Simvastatin Improves Retinal Ganglion Cell Survival and Spatial Vision after Acute Retinal Ischemia/Reperfusion in Mice

Modulation of TRPV4-mediated TNF-α expression in Müller glia and subsequent RGC apoptosis by statins

In addition to regulating cholesterol synthesis, statins have neuroprotective effects. Apoptosis of retinal ganglion cells (RGCs) causes a gradual loss of visual function in glaucoma. This study aimed to investigate the neuroprotective effect of statins on the RGC apoptosis induced by activated Müller glia. Primary Müller cells and RGCs were cultured from the retina of C57BL6 mice. Müller cells were activated with GSK101, a transient receptor potential vanilloid 4 (TRPV4) agonist, and tumor necrosis factor-alpha (TNF-α) released to the medium was measured using an enzyme-linked immunosorbent assay. Cells were pretreated with simvastatin or lovastatin before GSK101. RGCs were treated with conditioned media from Müller glia cultures, and apoptosis was determined using flow cytometry. TRPV4 activation through GSK101 treatment induced gliosis of Müller cells, and the conditioned media from activated Müller cells was potent to induce RGC apoptosis. Statins suppress both gliosis in Müller cells and subsequent RGC apoptosis. TNF-α release to the media was increased in GSK101-treated Müller cells, and TNF-α in the conditioned media was the critical factor causing RGC apoptosis. The increase in TRPV4-mediated TNF-α expression occurred through the nuclear factor kappa-light chain enhancer of activated B cell pathway activation, which was inhibited by statins. Herein, we showed that statins can modulate gliosis and TNF-α expression in Müller cells, protecting RGCs. These data further support the neuroprotective effect of statins, promoting them as a potential treatment for glaucoma.

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.

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.

Simvastatin protects photoreceptors from oxidative stress induced by all-trans-retinal, through the up-regulation of interphotoreceptor retinoid binding protein

BACKGROUND AND PURPOSE

Simvastatin is a 3-hydroxy-3-methylglutaryl CoA reductase inhibitor with multiple targets and effects. It protects neurons in the brain, but its protective effects on photoreceptors are unclear. In this study, we evaluated the neuroprotective effect of simvastatin on photoreceptors exposed to stress induced by all-trans-retinal (atRAL).

EXPERIMENTAL APPROACH

AlamarBlue and LDH assays were used to evaluate the viability and metabolic activity of Y79 cells (a retinoblastoma cell line) exposed to atRAL-induced stress with or without simvastatin pretreatment. Changes in cellular ROS were evaluated using flow cytometry and mitochondrial stress markers JC-1 and HSP60. Changes in levels of two photoreceptor-specific markers, cone-rod homeobox protein (CRX) and interphotoreceptor retinoid binding protein (IRBP), were evaluated with western blot. The results were validated in ex vivo human retinal explants and a mouse model of photoreceptor degeneration.

KEY RESULTS

Simvastatin improved mitochondrial function, alleviated oxidative stress and up-regulated the photoreceptor-specific markers IRBP and its upstream regulator CRX in Y79 cells and ex vivo human retinal explants under atRAL-induced stress. Simvastatin attenuated photoreceptor degeneration in association with up-regulation of IRBP and CRX expression after knockdown of IRBP in a murine model.

CONCLUSION AND IMPLICATIONS

Our findings suggest that simvastatin has a novel role in protecting photoreceptors from atRAL-induced stress. Simvastatin treatment resulted in up-regulation of IRBP and its upstream transcription factor CRX in Y79 cells, ex vivo human retinal explants, and murine retinas in vivo. Further studies of simvastatin to treat photoreceptor degeneration are warranted.

