Caspase-cleaved transactivation response DNA-binding protein 43 in Parkinson's disease and dementia with Lewy bodies

Nuclear pore dysfunction and disease: a complex opportunity

The separation of genetic material from bulk cytoplasm has enabled the evolution of increasingly complex organisms, allowing for the development of sophisticated forms of life. However, this complexity has created new categories of dysfunction, including those related to the movement of material between cellular compartments. In eukaryotic cells, nucleocytoplasmic trafficking is a fundamental biological process, and cumulative disruptions to nuclear integrity and nucleocytoplasmic transport are detrimental to cell survival. This is particularly true in post-mitotic neurons, where nuclear pore injury and errors to nucleocytoplasmic trafficking are strongly associated with neurodegenerative disease. In this review, we summarize the current understanding of nuclear pore biology in physiological and pathological contexts and discuss potential therapeutic approaches for addressing nuclear pore injury and dysfunctional nucleocytoplasmic transport.

Mitochondrial oxidative stress regulates LonP1-TDP-43 pathway and rises mitochondrial damage in carbon tetrachloride-induced liver fibrosis

Carbon tetrachloride (CCl4)-mediated liver damage has been well recognized, but the sources and mechanisms of mitochondrial damage during this progress still remain poorly understood. Accumulating evidence has revealed that LonP1-TDP-43 pathway affect proper mitochondrial integrity and function in neurodegenerative diseases. The current study aims to investigate whether mitochondrial oxidative stress regulate LonP1-TDP-43 pathway and the possible roles of this pathway in CCl4-driven liver fibrosis. We found that TDP-43 interacted with LonP1 in chronic CCl4 exposure-induced hepatic fibrogenesis. Moreover, CCl4 led to deficiency of LonP1 and excessive accumulation of TDP-43 on mitochondria. Particularly, the gene correlation analysis for liver fibrosis patients RNA sequencing (RNA-seq) results (GSE159676) showed an obvious negative correlation between LonP1 and TDP-43. By contrast, MitoQ enhanced the occurrence of mitochondrial unfolded protein response (mtUPR), especially the activation of LonP1 after CCl4 treatment. Importantly, mitochondrial antioxidant also promoted the degradation of TDP-43 and alleviated mitochondrial damage. In addition, our results showed that CCl4 induced the release of mitochondrial DNA (mtDNA) and effectively elevated cGAS-STING-mediated immune response, which can be inhibited by MitoQ. Finally, MitoQ prevented CCl4-induced liver fibrosis. Together, our study revealed that LonP1-TDP-43 pathway mediated by mitochondrial oxidative stress participated in the progress of CCl4-drived liver fibrosis. Therefore, mitigating or reversing mitochondrial damage through targeting LonP1-TDP-43 pathway may serve as a promising therapeutic strategy for CCl4 exposure-induced liver diseases.

Aberrant TDP-43 phosphorylation: a key wind gap from TDP-43 to TDP-43 proteinopathy

TDP-43 proteinopathy is a kind of neurodegenerative diseases related to the TAR DNA-binding protein of 43-kDa molecular weight (TDP-43). The typical neurodegenerative diseases include amyotrophic lateral sclerosis (ALS), frontotemporal lobar degeneration (FTLD), Alzheimer's disease (AD), Parkinson's disease (PD) and so on. As the disease process cannot be blocked or slowed down, these patients have poor quality of life and poor prognosis, and bring a huge burden to the family and society. So far, the specific pathogenesis of TDP-43 proteinopathy is not clear, and there is no effective preventive measure and treatment program for this kind of disease. TDP-43 plays an important role in triggering or promoting the occurrence and progression of TDP-43 proteinopathy. The hyperphosphorylation of TDP-43 is undoubtedly an important factor in triggering or promoting the process of TDP-43 proteinopathy. Hyperphosphorylation of TDP-43 can inhibit the degradation of TDP-43, aggravate the aggregation of TDP-43 protein, increase the wrong localization of TDP-43 in cells, and enhance the cytotoxicity of TDP-43. More and more evidences show that the hyperphosphorylation of TDP-43 plays an important role in the pathogenesis of TDP-43 proteinopathy. Inhibition of TDP-43 hyperphosphorylation may be one of the important strategies for the treatment of TDP-43 proteinopathy. Therefore, this article reviews the role of TDP-43 phosphorylation in TDP-43 proteinopathy and the related mechanisms.

