α-Synuclein is involved in manganese-induced ER stress via PERK signal pathway in organotypic brain slice cultures

Comprehensive analysis of an endoplasmic reticulum stress-related gene prediction model and immune infiltration in idiopathic pulmonary fibrosis

Background

Idiopathic pulmonary fibrosis (IPF) is a chronic progressive interstitial lung disease. This study aimed to investigate the involvement of endoplasmic reticulum stress (ERS) in IPF and explore its correlation with immune infiltration.

Methods

ERS-related differentially expressed genes (ERSRDEGs) were identified by intersecting differentially expressed genes (DEGs) from three Gene Expression Omnibus datasets with ERS-related gene sets. Gene Set Variation Analysis and Gene Ontology were used to explore the potential biological mechanisms underlying ERS. A nomogram was developed using the risk signature derived from the ERSRDEGs to perform risk assessment. The diagnostic value of the risk signature was evaluated using receiver operating characteristics, calibration, and decision curve analyses. The ERS score of patients with IPF was measured using a single-sample Gene Set Enrichment Analysis (ssGSEA) algorithm. Subsequently, a prognostic model based on the ERS scores was established. The proportion of immune cell infiltration was assessed using the ssGSEA and CIBERSORT algorithms. Finally, the expression of ERSRDEGs was validated in vivo and in vitro via RT-qPCR.

Results

This study developed an 8-ERSRDEGs signature. Based on the expression of these genes, we constructed a diagnostic nomogram model in which agouti-related neuropeptide had a significantly greater impact on the model. The area under the curve values for the predictive value of the ERSRDEGs signature were 0.975 and 1.000 for GSE70866 and GSE110147, respectively. We developed a prognostic model based on the ERS scores of patients with IPF. Furthermore, we classified patients with IPF into two subtypes based on their signatures. The RT-qPCR validation results supported the reliability of most of our conclusions.

Conclusion

We developed and verified a risk model using eight ERSRDEGs. These eight genes can potentially affect the progression of IPF by regulating ERS and immune responses.

NTRK1-mediated protection against manganese-induced neurotoxicity and cell apoptosis via IGF2 in SH-SY5Y cells

BACKGROUND

Excessive manganese (Mn) exposure has been linked to neurotoxicity, cognitive impairments. Neurotrophic Receptor Kinase 1 (NTRK1) encodes Tropomyosin kinase A (TrkA), a neurotrophic receptor, as a mediator of neuron differentiation and survival. Insulin-like growth factor 2 (IGF2), a pivotal member of the insulin gene family, plays a crucial role in brain development and neuroprotection. Despite this knowledge, the precise mechanisms through which NTRK1 and IGF2 influence cell responses to Mn-induced neuronal damage remain elusive.

METHODS

Cell apoptosis was assessed using CCK8, TUNEL staining, and Western blot analysis of cleaved Caspase-3. Lentiviral vectors facilitated NTRK1 overexpression, while small interfering RNAs (siRNAs) facilitated IGF2 knockdown. Real-time Quantitative PCR (qPCR) determined gene expression levels, while Western blotting measured protein expression.

RESULTS

The study reveals that NTRK1 inhibits MnCl2-induced apoptosis in SH-SY5Y cells. NTRK1 overexpression significantly upregulated IGF2 expression, and subsequent siRNA-IGF2 experiments confirmed IGF2's pivotal role in NTRK1-mediated neuroprotection. Notably, the study identifies that NTRK1 regulates the expression of IGF2 in the neuroprotective mechanism with the involvement of ER stress pathways.

DISCUSSION

The study reveals NTRK1's neuroprotective role via IGF2 against Mn-induced neurotoxicity and ER stress modulation in SH-SY5Y cells. These findings offer insights into potential therapies for neurodegenerative disorders related to Mn exposure and NTRK1 dysfunction, driving future research in this domain.

