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James C Tan, Jose Gonzalez, MinHee K. Ko, Andrius Masedunskas, Roberto Weigert, Young Hong; Contractile features of the distal aqueous drainage tract. Invest. Ophthalmol. Vis. Sci. 2017;58(8):3771.
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Outflow resistance in the aqueous drainage tract distal to trabecular meshwork (TM) is potentially an important determinant of intraocular pressure (IOP). It may also influence the success of treatments and surgeries directing aqueous into the distal system. Mechanisms controlling distal resistance are unclear. We hypothesize that contractility is a mechanism influencing aqueous vessel caliber and resistance in analogous fashion to its role in controlling blood vessel tone.
We determined if cells with a smooth muscle identity populate the distal aqueous vessel walls. 2-photon imaging was performed of live and postmortem mouse eyes. Transgenic reporter mice expressing a fluorescent endothelial marker (Prox1) and wild-type control mice were studied as models of the human system. Hoechst 33342-nuclear staining and F-actin labeling with fluorescence-conjugated phalloidin were used to characterize the cellularity of the cells lining aqueous vessels.
We imaged deep in the sclera to identify distal aqueous vessels. Aqueous vessels appeared as second harmonic generation signal voids amongst the scleral collagen fibers. Vessels and their cells were tracked from episcleral veins to their origins in Schlemm’s Canal. The Prox1 reporter revealed that endothelium was present in the outer wall of Schlemm’s Canal, collector channels and the proximal regions of aqueous vessels. Two distinct cells layers were identified surrounding the lumen of aqueous vessels: (1) endothelium immediately bordered the lumen of aqueous vessels and (2) external to endothelium were cells in a contracted state that expressed smooth muscle markers (eg., alpha smooth muscle actin) in a profile similar to that of arterial walls and ciliary muscle.
Our findings support an organization of aqueous vessel walls resembling that of blood vessels. A central lumen lined by endothelium is surrounded by cells with contractile features bearing a smooth muscle identity. This reflects a capacity to contract and could support dynamic alteration of aqueous vessel caliber and resistance analogous to the role of vascular tone in regulating blood flow.
This is an abstract that was submitted for the 2017 ARVO Annual Meeting, held in Baltimore, MD, May 7-11, 2017.
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