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The role of calcium-independent phospholipase A2? in modulation of aqueous humor drainage and Ca2+ sensitization of trabecular meshwork contraction.

ABSTRACT: The contractile and relaxation characteristics of trabecular meshwork (TM) are presumed to influence aqueous humor (AH) drainage and intraocular pressure. The mechanisms underlying regulation of TM cell contractile properties, however, are not well understood. This study investigates the role of calcium-independent phospholipase A(2) (iPLA(2)), which controls eicosanoid synthesis, in regulation of TM cell contraction and AH outflow using mechanism-based isoform specific inhibitors (R)-bromoenol lactone (R-BEL, iPLA(2)? specific) and (S)-bromoenol lactone (S-BEL, iPLA(2)? specific). Immunohistochemical analysis revealed intense staining for both iPLA(2)? and ? isoforms throughout the TM, juxtacanalicular tissue, and Schlemm's canal of human eye. Inhibition of iPLA(2)? by R-BEL or small interfering RNA-mediated silencing of iPLA(2)? expression induced dramatic changes in TM cell morphology, and decreased actin stress fibers, focal adhesions, and myosin light-chain (MLC) phosphorylation. AH outflow facility increased progressively and significantly in enucleated porcine eyes perfused with R-BEL. This response was associated with a significant decrease in TM tissue MLC phosphorylation and alterations in the morphology of aqueous plexi in R-BEL-perfused eyes. In contrast, S-BEL did not affect either of these parameters. Additionally, R-BEL-induced cellular relaxation of the TM was associated with a significant decrease in the levels of active Rho GTPase, phospho-MLC phosphatase, phospho-CPI-17, and arachidonic acid. Taken together, these observations demonstrate that iPLA(2)? plays a significant and isoform-specific role in regulation of AH outflow facility by altering the contractile characteristics of the TM. The effects of iPLA(2)? on TM contractile status appear to involve arachidonic acid and Rho GTPase signaling pathways.

SUBMITTER: Pattabiraman PP

PROVIDER: S-EPMC3330734 | biostudies-literature | 2012 Apr

REPOSITORIES: biostudies-literature

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The role of calcium-independent phospholipase A2γ in modulation of aqueous humor drainage and Ca2+ sensitization of trabecular meshwork contraction.

Pattabiraman Padmanabhan P PP Lih Fred B FB Tomer Kenneth B KB Rao Ponugoti Vasantha PV

American journal of physiology. Cell physiology 20120111 7

The contractile and relaxation characteristics of trabecular meshwork (TM) are presumed to influence aqueous humor (AH) drainage and intraocular pressure. The mechanisms underlying regulation of TM cell contractile properties, however, are not well understood. This study investigates the role of calcium-independent phospholipase A(2) (iPLA(2)), which controls eicosanoid synthesis, in regulation of TM cell contraction and AH outflow using mechanism-based isoform specific inhibitors (R)-bromoenol ...[more]

PMID: 22237407

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Project description:Key pointsTrabecular meshwork (TM) is a highly mechanosensitive tissue in the eye that regulates intraocular pressure through the control of aqueous humour drainage. Its dysfunction underlies the progression of glaucoma but neither the mechanisms through which TM cells sense pressure nor their role in aqueous humour outflow are understood at the molecular level. We identified the Piezo1 channel as a key TM transducer of tensile stretch, shear flow and pressure. Its activation resulted in intracellular signals that altered organization of the cytoskeleton and cell-extracellular matrix contacts and modulated the trabecular component of aqueous outflow whereas another channel, TRPV4, mediated a delayed mechanoresponse. This study helps elucidate basic mechanotransduction properties that may contribute to intraocular pressure regulation in the vertebrate eye.AbstractChronic elevations in intraocular pressure (IOP) can cause blindness by compromising the function of trabecular meshwork (TM) cells in the anterior eye, but how these cells sense and transduce pressure stimuli is poorly understood. Here, we demonstrate functional expression of two mechanically activated channels in human TM cells. Pressure-induced cell stretch evoked a rapid increase in transmembrane current that was inhibited by antagonists of the mechanogated channel Piezo1, Ruthenium Red and GsMTx4, and attenuated in Piezo1-deficient cells. The majority of TM cells exhibited a delayed stretch-activated current that was mediated independently of Piezo1 by TRPV4 (transient receptor potential cation channel, subfamily V, member 4) channels. Piezo1 functions as the principal TM transducer of physiological levels of shear stress, with both shear and the Piezo1 agonist Yoda1 increasing the number of focal cell-matrix contacts. Analysis of TM-dependent fluid drainage from the anterior eye showed significant inhibition by GsMTx4. Collectively, these results suggest that TM mechanosensitivity utilizes kinetically, regulatory and functionally distinct pressure transducers to inform the cells about force-sensing contexts. Piezo1-dependent control of shear flow sensing, calcium homeostasis, cytoskeletal dynamics and pressure-dependent outflow suggests potential for a novel therapeutic target in treating glaucoma.

Dataset Information

The role of calcium-independent phospholipase A2? in modulation of aqueous humor drainage and Ca2+ sensitization of trabecular meshwork contraction.

Publications

The role of calcium-independent phospholipase A2γ in modulation of aqueous humor drainage and Ca2+ sensitization of trabecular meshwork contraction.

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