SIRT1 promotes RGC survival and delays loss of function following optic nerve crush

Melatonin ameliorates retinal ganglion cell senescence and apoptosis in a SIRT1-dependent manner in an optic nerve injury model

Melatonin is involved in exerting protective effects in aged-related and neurodegenerative diseases through a silent information regulator type 1 (SIRT1)-dependent pathway. However, little was known about the impact of melatonin on retinal ganglion cell (RGC) senescence and apoptosis following optic nerve crush (ONC). Thus, this study aimed to examine the effects of melatonin on RGC senescence and apoptosis after ONC and investigate the involvement of SIRT1 in this process. To study this, an ONC model was established. EX-527, an inhibitor of SIRT1, was injected intraperitoneally into mice. And melatonin was administrated abdominally into mice after ONC every day. Hematoxylin & eosin staining, retina flat-mounts and optical coherence tomography were used to evaluate the loss of retina cells/neurons. Pattern electroretinogram (p-ERG) was performed to evaluate the function of RGCs. Immunofluorescence and western blot were used to evaluate protein expression. SA-β-gal staining was employed to detect senescent cells. The results demonstrated that melatonin partially rescued the expression of SIRT1 in RGC 3 days after ONC. Additionally, melatonin administration partly rescued the decreased RGC number and ganglion cell complex thickness observed 14 days after ONC. Melatonin also suppressed ONC-induced senescence and apoptosis index. Furthermore, p-ERG showed that melatonin improved the amplitude of P50, N95 and N95/P50 following ONC. Importantly, the protective effects of melatonin were reversed when EX-527 was administered. In summary, this study revealed that melatonin attenuated RGC senescence and apoptosis through a SIRT1-dependent pathway after ONC. These findings provide valuable insights for the treatment of RGC senescence and apoptosis.

AAV2 vector optimization for retinal ganglion cell-targeted delivery of therapeutic genes

Recombinant adeno-associated virus (AAV)-2 has significant potential as a delivery vehicle of therapeutic genes to retinal ganglion cells (RGCs), which are key interventional targets in optic neuropathies. Here we show that when injected intravitreally, AAV2 engineered with a reporter gene driven by cytomegalovirus (CMV) enhancer and chicken β-actin (CBA) promoters, displays ubiquitous and high RGC expression, similar to its synthetic derivative AAV8BP2. A novel AAV2 vector combining the promoter of the human RGC-selective γ-synuclein (hSNCG) gene and woodchuck hepatitis post-transcriptional regulatory element (WPRE) inserted upstream and downstream of a reporter gene, respectively, induces widespread transduction and strong transgene expression in RGCs. High transduction efficiency and selectivity to RGCs is further achieved by incorporating in the vector backbone a leading CMV enhancer and an SV40 intron at the 5' and 3' ends, respectively, of the reporter gene. As a delivery vehicle of hSIRT1, a 2.2-kb therapeutic gene with anti-apoptotic, anti-inflammatory and anti-oxidative stress properties, this recombinant vector displayed improved transduction efficiency, a strong, widespread and selective RGC expression of hSIRT1, and increased RGC survival following optic nerve crush. Thus, AAV2 vector carrying hSNCG promoter with additional regulatory sequences may offer strong potential for enhanced effects of candidate gene therapies targeting RGCs.

Molecular aspects of optic nerve autophagy in glaucoma

The optic nerve consists of the glia, vessels, and axons including myelin and axoplasm. Since axonal degeneration precedes retinal ganglion cell death in glaucoma, the preceding axonal degeneration model may be helpful for understanding the molecular mechanisms of optic nerve degeneration. Optic nerve samples from these models can provide information on several aspects of autophagy. Autophagosomes, the most typical organelles expressing autophagy, are found much more frequently inside axons than around the glia. Thus, immunoblot findings from the optic nerve can reflect the autophagy state in axons. Autophagic flux impairment may occur in degenerating optic nerve axons, as in other central nervous system neurodegenerative diseases. Several molecular candidates are involved in autophagy enhancement, leading to axonal protection. This concept is an attractive approach to the prevention of further retinal ganglion cell death. In this review, we describe the factors affecting autophagy, including nicotinamide riboside, p38, ULK, AMPK, ROCK, and SIRT1, in the optic nerve and propose potential methods of axonal protection via enhancement of autophagy.

Microglial SIRT1 activation attenuates synapse loss in retinal inner plexiform layer via mTORC1 inhibition

BACKGROUND

Optic nerve injury (ONI) is a key cause of irreversible blindness and triggers retinal ganglion cells (RGCs) change and synapse loss. Microglia is the resistant immune cell in brain and retina and has been demonstrated to be highly related with neuron and synapse injury. However, the function of Sirtuin 1 (SIRT1), a neuroprotective molecule, in mediating microglial activation, retinal synapse loss and subsequent retinal ganglion cells death in optic nerve injury model as well as the regulatory mechanism remain unclear.

METHOD

To this end, optic nerve crush (ONC) model was conducted to mimic optic nerve injury. Resveratrol and EX527, highly specific activator and inhibitor of SIRT1, respectively, were used to explore the function of SIRT1 in vivo and vitro. Cx3Cr1-CreERT2/RaptorF/F mice were used to delete Raptor for inhibiting mammalian target of rapamycin complex 1 (mTORC1) activity in microglia. HEK293 and BV2 cells were transfected with plasmids to explore the regulatory mechanism of SIRT1.

RESULTS

We discovered that microglial activation and synapse loss in retinal inner plexiform layer (IPL) occurred after optic nerve crush, with later-development retinal ganglion cells death. SIRT1 activation induced by resveratrol inhibited microglial activation and attenuated synapse loss and retinal ganglion cells injury. After injury, microglial phagocytosed synapse and SIRT1 inhibited this process to protect synapse and retinal ganglion cells. Moreover, SIRT1 exhibited neuron protective effects via activating tuberous sclerosis complex 2 (TSC2) through deacetylation, and enhancing the inhibition effect of tuberous sclerosis complex 2 on mammalian target of rapamycin complex 1 activity.

CONCLUSION

Our research provides novel insights into microglial SIRT1 in optic nerve injury and suggests a potential strategy for neuroprotective treatment of optic nerve injury disease.

Knockdown of Porf-2 restores visual function after optic nerve crush injury

Retinal ganglion cells (RGCs), the sole output neurons in the eyes, are vulnerable to diverse insults in many pathological conditions, which can lead to permanent vision dysfunction. However, the molecular and cellular mechanisms that contribute to protecting RGCs and their axons from injuries are not completely known. Here, we identify that Porf-2, a member of the Rho GTPase activating protein gene group, is upregulated in RGCs after optic nerve crush. Knockdown of Porf-2 protects RGCs from apoptosis and promotes long-distance optic nerve regeneration after crush injury in both young and aged mice in vivo. In vitro, we find that inhibition of Porf-2 induces axon growth and growth cone formation in retinal explants. Inhibition of Porf-2 provides long-term and post-injury protection to RGCs and eventually promotes the recovery of visual function after crush injury in mice. These findings reveal a neuroprotective impact of the inhibition of Porf-2 on RGC survival and axon regeneration after optic nerve injury, providing a potential therapeutic strategy for vision restoration in patients with traumatic optic neuropathy.

Neuroprotection in glaucoma: Mechanisms beyond intraocular pressure lowering

Glaucoma is a common, complex, multifactorial neurodegenerative disease characterized by progressive dysfunction and then loss of retinal ganglion cells, the output neurons of the retina. Glaucoma is the most common cause of irreversible blindness and affects ∼80 million people worldwide with many more undiagnosed. The major risk factors for glaucoma are genetics, age, and elevated intraocular pressure. Current strategies only target intraocular pressure management and do not directly target the neurodegenerative processes occurring at the level of the retinal ganglion cell. Despite strategies to manage intraocular pressure, as many as 40% of glaucoma patients progress to blindness in at least one eye during their lifetime. As such, neuroprotective strategies that target the retinal ganglion cell and these neurodegenerative processes directly are of great therapeutic need. This review will cover the recent advances from basic biology to on-going clinical trials for neuroprotection in glaucoma covering degenerative mechanisms, metabolism, insulin signaling, mTOR, axon transport, apoptosis, autophagy, and neuroinflammation. With an increased understanding of both the basic and clinical mechanisms of the disease, we are closer than ever to a neuroprotective strategy for glaucoma.

