ABSTRACT
ß-Site amyloid precursor protein cleaving enzyme (BACE1) is the rate-limiting enzyme for production of Aß peptides, proposed to drive the pathological changes found in Alzheimer's disease (AD). Reticulon 3 (RTN3) is a negative modulator of BACE1 (ß-secretase) proteolytic activity, while peptidylprolyl isomerase (cyclophilin)-like 2 (PPIL2) positively regulated BACE1 gene expression in a cell-based assay. This study aimed to analyze RTN3 and PPIL2 mRNA levels in four brain regions from individuals with AD and controls. BACE1 mRNA had been previously quantified in the samples, as had glial fibrillary acidic protein (GFAP) and neuron-specific enolase (NSE), to track changing cell populations in the tissue. mRNA levels in the human post mortem brain tissue were assayed using quantitative real-time polymerase chain reaction (qPCR) and qbase(PLUS), employing validated stably expressed reference genes. No differences in RTN3 or PPIL2 mRNA levels were found in individuals with AD, compared to controls. Both RTN3 and PPIL2 mRNA levels correlated significantly with BACE1 mRNA and all three showed similar disease stage-dependent changes with respect to NSE and GFAP. These findings indicated that the in vitro data demonstrating an effect of PPIL2 on BACE1 expression have functional relevance in vivo. Further research into BACE1-interacting proteins could provide a fruitful approach to the modulation of this protease and consequently Aß production.
Subject(s)
Alzheimer Disease/metabolism , Amyloid Precursor Protein Secretases/analysis , Aspartic Acid Endopeptidases/analysis , Brain/metabolism , Carrier Proteins/analysis , Cyclophilins/analysis , Membrane Proteins/analysis , Nerve Tissue Proteins/analysis , Aged , Aged, 80 and over , Female , Humans , Male , Middle Aged , RNA, Messenger/analysisABSTRACT
beta-Secretase activity is the rate-limiting step in Abeta peptide production from amyloid precursor protein. Abeta is a major component of Alzheimer's disease (AD) cortical amyloid plaques. beta-Secretase activity is elevated in post mortem brain tissue in AD. The current study investigated whether beta-secretase activity was also elevated in peripheral blood platelets. We developed a novel fluorimetric beta-secretase activity assay to investigate platelets isolated from individuals with AD (n=86), and age-matched controls (n=115). Platelet membrane beta-secretase activity (expressed as initial rate) varied over fourfold between individuals, raising important questions about in vivo regulation of this proteolytic activity. Nonetheless, we identified a significant 17% increase in platelet membrane beta-secretase activity in individuals with AD compared to controls (p=0.0003, unpaired t-test). Platelet membrane beta-secretase activity did not correlate with mini-mental state examination (MMSE) score in the AD group (mean MMSE=17.7, range 1-23), indicating that the increase did not occur as a secondary result of the disease process, and may even have preceded symptom onset.
Subject(s)
Alzheimer Disease/blood , Alzheimer Disease/enzymology , Amyloid Precursor Protein Secretases/blood , Blood Platelets/enzymology , Aged , Aged, 80 and over , Enzyme Activation , Female , Humans , MaleABSTRACT
BACKGROUND/AIMS: We have recently reported that platelet activity of the rate-limiting enzyme for beta-amyloid peptide production is elevated in established Alzheimer's disease. Laboratory investigation of the very early stages of dementia provides an opportunity to investigate pathological mechanisms before advanced disease hinders interpretation. Mild cognitive impairment (MCI) exists prior to obvious dementia, and is associated with increased risk of conversion to overt disease. METHODS: We developed and used a fluorimetric assay to quantify platelet membrane beta-secretase activity in 52 patients with MCI and 75 controls. RESULTS: Platelet membrane beta-secretase activity was 24% higher in individuals with MCI compared to controls (p = 0.001, unpaired t test with Welch correction). CONCLUSION: Elevated platelet beta-secretase activity in subjects with MCI is an area for further study in relation to the etiology and diagnosis of MCI.
Subject(s)
Amyloid Precursor Protein Secretases/blood , Blood Platelets/metabolism , Cognition Disorders/blood , Cognition Disorders/diagnosis , Aged , Brain/pathology , Female , Humans , Male , Nerve Degeneration/pathology , Neuropsychological Tests , ROC Curve , Severity of Illness IndexABSTRACT
Several lines of evidence indicate that the Abeta peptide is involved at some level in the pathological process that results in the clinical symptoms of AD (Alzheimer's disease). The N-terminus of Abeta is generated by cleavage of the Met-Asp bond at position 671-672 of APP (amyloid precursor protein), catalysed by a proteolytic activity called beta-secretase. Two 'beta-secretase' proteases have been identified: BACE (beta-site APP-cleaving enzyme) and BACE2. The cause of sporadic AD is currently unknown, but some studies have reported elevated BACE/beta-secretase activity in brain regions affected by the disease. We have demonstrated that robust beta-secretase activity is also detectable in platelets that contain APP and release Abeta. This review considers the current evidence for alterations in beta-secretase activity, and/or alterations in BACE expression, in post-mortem brain tissue and platelets from individuals with AD.