Regulation of voltage-gated sodium channels by TNF-α during herpes simplex virus latency establishment.

During lytic or latent infection of sensory neurons with herpes simplex virus type 1 (HSV-1) there are significant changes in the expression of voltage-gated Na+ channels, which may disrupt the transmission of pain information. HSV-1 infection can also evoke the secretion of various pro-inflammatory cytokines, including TNF-α and IL-6. In this work, we hypothesized that TNF-α regulates the expression of Na+ channels during HSV-1 latency establishment in ND7/23 sensory-like neurons. Latency establishment was mimicked by culturing HSV-1 infected ND7/23 cells in the presence of acyclovir (ACV) for 3 days. Changes in the functional expression of voltage-gated Na+ channels were assessed by whole-cell recordings. Our results demonstrate that infection of ND7/23 cells with the HSV-1 strain McKrae with GFP expression (M-GFP) causes a significant decrease in sodium currents during latency establishment. Exposure of ND7/23 cells to TNF-α during latency establishment reverses the effect of HSV-1, resulting in a significant increase in sodium current density. However, Na+ currents were not restored by 3 day-treatment with IL-6. There were no changes in the pharmacological and biophysical properties of sodium currents promoted by TNF-α, including sensitivity to tetrodotoxin and the current-voltage relationship. TNF-α stimulation of ND7/23 cells increases p38 signaling. Inhibition of p38 signaling with SB203580 or SB202190 eliminates the stimulatory effect of TNF-α on sodium currents. These results indicate that TNF-α signaling in sensory neurons during latency establishment upregulates the expression of voltage-gated Na+ channels in order to maintain the transmission of pain information.

Regulation of Molecular Biomarkers Associated with the Progression of Prostate Cancer.

Androgen receptor signaling regulates the normal and pathological growth of the prostate. In particular, the growth and survival of prostate cancer cells is initially dependent on androgen receptor signaling. Exposure to androgen deprivation therapy leads to the development of castration-resistant prostate cancer. There is a multitude of molecular and cellular changes that occur in prostate tumor cells, including the expression of neuroendocrine features and various biomarkers, which promotes the switch of cancer cells to androgen-independent growth. These biomarkers include transcription factors (TP53, REST, BRN2, INSM1, c-Myc), signaling molecules (PTEN, Aurora kinases, retinoblastoma tumor suppressor, calcium-binding proteins), and receptors (glucocorticoid, androgen receptor-variant 7), among others. It is believed that genetic modifications, therapeutic treatments, and changes in the tumor microenvironment are contributing factors to the progression of prostate cancers with significant heterogeneity in their phenotypic characteristics. However, it is not well understood how these phenotypic characteristics and molecular modifications arise under specific treatment conditions. In this work, we summarize some of the most important molecular changes associated with the progression of prostate cancers and we describe some of the factors involved in these cellular processes.

IL-6 evoked biochemical changes in prostate cancer cells.

The pro-inflammatory cytokine IL-6 has been associated with the progression of PCa to a castration-resistant phenotype. In this work, we characterized the biochemical changes evoked by IL-6 in three different models of PCa cells, including LNCaP, C4-2, and PC3. The effect of IL-6 on PCa cells was compared with the effect obtained by co-stimulation with the cAMP-inducing agent forskolin (FSK). Stimulation of LNCaP cells with IL-6 or IL-6 + FSK evoked increased expression of the neuroendocrine marker tubulin IIIß and Cav3.2 T-type Ca2+ channel subunit. PC3 cells, representing a more advanced state of PCa, had high levels of tubulin IIIß expression without any further changes observed by treatment with IL-6 or IL-6 + FSK. Elevated expression of the glucocorticoid receptor was observed in PC3, but not in LNCaP or C4-2 cells. Glucocorticoid receptor expression was not regulated by IL-6 stimulation of LNCaP or C4-2 cells. IL-6 acting alone or together with FSK evoked a significant reduction in the expression of the transcription factor REST and retinoblastoma tumor suppressor protein Rb1. In LNCaP cells, IL-6 acting alone or together with FSK had no effect on the expression of several biological markers of advanced PCa, including Aurora kinase A, valosin-containing protein, calcium-sensing receptor, calreticulin, S100A protein, and Protein S. In PC3 cells, co-treatment with IL-6 + FSK evoked increased expression of REST and S100A proteins, as well as a reduction in Protein S levels. These findings reveal a complex pattern of biochemical changes in PCa cells under the influence of IL-6.