Oxidative Stress: A Suitable Therapeutic Target for Optic Nerve Diseases?

Optic nerve disorders encompass a wide spectrum of conditions characterized by the loss of retinal ganglion cells (RGCs) and subsequent degeneration of the optic nerve. The etiology of these disorders can vary significantly, but emerging research highlights the crucial role of oxidative stress, an imbalance in the redox status characterized by an excess of reactive oxygen species (ROS), in driving cell death through apoptosis, autophagy, and inflammation. This review provides an overview of ROS-related processes underlying four extensively studied optic nerve diseases: glaucoma, Leber's hereditary optic neuropathy (LHON), anterior ischemic optic neuropathy (AION), and optic neuritis (ON). Furthermore, we present preclinical findings on antioxidants, with the objective of evaluating the potential therapeutic benefits of targeting oxidative stress in the treatment of optic neuropathies.

Cell-Specific Expression of Human SIRT1 by Gene Therapy Reduces Retinal Ganglion Cell Loss Induced by Elevated Intraocular Pressure

SIRT1 prevents retinal ganglion cell (RGC) loss in several acute and subacute optic neuropathy models following pharmacologic activation or genetic overexpression. We hypothesized that adeno-associated virus (AAV)-mediated overexpression of SIRT1 in RGCs in a chronic ocular hypertension model can reduce RGC loss, thereby preserving visual function by sustained therapeutic effect. A control vector AAV-eGFP and therapeutic vector AAV-SIRT1 were constructed and optimized for transduction efficiency. A magnetic microbead mouse model of ocular hypertension was optimized to induce a time-dependent and chronic loss of visual function and RGC degeneration. Mice received intravitreal injection of control or therapeutic AAV in which a codon-optimized human SIRT1 expression is driven by a RGC selective promoter. Intraocular pressure (IOP) was measured, and visual function was examined by optokinetic response (OKR) weekly for 49 days following microbead injection. Visual function, RGC survival, and axon numbers were compared among control and therapeutic AAV-treated animals. AAV-eGFP and AAV-SIRT1 showed transduction efficiency of ~ 40%. AAV-SIRT1 maintains the transduction of SIRT1 over time and is selectively expressed in RGCs. Intravitreal injections of AAV-SIRT1 in a glaucoma model preserved visual function, increased RGC survival, and reduced axonal degeneration compared with the control construct. Over-expression of SIRT1 through AAV-mediated gene transduction indicates a RGC-selective component of neuroprotection in multiple models of acute optic nerve degeneration. Results here show a neuroprotective effect of RGC-selective gene therapy in a chronic glaucoma model characterized by sustained elevation of IOP and subsequent RGC loss. Results suggest that this strategy may be an effective therapeutic approach for treating glaucoma, and warrants evaluation for the treatment of other chronic neurodegenerative diseases.

The role of SIRT1 level and SIRT1 gene polymorphisms in optic neuritis patients with multiple sclerosis

THE AIM

To investigate the role of Sirtuin 1 (SIRT1) level and SIRT1 (rs3818292, rs3758391, rs7895833) gene polymorphisms in patients with optic neuritis (ON) and multiple sclerosis (MS).

METHODS

79 patients with ON and 225 healthy subjects were included in the study. ON patients were divided into 2 subgroups: patients with MS (n = 30) and patients without MS (n = 43). 6 ON patients did not have sufficient data for MS diagnosis and were excluded from the subgroup analysis. DNA was extracted from peripheral blood leukocytes and genotyped by real-time polymerase chain reaction. Results were analysed using the program "IBM SPSS Statistics 27.0".

RESULTS

We discovered that SIRT1 rs3758391 was associated with a twofold increased odds of developing ON under the codominant (p = 0.007), dominant (p = 0.011), and over-dominant (p = 0.008) models. Also, it was associated with a threefold increased odds ofON with MS development under the dominant (p = 0.010), twofold increased odds under the over-dominant (p = 0.032) models and a 1.2-fold increased odds of ON with MS development (p = 0.015) under the additive model. We also discovered that the SIRT1 rs7895833 was significantly associated with a 2.5-fold increased odds of ON development under the codominant (p = 0.001), dominant (p = 0.006), and over-dominant (p < 0.001) models, and a fourfold increased odds of ON with MS development under the codominant (p < 0.001), dominant (p = 0.001), over-dominant (p < 0.001) models and with a twofold increased odds of ON with MS development (p = 0.013) under the additive genetic model. There was no association between SIRT1 levels and ON with/without MS development.

CONCLUSIONS

SIRT1 rs3758391 and rs7895833 polymorphisms are associated with ON and ON with MS development.

Mitochondrial Open Reading Frame of the 12S rRNA Type-c: Potential Therapeutic Candidate in Retinal Diseases

Mitochondrial open reading frame of the 12S rRNA type-c (MOTS-c) is the most unearthed peptide encoded by mitochondrial DNA (mtDNA). It is an important regulator of the nuclear genome during times of stress because it promotes an adaptive stress response to maintain cellular homeostasis. Identifying MOTS-c specific binding partners may aid in deciphering the complex web of mitochondrial and nuclear-encoded signals. Mitochondrial damage and dysfunction have been linked to aging and the accelerated cell death associated with many types of retinal degenerations. Furthermore, research on MOTS-c ability to revive oxidatively stressed RPE cells has revealed a significant protective role for the molecule. Evidence suggests that senescent cells play a role in the development of age-related retinal disorders. This review examines the links between MOTS-c, mitochondria, and age-related diseases of the retina. Moreover, the untapped potential of MOTS-c as a treatment for glaucoma, diabetic retinopathy, and age-related macular degeneration is reviewed.

Inhibition of ferroptosis promotes retina ganglion cell survival in experimental optic neuropathies

Retinal ganglion cell (RGC) death is a hallmark of traumatic optic neuropathy, glaucoma, and other optic neuropathies that result in irreversible vision loss. However, therapeutic strategies for rescuing RGC loss still remain challenging, and the molecular mechanism underlying RGC loss has not been fully elucidated. Here, we highlight the role of ferroptosis, a non-apoptotic form of programmed cell death characterized by iron-dependent lethal lipid peroxides accumulation, in RGC death using an experimental model of glaucoma and optic nerve crush (ONC). ONC treatment resulted in significant downregulation of glutathione peroxidase 4 (GPx4) and system xc(-) cystine/glutamate antiporter (xCT) in the rat retina, accompanied by increased lipid peroxide and iron levels. The reduction of GPx4 expression in RGCs after ONC was confirmed by laser-capture microdissection and PCR. Transmission electron microscopy (TEM) revealed alterations in mitochondrial morphology, including increased membrane density and reduced mitochondrial cristae in RGCs after ONC. Notably, the ferroptosis inhibitor ferrostatin-1 (Fer-1) significantly promoted RGC survival and preserved retinal function in ONC and microbead-induced glaucoma mouse models. In addition, compared to the apoptosis inhibitor Z-VAD-FMK, Fer-1 showed better effect in rescuing RGCs death in ONC retinas. Mechanistically, we found the downregulation of GPx4 mainly occurred in the mitochondrial compartment, accompanied by increased mitochondrial reactive oxygen species (ROS) and lipid peroxides. The mitochondria-selective antioxidant MitoTEMPO attenuated RGC loss after ONC, implicating mitochondrial ROS and lipid peroxides as major mechanisms in ferroptosis-induced RGC death in ONC retinas. Notably, administering Fer-1 effectively prevented the production of mitochondrial lipid peroxides, the impairment of mitochondrial adenosine 5'-triphosphate (ATP) production, and the downregulation of mitochondrial genes, such as mt-Cytb and MT-ATP6, in ONC retinas. Our findings suggest that ferroptosis is a major form of regulated cell death for RGCs in experimental glaucoma and ONC models and suggesting targeting mitochondria-dependent ferroptosis as a protective strategy for RGC injuries in optic neuropathies.

