Bardoxolone methyl induces neuritogenesis in Neuro2a cells

BACKGROUND

Bardoxolone methyl (RTA 402, CDDOMe) has been long known for its anti-inflammatory and exceptional cytotoxic activity. The biological responses to CDDOMe are truly dose dependent. And owing to the structural modifications introduced in its parent molecule oleanolic acid, CDDOMe is able to form reversible adducts with cellular proteins containing redox sensitive cysteine residues. This nature of CDDOMe makes it a multifunctional molecule targeting multiple signaling pathways. This study was initiated to study the response of Neuro2a, a mouse neuroblastoma cell line to CDDOMe.

METHODS

Neuro2a cells were treated with CDDOMe and all trans retinoic acid (ATRA) for 4days and observed for neurite outgrowth. The neurite length was estimated using ImageJ software (Neuron growth plugin). Cell viability was investigated using MTT dye reduction and trypan blue dye exclusion method. Gene expression of differentiation markers was analyzed using quantitative PCR. Cellular localization of Tuj1 and synaptophysin in differentiated Neuro2a cells was observed using immunofluorescence.

RESULTS

CDDOMe ceased proliferation and induced dramatic neurite outgrowth in Neuro2a cells. These morphological changes were accompanied by time dependent increase in the mRNA levels of tyrosine hydroxylase, neurofilament 200 and synaptophysin. Besides, cytoskeleton protein Tuj1 and the synaptic vesicle protein synaptophysin were also observed to be localized in the neurites induced by CDDOMe.

CONCLUSIONS

These early shreds of evidence suggest that CDDOMe induces differentiation in Neuro2a cells at concentrations ranging from 0.2 to 0.4μM and indeed contributes the existing knowledge on CDDOMe induced activities in cells.

Changes in neurofilament 200 and tyrosine hydroxylase expression in the cardiac innervation of diabetic rats during aging

Changes in sensory and sympathetic innervation during diabetes mellitus (DM) can be a predictor of arrhythmias, silent myocardial ischemia, and chronic heart failure, but knowledge about these changes is still unsatisfactory. We analyzed whether prolonged DM induces changes in density of sensory and sympathetic nerve terminals of rat's heart and whether it contributes to cardiomyopathy during aging. DM was induced by i/p injecting 55 mg/kg streptozotocin to male Sprague-Dawley rats, while a control group received a citrate buffer. DM in the rats was validated by measuring blood glucose level. Animals were sacrificed after 2 weeks, 2 months, 6 months, and 12 months. Five areas of cardiac sections were analyzed. Antibodies raised against tyrosine hydroxylase (TH) and neurofilament 200 kDa (NF 200) were used to detect sympathetic and sensory fibers. TH immunoreactive fiber density increased in DM groups 2 weeks after induction, reaching a peek after 2 months, while in the later stages of DM (6 and 12 months), there was no significant difference compared to control. NF 200 immunoreactive fiber density increased 2 weeks after induction compared to control. There was no consistent pattern of change during the given period in both the DM or control groups. In the DM group, we found thickening of the left ventricle wall (P<.05) as the sign of cardiomyopathy. Our findings suggest that hyperglycemia as a hallmark of DM in early stages can lead to proliferation of sympathetic and sensory nerve terminals. This finding can contribute to a better understanding of the occurrence of arrhythmias and silent myocardial ischemia in DM.

Selective regional alterations in the content or distribution of neuronal and glial cytoskeletal proteins in brain of rats chronically exposed to 2,5-hexanedione

Hexane is used in many industrial processes and induces neurotoxic effects in the central and peripheral nervous system. Hexane is metabolized to 2,5-hexanedione, which is the neurotoxic agent. Continued exposure to hexane or 2,5-hexanedione results in loss of sensorial and motor function in arms and legs and to alterations in axonal neurofilament proteins. The effects of 2,5-hexanedione on different cytoskeletal proteins in different brain areas have not been studied in detail. The aim of this work was to study the effects of chronic exposure of rats to 2,5-hexanedione (1% in the drinking water) on tubulin, neurofilament NF-L, microtubule-associated protein MAP-2, and on glial fibrillary acidic protein (GFAP), in cerebellum, hippocampus and cerebral cortex. The amount of each protein was determined by immunoblotting and its distribution was analysed by immunohistochemistry. The results obtained show a regional selectivity in the 2,5-hexanedione effects on cytoskeletal proteins. NF-L content decreased in all brain areas. MAP-2 decreased in cerebellum and hippocampus and tubulin decreased only in cerebellum. GFAP decreased only in cerebral cortex, but its distribution was altered in cerebellum, with increased content in the granular layer and decreased content in the molecular layer. The area most affected was the cerebellum, where all the proteins analysed were altered. These cytoskeletal proteins alterations may impair the transfer of information involved in the regulation by the cerebellum of motor function and contribute to the altered motor performance in rats exposed to 2,5-hexanedione and humans exposed to hexane.

