Neuroprotection, Growth Factors and BDNF-TrkB Signalling in Retinal Degeneration

Crosstalk Between Microglia and Müller Glia in the Age-Related Macular Degeneration: Role and Therapeutic Value of Neuroinflammation

Age-related macular degeneration (AMD) is a progressive neurodegeneration disease that causes photoreceptor demise and vision impairments. In AMD pathogenesis, the primary death of retinal neurons always leads to the activation of resident microglia. The migration of activated microglia to the ongoing retinal lesion and their morphological transformation from branching to ameboid-like are recognized as hallmarks of AMD pathogenesis. Activated microglia send signals to Müller cells and promote them to react correspondingly to damaging stimulus. Müller cells are a type of neuroglia cells that maintain the normal function of retinal neurons, modulating innate inflammatory responses, and stabilize retinal structure. Activated Müller cells can accelerate the progression of AMD by damaging neurons and blood vessels. Therefore, the crosstalk between microglia and Müller cells plays a homeostatic role in maintaining the retinal environment, and this interaction is complicatedly modulated. In particular, the mechanism of mutual regulation between the two glia populations is complex under pathological conditions. This paper reviews recent findings on the crosstalk between microglia and Müller glia during AMD pathology process, with special emphasis on its therapeutic potentials.

Addressing neurodegeneration in glaucoma: Mechanisms, challenges, and treatments

Glaucoma is the leading cause of irreversible blindness globally. The disease causes vision loss due to neurodegeneration of the retinal ganglion cell (RGC) projection to the brain through the optic nerve. Glaucoma is associated with sensitivity to intraocular pressure (IOP). Thus, mainstay treatments seek to manage IOP, though many patients continue to lose vision. To address neurodegeneration directly, numerous preclinical studies seek to develop protective or reparative therapies that act independently of IOP. These include growth factors, compounds targeting metabolism, anti-inflammatory and antioxidant agents, and neuromodulators. Despite success in experimental models, many of these approaches fail to translate into clinical benefits. Several factors contribute to this challenge. Firstly, the anatomic structure of the optic nerve head differs between rodents, nonhuman primates, and humans. Additionally, animal models do not replicate the complex glaucoma pathophysiology in humans. Therefore, to enhance the success of translating these findings, we propose two approaches. First, thorough evaluation of experimental targets in multiple animal models, including nonhuman primates, should precede clinical trials. Second, we advocate for combination therapy, which involves using multiple agents simultaneously, especially in the early and potentially reversible stages of the disease. These strategies aim to increase the chances of successful neuroprotective treatment for glaucoma.

Molecular pathways in experimental glaucoma models

Glaucoma is a complex and progressive disease that primarily affects the optic nerve axons, leading to irreversible vision loss. Although the exact molecular mechanisms underlying glaucoma pathogenesis are not fully understood, it is believed that except increased intraocular pressure, a combination of genetic and environmental factors play a role in the development of the disease. Animal models have been widely used in the study of glaucoma, allowing researchers to better understand the underlying mechanisms of the disease and test potential treatments. Several molecular pathways have been implicated in the pathogenesis of glaucoma, including oxidative stress, inflammation, and excitotoxic-induced neurodegeneration. This review summarizes the most important knowledge about molecular mechanisms involved in the glaucoma development. Although much research has been done to better understand the molecular mechanisms underlying this disease, there is still much to be learned to develop effective treatments and prevent vision loss in those affected by glaucoma.

The concept of gene therapy for glaucoma: the dream that has not come true yet

Gene therapies, despite of being a relatively new therapeutic approach, have a potential to become an important alternative to current treatment strategies in glaucoma. Since glaucoma is not considered a single gene disease, the identified goals of gene therapy would be rather to provide neuroprotection of retinal ganglion cells, especially, in intraocular-pressure-independent manner. The most commonly reported type of vector for gene delivery in glaucoma studies is adeno-associated virus serotype 2 that has a high tropism to retinal ganglion cells, resulting in long-term expression and low immunogenic profile. The gene therapy studies recruit inducible and genetic animal models of optic neuropathy, like DBA/2J mice model of high-tension glaucoma and the optic nerve crush-model. Reported gene therapy-based neuroprotection of retinal ganglion cells is targeting specific genes translating to growth factors (i.e., brain derived neurotrophic factor, and its receptor TrkB), regulation of apoptosis and neurodegeneration (i.e., Bcl-xl, Xiap, FAS system, nicotinamide mononucleotide adenylyl transferase 2, Digit3 and Sarm1), immunomodulation (i.e., Crry, C3 complement), modulation of neuroinflammation (i.e., erythropoietin), reduction of excitotoxicity (i.e., CamKIIα) and transcription regulation (i.e., Max, Nrf2). On the other hand, some of gene therapy studies focus on lowering intraocular pressure, by impacting genes involved in both, decreasing aqueous humor production (i.e., aquaporin 1), and increasing outflow facility (i.e., COX2, prostaglandin F2α receptor, RhoA/RhoA kinase signaling pathway, MMP1, Myocilin). The goal of this review is to summarize the current state-of-art and the direction of development of gene therapy strategies for glaucomatous neuropathy.

The Role of Retinal Ganglion Cell Structure and Function in Glaucoma

Glaucoma, a leading cause of irreversible blindness globally, primarily affects retinal ganglion cells (RGCs). This review dives into the anatomy of RGC subtypes, covering the different underlying theoretical mechanisms that lead to RGC susceptibility in glaucoma, including mechanical, vascular, excitotoxicity, and neurotrophic factor deficiency, as well as oxidative stress and inflammation. Furthermore, we examined numerous imaging methods and functional assessments to gain insight into RGC health. Finally, we investigated the current possible neuroprotective targets for RGCs that could help with future glaucoma research and management.

Reduced Levels of Lacrimal Glial Cell Line-Derived Neurotrophic Factor (GDNF) in Patients with Focal Epilepsy and Focal Epilepsy with Comorbid Depression: A Biomarker Candidate

Our previous studies showed that in patients with brain diseases, neurotrophic factors in lacrimal fluid (LF) may change more prominently than in blood serum (BS). Since glial cell line-derived neurotrophic factor (GDNF) is involved in the control of neuronal networks in an epileptic brain, we aimed to assess the GDNF levels in LF and BS as well as the BDNF and the hypothalamic-pituitary-adrenocortical and inflammation indices in BS of patients with focal epilepsy (FE) and epilepsy and comorbid depression (FE + MDD) and to compare them with those of patients with major depressive disorder (MDD) and healthy controls (HC). GDNF levels in BS were similar in patients and HC and higher in FE taking valproates. GDNF levels in LF were significantly lower in all patient groups compared to controls, and independent of drugs used. GDNF concentrations in LF and BS positively correlated in HC, but not in patient groups. BDNF level was lower in BS of patients compared with HC and higher in FE + MDD taking valproates. A reduction in the GDNF level in LF might be an important biomarker of FE. Logistic regression models demonstrated that the probability of FE can be evaluated using GDNF in LF and BDNF in BS; that of MDD using GDNF in LF and cortisol and TNF-α in BS; and that of epilepsy with MDD using GDNF in LF and TNF-α and BDNF in BS.

Molecular Mechanisms of Glaucoma Pathogenesis with Implications to Caveolin Adaptor Protein and Caveolin-Shp2 Axis

Glaucoma is a common retinal disorder characterized by progressive optic nerve damage, resulting in visual impairment and potential blindness. Elevated intraocular pressure (IOP) is a major risk factor, but some patients still experience disease progression despite IOP-lowering treatments. Genome-wide association studies have linked variations in the Caveolin1/2 (CAV-1/2) gene loci to glaucoma risk. Cav-1, a key protein in caveolae membrane invaginations, is involved in signaling pathways and its absence impairs retinal function. Recent research suggests that Cav-1 is implicated in modulating the BDNF/TrkB signaling pathway in retinal ganglion cells, which plays a critical role in retinal ganglion cell (RGC) health and protection against apoptosis. Understanding the interplay between these proteins could shed light on glaucoma pathogenesis and provide potential therapeutic targets.

