Role of epigenetic regulation in glaucoma

Integration of single-cell and bulk transcriptomics reveals β-hydroxybutyrylation-related signatures in primary open-angle glaucoma

The pathophysiology of primary open-angle glaucoma (POAG), the most prevalent glaucoma type, is poorly understood. Although it is well known that epigenetic factors affect the progression of POAG, the impact of β-hydroxybutyrylation (Kbhb) on POAG remains unknown. Based on POAG-related datasets (GSE27276, GSE4316, and GSE231749) retrieved from the Gene Expression Omnibus (GEO) database, four biomarkers (FABP5, GLS, PDLIM1, and TAGLN) with a diagnostic value for POAG were identified by combining differential expression analysis, machine learning algorithms, and receiver operating characteristic (ROC) analysis. Immune infiltration analysis demonstrated significant differences in the infiltration abundances of 10 immune cells between POAG and controls, including regulatory T cells, monocytes, and macrophages, with notable positive correlations between TAGLN expression and these immune cells. Subsequently, single-cell analysis revealed that GLS, PDLIM1, and TAGLN were higher expressed in chondrocytes, smooth muscle cells, and endothelial cells. In addition, in vitro cellular experiments and animal models revealed that the TAGLN expression trend was consistent with the data from GSE27276 and GSE4316. In conclusion, TAGLN may play an important role in understanding of the molecular mechanisms of POAG and exploration of therapeutic targets.

Cellular senescence and glaucoma

Cellular senescence, a characteristic feature of the aging process, is induced by diverse stressors. In recent years, glaucoma has emerged as a blinding ocular disease intricately linked to cellular senescence. The principal pathways implicated are oxidative stress, mitochondrial dysfunction, DNA damage, autophagy impairment, and the secretion of various senescence- associated secretory phenotype factors. Research on glaucoma-associated cellular senescence predominantly centers around the increased resistance of the aqueous humor outflow pathway, which is attributed to the senescence of the trabecular meshwork and Schlemm's canal. Additionally, it focuses on the mechanisms underlying retinal ganglion cell senescence in glaucoma and the corresponding intervention measures. Given that cell senescence represents an irreversible phase preceding cell death, an in-depth investigation into its mechanisms in the pathogenesis and progression of glaucoma, particularly by specifically blocking the signal transduction of cell senescence, holds the potential to decrease the outflow resistance of aqueous humor. This, in turn, could provide a novel avenue for safeguarding the optic nerve in glaucoma.

RNA methylation homeostasis in ocular diseases: All eyes on Me

RNA methylation is a pivotal epigenetic modification that adjusts various aspects of RNA biology, including nuclear transport, stability, and the efficiency of translation for specific RNA candidates. The methylation of RNA involves the addition of methyl groups to specific bases and can occur at different sites, resulting in distinct forms, such as N6-methyladenosine (m6A), N1-methyladenosine (m1A), 5-methylcytosine (m5C), and 7-methylguanosine (m7G). Maintaining an optimal equilibrium of RNA methylation is crucial for fundamental cellular activities such as cell survival, proliferation, and migration. The balance of RNA methylation is linked to various pathophysiological conditions, including senescence, cancer development, stress responses, and blood vessel formation, all of which are pivotal for comprehending a spectrum of eye diseases. Recent findings have highlighted the significant role of diverse RNA methylation patterns in ophthalmological conditions such as age-related macular degeneration, diabetic retinopathy, cataracts, glaucoma, uveitis, retinoblastoma, uveal melanoma, thyroid eye disease, and myopia, which are critical for vision health. This thorough review endeavors to dissect the influence of RNA methylation on common and vision-impairing ocular disorders. It explores the nuanced roles that RNA methylation plays in key pathophysiological mechanisms, such as oxidative stress and angiogenesis, which are integral to the onset and progression of these diseases. By synthesizing the latest research, this review offers valuable insights into how RNA methylation could be harnessed for therapeutic interventions in the field of ophthalmology.