Inhibition of Protein Aggregation and Endoplasmic Reticulum Stress as a Targeted Therapy for α-Synucleinopathy

α-synuclein (α-syn) is an intrinsically disordered protein abundant in the central nervous system. Physiologically, the protein regulates vesicle trafficking and neurotransmitter release in the presynaptic terminals. Pathologies related to misfolding and aggregation of α-syn are referred to as α-synucleinopathies, and they constitute a frequent cause of neurodegeneration. The most common α-synucleinopathy, Parkinson's disease (PD), is caused by abnormal accumulation of α-syn in the dopaminergic neurons of the midbrain. This results in protein overload, activation of endoplasmic reticulum (ER) stress, and, ultimately, neural cell apoptosis and neurodegeneration. To date, the available treatment options for PD are only symptomatic and rely on dopamine replacement therapy or palliative surgery. As the prevalence of PD has skyrocketed in recent years, there is a pending issue for development of new disease-modifying strategies. These include anti-aggregative agents that target α-syn directly (gene therapy, small molecules and immunization), indirectly (modulators of ER stress, oxidative stress and clearance pathways) or combine both actions (natural compounds). Herein, we provide an overview on the characteristic features of the structure and pathogenic mechanisms of α-syn that could be targeted with novel molecular-based therapies.

Manganese-induced neuronal apoptosis: new insights into the role of endoplasmic reticulum stress in regulating autophagy-related proteins

Manganese (Mn) is an essential trace element that participates in various physiological and pathological processes. However, epidemiological observations indicate that overexposure to Mn is strongly associated with neurodegenerative disorders and has been recognized as a potential risk factor of neuronal apoptosis. Many mechanisms are involved in the pathogenesis of Mn-induced neuronal apoptosis, such as reactive oxygen species generation, neuroinflammation reactions, protein accumulation, endoplasmic reticulum stress (ER stress), and autophagy, all of which collectively accelerate the process of nerve cell damage. As sophisticated cellular processes for maintaining intracellular homeostasis, ER-mediated unfolded protein response and autophagy both play bilateral roles including cell protection and cell injury under pathophysiological conditions, which might interact with each other. Although emerging evidence suggests that ER stress is involved in regulating the compensatory activation of autophagy to promote cell survival, the inherent relationship between ER stress and autophagy on Mn-induced neurotoxicity remains obscure. Here, our review focuses on discussing the existing mechanisms and connections between ER stress, autophagy, and apoptosis, which provide a new perspective on Mn-induced neuronal apoptosis, and the pathogenesis of neurodegenerative diseases.

Sodium P-aminosalicylic Acid Attenuates Manganese-Induced Neuroinflammation in BV2 Microglia by Modulating NF-κB Pathway

Exposure to high levels of manganese (Mn) leads to brain Mn accumulation, and a disease referred to as manganism. Activation of microglia plays an important role in Mn-induced neuroinflammation. Sodium p-aminosalicylic acid (PAS-Na) is a non-steroidal anti-inflammatory drug that inhibits Mn-induced neuroinflammation. The aim of the current study was to explore the role of NF-κB in the protective mechanism of PAS-Na on Mn-induced neuroinflammation in BV2 microglial experimental model. We treated BV2 microglia with 200 μM Mn for 24 h followed by 48 h treatment with graded concentrations of PAS-Na, using an NF-kB inhibitor, JSH-23, as a positive control. MTT results established that 200 and 400 μM PAS-Na treatment increased the Mn-induced cell viability reduction. NF-κB (P65) mRNA expression and the phosphorylation of p65 were increased in Mn-treated BV2 cell, and suppressed by PAS-Na, analogous to the effect of JSH-23 pretreatment. Furthermore, PAS-Na significantly reduced the contents of the inflammatory cytokine TNF-α and IL-1β, both of which were increased by Mn treatment. The current results show that PAS-Na attenuated Mn-induced inflammation by abrogating the activation of the NF-κB signaling pathways and reduced the release of pro-inflammatory cytokines.

Regional specific activations of ERK1/2 and CDK5 differently regulate astroglial responses to ER stress in the rat hippocampus following status epilepticus

