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Enzyme histochemical studies of membrane proteases in rat subfornical organ
1Department of Pathology, University of Oklahoma Health Sciences Center Oklahoma City 73190.
Abstract:
Localization of membrane proteases glutamyl aminopeptidase (EAP), microsomal alanyl aminopeptidase (mAAP), dipeptidyl peptidase IV (DPP IV) and gamma-glutamyl transpeptidase (gamma-GTP) were studied in vessels of the rat subfornical organ (SFO), ependyma which cover the surface of the SFO, and adjacent brain structures. Results of enzyme histochemical reactions showed strong activity for EAP, mAAP, and gamma-GTP, but absence of DPP IV in microvessels of SFO. The ependyma which cover the SFO was positive for gamma-GTP, but negative for other studied proteases. Our results showed that the spectrum of enzymes in the majority of the vessels of SFO is similar to that of the microvessels of the adjacent brain tissue which were positive for EAP, mAAP, and gamma-GTP, but negative for DPP IV. The relative intensity of the enzyme reactions in vessels varied from central to lateral locations in the SFO and the adjacent brain tissue. There was also a difference in the relative reaction intensity from one enzyme to the other. The presence and heterogeneous distribution of the enzymes are consistent with the hypothesis that membrane proteases of the microvascular endothelium constitute an enzyme-barrier between blood and parenchyma of the SFO and between blood and brain tissue, and may be involved in metabolism or modulation of various peptides when they contact the plasma membrane of the endothelial cells of the vessels.
Insights
Membrane proteases like glutamyl aminopeptidase were found in rat subfornical organ microvessels, suggesting an enzyme barrier. This barrier may regulate peptides interacting with endothelial cells.
Area of Science:
- Neuroscience
- Biochemistry
- Histology
Background:
- The subfornical organ (SFO) is a circumventricular organ crucial for regulating body fluid homeostasis.
- Understanding the microvascular environment of the SFO is key to deciphering its function.
- Membrane proteases play roles in peptide metabolism and signaling at the blood-brain interface.
Purpose of the Study:
- To investigate the localization of specific membrane proteases in the rat SFO microvasculature.
- To compare enzyme distribution in the SFO with adjacent brain tissue.
- To explore the potential role of these enzymes as an endothelial barrier.
Main Methods:
- Enzyme histochemistry was used to detect glutamyl aminopeptidase (EAP), microsomal alanyl aminopeptidase (mAAP), dipeptidyl peptidase IV (DPP IV), and gamma-glutamyl transpeptidase (gamma-GTP).
- Localization studies were performed on microvessels of the SFO, its covering ependyma, and adjacent brain structures in rats.
Main Results:
- Strong activity of EAP, mAAP, and gamma-GTP was observed in SFO microvessels, while DPP IV was absent.
- Ependyma showed positivity for gamma-GTP but not other studied proteases.
- Enzyme distribution in SFO vessels resembled that of adjacent brain tissue, with variations in intensity across locations.
Conclusions:
- The presence and heterogeneous distribution of membrane proteases suggest an enzyme-barrier function of the SFO microvascular endothelium.
- This barrier may be involved in the metabolism or modulation of peptides at the blood-brain interface.
- The findings contribute to understanding neurovascular regulation in the SFO.