α-Synuclein induced cell death in mouse hippocampal (HT22) cells is mediated by nitric oxide-dependent activation of caspase-3

Age-related Mitochondrial Dysfunction in Parkinson's Disease: New Insights Into the Disease Pathology

Aging is a progressive loss of physiological function that increases risk of disease and death. Among the many factors that contribute to human aging, mitochondrial dysfunction has emerged as one of the most prominent features of the aging process. It has been linked to the development of various age-related pathologies, including Parkinson's disease (PD). Mitochondria has a complex quality control system that ensures mitochondrial integrity and function. Perturbations in these mitochondrial mechanisms have long been linked to various age-related neurological disorders. Even though research has shed light on several aspects of the disease pathology, the underlying mechanism of age-related factors responsible for individuals developing this disease is still unknown. This review article aims to discuss the role of mitochondria in the transition from normal brain aging to pathological brain aging, which leads to the progression of PD. We have discussed the emerging evidence on how age-related disruption of mitochondrial quality control mechanisms contributes to the development of PD-related pathophysiology.

Recent Insights into the Interplay of Alpha-Synuclein and Sphingolipid Signaling in Parkinson's Disease

Molecular studies have provided increasing evidence that Parkinson’s disease (PD) is a protein conformational disease, where the spread of alpha-synuclein (ASN) pathology along the neuraxis correlates with clinical disease outcome. Pathogenic forms of ASN evoke oxidative stress (OS), neuroinflammation, and protein alterations in neighboring cells, thereby intensifying ASN toxicity, neurodegeneration, and neuronal death. A number of evidence suggest that homeostasis between bioactive sphingolipids with opposing function—e.g., sphingosine-1-phosphate (S1P) and ceramide—is essential in pro-survival signaling and cell defense against OS. In contrast, imbalance of the “sphingolipid biostat” favoring pro-oxidative/pro-apoptotic ceramide-mediated changes have been indicated in PD and other neurodegenerative disorders. Therefore, we focused on the role of sphingolipid alterations in ASN burden, as well as in a vast range of its neurotoxic effects. Sphingolipid homeostasis is principally directed by sphingosine kinases (SphKs), which synthesize S1P—a potent lipid mediator regulating cell fate and inflammatory response—making SphK/S1P signaling an essential pharmacological target. A growing number of studies have shown that S1P receptor modulators, and agonists are promising protectants in several neurological diseases. This review demonstrates the relationship between ASN toxicity and alteration of SphK-dependent S1P signaling in OS, neuroinflammation, and neuronal death. Moreover, we discuss the S1P receptor-mediated pathways as a novel promising therapeutic approach in PD.

Regulation of Mitochondrial Dynamics in Parkinson's Disease-Is 2-Methoxyestradiol a Missing Piece?

Mitochondria, as "power house of the cell", are crucial players in cell pathophysiology. Beyond adenosine triphosphate (ATP) production, they take part in a generation of reactive oxygen species (ROS), regulation of cell signaling and cell death. Dysregulation of mitochondrial dynamics may lead to cancers and neurodegeneration; however, the fusion/fission cycle allows mitochondria to adapt to metabolic needs of the cell. There are multiple data suggesting that disturbed mitochondrial homeostasis can lead to Parkinson's disease (PD) development. 2-methoxyestradiol (2-ME), metabolite of 17β-estradiol (E2) and potential anticancer agent, was demonstrated to inhibit cell growth of hippocampal HT22 cells by means of nitric oxide synthase (NOS) production and oxidative stress at both pharmacologically and also physiologically relevant concentrations. Moreover, 2-ME was suggested to inhibit mitochondrial biogenesis and to be a dynamic regulator. This review is a comprehensive discussion, from both scientific and clinical point of view, about the influence of 2-ME on mitochondria and its plausible role as a modulator of neuron survival.

