Corneal Regeneration Using Gene Therapy Approaches.

One of the most remarkable advancements in medical treatments of corneal diseases in recent decades has been corneal transplantation. However, corneal transplants, including lamellar strategies, have their own set of challenges, such as graft rejection, delayed graft failure, shortage of donor corneas, repeated treatments, and post-surgical complications. Corneal defects and diseases are one of the leading causes of blindness globally; therefore, there is a need for gene-based interventions that may mitigate some of these challenges and help reduce the burden of blindness. Corneas being immune-advantaged, uniquely avascular, and transparent is ideal for gene therapy approaches. Well-established corneal surgical techniques as well as their ease of accessibility for examination and manipulation makes corneas suitable for in vivo and ex vivo gene therapy. In this review, we focus on the most recent advances in the area of corneal regeneration using gene therapy and on the strategies involved in the development of such therapies. We also discuss the challenges and potential of gene therapy for the treatment of corneal diseases. Additionally, we discuss the translational aspects of gene therapy, including different types of vectors, particularly focusing on recombinant AAV that may help advance targeted therapeutics for corneal defects and diseases.

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.

CRISPR/Cas9 directed to the Ube3a antisense transcript improves Angelman syndrome phenotype in mice.

Gene editing holds the potential to correct mutations and cure devastating genetic disorders. The technology has not yet proven efficacious for therapeutic use in CNS diseases with ubiquitous neuronal defects. Angelman syndrome (AS), a severe neurodevelopmental disorder, is caused by a lack of maternal expression of the UBE3A gene. Because of genomic imprinting, only neurons are affected. One therapeutic approach focuses on the intact paternal UBE3A copy in patients with AS that is silenced by an antisense transcript (UBE3A-ATS). We show here that gene editing of Ube3a-ATS in the mouse brain resulted in the formation of base pair insertions/deletions (indels) in neurons and the subsequent unsilencing of the paternal Ube3a allele in neurons, which partially corrected the behavioral phenotype of a murine AS model. This study provides compelling evidence to further investigate editing of the homologous region of the human UBE3A-ATS because this may provide a lasting therapeutic effect for patients with AS.

Disruption of Tip60 HAT mediated neural histone acetylation homeostasis is an early common event in neurodegenerative diseases.

Epigenetic dysregulation is a common mechanism shared by molecularly and clinically heterogenous neurodegenerative diseases (NDs). Histone acetylation homeostasis, maintained by the antagonistic activity of histone acetyltransferases (HATs) and histone deacetylases (HDACs), is necessary for appropriate gene expression and neuronal function. Disruption of neural acetylation homeostasis has been implicated in multiple types of NDs including Alzheimer's disease (AD), yet mechanisms underlying alterations remain unclear. We show that like AD, disruption of Tip60 HAT/HDAC2 balance with concomitant epigenetic repression of common Tip60 target neuroplasticity genes occurs early in multiple types of Drosophila ND models such as Parkinson's Disease (PD), Huntington's Disease (HD) and Amyotrophic Lateral Sclerosis (ALS). Repressed neuroplasticity genes show reduced enrichment of Tip60 and epigentic acetylation signatures at all gene loci examined with certain genes showing inappropriate HDAC2 repressor enrichment. Functional neuronal consequences for these disease conditions are reminiscent of human pathology and include locomotion, synapse morphology, and short-term memory deficits. Increasing Tip60 HAT levels specifically in the mushroom body learning and memory center in the Drosophila brain protects against locomotion and short-term memory function deficits in multiple NDs. Together, our results support a model by which Tip60 protects against neurological impairments in different NDs via similar modes of action.

Deletion of Glycogen Synthase Kinase-3ß in D2 Receptor-Positive Neurons Ameliorates Cognitive Impairment via NMDA Receptor-Dependent Synaptic Plasticity.

BACKGROUND: Cortical dopaminergic systems are critically involved in prefrontal cortex (PFC) functions, especially in working memory and neurodevelopmental disorders such as schizophrenia. GSK-3ß (glycogen synthase kinase-3ß) is highly associated with cAMP (cyclic adenosine monophosphate)-independent dopamine D2 receptor (D2R)-mediated signaling to affect dopamine-dependent behaviors. However, the mechanisms underlying the GSK-3ß modulation of cognitive function via D2Rs remains unclear. METHODS: This study explored how conditional cell-type-specific ablation of GSK-3ß in D2R+ neurons (D2R-GSK-3ß-/-) in the brain affects synaptic function in the medial PFC (mPFC). Both male and female (postnatal days 60-90) mice, including 140 D2R, 24 D1R, and 38 DISC1 mice, were used. RESULTS: This study found that NMDA receptor (NMDAR) function was significantly increased in layer V pyramidal neurons in mPFC of D2R-GSK-3ß-/- mice, along with increased dopamine modulation of NMDAR-mediated current. Consistently, NR2A and NR2B protein levels were elevated in mPFC of D2R-GSK-3ß-/- mice. This change was accompanied by a significant increase in enrichment of activator histone mark H3K27ac at the promoters of both Grin2a and Grin2b genes. In addition, altered short- and long-term synaptic plasticity, along with an increased spine density in layer V pyramidal neurons, were detected in D2R-GSK-3ß-/- mice. Indeed, D2R-GSK-3ß-/- mice also exhibited a resistance of working memory impairment induced by injection of NMDAR antagonist MK-801. Notably, either inhibiting GSK-3ß or disrupting the D2R-DISC1 complex was able to reverse the mutant DISC1-induced decrease of NMDAR-mediated currents in the mPFC. CONCLUSIONS: This study demonstrates that GSK-3ß modulates cognition via D2R-DISC1 interaction and epigenetic regulation of NMDAR expression and function.

