Na-K-Cl cotransport regulates intracellular volume and monolayer permeability of trabecular meshwork cells

1995 ◽  
Vol 268 (4) ◽  
pp. C1067-C1074 ◽  
Author(s):  
M. E. O'Donnell ◽  
J. D. Brandt ◽  
F. R. Curry
Keyword(s):  
Trabecular Meshwork ◽  
Ethacrynic Acid ◽  
Vascular Endothelial Cells ◽  
Critical Role ◽  
Cell Types ◽  
Cell Monolayers ◽  
Aqueous Humor Outflow ◽  
Trabecular Meshwork Cells ◽  
Intracellular Volume ◽  
Underlying Mechanisms

The trabecular meshwork (TM) of the eye plays a critical role in modulating intraocular pressure (IOP) through regulation of aqueous humor outflow, although the underlying mechanisms remain unknown. Ethacrynic acid, an agent known to inhibit Na-K-Cl cotransport of a number of cell types, recently has been reported to increase aqueous outflow and lower IOP through an unknown effect on the TM. In vascular endothelial cells and a variety of other cell types, the Na-K-Cl cotransporter functions to regulate intracellular volume. The present study was conducted to evaluate TM cells for the presence of Na-K-Cl cotransport activity and to test the hypothesis that modulation of cotransport activity alters intracellular volume and, consequently, permeability of the TM. We demonstrate here that bovine and human TM cells exhibit robust Na-K-Cl cotransport activity that is inhibited by bumetanide and by ethacrynic acid. Our studies also show that TM cell Na-K-Cl cotransport is modulated by a variety of hormones and neurotransmitters. Inhibition of the cotransporter either by bumetanide, ethacrynic acid, or inhibitory hormones reduces TM intracellular volume, whereas stimulatory hormones increase cell volume. In addition, shrinkage of the cells by hypertonic media stimulates cotransport activity and initiates a subsequent regulatory volume increase. Permeability of TM cell monolayers, assessed as transmonolayer flux of [14C]sucrose, is increased by hypertonicity-induced cell shrinkage and by bumetanide. These findings suggest that Na-K-Cl cotransport of TM cells is of central importance to regulation of intracellular volume and TM permeability. Defects of Na-K-Cl cotransport may underlie the pathophysiology of glaucoma.

Intracellular Cl regulates Na-K-Cl cotransport activity in human trabecular meshwork cells

1999 ◽  
Vol 277 (3) ◽  
pp. C373-C383 ◽  
Author(s):  
Luanna K. Putney ◽  
Cecile Rose T. Vibat ◽  
Martha E. O’Donnell
Keyword(s):  
Cell Volume ◽  
Aqueous Humor ◽  
Trabecular Meshwork ◽  
Cell Types ◽  
Cellular Mechanisms ◽  
Outflow Facility ◽  
Aqueous Humor Outflow ◽  
Trabecular Meshwork Cells ◽  
Cotransport System ◽  
Stimulation Of

The trabecular meshwork (TM) of the eye plays a central role in modulating intraocular pressure by regulating aqueous humor outflow, although the mechanisms are largely unknown. We and others have shown previously that aqueous humor outflow facility is modulated by conditions that alter TM cell volume. We have also shown that the Na-K-Cl cotransport system is a primary regulator of TM cell volume and that its activity appears to be coordinated with net efflux pathways to maintain steady-state volume. However, the cellular mechanisms that regulate cotransport activity and cell volume in TM cells have yet to be elucidated. The present study was conducted to investigate the hypothesis that intracellular Cl concentration ([Cl]i) acts to regulate TM cell Na-K-Cl cotransport activity, as has been shown previously for some other cell types. We demonstrate here that the human TM cell Na-K-Cl cotransporter is highly sensitive to changes in [Cl]i. Our findings reveal a marked stimulation of Na-K-Cl cotransport activity, assessed as ouabain-insensitive, bumetanide-sensitive K influx, in TM cells following preincubation of cells with Cl-free medium as a means of reducing [Cl]i. In contrast, preincubation of cells with media containing elevated K concentrations as a means of increasing [Cl]i results in inhibition of Na-K-Cl cotransport activity. The effects of reducing [Cl]i, as well as elevating [Cl]i, on Na-K-Cl cotransport activity are concentration dependent. Furthermore, the stimulatory effect of reduced [Cl]i is additive with cell-shrinkage-induced stimulation of the cotransporter. Our studies also show that TM cell Na-K-Cl cotransport activity is altered by a variety of Cl channel modulators, presumably through changes in [Cl]i. These findings support the hypothesis that regulation of Na-K-Cl cotransport activity, and thus cell volume, by [Cl]i may participate in modulating outflow facility across the TM.

scholarly journals Optogenetic stimulation of phosphoinositides reveals a critical role of primary cilia in eye pressure regulation

