Ciliary Neurotrophic Factor Derived From Astrocytes Protects Retinal Ganglion Cells Through PI3K/AKT, JAK/STAT, and MAPK/ERK Pathways

Crosstalk between signaling pathways (Rho/ROCK, TGF-β and Wnt/β-Catenin Pathways/ PI3K-AKT-mTOR) in Cataract: A Mechanistic Exploration and therapeutic strategy

Cataract are a leading cause of visual impairment that is characterized by clouding or lens opacification of the healthy clear lens of the eye or its capsule. It can be classified based on their etiology and clinical presentation such as congenital, age-related, and secondary cataracts. Clinically, it may be further classified as a cortical or nuclear cataract. Cortical cataracts are responsible for opacification of the lens cortex, while nuclear cataracts cause age-related degeneration of the lens nucleus. This review aims to explore the molecular mechanism associated with various signaling pathways underlying cataract formation. Additionally, explore the potential therapeutic strategies for the management of cataracts. A comprehensive literature search was performed utilizing different keywords such as cataract, pathogenesis, signaling pathways, therapeutic approaches, RNA therapeutics, and surgery. Electronic databases such as PubMed, Google Scholar, Springer Link, and Web of Science were used for the literature search. The cataract formation is responsible for protein aggregation, primarily of γ-crystallin, and causes disruptions in signaling pathways. Key pathways include Rho/ROCK, TGF-β, Wnt/β-catenin, NF-κB, and PI3K-AKT-mTOR. Signaling pathways governing lens epithelial cell differentiation and epithelial-to-mesenchymal transition (EMT) are essential for maintaining lens transparency. Disruptions in these pathways, often caused by genetic mutations in genes like MIP, TDRD7, PAX6, FOXE3, HSF4, MAF, and PITX3 lead to cataract formation. While surgical intervention remains the primary treatment, pharmacological therapies and emerging RNA-based strategies offer promising strategies for the prevention and management of cataracts. A deeper understanding of the underlying molecular mechanisms is essential to develop innovative therapeutic strategies and improve the quality of life for individuals affected by cataracts.

Glaucomatous retinal ganglion cells: death and protection

Glaucoma is a group of diseases characterized by progressive optic nerve degeneration, with the characteristic pathological change being death of retinal ganglion cells (RGCs), which ultimately causes visual field loss and irreversible blindness. Elevated intraocular pressure (IOP) remains the most important risk factor for glaucoma, but the exact mechanism responsible for the death of RGCs is currently unknown. Neurotrophic factor deficiency, impaired mitochondrial structure and function, disrupted axonal transport, disturbed Ca2+ homeostasis, and activation of apoptotic and autophagic pathways play important roles in RGC death in glaucoma. This review was conducted using Web of Science, PubMed, Project, and other databases to summarize the relevant mechanisms of death of RGCs in glaucoma, in addition to outlining protective treatments to improve the degradation of RGCs.

Estrogen, via ESR2 receptor, prevents oxidative stress-induced Müller cell death and stimulates FGF2 production independently of NRF2, attenuating retinal degeneration

