Synucleins in glaucoma: implication of gamma-synuclein in glaucomatous alterations in the optic nerve

Glial Cell Activation and Immune Responses in Glaucoma: A Systematic Review of Human Postmortem Studies of the Retina and Optic Nerve

Although researched extensively the understanding regarding mechanisms underlying glaucoma pathogenesis remains limited. Further, the exact mechanism behind neuronal death remains elusive. The role of neuroinflammation in retinal ganglion cell (RGC) death has been prominently theorised. This review provides a comprehensive summary of neuroinflammatory responses in glaucoma. A systematic search of Medline and Embase for articles published up to 8th March 2023 yielded 32 studies using post-mortem tissues from glaucoma patients. The raw data were extracted from tables and text to calculate the standardized mean differences (SMDs). These studies utilized post-mortem tissues from glaucoma patients, totalling 490 samples, compared with 380 control samples. Among the included studies, 27 reported glial cell activation based on changes to cellular morphology and molecular staining. Molecular changes were predominantly attributed to astrocytes (62.5%) and microglia (15.6%), with some involvement of Muller cells. These glial cell changes included amoeboid microglial cells with increased CD45 or HLA-DR intensity and hypertrophied astrocytes with increased glial fibrillary acidic protein labelling. Further, changes to extracellular matrix proteins like collagen, galectin, and tenascin-C suggested glial cells' influence on structural changes in the optic nerve head. The activation of DAMPs-driven immune response and the classical complement cascade was reported and found to be associated with activated glial cells in glaucomatous tissue. Increased pro-inflammatory markers such as interleukin-6 (IL-6) and tumor necrosis factor-alpha (TNF-α) were also linked to glial cells. Glial cell activation was also associated with mitochondrial, vascular, metabolic and antioxidant component disruptions. Association of the activated glial cells with pro-inflammatory responses, dysregulation of homeostatic components and antigen presentation indicates that glial cell responses influence glaucoma progression. However, the exact mechanism triggering these responses and underlying interactions remains unexplored. This necessitates further research using human samples for an increased understanding of the precise role of neuroinflammation in glaucoma progression.

Cyclic-NDGA Effectively Inhibits Human γ-Synuclein Fibrillation, Forms Nontoxic Off-Pathway Species, and Disintegrates Preformed Mature Fibrils

Parkinson's disease arises from protein misfolding, aggregation, and fibrillation and is characterized by LB (Lewy body) deposits, which contain the protein α-synuclein (α-syn) as their major component. Another synuclein, γ-synuclein (γ-syn), coexists with α-syn in Lewy bodies and is also implicated in various types of cancers, especially breast cancer. It is known to seed α-syn fibrillation after its oxidation at methionine residue, thereby contributing in synucleinopathy. Despite its involvement in synucleinopathy, the search for small molecule inhibitors and modulators of γ-syn fibrillation remains largely unexplored. This work reveals the modulatory properties of cyclic-nordihydroguaiaretic acid (cNDGA), a natural polyphenol, on the structural and aggregational properties of human γ-syn employing various biophysical and structural tools, namely, thioflavin T (ThT) fluorescence, Rayleigh light scattering, 8-anilinonaphthalene-1-sulfonic acid binding, far-UV circular dichroism (CD), Fourier transform infrared spectroscopy (FTIR) spectroscopy, atomic force microscopy, ITC, molecular docking, and MTT-toxicity assay. cNDGA was observed to modulate the fibrillation of γ-syn to form off-pathway amorphous species that are nontoxic in nature at as low as 75 μM concentration. The modulation is dependent on oxidizing conditions, with cNDGA weakly interacting (Kd ∼10-5 M) with the residues at the N-terminal of γ-syn protein as investigated by isothermal titration calorimetry and molecular docking, respectively. Increasing cNDGA concentration results in an increased recovery of monomeric γ-syn as shown by sodium dodecyl sulfate and native-polyacrylamide gel electrophoresis. The retention of native structural properties of γ-syn in the presence of cNDGA was further confirmed by far-UV CD and FTIR. In addition, cNDGA is most effective in suppression of fibrillation when added at the beginning of the fibrillation kinetics and is also capable of disintegrating the preformed mature fibrils. These findings could, therefore, pave the ways for further exploring cNDGA as a potential therapeutic against γ-synucleinopathies.

Association between Parkinson's Disease and Cancer: New Findings and Possible Mediators

Epidemiological evidence points to an inverse association between Parkinson's disease (PD) and almost all cancers except melanoma, for which this association is positive. The results of multiple studies have demonstrated that patients with PD are at reduced risk for the majority of neoplasms. Several potential biological explanations exist for the inverse relationship between cancer and PD. Recent results identified several PD-associated proteins and factors mediating cancer development and cancer-associated factors affecting PD. Accumulating data point to the role of genetic traits, members of the synuclein family, neurotrophic factors, the ubiquitin-proteasome system, circulating melatonin, and transcription factors as mediators. Here, we present recent data about shared pathogenetic factors and mediators that might be involved in the association between these two diseases. We discuss how these factors, individually or in combination, may be involved in pathology, serve as links between PD and cancer, and affect the prevalence of these disorders. Identification of these factors and investigation of their mechanisms of action would lead to the discovery of new targets for the treatment of both diseases.

Differential Responses of Retinal Neurons and Glia Revealed via Proteomic Analysis on Primary and Secondary Retinal Ganglion Cell Degeneration

To explore the temporal profile of retinal proteomes specific to primary and secondary retinal ganglion cell (RGC) loss. Unilateral partial optic nerve transection (pONT) was performed on the temporal side of the rat optic nerve. Temporal and nasal retinal samples were collected at 1, 4 and 8 weeks after pONT (n = 4 each) for non-biased profiling with a high-resolution hybrid quadrupole time-of-flight mass spectrometry running on label-free SWATHTM acquisition (SCIEX). An information-dependent acquisition ion library was generated using ProteinPilot 5.0 and OneOmics cloud bioinformatics. Combined proteome analysis detected 2531 proteins with a false discovery rate of <1%. Compared to the nasal retina, 10, 25 and 61 significantly regulated proteins were found in the temporal retina at 1, 4, and 8 weeks, respectively (p < 0.05, FC ≥ 1.4 or ≤0.7). Eight proteins (ALDH1A1, TRY10, GFAP, HBB-B1, ALB, CDC42, SNCG, NEFL) were differentially expressed for at least two time points. The expressions of ALDH1A1 and SNCG at nerve fibers were decreased along with axonal loss. Increased ALDH1A1 localization in the inner nuclear layer suggested stress response. Increased GFAP expression demonstrated regional reactivity of astrocytes and Muller cells. Meta-analysis of gene ontology showed a pronounced difference in endopeptidase and peptidase inhibitor activity. Temporal proteomic profiling demonstrates established and novel protein targets associated with RGC damage.

Age-Related Changes of the Synucleins Profile in the Mouse Retina

Alpha-synuclein (aSyn) plays a central role in Parkinson's disease (PD) and has been extensively studied in the brain. This protein is part of the synuclein family, which is also composed of beta-synuclein (bSyn) and gamma-synuclein (gSyn). In addition to its neurotoxic role, synucleins have important functions in the nervous system, modulating synaptic transmission. Synucleins are expressed in the retina, but they have been poorly characterized. However, there is evidence that they are important for visual function and that they can play a role in retinal degeneration. This study aimed to profile synucleins in the retina of naturally aged mice and to correlate their patterns with specific retinal cells. With aging, we observed a decrease in the thickness of specific retinal layers, accompanied by an increase in glial reactivity. Moreover, the aSyn levels decreased, whereas bSyn increased with aging. The colocalization of both proteins was decreased in the inner plexiform layer (IPL) of the aged retina. gSyn presented an age-related decrease at the inner nuclear layer but was not significantly changed in the ganglion cell layer. The synaptic marker synaptophysin was shown to be preferentially colocalized with aSyn in the IPL with aging. At the same time, aSyn was found to exist at the presynaptic endings of bipolar cells and was affected by aging. Overall, this study suggests that physiological aging can be responsible for changes in the retinal tissue, implicating functional alterations that could affect synuclein family function.

