PKCδ mediates paraquat-induced Nox1 expression in dopaminergic neurons

MicroRNA-124-3p Modulates Alpha-Synuclein Expression Levels in a Paraquat-Induced in vivo Model for Parkinson's Disease

Parkinson's disease (PD) is the second most prevalent neurodegenerative disease and the most common movement disorder. Although PD etiology is not fully understood, alpha (α)-synuclein is a key protein involved in PD pathology. MicroRNAs (miRNA), small gene regulatory RNAs that control gene expression, have been identified as biomarkers and potential therapeutic targets for brain diseases, including PD. In particular, miR-124 is downregulated in the plasma and brain samples of PD patients. Recently we showed that the brain delivery of miR-124 counteracts 6-hydroxydopamine-induced motor deficits. However, its role in α-synuclein pathology has never been addressed. Here we used paraquat (PQ)-induced rat PD model to evaluate the role of miR-124-3p in α-synuclein accumulation and dopaminergic neuroprotection. Our results showed that an intranigral administration of miR-124-3p reduced the expression and aggregation of α-synuclein in the substantia nigra (SN) of rats exposed to PQ. NADPH oxidases (NOX), responsible for reactive oxygen species generation, have been considered major players in the development of α-synuclein pathology. Accordingly, miR-124-3p decreased protein expression levels of NOX1 and its activator, small GTPase Rac1, in the SN of PQ-lesioned rats. Moreover, miR-124-3p was able to counteract the reduced levels of pituitary homeobox 3 (PITX3), a protein required for the dopaminergic phenotype, induced by PQ in the SN. This is the first study showing that miR-124-3p decreases PQ-induced α-synuclein levels and the associated NOX1/Rac1 signaling pathway, and impacts PITX3 protein levels, supporting the potential of miR-124-3p as a disease-modifying agent for PD and related α-synucleinopathies.

The Association between NADPH Oxidase 2 (NOX2) and Drug Resistance in Cancer

NADPH oxidase, as a major source of intracellular reactive oxygen species (ROS), assumes an important role in the immune response and oxidative stress response of the body. NADPH oxidase 2 (NOX2) is the first and most representative member of the NADPH oxidase family, and its effects on the development of tumor cells are gaining more and more attention. Our previous study suggested that NCF4 polymorphism in p40phox, a key subunit of NOX2, affected the outcome of diffuse large B-cell lymphoma patients treated with rituximab. It hypothesized that NOX2-mediated ROS could enhance the cytotoxic effects of some anti-tumor drugs in favor of patients with tumors. Several reviews have summarized the role of NOX2 and its congeners-mediated ROS in anti-tumor therapy, but few studies focused on the relationship between the expression of NOX2 and anti-tumor drug resistance. In this article, we systematically introduced the NOX family, represented by NOX2, and a classification of the latest inhibitors and agonists of NOX2. It will help researchers to have a more rational and objective understanding of the dual role of NOX2 in tumor drug resistance and is expected to provide new ideas for oncology treatment and overcoming drug resistance in cancer.

Role of NADPH Oxidases in Blood-Brain Barrier Disruption and Ischemic Stroke

NADPH oxidases (Nox) are one of the main sources of reactive oxygen species (ROS) in the central nervous system (CNS). While these enzymes have been shown to be involved in physiological regulation of cerebral vascular tone, excessive ROS produced by Nox1-5 play a critical role in blood–brain barrier (BBB) dysfunction in numerous neuropathologies. Nox-derived ROS have been implicated in mediating matrix metalloprotease (MMP) activation, downregulation of junctional complexes between adjacent brain endothelial cells and brain endothelial cell apoptosis, leading to brain microvascular endothelial barrier dysfunction and consequently, increases in BBB permeability. In this review, we will highlight recent findings on the role played by these enzymes in BBB disruption induced by ischemic stroke.

