Abortive cell cycle events in the brains of scrapie-infected hamsters with remarkable decreases of PLK3/Cdc25C and increases of PLK1/cyclin B1

Chaperone-mediated autophagy in neurodegenerative diseases: mechanisms and therapy

Chaperone-mediated autophagy (CMA) is the selective degradation process of intracellular components by lysosomes, which is required for the degradation of aggregate-prone proteins and contributes to proteostasis maintenance. Proteostasis is essential for normal cell function and survival, and it is determined by the balance of protein synthesis and degradation. Because postmitotic neurons are highly susceptible to proteostasis disruption, CMA is vital for the nervous system. Since Parkinson's disease (PD) was first linked to CMA dysfunction, an increasing number of studies have shown that CMA loss, as seen during aging, occurs in the pathogenetic process of neurodegenerative diseases. Here, we review the molecular mechanisms of CMA, as well as the physiological function and regulation of this autophagy pathway. Following, we highlight its potential role in neurodegenerative diseases, and the latest advances and challenges in targeting CMA in therapy of neurodegenerative diseases.

Microscopic lesions and modulation of gene expression in cervical medulla during BoAHV-1and BoAHV-5 infection: A mini-review

Bovine herpesvirus (BoAHV) types 1 and 5 are closely-related neurotropic alpha-herpesviruses. BoAHV-1 generally causes respiratory and genital disease but can occasionally cause encephalitis. BoAHV-5 is the causative agent of non suppurative meningoencephalitis in calves. During neuroinvasion, both viruses reach the central and peripheral nervous system. While brain alterations are well-described, the changes that occur in the medulla have not been fully detailed. In this work, we integrated and analyzed the virological findings, the microscopic lesions and the changes that occur in the expression of genes related to the innate immunity, cell cycle and apoptosis in the cervical medulla of calves experimentally-infected with BoAHV-1 and BoAHV-5. This will contribute to the understanding of the differential neuropathogenesis of these alpha-herpesviruses of cattle.

Downregulation of CDC25C in NPCs Disturbed Cortical Neurogenesis

Cell division regulators play a vital role in neural progenitor cell (NPC) proliferation and differentiation. Cell division cycle 25C (CDC25C) is a member of the CDC25 family of phosphatases which positively regulate cell division by activating cyclin-dependent protein kinases (CDKs). However, mice with the Cdc25c gene knocked out were shown to be viable and lacked the apparent phenotype due to genetic compensation by Cdc25a and/or Cdc25b. Here, we investigate the function of Cdc25c in developing rat brains by knocking down Cdc25c in NPCs using in utero electroporation. Our results indicate that Cdc25c plays an essential role in maintaining the proliferative state of NPCs during cortical development. The knockdown of Cdc25c causes early cell cycle exit and the premature differentiation of NPCs. Our study uncovers a novel role of CDC25C in NPC division and cell fate determination. In addition, our study presents a functional approach to studying the role of genes, which elicit genetic compensation with knockout, in cortical neurogenesis by knocking down in vivo.

Extensive Disturbances of Intracellular Components and Dysfunctions of Biological Pathways in the Brain Tissues During Prion Infection - China's Studies

The study describes some of the major findings of changes in intracellular components and biological pathways in the brain during prion infection and hypothesizes some important physiological and pathological approaches mainly based on our studies. Omics techniques analysis of messenger RNA (mRNA) and proteins were carried out in the study. Meanwhile, Western blot, immunohistochemistry, and immunofluorescence were used for protein analysis in different signaling pathways. Statistical analyses were used to describe the protein differences in signaling pathways of infected and normal samples. This report reviewed and summarized our studies on the aberrant changes in intracellular components and biological functions in the brains of prion disease (PrD). Omics analyses proposed extensive abnormal alterations of brain mRNAs transcriptions, protein expressions, and post-translational modifications. The molecular disturbances for microtubule instability and depolymerization, the dysregulations of different signals related with neuron loss and synaptic plasticity, the abnormalities of mitochondrial and endoplasmic reticulum stress, and disturbance of intracellular reactive oxygen species homeostasis during prion infection were precisely analyzed and reviewed. Aberrant disturbances of numerous biological molecules and signals in brain tissues were found during prion infection.

