Expressional and functional involvement of gap junctions in aqueous humor outflow into the ocular trabecular meshwork of the anterior chamber

PURPOSE: The ocular trabecular meshwork (TM) responsible for aqueous humor (AH) drainage is crucial for regulating intraocular pressure (IOP) of the eye. An IOP elevation that causes distended TM is involved in the pathogenesis of glaucoma, suggesting intercellular connections important for the TM pathophysiology. The goal of this study was to examine whether gap junction proteins between endothelial cells in the TM are expressional and functional. METHODS: The expression levels of the gap junction channels in normal human TM cells were determined with real-time PCR and western blot assays. Immunohistochemistry (IHC) staining was performed to examine the localization of gap junction proteins in normal human TM cells and tissues. IOP and the outflow of AH were measured after intercameral injection of gap junction blockers in C57/BL6 mice. RESULTS: Gap junction proteins GJA1, GJA8, GJB6, and GJC1 were robustly expressed in human TM cells from three individuals. Among the four gap junction channels, GJA1 and GJA8 exhibited the most abundance in the TM. The IHC analysis further confirmed that these proteins were expressed on the membrane between adjacent cells. In the human TM tissues, GJA1, GJA8, GJB6, and GJC1 were also observed along the trabecular beams. Inhibition of gap junctions with intracameral injection of blockers resulted in a statistically significant increase in aqueous humor outflow resistance and IOP elevation in mice. CONCLUSIONS: The GJA1 and GJA8 gap junction proteins, in particular, are robustly expressed in human TM cells and tissues. Pharmacological inhibition of gap junction channels causes an increased resistance of AH outflow and an elevation of IOP in mice. The present findings suggest the functional role of gap junction channels for regulation of AH outflow in the TM, and activation of gap junctions might represent a therapeutic strategy for treatment of glaucoma.