Regulation of neuronal plasticity by the DNA repair associated Gadd45 proteins

Gadd45A-mediated autophagy regulation and its impact on Alzheimer's disease pathogenesis: Deciphering the molecular Nexus

BACKGROUND

The growth arrest and DNA damage-inducible 45 (Gadd45) gene has been implicated in various central nervous system (CNS) functions, both normal and pathological, including aging, memory, and neurodegenerative diseases. In this study, we examined whether Gadd45A deletion triggers pathways associated with neurodegenerative diseases including Alzheimer's disease (AD).

METHODS

Utilizing transcriptome data from AD-associated hippocampus samples, we identified Gadd45A as a pivotal regulator of autophagy. Comprehensive analyses, including Gene Ontology enrichment and protein-protein interaction network assessments, highlighted Cdkn1A as a significant downstream target of Gadd45A. Experimental validation confirmed Gadd45A's role in modulating Cdkn1A expression and autophagy levels in hippocampal cells. We also examined the effects of autophagy on hippocampal functions and proinflammatory cytokine secretion. Additionally, a murine model was employed to validate the importance of Gadd45A in neuroinflammation and AD pathology.

RESULTS

Our study identified 20 autophagy regulatory factors associated with AD, with Gadd45A emerging as a critical regulator. Experimental findings demonstrated that Gadd45A influences hippocampal cell fate by reducing Cdkn1A expression and suppressing autophagic activity. Comparisons between wild-type (WT) and Gadd45A knockout (Gadd45A-/-) mice revealed that Gadd45A-/- mice exhibited significant cognitive impairments, including deficits in working and spatial memory, increased Tau hyperphosphorylation, and elevated levels of kinases involved in Tau phosphorylation in the hippocampus. Additionally, Gadd45A-/- mice showed significant increases in pro-inflammatory cytokines and decreases autophagy markers in the brain. Neurotrophin levels and dendritic spine length were also reduced in Gadd45A-/- mice, likely contributing to the observed cognitive deficits.

CONCLUSIONS

These findings support the direct involvement of the Gadd45A gene in AD pathogenesis, and enhancing the expression of Gadd45A may represent a promising therapeutic strategy for the treatment of AD.

Deletion of Gadd45a Expression in Mice Leads to Cognitive and Synaptic Impairment Associated with Alzheimer's Disease Hallmarks

Gadd45 genes have been implicated in survival mechanisms, including apoptosis, autophagy, cell cycle arrest, and DNA repair, which are processes related to aging and life span. Here, we analyzed if the deletion of Gadd45a activates pathways involved in neurodegenerative disorders such as Alzheimer's Disease (AD). This study used wild-type (WT) and Gadd45a knockout (Gadd45a-/-) mice to evaluate AD progression. Behavioral tests showed that Gadd45a-/- mice presented lower working and spatial memory, pointing out an apparent cognitive impairment compared with WT animals, accompanied by an increase in Tau hyperphosphorylation and the levels of kinases involved in its phosphorylation in the hippocampus. Moreover, Gadd45a-/- animals significantly increased the brain's pro-inflammatory cytokines and modified autophagy markers. Notably, neurotrophins and the dendritic spine length of the neurons were reduced in Gadd45a-/- mice, which could contribute to the cognitive alterations observed in these animals. Overall, these findings demonstrate that the lack of the Gadd45a gene activates several pathways that exacerbate AD pathology, suggesting that promoting this protein's expression or function might be a promising therapeutic strategy to slow down AD progression.

Advances in the role of the GADD45 family in neurodevelopmental, neurodegenerative, and neuropsychiatric disorders

The growth arrest and DNA damage inducible protein 45 (GADD45) family comprises stress-induced nuclear proteins that interact with DNA demethylases to facilitate DNA demethylation, thereby regulating diverse cellular processes including oxidative stress, DNA damage repair, apoptosis, proliferation, differentiation, inflammation, and neuroplasticity by modulating the expression patterns of specific genes. Widely expressed in the central nervous system, the GADD45 family plays a pivotal role in various neurological disorders, rendering it a potential therapeutic target for central nervous system diseases. This review presented a comprehensive overview of the expression patterns and potential mechanisms of action associated with each member of GADD45 family (GADD45α, GADD45β, and GADD45γ) in neurodevelopmental, neurodegenerative, and neuropsychiatric disorders, while also explored strategies to harness these mechanisms for intervention and treatment. Future research should prioritize the development of effective modulators targeting the GADD45 family for clinical trials aimed at treating central nervous system diseases.

CDK7 and CDK9 inhibition interferes with transcription, translation, and stemness, and induces cytotoxicity in GBM irrespective of temozolomide sensitivity

BACKGROUND

Glioblastoma (GBM) is refractory to current treatment modalities while side effects of treatments result in neurotoxicity and cognitive impairment. Here we test the hypothesis that inhibiting CDK7 or CDK9 would effectively combat GBM with reduced neurotoxicity.

