Reduced vascular endothelial growth factor and capillary density in the occipital cortex in dementia with Lewy bodies

A single nuclear transcriptomic characterisation of mechanisms responsible for impaired angiogenesis and blood-brain barrier function in Alzheimer's disease

Brain perfusion and blood-brain barrier (BBB) integrity are reduced early in Alzheimer's disease (AD). We performed single nucleus RNA sequencing of vascular cells isolated from AD and non-diseased control brains to characterise pathological transcriptional signatures responsible for this. We show that endothelial cells (EC) are enriched for expression of genes associated with susceptibility to AD. Increased β-amyloid is associated with BBB impairment and a dysfunctional angiogenic response related to a failure of increased pro-angiogenic HIF1A to increased VEGFA signalling to EC. This is associated with vascular inflammatory activation, EC senescence and apoptosis. Our genomic dissection of vascular cell risk gene enrichment provides evidence for a role of EC pathology in AD and suggests that reducing vascular inflammatory activation and restoring effective angiogenesis could reduce vascular dysfunction contributing to the genesis or progression of early AD.

Impaired neuronal activity as a potential factor contributing to the underdeveloped cerebrovasculature in a young Parkinson's disease mouse model

Misfolding of α-synuclein (α-Syn) in the brain causes cellular dysfunction, leading to cell death in a group of neurons, and consequently causes the progression of Parkinson's disease (PD). Although many studies have demonstrated the pathological connections between vascular dysfunction and neurodegenerative diseases, it remains unclear how neuronal accumulation of α-Syn affects the structural and functional aspects of the cerebrovasculature to accelerate early disease progression. Here, we demonstrated the effect of aberrant α-Syn expression on the brain vasculature using a PD mouse model expressing a familial mutant form of human α-Syn selectively in neuronal cells. We showed that young PD mice have an underdeveloped cerebrovasculature without significant α-Syn accumulation in the vasculature. During the early phase of PD, toxic α-Syn was selectively increased in neuronal cells, while endothelial cell proliferation was decreased in the absence of vascular cell death or neuroinflammation. Instead, we observed altered neuronal activation and minor changes in the activity-dependent gene expression in brain endothelial cells (ECs) in young PD mice. These findings demonstrated that neuronal expression of mutant α-Syn in the early stage of PD induces abnormal neuronal activity and contributes to vascular patterning defects, which could be associated with a reduced angiogenic potential of ECs.

Is later-life depression a risk factor for Alzheimer's disease or a prodromal symptom: a study using post-mortem human brain tissue?

BACKGROUND

Depression and dementia are both common diseases. Although new cases of depression are more common in younger adults, there is a second peak at the age of 50 years suggesting a different pathological process. Late-life depression (LLD) is associated with dementia. However, it remains unclear whether depression represents a dementia prodrome or is a true risk factor for its development. LLD is thought to have a vascular component and this may be a possible link between depression and dementia. We hypothesised that later-life depression is a prodromal manifestation of dementia and would therefore be associated with more AD, and/or ischaemic brain abnormalities that are present in earlier-life depression or in age- and sex-matched controls.

METHODS

We assessed post-mortem orbitofrontal cortex and dorsolateral pre-frontal cortex from 145 individuals in 4 groups: 28 18-50-year-olds with depression, 30 older individuals (ages 51-90) with depression, 28 with early AD (Braak tangle stages III-IV) and 57 matched controls (17 early-life, 42 later-life). Levels of Aβ, phospho-tau and α-synuclein were assessed by immunohistochemistry and ELISA. To quantify chronic ischaemia, VEGF, MAG and PLP1 were measured by ELISA. To assess pericyte damage, PDGFRB was measured by ELISA. For blood-brain barrier leakiness, JAM-A, claudin 5 and fibrinogen were measured by ELISA. To quantity endothelial activation, the ratio of ICAM1:collagen IV was assessed by immunohistochemistry.

RESULTS

There was no evidence of chronic cerebral hypoperfusion or increased Aβ/tau in either depression group. There was also no indication of pericyte damage, increased blood-brain barrier leakiness or endothelial activation in the OFC or DLPFC in the depression groups.

CONCLUSIONS

Contrary to some previous findings, we have not found evidence of impaired vascular function or increased Aβ in LLD. Our study had a relatively small sample size and limitations in the availability of clinical data. These results suggest that depression is a risk factor for dementia rather than an early manifestation of AD or a consequence of cerebral vascular insufficiency.

Effects of Cerebrovascular and Lewy Body Pathology on Parkinsonian Signs in Community-Dwelling Older Adults

BACKGROUND AND OBJECTIVES

The roles of Lewy body (LB) and separately of cerebrovascular disease (CVD) pathologies in the severity of parkinsonian signs are well recognized in old age. We investigated whether the 2 pathologies act synergistically to further potentiate the severity of parkinsonism beyond their separate effects.

METHODS

We used postmortem data of decedents from 3 longitudinal community-based studies of aging who underwent annual clinical evaluation to assess parkinsonian signs using 26 items of the motor portion of a modified Unified Parkinson Disease Rating Scale. A summary score was developed from each item score to construct a global parkinsonian score, with a higher score indicating more severe parkinsonism. A detailed neuropathologic evaluation was performed to identify LB, Alzheimer disease pathology, nigral neuronal loss, atherosclerosis, macroscopic infarcts, and other CVD pathologies (arteriolosclerosis, cerebral amyloid angiopathy, and microscopic infarcts). A series of regression models with terms for LB, CVD pathology, and the interaction of LB with CVD pathologies was fit for global parkinsonism proximate to death and for individual parkinsonian signs scores including, parkinsonian gait, rigidity, tremor, and bradykinesia.

RESULTS

In 1,753 participants (mean age at death = 89 years; 68% women), LB was observed in 26% of participants, and CVD pathologies were present in more than two-thirds of participants. LB and 3 CVD pathologies (atherosclerosis, arteriolosclerosis, and macroscopic infarcts) were each independently associated with the severity of global parkinsonism proximate to death (LB: β = 0.318, SE = 0.08, p < 0.001; atherosclerosis: β = 0.373, SE = 0.079, p < 0.001; arteriolosclerosis: β = 0.253, SE = 0.078, p = 0.001; macroscopic infarcts: β = 0.333, SE = 0.077, p < 0.001). A linear regression model adjusted for demographics, CVD, and neurodegenerative pathologies showed interaction between LB and macroscopic infarcts (β = 0.463, SE = 0.168, p = 0.006), with LBs being associated with worse global parkinsonism when macroinfarcts are present. Similar interactions were found for atherosclerosis and LBs (β = 0.371, SE = 0.173, p = 0.032) and for parkinsonian gait as the outcome (macroscopic infarcts: β = 0.662, SE = 0.239, p = 0.005; atherosclerosis: β = 0.509, SE = 0.246, p = 0.038). Findings were not affected when the 66 participants with a clinical diagnosis of Parkinson disease were excluded. By contrast, there were no interactions between LB and other CVD pathologies or between atherosclerosis and macroscopic infarcts for global parkinsonism proximate to death.

