Protein kinase C delta negatively regulates tyrosine hydroxylase activity and dopamine synthesis by enhancing protein phosphatase-2A activity in dopaminergic neurons

Phosphoproteomics implicates glutamatergic and dopaminergic signalling in the antidepressant-like properties of the iron chelator deferiprone

BACKGROUND

Current antidepressants have limitations due to insufficient efficacy and delay before improvement in symptoms. Polymorphisms of the serotonin transporter (5-HTT) gene have been linked to depression (when combined with stressful life events) and altered response to selective serotonergic reuptake inhibitors. We have previously revealed the antidepressant-like properties of the iron chelator deferiprone in the 5-HTT knock-out (KO) mouse model of depression. Furthermore, deferiprone was found to alter neural activity in the prefrontal cortex of both wild-type (WT) and 5-HTT KO mice.

METHODS

In the current study, we examined the molecular effects of acute deferiprone treatment in the prefrontal cortex of both genotypes via phosphoproteomics analysis.

RESULTS

In WT mice treated with deferiprone, there were 22 differentially expressed phosphosites, with gene ontology analysis implicating cytoskeletal proteins. In 5-HTT KO mice treated with deferiprone, we found 33 differentially expressed phosphosites. Gene ontology analyses revealed phosphoproteins that were predominantly involved in synaptic and glutamatergic signalling. In a drug-naïve cohort (without deferiprone administration), the analysis revealed 21 differentially expressed phosphosites in 5-HTT KO compared to WT mice. We confirmed the deferiprone-induced increase in tyrosine hydroxylase serine 40 residue phosphorylation (pTH-Ser40) (initially revealed in our phosphoproteomics study) by Western blot analysis, with deferiprone increasing pTH-Ser40 expression in WT and 5-HTT KO mice.

CONCLUSION

As glutamatergic and synaptic signalling are dysfunctional in 5-HTT KO mice (and are the target of fast-acting antidepressant drugs such as ketamine), these molecular effects may underpin deferiprone's antidepressant-like properties. Furthermore, dopaminergic signalling may also be involved in deferiprone's antidepressant-like properties.

Exploring Parkinson-associated kinases for CRISPR/Cas9-based gene editing: beyond alpha-synuclein

Parkinson's disease (PD) is a debilitating neurodegenerative disorder characterized by the loss of dopaminergic neurons in the substania nigra (SN) and is associated with progressive motor impairment. PD is classified into familial and sporadic forms. The first genetic association studies in PD reported the involvement of Synuclein alpha (SNCA) mutations in the pathobiology of familial PD. Subsequent studies suggested mutations in PTEN-induced putative kinase 1 (PINK1), PARKIN, leucine repeat kinase-2 (LRRK2), and DJ-1 causing familial PD. In addition, kinase dysregulation has been embroiled in the pathogenesis of PD. The genome-editing mechanism CRISPR (clustered regularly interspaced short palindromic repeats) has recently influenced industry and scientific discoveries and is expected to expedite neurodegenerative disease research. This review will discuss the structure, function, and history of the CRISPR/Cas9 genome editing system. Moreover, it summarizes genes-encoding kinases involved in PD pathogenesis and targeted by CRISPR/Cas9 technology, including LRRK2, PINK1, Protein kinase C-delta (PKC-γ), and adenosine monophosphate-activated protein kinase (AMPK). We provide an overview of novel kinases to be targeted by the CRISPR/Cas9 system such as G-protein coupled receptor kinases (GRKs), cyclin-G-associated kinases (GAKs), cyclin-dependent kinase 5 (CDK5), Ataxia telangiectasia mutated (ATM), c-ABL, and rearranged during transfection (RET) receptors. Additionally, we will explain the off-target effects of CRISPR/Cas9 system and how to address them. Also, we will shed light on the associated challenges and future directions that are enabling the efficient use of CRISPR/Cas9 technology in kinases research in PD. In conclusion, gene editing, in addition to gene therapy, might be a possible promising strategy for PD therapy.

Neuroprotective role for RORA in Parkinson's disease revealed by analysis of post-mortem brain and a dopaminergic cell line

Parkinson's disease (PD) is almost twice as prevalent in men, which has largely been attributed to neuroprotective effect of oestradiol in women. RORA (retinoic acid receptor-related orphan receptor alpha) regulates the transcription of central aromatase, the enzyme responsible for local oestradiol synthesis, simultaneously, RORA expression is regulated by sex hormones. Moreover, RORA protects neurones against oxidative stress, a key mechanism contributing to the loss of dopaminergic neurones in PD. Therefore, we hypothesized that there would be sex differences in RORA expression in the substantia nigra pars compacta (SNpc), which could contribute to sex differences observed in PD prevalence and pathogenesis. In a case control study, qPCR and western blot analyses were used to quantify gene and protein expression in the SNpc of post-mortem brains (n = 14 late-stage PD and 11 age and sex matched controls). The neuroprotective properties of a RORA agonist were then investigated directly using a cell culture toxin-based model of PD coupled with measures of viability, mitochondrial function and apoptosis. RORA was expressed at significantly higher levels in the SNpc from control females' brains compared to males. In PD, we found a significant increase in SNpc RORA expression in male PD compared to female PD. Treatment with a RORA agonist showed a significant neuroprotection in our cell culture model of PD and revealed significant effects on intracellular factors involved in neuronal survival and demise. This study is the first to demonstrate a sex specific pattern of RORA protein and gene expression in the SNpc of controls post-mortem human brains, and to show that this is differentially altered in male and female PD subjects, thus supporting a role for RORA in sex-specific aspects of PD. Furthermore, our in vitro PD model indicates mechanisms whereby a RORA agonist exerts its neuroprotective effect, thereby highlighting the translational potential for RORA ligands in PD.

CRISPR/Cas9 assisted stem cell therapy in Parkinson's disease

Since its discovery in 2012, CRISPR Cas9 has been tried as a direct treatment approach to correct the causative gene mutation and establish animal models in neurodegenerative disorders. Since no strategy developed until now could completely cure Parkinson's disease (PD), neuroscientists aspire to use gene editing technology, especially CRISPR/Cas9, to induce a permanent correction in genetic PD patients expressing mutated genes. Over the years, our understanding of stem cell biology has improved. Scientists have developed personalized cell therapy using CRISPR/Cas9 to edit embryonic and patient-derived stem cells ex-vivo. This review details the importance of CRISPR/Cas9-based stem cell therapy in Parkinson's disease in developing PD disease models and developing therapeutic strategies after elucidating the possible pathophysiological mechanisms.

Alzheimer's disease: Ablating single master site abolishes tau hyperphosphorylation

Hyperphosphorylation of the neuronal tau protein is a hallmark of neurodegenerative tauopathies such as Alzheimer's disease. A central unanswered question is why tau becomes progressively hyperphosphorylated. Here, we show that tau phosphorylation is governed by interdependence- a mechanistic link between initial site-specific and subsequent multi-site phosphorylation. Systematic assessment of site interdependence identified distinct residues (threonine-50, threonine-69, and threonine-181) as master sites that determine propagation of phosphorylation at multiple epitopes. CRISPR point mutation and expression of human tau in Alzheimer's mice showed that site interdependence governs physiologic and amyloid-associated multi-site phosphorylation and cognitive deficits, respectively. Combined targeting of master sites and p38α, the most central tau kinase linked to interdependence, synergistically ablated hyperphosphorylation. In summary, our work delineates how complex tau phosphorylation arises to inform therapeutic and biomarker design for tauopathies.

In vivo study of a novel protein kinase C that mediates immunocompetence and catecholamine biosynthesis in hemocytes of Litopenaeus vannamei by using its potential competitive inhibitor, bisindolylmaleimide I

This study applied bisindolylmaleimide I (BSM), a pharmacological competitive inhibitor of protein kinase C (PKC) enzymatic activity, at 1.25 pmol shrimp^-1 for 60 min to investigate the potential involvement of PKC in signal transduction pathways in the hemocytes of Litopenaeus vannamei. A novel PKC in L. vannamei (LvnPKC) was identified and characterized and was determined to be involved in mediating the neuroendocrine-immune regulatory network. The hemocytes of L. vannamei that receive BSM exhibit significantly decreased PKC activity and LvnPKC gene and protein expression levels. Furthermore, the total hemocyte count, hyaline cells, and semigranular cells increased significantly along with significant decreases in granular cells, and meanwhile, the significantly increased phenoloxidase activity, respiratory bursts, superoxide dismutase (SOD) activity, phagocytic activity, and neutrophil extracellular trap were observed; however, phagocytic activity decreased significantly. In a molecular model, the gene expressions of lipopolysaccharide- and β-1,3-glucan-binding protein, peroxinectin, cytosolic manganese SOD, mitochondrial manganese SOD, and copper/zinc SOD in the hemocytes of L. vannamei that had received BSM decreased significantly, but prophenoloxidase I increased significantly. In catecholamine biosynthesis, tyrosine, dopamine, and norepinephrine decreased significantly in the hemocytes of L. vannamei that had received BSM, and l-dihydroxyphenylalanine increased. Moreover, tyrosine hydroxylase (TH) activity increased significantly, whereas TH and dihydroxyphenylalanine decarboxylase gene expression decreased significantly. These findings suggest that BSM inhibits PKC activity in hemocytes in which LvnPKC gene and protein expression are also inhibited. Additionally, the hemocytes' immunocompetence, including their prophenoloxidase and antioxidant systems, phagocytic activity, and catecholamine biosynthesis, was disrupted, confirming the roles of LvnPKC in mediating the neuroendocrine-immune regulatory network in hemocytes.