Efficacy of a Spearmint (Mentha spicata L.) Extract as Nutritional Support in a Rat Model of Hypertensive Glaucoma

Purpose

Glaucoma is an eye-brain axis disorder characterized by loss of retinal ganglion cells (RGCs). Although the role of intraocular pressure (IOP) elevation in glaucoma has been established, the reduction of oxidative stress and inflammation has emerged as a promising target for neuronal tissue-supporting glaucoma management. Therefore, we evaluated the effect of a proprietary spearmint extract (SPE) on RGC density, activity, and neuronal health markers in a rat model of hypertensive glaucoma.

Methods

Animals were divided in four groups: untreated healthy control and three glaucomatous groups receiving orally administered vehicle, SPE-low dose, or SPE-high dose for 28 days. Ocular hypertension was induced through intracameral injection of methylcellulose at day 15. At day 29, rats underwent electroretinogram (ERG) recordings, and retinas were analyzed for RGC density and markers of neural trophism, oxidative stress, and inflammation.

Results

SPE exerted dose-dependent response benefits on all markers except for IOP elevation. SPE significantly improved RGC-related ERG responses, cell density, neurotrophins, oxidative stress, and inflammation markers. Also, in SPE-high rats, most of the parameters were not statistically different from those of healthy controls.

Conclusions

SPE, a plant-based, polyphenolic extract, could be an effective nutritional support for neuronal tissues.

Translational Relevance

These results suggest that SPE not only may be a complementary approach in support to hypotensive treatments for the management of glaucoma but may also serve as nutritional support in other ocular conditions where antioxidant, anti-inflammatory, and neuroprotective mechanism are often disrupted.

Brain-derived neurotrophic factor in degenerative retinal diseases: Update and novel perspective

Dysfunction and death of neuronal cells are cardinal features of degenerative retinal diseases that are known to arise as the disease progresses. Increasingly evidence suggests that abnormal expression of brain-derived neurotrophic factor (BDNF) may serve as an obligatory relay of the dysfunction and death of neuronal cells in degenerative retinal diseases. Although disorder of BDNF, whether depletion or augmentation, has been connected with neuronal apoptosis and neuroinflammation, the exact mechanisms underlying the effect of impaired BDNF expression on degenerative retinal diseases remain unclear. Here, we present an overview of how BDNF is linked to pathological mechanism of retinal degenerative diseases, summarize BDNF-based treatment strategies, and discuss possible research perspectives in the future.

Neuroprotective Effect of Nosustrophine in a 3xTg Mouse Model of Alzheimer's Disease

Neurodegeneration, characterized by the progressive deterioration of neurons and glial cells, is a feature of Alzheimer's disease (AD). The present study aims to demonstrate that the onset and early progression of neurodegenerative processes in transgenic mice models of AD can be delayed by a cocktail of neurotrophic factors and derived peptides named Nosustrophine, a nootropic supplement made by a peptide complex extracted from the young porcine brain, ensuring neuroprotection and improving neuro-functional recovery. Experimental 3xTg-APP/Bin1/COPS5 transgenic mice models of AD were treated with Nosustrophine at two different early ages, and their neuropathological hallmark and behavior response were analyzed. Results showed that Nosustrophine increased the activity of the immune system and reduced pathological changes in the hippocampus and cortex by halting the development of amyloid plaques, mainly seen in mice of 3-4 months of age, indicating that its effect is more preventive than therapeutic. Taken together, the results indicate the potent neuroprotective activity of Nosustrophine and its stimulating effects on neuronal plasticity. This study shows for the first time an effective therapy using nootropic supplements against degenerative diseases, although further investigation is needed to understand their molecular pathways.

The Neuroprotective Effect of Activation of Sigma-1 Receptor on Neural Injury by Optic Nerve Crush

Purpose

This study aimed to explore the neuroprotective effects of sigma-1 receptor (S1R) on optic nerve crush (ONC) mice by upregulating its expression through intravitreal injection of adeno-associated virus (AAV).

Methods

The animals were divided into four groups. Mice that underwent ONC were administered an intravitreal injection with blank vector (ONC group), with AAV targeting downregulation of S1R (S1R-sh group), or with AAV targeting overexpression of S1R (S1R-AAV group). Mice in the control group underwent intravitreal injection with blank vector. The thickness of each layer of the retina was measured through optical coherence tomography, and the apoptotic rate of retinal neurons was determined using the TUNEL assay. The expression levels of brain-derived neurotrophic factor (BDNF) and S1R were quantified through western blot. Electroretinogram (ERG) was performed to evaluate the visual function.

Results

The thickness of the total retina (P = 0.001), ganglion cell layer (P = 0.017), and inner nuclear layer (P = 0.002) in S1R-AAV group was significantly thicker than that of the ONC group. The number of retinal apoptotic cells in the S1R-AAV group was 23% lower than that in the ONC group (P = 0.002). ERG results showed that, compared to the ONC group, the amplitudes of the a- and b-waves were higher in the S1R-AAV group (a-wave, P < 0.001; b-wave, P = 0.007). Western blot showed that the expression of BDNF in the S1R-AAV group was higher than that in the ONC group (P < 0.001).

Conclusions

Activation of S1R in the retina through intravitreal injection of AAV can effectively maintain the retina structure, promote neuronal cell survival, and protect visual function.

Valproate reduces retinal ganglion cell apoptosis in rats after optic nerve crush

The retinal ganglion cells of the optic nerve have a limited capacity for self-repair after injury. Valproate is a histone deacetylase inhibitor and multitarget drug, which has been demonstrated to protect retinal neurons. In this study, we established rat models of optic nerve-crush injury and injected valproate into the vitreous cavity immediately after modeling. We evaluated changes in the ultrastructure morphology of the endoplasmic reticulum of retinal ganglion cells over time via transmission electron microscope. Immunohistochemistry and western blot assay revealed that valproate upregulated the expression of the endoplasmic reticulum stress marker glucose-regulated protein 78 and downregulated the expression of transcription factor C/EBP homologous protein, phosphorylated eukaryotic translation initiation factor 2α, and caspase-12 in the endoplasmic reticulum of retinal ganglion cells. These findings suggest that valproate reduces apoptosis of retinal ganglion cells in the rat after optic nerve-crush injury by attenuating phosphorylated eukaryotic translation initiation factor 2α-C/EBP homologous protein signaling and caspase-12 activation during endoplasmic reticulum stress. These findings represent a newly discovered mechanism that regulates how valproate protects neurons.

Polarized RPE Secretome Preserves Photoreceptors in Retinal Dystrophic RCS Rats

Retinal degenerative diseases, including age-related macular degeneration (AMD) and retinitis pigmentosa, lack effective therapies. Conventional monotherapeutic approaches fail to target the multiple affected pathways in retinal degeneration. However, the retinal pigment epithelium (RPE) secretes several neurotrophic factors addressing diverse cellular pathways, potentially preserving photoreceptors. This study explored human embryonic stem cell-derived, polarized RPE soluble factors (PRPE-SF) as a combination treatment for retinal degeneration. PRPE-SF promoted retinal progenitor cell survival, reduced oxidative stress in ARPE-19 cells, and demonstrated critical antioxidant and anti-inflammatory effects for preventing retinal degeneration in the Royal College of Surgeons (RCS) rat model. Importantly, PRPE-SF treatment preserved retinal structure and scotopic b-wave amplitudes, suggesting therapeutic potential for delaying retinal degeneration. PRPE-SF is uniquely produced using biomimetic membranes for RPE polarization and maturation, promoting a protective RPE secretome phenotype. Additionally, PRPE-SF is produced without animal serum to avoid immunogenicity in future clinical development. Lastly, PRPE-SF is a combination of neurotrophic factors, potentially ameliorating multiple dysfunctions in retinal degenerations. In conclusion, PRPE-SF offers a promising therapeutic candidate for retinal degenerative diseases, advancing the development of effective therapeutic strategies for these debilitating conditions.