DISCUSSION

These findings suggest that atherosclerosis and macroscopic infarcts interact with LB pathology to increase the severity of parkinsonism beyond their additive effects in older persons.

The Mediating Role of Inflammation in the Relationship Between α-Synuclein and Cognitive Functioning

Accumulating evidence suggests that α-synuclein plays a role in the pathophysiology of Alzheimer's disease (AD). This study examined whether α-synuclein level in cerebrospinal fluid (CSF) was associated with cognitive functioning among older adults. We also explored whether this relationship was mediated by proinflammatory cytokines TNF-α and IL-6, along with sIL-6R and vascular endothelial growth factor (VEGF). Using a cross-sectional Alzheimer's Disease Neuroimaging Initiative (ADNI; N = 148) sample, we examined the relationship between α-synuclein and participants' performance on Mini-Mental State Examination (MMSE) and Alzheimer's Disease Assessment Scale Cognitive Subscale (ADAS-Cog 13) at baseline. Mediation analyses were utilized, adjusting for age, education, APOEe4, and Geriatric Depression Scale scores. All biological markers were measured in CSF. Participants in the current sample were 58.3% males, 41.7% females, and Caucasian (95.5%); their average education and age were 15.5 (standard deviation [SD] = 2.97) and 74.4 (SD = 7.51) years, respectively. Higher accumulation of α-synuclein was associated with poorer MMSE scores (β = -0.41, standard error [SE] = 1.54, p < .001). This relationship appeared to be mediated by VEGF (β = 0.27, SE = 2.15, p = .025) and IL-6r (β = 0.22, SE = 1.66, p < .026). In addition, α-synuclein was associated with poorer performance on the ADAS-Cog 13 (β = 0.34, p = .005) and mediated by VEGF (β = -0.19, SE = 4.13, p = .025) after adjusting for age, education, APOEe4, and depressive symptoms. α-Synuclein may serve as an additional biomarker for determining poor cognitive functioning. VEGF and IL-6 soluble receptors were significant mediators of the relationship between α-synuclein and cognitive functioning. If confirmed in prospective analyses, these findings can further inform the pathologic cascade and early diagnosis of AD.

Vascular smooth muscle cell dysfunction in neurodegeneration

Vascular smooth muscle cells (VSMCs) are the key moderators of cerebrovascular dynamics in response to the brain's oxygen and nutrient demands. Crucially, VSMCs may provide a sensitive biomarker for neurodegenerative pathologies where vasculature is compromised. An increasing body of research suggests that VSMCs have remarkable plasticity and their pathophysiology may play a key role in the complex process of neurodegeneration. Furthermore, extrinsic risk factors, including environmental conditions and traumatic events can impact vascular function through changes in VSMC morphology. VSMC dysfunction can be characterised at the molecular level both preclinically, and clinically ex vivo. However the identification of VSMC dysfunction in living individuals is important to understand changes in vascular function at the onset and progression of neurological disorders such as dementia, Alzheimer's disease, and Parkinson's disease. A promising technique to identify changes in the state of cerebral smooth muscle is cerebrovascular reactivity (CVR) which reflects the intrinsic dynamic response of blood vessels in the brain to vasoactive stimuli in order to modulate regional cerebral blood flow (CBF). In this work, we review the role of VSMCs in the most common neurodegenerative disorders and identify physiological systems that may contribute to VSMC dysfunction. The evidence collected here identifies VSMC dysfunction as a strong candidate for novel therapeutics to combat the development and progression of neurodegeneration, and highlights the need for more research on the role of VSMCs and cerebrovascular dynamics in healthy and diseased states.

Possible Contribution of Altered Cholinergic Activity in the Visual Cortex in Visual Hallucinations in Parkinson's Disease

OBJECTIVE

Up to one-third of patients with Parkinson's disease (PD) experience visual hallucinations (VHs). Lewy bodies are sparse in the visual cortices and seem unlikely to explain the hallucinations. Some neuroimaging studies have found that perfusion is reduced in the occipital lobe in individuals with VHs. Recent work has suggested that decreased cholinergic input may directly lead to the decreased perfusion. The investigators hypothesized that individuals with PD and VHs would have biochemical evidence of reduced microvascular perfusion and reduced cholinergic activity in areas of the brain that process visual images.

METHODS

Tissue from Brodmann's area (BA) 18 and BA 19 was obtained from a well-characterized cohort matched for age, gender, and postmortem interval in 69 individuals (PD without VHs, N=11; PD without dementia plus VHs N=10, N=10; PD with dementia plus VHs, N=16; and control subjects, N=32). Von Willebrand factor, vascular endothelial growth factor A, and myelin-associated glycoprotein:proteolipid protein-1 (MAG:PLP1) ratio-a measure of tissue oxygenation relative to metabolic demand, acetylcholinesterase (AChE), butyrylcholinesterase (BChE), choline acetyltransferase, and α-synuclein-were quantified by enzyme-linked immunosorbent assay. The primary outcome was the MAG:PLP1 ratio.

RESULTS

There was no biochemical evidence of chronic hypoperfusion in PD, although microvessel density was decreased in ventral BA 18 and BA 19. There was no between-group difference in BChE in either dorsal BA 18 or BA 19. AChE concentration was reduced in individuals with PD compared with control subjects in dorsal and ventral BA 18 and dorsal BA 19, and it was increased in ventral BA 19. These changes were most marked in the PD plus VHs group.

CONCLUSIONS

These results suggest that changes in cholinergic activity rather than chronic hypoperfusion may underlie VHs in PD.

Cerebrospinal Fluid Neurotransmitters, Cytokines, and Chemokines in Alzheimer's and Lewy Body Diseases

BACKGROUND

Alzheimer's disease (AD) and Lewy body disease (LBD) are complex neurodegenerative disorders that have been associated with brain inflammation and impaired neurotransmission.

OBJECTIVE

We aimed to determine concentrations of multiple cytokines, chemokines, and neurotransmitters previously associated with brain inflammation and synapse function in cerebrospinal fluid (CSF) from AD and LBD patients.

METHODS

We examined a panel of 50 analytes comprising neurotransmitters, cytokines, chemokines, and hormones in CSF in a cohort of patients diagnosed with mild cognitive impairment (MCI), AD, LBD, or non-demented controls (NDC).

RESULTS

Among neurotransmitters, noradrenaline (NA) was increased in AD CSF, while homovanillic acid (HVA), a dopamine metabolite, was reduced in both AD and LBD CSF relative to NDC. Six cytokines/chemokines out of 30 investigated were reliably detected in CSF. CSF vascular endothelial growth factor (VEGF) was significantly reduced in LBD patients relative to NDC.

CONCLUSIONS

CSF alterations in NA, HVA, and VEGF in AD and LBD may reflect pathogenic features of these disorders and provide tools for improved diagnosis. Future studies are warranted to replicate current findings in larger, multicenter cohorts.