2020 ◽  
Vol 6 (18) ◽  
pp. eaay8699
Author(s):  
Philipp P. Prosseda ◽  
Jorge A. Alvarado ◽  
Biao Wang ◽  
Tia J. Kowal ◽  
Ke Ning ◽  
...  
Keyword(s):  
Aqueous Humor ◽  
Primary Cilia ◽  
Vision Loss ◽  
Critical Role ◽  
Calcium Dependent ◽  
Aqueous Humor Outflow ◽  
Trabecular Meshwork Cells ◽  
Eye Pressure ◽  
Stimulation Of

Glaucoma is a group of progressive optic neuropathies that cause irreversible vision loss. Although elevated intraocular pressure (IOP) is associated with the development and progression of glaucoma, the mechanisms for its regulation are not well understood. Here, we have designed CIBN/CRY2-based optogenetic constructs to study phosphoinositide regulation within distinct subcellular compartments. We show that stimulation of CRY2-OCRL, an inositol 5-phosphatase, increases aqueous humor outflow and lowers IOP in vivo, which is caused by a calcium-dependent actin rearrangement of the trabecular meshwork cells. Phosphoinositide stimulation also rescues defective aqueous outflow and IOP in a Lowe syndrome mouse model but not in IFT88fl/fl mice that lack functional cilia. Thus, our study is the first to use optogenetics to regulate eye pressure and demonstrate that tight regulation of phosphoinositides is critical for aqueous humor homeostasis in both normal and diseased eyes.

scholarly journals Primary cilia and the reciprocal activation of AKT and SMAD2/3 regulate stretch-induced autophagy in trabecular meshwork cells

2021 ◽  
Vol 118 (13) ◽  
pp. e2021942118
Author(s):  
Myoung Sup Shim ◽  
April Nettesheim ◽  
Angela Dixon ◽  
Paloma B. Liton
Keyword(s):  
Trabecular Meshwork ◽  
Primary Cilia ◽  
Molecular Mechanisms ◽  
Ex Vivo ◽  
Mechanical Stretch ◽  
Cell Types ◽  
Elevated Pressure ◽  
Compensatory Response ◽  
Protein Levels ◽  
Trabecular Meshwork Cells

Activation of autophagy is one of the responses elicited by high intraocular pressure (IOP) and mechanical stretch in trabecular meshwork (TM) cells. However, the mechanosensor and the molecular mechanisms by which autophagy is induced by mechanical stretch in these or other cell types is largely unknown. Here, we have investigated the mechanosensor and downstream signaling pathway that regulate cyclic mechanical stretch (CMS)-induced autophagy in TM cells. We report that primary cilia act as a mechanosensor for CMS-induced autophagy and identified a cross-regulatory talk between AKT1 and noncanonical SMAD2/3 signaling as critical components of primary cilia-mediated activation of autophagy by mechanical stretch. Furthermore, we demonstrated the physiological significance of our findings in ex vivo perfused eyes. Removal of primary cilia disrupted the homeostatic IOP compensatory response and prevented the increase in LC3-II protein levels in response to elevated pressure challenge, strongly supporting a role of primary cilia-mediated autophagy in regulating IOP homeostasis.

scholarly journals Mechanisms of ATP release by human trabecular meshwork cells, the enabling step in purinergic regulation of aqueous humor outflow

2011 ◽  
Vol 227 (1) ◽  
pp. 172-182 ◽  
Author(s):  
Ang Li ◽  
Chi Ting Leung ◽  
Kim Peterson-Yantorno ◽  
W. Daniel Stamer ◽  
Claire H. Mitchell ◽  
...  
Keyword(s):  
Aqueous Humor ◽  
Trabecular Meshwork ◽  
Atp Release ◽  
Aqueous Humor Outflow ◽  
Trabecular Meshwork Cells

scholarly journals Role of MCP-1 and IL-8 in viral anterior uveitis, and contractility and fibrogenic activity of trabecular meshwork cells

2021 ◽  
Vol 11 (1) ◽  
Author(s):  
Jiyoung Lee ◽  
Jin A. Choi ◽  
Hyun-hee Ju ◽  
Ju-Eun Kim ◽  
Soon-Young Paik ◽  
...  
Keyword(s):  
Viral Infection ◽  
Aqueous Humor ◽  
Trabecular Meshwork ◽  
Anterior Uveitis ◽  
Rho Gtpase ◽  
Open Angle Glaucoma ◽  
Focal Adhesions ◽  
Aqueous Humor Outflow ◽  
Trabecular Meshwork Cells ◽  
Aqueous Outflow