In this study, we aimed to investigate the effects of the deficient antioxidative gene, nuclear factor-erythroid 2-related factor 2 (Nrf2), on 17β-estradiol (E2)-mediated oxidative stress response, with a specific focus on growth factor production and cell death in Müller cells and retinal tissue. Administration of hydrogen peroxide (H2O2) reduced the viability of Müller cells derived from Nrf2 wild-type (WT) and knockout (KO) mice. However, this effect was more significant in the KO cells than in the WT cells. Pretreatment with E2 inhibited H2O2-induced cell death in both Nrf2 WT and KO Müller cell genotypes. Small interfering RNA-mediated gene silencing of estrogen receptor 2 (Esr2) attenuated the cell survival-promoting activity of E2 in Nrf2 KO Müller cells, while other identified estrogen receptors, Esr1 or G protein-coupled estrogen receptor 1 (Gper1), had no effect. Western blotting revealed higher ESR2 expression levels in Nrf2 KO cells than in WT Müller cells. Conditioned media from E2-and H2O2-treated Nrf2 WT or KO Müller cells enhanced the dissociated retinal cell viability compared with H2O2-treated cells. Both quantitative reverse-transcription polymerase chain reaction assay (qRT-PCR) and enzyme-linked immunosorbent assay exhibited a significant increase in fibroblast growth factor 2 (FGF2) expression levels in E2-and H2O2-treated Nrf2 WT and KO Müller cells compared to those in E2-treated cells. In vivo, administration of N-methyl-N-nitrosourea (MNU) reduced the thickness and cell density of the outer nuclear layer (ONL) in Nrf2 KO mice and enhanced the number of terminal deoxynucleotidyl transferase dUTP nick-end labeling-positive cells in the ONL. However, E2 administration attenuated these defects in MNU-treated mice. Concomitant administration of MNU and E2 enhanced FGF2 protein levels in retinal lysates of Nrf2 KO mice. In conclusion, E2 demonstrated a significant role in preventing oxidative stress-induced retinal cell death by stimulating FGF2 production in Müller cells, independent of the Nrf2 gene. Based on these findings, we anticipate that exogenous administration of estrogens or ESR2-selective agonists could aid in treating patients with oxidative stress-related retinal degenerative diseases such as age-related macular degeneration and retinitis pigmentosa.

Advances in Neuroprotection in Glaucoma: Pharmacological Strategies and Emerging Technologies

Glaucoma is a major global health concern and the leading cause of irreversible blindness worldwide, characterized by the progressive degeneration of retinal ganglion cells (RGCs) and their axons. This review focuses on the need for neuroprotective strategies in glaucoma management, addressing the limitations of current treatments that primarily target intraocular pressure (IOP) reduction. Despite effective IOP management, many patients continue to experience RGC degeneration, leading to irreversible blindness. This review provides an overview of both pharmacological interventions and emerging technologies aimed at directly protecting RGCs and the optic nerve, independent of IOP reduction. Pharmacological agents such as brimonidine, neurotrophic factors, memantine, Ginkgo biloba extract, citicoline, nicotinamide, insulin, and resveratrol show promise in preclinical and early clinical studies for their neuroprotective properties. Emerging technologies, including stem cell therapy, gene therapy, mitochondrial-targeted therapies, and nanotechnologies, offer innovative approaches for neuroprotection and regeneration of damaged RGCs. While these interventions hold significant potential, further research and clinical trials are necessary to confirm their efficacy and establish their role in clinical practice. This review highlights the multifaceted nature of neuroprotection in glaucoma, aiming to guide future research and clinical practice toward more effective management of glaucoma-induced neurodegeneration.

Synergistic amelioration between Ligusticum striatum DC and borneol against cerebral ischemia by promoting astrocytes-mediated neurogenesis

ETHNOPHARMACOLOGICAL RELEVANCE

Ligusticum chuanxiong Hort (LCH), with the accepted name of Ligusticum striatum DC in "The Plant List" database, is a widely used ethnomedicine in treating ischemic stroke, and borneol (BO) is usually prescribed with LCH for better therapy. Our previous study confirmed their synergistic effect on neurogenesis against cerebral ischemia. However, the underlying mechanism is still unclear.

AIM OF THE STUDY

More and more evidence indicated that astrocytes (ACs) might be involved in the modulation of neurogenesis via polarization reaction. The study was designed to explore the synergic mechanism between LCH and BO in promoting astrocyte-mediated neurogenesis.