Garcinol blocks motor behavioural deficits by providing dopaminergic neuroprotection in MPTP mouse model of Parkinson's disease: involvement of anti-inflammatory response

Although the etiology of Parkinson's disease (PD) is poorly understood, studies in animal models revealed loss of dopamine and the dopaminergic neurons harbouring the neurotransmitter to be the principal cause behind this neuro-motor disorder. Neuroinflammation with glial cell activation is suggested to play a significant role in dopaminergic neurodegeneration. Several biomolecules have been reported to confer dopaminergic neuroprotection in different animal models of PD, owing to their anti-inflammatory potentials. Garcinol is a tri-isoprenylated benzophenone isolated from Garcinia sp. and accumulating evidences suggest that this molecule could provide neuroprotection by modulating oxidative stress and inflammation. However, direct evidence of dopaminergic neuroprotection by garcinol in the pre-clinical model of PD is not yet reported. The present study aims to investigate whether administration of garcinol in the MPTP mouse model of PD may ameliorate the cardinal motor behavioural deficits and prevent the loss of dopaminergic neurons. As expected, garcinol blocked the parkinsonian motor behavioural deficits which include akinesia, catalepsy, and rearing anomalies in the mice model. Most importantly, the degeneration of dopaminergic cell bodies in the substantia nigra region was significantly prevented by garcinol. Furthermore, garcinol reduced the inflammatory marker, glial fibrillary acidic protein, in the substantia nigra region. Since glial hyperactivation-mediated inflammation is inevitably associated with the loss of dopaminergic neurons, our study suggests the anti-inflammatory role of garcinol in facilitating dopaminergic neuroprotection in PD mice. Hence, in the light of the present study, it is suggested that garcinol is an effective anti-parkinsonian agent to block motor behavioural deficits and dopaminergic neurodegeneration in PD.

Clustered regularly interspaced short palindromic repeats as an advanced treatment for Parkinson's disease

Recently, genome-editing technology like clustered regularly interspaced short palindromic repeats (CRISPR)/Cas9 has improved the translational gap in the treatments mediated through gene therapy. The advantages of the CRISPR system, such as, work in the living cells and tissues, candidate this technique for the employing in experiments and the therapy of central nervous system diseases. Parkinson's disease (PD) is a widespread, disabling, neurodegenerative disease induced by dopaminergic neuron loss and linked to progressive motor impairment. Pathophysiological basis knowledge of PD has modified the PD classification model and expresses in the sporadic and familial types. Analyses of the earliest genetic linkage have shown in PD the inclusion of synuclein alpha (SNCA) genomic duplication and SNCA mutations in the familial types of PD pathogenesis. This review analyzes the structure, development, and function in genome editing regulated through the CRISPR/Cas9. Also, it explains the genes associated with PD pathogenesis and the appropriate modifications to favor PD. This study follows the direction by understanding the PD linking analyses in which the CRISPR technique is applied. Finally, this study explains the limitations and future trends of CRISPR service in relation to the genome-editing process in PD patients' induced pluripotent stem cells.

Fyn Kinase-Mediated PKCδ Y311 Phosphorylation Induces Dopaminergic Degeneration in Cell Culture and Animal Models: Implications for the Identification of a New Pharmacological Target for Parkinson's Disease

Oxidative stress, neuroinflammation and apoptosis are some of the key etiological factors responsible for dopamin(DA)ergic degeneration during Parkinson's disease (PD), yet the downstream molecular mechanisms underlying neurodegeneration are largely unknown. Recently, a genome-wide association study revealed the FYN gene to be associated with PD, suggesting that Fyn kinase could be a pharmacological target for PD. In this study, we report that Fyn-mediated PKCδ tyrosine (Y311) phosphorylation is a key event preceding its proteolytic activation in a 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) model of Parkinsonism. MPP+/MPTP induced Fyn kinase activation in N27 DAergic neuronal cells and the mouse substantia nigra. PKCδ-Y311 phosphorylation by activated Fyn initiates the apoptotic caspase-signaling cascade during DAergic degeneration. Pharmacological attenuation of Fyn activity protected DAergic neurons from MPP+-induced degeneration in primary mesencephalic neuronal cultures. We further employed Fyn wild-type and Fyn knockout (KO) mice to confirm whether Fyn is a valid pharmacological target of DAergic neurodegeneration. Primary mesencephalic neurons from Fyn KO mice were greatly protected from MPP+-induced DAergic cell death, neurite loss and DA reuptake loss. Furthermore, Fyn KO mice were significantly protected from MPTP-induced PKCδ-Y311 phosphorylation, behavioral deficits and nigral DAergic degeneration. This study thus unveils a mechanism by which Fyn regulates PKCδ's pro-apoptotic function and DAergic degeneration. Pharmacological inhibitors directed at Fyn activation could prove to be a novel therapeutic target in the delay or halting of selective DAergic degeneration during PD.

Role of novel protein kinase C in neuroendocrine-immune regulatory network in haemocytes of Litopenaeus vannamei: An in vitro approach

Shrimp lack adaptive immune systems and mainly rely on the cellular and humoral defences, involving the haemocytes (functionally analogous to vertebrate leukocytes) in non-self matter recognition, elimination, and in downstream coagulation. Furthermore, the linkage between stress-induced catecholamine (CA), a class of biogenic amines (BAs), releasing and immunological responses has been detected in shrimp. Varied isotypes of protein kinase C (PKC) regulate multiple cellular processes following their specific location and distribution within the cells, and a novel PKC identified in Litopenaeus vannamei (termed as LvnPKC) is proposed to mediate signaling transduction of immunocompetence and BA biosynthesis. In the present study, we analyzed the effects of the LvnPKC-silenced haemocytes by co-incubating with its dsRNA on the immune responses specific to prophenoloxidase (proPO) and antioxidant systems as well as phagocytic activity. In addition, the capability of haemocytes to produce BAs was assessed. The results revealed that LvnPKC-silenced haemocytes can induce interference in phenoloxidase and superoxide dismutase activities, respiratory bursts, and phagocytic activity; meanwhile, the disturbed gene expressions of proPO activating enzyme, proPOII, lipopolysaccharide- and β-1,3-glucan-binding protein, and cytosolic manganese superoxide dismutase were detected. The same deviated pattern was observed in tyrosine, dopamine, and norepinephrine levels, and in dopamine β-hydroxylase (DBH) activity and gene expressions of tyrosine hydroxylase, DOPA decarboxylase, and DBH involving in BA biosynthesis. Taken together, these results suggest that the immunocompetence and BA biosynthesis of haemocytes can be mediated via LvPKC signaling transduction, which proved the presence of a neuroendocrine-immune regulatory network in haemocytes.

NT5DC2 affects the phosphorylation of tyrosine hydroxylase regulating its catalytic activity

5'-Nucleotidase domain-containing protein 2 (NT5DC2) has been revealed by genome-wide association studies (GWAS) as a gene implicated in neuropsychiatric disorders related to the abnormality of dopamine (DA) activity in the brain. Based on its amino acid sequence, NT5DC2 is assumed to be a member of the family of haloacid dehalogenase-type phosphatases; although there is no information about its function and structural conformation. We recently reported that NT5DC2 binds to tyrosine hydroxylase (TH) and that the down-regulation of NT5DC2 tended to increase DA synthesis. In this study, we investigated whether NT5DC2 could regulate the catalytic activity of TH, which converts tyrosine to DOPA, because the phosphorylation level of TH, controlled by protein kinases and phosphatases, is well known to regulate its catalytic activity. The down-regulation of NT5DC2 by siRNA increased mainly DOPA synthesis by TH in PC12D cells, although this down-regulation tended to increase the conversion of DOPA to DA by aromatic L-amino acid decarboxylase. The increased DOPA synthesis should be attributed to the catalytic activity of TH controlled by its phosphorylation, because Western blot analysis revealed that the down-regulation of NT5DC2 tended to increase the level of TH phosphorylated at its Ser residues, but not that of the TH protein. Moreover, the induction of kinase activity by forskolin markedly potentiated the phosphorylation of TH at its Ser40 in PC12D cells having down-regulated NT5DC2. Immunocytochemical analysis of PC12D cells demonstrated that NT5DC2, TH protein, and TH phosphorylated at its Ser40 were predominantly localized in the cytoplasm and that the localization of NT5DC2 and TH proteins partially overlapped. Collectively, our results indicate that NT5DC2 could work to inhibit the DOPA synthesis by decreasing the phosphorylation of TH at its Ser40. We propose that NT5DC2 might decrease this phosphorylation of TH by promoting dephosphorylation or by inhibiting kinase activity.

