Platelets Of Alzheimer's Disease Patients Research Articles

MPTAC Determines APP Fragmentation via Sensing Sulfur Amino Acid Catabolism

Metabolic disorder has been suggested to underlie Alzheimer's disease (AD). However, the decisive molecular linkages remain unclear. We discovered that human Molybdopterin Synthase Associating Complex, MPTAC, promotes sulfur amino acid catabolism to prevent oxidative damage from excess sulfur amino acids, which, in turn, advances fatty acid oxidation and acetyl coenzyme A (acetyl-CoA) synthesis. The association of MPTAC with Protein arginine (R) Methyltransferase 5 (PRMT5) complex and small nuclear ribonucleoprotein (SNRP) splicing factors enables SNRPs to sense metabolic states through their methylation. This promotes the splicing fidelity of amyloid precursor protein (APP) pre-mRNA and proper APP fragmentation, abnormalities of which have been observed in the platelets of AD patients. The functions of MPTAC are crucial to maintain expression of drebrin 1, which is required for synaptic plasticity, through prevention from oxidative damage. Thus, adjustment of sulfur amino acid catabolism by MPTAC prevents events that occur early in the onset of AD.

ADAM10 gene expression in the blood cells of Alzheimer's disease patients and mild cognitive impairment subjects

ADAM10 is a potential biomarker for Alzheimer's disease (AD). ADAM10 protein levels are reduced in platelets of AD patients. The aim was to verify the total blood and platelet ADAM10 gene expression in AD patients and to compare with mild cognitive impairment (MCI) and healthy subjects. No significant differences in ADAM10 gene expression were observed. Therefore, the decrease of ADAM10 protein in platelets of AD patients is not caused by a reduction in ADAM10 mRNA. Further studies must be performed to investigate other pathways in the down regulation of ADAM10 protein.

GSK3β, CREB, and BDNF in peripheral blood of patients with Alzheimer's disease and depression

Glycogen synthase kinase-3β (GSK3β), cAMP-response element-binding protein (CREB) and brain-derived neurotrophic factor (BDNF) play critical roles in neuronal survival, synaptic plasticity and memory and participate in the pathophysiology of both depressive disorder and Alzheimer's disease (AD). This study was designed to determine the association of GSK3β activity, CREB activity and BDNF concentration in peripheral blood of patients with AD with or without depressive symptoms and in depressive patients without AD. GSK3β activity in platelets, CREB activity in lymphocytes and BDNF concentration in plasma, platelet-rich plasma or platelets were measured in 85 AD patients (36 of whom displayed co-morbid depressive symptoms), 65 non-AD patients with depressive disorder and 96 healthy controls. AD patients were clinically assessed for stage of dementia, cognitive impairment and severity of depressive symptoms. Depressive patients were clinically assessed for severity of depression. We observed increased CREB activity and GSK3β activity in AD with depressive symptoms or in AD at mild stage of dementia. Decreased BDNF concentration was found in platelet-rich plasma of AD patients at moderate to severe stages of dementia or in AD without depressive symptoms. An association was revealed of the severity of cognitive impairment with the increase of GSK3β in the platelets of AD patients with mild dementia. In depressive patients, a lower concentration of phosphorylated GSK3β was associated with a higher severity of depression. Association was confirmed between severity of depression, CREB activation, and BDNF concentration in drug-naïve depressive patients. Our data demonstrated that AD is accompanied by increased CREB activity in lymphocytes and a decreased concentration of BDNF in platelet-rich plasma. The decreased BDNF concentration appears to correlate with moderate to severe stages of dementia in AD. Observation of decreased phosphorylation of GSK3β in platelets of both AD patients with depressive symptoms and depressive patients after treatment confirms the role of increased GSK3β activity in the pathophysiology of both AD and depressive disorder. Associations were confirmed between AD and platelet GSK3β activity, lymphocyte CREB activity and plasma BDNF. CREB activity and platelet BDNF concentration seems to be related to depressive disorder.

