Alternative splicing of the beta A4 amyloid gene of Alzheimer's disease in cortex of control and Alzheimer's disease patients

Differential APP gene expression in rat cerebral cortex, meninges, and primary astroglial, microglial and neuronal cultures

Differential amyloid precursor protein (APP) gene expression was investigated in primary cultures of astrocytes, neurons and microglia from neonatal rat cerebral cortex as well as in meninges, and young and adult cerebral cortex tissues in order to define the possible contribution of individual CNS cell types in beta AP deposition. Meninges and neurons contained higher levels of total APP mRNA than glial cells and APP695 mRNA was abundant in neurons while glial cells and meninges contained higher levels of KPI-containing mRNAs. These results demonstrate cell-specific transcriptional and post-transcriptional regulation of APP gene expression in CNS cell types. In addition, the steady-state level of APPs in each cell type did not reflect mRNA levels indicating translational or post-translational regulation.

Interleukin-6 and alpha-2-macroglobulin indicate an acute-phase state in Alzheimer's disease cortices

Recent studies indicated that the formation of a major constituent of Alzheimer's disease (AD) senile plaques, called beta A4-peptide, does not result from normal processing of its precursor, amyloid precursor protein (APP). Since proteolytic cleavage of APP inside its beta A4 sequence was found to be part of APP processing the formation of the beta A4-peptide seems to be prevented under normal conditions. We considered whether in AD one of the endogenous proteinase inhibitors might interfere with APP processing. After we had recently found that cultured human neuronal cells synthesize the most potent of the known human proteinase inhibitors, alpha-2-macroglobulin (alpha 2M), upon stimulation with the inflammatory mediator interleukin-6 (IL-6) we now investigated whether alpha 2M and IL-6 could be detected in AD brains. Here we report that AD cortical senile plaques display strong alpha 2M and IL-6 immunoreactivity while no such immunoreactivity was found in age-matched control brains. Strong perinuclear alpha 2M immunoreactivity in hippocampal CA1 neurons of Alzheimer's disease brains indicates that neuronal cells are the site of alpha 2M synthesis in AD brains. We did not detect elevated IL-6 or alpha 2M levels in the cerebrospinal fluid of AD patients. Our data indicate that a sequence of immunological events which seem to be restricted to the local cortical environment is part of AD pathology.

Quantitative changes in the amyloid beta A4 precursor protein in Alzheimer cerebrospinal fluid

The major three secretory isoforms of Alzheimer beta A4 amyloid precursor protein (APP) were quantified in cerebrospinal fluid (CSF) using (1) a newly developed enzyme-linked immunosorbent assay (ELISA) and (2) densitometric analysis of CSF Western blots. The protease inhibitor-containing APP751/770 isoforms represented an average of 10.5% of total APP in CSF of patients with Alzheimer's disease (AD, n = 22), multi-infarct dementia (MID, n = 5) and normal controls (n = 10). APP levels in CSF did not depend on total CSF protein. Both findings are inconsistent with a hematogeneous origin of APP in CSF and suggest an intracerebral source. Total APP, APP695 and APP751/770 were significantly decreased in the AD and in the MID groups, but were not correlated to the ages of patients or controls.