Establishing a Herpesvirus Quiescent Infection in Differentiated Human Dorsal Root Ganglion Neuronal Cell Line Mediated by Micro-RNA Overexpression.

HSV-1 is a neurotropic pathogen associated with severe encephalitis, excruciating orofacial sensation, and other chronic neuropathic complications. After the acute infection, the virus may establish a lifelong latency in the neurons of trigeminal ganglia (TG) and other sensory and autonomic ganglia, including the dorsal root ganglia (DRG), etc. The reactivation occurred periodically by a variety of physical or emotional stressors. We have been developing a human DRG neuronal cell-culture model HD10.6, which mimics the mature neurons for latency and reactivation with robust neuronal physiology. We found that miR124 overexpression without acyclovir (ACV) could maintain the virus in a quiescent infection, with the accumulation of latency-associate transcript (LAT). The immediate-early (IE) gene ICP0, on the other hand, was very low and the latent viruses could be reactivated by trichostatin A (TSA) treatment. Together, these observations suggested a putative role of microRNA in promoting HSV-1 latency in human neurons.

Evaluation of potential anticonvulsant fluorinated N-benzamide enaminones as T-type Ca2+ channel blockers.

Trifluoromethylated N-benzamide enaminones have been identified as potential anticonvulsants for the treatment of drug-resistant epilepsy. T-type Ca2+ channels are an important target for anti-seizure medications. Our laboratory has developed several fluorinated N-benzamide enaminone analogs that were evaluated by their ability to target T-type Ca2+ channels. Using whole cell voltage-clamp recordings, we identified two meta-trifluoromethyl N-benzamide enaminones with a significant inhibitory effect on T-type Ca2+ channels. These compounds had no effect on voltage-activated Na+ channels. We also evaluated the effect of the fluorinated N-benzamide enaminone analogs on the T-type Ca2+ channel subunits Cav3.2 and Cav3.3. The meta-trifluoromethyl N-benzamide enaminone lead analogs altered the steady-state inactivation of Cav3.2 T-type Ca2+ channels, which resulted in a significant increase in the inactivation recovery time of the channels. There was no effect of fluorinated N-benzamide enaminone analogs on the gating mechanism of T-type Ca2+ channels, as proven by the lack of effect on the activation and inactivation time constant of Ca2+ currents. On the contrary, the meta-trifluoromethyl N-benzamide enaminone lead analogs altered the gating mechanism of Cav3.3 T-type Ca2+ channels, as proven by the reduction in the activation and inactivation time constant of the channels. There was no effect on the inactivation kinetics of Cav3.3 T-type Ca2+ channels. The present results demonstrate that meta-substituted trifluoromethyl N-benzamide enaminone analogs target T-type Ca2+ channels by different mechanisms depending on the channel subunit. Meta-trifluoromethyl N-benzamide enaminone analogs can potentially lead to the design of more specific blockers of T-type Ca2+ channels for the treatment of epileptic seizures.

Major differences in glycosylation and fucosyltransferase expression in low-grade versus high-grade bladder cancer cell lines.