NADPH Oxidases in the Central Nervous System: Regional and Cellular Localization and the Possible Link to Brain Diseases

Significance: The significant role of reduced nicotinamide adenine dinucleotide phosphate (NADPH) oxidase (Nox) in signal transduction is mediated by the production of reactive oxygen species (ROS), especially in the central nervous system (CNS). The pathogenesis of some neurologic and psychiatric diseases is regulated by ROS, acting as a second messenger or pathogen. Recent Advances: In the CNS, the involvement of Nox-derived ROS has been implicated in the regulation of multiple signals, including cell survival/apoptosis, neuroinflammation, migration, differentiation, proliferation, and synaptic plasticity, as well as the integrity of the blood/brain barrier. In these processes, the intracellular signals mediated by the members of the Nox family vary among different tissues. The present review illuminates the regions and cellular, subcellular localization of Nox isoforms in the brain, the signal transduction, and the role of NOX enzymes in pathophysiology, respectively. Critical Issues: Different signal transduction cascades are coupled to ROS derived from various Nox homologues with varying degrees. Therefore, a critical issue worth noting is the varied role of the homologues of NOX enzymes in different signaling pathways and also they mediate different phenotypes in the diverse pathophysiological condition. This substantiates the effectiveness of selective Nox inhibitors in the CNS. Future Directions: Further investigation to elucidate the role of various homologues of NOX enzymes in acute and chronic brain diseases and signaling mechanisms, and the development of more specific NOX inhibitors for the treatment of CNS disease are urgently needed. Antioxid. Redox Signal. 35, 951-973.

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.

Adeno-associated virus vector-mediated expression of DJ-1 attenuates learning and memory deficits in 2, 2´, 4, 4´-tetrabromodiphenyl ether (BDE-47)-treated mice

Evidence indicates that oxidative stress is the central pathological feature of 2, 2´, 4, 4´-tetrabromodiphenyl ether (BDE-47)-induced neurotoxicity. Protein kinase C delta (PKCδ), an oxidative stress-sensitive kinase, can be proteolytically cleaved to yield a catalytically active fragment (PKCδ-CF) that is involved in various neurodegenerative disorders. Here, we showed that BDE-47 treatment increased ROS, malondialdehyde, and protein carbonyl levels in the mouse hippocampus. In turn, excessive ROS induced caspase-3-dependent PKCδ activation and stimulated NF-κB p65 nuclear translocation, resulting in inflammation in the mouse hippocampus. These changes caused learning and memory deficits in BDE-47-treated mice. Treatment with Z-DEVD-fmk, a caspase-3 inhibitor, or N-acetyl-L-cysteine, an antioxidant, blocked PKCδ activation and subsequently inhibited inflammation, thereby improving learning and memory deficits in BDE-47-treated mice. Our data further showed that activation of ROS-PKCδ signaling was associated with DJ-1 downregulation, which exerted neuroprotective effects against oxidative stress induced by different neurotoxic agents. Adeno-associated viral vector-mediated DJ-1 overexpression in the hippocampus effectively inhibited excessive ROS production, suppressed caspase-3-dependent PKCδ cleavage, blunted inflammation and ultimately reversed learning and memory deficits in BDE-47-treated mice. Taken together, our results demonstrate that DJ-1 plays a pivotal role in BDE-47-induced neurotoxic effects and learning and memory deficits.

Histamine induces microglia activation and dopaminergic neuronal toxicity via H1 receptor activation

Background

Histamine is an amine widely known as a peripheral inflammatory mediator and as a neurotransmitter in the central nervous system. Recently, it has been suggested that histamine acts as an innate modulator of microglial activity. Herein, we aimed to disclose the role of histamine in microglial phagocytic activity and reactive oxygen species (ROS) production and to explore the consequences of histamine-induced neuroinflammation in dopaminergic (DA) neuronal survival.

Methods

The effect of histamine on phagocytosis was assessed both in vitro by using a murine N9 microglial cell line and primary microglial cell cultures and in vivo. Cells were exposed to IgG-opsonized latex beads or phosphatidylserine (PS) liposomes to evaluate Fcγ or PS receptor-mediated microglial phagocytosis, respectively. ROS production and protein levels of NADPH oxidases and Rac1 were assessed as a measure of oxidative stress. DA neuronal survival was evaluated in vivo by counting the number of tyrosine hydroxylase-positive neurons in the substantia nigra (SN) of mice.