Dysfunctional proteins in neuropsychiatric disorders: From neurodegeneration to autism spectrum disorders

Despite fundamental differences in disease course and outcomes, neurodevelopmental (autism spectrum disorders - ASD) and neurodegenerative disorders (Alzheimer's disease - AD and Parkinson's disease - PD) present surprising, common traits in their molecular pathomechanisms. Uncontrolled oligomerization and aggregation of amyloid β (Aβ), microtubule-associated protein (MAP) tau, or α-synuclein (α-syn) contribute to synaptic impairment and the ensuing neuronal death in both AD and PD. Likewise, the pathogenesis of ASD may be attributed, at least in part, to synaptic dysfunction; attention has also been recently paid to irregularities in the metabolism and function of the Aβ precursor protein (APP), tau, or α-syn. Commonly affected elements include signaling pathways that regulate cellular metabolism and survival such as insulin/insulin-like growth factor (IGF) - PI3 kinase - Akt - mammalian target of rapamycin (mTOR), and a number of key synaptic proteins critically involved in neuronal communication. Understanding how these shared pathomechanism elements operate in different conditions may help identify common targets and therapeutic approaches.

P2X7 Receptor is Involved in Mitochondrial Dysfunction Induced by Extracellular Alpha Synuclein in Neuroblastoma SH-SY5Y Cells

The purinergic P2X7 receptor (P2X7R) belongs to a family of trimeric ion channels that are gated by extracellular adenosine 5′-triphosphate (ATP). Several studies have pointed to a role of P2X7R-dependent signalling in Parkinson's disease (PD)-related neurodegeneration. The pathology of (PD) is characterized by the formation of insoluble alpha-synuclein (α-Syn) aggregates—Lewy bodies, but the mechanisms underlying α-Syn-induced dopaminergic cell death are still partially unclear. Our previous studies indicate that extracellular α-Syn directly interact with neuronal P2X7R and induces intracellular free calcium mobilization in neuronal cells. The main objective of this study was to examine the involvement of P2X7R receptor in α-Syn-induced mitochondrial dysfunction and cell death. We found that P2X7R stimulation is responsible for α-Syn-induced oxidative stress and activation of the molecular pathways of programmed cell death. Exogenous α-Syn treatment led to P2X7R-dependent decrease in mitochondrial membrane potential as well as elevation of mitochondrial ROS production resulting in breakdown of cellular energy production. Moreover, P2X7R-dependent deregulation of AMP-activated protein kinase as well as decrease in parkin protein level could be responsible for α-Syn-induced mitophagy impairment and accumulation of dysfunctional mitochondria. P2X7R might be putative pharmacological targets in molecular mechanism of extracellular α-Syn toxicity.

Mitochondrial damage by α-synuclein causes cell death in human dopaminergic neurons

Evolving concepts on Parkinson’s disease (PD) pathology suggest that α-synuclein (aSYN) promote dopaminergic neuron dysfunction and death through accumulating in the mitochondria. However, the consequence of mitochondrial aSYN localisation on mitochondrial structure and bioenergetic functions in neuronal cells are poorly understood. Therefore, we investigated deleterious effects of mitochondria-targeted aSYN in differentiated human dopaminergic neurons in comparison with wild-type (WT) aSYN overexpression and corresponding EGFP (enhanced green fluorescent protein)-expressing controls. Mitochondria-targeted aSYN enhanced mitochondrial reactive oxygen species (ROS) formation, reduced ATP levels and showed severely disrupted structure and function of the dendritic neural network, preceding neuronal death. Transmission electron microscopy illustrated distorted cristae and many fragmented mitochondria in response to WT-aSYN overexpression, and a complete loss of cristae structure and massively swollen mitochondria in neurons expressing mitochondria-targeted aSYN. Further, the analysis of mitochondrial bioenergetics in differentiated dopaminergic neurons, expressing WT or mitochondria-targeted aSYN, elicited a pronounced impairment of mitochondrial respiration. In a pharmacological compound screening, we found that the pan-caspase inhibitors QVD and zVAD-FMK, and a specific caspase-1 inhibitor significantly prevented aSYN-induced cell death. In addition, the caspase inhibitor QVD preserved mitochondrial function and neuronal network activity in the human dopaminergic neurons overexpressing aSYN. Overall, our findings indicated therapeutic effects by caspase-1 inhibition despite aSYN-mediated alterations in mitochondrial morphology and function.