Effect of stab injury in the rat cerebral cortex on temporal pattern of expression of neuronal cytoskeletal proteins: an immunohistochemical study

Compelling evidence now points to the critical role of the cytoskeleton in neurodegeneration. In the present study, using an immunohistochemical approach, we have shown that cortical stab injury (CSI) in adult Wistar rats significantly affects temporal pattern of expression of neurofilament proteins (NFs), a major cytoskeleton components of neurons, and microtubule-associated proteins (MAP2). At 3 days post-injury (dpi) most of the NFs immunoreactivity was found in pyknotic neurons and in fragmentized axonal processes in the perilesioned cortex. These cytoskeletal alterations became more pronounced by 10dpi. At the subcellular level CSI also showed significant impact on NFs and MAP-2 expression. Thus, at 3dpi most of the dendrites disappeared, while large neuronal somata appeared like open circles pointing to membrane disintegration. Conversely, at 10dpi neuronal perikarya and a few new apical dendrites were strongly labeled. Since aberrant NF phosphorylation is a pathological hallmark of many human neurodegenerative disorders, as well as is found after stressor stimuli, the present results shed light into the expression of neurofilaments after the stab brain injury.

Elevated neurofilament light chain (NFL) mRNA levels in prediabetic peripheral neuropathy

Evidence suggests that peripheral nerve injury occurs during the early stages of disease with mild glycemic dysregulation. Two proteins, neuron-specific enolase (NSE) and neurofilament light chain (NFL), have been examined previously as possible markers of neuronal damage in the pathophysiology of neuropathies. Herein, we aimed to determine the potential value of circulatory NSE and NFL mRNA levels in prediabetic patients and in those with peripheral neuropathy. This prospective clinical study included 45 prediabetic patients and 30 age- and sex-matched controls. All prediabetic patients were assessed with respect to diabetes-related microvascular complications, such as peripheral neuropathy, retinopathy and nephropathy. mRNA levels of NSE and NFL were determined in the blood by real-time polymerase chain reaction. NSE mRNA levels were similar between prediabetic and control groups (p > 0.05), whereas NFL mRNA levels were significantly higher in prediabetics than in controls (p < 0.001). NSE mRNA levels did not significantly differ between prediabetic patients with and without peripheral neuropathy (p > 0.05), while NFL mRNA levels were significantly higher in prediabetics with peripheral neuropathy than in those without (p = 0.038). According to correlation analysis, NFL mRNA levels were positively correlated with the Douleur Neuropathique 4 questionnaire score in prediabetic patients (r = 0.302, p = 0.044). This is the first study to suggest blood NFL mRNA as a surrogate marker for early prediction of prediabetic peripheral neuropathy, while NSE mRNA levels may be of no diagnostic value in prediabetic patients.

[Morphological changes in the lumbar dorsal root ganglion of the domestic porcine after pulsed radiofrequency stimulation]

Pulsed radiofrequency (PRF) is a percutaneous minimal invasive procedure that can be used when conservative pain therapy methods have been ineffective. The effectiveness of PRF was demonstrated in various good quality randomized control studies, but mechanisms of action are still unclear. The aim of our study is to analyse the histological effects of PRF on the domestic porcine dorsal root ganglion (DRG), and evaluate the expression of biomarkers in gangliocytes. 3 domestic porcines were investigated. Under general anaesthesia and X-ray control, DRG PRF was performed. Four lumbar DRGs (L1, L2, L3, L4) were randomly treated. The opposite side DRGs was used as control. One month after the procedure the animal was euthanized. The lumbar region of the spine was placed in 10% formaldehyde for a month. After this fixation DRG samples were prepared for slide analysis. They were embedded in paraffin in order to obtain 3 microm thick sections, which were then cut by microtome and collected on slide glasses. Using standard immunohistochemical reactions, the materials were tinted to define biomarkers NF, GFAP, Hsp-70 expression and apoptosis by TUNEL kit. The number of cells with NF (26.0 +/- 3.0 vs 16.1 +/- 3.3; p < 0.05), GFAP (12.0 +/- 1.3 vs 3.2 +/- 0.9; p < 0.05) and Hsp-70 (10.0 +/- 1.6 vs 4.2 +/- 1.0; p < 0.05) expression, were larger in the PRF side comparing with the control side. Additionally, glial cells in spinal ganglia of both sides demonstrated immunoreactivity. The instances of apoptosis were not significantly different, in statistical terms, between the control and experimental sides (18.0 +/- 4.0 vs 20.0 +/- 4.0; p = 0.35). PRF in spinal gangliocytes of lumbar region increases neural tissue cytoskeleton factors like NF and GFAP suggesting about active regeneration processes into the cells 1 month after the procedure. Spinal gangliocytes one month after PRF treatment notably increases Hsp-70 expression suggesting about activation of cellular activity and inhibitory role reducing of oxidative stress. Similar number of apoptotic cells in spinal ganglia of lumbar region after PRF and control side suggests about inhibitory role of PRF on programmed cell death and stimulation of cell survival.