Nanocarriers for the Delivery of Neuroprotective Agents in the Treatment of Ocular Neurodegenerative Diseases

Retinal neurodegeneration is considered an early event in the pathogenesis of several ocular diseases, such as diabetic retinopathy, age-related macular degeneration, and glaucoma. At present, there is no definitive treatment to prevent the progression or reversal of vision loss caused by photoreceptor degeneration and the death of retinal ganglion cells. Neuroprotective approaches are being developed to increase the life expectancy of neurons by maintaining their shape/function and thus prevent the loss of vision and blindness. A successful neuroprotective approach could prolong patients' vision functioning and quality of life. Conventional pharmaceutical technologies have been investigated for delivering ocular medications; however, the distinctive structural characteristics of the eye and the physiological ocular barriers restrict the efficient delivery of drugs. Recent developments in bio-adhesive in situ gelling systems and nanotechnology-based targeted/sustained drug delivery systems are receiving a lot of attention. This review summarizes the putative mechanism, pharmacokinetics, and mode of administration of neuroprotective drugs used to treat ocular disorders. Additionally, this review focuses on cutting-edge nanocarriers that demonstrated promising results in treating ocular neurodegenerative diseases.

Vision protection and robust axon regeneration in glaucoma models by membrane-associated Trk receptors

Activation of neurotrophic factor signaling is a promising therapy for neurodegeneration. However, the transient nature of ligand-dependent activation limits its effectiveness. In this study, we solved this problem by inventing a system that forces membrane localization of the intracellular domain of tropomyosin receptor kinase B (iTrkB), which results in constitutive activation without ligands. Our system overcomes the small size limitation of the genome packaging in adeno-associated virus (AAV) and allows high expression of the transgene. Using AAV-mediated gene therapy in the eyes, we demonstrate that iTrkB expression enhances neuroprotection in mouse models of glaucoma and stimulates robust axon regeneration after optic nerve injury. In addition, iTrkB expression in the retina was also effective in an optic tract transection model, in which the injury site is near the superior colliculus. Regenerating axons successfully formed pathways to their brain targets, resulting in partial recovery of visual behavior. Our system may also be applicable to other trophic factor signaling pathways and lead to a significant advance in the field of gene therapy for neurotrauma and neurodegenerative disorders, including glaucoma.

In Vitro Neurotrophic Properties and Structural Characterization of a New Polysaccharide LTC-1 from Pyrola corbieri Levl (Luticao)

Pyrola corbieri Levl has been used to strengthen bones and nourish the kidney (the kidney governs the bone and is beneficial to the brain) by the local Miao people in China. However, the functional components and neurotrophic activity have not been reported. A new acidic homogeneous heteropolysaccharide named LTC-1 was obtained and characterized by periodate oxidation, Smith degradation, partial acid hydrolysis, GC-MS spectrometry, methylation analysis, and Fourier transform infrared spectroscopy, and its molecular weight was 3239 Da. The content of mannuronic acid (Man A) in LTC-1 was 46%, and the neutral sugar was composed of L-rhamnose (L-Rha), L-arabinose (L-Ara), D-xylose (D-Xyl), D-mannose (D-Man), D-glucose (D-Glc) and D-galactose (D-Gal) with a molar ratio of 1.00:3.63:0.86:1.30:6.97:1.30. The main chain of LTC-1 was composed of Glc, Gal, Man, Man A and the branched chain Ara, Glc, Gal. The terminal residues were composed of Glc and Gal. The main chain and branched chains were linked by (1→5)-linked-Ara, (1→3)-linked-Glc, (1→4)-linked-Glc, (1→6)-linked-Glc, (1→3)-linked-Gal, (1→6)-linked-Gal, (1→3, 6)-linked-Man and ManA. Meanwhile, neurotrophic activity was evaluated through PC12 and primary hippocampal neuronal cell models. LTC-1 exhibited neurotrophic activity in a concentration-dependent manner, which significantly induced the differentiation of PC12 cells, promoted the neurite outgrowth of PC12 cells, enhanced the formation of the web architecture of dendrites, and increased the density of dendritic spines in hippocampal neurons and the expression of PSD-95. These results displayed significant neurotrophic factor-like activity of LTC-1, which suggests that LTC-1 is a potential treatment option for neurodegenerative diseases.

S1PR1 signaling attenuates apoptosis of retinal ganglion cells via modulation of cJun/Bim cascade and Bad phosphorylation in a mouse model of glaucoma

Glaucoma is a complex neurodegenerative disease characterized by optic nerve damage and apoptotic retinal ganglion cell (RGC) death, and is the leading cause of irreversible blindness worldwide. Among the sphingosine 1-phosphate receptors (S1PRs) family, S1PR1 is a highly expressed subtype in the central nervous system and has gained rapid attention as an important mediator of pathophysiological processes in the brain and the retina. Our recent study showed that mice treated orally with siponimod drug exerted neuroprotection via modulation of neuronal S1PR1 in experimental glaucoma. This study identified the molecular signaling pathway modulated by S1PR1 activation with siponimod treatment in RGCs in glaucomatous injury. We investigated the critical neuroprotective signaling pathway in vivo using mice deleted for S1PR1 in RGCs. Our results showed marked upregulation of the apoptotic pathway was associated with decreased Akt and Erk1/2 activation levels in the retina in glaucoma conditions. Activation of S1PR1 with siponimod treatment significantly increased neuroprotective Akt and Erk1/2 activation and attenuated the apoptotic signaling via suppression of c-Jun/Bim cascade and by increasing Bad phosphorylation. Conversely, deletion of S1PR1 in RGCs significantly increased the apoptotic cells in the ganglion cell layer in glaucoma and diminished the neuroprotective effects of siponimod treatment on Akt/Erk1/2 activation, c-Jun/Bim cascade, and Bad phosphorylation. Our data demonstrated that activation of S1PR1 in RGCs induces crucial neuroprotective signaling that suppresses the proapoptotic c-Jun/Bim cascade and increases antiapoptotic Bad phosphorylation. Our findings suggest that S1PR1 is a potential therapeutic target for neuroprotection of RGCs in glaucoma.

Axonal Regeneration: Underlying Molecular Mechanisms and Potential Therapeutic Targets

Axons in the peripheral nervous system have the ability to repair themselves after damage, whereas axons in the central nervous system are unable to do so. A common and important characteristic of damage to the spinal cord, brain, and peripheral nerves is the disruption of axonal regrowth. Interestingly, intrinsic growth factors play a significant role in the axonal regeneration of injured nerves. Various factors such as proteomic profile, microtubule stability, ribosomal location, and signalling pathways mark a line between the central and peripheral axons' capacity for self-renewal. Unfortunately, glial scar development, myelin-associated inhibitor molecules, lack of neurotrophic factors, and inflammatory reactions are among the factors that restrict axonal regeneration. Molecular pathways such as cAMP, MAPK, JAK/STAT, ATF3/CREB, BMP/SMAD, AKT/mTORC1/p70S6K, PI3K/AKT, GSK-3β/CLASP, BDNF/Trk, Ras/ERK, integrin/FAK, RhoA/ROCK/LIMK, and POSTN/integrin are activated after nerve injury and are considered significant players in axonal regeneration. In addition to the aforementioned pathways, growth factors, microRNAs, and astrocytes are also commendable participants in regeneration. In this review, we discuss the detailed mechanism of each pathway along with key players that can be potentially valuable targets to help achieve quick axonal healing. We also identify the prospective targets that could help close knowledge gaps in the molecular pathways underlying regeneration and shed light on the creation of more powerful strategies to encourage axonal regeneration after nervous system injury.