Tumor Necrosis Factor-Like Weak Inducer of Apoptosis (TWEAK) Enhances Activation of STAT3/NLRC4 Inflammasome Signaling Axis through PKCδ in Astrocytes: Implications for Parkinson's Disease

Astrocytic dysfunction has been implicated in Parkinson's disease (PD) pathogenesis. While the Tumor necrosis factor-like weak inducer of apoptosis (TWEAK)/Fn14 signaling axis is known to play a role in PD-like neuropathology, the molecular mechanisms that govern this process remain poorly understood. Herein, we show that TWEAK levels are elevated in PD serum compared to controls. Moreover, using both U373 human astrocyte cells and primary mouse astrocytes, we demonstrate that TWEAK induces mitochondrial oxidative stress as well as protein kinase C delta (PKCδ) and signal transducer and activator of transcription 3 (STAT3) activation, accompanied by NLRC4 inflammasome activation and upregulation and release of proinflammatory cytokines, including IL-1β, TNF-α, and IL-18. Mechanistically, TWEAK-induced PKCδ activation enhances the STAT3/NLRC4 signaling pathway and other proinflammatory mediators through a mitochondrial oxidative stress-dependent mechanism. We further show that PKCδ knockdown and mito-apocynin, a mitochondrial antioxidant, suppress TWEAK-induced proinflammatory NLRC4/STAT3 signaling and cellular oxidative stress response. Notably, we validated our in vitro findings in an MPTP mouse model of PD and in mice receiving intrastriatal administration of TWEAK. These results indicate that TWEAK is a key regulator of astroglial reactivity and illustrate a novel mechanism by which mitochondrial oxidative stress may influence dopaminergic neuronal survival in PD.

Mechanistic Interplay Between Autophagy and Apoptotic Signaling in Endosulfan-Induced Dopaminergic Neurotoxicity: Relevance to the Adverse Outcome Pathway in Pesticide Neurotoxicity

Chronic exposure to pesticides is implicated in the etiopathogenesis of Parkinson's disease (PD). Previously, we showed that dieldrin induces dopaminergic neurotoxicity by activating a cascade of apoptotic signaling pathways in experimental models of PD. Here, we systematically investigated endosulfan's effect on the interplay between apoptosis and autophagy in dopaminergic neuronal cell models of PD. Exposing N27 dopaminergic neuronal cells to endosulfan rapidly induced autophagy, indicated by an increased number of autophagosomes and LC3-II accumulation. Prolonged endosulfan exposure (>9 h) triggered apoptotic signaling, including caspase-2 and -3 activation and protein kinase C delta (PKCδ) proteolytic activation, ultimately leading to cell death, thus demonstrating that autophagy precedes apoptosis during endosulfan neurotoxicity. Furthermore, inhibiting autophagy with wortmannin, a phosphoinositide 3-kinase inhibitor, potentiated endosulfan-induced apoptosis, suggesting that autophagy is an early protective response against endosulfan. Additionally, Beclin-1, a major regulator of autophagy, was cleaved during the initiation of apoptotic cell death, and the cleavage was predominantly mediated by caspase-2. Also, caspase-2 and caspase-3 inhibitors effectively blocked endosulfan-induced apoptotic cell death. CRISPR/Cas9-based stable knockdown of PKCδ significantly attenuated endosulfan-induced caspase-3 activation, indicating that the kinase serves as a regulatory switch for apoptosis. Additional studies in primary mesencephalic neuronal cultures confirmed endosulfan's effect on autophagy and neuronal degeneration. Collectively, our results demonstrate that a functional interplay between autophagy and apoptosis dictate pesticide-induced neurodegenerative processes in dopaminergic neuronal cells. Our study provides insight into cell death mechanisms in environmentally linked neurodegenerative diseases.

Novel protein kinase C participates catecholamine biosynthesis and immunocompetence modulation in haemocytes of Litopenaeus vannamei

The catecholamine biosynthesis is required for physiological and immunological responses against stress, and the neuroendocrine-immune regulatory network plays a crucial role in immunocompetence of shrimp. A novel protein kinase C of Litopenaeus vannamei (LvnPKC) is involved in immune defense and signaling transduction in haemocytes, and in the present study, the gene silence technique is conducted to identify the role of LvnPKC on catecholamine biosynthesis and immunocompetence modulation in haemocytes of L. vannamei. The results show that tyrosine significantly increases in haemocytes of LvnPKC-silenced shrimp, and in the meantime, the obvious decrease of L-3, 4-dihydroxyphenylalanine and increase of dopamine as well as the consistent norepinephrine levels are detected. Tyrosine hydroxylase and dopamine β-hydroxylase activities are significantly reduced in haemocytes of LvnPKC-silenced shrimp. Total haemocyte count, hyaline cells and granulocytes insignificantly differ among treatments, and the obvious increase of phenoloxidase activity, respiratory bursts, superoxide dismutase and glutathione peroxidase activities are observed in haemocytes of LvnPKC-silenced shrimp, and furthermore, the downregulated phagocytic activity was observed. It is therefore concluded that the LvnPKC mediates catecholamine biosynthesis and immunocompetence in haemocytes, and plays a crucial role in the neuroendocrine-immune regulatory network.

CRISPR System: A High-throughput Toolbox for Research and Treatment of Parkinson's Disease

In recent years, the innovation of gene-editing tools such as the CRISPR/Cas9 system improves the translational gap of treatments mediated by gene therapy. The privileges of CRISPR/Cas9 such as working in living cells and organs candidate this technology for using in research and treatment of the central nervous system (CNS) disorders. Parkinson's disease (PD) is a common, debilitating, neurodegenerative disorder which occurs due to loss of dopaminergic neurons and is associated with progressive motor dysfunction. Knowledge about the pathophysiological basis of PD has altered the classification system of PD, which manifests in familial and sporadic forms. The first genetic linkage studies in PD demonstrated the involvement of Synuclein alpha (SNCA) mutations and SNCA genomic duplications in the pathogenesis of PD familial forms. Subsequent studies have also insinuated mutations in leucine repeat kinase-2 (LRRK2), Parkin, PTEN-induced putative kinase 1 (PINK1), as well as DJ-1 causing familial forms of PD. This review will attempt to discuss the structure, function, and development in genome editing mediated by CRISP/Cas9 system. Further, it describes the genes involved in the pathogenesis of PD and the pertinent alterations to them. We will pursue this line by delineating the PD linkage studies in which CRISPR system was employed. Finally, we will discuss the pros and cons of CRISPR employment vis-à-vis the process of genome editing in PD patients' iPSCs.

Protein kinase Cδ mediates methamphetamine-induced dopaminergic neurotoxicity in mice via activation of microsomal epoxide hydrolase

We previously demonstrated that activation of protein kinase Cδ (PKCδ) is critical for methamphetamine (MA)-induced dopaminergic toxicity. It was recognized that microsomal epoxide hydrolase (mEH) also induces dopaminergic neurotoxicity. It was demonstrated that inhibition of PKC modulates the expression of mEH. We investigated whether MA-induced PKCδ activation requires mEH induction in mice. MA treatment (8 mg/kg, i.p., × 4; 2 h interval) significantly enhanced the level of phosphorylated PKCδ in the striatum of wild type (WT) mice. Subsequently, treatment with MA resulted in significant increases in the expression of cleaved PKCδ and mEH. Treatment with MA resulted in enhanced interaction between PKCδ and mEH. PKCδ knockout mice exhibited significant attenuation of the enhanced mEH expression induced by MA. MA-induced hyperthermia, oxidative stress, proapoptotic potentials, and dopaminergic impairments were attenuated by PKCδ knockout or mEH knockout in mice. However, treating mEH knockout in mice with PKCδ inhibitor, rottlerin did not show any additive beneficial effects, indicating that mEH is a critical mediator of neurotoxic potential of PKCδ. Our results suggest that MA-induced PKCδ activation requires mEH induction as a downstream signaling pathway and that the modulation of the PKCδ and mEH interaction is important for the pharmacological intervention against MA-induced dopaminergic neurotoxicity.