Covalent Organic Framework (COF): A Drug and Carrier to Attenuate Retinal Ganglion Cells Death in an Acute Glaucoma Mouse Model

Purpose: We aim to investigate the use of covalent organic framework (COF) nanoparticles in the local treatment of glaucoma, both as a means of protecting retinal ganglion cells (RGCs), and as a carrier for delayed release of the medication rapamycin following a single intravitreal injection. Methods: a water-dispersible COF, and a COF-based nanoplatform for rapamycin release (COF-Rapa) was constructed. C57BL/6J mice were randomly divided into four groups: intravitreal injection of 1.5 µL normal saline (NS), COF (0.67 ng/µL), rapamycin (300 µM) or COF-Rapa (0.67 ng/µL-300 µM), respectively. The ischemia–reperfusion (I/R) model was established to mimic high intraocular pressure (IOP)-induced retinal injury in glaucoma. Labeling of RGCs by Fluoro-Gold and retinal electroretinogram were used to evaluate retinal function. Immunohistochemistry and Western blotting analyses of retinas were performed. Results: COF nanoparticles were delivered in vitro and in vivo. Six weeks after the COF injection, the number of RGCs was unaffected. In addition, the number of RBPMS-positive RGCs, GFAP-positive astrocytes and Iba1-positive microglia did not differ from the normal control. COF could effectively reduce RGCs death, improve phototransduction function and alleviate the overactivation of microglia compared to NS control after retinal I/R injury. Within six weeks, the mammalian target of rapamycin complex 1 (mTORC1) signaling pathway in the retinas could be inhibited by a single intravitreal injection of COF-Rapa. Compared with single COF administration, COF-Rapa significantly reduced the inflammatory reaction after retinal I/R injury. Conclusions: COF may act as both an RGC protection agent and a carrier for prolonged rapamycin release. This research may lead to the development of novel RGC protection agents and drug delivery techniques, as well as the creation of multifunctional COF-based biomaterials for glaucoma retinopathy.

Selective Upregulation of SIRT1 Expression in Retinal Ganglion Cells by AAV-Mediated Gene Delivery Increases Neuronal Cell Survival and Alleviates Axon Demyelination Associated with Optic Neuritis

Optic neuritis (ON), the most common ocular manifestation of multiple sclerosis, is an autoimmune inflammatory demyelinating disease also characterized by degeneration of retinal ganglion cells (RGCs) and their axons, which commonly leads to visual impairment despite attempted treatments. Although ON disease etiology is not known, changes in the redox system and exacerbated optic nerve inflammation play a major role in the pathogenesis of the disease. Silent information regulator 1 (sirtuin-1/SIRT1) is a ubiquitously expressed NAD+-dependent deacetylase, which functions to reduce/prevent both oxidative stress and inflammation in various tissues. Non-specific upregulation of SIRT1 by pharmacologic and genetic approaches attenuates RGC loss in experimental ON. Herein, we hypothesized that targeted expression of SIRT1 selectively in RGCs using an adeno-associated virus (AAV) vector as a delivery vehicle is an effective approach to reducing neurodegeneration and preserving vision in ON. We tested this hypothesis through intravitreal injection of AAV7m8.SNCG.SIRT1, an AAV2-derived vector optimized for highly efficient SIRT1 transgene transfer and protein expression into RGCs in mice with experimental autoimmune encephalomyelitis (EAE), a model of multiple sclerosis that recapitulates optic neuritis RGC loss and axon demyelination. Our data show that EAE mice injected with a control vehicle exhibit progressive alteration of visual function reflected by decreasing optokinetic response (OKR) scores, whereas comparatively, AAV7m8.SNCG.SIRT1-injected EAE mice maintain higher OKR scores, suggesting that SIRT1 reduces the visual deficit imparted by EAE. Consistent with this, RGC survival determined by immunolabeling is increased and axon demyelination is decreased in the AAV7m8.SNCG.SIRT1 RGC-injected group of EAE mice compared to the mouse EAE counterpart injected with a vehicle or with control vector AAV7m8.SNCG.eGFP. However, immune cell infiltration of the optic nerve is not significantly different among all EAE groups of mice injected with either vehicle or AAV7m8.SNCG.SIRT1. We conclude that despite minimally affecting the inflammatory response in the optic nerve, AAV7m8-mediated SIRT1 transfer into RGCs has a neuroprotective potential against RGC loss, axon demyelination and vison deficits associated with EAE. Together, these data suggest that SIRT1 exerts direct effects on RGC survival and function.

Curcumin and Wnt/β‑catenin signaling in exudative age‑related macular degeneration (Review)

Curcumin is a natural product widely used due to its pharmacological effects. Nevertheless, only a limited number of studies concerning the effects of curcumin on exudative age‑related macular degeneration (AMD) is currently available. Since ophthalmic diseases, including exudative AMD, have a marked impact on public health, the prevention and therapy of ophthalmic disorders remain of increasing concern. Exudative AMD is characterized by choroidal neovascularization (CNV) invading the subretinal space, ultimately enhancing exudation and hemorrhaging. The exudative AMD subtype corresponds to 10 to 15% of cases of macular degeneration; however, the occurrence of this subtype has been reported as the major cause of vision loss and blindness, with the occurrence of CNV being responsible for 80% of the cases with vision loss. In CNV increased expression of VEGF has been observed, stimulated by the overactivation of Wnt/β‑catenin signaling pathway. The stimulation of the Wnt/β‑catenin signaling pathway is responsible for the activation of several cellular mechanisms, simultaneously enhancing inflammation, oxidative stress and angiogenesis in numerous diseases, including ophthalmic disorders. Some studies have previously demonstrated the possible advantage of the use of curcumin for the inhibition of Wnt/β‑catenin signaling. In the present review article, the different mechanisms of curcumin are described concerning its effects on oxidative stress, inflammation and angiogenesis in exudative AMD, by interacting with Wnt/β‑catenin signaling.

SIRT1: Genetic Variants and Serum Levels in Age-Related Macular Degeneration

Background: The aim of this paper was to determine the frequency of SIRT1 rs3818292, rs3758391, rs7895833 single nucleotide polymorphism genotypes and SIRT1 serum levels associated with age-related macular degeneration (AMD) in the Lithuanian population. Methods: Genotyping of SIRT1 rs3818292, rs3758391 and rs7895833 was performed using RT-PCR. SIRT1 serum level was determined using the ELISA method. Results: We found that rs3818292 and rs7895833 were associated with an increased risk of developing exudative AMD. Additional sex-differentiated analysis revealed only rs7895833 was associated with an increased risk of developing exudative AMD in women after strict Bonferroni correction. The analysis also revealed that individuals carrying rs3818292, rs3758391 and rs7895833 haplotype G-T-G are associated with increased odds of exudative AMD. Still, the rare haplotypes were associated with the decreased odds of exudative AMD. After performing an analysis of serum SIRT1 levels and SIRT1 genetic variant, we found that carriers of the SIRT1 rs3818292 minor allele G had higher serum SIRT1 levels than the AA genotype. In addition, individuals carrying at least one SIRT1 rs3758391 T allele also had elevated serum SIRT1 levels compared with individuals with the wild-type CC genotype. Conclusions: Our study showed that the SIRT1 polymorphisms rs3818292 and rs7895833 and rs3818292-rs3758391-rs7895833 haplotype G-T-G could be associated with the development of exudative AMD. Also, two SNPs (rs3818292 and rs3758391) are associated with elevated SIRT1 levels.