Characterization of the small RNA transcriptomes of cell protrusions and cell bodies of highly metastatic hepatocellular carcinoma cells via RNA sequencing

Increasing evidence suggest that hepatocellular carcinoma (HCC) HCCLM3 cells initially develop pseudopodia when they metastasize, and microRNAs (miRNAs/miRs) and circular RNAs (circRNAs) have been demonstrated to serve important roles in the development, progression and metastasis of cancer. The present study aimed to isolate the cell bodies (CBs) and cell protrusions (CPs) from HCCLM3 cells, and screen the miRNAs and circRNAs associated with HCC infiltration and metastasis in CBs and CPs. The Boyden chamber assay has been confirmed to effectively isolate the CBs and CPs from HCCLM3 cells via observation of microtubule immunofluorescence, DAPI staining and nuclear protein H3 western blotting. Following high-throughput sequencing of the successfully isolated CBs and CPs, 64 pairs of miRNAs, including 23 pairs of upregulated genes and 41 pairs of downregulated genes, and 260 sets of circRNAs, including 127 upregulated genes and 133 downregulated genes, were significantly differentially expressed, using the following criteria: HP/HB ratio, fold change ≥|1.5|, P<0.05). PCR analysis verified that changes in the expression levels of hsa-let-7a-5p, hsa-let-7c-3p, hsa-miR-30c-5p, hsa_circ_0059580, hsa_circ_0067475, hsa_circ_0002100 and hsa_circ_00072309 were consistent with the sequencing results. Gene Ontology and Kyoto Encyclopedia of Genes and Genomes analyses were performed to analyze the functions and roles of the differentially expressed miRNAs and circRNAs. The interaction maps between miRNAs and circRNAs were constructed, and signaling pathway maps were analyzed to determine the molecular mechanism and regulation of the differentially expressed miRNAs and circRNAs. Taken together, the results of the present study suggest that the Boyden chamber assay can be used to effectively isolate the somatic CBs and CPs of HCC, which can be used to screen the miRNAs and circRNAs associated with invasion and metastasis of HCC.

Molecular, functional, and pathological aspects of TDP-43 fragmentation

Transactive response DNA binding protein 43 (TDP-43) is a DNA/RNA binding protein involved in transcriptional regulation and RNA processing. It is linked to sporadic and familial amyotrophic lateral sclerosis and frontotemporal lobar degeneration. TDP-43 is predominantly nuclear, but it translocates to the cytoplasm under pathological conditions. Cytoplasmic accumulation, phosphorylation, ubiquitination and truncation of TDP-43 are the main hallmarks of TDP-43 proteinopathies. Among these processes, the pathways leading to TDP-43 fragmentation remain poorly understood. We review here the molecular and biochemical properties of several TDP-43 fragments, the mechanisms and factors mediating their production, and their potential role in disease progression. We also address the presence of TDP-43 C-terminal fragments in several neurological disorders, including Alzheimer's disease, and highlight their respective implications. Finally, we discuss features of animal models expressing TDP-43 fragments as well as recent therapeutic strategies to approach TDP-43 truncation.

Nuclear Envelope and Nuclear Pore Complexes in Neurodegenerative Diseases-New Perspectives for Therapeutic Interventions

Transport of proteins, transcription factors, and other signaling molecules between the nucleus and cytoplasm is necessary for signal transduction. The study of these transport phenomena is particularly challenging in neurons because of their highly polarized structure. The bidirectional exchange of molecular cargoes across the nuclear envelope (NE) occurs through nuclear pore complexes (NPCs), which are aqueous channels embedded in the nuclear envelope. The NE and NPCs regulate nuclear transport but are also emerging as relevant regulators of chromatin organization and gene expression. The alterations in nuclear transport are regularly identified in affected neurons associated with human neurodegenerative diseases. This review presents insights into the roles played by nuclear transport defects in neurodegenerative disease, focusing primarily on NE proteins and NPCs. The subcellular mislocalization of proteins might be a very desirable means of therapeutic intervention in neurodegenerative disorders.