Results

We found that histamine triggers microglial phagocytosis via histamine receptor 1 (H1R) activation and ROS production via H1R and H4R activation. By using apocynin, a broad NADPH oxidase (Nox) inhibitor, and Nox1 knockout mice, we found that the Nox1 signaling pathway is involved in both phagocytosis and ROS production induced by histamine in vitro. Interestingly, both apocynin and annexin V (used as inhibitor of PS-induced phagocytosis) fully abolished the DA neurotoxicity induced by the injection of histamine in the SN of adult mice in vivo. Blockade of H1R protected against histamine-induced Nox1 expression and death of DA neurons in vivo.

Conclusions

Overall, our results highlight the relevance of histamine in the modulation of microglial activity that ultimately may interfere with neuronal survival in the context of Parkinson’s disease (PD) and, eventually, other neurodegenerative diseases which are accompanied by microglia-induced neuroinflammation. Importantly, our results also open promising new perspectives for the therapeutic use of H1R antagonists to treat or ameliorate neurodegenerative processes.

Electronic supplementary material

The online version of this article (doi:10.1186/s12974-016-0600-0) contains supplementary material, which is available to authorized users.

Sphingosine 1-Phosphate-Induced ICAM-1 Expression via NADPH Oxidase/ROS-Dependent NF-κB Cascade on Human Pulmonary Alveolar Epithelial Cells

The intercellular adhesion molecule-1 (ICAM-1) expression is frequently correlated with the lung inflammation. In lung injury, sphingosine-1-phosphate (S1P, bioactive sphingolipid metabolite), participate gene regulation of adhesion molecule in inflammation progression and aggravate tissue damage. To investigate the transduction mechanisms of the S1P in pulmonary epithelium, we demonstrated that exposure of HPAEpiCs (human pulmonary alveolar epithelial cells) to S1P significantly induces ICAM-1 expression leading to increase monocyte adhesion on the surface of HPAEpiCs. These phenomena were effectively attenuated by pretreatments with series of inhibitors such as Rottlerin (PKCδ), PF431396 (PYK2), diphenyleneiodonium chloride (DPI), apocynin (NADPH oxidase), Edaravone (ROS), and Bay11-7082 (NF-κB). Consistently, knockdown with siRNA transfection of PKCδ, PYK2, p47^phox, and p65 exhibited the same results. Pretreatment with both Gq-coupled receptor antagonist (GPA2A) and Gi/o-coupled receptor antagonist (GPA2) also blocked the upregulation of ICAM-1 protein and mRNA induced by S1P. We observed that S1P induced PYK2 activation via a Gq-coupled receptor/PKCδ-dependent pathway. In addition, S1P induced NADPH oxidase activation and intracellular ROS generation, which were also reduced by Rottlerin or PF431396. We demonstrated that S1P induced NF-κB p65 phosphorylation and nuclear translocation in HPAEpiCs. Activated NF-κB was blocked by Rottlerin, PF431396, APO, DPI, or Edaravone. Besides, the results of monocyte adhesion assay indicated that S1P-induced ICAM-1 expression on HPAEpiCs can enhance the monocyte attachments. In the S1P-treated mice, we found that the levels of ICAM-1 protein and mRNA in the lung fractions, the pulmonary hematoma and leukocyte count in bronchoalveolar lavage fluid were enhanced through a PKCδ/PYK2/NADPH oxidase/ROS/NF-κB signaling pathway. We concluded that S1P-accelerated lung damage is due to the ICAM-1 induction associated with leukocyte recruitment.

The signaling pathway of NADPH oxidase and its role in glomerular diseases

Nicotinamide adenine dinucleotide phosphate (NADPH) oxidase (Nox), a major source of reactive oxygen species, is a critical mediator of redox signaling. It is well-documented that oxidative stress is associated with the development of glomerular diseases (GN). Hence, the Nox was also thought to be involved in the pathogenesis of GN. However, the expression of Nox in various GN was not consistent, the mechanisms by which the activity of the Nox enzymes in regulating renal cells remains unclear. Signaling pathways might be very important in the pathogenesis of GN. We performed this review to provide a relatively complete signaling pathways flowchart for Nox to the investigators who were interested in the role of Nox in the pathogenesis of GN. Here, we reviewed the signal transduction pathway of Nox and its role in the pathogenesis of GN.