Garcinol, a multifaceted sword for the treatment of Parkinson's disease

Garcinol, the principal phytoconstituent of plants belonging to the genus Garcinia, is known for its anti-oxidant as well as anti-inflammatory properties, which can be extended to its possible neuroprotective role. Recent reports disseminate the capacity of garcinol to influence neuronal growth and survival, alter the neurochemical status in brain, as well as regulate memory and cognition. The concomitant neuro-rescue property of garcinol may render it as an effective compound in Parkinson's disease (PD) therapeutics since it is capable of ameliorating the related pathophysiological changes. Emerging pieces of evidence linking histone acetylation defects to the progression of neurodegenerative diseases provide an effective basis for targeting PD. Hyperacetylation of histones has been reported in Parkinsonian brain, which demands the use of pharmacological inhibitors of histone acetyltransferases (HAT). Garcinol serves as a potent natural HAT inhibitor and has unveiled promising results in molecular interaction studies against Monoamine oxidase B (MAO-B) and Catechol-O-Methyltransferase (COMT), as well as in L-DOPA induced dyskinesia. This review highlights the prospective implications of garcinol as a novel anti-Parkinsonian agent, and establishes a bridge between histone acetylation defects and the pathological aspects of PD.

Involvement of a novel protein kinase C (nPKC) in immunocompetence in hemocytes of white shrimp, Litopenaeus vannamei

Complementary (c)DNA encoding novel protein kinase C (PKC) messenger (m)RNA of the white shrimp Litopenaeus vannamei, consisted of 2454-bp cDNA containing an open reading frame (ORF) of 2232 bp, belonging to the novel (n)PKC family of proteins characterized by their containing two phorbol ester/diacylglycerol-binding domains (C1 domain), a C2 domain, and a catalytic domain of the serine/threonine kinase, designated LvnPKC. A comparison of amino acid sequences showed that LvnPKC was closely related to arthropod nPKC. LvnPKC cDNA was detected in all tested tissues with a real-time PCR including the hepatopancreas, gills, muscles, subcuticular epithelium, abdominal nerve, thoracic nerve, brain, the stomach, heart, and especially in hemocytes and the intestines. Moreover, significantly upregulated LvnPKC expression was only observed in the eyestalk, brain, and hepatopancreas of shrimp transferred from 28 °C to 18 °C for 30 min. Induction of LvnPKC expression in hemocytes of L. vannamei injected with Vibrio alginolyticus at 10⁵ cfu shrimp^-1 was detected earlier than in those injected with 10³ cfu shrimp^-1. Shrimp received LvnPKC-dsRNA for 1 days specifically depleted the expression of LvnPKC mRNA in hemocytes compared those of diethylpyrocarbonate water treatment. After that, significantly decreased expressions of lipopolysaccharide - and β-1,3-glucan-binding protein, prophenoloxidase-activating enzyme, peroxinectin, prophenoloxidase I, and prophenoloxidase II in the prophenoloxidase-activating system; lysozyme and cytosolic manganese superoxide dismutase and mitochondrial manganese superoxide dismutase in the antioxidant system were observed. We therefore concluded that LvnPKC is involved in immune defense of L. vannamei exposed to hypothermal stress or infected with V. alginolyticus.

p38 mitogen activated protein kinase mediates cardiac Na+/H+ exchanger inhibition induced by Sildenafil

Since the original description as potent antianginal compounds, phosphodiesterase 5A inhibitors have continuously increased their possible therapeutic applications. In the heart, Sildenafil was shown to protect against an ischemic insult by decreasing cardiac Na⁺/H⁺ exchanger (NHE1) activity, action that was mediated by protein kinase G. p38 mitogen activated protein kinase (p38MAPK) activation was described in cardiac ischemia, but its precise role remains elusive. It has been shown that p38MAPK is activated by protein kinase G (PKG) in certain non-cardiac tissues, while in others modulates NHE1 activity. Current study was aimed to seek the role of p38MAPK in the Sildenafil-triggered pathway leading to NHE1 inhibition in myocardium. Rat isolated papillary muscles were used to evaluate NHE1 activity during intracellular pH recovery from an acidic load. Protein kinases phosphorylation (activation) was determined by western blot. Sustained acidosis promoted NHE1 hyperactivity by enhancing Ser703 phosphorylation, effect that was blunted by Sildenafil. p38MAPK inhibition reversed the effect of Sildenafil on NHE1. Activation of p38MAPK, by Sodium Arsenite or Anisomycin, mimicked the inhibitory effect of Sildenafil on the exchanger. Consistently, Sildenafil induced p38MAPK phosphorylation/activation during acidosis. Neither Sildenafil nor p38MAPK inhibition affected extracellular signal-regulated kinases 1/2 phosphorylation, kinases upstream NHE1. Furthermore, inhibition of NHE1 after p38MAPK activation was precluded by preventing the activation of protein phosphatase 2A with Okadaic Acid. Taken together, these results suggest that activation of p38MAPK is a necessary step to trigger the inhibitory effect of Sildenafil on cardiac NHE1 activity, thorough a mechanism that involves protein phosphatase 2A-mediated exchanger dephosphorylation.

Role of protein kinase Cδ in dopaminergic neurotoxic events

The pro-apoptotic role of Protein kinase Cδ (PKCδ), a member of the novel PKC subfamily, has been well-documented in various pathological conditions. In the central nervous system, the possible role of PKCδ has been studied, mainly in the condition of dopaminergic loss. It has been suggested that the phosphorylation of PKCδ at tyrosine 311 residue (Tyr³¹¹) by redox-sensitive Src family kinases (SFKs) is critical for the caspase-3-mediated proteolytic cleavage, which produces the constitutively active cleaved form of PKCδ. Mitochondrial translocation of cleaved PKCδ has been suggested to facilitate mitochondria-derived apoptosis and oxidative burdens. Moreover, it has been suggested that PKCδ contribute to neuroinflammation through the transformation of microglia into the pro-inflammatory M1 phenotype and the assembly of membrane NADPH oxidase in dopaminergic impairments. Interestingly, mitochondrial respiratory chain inhibitors or neuroinflammogens have shown to induce PKCδ activation in dopaminergic systems. Thus, PKCδ activation may be one of the pivotal causes of neuropathologic events, and could amplify these processes further in a positive feedback manner. Furthermore, PKCδ may play an intermediary role in connecting each neuropathologic event. This review affords insight into the role of PKCδ in various dopaminergic neurotoxic models, which could provide a potential target for mitigating dopaminergic neurotoxicity.

Tyrosine hydroxylase regulation in adult rat striatum following short-term neonatal exposure to manganese

Manganese (Mn) is an essential trace element required for a range of physiological processes, but Mn can also be neurotoxic especially during development. Excess levels of Mn accumulate preferentially in the striatum and can induce a syndrome called manganism, characterized by an initial stage of psychiatric disorder followed by motor impairment. In the present study, we investigated the effects of Mn exposure on the developing dopaminergic system, specifically tyrosine hydroxylase (TH) protein and phosphorylation levels in the striatum of rats. Neonatal rats were exposed to Mn intraperitoneally (ip) from post-natal day 8 up to day 12 (PND8-12). Striatal tissue was analysed on PND14 or PND70, to detect either short-term or long-term effects induced by Mn exposure. There was a dose dependent increase in TH protein levels in the striatum at PND14, reaching significance at 20 mg kg(-1) Mn, and this correlated with an increase in TH phosphorylation at serines 40, 31 and 19. However, in the striatum at PND70, a time by which Mn levels were no longer elevated, there was a dose dependent decrease in TH protein levels, reaching significance at 20 mg kg(-1) Mn, and this correlated with TH phosphorylation at Ser40 and Ser19. There was however a significant increase in phosphorylation of TH at serine 31 at 20 mg kg(-1) Mn, which did not correlate with TH protein levels. Taken together our findings suggest that neonatal Mn exposure can have both short-term and long-term effects on the regulation of TH in the striatal dopaminergic system.

The Anti-allergic Cromones: Past, Present, and Future

The anti-allergic cromones were originally synthesized in the 1960s by Fisons Plc, and the first drug to emerge from this program, disodium cromoglycate was subsequently marketed for the treatment of asthma and other allergic conditions. Whilst early studies demonstrated that the ability of the cromones to prevent allergic reactions was due to their 'mast cell stabilizing' properties, the exact pharmacological mechanism by which this occurred, remained a mystery. Here, we briefly review the history of these drugs, recount some aspects of their pharmacology, and discuss two new explanations for their unique actions. We further suggest how these findings could be used to predict further uses for the cromones.

Melatonin as a mitochondrial protector in neurodegenerative diseases

Mitochondria are crucial organelles as their role in cellular energy production of eukaryotes. Because the brain cells demand high energy for maintaining their normal activities, disturbances in mitochondrial physiology may lead to neuropathological events underlying neurodegenerative conditions such as Alzheimer's disease, Parkinson's disease and Huntington's disease. Melatonin is an endogenous compound with a variety of physiological roles. In addition, it possesses potent antioxidant properties which effectively play protective roles in several pathological conditions. Several lines of evidence also reveal roles of melatonin in mitochondrial protection, which could prevent development and progression of neurodegeneration. Since the mitochondrial dysfunction is a primary event in neurodegeneration, the neuroprotection afforded by melatonin is thereby more effective in early stages of the diseases. This article reviews mechanisms which melatonin exerts its protective roles on mitochondria as a potential therapeutic strategy against neurodegenerative disorders.

