Changes in Retinal Glial Cells with Age and during Development of Age-Related Macular Degeneration

The impact of sestrin2 on reactive oxygen species in diabetic retinopathy

Diabetic retinopathy (DR) is a significant complication of diabetes that often leads to blindness, impacting Müller cells, the primary retinal macroglia involved in DR pathogenesis. Reactive oxygen species (ROS) play a crucial role in the development of DR. The objective of this study was to investigate the involvement of sestrin2 in DR using a high-glucose (HG)-induced Müller cell model and assessing cell proliferation with 5-ethynyl-2-deoxyuridine (EdU) labeling. Following this, sestrin2 was upregulated in Müller cells to investigate its effects on ROS, tube formation, and inflammation both in vitro and in vivo, as well as its interaction with the nuclear factor erythroid2-related factor 2 (Nrf2) signaling pathway. The findings demonstrated a gradual increase in the number of EdU-positive cells over time, with a subsequent decrease after 72 h of exposure to high glucose levels. Additionally, the expression of sestrin2 exhibited a progressive increase over time, followed by a decrease at 72 h. The rh-sestrin2 treatment suppressed the injury of Müller cells, decreased ROS level, and inhibited the tube formation. Rh-sestrin2 treatment enhanced the expression of sestrin2, Nrf2, heme oxygenase-1 (HO-1), and glutamine synthetase (GS); however, the ML385 treatment reversed the protective effect of rh-sestrin2. Finally, we evaluated the effect of sestrin2 in a DR rat model. Sestrin2 overexpression treatment improved the pathological injury of retina and attenuated the oxidative damage and inflammatory reaction. Our results highlighted the inhibitory effect of sestrin2 in the damage of retina, thus presenting a novel therapeutic sight for DR.

Age-related dysregulation of the retinal transcriptome in African turquoise killifish

Age-related vision loss caused by retinal neurodegenerative pathologies is becoming more prevalent in our ageing society. To understand the physiological and molecular impact of ageing on retinal homeostasis, we used the short-lived African turquoise killifish, a model known to naturally develop central nervous system (CNS) ageing hallmarks and vision loss. Bulk and single-cell RNA-sequencing (scRNAseq) of three age groups (6-, 12-, and 18-week-old) identified transcriptional ageing fingerprints in the killifish retina, unveiling pathways also identified in the aged brain, including oxidative stress, gliosis, and inflammageing. These findings were comparable to observations in the ageing mouse retina. Additionally, transcriptional changes in genes related to retinal diseases, such as glaucoma and age-related macular degeneration, were observed. The cellular heterogeneity in the killifish retina was characterized, confirming the presence of all typical vertebrate retinal cell types. Data integration from age-matched samples between the bulk and scRNAseq experiments revealed a loss of cellular specificity in gene expression upon ageing, suggesting potential disruption in transcriptional homeostasis. Differential expression analysis within the identified cell types highlighted the role of glial/immune cells as important stress regulators during ageing. Our work emphasizes the value of the fast-ageing killifish in elucidating molecular signatures in age-associated retinal disease and vision decline. This study contributes to the understanding of how age-related changes in molecular pathways may impact CNS health, providing insights that may inform future therapeutic strategies for age-related pathologies.

Müller Glial Cells in the Macula: Their Activation and Cell-Cell Interactions in Age-Related Macular Degeneration

Müller glia, the main glial cell of the retina, are critical for neuronal and vascular homeostasis in the retina. During age-related macular degeneration (AMD) pathogenesis, Müller glial activation, remodeling, and migrations are reported in the areas of retinal pigment epithelial (RPE) degeneration, photoreceptor loss, and choroidal neovascularization (CNV) lesions. Despite this evidence indicating glial activation localized to the regions of AMD pathogenesis, it is unclear whether these glial responses contribute to AMD pathology or occur merely as a bystander effect. In this review, we summarize how Müller glia are affected in AMD retinas and share a prospect on how Müller glial stress might directly contribute to the pathogenesis of AMD. The goal of this review is to highlight the need for future studies investigating the Müller cell's role in AMD. This may lead to a better understanding of AMD pathology, including the conversion from dry to wet AMD, which has no effective therapy currently and may shed light on drug intolerance and resistance to current treatments.

A novel capsid-XL32-derived adeno-associated virus serotype prompts retinal tropism and ameliorates choroidal neovascularization

Gene therapy has been adapted, from the laboratory to the clinic, to treat retinopathies. In contrast to subretinal route, intravitreal delivery of AAV vectors displays the advantage of bypassing surgical injuries, but the viral particles are more prone to be nullified by the host neutralizing factors. To minimize such suppression of therapeutic effect, especially in terms of AAV2 and its derivatives, we introduced three serine-to-glycine mutations, based on the phosphorylation sites identified by mass spectrum analysis, to the XL32 capsid to generate a novel serotype named AAVYC5. Via intravitreal administration, AAVYC5 was transduced more effectively into multiple retinal layers compared with AAV2 and XL32. AAVYC5 also enabled successful delivery of anti-angiogenic molecules to rescue laser-induced choroidal neovascularization and astrogliosis in mice and non-human primates. Furthermore, we detected fewer neutralizing antibodies and binding IgG in human sera against AAVYC5 than those specific for AAV2 and XL32. Our results thus implicate this capsid-optimized AAVYC5 as a promising vector suitable for a wide population, particularly those with undesirable AAV2 seroreactivity.

Astrocytes and brain-derived neurotrophic factor (BDNF)

Astrocytes are emerging in the neuroscience field as crucial modulators of brain functions, from the molecular control of synaptic plasticity to orchestrating brain-wide circuit activity for cognitive processes. The cellular pathways through which astrocytes modulate neuronal activity and plasticity are quite diverse. In this review, we focus on neurotrophic pathways, mostly those mediated by brain-derived neurotrophic factor (BDNF). Neurotrophins are a well-known family of trophic factors with pleiotropic functions in neuronal survival, maturation and activity. Within the brain, BDNF is the most abundantly expressed and most studied of all neurotrophins. While we have detailed knowledge of the effect of BDNF on neurons, much less is known about its physiology on astroglia. However, over the last years new findings emerged demonstrating that astrocytes take an active part into BDNF physiology. In this work, we discuss the state-of-the-art knowledge about astrocytes and BDNF. Indeed, astrocytes sense extracellular BDNF through its specific TrkB receptors and activate intracellular responses that greatly vary depending on the brain area, stage of development and receptors expressed. Astrocytes also uptake and recycle BDNF / proBDNF at synapses contributing to synaptic plasticity. Finally, experimental evidence is now available describing deficits in astrocytic BDNF in several neuropathologies, suggesting that astrocytic BDNF may represent a promising target for clinical translation.

CCR1 mediates Müller cell activation and photoreceptor cell death in macular and retinal degeneration

Mononuclear cells are involved in the pathogenesis of retinal diseases, including age-related macular degeneration (AMD). Here, we examined the mechanisms that underlie macrophage-driven retinal cell death. Monocytes were extracted from patients with AMD and differentiated into macrophages (hMdɸs), which were characterized based on proteomics, gene expression, and ex vivo and in vivo properties. Using bioinformatics, we identified the signaling pathway involved in macrophage-driven retinal cell death, and we assessed the therapeutic potential of targeting this pathway. We found that M2a hMdɸs were associated with retinal cell death in retinal explants and following adoptive transfer in a photic injury model. Moreover, M2a hMdɸs express several CCRI (C-C chemokine receptor type 1) ligands. Importantly, CCR1 was upregulated in Müller cells in models of retinal injury and aging, and CCR1 expression was correlated with retinal damage. Lastly, inhibiting CCR1 reduced photic-induced retinal damage, photoreceptor cell apoptosis, and retinal inflammation. These data suggest that hMdɸs, CCR1, and Müller cells work together to drive retinal and macular degeneration, suggesting that CCR1 may serve as a target for treating these sight-threatening conditions.