The interplay of autophagy and oxidative stress in the pathogenesis and therapy of retinal degenerative diseases

Oxidative stress is mainly caused by intracellular reactive oxygen species (ROS) production, which is highly associated with normal physiological homeostasis and the pathogenesis of diseases, particularly ocular diseases. Autophagy is a self-clearance pathway that removes oxidized cellular components and regulates cellular ROS levels. ROS can modulate autophagy activity through transcriptional and posttranslational mechanisms. Autophagy further triggers transcription factor activation and degrades impaired organelles and proteins to eliminate excessive ROS in cells. Thus, autophagy may play an antioxidant role in protecting ocular cells from oxidative stress. Nevertheless, excessive autophagy may cause autophagic cell death. In this review, we summarize the mechanisms of interaction between ROS and autophagy and their roles in the pathogenesis of several ocular diseases, including glaucoma, age-related macular degeneration (AMD), diabetic retinopathy (DR), and optic nerve atrophy, which are major causes of blindness. The autophagy modulators used to treat ocular diseases are further discussed. The findings of the studies reviewed here might shed light on the development and use of autophagy modulators for the future treatment of ocular diseases.

Plasma levels of sirtuin and adiponectin in patients with primary open-angle glaucoma, exfoliative glaucoma, and healthy controls

PURPOSE

To compare plasma levels of sirtuin 1 (SIRT1) and adiponectin (APN) in patients with primary open-angle glaucoma (POAG), exfoliative glaucoma (XFG), and healthy control subjects.

METHODS

This prospective case-control study collected plasma samples from 118 participants. All subjects underwent a comprehensive ophthalmologic examination before the acquisition of a plasma sample. Plasma samples were obtained from 40 POAG, 38 XFG, and 40 healthy control subjects without any evidence of systemic or ocular disease. Serum SIRT1 and APN levels were estimated by an enzyme-linked immunosorbent assay, ELISA (Elabscience, Houston, USA) method. Statistical analysis of results relied on Kolmogorov-Smirnov, Kruskal-Wallis, Chi-square, analysis of variance (ANOVA) tests, and linear regression analysis, where appropriate.

RESULTS

A significant decrease in SIRT1 levels was observed in POAG patients compared to healthy controls (p = 0.004, Dunn's test). In contrast, no difference was detected between XFG and POAG patients or healthy controls (p = 0.32 and p = 0.34, respectively, Dunn's test). There was no significant difference in plasma APN levels between the three groups under investigation (p = 0.59, ANOVA).

CONCLUSION

Alterations in serum level of SIRT1 may suggest a possible role in POAG via potential effects in neuroprotection and oxidative stress.

Pinosylvin Extract Retinari™ Sustains Electrophysiological Function, Prevents Thinning of Retina, and Enhances Cellular Response to Oxidative Stress in NFE2L2 Knockout Mice

Chronic oxidative stress eventually leads to protein aggregation in combination with impaired autophagy, which has been observed in age-related macular degeneration. We have previously shown an effective age-related macular degeneration disease model in mice with nuclear factor-erythroid 2-related factor-2 (NFE2L2) knockout. We have also shown pinosylvin, a polyphenol abundant in bark waste, to increase human retinal pigment epithelium cell viability in vitro. In this work, the effects of commercial natural pinosylvin extract, Retinari™, were studied on the electroretinogram, optical coherence tomogram, autophagic activity, antioxidant capacity, and inflammation markers. Wild-type and NFE2L2 knockout mice were raised until the age of 14.8 ± 3.8 months. They were fed with either regular or Retinari™ chow (141 ± 17.0 mg/kg/day of pinosylvin) for 10 weeks before the assays. Retinari™ treatment preserved significant retinal function with significantly preserved a- and b-wave amplitudes in the electroretinogram responses. Additionally, the treatment prevented thinning of the retina in the NFE2L2 knockout mice. The NFE2L2 knockout mice showed reduced ubiquitin-tagged protein accumulation in addition to local upregulation of complement factor H and antioxidant enzymes superoxide dismutase 1 and catalase. Therefore, the treatment in the NFE2L2 KO disease model led to reduced chronic oxidative stress and sustained retinal function and morphology. Our results demonstrate that pinosylvin supplementation could potentially lower the risk of age-related macular degeneration onset and slow down its progression.

Resveratrol attenuates retinal ganglion cell loss in a mouse model of retinal ischemia reperfusion injury via multiple pathways

BACKGROUND

Resveratrol (RES) is a natural polyphenol that has been shown to protect retinal ganglion cells (RGCs) following retinal ischemia reperfusion (I/R) injury. However, the molecular mechanisms of resveratrol function are yet to be fully elucidated. Thus, this study explored the potential mechanisms of resveratrol in vivo.

METHODS

A retinal ischemia reperfusion injury model was established in adult male C57BL/6 J mice. Intraperitoneal injection of resveratrol was administered continuously for 5 days. RGC survival was determined by immunofluorescence staining with Brn3a. Flash electroretinography (ERG) was conducted to assess visual function. Proteins of HIF-1a, VEGF, p38, p53, PI3K, Akt, Bax, Bcl2, and Cleaved Caspase3 were detected using Western blot.

RESULTS

RES administration significantly ameliorated retinal thickness damage and increased Brn3a stained RGCs 7 days after I/R injury. We also found that administration of RES remarkably inhibited the upregulation of mitochondrial apoptosis-related protein Bax and Cleaved Caspase3, as well as increased the expression of Bcl2. Furthermore, RES administration significantly suppressed the I/R injury-induced upregulation of the HIF-1a/VEGF and p38/p53 pathways, while activating the I/R injury-induced downregulation of the PI3K/Akt pathway. Moreover, RES administration remarkably improved retinal function after I/R injury-induced functional impairment.

CONCLUSIONS

Our data demonstrated that resveratrol can mitigate retinal ischemic injury induced RGC loss and retinal function impairment by inhibiting the HIF-1a/VEGF and p38/p53 pathways while activating the PI3K/Akt pathway. Therefore, our results further reinforce that resveratrol has potential for treating glaucoma.

Protection against experimental cisplatin-induced optic nerve toxicity using resveratrol: A rat model study

AIM

To investigate the effects of resveratrol on oxidative stress and inflammation parameters and histological alterations in cisplatin-induced optic nerve damage in a mouse model.

MATERIAL AND METHOD

Thirty-six albino Wistar male rats were divided into three groups as control, 5 mg/kg cisplatin-administered (Cis) and 5 mg/kg cisplatin + 25 mg/kg resveratrol-administered (Cis + Res) animals. At the end of the experimental period, the rats were sacrificed with high-dose (50 mg/kg) thiopental sodium, and their optic nerves were dissected. Malondialdehyde (MDA), total glutathione (tGSH), total oxidant status (TOS), total antioxidant status (TAS), tumour necrosis factor alpha (TNF-α), nuclear factor kappa B (NF-KB) levels, and histopathological findings were assessed using the optic nerve tissues.

RESULTS

In the Cis + Res group, the MDA, TOS, OSI, TNF-a and NFK-B levels were significantly lower and the tGSH and TAS levels were significantly higher compared with the Cis group (P = 0.001). In histological evaluations, there were dilated and congested blood vessels, destruction, oedema, degeneration, haemorrhage, and proliferating capillaries indicating the presence of inflammation and damage only in the Cis-administered group. However, in the Cis + Res group, the histological findings were very similar to the healthy controls.

CONCLUSION

Resveratrol is a promising neuroprotective agent for cisplatin-induced optic nerve toxicity with its anti-oxidant and anti-inflammatory effects. Further investigations are needed to evaluate the possible therapeutic effects on other optic nerve toxicities.

