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- Block of GABAA receptor ion channel by penicillin: Electrophysiological and modeling insights toward the mechanism. [JOURNAL ARTICLE]
- Mol Cell Neurosci 2014 Oct 8.
GABAA receptors (GABAAR) mainly mediate fast inhibitory neurotransmission in the central nervous system. Different classes of modulators target GABAAR properties. Penicillin G (PNG) belongs to the class of noncompetitive antagonists blocking the open GABAAR and is a prototype of β-lactam antibiotics. In this study, we combined electrophysiological and modeling approaches to investigate the peculiarities of PNG blockade of GABA-activated currents recorded from isolated rat Purkinje cells and to predict the PNG binding site. Whole-cell patch-сlamp recording and fast application system was used in the electrophysiological experiments. PNG block developed after channel activation and increased with membrane depolarization suggesting that the ligand binds within the open channel pore. PNG blocked stationary component of GABA-activated currents in a concentration-dependent manner with IC50 value of 1.12mM at -70mV. The termination of GABA and PNG co-application was followed by a transient tail current. Protection of the tail current from bicuculline block and dependence of its kinetic parameters on agonist affinity suggest that PNG acts as a sequential open channel blocker that prevents agonist dissociation while the channel remains blocked. We built the GABAAR models based on nAChR and GLIC structures and performed an unbiased systematic search of the PNG binding site. Monte-Carlo energy minimization was used to find the lowest energy binding modes. We have shown that PNG binds close to the intracellular vestibule. In both models the maximum contribution to the energy of ligand-receptor interactions revealed residues located on the level of 2', 6' and 9' rings formed by a bundle of M2 transmembrane segments, indicating that these residues most likely participate in PNG binding. The predicted structural models support the described mechanism of PNG block.
- Time-lapse analysis of tangential migration in Sema6A and PlexinA2 knockouts. [JOURNAL ARTICLE]
- Mol Cell Neurosci 2014 Oct 2.
In the developing cerebellum, granule cells migrate tangentially in the external granule cell layer and then radially and inward, across the molecular layer and Purkinje cell layer. We showed previously that the transmembrane semaphorin Sema6A and its receptor PlexinA2 control the ability of migrating granule cells to switch from one mode of migration to the other. In both Sema6A and PlexinA2 knockouts, a large number of granule cells remain in the molecular layer, a defect that is most likely due to abnormal nuclear translocation. We show here that the lack of Sema6A or PlexinA2 preferentially much more severely perturbs the migration of later-born granule cells than early-born ones. We also use a cerebellum slice model system and electroporation to perform time-lapse analysis of of granule cell migration in wild-type mice, Sema6A and PlexinA2 knockouts. This study reveals that defects of tangential migration can be detected in bipolar granule cells before the initiation of radial migration. Our results also directly confirm that the absence of Sema6A does not perturb radial migration.
- A novel protective role for the innate immunity Toll-Like Receptor 3 (TLR3) in the retina via Stat3. [JOURNAL ARTICLE]
- Mol Cell Neurosci 2014 Sep 28.:38-48.
The innate immune system and inflammatory pathways play key roles in numerous diseases of the central nervous system (CNS). Recent evidence indicates that innate immunity induces both pathogenesis and protection during neuronal injury. To test the possibility that the conflicting roles of innate immunity in the CNS depends on the cellular environment in which innate immunity is stimulated, we analyzed the effect of Toll-Like Receptor 3 (TLR3) activation on neuronal survival in the presence and absence of oxidative injury in a mouse model system. We demonstrated that activation of TLR3 by the double stranded RNA activator, Poly (I:C), during paraquat induced oxidative stress, significantly protected mouse photoreceptors, as measured by increased retinal structure, function, and improved visual acuity. In contrast, TLR3 activation without concurrent oxidative injury was neurotoxic. The neurotoxic and protective effects of Poly (I:C) stimulation were absent in TLR3 knockout animals, which indicates that protection by Poly (I:C) is dependent on the TLR3 signaling pathway. Furthermore, we identified the pro-survival transcription factor Stat3 as a necessary mechanism for protection. Knockdown of Stat3 using lentivirally delivered shRNA abolished the protective effects of TLR3 signaling in the retina during oxidative stress. Therefore, TLR3 activation in the context of oxidative stress triggers protective instead of pathogenic signaling, suggesting that TLR3 is a potential therapeutic target for neurodegeneration where oxidative stress is a significant contributor.
- Kinesin KIF4A transports integrin β1 in developing axons of cortical neurons. [JOURNAL ARTICLE]
- Mol Cell Neurosci 2014 Sep 23.
