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Brain membrane serine protease activity in human cortex compared with rat: implication for Alzheimer's disease
G C Stratmann1, M T Webster, P T Francis
1Institute of Neurology, Guy's Hospital Campus, London, UK.
Dementia (Basel, Switzerland)
|March 1, 1994
Summary
Researchers investigated the degradation of amyloid precursor protein-like immunoreactivity (APPLIR) in human and rat brain extracts. Human brain enzymes were more effective, suggesting specific proteolytic activity related to neuronal count, not Alzheimer's disease.
Area of Science:
- Neuroscience
- Biochemistry
- Proteomics
Background:
- Amyloid precursor protein (APP) processing is central to Alzheimer's disease (AD) pathogenesis.
- Understanding the enzymes involved in APP degradation is crucial for therapeutic development.
- Proteolytic activity in the brain, particularly in the cerebral cortex, warrants further investigation.
Purpose of the Study:
- To characterize and compare the enzyme activity responsible for degrading amyloid precursor protein-like immunoreactivity (APPLIR) in human and rat cerebral cortex.
- To investigate factors influencing this proteolytic activity, including post-mortem delay and cell type specificity.
- To assess the potential role of this activity in the context of Alzheimer's disease.
Main Methods:
- Sequential extraction of cerebral cortex from humans and rats using detergent and buffer solutions to isolate enzyme preparations.
- Incubation of soluble enzyme preparations with rat cerebral cortical membranes containing APPLIR.
- Analysis of APPLIR degradation products and enzyme activity using molecular mass determination.
- Inhibition studies with phenylmethylsulphonylfluoride and assessment of calcium ion (Ca2+) sensitivity.
- Correlation of enzyme activity with pyramidal neuron and astrocyte numbers.
Main Results:
- Enzyme preparations from human brain exhibited greater APPLIR degradation effectiveness than those from rat pups and adult rats, with effectiveness varying by post-mortem delay.
- Incubation with human samples resulted in the accumulation of a 100-kD product.
- The observed activity was inhibited by phenylmethylsulphonylfluoride, insensitive to Ca2+, and correlated with pyramidal neuron numbers, but not astrocyte numbers.
- No significant difference in activity was found between Alzheimer's disease patients and control groups.
Conclusions:
- Human brain enzymes possess significant APPLIR-degrading activity, distinct from rat enzymes, with higher efficacy in non-delayed post-mortem samples.
- This proteolytic activity is neuron-associated and its characteristics do not directly implicate it in the altered deposition of beta-amyloid protein observed in Alzheimer's disease.
- Further research into specific proteolytic pathways is needed to fully understand APP processing and its role in neurodegenerative diseases.