Gamma-Synuclein Dysfunction Causes Autoantibody Formation in Glaucoma Patients and Dysregulation of Intraocular Pressure in Mice

Dysregulation of intraocular pressure (IOP) is one of the main risk factors for glaucoma. γ-synuclein is a member of the synuclein family of widely expressed synaptic proteins within the central nervous system that are implicated in certain types of neurodegeneration. γ-synuclein expression and localization changes in the retina and optic nerve of patients with glaucoma. However, the mechanisms by which γ-synuclein could contribute to glaucoma are poorly understood. We assessed the presence of autoantibodies to γ-synuclein in the blood serum of patients with primary open-angle glaucoma (POAG) by immunoblotting. A positive reaction was detected for five out of 25 patients (20%) with POAG. Autoantibodies to γ-synuclein were not detected in a group of patients without glaucoma. We studied the dynamics of IOP in response to IOP regulators in knockout mice (γ-KO) to understand a possible link between γ-synuclein dysfunction and glaucoma-related pathophysiological changes. The most prominent decrease of IOP in γ-KO mice was observed after the instillation of 1% phenylephrine and 10% dopamine. The total protein concentration in tear fluid of γ-KO mice was approximately two times higher than that of wild-type mice, and the activity of neurodegeneration-linked protein α2-macroglobulin was reduced. Therefore, γ-synuclein dysfunction contributes to pathological processes in glaucoma, including dysregulation of IOP.

Synaptic vesicle binding of α-synuclein is modulated by β- and γ-synucleins

α-synuclein, β-synuclein, and γ-synuclein are abundantly expressed proteins in the vertebrate nervous system. α-synuclein functions in neurotransmitter release by binding to and clustering synaptic vesicles and chaperoning SNARE-complex assembly. Pathologically, aggregates originating from soluble pools of α-synuclein are deposited into Lewy bodies in Parkinson's disease and related synucleinopathies. The functions of β-synuclein and γ-synuclein in presynaptic terminals remain poorly studied. Using in vitro liposome binding studies, circular dichroism spectroscopy, immunoprecipitation, and fluorescence resonance energy transfer (FRET) experiments on isolated synaptic vesicles in combination with subcellular fractionation of brains from synuclein mouse models, we show that β-synuclein and γ-synuclein have a reduced affinity toward synaptic vesicles compared with α-synuclein, and that heteromerization of β-synuclein or γ-synuclein with α-synuclein results in reduced synaptic vesicle binding of α-synuclein in a concentration-dependent manner. Our data suggest that β-synuclein and γ-synuclein are modulators of synaptic vesicle binding of α-synuclein and thereby reduce α-synuclein's physiological activity at the neuronal synapse.

Severe Primary Open-Angle Glaucoma and Agricultural Profession: A Retrospective Cohort Study

While exposure to pesticides is a known risk factor for neurodegenerative brain diseases, little is known about the influence of environment on glaucoma neuropathy. We aimed to determine whether farmers are at higher risk of developing severe primary open-angle glaucoma (POAG). This retrospective cohort study (tertiary referral center, Reims University Hospital, France) included patients diagnosed with POAG in the last two years. Univariate analysis and adjusted multivariate logistic regression were performed to evaluate the association between agricultural profession and all recorded data. Glaucoma severity (primary outcome) and the number of patients who underwent filtering surgery (secondary outcome) were analyzed. In total, 2065 records were screened, and 772 patients were included (66 in the farmer group and 706 in the nonfarmer group). The risk of severe glaucoma was higher in the farmer group (adjusted odds ratio (aOR) 1.87, p = 0.03). More patients underwent filtering surgery in the farmer group in univariate analysis (p = 0.02) but with no statistical significance after adjustment (p = 0.08). These results suggest pesticide exposure may be a factor accelerating the neurodegeneration in POAG, although a direct link between the agricultural profession and the disease requires further extended studies to be demonstrated.

A Precise Method to Evaluate 360 Degree Measures of Optic Cup and Disc Morphology in an African American Cohort and Its Genetic Applications

(1) Background: Vertical cup-to-disc ratio (CDR) is an important measure for evaluating damage to the optic nerve head (ONH) in glaucoma patients. However, this measure often does not fully capture the irregular cupping observed in glaucomatous nerves. We developed and evaluated a method to measure cup-to-disc ratio (CDR) at all 360 degrees of the ONH. (2) Methods: Non-physician graders from the Scheie Reading Center outlined the cup and disc on digital stereo color disc images from African American patients enrolled in the Primary Open-Angle African American Glaucoma Genetics (POAAGG) study. After converting the resultant coordinates into polar representation, the CDR at each 360-degree location of the ONH was obtained. We compared grader VCDR values with clinical VCDR values, using Spearman correlation analysis, and validated significant genetic associations with clinical VCDR, using grader VCDR values. (3) Results: Graders delineated outlines of the cup contour and disc boundaries twice in each of 1815 stereo disc images. For both cases and controls, the mean CDR was highest at the horizontal bisector, particularly in the temporal region, as compared to other degree locations. There was a good correlation between grader CDR at the vertical bisector and clinical VCDR (Spearman Correlation OD: r = 0.78 [95% CI: 0.76–0.79]). An SNP in the MPDZ gene, associated with clinical VCDR in a prior genome-wide association study, showed a significant association with grader VCDR (p = 0.01) and grader CDR area ratio (p = 0.02). (4) Conclusions: The CDR of both glaucomatous and non-glaucomatous eyes varies by degree location, with the highest measurements in the temporal region of the eye. This method can be useful for capturing innate eccentric ONH morphology, tracking disease progression, and identifying genetic associations.

Suppression of synuclein gamma inhibits the movability of endometrial carcinoma cells by PI3K/AKT/ERK signaling pathway

BACKGROUND

Although overexpression of synuclein gamma (SNCG) has been reported in several cancers, few studies have been performed onSNCG in endometrial carcinomas.

OBJECTIVE

This study aimed to investigate the role of SNCG in the progression of endometrial carcinoma.

METHODS

The expression pattern and function ofSNCG gene were analyzed using the Gene Expression Omnibus (GEO) and Gene Set Enrichment Analysis (GSEA) datasets. Two vector types, containing either SNCG or negative control shRNAs, were used to evaluate cell proliferation, apoptosis, and metastasis using Cell Counting Kit 8, colony formation, flow cytometry, wound-healing, transwell, and invasion assays. The relative protein levels of N-cadherin, E-cadherin, vimentin, p-PI3K, PI3K, p-AKT, AKT, p-ERK, and ERK were determined by western bloting.

RESULTS

Our results revealed thatSNCG mRNA expression and SNCG protein levels in shRNA-treated SPEC2 cells were lower than in the negative control cells. Furthermore, cell proliferation, migration, and invasion were significantly inhibited in SNCG shRNA-treated cells, but apoptosis was increased. The results of western blot analysis indicated that SNCG silencing reduced the protein levels of N-cadherin, vimentin, p-PI3K, p-AKT, and p-ERK, but not those of total PI3K, AKT, and ERK.

CONCLUSIONS

Therefore, shRNA-mediated suppression of SNCG inhibited SPEC2 cell proliferation, migration, and invasion, and promoted SPEC2 cell apoptosis, which was presumably accomplished via regulation of the PI3K/AKT/ERK signaling pathway.

Electroacupuncture Attenuates Cognitive Impairment in Rat Model of Chronic Cerebral Hypoperfusion via miR-137/NOX4 Axis

Electroacupuncture has shown protective effects on cognitive decline. However, the underlying molecular mechanisms are not clear. The present study was conducted to determine whether the cognitive function was ameliorated in cerebral hypoperfusion rats following electroacupuncture and to investigate the role of miR-137/NOX4 axis. In this study, chronic cerebral hypoperfusion (CCH) model was established by bilateral common carotid artery occlusion. Electroacupuncture treatment attenuated brain injury in CCH model group via regulating miR-137/NOX4 axis. Furthermore, the data of neuronal apoptosis and oxidative stress were observed. Our findings indicated that (1) neuronal apoptosis and oxidative stress in CCH rats were significantly increased compared with control group; (2) the animal cognitive performance was evaluated using the Morris water maze (MWM). The results showed that electroacupuncture therapy ameliorated spatial learning and memory impairment in cerebral hypoperfusion rats; and (3) electroacupuncture therapy reduces neuronal apoptosis and oxidative stress by activating miR-137/NOX4 axis. These results suggest that electroacupuncture therapy for CCH may be mediated by miR-137/NOX4 axis. Electroacupuncture therapy may act as a potential therapeutic approach for chronic cerebral hypoperfusion.