Neuregulin-1β regulates outgrowth of neurites and migration of neurofilament 200 neurons from dorsal root ganglial explants in vitro

Neuregulin-1β (NRG-1β) signaling has multiple functions in neurons. To assess NRG-1β on neurite outgrowth and neuronal migration in vitro, organotypic dorsal root ganglion (DRG) neuronal culture model was established. Neurite outgrowth and neuronal migration were evaluated using this culture model in the presence (5nmol/L, 10nmol/L, 20nmol/L) or absence of NRG-1β. Neurofilament 200 (NF-200)-immunoreactive (IR) neurons were determined as the migrating neurons. The number of nerve fiber bundles extended from DRG explant increased significantly in the presence of NRG-1β (5nmol/L, 23.0±2.2, P<0.05; 10nmol/L, 27.0±2.7, P<0.001; 20nmol/L, 30.8±3.7, P<0.001) as compared with that in the absence of NRG-1β (19.0±2.2). The number of neurons migrating from DRG explants increased significantly in the presence of NRG-1β (5nmol/L, 39.6±5.0, P<0.05; 10nmol/L, 54.6±6.7, P<0.001; 20nmol/L, 62.2±5.7, P<0.001) as compared with that in the absence of NRG-1β (31.6±4.0). Moreover, the increase of the number of nerve fiber bundles and the number of migrating NF-200-IR neurons was dose-dependent for NRG-1β addition. The data in this study imply that NRG-1β promotes neurite outgrowth and neuronal migration from DRG explants in vitro.

Cannabinoid receptor CB1-immunoreactive nerve fibres in painful and non-painful human tooth pulp

The cannabinoid receptor CB1 is involved in modulation of neuronal hypersensitivity and pain. The aim of this study was to evaluate CB1 receptor levels for the first time in dental pain. A total of 19 patients due for molar extraction were divided into two groups, those with existing dental pain (n=9), and those with no history of pain (n=10). Immunohistochemistry and computer image analysis was used to evaluate CB1-positive nerve fibres in tooth pulp, with neurofilament-immunostaining as a structural nerve marker. CB1-immunoreactive nerve fibres were scattered throughout the tooth pulp and often seen in nerve bundles, but the fibres did not penetrate the subodontoblastic layer. There was no statistically significant change in the CB1 nerve fibre percentage area in the painful group compared to the non-painful group (p=0.146); the neurofilament fibres were significantly reduced in the painful group compared to the controls (p=0.028), but there was no difference in the ratio of CB1 to neurofilaments between the two groups. Thus, CB1 expression is maintained by nerve fibres in painful human dental pulp, and peripherally-restricted CB1 agonists currently in development may advance the treatment of dental pain.

Nrf2 promotes neuronal cell differentiation

The transcription factor Nrf2 has emerged as a master regulator of the endogenous antioxidant response, which is critical in defending cells against environmental insults and in maintaining intracellular redox balance. However, whether Nrf2 has any role in neuronal cell differentiation is largely unknown. In this report, we have examined the effects of Nrf2 on cell differentiation using a neuroblastoma cell line, SH-SY5Y. Retinoic acid (RA) and 12-O-tetradecanoylphorbol 13-acetate, two well-studied inducers of neuronal differentiation, are able to induce Nrf2 and its target gene NAD(P)H quinone oxidoreductase 1 in a dose- and time-dependent manner. RA-induced Nrf2 up-regulation is accompanied by neurite outgrowth and an induction of two neuronal differentiation markers, neurofilament-M and microtubule-associated protein 2. Overexpression of Nrf2 in SH-SY5Y cells promotes neuronal differentiation, whereas inhibition of endogenous Nrf2 expression inhibited neuronal differentiation. More remarkably, the positive role of Nrf2 in neuronal differentiation was verified ex vivo in primary neuron culture. Primary neurons isolated from Nrf2-null mice showed a retarded progress in differentiation, compared to those from wild-type mice. Collectively, our data demonstrate a novel role for Nrf2 in promoting neuronal cell differentiation, which will open new perspectives for therapeutic uses of Nrf2 activators in patients with neurodegenerative diseases.