Extracellular Vesicles and Glaucoma: Opportunities and Challenges

PURPOSE

Glaucoma is one of the leading causes of irreversible blindness, characterized by progressive visual field loss. Several risk factors are associated with developing the disease. However, the exact mechanisms or pathological pathways involved are still unknown. There is an urgent need to find the mechanisms and biomarkers for early detection and therapy to halt progression or cure the disease. Extracellular vesicles (EVs), specifically exosomes, have emerged as a crucial player in all aspects of glaucoma, including pathogenesis to therapeutic application with their cell-cell communication properties.

METHODS

We performed a literature search on PubMed, Google Scholar, and Web of Science using different keywords. Next, we reviewed the literature with studies focusing on the role of EVs as a causative factor in disease progression, biomarker discovery based on their contents, and protection from glaucoma.

RESULTS

Studies summarized here provide reports of differential EV miRNA and protein expression alterations when communicating with aqueous humor drainage tissues. We described how EV contents are involved in various pathways, including extracellular matrix remodeling and miRNA-mediated oxidative stress transmission between outflow tissues, thereby contributing to glaucoma. Extracellular vesicles, mainly derived from mesenchymal stem cells protecting the optic nerve from degeneration, have also been discussed as potential therapies for glaucoma.

CONCLUSIONS

Overall, this review provides a comprehensive discussion of the role of extracellular vesicles in glaucoma. We identified the challenges in finding major signaling molecules of glaucoma etiology. Lastly, we highlighted future directions to improve the treatment of glaucoma by extracellular vesicles.

Mettl3-Mediated N6-Methyladenosine Modification Mitigates Ganglion Cell Loss and Retinal Dysfunction in Retinal Ischemia-Reperfusion Injury by Inhibiting FoxO1-Mediated Autophagy

Purpose

N6-methyladenosine (m6A) modification has been implicated in ischemia-reperfusion injury in various systems and in several neurodegenerative diseases. Glaucoma is characterized by degeneration of retinal ganglion cells (RGCs) and shares similar pathologic injury characteristics with retinal ischemia-reperfusion (RIR) injury. However, the specific role of m6A modification in RIR injury is unclear, and the involvement of autophagy in RIR injury also remains controversial. Therefore, our study explored the role of m6A modification and autophagy in RIR injury.

Methods

Male wild-type C57BL/6J mice (6-8 weeks old) were used to induce RIR injury. Retinal flat-mount immunofluorescence was performed to assess RGC survival rate. Electroretinogram and optomotor response were conducted to evaluate the retinal electrophysiologic function and visual acuity. Autophagy level was reflected by Western blot and transmission electron microscope images. M6A modification levels were determined via m6A dot blot. Methyltransferase-like protein 3 (Mettl3) and forkhead box O1 (FoxO1) protein expressions were tested by Western blot. Methylated RNA immunoprecipitation-quantitative PCR was conducted to examine m6A modification level on FoxO1 mRNA. We also employed 3-methyladenine and rapamycin to regulate autophagy level in RIR injury.

Results

Inhibiting autophagy ameliorated RGC loss and preserved retinal electrophysiologic function in RIR injury. Additionally, a decrease in Mettl3-mediated m6A modification was observed in RIR injury mice. By overexpressing Mettl3 via intravitreal injection of type 2 recombinant adeno-associated virus before RIR injury, we established that Mettl3 overexpression can also ameliorate RGC loss and retinal electrophysiologic dysfunction induced by RIR injury. Furthermore, Mettl3 overexpression inhibited autophagy and reduced FoxO1 expression by upregulating m6A modifications on FoxO1 mRNA.

Conclusions

Mettl3-mediated m6A modification mitigates RGC loss and retinal electrophysiologic dysfunction by inhibiting FoxO1-mediated autophagy in RIR injury.

Relationship Between Changes in the Expression Levels of miR-134 and E2F6 in Mediating Control of Apoptosis in NMDA-Induced Glaucomatous Mice

OBJECTIVE

This investigation was to determine the relationship between changes in the expression levels of miR-134 and the E2F transcription factor 6 (E2F6) in mediating control of apoptosis in N-methyl-D-aspartate (NMDA)-induced glaucomatous mice.

METHODS

Morphological and structural changes were quantitatively analyzed along with apoptosis in the retinal ganglion cell (RGC) layer, internal plexiform layer and RGCs. Glaucomatous RGCs were transfected, and cell viability and apoptosis were examined. The targeting relationship between miR-134 and E2F6 was analyzed, as well as their expression pattern.