Association of Caspase 3 Activation and H2AX γ Phosphorylation in the Aging Brain: Studies on Untreated and Irradiated Mice

Phosphorylation of H2AX is a response to DNA damage, but γH2AX also associates with mitosis and/or apoptosis. We examined the effects of X-rays on DNA integrity to shed more light on the significance of H2AX phosphorylation and its relationship with activation of caspase 3 (CASP3), the main apoptotic effector. After administration of the S phase marker BrdU, brains were collected from untreated and irradiated (10 Gray) 24-month-old mice surviving 15 or 30 min after irradiation. After paraffin embedding, brain sections were single- or double-stained with antibodies against γH2AX, p53-binding protein 1 (53BP1) (which is recruited during the DNA damage response (DDR)), active CASP3 (cCASP3), 5-Bromo-2-deoxyuridine (BrdU), and phosphorylated histone H3 (pHH3) (which labels proliferating cells). After statistical analysis, we demonstrated that irradiation not only induced a robust DDR with the appearance of γH2AX and upregulation of 53BP1 but also that cells with damaged DNA attempted to synthesize new genetic material from the rise in BrdU immunostaining, with increased expression of cCASP3. Association of γH2AX, 53BP1, and cCASP3 was also evident in normal nonirradiated mice, where DNA synthesis appeared to be linked to disturbances in DNA repair mechanisms rather than true mitotic activity.

Transcriptional signature of prion-induced neurotoxicity in a Drosophila model of transmissible mammalian prion disease

Prion diseases are fatal transmissible neurodegenerative conditions of humans and animals that arise through neurotoxicity induced by PrP misfolding. The cellular and molecular mechanisms of prion-induced neurotoxicity remain undefined. Understanding these processes will underpin therapeutic and control strategies for human and animal prion diseases, respectively. Prion diseases are difficult to study in their natural hosts and require the use of tractable animal models. Here we used RNA-Seq-based transcriptome analysis of prion-exposed Drosophila to probe the mechanism of prion-induced neurotoxicity. Adult Drosophila transgenic for pan neuronal expression of ovine PrP targeted to the plasma membrane exhibit a neurotoxic phenotype evidenced by decreased locomotor activity after exposure to ovine prions at the larval stage. Pathway analysis and quantitative PCR of genes differentially expressed in prion-infected Drosophila revealed up-regulation of cell cycle activity and DNA damage response, followed by down-regulation of eIF2 and mTOR signalling. Mitochondrial dysfunction was identified as the principal toxicity pathway in prion-exposed PrP transgenic Drosophila. The transcriptomic changes we observed were specific to PrP targeted to the plasma membrane since these prion-induced gene expression changes were not evident in similarly treated Drosophila transgenic for cytosolic pan neuronal PrP expression, or in non-transgenic control flies. Collectively, our data indicate that aberrant cell cycle activity, repression of protein synthesis and altered mitochondrial function are key events involved in prion-induced neurotoxicity, and correlate with those identified in mammalian hosts undergoing prion disease. These studies highlight the use of PrP transgenic Drosophila as a genetically well-defined tractable host to study mammalian prion biology.

miR-593-5p inhibit cell proliferation by targeting PLK1 in non small cell lung cancer cells

Worldwide, lung cancer has the highest rates of mortality and morbidity, with the majority of its pathology attributable to non-small cell lung cancer (NSCLC). MicroRNAs are pivotal in the occurrence and development of cancer. However, the role of miRNA-593-5p in the progression of NSCLC is not clear. In this study, we investigate, in vitro, whether miRNA-593-5p inhibits NSCLC cell proliferation. To clarify its specific mechanism of inhibition, we used bioinformatics to predict its target genes and identified PLK1. Luciferase reporter assay confirmed the binding of miR-593-5p to the PLK1 3'-UTR in a sequence-specific manner in NSCLC cells. Additionally, we also found through Western blot and quantitative RT-PCR that miR-593-5p down-regulates the expression of PLK1 protein. Finally, PLK1 overexpression was shown to disinhibit NSCLC cell proliferation. Taken together, this evidence suggests that miR-593-5p inhibits NSCLC cell proliferation by inhibiting PLK1 expression.

