Cell death caused by the synergistic effects of zinc and dopamine is mediated by a stress sensor gene Gadd45b - implication in the pathogenesis of Parkinson's disease

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.

PCBP-1 Regulates the Transcription and Alternative Splicing of Inflammation and Ubiquitination-Related Genes in PC12 Cell

PCBP-1, a multifunctional RNA binding protein, is expressed in various human cell/tissue types and involved in post-transcriptional gene regulation. PCBP-1 has important roles in cellular Iron homeostasis, mitochondrial stability, and other cellular activities involved in the pathophysiological process of neurodegenerative diseases, such as amyotrophic lateral sclerosis (ALS) and Huntington's disease (HD). However, it remains enigmatic whether PCPB-1 is associated with the pathogenesis of PD. In this study, we cloned and constitutively overexpressed PCBP-1 in rat PC12 cells (PC12 cell is the common cell line studying neurodegenerative disease include PD). RNA-seq was performed to analyze PCBP-1-regulated differentially expressed genes (DEGs) and alternative splicing events (ASEs) between control and PCBP1-overexpressed cells. GO and KEGG pathway analyses were performed to identify functional DEGs and alternatively spliced genes. Consequently, we validated PCBP-1-regulated genes using RT-qPCR. Finally, we downloaded CLIP-seq data from GEO (GSE84700) to analyze the mechanisms of PCBP-1's regulation of gene expression and ASEs by revealing the binding profile of PCBP-1 on its target pre-mRNAs. Overexpression of PCBP-1 partially regulated the ASE and expression of genes enriched in neuroinflammation and protein ubiquitination, which were also associated with PD pathogenesis. Moreover, RT-qPCR assay verified the PCBP-1-modulated expression of neuroinflammatory genes, like LCN-2, and alternative splicing (AS) of ubiquitination-related gene WWP-2. Finally, CLIP-seq data analysis indicated that the first UC motif was the critical site for PCBP-1 binding to its targets. In this study, we provided evidence that PCBP-1 could regulate the expression of LCN-2 gene expression associated with neuroinflammation and AS of WWP-2 in relation to protein ubiquitination. These findings thus provided novel insights into the potential application of PCBP-1 as the disease pathophysiological or therapeutic target for neurodegenerative disease.

High-Affinity Ratiometric Fluorescence Probe Based on 6-Amino-2,2'-Bipyridine Scaffold for Endogenous Zn2+ and Its Application to Living Cells

Zinc is an essential trace element involved in many biological activities; however, its functions are not fully understood. To elucidate the role of endogenous labile Zn²⁺, we developed a novel ratiometric fluorescence probe, 5-(4-methoxyphenyl)-4-(methylsulfanyl)-[2,2′-bipyridin]-6-amine (6 (rBpyZ)) based on the 6-amino-2,2′-bipyridine scaffold, which acts as both the chelating agent for Zn²⁺ and the fluorescent moiety. The methoxy group acted as an electron donor, enabling the intramolecular charge transfer state of 6 (rBpyZ), and a ratiometric fluorescence response consisting of a decrease at the emission wavelength of 438 nm and a corresponding increase at the emission wavelength of 465 nm was observed. The ratiometric probe 6 (rBpyZ) exhibited a nanomolar-level dissociation constant (K_d = 0.77 nM), a large Stokes shift (139 nm), and an excellent detection limit (0.10 nM) under physiological conditions. Moreover, fluorescence imaging using A549 human lung adenocarcinoma cells revealed that 6 (rBpyZ) had good cell membrane permeability and could clearly visualize endogenous labile Zn²⁺. These results suggest that the ratiometric fluorescence probe 6 (rBpyZ) has considerable potential as a valuable tool for understanding the role of Zn²⁺ in living systems.