Endoplasmic reticulum (ER) triggers the regional specific astroglial responses to status epilepticus (SE, a prolonged seizure activity). However, the epiphenomena/downstream effecters for ER stress and the mechanism of ER stress signaling in astroglial apoptosis have not been fully understood. In the present study, tunicamycin-induced ER stress resulted in reactive astrogliosis-like events showing astroglial hypertrophy with the elevated extracellular signal-activated protein kinase 1/2 (ERK1/2) and cyclin-dependent kinase 5 (CDK5) phosphorylations in the CA1 region of the rat hippocampus. However, tunicamycin increased CDK5, but not ERK1/2, phosphorylation in the molecular layer of the dentate gyrus. Roscovitine (a CDK5 inhibitor) suppressed the effect of tunicamycin in the molecular layer of the dentate gyrus and the CA1 region, while U0126 (an ERK1/2 inhibitor) reversed it in the CA1 region. Salubrinal (an ER stress inhibitor) abrogated activations of ERK1/2 and CDK5, and attenuated reactive astrogliosis in the CA1 region and astroglial apoptosis in the molecular layer of the dentate gyrus following status epilepticus (SE, a prolonged seizure activity). These findings indicate that ER stress may induce reactive astrogliosis via ERK1/2-mediated CDK5 activation in the CA1 region. In the molecular layer of the dentate gyrus, however, ER stress may participate in astroglial apoptosis through ERK1/2-independent CDK5 activation following SE.

Alpha-synuclein is involved in manganese-induced spatial memory and synaptic plasticity impairments via TrkB/Akt/Fyn-mediated phosphorylation of NMDA receptors

Manganese (Mn) overexposure produces long-term cognitive deficits and reduces brain-derived neurotrophic factor (BDNF) in the hippocampus. However, it remains elusive whether Mn-dependent enhanced alpha-synuclein (α-Syn) expression, suggesting a multifaceted mode of neuronal toxicities, accounts for interference with BDNF/TrkB signaling. In this study, we used C57BL/6J WT and α-Syn knockout (KO) mice to establish a model of manganism and found that Mn-induced impairments in spatial memory and synaptic plasticity were related to the α-Syn protein. In addition, consistent with the long-term potentiation (LTP) impairments that were observed, α-Syn KO relieved Mn-induced degradation of PSD95, phosphorylated CaMKIIα, and downregulated SynGAP protein levels. We transfected HT22 cells with lentivirus (LV)-α-Syn shRNA, followed by BDNF and Mn stimulation. In vitro experiments indicated that α-Syn selectively interacted with TrkB receptors and inhibited BDNF/TrkB signaling, leading to phosphorylation and downregulation of GluN2B. The binding of α-Syn to TrkB and Fyn-mediated phosphorylation of GluN2B were negatively regulated by BDNF. Together, these findings indicate that Mn-dependent enhanced α-Syn expression contributes to further exacerbate BDNF protein-level reduction and to inhibit TrkB/Akt/Fyn signaling, thereby disturbing Fyn-mediated phosphorylation of the NMDA receptor GluN2B subunit at tyrosine. In KO α-Syn mice treated with Mn, spatial memory and LTP impairments were less pronounced than in WT mice. However, the same robust neuronal death was observed as a result of Mn-induced neurotoxicity.

The Role of Autophagy in Manganese-Induced Neurotoxicity

Manganese (Mn), an essential micronutrient, acts as a cofactor for multiple enzymes. Epidemiological investigations have shown that an excessive level of Mn is an important environmental factor involved in neurotoxicity. Frequent pollution of air and water by Mn is a serious threat to the health of the population. Overexposure to Mn is particularly detrimental to the central nervous system, leading to symptoms similar to several neurological disorders. Many different mechanisms have been implicated in Mn-induced neurotoxicity, including oxidative/nitrosative stress, toxic protein aggregation, endoplasmic reticulum (ER) stress, mitochondrial dysfunction, dysregulation of autophagy, and the apoptotic cascade, which together promote the progressive neurodegeneration of nerve cells. As a compensatory regulatory mechanism, autophagy plays dual roles in various biological activities under pathological stress conditions. Dysregulation of autophagy is involved in the development of neurodegenerative disorders, with recent emerging evidence indicating a strong, complex relationship between autophagy and Mn-induced neurotoxicity. This review discusses the connection between autophagy and Mn-induced neurotoxicity, especially alpha-synuclein oligomerization, ER stress, and aberrated protein S-nitrosylation, which will provide new insights to profoundly explore the precise mechanisms of Mn-induced neurotoxicity.