Differential expression of cyclins mRNA in neural tissues of BoHV-1- and BoHV-5- infected cattle

Bovine alphaherpesvirus types 1 (BoHV-1) and 5 (BoHV-5) are closely related alphaherpesviruses. BoHV-5 causes non-suppurative meningoencephalitis in calves. BoHV-1 is associated with several syndromes and, occasionally, can cause encephalitis. Although both viruses are neurotropic and they share similar biological properties, it is unknown why these alphaherpesviruses differ in their ability to cause neurological disease. Neural tissue samples were collected from BoHV-1- and BoHV-5-intranasally inoculated calves during acute infection, latency and reactivation and the levels of cyclins mRNA expression were analyzed by qRT-PCR. Striking differences in the levels of cyclins mRNA were particularly detected in trigeminal ganglion (TG). The expression levels of cyclins in TG during BoHV-5 latency suggest that these viruses utilize different strategies to persist in the host. It is apparent that a relationship between virus loads and cyclin mRNA levels can be established only during acute infection and other factors might be involved in the regulation of cell cycle components during BoHV latency and reactivation. Bovine alphaherpesviruses neuropathogenicity might be influenced by the differential control of cell cycle components by these herpesviruses. This is the first report on BoHV-5 modulation of cyclins expression in neural tissues from its natural host.

Review: PrP 106-126 - 25 years after

A quarter of a century ago, we proposed an innovative approach to study the pathogenesis of prion disease, one of the most intriguing biomedical problems that remains unresolved. The synthesis of a peptide homologous to residues 106-126 of the human prion protein (PrP106-126), a sequence present in the PrP amyloid protein of Gerstmann-Sträussler-Scheinker syndrome patients, provided a tractable tool for investigating the mechanisms of neurotoxicity. Together with several other discoveries at the beginning of the 1990s, PrP106-126 contributed to underpin the role of amyloid in the pathogenesis of protein-misfolding neurodegenerative disorders. Later, the role of oligomers on one hand and of prion-like spreading of pathology on the other further clarified mechanisms shared by different neurodegenerative conditions. Our original report on PrP106-126 neurotoxicity also highlighted a role for programmed cell death in CNS diseases. In this review, we analyse the prion research context in which PrP106-126 first appeared and the advances in our understanding of prion disease pathogenesis and therapeutic perspectives 25 years later.

Plk1 promotes the migration of human lung adenocarcinoma epithelial cells via STAT3 signaling

Polo-like kinase (Plk)1 contributes to the development of human cancer via multiple mechanisms, such as promoting the migration of cancer cells. However, the mechanistic basis for the regulation of cell migration by Plk1 remains unknown. To address this question, the present study investigated the effect of Plk1 inhibition on the migration of human lung adenocarcinoma epithelial A549 cells and the molecular factors involved. A549 cells were treated with the Plk1 inhibitor, BI2536, and cell migration was evaluated with the wound-healing assay. The expression of matrix metallopeptidase (MMP)2, vascular endothelial growth factor (VEGF)A, total and phosphorylated signal transducer and activator of transcription (STAT)3 was assessed by western blotting and reverse transcription-polymerase chain reaction following Plk1 knockdown and/or STAT3 overexpression. The interaction between Plk1 and STAT3 was evaluated by co-immunoprecipitation. The levels of MMP2 and VEGFA were decreased by treatment with Plk1 inhibitor. The phosphorylation of STAT3, which acts upstream of MMP2 and VEGFA, was also decreased by Plk1 knockdown, an effect that was abrogated by STAT3 overexpression. In addition, Plk1 was detected to bind with STAT3 either directly or as part of a complex by co-immunoprecipitation experiments. These results indicated that Plk1 may promote the migration of A549 cells via regulation of STAT3 signaling.

Decrease of RyR2 in the prion infected cell line and in the brains of the scrapie infected mice models and the patients of human prion diseases

The levels of ryanodine receptors (RyRs) are usually increased in the brains of human Alzheimer disease (AD) and AD animal models. To evaluate the underlying alteration of brain RyRs in prion disease, scrapie infected cell line SMB-S15 and its infected mice were tested. RyR2 specific Western blots revealed markedly decreased RyR2 levels both in the cells and in the brains of infected mice. Assays of the brain samples of other scrapie (agents 139A and ME7) infected mice collected at different time-points during incubation period showed time-dependent decreases of RyR2. Immunofluorescent assays (IFA) verified that the expression of RyR2 locates predominantly in cytoplasm of SMB cells and overlapped with the neurons in the brain slices of mice. Furthermore, significant down-regulation of RyR2 was also detected in the postmortem cortical brains of the patients of various types of human prion diseases, including sporadic Creutzfeldt-Jakob disease (sCJD), fatal familial insomnia (FFI) and G114V-genetic CJD. Our data here propose the evidences of remarkably decreased brain RyR2 at terminal stages of both human prion diseases and prion infected rodent models. It also highlights that the therapeutic strategy with antagonist of RyRs in AD may not be suitable for prion disease.