Diosbulbin B-Induced Mitochondria-Dependent Apoptosis in L-02 Hepatocytes is Regulated by Reactive Oxygen Species-Mediated Autophagy

Aim: Diosbulbin B (DB) is a major diterpenoid compound found in Dioscorea bulbifera L, a traditional medicinal herb in China. Clinical reports have confirmed that Dioscorea bulbifera L. can induce significant hepatotoxicity. In this study, we showed that DB can induce mitochondria-dependent apoptosis and investigated the role of autophagy in DB-induced hepatotoxicity in L-02 hepatocytes.

Methods: L-02 hepatocytes were treated with different concentrations of DB for 48 h, after which indicators of autophagy and apoptosis were measured. 3-Methyladenine (3-MA) and rapamycin (Rapa) were used as inhibitor and agonist of autophagy, respectively. Furthermore, the reactive oxygen species (ROS) scavenger N-acetyl-l-cysteine (NAC) was used in combination with DB to evaluate the relationship between ROS and autophagy.

Results: L-02 cell viability was significantly decreased after treatment with DB for 48 h. Additionally, DB induced concentration-dependent apoptosis and autophagy and increased the activities of caspase-3, caspase-9, alanine aminotransferase (ALT), and aspartate transaminase (AST), and induced excessive leakage of lactate dehydrogenase (LDH). Inhibition of autophagy by 3-MA increased DB-induced apoptosis, resulting in aggravation of hepatotoxicity. Conversely, treatment with Rapa increased malondialdehyde (MDA) content and reduced superoxide dismutase (SOD) activity. Moreover, we found that DB treatment increased the level of intracellular ROS, decreased the mitochondrial membrane potential (MMP) and adenosine triphosphate (ATP) production, and caused abnormal opening of the mitochondrial permeability transition pore (mPTP), which were finally restored by the ROS scavenger NAC.

Conclusions: Accumulation of ROS can induce mitochondria-dependent apoptosis and likely to play a key role in DB-induced hepatocellular injury. Activation of autophagy may inhibit apoptosis, but also reduces antioxidant capacity.

In vitro models of synucleinopathies: informing on molecular mechanisms and protective strategies

Alpha-synuclein (α-Syn) is a central player in Parkinson's disease (PD) and in a spectrum of neurodegenerative diseases collectively known as synucleinopathies. The protein was first associated with PD just over 20 years ago, when it was found to (i) be a major component of Lewy bodies and (ii) to be also associated with familial forms of PD. The characterization of α-Syn pathology has been achieved through postmortem studies of human brains. However, the identification of toxic mechanisms associated with α-Syn was only achieved through the use of experimental models. In vitro models are highly accessible, enable relatively rapid studies, and have been extensively employed to address α-Syn-associated neurodegeneration. Given the diversity of models used and the outcomes of the studies, a cumulative and comprehensive perspective emerges as indispensable to pave the way for further investigations. Here, we subdivided in vitro models of α-Syn pathology into three major types: (i) models simulating α-Syn fibrillization and the formation of different aggregated structures in vitro, (ii) models based on the intracellular expression of α-Syn, reporting on pathogenic conditions and cellular dysfunctions induced, and (iii) models using extracellular treatment with α-Syn aggregated species, reporting on sites of interaction and their downstream consequences. In summary, we review the underlying molecular mechanisms discovered and categorize protective strategies, in order to pave the way for future studies and the identification of effective therapeutic strategies. This article is part of the Special Issue "Synuclein".

Extracellular Alpha-Synuclein Oligomers Induce Parkin S-Nitrosylation: Relevance to Sporadic Parkinson's Disease Etiopathology

