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Tubular lysosome morphology and distribution within macrophages depend on the integrity of cytoplasmic microtubules
Abstract:
Pinocytosis of the fluorescent dye lucifer yellow labels elongated, membrane-bound tubular organelles in several cell types, including cultured human monocytes, thioglycolate-elicited mouse peritoneal macrophages, and the macrophage-like cell line J774.2. These tubular structures can be identified as lysosomes by acid phosphatase histochemistry and immunofluorescence localization of cathepsin L. The abundance of tubular lysosomes is markedly increased by treatment with phorbol 12-myristate 13-acetate (10 ng/ml). When labeled by pinocytosis of microperoxidase and examined by electron microscopic histochemistry, the tubular lysosomes have an outside diameter of approximately 75 nm and a length of several micrometers; they radiate from the cell's centrosphere in alignment with cytoplasmic microtubules and intermediate filaments. Incubation of phorbol myristate acetate-treated macrophages at 4 degrees C or in medium containing 5 microM colchicine or nocodazole at 37 degrees C leads to disassembly of microtubules and fragmentation of the tubular lysosomes. Return of the cultures to 37 degrees C or removal of nocodazole from the medium leads to reassembly of microtubules and the reappearance of tubular lysosomes within 10-20 min. We conclude that microtubules are essential for the maintenance of tubular lysosome morphology and that, in macrophages, a significant proportion of the lysosomal compartment is contained within these tubular structures.
Insights
Microtubules maintain the tubular shape of lysosomes in macrophages. Disrupting microtubules fragments these lysosomes, while their reassembly restores tubular lysosome morphology, highlighting microtubule importance.
Area of Science:
- Cell Biology
- Organelle Biology
Background:
- Lysosomes are key organelles for cellular waste disposal and recycling.
- The morphology of lysosomes can vary significantly depending on cell type and physiological conditions.
Purpose of the Study:
- To investigate the role of microtubules in maintaining the morphology of tubular lysosomes.
- To characterize the structure and dynamics of tubular lysosomes in macrophages.
Main Methods:
- Pinocytosis of fluorescent dyes (lucifer yellow, microperoxidase) for organelle labeling.
- Acid phosphatase histochemistry and cathepsin L immunofluorescence for lysosome identification.
- Electron microscopy for ultrastructural analysis.
- Treatment with phorbol 12-myristate 13-acetate (PMA) to modulate lysosome abundance.
- Disruption and reassembly of microtubules using cold shock, colchicine, and nocodazole.
Main Results:
- Pinocytosis labels elongated, membrane-bound tubular organelles as lysosomes in various macrophage types.
- Phorbol 12-myristate 13-acetate treatment significantly increases the abundance of these tubular lysosomes.
- Tubular lysosomes radiate from the centrosphere, aligned with microtubules and intermediate filaments.
- Microtubule disruption leads to fragmentation of tubular lysosomes, while microtubule reassembly restores their tubular morphology.
Conclusions:
- Microtubules are essential for maintaining the characteristic tubular morphology of lysosomes in macrophages.
- A significant portion of the lysosomal compartment in macrophages exists as these dynamic tubular structures.
- The dynamics of tubular lysosomes are closely linked to the state of the microtubule cytoskeleton.