Protein kinase Cδ upregulation in microglia drives neuroinflammatory responses and dopaminergic neurodegeneration in experimental models of Parkinson's disease

Chronic microglial activation has been linked to the progressive degeneration of the nigrostriatal dopaminergic neurons evidenced in Parkinson's disease (PD) pathogenesis. The exact etiology of PD remains poorly understood. Although both oxidative stress and neuroinflammation are identified as co-contributors in PD pathogenesis, signaling mechanisms underlying neurodegenerative processes have yet to be defined. Indeed, we recently identified that protein kinase C delta (PKCδ) activation is critical for induction of dopaminergic neuronal loss in response to neurotoxic stressors. However, it remains to be defined whether PKCδ activation contributes to immune signaling events driving microglial neurotoxicity. In the present study, we systematically investigated whether PKCδ contributes to the heightened microglial activation response following exposure to major proinflammatory stressors, including α-synuclein, tumor necrosis factor α (TNFα), and lipopolysaccharide (LPS). We report that exposure to the aforementioned inflammatory stressors dramatically upregulated PKCδ with a concomitant increase in its kinase activity and nuclear translocation in both BV-2 microglial cells and primary microglia. Importantly, we also observed a marked upregulation of PKCδ in the microglia of the ventral midbrain region of PD patients when compared to age-matched controls, suggesting a role for microglial PKCδ in neurodegenerative processes. Further, shRNA-mediated knockdown and genetic ablation of PKCδ in primary microglia blunted the microglial proinflammatory response elicited by the inflammogens, including ROS generation, nitric oxide production, and proinflammatory cytokine and chemokine release. Importantly, we found that PKCδ activated NFκB, a key mediator of inflammatory signaling events, after challenge with inflammatory stressors, and that transactivation of NFκB led to translocation of the p65 subunit to the nucleus, IκBα degradation and phosphorylation of p65 at Ser536. Furthermore, both genetic ablation and siRNA-mediated knockdown of PKCδ attenuated NFκB activation, suggesting that PKCδ regulates NFκB activation subsequent to microglial exposure to inflammatory stimuli. To further investigate the pivotal role of PKCδ in microglial activation in vivo, we utilized pre-clinical models of PD. We found that PKCδ deficiency attenuated the proinflammatory response in the mouse substantia nigra, reduced locomotor deficits and recovered mice from sickness behavior in an LPS-induced neuroinflammation model of PD. Likewise, we found that PKCδ knockout mice treated with MPTP displayed a dampened microglial inflammatory response. Moreover, PKCδ knockout mice exhibited reduced susceptibility to the neurotoxin-induced dopaminergic neurodegeneration and associated motor impairments. Taken together, our studies propose a pivotal role for PKCδ in PD pathology, whereby sustained PKCδ activation drives sustained microglial inflammatory responses and concomitant dopaminergic neurotoxicity consequently leading to neurobehavioral deficits. We conclude that inhibiting PKCδ activation may represent a novel therapeutic strategy in PD treatment.

p73 gene in dopaminergic neurons is highly susceptible to manganese neurotoxicity

Chronic exposure to elevated levels of manganese (Mn) has been linked to a Parkinsonian-like movement disorder, resulting from dysfunction of the extrapyramidal motor system within the basal ganglia. However, the exact cellular and molecular mechanisms of Mn-induced neurotoxicity remain elusive. In this study, we treated C57BL/6J mice with 30mg/kg Mn via oral gavage for 30 days. Interestingly, in nigral tissues of Mn-exposed mice, we found a significant downregulation of the truncated isoform of p73 protein at the N-terminus (ΔNp73). To further determine the functional role of Mn-induced p73 downregulation in Mn neurotoxicity, we examined the interrelationship between the effect of Mn on p73 gene expression and apoptotic cell death in an N27 dopaminergic neuronal model. Consistent with our animal study, 300μM Mn treatment significantly suppressed p73 mRNA expression in N27 dopaminergic cells. We further determined that protein levels of the ΔNp73 isoform was also reduced in Mn-treated N27 cells and primary striatal cultures. Furthermore, overexpression of ΔNp73 conferred modest cellular protection against Mn-induced neurotoxicity. Taken together, our results demonstrate that Mn exposure downregulates p73 gene expression resulting in enhanced susceptibility to apoptotic cell death. Thus, further characterization of the cellular mechanism underlying p73 gene downregulation will improve our understanding of the molecular underpinnings of Mn neurotoxicity.

Physiological TLR5 expression in the intestine is regulated by differential DNA binding of Sp1/Sp3 through simultaneous Sp1 dephosphorylation and Sp3 phosphorylation by two different PKC isoforms

Toll-like receptor 5 (TLR5) expression in the intestinal epithelial cells (IECs) is critical to maintain health, as underscored by multiple intestinal and extra-intestinal diseases in mice genetically engineered for IEC-specific TLR5 knockout. A gradient of expression exists in the colonic epithelial cells from the cecum to the distal colon. Intriguingly, an identical gradient for the dietary metabolite, butyrate also exists in the luminal contents. However, both being critical for intestinal homeostasis and immune response, no studies examined the role of butyrate in the regulation of TLR5 expression. We showed that butyrate transcriptionally upregulates TLR5 in the IECs and augments flagellin-induced immune responses. Both basal and butyrate-induced transcription is regulated by differential binding of Sp-family transcription factors to the GC-box sequences over the TLR5 promoter. Butyrate activates two different protein kinase C isoforms to dephosphorylate/acetylate Sp1 by serine/threonine phosphatases and phosphorylate Sp3 by ERK-MAPK, respectively. This resulted in Sp1 displacement from the promoter and binding of Sp3 to it, leading to p300 recruitment and histone acetylation, activating transcription. This is the first study addressing the mechanisms of physiological TLR5 expression in the intestine. Additionally, a novel insight is gained into Sp1/Sp3-mediated gene regulation that may apply to other genes.

Dopaminergic lesioning impairs adult hippocampal neurogenesis by distinct modification of α-synuclein

Nonmotor symptoms of cognitive and affective nature are present in premotor and motor stages of Parkinson's disease (PD). Neurogenesis, the generation of new neurons, persists throughout the mammalian life span in the hippocampal dentate gyrus. Adult hippocampal neurogenesis may be severely affected in the course of PD, accounting for some of the neuropsychiatric symptoms such as depression and cognitive impairment. Two important PD-related pathogenic factors have separately been attributed to contribute to both PD and adult hippocampal neurogenesis: dopamine depletion and accumulation of α-synuclein (α-syn). In the acute 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine model, altered neurogenesis has been linked merely to a reduced dopamine level. Here, we seek to determine whether a distinct endogenous α-syn expression pattern is associated, possibly contributing to the hippocampal neurogenic deficit. We observed a persistent reduction of striatal dopamine and a loss of tyrosine hydroxylase-expressing neurons in the substantia nigra pars compacta in contrast to a complete recovery of tyrosine hydroxylase-immunoreactive dopaminergic fibers within the striatum. However, dopamine levels in the hippocampus were significantly decreased. Survival of newly generated neurons was significantly reduced and paralleled by an accumulation of truncated, membrane-associated, insoluble α-syn within the hippocampus. Specifically, the presence of truncated α-syn species was accompanied by increased activity of calpain-1, a calcium-dependent protease. Our results further substantiate the broad effects of dopamine loss in PD-susceptible brain nuclei, gradually involved in the PD course. Our findings also indicate a detrimental synergistic interplay between dopamine depletion and posttranslational modification of α-syn, contributing to impaired hippocampal plasticity in PD.

Alterations in mitochondrial dynamics induced by tebufenpyrad and pyridaben in a dopaminergic neuronal cell culture model

Tebufenpyrad and pyridaben are two agro-chemically important acaricides that function like the known mitochondrial toxicant rotenone. Although these two compounds have been commonly used to kill populations of mites and ticks in commercial greenhouses, their neurotoxic profiles remain largely unknown. Therefore, we investigated the effects of these two pesticides on mitochondrial structure and function in an in vitro cell culture model using the Seahorse bioanalyzer and confocal fluorescence imaging. The effects were compared with rotenone. Exposing rat dopaminergic neuronal cells (N27 cells) to tebufenpyrad and pyridaben for 3h induced dose-dependent cell death with an EC50 of 3.98μM and 3.77μM, respectively. Also, tebufenpyrad and pyridaben (3μM) exposure induced reactive oxygen species (ROS) generation and m-aconitase damage, suggesting that the pesticide toxicity is associated with oxidative damage. Morphometric image analysis with the MitoTracker red fluorescent probe indicated that tebufenpyrad and pyridaben, as well as rotenone, caused abnormalities in mitochondrial morphology, including reduced mitochondrial length and circularity. Functional bioenergetic experiments using the Seahorse XF96 analyzer revealed that tebufenpyrad and pyridaben very rapidly suppressed the basal mitochondrial oxygen consumption rate similar to that of rotenone. Further analysis of bioenergetic curves also revealed dose-dependent decreases in ATP-linked respiration and respiratory capacity. The luminescence-based ATP measurement further confirmed that pesticide-induced mitochondrial inhibition of respiration is accompanied by the loss of cellular ATP. Collectively, our results suggest that exposure to the pesticides tebufenpyrad and pyridaben induces neurotoxicity by rapidly initiating mitochondrial dysfunction and oxidative damage in dopaminergic neuronal cells. Our findings also reveal that monitoring the kinetics of mitochondrial respiration with Seahorse could be used as an early neurotoxicological high-throughput index for assessing the risk that pesticides pose to the dopaminergic neuronal system.