α-Synuclein (ASN) and parkin, a multifunctional E3 ubiquitin ligase, are two proteins that are associated with the pathophysiology of Parkinson’s disease (PD). Excessive release of ASN, its oligomerization, aggregation, and deposition in the cytoplasm contribute to neuronal injury and cell death through oxidative-nitrosative stress induction, mitochondrial impairment, and synaptic dysfunction. In contrast, overexpression of parkin provides protection against cellular stresses and prevents dopaminergic neural cell loss in several animal models of PD. However, the influence of ASN on the function of parkin is largely unknown. Therefore, the aim of this study was to investigate the effect of extracellular ASN oligomers on parkin expression, S-nitrosylation, as well as its activity. For these investigations, we used rat pheochromocytoma (PC12) cell line treated with exogenous oligomeric ASN as well as PC12 cells with parkin overexpression and parkin knock-down. The experiments were performed using spectrophotometric, spectrofluorometric, and immunochemical methods. We found that exogenous ASN oligomers induce oxidative/nitrosative stress leading to parkin S-nitrosylation. Moreover, this posttranslational modification induced the elevation of parkin autoubiquitination and degradation of the protein. The decreased parkin levels resulted in significant cell death, whereas parkin overexpression protected against toxicity induced by extracellular ASN oligomers. We conclude that lowering parkin levels by extracellular ASN may significantly contribute to the propagation of neurodegeneration in PD pathology through accumulation of defective proteins as a consequence of parkin degradation.

Neuroprotective effects of melatonin on amphetamine-induced dopaminergic fiber degeneration in the hippocampus of postnatal rats

Chronic amphetamine (AMPH) abuse leads to damage of the hippocampus, the brain area associated with learning and memory process. Previous results have shown that AMPH-induced dopamine neurotransmitter release, reactive oxygen species formation, and degenerative protein aggregation lead to neuronal death. Melatonin, a powerful antioxidant, plays a role as a neuroprotective agent. The objective of this study was to investigate whether the protective effect of melatonin on AMPH-induced hippocampal damage in the postnatal rat acts through the dopaminergic pathway. Four-day-old postnatal rats were subcutaneously injected with 5-10 mg/kg AMPH and pretreated with 10 mg/kg melatonin prior to AMPH exposure for seven days. The results showed that melatonin decreased the AMPH-induced hippocampal neuronal degeneration in the dentate gyrus, CA1, and CA3. Melatonin attenuated the reduction in the expression of hippocampal synaptophysin, PSD-95, α-synuclein, and N-methyl-D-aspartate (NMDA) receptor protein and mRNA caused by AMPH. Melatonin attenuated the AMPH-induced reduction in dopamine transporter (DAT) protein expression in the hippocampus and the reduction in mRNA expression in the ventral tegmental area (VTA). Immunofluorescence demonstrated that melatonin not only prevented the AMPH-induced loss of DAT and NMDA receptor but also prevented AMPH-induced α-synuclein overexpression in the dentate gyrus, CA1, and CA3. Melatonin decreased the AMPH-induced reduction in the protein and mRNA of the NMDA receptor downstream signaling molecule, calcium/calmodulin-dependent protein kinase II (CaMKII), and the melatonin receptors (MT1 and MT2). This study showed that melatonin prevented AMPH-induced toxicity in the hippocampus of postnatal rats possibly via its antioxidative effect and mitochondrial protection.

Exogenous α-synuclein hinders synaptic communication in cultured cortical primary rat neurons

Amyloid aggregates of the protein α-synuclein (αS) called Lewy Bodies (LB) and Lewy Neurites (LN) are the pathological hallmark of Parkinson's disease (PD) and other synucleinopathies. We have previously shown that high extracellular αS concentrations can be toxic to cells and that neurons take up αS. Here we aimed to get more insight into the toxicity mechanism associated with high extracellular αS concentrations (50-100 μM). High extracellular αS concentrations resulted in a reduction of the firing rate of the neuronal network by disrupting synaptic transmission, while the neuronal ability to fire action potentials was still intact. Furthermore, many cells developed αS deposits larger than 500 nm within five days, but otherwise appeared healthy. Synaptic dysfunction clearly occurred before the establishment of large intracellular deposits and neuronal death, suggesting that an excessive extracellular αS concentration caused synaptic failure and which later possibly contributed to neuronal death.