Pre-Stroke Cholinesterase Inhibitor Treatment Is Beneficially Associated with Functional Outcome in Patients with Acute Ischemic Stroke and Pre-Stroke Dementia: The Fukuoka Stroke Registry

INTRODUCTION

Pre-stroke dementia is significantly associated with poor stroke outcome. Cholinesterase inhibitors (ChEIs) might reduce the risk of stroke in patients with dementia. However, the association between pre-stroke ChEI treatment and stroke outcome remains unresolved. Therefore, we aimed to determine this association in patients with acute ischemic stroke and pre-stroke dementia.

METHODS

We enrolled 805 patients with pre-stroke dementia among 13,167 with ischemic stroke within 7 days of onset who were registered in the Fukuoka Stroke Registry between June 2007 and May 2019 and were independent in basic activities of daily living (ADLs) before admission. Primary and secondary study outcomes were poor functional outcome (modified Rankin Scale [mRS] score: 3-6) at 3 months after stroke onset and neurological deterioration (≥2-point increase in the NIH Stroke Scale [NIHSS] during hospitalization), respectively. Logistic regression analysis was used to evaluate associations between pre-stroke ChEI treatment and study outcomes. To improve covariate imbalance, we further conducted a propensity score (PS)-matched cohort study.

RESULTS

Among the participants, 212 (26.3%) had pre-stroke ChEI treatment. Treatment was negatively associated with poor functional outcome (odds ratio: 0.68 [95% confidence interval: 0.46-0.99]) and neurological deterioration (0.52 [0.31-0.88]) after adjusting for potential confounding factors. In the PS-matched cohort study, the same trends were observed between pre-stroke ChEI treatment and poor functional outcome (0.61 [0.40-0.92]) and between the treatment and neurological deterioration (0.47 [0.25-0.86]).

CONCLUSIONS

Our findings suggest that pre-stroke ChEI treatment is associated with reduced risks for poor functional outcome and neurological deterioration after acute ischemic stroke in patients with pre-stroke dementia who are independent in basic ADLs before the onset of stroke.

Mediators of cerebral hypoperfusion and blood-brain barrier leakiness in Alzheimer's disease, vascular dementia and mixed dementia

In vascular dementia (VaD) and Alzheimer’s disease (AD), cerebral hypoperfusion and blood‐brain barrier (BBB) leakiness contribute to brain damage. In this study, we have measured biochemical markers and mediators of cerebral hypoperfusion and BBB in the frontal (BA6) and parietal (BA7) cortex and underlying white matter, to investigate the pathophysiology of vascular dysfunction in AD, VaD and mixed dementia. The ratio of myelin‐associated glycoprotein to proteolipid protein‐1 (MAG:PLP1), a post‐mortem biochemical indicator of the adequacy of ante‐mortem cerebral perfusion; the concentration of fibrinogen adjusted for haemoglobin level, a marker of blood‐brain barrier (BBB) leakiness; the level of vascular endothelial growth factor‐A (VEGF), a marker of tissue hypoxia; and endothelin‐1 (EDN1), a potent vasoconstrictor, were measured by ELISA in the frontal and parietal cortex and underlying white matter in 94 AD, 20 VaD, 33 mixed dementia cases and 58 age‐matched controls. All cases were assessed neuropathologically for small vessel disease (SVD), cerebral amyloid angiopathy (CAA) severity, Aβ and phospho‐tau parenchymal load, and Braak tangle stage. Aβ40 and Aβ42 were measured by ELISA in guanidine‐HCl tissue extracts. We found biochemical evidence of cerebral hypoperfusion in AD, VaD and mixed dementia to be associated with SVD, Aβ level, plaque load, EDN1 level and Braak tangle stage, and to be most widespread in mixed dementia. There was evidence of BBB leakiness in AD—limited to the cerebral cortex and related to EDN1 level. In conclusion, abnormalities of cerebral perfusion and BBB function in common types of dementia can largely be explained by a combination of arteriolosclerosis, and Aβ‐, tau‐ and endothelin‐related vascular dysfunction. The relative contributions of these processes vary considerably both between and within the diseases.

Research Progress of Alzheimer's Disease Therapeutic Drugs: Based on Renin-Angiotensin System Axis

It is widely recognized that Alzheimer's disease (AD) has a complicate link to renin-angiotensin system (RAS). It is known that cerebrovascular disease has some connections with AD, but most of the studies are still conducted in parallel or independently. Although previous research came up with large number of hypotheses about the pathogenesis of AD, it does not include the mechanism of RAS-related regulation of AD. It has been found that many components of RAS have been changed in AD. For example, the multifunctional and high-efficiency vasoconstrictor Ang II and Ang III with similar effects are changed under the action of other RAS signal peptides; these signal peptides are believed to help improve nerve injury and cognitive function. These changes may lead to neuropathological changes of AD, and progressive defects of cognitive function, which are association with some hypotheses of AD. The role of RAS in AD gradually attracts our attention, and RAS deserved to be considered carefully in the pathogenesis of AD. This review discusses the mechanisms of RAS participating in the three current hypotheses of AD: neuroinflammation, oxidative stress and amyloid-β protein (Aβ) hypothesis, as well as the drugs that regulate RAS systems already in clinical or in clinical trials. It further demonstrates the importance of RAS in the pathogenesis of AD, not only because of its multiple aspects of participation, which may be accidental, but also because of the availability of RAS drugs, which can be reused as therapies of AD.

Sildenafil ameliorates Alzheimer disease via the modulation of vascular endothelial growth factor and vascular cell adhesion molecule-1 in rats

Alzheimer disease (AD) is a chronic neurodegenerative disease with multi-pathways pathogenesis. Sildenafil is a selective phosphodiesterase-5 inhibitor with a potential benefit in the treatment of AD. This study investigated the possible mechanisms underlying the effect of sildenafil in AD with emphasis on vascular endothelial growth factor (VEGF), and vascular cell adhesion molecule-1 (VCAM-1). Twenty-four adult male rats were classified into four groups; control group: received vehicles, sildenafil-control: received sildenafil (15 mg/kg/day, p.o.), AD group received Aluminum (25 mg/kg/day, p.o.), AD-treated group: received sildenafil (15 mg/kg/day, p.o.) for 6 weeks. AD was assessed by memory performance test and confirmed by histopathological examination and immunostaining of, neurogenesis marker nestin and α-synuclein. The levels of VEGF-A, VCAM-1, oxidative stress markers and TNF-α in brain tissue were evaluated. AD rats showed histopathological evidences of AD; along with increased latency time in the memory test. There was a decrease in VEGF-A, and an increase in VCAM-1, TNF-α, and oxidative stress markers. Immunohistochemical study showed a significant increase in α-synuclein and a significant decrease in nestin expressions in brain tissues. Sildenafil administration ameliorated the histopathological changes and decreased latency time. Such effect was associated with a decrease in VCAM-1, TNF-α and oxidative stress as well as an increase in VEGF-A. Sildenafil caused a significant increase in nestin and a decrease in α-synuclein immunostaining. These findings suggested a protective effect of sildenafil via modulation of VEGF-A, and VCAM-1.