MATERIALS AND METHODS

After primary cultures and identifications of ACs and neural stem cells (NSCs), the oxygen-glucose deprivation (OGD) model and the concentrations of LCH and BO were optimized. After the OGD-injured ACs were treated by LCH, BO, and their combination, the conditioned mediums were used to culture the OGD-injured NSCs. The proliferation, migration, and differentiation of NSCs were assessed, and the secretions of BDNF, CNTF, and VEGF from ACs were measured. Then the expressions of C3 and PTX3 were detected. Moreover, the mice were performed a global cerebral ischemia/reperfusion model and treated with LCH and (or) BO. After the assessments of Nissl staining, the expressions of Nestin, DCX, GFAP, C3, PTX3, p65 and p-p65 were probed.

RESULTS

The most appropriate duration of OGD for the injury of both NSCs and ACs was 6 h, and the optimized concentrations of LCH and BO were 1.30 μg/mL and 0.03 μg/mL, respectively. The moderate OGD environment induced NSCs proliferation, migration, astrogenesis, and neurogenesis, increased the secretions of CNTF and VEGF from ACs, and upregulated the expressions of C3 and PTX3. For the ACs, LCH further increased the secretions of BDNF and CNTF, enhanced PTX3 expression, and reduced C3 expression. Additionally, the conditioned medium from LCH-treated ACs further enhanced NSC proliferation, migration, and neurogenesis. The in vivo study showed that LCH markedly enhanced the Nissl score and neurogenesis, and decreased astrogenesis which was accompanied by downregulations of C3, p-p65, and p-p65/p65 and upregulation of PTX3. BO not only decreased the expression of C3 in ACs both in vitro and in vivo but also downregulated p-p65 and p-p65/p65 in vivo. Additionally, BO promoted the therapeutic effect of LCH for most indices.

CONCLUSION

A certain degree of OGD might induce ACs to stimulate the proliferation, astrogenesis, and neurogenesis of NSCs. LCH and BO exhibited a marked synergy in promoting ACs-mediated neurogenesis and reducing astrogenesis, in which LCH played a dominant role and BO boosted the effect of LCH. The mechanism of LCH might be involved in switching the polarization of ACs from A1 to A2, while BO preferred to inhibit the formation of A1 phenotype via downregulating NF-κB pathway.

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.

Role of Interleukin-21 in retinal ischemia-reperfusion injury: Unveiling the impact on retinal ganglion cell apoptosis

BACKGROUND

Retinal ischemia-reperfusion (I/R) serves as a significant contributor to ocular diseases, triggering a cascade of pathological processes. The interplay between neuroinflammation and the apoptosis of retinal ganglion cell (RGC) is a well-explored aspect of retinal I/R-induced tissue damage. Within this intricate landscape, the inflammatory cytokine Interleukin-21 (IL21) emerges as a potent mediator of neuroinflammation with known detrimental effects on neuronal integrity. However, its specific impact on RGC apoptosis in the context of retinal I/R has remains to be uncovered. This study aims to unravel the potential anti-apoptotic effects of IL21 siRNA on RGC, shedding light on the neuroprotection of retinal I/R.

METHODS

Sprague-Dawley (SD) rats underwent a controlled elevation of intraocular pressure (IOP) to 110 mmHg for 60 min to simulate retinal I/R conditions. To explore the influence of IL21 on RGC apoptosis and its underlying molecular mechanisms, a comprehensive array of techniques such immunohistochemistry, immunofluorescence, TUNEL, Hematoxylin-eosin (H&E), immunoblotting, and qRT-PCR were carried out.

RESULTS

The landscape of retinal I/R injury revealed an increase in the expression of IL21, reaching its peak at 72 h. Notably, IL21 markedly induced RGC apoptosis within the retinal I/R milieu. The introduction of IL21 siRNA showed promising outcomes, manifesting as an amelioration of neurological function deficits, a reduction in RGC loss, and an increase in the thickness of the inner retinal layer at the 72-hour reperfusion. Additionally, IL21 siRNA demonstrated its ability to hinder the release of proteins associated with apoptosis via the JAK/STAT signaling pathway. In the in vitro setting, IL21 siRNA efficiently reduced R28 cell apoptosis by suppressing the production of proteins associated with apoptosis by regulating the JAK/STAT signaling pathway.