Restoring Tip60 HAT/HDAC2 Balance in the Neurodegenerative Brain Relieves Epigenetic Transcriptional Repression and Reinstates Cognition.

Cognitive decline is a debilitating hallmark during preclinical stages of Alzheimer's disease (AD), yet the causes remain unclear. Because histone acetylation homeostasis is critical for mediating epigenetic gene control throughout neuronal development, we postulated that its misregulation contributes to cognitive impairment preceding AD pathology. Here, we show that disruption of Tip60 histone acetlytransferase (HAT)/histone deacetylase 2 (HDAC2) homeostasis occurs early in the brain of an AD-associated amyloid precursor protein (APP) Drosophila model and triggers epigenetic repression of neuroplasticity genes well before Aß plaques form in male and female larvae. Repressed genes display enhanced HDAC2 binding and reduced Tip60 and histone acetylation enrichment. Increasing Tip60 in the AD-associated APP brain restores Tip60 HAT/HDAC2 balance by decreasing HDAC2 levels, reverses neuroepigenetic alterations to activate synaptic plasticity genes, and reinstates brain morphology and cognition. Such Drosophila neuroplasticity gene epigenetic signatures are conserved in male and female mouse hippocampus and their expression and Tip60 function is compromised in hippocampus from AD patients. We suggest that Tip60 HAT/HDAC2-mediated epigenetic gene disruption is a critical initial step in AD that is reversed by restoring Tip60 in the brain.SIGNIFICANCE STATEMENT Mild cognitive impairment is a debilitating hallmark during preclinical stages of Alzheimer's disease (AD), yet its causes remain unclear. Although recent findings support elevated histone deacetylase 2 (HDAC2) as a cause for epigenetic repression of synaptic genes that contribute to cognitive deficits, whether alterations in histone acetlytransferase (HAT) levels that counterbalance HDAC2 repressor action occur and the identity of these HATs remain unknown. We demonstrate that disruption of Tip60 HAT/HDAC2 homeostasis occurs early in the AD Drosophila brain and triggers epigenetic repression of neuroplasticity genes before Aß plaques form. Increasing Tip60 in the AD brain restores Tip60 HAT/HDAC2 balance, reverses neuroepigenetic alterations to activate synaptic genes, and reinstates brain morphology and cognition. Our data suggest that disruption of the Tip60 HAT/HDAC2 balance is a critical initial step in AD.

Tip60 HAT Action Mediates Environmental Enrichment Induced Cognitive Restoration.

Environmental enrichment (EE) conditions have beneficial effects for reinstating cognitive ability in neuropathological disorders like Alzheimer's disease (AD). While EE benefits involve epigenetic gene control mechanisms that comprise histone acetylation, the histone acetyltransferases (HATs) involved remain largely unknown. Here, we examine a role for Tip60 HAT action in mediating activity- dependent beneficial neuroadaptations to EE using the Drosophila CNS mushroom body (MB) as a well-characterized cognition model. We show that flies raised under EE conditions display enhanced MB axonal outgrowth, synaptic marker protein production, histone acetylation induction and transcriptional activation of cognition linked genes when compared to their genotypically identical siblings raised under isolated conditions. Further, these beneficial changes are impaired in both Tip60 HAT mutant flies and APP neurodegenerative flies. While EE conditions provide some beneficial neuroadaptive changes in the APP neurodegenerative fly MB, such positive changes are significantly enhanced by increasing MB Tip60 HAT levels. Our results implicate Tip60 as a critical mediator of EE-induced benefits, and provide broad insights into synergistic behavioral and epigenetic based therapeutic approaches for treatment of cognitive disorder.

Epigenetic control of learning and memory in Drosophila by Tip60 HAT action.

Disruption of epigenetic gene control mechanisms in the brain causes significant cognitive impairment that is a debilitating hallmark of most neurodegenerative disorders, including Alzheimer's disease (AD). Histone acetylation is one of the best characterized of these epigenetic mechanisms that is critical for regulating learning- and memory- associated gene expression profiles, yet the specific histone acetyltransferases (HATs) that mediate these effects have yet to be fully characterized. Here, we investigate an epigenetic role for the HAT Tip60 in learning and memory formation using the Drosophila CNS mushroom body (MB) as a well-characterized cognition model. We show that Tip60 is endogenously expressed in the Kenyon cells, the intrinsic neurons of the MB, and in the MB axonal lobes. Targeted loss of Tip60 HAT activity in the MB causes thinner and shorter axonal lobes while increasing Tip60 HAT levels cause no morphological defects. Functional consequences of both loss and gain of Tip60 HAT levels in the MB are evidenced by defects in immediate-recall memory. Our ChIP-Seq analysis reveals that Tip60 target genes are enriched for functions in cognitive processes, and, accordingly, key genes representing these pathways are misregulated in the Tip60 HAT mutant fly brain. Remarkably, we find that both learning and immediate-recall memory deficits that occur under AD-associated, amyloid precursor protein (APP)-induced neurodegenerative conditions can be effectively rescued by increasing Tip60 HAT levels specifically in the MB. Together, our findings uncover an epigenetic transcriptional regulatory role for Tip60 in cognitive function and highlight the potential of HAT activators as a therapeutic option for neurodegenerative disorders.