Lesions in the hippocampus (HC), the entorhinal cortex (EC), and the prefrontal cortex (PFC) are associated with impairment of episodic memory; reduced HC volume is linked to memory declines in dementia; and decline in EC volume predicts progression from mild cognitive impairment to dementia. However, in healthy adults, the relationship between memory and regional volumes is unclear, and no data are available on the relationship of longitudinal regional shrinkage to memory performance in a cognitively intact population. The objective of this study was to examine whether shrinkage of the EC, HC, and PFC over a 5 year period can predict declarative memory performance in healthy adults. The volumes of three brain regions were measured on magnetic resonance images that were acquired twice, 5 years apart. Multiple measures of episodic memory were administered at follow-up. Results indicated that the volume of HC and PFC (but not EC) correlated with age at baseline and follow-up. However, after age differences in memory were taken into account, none of the regional volumes was associated with memory performance at follow-up. In contrast, greater annual rate of shrinkage in EC (but not HC or PFC) predicted poorer memory performance. Thus, in a healthy and educated population, even mild age-related shrinkage of the EC may be a sensitive predictor of memory decline.

https://www.jneurosci.org/content/jneuro/24/4/956.full.pdf

Shrinkage of the Entorhinal Cortex over Five Years Predicts Memory Performance in Healthy Adults

Members of membrane-bound disintegrin metalloproteinases (ADAMs) were shown to be capable of cleaving amyloid precursor protein (APP) at the α-cleavage site in different cell systems. One of the candidate α-secretases identified in this family is ADAM10. The present study addresses the following major questions: 1) Are the levels of an α-secretase candidate (i.e., ADAM10) reduced in accessible cells of Alzheimer Disease (AD) patients? 2) Are ADAM10 levels in the peripheral cells of AD patients related to a concomitant decrease in αAPPs? Western Blot analysis of ADAM10 is performed on platelet homogenates from 33 sporadic AD patients and on 26 age-matched control subjects. Moreover, the levels of α-secretase metabolite (αAPPs) are tested both in platelets and cerebrospinal fluid (CSF) of the same pool of subjects by means of Western blot with a specific antibody. A significant decrease of platelet ADAM10 levels is observed in patients affected by probable AD when compared to control subjects and this is paralleled by a reduced level of αAPPs released from platelets. Moreover, in the same pool of AD patients, αAPPs levels were reduced concomitantly in CSF. ADAM10 is expressed in platelets. A reduced level of ADAM10 is observed in platelets obtained from AD patients compared to age-matched controls. Further, in the same pool of AD patients, a qualitatively and quantitatively similar decrease in αAPPs is present both in thrombin-activated platelets and CSF, thus suggesting that alterations of APP processing might occur both in the neuronal compartment and peripheral cells.

/pdf/a-secretase-adam10-as-well-as-aapps-is-reduced-in-platelets-y728av4r1o.pdf

α-Secretase ADAM10 as Well as αAPPs Is Reduced in Platelets and CSF of Alzheimer Disease Patients

Platelet activation results in changes in a number of cell surface molecules including an increase in P-Selectin (CD62P) that may be rapidly and conveniently measured by immunofluorescent flow cytometry. The ADVIA 120 (Bayer) is a new system that facilitates more accurate measurement of platelet volume and in addition provides an approximate measure of the mean refractive index (RI) of the platelets reported as mean platelet component (MPC) concentration. We were interested to determine whether changes in MPC might reflect changes in platelet activation status. To investigate this, the platelet CD62P expression, determined by flow cytometry, and change in MPC, measured on the ADVIA 120 system, was first examined in vitro after stimulation of EDTA anticoagulated whole blood with submaximal concentrations of bovine thrombin in the presence or absence of the thromboxane synthase inhibitor, Ridogrel. Thrombin produced a dose-dependent increase in platelet CD62P expression and a decrease in MPC that could be inhibited by Ridogrel at physiological concentrations. In the second set of experiments, blood from 20 normal controls was collected into both EDTA and sodium citrate (SC) anticoagulants. Within 30 min of venesection and again at 3 h post-venesection after storage at room temperature, the platelet MPC and CD62P expression were determined. Platelets in all samples with both anticoagulants showed very low levels of CD62P expression when first analysed. At 3 h there was a small increase in CD62P expression on platelets in whole blood anticoagulated with SC, but a significant (P < 0.001) increase was observed on platelets anti-coagulated with EDTA. A negative correlation was found between the change in MPC of the platelets and the increase in the mean fluorescence intensity (MFI) (r = -0.69, P < 0.001, n = 20) and the percentage (r = -0.72, P < 0.001, n = 20) of CD62P positive platelets at 3 h in blood anticoagulated with EDTA. We conclude that a reduction in MPC as measured by the ADVIA 120 may be used to detect anticoagulant induced, as well as thrombin stimulated, in vitro platelet activation in blood anticoagulated with EDTA. Further, we conclude that platelet activation is negligible for up to 3 h in sodium citrate anticoagulated whole blood.

https://onlinelibrary.wiley.com/doi/pdf/10.1002/%28SICI%291097-0320%2819991015%2938%3A5%3C250%3A%3AAID-CYTO8%3E3.0.CO%3B2-K

Use of mean platelet component to measure platelet activation on the ADVIA 120 haematology system.

Studies of the metabolism and function of the amyloid precursor protein (APP) and its proteolytic fragment A beta in cultured cells, transgenic mice, and post-mortem brain tissue have advanced our understanding of Alzheimer disease (AD). However, the molecular pathogenesis of the disease is still not clear, and we are a long way from finding a cure for the disease. Studies carried out on human platelets and leukocytes have also helped shed light on APP and A beta metabolism and function. Platelet and leukocyte APP isoforms are processed using mechanisms similar to those in neuronal cells to generate A beta and soluble forms of APP. The activation of platelets and leukocytes leads to the secretion of APP and A beta, resulting in higher levels of these proteins in serum. APP and A beta in the circulation may be involved in the regulation of platelet function and in the modulation of immune responses. Because human platelets and lymphocytes produce all forms of APP and secrete amyloidogenic A beta peptides, these tissues may be useful in monitoring responses to therapeutic interventions directed at APP metabolism. Although not of neuronal origin, further studies on the more accessible ex vivo tissues, including platelets and leukocytes and other blood components, may reveal potential peripheral markers for AD and will further our understanding of the molecular pathogenesis of AD.

https://jlb.onlinelibrary.wiley.com/doi/pdf/10.1002/jlb.66.4.567

The amyloid precursor protein of Alzheimer disease in human brain and blood.

Platelets as a peripheral district where to study pathogenetic mechanisms of alzheimer disease: the case of amyloid precursor protein.

Moderate and Advanced Alzheimer's Patients Exhibit Platelet Activation Differences

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Moderate and Advanced Alzheimer's Patients Exhibit Platelet Activation Differences