IRE1 signaling pathway mediates protective autophagic response against manganese-induced neuronal apoptosis in vivo and in vitro

Overexposure to manganese (Mn) can result in neurotoxicity and is associated with manganism, a Parkinson's-like neurological disorder. In addition, Mn can induce endoplasmic reticulum (ER) stress and autophagy. In this study, we used C57BL/6 mice to establish a model of manganism and found that Mn could induce cell injury. Our results also showed that Mn could initiate the unfolded protein response (UPR) signaling and autophagy, via initiation of the UPR signaling occurring earlier than autophagy. We further investigated the intrinsic relationship between the endoplasmic reticulum to nucleus 1(ERN1, also known as inositol requiring enzyme 1, IRE1) signaling pathway and autophagy induction in SH-SY5Y cells exposed to Mn. Our results revealed that autophagy activation was a protective response in Mn-induced toxicity. Additionally, we found that Jun N-terminal kinase (JNK) inhibition downregulated autophagy and interaction of c-Jun with the Beclin1 promoter. In addition, knockdown of IRE1 with the LV-IRE1 shRNA suppressed the expression of IRE1, TRAF2, p-ASK1, and p-JNK in Mn-treated SH-SY5Y cells. Furthermore, the expression of proteins associated with ASK1-TRAF2 complex formation and autophagy activation were reversed by the LV-IRE1 shRNA. These findings suggest that IRE1 was involved in the activation of JNK through the formation of the ASK1-TRAF2 complex, and JNK activation led to the induction of autophagy, which required Beclin1 transcription by c-Jun. In this study, we demonstrated that the IRE1 signaling pathway mediated the activation of JNK signaling via the formation of the ASK1-TRAF2 complex which could initiate autophagy and the protein c-Jun which regulates Beclin1 transcription in Mn-induced neurotoxicity.

Endoplasmic reticulum stress and NLRP3 inflammasome: Crosstalk in cardiovascular and metabolic disorders

When endoplasmic reticulum (ER) homeostasis is disrupted, known as ER stress (ERS), the ER generates an adaptive signaling pathway called the unfolded protein response to maintain the homeostasis of this organelle. However, if homeostasis is not restored, the ER initiates death signaling pathways, which contribute to the pathogenesis of various disorders. The activation of inflammatory mechanisms is also emerging as a crucial component of cardiovascular and metabolic disorders. Furthermore, the nucleotide-binding oligomerization domain-like receptor family, pyrin domain containing 3 (NLRP3) inflammasome has attracted more attention than others and is the best-characterized member of the NLR family of inflammasomes to date. ERS intersects with many different inflammatory pathways, particularly the NLRP3 inflammasome. In this review, we focus on the interactions between ERS and the NLRP3 inflammasome. The pharmacologic and nonpharmaceutical manipulation of these two processes may offer novel opportunities for the treatment of cardiovascular and metabolic disorders.

Sec62 Suppresses Foot-and-Mouth Disease Virus Proliferation by Promotion of IRE1α-RIG-I Antiviral Signaling

Foot-and-mouth disease virus (FMDV) is highly infectious and causes a major plague in animal farming. Unfolded protein response is one of the major cellular responses to pathogenic infections, which performs a crucial role in cell survival, apoptosis, and antiviral innate immune response. In this study, we showed that FMDV infection activated two unfolded protein response branches (PERK-eIF2α and ATF6 signaling) in both baby hamster kidney cells (BHK-21) and porcine kidney (PK-15) cells, whereas it suppressed the IRE1α-XBP1 signaling by decreasing IRE1α level. Further study revealed IRE1α signaling as an important antiviral innate immune mechanism against FMDV. Sec62, the transport protein, was greatly decreased at the late stages of FMDV infection. By overexpression and knockdown study, we also found that the expression of Sec62 was positively involved in the levels of IRE1α and RIG-I and subsequent activation of downstream antiviral signaling pathways in FMDV-infected PK-15 cells. Taken together, our study demonstrates that Sec62 is an important antiviral factor that upregulates IRE1α-RIG-I-dependent antiviral innate immune responses, and FMDV evades antiviral host defense mechanism by downregulating Sec62-IRE1α/RIG-I.