Glutathione trisulfide prevents lipopolysaccharide-induced retinal inflammation via inhibition of proinflammatory cytokine production in glial cells

We aimed to investigate the impact of glutathione trisulfide (GSSSG) on lipopolysaccharide (LPS)-induced inflammation in retinal glia. Inflammatory responses in mouse-derived glial cells and Wistar rat retinas were stimulated with administration of LPS. Cell survival and proinflammatory cytokine production were examined using the Calcein-AM assay, and reverse transcription-quantitative polymerase chain reaction (RT-qPCR) and enzyme-linked immunosorbent assay (ELISA), respectively. Retinal microglia were visualized with immunohistochemistry for Iba1. Administration of LPS (10 µg/mL) or GSSSG (less than 100 µM) did not affect survival of cultured primary Müller cells and established microglial cells (BV-2). RT-qPCR and ELISA indicated that GSSSG inhibited LPS-induced gene upregulation and protein secretion of proinflammatory cytokines in these glial cells and rat retinas. GSSSG inhibited LPS-induced activation of TGF-β-activated kinase 1 (TAK1), which is an upstream kinase of NF-κB, in BV-2 cells. Finally, in vivo experiments indicated that intravitreal administration of GSSSG but not its relative glutathione disulfide (GSSG) inhibited LPS (500 ng)-induced accumulation of Iba1-immunopositive microglia in rat retinas. Taken together, GSSSG has the potential to prevent pathogenesis of inflammation-associated ocular diseases by inhibiting proinflammatory cytokine expression in retinal glial cells.

Aqueous Fluid Transcriptome Profiling Differentiates Between Non-Neovascular and Neovascular AMD

Purpose

Early and intermediate non-neovascular AMD (NN-AMD) has the potential to progress to either advanced NN-AMD with geographic atrophy, or to neovascular AMD (N-AMD) with CNV. This exploratory study performed an unbiased analysis of aqueous humor transcriptome in patients with early or intermediate NN-AMD vs. treatment-naïve N-AMD to determine the feasibility of using this method in future studies investigating pathways and triggers for conversion from one form to another.

Methods

Aqueous humor samples were obtained from 20 patients with early or intermediate NN-AMD and 20 patients with untreated N-AMD, graded on clinical examination and optical coherence tomography. Transcriptome profiles were generated using next-generation sequencing methods optimized for ocular samples. Top-ranked transcripts were compared between groups, and pathway enrichment analysis was performed.

Results

Seventy-eight differentially expressed transcripts were identified. Unsupervised clustering of differentially expressed transcripts was able to successfully differentiate between the two groups based on aqueous transcriptome alone. Pathway analysis highlighted changes in expression of genes associated with mitochondrial respiration, oxidative stress, ubiquitination, and neurogenesis between the two groups.

Conclusions

This pilot study compared the aqueous fluid transcriptome of patients with early or intermediate NN-AMD and untreated N-AMD. Differences in transcripts and transcriptome pathways identified in the aqueous of patients with early or intermediate NN-AMD compared with patients with N-AMD are consistent with those previously implicated in the pathogenesis of these distinct AMD subtypes. The findings from this exploratory study warrant further investigation using a larger, prospective study design, with the inclusion of a control group of eyes without AMD.

The central role of the NLRP3 inflammasome pathway in the pathogenesis of age-related diseases in the eye and the brain

With increasing age, structural changes occur in the eye and brain. Neuronal death, inflammation, vascular disruption, and microglial activation are among many of the pathological changes that can occur during ageing. Furthermore, ageing individuals are at increased risk of developing neurodegenerative diseases in these organs, including Alzheimer's disease (AD), Parkinson's disease (PD), glaucoma and age-related macular degeneration (AMD). Although these diseases pose a significant global public health burden, current treatment options focus on slowing disease progression and symptomatic control rather than targeting underlying causes. Interestingly, recent investigations have proposed an analogous aetiology between age-related diseases in the eye and brain, where a process of chronic low-grade inflammation is implicated. Studies have suggested that patients with AD or PD are also associated with an increased risk of AMD, glaucoma, and cataracts. Moreover, pathognomonic amyloid-β and α-synuclein aggregates, which accumulate in AD and PD, respectively, can be found in ocular parenchyma. In terms of a common molecular pathway that underpins these diseases, the nucleotide-binding domain, leucine-rich-containing family, and pyrin domain-containing-3 (NLRP3) inflammasome is thought to play a vital role in the manifestation of all these diseases. This review summarises the current evidence regarding cellular and molecular changes in the brain and eye with age, similarities between ocular and cerebral age-related diseases, and the role of the NLRP3 inflammasome as a critical mediator of disease propagation in the eye and the brain during ageing.

Developmental Expression of the Cell Cycle Regulator p16INK4a in Retinal Glial Cells: A Novel Marker for Immature Ocular Astrocytes?

Retinal astrocytes are vital for neuronal homeostasis in the retina. Together with Müller glia, they provide retinal cells with neurotrophic factors, antioxidative support, and defense mechanisms such as the formation of the blood-retinal barrier. Substantial heterogeneity of astrocyte morphology and function represents a challenge for identification of distinct subtypes which may be potential targets for therapeutic purposes. Hence, identification of novel markers of astrocyte subpopulations is highly relevant to better understand the molecular mechanisms involved in retinal development, homeostasis, and pathology. In this study, we observed that the cell cycle regulator, p16INK4a, is expressed in immature astrocytes in the mouse retina. Immunohistochemical analysis showed p16INK4a expression in the optic nerve of wild-type mice from 3 days to 3 months of age and in the nerve fiber layer of the adult mouse retina. Colocalization of p16INK4a expression and glial fibrillary acidic protein (immature/mature astrocyte marker) tends to decrease with age. However, colocalization of p16INK4a expression and vimentin (immature astrocyte marker) remains high in the optic nerve from the early postnatal period to adulthood. The observations from this study provide a valuable tool for further investigations of ocular astrocytes in the developing retina as well as in degenerative retinopathies.

Peptidyl arginine deiminase 4 deficiency protects against subretinal fibrosis by inhibiting Müller glial hypercitrullination

Retinal scarring with vision loss continues to be an enigma in individuals with advanced age-related macular degeneration (AMD). Müller glial cells are believed to initiate and perpetuate scarring in retinal degeneration as these glial cells participate in reactive gliosis and undergo hypertrophy. We previously showed in the murine laser-induced model of choroidal neovascularization that models wet-AMD that glial fibrillary acidic protein (GFAP) expression, an early marker of reactive gliosis, increases along with its posttranslational modification citrullination. This was related to increased co-expression of the citrullination enzyme peptidyl arginine deiminase-4 (PAD4), which also colocalizes to GFAP filaments. However, whether such hypercitrullination in Müller glial drives fibrotic pathology has remained understudied. Here, using male and female C57Bl6 mice subjected to laser injury, we investigated in a temporal study how citrullination impacts GFAP and PAD4 dynamics. We found that high molecular weight citrullinated species that accumulate in Müller glia corresponded with dynamic changes in GFAP and PAD4 showing their temporal redistribution from polymeric cytoskeletal to soluble protein fractions using immunostaining and western blot analysis. In conditional glial-specific PAD4 knockout (PAD4cKO) mice subjected to laser injury, there was a stark reduction of citrullination and of polymerized GFAP filaments. These injured PAD4cKO retinas showed improved lesion healing, as well as reduced fibronectin deposition in the subretinal space at 30 days. Taken together, these findings reveal that pathologically overexpressed PAD4 in reactive Müller glia governs GFAP filament dynamics and alters their stability, suggesting chronic PAD4-driven hypercitrullination may be a target for retinal fibrosis.