METHODS

We examined the effect of a CDK7 inhibitor, THZ1, and multiple CDK9 inhibitors (SNS032, AZD4573, NVP2, and JSH150) on GBM cell lines, patient-derived temozolomide (TMZ)-resistant and responsive primary tumor cells and glioma stem cells (GSCs). Biochemical changes were assessed by western blotting, immunofluorescence, multispectral imaging, and RT-PCR. In vivo, efficacy was assessed in orthotopic and subcutaneous xenograft models.

RESULTS

CDK7 and CDK9 inhibitors suppressed the viability of TMZ-responsive and resistant GBM cells and GSCs at low nanomolar concentrations, with limited cytotoxic effects in vivo. The inhibitors abrogated RNA Pol II and p70S6K phosphorylation and nascent protein synthesis. Furthermore, the self-renewal of GSCs was significantly reduced with a corresponding reduction in Sox2 and Sox9 levels. Analysis of TCGA data showed increased expression of CDK7, CDK9, SOX2, SOX9, and RPS6KB1 in GBM; supporting this, multispectral imaging of a TMA revealed increased levels of CDK9, Sox2, Sox9, phospho-S6, and phospho-p70S6K in GBM compared to normal brains. RNA-Seq results suggested that inhibitors suppressed tumor-promoting genes while inducing tumor-suppressive genes. Furthermore, the studies conducted on subcutaneous and orthotopic GBM tumor xenograft models showed that administration of CDK9 inhibitors markedly suppressed tumor growth in vivo.

CONCLUSIONS

Our results suggest that CDK7 and CDK9 targeted therapies may be effective against TMZ-sensitive and resistant GBM.

Irradiation and lithium treatment alter the global DNA methylation pattern and gene expression underlying a shift from gliogenesis towards neurogenesis in human neural progenitors

Central nervous system (CNS) tumors account for almost a third of pediatric cancers and are the largest contributor to cancer-related death in children. Cranial radiation therapy (CRT) is, often in combination with chemotherapy and surgery, effective in the treatment of high-grade childhood brain cancers, but it has been associated with late complications in 50-90% of survivors, such as decline in cognition and mood, decreased social competence, and fatigue. A leading hypothesis to explain the decline in cognition, at least partially, is injury to the neural stem and progenitor cells (NSPCs), which leads to apoptosis and altered fate choice, favoring gliogenesis over neurogenesis. Hence, treatments harnessing neurogenesis are of great relevance in this context. Lithium, a well-known mood stabilizer, has neuroprotective and antitumor effects and has been found to reverse irradiation-induced damage in rodents, at least in part by regulating the expression of the glutamate decarboxylase 2 gene (Gad2) via promoter demethylation in rat NSPCs. Additionally, lithium was shown to rescue irradiation-induced cognitive defects in mice. Here, we show that irradiation (IR) alone or in combination with lithium chloride (LiCl) caused major changes in gene expression and global DNA methylation in iPSC-derived human NSPCs (hNSPCs) compared to untreated cells, as well as LiCl-only-treated cells. The pattern of DNA methylation changes after IR-treatment alone was stochastic and observed across many different gene groups, whereas differences in DNA methylation after LiCl-treatment of irradiated cells were more directed to specific promoters of genes, including genes associated with neurogenesis, for example GAD2. Interestingly, IR and IR + LiCl treatment affected the promoter methylation and expression of several genes encoding factors involved in BMP signaling, including the BMP antagonist gremlin1. We propose that lithium in addition to promoting neuronal differentiation, also represses glial differentiation in hNSPCs with DNA methylation regulation being a key mechanism of action.

Induced Coma, Death, and Organ Transplantation: A Physiologic, Genetic, and Theological Perspective

In the clinic, the death certificate is issued if brain electrical activity is no longer detectable. However, recent research has shown that in model organisms and humans, gene activity continues for at least 96 h postmortem. The discovery that many genes are still working up to 48 h after death questions our definition of death and has implications for organ transplants and forensics. If genes can be active up to 48 h after death, is the person technically still alive at that point? We discovered a very interesting parallel between genes that were upregulated in the brain after death and genes upregulated in the brains that were subjected to medically-induced coma, including transcripts involved in neurotransmission, proteasomal degradation, apoptosis, inflammation, and most interestingly, cancer. Since these genes are involved in cellular proliferation, their activation after death could represent the cellular reaction to escape mortality and raises the question of organ viability and genetics used for transplantation after death. One factor limiting the organ availability for transplantation is religious belief. However, more recently, organ donation for the benefit of humans in need has been seen as “posthumous giving of organs and tissues can be a manifestation of love spreading also to the other side of death”.