Genetics of synucleins in neurodegenerative diseases

The SNCA locus currently has an indisputable role in Parkinson's disease and other synucleinopathies. The role of genetic variability in the other members of the synuclein family (SNCB and SNCG) in disease is far less clear. In this review, we critically assess the pathogenicity, main characteristics, and roles of genetic variants in these genes reported to be causative of synucleinopathies. We also summarize the different association signals identified in the SNCA locus that have been associated with risk for disease. We take a bird's eye view of the variability currently reported in the general population for the three genes and use these data to infer on the potential relationship between each of the genes and human disease.

Hydrogen Sulfide and β-Synuclein Are Involved and Interlinked in the Aging Glaucomatous Retina

Purpose

Glaucoma, one of the leading causes of irreversible blindness worldwide, is a group of disorders characterized by progressive retinal ganglion cell (RGC) loss. Synucleins, a family of small proteins, have been of interest in studies of neurodegeneration and CNS. However, their roles and functions in glaucoma are still not completely understood and remain to be explored. Our previous studies showed that α-synuclein and H₂S play a pivotal role in glaucoma. This study aims to (1) elucidate the potential roles and functions of synucleins in glaucoma throughout aging, (2) investigate the interaction between the synucleins and H₂S, and better understand the mechanism of H₂S in neuroprotection.

Methods

The chronic IOP elevation model was carried out in 12 animals at different ages (3 months and 14 months), and RGCs were quantified by Brn3a staining. Mass spectrometric-assisted proteomics analysis was employed to measure synuclein levels and H₂S producing proteins in retina. Secondly, the acute IOP elevation model was carried out in 12 juvenile animals, with or without intravitreal injection of GYY4137 (a H₂S donor). RGCs were quantified along with the abundancy of synucleins.

Results

RGCs and β-synuclein (SNCB) are significantly changed in old animals. Under chronic IOP elevation, there is a significant RGC loss in old animals, whereas no significant change in young animals; SNCB is significantly downregulated and 3MST is significantly upregulated in young animals due to IOP, while no significant changes in old ones are notable. Under acute IOP elevation (approx. 55 mmHg), a significant RGC loss is observed; exogenous H₂S significantly reduced RGC loss and downregulated SNCB levels.

Conclusion

The present study indicates a strong link between ageing and SNCB regulation. In young animals SNCB is downregulated going along with less RGC loss. Furthermore, increasing endogenous H₂S is effective to downregulate SNCB and is neuroprotective against acute IOP elevation.

Optic Nerve Lipidomics Reveal Impaired Glucosylsphingosine Lipids Pathway in Glaucoma

Purpose

To determine major differences in lipid profile between human control and glaucomatous optic nerve. To assess major enzymes in lipid pathway if aberration is revealed for a lipid class by profiling.

Methods

Optic nerve (ON) samples were obtained from human cadaveric donors [control (n = 11) and primary open-angle glaucoma (POAG; n = 12)]; the lipids were extracted using Bligh and Dyer methods. Control and glaucoma donors were all Caucasians age 72.3 ± 5.9 and 70.3 ± 10.5 (inclusive of both sexes), respectively. Lipids were extracted after weighing the tissue; the protein amounts in the corresponding aqueous phase of organic solvent extraction were recorded. High-resolution mass spectrometry was performed using a Q-exactive mass spectrometer coupled with an EASY-nLC 1000 liquid chromatograph instrument. Bioinformatics and statistical analysis were performed using LipidSearch v.4.1 and MetaboAnalyst 4.0/STATA 14.2. Protein amounts were determined using Bradford's method. Western blot, ELISA, and immunohistochemistry utilized established protocols and were performed for protein quantification and localization, respectively. Additional donor tissues were utilized for Western blot, ELISA, and immunohistochemistry.

Results

Principal component analysis (PCA) placed control and glaucomatous ONs in two distinct groups based on analysis of lipid profiles. Total lipid, total phospholipids, total ceramide, and total sphingolipids were similar (without significant difference) between control and glaucoma. However, we found a significant increase in glucosylsphingosine in glaucoma compared to control samples. We found similar levels of glucocerebrosidase (GBA), ceramide glucosyltransferase (UGCG), decreased nonlysosomal glucocerebrosidase (GBA2), and increased lysosomal and nonlysosomal acylsphingosine amidohydrolase (ASAH1 and ASAH2) levels in glaucomatous ON compared to control.

Conclusions

We found significant differences in glucosylsphingosine lipids, consistent with decreased GBA and GBA2 and increased ASAH1 and ASAH2 immunoreactivity in glaucoma, suggesting the potential impairment of sphingolipid enzymatic pathways in lysosomal and nonlysosomal cellular compartments.

Differential Gamma-Synuclein Expression in Acute and Chronic Retinal Ganglion Cell Death in the Retina and Optic Nerve

We used genetic naturally occurring glaucoma (DBA/2J) and experimentally induced optic nerve crush (ONC) as models to study gamma-synuclein expression change in retinal ganglion cells and optic nerves. Gene chip microarray analysis demonstrated downregulated expression of the gamma-synuclein gene in DBA/2J mice as they developed age-associated glaucoma with concomitant with retinal ganglion cell loss. Real-time PCR, Western blot, and immunostaining results confirmed that the expression of gamma-synuclein at the mRNA and protein level was significantly reduced in the retinas and optic nerves of aged DBA/2J mice. We also observed similar reduced expression of gamma-synuclein in the retinas from mice after optic nerve crush. Surprisingly, the expression of gamma-synuclein was increased in optic nerves after crush. This is the first study demonstrating gamma-synuclein-expressing cells accumulate in the optic nerve crush site. Gamma-synuclein was found in axons colocalizing largely with neurofilaments in control mice without injury but was found inside cells within the scar in the crush site. Gamma-synuclein expression is predominantly expressed at the optic nerve crush site associated with CD68⁺ macrophage-like cells, not GFAP-expressing astroglial cells, suggesting gamma-synuclein expression is associated with glial scar formation inhibitory to optic nerve regeneration. We propose gamma-synuclein labels macrophage-like cells recruited to the site of acute optic nerve injury.

γ-Synuclein Induces Human Cortical Astrocyte Proliferation and Subsequent BDNF Expression and Release

γ-Synuclein (γ-syn) is expressed by astrocytes in the human nervous system, and increased extracellularly in the brain and cerebrospinal fluid of individuals diagnosed with Alzheimer's disease. Upregulation of γ-syn also coincides with proliferation of glioblastomas and other cancers. In order to better understand regulation and function of extracellular γ-syn, primary human cortical astrocytes were treated with γ-syn conditioned media at various physiological concentrations (50, 100, 150 nM) after cell synchronization. Additionally, extracellular brain-derived neurotrophic factor (BDNF), a neuroprotective growth factor released by astrocytes that has been shown to be decreased extracellularly in neurodegenerative disease, was observed in response to γ-syn treatment. Analysis of 5-bromodeoxyuridine (BrdU) and propidium iodide through flow cytometry 24 h after release from synchronization revealed an increase in G₂/M phase of the cell cycle with 100 nM γ-syn during initial cell division, an effect that was reversed at 48 h. However, increased extracellular BDNF was observed at 48 h with 100 nM and 150 nM γ-syn treatment with no difference between controls at 24 h. Further analysis of cell cycle markers with immunocytochemistry of BrdU and Ki67 after treatment with 100 nM γ-syn confirmed increased initial cell proliferation and decreased non-proliferating cells. Western blot analysis demonstrated increased γ-syn levels after 100 nM treatment at 24 and 48 h, and increased pro-BDNF, mature BDNF and cell viability at 48 h. The results demonstrate that γ-syn internalization by human cortical astrocytes causes upregulation of the cell cycle, followed by subsequent BDNF expression and release.

