Experimental chronic cerebral hypoperfusion results in decreased pericyte coverage and increased blood-brain barrier permeability in the corpus callosum

Acute Ablation of Cortical Pericytes Leads to Rapid Neurovascular Uncoupling

Pericytes are perivascular mural cells that enwrap brain capillaries and maintain blood-brain barrier (BBB) integrity. Most studies suggest that pericytes regulate cerebral blood flow (CBF) and oxygen delivery to activated brain structures, known as neurovascular coupling. While we have previously shown that congenital loss of pericytes leads over time to aberrant hemodynamic responses, the effects of acute global pericyte loss on neurovascular coupling have not been studied. To address this, we used our recently reported inducible pericyte-specific Cre mouse line crossed to iDTR mice carrying Cre-dependent human diphtheria toxin (DT) receptor, which upon DT treatment leads to acute pericyte ablation. As expected, DT led to rapid progressive loss of pericyte coverage of cortical capillaries up to 50% at 3 days post-DT, which correlated with approximately 50% reductions in stimulus-induced CBF responses measured with laser doppler flowmetry (LDF) and/or intrinsic optical signal (IOS) imaging. Endothelial response to acetylcholine, microvascular density, and neuronal evoked membrane potential responses remained, however, unchanged, as well as arteriolar smooth muscle cell (SMC) coverage and functional responses to adenosine, as we previously reported. Together, these data suggest that neurovascular uncoupling in this model is driven by pericyte loss, but not other vascular deficits or neuronal dysfunction. These results further support the role of pericytes in CBF regulation and may have implications for neurological conditions associated with rapid pericyte loss such as hypoperfusion and stroke, as well as conditions where the exact time course of global regional pericyte loss is less clear, such as Alzheimer's disease (AD) and other neurogenerative disorders.

Glucagon-Like Peptide-2 Receptor is Involved in Spatial Cognitive Dysfunction in Rats After Chronic Cerebral Hypoperfusion

Chronic cerebral hypoperfusion (CCH) affects the aging population and especially patients with neurodegenerative diseases, such as Alzheimer's disease or Parkinson's disease. CCH is closely related to the cognitive dysfunction in these diseases. Glucagon-like peptide-2 receptor (GLP2R) mRNA and protein are highly expressed in the gut and in hippocampal neurons. This receptor is involved in the regulation of food intake and the control of energy balance and glucose homeostasis. The present study employed behavioral techniques, electrophysiology, western blotting, immunohistochemistry, quantitative real time polymerase chain reaction (qRT-PCR), and Golgi staining to investigate whether the expression of GLP2R changes after CCH and whether GLP2R is involved in cognitive impairment caused by CCH. Our findings show that CCH significantly decreased hippocampal GLP2R mRNA and protein levels. GLP2R upregulation could prevent CCH-induced cognitive impairment. It also improved the CCH-induced impairment of long-term potentiation and long-term depression. Additionally, GLP2R modulated after CCH the AKT-mTOR-p70S6K pathway in the hippocampus. Moreover, an upregulation of the GLP2R increased the neurogenesis in the dentate gyrus, neuronal activity, and density of dendritic spines and mushroom spines in hippocampal neurons. Our findings reveal the involvement of GLP2R via a modulation of the AKT-mTOR-p70S6K pathway in the mechanisms underlying CCH-induced impairments of spatial learning and memory. We suggest that the GLP2R and the AKT-mTOR-p70S6K pathway in the hippocampus are promising targets to treat cognition deficits in CCH.

CSF evidence of pericyte damage in Alzheimer's disease is associated with markers of blood-brain barrier dysfunction and disease pathology

Background

We aimed to assess the relationship between levels of a cerebrospinal fluid (CSF) marker of pericyte damage, soluble platelet-derived growth factor receptor β (sPDGFRβ) and CSF markers of blood-brain barrier (BBB) integrity (CSF albumin and CSF/serum albumin ratio) and disease pathology (reduced CSF Aβ42 and elevated CSF total and phosphorylated tau) in Alzheimer’s disease (AD).

