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Proteolytic action of thrombin is required for electrical activity-dependent synapse reduction
Y Liu1, R D Fields, B W Festoff
1Laboratory of Developmental Neurobiology, National Institute of Child Health and Human Development, National Institutes of Health, Bethesda, MD 20892.
Summary
Activity-dependent synapse reduction in mammals involves proteolysis. Specific thrombin inhibition completely blocked this process, implicating serine proteases like thrombin in neuromuscular junction remodeling.
Area of Science:
- Neuroscience
- Molecular Biology
- Biochemistry
Background:
- Synapse elimination is crucial for neural development and function.
- Activity-dependent synapse reduction is a key process in refining neural circuits.
- Proteolytic mechanisms are implicated in synapse remodeling.
Purpose of the Study:
- To investigate the molecular mechanisms underlying activity-dependent synapse reduction.
- To identify the specific proteases involved in synapse elimination at the neuromuscular junction.
Main Methods:
- Utilized an in vitro mammalian neuromuscular preparation.
- Assessed synapse reduction in the presence of various protease inhibitors.
- Examined the effects of thrombin inhibitors, serine protease inhibitors, and calpain inhibitors.
Main Results:
- Broad-spectrum protease inhibitor leupeptin reduced activity-dependent synapse reduction.
- Specific thrombin inhibitor hirudin completely blocked synapse reduction at nanomolar concentrations.
- Protease nexin I (PNI), a serine protease inhibitor, also inhibited synapse reduction.
- Cystatin, aprotinin, and calpain inhibitors did not affect synapse reduction.
Conclusions:
- Serine proteolytic activity, likely by thrombin or thrombin-like enzymes, is essential for activity-dependent synapse reduction.
- These findings highlight a specific enzymatic pathway in neuromuscular junction plasticity.