Caspase-4 mediates cytoplasmic accumulation of TDP-43 in the primate brains

The cytoplasmic accumulation of the nuclear TAR DNA-binding protein 43 (TDP-43) is a pathologic hallmark in amyotrophic lateral sclerosis, frontotemporal lobar degeneration, and other neurological disorders. However, most transgenic TDP-43 rodent models show predominant nuclear distribution of TDP-43 in the brain. By expressing mutant TDP-43 (M337V) in the brains of rhesus monkeys and mice, we verified that mutant TDP-43 is distributed in the cytoplasm of the monkey brain and that the majority of mutant TDP-43 remains in the nuclei of the mouse brain. The primate-specific caspase-4, but not mouse homologue caspase-11, could remove the NLS-containing N-terminal domain and generate fragmented TDP-43 that accumulates in the cytoplasm. Moreover, increased expression of caspase-4 in the monkey brain promotes the cytoplasmic accumulation of endogenous TDP-43, and suppressing caspase-4 reduces the cytoplasmic distribution of endogenous TDP-43 in cultured human neural cells. Our findings suggest that primate-specific caspase-4-mediated cleavage of TDP-43 accounts for its cytoplasmic mislocalization in the primate brains and may serve as a potential therapeutic target.

TDP-43 induces mitochondrial damage and activates the mitochondrial unfolded protein response

Mutations in or dys-regulation of the TDP-43 gene have been associated with TDP-43 proteinopathy, a spectrum of neurodegenerative diseases including Frontotemporal Lobar Degeneration (FTLD) and Amyotrophic Lateral Sclerosis (ALS). The underlying molecular and cellular defects, however, remain unclear. Here, we report a systematic study combining analyses of patient brain samples with cellular and animal models for TDP-43 proteinopathy. Electron microscopy (EM) analyses of patient samples revealed prominent mitochondrial impairment, including abnormal cristae and a loss of cristae; these ultrastructural changes were consistently observed in both cellular and animal models of TDP-43 proteinopathy. In these models, increased TDP-43 expression induced mitochondrial dysfunction, including decreased mitochondrial membrane potential and elevated production of reactive oxygen species (ROS). TDP-43 expression suppressed mitochondrial complex I activity and reduced mitochondrial ATP synthesis. Importantly, TDP-43 activated the mitochondrial unfolded protein response (UPR^mt) in both cellular and animal models. Down-regulating mitochondrial protease LonP1 increased mitochondrial TDP-43 levels and exacerbated TDP-43-induced mitochondrial damage as well as neurodegeneration. Together, our results demonstrate that TDP-43 induced mitochondrial impairment is a critical aspect in TDP-43 proteinopathy. Our work has not only uncovered a previously unknown role of LonP1 in regulating mitochondrial TDP-43 levels, but also advanced our understanding of the pathogenic mechanisms for TDP-43 proteinopathy. Our study suggests that blocking or reversing mitochondrial damage may provide a potential therapeutic approach to these devastating diseases.

TDP-43 proteinopathy is a group of fatal neurological diseases. Here, we report a systematic examination of the role of mitochondrial damage in TDP-43 proteinopathy using patient brain tissues, as well as cellular and animal models. Our data show that TDP-43 induces severe mitochondrial damage, accompanied by activation of UPR^mt in both cellular and animal models of TDP-43 proteinopathy. LonP1, one of the key mitochondrial proteases in UPR^mt, protects against TDP-43 induced cytotoxicity and neurodegeneration. Our study uncovers LonP1 as a modifier gene for TDP-43 proteinopathy and suggests protecting against or reversing mitochondrial damage as a potential therapeutic approach to these neurodegenerative disorders.

Biomarkers for diseases with TDP-43 pathology

The discovery that aggregated transactive response DNA-binding protein 43 kDa (TDP-43) is the major component of pathological ubiquitinated inclusions in amyotrophic lateral sclerosis (ALS) and frontotemporal lobar degeneration (FTLD) caused seminal progress in the unveiling of the genetic bases and molecular characteristics of these now so-called TDP-43 proteinopathies. Substantial increase in the knowledge of clinic-pathological coherencies, especially for FTLD variants, could be made in the last decade, but also revealed a considerable complexity of TDP-43 pathology and often a poor correlation of clinical and molecular disease characteristics. To date, an underlying TDP-43 pathology can be predicted only for patients with mutations in the genes C9orf72 and GRN, but is dependent on neuropathological verification in patients without family history, which represent the majority of cases. As etiology-specific therapies for neurodegenerative proteinopathies are emerging, methods to forecast TDP-43 pathology at patients' lifetime are highly required. Here, we review the current status of research pursued to identify specific indicators to predict or exclude TDP-43 pathology in the ALS-FTLD spectrum disorders and findings on candidates for prognosis and monitoring of disease progression in TDP-43 proteinopathies with a focus on TDP-43 with its pathological forms, neurochemical and imaging biomarkers.

