutic target for ischemia-induced neurodegeneration. Importantly, FAD mutant effects occur in absence of neuropathological hallmarks of AD, supporting such hallmarks may form downstream of mutant effects on neoangiogenesis and neuronal survival.

Interactions Between Kidney Function and Cerebrovascular Disease: Vessel Pathology That Fires Together Wires Together.

The kidney and the brain, as high-flow end organs relying on autoregulatory mechanisms, have unique anatomic and physiological hemodynamic properties. Similarly, the two organs share a common pattern of microvascular dysfunction as a result of aging and exposure to vascular risk factors (e.g., hypertension, diabetes and smoking) and therefore progress in parallel into a systemic condition known as small vessel disease (SVD). Many epidemiological studies have shown that even mild renal dysfunction is robustly associated with acute and chronic forms of cerebrovascular disease. Beyond ischemic SVD, kidney impairment increases the risk of acute cerebrovascular events related to different underlying pathologies, notably large artery stroke and intracerebral hemorrhage. Other chronic cerebral manifestations of SVD are variably associated with kidney disease. Observational data have suggested the hypothesis that kidney function influences cerebrovascular disease independently and adjunctively to the effect of known vascular risk factors, which affect both renal and cerebral microvasculature. In addition to confirming this independent association, recent large-scale human genetic studies have contributed to disentangling potentially causal associations from shared genetic predisposition and resolving the uncertainty around the direction of causality between kidney and cerebrovascular disease. Accelerated atherosclerosis, impaired cerebral autoregulation, remodeling of the cerebral vasculature, chronic inflammation and endothelial dysfunction can be proposed to explain the additive mechanisms through which renal dysfunction leads to cerebral SVD and other cerebrovascular events. Genetic epidemiology also can help identify new pathological pathways which wire kidney dysfunction and cerebral vascular pathology together. The need for identifying additional pathological mechanisms underlying kidney and cerebrovascular disease is attested to by the limited effect of current therapeutic options in preventing cerebrovascular disease in patients with kidney impairment.