Current Alzheimer Research - Volume 11, Issue 1, 2014

Accumulation, aggregation and deposition of the amyloid-β (Aβ) peptides in the brain are widely accepted as the central events in the pathogenesis of Alzheimer's disease (AD). Any factor that is capable of causing these events is potentially a risk factor for AD. In the last decade, evidence has accumulated to support the association between cerebral vascular diseases (CVD) and AD. CVD is known to induce amyloid deposition and affects the age of onset for sporadic AD; whereas, amyloid deposition has been shown to cause cerebrovascular degeneration. In this review, we propose a positive feedback loop between CVD and amyloid deposition. The disease cycle could be triggered by aging and/or other environmental factor-associated CVD, as in late-onset sporadic AD patients, or by over production of Aβ, as in the familial AD patients and amyloid precursor protein transgenic animals.

Background Understanding the relationship between vascular disease and Alzheimer’s disease (AD) will enhance our insight into this disease and pave the way for novel therapeutic research. Cerebrovascular dysfunction, expressed as impaired cerebral autoregulation and cerebral vasomotor reactivity, has been observed in transgenic mouse models for AD. Translation to human AD is limited and conflicting however. Objective To investigate if impaired cerebral autoregulation and cerebral vasomotor reactivity, found in animal models for AD, are present in human sporadic AD. Methods In 12 patients with mild to moderate AD (75 SD 4 yr) and 24 controls matched for age and history of hypertension, all without diabetes, we measured blood pressure (Finapres) and cerebral blood flow-velocity (transcranial Doppler). Cerebral autoregulation was assessed during changes in blood pressure induced by single and repeated sit-stand maneuvers. Cerebral vasomotor reactivity was assessed during hyperventilation and inhalation of 5 % carbon dioxide. Results During single sit-stands, controls had a 4% (SD 8) decrease in cerebrovascular resistance during a reduction in blood pressure, and an 8 % (SD 11) increase during a rise in blood pressure, indicating normal cerebral autoregulation. These changes were not seen in AD (p=0.04). During repeated sit-stands, blood pressure fluctuated by 20 % of baseline. This led to larger fluctuations in cerebral blood flow in AD (27 (6) %) than in controls (22 (6) %, p < 0.05). Cerebral vasomotor reactivity to hypercapnia was reduced in AD (42.7 % increase in CBFV, versus 79.5 % in controls, p = 0.03). Conclusion Observations of impaired cerebrovascular function (impaired autoregulation and vasoreactivity) in transgenic mouse models for AD were confirmed in patients with sporadic AD.

Objective: Preclinical and post-mortem studies suggest that Alzheimer disease (AD) causes cerebrovascular dysfunction, and therefore may enhance susceptibility to cerebrovascular disease (CVD). The objective of this study was to investigate this association in a memory clinic population. Methods: The AD biomarkers CSF amyloid β42, amyloid β40 and APOE-ε4 status have all been linked to increased CVD risk in AD, and therefore the first aim of this study was to analyze the association between these biomarkers and CVD. In 92 memory clinic patients the cross-sectional association between AD biomarkersand the severity of CVD was investigated with linear regression analysis. Additionally, we studied whether AD biomarkers modified the relation between vascular risk factors and CVD. CVD was assessed on MRI through a visual rating scale.Analyses were adjusted for age. The second aim of this study was to investigate the association between clinical AD and CVD, where ‘clinical AD’ was defined as follows: impairment in episodic memory, hippocampal atrophy and an aberrant concentration of cerebrospinal fluid (CSF) biomarkers. 47 of the 92 patients had AD. Results: No association between CSF amyloid β42, amyloid β40 or APOE-ε4 status and CVD severity was found, nor did these AD biomarkers modify the relation between vascular risk factors and CVD. Clinical AD was not associated with CVD severity (p=0.83). Patients with more vascular risk factors had more CVD, but this relationship was not convincingly modified by AD (p=0.06). Conclusions: In this memory clinic population, CVD in patients with AD was related to vascular risk factors and age, comparable to patients without AD. Therefore, in our study, the preclinical and post-mortem evidence that AD would predispose to CVD could not be translated clinically. Further work, including replication of this work in a different and larger sample, is warranted.