Bladder cancer is the ninth most frequently diagnosed cancer worldwide, and there is a need to develop new biomarkers for staging and prognosis of this disease. Here we report that cell lines derived from low-grade and high-grade bladder cancers exhibit major differences in expression of glycans in surface glycoproteins. We analyzed protein glycosylation in three low-grade bladder cancer cell lines RT4 (grade-1-2), 5637 (grade-2), and SW780 (grade-1), and three high-grade bladder cancer cell lines J82COT (grade-3), T24 (grade-3) and TCCSUP (grade-4), with primary bladder epithelial cells, A/T/N, serving as a normal bladder cell control. Using a variety of approaches including flow cytometry, immunofluorescence, glycomics and gene expression analysis, we observed that the low-grade bladder cancer cell lines RT4, 5637 and SW780 express high levels of the fucosylated Lewis-X antigen (Lex, CD15) (Galß1-4(Fucα1-3)GlcNAcß1-R), while normal bladder epithelial A/T/N cells lack Lex expression. T24 and TCCSUP cells also lack Lex, whereas J82COT cells express low levels of Lex. Glycomics analyses revealed other major differences in fucosylation and sialylation of N-glycans between these cell types. O-glycans are highly differentiated, as RT4 cells synthesize core 2-based O-glycans that are lacking in the T24 cells. These differences in glycan expression correlated with differences in RNA expression levels of their cognate glycosyltransferases, including α1-3/4-fucosyltransferase genes. These major differences in glycan structures and gene expression profiles between low- and high-grade bladder cancer cells suggest that glycans and glycosyltransferases are candidate biomarkers for grading bladder cancers.

Pathophysiological roles and therapeutic potential of voltage-gated ion channels (VGICs) in pain associated with herpesvirus infection.

Herpesvirus is ranked as one of the grand old members of all pathogens. Of all the viruses in the superfamily, Herpes simplex virus type 1 (HSV-1) is considered as a model virus for a variety of reasons. In a permissive non-neuronal cell culture, HSV-1 concludes the entire life cycle in approximately 18-20 h, encoding approximately 90 unique transcriptional units. In latency, the robust viral gene expression is suppressed in neurons by a group of noncoding RNA. Historically the lesions caused by the virus can date back to centuries ago. As a neurotropic pathogen, HSV-1 is associated with painful oral lesions, severe keratitis and lethal encephalitis. Transmission of pain signals is dependent on the generation and propagation of action potential in sensory neurons. T-type Ca2+ channels serve as a preamplifier of action potential generation. Voltage-gated Na+ channels are the main components for action potential production. This review summarizes not only the voltage-gated ion channels in neuropathic disorders but also provides the new insights into HSV-1 induced pain.

Modulation of Voltage-Gated Sodium Channel Activity in Human Dorsal Root Ganglion Neurons by Herpesvirus Quiescent Infection.

The molecular mechanisms of pain associated with alphaherpesvirus latency are not clear. We hypothesize that the voltage-gated sodium channels (VGSC) on the dorsal root ganglion (DRG) neurons controlling electrical impulses may have abnormal activity during latent viral infection and reactivation. We used herpes simplex virus 1 (HSV-1) to infect the human DRG-derived neuronal cell line HD10.6 in order to study the establishment and maintenance of viral latency, viral reactivation, and changes in the functional expression of VGSCs. Differentiated cells exhibited robust tetrodotoxin (TTX)-sensitive sodium currents, and acute infection significantly reduced the functional expression of VGSCs within 24 h and completely abolished VGSC activity within 3 days. A quiescent state of infection mimicking latency can be achieved in the presence of acyclovir (ACV) for 7 days followed by 5 days of ACV washout, and then the viruses can remain dormant for another 3 weeks. It was noted that during the establishment of HSV-1 latency, the loss of VGSC activity caused by HSV-1 infection could not be blocked by ACV treatment. However, neurons with continued ACV treatment for another 4 days showed a gradual recovery of VGSC functional expression. Furthermore, the latently infected neurons exhibited higher VGSC activity than controls. The overall regulation of VGSCs by HSV-1 during quiescent infection was proved by increased transcription and possible translation of Nav1.7. Together, these observations demonstrated a very complex pattern of electrophysiological changes during HSV infection of DRG neurons, which may have implications for understanding of the mechanisms of virus-mediated pain linked to latency and reactivation.IMPORTANCE The reactivation of herpesviruses, most commonly varicella-zoster virus (VZV) and pseudorabies virus (PRV), may cause cranial nerve disorder and unbearable pain. Clinical studies have also reported that HSV-1 causes postherpetic neuralgia and chronic occipital neuralgia in humans. The current work meticulously studies the functional expression profile changes of VGSCs during the processes of HSV-1 latency establishment and reactivation using human dorsal root ganglion-derived neuronal HD10.6 cells as an in vitro model. Our results indicated that VGSC activity was eliminated upon infection but steadily recovered during latency establishment and that latent neurons exhibited even higher VGSC activity. This finding advances our knowledge of how ganglion neurons generate uncharacteristic electrical impulses due to abnormal VGSC functional expression influenced by the latent virus.