Inflammation and retinal degenerative diseases

Vision is an ability that depends on the precise structure and functioning of the retina. Any kind of stress or injury can disrupt the retinal architecture and leads to vision impairment, vision loss, and blindness. Immune system and immune response function maintain homeostasis in the microenvironment. Several genetic, metabolic, and environmental factors may alter retinal homeostasis, and these events may initiate various inflammatory cascades. The prolonged inflammatory state may contribute to the initiation and development of retinal disorders such as glaucoma, age-related macular degeneration, diabetic retinopathy, and retinitis pigmentosa, which pose a threat to vision. In the current review, we attempted to provide sufficient evidence on the role of inflammation in these retinal disorders. Moreover, this review paves the way to focus on therapeutic targets of the disease, which are found to be promising.

Repeated Topical Administration of 3 nm Cerium Oxide Nanoparticles Reverts Disease Atrophic Phenotype and Arrests Neovascular Degeneration in AMD Mouse Models

Increased oxidative stress in the retina and retinal pigment epithelium is implicated in age-related macular degeneration (AMD). Antioxidant cerium oxide nanoparticles (CeO2NPs) have been used to treat degenerative retinal pathologies in animal models, although their delivery route is not ideal for chronic patient treatment. In this work, we prepared a formulation for ocular topical delivery that contains small (3 nm), nonaggregated biocompatible CeO2NPs. In vitro results indicate the biocompatible and protective character of the CeO2NPs, reducing oxidative stress in ARPE19 cells and inhibiting neovascularization related to pathological angiogenesis in both HUVEC and in in vitro models of neovascular growth. In the in vivo experiments, we observed the capacity of CeO2NPs to reach the retina after topical delivery and a subsequent reversion of the altered retinal transcriptome of the retinal degenerative mouse model DKOrd8 toward that of healthy control mice, together with signs of decreased inflammation and arrest of degeneration. Furthermore, CeO2NP eye drops' treatment reduced laser-induced choroidal neovascular lesions in mice by lowering VEGF and increasing PEDF levels. These results indicate that CeO2NP eye drops are a beneficial antioxidant and neuroprotective treatment for both dry and wet forms of AMD disease.

Single-cell transcriptome reveals diversity of Müller cells with different metabolic-mitochondrial signatures in normal and degenerated macula

Müller cell is the most abundant glial cell in mammalian retina, supporting the functions of photoreceptors and other retinal neurons via maintaining environmental homeostasis. In response to injury and/or neuronal degeneration, Müller cells undergo morphological and functional alternations, known as reactive gliosis documented in multiple retinal diseases, including age-related macular degeneration (AMD), retinitis pigmentosa, diabetic retinopathy, and traumatic retinal detachment. But the functional consequences of Müller glia cell reactivation or even the regulatory networks of the retinal gliosis are still controversial. In this study, we reveal different subpopulations of Müller cells with distinct metabolic-mitochondrial signatures by integrating single cell transcriptomic data from Early AMD patients and healthy donors. Our results show that a portion of Müller cells exhibits low mitochondrial DNA (mtDNA) expressions, reduced protein synthesis, impaired homeostatic regulation, decreased proliferative ability but enhanced proangiogenic function. Interestingly, the major alternation of Müller cells in Early AMD retina is the change of subpopulation abundance, rather than generation of new subcluster. Transcription factor enrichment analysis further highlights the key regulators of metabolic-mitochondrial states of Müller glias in Early AMD patients especially. Our study demonstrates new characteristics of retinal gliosis associated with Early AMD and suggests the possibility to prevent degeneration by intervening mitochondrial functions of Müller cells.

Increased efficacy of dietary supplement containing wax ester-rich marine oil and xanthophylls in a mouse model of dry macular degeneration

Age-related macular degeneration (AMD) is nowadays considered among the retinal diseases whose clinical management lacks established treatment approaches, mainly for its atrophic (dry) form. In this respect, the use of dietary patterns enriched in omega-3 and antioxidant xanthophylls has emerged as a promising approach to counteract dry AMD progression although the prophylactic potential of omega-3 of fish origin has been discussed. Whether enriched availability of omega-3 and xanthophylls may increase the effectiveness of diet supplementation in preventing dry AMD remains to be fully established. The present study aims at comparing the efficacy of an existing orally administered formulation based on lutein and fish oil, as a source of omega-3, with a novel formulation providing the combination of lutein and astaxanthin with Calanus oil (COil), which contains omega-3 together with their precursors policosanols. Using a mouse model of dry AMD based on subretinal injection of polyethylene glycol (PEG)-400, we assessed the comparative efficacy of both formulations on PEG-induced major hallmarks including oxidative stress, inflammation, glial reactivity and outer retinal thickness. Dietary supplementation with both mixtures has been found to exert a significant antioxidant and anti-inflammatory activity as reflected by the overall amelioration of the PEG-induced pathological hallmarks. Noteworthy, the formulation based on COil appeared to be more protective than the one based on fish oil, presumably because of the higher bioavailability of omega-3 in COil. These results support the use of dietary supplements combining omega-3 and xanthophylls in the prevention and treatment of AMD and suggest that the source of omega-3 might contribute to treatment efficacy.

Glial cell response to constant low light exposure in rat retina

To study the macroglia and microglia and the immune role in long-time light exposure in rat eyes, we performed glial cell characterization along the time-course of retinal degeneration induced by chronic exposure to low-intensity light. Animals were exposed to light for periods of 2, 4, 6, or 8 days, and the retinal glial response was evaluated by immunohistochemistry, western blot and real-time reverse transcription polymerase chain reaction. Retinal cells presented an increased expression of the macroglia marker GFAP, as well as increased mRNA levels of microglia markers Iba1 and CD68 after 6 days. Also, at this time-point, we found a higher number of Iba1-positive cells in the outer nuclear layer area; moreover, these cells showed the characteristic activated-microglia morphology. The expression levels of immune mediators TNF, IL-6, and chemokines CX3CR1 and CCL2 were also significantly increased after 6 days. All the events of glial activation occurred after 5-6 days of constant light exposure, when the number of photoreceptor cells has already decreased significantly. Herein, we demonstrated that glial and immune activation are secondary to neurodegeneration; in this scenario, our results suggest that photoreceptor death is an early event that occurs independently of glial-derived immune responses.

Transketolase in human Müller cells is critical to resist light stress through the pentose phosphate and NRF2 pathways

The Pentose Phosphate Pathway (PPP), a metabolic offshoot of the glycolytic pathway, provides protective metabolites and molecules essential for cell redox balance and survival. Transketolase (TKT) is the critical enzyme that controls the extent of “traffic flow” through the PPP. Here, we explored the role of TKT in maintaining the health of the human retina. We found that Müller cells were the primary retinal cell type expressing TKT in the human retina. We further explored the role of TKT in human Müller cells by knocking down its expression in primary cultured Müller cells (huPMCs), isolated from the human retina (11 human donors in total), under light-induced oxidative stress. TKT knockdown and light stress reduced TKT enzymatic activities and the overall metabolic activities of huPMCs with no detectable cell death. TKT knockdown restrained the PPP traffic flow, reduced the expression of NAD(P)H Quinone Dehydrogenase 1 (NQO1), impaired the antioxidative response of NRF2 to light stress and aggravated the endoplasmic reticulum (ER) stress. TKT knockdown also inhibited overall glucose intake, reduced expression of Dihydrolipoamide dehydrogenase (DLD) and impaired the energy supply of the huPMCs. In summary, Müller cell-mediated TKT activity plays a critical protective role in the stressed retina. Knockdown of TKT disrupted the PPP and impaired overall glucose utilisation by huPMCs and rendered huPMCs more vulnerable to light stress by impairing energy supply and antioxidative NRF2 responses.