Manganese-induced cellular disturbance in the baker's yeast, Saccharomyces cerevisiae with putative implications in neuronal dysfunction

Manganese (Mn) is an essential element, but in humans, chronic and/or acute exposure to this metal can lead to neurotoxicity and neurodegenerative disorders including Parkinsonism and Parkinson’s Disease by unclear mechanisms. To better understand the effects that exposure to Mn²⁺ exert on eukaryotic cell biology, we exposed a non-essential deletion library of the yeast Saccharomyces cerevisiae to a sub-inhibitory concentration of Mn²⁺ followed by targeted functional analyses of the positive hits. This screen produced a set of 43 sensitive deletion mutants that were enriched for genes associated with protein biosynthesis. Our follow-up investigations demonstrated that Mn reduced total rRNA levels in a dose-dependent manner and decreased expression of a β-galactosidase reporter gene. This was subsequently supported by analysis of ribosome profiles that suggested Mn-induced toxicity was associated with a reduction in formation of active ribosomes on the mRNAs. Altogether, these findings contribute to the current understanding of the mechanism of Mn-triggered cytotoxicity. Lastly, using the Comparative Toxicogenomic Database, we revealed that Mn shared certain similarities in toxicological mechanisms with neurodegenerative disorders including amyotrophic lateral sclerosis, Alzheimer’s, Parkinson’s and Huntington’s diseases.

Mn-Induced Neurocytes Injury and Autophagy Dysfunction in Alpha-Synuclein Wild-Type and Knock-Out Mice: Highlighting the Role of Alpha-Synuclein

Overexposure to manganese (Mn) is an important environmental risk factor for Parkinsonian-like symptoms referred to as manganism. Alpha-synuclein (α-Syn) oligomerization is a major cause in Mn-induced neurotoxicity. Autophagy, as an adjust response to control intracellular protein homeostasis, is involved in the degradation of α-Syn monomers or oligomers. Furthermore, autophagy dysregulation is also related to development of neurodegenerative disorders. Hence, we speculated that there was an interaction effect between α-Syn oligomerization and autophagy upon Mn exposure. In this study, we applied α-Syn gene knockout mice (α-Syn^-/-) and wild-type mice (α-Syn^+/+) treated with three different concentrations of MnCl₂ (50, 100, and 200 μmol/kg) to elucidate the physiological role of α-Syn in Mn-induced autophagy dysregulation and neurocytes injury. We found that activation of chaperone-mediated autophagy (CMA) pathway by Mn was independent of α-Syn. Additionally, α-Syn could ameliorate excessive autophagy induced by high dose Mn (200 μmol/kg). Next, we used 5 mg/kg Rapamycin (Rap) or 3-methyladenine (3-MA) to regulate autophagy. The study revealed that autophagy is involved in Mn-induced α-Syn oligomerization and neurocytes injury. Taken together, these findings indicated that α-Syn oligomerization might be the major responsible for the Mn-induced autophagy dysregulation and neurocytes injury.

Corynoxine B ameliorates HMGB1-dependent autophagy dysfunction during manganese exposure in SH-SY5Y human neuroblastoma cells

Manganese (Mn) has recently come into the limelight as an important environmental risk factor for neurodegenerative disorders. Although multiple neurotoxicity of Mn have been extensively studied, the exact mechanism of Mn-induced autophagic dysregulation is still poorly understood. The main aim of this study was to explore the role of cytosolic high-mobility group box 1 (HMGB1)-dependent autophagy in Mn-induced autophagic dysregulation and neurotoxicity. SH-SY5Y cells were treated with culture solution (control) and three different concentrations of Mn (50, 100, and 200 μM) for 24 h to detect the effect of Mn on HMGB1-dependent autophagy. We found Mn could increase the HMGB1 mRNA level and its cytosolic translocation and dysregulate autophagy, and Mn-induced alpha-synuclein overexpression interfered with the interaction of HMGB1 and Beclin1, to subsequently promote Beclin1 binding to Bcl2. Another important finding was the neuroprotective role of corynoxine B (Cory B) in Mn-induced autophagic dysregulation and neurotoxicity. We set up six experimental groups: control (culture solution); 200 μM Mn treatment; 100 μM Cory B-alone treatment; and three different pretreated concentrations of Cory B (25, 50, and 100 μM). Our results showed that Cory B ameliorated Mn-induced autophagic dysregulation and neurotoxicity partly by dissociating HMGB1 from alpha-synuclein and inhibiting mTOR signaling.