P2X7 receptor-pannexin 1 interaction mediates extracellular alpha-synuclein-induced ATP release in neuroblastoma SH-SY5Y cells

Abnormalities of alpha-synuclein (ASN), the main component of protein deposits (Lewy bodies), were observed in Parkinson’s disease (PD), dementia with Lewy bodies, Alzheimer’s disease, and other neurodegenerative disorders. These alterations include increase in the levels of soluble ASN oligomers in the extracellular space. Numerous works have identified several mechanisms of their toxicity, including stimulation of the microglial P2X7 receptor leading to oxidative stress. While the significant role of purinergic signaling—particularly, P2 family receptors—in neurodegenerative disorders is well known, the interaction of extracellular soluble ASN with neuronal purinergic receptors is yet to be studied. Therefore, in this study, we have investigated the effect of ASN on P2 purinergic receptors and ATP-dependent signaling. We used neuroblastoma SH-SY5Y cell line and rat synaptoneurosomes treated with exogenous soluble ASN. The experiments were performed using spectrofluorometric, radiochemical, and immunochemical methods. We found the following: (i) ASN-induced intracellular free calcium mobilization in neuronal cells and nerve endings depends on the activation of purinergic P2X7 receptors; (ii) activation of P2X7 receptors leads to pannexin 1 recruitment to form an active complex responsible for ATP release; and (iii) ASN greatly decreases the activity of extracellular ecto-ATPase responsible for ATP degradation. Thus, it is concluded that purinergic receptors might be putative pharmacological targets in the molecular mechanism of extracellular ASN toxicity. Interference with P2X7 signaling seems to be a promising strategy for the prevention or therapy of PD and other neurodegenerative disorders.

Selenium in the Therapy of Neurological Diseases. Where is it Going?

Selenium (₃₄Se), an antioxidant trace element, is an important regulator of brain function. These beneficial properties that Se possesses are attributed to its ability to be incorporated into selenoproteins as an amino acid. Several selenoproteins are expressed in the brain, in which some of them, e.g. glutathione peroxidases (GPxs), thioredoxin reductases (TrxRs) or selenoprotein P (SelP), are strongly involved in antioxidant defence and in maintaining intercellular reducing conditions. Since increased oxidative stress has been implicated in neurological disorders, including Parkinson’s disease, Alzheimer’s disease, stroke, epilepsy and others, a growing body of evidence suggests that Se depletion followed by decreased activity of Se-dependent enzymes may be important factors connected with those pathologies. Undoubtedly, the remarkable progress that has been made in understanding the biological function of Se in the brain has opened up new potential possibilities for the treatment of neurological diseases by using Se as a potential drug. However, further research in the search for optimal Se donors is necessary in order to achieve an effective and safe therapeutic income.

Identification and functional studies of regulatory variants responsible for the association of NRG3 with a delusion phenotype in schizophrenia

We previously reported genetic linkage for Schizophrenia (SZ) (NPL of 4.7) at 10q22 in the Ashkenazi Jewish (AJ) population. In follow up fine mapping we found strong evidence of association between three intronic single nucleotide variants (SNVs) in the 5' end of Neuregulin 3 (NRG3) and the delusion factor score of our phenotypic principal component analysis. Two independent groups replicated these findings, indicating that variants in NRG3 confer risk for a delusion-rich SZ subtype. To identify the causative variants, we sequenced the 162 kb linkage disequilibrium (LD) block covering the NRG3 5' end in 47 AJ SZ patients at the extremes of the delusion factor quantitative trait distribution. Among the identified variants we found 5 noncoding SNVs present on the high delusion factor haplotype and significantly overrepresented in high delusion factor subjects. We tested these for regulatory effects and found that risk alleles of rs10883866 and rs60827755 decreased and increased, respectively, the expression of a reporter gene as compared to the reference allele. In post-mortem brain RNA quantification experiments we found the same variants also perturb relative expression of alternative NRG3 isoforms. In summary, we have identified regulatory SNVs contributing to the association of NRG3 with delusion symptoms in SZ.

PARP-1 involvement in neurodegeneration: A focus on Alzheimer's and Parkinson's diseases

DNA damage is the prime activator of the enzyme poly(ADP-ribose)polymerase1 (PARP-1) whose overactivation has been proven to be associated with the pathogenesis of numerous central nervous system disorders, such as ischemia, neuroinflammation, and neurodegenerative diseases. Under oxidative stress conditions PARP-1 activity increases, leading to an accumulation of ADP-ribose polymers and NAD(+) depletion, that induces energy crisis and finally cell death. This review aims to explain the contribution of PARP-1 in neurodegenerative diseases, focusing on Alzheimer's and Parkinson's disease, to stimulate further studies on this issue and thereby engage a new perspective regarding the design of possible therapeutic agents or the identification of biomarkers.