Cerebral regional and network characteristics in asthma patients: a resting-state fMRI study

Asthma is a serious health problem that involves not only the respiratory system but also the central nervous system. Previous studies identified either regional or network alterations in patients with asthma, but inconsistent results were obtained. A key question remains unclear: are the regional and neural network deficits related or are they two independent characteristics in asthma? Answering this question is the aim of this study. By collecting resting-state functional magnetic resonance imaging from 39 patients with asthma and 40 matched health controls, brain functional measures including regional activity (amplitude of low-frequency fluctuations) and neural network function (degree centrality (DC) and functional connectivity) were calculated to systematically characterize the functional alterations. Patients exhibited regional abnormities in the left angular gyrus, right precuneus, and inferior temporal gyrus within the default mode network. Network abnormalities involved both the sensorimotor network and visual network with key regions including the superior frontal gyrus and occipital lobes. Altered DC in the lingual gyrus was correlated with the degree of airway obstruction. This study elucidated different patterns of regional and network changes, thereby suggesting that the two parameters reflect different brain characteristics of asthma. These findings provide evidence for further understanding the potential cerebral alterations in the pathophysiology of asthma.

Visual hallucinations in Alzheimer's disease do not seem to be associated with chronic hypoperfusion of to visual processing areas V2 and V3 but may be associated with reduced cholinergic input to these areas

Background

Up to 20% of patients with AD experience hallucinations. The pathological substrate is not known. Visual hallucinations (VH) are more common in dementia with Lewy bodies (DLB). In autopsy studies, up to 60% of patients with AD have concomitant Lewy body pathology. Decreased perfusion of the occipital lobe has been implicated in DLB patients with VH, and post-mortem studies point to both decreased cholinergic activity and reduced oxygenation of the occipital cortex in DLB.

Methods

We used biochemical methods to assess microvessel density (level of von Willebrand factor, a marker of endothelial cell content), ante-mortem oxygenation (vascular endothelial growth factor, a marker of tissue hypoxia; myelin-associated glycoprotein to proteolipid protein-1 ratio, a measure of tissue oxygenation relative to metabolic demand), cholinergic innervation (acetylcholinesterase and choline acetyltransferase), butyrylcholinesterase and insoluble α-synuclein content in the BA18 and BA19 occipital cortex obtained post-mortem from 23 AD patients who had experienced visual hallucinations, 19 AD patients without hallucinations, 19 DLB patients, and 36 controls. The cohorts were matched for age, gender and post-mortem interval.

Results

There was no evidence of reduced microvessel density, hypoperfusion or reduction in ChAT activity in AD with visual hallucinations. Acetylcholinesterase activity was reduced in both BA18 and BA19, in all 3 dementia groups, and the concentration was also reduced in BA19 in the DLB and AD without visual hallucinations groups. Insoluble α-synuclein was raised in the DLB group in both areas but not in AD either with or without visual hallucinations.

Conclusions

Our results suggest that visual hallucinations in AD are associated with cholinergic denervation rather than chronic hypoperfusion or α-synuclein accumulation in visual processing areas of the occipital cortex.

Electronic supplementary material

The online version of this article (10.1186/s13195-019-0519-7) contains supplementary material, which is available to authorized users.

Dementia with Lewy bodies: an update and outlook

Dementia with Lewy bodies (DLB) is an age-associated neurodegenerative disorder producing progressive cognitive decline that interferes with normal life and daily activities. Neuropathologically, DLB is characterised by the accumulation of aggregated α-synuclein protein in Lewy bodies and Lewy neurites, similar to Parkinson’s disease (PD). Extrapyramidal motor features characteristic of PD, are common in DLB patients, but are not essential for the clinical diagnosis of DLB. Since many PD patients develop dementia as disease progresses, there has been controversy about the separation of DLB from PD dementia (PDD) and consensus reports have put forward guidelines to assist clinicians in the identification and management of both syndromes. Here, we present basic concepts and definitions, based on our current understanding, that should guide the community to address open questions that will, hopefully, lead us towards improved diagnosis and novel therapeutic strategies for DLB and other synucleinopathies.

VEGFR1 and VEGFR2 in Alzheimer's Disease

Vascular endothelial growth factor (VEGF) is a potent angiogenic factor. Despite upregulation of VEGF in the brain in Alzheimer's disease (AD), probably in response to amyloid-β, vasoconstriction, and tissue hypoxia, there is no consequent increase in microvessel density. VEGF binds to and activates VEGF receptor 2 (VEGFR2), but also binds to VEGF receptor 1 (VEGFR1), which exists in less-active membrane-bound and inactive soluble (sVEGFR1) forms and inhibits pro-angiogenic signaling. We have investigated whether altered expression of VEGF receptors might account for the lack of angiogenic response to VEGF in AD. We assessed the cellular distribution and protein level of VEGFR1 and VEGFR2 in parietal cortex from 50 AD and 36 age-matched control brains, and related the findings to measurements of VEGF and von Willebrand factor level (a marker of microvessel density) in the same tissue samples. VEGFR2 was expressed by neurons, astrocytes and endothelial cells. VEGFR1 was expressed predominantly neuronally and was significantly reduced in AD (p = 0.02). Western blot analysis on a subset of brains showed reduction in VEGFR1:sVEGFR1 in AD (p = 0.046). The lack of angiogenesis despite cerebral hypoperfusion in AD is not explained by altered expression of VEGFR2 or total VEGFR1; indeed, the downregulation of VEGFR1 may represent a pro-angiogenic response to the hypoperfusion. However, the relative increase in sVEGFR1 would be expected to have an anti-angiogenic effect which may be a factor in AD.

Long-Term Intravitreal Ranibizumab as a Potential Additional Risk Factor for Neurodegeneration in Parkinson's Disease: A Case Report

In November 2012, a 72-year old patient was diagnosed with left eye wet age-related macular degeneration. The patient received three monthly intravitreal injections of ranibizumab, with complete resolution of retinal hemorrhage and edema and reinstatement of visual acuity. In May 2015, symptomatic relapse was detected. The patient was again treated with intravitreal ranibizumab, with overall six injections till the end of February 2016. In May 2016, the patient complained of left hand resting tremor, bradykinesia, and postural rigidity of head and trunk. A diagnosis of clinically established PD was made based on new criteria of the Movement Disorders Society. Single Photon Emission Computerized Tomography of the Dopamine Transporter with (123I) ioflupane documented a low Dopamine Transporter (DAT) uptake mostly in the right striatum. Due to the documented protective role of vascular endothelial growth factor (VEGF) on the dopaminergic neurons, intensive intravitreal injections of the anti-VEGF agent ranibizumab may have played as an additional risk factor accelerating the neurodegeneration process related to PD and the onset of the related clinical signs and symptoms.