RESULTS

Intravitreal injection of NMDA induced a significant reduction in the number of RGCs and thinning of IPL thickness. miR-134 was highly expressed and E2F6 was lowly expressed in glaucoma mice. Suppression of miR-134 or E2F6 overexpression inhibited apoptosis in the glaucomatous RGCs and instead their proliferative activity. MiR-134 targeted inhibition of E2F6 expression. Suppressing rises in E2F6 expression reduced the interfering effect of miR-134 on glaucomatous RGC development.

CONCLUSION

Depleting miR134 expression increases, in turn, E2F6 expression levels and in turn reduces glaucomatous RGC apoptosis expression.

Epigenetics in Glaucoma

Primary open angle glaucoma (POAG) is defined as a "genetically complex trait", where modifying factors act on a genetic predisposing background. For the majority of glaucomatous conditions, DNA variants are not sufficient to explain pathogenesis. Some genes are clearly underlying the more "Mendelian" forms, while a growing number of related polymorphisms in other genes have been identified in recent years. Environmental, dietary, or biological factors are known to influence the development of the condition, but interactions between these factors and the genetic background are poorly understood. Several studies conducted in recent years have led to evidence that epigenetics, that is, changes in the pattern of gene expression without any changes in the DNA sequence, appear to be the missing link. Different epigenetic mechanisms have been proven to lead to glaucomatous changes in the eye, principally DNA methylation, post-translational histone modification, and RNA-associated gene regulation by non-coding RNAs. The aim of this work is to define the principal epigenetic actors in glaucoma pathogenesis. The identification of such mechanisms could potentially lead to new perspectives on therapeutic strategies.

Molecular genetics of inherited normal tension glaucoma

Normal tension glaucoma (NTG) is a complex optic neuropathy characterized by progressive retinal ganglion cell death and glaucomatous visual field loss, despite normal intraocular pressure (IOP). This condition poses a unique clinical challenge due to the absence of elevated IOP, a major risk factor in typical glaucoma. Recent research indicates that up to 21% of NTG patients have a family history of glaucoma, suggesting a genetic predisposition. In this comprehensive review using PubMed studies from January 1990 to December 2023, our focus delves into the genetic basis of autosomal dominant NTG, the only known form of inheritance for glaucoma. Specifically exploring optineurin ( OPTN ), TANK binding kinase 1 ( TBK1 ), methyltransferase-like 23 ( METTL23 ), and myocilin ( MYOC ) mutations, we summarize their clinical manifestations, mutant protein behaviors, relevant animal models, and potential therapeutic pathways. This exploration aims to illuminate the intricate pathogenesis of NTG, unraveling the contribution of these genetic components to its complex development.

Exploring Epigenetic Modifications as Potential Biomarkers and Therapeutic Targets in Glaucoma

Glaucoma, a complex and multifactorial neurodegenerative disorder, is a leading cause of irreversible blindness worldwide. Despite significant advancements in our understanding of its pathogenesis and management, early diagnosis and effective treatment of glaucoma remain major clinical challenges. Epigenetic modifications, encompassing deoxyribonucleic acid (DNA) methylation, histone modifications, and non-coding RNAs, have emerged as critical regulators of gene expression and cellular processes. The aim of this comprehensive review focuses on the emerging field of epigenetics and its role in understanding the complex genetic and molecular mechanisms underlying glaucoma. The review will provide an overview of the pathophysiology of glaucoma, emphasizing the intricacies of intraocular pressure regulation, retinal ganglion cell dysfunction, and optic nerve damage. It explores how epigenetic modifications, such as DNA methylation and histone modifications, can influence gene expression, and how these mechanisms are implicated in glaucomatous neurodegeneration and contribute to glaucoma pathogenesis. The manuscript discusses evidence from both animal models and human studies, providing insights into the epigenetic alterations associated with glaucoma onset and progression. Additionally, it discusses the potential of using epigenetic modifications as diagnostic biomarkers and therapeutic targets for more personalized and targeted glaucoma treatment.