[Tetramethylpyrazine accelerated spinal cord repair through regulation of caspase-3 and neurofilament protein expression: an acute spinal cord injury model in rats]

OBJECTIVE

To investigate the effect of tetramethylpyrazine on spinal cord repair through hypothesized pathways including regulation of caspase-3, neurofilament protein NF-L, NF-H, and NF-M expression.

METHODS

Allenos weight drop method was used to establish acute spinal cord injury (SCI) rat model at T10 section and was conducted in 80 adult Sprague Dawley rats that were subsequently divided into pseudo-therapy group (sodium chloride group, n=40) and tetramethylpyrazine group (treatment group, n=40). Eight normal rats were included into the pseudo-surgery normal group (n=1 for each time point). The function of spinal cord was evaluated with animal behavioral scores by measuring modified Rivilin loxotic plate degree and counting BBB score at 1, 3, 7, 14, and 21 d postoperatively. The injured spinal cord tissue samples were harvested at 1 h, 3 h, 6 h, 1 d, 3 d, 7 d, 14 d, and 21 d postoperatively (n=5 for each time point) for the preparation of continuous histological sections that were analyzed the expression of caspase-3,NF-L,NF-H, and NF-M by immunohistochemistry method.

RESULTS

At postoperative Day 7, 14, and 21, animal behavioral scores revealed higher modified Rivlin loxotic plate degree and BBB scores in the treatment group when compared with those of the control group (P<0.05). The cells in the injured spinal cord tissue expressed significantly less caspase-3 and significantly more NF (NF-L, NF-H and NF-M) in the treatment group than those in the control group at Day 3, 7, and 14 (P<0.05). There was positive correlation between modified Rivlin loxotic plate degree and NF expression, BBB score and NF expression; and negative correlations between BBB score and caspase-3 expression, caspase-3 expression and NF expression.

CONCLUSION

Tetramethylpyrazine improves spinal cord healing through regulation of caspase-3 and neurofilament protein expression.

Marked effect of RhoA-specific shRNA-producing plasmids on neurite growth in PC12 cells

In order to promote neurite outgrowth, we constructed a plasmid producing RhoA-specific small hairpin RNA (shRNA) to block RhoA expression and tested its actions in PC12 cells. Our results show that the shRNA-mediated RNA interference (RNAi) successfully suppressed RhoA expression. As a consequence of RhoA knockdown, F-actin levels were significantly reduced and processes were markedly induced. These processes express two neurite markers, neurofilament and betaIII tubulin. This study demonstrates that plasmid-producing shRNA specific for RhoA can act as an effective tool to induce neurite outgrowth and further confirms the neurite growth-inhibitory role of RhoA. This shRNA may thus be a useful tool in promoting neurite outgrowth and could be applicable in neural repair after CNS injury.

Pathophysiologic characteristics of balloon cells in cortical dysplasia

OBJECTS

Balloon cells are histopathological hallmarks of cortical malformations, i.e., focal cortical dysplasia (FCD) of the Taylor type or the cortical tubers of tuberous sclerosis, and they are believed to be the epileptogenic substrate and cause therapeutic drug resistant epilepsy in man. This study was carried out to investigate the developmental histogenesis and epileptogenesis of balloon cells in FCD.

MATERIALS AND METHODS

We used an immunohistochemical approach to examine the expressions of primitive neuroepithelial cell antigens (CD34, nestin, and vimentin), ionotrophic glutamate receptor subunits (NR1, NR2A/B, GluR1, GluR2, GluR3, GluR4, and GluR5/6/7), and P-glycoprotein in balloon cells from FCD and normal cerebral cortex epileptogenic lesions.

CONCLUSION

Balloon cells presented in clusters or as scattered cells throughout FCD lesions involving the gray and white matter. We found the balloon cells to be classifiable into three subtypes based on glial fibrillary acidic protein (GFAP) and neurofilament protein (NF-L) immunohistochemistry, i.e., as neuronal, astrocytic, and uncommitted. Immunopositivity for nestin, CD34, and vimentin in balloon cells of FCD suggests that they may be derived from the abnormal development and differentiation of neural stem cells. Moreover, it appears that epileptogenesis in cortical dysplasia is partly caused by the upregulations of some glutamate receptor subunit proteins (NR1, NR2A/B, GluR1, and GluR3) in balloon cells and dysplastic neurons. We speculate that the presence of the drug resistance protein P-glycoprotein in balloon cells might explain medically refractory epilepsy in FCD.

[Expression of glutamate receptor 2 in retinal ganglion cells in the eyes with chronic elevated intraocular pressure: experiment with rats]

OBJECTIVE

To investigate the mechanism of selective damage of retinal ganglion cells (RGCs) in glaucoma.