The epinephrine increases tyrosine hydroxylase expression through upregulating thioredoxin-1 in PC12 cells

Epinephrine is a stress hormone which is sharply increased in response to acute stress and is continuously elevated during persistent stress. Thioredoxin-1 (Trx-1) is a redox regulating protein and is induced under various stresses. Our previous study has shown that epinephrine induces the expression of Trx-1. Tyrosine hydroxylase (TH) is the major rate-limiting enzyme in catecholamine biosynthesis in response to stress. However, how TH is regulated by epinephrine is still unknown. In the present study, we found that epinephrine increased the expression of TH in a dose- and time-dependent manner in PC12 cells, which was inhibited by propranolol (β-adrenergic receptor inhibitor), but not by phenoxybenzamine (α-adrenergic receptor inhibitor). The increase of TH was also inhibited by SQ22536 (adenylyl cyclase inhibitor), H-89(PKA inhibitor) and LY294002 (phosphatidylinositol 3 kinase inhibitor). More importantly, overexpression of Trx-1 significantly enhanced the expression of TH, while Trx-1 siRNA suppressed TH expression induced by epinephrine. These results suggest that Trx-1 is involved in TH expression induced by epinephrine in PC12 cells.

Histone hyperacetylation up-regulates protein kinase Cδ in dopaminergic neurons to induce cell death: relevance to epigenetic mechanisms of neurodegeneration in Parkinson disease

The oxidative stress-sensitive protein kinase Cδ (PKCδ) has been implicated in dopaminergic neuronal cell death. However, little is known about the epigenetic mechanisms regulating PKCδ expression in neurons. Here, we report a novel mechanism by which the PKCδ gene can be regulated by histone acetylation. Treatment with histone deacetylase (HDAC) inhibitor sodium butyrate (NaBu) induced PKCδ expression in cultured neurons, brain slices, and animal models. Several other HDAC inhibitors also mimicked NaBu. The chromatin immunoprecipitation analysis revealed that hyperacetylation of histone H4 by NaBu is associated with the PKCδ promoter. Deletion analysis of the PKCδ promoter mapped the NaBu-responsive element to an 81-bp minimal promoter region. Detailed mutagenesis studies within this region revealed that four GC boxes conferred hyperacetylation-induced PKCδ promoter activation. Cotransfection experiments and Sp inhibitor studies demonstrated that Sp1, Sp3, and Sp4 regulated NaBu-induced PKCδ up-regulation. However, NaBu did not alter the DNA binding activities of Sp proteins or their expression. Interestingly, a one-hybrid analysis revealed that NaBu enhanced transcriptional activity of Sp1/Sp3. Overexpression of the p300/cAMP-response element-binding protein-binding protein (CBP) potentiated the NaBu-mediated transactivation potential of Sp1/Sp3, but expressing several HDACs attenuated this effect, suggesting that p300/CBP and HDACs act as coactivators or corepressors in histone acetylation-induced PKCδ up-regulation. Finally, using genetic and pharmacological approaches, we showed that NaBu up-regulation of PKCδ sensitizes neurons to cell death in a human dopaminergic cell model and brain slice cultures. Together, these results indicate that histone acetylation regulates PKCδ expression to augment nigrostriatal dopaminergic cell death, which could contribute to the progressive neuropathogenesis of Parkinson disease.

Complex molecular regulation of tyrosine hydroxylase

Tyrosine hydroxylase, the rate-limiting enzyme in catecholamine biosynthesis, is strictly controlled by several interrelated regulatory mechanisms. Enzyme synthesis is controlled by epigenetic factors, transcription factors, and mRNA levels. Enzyme activity is regulated by end-product feedback inhibition. Phosphorylation of the enzyme is catalyzed by several protein kinases and dephosphorylation is mediated by two protein phosphatases that establish a sensitive process for regulating enzyme activity on a minute-to-minute basis. Interactions between tyrosine hydroxylase and other proteins introduce additional layers to the already tightly controlled production of catecholamines. Tyrosine hydroxylase degradation by the ubiquitin-proteasome coupled pathway represents yet another mechanism of regulation. Here, we revisit the myriad mechanisms that regulate tyrosine hydroxylase expression and activity and highlight their physiological importance in the control of catecholamine biosynthesis.

Protein kinase D1 (PKD1) phosphorylation promotes dopaminergic neuronal survival during 6-OHDA-induced oxidative stress

Oxidative stress is a major pathophysiological mediator of degenerative processes in many neurodegenerative diseases including Parkinson’s disease (PD). Aberrant cell signaling governed by protein phosphorylation has been linked to oxidative damage of dopaminergic neurons in PD. Although several studies have associated activation of certain protein kinases with apoptotic cell death in PD, very little is known about protein kinase regulation of cell survival and protection against oxidative damage and degeneration in dopaminergic neurons. Here, we characterized the PKD1-mediated protective pathway against oxidative damage in cell culture models of PD. Dopaminergic neurotoxicant 6-hydroxy dopamine (6-OHDA) was used to induce oxidative stress in the N27 dopaminergic cell model and in primary mesencephalic neurons. Our results indicated that 6-OHDA induced the PKD1 activation loop (PKD1S744/S748) phosphorylation during early stages of oxidative stress and that PKD1 activation preceded cell death. We also found that 6-OHDA rapidly increased phosphorylation of the C-terminal S916 in PKD1, which is required for PKD1 activation loop (PKD1S744/748) phosphorylation. Interestingly, negative modulation of PKD1 activation by RNAi knockdown or by the pharmacological inhibition of PKD1 by kbNB-14270 augmented 6-OHDA-induced apoptosis, while positive modulation of PKD1 by the overexpression of full length PKD1 (PKD1^WT) or constitutively active PKD1 (PKD1^S744E/S748E) attenuated 6-OHDA-induced apoptosis, suggesting an anti-apoptotic role for PKD1 during oxidative neuronal injury. Collectively, our results demonstrate that PKD1 signaling plays a cell survival role during early stages of oxidative stress in dopaminergic neurons and therefore, positive modulation of the PKD1-mediated signal transduction pathway can provide a novel neuroprotective strategy against PD.

Novel siRNA delivery strategy: a new "strand" in CNS translational medicine?

RNA interference has been envisaged as a powerful tool for molecular and clinical investigation with a great potential for clinical applications. In recent years, increased understanding of cancer biology and stem cell biology has dramatically accelerated the development of technology for cell and gene therapy in these areas. This paper is a review of the most recent report of innovative use of siRNA to benefit several central nervous system diseases. Furthermore, a description is made of innovative strategies of delivery into the brain by means of viral and non-viral vectors with high potential for translation into clinical use. Problems are also highlighted that might hamper the transition from bench to bed, analyzing the lack of reliable preclinical models with predictive validity and the lack of effective delivery systems, which are able to overcome biological barriers and specifically reach the brain site of action.

Proteolytic activation of proapoptotic kinase protein kinase Cδ by tumor necrosis factor α death receptor signaling in dopaminergic neurons during neuroinflammation

BACKGROUND

The mechanisms of progressive dopaminergic neuronal loss in Parkinson's disease (PD) remain poorly understood, largely due to the complex etiology and multifactorial nature of disease pathogenesis. Several lines of evidence from human studies and experimental models over the last decade have identified neuroinflammation as a potential pathophysiological mechanism contributing to disease progression. Tumor necrosis factor α (TNF) has recently emerged as the primary neuroinflammatory mediator that can elicit dopaminergic cell death in PD. However, the signaling pathways by which TNF mediates dopaminergic cell death have not been completely elucidated.

METHODS

In this study we used a dopaminergic neuronal cell model and recombinant TNF to characterize intracellular signaling pathways activated during TNF-induced dopaminergic neurotoxicity. Etanercept and neutralizing antibodies to tumor necrosis factor receptor 1 (TNFR1) were used to block TNF signaling. We confirmed the results from our mechanistic studies in primary embryonic mesencephalic cultures and in vivo using the stereotaxic lipopolysaccharide (LPS) model of nigral dopaminergic degeneration.

