RGC-specific ATF4 and/or CHOP deletion rescues glaucomatous neurodegeneration and visual function

From bench to bedside: Developing CRISPR/Cas-based therapy for ocular diseases

Vision-threatening disorders, including both hereditary and multifactorial ocular diseases, necessitate innovative therapeutic approaches. The Clustered Regularly Interspaced Short Palindromic Repeats (CRISPR)/CRISPR-associated protein (Cas) has emerged as a promising tool for treating ocular diseases through gene editing and expression regulation. This system has contributed to the development of representative disease models, including animal models, organoids, and cell lines, thereby facilitating investigations into the pathogenesis of disease-related genes. Besides, therapeutic applications of CRISPR/Cas have been extensively explored in preclinical in vitro and in vivo studies, targeting various ocular conditions, such as retinitis pigmentosa, Leber congenital amaurosis, Usher syndrome, fundus neovascular diseases, glaucoma, and corneal diseases. Recent advancements have demonstrated the technology's potential to restore cellular homeostasis and alleviate disease phenotypes, thereby prompting a variety of clinical trials. To date, active trials include treatments for primary open angle glaucoma with MYOC mutations, refractory herpetic viral keratitis, CEP290-associated inherited retinal degenerations, neovascular age-related macular degeneration, and retinitis pigmentosa with RHO mutations. However, challenges remain, primarily concerning off-target effects, immunogenicity, ethical considerations, and regulatory particularity. To reach higher safety and efficiency before truly transitioning from bench to bedside, future research should concentrate on improving the specificity and efficacy of Cas proteins, optimizing delivery vectors, and broadening the applicability of therapeutic targets. This review summarizes the application strategies and delivery methods of CRISPR/Cas, discusses recent progress in CRISPR/Cas-based disease models and therapies, and provides an overview of the landscape of clinical trials. Current obstacles and future directions regarding the bench-to-bedside transition are also discussed.

Unlocking NAC's potential ATF4 and m6A dynamics in rescuing cognitive impairments in PTSD

In this study, we investigated the therapeutic potential of N-acetylcysteine (NAC) in a mouse model of post-traumatic stress disorder (PTSD) induced by a single prolonged stress (SPS) protocol. Our findings demonstrate that NAC treatment significantly improved cognitive function and mitigated hippocampal neuronal apoptosis in PTSD model mice. These positive effects were accompanied by a reduction in m6A methylation levels and activating transcription factor 4 (ATF4) expression. Silencing ATF4 further attenuated hippocampal neuronal apoptosis and cognitive dysfunction, while ATF4 overexpression partially reversed the beneficial effects of NAC. It suggests that NAC's efficacy in PTSD may be mediated by its regulation of ATF4 expression and m6A methylation levels. Overall, our study provides valuable insights into the potential mechanism of action for NAC in PTSD treatment, offering promising avenues for future therapeutic strategies.

Endoplasmic reticulum stress-related deficits in calcium clearance promote neuronal dysfunction that is prevented by SERCA2 gene augmentation

Disruption of calcium (Ca2+) homeostasis in neurons is a hallmark of neurodegenerative diseases. Here, we investigate the mechanisms leading to Ca2+ dysregulation and ask whether altered Ca2+ dynamics impinge on neuronal stress and circuit dysfunction. Using two-photon microscopy, we show that ocular hypertension, a major risk factor in glaucoma, and optic nerve crush injury disrupt the capacity of retinal neurons to clear cytosolic Ca2+ leading to impaired light-evoked responses. Gene- and protein expression analysis reveal the loss of the sarco-endoplasmic reticulum (ER) Ca2+-ATPase2 pump (SERCA2/ATP2A2) in injured retinal neurons from mice and patients with primary open-angle glaucoma. Pharmacological activation or neuron-specific gene delivery of SERCA2 is sufficient to rescue single-cell Ca2+ dynamics and promote robust survival of damaged neurons. Furthermore, SERCA2 gene supplementation reduces ER stress, reestablishes circuit balance, and restores visual behaviors. Our findings reveal that enhancing the Ca2+ clearance capacity of vulnerable neurons alleviates organelle stress and promotes neurorecovery.

Differential enrichment of retinal ganglion cells underlies proposed core neurodegenerative transcription programs

In a published Correction 1 , a revised analysis updated two "core transcription programs" proposed to underlie axon injury-induced retinal ganglion cell (RGC) neurodegeneration. Though extensive, the Correction purported to leave the two principal conclusions of its parent study 2 unaltered. The first of those findings was that a core program mediated by the Activating Transcription Factor-4 (ATF4) and its likely heterodimeric partner does not include numerous canonical ATF4 target genes stimulated by RGC axon injury. The second was that the Activating Transcription Factor-3 (ATF3) and C/EBP Homologous Protein (CHOP) function with unprecedented coordination in a parallel program regulating innate immunity pathways. Here those unexpected findings are revealed to instead reflect insufficient knockout coupled with differences in RGC enrichment across conditions. This analysis expands on the published Correction's redefinition of the purported transcription programs to raise foundational questions about the proposed functions and relationships of these transcription factors in neurodegeneration.

