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In vitro induction of lysosomal enzymes by phagocytosis
Abstract:
The in vitro induction of lysosomal enzymes by phagocytosis was demonstrated in cultivated mouse peritoneal macrophages. The contribution of each of several steps in the endocytic process to enzyme induction was examined. The enzymatic response after the uptake of equal numbers of erythrocytes (RBC) and nondigestible particles were compared. Phagocytosis of RBC produced a marked increase in the levels of acid phosphatase, beta-glucuronidase, and cathepsin D. Puromycin (1 microg/ml) inhibited the enzyme response. In contrast, phagocytosis of polyvinyl toluene, polystyrene, and insoluble starch particles produced no increase in macrophage lysosomal enzymes, although fusion of phagosomes with preexisting lysosomes occurred normally. The endocytic stimulus to synthesis of inducible lysosomal enzymes, therefore, occurred at or beyond the stage of digestion. Purified protein (bovine gamma globulin) aggregates and homopolymer coacervates of poly-l-glutamic acid: poly-l-lysine were effective inducers of lysosomal acid phosphatase, beta-glucuronidase, and cathepsin D, whereas homopolymers of the same D-amino acids were ineffective as inducers. Both the quantity of phagocytized substrate and its rate of enzymatic hydrolysis appear to control the level and persistance of lysosomal hydrolases.
Insights
Phagocytosis of digestible materials like red blood cells (RBC) triggers macrophage lysosomal enzyme production. Indigestible particles do not, indicating digestion is key for this cellular response.
Area of Science:
- Cell Biology
- Immunology
- Biochemistry
Background:
- Phagocytosis is a key cellular process for immune defense and nutrient uptake.
- Lysosomal enzymes play crucial roles in degrading internalized material.
- The regulation of lysosomal enzyme synthesis during phagocytosis is not fully understood.
Purpose of the Study:
- To investigate the role of phagocytosis and subsequent digestion in inducing lysosomal enzymes in macrophages.
- To compare the effects of digestible and non-digestible particles on enzyme induction.
- To identify the specific stages of endocytosis that trigger enzyme synthesis.
Main Methods:
- Cultured mouse peritoneal macrophages were used for in vitro experiments.
- Macrophages were exposed to erythrocytes (RBC) and various non-digestible particles (polyvinyl toluene, polystyrene, starch).
- Enzyme levels (acid phosphatase, beta-glucuronidase, cathepsin D) were measured, and the effect of puromycin was assessed.
Main Results:
- Phagocytosis of RBC led to significant increases in acid phosphatase, beta-glucuronidase, and cathepsin D.
- Puromycin inhibited this enzyme induction, suggesting a requirement for protein synthesis.
- Phagocytosis of non-digestible particles did not induce these enzymes, despite normal phagosome-lysosome fusion.
- Digestible protein aggregates and specific amino acid polymers induced enzymes, while their D-amino acid counterparts did not.
Conclusions:
- The induction of lysosomal enzymes by phagocytosis is dependent on the digestion of the internalized material.
- The stimulus for enzyme synthesis occurs at or after the digestion stage of endocytosis.
- Both the amount and the rate of enzymatic hydrolysis of phagocytized substrates influence lysosomal hydrolase levels.