Alpha-Synuclein and Calpains Disrupt SNARE-Mediated Synaptic Vesicle Fusion During Manganese Exposure in SH-SY5Y Cells

Synaptic vesicle fusion is mediated by an assembly of soluble N-ethylmaleimide-sensitive fusion protein attachment protein receptors (SNAREs), composed of syntaxin 1, soluble NSF-attachment protein (SNAP)-25, and synaptobrevin-2/VAMP-2. Previous studies have suggested that over-exposure to manganese (Mn) could disrupt synaptic vesicle fusion by influencing SNARE complex formation, both in vitro and in vivo. However, the mechanisms underlying this effect remain unclear. Here we employed calpeptin, an inhibitor of calpains, along with a lentivirus vector containing alpha-synuclein (α-Syn) shRNA, to examine whether specific SNAP-25 cleavage and the over-expression of α-Syn disturbed the formation of the SNARE complex in SH-SY5Y cells. After cells were treated with Mn for 24 h, fragments of SNAP-25-N-terminal protein began to appear; however, this effect was reduced in the group of cells which were pre-treated with calpeptin. FM1-43-labeled synaptic vesicle fusion decreased with Mn treatment, which was consistent with the formation of SNARE complexes. The interaction of VAMP-2 and α-Syn increased significantly in normal cells in response to 100 μM Mn treatment, but decreased in LV-α-Syn shRNA cells treated with 100 μM Mn; similar results were observed in terms of the formation of SNARE complexes and FM1-43-labeled synaptic vesicle fusion. Our data suggested that Mn treatment could increase [Ca²⁺]_i, leading to abnormally excessive calpains activity, which disrupted the SNARE complex by cleaving SNAP-25. Our data also provided convincing evidence that Mn could induce the over-expression of α-Syn; when combined with VAMP-2, α-Syn prevented VAMP-2 from joining the SNARE complex cycle.

Exosomal secretion of α-synuclein as protective mechanism after upstream blockage of macroautophagy

Accumulation of pathological α-synuclein aggregates plays a major role in Parkinson’s disease. Macroautophagy is a mechanism to degrade intracellular protein aggregates by wrapping them into autophagosomes, followed by fusion with lysosomes. We had previously shown that pharmacological activation of macroautophagy protects against α-synuclein-induced toxicity in human neurons. Here, we hypothesized that inhibition of macroautophagy would aggravate α-synuclein-induced cell death.

Unexpectedly, inhibition of autophagosome formation by silencing of ATG5 protected from α-synuclein-induced toxicity. Therefore, we studied alternative cellular mechanisms to compensate for the loss of macroautophagy. ATG5 silencing did not affect the ubiquitin–proteasome system, chaperone systems, chaperone-mediated autophagy, or the unfolded protein response. However, ATG5 silencing increased the secretion of α-synuclein via exosomes. Blocking exosomal secretion exacerbated α-synuclein-induced cell death.

We conclude that exosomal secretion of α-synuclein is increased after impaired formation of autophagosomes to reduce the intracellular α-synuclein burden. This compensatory mechanism prevents α-synuclein-induced neuronal cell death.

Effect of the cross-talk between autophagy and endoplasmic reticulum stress on Mn-induced alpha-synuclein oligomerization

Overexposure to manganese (Mn) has been known to induce alpha-synuclein (α-Syn) oligomerization, which is degraded mainly depending on endoplasmic reticulum stress (ER stress) and autophagy pathways. However, little data reported the cross-talk between ER stress and autophagy on Mn-induced α-Syn oligomerization. To explore the relationship between ER stress and autophagy, we used 4-phenylbutyric acid (4-PBA, the ER stress inhibitor), rapamycin (Rap, autophagy activator) and 3-methyladenine (3-MA, autophagy inhibitor) in mice model of manganism. After 4 weeks of treatment with Mn, both ER stress and autophagy were activated. Exposed to Mn also resulted in α-Syn oligomerization and neuronal cell damage in the brain tissue of mice, which could be relieved by 4-PBA pretreatment. Moreover, when the ER stress was inhibited, the activation of autophagy was also inhibited. Rap pretreatment significantly activated autophagy and decreased α-Syn oligomers. However, 3-MA pretreatment inhibited autophagy resulting in increase of α-Syn oligomers, and compensatorily activated PERK signaling pathway. Our results also demonstrated that the inhibition of autophagy by 3-MA aggravated neuronal cell damage. The findings clearly demonstrated that the cross-talking between autophagy and ER stress might play an important role in the α-Syn oligomerization and neurotoxicity by Mn.