Protein folding, protein degradation, and protein stability are regulated by the molecular chaperones. Under pathogenic conditions, aberrant proteins can be dysfunctional, unregulated, or pathogenically mutated. These aberrant proteins are triaged by the chaperone network for the maintenance of cellular homeostasis. These species, called chaperone client proteins, include the pathogenic factors of numerous neurodegenerative disorders, including tau in Alzheimer’s disease, α-synuclein and LRRK2 in Parkinson’s disease, SOD-1, TDP-43 and FUS in amyotrophic lateral sclerosis, and polyQ-expanded proteins such as huntingtin in Huntington’s disease. In depth study of two molecular chaperones, Hsp90 and Hsc70, has led to a greater understanding of aberrant client fate and how retarding the chaperone system can promote clearance of these pathogenic clients. Here we discuss how chaperone interactions and small molecule inhibitors can regulate the burden of aberrant client signaling in these neurological disorders.

In Alzheimer’s disease (AD), synaptic alterations play a major role and are often correlated with cognitive changes. In order to better understand synaptic modifications, we compared alterations in NMDA receptors and postsynaptic protein PSD-95 expression in the entorhinal cortex (EC) and frontal cortex (FC; area 9) of AD and control brains. We combined immunohistochemical and image analysis methods to quantify on consecutive sections the distribution of PSD-95 and NMDA receptors GluN1, GluN2A and GluN2B in EC and FC from 25 AD and control cases. The density of stained receptors was analyzed using multivariate statistical methods to assess the effect of neurodegeneration. In both regions, the number of neuronal profiles immunostained for GluN1 receptors subunit and PSD-95 protein was significantly increased in AD compared to controls (3-6 fold), while the number of neuronal profiles stained for GluN2A and GluN2B receptors subunits was on the contrary decreased (3-4 fold). The increase in marked neuronal profiles was more prominent in a cortical band corresponding to layers 3 to 5 with large pyramidal cells. Neurons positive for GluN1 or PSD-95 staining were often found in the same localization on consecutive sections and they were also reactive for the anti-tau antibody AD2, indicating a neurodegenerative process. Differences in the density of immunoreactive puncta representing neuropile were not statistically significant. Altogether these data indicate that GluN1 and PSD-95 accumulate in the neuronal perikarya, but this is not the case for GluN2A and GluN2B, while the neuropile compartment is less subject to modifications. Thus, important variations in the pattern of distribution of the NMDA receptors subunits and PSD-95 represent a marker in AD and by impairing the neuronal network, contribute to functional deterioration.

Background:This study measured serum concentrations of vascular risk factors, asymmetric dimethylarginine (ADMA) and symmetric dimethylarginine (SDMA) in a representative sample of older community-dwelling adults and determined their associations with objective and subjective memory impairment. Methods: Data on clinical, lifestyle, and demographic characteristics, serum ADMA, SDMA, and L-arginine (measured using LC-MS/MS) were collected from a population-based sample of older Australian adults from the Hunter Community Study. Objective memory was measured with the Audio Recorded Cognitive Screen (ARCS) neuropsychological battery and subjective memory impairment was measured using the Memory Complaint Questionnaire (MAC-Q). Results: Multivariate analysis revealed that SDMA and diabetes were significantly associated with objective memory impairment (Adjusted Odd ratio (AOR) = 3.90; 95% CI. 1.21 – 12.52 for fourth quartile (Q4) of SDMA. ADMA, SDMA, education, number of general practitioner visits and atrial fibrillation were all significantly associated with subjective memory impairment. (AOR = 1.82; 95% CI. 1.04 – 3.18 for Q4 ADMA. Conclusions: Higher serum SDMA was associated with objective and subjective memory impairment while higher serum ADMA was associated with subjective memory impairment.