Regulation of T-type Ca2+ channel expression by interleukin-6 in sensory-like ND7/23 cells post-herpes simplex virus (HSV-1) infection.

Herpes simplex virus-type 1 (HSV-1) infection of sensory neurons may lead to a significant reduction in the expression of voltage-activated Na+ and Ca2+ channels, which can disrupt the transmission of pain information. Viral infection also results in the secretion of various pro-inflammatory cytokines, including interleukin (IL)-6. In this work, we tested whether IL-6 regulates the expression of Na+ and Ca2+ channels post-HSV-1 infection in ND7/23 sensory-like neurons. Our results demonstrate that HSV-1 infection causes a significant decrease in the protein expression of the Cav3.2 T-type Ca2+ channel subunit, despite increasing Cav3.2 mRNA synthesis. Neither Cav3.2 mRNA nor total protein content was affected by IL-6 treatment post-HSV-1 infection. In ND7/23 cells, HSV-1 infection caused a significant reduction in the expression of Na+ and T-type Ca2+ channels within 48 h. Exposure of ND7/23 cells to IL-6 for 24 h post-infection reverses the effect of HSV-1, resulting in a significant increase in T-type Ca2+ current density. However, Na+ currents were not restored by 24-h treatment with IL-6 post-HSV-1 infection of ND7/23 cells. The ability of IL-6 to increase the functional expression of T-type Ca2+ channels on the membrane was blocked by the inhibition of protein trafficking with brefeldin-A and ERK1/2 activation. These results indicate that IL-6 release following HSV-1 infection regulates the expression of T-type Ca2+ channels, which may alter the transmission of pain information.

T-type Calcium Channels in Cancer.

Although voltage-activated Ca2+ channels are a common feature in excitable cells, their expression in cancer tissue is less understood. T-type Ca2+ channels are particularly overexpressed in various cancers. Because of their activation profile at membrane potentials close to rest and the generation of a window current, T-type Ca2+ channels may regulate a variety of Ca2+-dependent cellular processes, including cell proliferation, survival, and differentiation. The expression of T-type Ca2+ channels is of special interest as a target for therapeutic interventions.

6 Hz Active Anticonvulsant Fluorinated N-Benzamide Enaminones and Their Inhibitory Neuronal Activity.

A small library of novel fluorinated N-benzamide enaminones were synthesized and evaluated in a battery of acute preclinical seizure models. Three compounds (GSA 62, TTA 35, and WWB 67) were found to have good anticonvulsant activity in the 6-Hz 'psychomotor' 44-mA rodent model. The focus of this study was to elucidate the active analogs' mode of action on seizure-related molecular targets. Electrophysiology studies were employed to evaluate the compounds' ability to inhibit neuronal activity in central olfactory neurons, mitral cells, and sensory-like ND7/23 cells, which express an assortment of voltage and ligand-gated ion channels. We did not find any significant effects of the three compounds on action potential generation in mitral cells. The treatment of ND7/23 cells with 50 µM of GSA 62, TTA 35, and WWB 67 generated a significant reduction in the amplitude of whole-cell sodium currents. Similar treatment of ND7/23 cells with these compounds had no effect on T-type calcium currents, indicating that fluorinated N-benzamide enaminone analogs may have a selective effect on voltage-gated sodium channels, but not calcium channels.