Are Major Dementias Triggered by Poor Blood Flow to the Brain? Theoretical Considerations

There is growing evidence that chronic brain hypoperfusion plays a central role in the development of Alzheimer's disease (AD) long before dyscognitive symptoms or amyloid-β accumulation in the brain appear. This commentary proposes that dementia with Lewy bodies (DLB), frontotemporal dementia (FTD), and Creutzfeldt-Jakob disease (CJD) may also develop from chronic brain hypoperfusion following a similar but not identical neurometabolic breakdown as AD. The argument to support this conclusion is that chronic brain hypoperfusion, which is found at the early stages of the three dementias reviewed here, will reduce oxygen delivery and lower oxidative phosphorylation promoting a steady decline in the synthesis of the cell energy fuel adenosine triphosphate (ATP). This process is known to lead to oxidative stress. Virtually all neurodegenerative diseases, including FTD, DLB, and CJD, are characterized by oxidative stress that promotes inclusion bodies which differ in structure, location, and origin, as well as which neurological disorder they typify. Inclusion bodies have one thing in common; they are known to diminish autophagic activity, the protective intracellular degradative process that removes malformed proteins, protein aggregates, and damaged subcellular organelles that can disrupt neuronal homeostasis. Neurons are dependent on autophagy for their normal function and survival. When autophagic activity is diminished or impaired in neurons, high levels of unfolded or misfolded proteins overwhelm and downregulate the neuroprotective activity of unfolded protein response which is unable to get rid of dysfunctional organelles such as damaged mitochondria and malformed proteins at the synapse. The endpoint of this neuropathologic process results in damaged synapses, impaired neurotransmission, cognitive decline, and dementia.

Differing associations between Aβ accumulation, hypoperfusion, blood-brain barrier dysfunction and loss of PDGFRB pericyte marker in the precuneus and parietal white matter in Alzheimer's disease

Recent studies implicate loss of pericytes in hypoperfusion and blood-brain barrier (BBB) leakage in Alzheimer's disease (AD). In this study, we have measured levels of the pericyte marker, platelet-derived growth factor receptor-β (PDGFRB), and fibrinogen (to assess blood-brain barrier leakage), and analyzed their relationship to indicators of microvessel density (von Willebrand factor level), ante-mortem oxygenation (myelin-associated glycoprotein:proteolipid protein-1 ratio and vascular endothelial growth factor level), Aβ level and plaque load, in precuneus and underlying white matter from 49 AD to 37 control brains. There was reduction in PDGFRB and increased fibrinogen in the precuneus in AD. These changes correlated with reduction in oxygenation and with plaque load. In the underlying white matter, increased fibrinogen correlated with reduced oxygenation, but PDGFRB level was unchanged. The level of platelet-derived growth factor-ββ (PDGF-BB), important for pericyte maintenance, was increased in AD but mainly in the insoluble tissue fraction, correlating with insoluble Aβ level. Loss of the PDGFRB within the precuneus in AD is associated with fibrinogen leakage and reduced oxygenation, and related to fibrillar Aβ accumulation. In contrast, fibrinogen leakage and reduced oxygenation of underlying white matter occur independently of loss of PDGFRB, perhaps secondary to reduced transcortical perfusion.

The Neurovascular Unit Coming of Age: A Journey through Neurovascular Coupling in Health and Disease

The concept of the neurovascular unit (NVU), formalized at the 2001 Stroke Progress Review Group meeting of the National Institute of Neurological Disorders and Stroke, emphasizes the intimate relationship between the brain and its vessels. Since then, the NVU has attracted the interest of the neuroscience community, resulting in considerable advances in the field. Here the current state of knowledge of the NVU will be assessed, focusing on one of its most vital roles: the coupling between neural activity and blood flow. The evidence supports a conceptual shift in the mechanisms of neurovascular coupling, from a unidimensional process involving neuronal-astrocytic signaling to local blood vessels to a multidimensional one in which mediators released from multiple cells engage distinct signaling pathways and effector systems across the entire cerebrovascular network in a highly orchestrated manner. The recently appreciated NVU dysfunction in neurodegenerative diseases, although still poorly understood, supports emerging concepts that maintaining neurovascular health promotes brain health.

[Diagnostic of prodromal dementia with Levy bodies]

The issues of diagnosis of prodromal dementia with Lewy bodies are considered. Despite numerous studies using international diagnostic criteria, clinical and diagnosis are often inconsistent. Early and more accurate detection of dementia with Lewy bodies is needed for prognosis, optimal management and effective pharmacotherapy.

Connexins in Cardiovascular and Neurovascular Health and Disease: Pharmacological Implications

Connexins are ubiquitous channel forming proteins that assemble as plasma membrane hemichannels and as intercellular gap junction channels that directly connect cells. In the heart, gap junction channels electrically connect myocytes and specialized conductive tissues to coordinate the atrial and ventricular contraction/relaxation cycles and pump function. In blood vessels, these channels facilitate long-distance endothelial cell communication, synchronize smooth muscle cell contraction, and support endothelial-smooth muscle cell communication. In the central nervous system they form cellular syncytia and coordinate neural function. Gap junction channels are normally open and hemichannels are normally closed, but pathologic conditions may restrict gap junction communication and promote hemichannel opening, thereby disturbing a delicate cellular communication balance. Until recently, most connexin-targeting agents exhibited little specificity and several off-target effects. Recent work with peptide-based approaches has demonstrated improved specificity and opened avenues for a more rational approach toward independently modulating the function of gap junctions and hemichannels. We here review the role of connexins and their channels in cardiovascular and neurovascular health and disease, focusing on crucial regulatory aspects and identification of potential targets to modify their function. We conclude that peptide-based investigations have raised several new opportunities for interfering with connexins and their channels that may soon allow preservation of gap junction communication, inhibition of hemichannel opening, and mitigation of inflammatory signaling.

Effect of APOE Genotype on Synaptic Proteins in Earlier Adult Life

Background:

Possession of APOEɛ4 is a strong risk factor for late-onset Alzheimer’s disease and is associated with loss of synaptic proteins in the elderly even in the absence of Alzheimer’s disease.

Objective:

We hypothesized that ɛ4 allele possession in non-demented adults aged under-75 would also be associated with alterations in the levels of synaptic proteins.

Methods:

We measured synaptophysin, PSD95, drebrin, SNAP-25, and septin 7 by ELISA in hippocampus and superior temporal gyrus from 103 adults aged <75 without dementia. Corresponding gene expression was measured by RT-PCR.

Results:

There was no evidence that ɛ4 affected levels of the proteins measured. Instead we found an increase in post-synaptic proteins in the hippocampi of those with an ɛ32 genotype. The evidence was strongest for drebrin (p = 0.011). There was some evidence of increased synaptic protein gene expression in ɛ4 carriers.

Conclusions:

People with an APOEɛ32 genotype have a reduced risk of Alzheimer’s disease. It may be relevant that they have a higher level of post-synaptic proteins in the hippocampus even in earlier adulthood.