Rapamycin and fasting sustain autophagy response activated by ischemia/reperfusion injury and promote retinal ganglion cell survival

Autophagy, the cellular process responsible for degradation and recycling of cytoplasmic components through the autophagosomal–lysosomal pathway, is fundamental for neuronal homeostasis and its deregulation has been identified as a hallmark of neurodegeneration. Retinal hypoxic–ischemic events occur in several sight-treating disorders, such as central retinal artery occlusion, diabetic retinopathy, and glaucoma, leading to degeneration and loss of retinal ganglion cells. Here we analyzed the autophagic response in the retinas of mice subjected to ischemia induced by transient elevation of intraocular pressure, reporting a biphasic and reperfusion time-dependent modulation of the process. Ischemic insult triggered in the retina an acute induction of autophagy that lasted during the first hours of reperfusion. This early upregulation of the autophagic flux limited RGC death, as demonstrated by the increased neuronal loss observed in mice with genetic impairment of basal autophagy owing to heterozygous ablation of the autophagy-positive modulator Ambra1 (Ambra1^+/gt). Upregulation of autophagy was exhausted 24 h after the ischemic event and reduced autophagosomal turnover was associated with build up of the autophagic substrate SQSTM-1/p62, decreased ATG12-ATG5 conjugate, ATG4 and BECN1/Beclin1 expression. Animal fasting or subchronic systemic treatment with rapamycin sustained and prolonged autophagy activation and improved RGC survival, providing proof of principle for autophagy induction as a potential therapeutic strategy in retinal neurodegenerative conditions associated with hypoxic/ischemic stresses.

Nogo-A inactivation improves visual plasticity and recovery after retinal injury

Myelin-associated proteins such as Nogo-A are major inhibitors of neuronal plasticity that contribute to permanent neurological impairments in the injured CNS. In the present study, we investigated the influence of Nogo-A on visual recovery after retinal injuries in mice. Different doses of N-methyl-d-aspartate (NMDA) were injected in the vitreous of the left eye to induce retinal neuron death. The visual function was monitored using the optokinetic response (OKR) as a behavior test, and electroretinogram (ERG) and local field potential (LFP) recordings allowed to assess changes in retinal and cortical neuron activity, respectively. Longitudinal OKR follow-ups revealed reversible visual deficits after injection of NMDA ≤ 1 nmole in the left eye and concomitant functional improvement in the contralateral visual pathway of the right eye that was let intact. Irreversible OKR loss observed with NMDA ≥ 2 nmol was correlated with massive retinal cell death and important ERG response decline. Strikingly, the OKR mediated by injured and intact eye stimulation was markedly improved in Nogo-A KO mice compared with WT animals, suggesting that the inactivation of Nogo-A promotes visual recovery and plasticity. Moreover, OKR improvement was associated with shorter latency of the N2 wave of Nogo-A KO LFPs relative to WT animals. Strikingly, intravitreal injection of anti-Nogo-A antibody (11C7) in the injured eye exerted positive effects on cortical LFPs. This study presents the intrinsic ability of the visual system to recover from NMDA-induced retinal injury and its limitations. Nogo-A neutralization may promote visual recovery in retinal diseases such as glaucoma.

Frataxin overexpression in Müller cells protects retinal ganglion cells in a mouse model of ischemia/reperfusion injury in vivo

Müller cells are critical for retinal function and neuronal survival but can become detrimental in response to retinal ischemia and increased oxidative stress. Elevated oxidative stress increases expression of the mitochondrial enzyme frataxin in the retina, and its overexpression is neuroprotective after ischemia. Whether frataxin expression in Müller cells might improve their function and protect neurons after ischemia is unknown. The aim of this study was to evaluate the effect of frataxin overexpression in Müller cells on neuronal survival after retinal ischemia/reperfusion in the mouse in vivo. Retinal ischemia/reperfusion was induced in mice overexpressing frataxin in Müller cells by transient elevation of intraocular pressure. Retinal ganglion cells survival was determined 14 days after lesion. Expression of frataxin, antioxidant enzymes, growth factors and inflammation markers was determined with qRT-PCR, Western blotting and immunohistochemistry 24 hours after lesion. Following lesion, there was a 65% increase in the number of surviving RGCs in frataxin overexpressing mice. Improved survival was associated with increased expression of the antioxidant enzymes Gpx1 and Sod1 as well as the growth factors Cntf and Lif. Additionally, microglial activation was decreased in these mice. Therefore, support of Müller cell function constitutes a feasible approach to reduce neuronal degeneration after ischemia.