Is Cadmium Toxicity Tissue-Specific? Toxicogenomics Studies Reveal Common and Specific Pathways in Pulmonary, Hepatic, and Neuronal Cell Models

Several harmful modifications in different tissues-organs, leading to relevant diseases (e.g., liver and lung diseases, neurodegeneration) are reported after exposure to cadmium (Cd), a wide environmental contaminant. This arises the question whether any common molecular signatures and/or Cd-induced modifications might represent the building block in initiating or contributing to address the cells towards different pathological conditions. To unravel possible mechanisms of Cd tissue-specificity, we have analyzed transcriptomics data from cell models representative of three major Cd targets: pulmonary (A549), hepatic (HepG2), and neuronal (SH-SY-5Y) cells. Further, we compared common features to identify any non-specific molecular signatures. The functional analysis of dysregulated genes (gene ontology and KEGG) shows GO terms related to metabolic processes significantly enriched only in HepG2 cells. GO terms in common in the three cell models are related to metal ions stress response and detoxification processes. Results from KEGG analysis show that only one specific pathway is dysregulated in a significant way in all cell models: the mineral absorption pathway. Our data clearly indicate how the molecular mimicry of Cd and its ability to cause a general metal ions dyshomeostasis represent the initial common feature leading to different molecular signatures and alterations, possibly responsible for different pathological conditions.

Factors Regulating the Activity of LINE1 Retrotransposons

LINE-1 (L1) is a class of autonomous mobile genetic elements that form somatic mosaicisms in various tissues of the organism. The activity of L1 retrotransposons is strictly controlled by many factors in somatic and germ cells at all stages of ontogenesis. Alteration of L1 activity was noted in a number of diseases: in neuropsychiatric and autoimmune diseases, as well as in various forms of cancer. Altered activity of L1 retrotransposons for some pathologies is associated with epigenetic changes and defects in the genes involved in their repression. This review discusses the molecular genetic mechanisms of the retrotransposition and regulation of the activity of L1 elements. The contribution of various factors controlling the expression and distribution of L1 elements in the genome occurs at all stages of the retrotransposition. The regulation of L1 elements at the transcriptional, post-transcriptional and integration into the genome stages is described in detail. Finally, this review also focuses on the evolutionary aspects of L1 accumulation and their interplay with the host regulation system.

Perturbed DNA methylation by Gadd45b induces chromatin disorganization, DNA strand breaks and dopaminergic neuron death

Age is a major risk factor for neurodegenerative diseases like Parkinson's disease, but few studies have explored the contribution of key hallmarks of aging, namely DNA methylation changes and heterochromatin destructuration, in the neurodegenerative process. Here, we investigated the consequences of viral overexpression of Gadd45b, a multifactorial protein involved in DNA demethylation, in the mouse midbrain. Gadd45b overexpression induced global and stable changes in DNA methylation, particularly in introns of genes related to neuronal functions, as well as on LINE-1 transposable elements. This was paralleled by disorganized heterochromatin, increased DNA damage, and vulnerability to oxidative stress. LINE-1 de-repression, a potential source of DNA damage, preceded Gadd45b-induced neurodegeneration, whereas prolonged Gadd45b expression deregulated expression of genes related to heterochromatin maintenance, DNA methylation, or Parkinson's disease. Our data indicates that aging-related alterations contribute to dopaminergic neuron degeneration with potential implications for Parkinson's disease.

Zinc

Since the discovery of manifest Zn deficiency in 1961, the increasing number of studies demonstrated the association between altered Zn status and multiple diseases. In this chapter, we provide a review of the most recent advances on the role of Zn in health and disease (2010-20), with a special focus on the role of Zn in neurodegenerative and neurodevelopmental disorders, diabetes and obesity, male and female reproduction, as well as COVID-19. In parallel with the revealed tight association between ASD risk and severity and Zn status, the particular mechanisms linking Zn2+ and ASD pathogenesis like modulation of synaptic plasticity through ProSAP/Shank scaffold, neurotransmitter metabolism, and gut microbiota, have been elucidated. The increasing body of data indicate the potential involvement of Zn2+ metabolism in neurodegeneration. Systemic Zn levels in Alzheimer's and Parkinson's disease were found to be reduced, whereas its sequestration in brain may result in modulation of amyloid β and α-synuclein processing with subsequent toxic effects. Zn2+ was shown to possess adipotropic effects through the role of zinc transporters, zinc finger proteins, and Zn-α2-glycoprotein in adipose tissue physiology, underlying its particular role in pathogenesis of obesity and diabetes mellitus type 2. Recent findings also contribute to further understanding of the role of Zn2+ in spermatogenesis and sperm functioning, as well as oocyte development and fertilization. Finally, Zn2+ was shown to be the potential adjuvant therapy in management of novel coronavirus infection (COVID-19), underlining the perspectives of zinc in management of old and new threats.