CONCLUSIONS

This study provides evidence for the pathogenic role of IL21 in retinal I/R. The findings underscore IL21 siRNA as a promising therapeutic target for ischemic retinal injury. Its efficacy lies in its ability to mitigate RGC apoptosis by suppressing the JAK/STAT signaling pathway. These findings not only enhance our comprehension of retinal I/R pathology but also suggests IL21 siRNA as a potential transformative factor in the development of targeted therapies for ischemic retinal injuries.

Synergistic Protection of Retinal Ganglion Cells (RGCs) by SARM1 Inactivation with CNTF in a Rodent Model of Nonarteritic Anterior Ischemic Optic Neuropathy

We evaluated whether inhibiting sterile alpha and (Toll/interleukin receptor (TIR)) motif-containing 1 (SARM1) activity protects retinal ganglion cells (RGCs) following ischemic axonopathy (rodent nonarteritic anterior ischemic optic neuropathy: rNAION) by itself and combined with ciliary neurotrophic factor (CNTF). Genetically modified SARM1(-) rats were rNAION-induced in one eye and compared against equivalently induced wild-type animals of the same background. Optic nerve (ON) diameters were quantified using optical coherence tomography (SD-OCT). RGCs were quantified 30 d post-induction using retinal stereology for Brn3a(+) nuclei. ON sections were analyzed by TEM and immunohistochemistry. SARM1(-)(-) and WT animals were then bilaterally sequentially rNAION-induced. One eye received intravitreal vehicle injection following induction; the contralateral side received CNTF and was analyzed 30 d post-induction. Inhibiting SARM1 activity suppressed axonal collapse following ischemic axonopathy. SARM1(-) animals significantly reduced RGC loss, compared with WT animals (49.4 ± 6.8% RGC loss in SARM1(-) vs. 63.6 ± 3.2% sem RGC loss in WT; Mann-Whitney one-tailed U-test, (p = 0.049)). IVT-CNTF treatment vs. IVT-vehicle in SARM1(-) animals further reduced RGC loss by 24% at 30 d post-induction, but CNTF did not, by itself, improve long-term RGC survival in WT animals compared with vehicle (Mann-Whitney one-tailed t-test; p = 0.033). While inhibiting SARM1 activity is itself neuroprotective, combining SARM1 inhibition and CNTF treatment generated a long-term, synergistic neuroprotective effect in ischemic neuropathy. Combinatorial treatments for NAION utilizing independent neuroprotective mechanisms may thus provide a greater effect than individual treatment modalities.

Regulated Cell Death of Retinal Ganglion Cells in Glaucoma: Molecular Insights and Therapeutic Potentials

Glaucoma is a group of diseases characterized by the degeneration of retinal ganglion cells (RGCs) and progressive, irreversible vision loss. High intraocular pressure (IOP) heightens the likelihood of glaucoma and correlates with RGC loss. While the current glaucoma therapy prioritizes lower the IOP; however, RGC, and visual loss may persist even when the IOP is well-controlled. As such, discovering and creating IOP-independent neuroprotective strategies for safeguard RGCs is crucial for glaucoma management. Investigating and clarifying the mechanism behind RGC death to counteract its effects is a promising direction for glaucoma control. Empirical studies of glaucoma reveal the role of multiple regulated cell death (RCD) pathways in RGC death. This review delineates the RCD of RGCs following IOP elevation and optic nerve damage and discusses the substantial benefits of mitigating RCD in RGCs in preserving visual function.