Neuroprotection in Glaucoma: Basic Aspects and Clinical Relevance

Glaucoma is a neurodegenerative disease that affects primarily the retinal ganglion cells (RGCs). Increased intraocular pressure (IOP) is one of the major risk factors for glaucoma. The mainstay of current glaucoma therapy is limited to lowering IOP; however, controlling IOP in certain patients can be futile in slowing disease progression. The understanding of potential biomolecular processes that occur in glaucomatous degeneration allows for the development of glaucoma treatments that modulate the death of RGCs. Neuroprotection is the modification of RGCs and the microenvironment of neurons to promote neuron survival and function. Numerous studies have revealed effective neuroprotection modalities in animal models of glaucoma; nevertheless, clinical translation remains a major challenge. In this review, we select the most clinically relevant treatment strategies, summarize preclinical and clinical data as well as recent therapeutic advances in IOP-independent neuroprotection research, and discuss the feasibility and hurdles of each therapeutic approach based on possible pathogenic mechanisms. We also summarize the potential therapeutic mechanisms of various agents in neuroprotection related to glutamate excitotoxicity.

Impact of Freeze-Drying on Cord Blood (CB), Serum (S), and Platelet-Rich Plasma (CB-PRP) Preparations on Growth Factor Content and In Vitro Cell Wound Healing

Blood-based preparations are used in clinical practice for the treatment of several eye disorders. The aim of this study is to analyze the effect of freeze-drying blood-based preparations on the levels of growth factors and wound healing behaviors in an in vitro model. Platelet-rich plasma (PRP) and serum (S) preparations from the same Cord Blood (CB) sample, prepared in both fresh frozen (FF) and freeze-dried (FD) forms (and then reconstituted), were analyzed for EGF and BDNF content (ELISA Quantikine kit). The human MIO-M1 glial cell line (Moorfield/Institute of Ophthalmology, London, UK) was incubated with FF and FD products and evaluated for cell migration with scratch-induced wounding (IncuCyte S3 Essen BioScience), proliferation with cyclin A2 and D1 gene expression, and activation with vimentin and GFAP gene expression. The FF and FD forms showed similar concentrations of EGF and BDNF in both the S and PRP preparations. The wound healing assay showed no significant difference between the FF and FD forms for both S and PRP. Additionally, cell migration, proliferation, and activation did not appear to change in the FD forms compared to the FF ones. Our study showed that reconstituted FD products maintained the growth factor concentrations and biological properties of FF products and could be used as a functional treatment option.

Treadmill exercise promotes retinal astrocyte plasticity and protects against retinal degeneration in a mouse model of light-induced retinal degeneration

Exercise is an effective neuroprotective intervention that preserves retinal function and structure in several animal models of retinal degeneration. However, the retinal cell types governing exercise-induced neuroprotection remain elusive. Previously, we found exercise-induced retinal neuroprotection was associated with increased levels of retinal brain-derived neurotrophic factor (BDNF) and required intact signal transduction with its high-affinity receptor, tropomyosin kinase B (TrkB). Brain studies have shown astrocytes express BDNF and TrkB and that decreased BDNF-TrkB signaling in astrocytes contributes to neurodegeneration. Additionally, exercise has been shown to alter astrocyte morphology. Using a light-induced retinal degeneration (LIRD) model, we investigated how exercise influences retinal astrocytes in adult male BALB/c mice. Treadmill exercise in dim control and LIRD groups had increased astrocyte density, GFAP labeling, branching, dendritic endpoints, and arborization. Meanwhile, inactive LIRD animals had significant reductions in all measured parameters. Additionally, exercised groups had increased astrocytic BDNF expression that was visualized using proximity ligase assay. Isolated retinal astrocytes from exercised LIRD groups had significantly increased expression of a specific isoform of TrkB associated with cell survival, TrkB.FL. Conversely, inactive LIRD isolated retinal astrocytes had significantly increased expression of TrkB.T1, which has been implicated in neuronal cell death. Our data indicate exercise not only alters retinal astrocyte morphology but also promotes specific BDNF-TrkB signaling associated with cell survival and protection during retinal degeneration. These findings provide novel insights into the effects of treadmill exercise on retinal astrocyte morphology and cellular expression, highlighting retinal astrocytes as a potential cell type involved in BDNF-TrkB signaling.

Advancing precision medicines for ocular disorders: Diagnostic genomics to tailored therapies

Successful sequencing of the human genome and evolving functional knowledge of gene products has taken genomic medicine to the forefront, soon combining broadly with traditional diagnostics, therapeutics, and prognostics in patients. Recent years have witnessed an extraordinary leap in our understanding of ocular diseases and their respective genetic underpinnings. As we are entering the age of genomic medicine, rapid advances in genome sequencing, gene delivery, genome surgery, and computational genomics enable an ever-increasing capacity to provide a precise and robust diagnosis of diseases and the development of targeted treatment strategies. Inherited retinal diseases are a major source of blindness around the world where a large number of causative genes have been identified, paving the way for personalized diagnostics in the clinic. Developments in functional genetics and gene transfer techniques has also led to the first FDA approval of gene therapy for LCA, a childhood blindness. Many such retinal diseases are the focus of various clinical trials, making clinical diagnoses of retinal diseases, their underlying genetics and the studies of natural history important. Here, we review methodologies for identifying new genes and variants associated with various ocular disorders and the complexities associated with them. Thereafter we discuss briefly, various retinal diseases and the application of genomic technologies in their diagnosis. We also discuss the strategies, challenges, and potential of gene therapy for the treatment of inherited and acquired retinal diseases. Additionally, we discuss the translational aspects of gene therapy, the important vector types and considerations for human trials that may help advance personalized therapeutics in ophthalmology. Retinal disease research has led the application of precision diagnostics and precision therapies; therefore, this review provides a general understanding of the current status of precision medicine in ophthalmology.

Newer advances in medical management of glaucoma

The burden of irreversible vision loss from Glaucoma continues to rise. While the disease pathogenesis is not well understood, intraocular pressure (IOP) is the only modifiable risk factor identified to prevent glaucomatous vision loss. Medical management remains the first-line of treatment in most adult glaucomas and the evolution of medical therapy for glaucoma has followed an exponential curve. This review tracks the rapid development of new medications and drug delivery systems in the recent years. Introduction of Rho kinase inhibitors with an entirely new mechanism of action from that of the currently used anti glaucoma medications has been a significant milestone. Latanoprostene Bunod is a novel, single molecule which provides two active metabolites that work through two different pathways for reducing intra ocular pressure. Bimatoprost implants and travoprost punctum plugs attempt to ease chronic medication use in glaucoma patients. Nanotechnology is an evolving route of drug delivery. Role of cannabinoids in medical management of glaucoma remain equivocal. The relatively short term effect on IOP, the risks of developing tolerance and side effects impacting patients' neurocognitive health greatly outweigh the potential benefit. Research on Latrunculin B, Adenosine receptor agonists, Specific gene silencing and Stem cell therapy are poised to make an impact on glaucoma treatment. While there is some evidence to support the role of Brimonidine in neuroprotection, further research is needed to clarify the role of Memantine and Neurotrophins. Evidence for benefit from dietary supplementation with Alpha lipoic acid, Forskolin , and Ginko Biloba is limited.