Neuroprotection in Glaucoma: NAD+/NADH Redox State as a Potential Biomarker and Therapeutic Target

Glaucoma is the leading cause of irreversible blindness worldwide. Its prevalence and incidence increase exponentially with age and the level of intraocular pressure (IOP). IOP reduction is currently the only therapeutic modality shown to slow glaucoma progression. However, patients still lose vision despite best treatment, suggesting that other factors confer susceptibility. Several studies indicate that mitochondrial function may underlie both susceptibility and resistance to developing glaucoma. Mitochondria meet high energy demand, in the form of ATP, that is required for the maintenance of optimum retinal ganglion cell (RGC) function. Reduced nicotinamide adenine dinucleotide (NAD⁺) levels have been closely correlated to mitochondrial dysfunction and have been implicated in several neurodegenerative diseases including glaucoma. NAD⁺ is at the centre of various metabolic reactions culminating in ATP production—essential for RGC function. In this review we present various pathways that influence the NAD⁺(H) redox state, affecting mitochondrial function and making RGCs susceptible to degeneration. Such disruptions of the NAD⁺(H) redox state are generalised and not solely induced in RGCs because of high IOP. This places the NAD⁺(H) redox state as a potential systemic biomarker for glaucoma susceptibility and progression; a hypothesis which may be tested in clinical trials and then translated to clinical practice.

Rescue of retinal ganglion cells in optic nerve injury using cell-selective AAV mediated delivery of SIRT1

SIRT1 prevents retinal ganglion cell (RGC) loss in models of optic neuropathy following pharmacologic activation or genetic overexpression. The exact mechanism of loss is not known, prior evidence suggests this is through oxidative stress to either neighboring cells or RGC specifically. We investigated the neuroprotective potential of RGC-selective SIRT1 gene therapy in the optic nerve crush (ONC) model. We hypothesized that AAV-mediated overexpression of SIRT1 in RGCs reduces RGC loss, thereby preserving visual function. Cohorts of C57Bl/6J mice received intravitreal injection of experimental or control AAVs using either a ganglion cell promoter or a constitutive promoter and ONC was performed. Visual function was examined by optokinetic response (OKR) for 7 days following ONC. Retina and optic nerves were harvested to investigate RGC survival by immunolabeling. The AAV7m8-SNCG.SIRT1 vector showed 44% transduction efficiency for RGCs compared with 25% (P > 0.05) by AAV2-CAG.SIRT1, and AAV7m8-SNCG.SIRT1 drives expression selectively in RGCs in vivo. Animals modeling ONC demonstrated reduced visual acuity compared to controls. Intravitreal delivery of AAV7m8-SNCG.SIRT1 mediated significant preservation of the OKR and RGC survival compared to AAV7m8-SNCG.eGFP controls, an effect not seen with the AAV2 vector. RGC-selective expression of SIRT1 offers a targeted therapy for an animal model with significant ganglion cell loss. Over-expression of SIRT1 through AAV-mediated gene transduction suggests a RGC selective component of neuro-protection using the ONC model. This study expands our understanding of SIRT1 mediated neuroprotection in the context of compressive or traumatic optic neuropathy, making it a strong therapeutic candidate for testing in all optic neuropathies.

Targeting Diet and Exercise for Neuroprotection and Neurorecovery in Glaucoma

Glaucoma is a leading cause of blindness worldwide. In glaucoma, a progressive dysfunction and death of retinal ganglion cells occurs, eliminating transfer of visual information to the brain. Currently, the only available therapies target the lowering of intraocular pressure, but many patients continue to lose vision. Emerging pre-clinical and clinical evidence suggests that metabolic deficiencies and defects may play an important role in glaucoma pathophysiology. While pre-clinical studies in animal models have begun to mechanistically uncover these metabolic changes, some existing clinical evidence already points to potential benefits in maintaining metabolic fitness. Modifying diet and exercise can be implemented by patients as an adjunct to intraocular pressure lowering, which may be of therapeutic benefit to retinal ganglion cells in glaucoma.

RGC and Vision Loss From Traumatic Optic Neuropathy Induced by Repetitive Closed Head Trauma Is Dependent on Timing and Force of Impact

Purpose

Traumatic optic neuropathy (TON) is often caused by blunt head trauma and has no currently effective treatment. Common animal models of TON induced by surgical crush injury are plagued by variability and do not mimic typical mechanisms of TON injury. Traumatic head impact models have recently shown evidence of TON, but the degree of head impact necessary to consistently induce TON is not well characterized, and it is examined here.

Methods

Traumatic skull impacts to C57BL/6J mice were induced using an electromagnetic controlled impact device. One impact performed at two depths (mild and severe), as well as three and five repetitive impacts with an interconcussion interval of 48 hours, were tested. Optokinetic responses (OKRs) and retinal ganglion cell (RGC) loss were measured.

Results

Five repetitive mild impacts significantly decreased OKR scores and RGC numbers compared with control mice 10 weeks after initial impact, with maximal pathology observed by 6 weeks and partial but significant loss present by 3 weeks. One severe impact induced similar TON. Three mild impacts also induced early OKR and RGC loss, but one mild impact did not. Equivalent degrees of TON were induced bilaterally, and a significant correlation was observed between OKR scores and RGC numbers.

Conclusions

Repetitive, mild closed head trauma in mice induces progressive RGC and vision loss that worsens with increasing impacts.

Translational Relevance

Results detail a reproducible model of TON that provides a reliable platform for studying potential treatments over a 3- to 6-week time course.

Curcumin Metabolite Tetrahydrocurcumin in the Treatment of Eye Diseases

Curcumin is one of the most valuable natural products due to its pharmacological activities. However, the low bioavailability of curcumin has long been a problem for its medicinal use. Large studies have been conducted to improve the use of curcumin; among these studies, curcumin metabolites have become a relatively new research focus over the past few years. Additionally, accumulating evidence suggests that curcumin or curcuminoid metabolites have similar or better biological activity than the precursor of curcumin. Recent studies focus on the protective role of plasma tetrahydrocurcumin (THC), a main metabolite of curcumin, against tumors and chronic inflammatory diseases. Nevertheless, studies of THC in eye diseases have not yet been conducted. Since ophthalmic conditions play a crucial role in worldwide public health, the prevention and treatment of ophthalmic diseases are of great concern. Therefore, the present study investigated the antioxidative, anti-inflammatory, antiangiogenic, and neuroprotective effects of THC on four major ocular diseases: age-related cataracts, glaucoma, age-related macular degeneration (AMD), and diabetic retinopathy (DR). While this study aimed to show curcumin as a promising potential solution for eye conditions and discusses the involved mechanistic pathways, further work is required for the clinical application of curcumin.

Natural Products: Evidence for Neuroprotection to Be Exploited in Glaucoma

Glaucoma, a leading cause of irreversible blindness worldwide, is an optic neuropathy characterized by the progressive death of retinal ganglion cells (RGCs). Elevated intraocular pressure (IOP) is recognized as the main risk factor. Despite effective IOP-lowering therapies, the disease progresses in a significant number of patients. Therefore, alternative IOP-independent strategies aiming at halting or delaying RGC degeneration is the current therapeutic challenge for glaucoma management. Here, we review the literature on the neuroprotective activities, and the underlying mechanisms, of natural compounds and dietary supplements in experimental and clinical glaucoma.

Resveratrol protects retinal ganglion cells against ischemia induced damage by increasing Opa1 expression

Loss of idiopathic retinal ganglion cells (RGCs) leads to irreversible vision defects and is considered the primary characteristic of glaucoma. However, effective treatment strategies in terms of RGC neuroprotection remain elusive. In the present study, the protective effects of resveratrol on RGC apoptosis, and the mechanisms underlying its effects were investigated, with a particular emphasis on the function of optic atrophy 1 (Opa1). In an ischemia/reperfusion (I/R) injury model, the notable thinning of the retina, significant apoptosis of RGCs, reduction in Opa1 expression and long Opa1 isoform to short Opa1 isoform ratios (L-Opa1/S-Opa1 ratio) were observed, all of which were reversed by resveratrol administration. Serum deprivation resulted in reductions in R28 cell viability, superoxide dismutase (SOD) activity, Opa1 expression and induced apoptosis, which were also partially reversed by resveratrol treatment. To conclude, results from the present study suggest that resveratrol treatment significantly reduced retinal damage and RGC apoptosis in I/R injury and serum deprivation models. In addition, resveratrol reversed the downregulated expression of Opa1 and reduced SOD activity. Mechanistically, resveratrol influenced mitochondrial dynamics by regulating the L-Opa1/S-Opa1 ratio. Therefore, these observations suggest that resveratrol may exhibit potential as a therapeutic agent for RGC damage in the future.