Neuroprotective effects of extract of Acanthopanax senticosus harms on SH-SY5Y cells overexpressing wild-type or A53T mutant α-synuclein

Extract of Acanthopanax senticosus harms (EAS) has been shown to have neuroprotective effects on dopaminergic neurons in Parkinson's disease (PD) mice model. α-Synuclein is a key player in the pathogenesis of PD, the elevated level of which is deleterious to dopaminergic neurons, and enhancing its clearance might be a promising strategy for treating PD. To assess the potential of EAS in this regard, we investigated its effect on the SH-SY5Y cells overexpressing wild-type α-synuclein (WT-α-Syn) or A53T mutant α-synuclein (A53T-α-Syn), and the implicated pathway it might mediate. After treatment with EAS, the changes of α-synuclein, caspase-3, parkin, phospho-protein kinase B (Akt), phospho-glycogen synthase kinase 3 beta (GSK3β), and phospho-microtubule-associated protein tau (Tau) in WT-α-Syn or A53T-α-Syn transgenic cells were reverted back to near normal levels, demonstrated by the western blotting and quantitative real-time PCR outcomes. The neuroprotective effects of EAS may be able to protect WT-α-Syn or A53T-α-Syn transgenic SH-SY5Y cells from α-synuclein overexpression and toxicity. Therefore, we speculate that EAS might be a promising candidate for prevention or treatment of α-synuclein-related neurodegenerative disorders such as PD.

Pentose-phosphate pathway disruption in the pathogenesis of Parkinson’s disease

Oxidative stress is known to be a key factor in the pathogenesis of Parkinson’s disease (PD). Neuronal redox status is maintained by glucose metabolism via the pentose-phosphate pathway and it is known that disruption of glucose metabolism is damaging to neurons. Accumulating evidence supports the idea that glucose metabolism is altered in PD and dysregulation of the pentose-phosphate pathway in this disease has recently been shown. In this review, we present an overview of the literature regarding neuronal glucose metabolism and PD, and discuss the implications of these findings for PD pathogenesis and possible future therapeutic avenues.

Extracellular alpha-synuclein induces calpain-dependent overactivation of cyclin-dependent kinase 5 in vitro

Extracellular alpha-synuclein (ASN) could be involved in the pathomechanism of Parkinson's disease (PD) via disturbances of calcium homeostasis, activation of nitric oxide synthase and oxidative/nitrosative stress. In this study we analyzed the role of cyclin-dependent kinase 5 (Cdk5) in the molecular mechanism(s) of ASN toxicity. We found that exposure of PC12 cells to ASN increases Cdk5 activity via calpain-dependent p25 formation and by enhancement of Cdk5 phosphorylation at Tyr15. Cdk5 and calpain inhibitors prevented ASN-evoked cell death. Our findings, indicating the participation of Cdk5 in ASN toxicity, provide new insight into how extracellular ASN may trigger dopaminergic cell dysfunction in PD.

Toxicity of extracellular secreted alpha-synuclein: Its role in nitrosative stress and neurodegeneration

It has been demonstrated that both oligomerisation and accumulation of α-synuclein (ASN) are the key molecular processes involved in the pathophysiology of neurodegenerative diseases such as Parkinson's disease, Alzheimer's disease and other synucleinopathies. Alterations of ASN expression and impairment of its degradation can lead to the formation of intracellular deposits of this protein, called Lewy bodies. Overexpressed or misfolded ASN could be secreted to the extracellular space. Today the prion-like transmission of ASN oligomers to neighbouring cells is believed to be responsible for protein modification and propagation of neurodegeneration in the brain. It was presented that oxidative/nitrosative stress may play a key role in ASN secretion and spread of ASN pathology. Moreover, ASN-evoked protein oxidation, nitration and nitrosylation lead to disturbances in synaptic transmission and cell death. The interaction of secreted ASN with other amyloidogenic proteins and its involvement in irreversible mitochondrial disturbances and oxidative stress were also described. A better understanding of the mechanisms of ASN secretion and dysfunction may help to explain the molecular mechanisms of neurodegeneration and may be the basis for the development of novel therapeutic strategies.