Brain-Derived Neurotrophic Factor-Mediated Neuroprotection in Glaucoma: A Review of Current State of the Art

Retinal ganglion cells (RGCs) are neurons of the visual system that are responsible for transmitting signals from the retina to the brain via the optic nerve. Glaucoma is an optic neuropathy characterized by apoptotic loss of RGCs and degeneration of optic nerve fibers. Risk factors such as elevated intraocular pressure and vascular dysregulation trigger the injury that culminates in RGC apoptosis. In the event of injury, the survival of RGCs is facilitated by neurotrophic factors (NTFs), the most widely studied of which is brain-derived neurotrophic factor (BDNF). Its production is regulated locally in the retina, but transport of BDNF retrogradely from the brain to retina is also crucial. Not only that the interruption of this retrograde transport has been detected in the early stages of glaucoma, but significantly low levels of BDNF have also been detected in the sera and ocular fluids of glaucoma patients, supporting the notion that neurotrophic deprivation is a likely mechanism of glaucomatous optic neuropathy. Moreover, exogenous NTF including BDNF administration was shown reduce neuronal loss in animal models of various neurodegenerative diseases, indicating the possibility that exogenous BDNF may be a treatment option in glaucoma. Current literature provides an extensive insight not only into the sources, transport, and target sites of BDNF but also the intracellular signaling pathways, other pathways that influence BDNF signaling and a wide range of its functions. In this review, the authors discuss the neuroprotective role of BDNF in promoting the survival of RGCs and its possible application as a therapeutic tool to meet the challenges in glaucoma management. We also highlight the possibility of using BDNF as a biomarker in neurodegenerative disease such as glaucoma. Further we discuss the challenges and future strategies to explore the utility of BDNF in the management of glaucoma.

Glial cell line-derived neurotrophic factor (GDNF) in patients with primary open-angle glaucoma and age-related cataract

PURPOSE

To study glial cell line-derived neurotrophic factor (GDNF) concentrations in aqueous humor (AH), lacrimal fluid (LF), and blood serum (BS) in patients with age-related cataract and primary open-angle glaucoma (POAG).

METHODS

GDNF was studied in AH, LF, and BS in 47 patients with age-related cataract, and 30 patients with POAG combined with cataract (one eye in each person). AH was sampled during cataract surgery.

RESULTS

GDNF concentration (pg/ml) in patients with POAG and cataract was lower than in cataract-only patients (p<0.001), both in AH (46.3±31.1 versus 88.9±46.9) and in LF (222±101 versus 344±134). The difference was not significant for the GDNF concentration in BS (194±56 versus 201±45). In the earlier (early and moderate) stages of POAG, compared to later (advanced and severe) stages, GDNF concentration was significantly lower in LF (176±99 versus 258±91; p = 0.027) and in BS (165±42 versus 217±55; p = 0.017), while GDNF concentration in AH showed an insignificant difference (40.0±25.7 versus 51.1±34.7). In patients with POAG, GDNF concentration in LF and BS was inversely correlated with the Humphrey visual field index: Pearson's correlation coefficient r = -0.465 (p = 0.01) for LF and r = -0.399 (p = 0.029) for BS. When compared to the cataract group, patients in the earlier stages of POAG showed significantly lower GDNF concentrations in all studied biologic fluids.

CONCLUSIONS

Compared to patients with cataract only, GDNF levels are lower in the AH and LF of patients with POAG and cataract, especially at earlier stages of the disease (at these stages, the GDNF level in BS is also lower). At earlier stages of POAG, compared to later stages, GDNF content is lower in LF and BS. These data could serve as a reason for the therapeutic use of GDNF in patients with POAG.

Retinal Glutamate Neurotransmission: From Physiology to Pathophysiological Mechanisms of Retinal Ganglion Cell Degeneration

Glutamate neurotransmission and metabolism are finely modulated by the retinal network, where the efficient processing of visual information is shaped by the differential distribution and composition of glutamate receptors and transporters. However, disturbances in glutamate homeostasis can result in glutamate excitotoxicity, a major initiating factor of common neurodegenerative diseases. Within the retina, glutamate excitotoxicity can impair visual transmission by initiating degeneration of neuronal populations, including retinal ganglion cells (RGCs). The vulnerability of RGCs is observed not just as a result of retinal diseases but has also been ascribed to other common neurodegenerative and peripheral diseases. In this review, we describe the vulnerability of RGCs to glutamate excitotoxicity and the contribution of different glutamate receptors and transporters to this. In particular, we focus on the N-methyl-d-aspartate (NMDA) receptor as the major effector of glutamate-induced mechanisms of neurodegeneration, including impairment of calcium homeostasis, changes in gene expression and signalling, and mitochondrial dysfunction, as well as the role of endoplasmic reticular stress. Due to recent developments in the search for modulators of NMDA receptor signalling, novel neuroprotective strategies may be on the horizon.

Behavioral genetics of alcohol's effects in three zebrafish (Danio rerio) populations

Alcohol abuse is one of the most dangerous and serious problems for patients and society. Interpopulation studies are important in understanding how genetic background contributes to the effects of alcohol. In this study, we applied a chronic alcohol exposure protocol in three zebrafish populations (Danio rerio; both sexes; AB, TU, and outbred fish - OB). We analyzed the behavioral responses and mRNA expression involved in neurotransmitter metabolism - th1, tph1, ache, ada1, gaba1, gad1b, and bdnf. Locomotion patterns were similar between populations (increased speed after acute alcohol and unaltered locomotion after chronic and withdrawal treatments). All populations exhibited increased expression of genes associated with locomotion (th1, gad1b, and gaba1) after acute alcohol exposure. Anxiety-like responses increased in AB and TU fish during withdrawal and decreased in AB fish after acute alcohol exposure. Genes related to anxiety-like behavior (tph1 and ada1) were overexpressed in AB and TU fish after acute and withdrawal treatments, while OB fish exhibited unaltered responses. Bdnf levels decreased during withdrawal in AB and OB fish, while TU showed upregulated levels in both chronic and withdrawal treatments. Our results suggest that zebrafish populations respond differently to alcohol exposure, which may contribute to understanding the mechanisms underlying alcohol use and dependence. Moreover, we found that a more diverse genetic background (OB) was related to higher variability in behavioral and mRNA expression, demonstrating that inbred populations (AB and TU) may be useful tools in identifying alcohol use and abuse mechanisms.

The BDNF/TrkB Neurotrophin System in the Sensory Organs of Zebrafish

The brain-derived neurotrophic factor (BDNF) was discovered in the last century, and identified as a member of the neurotrophin family. BDNF shares approximately 50% of its amino acid with other neurotrophins such as NGF, NT-3 and NT-4/5, and its linear amino acid sequences in zebrafish (Danio rerio) and human are 91% identical. BDNF functions can be mediated by two categories of receptors: p75NTR and Trk. Intriguingly, BDNF receptors were highly conserved in the process of evolution, as were the other NTs’ receptors. In this review, we update current knowledge about the distribution and functions of the BDNF-TrkB system in the sensory organs of zebrafish. In fish, particularly in zebrafish, the distribution and functions of BDNF and TrkB in the brain have been widely studied. Both components of the system, associated or segregated, are also present outside the central nervous system, especially in sensory organs including the inner ear, lateral line system, retina, taste buds and olfactory epithelium.

Caffeine Protects Against Retinal Inflammation

Caffeine, one of the most consumed central nervous system (CNS) stimulants, is an antagonist of A₁ and A_2A adenosine receptors. In this study, we investigated the potential protective effects of this methylxanthine in the retinal tissue. We tested caffeine by using in vitro and in vivo paradigms of retinal inflammation. Human retinal pigment epithelial cells (ARPE-19) were exposed to lipopolysaccharide (LPS) with or without caffeine. This latter was able to reduce the inflammatory response in ARPE-19 cells exposed to LPS, attenuating the release of IL-1β, IL-6, and TNF-α and the nuclear translocation of p-NFκB. Additionally, caffeine treatment restored the integrity of the ARPE-19 monolayer assessed by transepithelial electrical resistance (TEER) and the sodium fluorescein permeability test. Finally, the ischemia reperfusion (I/R) injury model was used in C57BL/6J mice to induce retinal inflammation and investigate the effects of caffeine treatment. Mouse eyes were treated topically with caffeine, and a pattern electroretinogram (PERG) was used to assess the retinal ganglion cell (RGC) function; furthermore, we evaluated the levels of IL-6 and BDNF in the retina. Retinal BDNF dropped significantly (p < 0.05) in the I/R group compared to the control group (normal mice); on the contrary, caffeine treatment maintained physiological levels of BDNF in the retina of I/R eyes. Caffeine was also able to reduce IL-6 mRNA levels in the retina of I/R eyes. In conclusion, these findings suggest that caffeine is a good candidate to counteract inflammation in retinal diseases.