Androgen receptor signaling regulates T-type Ca2+ channel expression and neuroendocrine differentiation in prostate cancer cells.

Therapies designed to reduce androgen production or receptor activation are effective in limiting prostate tumor growth. However, prolonged treatment with anti-androgen therapies results in the progression of prostate cancers into an androgen refractory state. Neuroendocrine differentiation (NED) has been associated with the progression of prostate cancers to an androgen resistant phenotype. In this work we investigated the effect of disrupting androgen receptor signaling in promoting NED of prostate carcinoma cells and whether it is accompanied by an increase in T-type Ca2+ channel expression. The effect of disrupting androgen signaling was assessed in LNCaP and 22Rv1 prostate cancer cells following treatment with the androgen receptor blocker, bicalutamide, or hormone-depleted media. Treatment of LNCaP cells with bicalutamide or hormone-depleted media for 4-10 d evoked considerable morphological and biochemical changes consistent with NED including the development of long neurite-like processes and the expression of the neuronal marker, tubulin IIIß. PCR analysis of bicalutamide-stimulated cells revealed no significant changes in Cav3.2 mRNA. However, stimulation of LNCaP cells with bicalutamide or hormone-depleted media for 10 d evoked a significant increase in Cav3.2 protein expression and the appearance of functional T-type Ca2+ channels. Inhibition of T-type Ca2+ channel function with various pharmacological blockers disrupted the morphological differentiation of LNCaP cells. Bicalutamide-evoked expression of functional T-type Ca2+ channels in LNCaP cells promoted chemoresistance to docetaxel. These findings indicate that disruption of androgen receptor signaling in prostate cancer cells evokes increased expression of functional T-type Ca2+ channels, which may result in significant morphological and biochemical changes.

Regulation of T-type Ca2+ channel expression by herpes simplex virus-1 infection in sensory-like ND7 cells.

Infection of sensory neurons by herpes simplex virus (HSV)-1 disrupts electrical excitability, altering pain sensory transmission. Because of their low threshold for activation, functional expression of T-type Ca2+ channels regulates various cell functions, including neuronal excitability and neuronal communication. In this study, we have tested the effect of HSV-1 infection on the functional expression of T-type Ca2+ channels in differentiated ND7-23 sensory-like neurons. Voltage-gated Ca2+ currents were measured using whole cell patch clamp recordings in differentiated ND7-23 neurons under various culture conditions. Differentiation of ND7-23 cells evokes a significant increase in T-type Ca2+ current densities. Increased T-type Ca2+ channel expression promotes the morphological differentiation of ND7-23 cells and triggers a rebound depolarization. HSV-1 infection of differentiated ND7-23 cells causes a significant loss of T-type Ca2+ channels from the membrane. HSV-1 evoked reduction in the functional expression of T-type Ca2+ channels is mediated by several factors, including decreased expression of Cav3.2 T-type Ca2+ channel subunits and disruption of endocytic transport. Decreased functional expression of T-type Ca2+ channels by HSV-1 infection requires protein synthesis and viral replication, but occurs independently of Egr-1 expression. These findings suggest that infection of neuron-like cells by HSV-1 causes a significant disruption in the expression of T-type Ca2+ channels, which can results in morphological and functional changes in electrical excitability.

Developmental plasticity of phrenic motoneuron and diaphragm properties with the inception of inspiratory drive transmission in utero.