NEUROTOXICITY OF METAL MIXTURES

Environmental exposures and/or alterations in the homeostasis of essential transition metals (ETM), such as Fe, Cu, Zn or Mn, are known to contribute to neurodegenerative diseases (ND), such as Alzheimer's Disease (AD) and Parkinson's Disease (PD). Aberrant ETM homeostasis leads to altered distributions, as significant amounts may accumulate in specific brain areas, while causing metal deficiency in others. The disruption of processes reliant on the interplay between these ETM, may lead to loss of metal balance and the ensuing neurotoxicity via shared mechanisms, such as the induction of oxidative stress (OS). Both ETM imbalance and OS may play a role, via complex positive loop processes, in primary neuropathological signatures of AD, such as the accumulation of amyloid plaques and neurofibrillary tangles (NTF), and in PD, α-Syn aggregation and loss of dopamine(DA)rgic neurons. The association between ETM imbalance and ND is rarely approached under the view that metals such as Fe, Cu, Zn and Mn, can act as dangerous endogenous neurotoxic mixtures when their control mechanisms became disrupted. In fact, their presence as mixtures implies intricacies, which should be kept in mind when developing therapies for complex disorders of metal dyshomeostasis, which commonly occur in ND.

GADD45B Facilitates Metastasis of Ovarian Cancer Through Epithelial-Mesenchymal Transition

Background

Growth arrest and DNA-damage-inducible 45 beta (GADD45B) is overexpressed and is associated with poor clinical outcomes in many human cancers, but the clinical implication of GADD45B in epithelial ovarian cancer (EOC) remains unclear.

Methods

Bioinformatics analysis of The Cancer Genome Atlas (TCGA) and gene expression omnibus (GEO) cohorts was used to illustrate the relationship between GADD45B expression and metastasis, as well as the survival time of EOC. GADD45B was downregulated by siRNAs in EOC cells, and migration ability was determined by a transwell assay and wound-healing assay. Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway enrichment analysis and gene set enrichment analysis (GSEA) were conducted to discover the downstream pathway of GADD45B. The regulation of epithelial–mesenchymal transition (EMT) by GADD45B was verified by Western blotting and qRT-PCR. Finally, the correlation of GADD45B expression with EOC metastasis was investigated in EOC tissues by immunohistochemistry.

Results

Overexpression of GADD45B indicates shorter overall survival time and progression-free survival time, and it is an independent risk factor for poor survival in EOC patients. Elevated GADD45B is related to venous invasion, lymphatic invasion and peritoneal carcinomatosis. Downregulation of GADD45B decreases the migration of ES2 and SKOV3 cells. Further KEGG enrichment analysis and GSEA revealed that EMT may be the downstream pathway of GADD45B. In addition, reduced GADD45B increases the expression of E-cadherin and decreases that of N-cadherin and vimentin. Finally, immunohistochemical analysis of GADD45B expression revealed that the expression of GADD45B in omental metastatic tissues was higher than that in matched primary ovarian cancer tissues. These results suggest that elevated GADD45B promotes the motility of ovarian cancer cells through EMT and is associated with EOC metastasis.

Conclusion

GADD45B can promote the motility of ovarian cancer cells through EMT, is associated with EOC metastasis, and may be a new biomarker of metastasis and prognosis.