Matrix Metalloproteinase-2 and Epidermal Growth Factor are Decreased in Platelets of Alzheimer Patients

Alzheimer's disease (AD) is the most prevalent type of dementia. Despite considerable advances in diagnostic accuracy, diagnostic procedures that are easily accessible are still sorely needed. Blood biomarkers are therefore in the focus of research. Platelets contain a high concentration of the amyloid precursor protein (APP), which has been mentioned as a potentially useful diagnostic marker. The aim of the present study was to analyze various cell adhesion molecules (CAMs), cytokines, growth factors, and matrix metalloproteinases (MMPs) in platelets of AD and mild cognitively impaired (MCI) patients as compared to healthy controls. Our data show a significant decrease in the levels of epidermal growth factor (EGF) and of MMP-2 in platelets of AD patients and decreased levels of MMP-2 in MCI. The APP ratio was slightly but not significantly decreased in AD patients, whereas CD40L and serotonin were unchanged. Our findings demonstrate specific changes in AD platelets. Whether these biomarkers can be established as potential early diagnostic biomarkers for AD remains to be established in longitudinal studies.

Effects of oxidative stress on amyloid precursor protein processing in rat and human platelets

Alzheimer's disease (AD) is the most common neurodegenerative illness affecting the elderly and is characterized by beta-amyloid (Aβ) deposition in the brain (plaques) and in microvessels (Aβ-angiopathy). The reasons for Aβ deposition are not clear, but an impaired clearance of Aβ at the blood-brain barrier may be implicated and oxidative stress possibly plays a major role in this process. Platelets are of particular interest, because they contain high levels of the amyloid precursor protein (APP) and in AD an abnormal expression of platelets APP fragments was found. The aim of the present study was to investigate (1) if oxidative stress induced by hydrogen peroxide (H2O2) affects APP expression in rat and human platelets and (2) to compare the APP changes with platelets of AD patients. In rat platelets, all three fragments of APP (130-110-106 kilo Dalton, kDa) were found. H2O2 (10 mM, 20 minutes) significantly reduced all three fragments in rat platelets, did not affect CD62P-staining and slightly increased the size of actin as seen in the Western blot. The effect was not seen at 1 mM H2O2 and was counteracted by glutathione. Immunohistochemistry for CD62P, CD61, APP and Annexin-V was used to verify the changes at the cellular level. In platelets of young volunteers (age = 33 ± 4 years), 10 mM H2O2 markedly reduced the smaller APP 110 and 106 kDa fragments after 20 minutes. Our data show that platelets of AD patients (age = 80 ± 1 years) had a significant reduced 130 kDa fragment compared to controls (age = 70 ± 2 years). In summary, oxidative stress may account for a dysfunctional processing of APP in rat and human control platelets and possibly in AD patients.

Expression of the Anti-amyloidogenic Secretase ADAM10 Is Suppressed by Its 5′-Untranslated Region

Proteolytic processing of the amyloid precursor protein by alpha-secretase prevents formation of the amyloid beta-peptide (Abeta), which is the main constituent of amyloid plaques in brains of Alzheimer disease (AD) patients. alpha-Secretase activity is decreased in AD, and overexpression of the alpha-secretase ADAM10 (a disintegrin and metalloprotease 10) in an AD animal model prevents amyloid pathology. ADAM10 has a 444-nucleotide-long, very GC-rich 5'-untranslated region (5'-UTR) with two upstream open reading frames. Because similar properties of 5'-UTRs are found in transcripts of many genes, which are regulated by translational control mechanisms, we asked whether ADAM10 expression is translationally controlled by its 5'-UTR. We demonstrate that the 5'-UTR of ADAM10 represses the rate of ADAM10 translation. In the absence of the 5'-UTR, we observed a significant increase of ADAM10 protein levels in HEK293 cells, whereas mRNA levels were not changed. Moreover, the 5'-UTR of ADAM10 inhibits translation of a luciferase reporter in an in vitro transcription/translation assay. Successive deletion of the first half of the ADAM10 5'-UTR revealed a striking increase in ADAM10 protein expression in HEK293 cells, suggesting that this part of the 5'-UTR contains inhibitory elements for translation. Moreover, we detect an enhanced alpha-secretase activity and consequently reduced Abeta levels in the conditioned medium of HEK293 cells expressing both amyloid precursor protein and a 5'-UTR-ADAM10 deletion construct lacking the first half of the 5'-UTR. Thus, we provide evidence that the 5'-UTR of ADAM10 may have an important role for post-transcriptional regulation of ADAM10 expression and consequently Abeta production.