Methods

sPDGFRβ and albumin were measured by sandwich ELISA in ante-mortem CSF from 39 AD and 39 age-matched controls that were grouped according to their biomarker profile (i.e. AD cases t-tau > 400 pg/mL, p-tau > 60 pg/mL and Aβ42 < 550 pg/mL). sPDGFRβ was also measured in matched serum and CSF samples (n = 23) in a separate neurologically normal group for which the CSF/serum albumin ratio had been determined.

Results

CSF sPDGFRβ level was significantly increased in AD (p = 0.0038) and correlated positively with albumin (r = 0.45, p = 0.007), total tau (r = 0.50, p = 0.0017) and phosphorylated tau (r = 0.41, p = 0.013) in AD but not in controls. CSF sPDGFRβ did not correlate with Aβ42. Serum and CSF sPDGFRβ were positively correlated (r = 0.547, p = 0.0085) in the independent neurologically normal CSF/serum matched samples.

Conclusions

We provide further evidence of an association between pericyte injury and BBB breakdown in AD and novel evidence that a CSF marker of pericyte injury is related to the severity of AD pathology.

Electronic supplementary material

The online version of this article (10.1186/s13195-019-0534-8) contains supplementary material, which is available to authorized users.

Huoluo Yinao decoction mitigates cognitive impairments after chronic cerebral hypoperfusion in rats

ETHNOPHARMACOLOGICAL RELEVANCE

Huoluo Yinao decoction (HLYND) has been used to ameliorate cognitive impairment induced by chronic cerebral hypoperfusion in clinical for years. However, the exact mechanisms remain unknown.

AIM OF THE STUDY

To investigate the effects and mechanisms underlying HLYND-mediated improvement in cognitive deficits associated with chronic cerebral hypoperfusion.

MATERIALS AND METHODS

Thirty-six Sprague-Dawley rats were randomly allocated to three groups: sham, model, and HLYND. Daily administration of HLYND or volume-matched vehicle by gavage was initiated 1 day after bilateral carotid artery stenosis (BCAS) and continued for 42 days. The Morris water maze (MWM) test was used to assess cognitive functions from days 36-42. Via western blot and immunofluorescent staining, restoration of neuronal plasticity and remyelination of white matter were evaluated by analyzing the expression profiles of MAP-2, synaptophysin and MBP. In addition, macrophage/microglial activation was assessed by quantifying changes in Iba1, and macrophage/microglial polarization was assessed by changes in iNOS and CD16 (M1 markers), as well as Arg1 and CD206 (M2 markers).

RESULTS

In the MWM test, BCAS rats showed significantly extended escape latency and reduced platform crossing times, while those in the HLYND group had shortened escape latency and increased frequency of platform crossing. In addition, rats in the model group showed decreased levels and abnormal morphological changes of MAP-2, synaptophysin and MBP, whereas HLYND administration reversed these effects. As expected, Iba1 levels were elevated in both the model and HLYND groups but rats in the model group showed increased levels of the M1 markers, iNOS and CD16, and a correspondent decrease in the M2 marker, Arg1. In contrast, in the HLYND group, iNOS and CD16 levels were suppressed, while Arg1 levels were elevated.

CONCLUSIONS

Our findings demonstrate that HLYND mitigates cognitive impairment after chronic cerebral hypoperfusion in rats through mechanisms involving increased neuronal plasticity and white matter remyelination, with a subtile modulation of macrophage/microglial polarization toward the M2 phenotype.

Tripchlorolide May Improve Spatial Cognition Dysfunction and Synaptic Plasticity after Chronic Cerebral Hypoperfusion

