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The calpain proteolytic system in neonatal hypoxic-ischemia
K Blomgren1, A McRae, A Elmered
1Institute of Anatomy and Cell Biology, University of Göteborg, Sweden. klas.blomgren@anatcell.gu.se
Annals of the New York Academy of Sciences
|November 25, 1997
Summary
Calpain activity increases in both brain hemispheres after hypoxic-ischemia (HI) in neonatal rats. This calpain activation, particularly in the ipsilateral hemisphere, precedes neuronal death and is linked to decreased calpastatin levels.
Area of Science:
- Neuroscience
- Biochemistry
- Pathology
Background:
- Cerebral hypoxic-ischemia (HI) is a major cause of neonatal brain injury.
- Calpains are calcium-dependent proteases implicated in various cellular processes, including cell death.
- Understanding calpain involvement in HI is crucial for developing therapeutic strategies.
Purpose of the Study:
- To investigate the role and activation patterns of calpains in the neonatal rat brain following transient cerebral HI.
- To examine the expression and activity of calpains and their endogenous inhibitor, calpastatin, in response to HI.
- To correlate calpain activity with markers of neuronal injury and proteolysis.
Main Methods:
- Neonatal rats were subjected to transient unilateral cerebral HI.
- Calpain caseinolytic activity was measured in different brain fractions.
- Immunohistochemistry was used to detect calpastatin, alpha-fodrin, its breakdown product (FBDP), and MAP-2.
- Western blotting analyzed calpain and calpastatin protein levels.
- mRNA levels of m-calpain were quantified.
Main Results:
- Calpain activity increased in both hemispheres post-HI, with a pronounced increase in the membrane-associated fraction.
- HI led to a loss of calpain activity in the cytosolic fraction, suggesting translocation.
- FBDP, a marker of calpain activity, accumulated in the ipsilateral hemisphere and transiently in the contralateral hemisphere.
- Calpastatin protein levels and inhibitory activity decreased in the ipsilateral hemisphere post-HI.
- Increased m-calpain mRNA and protein were observed in the HI hemisphere 48 hours after the insult.
- Neuronal injury marker MAP-2 showed a distinct loss in areas with brain injury.
Conclusions:
- Calpains are activated during and in the early reperfusion phase following neonatal cerebral HI.
- The observed decrease in calpastatin in the ipsilateral hemisphere likely facilitates calpain activation and subsequent neuronal damage.
- Calpain activation precedes observable neuronal death, highlighting its potential as a therapeutic target.