The Transcriptome Profile of Retinal Pigment Epithelium and Müller Cell Lines Protected by Risuteganib Against Hydrogen Peroxide Stress

Purpose:

Oxidative stress contributes to the pathogenesis of vision-impairing diseases. In the retina, retinal pigment epithelium (RPE) and Müller cells support neuronal homeostasis, but also contribute to pathological development under stressed conditions. Recent studies found that the investigational drug risuteganib (RSG) has a good safety profile, provided protection in experimental models, and improved visual acuity in patients. The present in vitro study evaluated the effects of RSG in RPE and Müller cell lines stressed with the oxidant hydrogen peroxide (H₂O₂).

Methods:

Human RPE (ARPE-19) and Müller (MIO-M1) cell lines were treated with various combinations of RSG and H₂O₂. Trypan blue assay was used to investigate the effect of compounds on cell viability. Gene expression was measured using RNA sequencing to identify regulated genes and the biological processes and pathways involved.

Results:

Trypan blue assay found RSG pre-treatment significantly protected against H₂O₂-induced cell death in ARPE-19 and MIO-M1 cells. Transcriptome analysis found H₂O₂ regulated genes in several disease-relevant biological processes, including cell adhesion, migration, death, and proliferation; ECM organization; angiogenesis; metabolism; and immune system processes. RSG pre-treatment modulated these gene expression profiles in the opposite direction of H₂O₂. Pathway analysis found genes in integrin, AP-1, and syndecan signaling pathways were regulated. Expression of selected RSG-regulated genes was validated using qRT-PCR.

Conclusions:

RSG protected cultured human RPE and Müller cell lines against H₂O₂-induced cell death and mitigated the associated transcriptome changes in biological processes and pathways relevant to the pathogenesis of retinal diseases. These results demonstrate RSG reduced oxidative stress-induced toxicity in two retinal cell lines with potential relevance to the treatment of human diseases.

Müller Glia maintain their regenerative potential despite degeneration in the aged zebrafish retina

Ageing is a significant risk factor for degeneration of the retina. Müller glia cells (MG) are key for neuronal regeneration, so harnessing the regenerative capacity of MG in the retina offers great promise for the treatment of age-associated blinding conditions. Yet, the impact of ageing on MG regenerative capacity is unclear. Here, we show that the zebrafish retina undergoes telomerase-independent, age-related neurodegeneration but that this is insufficient to stimulate MG proliferation and regeneration. Instead, age-related neurodegeneration is accompanied by MG morphological aberrations and loss of vision. Mechanistically, yes-associated protein (Yap), part of the Hippo signalling, has been shown to be critical for the regenerative response in the damaged retina, and we show that Yap expression levels decline with ageing. Despite this, morphologically and molecularly altered aged MG retain the capacity to regenerate neurons after acute light damage, therefore, highlighting key differences in the MG response to high-intensity acute damage versus chronic neuronal loss in the zebrafish retina.

Accumulation of systematic TPM1 mediates inflammation and neuronal remodeling by phosphorylating PKA and regulating the FABP5/NF-κB signaling pathway in the retina of aged mice

The molecular mechanisms underlying functional decline during normal brain aging are poorly understood. Here, we identified the actin‐associated protein tropomyosin 1 (TPM1) as a new systemic pro‐aging factor associated with function deficits in normal aging retinas. Heterochronic parabiosis and blood plasma treatment confirmed that systemic factors regulated age‐related inflammatory responses and the ectopic dendritic sprouting of rod bipolar (RBC) and horizontal (HC) cells in the aging retina. Proteomic analysis revealed that TPM1 was a potential systemic molecule underlying structural and functional deficits in the aging retina. Recombinant TPM1 protein administration accelerated the activation of glial cells, the dendritic sprouting of RBCs and HCs and functional decline in the retina of young mice, whereas anti‐TPM1 neutralizing antibody treatment ameliorated age‐related structural and function changes in the retina of aged mice. Old mouse plasma (OMP) induced glial cell activation and the dendritic outgrowth of RBCs and HCs in young mice, and yet TMP1‐depleted OMP failed to reproduce the similar effect in young mice. These results confirmed that TPM1 was a systemic pro‐aging factor. Moreover, we demonstrated that systematic TPM1 was an immune‐related molecule, which elicited endogenous TPM1 expression and inflammation by phosphorylating PKA and regulating FABP5/NF‐κB signaling pathway in normal aging retinas. Interestingly, we observed TPM1 upregulation and the ectopic dendritic sprouting of RBCs and HCs in young mouse models of Alzheimer's disease, indicating a potential role of TPM1 in age‐related neurodegenerative diseases. Our data indicate that TPM1 could be targeted for combating the aging process.

Compritol solid lipid nanoparticle formulations enhance the protective effect of betulinic acid derivatives in human Müller cells against oxidative injury

Müller cells maintain homeostatic functions in the retina. Their dysfunction leads to irreversible retinal diseases. Oxidative injury is a leading cause of retinal cytotoxicity. Our previous studies reported several betulinic acid (BA) derivatives can protect Müller cells from oxidative injury but achieving pharmacologically effective concentrations in the Müller cells could be a limitation. To optimise cellular delivery, we encapsulated the BA analogues H3, H5 and H7 into the clinically approved Compritol 888 and HD5 ATO solid lipid nanoparticles (SLNs) using the micro-emulsion method. The cytoprotective effects of these SLN-formulations were determined in human MIO-M1 cells. We found cytoprotection by H3 and H5 SLN-formulations was significantly enhanced, which was evident at concentrations much lower than those required with the free agents. Both SLN-formulations prolonged the duration of action of these agents. The most effective agent H5 delivered in 888 ATO SLNs attenuated glutamate-induced ROS formation and the associated necrosis in MIO-M1 cells. Overall, SLNs have emerged as promising delivery carriers for BA derivatives enhancing their protective effects against oxidative injury in human Müller cells. Our study is the first to show SLNs can be a viable route to delivery agents with improved efficacy and stability into human Müller cells favoring the treatment/prevention of retinal diseases.

Microglia-derived TNF-α mediates Müller cell activation by activating the TNFR1-NF-κB pathway

Microglia and its interaction with Müller cells are responsible to retinal surveillance during retinal neurodegeneration, however, the role and mechanism of microglia-derived tumor necrosis factor (TNF)-α in the activation of retinal Müller cells have not been fully elucidated. In the present study, primary microglia and Müller cells were isolated from newborn Sprague-Dawley (SD) rats with purities of 88.2 ± 6.2% and 92.2 ± 2.2%, respectively. By performing immunofluorescence and Western blot analysis, we found that TNF receptor (TNFR)-1 and TNFR2 were expressed in Müller cells. After co-cultured with microglia-conditioned medium (MCM), the elevated mRNA levels of glial fibrillary acidic protein (GFAP), proinflammatory factors (TNF-α, IL-1β, CXCL-1, CSF-1, NOS2, COX2) and decreased CNTF mRNA levels were found in Müller cells. However, pretreatment with R-7050 (a TNF-α receptor inhibitor) or anti-TNFR1 significantly abrogated the changes. Simultaneously, pretreatment with anti-TNFR2 slightly inhibited the expression of GFAP in MCM-incubated Müller cells. Meanwhile, anti-TNFR1 treatment reversed the increased expression of CSF-1 and IL-1β induced by TNF-α. Compared to the control groups, the phosphorylation of NF-κB P65, MAPK P38 and ERK1/2 in TNF-α-treated Müller cells was significantly increased. Nevertheless, pretreatment with anti-TNFR1 inhibited the phosphorylation of NF-κB P65 and MAPK p38, especially NF-κB P65. Additionally, pretreatment with Bay117082 (an NF-κB inhibitor) also significantly inhibited NF-κB P65 phosphorylation and GFAP expression. Moreover, anti-TNFR1 and Bay117082 treatment reduced NF-κB P65 phosphorylation of Müller cells induced by MCM. These results suggested that microglia-derived TNF-α served as a vital role in regulating Müller cells activation during retinal neurodegeneration.