The review outlines data consistent with the hypothesis that inspiratory drive transmission that generates fetal breathing movements (FBMs) is essential for the developmental plasticity of phrenic motoneurons (PMNs) and diaphragm musculature prior to birth. A systematic examination during the perinatal period demonstrated a very marked transformation of PMN and diaphragm properties coinciding with the onset and strengthening of inspiratory drive and FBMs in utero. This included studies of age-dependent changes of: i) morphology, neuronal coupling, passive and electrophysiological properties of PMNs; ii) rhythmic inspiratory activity in vitro; iii) FBMs generated in vivo detected by ultrasonography; iv) contractile and end-plate potential properties of diaphragm musculature. We also propose how the hypothesis can be further evaluated with studies of perinatal hypoglossal motoneuron-tongue musculature and the use of Dbx1 null mice that provide an experimental model lacking descending inspiratory drive transmission in utero.

Volatile Organic Compound Gamma-Butyrolactone Released upon Herpes Simplex Virus Type -1 Acute Infection Modulated Membrane Potential and Repressed Viral Infection in Human Neuron-Like Cells.

Herpes Simplex Virus Type -1 (HSV-1) infections can cause serious complications such as keratitis and encephalitis. The goal of this study was to identify any changes in the concentrations of volatile organic compounds (VOCs) produced during HSV-1 infection of epithelial cells that could potentially be used as an indicator of a response to stress. An additional objective was to study if any VOCs released from acute epithelial infection may influence subsequent neuronal infection to facilitate latency. To investigate these hypotheses, Vero cells were infected with HSV-1 and the emission of VOCs was analyzed using two-dimensional gas chromatograph/mass spectrometry (2D GC/MS). It was observed that the concentrations of gamma-butyrolactone (GBL) in particular changed significantly after a 24-hour infection. Since HSV-1 may establish latency in neurons after the acute infection, GBL was tested to determine if it exerts neuronal regulation of infection. The results indicated that GBL altered the resting membrane potential of differentiated LNCaP cells and promoted a non-permissive state of HSV-1 infection by repressing viral replication. These observations may provide useful clues towards understanding the complex signaling pathways that occur during the HSV-1 primary infection and establishment of viral latency.

Posttranscriptional regulation of T-type Ca(2+) channel expression by interleukin-6 in prostate cancer cells.

BACKGROUND: At early stages, the growth of prostate cancers is androgen dependent. At later stages, however, the growth of prostate cancers becomes androgen independent, which leads to an increase in mortality. The switch to an androgen-refractory state is associated with neuroendocrine differentiation (NED) of prostate cancer cells. Several factors including interleukin-6 (IL-6) and increased cAMP production promote NED of prostate cancer cells. In this work we investigated whether IL-6 evoked NED of LNCaP cells results in a significant change in T-type Ca(2+) channel expression in comparison to non-stimulated LNCaP cells. METHODS: T-type Ca(2+) channel subunit Cav3.2 expression was studied using PCR analysis, western blot and whole cell recordings. Tubulin IIIß expression and neurite-like morphology was assessed to investigate the role of T-type Ca(2+) channels in the differentiation of prostate cancer cells. RESULTS: Treatment of LNCaP cells with IL-6 for 4days evokes considerable morphological and biochemical changes consistent with NED. Transcripts of the T-type Ca(2+) channel subunit Cav3.2 but not Cav3.1 or Cav3.3 are detected in IL-6 stimulated cells. Real time PCR analysis of IL-6 stimulated cells indicates no significant change in Cav3.2 mRNA expression in comparison to non-stimulated cells. LNCaP cells stimulated with IL-6 show a threefold increase in T-type Ca(2+) channel subunit Cav3.2 protein expression, suggesting that channel expression is upregulated by a posttranscriptional mechanism. Electrophysiological recordings reveal that increased Cav3.2 protein expression following IL-6 stimulation of LNCaP cells does not result in increased expression of functional channels in the membrane. Functional expression of Cav3.2 channels in LNCaP cells is facilitated by co-stimulation with IL-6 and the cAMP-stimulating agent, forskolin (FSK). Inhibition of T-type Ca(2+) channel activity in IL-6 stimulated LNCaP cells prevents the development of morphological characteristics consistent with NED. CONCLUSIONS: These results indicate that the functional expression of T-type Ca(2+) channels is regulated by the interplay of multiple factors in LNCaP cells.