Small vessel disease, neurovascular regulation and cognitive impairment: post-mortem studies reveal a complex relationship, still poorly understood

The contribution of vascular disease to cognitive impairment is under-recognized and the pathogenesis is poorly understood. This information gap has multiple causes, including a lack of post-mortem validation of clinical diagnoses of vascular cognitive impairment (VCI) or vascular dementia (VaD), the exclusion of cases with concomitant neurodegenerative disease when diagnosing VCI/VaD, and a lack of standardization of neuropathological assessment protocols for vascular disease. Other contributors include a focus on end-stage destructive lesions to the exclusion of more subtle types of diffuse brain injury, on structural abnormalities of arteries and arterioles to the exclusion of non-structural abnormalities and capillary damage, and the use of post-mortem sampling strategies that are biased towards the identification of neurodegenerative pathologies. Recent studies have demonstrated the value of detailed neuropathology in characterizing vascular contributions to cognitive impairment (e.g. in diabetes), and highlight the importance of diffuse white matter changes, capillary damage and vasoregulatory abnormalities in VCI/VaD. The use of standardized, evidence-based post-mortem assessment protocols and the inclusion of biochemical as well as morphological methods in neuropathological studies should improve the accuracy of determination of the contribution of vascular disease to cognitive impairment and clarify the relative contribution of different pathogenic processes to the tissue damage.

Endothelin-converting enzymes degrade α-synuclein and are reduced in dementia with Lewy bodies

We have examined the roles of the endothelin-converting enzyme-1 and -2 (ECE-1 and ECE-2) in the homeostasis of α-synuclein (α-syn) and pathogenesis of Lewy body disease. The ECEs are named for their ability to convert inactive big endothelin to the vasoactive peptide endothelin-1 (EDN1). We have found that ECE-1 and ECE-2 cleave and degrade α-syn in vitro and siRNA-mediated knockdown of ECE-1 and ECE-2 in SH-SY5Y neuroblastoma cells significantly increased α-syn both intracellularly (within the cell lysate) (p < 0.05 for both ECE-1 and -2) and extracellularly (in the surrounding medium) (p < 0.05 for ECE-1 and p = 0.07 for ECE-2). Double immunofluorescent labelling showed co-localization of ECE-1 and ECE-2 with α-syn within the endolysosomal system (confirmed by a proximity ligation assay). To assess the possible relevance of these findings to human Lewy body disease, we measured ECE-1 and ECE-2 levels by sandwich ELISA in post-mortem samples of cingulate cortex (a region with a predilection for Lewy body pathology) in dementia with Lewy bodies (DLB) and age-matched controls. ECE-1 (p < 0.001) and ECE-2 (p < 0.01) levels were significantly reduced in DLB and both enzymes correlated inversely with the severity of Lewy body pathology as indicated by the level of α-syn phosphorylated at Ser129 (r = -0.54, p < 0.01 for ECE-1 and r = -0.49, p < 0.05 for ECE-2). Our novel findings suggest a role for ECEs in the metabolism of α-syn that could contribute to the development and progression of DLB.

The concept of sporadic cerebral small vessel disease: A road map on key definitions and current concepts

Sporadic cerebral small vessel disease is considered to be among the most common known neuropathological processes and has an important role in stroke, cognitive impairment, and functional loss in elderly persons. The term is now commonly used to describe a range of neuroimaging, neuropathological, and associated clinical features, the pathogenesis of which is largely unclear but that are thought to arise from disease affecting the perforating cerebral arterioles, capillaries, and venules. Modern neuroimaging has revolutionized our understanding of the consequences of small vessels disease on the brain parenchyma, even though small arteries, arterioles, capillaries, and venules are difficult to be directly visualized with current techniques used in clinical practice. In this short review, we focus on histopathological and neuroimaging perspectives, basic definitions, and recent advances in the field.

Post-mortem assessment in vascular dementia: advances and aspirations

BACKGROUND

Cerebrovascular lesions are a frequent finding in the elderly population. However, the impact of these lesions on cognitive performance, the prevalence of vascular dementia, and the pathophysiology behind characteristic in vivo imaging findings are subject to controversy. Moreover, there are no standardised criteria for the neuropathological assessment of cerebrovascular disease or its related lesions in human post-mortem brains, and conventional histological techniques may indeed be insufficient to fully reflect the consequences of cerebrovascular disease.

DISCUSSION

Here, we review and discuss both the neuropathological and in vivo imaging characteristics of cerebrovascular disease, prevalence rates of vascular dementia, and clinico-pathological correlations. We also discuss the frequent comorbidity of cerebrovascular pathology and Alzheimer's disease pathology, as well as the difficult and controversial issue of clinically differentiating between Alzheimer's disease, vascular dementia and mixed Alzheimer's disease/vascular dementia. Finally, we consider additional novel approaches to complement and enhance current post-mortem assessment of cerebral human tissue.

CONCLUSION

Elucidation of the pathophysiology of cerebrovascular disease, clarification of characteristic findings of in vivo imaging and knowledge about the impact of combined pathologies are needed to improve the diagnostic accuracy of clinical diagnoses.

Investigation of Aβ phosphorylated at serine 8 (pAβ) in Alzheimer's disease, dementia with Lewy bodies and vascular dementia

AIMS

Deposition of amyloid beta (Aβ) in the brain is one of the defining abnormalities of Alzheimer's disease (AD). Phosphorylation of Aβ at serine 8 (pAβ) has been implicated in its aggregation in vitro and pAβ level has been shown to be significantly elevated in AD. We aimed to assess the specificity of pAβ for AD and have investigated associations of pAβ with parenchymal and cerebrovascular accumulation of Aβ, disease progression, angiotensin-converting enzyme activity and APOE genotype.

METHODS

The distribution of pAβ was studied by immunohistochemistry in sporadic and familial AD, pure dementia with Lewy bodies (DLB), pure vascular dementia (VaD) and age-matched controls. Soluble and insoluble (guanidine-extractable) pAβ level was measured by enzyme-linked immunosorbent assay (ELISA) in the midfrontal and parahippocampal cortex in sporadic AD (n = 20, 10 with Braak tangle stages of III-IV and 10 of stages V-VI), DLB (n = 10), VaD (n = 10) and age-matched controls (n = 20).

RESULTS

We found pAβ to be associated with only a subset of Aβ plaques and vascular deposits in sporadic and familial AD, with absent or minimal immunohistochemically detectable pAβ in control, DLB and VaD brains. In both brain regions, insoluble pAβ level was significantly elevated only in advanced AD (Braak tangle stage of V or VI) and in the parahippocampus soluble and insoluble pAβ level increased with the number of APOE ε4 alleles.

CONCLUSIONS

These results indicate that pAβ accumulation in the parenchyma and vasculature is largely restricted to late-stage AD (Braak tangle stage V-VI).

The neuropathology and cerebrovascular mechanisms of dementia

The prevalence of dementia is increasing in our aging population at an alarming rate. Because of the heterogeneity of clinical presentation and complexity of disease neuropathology, dementia classifications remain controversial. Recently, the National Plan to address Alzheimer’s Disease prioritized Alzheimer’s disease-related dementias to include: Alzheimer’s disease, dementia with Lewy bodies, frontotemporal dementia, vascular dementia, and mixed dementias. While each of these dementing conditions has their unique pathologic signature, one common etiology shared among all these conditions is cerebrovascular dysfunction at some point during the disease process. The goal of this comprehensive review is to summarize the current findings in the field and address the important contributions of cerebrovascular, physiologic, and cellular alterations to cognitive impairment in these human dementias. Specifically, evidence will be presented in support of small-vessel disease as an underlying neuropathologic hallmark of various dementias, while controversial findings will also be highlighted. Finally, the molecular mechanisms shared among all dementia types including hypoxia, oxidative stress, mitochondrial bioenergetics, neuroinflammation, neurodegeneration, and blood–brain barrier permeability responsible for disease etiology and progression will be discussed.

