Cross-linked actin networks (CLANs) affect stiffness and/or actin dynamics in transgenic transformed and primary human trabecular meshwork cells

GSK3β Inhibitors Inhibit TGFβ Signaling in the Human Trabecular Meshwork

Purpose

Primary open-angle glaucoma (POAG) is a leading cause of blindness, and its primary risk factor is elevated intraocular pressure (IOP) due to pathologic changes in the trabecular meshwork (TM). We previously showed that there is a cross-inhibition between TGFβ and Wnt signaling pathways in the TM. In this study, we determined if activation of the Wnt signaling pathway using small-molecule Wnt activators can inhibit TGFβ2-induced TM changes and ocular hypertension (OHT).

Methods

Primary human TM (pHTM) cells and transduced SBE-GTM3 cells were treated with or without Wnt and/or TGFβ signaling activators and used for luciferase assays; for the extraction of whole-cell lysate, conditioned medium, cytosolic proteins, and nuclear proteins for Western immunoblotting (WB); or for immunofluorescent staining. Human donor eyes were perfusion cultured to study the effect of Wnt activators on IOP.

Results

We found that the small-molecule Wnt activators (GSK3β inhibitors) (BIO, SB216763, and CHIR99021) activated canonical Wnt signaling in pHTM cells without toxicity at tested concentrations. This activation inhibited TGFβ signaling as well as TGFβ2-induced extracellular matrix deposition and formation of cross-linked actin networks in pHTM cells or SBE-GTM3 cells. We also observed nuclear translocation of both Smad4 and β-catenin in pHTM cells, which suggested that the cross-inhibition between the TGFβ and Wnt signaling pathways may occur in the nucleus. Using our ex vivo model, we found that CHIR99021 inhibited TGFβ2-induced OHT in perfusion-cultured human eyes.

Conclusions

Our results showed that small-molecule Wnt activators have the potential for treating TGFβ signaling-induced OHT in patients with POAG.

Glucocorticoid-Induced Ocular Hypertension and Glaucoma

Glucocorticoid (GC) therapy is indicated in many diseases, including ocular diseases. An important side-effect of GC therapy is GC-induced ocular hypertension (GIOHT), which may cause irreversible blindness known as GC-induced glaucoma (GIG). Here, we reviewed the pathological changes that contribute to GIOHT including in the trabecular meshwork and Schlemm's canal at cellular and molecular levels. We also discussed the clinical aspects of GIOHT/GIG including disease prevalence, risk factors, the type of GCs, the route of GC administration, and management strategies.

Inhibition of TGF-β2-Induced Trabecular Meshwork Fibrosis by Pirfenidone

Purpose

Trabecular meshwork (TM) fibrosis is a crucial pathophysiological process in the development of primary open-angle glaucoma. Pirfenidone (PFD) is a new, broad-spectrum antifibrotic agent approved for the treatment of idiopathic pulmonary fibrosis. This study investigated the inhibitory effect of PFD on TM fibrosis and evaluated its efficacy in lowering intraocular pressure (IOP).

Methods

Human TM cells were isolated, cultured, and characterized. Cell Counting Kit-8 was used to evaluate the proliferation and toxicity of different concentrations of PFD on normal or fibrotic TM cells. TM cells were treated with transforming growth factor beta-2 (TGF-β2) in the absence or presence of PFD. Western blotting and immunofluorescence analyses were used to analyze changes in the TM cell cytoskeleton and extracellular matrix (ECM) proteins, including alpha-smooth muscle actin (α-SMA), F-actin, collagen IV (COL IV), and fibronectin (FN). An ocular hypertension (OHT) mouse model was induced with Ad-TGF-β2C226/228S and then treated with PFD or latanoprost (LT) eye drops to confirm the efficacy of PFD in lowering IOP.

Results

PFD inhibited the proliferation of fibrotic TM cells in a dose-dependent manner and inhibited TGF-β2-induced overexpression of α-SMA, COL IV, and FN in TM cells. PFD stabilized F-actin. In vivo, PFD eye drops reduced the IOP of the OHT models and showed no significant difference compared with LT eye drops.

Conclusions

PFD inhibited TGF-β2-induced TM cell fibrosis by rearranging the disordered cytoskeleton and decreasing ECM deposition, thereby enhancing the aqueous outflow from the TM outflow pathway and lowering IOP, which provides a potential new approach to treating glaucoma.

Translational Relevance

Our work with pirfenidone provides a new approach to treat glaucoma.

A Novel Mouse Model of TGFβ2-Induced Ocular Hypertension Using Lentiviral Gene Delivery

Glaucoma is a multifactorial disease leading to irreversible blindness. Primary open-angle glaucoma (POAG) is the most common form and is associated with the elevation of intraocular pressure (IOP). Reduced aqueous humor (AH) outflow due to trabecular meshwork (TM) dysfunction is responsible for IOP elevation in POAG. Extracellular matrix (ECM) accumulation, actin cytoskeletal reorganization, and stiffening of the TM are associated with increased outflow resistance. Transforming growth factor (TGF) β2, a profibrotic cytokine, is known to play an important role in the development of ocular hypertension (OHT) in POAG. An appropriate mouse model is critical in understanding the underlying molecular mechanism of TGFβ2-induced OHT. To achieve this, TM can be targeted with recombinant viral vectors to express a gene of interest. Lentiviruses (LV) are known for their tropism towards TM with stable transgene expression and low immunogenicity. We, therefore, developed a novel mouse model of IOP elevation using LV gene transfer of active human TGFβ2 in the TM. We developed an LV vector-encoding active hTGFβ2C226,228S under the control of a cytomegalovirus (CMV) promoter. Adult C57BL/6J mice were injected intravitreally with LV expressing null or hTGFβ2C226,228S. We observed a significant increase in IOP 3 weeks post-injection compared to control eyes with an average delta change of 3.3 mmHg. IOP stayed elevated up to 7 weeks post-injection, which correlated with a significant drop in the AH outflow facility (40.36%). Increased expression of active TGFβ2 was observed in both AH and anterior segment samples of injected mice. The morphological assessment of the mouse TM region via hematoxylin and eosin (H&E) staining and direct ophthalmoscopy examination revealed no visible signs of inflammation or other ocular abnormalities in the injected eyes. Furthermore, transduction of primary human TM cells with LV_hTGFβ2C226,228S exhibited alterations in actin cytoskeleton structures, including the formation of F-actin stress fibers and crossed-linked actin networks (CLANs), which are signature arrangements of actin cytoskeleton observed in the stiffer fibrotic-like TM. Our study demonstrated a mouse model of sustained IOP elevation via lentiviral gene delivery of active hTGFβ2C226,228S that induces TM dysfunction and outflow resistance.