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Leonie Herrnberger, Kathrin Ebner, Margit Schimmel, Ernst R. Tamm; First Molecular Insights Into The Mechanisms Of Intracellular Pore Formation In Schlemm`s Canal Endothelium. Invest. Ophthalmol. Vis. Sci. 2011;52(14):6621.
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The transient formation of micron-size intracellular (i)-pores is a characteristic of Schlemm’s canal (SC) endothelium which is regarded as critical for aqueous humor outflow. The molecular mechanisms of i-pore formation are completely unknown. We hypothesized that i-pores originate from endothelial structures covered with a thin non-membranous diaphragm such as diaphragmed caveolae (DC), fenestrae (DF) and transendothelial channels (DTC). We investigated by transmission electron microscopy (TEM), if such structures preferentially localize to those parts of the SC endothelium that form giant vacuoles indicating flow of aqueous humor. In addition, we studied by immunohistochemistry the presence of plasmalemmal vesicle associated protein-1 (PV-1), an essential molecule for diaphragm formation in DC, DF, and DTC.
Mouse eyes were fixed by anterior chamber perfusion and the circumference of SC endothelium was studied on frontal sections by TEM. Immunoreactivity for PV-1 was analyzed by immunohistochemistry and confocal microscopy on fresh frozen sections. Double-staining experiments were performed with antibodies against the endothelial marker CD-31.
Strong immunoreactivity for PV-1 was observed in both inner and outer wall of the circumferential mouse SC, and in the endothelial wall of collector channels. In addition, capillaries that form DF such as those in choroid and ciliary body were intensely labeled. In contrast, positive staining was neither observed in non-fenestrated capillaries such as in those of iris and retina nor in control sections without primary antibody. Staining for PV-1 entirely overlapped with that of CD-31. No staining for CD-31 was seen in trabecular meshwork cells. DC, DF, and DTC as well as i-pores were observed frequently in those areas of SC endothelium forming giant vacuoles.
DC, DF, and DTC are associated with i-pore formation. PV-1 is the first molecular target to experimentally study the formation of i-pores and to shed more light on the role of SC endothelium for aqueous humor outflow in the mammalian eye.
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