Vascular mTOR-dependent mechanisms linking the control of aging to Alzheimer's disease

Aging is the strongest known risk factor for Alzheimer's disease (AD). With the discovery of the mechanistic target of rapamycin (mTOR) as a critical pathway controlling the rate of aging in mice, molecules at the interface between the regulation of aging and the mechanisms of specific age-associated diseases can be identified. We will review emerging evidence that mTOR-dependent brain vascular dysfunction, a universal feature of aging, may be one of the mechanisms linking the regulation of the rate of aging to the pathogenesis of Alzheimer's disease. This article is part of a Special Issue entitled: Vascular Contributions to Cognitive Impairment and Dementia edited by M. Paul Murphy, Roderick A. Corriveau and Donna M. Wilcock.

Pathophysiology of Hypoperfusion of the Precuneus in Early Alzheimer's Disease

The earliest decline in cerebral perfusion in Alzheimer's disease (AD) is in the medial parietal cortex (precuneus). We have analyzed precuneus in post‐mortem tissue from 70 AD and 37 control brains to explore the pathophysiology of the hypoperfusion: the contribution of arteriolosclerotic small vessel disease (SVD) and cerebral amyloid angiopathy (CAA), and of the vasoconstrictors endothelin‐1 (EDN1) and angiotensin II (Ang II), and the association with Aβ. The myelin‐associated glycoprotein:proteolipid protein‐1 ratio (MAG:PLP1) was used as an indicator of oxygenation of the precuneus prior to death. MAG:PLP1 was reduced ∼50% in early AD (Braak stage III–IV). Although MAG:PLP1 remained low in advanced AD (stage V–VI), the reduction was less pronounced, possibly reflecting falling oxygen demand. Reduction in cortical MAG:PLP1 correlated with elevation in vascular endothelial growth factor (VEGF), another marker of hypoperfusion. Cortical MAG:PLP1 declined nonsignificantly with increasing SVD and CAA, but significantly with the concentration of EDN1, which was elevated approximately 75% in AD. In contrast, with reduction in cortical MAG:PLP1, Ang II level and angiotensin‐converting enzyme (ACE) activity declined, showing a normal physiological response to hypoperfusion. MAG:PLP1 was reduced in the parietal white matter (WM) in AD but here the decline correlated positively (ie, physiologically) with WM EDN1. However, the decline of MAG:PLP1 in the WM was associated with increasing cortical EDN1 and perhaps reflected vasoconstriction of perforating arterioles, which traverse the cortex to perfuse the WM. EDN1 in the cortex correlated highly significantly with both soluble and insoluble Aβ42, shown previously to upregulate neuronal endothelin‐converting enzyme‐2 (ECE2), but not with Aβ40. Our findings demonstrate reduced oxygenation of the precuneus in early AD and suggest that elevated EDN1, resulting from Aβ42‐mediated upregulation of ECE2, is a contributor.

White matter hypoperfusion and damage in dementia: post-mortem assessment

Neuroimaging has revealed a range of white matter abnormalities that are common in dementia, some that predict cognitive decline. The abnormalities may result from structural diseases of the cerebral vasculature, such as arteriolosclerosis and amyloid angiopathy, but can also be caused by nonstructural vascular abnormalities (eg, of vascular contractility or permeability), neurovascular instability or extracranial cardiac or vascular disease. Conventional histopathological assessment of the white matter has tended to conflate morphological vascular abnormalities with changes that reflect altered interstitial fluid dynamics or white matter ischemic damage, even though the latter may be of extracranial or nonstructural etiology. However, histopathology is being supplemented by biochemical approaches, including the measurement of proteins involved in the molecular responses to brain ischemia, myelin proteins differentially susceptible to ischemic damage, vessel-associated proteins that allow rapid measurement of microvessel density, markers of blood-brain barrier dysfunction and axonal injury, and mediators of white matter damage. By combining neuroimaging with histopathology and biochemical analysis, we can provide reproducible, quantitative data on the severity of white matter damage, and information on its etiology and pathogenesis. Together these have the potential to inform and improve treatment, particularly in forms of dementia to which white matter hypoperfusion makes a significant contribution.

Synaptic protein levels altered in vascular dementia

Introduction

Cerebral ischaemia is the defining pathophysiological abnormality in most forms of vascular dementia (VAD), but the pathogenesis of the dementia remains poorly understood. In Alzheimer's disease (AD), there is early loss of synaptic proteins, but these have been little studied in VAD.

Materials and Methods

We measured synaptophysin, postsynaptic density protein 95 (PSD-95), drebrin, synaptosomal-associated protein 25 (SNAP-25) and vascular endothelial growth factor (VEGF) by enzyme-linked immunosorbent assays in superior temporal cortex from 11 patients with VAD and, initially, 11 non-dementia controls. We corrected for neuronal content by measurement of neuron-specific enolase. A further 11 controls were subsequently used in a validation study. Simulation of post-mortem delay found that PSD-95 was stable at 4°C but declined slightly at RT. SNAP-25 and drebrin showed good post-mortem stability. Previous studies had shown good post-mortem preservation of synaptophysin and VEGF.

Results

The VAD cases had lower synaptophysin (but P > 0.05 in initial study), significantly lower SNAP-25 (P = 0.024) and significantly higher drebrin (P = 0.020). On comparison with the second control group, the reduction in synaptophysin was significant (P = 0.008), and the other results were confirmed.

Conclusion

There is probably a reduction in presynaptic proteins in the temporal cortex in VAD, although not as marked as in AD. In VAD, there is also an increase in drebrin, which may be a response to reduced synaptic input.

Post-mortem assessment of hypoperfusion of cerebral cortex in Alzheimer's disease and vascular dementia