Modulation of the Immune System for the Treatment of Glaucoma

Background:

At present intraocular pressure (IOP) lowering therapies are the only approach to treat glaucoma. Neuroprotective strategies to protect the retinal ganglion cells (RGC) from apoptosis are lacking to date. Substantial amount of research concerning the role of the immune system in glaucoma has been performed in the recent years. This review aims to analyse changes found in the peripheral immune system, as well as selected local changes of retina immune cells in the glaucomatous retina.

Methods:

By dividing the immune system into the innate and the adaptive immune system, a systematic literature research was performed to find recent approaches concerning the modulation of the immune system in the context of glaucoma. Also ClinicalTrials.gov was assessed to identify studies with a translational context.

Results:

We found that some aspects of the immune system, such as changes in antibody levels, changes in toll like receptor signalling, T cells and retinal microglial cells, experience more research activity than other areas such as changes in dendritic cells or macrophages. Briefly, results from clinical studies revealed altered immunoreactivities against retinal and optic nerve antigens in sera and aqueous humor of glaucoma patients and point toward an autoimmune involvement in glaucomatous neurodegeneration and RGC death. IgG accumulations along with plasma cells were found localised in human glaucomatous retinae in a pro-inflammatory environment possibly maintained by microglia. Animal studies show that antibodies (e.g. anti- heat shock protein 60 and anti-myelin basic protein) elevated in glaucoma patients provoke autoaggressive RGC loss and are associated with IgG depositions and increased microglial cells. Also, studies addressing changes in T lymphocytes, macrophages but also local immune responses in the retina have been performed and also hold promising results.

Conclusions:

This recapitulation of recent literature demonstrates that the immune system definitely plays a role in the pathogenesis of glaucoma. Multiple changes in the peripheral innate as well as adaptive immune system have been detected and give room for further research concerning valuable therapeutic targets. We conclude that there still is a great need to bring together the results derived from basic research analysing different aspects of the immune system in glaucoma to understand the immune context of the disease. Furthermore local immune changes in the retina of glaucoma patients still leave room for further therapeutic targets

Analysis of Autoantibody Repertoires in Sera of Patients with Glaucoma

PURPOSE

Glaucoma is the second cause of blindness worldwide. It is usually considered a neurodegenerative disease. There is evidence that an autoimmune mechanism is involved in the development of glaucoma in some patients. The aim of this study was to analyze the IgG autoantibody repertoires in sera of glaucoma patients and healthy subjects.

METHODS

A total of 82 patients were divided into four groups: healthy volunteers without any ocular disorders (CO, n = 30), patients with primary open-angle glaucoma (POAG, n = 19), ocular hypertension (OHT, n = 16), and normal tension glaucoma (NTG, n = 17). All groups were matched for age and gender. The sera of these patients were tested against Western blots of retinal antigens. Immunodetection was done using 4-chloro-1-naphthol staining. The autoantibody patterns were digitized and subsequently analyzed by multivariate statistical techniques.

RESULTS

All patients showed different, complex staining patterns of autoantibodies against retinal antigens. There was an increase in the number of peaks in sera of patients with primary open-angle glaucoma (POAG) compared to healthy subjects (CO). Including all peaks the analysis of discriminance revealed a statistically significant difference between the patterns of POAG compared to all other groups (p < 0.01). Sera of normal tension glaucoma (NTG) had no statistically different autoantibody pattern compared to those of control subjects.

CONCLUSIONS

In this study, we demonstrated a difference in the IgG autoantibody patterns of primary open-angle glaucoma patients compared to healthy subjects. However, the patterns were not significantly different in normal tension glaucoma compared to control subjects.

Decelerated neurodegeneration after intravitreal injection of α-synuclein antibodies in a glaucoma animal model

Although elevated intraocular pressure (IOP) remains the major risk factor in glaucoma, neurodegenerative processes continue despite effective IOP lowering. Altered α-synuclein antibody (Abs) levels have been reported to play a crucial role. This study aimed at identifying whether α-synuclein Abs are capable to decelerate neuronal decay while providing insights into proteomic changes. Four groups of Sprague Dawley rats received episcleral vein occlusion: (1) CTRL, no intravitreal injection, n = 6, (2) CTRL IgG, intravitreal injection of unspecific IgG, n = 5, (3) Buffer, intravitreal injection of buffer, n = 6, (4), α-synuclein Ab, intravitreal injection of α-synuclein Ab, n = 5. IOP and retinal nerve fiber layer thickness (RNFLT) were monitored and immunohistochemistry, microarray and proteomic analysis were performed. RNFLT was reduced in CTRL, CTRL IgG and Buffer group (all p < 0.01) and α-synuclein Ab group (p = 0.17). Axon and RGC density showed an increased neurodegeneration in CTRL, CTRL IgG and Buffer group (all p < 0.01) and increased neuronal survival in α-synuclein Ab group (p = 0.38 and 0.06, respectively) compared with fellow eyes. Proteomic analysis revealed alterations of cofilin 1 and superoxide dismutase 1 expression. This data indicate that α-synuclein Ab might indirectly modulate the actin cytoskeleton organization and negatively regulate apoptotic processes via cofilin 1 and superoxide dismutase 1.

The Role of Microglia in Retinal Neurodegeneration: Alzheimer's Disease, Parkinson, and Glaucoma

Microglia, the immunocompetent cells of the central nervous system (CNS), act as neuropathology sensors and are neuroprotective under physiological conditions. Microglia react to injury and degeneration with immune-phenotypic and morphological changes, proliferation, migration, and inflammatory cytokine production. An uncontrolled microglial response secondary to sustained CNS damage can put neuronal survival at risk due to excessive inflammation. A neuroinflammatory response is considered among the etiological factors of the major aged-related neurodegenerative diseases of the CNS, and microglial cells are key players in these neurodegenerative lesions. The retina is an extension of the brain and therefore the inflammatory response in the brain can occur in the retina. The brain and retina are affected in several neurodegenerative diseases, including Alzheimer's disease (AD), Parkinson's disease (PD), and glaucoma. AD is an age-related neurodegeneration of the CNS characterized by neuronal and synaptic loss in the cerebral cortex, resulting in cognitive deficit and dementia. The extracellular deposits of beta-amyloid (Aβ) and intraneuronal accumulations of hyperphosphorylated tau protein (pTau) are the hallmarks of this disease. These deposits are also found in the retina and optic nerve. PD is a neurodegenerative locomotor disorder with the progressive loss of dopaminergic neurons in the substantia nigra. This is accompanied by Lewy body inclusion composed of α-synuclein (α-syn) aggregates. PD also involves retinal dopaminergic cell degeneration. Glaucoma is a multifactorial neurodegenerative disease of the optic nerve, characterized by retinal ganglion cell loss. In this pathology, deposition of Aβ, synuclein, and pTau has also been detected in retina. These neurodegenerative diseases share a common pathogenic mechanism, the neuroinflammation, in which microglia play an important role. Microglial activation has been reported in AD, PD, and glaucoma in relation to protein aggregates and degenerated neurons. The activated microglia can release pro-inflammatory cytokines which can aggravate and propagate neuroinflammation, thereby degenerating neurons and impairing brain as well as retinal function. The aim of the present review is to describe the contribution in retina to microglial-mediated neuroinflammation in AD, PD, and glaucomatous neurodegeneration.