AbstractThe inflammatory chemokines, monocyte chemoattractant protein (MCP)-1 and IL-8, are produced by normal trabecular meshwork cells (TM) and elevated in the aqueous humor of primary open angle glaucoma (POAG) and hypertensive anterior uveitis associated with viral infection. However, their role in TM cells and aqueous humor outflow remains unclear. Here, we explored the possible involvement of MCP-1 and IL-8 in the physiology of TM cells in the context of aqueous outflow, and the viral anterior uveitis. We found that the stimulation of human TM cells with MCP-1 and IL-8 induced significant increase in the formation of actin stress fibers and focal adhesions, myosin light chain phosphorylation, and the contraction of TM cells. MCP-1 and IL-8 also demonstrated elevation of extracellular matrix proteins, and the migration of TM cells. When TM cells were infected with HSV-1 and CMV virus, there was a significant increase in cytoskeletal contraction and Rho-GTPase activation. Viral infection of TM cells revealed significantly increased expression of MCP-1 and IL-8. Taken together, these results indicate that MCP-1 and IL-8 induce TM cell contractibility, fibrogenic activity, and plasticity, which are presumed to increase resistance to aqueous outflow in viral anterior uveitis and POAG.

scholarly journals New Insights Into Pathophysiological Mechanisms Regulating Conventional Aqueous Humor Outflow

Medicina ◽  
2013 ◽  
Vol 49 (4) ◽  
pp. 26 ◽  
Author(s):  
Daiva Paulavičiūtė-Baikštienė ◽  
Rūta Baršauskaitė ◽  
Ingrida Janulevičienė
Keyword(s):  
Intraocular Pressure ◽  
Aqueous Humor ◽  
Trabecular Meshwork ◽  
Kinase Inhibitors ◽  
Transforming Growth Factor ◽  
Protein Kinase Inhibitors ◽  
Pathophysiological Mechanisms ◽  
Aqueous Humor Outflow ◽  
Trabecular Meshwork Cells ◽  
Glaucoma Treatment

The aim of the article was to overview the pathophysiology of the conventional outflow pathway, trabecular meshwork, and intraocular pressure and to discuss the options of future glaucoma treatment directed to improvement in aqueous outflow. The literature search in the Medline, Embase, and Cochrane databases from April to May 2012 was performed; a total of 47 articles analyzed. The diminished conventional pathway may be altered by several pathophysiological mechanisms like TM obstruction caused by transforming growth factor-β2, clastic nondeformable cells, macrophages leaking from hypermature cataract, iris pigment, lens capsular fragments after YAG-laser posterior capsulotomy, proteins and their subfragments. It is known that trabecular meshwork contraction reduces outflow, and the actomyosin system is directly linked to this mechanism. New glaucoma drugs are still under investigation, but it is already proven that agents such as latranculin-B are effective in improving aqueous drainage. Selective Rho-associated coiled coilforming protein kinase inhibitors have been shown to cause a significant improvement in outflow facility and may become a new option for glaucoma treatment. Caldesmon negatively regulates actin-myosin interactions and thus increases outflow. Stem cells may replace missing or nonfunctional trabecular meshwork cells and hopefully will bring a new treatment solution. Pathophysiological mechanisms regulating conventional aqueous humor outflow are still not fully understood and require further investigations. Future treatment decisions should be directed to a specific mechanism regulating an elevation in intraocular pressure.

scholarly journals Dexamethasone Downregulates Autophagy through Accelerated Turn-Over of the Ulk-1 Complex in a Trabecular Meshwork Cells Strain: Insights on Steroid-Induced Glaucoma Pathogenesis

2021 ◽  
Vol 22 (11) ◽  
pp. 5891
Author(s):  
Diego Sbardella ◽  
Grazia Raffaella Tundo ◽  
Massimo Coletta ◽  
Gianluca Manni ◽  
Francesco Oddone
Keyword(s):  
Trabecular Meshwork ◽  
Pathological Condition ◽  
Anterior Segment ◽  
Cell Types ◽  
Ubiquitin Proteasome System ◽  
Progressive Increase ◽  
Trabecular Meshwork Cells ◽  
Metabolic Dysregulation ◽  
Autophagy Induction ◽  
Turn Over

Steroid-induced glaucoma is a severe pathological condition, sustained by a rapidly progressive increase in intraocular pressure (IOP), which is diagnosed in a subset of subjects who adhere to a glucocorticoid (GC)-based therapy. Molecular and clinical studies suggest that either natural or synthetic GCs induce a severe metabolic dysregulation of Trabecular Meshwork Cells (TMCs), an endothelial-derived histotype with phagocytic and secretive functions which lay at the iridocorneal angle in the anterior segment of the eye. Since TMCs physiologically regulate the composition and architecture of trabecular meshwork (TM), which is the main outflow pathway of aqueous humor, a fluid which shapes the eye globe and nourishes the lining cell types, GCs are supposed to trigger a pathological remodeling of the TM, inducing an IOP increase and retina mechanical compression. The metabolic dysregulation of TMCs induced by GCs exposure has never been characterized at the molecular detail. Herein, we report that, upon dexamethasone exposure, a TMCs strain develops a marked inhibition of the autophagosome biogenesis pathway through an enhanced turnover of two members of the Ulk-1 complex, the main platform for autophagy induction, through the Ubiquitin Proteasome System (UPS).

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