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Reduction of NMNAT2 increases retinal ganglion cell susceptibility to injury A Crossing mice heterozygous for Nmnat2 gene-trap alleles gtBay (predicted 50% silencing) or gtE (predicted 100% silencing) allowed Nmnat2 titration. In these mice, retinal Nmnat2 was depleted to (observed vs. expected based on allele penetrance) 80% (expected 75%; Nmnat2gtBay/+, n = 10), 39% (expected 50%; Nmnat2gtE/+, n = 12), or 10% (expected 25%; Nmnat2gtBay/gtE, n = 12) of normal levels relative to wild type controls (100%; Nmnat2+/+, n = 10). B RGC density was significantly lower in Nmnat2gtBay/gtE retina than in Nmnat2+/+ retina at 3 months without further change at 6 months (indicating a developmental loss). By 12 months of age, Nmnat2gtBay/gtE mice had significantly fewer RGCs than at 3 and 6 months, and this is stable to 22 months (indicating an additional early age-related decline). For Nmnat2+/+: 3 months, n = 6; 6 months, n = 8; 12 months, n = 8; 22 months, n = 8; for Nmnat2gtBay/gtE: 3 months, n = 6; 6 months, n = 8; 12 months, n = 8; 22 months, n = 6. Scale bar = 20 µm. C RGC density was significantly reduced in all Nmnat2 gene-trap allele mouse strains at 3 days ex vivo following RGC axotomy (RBPMS = specific marker of RGCs in the retina) relative to naïve controls (0 days ex vivo), and this was greatest in Nmnat2gtBay/gtE mice supporting a threshold of Nmnat2 loss beyond which RGC susceptibility to injury is increased (Day 0: Nmnat2+/+, n = 6; Nmnat2+/gtBay, n = 6; Nmnat2+/gtE, n = 6; Nmnat2gtBay/gtE, n = 6; Day 3: Nmnat2+/+, n = 8; Nmnat2+/gtBay, n = 6; Nmnat2+/gtE, n = 7; Nmnat2gtBay/gtE, n = 5; scale bar = 20 µm). For B and C, *P < 0.05, **P < 0.01, ***P < 0.001, NS = non-significant (P > 0.05); One-way ANOVA with Tukey’s HSD. For box plots, the centre hinge represents the median with upper and lower hinges representing the first and third quartiles; whiskers represent 1.5 times the interquartile range.
Source publication
Maintenance of NAD pools is critical for neuronal survival. The capacity to maintain NAD pools declines in neurodegenerative disease. We identify that low NMNAT2, the critical neuronal NAD producing enzyme, drives retinal susceptibility to neurodegenerative insults. As proof of concept, gene therapy over-expressing full length human NMNAT2 is neuro...
Citations
... Blocking these pathways weakens EGCG's protective effect, showing its role in promoting RGC survival by inhibiting proapoptotic signals and activating cell survival mechanisms [92]. Additionally, EGCG boosts NAD production by activating NMNAT2, an enzyme critical for neuron survival, which further protects RGCs from degeneration [93,94]. In AMD, EGCG reduces UVB-induced apoptosis in retinal pigment epithelial cells by modulating the JNK and ERK pathways [82]. ...
This review highlights the therapeutic potential of epigallocatechin gallate (EGCG) and forskolin in managing retinal diseases, with a focus on glaucoma, age-related macular degeneration (AMD), and diabetic retinopathy. EGCG, a potent polyphenol from green tea, exhibits significant antioxidant, anti-inflammatory, and neuroprotective effects, making it a promising candidate for reducing oxidative stress and inflammation in ocular tissues. Forskolin, a diterpene from Coleus forskohlii, increases cyclic AMP (cAMP) levels, which helps lower intraocular pressure (IOP) and provides neuroprotection. Both compounds target critical pathways involved in retinal disease progression, including oxidative stress, mitochondrial dysfunction, and inflammation, offering complementary therapeutic benefits. This review consolidates preclinical and clinical studies, highlighting the potential of EGCG and forskolin as adjunctive or alternative treatments for retinal diseases. Future research should explore the synergistic effects of these compounds, particularly in combination therapies aimed at addressing multiple pathogenic mechanisms in retinal health.