Longitudinal live imaging of retinal α-synuclein::GFP deposits in a transgenic mouse model of Parkinson's Disease/Dementia with Lewy Bodies

Abnormal α-synuclein (α-syn) accumulation in the CNS may underlie neuronal cell and synaptic dysfunction leading to motor and cognitive deficits in synucleinopathies including Parkinson’s disease (PD) and Dementia with Lewy Bodies (DLB). Multiple groups demonstrated α-syn accumulation in CNS accessory structures, including the eyes and olfactory terminals, as well as in peripheral organs of Parkinsonian patients. Retinal imaging studies of mice overexpressing fused α-syn::GFP were conducted to evaluate the presence and progression of retinal pathology in a PD/DLB transgenic mouse model. Bright-field image retinal maps and fluorescent images were acquired at 1-month intervals for 3 months. Retinal imaging revealed the accumulation of GFP-tagged α-syn in retinal ganglion cell layer and in the edges of arterial blood vessels in the transgenic mice. Double labeling studies confirmed that the α-syn::GFP-positive cells were retinal ganglion cells containing α-syn. Accumulation of α-syn persisted in the same cells and increased with age. Accumulation of α-syn::GFP was reduced by immunization with single chain antibodies against α-syn. In conclusion, longitudinal live imaging of the retina in the PDGF-α-syn::GFP mice might represent a useful, non-invasive tool to monitor the fate of α-syn accumulation in the CNS and to evaluate the therapeutic effects of compounds targeting α-syn.

Sub-Chronic Neuropathological and Biochemical Changes in Mouse Visual System after Repetitive Mild Traumatic Brain Injury

Repetitive mild traumatic brain injury (r-mTBI) results in neuropathological and biochemical consequences in the human visual system. Using a recently developed mouse model of r-mTBI, with control mice receiving repetitive anesthesia alone (r-sham) we assessed the effects on the retina and optic nerve using histology, immunohistochemistry, proteomic and lipidomic analyses at 3 weeks post injury. Retina tissue was used to determine retinal ganglion cell (RGC) number, while optic nerve tissue was examined for cellularity, myelin content, protein and lipid changes. Increased cellularity and areas of demyelination were clearly detectable in optic nerves in r-mTBI, but not in r-sham. These changes were accompanied by a ~25% decrease in the total number of Brn3a-positive RGCs. Proteomic analysis of the optic nerves demonstrated various changes consistent with a negative effect of r-mTBI on major cellular processes like depolymerization of microtubules, disassembly of filaments and loss of neurons, manifested by decrease of several proteins, including neurofilaments (NEFH, NEFM, NEFL), tubulin (TUBB2A, TUBA4A), microtubule-associated proteins (MAP1A, MAP1B), collagen (COL6A1, COL6A3) and increased expression of other proteins, including heat shock proteins (HSP90B1, HSPB1), APOE and cathepsin D. Lipidomic analysis showed quantitative changes in a number of phospholipid species, including a significant increase in the total amount of lysophosphatidylcholine (LPC), including the molecular species 16:0, a known demyelinating agent. The overall amount of some ether phospholipids, like ether LPC, ether phosphatidylcholine and ether lysophosphatidylethanolamine were also increased, while the majority of individual molecular species of ester phospholipids, like phosphatidylcholine and phosphatidylethanolamine, were decreased. Results from the biochemical analysis correlate well with changes detected by histological and immunohistochemical methods and indicate the involvement of several important molecular pathways. This will allow future identification of therapeutic targets for improving the visual consequences of r-mTBI.

Yeast reveals similar molecular mechanisms underlying alpha- and beta-synuclein toxicity

Synucleins belong to a family of intrinsically unstructured proteins that includes alpha-synuclein (aSyn), beta-synuclein (bSyn) and gamma-synuclein (gSyn). aSyn is the most studied member of the synuclein family due to its central role in genetic and sporadic forms of Parkinson's disease and other neurodegenerative disorders known as synucleionopathies. In contrast, bSyn and gSyn have been less studied, but recent reports also suggest that, unexpectedly, these proteins may also cause neurotoxicity. Here, we explored the yeast toolbox to investigate the cellular effects of bSyn and gSyn. We found that bSyn is toxic and forms cytosolic inclusions that are similar to those formed by aSyn. Moreover, we found that bSyn shares similar toxicity mechanisms with aSyn, including vesicular trafficking impairment and induction of oxidative stress. We demonstrate that co-expression of aSyn and bSyn exacerbates cytotoxicity, due to increased dosage of toxic synuclein forms, and that they are able to form heterodimers in both yeast and in human cells. In contrast, gSyn is not toxic and does not form inclusions in yeast cells. Altogether, our findings shed light into the question of whether bSyn can exert toxic effects and confirms the occurrence of aSyn/bSyn heterodimers, opening novel perspectives for the development of novel strategies for therapeutic intervention in synucleinopathies.

Intracellular Dynamics of Synucleins: "Here, There and Everywhere"

Synucleins are small, soluble proteins expressed primarily in neural tissue and in certain tumors. The synuclein family consists of three members: α-, β-, and γ-synucleins present only in vertebrates. Members of the synuclein family have high sequence identity, especially in the N-terminal regions. The synuclein gene family came into the spotlight, when one of its members, α-synuclein, was found to be associated with Parkinson's disease and other neurodegenerative disorders, whereas γ-synuclein was linked to several forms of cancer. There are a lot of controversy and exciting debates concerning members of the synuclein family, including their normal functions, toxicity, role in pathology, transmission between cells and intracellular localization. Important findings which remain undisputable for many years are synuclein localization in synapses and their role in the regulation of synaptic vesicle trafficking, whereas their presence and function in mitochondria and nucleus is a debated topic. In this review, we present the data on the localization of synucleins in two intracellular organelles: the nucleus and mitochondria.

Role of synucleins in traumatic brain injury — an experimental in vitro and in vivo study in mice

Synucleins are small prone to aggregate proteins associated with several neurodegenerative diseases (NDDs), however their role in traumatic brain injury (TBI) is an emerging area of investigation. Using in vitro scratch injury model and in vivo mouse weight-drop model we have found that the injury causes alterations in the expression and localization of synucleins near the damaged area. Before injury, α-synuclein is diffused in the cytoplasm of neurons and γ-synuclein is both in the cytoplasm and nucleus of oligodendrocytes. After the scratch injury of the mixed neuronal and glial culture, α-synuclein forms punctate structures in the cytoplasm of neurons and γ-synuclein is almost completely localized to the nucleus of the oligodendrocytes. Furthermore, the amount of post-translationally modified Met38-oxidized γ-synuclein is increased 3.8 fold 24 h after the scratch. α- and γ-synuclein containing cells increased in the initially cell free scratch zone up to 24 h after the scratch.Intracellular expression and localization of synucleins are also changed in a mouse model of focal closed head injury, using a standardized weight drop device. γ-Synuclein goes from diffuse to punctate staining in a piriform cortex near the amygdala, which may reflect the first steps in the formation of deposits/inclusions. Surprisingly, oxidized γ-synuclein co-localizes with cofilin-actin rods in the thalamus, which are absent in all other regions of the brain. These structures reach their peak amounts 7 days after injury. The changes in γ-synuclein localization are accompanied by injury-induced alterations in the morphology of both astrocytes and neurons.

Mini-Review: Impaired Axonal Transport and Glaucoma

Glaucoma is increasingly recognized as a neurodegenerative disorder, characterized by the accelerated loss of retinal ganglion cells (RGCs) and their axons. Impaired axonal transport has been implicated as a pathogenic mechanism in a number of neurodegenerative diseases, including glaucoma. The long RGC axon, with its high metabolic demand and crucial role in conveying neurotrophic signals, relies heavily on intact axonal transport. In this mini review, we consider the evidence for transport disruption along RGCs in association with glaucoma and other intraocular pressure models. We give a brief overview of the axonal transport process and the methods by which it is assessed. Spatial and temporal patterns of axonal transport disruption are considered as well as the reversibility of these changes. Biomechanical, metabolic and cytoskeletal insults may underlie the development of axonal transport deficits, and there are multiple perspectives on the impact that transport disruption has on the RGC. Eliciting the role of impaired axonal transport in glaucoma pathogenesis may uncover novel therapeutic targets for protecting the optic nerve and preventing vision loss in glaucoma.