Nitric oxide promotes MPK6-mediated caspase-3-like activation in cadmium-induced Arabidopsis thaliana programmed cell death

Nitric oxide (NO), a vital cell-signalling molecule, has been reported to regulate toxic metal responses in plants. This work investigated the effects of NO and the relationship between NO and mitogen-activated protein kinase (MAPK) in Arabidopsis (Arabidopsis thaliana) programmed cell death (PCD) induced by cadmium (Cd(2+) ) exposure. With fluorescence resonance energy transfer (FRET) analysis, caspase-3-like protease activation was detected after Cd(2+) treatment. This was further confirmed with a caspase-3 substrate assay. Cd(2+) -induced caspase-3-like activity was inhibited in the presence of the NO-specific scavenger 2-(4-carboxyphenyl)-4,4,5,5-tetramethylimidazoline-1-oxyl-3-oxide (cPTIO), suggesting that NO mediated caspase-3-like protease activation under Cd(2+) stress conditions. Pretreatment with cPTIO effectively inhibited Cd(2+) -induced MAPK activation, indicating that NO also affected the MAPK pathway. Interestingly, Cd(2+) -induced caspase-3-like activity was significantly suppressed in the mpk6 mutant, suggesting that MPK6 was required for caspase-3-like protease activation. To our knowledge, this is the first demonstration that NO promotes Cd(2+) -induced Arabidopsis PCD by promoting MPK6-mediated caspase-3-like activation.

Redox regulation of cysteine-dependent enzymes in neurodegeneration

Evidence of increased oxidative stress has been found in various neurodegenerative diseases and conditions. While it is unclear whether oxidative stress is a cause or effect, protein, lipid, and DNA have all been found to be susceptible to oxidant-induced modifications that alter their function. Results of clinical trials based on the oxidative-stress theory have been mixed, though data continues to indicate that prevention of high levels of oxidative stress is beneficial for health and increases longevity. Due to the highly reactive nature of the sulfhydryl group, the focus of this paper is on the impact of oxidative stress on cysteine-dependent enzymes and how oxidative stress may contribute to neurological dysfunction through this selected group of proteins.

Insulin promotes neuronal survival via the alternatively spliced protein kinase CδII isoform

Insulin signaling pathways in the brain regulate food uptake and memory and learning. Insulin and protein kinase C (PKC) pathways are integrated and function closely together. PKC activation in the brain is essential for learning and neuronal repair. Intranasal delivery of insulin to the central nervous system (CNS) has been shown to improve memory, reduce cerebral atrophy, and reverse neurodegeneration. However, the neuronal molecular mechanisms of these effects have not been studied in depth. PKCδ plays a central role in cell survival. Its splice variants, PKCδI and PKCδII, are switches that determine cell survival and fate. PKCδI promotes apoptosis, whereas PKCδII promotes survival. Here, we demonstrate that insulin promotes alternative splicing of PKCδII isoform in HT22 cells. The expression of PKCδI splice variant remains unchanged. Insulin increases PKCδII alternative splicing via the PI3K pathway. We further demonstrate that Akt kinase mediates phosphorylation of the splicing factor SC35 to promote PKCδII alternative splicing. Using overexpression and knockdown assays, we demonstrate that insulin increases expression of Bcl2 and bcl-xL via PKCδII. We demonstrate increased cell proliferation and increased BrdU incorporation in insulin-treated cells as well as in HT22 cells overexpressing PKCδII. Finally, we demonstrate in vivo that intranasal insulin promotes cognitive function in mice with concomitant increases in PKCδII expression in the hippocampus. This is the first report of insulin, generally considered a growth or metabolic hormone, regulating the alternative isoform expression of a key signaling kinase in neuronal cells such that it results in increased neuronal survival.

