A Small Natural Molecule S3 Protects Retinal Ganglion Cells and Promotes Parkin-Mediated Mitophagy against Excitotoxicity.

Glutamate excitotoxicity may contribute to retinal ganglion cell (RGC) degeneration in glaucoma and other optic neuropathies, leading to irreversible blindness. Growing evidence has linked impaired mitochondrial quality control with RGCs degeneration, while parkin, an E3 ubiquitin ligase, has proved to be protective and promotes mitophagy in RGCs against excitotoxicity. The purpose of this study was to explore whether a small molecule S3 could modulate parkin-mediated mitophagy and has therapeutic potential for RGCs. The results showed that as an inhibitor of deubiquitinase USP30, S3 protected cultured RGCs and improved mitochondrial health against NMDA-induced excitotoxicity. Administration of S3 promoted the parkin expression and its downstream mitophagy-related proteins in RGCs. An upregulated ubiquitination level of Mfn2 and protein level of OPA1 were also observed in S3-treated RGCs, while parkin knockdown resulted in a major loss of the protective effect of S3 on RGCs under excitotoxicity. These findings demonstrated that S3 promoted RGC survival mainly through enhancing parkin-mediated mitophagy against excitotoxicity. The neuroprotective value of S3 in glaucoma and other optic neuropathies deserves further investigation.

Comparative analysis of OCT-defined parapapillary beta and gamma zones between primary open angle glaucoma and primary angle closure glaucoma.

The ophthalmoscopic beta zone of parapapillary atrophy has recently been proposed to divide into a gamma zone and a (new) beta zone based on OCT imaging. The present study was undertaken to compare the microstructural characteristics of parapapillary gamma and beta zones and their influencing factors between primary open angle glaucoma (POAG) and primary angle closure glaucoma (PACG). Seventy-three PACG patients that had no evidence of an acute attack and 78 POAG patients were enrolled. Patients were matched by propensity scores for age and visual field mean defect (MD) value. The area and angular extent of both zones were measured. In multivariate analysis, a larger beta zone was correlated with older age, severe MD value and longer axial length. A larger gamma zone was correlated with longer axial length. Older age and severe MD value were correlated with the concentric shape of beta zone. Comparing the PACG and POAG groups that adjusted for age and MD value, gamma zone was larger and more prevalent in the POAG group, while beta zone showed no significant difference. Taken separately, MD value was associated with the area and shape of beta zone in the PACG group. Axial length was associated with the temporal shape of beta zone in the POAG group. These data indicated that OCT-defined parapapillary beta and gamma zones exhibited different characteristics in two types of glaucoma. Clinically, the size of parapapillary beta zone may serve as a better indicator of glaucoma severity in eyes with PACG than that in POAG.

Nicotinamide ameliorates energy deficiency and improves retinal function in Cav-1-/- mice.

Caveolin-1(Cav-1) is involved in lipid metabolism and energy homeostasis, which is important for the energetically demanding retina. Although retinal function deficits were noted in Cav-1 knockout (Cav-1-/- ) mice, the underlying causes remain largely unknown. Here, we investigate if the disruption in energy homeostasis presents a potential mechanism for retinal function deficits in Cav-1-/- retina and if it can be ameliorated by nicotinamide (NAM). In this study, NAM was administrated orally for 2 weeks in Cav-1-/- mice before experiments. Oxidative lipidomics was conducted to detect the oxylipin changes, the retinal energy flux was measured by seahorse assay, and the retinal function was assessed by electroretinogram (ERG). Cav-1 deficiency induced the dysregulation of oxidative lipidomics and reduction in energy consumption/production in the retina by decreasing Na+ /K+ -ATPase, oxidative phosphorylation CII, cytochrome c, and oxygen consumption rate (OCR). A decrease in Sirt1 was also detected. Therapeutic administration of NAM significantly increased Sirt1 expression and improved energy deficiency by increasing Na+ /K+ -ATPase, cytochrome c, and OCR. The dysregulation of oxidative lipidomics was partially recovered, and the retinal function was improved as assessed by ERG compared to Cav-1-/- mice. Our study demonstrated the dysregulation of oxidative lipidomics in Cav-1-/- retina and established a link between energy deficiency and retinal function deficits in Cav-1-/- mice. Administration of NAM ameliorated energy deficiency, increased the expression of Sirt1, and improved retinal function, which presents a potential therapeutic strategy for Cav-1 deficiency-induced retinal function deficits.