A novel viewpoint in glaucoma therapeutics: enriched environment

Glaucoma is one of the world's most frequent visual impairment causes and leads to selective damage to retinal ganglion cells and their axons. Despite glaucoma's most accepted risk factor is increased intraocular pressure (IOP), the mechanisms behind the disease have not been fully elucidated. To date, IOP lowering remains the gold standard; however, glaucoma patients may still lose vision regardless of effective IOP management. Therefore, the exclusive IOP control apparently is not enough to stop the disease progression, and developing new resources to protect the retina and optic nerve against glaucoma is a goal of vast clinical importance. Besides pharmacological treatments, environmental conditions have been shown to prevent neurodegeneration in the central nervous system. In this review, we discuss current concepts on key pathogenic mechanisms involved in glaucoma, the effect of enriched environment on these mechanisms in different experimental models, as well as recent evidence supporting the preventive and therapeutic effect of enriched environment exposure against experimental glaucomatous damage. Finally, we postulate that stimulating vision may become a non-invasive and rehabilitative therapy that could be eventually translated to the human disease, preventing glaucoma-induced terrible sequelae resulting in permanent visual disability.

Effect and mechanism of BDNF/TrkB signaling on vestibular compensation

Brain-derived neurotrophic factor (BDNF) regulates neuronal plasticity by targeting the tyrosine kinase B receptor (TrkB) receptor, but limited researches concentrate on the role of BDNF/TrkB signaling in vestibular compensation. In this study, rats with unilateral vestibular dysfunction were established by unilateral labyrinthectomy (UL) and infusion with siBDNF or 7, 8-Dihydroxyflavone (7,8-DHF, a TrkB receptor agonist). The behavioral scores of rats with vestibular deficits were determined and the rotarod test was performed after UL. BDNF and TrkB levels after UL were determined by western blot and quantitative reverse transcription PCR (qRT-PCR). 5-bromo-2'-deoxyuridine (BrdU)-positive cells (newly generated cells) and GAD67-positive cells (GABAergic neurons) were identified by immunohistochemistry. Glial fibrillary acidic protein (GFAP) (astrocyte marker)-positive cells were identified and GABA type A receptor (GABAAR) expression was detected by immunofluorescence. We found that after UL, BDNF and TrkB levels were up-regulated with a maximum value at 4 h, and then progressively down-regulated during 4 h ~ 7 d. Blocking BDNF/TrkB signaling inhibited the recovery from vestibular deficits, decreased the numbers of newly generated cells and astrocytes in medial vestibular nucleus (MVN), inferior vestibular nerve (IVN), superior vestibular nerve (SVN) and lateral vestibular nucleus (LVN), and disrupted the balances of GABAergic neurons and GABAAR expressions in the left (lesioned) side and right (intact) side of MVN, whereas activation of BDNF/TrkB signaling caused opposite results. The current study indicated that BDNF/TrkB signaling avails vestibular compensation, depending on the number of newly generated cells and astrocytes, the rebalance of GABAergic neurons, and GABAAR expression in bilateral MVN.

Neuroprotection of retinal ganglion cells by the sigma-1 receptor agonist pridopidine in models of experimental glaucoma

Optic neuropathies such as glaucoma are characterized by retinal ganglion cell (RGC) degeneration and death. The sigma-1 receptor (S1R) is an attractive target for treating optic neuropathies as it is highly expressed in RGCs, and its absence causes retinal degeneration. Activation of the S1R exerts neuroprotective effects in models of retinal degeneration. Pridopidine is a highly selective and potent S1R agonist in clinical development. We show that pridopidine exerts neuroprotection of retinal ganglion cells in two different rat models of glaucoma. Pridopidine strongly binds melanin, which is highly expressed in the retina. This feature of pridopidine has implications to its ocular distribution, bioavailability, and effective dose. Mitochondria dysfunction is a key contributor to retinal ganglion cell degeneration. Pridopidine rescues mitochondrial function via activation of the S1R, providing support for the potential mechanism driving its neuroprotective effect in retinal ganglion cells.

TGFβ-Neurotrophin Interactions in Heart, Retina, and Brain

Ischemic insults to the heart and brain, i.e., myocardial and cerebral infarction, respectively, are amongst the leading causes of death worldwide. While there are therapeutic options to allow reperfusion of ischemic myocardial and brain tissue by reopening obstructed vessels, mitigating primary tissue damage, post-infarction inflammation and tissue remodeling can lead to secondary tissue damage. Similarly, ischemia in retinal tissue is the driving force in the progression of neovascular eye diseases such as diabetic retinopathy (DR) and age-related macular degeneration (AMD), which eventually lead to functional blindness, if left untreated. Intriguingly, the easily observable retinal blood vessels can be used as a window to the heart and brain to allow judgement of microvascular damages in diseases such as diabetes or hypertension. The complex neuronal and endocrine interactions between heart, retina and brain have also been appreciated in myocardial infarction, ischemic stroke, and retinal diseases. To describe the intimate relationship between the individual tissues, we use the terms heart-brain and brain-retina axis in this review and focus on the role of transforming growth factor β (TGFβ) and neurotrophins in regulation of these axes under physiologic and pathologic conditions. Moreover, we particularly discuss their roles in inflammation and repair following ischemic/neovascular insults. As there is evidence that TGFβ signaling has the potential to regulate expression of neurotrophins, it is tempting to speculate, and is discussed here, that cross-talk between TGFβ and neurotrophin signaling protects cells from harmful and/or damaging events in the heart, retina, and brain.

Cell Ferroptosis: New Mechanism and New Hope for Retinitis Pigmentosa

Retinitis pigmentosa (RP) is a leading cause of inherited retinal degeneration, with more than 60 gene mutations. Despite the genetic heterogenicity, photoreceptor cell damage remains the hallmark of RP pathology. As a result, RP patients usually suffer from reduced night vision, loss of peripheral vision, decreased visual acuity, and impaired color perception. Although photoreceptor cell death is the primary outcome of RP, the underlying mechanisms are not completely elucidated. Ferroptosis is a novel programmed cell death, with characteristic iron overload and lipid peroxidation. Recent studies, using in vitro and in vivo RP models, discovered the involvement of ferroptosis-associated cell death, suggesting a possible new mechanism for RP pathogenesis. In this review, we discuss the association between ferroptosis and photoreceptor cell damage, and its implication in the pathogenesis of RP. We propose that ferroptotic cell death not only opens up a new research area in RP, but may also serve as a novel therapeutic target for RP.

Risk Factors for Retinal Ganglion Cell Distress in Glaucoma and Neuroprotective Potential Intervention

Retinal ganglion cells (RGCs) are a population of neurons of the central nervous system (CNS) extending with their soma to the inner retina and with their axons to the optic nerve. Glaucoma represents a group of neurodegenerative diseases where the slow progressive death of RGCs results in a permanent loss of vision. To date, although Intra Ocular Pressure (IOP) is considered the main therapeutic target, the precise mechanisms by which RGCs die in glaucoma have not yet been clarified. In fact, Primary Open Angle Glaucoma (POAG), which is the most common glaucoma form, also occurs without elevated IOP. This present review provides a summary of some pathological conditions, i.e., axonal transport blockade, glutamate excitotoxicity and changes in pro-inflammatory cytokines along the RGC projection, all involved in the glaucoma cascade. Moreover, neuro-protective therapeutic approaches, which aim to improve RGC degeneration, have also been taken into consideration.