METHODS

(1) The right eyes of 12 SD rats underwent ligation of 2 episcleral veins and subconjunctival injection 5-fluoro-uracilum so as to establish chronic elevated intraocular pressure glaucoma rat model. Six SD rats were used as controls. Intraocular pressure (IOP) was measured every week. (2) One week and 4 weeks after the operation 6 glaucoma rats and 3 control rats were killed with their eyes taken out to undergo immuno-histological assays to observe the expression of glutamate receptor (GluR)-2 and neurofilament (NF)-68 in the RGCs with different sizes by confocal laser scanning microscope.

RESULTS

(1) The IOP was increased since 1 week after the operation. The elevated IOP was consistently maintained for up to 4 weeks in the glaucoma group. (2) All the RGCs of both groups were NF-68 positive, especially the larger RGCs. (3) GluR2 was not expressed in the larger RGCs of both the glaucoma and control groups, and was expressed in the small and intermediate RGCs of the glaucoma group up to the end of experiment. However, 4 weeks after the operation the residual NF-68 positive larger RGCs of the glaucoma group showed GluR-2 expression.

CONCLUSION

The vulnerability of the RGCs may be related to the specific deficiency of GluR-2 expression.

[Experimental study on effect of Suifukang in promoting repairing and regeneration of nerve fibers in spinal cord]

OBJECTIVE

To study the change in expressions of nerve growth related protein (GAP-43) and neurofilament (NF) after experimental injury of spinal cord, and the regulatory effect of Chinese medicine Suifukang (SFK) on them.

METHODS

Forty-eight from the 54 selected adult SD rats were established into spinal cord injury model by making hemitransection at the T12 level, and randomly divided into two groups, the SFK group feed with SKF contained liquor and the model group feeding with equal volume of saline. The another 6 rats were untreated and taken as the normal group. All rats were sacrificed in batches at different time points of day 3, 7, 15 and 30 after modeling. The spinal cord was obtained for determining the optic density (OD) of positive expression of GAP-43 and NF with immunohistochemical stain by microscopic and semi-quantitative image analysis.

RESULTS

(1) OD of NF in the model group was obviously decreased on day 7, showing significant difference to that in the normal group and that in the SFK group (P < 0.05), and it maintained at low level after then, while the OD of NF in the SFK group was obviously higher than that in the model group (P < 0.05), it arrived the peak on day 15 and then dropped near the level in the normal group on day 30; (2) OD and of GAP-43 in the model group obviously decreased on day 3 (P < 0.05), showing significant difference to that in the normal group (P < 0.05), then it returned to approach to the level in the normal group on day 7. It was higher in the SFK group than in the model group on day 3, and maintained the high level to day 7, at that time, it was still higher than that in the model group and also higher than that in the normal group (P < 0.05).

CONCLUSION

SFK can promote the repair and regeneration of injured nerve fibers in spinal cord by up-regulating the expression of GAP-43 and NF.

Molecular heterogeneity of developing retinal ganglion and amacrine cells revealed through single cell gene expression profiling

During development of the central nervous system (CNS), cycling uncommitted progenitor cells give rise to a variety of distinct neuronal and glial cell types. As these different cell types are born they progress from newly specified cells to fully differentiated neurons and glia. In order to define the developmental processes of individual cell types, single cell expression profiling was carried out on developing ganglion and amacrine cells of the murine retina. Individual cells from multiple developmental stages were isolated and profiled on Affymetrix oligonucleotide arrays. Two-color fluorescent in situ hybridization on dissociated retinas was used to verify and extend the microarray results by allowing quantitative measurements of a large number of cells coexpressing two genes. Together, these experiments have yielded an expanded view of the processes underway in developing retinal ganglion and amacrine cells, as well as several hundred new marker genes for these cell types. In addition, this study has allowed for the definition of some of the molecular heterogeneity both between developing ganglion and amacrine cells and among subclasses of each cell type.

The polypeptide composition of moving and stationary neurofilaments in cultured sympathetic neurons

Studies on the axonal transport of neurofilament proteins in cultured neurons have shown they move at fast rates, but their overall rate of movement is slow because they spend most of their time not moving. Using correlative light and electron microscopy, we have shown that these proteins move in the form of assembled neurofilament polymers. However, the polypeptide composition of these moving polymers is not known. To address this, we visualized neurofilaments in cultured neonatal mouse sympathetic neurons using GFP-tagged neurofilament protein M and performed time-lapse fluorescence microscopy of naturally occurring gaps in the axonal neurofilament array. When neurofilaments entered the gaps, we stopped them in their tracks using a rapid perfusion and permeabilization technique and then processed them for immunofluorescence microscopy. To compare moving neurofilaments to the total neurofilament population, most of which are stationary at any point in time, we also performed immunofluorescence microscopy on neurofilaments in detergent-splayed axonal cytoskeletons. All neurofilaments, both moving and stationary, contained NFL, NFM, peripherin and alpha-internexin along>85% of their length. NFH was absent due to low expression levels in these neonatal neurons. These data indicate that peripherin and alpha-internexin are integral and abundant components of neurofilament polymers in these neurons and that both moving and stationary neurofilaments in these neurons are complex heteropolymers of at least four different neuronal intermediate filament proteins.