CNS axons have poor regenerative ability compared to PNS axons, and mature axons regenerate less well than immature embryonic axons. The loss of regenerative ability with maturity is accompanied by the setting up of a selective transport filter in axons, restricting the types of molecule that are present. We confirm that integrins (represented by subunits β1 and α5) are present in early cortical axons in vitro but are excluded from mature axons. Ribosomal protein and L1 show selective axonal transport through association with kinesin kif4A; we have therefore examined the hypothesis that integrin transport might also be in association with kif4A. Kif4A is present in all processes of immature cortical neurons cultured at E18, then downregulated by 14days in vitro, coinciding with the exclusion of integrin from axons. Kif4a co-localizes with β1 integrin in vesicles in neurons and non-neuronal cells, and the two molecules co-immunoprecipitate. Knockdown of KIF4A expression with shRNA reduced the level of integrin β1 in axons of developing neurons and reduced neurite elongation on Laminin, an integrin-dependent substrate. Overexpression of kif4A triggered apoptosis in neuronal and non-neuronal cells. In mature neurons expression of kif4A-GFP at a modest level did not kill the cells, and the kif4A was detectable in their axons. However this was not accompanied by an increase in integrin β1 axonal transport, suggesting that kif4A is not the only integrin transporter, and that integrin exclusion from axons is controlled by factors other than the kif4A level.
- Nrf-2 regulation of prion protein expression is independent of oxidative stress. [JOURNAL ARTICLE]
- Mol Cell Neurosci 2014 Sep 16.:31-37.
Cellular expression of host prion protein (PrP) is essential to infection with prion disease. Understanding the mechanisms that regulate prion protein expression at both the transcriptional and translational levels is therefore an important goal. The cellular prion protein has been associated with resistance to oxidative, and its expression is also increased by oxidative stress. The transcription factor Nrf-2 is associated with cellular responses to oxidative stress and is known to induce upregulation of antioxidant defense mechanisms. We have identified an Nrf-2 binding site in the prion protein promoter (Prnp) and shown that Nrf-2 downregulated PrP expression. However, this effect is independent of oxidative stress as oxidative stress can up-regulate PrP expression regardless of the level of Nrf-2 expression. Furthermore, Nrf-2 has no impact on PrP expression when cells are infected with scrapie. These findings highlight that Nrf-2 can regulate PrP expression, but that this regulation becomes uncoupled during cellular stress.
- Mitochondria-derived reactive oxygen species mediate caspase-dependent and -independent neuronal deaths. [JOURNAL ARTICLE]
- Mol Cell Neurosci 2014 Sep 16.:13-23.
Mitochondrial dysfunction and oxidative stress are implicated in many neurodegenerative diseases. Mitochondria-targeted drugs that effectively decrease oxidative stress, protect mitochondrial energetics, and prevent neuronal loss may therefore lend therapeutic benefit to these currently incurable diseases. To investigate the efficacy of such drugs, we examined the effects of mitochondria-targeted antioxidants MitoQ10 and MitoE2 on neuronal death induced by neurotrophin deficiency. Our results indicate that MitoQ10 blocked apoptosis by preventing increased mitochondria-derived reactive oxygen species (ROS) and subsequent cytochrome c release, caspase activation, and mitochondrial damage in nerve growth factor (NGF)-deprived sympathetic neurons, while MitoE2 was largely ineffective. In this paradigm, the most proximal point of divergence was the ability of MitoQ10 to scavenge mitochondrial superoxide (O2(-)). MitoQ10 also prevented caspase-independent neuronal death in these cells demonstrating that the mitochondrial redox state significantly influences both apoptotic and nonapoptotic pathways leading to neuronal death. We suggest that mitochondria-targeted antioxidants may provide tools for delineating the role and significance of mitochondrial ROS in neuronal death and provide a new therapeutic approach for neurodegenerative conditions involving trophic factor deficits and multiple modes of cell death.
- PACAP induces plasticity at autonomic synapses by nAChR-dependent NOS1 activation and AKAP-mediated PKA targeting. [JOURNAL ARTICLE]
- Mol Cell Neurosci 2014 Aug 25.
Pituitary adenylate cyclase-activating polypeptide (PACAP) is a pleitropic neuropeptide found at synapses throughout the central and autonomic nervous system. We previously found that PACAP engages a selective G-protein coupled receptor (PAC1R) on ciliary ganglion neurons to rapidly enhance quantal acetylcholine (ACh) release from presynaptic terminals via neuronal nitric oxide synthase (NOS1) and cyclic AMP/protein kinase A (PKA) dependent processes. Here, we examined how PACAP stimulates NO production and targets resultant outcomes to synapses. Scavenging extracellular NO blocked PACAP-induced plasticity supporting a retrograde (post- to presynaptic) NO action on ACh release. Live-cell imaging revealed that PACAP stimulates NO production by mechanisms requiring NOS1, PKA and Ca(2+) influx. Ca(2+)-permeable nicotinic ACh receptors composed of α7 subunits (α7-nAChRs) are potentiated by PKA-dependent PACAP/PAC1R signaling and were required for PACAP-induced NO production and synaptic plasticity since both outcomes were blocked following their selective inhibition. Co-precipitation experiments showed that NOS1 associates with α7-nAChRs, many of which are perisynaptic, as well as with heteromeric α3*-nAChRs that generate the bulk of synaptic activity. NOS1-nAChR physical association would facilitate NO production at perisynaptic and adjacent postsynaptic sites to enhance focal ACh release from juxtaposed presynaptic terminals. The synaptic outcomes of PACAP/PAC1R signaling are localized by PKA anchoring proteins (AKAPs). PKA regulatory-subunit overlay assays identified five AKAPs in ganglion lysates, including a prominent neuronal subtype. Moreover, PACAP-induced synaptic plasticity was selectively blocked when PKA regulatory-subunit binding to AKAPs was inhibited. Taken together, our findings indicate that PACAP/PAC1R signaling coordinates nAChR, NOS1 and AKAP activities to induce targeted, retrograde plasticity at autonomic synapses. Such coordination has broad relevance for understanding the control of autonomic synapses and consequent visceral functions.
