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Quantification of APP and APLP2 mRNA in APOE genotyped Alzheimer's disease brains
J A Johnston1, S Norgren, R Ravid
1Department of Clinical Neuroscience and Family Medicine, Karolinska Institute, Novum KFC, Huddinge, Sweden. janet.johnston@kfcm13.hs.sll.se
Abstract:
Amyloid precursor protein (APP) is metabolised to produce A beta, a peptide found aggregated in Alzheimer's disease neuritic plaques. APP is a member of a multigene protein family which includes amyloid precursor-like protein 2 (APLP2). Since A beta accumulation can be triggered by factors acting up- or downstream of APP processing, we investigated whether APP mRNA expression was altered in Alzheimer's disease post-mortem cerebral cortex. In addition, we characterised cortical APLP2 mRNA levels. Quantitative RNA-RNA solution hybridisation-RNase protection was used to assay total APP. APP containing the Kunitz-type protease inhibitor (KPI) insert and APLP2 mRNA in mid-temporal and superior frontal cortices from apolipoprotein E-genotyped subjects with Alzheimer's disease, other neurological diseases and non-demented controls. Approximately 3 times more APP than APLP2 mRNA was detected and about 70% of total APP mRNA contained the KPI insert in the control subjects. Total APP and APLP2 mRNA levels were significantly reduced in Alzheimer's disease mid-temporal, but not superior frontal cortex, suggesting that regional reductions in these mRNA correlate with severity of disease pathology. A small significant increase in the proportion of APP KPI mRNA was seen in both cortical regions in Alzheimer's disease. Apolipoprotein E genotype did not influence cortical levels of total APP, APP KPI or APLP2 mRNA. Alzheimer's disease-related increases in tissue DNA content were seen in both regions studied, while tissue RNA levels were reduced in the positive disease controls. In summary, these results indicate that Alzheimer's disease is not associated with over-expression of either APP or APLP2 mRNA. Our findings reveal a disease-associated increase in the proportion of APP KPI-containing isoforms, and further investigation should clarify whether this predisposes affected individuals to A beta production and aggregation, or reflects later events such as gliosis and neuronal cell death.
Insights
Alzheimer's disease does not involve increased amyloid precursor protein (APP) or amyloid precursor-like protein 2 (APLP2) mRNA. However, the proportion of APP mRNA with the Kunitz-type protease inhibitor (KPI) insert increases, potentially impacting A beta aggregation.
Area of Science:
- Neuroscience
- Molecular Biology
- Genetics
Background:
- Amyloid precursor protein (APP) metabolism produces A beta, implicated in Alzheimer's disease (AD) plaques.
- APP and amyloid precursor-like protein 2 (APLP2) are related proteins.
- Investigating mRNA expression alterations in AD is crucial for understanding disease mechanisms.
Purpose of the Study:
- To determine if Alzheimer's disease alters cortical mRNA expression of APP and APLP2.
- To characterize the levels of APP containing the Kunitz-type protease inhibitor (KPI) insert and APLP2 mRNA in AD.
Main Methods:
- Quantitative RNA-RNA solution hybridization-RNase protection assays were employed.
- Analysis was performed on post-mortem cerebral cortex (mid-temporal and superior frontal) from AD patients, other neurological diseases, and controls.
- Apolipoprotein E genotyping was used to stratify subjects.
Main Results:
- Total APP and APLP2 mRNA levels were significantly reduced in the mid-temporal cortex of AD patients, correlating with disease severity.
- A small but significant increase in the proportion of APP KPI mRNA was observed in both cortical regions in AD.
- Apolipoprotein E genotype did not affect cortical mRNA levels of APP or APLP2.
Conclusions:
- Alzheimer's disease is not associated with the over-expression of APP or APLP2 mRNA.
- A disease-associated increase in APP KPI-containing isoforms suggests a potential role in AD pathogenesis.
- Further research is needed to clarify if increased APP KPI isoforms predispose to A beta production or reflect later pathological events like gliosis.