The influence of oral statin medications on progression of glaucomatous visual field loss: A propensity score analysis

PURPOSE

The purpose of this study was to examine the association between oral statin use and the progression of open angle glaucoma.

METHODS

Medical records of 847 Veterans were reviewed to collect statin use history, record demographic and comorbid medical conditions, and review visual fields. Visual field progression was judged by an ophthalmologist masked to statin use history. Progression rates in a propensity score matched cohort were compared between statin users and nonusers using McNemar's test with the propensity model derived using associated medical and demographic factors.

RESULTS

The mean length of observation was 1324 days with a standard deviation of 464 days. Thirty-one per cent of Veterans demonstrated glaucomatous progression in at least one eye, 49% did not demonstrate progression, and 20% were indeterminate. Approximately 74% of subjects had previously used a statin, with this group having heavier burdens of several comorbid medical conditions and less severe baseline glaucoma than nonusers. The matched cohort was 196 statin users and 196 nonusers, each with similar baseline characteristics (standardised differences <0.10). Progression rates were 35% for statin users compared to 56% for nonusers in the matched cohort (McNemar's p<0.001).

CONCLUSIONS

In this population of Veterans, glaucoma patients with any history of statin use have lower visual field progression rates than statin nonusers.

The ocular toxicity and pharmacokinetics of simvastatin following intravitreal injection in mice

AIM

To investigate the retinal toxicity and pharmacokinetics of simvastatin intravitreally injected into mice.

METHODS

Forty-eight 6-8-week-old C57BL/6J mice were used in this study. Simvastatin was intravitreally injected into the right eye of each mouse; the left eye was injected with vehicle and was used as a control. Bilateral dark-adapted electroretinography (ERG) was performed 1 and 7d following injection. Histology was examined using a combination of light, fluorescence and electron microscopy. High-performance liquid chromatography (HPLC) was used to determine the decay in the retinal simvastatin concentration.

RESULTS

ERG revealed no significant changes in the simvastatin-injected eyes compared to control. Histologic studies showed normal retinal morphology in eyes injected with simvastatin up to a final vitreal concentration of 200 µmol/L. No significant changes in the number of photoreceptors, bipolar cells or ganglion cells were found. The retinal simvastatin concentration decayed exponentially, with a half-life of 1.92-2.41h.

CONCLUSION

Intravitreal injection of up to 200 µmol/L simvastatin produced no signs of adverse effects in the mouse retina. Simvastatin reaches the retina shortly after intravitreal injectionand has a short half-life.

Psychophysical testing in rodent models of glaucomatous optic neuropathy

Processing of visual information begins in the retina, with photoreceptors converting light stimuli into neural signals. Ultimately, signals are transmitted to the brain through signaling networks formed by interneurons, namely bipolar, horizontal and amacrine cells providing input to retinal ganglion cells (RGCs), which form the optic nerve with their axons. As part of the chronic nature of glaucomatous optic neuropathy, the increasing and irreversible damage and ultimately loss of neurons, RGCs in particular, occurs following progressive damage to the optic nerve head (ONH), eventually resulting in visual impairment and visual field loss. There are two behavioral assays that are typically used to assess visual deficits in glaucoma rodent models, the visual water task and the optokinetic drum. The visual water task can assess an animal's ability to distinguish grating patterns that are associated with an escape from water. The optokinetic drum relies on the optomotor response, a reflex turning of the head and neck in the direction of the visual stimuli, which usually consists of rotating black and white gratings. This reflex is a physiological response critical for keeping the image stable on the retina. Driven initially by the neuronal input from direction-selective RGCs, this reflex is comprised of a number of critical sensory and motor elements. In the presence of repeatable and defined stimuli, this reflex is extremely well suited to analyze subtle changes in the circuitry and performance of retinal neurons. Increasing the cycles of these alternating gratings per degree, or gradually reducing the contrast of the visual stimuli, threshold levels can be determined at which the animal is no longer tracking the stimuli, and thereby visual function of the animal can be determined non-invasively. Integrating these assays into an array of outcome measures that determine multiple aspects of visual function is a central goal in vision research and can be realized, for example, by the combination of measuring optomotor reflex function with electroretinograms (ERGs) and optical coherence tomography (OCT) of the retina. These structure-function correlations in vivo are urgently needed to identify disease mechanisms as potential new targets for drug development. Such a combination of the experimental assessment of the optokinetic reflex (OKR) or optomotor response (OMR) with other measures of retinal structure and function is especially valuable for research on GON. The chronic progression of the disease is characterized by a gradual decrease in function accompanied by a concomitant increase in structural damage to the retina, therefore the assessment of subtle changes is key to determining the success of novel intervention strategies.