Regulation of T-type calcium channel expression by sodium butyrate in prostate cancer cells.

Several cellular mechanisms contribute to the neuroendocrine differentiation of prostate cancer cells, including exposure to sodium butyrate (NaBu), a naturally occurring salt of the short chain fatty acid n-butyric acid. NaBu belongs to a class of histone deacetylase inhibitors with potential anticancer function. T-type calcium channel expression constitutes an important route for calcium influx in tumor cells that may trigger changes in cell proliferation and differentiation. In this work we investigated the role NaBu on the differentiation of lymph node carcinoma of the prostate (LNCaP) cells and its effect on T-type Ca(2+) channel expression. NaBu stimulates the morphological and molecular differentiation of LNCaP cells. Stimulation of LNCaP cells with NaBu evokes a significant increase in the expression of the Cav3.2 T-type channel subunits. Furthermore, the increased Cav3.2 expression promotes membrane insertion of T-type Ca(2+) channels capable of generating fast inactivating Ca(2+) currents, sensitive to 100µM Ni(2+) ions. Inhibition of T-type Ca(2+) channel function reduces the outgrowth of neurite-like processes in LNCaP cells. NaBu-evoked expression of T-type Ca(2+) channels is also involved in the regulation of cell viability. Inhibition of T-type Ca(2+) channels causes a significant reduction in the viability of LNCaP cells treated with 1mM NaBu, suggesting that Ca(2+) influx via T-type channels can promote cell proliferation. However, increased expression of T-type Ca(2+) channels enhanced the cytotoxic effect of thapsigargin and paclitaxel on cell proliferation. These findings demonstrate that NaBu stimulates T-type Ca(2+) channel expression, thereby regulating both the morphological differentiation and growth of prostate cancer cells.

Downregulation of GluA2 AMPA receptor subunits reduces the dendritic arborization of developing spinal motoneurons.

AMPA receptors lacking the GluA2 subunit allow a significant influx of Ca(2+) ions. Although Ca(2+)-permeable AMPA receptors are a familiar feature at early stages of development, the functional significance of these receptors during the maturation of the nervous system remains to be established. Chicken lumbar motoneurons express Ca(2+)-permeable AMPA receptors at E6 but the Ca(2+) permeability of AMPA receptors decreases ∼3-fold by E11. Considering that activity-dependent changes in intracellular Ca(2+) regulates dendritic outgrowth, in this study we investigated whether downregulation of GluA2 expression during a critical period of development alters the dendritic arborization of spinal motoneurons in ovo. We use an avian replication-competent retroviral vector RCASBP (B) carrying the marker red fluorescent protein (RFP) and a GluA2 RNAi construct to downregulate GluA2 expression. Chicken embryos were infected at E2 with one of the following constructs: RCASBP(B)-RFP, RCASBP(B)-RFP-scrambled RNAi, or RCASBP(B)-RFP-GluA2 RNAi. Infection of chicken embryos at E2 resulted in widespread expression of RFP throughout the spinal cord with ≥60% of Islet1/2-positive motoneurons infected, resulting in a significant reduction in GluA2 protein expression. Downregulation of GluA2 expression had no effect on the dendritic arborization of E6 motoneurons. However, downregulation of GluA2 expression caused a significant reduction in the dendritic arborization of E11 motoneurons. Neither motoneuron survival nor maturation of network activity was affected by changes in GluA2 expression. These findings demonstrate that increased GluA2 expression and changes in the Ca(2+) permeability of AMPA receptors regulate the dendritic arborization of spinal cord motoneurons during a critical period of development.

Leukemia inhibitory factor regulates trafficking of T-type Ca2+ channels.