Oxidative stress and cellular pathologies in Parkinson's disease

Parkinson’s disease (PD) is a chronic and progressive neurodegeneration of dopamine neurons in the substantia nigra. The reason for the death of these neurons is unclear; however, studies have demonstrated the potential involvement of mitochondria, endoplasmic reticulum, α-synuclein or dopamine levels in contributing to cellular oxidative stress as well as PD symptoms. Even though those papers had separately described the individual roles of each element leading to neurodegeneration, recent publications suggest that neurodegeneration is the product of various cellular interactions. This review discusses the role of oxidative stress in mediating separate pathological events that together, ultimately result in cell death in PD. Understanding the multi-faceted relationships between these events, with oxidative stress as a common denominator underlying these processes, is needed for developing better therapeutic strategies.

Isorhynchophylline Attenuates MPP+-Induced Apoptosis Through Endoplasmic Reticulum Stress- and Mitochondria-Dependent Pathways in PC12 Cells: Involvement of Antioxidant Activity

Endoplasmic reticulum stress (ERS) and mitochondrial dysfunctions are thought to be involved in the dopaminergic neuronal death in Parkinson's disease (PD). In this study, we found that isorhynchophylline (IRN) significantly attenuated 1-methyl-4-phenylpyridinium (MPP⁺)-induced apoptotic cell death and oxidative stress in PC12 cells. IRN markedly reduced MPP⁺-induced-ERS responses, indicative of inositol-requiring enzyme 1 (IRE1) phosphorylation and caspase-12 activation. Furthermore, IRN inhibits MPP⁺-triggered apoptosis signal-regulating kinase 1 (ASK1)/c-Jun N-terminal Kinase (JNK) signaling-mediated mitochondria-dependent apoptosis pathway. IRN-mediated attenuation of endoplasmic reticulum modulator caspase-12 activation was abolished by diphenyleneiodonium (DPI) or IRE-1α shRNA, but not by SP600125 or pifithrin-α in MPP⁺-treated PC12 cells. Inhibitions of MPP⁺-induced both cytochrome c release and caspase-9 activation by IRN were blocked by pre-treatment with DPI or pifithrin-α, but not by IRE-1α shRNA. IRN blocks the generation of reactive oxygen species upstream of both ASK1/JNK pathway and IRE1/caspase-12 pathway. Altogether, our in vitro findings suggest that IRN possesses potent neuroprotective activity and may be a potential candidate for the treatment of PD.

Inhibition of Calpains Protects Mn-Induced Neurotransmitter release disorders in Synaptosomes from Mice: Involvement of SNARE Complex and Synaptic Vesicle Fusion

Overexposure to manganese (Mn) could disrupt neurotransmitter release via influencing the formation of SNARE complex, but the underlying mechanisms are still unclear. A previous study demonstrated that SNAP-25 is one of substrate of calpains. The current study investigated whether calpains were involved in Mn-induced disorder of SNARE complex. After mice were treated with Mn for 24 days, Mn deposition increased significantly in basal nuclei in Mn-treated and calpeptin pre-treated groups. Behaviorally, less time spent in the center of the area and decreased average velocity significantly in an open field test after 24 days of Mn exposure. With the increase in MnCl₂ dosage, intracellular Ca²⁺ increased significantly, but pretreatment with calpeptin caused a dose-dependent decrease in calpains activity. There were fragments of N-terminal of SNAP-25 protein appearance in Mn-treated groups, but it is decreased with pretreatment of calpeptin. FM1-43-labeled synaptic vesicles also provided evidence that the treatment with Mn resulted in increasing first and then decreasing, which was consistent with Glu release and the 80 kDa protein levels of SNARE complexes. In summary, Mn induced the disorder of neurotransmitter release through influencing the formation of SNARE complex via cleaving SNAP-25 by overactivation of calpains in vivo.