Conditional NF-L transgene expression in mice for in vivo analysis of turnover and transport rate of neurofilaments

We generated mice with doxycycline control of a human neurofilament light (NF-L) transgene in the context of the absence (tTA;hNF-L;NF-L(-/-)) or presence (tTA;hNF-L;NF-L(+/-)) of endogenous mouse NF-L proteins. Doxycycline treatment caused the rapid disappearance of human NF-L (hNF-L) mRNA in tTA;hNF-L mice, but the hNF-L proteins remained with a half-life of 3 weeks in the brain. In the sciatic nerve, the disappearance of hNF-L proteins after doxycycline treatment occurred in synchrony along the sciatic nerve, suggesting a proteolysis of NF proteins along the entire axon. The presence of permanent NF network in tTA;hNF-L;NF-L(+/-) mice further stabilized and extended longevity of hNF-L proteins by several months. Surprisingly, after cessation of doxycycline treatment, there was no evidence of leading front of newly synthesized hNF-L proteins migrating into sciatic nerve axons devoid of NF structures. The hNF-L proteins detected at weekly intervals reappeared and accumulated in synchrony at similar rate along nerve segments, a phenomenon consistent with a fast hNF-L transport into axons. We estimated the hNF-L transport rate to be of approximately 10 mm/d in axons devoid of NF structures based on the use of an adenovirus encoding tet-responsive transcriptional activator to transactivate the hNF-L transgene in hypoglossal motor neurons. These results provide in vivo evidence that the stationary NF network in axons is a key determinant of half-life and transport rate of NF proteins.

Post-transcriptional control of neurofilaments in development and disease

Tight coordination of the expression of neurofilament subunits is integral to the normal development and function of the nervous system. Imbalances in their expression are increasingly implicated in the induction of neurodegeneration in which formation of neurofilamentous aggregates is central to the pathology. Neurofilament expression can be controlled not only at the transcriptional level but also through post-transcriptional regulation of mRNA localization, stability, and translational efficiency. The critical role that post-transcriptional mechanisms play in maintaining neurofilament homeostasis is highlighted, for example, by the human disease amyotrophic lateral sclerosis, in which selective destabilization of NF-L mRNA (or failure to stabilize it) is associated with the formation of neurofilamentous aggregates - a hallmark of the disease process. This review discusses the post-transcriptional regulatory mechanisms and associated ribonucleoproteins that have been implicated to date in controlling neurofilament expression during normal development and in disrupting neurofilament homeostasis during neurodegenerative disease.

Neuroimmune connections in jejunal and ileal Peyer’s patches at various bovine ages: potential sites for prion neuroinvasion

During preclinical stages of cattle orally infected with bovine spongiform encephalopathy (BSE), the responsible agent is confined to ileal Peyer's patches (IPP), namely in nerve fibers and in lymph follicles, before reaching the peripheral and central nervous systems. No infectivity has been reported in other bovine lymphoid organs, including jejunal Peyer's patches (JPP). To determine the potential sites for prion neuroinvasion in IPP, we analyzed the mucosal innervation and the interface between nerve fibers and follicular dendritic cells (FDC), two dramatic influences on neuroinvasion. Bovine IPP were studied at three ages, viz., newborn calves, calves less than 12 months old, and bovines older than 24 months, and the parameters obtained were compared with those of JPP. No differences in innervation patterns between IPP and JPP were found. The major difference observed was that, in calves of less than 12 months, IPP were the major mucosal-associated lymphoid organ that possessed a large number of follicles with extended FDC networks. Using a panel of antibodies, we showed that PP in 24-month-old bovines were highly innervated at various strategic sites assumed to be involved in the invasion and replication of the BSE pathogen: the suprafollicular dome, T cell area, and germinal centers. In PP in calves of less than 12 months old, no nerve fibers positive for the neurofilament markers NF-L (70 kDa) and NF-H (200 kDa) were observed in contact with FDC. Thus, in view of the proportion of these protein subunits present in neurofilaments, the innervation of the germinal centers can be said to be an age-dependent dynamic process. This variation in innervation might influence the path of neuroinvasion and, thus, the susceptibility of bovines to the BSE agent.