Neuropoietic cytokines such as ciliary neurotrophic factor (CNTF) and leukemia inhibitory factor (LIF) stimulate the functional expression of T-type Ca(2+) channels in developing sensory neurons. However, the molecular and cellular mechanisms involved in the cytokine-evoked membrane expression of T-type Ca(2+) channels are not fully understood. In this study we investigated the role of LIF in promoting the trafficking of T-type Ca(2+) channels in a heterologous expression system. Our results demonstrate that transfection of HEK-293 cells with the rat green fluorescent protein (GFP)-tagged T-type Ca(2+) channel α(1H)-subunit resulted in the generation of transient Ca(2+) currents. Overnight treatment of α(1H)-GFP-transfected cells with LIF caused a significant increase in the functional expression of T-type Ca(2+) channels as indicated by changes in current density. LIF also evoked a significant increase in membrane fluorescence compared with untreated cells. Disruption of the Golgi apparatus with brefeldin A inhibited the stimulatory effect of LIF, indicating that protein trafficking regulates the functional expression of T-type Ca(2+) channels. Trafficking of α(1H)-GFP was also disrupted by cotransfection of HEK-293 cells with the dominant-negative form of ADP-ribosylation factor (ARF)1 but not ARF6, suggesting that ARF1 regulates the LIF-evoked membrane trafficking of α(1H)-GFP subunits. Trafficking of T-type Ca(2+) channels required transient activation of the JAK and ERK signaling pathways since stimulation of HEK-293 cells with LIF evoked a considerable increase in the phosphorylation of the downstream JAK targets STAT3 and ERK. Pretreatment of HEK-293 cells with the JAK inhibitor P6 or the ERK inhibitor U0126 blocked ERK phosphorylation. Both P6 and U0126 also inhibited the stimulatory effect of LIF on T-type Ca(2+) channel expression. These findings demonstrate that cytokines like LIF promote the trafficking of T-type Ca(2+) channels.

Pharmacological manipulation of GABA-driven activity in ovo disrupts the development of dendritic morphology but not the maturation of spinal cord network activity.

BACKGROUND: In the adult nervous system, GABA acts as a major inhibitory neurotransmitter; however, at early stages of neurodevelopment, GABA receptor activation leads to membrane depolarization and accumulation of [Ca2+]i. The role of excitatory GABAergic neurotransmission in the development of the nervous system is not fully understood. In this study, we investigated the role of excitatory GABA-driven activity in regulating the dendritic morphology and network function in the developing chicken spinal cord. RESULTS: Both bicuculline, a GABA receptor antagonist, and muscimol, a GABA agonist, inhibit the generation of spontaneous network activity in the isolated spinal cord at E8 or E10, indicating that altering GABA receptor activation disrupts the generation of spontaneous network activity in the chicken spinal cord. Treatment of chicken embryos with bicuculline or muscimol between E5 and E8 (or between E8 and E10), inhibits the dendritic outgrowth of motoneurons when compared to vehicle-treated embryos. The inhibitory effect of bicuculline or muscimol on the dendritic morphology of motoneurons was likely due to inhibition of GABA-driven network activity since a similar effect was also observed following reduction of network activity by Kir2.1 overexpression in the spinal cord. The inhibitory effect of bicuculline or muscimol was not caused by an adverse effect on cell survival. Surprisingly, chronic treatment of chicken embryos with bicuculline or muscimol has no effect on the shape and duration of the episodes of spontaneous activity, suggesting that maturation of network activity is not altered by disruption of the dendritic outgrowth of motoneurons. CONCLUSIONS: Taken together, these findings indicate that excitatory GABA receptor activation regulates the maturation of dendritic morphology in the developing spinal cord by an activity-dependent mechanism. However, inhibition of dendritic outgrowth caused by disruption of GABA-driven activity does not alter the maturation of spontaneous electrical activity generated by spinal cord networks, suggesting that compensatory mechanisms can reverse any adverse effect of dendritic morphology on network function.