Assessment of retinal ganglion cell damage in glaucomatous optic neuropathy: Axon transport, injury and soma loss

Glaucoma is a disease characterized by progressive axonal pathology and death of retinal ganglion cells (RGCs), which causes structural changes in the optic nerve head and irreversible vision loss. Several experimental models of glaucomatous optic neuropathy (GON) have been developed, primarily in non-human primates and, more recently and commonly, in rodents. These models provide important research tools to study the mechanisms underlying glaucomatous damage. Moreover, experimental GON provides the ability to quantify and monitor risk factors leading to RGC loss such as the level of intraocular pressure, axonal health and the RGC population. Using these experimental models we are able to gain a better understanding of GON, which allows for the development of potential neuroprotective strategies. Here we review the advantages and disadvantages of the relevant and most often utilized methods for evaluating axonal degeneration and RGC loss in GON. Axonal pathology in GON includes functional disruption of axonal transport (AT) and structural degeneration. Horseradish peroxidase (HRP), rhodamine-B-isothiocyanate (RITC) and cholera toxin-B (CTB) fluorescent conjugates have proven to be effective reporters of AT. Also, immunohistochemistry (IHC) for endogenous AT-associated proteins is often used as an indicator of AT function. Similarly, structural degeneration of axons in GON can be investigated via changes in the activity and expression of key axonal enzymes and structural proteins. Assessment of axonal degeneration can be measured by direct quantification of axons, qualitative grading, or a combination of both methods. RGC loss is the most frequently quantified variable in studies of experimental GON. Retrograde tracers can be used to quantify RGC populations in rodents via application to the superior colliculus (SC). In addition, in situ IHC for RGC-specific proteins is a common method of RGC quantification used in many studies. Recently, transgenic mouse models that express fluorescent proteins under the Thy-1 promoter have been examined for their potential to provide specific and selective labeling of RGCs for the study of GON. While these methods represent important advances in assessing the structural and functional integrity of RGCs, each has its advantages and disadvantages; together they provide an extensive toolbox for the study of GON.

Gamma-synuclein pathology in amyotrophic lateral sclerosis

Objective

The prominent histopathological feature of the amyotrophic lateral sclerosis (ALS) is the presence of intracellular inclusions in degenerating neurons and their axons. The appearance and localization of these pathological structures depend on an aggregated protein that forms their scaffold. We investigated if γ-synuclein, an aggregation-prone protein highly expressed in healthy motor neurons, and predominantly localized in their axons and synaptic terminals is involved in ALS pathology.

Methods

Immunostaining of histological sections and sequential protein extraction from postmortem neural samples followed by immunoblotting.

Results

Immunohistochemical screening revealed a subset of sporadic (9 of 31) and familial (8 of 23) ALS cases with a novel type of pathology characterized by the accumulation of γ-synuclein in distinct profiles within the dorsolateral column. Sequential fractionation of proteins from the spinal cord tissues revealed detergent-insoluble γ-synuclein species specifically in the dorsolateral corticospinal tracts of a ALS patient with γ-synuclein-positive profiles in this region. These profiles are negative for protein markers commonly found in pathological inclusions in the spinal cord of ALS patients and most probably represent degenerated axons of upper motor neurons that have lost their neurofilaments. A subset of these profiles was found in association with phagocytic cells positive for Mac-2/Galectin-3. A smaller subset of studied ALS cases (4 of 54) contained large cytoplasmic inclusions in the cell body of remaining spinal motor neurons.

Interpretation

Our observations suggest that pathological aggregation of γ-synuclein might contribute to the pathogenesis of ALS.

Synuclein-gamma predicts poor clinical outcome in esophageal cancer patients

The synuclein gamma (SNCG) protein, a member of neuronal protein family synuclein, has been considered as a promising potential biomarker as an indicator of cancer stage and survival in patients with cancer. The present study was conducted to evaluate the prognostic value of SNCG in patients with esophageal carcinoma (EC). SNCG levels were assessed immunohistochemically in cancer tissues from 73 EC patients. Median age was 57 (range, 29-78) years old. Forty-seven percent of the patients were male. Thirty-seven percent of the patients had upper or middle localized tumor whereas 59 % had epidermoid carcinoma. More than half of the patients (61 %) had undergone operation where 57 % received adjuvant treatment including chemotherapy or chemotherapy plus radiotherapy. Median overall survival was 11.3 ± 1.8 months (95% confidence interval (CI): 7.7-14.9 months). SNCG positivity was significantly associated with the histological type of EC and inoperability (for SNCG positive vs. negative group; epidermoid 80 vs. 53 %; p = 0.05 and inoperable 59 vs.32 %; p = 0.04, respectively). Lymph node metastasis, inoperability and receiving no adjuvant treatment had significantly adverse effect on survival in the univariate analysis (p = 0.01, p < 0.001, and p = 0.001, respectively). SNCG positivity had significantly adverse effect on survival in both univariate and multivariate analysis (p = 0.02 and p = 0.01, respectively). Our results are the first to suggest that SNCG is a new independent predictor for poor prognosis in EC patients in the literature.

New α- and γ-synuclein immunopathological lesions in human brain

Introduction

Several neurodegenerative diseases are classified as proteopathies as they are associated with the aggregation of misfolded proteins. Synucleinopathies are a group of neurodegenerative disorders associated with abnormal deposition of synucleins. α-Synucleinopathies include Parkinson’s disease, dementia with Lewy bodies, and multiple system atrophy. Recently accumulation of another member of the synuclein family- γ−synuclein in neurodegenerative diseases compelled the introduction of the term γ−synucleinopathy. The formation of aggregates and deposits of γ−synuclein is facilitated after its oxidation at methionine 38 (Met³⁸).

Results

Several types of intracytoplasmic inclusions containing post-translationally modified α- and γ−synucleins are detected. Oxidized Met³⁸-γ-synuclein forms aberrant inclusions in amygdala and substantia nigra. Double staining revealed colocalization of oxidized-γ-synuclein with α-synuclein in the cytoplasm of neurons. Another type of synuclein positive inclusions in the amygdala of dementia with Lewy bodies patients has the appearance of Lewy bodies. These inclusions are immunoreactive when analyzed with antibodies to α-synuclein phosphorylated on serine 129, as well as with antibodies to oxidized-γ-synuclein. Some of these Lewy bodies have doughnut-like shape with round or elongated shape. The separate immunofluorescent images obtained with individual antibodies specific to oxidized-γ-synuclein and phospho-α-synuclein clearly shows the colocalization of these synuclein isoforms in substantia nigra inclusions. Phospho-α-synuclein is present almost exclusively at the periphery of these structures, whereas oxidized-γ-syn immunoreactivity is also located in the internal parts forming dot-like pattern of staining.

We also identified several types of oxidized-γ-syn positive astrocytes with different morphology and examined their immunohistochemical phenotypes. Some of them are compact cells with short processes, others have longer processes. Oxidized-γ-synuclein positive astrocytes may also display mixed morphological and immunocytochemical phenotypes between protoplasmic and fibrous astrocytes.

Conclusions

These results reveal new γ−synuclein positive lesions in human brain. Oxidized-γ-synuclein is colocalized with phospho-α-synuclein in doughnut-like inclusions. Several types of astrocytes with different morphology are immunopositive for oxidized-γ-synuclein.

γ-Synuclein antibodies have neuroprotective potential on neuroretinal cells via proteins of the mitochondrial apoptosis pathway

The family of synuclein proteins (α, β and γ) are related to neurodegenerative disease e.g. Parkinson disease and Morbus Alzheimer. Additionally, a connection between γ-synuclein and glaucoma, a neurodegenerative disease characterized by a progressive loss of retinal ganglion cells, which finally leads to blindness, exists. The reason for the development of glaucoma is still unknown. Recent studies evaluating the participation of immunological components, demonstrate complex changed antibody reactivities in glaucoma patients in comparison to healthy people, showing not only up-regulations (e.g. alpha-fodrin antibody) but also down-regulations (e.g. γ-synuclein antibody) of antibodies in glaucoma patients. Up-regulated antibodies could be auto-aggressive, but the role of down-regulated antibodies is still unclear. Previous studies show a significant influence of the serum and the antibodies of glaucoma patients on protein expression profiles of neuroretinal cells. The aim of this study was to investigate the effect of γ-synuclein antibody on the viability and reactive oxygen species levels of a neuroretinal cell line (RGC-5) as well as their interaction with cellular proteins. We found a protective effect of γ-synuclein antibody resulting in an increased viability (up to 15%) and decreased reactive oxygen species levels (up to −12%) of glutamate and oxidative stressed RGC-5. These can be traced back to anti-apoptotic altered protein expressions in the mitochondrial apoptosis pathway indicated by mass spectrometry and validated by microarray analysis such as active caspase 3, bcl-2 associated-x-protein, S100A4, voltage-dependent anion channel, extracellular-signal-regulated-kinase (down-regulated) and baculoviral IAP repeat-containing protein 6, phosphorylated extracellular-signal-regulated-kinase (up-regulated). These changed protein expression are triggered by the γ-synuclein antibody internalization of RGC-5 we could see in immunohistochemical stainings. These findings let us assume a novel physiological function of γ-synuclein antibodies and give insights in the role of autoantibodies in glaucoma. We hypothesize that the down-regulation of autoantibodies found in glaucoma patients lead to a loss of protective autoimmunity.