Aberrant alterations of the expressions and S-nitrosylation of calmodulin and the downstream factors in the brains of the rodents during scrapie infection

The aberrant alterations of calmodulin (CaM) and its downstream substrates have been reported in some neurodegenerative diseases, but rarely described in prion disease. In this study, the potential changes of Ca²⁺/CaM and its associated agents in the brains of scrapie agent 263K-infected hamsters and the prion infected cell line SMB-S15 were evaluated by various methodologies. We found that the level of CaM in the brains of 263K-infected hamsters started to increase at early stage and maintained at high level till terminal stage. The increased CaM mainly accumulated in the regions of cortex, thalamus and cerebellum of 263K-infected hamsters and well localization of CaM with NeuN positive cells. However, the related kinases such as total and phosphorylated forms of CaMKII and CaMKIV, as well as the downstream proteins such as CREB and BDNF in the brain of 263K-infected hamsters were decreased. Further analysis showed a remarkable increase of S-nitrosylated (SNO) form of CaM in the brains of 263K-infected hamsters. Dynamic analysis of S-nitrosylated CaM showed the SNO form of CaM abnormally increases in a time-dependent manner during prion infection. Compared with that of the normal partner cell line SMB-PS, the CaM level in SMB-S15 cells was increased, meanwhile, the downstream proteins, such as CaMKII, p-CaMKII, CREB, as well as BDNF, were also increased, especially in the nucleic fraction. No SNO-CaM was detected in the cell lines SMB-S15 and SMB-PS. Our data indicate an aberrant increase of CaM during prion infection in vivo and in vitro.

Overexpression of PLK3 Mediates the Degradation of Abnormal Prion Proteins Dependent on Chaperone-Mediated Autophagy

Polo-like kinase 3 (PLK3) is the main cause of cell cycle reentry-related neuronal apoptosis which has been implicated in the pathogenesis of prion diseases. Previous work also showed the regulatory activity of exogenous PLK3 on the degradation of PrP (prion protein) mutants and pathogenic PrP^Sc; however, the precise mechanisms remain unknown. In this study, we identified that the overexpression of PLK3-mediated degradation of PrP mutant and PrP^Sc was repressed by lysosome rather than by proteasomal and macroautophagy inhibitors. Core components of chaperone-mediated autophagy (CMA) effectors, lysosome-associated membrane protein type 2A (LAMP2a), and heat shock cognate protein 70 (Hsc70) are markedly decreased in the HEK293T cells expressing PrP mutant and scrapie-infected cell line SMB-S15. Meanwhile, PrP mutant showed ability to interact with LAMP2a and Hsc70. Overexpression of PLK3 sufficiently increased the cellular levels of LAMP2a and Hsc70, accompanying with declining the accumulations of PrP mutant and PrP^Sc. The kinase domain (KD) of PLK3 was responsible for elevating LAMP2a and Hsc70. Knockdown of endogenous PLK3 enhanced the activity of macroautophagy in the cultured cells. Moreover, time-dependent reductions of LAMP2a and Hsc70 were also observed in the brain tissues of hamster-adapted scrapie agent 263K-infected hamsters, indicating an impairment of CMA during prion infection. Those data indicate that the overexpression of PLK3-mediated degradation of abnormal PrP is largely dependent on CMA pathway.

Increases of Galectin-1 and its S-nitrosylated form in the Brain Tissues of Scrapie-Infected Rodent Models and Human Prion Diseases

Galectin-1 (Gal-1) shows neuroprotective activity in brain ischemia, spinal cord injury, and autoimmune neuroinflammation. To evaluate the Gal-1 situation in the brains of prion disease, the brain levels of Gal-1 in several scrapie-infected experimental rodent models were tested by Western blot, including agents 263K-infected hamsters, 139A-, ME7-, and S15-infected mice. Remarkable increases of brain Gal-1 were observed in all tested scrapie-infected rodents at the terminal stage. The brain levels of Gal-1 showed time-dependent increases along with the prolonging of incubation times. Immunohistochemical assays illustrated much stronger stainings in the brain sections of scrapie-infected rodents. Quantitative RT-PCR of Gal-1 gene demonstrated increased transcription in the brains of scrapie-infected mice. Gal-1 was colocalized with GFAP- and NeuN-positive cells, but not with Iba-1-positive cells in immunofluorescent test. Increases of Gal-1 were also detected in the several postmortem cortex regions of human prion diseases. Moreover, the S-nitrosylated forms of Gal-1 in the brains of scrapie-infected rodents were significantly higher than those of normal ones. Our finding here demonstrates markedly increased brain Gal-1 and S-nitrosylated Gal-1 both in scrapie-infected rodents and human prion diseases.

