Remodeling of the Lamina Cribrosa: Mechanisms and Potential Therapeutic Approaches for Glaucoma

Glaucomatous optic neuropathy is the leading cause of irreversible blindness in the world. The chronic disease is characterized by optic nerve degeneration and vision field loss. The reduction of intraocular pressure remains the only proven glaucoma treatment, but it does not prevent further neurodegeneration. There are three major classes of cells in the human optic nerve head (ONH): lamina cribrosa (LC) cells, glial cells, and scleral fibroblasts. These cells provide support for the LC which is essential to maintain healthy retinal ganglion cell (RGC) axons. All these cells demonstrate responses to glaucomatous conditions through extracellular matrix remodeling. Therefore, investigations into alternative therapies that alter the characteristic remodeling response of the ONH to enhance the survival of RGC axons are prevalent. Understanding major remodeling pathways in the ONH may be key to developing targeted therapies that reduce deleterious remodeling.

Neuroprotective Effect of Statins in a Rat Model of Chronic Ocular Hypertension

Glaucoma is an optic neuropathy in which the degeneration of retinal ganglion cells (RGCs) results in irreversible vison loss. Therefore, neuroprotection of RGCs from glaucomatous afflictions is crucial for glaucoma treatment. In this study, we aimed to investigate the beneficial effects of statins in the protection of RGCs using a rat model. Glaucomatous injury was induced in rats by chronic ocular hypertension (OHT) achieved after performing a circumlimbal suture. The rats were given either statins such as simvastatin and atorvastatin or a solvent weekly for 6 weeks. Retina sections underwent hematoxylin and eosin, Brn3a, or cleaved casepase-3 staining to evaluate RGC survival. In addition, modulation of glial activation was assessed. While the retinas without statin treatment exhibited increased RGC death due to chronic OHT, statins promoted the survival of RGCs and reduced apoptosis. Statins also suppressed chronic OHT-mediated glial activation in the retina. Our results demonstrate that statins exert neuroprotective effects in rat retinas exposed to chronic OHT, which may support the prospect of statins being a glaucoma treatment.

Statins Suppress TGF-β2-Mediated MMP-2 and MMP-9 Expression and Activation Through RhoA/ROCK Inhibition in Astrocytes of the Human Optic Nerve Head

Purpose

Matrix metalloproteinases (MMPs) are involved in extracellular matrix (ECM) maintenance and remodeling. The present study aimed to determine whether transforming growth factor (TGF)-β2 regulates MMP-2 and MMP-9 levels and activities in astrocytes derived from the optic nerve head (ONH) and the role of statins in such modulation.

Methods

Primary astrocytes cultured from the lamina cribrosa of human donor ONHs were incubated with three types of statins (5 µg/mL) for 1 hour followed by recombinant TGF-β2 (5 ng/mL) for various periods to test their effects. Levels and activities of MMP-2 and MMP-9 in astrocytes in vitro were determined by western blotting and zymography, respectively. Levels of phosphorylated myosin phosphatase target subunit 1 (MYPT1) in astrocyte lysates were determined by western blotting, and those of phosphorylated myosin light chain (MLC) were determined by western blotting and immunocytochemistry.

Results

MMP-2 and MMP-9 levels were upregulated by TGF-β2 in human ONH astrocytes. Prior incubation with simvastatin, lovastatin, and atorvastatin inhibited TGF-β2-mediated MMP-2 and MMP-9 expression and activities. Prior incubation with statins downregulated the TGF-β2-induced phosphorylation of MYPT1 and MLC, which are downstream substrates of RhoA and ROCKs.

Conclusions

Statins inhibited the TGF-β2-mediated regulation of MMP-2 and MMP-9 by inhibiting the RhoA/ROCK signaling pathway. Considering the role of MMP in ECM remodeling, the present findings support the notion that statins positively impact ECM remodeling within the ONH.

Association of Statin Use and High Serum Cholesterol Levels With Risk of Primary Open-Angle Glaucoma

Importance

The use of statins (hydroxymethylglutaryl coenzyme A inhibitors) has been associated with a lower risk of primary open-angle glaucoma (POAG); however, results have been conflicting, and little is known about the association between high cholesterol levels and POAG.

Objective

To assess the association of elevated cholesterol levels and statin use with incident POAG.

Design, Setting, and Participants

This study used data collected biennially from participants aged 40 years or older who were free of glaucoma and reported eye examinations, within 3 population-based cohorts: the Nurses' Health Study (N = 50 710; followed up from 2000 to 2014), the Nurses' Health Study 2 (N = 62 992; 1999-2015), and the Health Professionals Follow-up Study (N = 23 080; 2000-2014). Incident cases of POAG were confirmed by medical record review. The analyses were performed in January 2019.