Effects of tACS-Like Electrical Stimulation on On-Center Retinal Ganglion Cells: Part I

Purpose

Electrical stimulation of the human central nervous system via surface electrodes has been used for both learning enhancement and the amelioration of neurodegenerative or psychiatric disorders. However, data are sparse on how such electrical stimulation affects neural circuits at the cellular level. This study assessed the effects of tACS-like currents at 10 Hz on On-center retinal ganglion cell responsiveness, using the rabbit retina eyecup preparation as a model for central nervous system effects.

Methods

We made extracellular recordings of light-evoked spike responses in different classes of On-center retinal ganglion cells before, during and after brief applications of 1 microampere alternating currents using single electrodes and microelectrode arrays.

Results

tACS-like currents (tACS) of 1 microampere produced effects on On-center ganglion cell response profiles immediately after initiation or cessation of tACS, without driving phase-locked firing in the absence of light stimuli. tACS affected the initial transient responses to light stimulation for all cells, sustained response components (if any) more strongly for sustained cells, and the center-surround balance more strongly for transient cells.

Conclusion

tACS sculpted light-evoked responses that lasted for one or more hours after cessation of current without, itself, directly inducing significant firing changes. Functionally, tACS effects could result in effects on contrast thresholds for both broad classes of cells, but because tACs differentially affects the center-surround balance of transient On-center cells, there may be greater effects on the spatial resolution and gain. The isolated retina appears to be a useful model to understand tACS actions at the neuronal level.

Differential Expression of BDNF and BIM in Streptozotocin-induced Diabetic Rat Retina After Fluoxetine Injection

BACKGROUND

Chronic diabetic retinopathy (DR) is a diabetic complication that causes blindness. Brain-derived neurotrophic factor (BDNF) expression is induced by fluoxetine. We observed the effects of fluoxetine on a streptozotocin (STZ)-induced diabetic rat model in this study.

MATERIALS AND METHODS

Rats were divided into three groups: Control, diabetic (65 mg/kg STZ injection), and diabetic with fluoxetine injection (20 mg/kg/week, six times). Western blotting was performed using anti-BDNF and anti-hexaribonucleotide-binding protein-3. Expression of BCL2 apoptosis regulator-like protein 11 (BIM) was analysed using a reverse transcription-polymerase chain reaction.

RESULTS

BDNF levels were significantly higher in the diabetic group treated with fluoxetine than in the untreated diabetic group. BIM expression was higher in the diabetic group than in the control group. BIM gene expression was lower in fluoxetine-treated diabetic group than in the untreated diabetic group.

CONCLUSION

Fluoxetine had an anti-apoptotic effect with upregulation of BDNF expression in retina of rats with STZ-induced diabetes.

Neurogenic and Neuroprotective Potential of Stem/Stromal Cells Derived from Adipose Tissue

Currently, the number of stem-cell based experimental therapies in neurological injuries and neurodegenerative disorders has been massively increasing. Despite the fact that we still have not obtained strong evidence of mesenchymal stem/stromal cells’ neurogenic effectiveness in vivo, research may need to focus on more appropriate sources that result in more therapeutically promising cell populations. In this study, we used dedifferentiated fat cells (DFAT) that are proven to demonstrate more pluripotent abilities in comparison with standard adipose stromal cells (ASCs). We used the ceiling culture method to establish DFAT cells and to optimize culture conditions with the use of a physioxic environment (5% O₂). We also performed neural differentiation tests and assessed the neurogenic and neuroprotective capability of both DFAT cells and ASCs. Our results show that DFAT cells may have a better ability to differentiate into oligodendrocytes, astrocytes, and neuron-like cells, both in culture supplemented with N21 and in co-culture with oxygen–glucose-deprived (OGD) hippocampal organotypic slice culture (OHC) in comparison with ASCs. Results also show that DFAT cells have a different secretory profile than ASCs after contact with injured tissue. In conclusion, DFAT cells constitute a distinct subpopulation and may be an alternative source in cell therapy for the treatment of nervous system disorders.

Retinal Ganglion Cell Transplantation: Approaches for Overcoming Challenges to Functional Integration

As part of the central nervous system, mammalian retinal ganglion cells (RGCs) lack significant regenerative capacity. Glaucoma causes progressive and irreversible vision loss by damaging RGCs and their axons, which compose the optic nerve. To functionally restore vision, lost RGCs must be replaced. Despite tremendous advancements in experimental models of optic neuropathy that have elucidated pathways to induce endogenous RGC neuroprotection and axon regeneration, obstacles to achieving functional visual recovery through exogenous RGC transplantation remain. Key challenges include poor graft survival, low donor neuron localization to the host retina, and inadequate dendritogenesis and synaptogenesis with afferent amacrine and bipolar cells. In this review, we summarize the current state of experimental RGC transplantation, and we propose a set of standard approaches to quantifying and reporting experimental outcomes in order to guide a collective effort to advance the field toward functional RGC replacement and optic nerve regeneration.

Increased ciliary neurotrophic factor in blood serum and lacrimal fluid as a potential biomarkers of focal epilepsy

PURPOSE

To evaluate ciliary neurotrophic factor (CNTF) level in blood serum (BS) and lacrimal fluid (LF) of people with epilepsy (PWE).

METHODS

A case-control study of 72 consecutive patients with focal epilepsy (cases, epilepsy group) and 60 age- and gender-matched healthy volunteers (controls) was performed. Based on comorbid depression, two subgroups of PWE were formed. CNTF level was measured by an enzyme-linked immunosorbent assay (ELISA) in the BS and LF. For measurements of low CNTF levels in the BS, the methodology previously improved by the authors was applied.

RESULTS

As compared to controls, CNTF level (pg/mL) in PWE was increased both in the BS (7.0±2.9 vs. 3.7±2.0, P<0.000) and in LF (34.0±8.0 vs. 30.6±4.8, P=0.005). No significant correlation was found between CNTF level in the BS and LF either in PWE or in controls. No impact of comorbid depression or any demographic or clinical parameters studied on CNTF level in the BS or LF of PWE could be detected.

CONCLUSIONS

In patients with focal epilepsy, CNTF level is increased both in the BS and LF, though without correlation between them. No association of CNTF levels with age, gender, or clinical parameters, as well as depression occurrence, was found. High CNTF levels in the BS and LF could be considered as non-invasive biomarkers of focal epilepsy.

Effect of Sodium Valproate on the Conformational Stability of the Visual G Protein-Coupled Receptor Rhodopsin

Rhodopsin is the G protein-coupled receptor of rod photoreceptor cells that mediates vertebrate vision at low light intensities. Mutations in rhodopsin cause inherited retinal degenerative diseases such as retinitis pigmentosa. Several therapeutic strategies have attempted to address and counteract the deleterious effect of rhodopsin mutations on the conformation and function of this photoreceptor protein, but none has been successful in efficiently preventing retinal degeneration in humans. These approaches include, among others, the use of small molecules, known as pharmacological chaperones, that bind to the receptor stabilizing its proper folded conformation. Valproic acid, in its sodium valproate form, has been used as an anticonvulsant in epileptic patients and in the treatment of several psychiatric disorders. More recently, this compound has been tested as a potential therapeutic agent for the treatment of retinal degeneration associated with retinitis pigmentosa caused by rhodopsin mutations. We now report on the effect of sodium valproate on the conformational stability of heterologously expressed wild-type rhodopsin and a rhodopsin mutant, I307N, which has been shown to be an appropriate model for studying retinal degeneration in mice. We found no sign of enhanced stability for the dark inactive conformation of the I307N mutant. Furthermore, the photoactivated conformation of the mutant appears to be destabilized by sodium valproate as indicated by a faster decay of its active conformation. Therefore, our results support a destabilizing effect of sodium valproate on rhodopsin I307N mutant associated with retinal degeneration. These findings, at the molecular level, agree with recent clinical studies reporting negative effects of sodium valproate on the visual function of retinitis pigmentosa patients.