Heat sensitization in skin and muscle nociceptors expressing distinct combinations of TRPV1 and TRPV2 protein

Recordings were made from small and medium diameter dorsal root ganglia (DRG) neurons that expressed transient receptor potential (TRP) proteins. Physiologically characterized skin nociceptors expressed either TRPV1 (type 2) or TRPV2 (type 4) in isolation. Other nociceptors co-expressed both TRP proteins and innervated deep tissue sites (gastrocnemius muscle, distal colon; type 5, type 8) and skin (type 8). Subpopulations of myelinated (type 8) and unmyelinated (type 5) nociceptors co-expressed both TRPs. Cells that expressed TRPV1 were excellent transducers of intense heat. Proportional inward currents were obtained from a threshold of approximately 46.5 to approximately 56 degrees C. In contrast, cells expressing TRPV2 alone (52 degrees C threshold) did not reliably transduce the intensity of thermal events. Studies were undertaken to assess the capacity of skin and deep nociceptors to exhibit sensitization to repeated intense thermal stimuli [heat-heat sensitization (HHS)]. Only nociceptors that expressed TRPV2, alone or in combination with TRPV1, exhibited HHS. HHS was shown to be Ca(2+) dependent in either case. Intracellular Ca(2+) dependent pathways to HHS varied with the pattern of TRP protein expression. Cells co-expressing both TRPs modulated heat reactivity through serine/threonine phosphorylation or PLA(2)-dependent pathways. Cells expressing only TRPV2 may have relied on tyrosine kinases for HHS. We conclude that heat sensitization in deep and superficial capsaicin and capsaicin-insensitive C and Adelta nociceptors varies with the distribution of TRPV1 and TRPV2 proteins. The expression pattern of these proteins are specific to subclasses of physiologically identified C and A fiber nociceptors with highly restricted tissue targets.

14-3-3 protein binds to the low molecular weight neurofilament (NFL) mRNA 3′ UTR

We have previously reported that altered stability of low molecular weight neurofilament (NFL) mRNA in lumbar spinal cord homogenates in amyotrophic lateral sclerosis (ALS) is associated with altered expression of trans-acting 3' UTR mRNA binding proteins. We have identified two hexanucleotide motifs as the main cis elements and, using LC/MS/MS of peptide digests of NFL 3' UTR interacting proteins from human spinal cord, observed that 14-3-3 proteins interact with these motifs. 14-3-3 beta, zeta, tau, gamma, and eta isoforms were found to be expressed in human spinal cord. Each isoform was expressed in vitro and shown to interact with NFL 3' UTR mRNA. Mutation of one or both motifs resulted in decreased 14-3-3 interaction, changes in predicted mRNA structure or alteration in stability of the mRNA. These data show a novel interaction for 14-3-3 with NFL mRNA, and suggests that 14-3-3 may play a role in regulating NFL mRNA stability.

Activation of mammalian target of rapamycin in cytomegalic neurons of human cortical dysplasia

OBJECTIVE

The cortex of patients with cortical dysplasia contains several abnormal cell types. Among the dysplastic cells, cytomegalic neurons are known to be electrically hyperactive and may contribute to epileptic activity. In this study, we sought to identify molecular markers of cytomegalic neurons in focal or hemispheric cortical dysplasia and to determine whether the activity of the mammalian target of rapamycin (mTOR) kinase is abnormally high in these cells.

METHODS

Microarray analysis of gene expression in large dysplastic cells microdissected from cortical dysplasia surgical specimens was used to identify markers of cytomegalic neurons. Immunohistochemistry and immunofluorescence analysis of cortical sections was used to validate the microarray results and to probe the activity of mTOR in cytomegalic neurons using phospho-specific antibodies directed against known mTOR targets.

RESULTS

We demonstrate that the neurofilament heavy chain is a reliable marker of cytomegalic neurons and that targets of the mTOR kinase, such as the ribosomal protein S6, eIF4G, and Akt, are hyperphosphorylated in these dysplastic neurons.

INTERPRETATION

We conclude that mTOR kinase hyperactivation is a molecular mechanism underlying the development of cytomegalic neurons. This finding may lead to the development of novel therapeutic approaches for childhood epilepsy associated with cortical dysplasia.