Effects of caloric restriction on retinal aging and neurodegeneration

Glaucoma is the most common neurodegenerative cause of irreversible blindness worldwide. Restricted caloric regimens are an attractive approach for delaying the progression of neurodegenerative diseases. Here we review the current literature on the effects of caloric restriction on retinal neurons, under physiological and pathological conditions. We focused on autophagy as one of the mechanisms modulated by restricted caloric regimens and involved in the death of retinal ganglion cells (RGCs) over the course of glaucoma.

Axonal protection by a small molecule SIRT1 activator, SRT2104, with alteration of autophagy in TNF-induced optic nerve degeneration

PURPOSE

To examine the effects of SRT2104, an SIRT1 activator, in optic nerve degeneration induced by TNF and to investigate whether it affects the autophagic status after induction of axonal degeneration.

STUDY DESIGN

Experimental.

METHODS

Adult male Wistar rats received intravitreal injection of TNF alone, concomitant injection of SRT2104 and TNF, or injection of SRT2104 alone. The autophagic status in the optic nerve was evaluated to examine p62 and LC3-II expression by immunoblot analysis. The effect of SRT2104 on TNF-induced axon loss was determined by counting the number of axons.

RESULTS

Intravitreal injection of SRT2104 showed a modest protective tendency in the 2-pmol-treated groups against TNF-induced axon loss, although the tendency was not significant on quantitative analysis. However, significant protective effects were found in the 20- or 200-pmol-treated groups. Injection of SRT2104 alone significantly decreased the p62 levels and increased the LC3-II levels as compared with the basal levels. Similarly, concomitant injection of SRT2104 and TNF significantly decreased the p62 levels and increased the LC3-II levels as compared with the TNF-treated group. Upregulation of SIRT1 expression was observed in the optic nerve after SRT2104 treatment.

CONCLUSION

The SIRT1 activator SRT2104 exerts axonal protection in TNF-induced optic nerve degeneration. This effect may be associated with upregulated autophagic status in the optic nerve.

SIRT1 is required for the neuroprotection of resveratrol on retinal ganglion cells after retinal ischemia-reperfusion injury in mice

PURPOSE

Retinal ganglion cells (RGCs) loss is closely related to visual impairment in glaucoma, so the neuroprotection on RGCs is important and novel for glaucoma research. SIRT1, a family member of sirtuins, is implicated in many crucial processes of eye diseases. The purpose of this study is to determine the neuroprotection of SIRT1 on RGCs and to investigate the underlying mechanisms of these effects in an experimental model for acute glaucoma.

METHODS

Retinal ischemia-reperfusion (IR) injury was induced in C57BL/6J mice. Resveratrol (RSV, activator of SIRT1) and sirtinol (inhibitor of SIRT1) were injected intravitreally 1 day before IR injury. RGCs survival rate was quantified by immunofluorescence staining. RGCs apoptosis was evaluated by the staining of TUNEL and cleaved caspase-3, and SIRT1 level was detected by western blot. Expressions of phospho-Akt, Akt, Bax, and Bcl-2 were further determined by western blot to investigate the neuroprotective mechanisms of SIRT1.

RESULTS

RGCs survival rates and SIRT1 levels were decreased over time after IR injury. Intravitreal injection of RSV remarkably attenuated RGCs loss in a dose-dependent manner, and the most effective concentration of RSV was 100 μM. Up-regulation of SIRT1 by RSV significantly inhibited RGCs apoptosis, increased p-Akt level, decreased Bax and cleaved caspase-3 expressions, and all these effects were diminished by 100 μM sirtinol. Moreover, there were no significant changes in total Akt and Bcl-2 levels.

CONCLUSION

SIRT1 activation by RSV confers neuroprotection on RGCs in retinal IR injury through the activation of Akt pathway and subsequent suppression of mitochondrial apoptotic pathway. Determination of the effective concentration of intravitreal injection of RSV also provides a theoretical basis for the clinical application of RSV.

Role of Sirtuins in Retinal Function Under Basal Conditions

Sirtuins are NAD⁺-dependent enzymes that govern cellular homeostasis by regulating the acylation status of their diverse target proteins. We recently demonstrated that both rod and cone photoreceptors rely on NAMPT-mediated NAD⁺ biosynthesis to meet their energetic requirements. Moreover, we found that this NAD⁺-dependent retinal homeostasis relies, in part, on maintenance of optimal activity of the mitochondrial sirtuins and of SIRT3 in particular. Nonetheless, it is unknown whether other sirtuin family members also play important roles in retinal homeostasis. Our results suggest that SIRT1, SIRT2, SIRT4, and SIRT6 are dispensable for retinal survival at baseline, as individual deletion of each of these sirtuins does not cause retinal degeneration by fundus biomicroscopy or retinal dysfunction by ERG. These findings have significant implications and inform future studies investigating the mechanisms underlying the central role of NAD⁺ biosynthesis in retinal survival and function.

Resveratrol Delays Retinal Ganglion Cell Loss and Attenuates Gliosis-Related Inflammation From Ischemia-Reperfusion Injury

Purpose

Resveratrol has been shown to enhance the survival of retinal ganglion cells (RGCs) following ischemia-reperfusion (I/R) injury for glaucoma. However, the precise mechanisms for resveratrol's protective effects are still unclear. The aim of this study is to determine whether resveratrol can inhibit RGC apoptosis, retinal gliosis, and inflammation, all of which are critical events in retinal degeneration following I/R injury.

Methods

Right retinal ischemia was induced in adult male Sprague Dawley rats by increasing intraocular pressure to 110 mm Hg for 60 minutes, and the left eyes maintained at normal pressure serve as the control. Intraperitoneal injection of resveratrol or control buffer was performed continuously for 3 days from pre- to post-I/R injury and the protective effects were evaluated and compared. RGCs were retrogradely labeled with Fluoro-Gold by injection into superior colliculi. Apoptosis was detected by TUNEL staining. Western blotting and immunostaining for Bax, Bcl-2, and Caspase-3 were used to explore the Bax-associated apoptotic pathway. Gliosis was assessed by western blotting and immunostaining of retinal cross sections with anti-glial fibrillary acidic protein (GFAP) antibodies.

Results

In this study, resveratrol treatment significantly reduced retinal damage and RGC loss as demonstrated by the relatively intact tissue structure in hematoxylin and eosin staining at day 7 and increased Fluoro-Gold labeling of RGCs at day 14, respectively. We found that resveratrol exhibited an anti-apoptotic effect as assessed by reduced TUNEL staining, inhibition of the early upregulated expression of the apoptosis-related protein Bax, and decreased subsequently cleaved caspase-3. However, it did not affect Bcl-2 levels. Moreover, in our I/R injury model, the combined response of reactive gliosis and related inflammation, which were demonstrated by an early induction of pro-inflammatory mediators and subsequently increased GFAP level, were significantly attenuated after resveratrol treatment.

Conclusions

These results demonstrate that resveratrol can prevent RGC death by blocking the Bax-caspase-3-dependent apoptotic pathway and suppressed gliosis-related inflammation in the retina after I/R injury. Together these results support the use of resveratrol as a possible therapeutic strategy for glaucoma.

RGC Neuroprotection Following Optic Nerve Trauma Mediated By Intranasal Delivery of Amnion Cell Secretome

Purpose

Intranasally delivered ST266, the biological, proteinaceous secretome of amnion-derived multipotent progenitor cells, reduces retinal ganglion cell (RGC) loss, optic nerve inflammation, and demyelination in experimental optic neuritis. This unique therapy and novel administration route delivers numerous cytokines and growth factors to the eye and optic nerve, suggesting a potential to also treat other optic neuropathies. Thus, ST266-mediated neuroprotection was examined following traumatic optic nerve injury.