Progesterone alters the activation and typing of the microglia in the optic nerve crush model

Microglia have a protective effect on the central nervous system (CNS), but their over-proliferation can cause secondary injury to the retina following optic nerve crush (ONC). Progesterone as a steroid gonadal hormone has been used in some experimental animal models for its neuroprotective effect. However, there is limited attention on the interactions between progesterone and microglia in retinal diseases. This study investigated the proliferation, morphology changes, and cell types of microglia at 3 days and 7 days after ONC. We found that progesterone treatment in unilateral optic nerve injury mice significantly reduced densities and morphological change of microglia at 7 days in the ganglion cell layer (GCL), especially in the retinal central. Inhibition of the microglia proliferation and transformation of ramified microglia into ameboid macrophages also appeared in the inner plexiform layer (IPL). Moreover, progesterone also regulated the TNF signal pathway, which was similar to the specific elimination of the M1 phenotype. M1 marks such as tumor necrosis factor alpha (TNF-α), inducible NOS(iNOS), interleukin-6 (IL-6), and Fc receptor (CD16 and CD32) significantly downregulated by progesterone treatment whether at 3 days or 7 days after ONC. On the other hand, progesterone continuously increased the expression of the M2 marks, including interleukin-4 (IL-4), arginase 1 (Arg1), and mannose receptor (CD206) since the third day, while the expression levels of transforming growth factor (TGF-β) only increased at 7 days. In general, this study elucidated the mechanism that progesterone prevented further damage on the retina by inhibiting proliferation, activation, and changing the type of microglia.

The killifish visual system as an in vivo model to study brain aging and rejuvenation

Worldwide, people are getting older, and this prolonged lifespan unfortunately also results in an increased prevalence of age-related neurodegenerative diseases, contributing to a diminished life quality of elderly. Age-associated neuropathies typically include diseases leading to dementia (Alzheimer's and Parkinson's disease), as well as eye diseases such as glaucoma and age-related macular degeneration. Despite many research attempts aiming to unravel aging processes and their involvement in neurodegeneration and functional decline, achieving healthy brain aging remains a challenge. The African turquoise killifish (Nothobranchius furzeri) is the shortest-lived reported vertebrate that can be bred in captivity and displays many of the aging hallmarks that have been described for human aging, which makes it a very promising biogerontology model. As vision decline is an important hallmark of aging as well as a manifestation of many neurodegenerative diseases, we performed a comprehensive characterization of this fish's aging visual system. Our work reveals several aging hallmarks in the killifish retina and brain that eventually result in a diminished visual performance. Moreover, we found evidence for the occurrence of neurodegenerative events in the old killifish retina. Altogether, we introduce the visual system of the fast-aging killifish as a valuable model to understand the cellular and molecular mechanisms underlying aging in the vertebrate central nervous system. These findings put forward the killifish for target validation as well as drug discovery for rejuvenating or neuroprotective therapies ensuring healthy aging.

Implication of specific retinal cell-type involvement and gene expression changes in AMD progression using integrative analysis of single-cell and bulk RNA-seq profiling

Age-related macular degeneration (AMD) is a blinding eye disease with no unifying theme for its etiology. We used single-cell RNA sequencing to analyze the transcriptomes of ~ 93,000 cells from the macula and peripheral retina from two adult human donors and bulk RNA sequencing from fifteen adult human donors with and without AMD. Analysis of our single-cell data identified 267 cell-type-specific genes. Comparison of macula and peripheral retinal regions found no cell-type differences but did identify 50 differentially expressed genes (DEGs) with about 1/3 expressed in cones. Integration of our single-cell data with bulk RNA sequencing data from normal and AMD donors showed compositional changes more pronounced in macula in rods, microglia, endothelium, Müller glia, and astrocytes in the transition from normal to advanced AMD. KEGG pathway analysis of our normal vs. advanced AMD eyes identified enrichment in complement and coagulation pathways, antigen presentation, tissue remodeling, and signaling pathways including PI3K-Akt, NOD-like, Toll-like, and Rap1. These results showcase the use of single-cell RNA sequencing to infer cell-type compositional and cell-type-specific gene expression changes in intact bulk tissue and provide a foundation for investigating molecular mechanisms of retinal disease that lead to new therapeutic targets.

Features of Retinal Neurogenesis as a Key Factor of Age-Related Neurodegeneration: Myth or Reality?

Age-related macular degeneration (AMD) is a complex multifactorial neurodegenerative disease that constitutes the most common cause of irreversible blindness in the elderly in the developed countries. Incomplete knowledge about its pathogenesis prevents the search for effective methods of prevention and treatment of AMD, primarily of its "dry" type which is by far the most common (90% of all AMD cases). In the recent years, AMD has become "younger": late stages of the disease are now detected in relatively young people. It is known that AMD pathogenesis-according to the age-related structural and functional changes in the retina-is linked with inflammation, hypoxia, oxidative stress, mitochondrial dysfunction, and an impairment of neurotrophic support, but the mechanisms that trigger the conversion of normal age-related changes to the pathological process as well as the reason for early AMD development remain unclear. In the adult mammalian retina, de novo neurogenesis is very limited. Therefore, the structural and functional features that arise during its maturation and formation can exert long-term effects on further ontogenesis of this tissue. The aim of this review was to discuss possible contributions of the changes/disturbances in retinal neurogenesis to the early development of AMD.

Sex and Age-Related Differences in Neuroinflammation and Apoptosis in Balb/c Mice Retina Involve Resolvin D1

(1) Background: The pro-resolving lipid mediator Resolvin D1 (RvD1) has already shown protective effects in animal models of diabetic retinopathy. This study aimed to investigate the retinal levels of RvD1 in aged (24 months) and younger (3 months) Balb/c mice, along with the activation of macro- and microglia, apoptosis, and neuroinflammation. (2) Methods: Retinas from male and female mice were used for immunohistochemistry, immunofluorescence, transmission electron microscopy, Western blotting, and enzyme-linked immunosorbent assays. (3) Results: Endogenous retinal levels of RvD1 were reduced in aged mice. While RvD1 levels were similar in younger males and females, they were markedly decreased in aged males but less reduced in aged females. Both aged males and females showed a significant increase in retinal microglia activation compared to younger mice, with a more marked reactivity in aged males than in aged females. The same trend was shown by astrocyte activation, neuroinflammation, apoptosis, and nitrosative stress, in line with the microglia and Müller cell hypertrophy evidenced in aged retinas by electron microscopy. (4) Conclusions: Aged mice had sex-related differences in neuroinflammation and apoptosis and low retinal levels of endogenous RvD1.

Age-Related Retinal Changes in Wild-Type C57BL/6J Mice Between 2 and 32 Months

Purpose

The purpose of this study was to extend our understanding of how aging affects normal retina function and morphology in wild-type C57BL/6J mice, by analyzing electrophysiological recordings and in vivo and post mortem anatomy.

Methods

Electroretinograms (ERGs), spectral domain optical coherence tomography (SD-OCT), and confocal scanning laser ophthalmoscope (cSLO) in vivo images were obtained from mice between the ages of 2 and 32 months in four groups: group 1 (<0.5 years), group 2 (1.0-1.5 years), group 3 (1.5-2.0 years), and group 4 (>2.0 years). Afterward, mouse bodies and eyes were weighed. Eyes were stained with hematoxylin and eosin (H&E) and cell nuclei were quantified.

Results

With aging, mice showed a significant reduction in both a- and b-wave ERG amplitudes in scotopic and photopic conditions. Additionally, total retina and outer nuclear layer (ONL) thickness, as measured by SD-OCT images, were significantly reduced in older groups. The cSLO images showed an increase in auto-fluorescence at the photoreceptor-RPE interface as age increases. H&E cell nuclei quantification showed significant reduction in the ONL in older ages, but no differences in the inner nuclear layer (INL) or ganglion cell layer (GCL).