Influence of apolipoprotein E genotype on blood redox status of Alzheimer's disease patients.

The blood redox status of probable Alzheimer's Disease (AD) patients and control subjects with distinct Apo E genotypes was investigated. It was assessed by measuring the levels of hydroperoxides (MDA) in plasma and erythrocytes, the levels of the antioxidant defense system (enzymatic and non-enzymatic) in plasma, erythrocytes, platelets and leukocytes, the activities of catechol-O-methyltransferase (COMT) in erythrocytes and monoamine oxidase-B (MAO-B) in platelets and also the activity of the mitochondrial respiratory chain in leukocytes. No significant differences were found between the Apo E genotype and MDA, uric acid, vitamin E and reduced-glutathione (GSH) levels in plasma; MDA, vitamin E, GSH, superoxide-dismutase (SOD), glutathione-peroxidase (GSH-Px) and COMT levels in erythrocytes; vitamin E levels in the platelets of AD patients and control subjects. However, the uric acid levels in plasma and the COMT levels in erythrocytes of AD patients and control subjects with the epsilon4 allele were significantly lower than those observed in control subjects without the epsilon4 allele. Moreover, the duraquinol oxidation level in leukocytes of AD patients with the epsilon4 allele was significantly higher than that in AD patients without the epsilon4 allele and control subjects with and without the epsilon4 allele. The meaning of these results is discussed in terms of involvement of oxidative stress in the etiopathogenesis of AD.

Reduction of Platelet Phospholipase C Activity in Patients with Alzheimer Disease

Phosphoinositide-specific phospholipase C (PLC) is a key enzyme in signal transduction. We have previously demonstrated that a PLC isozyme is abnormally accumulated in the brain tissue in Alzheimer's disease (AD). AD has been suggested to be a systemic disease in which the expression of abnormalities is most prominent in neuronal tissues. In a recent study, we have revealed the increase of the cytosolic protein kinase C (PKC) concentration in platelets of AD patients, suggesting the change of PLC, which is upstream to PKC in phosphoinositide metabolism. In this study, we examined phosphatidylinositol-specific PLC activity in platelets from patients with AD and age-matched controls by measuring the formation of radioactive inositol phosphate. The PLC activity was significantly lower in the AD platelets than in the controls. These findings suggest that aberrant phosphoinositide metabolism is present in nonneuronal tissues as well as the brain in AD.

Platelet Protein Kinase C levels in Alzheimer's disease

Alzheimer's disease (AD) has been suggested to be a systemic disease, and signal transduction abnormalities have been reported in non-neuronal AD cells. We have previously quantified the protein kinase C (PKC) subtypes in AD and control brains using a two-site enzyme immunoassay (EIA), and have shown that type II PKC levels were significantly reduced in the temporal cortex of AD patients. In this study, we used this EIA to assess the platelet levels of type II PKC in age-matched groups of AD patients and normal controls. The cytosolic level of type II PKC was significantly higher in AD platelets than in control platelets but was unchanged in the membranous fraction. Platelet proteins showed no differences between the AD and control groups. Therefore, the type II PKC content of the cytosolic fraction was increased in AD platelets. These results suggest that type II PKC may be altered in both the brain and platelets of AD patients and support the hypothesis that AD is a systemic disease.