New insight into Parkinson's disease pathogenesis from reactive oxygen species-mediated extracellular Zn2+ influx

BACKGROUND

Parkinson's disease (PD) is the common neurodegenerative disorder in the elderly characterized by motor symptoms such as tremors, which is caused by selective loss of nigral dopaminergic neurons. Oxidative stress induced by the auto-oxidation of dopamine has been implicated as a key cause of the selective loss of dopaminergic neurons.

METHODS

To understand the selective loss of nigral dopaminergic neurons, the PD pathogenesis is reviewed focused on paraquat (PQ) and 6-hydroxydopamine (6-OHDA)-induced PD in rats.

RESULTS

Reactive oxygen species (ROS), which are produced by PQ and 6-OHDA, are retrogradely transported to presynaptic glutamatergic neuron terminals. ROS activate presynaptic transient receptor potential melastatin 2 (TRPM2) cation channels and induce extracellular glutamate accumulation in the substantia nigra pars compacta (SNpc), followed by age-related intracellular Zn2+ dysregulation. Loss of nigral dopaminergic neurons is accelerated by age-related intracellular Zn2+ dysregulation in the SNpc of rat PD models. The intracellular Zn2+ dysregulation in nigral dopaminergic neurons is linked with the rapid influx of extracellular Zn2+ via postsynaptic AMPA receptor activation, suggesting that PQ- and 6-OHDA-induced pathogenesis is linked with age-related intracellular Zn2+ dysregulation in the SNpc. Postsynaptic TRPM2 channels may be also involved in intracellular Zn2+ dysregulation in the SNpc.

CONCLUSION

A novel mechanism of nigral dopaminergic degeneration, in which ROS induce rapid intracellular Zn2+ dysregulation, figures out the PD pathogenesis induced by PQ and 6-OHDA in rats. This review deals with new insight into PD pathogenesis from ROS-mediated extracellular Zn2+ influx and its proposed defense strategy.

Synaptic zinc contributes to motor and cognitive deficits in 6-hydroxydopamine mouse models of Parkinson's disease

Hyperactivity of glutamatergic corticostrial pathways is recognized as a key pathophysiological mechanism contributing to development of PD symptoms and dopaminergic neurotoxicity. Subset of corticostriatal projection neurons uses Zn²⁺ as a co-transmitter alongside glutamate, but the role of synaptically released Zn²⁺ in PD remains unexplored. We used genetically modified mice and pharmacological tools in combination with 6-hydroxydopamine (6-OHDA) lesion models of PD to investigate the contribution of synaptic zinc to disease associated behavioral deficits and neurodegeneration. Vesicular zinc transporter-3 (ZnT3) knockout mice lacking releasable Zn²⁺ were more resistant to locomotor deficit and memory impairment of nigrostriatal dopamine (DA) denervation compared to wildtype littermates. The loss of striatal dopaminergic fibers was comparable between genotypes, indicating that synaptically released Zn²⁺ contributes to behavioral deficits but not neurotoxic effects of 6-OHDA. To gain further insight into the mechanisms of Zn²⁺ actions, we used the extracellular Zn²⁺ chelator CaEDTA and knock-in mice lacking the high affinity Zn²⁺ inhibition of GluN2A-containing NMDA receptors (GluN2A-NMDARs). Acute chelation of extracellular Zn²⁺ in the striatum restored locomotor deficit of 6-OHDA lesion, confirming that synaptic Zn²⁺ suppresses locomotor behavior. Disruption of the Zn²⁺-GluN2A interaction had, on the other hand, no impact on locomotor deficit or neurotoxic effect of 6-OHDA. Collectively, these findings provide clear evidence for the implication of striatal synaptic Zn²⁺ in the pathophysiology of PD. They unveil that synaptic Zn²⁺ plays predominantly a detrimental role by promoting motor and cognitive deficits caused by nigrostriatal DA denervation, pointing towards new therapeutic interventions.