Conclusions

By using multiple age groups and extending the upper age limit of our animals to approximately 2.65 years (P970), we found that natural aging causes negative effects on retinal function and morphology in a gradual, rather than abrupt, process. Future studies should investigate the exact mechanisms that contribute to these gradual declines in order to discover pathways that could potentially serve as therapeutic targets.

Glial cells modulate retinal cell survival in rotenone-induced neural degeneration

Administration of the mitochondrial complex I inhibitor rotenone provides an excellent model to study the pathomechanism of oxidative stress-related neural degeneration diseases. In this study, we examined the glial roles in retinal cell survival and degeneration under the rotenone-induced oxidative stress condition. Mouse-derived Müller, microglial (BV-2), and dissociated retinal cells were used for in vitro experiments. Gene expression levels and cell viability were determined using quantitative reverse transcription-polymerase chain reaction and the alamarBlue assay, respectively. Conditioned media were prepared by stimulating glial cells with rotenone. Retinal ganglion cells (RGCs) and inner nuclear layer (INL) were visualized on rat retinal sections by immunohistochemistry and eosin/hematoxylin, respectively. Rotenone dose-dependently induced glial cell death. Treatment with rotenone or rotenone-stimulated glial cell-conditioned media altered gene expression of growth factors and inflammatory cytokines in glial cells. The viability of dissociated retinal cells significantly increased upon culturing in media conditioned with rotenone-stimulated or Müller cell-conditioned media-stimulated BV-2 cells. Furthermore, intravitreal neurotrophin-5 administration prevented the rotenone-induced reduction of RGC number and INL thickness in rats. Thus, glial cells exerted both positive and negative effects on retinal cell survival in rotenone-induced neural degeneration via altered expression of growth factors, especially upregulation of microglia-derived Ntf5, and proinflammatory cytokines.

Spontaneous Closure of a Macular Hole in Macular Telangiectasia Type 2

Purpose:

Spontaneous closure of a macular hole in macular telangiectasia type 2 (MacTel) with vision improvement is described.

Methods:

A case report is presented.

Results:

A 71-year-old man presented with a 1-week history of distorted vision in his left eye. Left visual acuity (LVA) was 20/80. Optical coherence tomography showed an almost full-thickness left macular hole with an intact internal limiting membrane drape. Small inner retinal cavitations were present at the right macula; multimodal imaging confirmed MacTel. Managed conservatively, at 5 months the patient’s LVA had improved to 20/60, the defect was no longer full thickness, and the external limiting membrane had reconstituted. At the right macula, the inner cavitations grew and outer cavitations developed, but the external limiting membrane remained intact. At 32 months, right VA was 20/20 and LVA was 20/40.

Conclusions:

This case of MacTel with spontaneous closure of a macular hole was associated with an overlying internal limiting membrane drape.

The phase changes of M1/M2 phenotype of microglia/macrophage following oxygen-induced retinopathy in mice

OBJECTIVE

Microglia/macrophage activation is previously reported to be involved in various ocular diseases. However, the separate role of M1/M2 phenotype microglia/macrophage in the pathological process of oxygen-induced retinopathy (OIR) remains unknown. In this research, we explored the role and regulatory mechanism of M1/M2 microglia/macrophage in OIR in C57BL/6J mice. Furthermore, we demonstrated the time phase of M1/M2 shifting of microglia/macrophage during the natural process of OIR, which is very essential for further investigations.

MATERIALS AND METHODS

C57BL/6j pups were exposed to hyperoxia environment from postnatal 7(P7) to P12 then returned to normoxia. The mice were then euthanized, and the eyes were harvested at a series of time points for further investigation. The M1/M2 phenotype microglia/macrophage activity was presented by immunofluorescent staining and real-time quantitative polymerase chain reaction (qPCR). The NF-κb-STAT3 signaling and IL-4-STAT6-PPAR-γ signaling pathway activity was examined by western blot analysis.

RESULTS

The microglia/macrophage were activated when the OIR model was set up after P12. The M1 microglia/macrophage activation was found in neovascularization (NV) tufts in both central and peripheral retina, which started from P12 when the mice were returned to normoxia environment and peaked at P17. During this period of time, the NF-κb-STAT3 signaling pathway was activated, resulting in the upregulated M1 phenotype microglia/macrophage polarization, along with the enhanced inflammatory cytokine expression including tumor necrosis factor-α (TNF-α), interleukin-6 (IL-6), and IL-1β. Consequently, the NV tufts were observed from P12 and the volume continued to increase until P17. However, the M2 phenotype microglia/macrophage activity took over during the late phase of OIR started from P17. The IL-4-STAT6-PPAR-γ signaling activity was upregulated from P17 and peaked at P20, inducing M2 phenotype microglia polarization, which consequently led to the inhibition of inflammatory cytokines and spontaneous regression of NV tufts.

CONCLUSIONS

Microglia/macrophage participate actively in the natural process of OIR in mice, and two phenotypes exert different functions. Treatment modulating microglia/macrophage polarize toward M2 phenotype might be a novel and promising method for ocular neovascular diseases such as retinopathy of prematurity (ROP), wet age-related macular degeneration (wAMD), and diabetic retinopathy (DR).

Glutathione Trisulfide Prevents Lipopolysaccharide-induced Inflammatory Gene Expression in Retinal Pigment Epithelial Cells

We investigated the effects of glutathione trisulfide (GSSSG) on lipopolysaccharide (LPS)-induced inflammatory gene expression in immortalized ARPE-19, and primary human and mouse retinal pigment epithelial (RPE) cells. Sulfane sulfur molecules were significantly increased in GSSSG-treated ARPE-19 cells. GSSSG prevented the LPS-induced upregulation of interleukin (IL)-1β, IL-6, and C-C motif chemokine ligand 2 (CCL2) in ARPE-19/primary RPE cells. Moreover, GSSSG prevented the activation of the nuclear factor-kappa B p65 subunit, and promoted the activation of extracellular signal-regulated kinase 1/2 (ERK1/2) in LPS-treated ARPE-19 cells. ERK1/2 inhibition prevented the GSSSG-mediated inhibition of LPS-induced IL-6 and CCL2 upregulation. Additionally, ERK1/2 activation prevented the upregulation of these genes in the absence of GSSSG. Knockdown of HMOX1 or NRF2, known as anti-oxidative genes, did not affect the activity of GSSSG in the context of LPS stimulation. These findings suggest that GSSSG attenuates LPS-induced inflammatory gene expression via ERK signaling hyperactivation, independently of the NRF2/HMOX1 pathway.

The Role of Inflammation in Age-Related Macular Degeneration

Age-related macular degeneration (AMD) is a blinding eye disease which incidence gradually increases with age. Inflammation participates in AMD pathogenesis, including choroidal neovascularization and geographic atrophy. It is also a kind of self-protective regulation from injury for the eyes. In this review, we described inflammation in AMD pathogenesis, summarized the roles played by inflammation-related cytokines, including pro-inflammatory and anti-inflammatory cytokines, as well as leukocytes (macrophages, dendritic cells, neutrophils, T lymphocytes and B lymphocytes) in the innate or adaptive immunity in AMD. Possible clinical applications such as potential diagnostic biomarkers and anti-inflammatory therapies were also discussed. This review overviews the inflammation as a target of novel effective therapies in treating AMD.