[Role of genetics in the etiology of synucleinopathies]

The protein family known as synucleins is composed of α-, β- and γ-synuclein. The most widely studied is the α-synuclein protein due to its participation in essential processes of the central nervous system. Neurotoxicity of this protein is related to the presence of multiplications (duplications and triplications) and point mutations in the gene sequence of the α-synuclein gene (SNCA), differential expression of its isoforms and variations in post-transductional modifications. Neurotoxicity is also related to cytoplasmic inclusions known as Lewy bodies (LBs) and Lewy neurites (LNs), which are also present in α-synucleinopathies. In general, the β-synuclein protein, codified by the SNCB gene, acts as a regulator of processes triggered by α-synuclein and its function is altered by variations in the gene sequence, while γ-synuclein, codified by the SNCG gene, seems to play a major role in certain tumoral processes.

The biochemical and cellular basis for nutraceutical strategies to attenuate neurodegeneration in Parkinson's disease

Future therapeutic intervention that could effectively decelerate the rate of degeneration within the substantia nigra pars compacta (SNc) could add years of mobility and reduce morbidity associated with Parkinson’s disease (PD). Neurodegenerative decline associated with PD is distinguished by extensive damage to SNc dopaminergic (DAergic) neurons and decay of the striatal tract. While genetic mutations or environmental toxins can precipitate pathology, progressive degenerative succession involves a gradual decline in DA neurotransmission/synaptic uptake, impaired oxidative glucose consumption, a rise in striatal lactate and chronic inflammation. Nutraceuticals play a fundamental role in energy metabolism and signaling transduction pathways that control neurotransmission and inflammation. However, the use of nutritional supplements to slow the progression of PD has met with considerable challenge and has thus far proven unsuccessful. This review re-examines precipitating factors and insults involved in PD and how nutraceuticals can affect each of these biological targets. Discussed are disease dynamics (Sections 1 and 2) and natural substances, vitamins and minerals that could impact disease processes (Section 3). Topics include nutritional influences on α-synuclein aggregation, ubiquitin proteasome function, mTOR signaling/lysosomal-autophagy, energy failure, faulty catecholamine trafficking, DA oxidation, synthesis of toxic DA-quinones, o-semiquinones, benzothiazolines, hyperhomocyseinemia, methylation, inflammation and irreversible oxidation of neuromelanin. In summary, it is clear that future research will be required to consider the multi-faceted nature of this disease and re-examine how and why the use of nutritional multi-vitamin-mineral and plant-based combinations could be used to slow the progression of PD, if possible.

Stimulation of natriuretic peptide receptor C attenuates accumulation of reactive oxygen species and nitric oxide synthesis in ammonia-treated astrocytes

Oxidative and nitrosative stress contribute to ammonia-induced astrocytic dysfunction in hepatic encephalopathy. Treatment of cultured astrocytes with 5 mmol/L ammonium chloride ('ammonia') increased the production of reactive oxygen species (ROS), including the toxic NADPH oxidase reaction product, •O(2)(-). Atrial natriuretic peptide (ANP), natriuretic peptide C and a selective natriuretic peptide receptor (NPR)-C ligand, cANP((4-23),) each decreased the total ROS content both in control cells and cells treated with ammonia. However, attenuation of •O(2)(-) accumulation by ANP and cANP((4-23),) was observed in ammonia-treated cells only and the effect of cANP((4-23)) was decreased when the NADPH oxidase-regulatory protein G(iα-2) was blocked with a specific anti-G(iα-2) antibody. Although in contrast to ANP, cANP((4-23)) did not elevate the cGMP content in control astrocytes, it decreased cAMP content and reduced the expression of G(iα-2), the NADPH oxidase-regulatory protein. The results show the presence of functional NPR-C in astrocytes, activation of which (i) attenuates basal ROS production, and (ii) prevents excessive accumulation of the toxic ROS species, •O(2)(-) by ammonia. Ammonia, ANP and cANP((4-23)) added separately, each stimulated formation of NO(x) (nitrates + nitrites) which was associated with up-regulation of the activity [cANP((4-23))] or/and expression (ammonia) of the endothelial isoform of nitric oxide synthase. However, the ammonia-induced increase of NO(x) was not augmented by co-addition of ANP, and was reduced to the control level by co-addition of cANP((4-23)) , indicating that activation of NPR-C may also reduce nitrosative stress. Future hepatic encephalopathy therapy might include the use of cANP((4-23)) or other NPR-C agonists to control oxidative/nitrosative stress induced by ammonia.