Perfusion is reduced in the cerebral neocortex in Alzheimer's disease. We have explored some of the mechanisms, by measurement of perfusion-sensitive and disease-related proteins in post-mortem tissue from Alzheimer's disease, vascular dementia and age-matched control brains. To distinguish physiological from pathological reduction in perfusion (i.e. reduction exceeding the decline in metabolic demand), we measured the concentration of vascular endothelial growth factor (VEGF), a protein induced under conditions of tissue hypoxia through the actions of hypoxia-inducible factors, and the myelin associated glycoprotein to proteolipid protein 1 (MAG:PLP1) ratio, which declines in chronically hypoperfused brain tissue. To evaluate possible mechanisms of hypoperfusion, we also measured the levels of amyloid-β40, amyloid-β42, von Willebrand factor (VWF; a measure of microvascular density) and the potent vasoconstrictor endothelin 1 (EDN1); we assayed the activity of angiotensin I converting enzyme (ACE), which catalyses the production of another potent vasoconstrictor, angiotensin II; and we scored the severity of arteriolosclerotic small vessel disease and cerebral amyloid angiopathy, and determined the Braak tangle stage. VEGF was markedly increased in frontal and parahippocampal cortex in Alzheimer's disease but only slightly and not significantly in vascular dementia. In frontal cortex the MAG:PLP1 ratio was significantly reduced in Alzheimer's disease and even more so in vascular dementia. VEGF but not MAG:PLP1 increased with Alzheimer's disease severity, as measured by Braak tangle stage, and correlated with amyloid-β42 and amyloid-β42: amyloid-β40 but not amyloid-β40. Although MAG:PLP1 tended to be lowest in cortex from patients with severe small vessel disease or cerebral amyloid angiopathy, neither VEGF nor MAG:PLP1 correlated significantly with the severity of structural vascular pathology (small vessel disease, cerebral amyloid angiopathy or VWF). However, MAG:PLP1 showed a significant negative correlation with the level of EDN1, which we previously showed to be elevated in the cerebral cortex Alzheimer's disease. These finding are in contrast with the previously demonstrated reduction in EDN1, and positive correlation with MAG:PLP1, in the hypoperfused white matter in Alzheimer's disease. The decline in MAG:PLP1 strongly suggests pathological hypoperfusion of the frontal cortex in Alzheimer's disease. Although severe small vessel disease or cerebral amyloid angiopathy may contribute in some cases, abnormal vascular contractility mediated by EDN1 is likely to be a more important overall contributor. Both amyloid-β accumulation and hypoperfusion are likely to cause the upregulation of VEGF.

Accumulation of α-synuclein in dementia with Lewy bodies is associated with decline in the α-synuclein-degrading enzymes kallikrein-6 and calpain-1

Kallikrein-6 and calpain-1 are amongst a small group of proteases that degrade α-synuclein. We have explored the possibility that reduction in the level or activity of these enzymes contributes to the accumulation of α-synuclein in Lewy body diseases. We measured calpain-1 activity by fluorogenic activity assay, kallikrein-6 level by sandwich ELISA, and levels of α-synuclein and α-synuclein phosphorylated at serine 129 (α-synuclein-P129), in post-mortem brain tissue in pure dementia with Lewy bodies (DLB, n = 12), Alzheimer’s disease (AD, n = 20) and age-matched controls (n = 19). Calpain-1 activity was significantly reduced in DLB within the cingulate and parahippocampal cortex, regions with highest α-synuclein and α-synuclein-P129 load, and correlated inversely with the levels of α-synuclein and α-synuclein-P129. Calpain-1 was unaltered in the thalamus and frontal cortex, regions with less α-synuclein pathology. Kallikrein-6 level was reduced in the cingulate cortex in the DLB cohort, and correlated inversely with α-synuclein and α-synuclein-P129. Kallikrein-6 was also reduced in DLB in the thalamus but not in relation to α-synuclein or α-synuclein-P129 load and was unaltered in the frontal and parahippocampal cortex. In SH-SY5Y cells overexpressing wild-type α-synuclein there was partial co-localisation of kallikrein-6 and calpain-1 with α-synuclein, and siRNA-mediated knock-down of kallikrein-6 and calpain-1 increased the amount of α-synuclein in cell lysates. Our results indicate that reductions in kallikrein-6 and calpain-1 may contribute to the accumulation of α-synuclein in DLB.

Evaluating the relationship between amyloid-β and α-synuclein phosphorylated at Ser129 in dementia with Lewy bodies and Parkinson's disease

Introduction

Lewy body and Alzheimer-type pathologies often co-exist. Several studies suggest a synergistic relationship between amyloid-β (Aβ) and α-synuclein (α-syn) accumulation. We have explored the relationship between Aβ accumulation and the phosphorylation of α-syn at serine-129 (pSer129 α-syn), in post-mortem human brain tissue and in SH-SY5Y neuroblastoma cells transfected to overexpress human α-syn.

Methods

We measured levels of Aβ40, Aβ42, α-syn and pSer129 α-syn by sandwich enzyme-linked immunosorbent assay, in soluble and insoluble fractions of midfrontal, cingulate and parahippocampal cortex and thalamus, from cases of Parkinson’s disease (PD) with (PDD; n = 12) and without dementia (PDND; n = 23), dementia with Lewy bodies (DLB; n = 10) and age-matched controls (n = 17). We also examined the relationship of these measurements to cognitive decline, as measured by time-to-dementia and the mini-mental state examination (MMSE) score in the PD patients, and to Braak tangle stage.

Results

In most brain regions, the concentration of insoluble pSer129 α-syn correlated positively, and soluble pSer129 α-syn negatively, with the levels of soluble and insoluble Aβ. Insoluble pSer129 α-syn also correlated positively with Braak stage. In most regions, the levels of insoluble and soluble Aβ and the proportion of insoluble α-syn that was phosphorylated at Ser129 were significantly higher in the PD and DLB groups than the controls, and higher in the PDD and DLB groups than the PDND brains. In PD, the MMSE score correlated negatively with the level of insoluble pSer129 α-syn. Exposure of SH-SY5Y cells to aggregated Aβ42 significantly increased the proportion of α-syn that was phosphorylated at Ser129 (aggregated Aβ40 exposure had a smaller, non-significant effect).

Conclusions

Together, these data show that the concentration of pSer129 α-syn in brain tissue homogenates is directly related to the level of Aβ and Braak tangle stage, and predicts cognitive status in Lewy body diseases.

Electronic supplementary material

The online version of this article (doi:10.1186/s13195-014-0077-y) contains supplementary material, which is available to authorized users.

Aβ degradation or cerebral perfusion? Divergent effects of multifunctional enzymes

There is increasing evidence that deficient clearance of β-amyloid (Aβ) contributes to its accumulation in late-onset Alzheimer disease (AD). Several Aβ-degrading enzymes, including neprilysin (NEP), endothelin-converting enzyme (ECE), and angiotensin-converting enzyme (ACE) reduce Aβ levels and protect against cognitive impairment in mouse models of AD. In post-mortem human brain tissue we have found that the activity of these Aβ-degrading enzymes rise with age and increases still further in AD, perhaps as a physiological response that helps to minimize the build-up of Aβ. ECE-1/-2 and ACE are also rate-limiting enzymes in the production of endothelin-1 (ET-1) and angiotensin II (Ang II), two potent vasoconstrictors, increases in the levels of which are likely to contribute to reduced blood flow in AD. This review considers the possible interdependence between Aβ-degrading enzymes, ischemia and Aβ in AD: ischemia has been shown to increase Aβ production both in vitro and in vivo, whereas increased Aβ probably enhances ischemia by vasoconstriction, mediated at least in part by increased ECE and ACE activity. In contrast, NEP activity may help to maintain cerebral perfusion, by reducing the accumulation of Aβ in cerebral blood vessels and lessening its toxicity to vascular smooth muscle cells. In assessing the role of Aβ-degrading proteases in the pathogenesis of AD and, particularly, their potential as therapeutic agents, it is important to bear in mind the multifunctional nature of these enzymes and to consider their effects on other substrates and pathways.