Utilizing extracellular vesicles as a drug delivery system in glaucoma and RGC degeneration

Retinal diseases are the leading cause of blindness, resulting in irreversible degeneration and death of retinal neurons. One such cell type, the retinal ganglion cell (RGC), is responsible for connecting the retina to the rest of the brain through its axons that make up the optic nerve and is the primary cell lost in glaucoma and traumatic optic neuropathy. To date, different therapeutic strategies have been investigated to protect RGCs from death and preserve vision, yet currently available strategies are restricted to treating neuron loss by reducing intraocular pressure. A major barrier identified by these studies is drug delivery to RGCs, which is in large part due to drug stability, short duration time at target, low delivery efficiency, and undesired off-target effects. Therefore, a delivery system to deal with these problems is needed to ensure maximum benefit from the candidate therapeutic material. Extracellular vesicles (EV), nanocarriers released by all cells, are lipid membranes encapsulating RNAs, proteins, and lipids. As they naturally shuttle these encapsulated compounds between cells for communicative purposes, they may be exploitable and offer opportunities to overcome hurdles in retinal drug delivery, including drug stability, drug molecular weight, barriers in the retina, and drug adverse effects. Here, we summarize the potential of an EV drug delivery system, discussing their superiorities and potential application to target RGCs.

Biologically Driven In Vivo Occlusion Design Provides a Reliable Experimental Glaucoma Model

Fluid flow transport through the trabecular meshwork tissues is a major regulator of intraocular pressure (IOP) modulation in healthy and glaucomatous individuals. Microbead occlusion models of ocular hypertension regulate aqueous humor drainage to induce high IOP to allow for in vivo study of pressure-related glaucomatous pathology. However, the reliability and application of current injectable microbeads are hindered by inadequate design of the beads-tissue interfaces to maintain a stable IOP elevation over the long term. Considering the graded, porous architecture and fluid transport of the trabecular meshwork, we developed a tailored, injectable "viscobeads" technique, which induced a sustained elevation of IOP for at least 8 weeks. These composite viscobeads contain a non-degradable polystyrene (PS) core for structural support and a biodegradable polylactic-co-glycolic acid (PLGA) viscoelastic surface. This approach enhances the obstruction of aqueous humor drainage through heterogeneous sizes of trabecular meshwork fenestrations and reliably modulates the magnitude and duration of ocular hypertension. In a mouse model, a single viscobeads injection resulted in sustained IOP elevation (average 21.4±1.39 mm Hg), leading to a 34% retinal ganglion cell (RGC) loss by 56 days. In an earlier stage of glaucoma progression, we conducted non-invasive electroretinography (ERG) recording and revealed glaucomatous progression by analyzing high-frequency oscillatory potentials. To further explore the application of the viscobeads glaucoma models, we assayed a series of genes through adeno-associated virus (AAV)-mediated screening in mice and assessed the impact of genetic manipulation on RGC survivals. CRISPR mediated disruption of the genes, PTEN, ATF3 and CHOP enhanced RGC survival while LIN 28 disruption negatively impacted RGC survival. This biologically driven viscobeads design provides an accessible approach to investigate chronic intraocular hypertension and glaucoma-like neurodegeneration and ultimately tenders the opportunity to evaluate genetic and pharmacological therapeutics.

A beneficial adaptive role for CHOP in driving cell fate selection during ER stress

Cellular stresses elicit signaling cascades that are capable of either mitigating the inciting dysfunction or initiating cell death. During endoplasmic reticulum (ER) stress, the transcription factor CHOP is widely recognized to promote cell death. However, it is not clear whether CHOP also has a beneficial role during adaptation. Here, we combine a new, versatile, genetically modified Chop allele with single cell analysis and with stresses of physiological intensity, to rigorously examine the contribution of CHOP to cell fate. Paradoxically, we find that CHOP promotes death in some cells, but proliferation-and hence recovery-in others. Strikingly, this function of CHOP confers to cells a stress-specific competitive growth advantage. The dynamics of CHOP expression and UPR activation at the single cell level suggest that CHOP maximizes UPR activation, which in turn favors stress resolution, subsequent UPR deactivation, and proliferation. Taken together, these findings suggest that CHOP's function can be better described as a "stress test" that drives cells into either of two mutually exclusive fates-adaptation or death-during stresses of physiological intensity.