Functional impairment of TRPV4-eNOS signaling in glaucomatous trabecular meshwork contributes to elevation of intraocular pressure.

Purpose: Nitric oxide (NO) is known to reduce intraocular pressure (IOP) by relaxation of the trabecular meshwork (TM). However, the intrinsic mechanism regulating NO production in the TM is yet to be elucidated. Here, we examined whether transient receptor potential vanilloid 4 (TRPV4) channels regulate IOP via endothelial nitic oxide synthase (eNOS) signaling. We also assess whether TRPV4-eNOS signaling is impaired in glaucoma. Methods: In WT C57BL/6J mice, the effect of the TRPV4 agonist GSK1016790A (GSK101) on IOP and outflow facility was determined using rebound tonometry and constant-flow infusion method, respectively. The effect of GSK101 on eNOS activation and NO production was determined using Western blot and a fluorometric DAF-FM assay in normal and glaucomatous primary human TM cells. We further examined whether TRPV4 channel function is impaired in glaucoma using high-speed Calcium imaging in normal and glaucomatous human primary TM cells. Results: Topical administration of GSK101 (20 µM) significantly improved outflow facility (P=0.05) and reduced IOP (P< 0.0001) in WT mice. GSK101 (20 nM) treatment resulted in increased eNOS phosphorylation in primary human TM cells and donor tissues. GSK101 treatment also resulted in increased DAF-FM fluorescence, which signifies an increase in NO production. Importantly, human glaucomatous primary TM cells exhibited significantly attenuated Calcium influx, eNOS phosphorylation, and NO production in response to GSK101 when compared to normal human primary TM cells. Conclusion: TRPV4 channel activation lowers IOP by regulating NO in the TM. Functional impairment of these channels may contribute to glaucomatous pathophysiology.