... Decreased NMNAT2 mRNA levels have been reported in the cortex of several neurodegenerative diseases, such as Alzheimer's disease (AD), Parkinson's disease (PD), and Huntington's disease (HD) [21,11,[22][23][24]. NMNAT2 transcription was also reduced by Wallerian-like axonal degeneration [25] and glaucoma [26,27], and over-expression of full-length human NMNAT2 exerts neuroprotective effects against glaucoma [28]. Deleting NMNAT2 in cortical neurons results in axonopathy and severe neurodegenerative-like phenotypes [18]. ...
... Low NMNAT2 increases neuronal susceptibility to neurodegenerative insults [67,68]. Many studies show that various pathological conditions can result in reduced NMNAT2 mRNA levels, such as nerve injury, proteinopathy, and glaucoma (Table 5), while NMNAT2 overexpression is neuroprotective against these insults [69,27,28]. Thus, NMNAT2 has been considered as a valuable drug target [70,71,28]. ...
... Many studies show that various pathological conditions can result in reduced NMNAT2 mRNA levels, such as nerve injury, proteinopathy, and glaucoma (Table 5), while NMNAT2 overexpression is neuroprotective against these insults [69,27,28]. Thus, NMNAT2 has been considered as a valuable drug target [70,71,28]. To elucidate the transcriptional regulation on NMNAT2 expression, we conducted a 4C-seq experiment to unbiasedly identify genomic regions containing NMNAT2 regulatory (which was not certified by peer review) is the author/funder. ...
Nicotinamide mononucleotide adenylyl transferases 2 (NMNAT2) is a crucial nicotinamide adenine dinucleotide (NAD)-synthesizing enzyme essential for neuronal health. In the Religious Orders Study/Memory and Aging Project (ROSMAP), human brain levels of NMNAT2 mRNA positively correlated with cognitive capabilities in older adults. NMNAT2 mRNA abundance is significantly reduced following various insults or proteinopathies. To elucidate the transcriptional regulation of NMNAT2, we employed circular chromosome conformation capture followed by high-throughput sequencing (4C-seq) to identify potential NMNAT2 enhancer and silencer regions by determining genomic regions interacting with the NMNAT2 promoter in human SH-SY5Y cells. We discovered distinct NMNAT2 promoter interactomes in undifferentiated versus neuron-like SH-SY5Y cells. Utilizing bioinformatics analyses, we identified putative transcriptional factors and NMNAT2-associated genes. Notably, the mRNA levels of many of these genes showed a significant correlation with NMNAT2 mRNA levels in single-nuclei RNA-seq datasets from ~400 human subjects in ROSMAP. Additionally, using CRISPR-Cas9 strategies, we confirmed the requirement of two specific genomic regions within the interactomes and four transcription factors in regulating NMNAT2 transcription. In summary, our study identifies genomic loci containing NMNAT2 regulatory elements and predicts associated genes and transcription factors through computational analyses.
Background
The understanding of disease pathophysiology is pivotal for tailored treatments. The spatial distribution of brain damage relies on the regional antigen expression and the local balance of susceptibility and protective elements.
Objective
As proof-of-concept, we investigated the spatial association between brain damage and gene expression in aquaporin-4-IgG-positive neuromyelitis optica spectrum disorder (AQP4 + NMOSD).
Methods
In this multicenter cross-sectional study, 90 AQP4 + NMOSD patients and 94 age-matched healthy controls underwent a brain magnetic resonance imaging (MRI). We used T2-hyperintense lesion probability maps and white/gray matter atrophy as proxies of inflammation and neurodegeneration. The association with the expression of 266 candidate genes was obtained with the Multimodal Environment for Neuroimaging and Genomic Analysis platform. A functional-enrichment analysis investigated overrepresented biological processes.
Results
In AQP4 + NMOSD, T2-hyperintense lesions were mainly periventricular; atrophy mostly involved the visual pathway. The expression of AQP4 and complement (C4a and C5) was associated with both inflammation and neurodegeneration. Complement activation and regulation/uptake of the insulin-like growth factor were the most relevant enriched pathways. Nonspecific pathways related to DNA synthesis and repair were associated with brain atrophy.
Conclusions
Quantitative MRI and gene expression atlas identified the key elements of AQP4 + NMOSD pathophysiology. This analysis could help in understanding the pathophysiology of antibody-mediated autoimmune disorders.
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.
