Proteolytic processing of beta-amyloid precursor by calpain I

Area of Science:

• Neuroscience
• Biochemistry
• Cell Biology

Background:

• Alzheimer's disease is characterized by beta-amyloid plaques.
• Beta-amyloid peptide originates from amyloid precursor protein (APP).
• Proteolytic processing of APP is crucial for beta-amyloid deposition.

Purpose of the Study:

• Investigate the role of calpain I in APP processing.
• Determine if calpain I cleaves APP and identify cleavage sites.
• Examine the in vivo relevance of calpain I in APP metabolism.

Main Methods:

• In vitro degradation assays using immunoblotting of rat brain APP.
• Immunohistochemistry to assess colocalization of APP and calpain I in neurons.
• Intraventricular kainate infusion to induce calpain I activation in vivo.

Main Results:

• Activated calpain I efficiently degraded both soluble and membrane-bound APP in vitro.
• Identified three distinct calpain I cleavage sites on APP, one yielding a beta-peptide-containing fragment.
• Observed extensive colocalization of APP and calpain I in rat brain neurons.
• Kainate infusion led to decreased APP levels, suggesting in vivo degradation by calpain I.
• APP and calpain I immunoreactivity shifted to reactive astrocytes after kainate-induced neuronal loss.

Conclusions:

• Calpain I plays a significant role in both normal and pathological APP processing.
• APP processing by calpain I can occur in neurons and reactive astrocytes.
• Calcium influx and calpain I activation may link excitatory neurotransmission to APP metabolism.