Prevalence and risk factors of retinal vein occlusion: the Gutenberg Health Study

OBJECTIVE

To determine the age- and sex-specific prevalence and determinants of retinal vein occlusions (RVOs) in a large population-based German cohort.

METHODS

The investigation included 15,010 participants (aged 35-74 years) from the Gutenberg Health Study. We determined the prevalence of RVO (central retinal vein occlusion [CRVO] and branch retinal vein occlusion [BRVO]) for the local population by assessing fundus photographs of 12 954 (86.3%; 49.8% women and 50.2% men) participants. Further, we analyzed the associations of RVO with cardiovascular, anthropometric, and ophthalmic parameters.

RESULTS

The weighted prevalences of RVO, CRVO, and BRVO were 0.40%, 0.08%, and 0.32%, respectively. Men were 1.7 times more frequently affected by RVO than were women. Prevalence of RVO was 0.2% in participants aged 35-44 and 45-54 years, respectively, 0.48% in those aged 55-64 years, and 0.92% in those aged 65-74 years. Of persons with RVO, 91.5% had one or more cardiovascular risk factor or disease vs. 75.9% of persons without RVO. BRVO was associated with arterial hypertension (odds ratio 2.69, 95% confidence interval 1.27-5.70) and atrial fibrillation (3.37, 1.24-9.12) and CRVO with higher age (7.02, 1.63-30.19) and a family history of stroke (4.64, 1.18-18.25). Median visual acuity (base 10 logarithm of minimum angle of resolution) was 0.2 in persons with RVO vs. 0.05 in those without.

CONCLUSION

The prevalence of RVO in this German population was 0.4%, and men were 1.7 times more frequently affected than women. CRVO was associated with higher age and a family history of stroke, and BRVO was associated with arterial hypertension and atrial fibrillation.

Simvastatin inhibits ischemia/reperfusion injury-induced apoptosis of retinal cells via downregulation of the tumor necrosis factor-α/nuclear factor-κB pathway

Simvastatin, which is widely used in the prevention and treatment of hyperlipidemia-associated diseases, has been reported to enhance the survival of retinal ganglion cells (RGCs) in a model of retinal ischemia/reperfusion (IR) injury. However, the underlying mechanism of the anti-apoptotic effects of simvastatin on the retina have yet to be elucidated. In the present study, rats were treated with simvastatin or saline for 7 days prior to IR via ligation of the right cephalic artery. The results showed that simvastatin prevented the apoptosis of RGCs and cells in the inner nuclear layer. Furthermore, simvastatin regulated the expression of apoptosis-associated proteins. The expression levels of the anti-apoptotic protein B-cell lymphoma-2 were upregulated 4 and 24 h after IR in the simvastatin/IR group compared to those in the saline/IR group. Conversely, the levels of pro-apoptotic protein Bax were downregulated in the simvastatin/IR group compared to those in the saline/IR group. Furthermore, the results of the present study showed for the first time, to the best of our knowledge, that simvastatin decreased IR injury-induced tumor necrosis factor-α (TNF-α) and nuclear factor-κB (NF-κB) expression in the retina. These findings strongly suggested that simvastatin inhibits apoptosis following IR-induced retinal injury by inhibition of the TNF-α/NF-κB pathway. The present study also provided a rationale for developing therapeutic methods to treat IR-induced retinal injury in the clinic.