7,8-Dihydroxyflavone protects retinal ganglion cells against chronic intermittent hypoxia-induced oxidative stress damage via activation of the BDNF/TrkB signaling pathway

PURPOSE

Chronic intermittent hypoxia (CIH) plays a key role in the complications of obstructive sleep apnea (OSA), which is strongly associated with retinal and optic nerve diseases. Additionally, the brain-derived neurotrophic factor (BDNF)/tropomyosin receptor kinase B (TrkB) signaling pathway plays an important protective role in neuronal injury. In the present study, we investigated the role of 7,8-dihydroxyflavone (7,8-DHF) in regulating CIH-induced injury in mice retinas and rat primary retinal ganglion cells (RGCs).

METHODS

C57BL/6 mice and in vitro primary RGCs were exposed to CIH or normoxia and treated with or without 7,8-DHF. The mice eyeballs or cultured cells were then taken for histochemistry, immunofluorescence or biochemistry, and the protein expression of the BDNF/TrkB signaling pathway analysis.

RESULTS

Our results showed that CIH induced oxidative stress (OS) in in vivo and in vitro models and inhibited the conversion of BDNF precursor (pro-BDNF) to a mature form of BDNF, which increased neuronal cell apoptosis. 7,8-DHF reduced the production of reactive oxygen species (ROS) caused by CIH and effectively activated TrkB signals and downstream protein kinase B (Akt) and extracellular signal-regulated kinase (Erk) survival signaling pathways, which upregulated the expression of mature BDNF. ANA-12 (a TrkB specific inhibitor) blocked the protective effect of 7,8-DHF.

CONCLUSION

In short, the activation of the BDNF/TrkB signaling pathway alleviated CIH-induced oxidative stress damage of the optic nerve and retinal ganglion cells. 7,8-DHF may serve as a promising agent for OSA related neuropathy.

Plasmalogen attenuates the development of hepatic steatosis and cognitive deficit through mechanism involving p75NTR inhibition

Emerging evidence suggests that the reduction of ethanolamine plasmalogen (PlsEtn) is associated with in Alzheimer's disease and metabolic diseases. However, the mechanistic bases for PlsEtn on the these diseases are not well understood. Plasmalogens are primarily synthesized in the liver and enriched in brain. To this end, the present study sought to investigate the potential role of PlsEtn on steatohepatitis and memory impairments and its underlying mechanism. Here we show that peroxisome dysfunction and impairment of PlsEtn synthesis pathway occurs in both of hippocampus and liver, resulting in the decrease of PlsEtn level in APP/PS1 mice and HFD-fed mice. shGNPAT induced PlsEtn deficiency in hepatocytes induces p75NTR enhancement leading to decreased lipolysis activity, thereby exacerbating steatosis. Moreover, in the brain, PlsEtn administration appears to not only improve steatosis but also prevent Alzheimer's disease through restoration of TrkA/p75NTR balance. Together, our findings reveal a molecular mechanistic insight into the preventive role of plasmalogen modulation against steatosis and memory impairments via p75NTR inhibition.

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Peroxisome dysfunction and impairment of plasmalogen synthesis pathway resulted in the decrease of plasmalogen level.

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Plasmalogen deficiency in hepatocytes induces p75NTR enhancement leading to decreased lipolysis activity.

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Ethanolamine plasmalogen administration improves memory impairments by restoration of TrkA/p75NTR balance.

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Ethanolamine plasmalogen administration attenuates neurodegeneration and neuronal death, and mitigates oxidative stress.

Emerging treatments for geographic atrophy in age-related macular degeneration

PURPOSE OF REVIEW

This review describes therapeutic research programs for geographic atrophy (GA) due to age-related macular degeneration (AMD). We highlight clinical trial data from phase I, II, and III studies.

RECENT FINDINGS

There are currently no treatments for GA, a form of advanced AMD that causes significant visual morbidity. Currently, therapeutic candidates are being developed to delay further progression of GA or even attempt to reverse some of the damage. The approaches to therapy range from molecular targets to cell transplantation. Studies of these novel treatment approaches have demonstrated varying degrees of success. The progress in understanding the disease pathophysiology as well as clinical trial data is reviewed.

SUMMARY

There are promising new treatments to prevent GA progression as well as some that may reverse the disease course.

Focused Update on AAV-Based Gene Therapy Clinical Trials for Inherited Retinal Degeneration

Inherited retinal diseases (IRDs) comprise a clinically and genetically heterogeneous group of disorders that can ultimately result in photoreceptor dysfunction/death and vision loss. With over 270 genes known to be involved in IRDs, translation of treatment strategies into clinical applications has been historically difficult. However, in recent years there have been significant advances in basic research findings as well as translational studies, culminating in an increasing number of clinical trials with the ultimate goal of reducing vision loss and associated morbidities. The recent approval of Luxturna^® (voretigene neparvovec-rzyl) for Leber congenital amaurosis type 2 (LCA2) prompts a review of the current clinical trials for IRDs, with a particular focus on the importance of adeno-associated virus (AAV)-based gene therapies. The present article reviews the current state of AAV use in gene therapy clinical trials for IRDs, with a brief background on AAV and the reasons behind its dominance in ocular gene therapy. It will also discuss pre-clinical progress in AAV-based therapies aimed at treating other ocular conditions that can have hereditable links, and what alternative technologies are progressing in the same therapeutic space.

Immunological and molecular basics of the primary open angle glaucoma pathomechanism

Glaucoma is a degenerative process of the optic nerve. Increased intraocular pressure is believed to be the main factor leading to the glaucomatous damage. The in vitro and in vivo animal glaucoma research models provide insight into the molecular changes in the retina in response to the injury factor. The damage is a complex process incorporating molecular and immunological changes. Such changes involve NF kB activity and complement activation. The processes affect the human antigen, JNK, MAPK, p53, MT2 and DBA/2J molecular pathways, activate the autophagy processes and compromise neuroprotective mechanisms. Activation and inhibition of immunological responses contribute to cell injury. The immunological mechanisms of glaucomatous degeneration include glial response, the complement, tumor necrosis factor α (TNF-α) pathways and toll-like receptors athways. Oxidative stress and excitotoxicity are factors contributing to cell death in glaucoma. The authors present an up-to-date review of the mechanisms involved and update on research focusing on a possible innovative glaucoma treatment.

Mechanisms and repair strategies for white matter degeneration in CNS injury and diseases

White matter degeneration is an important pathophysiological event of the central nervous system that is collectively characterized by demyelination, oligodendrocyte loss, axonal degeneration and parenchymal changes that can result in sensory, motor, autonomic and cognitive impairments. White matter degeneration can occur due to a variety of causes including trauma, neurotoxic exposure, insufficient blood flow, neuroinflammation, and developmental and inherited neuropathies. Regardless of the etiology, the degeneration processes share similar pathologic features. In recent years, a plethora of cellular and molecular mechanisms have been identified for axon and oligodendrocyte degeneration including oxidative damage, calcium overload, neuroinflammatory events, activation of proteases, depletion of adenosine triphosphate and energy supply. Extensive efforts have been also made to develop neuroprotective and neuroregenerative approaches for white matter repair. However, less progress has been achieved in this area mainly due to the complexity and multifactorial nature of the degeneration processes. Here, we will provide a timely review on the current understanding of the cellular and molecular mechanisms of white matter degeneration and will also discuss recent pharmacological and cellular therapeutic approaches for white matter protection as well as axonal regeneration, oligodendrogenesis and remyelination.