Methods

Optic nerve crush injury was surgically induced in C57BL/6J mice. Mice were treated daily with intranasal PBS or ST266. RGC function was assessed by optokinetic responses (OKRs), RGCs were counted, and optic nerve sections were stained with luxol fast blue and anti-neurofilament antibodies to assess myelin and RGC axon damage.

Results

Intranasal ST266 administered daily for 5 days, beginning at the time that a 1-second optic nerve crush was performed, significantly attenuated OKR decreases. Furthermore, ST266 treatment reduced damage to RGC axons and myelin within optic nerves, and blocked RGC loss. Following a 4-second optic nerve crush, intranasal ST266 increased RGC survival and showed a trend toward reduced RGC axon and myelin damage. Ten days following optic nerve crush, ST266 prevented myelin damage, while also inducing a trend toward increased RGC survival and visual function.

Conclusions

ST266 significantly attenuates traumatic optic neuropathy. Neuroprotective effects of this unique combination of biologic molecules observed here and previously in optic neuritis suggest potential broad application for preventing neuronal damage in multiple optic nerve disorders. Furthermore, results support intranasal delivery as a novel, noninvasive therapeutic modality for eyes and optic nerves.

SIRT1 and NRF2 Gene Transfer Mediate Distinct Neuroprotective Effects Upon Retinal Ganglion Cell Survival and Function in Experimental Optic Neuritis

Purpose

Optic neuritis is a condition defined by autoimmune-mediated demyelination of the optic nerve and death of retinal ganglion cells. SIRT1 and NRF2 stimulate anti-inflammatory mechanisms and have previously demonstrated therapeutic value in preclinical models of neurodegenerative disease. Here we investigated the neuroprotective potential of SIRT1 or NRF2 gene transfer using adeno-associated virus (AAV) vectors in the experimental autoimmune encephalomyelitis (EAE) model of multiple sclerosis.

Methods

C57Bl/6J mice were administered intravitreal doses of AAV2 vectors and immunized to induce EAE symptoms. Visual function was examined by recording the optokinetic response (OKR) just prior to EAE induction and once every 7 days postinduction for 7 weeks. Retina and optic nerves were harvested to investigate retinal ganglion cell survival (immunolabeling with Brn3a antibodies); inflammation (hematoxylin and eosin staining); and demyelination (luxol fast blue staining).

Results

Animals modeling EAE demonstrate reduced visual acuity compared to sham-induced controls. Intravitreal delivery of AAV2-NRF2 did not preserve visual function. However, AAV2-SIRT1 mediated significant preservation of the OKR compared to AAV2-eGFP controls. Treatment with AAV2-NRF2 promoted RGC survival while AAV2-SIRT1 mediated an upward trend in protection compared to vehicle and AAV2-eGFP controls. Neither NRF2 nor SIRT1 gene augmentation was able to suppress optic nerve inflammation or demyelination.

Conclusions

AAV-mediated overexpression of NRF2 or SIRT1 within RGCs mediates distinct neuroprotective effects upon visual function and RGC survival. This study expands our understanding of SIRT1 and NRF2-mediated neuroprotection in the context of MS pathogenesis and optic neuropathies.

Role of Sirtuin 1 in the pathogenesis of ocular disease (Review)

Sirtuin (SIRT)1, a member of the SIRT family, is a highly conserved NAD+‑dependent histone deacetylase, which has a regulatory role in numerous physiological and pathological processes by removing acetyl groups from various proteins. SIRT1 controls the activity of numerous transcription factors and cofactors, which impacts the downstream gene expression, and eventually alleviates oxidative stress and associated damage. Numerous studies have revealed that dysfunction of SIRT1 is linked with ocular diseases, including cataract, age‑associated macular degeneration, diabetic retinopathy and glaucoma, while ectopic upregulation of SIRT1 protects against various ocular diseases. In the present review, the significant role of SIRT1 and the potential therapeutic value of modulating SIRT1 expression in ocular development and eye diseases is summarized.

Role and Possible Mechanisms of Sirt1 in Depression

Depression is a common, devastating illness. Due to complicated causes and limited treatments, depression is still a major problem that plagues the world. Silent information regulator 1 (Sirt1) is a deacetylase at the consumption of NAD⁺ and is involved in gene silencing, cell cycle, fat and glucose metabolism, cellular oxidative stress, and senescence. Sirt1 has now become a critical therapeutic target for a number of diseases. Recently, a genetic study has received considerable attention for depression and found that Sirt1 is a potential gene target. In this short review article, we attempt to present an up-to-date knowledge of depression and Sirt1 of the sirtuin family, describe the different effects of Sirt1 on depression, and further discuss possible mechanisms of Sirt1 including glial activation, neurogenesis, circadian control, and potential signaling molecules. Thus, it will open a new avenue for clinical treatment of depression.

Expression of Sirtuins in the Retinal Neurons of Mice, Rats, and Humans

Sirtuins are a class of histone deacetylases (HDACs) that have been shown to regulate a range of pathophysiological processes such as cellular aging, inflammation, metabolism, and cell proliferation. There are seven mammalian Sirtuins (SIRT1-7) that play important roles in stress response, aging, and neurodegenerative diseases. However, the location and function of Sirtuins in neurons are not well defined. This study assessed the retinal expression of Sirtuins in mice, rats, and humans and measured the expression of Sirtuins in aged and injured retinas. Expression of all 7 Sirtuins was confirmed by Western blot and Real-Time PCR analysis in all three species. SIRT1 is highly expressed in mouse, rat, and human retinas, whereas SIRT2-7 expression was relatively lower in human retinas. Immunofluorescence was also used to examine the expression and localization of Sirtuins in rat retinal neurons. Importantly, we demonstrate a marked reduction of SIRT1 expression in aged retinal neurons as well as retinas injured by acute ischemia-reperfusion. On the other hand, none of the other Sirtuins exhibit any significant age-related changes in expression except for SIRT5, which was significantly higher in the retinas of adults compared to both young and aged rats. Our work presents the first composite analysis of Sirtuins in the retinal neurons of mice, rats, and humans, and suggests that increasing the expression and activity of SIRT1 may be beneficial for the treatment of glaucoma and other age-related eye dysfunction.

The role and therapeutic potential of melatonin in age-related ocular diseases

The eye is continuously exposed to solar UV radiation and pollutants, making it prone to oxidative attacks. In fact, oxidative damage is a major cause of age-related ocular diseases including cataract, glaucoma, age-related macular degeneration, and diabetic retinopathy. As the nature of lens cells, trabecular meshwork cells, retinal ganglion cells, retinal pigment epithelial cells, and photoreceptors is postmitotic, autophagy plays a critical role in their cellular homeostasis. In age-related ocular diseases, this process is impaired, and thus, oxidative damage becomes irreversible. Other conditions such as low-grade chronic inflammation and angiogenesis also contribute to the development of retinal diseases (glaucoma, age-related macular degeneration and diabetic retinopathy). As melatonin is known to have remarkable qualities such as antioxidant/antinitridergic, mitochondrial protector, autophagy modulator, anti-inflammatory, and anti-angiogenic, it can represent a powerful tool to counteract all these diseases. The present review analyzes the role and therapeutic potential of melatonin in age-related ocular diseases, focusing on nitro-oxidative stress, autophagy, inflammation, and angiogenesis mechanisms.

Mitochondrial Uncoupler Prodrug of 2,4-Dinitrophenol, MP201, Prevents Neuronal Damage and Preserves Vision in Experimental Optic Neuritis

The ability of novel mitochondrial uncoupler prodrug of 2,4-dinitrophenol (DNP), MP201, to prevent neuronal damage and preserve visual function in an experimental autoimmune encephalomyelitis (EAE) model of optic neuritis was evaluated. Optic nerve inflammation, demyelination, and axonal loss are prominent features of optic neuritis, an inflammatory optic neuropathy often associated with the central nervous system demyelinating disease multiple sclerosis. Currently, optic neuritis is frequently treated with high-dose corticosteroids, but treatment fails to prevent permanent neuronal damage and associated vision changes that occur as optic neuritis resolves, thus suggesting that additional therapies are required. MP201 administered orally, once per day, attenuated visual dysfunction, preserved retinal ganglion cells (RGCs), and reduced RGC axonal loss and demyelination in the optic nerves of EAE mice, with limited effects on inflammation. The prominent mild mitochondrial uncoupling properties of MP201, with slow elimination of DNP, may contribute to the neuroprotective effect by modulating the entire mitochondria's physiology directly. Results suggest that MP201 is a potential novel treatment for optic neuritis.

