Comparative Genomic and Proteomic Analysis of Cytoskeletal Changes in Dexamethasone-Treated Trabecular Meshwork Cells

Abstract

Steroid-induced glaucoma is an iatrogenic condition resulting from the use of glucocorticoids. Glucocorticoids such as dexamethasone (DEX) 1 raise intraocular pressure (IOP) in ϳ40% of patients in the general population, and ϳ6% of these patients will go on to develop glaucoma (1, 2). This condition is similar to primary open angle glaucoma (1-3), and is caused by a restriction in fluid outflow through the trabecular meshwork (TM), resulting in an imbalance between the amount of aqueous humor produced and the amount drained. This imbalance results in a higher IOP.It is thought that an alteration in the cytoskeletal structure or contractile properties of TM cells may result in the disruption of normal fluid flow. In support of this idea, cross-linked actin networks, referred to as CLANs, have been observed with increased frequency in the TM of glaucomatous patients and in glucocorticoid treated anterior segments as well as in TM cells in culture. CLANs are thought to alter the contractility of the TM by holding the cells in a rigid conformation, making the cells unresponsive to the change in pressure and blocking the aqueous humor outflow pathway (1,4,5). Thus, agents such as H7 and the latrunculins A and B, which disrupt the organization of the cytoskeleton, decrease IOP in porcine and monkey cultured anterior segments (6 -9).Control of the actin cytoskeleton is mediated by the Rho family of small GTPases. The Rho effector ROCK has been shown to play a part in TM contractility and modulation of IOP. Inhibition of ROCK using a dominant negative mutant or the inhibitor Y-27632 causes TM cells to "relax" by decreasing actin stress fiber formation and phosphorylation of myosin light chain (MLC) (10, 11). ROCK inhibition also decreases IOP in cultured human and porcine anterior segments (10, 11). In contrast, constitutively active RhoA (RhoA V14) increases From the ‡Departments

Activated αvβ3 Integrin Regulates αvβ5 Integrin–Mediated Phagocytosis in Trabecular Meshwork Cells

“…We then investigated whether the level of activated avb3 integrin was also increased in DEX-treated cells, since our previous studies have shown that DEX treatment not only upregulates the expression of avb3 integrin, but it causes an increase in its activation state. 19,20,32,33 Not surprisingly, both total and activated levels of avb3 integrin were increased in DEX-treated HTM cells compared with untreated (Figs. 7A, 7B) and EtOHtreated cells (Figs.…”

“…51,52 Interestingly, a number of the molecules that could control the activity of avb5 and avb3 integrin signaling events have been reported to be upregulated in DEX treated TM cells. 32 Among them are filamin-B, caveolin-1, talin-1, paxillin, Src, and EPS8. Upregulation of caveolin-1 is particularly interesting since it has been reported to be a risk factor in glaucoma, [53][54][55] suggesting that alterations in caveolin-1/integrin signaling pathways could be involved in some glaucomas.…”

Cellular softening mediates leukocyte demargination and trafficking, thereby increasing clinical blood counts

“…S6). Previous studies in other cell types have shown that activation of glucocorticoid receptors and adrenergic receptors (i.e., catecholamine receptors) leads to downstream rearrangements of cytoskeletal actin via multiple pathways including SGK1, ERK, RhoA/ROCK1, and cAMPdependent protein kinase A signaling (26)(27)(28)(29)(30)(31), providing candidate pathways that could provide further insight into our observed phenomenon. Of note, erythrocyte exposure to dexamethasone or epinephrine revealed no measurable changes in red cell concentration (i.e., no aggregation), size, shape, deformability, or margination (Figs.…”

Intraocular Pressure Regulation: Findings of Pulse-Dependent Trabecular Meshwork Motion Lead to Unifying Concepts of Intraocular Pressure Homeostasis

“…2,27 Studies implicate changes in cell and ECM stiffness as probable factors in the glaucoma process. 8,28,29 Recent elastic modulus determination in normal and glaucoma conditions [30][31][32] has indicated a relationship between increased TM tissue stiffness and open angle glaucoma, a change also identified in clinical studies. 7,33,34 Recognition of the Importance of Trabecular Tissue Motion Morton Grant can be credited with initiating the first studies to characterize TM motion.…”