Carbon Disulfide-Induced Alterations of Neurofilaments and Calpains Content in Rat Spinal Cord

To investigate the mechanism of carbon disulfide-induced neuropathy, male Wistar rats were randomly divided into two experimental groups and one control group. The rats in two experimental groups were treated with carbon disulfide by gavage at dosages of 300 and 500 mg/kg/day, respectively, five times per week for 12 weeks. Spinal cords of carbon disulfide-intoxicated rats and their age-matched controls were Triton-extracted and ultracentrifuged to yield a pellet fraction of neurofilament (NF) polymer and a corresponding supernatant fraction. Then, the contents of NF triplet proteins (NF-H, NF-M, NF-L) and two calpain isoforms (m-calpain and mu-calpain) in both fractions were determined by immunoblotting. In the meantime, the mRNA levels of NF-H, NF-M, and NF-L in spinal cords were quantified using reverse transcriptase-polymerase chain reaction. Results showed that in the pellet fraction, the contents of three NF subunits in both treated groups decreased significantly except NF-L in low dose group. In the supernatant fraction, the pattern of NFs alteration varied according to dose-levels. Compared to controls, three neurofilmant subunits in the high dose group displayed significant reduction consistently. However, in the low dose group, they remained unaffected. As for calpains, the contents of mu-calpain in both fractions increased significantly regardless of carbon disulfide dose-levels. Meanwhile, m-calpain demonstrated a significant decline in the supernatant fraction, and remained unchangeable in the pellet fraction compared to the control group. Furthermore, the levels of mRNA expression of NF-H, NF-M, and NF-L genes were elevated consistently in CS(2)-treated groups. These findings suggested that carbon disulfide intoxication was associated with obvious alterations of NFs content in rat spinal cord, which might be involved in the development of carbon disulfide neurotoxicity.

Postganglionic nerve stimulation induces temporal inhibition of excitability in rabbit sinoatrial node

Vagal stimulation results in complex changes of pacemaker excitability in the sinoatrial node (SAN). To investigate the vagal effects in the rabbit SAN, we used optical mapping, which is the only technology that allows resolving simultaneous changes in the activation pattern and action potentials morphologies. With the use of immunolabeling, we identified the SAN as a neurofilament 160-positive but connexin 43-negative region ( n = 5). Normal excitation originated in the SAN center with a cycle length (CL) of 405 ± 14 ms ( n = 14), spread anisotropically along the crista terminalis (CT), and failed to conduct toward the septum. Postganglionic nerve stimulation (PNS, 400–800 ms) reduced CL by 74 ± 7% transiently and shifted the leading pacemaker inferiorly (78%) or superiorly (22%) from the SAN center by 2–10 mm. In the intercaval region between the SAN center and the septal block zone, PNS produced an 8 ± 1-mm2 region of transient hyperpolarization and inexcitability. The first spontaneous or paced excitation following PNS could not enter this region for 500–1,500 ms. Immunolabeling revealed that the PNS-induced inexcitable region is located between the SAN center and the block zone and has a 2.5-fold higher density of choline acetyltransferase than CT but is threefold lower than the SAN center. The fact that the inexcitability region does not coincide with the most innervated area indicates that the properties of the myocytes themselves, as well as intercellular coupling, must play a role in the inexcitability induction. Optically mapping revealed that PNS resulted in transient loss of pacemaker cell excitability and unidirectional entrance conduction block in the periphery of SAN.

NG2 colocalizes with axons and is expressed by a mixed cell population in spinal cord lesions

The NG2 proteoglycan is of general interest after spinal cord injury because it is expressed by oligodendrocyte progenitors (OPCs), which contribute to central nervous system remyelination; however, NG2 may inhibit axon regeneration. We and others have examined the spatiotemporal expression of NG2 after spinal cord injury (SCI). Here, we extend those observations and provide a comprehensive analysis of the distribution, phenotype, and colocalization of NG2 cells with axons in a clinically relevant model of spinal contusion. Because contusion models mimic the majority of human SCI, this information is important for understanding endogenous processes that promote and/or prevent repair. The data demonstrate that NG2 levels rise significantly between 3 and 7 days postinjury (dpi) and remain elevated chronically throughout the lesions. NG2 within the lesions could be derived from an array of infiltrating cells; thus, a panel of antibodies was used to investigate NG2 cell phenotypes. First, platelet-derived growth factor-alpha receptor (PDGFalphaR) colocalization was examined because OPCs normally express both markers. PDGFalphaR cells were present in lesions at all times examined. However, only 37% of NG2 cells coexpressed PDGFalphaR at 14 dpi, which dropped to <1% by 70 dpi. This contrasts with the nearly complete overlap in spared tissue surrounding the lesion. In contrast, 40% to 60% of NG2 cells expressed p75 and approximately 84% expressed Sox10, suggesting that many NG2 cells were nonmyelinating Schwann cells. Despite rising levels of NG2, we noted robust and sustained axon growth into the lesions, many of which were located along NG2 profiles. Thus, spinal contusion produces an NG2-rich environment into which axons grow and in which the source of NG2 appears considerably different from that in surrounding spared tissue.