The pivotal role of JAK/STAT and IRS/PI3K signaling pathways in neurodegenerative diseases: Mechanistic approaches to polyphenols and alkaloids

BACKGROUND

Neurodegenerative diseases (NDDs) are characterized by progressive neuronal dysfunctionality which results in disability and human life-threatening events. In recent decades, NDDs are on the rise. Besides, conventional drugs have not shown potential effectiveness to attenuate the complications of NDDs. So, exploring novel therapeutic agents is an urgent need to combat such disorders. Accordingly, growing evidence indicates that polyphenols and alkaloids are promising natural candidates, possessing several beneficial pharmacological effects against diseases. Considering the complex pathophysiological mechanisms behind NDDs, Janus kinase (JAK), insulin receptor substrate (IRS), phosphoinositide 3-kinase (PI3K), and signal transducer and activator of transcription (STAT) seem to play critical roles during neurodegeneration/neuroregeneration. In this line, modulation of the JAK/STAT and IRS/PI3K signaling pathways and their interconnected mediators by polyphenols/alkaloids could play pivotal roles in combating NDDs, including Alzheimer's disease (AD), Parkinson's disease (PD), Huntington's disease (HD), stroke, aging, multiple sclerosis (MS), amyotrophic lateral sclerosis (ALS), depression and other neurological disorders.

PURPOSE

Thus, the present study aimed to investigate the neuroprotective roles of polyphenols/alkaloids as multi-target natural products against NDDs which are critically passing through the modulation of the JAK/STAT and IRS/PI3K signaling pathways.

STUDY DESIGN AND METHODS

A systematic and comprehensive review was performed to highlight the modulatory roles of polyphenols and alkaloids on the JAK/STAT and IRS/PI3K signaling pathways in NDDs, according to the PRISMA guideline, using scholarly electronic databases, including Scopus, PubMed, ScienceDirect, and associated reference lists.

RESULTS

In the present study 141 articles were included from a total of 1267 results. The results showed that phenolic compounds such as curcumin, epigallocatechin-3-gallate, and quercetin, and alkaloids such as berberine could be introduced as new strategies in combating NDDs through JAK/STAT and IRS/PI3K signaling pathways. This is the first systematic review that reveals the correlation between the JAK/STAT and IRS/PI3K axis which is targeted by phytochemicals in NDDs. Hence, this review highlighted promising insights into the neuroprotective potential of polyphenols and alkaloids through the JAK/STAT and IRS/PI3K signaling pathway and interconnected mediators toward neuroprotection.

CONCLUSION

Amongst natural products, phenolic compounds and alkaloids are multi-targeting agents with the most antioxidants and anti-inflammatory effects possessing the potential of combating NDDs with high efficacy and lower toxicity. However, additional reports are needed to prove the efficacy and possible side effects of natural products.

The Protective Role of Apelin in the Early Stages of Diabetic Retinopathy

Diabetic retinopathy (DR) is one of the most common and serious microvascular complications of diabetes. Although current treatments can control the progression of DR to a certain extent, there is no effective treatment for early DR. Apart from vascular endothelial growth factor, it has been noted that the apelin/APJ system contributes to the pathogenesis of DR. We used a high-fat diet/streptozotocin-induced type 2 diabetic mouse model. The mice were divided into a lentivirus control group (LV-EGFP), an apelin-overexpression group (LV-Apelin+), and an apelin-knockdown group (LV-Apelin-), all of which were administrated intravitreal injections. LV-Apelin+ ameliorated the loss of pericytes in DR mice, whereas LV-Apelin- aggravated the loss of pericytes. Similarly, LV-Apelin+ reduced the leakage of retinal vessels, whereas LV-Apelin- exacerbated it. The genes and signaling pathway related to cell adhesion molecules were downregulated, whereas the cell-cell tight junctions and anti-apoptotic genes were upregulated in response to apelin overexpression. However, the alterations of these same genes and signaling pathways were reversed in the case of apelin knockdown. Additionally, LV-Apelin+ increased ZO-1 and occludin levels, whereas LV-Apelin- decreased them. Our results suggest that apelin can reduce vascular leakage by protecting pericytes, which offers a promising new direction for the early treatment of DR.