Metabolic Vulnerability in the Neurodegenerative Disease Glaucoma

Axons can be several orders of magnitude longer than neural somas, presenting logistical difficulties in cargo trafficking and structural maintenance. Keeping the axon compartment well supplied with energy also presents a considerable challenge; even seemingly subtle modifications of metabolism can result in functional deficits and degeneration. Axons require a great deal of energy, up to 70% of all energy used by a neuron, just to maintain the resting membrane potential. Axonal energy, in the form of ATP, is generated primarily through oxidative phosphorylation in the mitochondria. In addition, glial cells contribute metabolic intermediates to axons at moments of high activity or according to need. Recent evidence suggests energy disruption is an early contributor to pathology in a wide variety of neurodegenerative disorders characterized by axonopathy. However, the degree to which the energy disruption is intrinsic to the axon vs. associated glia is not clear. This paper will review the role of energy availability and utilization in axon degeneration in glaucoma, a chronic axonopathy of the retinal projection.

Intranasal Delivery of A Novel Amnion Cell Secretome Prevents Neuronal Damage and Preserves Function In A Mouse Multiple Sclerosis Model

The ability of a novel intranasally delivered amnion cell derived biologic to suppress inflammation, prevent neuronal damage and preserve neurologic function in the experimental autoimmune encephalomyelitis animal model of multiple sclerosis was assessed. Currently, there are no existing optic nerve treatment methods for disease or trauma that result in permanent vision loss. Demyelinating optic nerve inflammation, termed optic neuritis, induces permanent visual dysfunction due to retinal ganglion cell damage in multiple sclerosis and experimental autoimmune encephalomyelitis. ST266, the biological secretome of Amnion-derived Multipotent Progenitor cells, contains multiple anti-inflammatory cytokines and growth factors. Intranasally administered ST266 accumulated in rodent eyes and optic nerves, attenuated visual dysfunction, and prevented retinal ganglion cell loss in experimental optic neuritis, with reduced inflammation and demyelination. Additionally, ST266 reduced retinal ganglion cell death in vitro. Neuroprotective effects involved oxidative stress reduction, SIRT1-mediated mitochondrial function promotion, and pAKT signaling. Intranasal delivery of neuroprotective ST266 is a potential novel, noninvasive therapeutic modality for the eyes, optic nerves and brain. The unique combination of biologic molecules in ST266 provides an innovative approach with broad implications for suppressing inflammation in autoimmune diseases, and for preventing neuronal damage in acute neuronal injury and chronic neurodegenerative diseases such as multiple sclerosis.

Sirtuins Expression and Their Role in Retinal Diseases

Sirtuins have received considerable attention since the discovery that silent information regulator 2 (Sir2) extends the lifespan of yeast. Sir2, a nicotinamide adenine dinucleotide- (NAD-) dependent histone deacetylase, serves as both a transcriptional effector and energy sensor. Oxidative stress and apoptosis are implicated in the pathogenesis of neurodegenerative eye diseases. Sirtuins confer protection against oxidative stress and retinal degeneration. In mammals, the sirtuin (SIRT) family consists of seven proteins (SIRT1–SIRT7). These vary in tissue specificity, subcellular localization, and enzymatic activity and targets. In this review, we present the current knowledge of the sirtuin family and discuss their structure, cellular location, and biological function with a primary focus on their role in different neuroophthalmic diseases including glaucoma, optic neuritis, and age-related macular degeneration. The potential role of certain therapeutic targets is also described.

Evaluating retinal ganglion cell loss and dysfunction

Retinal ganglion cells (RGC) bear the sole responsibility of propagating visual stimuli to the brain. Their axons, which make up the optic nerve, project from the retina to the brain through the lamina cribrosa and in rodents, decussate almost entirely at the optic chiasm before synapsing at the superior colliculus. For many traumatic and degenerative ocular conditions, the dysfunction and/or loss of RGC is the primary determinant of visual loss and are the measurable endpoints in current research into experimental therapies. To actually measure these endpoints in rodent models, techniques must ascertain both the quantity of surviving RGC and their functional capacity. Quantification techniques include phenotypic markers of RGC, retrogradely transported fluorophores and morphological measurements of retinal thickness whereas functional assessments include electroretinography (flash and pattern) and visual evoked potential. The importance of the accuracy and reliability of these techniques cannot be understated, nor can the relationship between RGC death and dysfunction. The existence of up to 30 types of RGC complicates the measuring process, particularly as these may respond differently to disease and treatment. Since the above techniques may selectively identify and ignore particular subpopulations, their appropriateness as measures of RGC survival and function may be further limited. This review discusses the above techniques in the context of their subtype specificity.

The glucagon like peptide 1 analogue, exendin-4, attenuates oxidative stress-induced retinal cell death in early diabetic rats through promoting Sirt1 and Sirt3 expression

This study was aimed to further investigate the possible mechanisms by which the glucagon like peptide 1 analogue, exendin-4 (EX4), protects rat retinal cells at the early stage of diabetes. EX4 was injected intravitreally into normal and early-stage streptozotocin-diabetic rats. Cell death, reactive oxygen species (ROS), and electroretinogram (ERG) were measured. Sirtuin (Sirt) mRNA and protein were analyzed. In retinas of diabetic rats 1 month after diabetes onset, cell death and ROS level increased significantly, and the b-wave amplitudes and OPs were significantly reduced. Four days after intravitreal EX4 treatment, retinal cell death and ROS level in retinas reduced significantly, and visual function was recovered. In the retinas of early-stage diabetic rats, the expressions of Sirt1 and Sirt3 were also found to be significantly decreased, and both were back to normal levels after intravitreal injection of EX4. In R28 cells, hydrogen peroxide (H2O2) treatment increased ROS and cell death and decreased Sirt1 and Sirt3. With the addition of EX4 into the culture system, the expressions of Sirt1 and Sirt3 were increased, and the H2O2-induced ROS and cell death were significantly reduced. These results confirm a mechanism for EX4 to protect retinal cells from diabetic damage and oxidative injury. EX4 reduces retinal cell death and ROS generation by upregulating Sirt1 and Sirt3 expressions in the retina of early-stage diabetic rats as well as in H2O2-treated R28 cells.

The involvement of sirtuins during optic nerve injury of rats

Sirtuins, comprised of seven members, protect cells from injury, possibly through different roles. In this study, we used two young rat optic nerve injury models to analyze the changes in Sirts 1-7 at different time points to better understand the role of sirtuins during optic nerve injury. Twelve-week-old adult male F344 rats (total n=42) were divided randomly into two groups. One group was subjected to optic nerve cut (ON-cut) and the other group was subjected to a peripheral nerve-optic nerve graft (PN-ON graft) on the left eye. At 1 and 3 days and 1, 2, and 4 weeks, rats were euthanized and retinas of both eyes were removed. Total RNA was extracted and first-strand cDNA was synthesized. Sirts 1-7 and housekeeping β-actin quantitative real-time PCR were performed. The quantitative real-time PCR profile showed that sirtuin mRNAs in both groups increased following optic nerve injury with and without peripheral nerve grafting. Sirt1 mRNA increased rapidly, reaching its peak at 3 days after surgery. Sirts 2-7 showed an increasing trend and remained high through 4 weeks after surgery. Sirts 4 and 6 were the only Sirts that increased in number in the PN-graft group at 4 weeks after surgery, where neuronal survival should be higher. Our data indicate that Sirt1 and Sirts 2-7 may play different or complementary roles in optic nerve injury and that Sirts 4 and 6 may play a greater role than the remaining Sirts in axon regeneration.