Zinc Chloride Exposure Inhibits Brain Acetylcholine Levels, Produces Neurotoxic Signatures, and Diminishes Memory and Motor Activities in Adult Zebrafish

In this study, we evaluated the acute (24, 48, 72, and 96 h) and chronic (21 days) adverse effects induced by low doses (0.1, 0.5, 1, and 1.5 mg/L) of zinc chloride (ZnCl₂) exposure in adult zebrafish by using behavioral endpoints like three-dimensional (3D) locomotion, passive avoidance, aggression, circadian rhythm, and predator avoidance tests. Also, brain tissues were dissected and subjected to analysis of multiple parameters related to oxidative stress, antioxidant responses, superoxide dismutase (SOD), neurotoxicity, and neurotransmitters. The results showed that ZnCl₂-exposed fishes displayed decreased locomotor behavior and impaired short-term memory, which caused an Alzheimer’s Disease (AD)-like syndrome. In addition, low concentrations of ZnCl₂ induced amyloid beta (amyloid β) and phosphorylated Tau (p-Tau) protein levels in brains. In addition, significant induction in oxidative stress indices (reactive oxygen species (ROS) and malondialdehyde (MDA)), reduction in antioxidant defense system (glutathione (GSH), GSH peroxidase (GSH-Px) and SOD) and changes in neurotransmitters were observed at low concentrations of ZnCl₂. Neurotoxic effects of ZnCl₂ were observed with significant inhibition of acetylcholine (ACh) activity when the exposure dose was higher than 1 ppm. Furthermore, we found that zinc, metallothionein (MT), and cortisol levels in brain were elevated compared to the control group. A significantly negative correlation was observed between memory and acetylcholinesterase (AChE) activity. In summary, these findings revealed that exposure to ZnCl₂ affected the behavior profile of zebrafish, and induced neurotoxicity which may be associated with damaged brain areas related to memory. Moreover, our ZnCl₂-induced zebrafish model may have potential for AD-associated research in the future.

Extracellular Zn2+ Influx into Nigral Dopaminergic Neurons Plays a Key Role for Pathogenesis of 6-Hydroxydopamine-Induced Parkinson's Disease in Rats

Parkinson's disease (PD) is a progressive neurological disease characterized by a selective loss of nigrostriatal dopaminergic neurons. The exact cause of the neuronal loss remains unclear. Here, we report a unique mechanism of nigrostriatal dopaminergic neurodegeneration, in which extracellular Zn²⁺ influx plays a key role for PD pathogenesis induced with 6-hydroxydopamine (6-OHDA) in rats. 6-OHDA rapidly increased intracellular Zn²⁺ only in the substantia nigra pars compacta (SNpc) of brain slices and this increase was blocked in the presence of CaEDTA, an extracellular Zn²⁺ chelator, and 6-cyano-7-nitroquinoxaline-2,3-dione (CNQX), an α-amino-3-hydroxy-5-methyl-4-isoxazolepropionate (AMPA) receptor antagonist, indicating that 6-OHDA rapidly increases extracellular Zn²⁺ influx via AMPA receptor activation in the SNpc. Extracellular Zn²⁺ concentration was decreased under in vivo SNpc perfusion with 6-OHDA and this decrease was blocked by co-perfusion with CNQX, supporting 6-OHDA-induced Zn²⁺ influx via AMPA receptor activation in the SNpc. Interestingly, both 6-OHDA-induced loss of nigrostriatal dopaminergic neurons and turning behavior to apomorphine were ameliorated by co-injection of intracellular Zn²⁺ chelators, i.e., ZnAF-2DA and N,N,N',N'-Tetrakis(2-pyridylmethyl)ethylenediamine (TPEN). Co-injection of TPEN into the SNpc blocked 6-OHDA-induced increase in intracellular Zn²⁺ but not in intracellular Ca²⁺. These results suggest that the rapid influx of extracellular Zn²⁺ into dopaminergic neurons via AMPA receptor activation in the SNpc induces nigrostriatal dopaminergic neurodegeneration, resulting in 6-OHDA-induced PD in rats.