The effect of manganese exposure in Atp13a2-deficient mice

Loss of function mutations in the P₅-ATPase ATP13A2 are associated with Kufor-Rakeb Syndrome and Neuronal Ceroid Lipofuscinosis. While the function of ATP13A2 is unclear, in vitro studies suggest it is a lysosomal protein that interacts with the metals manganese (Mn) and zinc and the presynaptic protein alpha-synuclein. Loss of ATP13A2 function in mice causes sensorimotor deficits, enhanced autofluorescent storage material, and accumulation of alpha-synuclein. The present study sought to determine the effect of Mn administration on these same outcomes in ATP13A2-deficient mice. Wildtype and ATP13A2-deficient mice received saline or Mn at 5-9 or 12-19 months for 45days. Sensorimotor function was assessed starting at day 30. Autofluorescence was quantified in multiple brain regions and alpha-synuclein protein levels were determined in the ventral midbrain. Brain Mn, iron, zinc, and copper concentrations were measured in 5-9 month old mice. The results show Mn enhanced sensorimotor function, increased autofluorescence in the substantia nigra, and increased insoluble alpha-synuclein in the ventral midbrain in older ATP13A2-deficient mice. In addition, the Mn regimen used increased Mn concentration in the brain and levels were higher in Mn-treated mutants than controls. These results indicate loss of ATP13A2 function leads to increased sensitivity to Mn in vivo.

A familial ATP13A2 mutation enhances alpha-synuclein aggregation and promotes cell death

Aberrant protein-protein interactions are a common pathological hallmark among neurodegenerative diseases, including Parkinson's disease (PD). Thus far, mutations in more than 20 genes have been associated with PD. These genes encode for proteins involved in distinct intracellular pathways, complicating our understanding of the precise molecular mechanisms underlying the disease. Recent reports suggested that the endolysosomal protein ATP13A2 can determine the fate of alpha-synuclein (α-Syn), although no consensus has yet been reached on the mechanisms underlying this effect. Here, we describe, for the first time, the deleterious effect arising from the interaction between the ATP13A2 familial mutant Dup22 with α-Syn. We show that this ATP13A2 mutant can enhance α-Syn oligomerization and aggregation in cell culture. Additionally, we report the accumulation of both proteins in abnormal endoplasmic reticulum membranous structures and the activation of the protein kinase RNA-like endoplasmic reticulum kinase pathway. Ultimately, our data bring new insight into the molecular mechanisms underlying the interplay of these two proteins, opening novel perspectives for therapeutic intervention.

Organotypic brain slice cultures: A review

In vitro cell cultures are an important tool for obtaining insights into cellular processes in an isolated system and a supplement to in vivo animal experiments. While primary dissociated cultures permit a single homogeneous cell population to be studied, there is a clear need to explore the function of brain cells in a three-dimensional system where the main architecture of the cells is preserved. Thus, organotypic brain slice cultures have proven to be very useful in investigating cellular and molecular processes of the brain in vitro. This review summarizes (1) the historical development of organotypic brain slices focusing on the membrane technology, (2) methodological aspects regarding culturing procedures, age of donors or media, (3) whether the cholinergic neurons serve as a model of neurodegeneration in Alzheimer’s disease, (4) or the nigrostriatal dopaminergic neurons as a model of Parkinson’s disease and (5) how the vascular network can be studied, especially with regard to a synthetic blood–brain barrier. This review will also highlight some limits of the model and give an outlook on future applications.

Inhibition of calpain prevents manganese-induced cell injury and alpha-synuclein oligomerization in organotypic brain slice cultures

Overexposure to manganese has been known to promote alpha-synuclein oligomerization and enhance cellular toxicity. However, the exact mechanism of Mn-induced alpha-synuclein oligomerization is unclear. To explore whether alpha-synuclein oligomerization was associated with the cleavage of alpha-synuclein by calpain, we made a rat brain slice model of manganism and pretreated slices with calpain inhibitor II, a cell-permeable peptide that restricts the activity of calpain. After slices were treated with 400 μM Mn for 24 h, there were significant increases in the percentage of apoptotic cells, lactate dehydrogenase release, intracellular [Ca²⁺]_i, calpain activity, and the mRNA and protein expression of calpain 1 and alpha-synuclein. Moreover, the number of C- and N-terminal fragments of alpha-synuclein and the amount of alpha-synuclein oligomerization also increased. These results also showed that calpain inhibitor II pretreatment could reduce Mn-induced nerve cell injury and alpha-synuclein oligomerization. Additionally, there was a significant decrease in the number of C- and N-terminal fragments of alpha-synuclein in calpain inhibitor II-pretreated slices. These findings revealed that Mn induced the cleavage of alpha-synuclein protein via overactivation of calpain and subsequent alpha-synuclein oligomerization in cultured slices. Moreover, the cleavage of alpha-synuclein by calpain 1 is an important signaling event in Mn-induced alpha-synuclein oligomerization.