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Intracellular reactions in single human granulocytes upon phorbol myristate acetate activation using confocal Raman
N M Sijtsema1, A G Tibbe, I G Segers-Nolten
1University of Twente, Institute for Biomedical Technology, Department of Applied Physics, Applied Optics Group (TOP), 7500 AE Enschede, the Netherlands.
Abstract:
We have obtained new evidence for the occurrence of intracellular NADPH-oxidase activity in neutrophilic and eosinophilic granulocytes upon stimulation with phorbol myristate acetate (PMA). PMA activation leads to a partial translocation of cytochrome b(558) from the membranes of the specific granules to the plasma membrane. It was suggested that NADPH-oxidase activity only takes place in the plasma membrane, leading to an extracellular release of oxygen metabolites because cellular self-destruction can be avoided in this way. The effects of PMA activation were indirectly studied in recent experiments employing scavengers of extracellular superoxide anion and hydrogen peroxide, and support for intracellular NADPH-oxidase activity was obtained. In this paper we use Raman microspectroscopy as a direct method to study intracellular molecular reactions that result from cellular triggering by PMA. The molecular specificity of this microscopic method enables us to show that intracellular reduction of both myeloperoxidase (MPO) and cytochrome b(558) occurs in neutrophilic granulocytes. Control measurements with cytochrome b(558)-deficient neutrophilic granulocytes did not show a reduction of intracellular MPO. This is direct support for the occurrence of intracellular NADPH-oxidase activity in organelles that must be in close contact with the azurophilic granules that contain MPO. Furthermore, a comparison was made with chemical reactions occurring in eosinophilic granulocytes after activation with PMA. Moreover, in these cells an intracellular reduction of eosinophil peroxidase was observed.
Insights
New evidence shows intracellular NADPH-oxidase activity in granulocytes after phorbol myristate acetate (PMA) stimulation. Raman microspectroscopy directly confirms intracellular reactions, supporting NADPH-oxidase activity within these cells.
Area of Science:
- Cellular Biology
- Immunology
- Biochemistry
Background:
- Neutrophilic and eosinophilic granulocytes play key roles in immune responses.
- NADPH-oxidase activity is crucial for producing reactive oxygen species (ROS) in phagocytes.
- Previous studies suggested extracellular NADPH-oxidase activity, but intracellular mechanisms remained unclear.
Purpose of the Study:
- To directly investigate intracellular NADPH-oxidase activity in granulocytes using Raman microspectroscopy.
- To elucidate the subcellular localization and molecular events associated with NADPH-oxidase activation by phorbol myristate acetate (PMA).
- To compare intracellular reactions in neutrophilic and eosinophilic granulocytes following PMA stimulation.
Main Methods:
- Raman microspectroscopy was employed as a direct, molecularly specific method to analyze intracellular reactions.
- Phorbol myristate acetate (PMA) was used to stimulate neutrophilic and eosinophilic granulocytes.
- Control experiments were performed using cytochrome b(558)-deficient neutrophilic granulocytes.
Main Results:
- Direct evidence for intracellular reduction of myeloperoxidase (MPO) and cytochrome b(558) in PMA-activated neutrophilic granulocytes was obtained.
- Intracellular MPO reduction was absent in cytochrome b(558)-deficient cells, indicating a dependence on this component.
- Intracellular reduction of eosinophil peroxidase was observed in PMA-activated eosinophilic granulocytes.
Conclusions:
- The study provides direct evidence for intracellular NADPH-oxidase activity in both neutrophilic and eosinophilic granulocytes.
- Intracellular NADPH-oxidase activity appears to occur in organelles in close proximity to azurophilic granules containing MPO.
- These findings challenge previous assumptions and highlight the importance of intracellular ROS production in granulocyte function.