Activation of the AMPK-ULK1 pathway plays an important role in autophagy during prion infection

AMPK is a serine/threonine protein kinase that acts as a positive regulator of autophagy, by phosphorylating ULK1 at specific sites. A previous study demonstrated activation of the macroautophagic system in scrapie-infected experimental rodents and in certain human prion diseases, in which the essential negative regulator mTOR is severely inhibited. In this study, AMPK and ULK1 in the brains of hamsters infected with scrapie strain 263 K and in the scrapie-infected cell line SMB-S15 were analysed. The results showed an up-regulated trend of AMPK and AMPK-Thr172, ULK1 and ULK1-Ser555. Increases in brain AMPK and ULK1 occurred at an early stage of agent 263 K infection. The level of phosphorylated ULK1-Ser757 decreased during mid-infection and was only negligibly present at the terminal stage, a pattern that suggested a close relationship of the phosphorylated protein with altered endogenous mTOR. In addition, the level of LKB1 associated with AMPK activation was selectively increased at the early and middle stages of infection. Knockdown of endogenous ULK1 in SMB-S15 cells inhibited LC3 lipidation. These results showed that, in addition to the abolishment of the mTOR regulatory pathway, activation of the AMPK-ULK1 pathway during prion infection contributes to autophagy activation in prion-infected brain tissues.

Prion-induced neurotoxicity: Possible role for cell cycle activity and DNA damage response

Protein misfolding neurodegenerative diseases arise through neurotoxicity induced by aggregation of host proteins. These conditions include Alzheimer’s disease, Huntington’s disease, Parkinson’s disease, motor neuron disease, tauopathies and prion diseases. Collectively, these conditions are a challenge to society because of the increasing aged population and through the real threat to human food security by animal prion diseases. It is therefore important to understand the cellular and molecular mechanisms that underlie protein misfolding-induced neurotoxicity as this will form the basis for designing strategies to alleviate their burden. Prion diseases are an important paradigm for neurodegenerative conditions in general since several of these maladies have now been shown to display prion-like phenomena. Increasingly, cell cycle activity and the DNA damage response are recognised as cellular events that participate in the neurotoxic process of various neurodegenerative diseases, and their associated animal models, which suggests they are truly involved in the pathogenic process and are not merely epiphenomena. Here we review the role of cell cycle activity and the DNA damage response in neurodegeneration associated with protein misfolding diseases, and suggest that these events contribute towards prion-induced neurotoxicity. In doing so, we highlight PrP transgenic Drosophila as a tractable model for the genetic analysis of transmissible mammalian prion disease.

Polo-like kinase 3 (PLK3) mediates the clearance of the accumulated PrP mutants transiently expressed in cultured cells and pathogenic PrP(Sc) in prion infected cell line via protein interaction

Polo-like kinases (PLKs) family has long been known to be critical for cell cycle and recent studies have pointed to new dimensions of PLKs function in the nervous system. Our previous study has verified that the levels of PLK3 in the brain are severely downregulated in prion-related diseases. However, the associations of PLKs with prion protein remain unclear. In the present study, we confirmed that PrP protein constitutively interacts with PLK3 as determined by both in vitro and in vivo assays. Both the kinase domain and polo-box domain of PLK3 were proved to bind PrP proteins expressed in mammalian cell lines. Overexpression of PLK3 did not affect the level of wild-type PrP, but significantly decreased the levels of the mutated PrPs in cultured cells. The kinase domain appeared to be responsible for the clearance of abnormally aggregated PrPs, but this function seemed to be independent of its kinase activity. RNA-mediated knockdown of PLK3 obviously aggravated the accumulation of cytosolic PrPs. Moreover, PLK3 overexpression in a scrapie infected cell line caused notable reduce of PrP(Sc) level in a dose-dependent manner, but had minimal effect on the expression of PrP(C) in its normal partner cell line. Our findings here confirmed the molecular interaction between PLK3 and PrP and outlined the regulatory activity of PLK3 on the degradation of abnormal PrPs, even its pathogenic isoform PrP(Sc). We, therefore, assume that the recovery of PLK3 in the early stage of prion infection may be helpful to prevent the toxic accumulation of PrP(Sc) in the brain tissues.