RESULTS

TNF signaling in dopaminergic neuronal cells triggered the activation of protein kinase Cδ (PKCδ), an isoform of the novel PKC family, by caspase-3 and caspase-8 dependent proteolytic cleavage. Both TNFR1 neutralizing antibodies and the soluble TNF receptor Etanercept blocked TNF-induced PKCδ proteolytic activation. Proteolytic activation of PKCδ was accompanied by translocation of the kinase to the nucleus. Notably, inhibition of PKCδ signaling by small interfering (si)RNA or overexpression of a PKCδ cleavage-resistant mutant protected against TNF-induced dopaminergic neuronal cell death. Further, primary dopaminergic neurons obtained from PKCδ knockout (-/-) mice were resistant to TNF toxicity. The proteolytic activation of PKCδ in the mouse substantia nigra in the neuroinflammatory LPS model was also observed.

CONCLUSIONS

Collectively, these results identify proteolytic activation of PKCδ proapoptotic signaling as a key downstream effector of dopaminergic cell death induced by TNF. These findings also provide a rationale for therapeutically targeting PKCδ to mitigate progressive dopaminergic degeneration resulting from chronic neuroinflammatory processes.

Role of oxidative stress in methamphetamine-induced dopaminergic toxicity mediated by protein kinase Cδ

This study examined the role of protein kinase C (PKC) isozymes in methamphetamine (MA)-induced dopaminergic toxicity. Multiple-dose administration of MA did not significantly alter PKCα, PKCβI, PKCβII, or PKCζ expression in the striatum, but did significantly increase PKCδ expression. Gö6976 (a co-inhibitor of PKCα and -β), hispidin (PKCβ inhibitor), and PKCζ pseudosubstrate inhibitor (PKCζ inhibitor) did not significantly alter MA-induced behavioral impairments. However, rottlerin (PKCδ inhibitor) significantly attenuated behavioral impairments in a dose-dependent manner. In addition, MA-induced behavioral impairments were not apparent in PKCδ knockout (-/-) mice. MA-induced oxidative stress (i.e., lipid peroxidation and protein oxidation) was significantly attenuated in rottlerin-treated mice and was not apparent in PKCδ (-/-) mice. Consistent with this, MA-induced apoptosis (i.e., terminal deoxynucleotidyl transferase-mediated dUTP nick-end labeling-positive apoptotic cells) was significantly attenuated in rottlerin-treated mice. Furthermore, MA-induced increases in the dopamine (DA) turnover rate and decreases in tyrosine hydroxylase (TH) activity and the expression of TH, dopamine transporter (DAT), and vesicular monoamine transporter 2 (VMAT2) were not significantly observed in rottlerin-treated or PKCδ (-/-) mice. Our results suggest that PKCδ gene expression is a key mediator of oxidative stress and dopaminergic damage induced by MA. Thus, inhibition of PKCδ may be a useful target for protection against MA-induced neurotoxicity.

Methamphetamine-induced neurotoxicity linked to ubiquitin-proteasome system dysfunction and autophagy-related changes that can be modulated by protein kinase C delta in dopaminergic neuronal cells

A compromised protein degradation machinery has been implicated in methamphetamine (MA)-induced neurodegeneration. However, the signaling mechanisms that induce autophagy and ubiquitin-proteasome system (UPS) dysfunction are not well understood. The present study investigates the contributions of protein kinase C delta (PKCδ)-mediated signaling events in MA-induced autophagy, UPS dysfunction, and cell death. Using an in vitro mesencephalic dopaminergic cell culture model, we demonstrate that MA-induced early induction of autophagy is associated with reduction in proteasomal function and concomitant dissipation of mitochondrial membrane potential (MMP), followed by significantly increased PKCδ activation, caspase-3 activation, accumulation of ubiquitin-positive aggregates and microtubule-associated light chain-3 (LC3-II) levels. Interestingly, siRNA-mediated knockdown of PKCδ or overexpression of cleavage-resistant mutant of PKCδ dramatically reduced MA-induced autophagy, proteasomal function, and associated accumulation of ubiquitinated protein aggregates, which closely paralleled cell survival. Importantly, when autophagy was inhibited either pharmacologically (3-MA) or genetically (siRNA-mediated silencing of LC3), the dopaminergic cells became sensitized to MA-induced apoptosis through caspase-3 activation. Conversely, overexpression of LC3 partially protected against MA-induced apoptotic cell death, suggesting a neuroprotective role for autophagy in MA-induced neurotoxicity. Notably, rat striatal tissue isolated from MA-treated rats also exhibited elevated LC3-II, ubiquitinated protein levels, and PKCδ cleavage. Taken together, our data demonstrate that MA-induced autophagy serves as an adaptive strategy for inhibiting mitochondria-mediated apoptotic cell death and degradation of aggregated proteins. Our results also suggest that the sustained activation of PKCδ leads to UPS dysfunction, resulting in the activation of caspase-3-mediated apoptotic cell death in the nigrostriatal dopaminergic system.

PED/PEA-15 induces autophagy and mediates TGF-beta1 effect on muscle cell differentiation

TGF-beta1 has been shown to induce autophagy in certain cells but whether and how this action is exerted in muscle and whether this activity relates to TGF-beta1 control of muscle cell differentiation remains unknown. Here, we show that expression of the autophagy-promoting protein phosphoprotein enriched in diabetes/phosphoprotein enriched in astrocytes (PED/PEA-15) progressively declines during L6 and C2C12 skeletal muscle cell differentiation. PED/PEA-15 underwent rapid induction upon TGF-beta1 exposure of L6 and C2C12 myoblasts, accompanied by impaired differentiation into mature myotubes. TGF-beta1 also induced autophagy in the L6 and C2C12 cells through a PP2A/FoxO1-mediated mechanism. Both the TGF-beta1 effect on differentiation and that on autophagy were blocked by specific PED/PEA-15 ShRNAs. Myoblasts stably overexpressing PED/PEA-15 did not differentiate and showed markedly enhanced autophagy. In these same cells, the autophagy inhibitor 3-methyladenine rescued TGF-beta1 effect on both autophagy and myogenesis, indicating that PED/PEA-15 mediates TGF-beta1 effects in muscle. Muscles from transgenic mice overexpressing PED/PEA-15 featured a significant number of atrophic fibers, accompanied by increased light chain 3 (LC3)II to LC3I ratio and reduced PP2A/FoxO1 phosphorylation. Interestingly, these mice showed significantly impaired locomotor activity compared with their non-transgenic littermates. TGF-beta1 causes transcriptional upregulation of the autophagy-promoting gene PED/PEA-15, which in turn is capable to induce atrophic responses in skeletal muscle in vivo.

Dichotomy of tyrosine hydroxylase and dopamine regulation between somatodendritic and terminal field areas of nigrostriatal and mesoaccumbens pathways

Measures of dopamine-regulating proteins in somatodendritic regions are often used only as static indicators of neuron viability, overlooking the possible impact of somatodendritic dopamine (DA) signaling on behavior and the potential autonomy of DA regulation between somatodendritic and terminal field compartments. DA reuptake capacity is less in somatodendritic regions, possibly placing a greater burden on de novo DA biosynthesis within this compartment to maintain DA signaling. Therefore, regulation of tyrosine hydroxylase (TH) activity may be particularly critical for somatodendritic DA signaling. Phosphorylation of TH at ser31 or ser40 can increase activity, but their impact on L-DOPA biosynthesis in vivo is unknown. Thus, determining their relationship with L-DOPA tissue content could reveal a mechanism by which DA signaling is normally maintained. In Brown-Norway Fischer 344 F₁ hybrid rats, we quantified TH phosphorylation versus L-DOPA accumulation. After inhibition of aromatic acid decarboxylase, L-DOPA tissue content per recovered TH protein was greatest in NAc, matched by differences in ser31, but not ser40, phosphorylation. The L-DOPA per catecholamine and DA turnover ratios were significantly greater in SN and VTA, suggesting greater reliance on de novo DA biosynthesis therein. These compartmental differences reflected an overall autonomy of DA regulation, as seen by decreased DA content in SN and VTA, but not in striatum or NAc, following short-term DA biosynthesis inhibition from local infusion of the TH inhibitor α-methyl-p-tyrosine, as well as in the long-term process of aging. Such data suggest ser31 phosphorylation plays a significant role in regulating TH activity in vivo, particularly in somatodendritic regions, which may have a greater reliance on de novo DA biosynthesis. Thus, to the extent that somatodendritic DA release affects behavior, TH regulation in the midbrain may be critical for DA bioavailability to influence behavior.

Catecholamines up integrates dopamine synthesis and synaptic trafficking

The highly reactive nature of dopamine renders dopaminergic neurons vulnerable to oxidative damage. We recently demonstrated that loss-of-function mutations in the Drosophila gene Catecholamines up (Catsup) elevate dopamine pools but, paradoxically, also confer resistance to paraquat, an herbicide that induces oxidative stress-mediated toxicity in dopaminergic neurons. We now report a novel association of the membrane protein, Catsup, with GTP cyclohydrolase rate-limiting enzyme for tetrahydrobiopterin (BH(4)) biosynthesis and tyrosine hydroxylase, rate-limiting enzyme for dopamine biosynthesis, which requires BH(4) as a cofactor. Loss-of-function Catsup mutations cause dominant hyperactivation of both enzymes. Elevated dopamine levels in Catsup mutants coincide with several distinct characteristics, including hypermobility, minimal basal levels of 3,4-dihydroxy-phenylacetic acid, an oxidative metabolite of dopamine, and resistance to the vesicular monoamine transporter inhibitor, reserpine, suggesting that excess dopamine is synaptically active and that Catsup functions in the regulation of synaptic vesicle loading and release of dopamine. We conclude that Catsup regulates and links the dopamine synthesis and transport networks.

