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Ultrastructural immunolocalization of basic fibroblast growth factor in mast cell secretory granules. Morphological
1Oregon Health Sciences University, Casey Eye Institute, Portland, Oregon, USA.
Abstract:
We previously reported that mast cells (MCs) serve as a source of basic fibroblast growth factor (bFGF), a potent angiogenic and mitogenic polypeptide, suggesting that bFGF may mediate MC-related neovascularization and fibroproliferation. Unlike many other growth factors, bFGF lacks a classic peptide sequence for its secretion, and the mechanism(s) for its release remains controversial. Because MCs release a wide spectrum of bioactive products via degranulation, we hypothesized that MC degranulation may be a mechanism of bFGF release and used ultrastructural immunohistochemistry to test the hypothesis. We reasoned that if bFGF is released through degranulation, it should be localized to MC secretory granules. Human tissues with chronic inflammation and rat/mouse tissues with anaphylaxis were studied. In all tissue samples examined, positive staining (or immunogold particle localization) for bFGF in MCs was predominantly in the cytoplasmic granules. Moderate bFGF immunoreactivity was also found in the nucleus, whereas the cytosol and other subcellular organelles exhibited minimal immunogold particle localization. In contrast, no immunogold particle localization for bFGF was observed in lymphocytes or plasma cells. In rat/mouse lingual tissue undergoing anaphylaxis, immunogold particle localization for bFGF was found not only in swollen cytoplasmic granules but also in the extruded granules of MCs. Three different anti-bFGF antibodies gave similar immunogold particle localization patterns, whereas all controls were negative. These results provide morphological evidence suggesting that, despite the lack of a classic secretory peptide in its structure, bFGF is localized to the secretory granules in MCs and may be released through degranulation.
Insights
Mast cells (MCs) release basic fibroblast growth factor (bFGF) through degranulation. Ultrastructural immunohistochemistry confirmed bFGF is stored in MC secretory granules, supporting this release mechanism.
Area of Science:
- Immunology
- Cell Biology
- Histology
Background:
- Mast cells (MCs) are known sources of basic fibroblast growth factor (bFGF).
- The secretion mechanism of bFGF is unclear due to its lack of a classic secretion signal sequence.
- MCs release various bioactive molecules via degranulation.
Purpose of the Study:
- To investigate if mast cell degranulation is a mechanism for releasing basic fibroblast growth factor (bFGF).
- To determine the subcellular localization of bFGF within mast cells.
Main Methods:
- Ultrastructural immunohistochemistry was employed to examine bFGF localization in MCs.
- Human tissues with chronic inflammation and rat/mouse tissues with anaphylaxis were analyzed.
- Immunogold particle localization was used to identify bFGF in MCs and other cells.
Main Results:
- Basic fibroblast growth factor (bFGF) was predominantly localized to the cytoplasmic granules of mast cells (MCs).
- Moderate bFGF immunoreactivity was observed in the nucleus, with minimal presence in the cytosol.
- In anaphylaxis models, bFGF was found in both extruded and swollen cytoplasmic granules of MCs.
- No bFGF localization was detected in lymphocytes or plasma cells.
Conclusions:
- Morphological evidence suggests bFGF is stored in mast cell secretory granules.
- Mast cell degranulation is a likely mechanism for the release of bFGF.
- This finding clarifies a controversial aspect of bFGF secretion, linking it to mast cell biology.