A sticky situation: Aberrant protein-protein interactions in Parkinson's disease

The aberrant aggregation of normally soluble proteins into amyloid fibrils is the pathological hallmark of several neurodegenerative disorders, including Alzheimer's and Parkinson's diseases. Understanding this process will be key to developing both diagnostic and therapeutic approaches for neurodegenerative diseases. Recent advances in biophysical techniques, coupled with kinetic analyses have enabled a thorough description of the key molecular steps involved in protein aggregation. In this review, we discuss these advances and how they have been applied to study the ability of one such protein, α-Synuclein, to form neurotoxic oligomers.

Apolipoprotein E Fragmentation within Lewy Bodies of the Human Parkinson's Disease Brain

Although harboring the Apolipoprotein E4 (APOE4) allele is a well-known risk factor in Alzheimer’s disease (AD), whether a similar risk holds true for Parkinson’s disease (PD) is currently not known. To investigate whether apoE pathology is present in PD, an immunohistochemical study was undertaken with fixed, human PD brain sections from the substantia nigra utilizing a recently characterized antibody that detects an amino-terminal fragment of apoE. This antibody, termed the apoE cleavage fragment p17 (nApoECFp17) antibody specifically detects an amino-terminal 17 kDa fragment of apoE without reacting with full-length forms of the protein. Application of this antibody revealed the presence of this fragment in Lewy bodies in all cases examined. Colocalization of nApoECFp17 with an antibody to alpha-synuclein (α-Syn), which served as a general marker for Lewy bodies, indicated the presence of this apoE fragment in 87.5% of all identified Lewy bodies. In addition, localization of nApoECFp17 was also evident within oligodendrocytes, the nucleus of melatonin-containing neurons, and blood vessels. Conversely, little staining was observed in the substantia nigra from Pick’s disease or in the frontal cortex of dementia with Lewy bodies (DLB) cases, suggesting a specificity for nApoECFp17 immunoreactivity in PD. Collectively, these data have identified widespread evidence for apoE fragmentation in the human PD brain and documented for the first time the presence of apoE within Lewy bodies, the major pathological marker for this neurodegenerative disease.

The Amygdala as a Locus of Pathologic Misfolding in Neurodegenerative Diseases

Over the course of most common neurodegenerative diseases the amygdala accumulates pathologically misfolded proteins. Misfolding of 1 protein in aged brains often is accompanied by the misfolding of other proteins, suggesting synergistic mechanisms. The multiplicity of pathogenic processes in human amygdalae has potentially important implications for the pathogenesis of Alzheimer disease, Lewy body diseases, chronic traumatic encephalopathy, primary age-related tauopathy, and hippocampal sclerosis, and for the biomarkers used to diagnose those diseases. Converging data indicate that the amygdala may represent a preferential locus for a pivotal transition from a relatively benign clinical condition to a more aggressive disease wherein multiple protein species are misfolded. Thus, understanding of amygdalar pathobiology may yield insights relevant to diagnoses and therapies; it is, however, a complex and imperfectly defined brain region. Here, we review aspects of amygdalar anatomy, connectivity, vasculature, and pathologic involvement in neurodegenerative diseases with supporting data from the University of Kentucky Alzheimer's Disease Center autopsy cohort. Immunohistochemical staining of amygdalae for Aβ, Tau, α-synuclein, and TDP-43 highlight the often-coexisting pathologies. We suggest that the amygdala may represent an "incubator" for misfolded proteins and that it is possible that misfolded amygdalar protein species are yet to be discovered.

The neuroprotective effect of nicotine in Parkinson's disease models is associated with inhibiting PARP-1 and caspase-3 cleavage

Clinical evidence points to neuroprotective effects of smoking in Parkinson’s disease (PD), but the molecular mechanisms remain unclear. We investigated the pharmacological pathways involved in these neuroprotective effects, which could provide novel ideas for developing targeted neuroprotective treatments for PD. We used the ETC complex I inhibitor methylpyridinium ion (MPP⁺) to induce cell death in SH-SY5Y cells as a cellular model for PD and found that nicotine inhibits cell death. Using choline as a nicotinic acetylcholine receptor (nAChR) agonist, we found that nAChR stimulation was sufficient to protect SH-SY5Y cells against cell death from MPP⁺. Blocking α7 nAChR with methyllycaconitine (MLA) prevented the protective effects of nicotine, demonstrating that these receptors are necessary for the neuroprotective effects of nicotine. The neuroprotective effect of nicotine involves other pathways relevant to PD. Cleaved Poly (ADP-ribose) polymerase-1 (PARP-1) and cleaved caspase-3 were decreased by nicotine in 6-hydroxydopamine (6-OHDA) lesioned mice and in MPP⁺-treated SH-SY5Y cells. In conclusion, our data indicate that nicotine likely exerts neuroprotective effects in PD through the α7 nAChR and downstream pathways including PARP-1 and caspase-3. This knowledge could be pursued in future research to develop neuroprotective treatments for PD.