Systemic simvastatin rescues retinal ganglion cells from optic nerve injury possibly through suppression of astroglial NF-κB activation

Neuroinflammation is involved in the death of retinal ganglion cells (RGCs) after optic nerve injury. The purpose of this study was to determine whether systemic simvastatin can suppress neuroinflammation in the optic nerve and rescue RGCs after the optic nerve is crushed. Simvastatin or its vehicle was given through an osmotic minipump beginning one week prior to the crushing. Immunohistochemistry and real-time PCR were used to determine the degree of neuroinflammation on day 3 after the crushing. The density of RGCs was determined in Tuj-1 stained retinal flat mounts on day 7. The effect of simvastain on the TNF-α-induced NF-κB activation was determined in cultured optic nerve astrocytes. On day 3, CD68-positive cells, most likely microglia/macrophages, were accumulated at the crushed site. Phosphorylated NF-κB was detected in some astrocytes at the border of the lesion where the immunoreactivity to MCP-1 was intensified. There was an increase in the mRNA levels of the CD68 (11.4-fold), MCP-1 (22.6-fold), ET-1 (2.3-fold), GFAP (1.6-fold), TNF-α (7.0-fold), and iNOS (14.8-fold) genes on day 3. Systemic simvastatin significantly reduced these changes. The mean ± SD number of RGCs was 1816.3±232.6/mm² (n = 6) in the sham controls which was significantly reduced to 831.4±202.5/mm² (n = 9) on day 7 after the optic nerve was crushed. This reduction was significantly suppressed to 1169.2±201.3/mm² (P = 0.01, Scheffe; n = 9) after systemic simvastatin. Simvastatin (1.0 µM) significantly reduced the TNF-α-induced NF-κB activation in cultured optic nerve astrocytes. We conclude that systemic simvastatin can reduce the death of RGCs induced by crushing the optic nerve possibly by suppressing astroglial NF-κB activation.

Progressive morphological changes and impaired retinal function associated with temporal regulation of gene expression after retinal ischemia/reperfusion injury in mice

Retinal ischemia/reperfusion (I/R) injury is an important cause of visual impairment. However, questions remain on the overall I/R mechanisms responsible for progressive damage to the retina. In this study, we used a mouse model of I/R and characterized the pathogenesis by analyzing temporal changes of retinal morphology and function associated with changes in retinal gene expression. Transient ischemia was induced in one eye of C57BL/6 mice by raising intraocular pressure to 120 mmHg for 60 min followed by retinal reperfusion by restoring normal pressure. At various time points post I/R, retinal changes were monitored by histological assessment with H&E staining and by SD-OCT scanning. Retinal function was also measured by scotopic ERG. Temporal changes in retinal gene expression were analyzed using cDNA microarrays and real-time RT-PCR. In addition, retinal ganglion cells and gliosis were observed by immunohistochemistry. H&E staining and SD-OCT scanning showed an initial increase followed by a significant reduction of retinal thickness in I/R eyes accompanied with cell loss compared to contralateral control eyes. The greatest reduction in thickness was in the inner plexiform layer (IPL) and inner nuclear layer (INL). Retinal detachment was observed at days 3 and 7 post- I/R injury. Scotopic ERG a- and b-wave amplitudes and implicit times were significantly impaired in I/R eyes compared to contralateral control eyes. Microarray data showed temporal changes in gene expression involving various gene clusters such as molecular chaperones and inflammation. Furthermore, immunohistochemical staining confirmed Müller cell gliosis in the damaged retinas. The time-dependent changes in retinal morphology were significantly associated with functional impairment and altered retinal gene expression. We demonstrated that I/R-mediated morphological changes the retina closely associated with functional impairment as well as temporal changes in retinal gene expression. Our findings will provide further understanding of molecular pathogenesis associated with ischemic injury to the retina.