Therapeutic Targeting of Retinal Immune Microenvironment With CSF-1 Receptor Antibody Promotes Visual Function Recovery After Ischemic Optic Neuropathy.

Retinal ischemia/reperfusion injury (RI) is a common cause of irreversible visual impairment and blindness in elderly and critical unmet medical need. While no effective treatment is available for RI, microglial activation and local immune responses in the retina are thought to play important roles in the pathophysiology of neurodegeneration. While survival and activation of microglia depend critically on colony-stimulating factor receptor (CSF-1R) signaling, it remains unclear if targeting the retinal immune microenvironments by CSF-1RAb after RI is sufficient to rescue vision and present a potentially effective therapy. Here we used rodent models of RI and showed that retinal ischemia induced by acute elevation of intraocular pressure triggered an early activation of microglia and macrophages in the retina within 12 h. This was followed by lymphocyte infiltration and increased production of pro-inflammatory cytokines. Intravitreal injection of CSF-1R neutralizing antibody (CSF-1RAb) after RI significantly blocked microglial activation and the subsequent T cell recruitment. This also led to improved retinal ganglion cell survival and function measured by cell quantification and electroretinogram positive scotopic threshold responses, as well as increased visual acuity and contrast sensitivity as assessed by optomotor reflex-based assays, when compared to the isotype-treated control group. Moreover, the administration of CSF-1RAb efficiently attenuated inflammatory responses and activation of human microglia in culture, suggesting a therapeutic target with human relevance. These results, together with the existing clinical safety profiles, support that CSF-1RAb may present a promising therapeutic avenue for RI, a currently untreatable condition, by targeting microglia and the immune microenvironment in the retina to facilitate neural survival and visual function recovery.

The small molecule inhibitor PR-619 protects retinal ganglion cells against glutamate excitotoxicity.

Glutamate excitotoxicity may contribute to the death of retinal ganglion cell (RGC) in glaucoma and other retinal diseases such as ischemia. Deubiquitinating enzyme (DUB) inhibitors are emerging as attractive targets for pharmacological intervention in neurodegenerative diseases. However, the role of PR-619, the broad spectrum DUB inhibitor, on RGCs under different stressful environment remains largely unknown. This study was designed to investigate the role of PR-619 in regulating mitophagy of RGCs under glutamate excitotoxicity. Primary cultured RGCs were incubated with PR-619 or vehicle control in the excitotoxicity model of 100 µM glutamate treatment. Mitochondrial membrane potential was assessed by JC-1 assay. Cytotoxicity of RGCs was measured by LDH activity. Proteins levels of parkin, optineurin, LAMP1, Bax, Bcl-2 and the LC3-II/I ratio were analyzed by western blot. The distribution and morphology of mitochondria in RGCs was stained by MitoTracker and antibody against mitochondria membrane protein, and examined by confocal microscopy. We show here that in the presence of glutamate-induced excitotoxicity, PR-619 stabilized the mitochondrial membrane potential of RGCs, decreased cytotoxicity and apoptosis, attenuated the expression of Bax. Meanwhile, PR-619 promoted the protein levels of Bcl-2, parkin, optineurin, LAMP1 and the LC3-II/I ratio. While knockdown of parkin by siRNA diminished the neuroprotective effect of PR-619 on RGCs. These findings demonstrate that PR-619 exerted a neuroprotective effect and promoted parkin-mediated mitophagy on cultured RGCs against glutamate excitotoxicity. DUB inhibitors may be useful in protecting RGCs through modulating the parkin-mediated mitophagy pathway against excitotoxicity.