New α- and γ-synuclein immunopathological lesions in human brain

Introduction

Several neurodegenerative diseases are classified as proteopathies as they are associated with the aggregation of misfolded proteins. Synucleinopathies are a group of neurodegenerative disorders associated with abnormal deposition of synucleins. α-Synucleinopathies include Parkinson’s disease, dementia with Lewy bodies, and multiple system atrophy. Recently accumulation of another member of the synuclein family- γ−synuclein in neurodegenerative diseases compelled the introduction of the term γ−synucleinopathy. The formation of aggregates and deposits of γ−synuclein is facilitated after its oxidation at methionine 38 (Met³⁸).

Results

Several types of intracytoplasmic inclusions containing post-translationally modified α- and γ−synucleins are detected. Oxidized Met³⁸-γ-synuclein forms aberrant inclusions in amygdala and substantia nigra. Double staining revealed colocalization of oxidized-γ-synuclein with α-synuclein in the cytoplasm of neurons. Another type of synuclein positive inclusions in the amygdala of dementia with Lewy bodies patients has the appearance of Lewy bodies. These inclusions are immunoreactive when analyzed with antibodies to α-synuclein phosphorylated on serine 129, as well as with antibodies to oxidized-γ-synuclein. Some of these Lewy bodies have doughnut-like shape with round or elongated shape. The separate immunofluorescent images obtained with individual antibodies specific to oxidized-γ-synuclein and phospho-α-synuclein clearly shows the colocalization of these synuclein isoforms in substantia nigra inclusions. Phospho-α-synuclein is present almost exclusively at the periphery of these structures, whereas oxidized-γ-syn immunoreactivity is also located in the internal parts forming dot-like pattern of staining.

We also identified several types of oxidized-γ-syn positive astrocytes with different morphology and examined their immunohistochemical phenotypes. Some of them are compact cells with short processes, others have longer processes. Oxidized-γ-synuclein positive astrocytes may also display mixed morphological and immunocytochemical phenotypes between protoplasmic and fibrous astrocytes.

Conclusions

These results reveal new γ−synuclein positive lesions in human brain. Oxidized-γ-synuclein is colocalized with phospho-α-synuclein in doughnut-like inclusions. Several types of astrocytes with different morphology are immunopositive for oxidized-γ-synuclein.

The Lewy body in Parkinson's disease and related neurodegenerative disorders

The histopathological hallmark of Parkinson's disease (PD) is the presence of fibrillar aggregates referred to as Lewy bodies (LBs), in which α-synuclein is a major constituent. Pale bodies, the precursors of LBs, may serve the material for that LBs continue to expand. LBs consist of a heterogeneous mixture of more than 90 molecules, including PD-linked gene products (α-synuclein, DJ-1, LRRK2, parkin, and PINK-1), mitochondria-related proteins, and molecules implicated in the ubiquitin-proteasome system, autophagy, and aggresome formation. LB formation has been considered to be a marker for neuronal degeneration because neuronal loss is found in the predilection sites for LBs. However, recent studies have indicated that nonfibrillar α-synuclein is cytotoxic and that fibrillar aggregates of α-synuclein (LBs and pale bodies) may represent a cytoprotective mechanism in PD.

Immunolocalization of influenza A virus and markers of inflammation in the human Parkinson's disease brain

Although much is known regarding the molecular mechanisms leading to neuronal cell loss in Parkinson's disease (PD), the initiating event has not been identified. Prevailing theories including a chemical insult or infectious agent have been postulated as possible triggers, leading to neuroinflammation. We present immunohistochemical data indicating the presence of influenza A virus within the substantia nigra pars compacta (SNpc) from postmortem PD brain sections. Influenza A virus labeling was identified within neuromelanin granules as well as on tissue macrophages in the SNpc. Further supporting a role for neuroinflammation in PD was the identification of T-lymphocytes that colocalized with an antibody to caspase-cleaved Beclin-1 within the SNpc. The presence of influenza A virus together with macrophages and T-lymphocytes may contribute to the neuroinflammation associated with this disease.