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Lysosomal enzyme secretion by macrophages during intracellular storage of particles
Abstract:
Cultured mouse peritoneal macrophages containing previously endocytosed zymosan or small-fibre asbestos (but not latex or sucrose) were shown to release selectively into the medium the lysosomal hydrolase beta-N-acetylglucosaminidase. Thus macrophage lysosomal enzyem secretion was experimentally dissociated from endocytosis (as the residual external particles were washed away from the cells). The cells remained viable, and total activities of both N-acetyl-beta-D-glucosaminidase and of lactate dehydrogenase (a cytosol enzyme) rose with time. The relevance of such secretion by macrophages containing stored materials to chronic inflammatory processes is discussed.
Insights
Macrophages selectively release beta-N-acetylglucosaminidase when containing zymosan or asbestos particles. This lysosomal enzyme secretion is dissociated from endocytosis, suggesting a role in chronic inflammation.
Area of Science:
- Cell Biology
- Immunology
- Biochemistry
Background:
- Macrophages play a crucial role in the immune system, involved in both endocytosis and inflammatory responses.
- Lysosomal enzymes are essential for cellular degradation and can be released extracellularly.
Purpose of the Study:
- To investigate the selective secretion of lysosomal hydrolases by macrophages.
- To determine if enzyme secretion is linked to the presence of specific endocytosed materials.
- To explore the dissociation between endocytosis and enzyme secretion.
Main Methods:
- Cultured mouse peritoneal macrophages were incubated with zymosan, asbestos, latex, or sucrose.
- Cells were washed to remove external particles, dissociating secretion from ongoing endocytosis.
- Lysosomal (beta-N-acetylglucosaminidase) and cytosolic (lactate dehydrogenase) enzyme activities were measured in the medium and cell lysates.
Main Results:
- Macrophages selectively secreted beta-N-acetylglucosaminidase when containing zymosan or asbestos particles.
- No significant secretion was observed with latex or sucrose particles.
- Enzyme secretion was experimentally dissociated from the initial endocytosis event.
- Cell viability was maintained, with increased total enzyme activities over time.
Conclusions:
- Macrophages can selectively secrete lysosomal enzymes in response to specific endocytosed materials.
- This secretion mechanism is independent of continuous endocytosis.
- The findings suggest a potential role for stored materials and macrophage enzyme secretion in chronic inflammatory processes.