Retina in a dish: Cell cultures, retinal explants and animal models for common diseases of the retina

For many retinal diseases, including age-related macular degeneration (AMD), glaucoma, and diabetic retinopathy (DR), the exact pathogenesis is still unclear. Moreover, the currently available therapeutic options are often unsatisfactory. Research designed to remedy this situation heavily relies on experimental animals. However, animal models often do not faithfully reproduce human disease and, currently, there is strong pressure from society to reduce animal research. Overall, this creates a need for improved disease models to understand pathologies and develop treatment options that, at the same time, require fewer or no experimental animals. Here, we review recent advances in the field of in vitro and ex vivo models for AMD, glaucoma, and DR. We highlight the difficulties associated with studies on complex diseases, in which both the initial trigger and the ensuing pathomechanisms are unclear, and then delineate which model systems are optimal for disease modelling. To this end, we present a variety of model systems, ranging from primary cell cultures, over organotypic cultures and whole eye cultures, to animal models. Specific advantages and disadvantages of such models are discussed, with a special focus on their relevance to putative in vivo disease mechanisms. In many cases, a replacement of in vivo research will mean that several different in vitro models are used in conjunction, for instance to analyze and validate causative molecular pathways. Finally, we argue that the analytical decomposition into appropriate cell and tissue model systems will allow making significant progress in our understanding of complex retinal diseases and may furthermore advance the treatment testing.

Alterations of STEP46 and STEP61 Expression in the Rat Retina with Age and AMD-Like Retinopathy Development

Tyrosine phosphatase STEP (striatal-enriched tyrosine protein phosphatase) is a brain-specific protein phosphatase and is involved in the pathogenesis of many neurodegenerative diseases. Here, we examined the impact of STEP on the development of age-related macular degeneration (AMD)-like pathology in senescence-accelerated OXYS rats. Using OXYS and Wistar rats (control), we for the first time demonstrated age-dependent changes in Ptpn5 mRNA expression, STEP46 and STEP61 protein levels, and their phosphatase activity in the retina. The increases in STEP protein levels and the decrease of total and STEP phosphatase activities in the retina (as compared with Wistar rats) preceded the manifestation of clinical signs of AMD in OXYS rats (age 20 days). There were no differences in these retinal parameters between 13-month-old Wistar rats and OXYS rats with pronounced signs of AMD. Inhibition of STEP with TC-2153 during progressive AMD-like retinopathy (from 9 to 13 months of age) reduced the thickness of the retinal inner nuclear layer, as evidenced by a decreased amount of parvalbumin-positive amacrine neurons. Prolonged treatment with TC-2153 had no effect on Ptpn5 mRNA expression, STEP46 and STEP61 protein levels, and their phosphatase activity in the OXYS retina. Thus, TC-2153 may negatively affect the retina through mechanisms unrelated to STEP.

Identification of epiretinal proliferation in various retinal diseases and vitreoretinal interface disorders

Background

To describe the presence of epiretinal proliferation in eyes with various retinal and vitreoretinal interface conditions.

Methods

Consecutive patients seen at the Stein Eye Institute, by one retina specialist, from December 2018 to March 2019, and demonstrating epiretinal proliferation on optical coherence tomography (OCT) were enrolled in this cross-sectional study. Included patients were divided into two groups: vitreoretinal interface pathologies group or retinal diseases group. Presence of epiretinal proliferation and its localization within the 9 macular sectors, as defined by the Early Treatment Diabetic Retinopathy Study (ETDRS), were assessed on OCT.

Results

77 eyes from 69 patients demonstrated epiretinal proliferation on OCT. The most frequently involved ETDRS sector was the 1-mm central subfield, followed by inner temporal and inner nasal sectors. Localization of epiretinal proliferation correlated with the presence of any retinal abnormalities in the same quadrant (r = 0.962; P < 0.0001). 31 eyes (40.3%) demonstrated symptomatic vitreoretinal interface pathologies including lamellar macular hole, full-thickness macular hole, epiretinal membrane and history of macular peeling. 46 eyes (59.7%) manifested various retinal diseases, including age-related macular degeneration, diabetic retinopathy, refractory macular edema, vein occlusion and high myopia.

Conclusions

Epiretinal proliferation was noted in several retinal conditions and not limited only to full-thickness and lamellar macular holes. Different mechanisms affecting retinal homeostasis might trigger Müller cells dysregulation, potentially leading to abnormal retinal remodeling.

Combined Transplantation of Olfactory Ensheathing Cells With Rat Neural Stem Cells Enhanced the Therapeutic Effect in the Retina of RCS Rats

Retinal degenerative diseases (RDDs) are the leading causes of blindness and currently lack effective treatment. Cytotherapy has become a promising strategy for RDDs. The transplantation of olfactory ensheathing cells (OECs) or neural stem cells (NSCs) has recently been applied for the experimental treatment of RDDs. However, the long-term outcomes of single-cell transplantation are poor. The combined transplantation of multiple types of cells might achieve better effects. In the present study, OECs [containing olfactory nerve fibroblasts (ONFs)] and NSCs were cotransplanted into the subretinal space of Royal College of Surgeons (RCS) rats. Using electroretinogram (ERG), immunofluorescence, Western blot, and in vitro Transwell system, the differences in the electrophysiological and morphological changes of single and combined transplantation as well as the underlying mechanisms were explored at 4, 8, and 12 weeks postoperation. In addition, using the Transwell system, the influence of OECs on the stemness of NSCs was discovered. Results showed that, compared to the single transplantation of OECs or NSCs, the combined transplantation of OECs and NSCs produced greater improvements in b-wave amplitudes in ERGs and the thickness of the outer nuclear layer at all three time points. More endogenous stem cells were found within the retina after combined transplantation. Glial fibrillary acidic protein (GFAP) expression decreased significantly when NSCs were cotransplanted with OECs. Both the vertical and horizontal migration of grafted cells were enhanced in the combined transplantation group. Meanwhile, the stemness of NSCs was also better maintained after coculture with OECs. Taken together, the results suggested that the combined transplantation of NSCs and OECs enhanced the improvement in retinal protection in RCS rats, providing a new strategy to treat RDDs in the future.

The expression and role of PIDD in retina after optic nerve crush

To examine the expression of P53-induced protein with a death domain (PIDD) at retina in animal model of optic nerve crush (ONC) and to investigate the role of PIDD in retinal glial activation and NF-κB activation induced by optic nerve damage, ONC animal model was established in Sprague-Dawley rats. PIDD has three isoforms (Isof); Western blot was performed to examine the expression of PIDD (Isof-1, Isof-2, and Isof-3, respectively) in retina at different time points after ONC. Retinal glial activation is closely associated with retinal neuronal death and is monitored by the expression of GFAP+ glial cells and IBA1+ microglia, then activated microglia leads to inflammatory cytokine production. NF-kB activation in glial cells also can promote neuronal death. In our study, the role of PIDD in retinal glial activation and NF-kB activation was investigated with PIDD inhibition selectively. PIDD expression (Isof-1 and Isof-3) was dramatically increased, and peaked at 3 days after ONC, while Isof-2 did not show any difference. In the ONC animal model, the number of GFAP+ glial cells and IBA1+ microglia in retinal layers was increased significantly, inflammatory cytokine production was upregulated, and NF-κB in glial cell was also activated. Moreover, those responses induced by optic nerve damage were attenuated with PIDD inhibition, which indicated that PIDD could regulate retinal glial activation, neuro-inflammation, and NF-κB activation. These results provided the direct demonstration that the PIDD (Isof-1and Isof-3) was overexpressed in retina after ONC, and PIDD may be involved in retinal neurodegenerative diseases by regulating retinal glial activation and NF-κB activation.