Chronic cerebral hypoperfusion (CCH) is a common pathophysiological mechanism that underlies cognitive decline and degenerative processes in dementia and other neurodegenerative diseases. Low cerebral blood flow (CBF) during CCH leads to disturbances in the homeostasis of hemodynamics and energy metabolism, which in turn results in oxidative stress, astroglia overactivation, and synaptic protein downregulation. These events contribute to synaptic plasticity and cognitive dysfunction after CCH. Tripchlorolide (TRC) is an herbal compound with potent neuroprotective effects. The potential of TRC to improve CCH-induced cognitive impairment has not yet been determined. In the current study, we employed behavioral techniques, electrophysiology, Western blotting, immunofluorescence, and Golgi staining to investigate the effect of TRC on spatial learning and memory impairment and on synaptic plasticity changes in rats after CCH. Our findings showed that TRC could rescue CCH-induced spatial learning and memory dysfunction and improve long-term potentiation (LTP) disorders. We also found that TRC could prevent CCH-induced reductions in N-methyl-D-aspartic acid receptor 2B, synapsin I, and postsynaptic density protein 95 levels. Moreover, TRC upregulated cAMP-response element binding protein, which is an important transcription factor for synaptic proteins. TRC also prevented the reduction in dendritic spine density that is caused by CCH. However, sham rats treated with TRC did not show any improvement in cognition. Because CCH causes disturbances in brain energy homeostasis, TRC therapy may resolve this instability by correcting a variety of cognitive-related signaling pathways. However, for the normal brain, TRC treatment led to neither disturbance nor improvement in neural plasticity. Additionally, this treatment neither impaired nor further improved cognition. In conclusion, we found that TRC can improve spatial learning and memory, enhance synaptic plasticity, upregulate the expression of some synaptic proteins, and increase the density of dendritic spines. Our findings suggest that TRC may be beneficial in the treatment of cognitive impairment induced by CCH.

Apoε4 disrupts neurovascular regulation and undermines white matter integrity and cognitive function

The ApoE4 allele is associated with increased risk of small vessel disease, which is a cause of vascular cognitive impairment. Here, we report that mice with targeted replacement (TR) of the ApoE gene with human ApoE4 have reduced neocortical cerebral blood flow compared to ApoE3-TR mice, an effect due to reduced vascular density rather than slowing of microvascular red blood cell flow. Furthermore, homeostatic mechanisms matching local delivery of blood flow to brain activity are impaired in ApoE4-TR mice. In a model of cerebral hypoperfusion, these cerebrovascular alterations exacerbate damage to the white matter of the corpus callosum and worsen cognitive dysfunction. Using 3-photon microscopy we found that the increased white matter damage is linked to an enhanced reduction of microvascular flow resulting in local hypoxia. Such alterations may be responsible for the increased susceptibility to hypoxic-ischemic lesions in the subcortical white matter of individuals carrying the ApoE4 allele.

ApoE4 is a risk factor for small vessel disease, which can lead to cognitive impairment. Here the authors assess the microvasculature of the corpus callosum using 3-photon microscopy and find that mice expressing the ApoE4 allele are more susceptible than wild-type to white matter injury and cognitive impairment in a model of hypoperfusion-induced hypoxia.

Understanding the role of the perivascular space in cerebral small vessel disease

Small vessel diseases (SVDs) are a group of disorders that result from pathological alteration of the small blood vessels in the brain, including the small arteries, capillaries and veins. Of the 35-36 million people that are estimated to suffer from dementia worldwide, up to 65% have an SVD component. Furthermore, SVD causes 20-25% of strokes, worsens outcome after stroke and is a leading cause of disability, cognitive impairment and poor mobility. Yet the underlying cause(s) of SVD are not fully understood. Magnetic resonance imaging has confirmed enlarged perivascular spaces (PVS) as a hallmark feature of SVD. In healthy tissue, these spaces are proposed to form part of a complex brain fluid drainage system which supports interstitial fluid exchange and may also facilitate clearance of waste products from the brain. The pathophysiological signature of PVS and what this infers about their function and interaction with cerebral microcirculation, plus subsequent downstream effects on lesion development in the brain has not been established. Here we discuss the potential of enlarged PVS to be a unique biomarker for SVD and related brain disorders with a vascular component. We propose that widening of PVS suggests presence of peri-vascular cell debris and other waste products that form part of a vicious cycle involving impaired cerebrovascular reactivity, blood-brain barrier dysfunction, perivascular inflammation and ultimately impaired clearance of waste proteins from the interstitial fluid space, leading to accumulation of toxins, hypoxia, and tissue damage. Here, we outline current knowledge, questions and hypotheses regarding understanding the brain fluid dynamics underpinning dementia and stroke through the common denominator of SVD.