Microglia isolated from rat brain secrete a urokinase-type plasminogen activator
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Updated: Sep 29, 2026
Primary Microglia Isolation from Mixed Glial Cell Cultures of Neonatal Rat Brain Tissue
Published on: August 15, 2012
K Nakajima1, N Tsuzaki, M Shimojo
1Department of Neurochemistry, National Institute of Neuroscience, Tokyo, Japan.
Abstract:
In a previous study, we found particular proteases which degrade myelin basic protein (MBP) in a conditioned medium of cultured rat brain microglia. The MBP degrading activity in microglial-conditioned medium (Mic-CM) increased markedly in the presence of plasminogen. By Sephadex G-150 column chromatography, plasminogen-dependent MBP degrading activity was eluted at the position of about 47 kDa and 28 kDa. Furthermore slight plasminogen-dependent protease activity in the presence of fibrin (tissue plasminogen activator activity) was detected at a molecular weight of about 68 kDa. The two molecular forms (47 kDa and 28 kDa) of plasminogen-dependent protease were demonstrated by casein-zymography, and it was suggested that they were urokinase type-plasminogen activators (uPA). This suggestion was confirmed by immunoblotting using anti-uPA antiserum. The unique 28 kDa type was considered to be produced from the 47 kDa form by limited proteolysis. Secretion of PA from microglia was demonstrated by cell zymography. In contrast, significant secretion of plasminogen activator inhibitor could not be detected in the Mic-CM. In addition, lipopolysaccharide significantly decreased the secretion of PA from microglia, while interleukin-1 and basic fibroblast growth factor enhanced the secretion.
Insights
Researchers identified urokinase-type plasminogen activators (uPA) secreted by microglia that degrade myelin basic protein (MBP). Microglial uPA secretion is modulated by inflammatory signals, impacting myelin breakdown in the brain.
Area of Science:
- Neuroscience
- Molecular Biology
- Biochemistry
Background:
- Microglia play a crucial role in central nervous system homeostasis and disease.
- Myelin basic protein (MBP) degradation is implicated in neuroinflammatory conditions.
Purpose of the Study:
- To identify and characterize proteases secreted by microglia responsible for myelin basic protein degradation.
- To investigate the regulation of these proteases by inflammatory mediators.
Main Methods:
- Cultured rat brain microglia conditioned medium (Mic-CM) analysis.
- Sephadex G-150 column chromatography and casein-zymography.
- Immunoblotting with anti-urokinase-type plasminogen activator (uPA) antiserum.
- Cell zymography to assess plasminogen activator (PA) secretion.
Main Results:
- Plasminogen-dependent MBP degrading activity was identified in Mic-CM at 47 kDa and 28 kDa.
- These activities were confirmed as urokinase-type plasminogen activators (uPA) via immunoblotting.
- A unique 28 kDa uPA form likely results from proteolysis of the 47 kDa form.
- Lipopolysaccharide decreased PA secretion, while interleukin-1 and basic fibroblast growth factor enhanced it.
Conclusions:
- Microglia secrete uPA, which can degrade myelin basic protein.
- Microglial uPA secretion is differentially regulated by inflammatory and growth factors.
- These findings suggest a role for microglial uPA in myelin pathology.