Protein kinase C-dependent dephosphorylation of tyrosine hydroxylase requires the B56δ heterotrimeric form of protein phosphatase 2A

Tyrosine hydroxylase, which plays a critical role in regulation of dopamine synthesis, is known to be controlled by phosphorylation at several critical sites. One of these sites, Ser40, is phosphorylated by a number of protein kinases, including protein kinase A. The major protein phosphatase that dephosphorylates Ser40 is protein phosphatase-2A (PP2A). A recent study has also linked protein kinase C to the dephosphorylation of Ser40 [1], but the mechanism is unclear. PP2A isoforms are comprised of catalytic, scaffold, and regulatory subunits, the regulatory B subunits being able to influence cellular localization and substrate selection. In the current study, we find that protein kinase C is able to phosphorylate a key regulatory site in the B56δ subunit leading to activation of PP2A. In turn, activation of the B56δ-containing heterotrimeric form of PP2A is responsible for enhanced dephosphorylation of Ser40 of tyrosine hydroylase in response to stimulation of PKC. In support of this mechanism, down-regulation of B56δ expression in N27 cells using RNAi was found to increase dopamine synthesis. Together these studies reveal molecular details of how protein kinase C is linked to reduced tyrosine hydroxylase activity via control of PP2A, and also add to the complexity of protein kinase/protein phosphatase interactions.

Protein kinases and phosphatases in the control of cell fate

Protein phosphorylation controls many aspects of cell fate and is often deregulated in pathological conditions. Several recent findings have provided an intriguing insight into the spatial regulation of protein phosphorylation across different subcellular compartments and how this can be finely orchestrated by specific kinases and phosphatases. In this review, the focus will be placed on (i) the phosphoinositide 3-kinase (PI3K) pathway, specifically on the kinases Akt and mTOR and on the phosphatases PP2a and PTEN, and on (ii) the PKC family of serine/threonine kinases. We will look at general aspects of cell physiology controlled by these kinases and phosphatases, highlighting the signalling pathways that drive cell division, proliferation, and apoptosis.

Modulation of TGFβ(2) and dopamine by PKC in retinal Müller cells of guinea pig myopic eye

AIM

To investigate the effect of protein kinase C (PKC) on transforming growth factor-β(2) (TGFβ(2)) and dopamine in retinal Müller cells of guinea pig myopic eye.

METHODS

Myopia was induced by translucent goggles in guinea pig, whose retinal Müller cells were cultured using the enzyme-digesting method. Retinal Müller cells were divided into 5 groups: normal control, myopia, myopia plus GF109203X, myopia plus PMA, myopia plus DMSO. PKC activities were detected by the non-radioactive methods. TGFβ(2) and tyrosine hydroxylase (TH) proteins were analyzed by Western Blotting in retinal Müller cells. Dopamine was determined by the high-performance liquid chromatography-electrochemical detection in suspensions.

RESULTS

After 14 days deprived, the occluded eyes became myopic with ocular axle elongating. Müller cells of guinea pigs were obtained using enzyme digestion. Compared with normal control group, the increase in PKC activity and the up-regulation in TGFβ(2) expression were found in retinal Müller cells of myopic eyes, with the decrease of TH and dopamine content (P<0.05). After PKC activated by PMA, TGFβ(2) and TH content were up-regulated with the increase of dopamine content (P<0.05). While the PKC activities was inhibited by GF109203X, proteins of TGFβ(2) and TH were down-regulated in the myopic eyes, with the decrease of dopamine content (P<0.05).

CONCLUSION

TGFβ(2) and dopamine are modulated by PKC in Müller cells of the myopic eyes in guinea pig.

PP2A targeting by viral proteins: a widespread biological strategy from DNA/RNA tumor viruses to HIV-1

Protein phosphatase 2A (PP2A) is a large family of holoenzymes that comprises 1% of total cellular proteins and accounts for the majority of Ser/Thr phosphatase activity in eukaryotic cells. Although initially viewed as constitutive housekeeping enzymes, it is now well established that PP2A proteins represent a family of highly and sophistically regulated phosphatases. The past decade, multiple complementary studies have improved our knowledge about structural and functional regulation of PP2A holoenzymes. In this regard, after summarizing major cellular regulation, this review will mainly focus on discussing a particulate biological strategy, used by various viruses, which is based on the targeting of PP2A enzymes by viral proteins in order to specifically deregulate, for their own benefit, cellular pathways of their hosts. The impact of such PP2A targeting for research in human diseases, and in further therapeutic developments, is also discussed.

Dopaminergic neurotoxicant 6-OHDA induces oxidative damage through proteolytic activation of PKCδ in cell culture and animal models of Parkinson's disease

The neurotoxicant 6-hydroxydopamine (6-OHDA) is used to investigate the cellular and molecular mechanisms underlying selective degeneration of dopaminergic neurons in Parkinson's disease (PD). Oxidative stress and caspase activation contribute to the 6-OHDA-induced apoptotic cell death of dopaminergic neurons. In the present study, we sought to systematically characterize the key downstream signaling molecule involved in 6-OHDA-induced dopaminergic degeneration in cell culture and animal models of PD. Treatment of mesencephalic dopaminergic neuronal N27 cells with 6-OHDA (100 μM) for 24h significantly reduced mitochondrial activity and increased cytosolic cytochrome c, followed by sequential activation of caspase-9 and caspase-3. Co-treatment with the free radical scavenger MnTBAP (10 μM) significantly attenuated 6-OHDA-induced caspase activities. Interestingly, 6-OHDA induced proteolytic cleavage and activation of protein kinase C delta (PKCδ) was completely suppressed by treatment with a caspase-3-specific inhibitor, Z-DEVD-FMK (50 μM). Furthermore, expression of caspase-3 cleavage site-resistant mutant PKCδ(D327A) and kinase dead PKCδ(K376R) or siRNA-mediated knockdown of PKCδ protected against 6-OHDA-induced neuronal cell death, suggesting that caspase-3-dependent PKCδ promotes oxidative stress-induced dopaminergic degeneration. Suppression of PKCδ expression by siRNA also effectively protected N27 cells from 6-OHDA-induced apoptotic cell death. PKCδ cleavage was also observed in the substantia nigra of 6-OHDA-injected C57 black mice but not in control animals. Viral-mediated delivery of PKCδ(D327A) protein protected against 6-OHDA-induced PKCδ activation in mouse substantia nigra. Collectively, these results strongly suggest that proteolytic activation of PKCδ is a key downstream event in dopaminergic degeneration, and these results may have important translational value for development of novel treatment strategies for PD.

Environmental neurotoxic pesticide dieldrin activates a non receptor tyrosine kinase to promote PKCδ-mediated dopaminergic apoptosis in a dopaminergic neuronal cell model

Oxidative stress and apoptosis are two key pathophysiological mechanisms underlying dopaminergic degeneration in Parkinson's disease (PD). Recently, we identified that proteolytic activation of protein kinase C-delta (PKCδ), a member of the novel PKC family, contributes to oxidative stress-induced dopaminergic degeneration and that phosphorylation of tyrosine residue 311 (tyr311) on PKCδ is a key event preceding the PKCδ proteolytic activation during oxidative damage. Herein, we report that a non-receptor tyrosine kinase Fyn is significantly expressed in a dopaminergic neuronal N27 cell model. Exposure of N27 cells to the dopaminergic toxicant dieldrin (60 μM) rapidly activated Fyn kinase, PKCδ-tyr311 phosphorylation and proteolytic cleavage. Fyn kinase activation precedes the caspase-3-mediated proteolytic activation of PKCδ. Pre-treatment with p60-tyrosine-specific kinase inhibitor (TSKI) almost completely attenuated dieldrin-induced phosphorylation of PKCδ-tyr311 and its proteolytic activation. Additionally, TSKI almost completely blocked dieldrin-induced apoptotic cell death. To further confirm Fyn's role in the pro-apoptotic function of PKCδ, we adopted the RNAi approach. siRNA-mediated knockdown of Fyn kinase also effectively attenuated dieldrin-induced phosphorylation of PKCδ-tyr311, caspase-3-mediated PKCδ proteolytic cleavage, and DNA fragmentation, suggesting that Fyn kinase regulates the pro-apoptotic function of PKCδ. Collectively, these results demonstrate for the first time that Fyn kinase is a pro-apoptotic kinase that regulates upstream signaling of the PKCδ-mediated apoptotic cell death pathway in neurotoxicity models of pesticide exposure.