Mechanisms of Neuronal Death in the Cerebral Cortex during Aging and Development of Alzheimer's Disease-Like Pathology in Rats

Alzheimer’s disease (AD) is the commonest type of late-life dementia and damages the cerebral cortex, a vulnerable brain region implicated in memory, emotion, cognition, and decision-making behavior. AD is characterized by progressive neuronal loss, but the mechanisms of cell death at different stages of the disease remain unknown. Here, by means of OXYS rats as an appropriate model of the most common (sporadic) AD form, we studied the main pathways of cell death during development of AD-like pathology, including the preclinical stage. We found that apoptosis is activated at the pre-symptomatic stage (age 20 days) correlating with the retardation of brain development in the OXYS strain early in life. Progression of the AD-like pathology was accompanied by activation of apoptosis and necroptosis resulting from a decline of autophagy-mediated proteostasis. Our results are consistent with the idea that the nature of changes in the pathways of apoptosis, autophagy, and necrosis depends on the stage of AD.

Prolactin mitigates deficiencies of retinal function associated with aging

Aging causes the progressive degeneration of retinal cells leading to the eventual loss of vision. The hormone prolactin (PRL) is a neurotrophic factor able to compensate for photoreceptor cell death and electroretinogram deficits induced by light retinal damage. Here, we used adult 4-month old and aged 20-month old pigmented mice, null or not for the PRL receptor to explore whether PRL provides trophic support against age-related retinal dysfunction. Retinal functionality, apoptosis, glia activation, and neurotrophin expression were assessed by electroretinogram, TUNEL, glial fibrillary acidic protein and ionized calcium binding adaptor molecule 1 immunohistochemistry, and real-time PCR, respectively. Lack of PRL signaling in aged mice, but not in adult mice, correlated with photosensitive retinal dysfunction, increased photoreceptor apoptosis, differential expression of proapoptotic mediators, and microglia activation. We conclude that PRL is required for maintaining retinal functionality in both female and male mice during aging and has potential therapeutic value against age-related retinal disorders.

p62 /SQSTM1 coding plasmid prevents age related macular degeneration in a rat model

P62/SQSTM1, a multi-domain protein that regulates inflammation, apoptosis, and autophagy, has been linked to age-related pathologies. For example, previously we demonstrated that administration of p62/SQSTM1-encoding plasmid reduced chronic inflammation and alleviated osteoporosis and metabolic syndrome in animal models. Herein, we built upon these findings to investigate effect of the p62-encoding plasmid on an age-related macular degeneration (AMD), a progressive neurodegenerative ocular disease, using spontaneous retinopathy in senescence-accelerated OXYS rats as a model. Overall, the p62DNA decreased the incidence and severity of retinopathy. In retinal pigment epithelium (RPE), p62DNA administration slowed down development of the destructive alterations of RPE cells, including loss of regular hexagonal shape, hypertrophy, and multinucleation. In neuroretina, p62DNA prevented gliosis, retinal thinning, and significantly inhibited microglia/macrophages migration to the outer retina, prohibiting their subretinal accumulation. Taken together, our results suggest that the p62DNA has a strong retinoprotective effect in AMD.

Inhibitory effect of Houttuynia cordata Thunb on LPS-induced retinal microglial activation

AIM

To identify the effect of Houttuynia cordata Thunb (HCT) on lipopolysaccharide (LPS)-induced microglial activation and investigate its possible molecular mechanisms.

METHODS

The primary retinal microglial cells were cultured from the retinas of newborn Sprague-Dawley rats and exposed to LPS, and/or HCT with different concentrations. The survival ability of retinal microglia cells was tested by standard MTT method. BrdU cell proliferation assay was used to evaluate the proliferation of retinal microglia. Inflammatory factors in the culture supernatants, including TNF-α, iNOS and IL-1β, were measured using ELISA. Microglia cells' migration was determined with Transwell migration assay. The total p38-MAPK and phosphorylation of p38-MAPK (p-p38-MAPK) were detected with Western blot.

RESULTS

Primary retinal microglia in culture exposed to LPS to induce microglia activation. Pretreatment with HCT significantly inhibited the LPS-induced cell proliferation, but not the cell viability. LPS induced inflammatory reaction in microglia and cell migration. HCT significantly reduced LPS-stimulated release of pro-inflammatory factors and decreased the number of migrating cells substantially in a concentration-dependent manner. Moreover, the protein levels of p-p38 MAPK were identified as the up regulation and co-treatment with HCT obviously inhibited the upregulation of p-p38 MAPK, but had no effect on the levels of total p38-MAPK.

CONCLUSION

The data suggest that HCT inhibits LPS-induced retinal microglial activation via suppression of the p-p38-MAPK. HCT may be used for the treatment of ocular diseases characterized by over-activated microglia.

Suppression of AMD-Like Pathology by Mitochondria-Targeted Antioxidant SkQ1 Is Associated with a Decrease in the Accumulation of Amyloid β and in mTOR Activity

Age-related macular degeneration (AMD) is a major cause of irreversible visual impairment and blindness in developed countries, and the molecular pathogenesis of AMD is poorly understood. Recent studies strongly indicate that amyloid β (Aβ) accumulation -found in the brain and a defining feature of Alzheimer's disease-also forms in the retina in both Alzheimer's disease and AMD. The reason why highly neurotoxic proteins of consistently aggregate in the aging retina, and to what extent they contribute to AMD, remains to be fully addressed. Nonetheless, the hypothesis that Aβ is a therapeutic target in AMD is debated. Here, we showed that long-term treatment with SkQ1 (250 nmol/[kg body weight] daily from the age of 1.5 to 22 months) suppressed the development of AMD-like pathology in senescence-accelerated OXYS rats by reducing the level of Aβ and suppressing the activity of mTOR in the retina. Inhibition of mTOR signaling activity, which plays key roles in aging and age-related diseases, can be considered a new mechanism of the prophylactic effect of SkQ1. It seems probable that dietary supplementation with mitochondria-targeted antioxidant SkQ1 can be a good prevention strategy to maintain eye health and possibly a treatment of AMD.

Immunohistochemical localization of NGF, BDNF, and their receptors in a normal and AMD-like rat retina

BACKGROUND

Age-related macular degeneration (AMD) is a major cause of blindness in developed countries, and the molecular pathogenesis of AMD is poorly understood. A large body of evidence has corroborated the key role of neurotrophins in development, proliferation, differentiation, and survival of retinal cells. Neurotrophin deprivation has been proposed to contribute to retinal-cell death associated with neurodegenerative diseases. Little is known about the expression of the immature form of neurotrophins (proneurotrophins) and their mature form [e.g., nerve growth factor (proNGF and mNGF) and brain-derived neurotrophic factor (proBDNF and mBDNF)] in the retina during physiological aging and against the background of AMD. In addition, cell-specific localization of proteins NGF and BDNF in the retina during AMD development is not clear. Here, we evaluated contributions of the age-related alterations in the neurotrophin system to the development of AMD-like retinopathy in OXYS rats.

METHODS

Male OXYS rats at preclinical (20 days), early (3 months), and late (18 months) stages of the disease and age-matched male Wistar rats (as controls) were used. We performed immunohistochemical localization of NGF, BDNF, and their receptors TrkA, TrkB, and p75NTR by fluorescence microscopy in retinal sections from OXYS and Wistar rats.

RESULTS

We found increased NGF staining in Muller cells in 18-month-old OXYS rats (progressive stage of retinopathy). In contrast, we observed only subtle changes in the labeling of mature BDNF (mBDNF) and TrkB during the development of AMD-like retinopathy in OXYS rats. Using colocalization with vimentin and NeuN, we detected a difference in the cell type-specific localization of mBDNF between OXYS and Wistar rats. We showed that the mBDNF protein was located in Muller cells in OXYS rats, whereas in the Wistar retina, mBDNF immunoreactivity was detected in Muller cells and ganglion cells. During the development of AMD-like retinopathy, proBDNF dominated over mBDNF during increasing cell loss in the OXYS retina.

CONCLUSIONS

These data indicate that alterations in the balance of neurotrophic factors in the retina are involved in the development of AMD-like retinopathy in OXYS rats and confirm their participation in the pathogenesis of AMD in humans.