- Neuroproteomics in the Auditory Brainstem: Candidate Proteins for Ultrafast and Precise Information Processing. [JOURNAL ARTICLE]
- Mol Cell Neurosci 2014 Aug 13.
In the mammalian auditory brainstem, the cochlear nuclear complex (CN) and the superior olivary complex (SOC) feature structural and functional specializations for ultrafast (<1ms) and precise information processing. Their proteome, the basis for structure and function, has been rarely analyzed so far. Here we identified and quantified the protein profiles of three major auditory brainstem regions of adult rats, the CN, the SOC, and the inferior colliculus (IC). The rest of the brain served as a reference. Via label-free quantitative mass spectrometry and 2-D DIGE/MALDI-MS, we identified 584 and 297 proteins in the plasma membrane/synaptic vesicle proteome and the cytosolic proteome, respectively. 'Region-typical' proteins, i.e., those with higher abundance in one region than in the other three, were considered candidates for functional specializations. Key proteins were validated via Western blots and immunohistochemistry. Functional annotation clustering revealed an overrepresentation of neurofilament proteins among the CN+SOC-typical proteins. These are related to regulation of axon diameter and, thereby, conduction velocity. Interestingly, the sets of synapse-associated proteins differed between regions. For example, synaptotagmin-2 (Syt2), a Ca(2+) sensor for fast exocytosis, was CN+SOC+IC-typical, whereas Syt1 was CN+SOC+IC-atypical. Together, our quantitative comparison of protein profiles has revealed several interesting candidate proteins for ultrafast and precise information processing.
- CD31(+) cell transplantation promotes recovery from peripheral neuropathy. [Journal Article]
- Mol Cell Neurosci 2014 Sep.:60-7.
Recently, we reported that human peripheral blood (PB)-derived CD31(+) cells are highly angiogenic. In this study, we investigated the beneficial effects of CD31(+) cells on peripheral neuropathy in mice. CD31(+) cells were collected from the peripheral blood using magnetic activated cell sorting. CD31(+) cells exhibited higher levels of expression of angiogenic genes on real-time reverse transcriptase polymerase chain reaction. Peripheral neuropathy was induced by crushing the sciatic nerve with a hemostat, and CD31(+) cells were then injected intramuscularly along the sciatic nerve. CD31(+) cell transplantation restored motor nerve conduction velocity and voltage amplitude and improved motor coordination. In addition, CD31(+) cell transplantation significantly improved blood perfusion and increased intraneural vascularity in the sciatic nerve. Whole-mount fluorescent imaging and dot blot analysis showed that CD31(+) cells in the nerve possessed high engraftment and anti-apoptotic properties. Additionally, injected CD31(+) cells displayed neurovascular tropism and are highly incorporated with vasculature. Angiogenic cytokines were augmented in CD31(+)-injected nerve tissue, suggesting increased neovascularization. Taken together, these results indicate that CD31(+) cells might be a novel therapeutic strategy in the treatment of peripheral neuropathy.
- Differential synaptic distribution of the scaffold proteins Cask and Caskin1 in the bovine retina. [Journal Article]
- Mol Cell Neurosci 2014 Sep.:19-29.
Scaffold proteins organize pre- and postsynaptic compartments and align pre- and postsynaptic events. Cask is a multi-domain scaffold protein essential for brain synaptic functions. Caskin1 is a recently discovered, brain-specific Cask-interacting multi-domain protein of unknown function. In the present study, we determined the localization of these scaffold proteins in the bovine retina. The retina contains tonically active ribbon synapses and conventional synapses. We found Cask highly enriched in virtually all retinal synapses. Cask was localized in close vicinity to the active zone protein RIM1/2 in ribbon and conventional synapses. Caskin1 is also enriched in retinal synapses but is present only in a subset of Cask-positive synapses. These findings suggest that Cask plays an important role in all retinal synapses. In contrast, Caskin1 appears to execute more specialized functions in distinct sets of retinal synapses, possibly for neuronal pathway formation and stabilization of distinct synaptic contacts.