Cell-specific post-transcriptional regulation of γ-synuclein gene by micro-RNAs

γ-Synuclein is a member of the synucleins family of small proteins, which consists of three members:α, β- and γ-synuclein. γ-Synuclein is abnormally expressed in a high percentage of advanced and metastatic tumors, but not in normal or benign tissues. Furthermore, γ-synuclein expression is strongly correlated with disease progression, and can stimulate proliferation, induce invasion and metastasis of cancer cells. γ-Synuclein transcription is regulated basically through the binding of AP-1 to specific sequences in intron 1. Here we show that γ-synuclein expression may be also regulated by micro RNAs (miRs) on post-transcriptional level. According to prediction by several methods, the 3′-untranslated region (UTR) of γ-synuclein gene contains targets for miRs. Insertion of γ-synuclein 3′-UTR downstream of the reporter luciferase (LUC) gene causes a 51% reduction of LUC activity after transfection into SKBR3 and Y79 cells, confirming the presence of efficient targets for miRs in this fragment. Expression of miR-4437 and miR-4674 for which putative targets in 3′-UTR were predicted caused a 61.2% and 60.1% reduction of endogenous γ-synuclein expression confirming their role in gene expression regulation. On the other hand, in cells overexpressing γ-synuclein no significant effect of miRs on γ-synuclein expression was found suggesting that miRs exert their regulatory effect only at low or moderate, but not at high level of γ-synuclein expression. Elevated level of γ-synuclein differentially changes the level of several miRs expression, upregulating the level of some miRs and downregulating the level of others. Three miRs upregulated as a result of γ-synuclein overexpression, i.e., miR-885-3p, miR-138 and miR-497 have putative targets in 3′-UTR of the γ-synuclein gene. Some of miRs differentially regulated by γ-synuclein may modulate signaling pathways and cancer related gene expression. This study demonstrates that miRs might provide cell-specific regulation of γ-synuclein expression and set the stage to further evaluate their role in pathophysiological processes.

Synucleins antagonize endoplasmic reticulum function to modulate dopamine transporter trafficking

Synaptic re-uptake of dopamine is dependent on the dopamine transporter (DAT), which is regulated by its distribution to the cell surface. DAT trafficking is modulated by the Parkinson's disease-linked protein alpha-synuclein, but the contribution of synuclein family members beta-synuclein and gamma-synuclein to DAT trafficking is not known. Here we use SH-SY5Y cells as a model of DAT trafficking to demonstrate that all three synucleins negatively regulate cell surface distribution of DAT. Under these conditions the synucleins limit export of DAT from the endoplasmic reticulum (ER) by impairment of the ER-Golgi transition, leading to accumulation of DAT in this compartment. This mechanism for regulating DAT export indirectly through effects on ER and Golgi function represents a previously unappreciated role for the extended synuclein family that is likely applicable to trafficking of the many proteins that rely on the secretory pathway.

Synucleins: are they two-edged swords?

The synuclein family consists of three distinct highly homologous genes, α-synuclein, β-synuclein, and γ-synuclein, which have so far been found only in vertebrates. Proteins encoded by these genes are characterized by an acidic C-terminal region and five or six imperfect repeat motifs (KTKEGV) distributed throughout the highly conserved N-terminal region. Numerous data demonstrate that synucleins are implicated in two groups of the most devastating human disorders, i.e., neurodegenerative diseases (NDDs) and cancer. Mutations in the α-synuclein gene are associated with familial forms of Parkinson's disease (PD), and accumulation of α-synuclein inclusions is a hallmark of this disorder. In breast cancer, increased expression of γ-synuclein correlates with disease progression. Conversely, some results indicate that the members of the synuclein family may have a protective effect. How might these small proteins combine such controversial properties? We present evidence that synuclein's features are basically regulated by two mechanisms, i.e., posttranslational modifications (PTMs) and the level of their expression. We also discuss a new, emerging area of investigation of synucleins, namely, their role in the cell-to-cell propagation of pathology.

Contrasting effects of α-synuclein and γ-synuclein on the phenotype of cysteine string protein α (CSPα) null mutant mice suggest distinct function of these proteins in neuronal synapses

In neuronal synapses, neurotransmitter-loaded vesicles fuse with presynaptic plasma membrane in a complex sequence of tightly regulated events. The assembly of specialized SNARE complexes plays a pivotal role in this process. The function of the chaperone cysteine string protein α (CSPα) is important for synaptic SNARE complex formation, and mice lacking this protein develop severe synaptic dysfunction and neurodegeneration that lead to their death within 3 months after birth. Another presynaptic protein, α-synuclein, also potentiates SNARE complex formation, and its overexpression rescues the phenotype of CSPα null mutant mice, although these two proteins use different mechanisms to achieve this effect. α-Synuclein is a member of a family of three related proteins whose structural similarity suggests functional redundancy. Here, we assessed whether γ-synuclein shares the ability of α-synuclein to bind synaptic vesicles and ameliorate neurodegeneration caused by CSPα deficiency in vivo. Although the N-terminal lipid-binding domains of the two synucleins showed similar affinity for purified synaptic vesicles, the C-terminal domain of γ-synuclein was not able to interact with synaptobrevin-2/VAMP2. Consequently, overexpression of γ-synuclein did not have any noticeable effect on the phenotype of CSPα null mutant mice. Our data suggest that the functions of α- and γ-synucleins in presynaptic terminals are not fully redundant.

Cell type-specific translational profiling in the Xenopus laevis retina

BACKGROUND

Translating Ribosome Affinity Purification (TRAP), a method recently developed to generate cell type-specific translational profiles, relies on creating transgenic lines of animals in which a tagged ribosomal protein is placed under regulatory control of a cell type-specific promoter. An antibody is then used to affinity purify the tagged ribosomes so that cell type-specific mRNAs can be isolated from whole tissue lysates.

RESULTS

Here, cell type-specific transgenic lines were generated to enable TRAP studies for retinal ganglion cells and rod photoreceptors in the Xenopus laevis retina. Using real time quantitative PCR for assessing expression levels of cell type-specific mRNAs, the TRAP method was shown to selectively isolate mRNAs expressed in the targeted cell and was efficient at purifying mRNAs expressed at both high and low levels. Statistical measures used to distinguish cell type-specific RNAs from low level background and non-specific RNAs showed TRAP to be highly effective in Xenopus.

CONCLUSIONS

TRAP can be used to purify mRNAs expressed in rod photoreceptors and retinal ganglion cells in X. laevis. The generated transgenic lines will enable numerous studies into the development, disease, and injury of the X. laevis retina.

Selective pattern of motor system damage in gamma-synuclein transgenic mice mirrors the respective pathology in amyotrophic lateral sclerosis

Amyotrophic lateral sclerosis (ALS) is characterised by substantial loss of both upper and lower motor neuron function, with sensory and cognitive systems less affected. Though heritable forms of the disease have been described, the vast majority of cases are sporadic with poorly defined underlying pathogenic mechanisms. Here we demonstrate that the neurological pathology induced in transgenic mice by overexpression of γ-synuclein, a protein not previously associated with ALS, recapitulates key features of the disease, namely selective damage and loss of discrete populations of upper and lower motor neurons and their axons, contrasted by limited effects upon the sensory system.