Exposures

Biennially updated self-reported information on elevated cholesterol level status, serum cholesterol levels, and duration of statin use.

Main Outcomes and Measures

Multivariable-adjusted relative risks (RRs) and 95% CIs were estimated using Cox proportional hazards regression models on pooled data, with stratification by cohort.

Results

Among the 136 782 participants in the 3 cohorts (113 702 women and 23 080 men), 886 incident cases of POAG were identified. Every 20-mg/dL increase in total serum cholesterol was associated with a 7% increase in risk of POAG (RR, 1.07 [95% CI, 1.02-1.11]; P = .004). Any self-reported history of elevated cholesterol was also associated with a higher risk of POAG (RR, 1.17 [95% CI, 1.00-1.37]). A history of any statin use was associated with a 15% lower risk of POAG (RR, 0.85 [95% CI, 0.73-0.99]). Use of statins for 5 or more years vs never use of statins was associated with a 21% lower risk of POAG (RR, 0.79 [95% CI, 0.65-0.97]; P = .02 for linear trend). The association between use of statins for 5 or more years vs never use of statins and risk of POAG was more inverse in those who were older (≥65 years: RR, 0.70 [95% CI, 0.56-0.87] vs <65 years: RR, 1.05 [95% CI, 0.68-1.63]; P = .01 for interaction).

Conclusions and Relevance

Among adults aged 40 years or older, higher serum cholesterol levels were associated with higher risk of POAG, while 5 or more years of statin use compared with never use of statins was associated with a lower risk of POAG.

Effects of atorvastatin on porcine aqueous humour outflow and trabecular meshwork cells

Primary open-angle glaucoma (POAG) with complex pathogenesis is one of the many major causes of blindness. It is widely accepted that the major cause of POAG is the dysregulation of the trabecular meshwork (TM), which regulates the resistance to aqueous humour outflow. Intraocular pressure is elevated with increasing outflow resistance in the conventional pathway, which consists of the TM and Schlemm's canal. The TM is a filter made up of extracellular matrix (e.g., collagens), most of which is organized into a network of beams covered by endothelial-like trabecular cells. Currently, lack of effective anti-glaucoma drugs acting on TM to normalize trabecular outflow represents a bottleneck for POAG therapy. Atorvastatin, a lipid-lowering drug, has been proven to be of benefit for POAG. The present study aimed to investigate the possible mechanisms of action of atorvastatin on the TM by using a porcine aqueous humour outflow model in vivo and TM cells in vitro. Perfusion of enucleated porcine eyes with atorvastatin (50-200 µM) for 2 h increased aqueous humour outflow (P<0.05, n=6), possibly via regulating the morphology of TM cells and the distribution of the cytoskeleton. Atorvastatin decreased adhesion molecules at the mRNA and protein level. No cytotoxicity of atorvastatin on TM cells was observed at concentrations of <100 µM. The atorvastatin-induced effects mentioned above were reversible after removal of the compound only if the atorvastatin concentration was <100 µM. The present study demonstrated that atorvastatin efficaciously elevated aqueous humour outflow, possibly due to affecting TM-cell morphology, cytoskeleton and cell junctions. Statins may be potential therapeutic agents for lowering intraocular pressure in POAG.

Statins reduce TGF-beta2-modulation of the extracellular matrix in cultured astrocytes of the human optic nerve head

Statins are cholesterol lowering drugs and have shown beneficial effects on glaucoma. With regard to the mechanism of statin action on glaucoma, we investigated the effects of statins on transforming growth factor-beta 2 (TGF-β2)-induced expression of extracellular matrix (ECM) proteins in human astrocytes of the optic nerve head (ONH) lamina cribrosa (LC). By using primary human ONH astrocytes, we found that both simvastatin and lovastatin inhibited TGF-β2-mediated expression of ECM proteins such as connective tissue growth factor, collagen I, fibronectin, and plasminogen activator inhibitor-1. Suppression of ECM related proteins is due to inhibition of Smad2/3 activation as statins inhibit TGF-β2-induced Smad2 phosphorylation and Smad2/3 nuclear accumulation. In ONH astrocytes, TGF-β2 does not induce MAPK activation. In this study we found an anti-fibrotic effect of statins in human astrocytes of the ONH and identified TGF-β2 as a mediator of statin action, which may support a beneficial role for statins in blocking glaucomatous axonal damage induced by ECM remodeling.