γ-Synuclein: seeding of α-synuclein aggregation and transmission between cells

Protein misfolding and aggregation is a ubiquitous phenomenon associated with a wide range of diseases. The synuclein family comprises three small naturally unfolded proteins implicated in neurodegenerative diseases and some forms of cancer. α-Synuclein is a soluble protein that forms toxic inclusions associated with Parkinson's disease and several other synucleinopathies. However, the triggers inducing its conversion into noxious species are elusive. Here we show that another member of the family, γ-synuclein, can be easily oxidized and form annular oligomers that accumulate in cells in the form of deposits. Importantly, oxidized γ-synuclein can initiate α-synuclein aggregation. Two amino acid residues in γ-synuclein, methionine and tyrosine located in neighboring positions (Met(38) and Tyr(39)), are most easily oxidized. Their oxidation plays a key role in the ability of γ-synuclein to aggregate and seed the aggregation of α-synuclein. γ-Synuclein secreted from neuronal cells into conditioned medium in the form of exosomes can be transmitted to glial cells and cause the aggregation of intracellular proteins. Our data suggest that post-translationally modified γ-synuclein possesses prion-like properties and may induce a cascade of events leading to synucleinopathies.

[Role of genetics in the etiology of synucleinopathies]

The protein family known as synucleins is composed of α-, β- and γ-synuclein. The most widely studied is the α-synuclein protein due to its participation in essential processes of the central nervous system. Neurotoxicity of this protein is related to the presence of multiplications (duplications and triplications) and point mutations in the gene sequence of the α-synuclein gene (SNCA), differential expression of its isoforms and variations in post-transductional modifications. Neurotoxicity is also related to cytoplasmic inclusions known as Lewy bodies (LBs) and Lewy neurites (LNs), which are also present in α-synucleinopathies. In general, the β-synuclein protein, codified by the SNCB gene, acts as a regulator of processes triggered by α-synuclein and its function is altered by variations in the gene sequence, while γ-synuclein, codified by the SNCG gene, seems to play a major role in certain tumoral processes.

Endothelin, astrocytes and glaucoma

It has become increasingly clear that astrocytes may play an important role in the genesis of glaucoma. Astrogliosis occurs in response to ocular stress or the presence of noxious stimuli. Agents that appear to stimulate reactive gliosis are becoming increasingly clear. One class of agents that is emerging is the endothelins (ETs; specifically, ET-1). In this review we examine the interactions of ET-1 with astrocytes and provide examples where ET-1 appears to contribute to activation of astrocytes and play a role in the neurodegenerative effects that accompany such reactivation resulting in astrogliosis. These actions are presented in the context of glaucoma although information is also presented with respect to ET-1's role in the central nervous system and brain. While much has been learned with respect to ET-1/astrocyte interactions, there are still a number of questions concerning the potential therapeutic implications of these findings. Hopefully this review will stimulate others to examine this potential.

Myelination transition zone astrocytes are constitutively phagocytic and have synuclein dependent reactivity in glaucoma

Optic nerve head (ONH) astrocytes have been proposed to play both protective and deleterious roles in glaucoma. We now show that, within the postlaminar ONH myelination transition zone (MTZ), there are astrocytes that normally express Mac-2 (also known as Lgals3 or galectin-3), a gene typically expressed only in phagocytic cells. Surprisingly, even in healthy mice, MTZ and other ONH astrocytes constitutive internalize large axonal evulsions that contain whole organelles. In mouse glaucoma models, MTZ astrocytes further up-regulate Mac-2 expression. During glaucomatous degeneration, there are dystrophic processes in the retina and optic nerve, including the MTZ, which contain protease resistant γ-synuclein. The increased Mac-2 expression by MTZ astrocytes during glaucoma likely depends on this γ-synuclein, as mice lacking γ-synuclein fail to up-regulate Mac-2 at the MTZ after elevation of intraocular pressure. These results suggest the possibility that a newly discovered normal degradative pathway for axons might contribute to glaucomatous neurodegeneration.

Conformational diseases: looking into the eyes

Conformational diseases, a general term comprising more than 40 disorders are caused by the accumulation of unfolded or misfolded proteins. Improper protein folding (misfolding) as well as accrual of unfolded proteins can lead to the formation of disordered (amorphous) or ordered (amyloid fibril) aggregates. The gradual accumulation of protein aggregates and the acceleration of their formation by stress explain the characteristic late or episodic onset of the diseases. The best studied in this group are neurodegenerative diseases and amyloidosis accompanied by the deposition of a specific aggregation-prone proteins or protein fragments and formation of insoluble fibrils. Amyloidogenic protein accumulation often occurs in the brain tissues, e.g. in Alzheimer's disease with the deposition of amyloid-beta and Tau, in scrapie and bovine spongiform encephalopathy with the accumulation of prion protein, in Parkinson's disease with the deposition of alpha-synuclein. Other examples of amyloid proteins are transthyretin, immunoglobulin light chain, gelsolin, etc. In addition to the brain, the accumulation of unfolded or misfolded proteins leading to pathology takes place in a wide variety of organs and tissues, including different parts of the eye. The best studied ocular conformational diseases are cataract in the lens and retinitis pigmentosa in the retina, but accumulation of misfolded proteins also occurs in other parts of the eye causing various disorders. Furthermore, ocular manifestation of systemic amyloidosis often causes the deposition of amyloidogenic proteins in different ocular tissues. Here we present the data regarding naturally unfolded and misfolded proteins in eye tissues, their structure-function relationships, and molecular mechanisms underlying their involvement in diseases. We also summarize the etiology of ocular conformational diseases and discuss approaches to their treatment.

Friend or foe? Resolving the impact of glial responses in glaucoma

Glaucomatous vision loss results from the progressive degeneration of optic nerve axons and the death of retinal ganglion cells. This process is accompanied by dramatic alterations in the functional properties and distribution of glial cells in both the retina and the optic nerve head in a reaction commonly referred to as glial activation. The recent availability of rodent and cell culture glaucoma models has substantially contributed to our knowledge of glial activation under glaucomatous conditions. Conclusions drawn from these studies have led to the refinement of existing hypotheses and the generation of new ones. Because these hypotheses encompass both protective and injurious roles for glia, the impact of specific aspects of glial activation are current topics of intensive research, speculation, and debate in the field. With these unresolved issues in mind, this review will summarize recent progress in our understanding of the process of glial activation in the glaucomatous optic nerve head and retina.

Gene expression changes in areas of focal loss of retinal ganglion cells in the retina of DBA/2J mice

Purpose. To determine whether differences in gene expression occur between areas of focal retinal ganglion cell (RGC) loss and of relative RGC preservation in the DBA/2 mouse retina and whether they can provide insight into the pathophysiology of glaucoma. Methods. Areas of focal RGC loss (judged by lack of Fluorogold labeling; Fluorochrome, Denver, CO), adjacent areas with relative RGC preservation in DBA/2 retina, and Fluorogold-labeled retina from DBA/2(-pe) (pearl) mice were dissected and used for microarray analysis. RT-PCR and immunoblot analysis were used to confirm differential gene expression. Bioinformatic analysis was used to identify gene networks affected in the glaucomatous retina. Results. Microarray analysis identified 372 and 115 gene chip IDs as up- and downregulated, respectively, by 0.5-fold in areas of RGC loss. Differentially expressed genes included those coding for cytoskeletal proteins, enzymes, transport proteins, extracellular matrix (ECM) proteins, and immune response proteins. Several genes were confirmed by RT-PCR. For at least two genes, differential protein expression was verified. Bioinformatics analysis identified multiple affected functional gene networks. Pearl mice appeared to have significantly different gene expression, even when compared with relatively preserved areas of the DBA/2 retina. Conclusions. Regional gene expression changes occur in areas of focal RGC loss in the DBA/2 retina. The genes involved code for proteins with diverse cellular functions. Further investigation is needed to determine the cellular localization of the expression of these genes during the development of spontaneous glaucoma in the DBA/2 mouse and to determine whether some of these gene expression changes are causative or protective of RGC loss.