SCN2B in the Rat Trigeminal Ganglion and Trigeminal Sensory Nuclei.

The beta-2 subunit of the mammalian brain voltage-gated sodium channel (SCN2B) was examined in the rat trigeminal ganglion (TG) and trigeminal sensory nuclei. In the TG, 42.6 % of sensory neurons were immunoreactive (IR) for SCN2B. These neurons had various cell body sizes. In facial skins and oral mucosae, corpuscular nerve endings contained SCN2B-immunoreactivity. SCN2B-IR nerve fibers formed nerve plexuses beneath taste buds in the tongue and incisive papilla. However, SCN2B-IR free nerve endings were rare in cutaneous and mucosal epithelia. Tooth pulps, muscle spindles and major salivary glands were also innervated by SCN2B-IR nerve fibers. A double immunofluorescence method revealed that about 40 % of SCN2B-IR neurons exhibited calcitonin gene-related peptide (CGRP)-immunoreactivity. However, distributions of SCN2B- and CGRP-IR nerve fibers were mostly different in facial, oral and cranial structures. By retrograde tracing method, 60.4 and 85.3 % of TG neurons innervating the facial skin and tooth pulp, respectively, showed SCN2B-immunoreactivity. CGRP-immunoreactivity was co-localized by about 40 % of SCN2B-IR cutaneous and tooth pulp TG neurons. In trigeminal sensory nuclei of the brainstem, SCN2B-IR neuronal cell bodies were common in deep laminae of the subnucleus caudalis, and the subnuclei interpolaris and oralis. In the mesencephalic trigeminal tract nucleus, primary sensory neurons also exhibited SCN2B-immunoreactivity. In other regions of trigeminal sensory nuclei, SCN2B-IR cells were very infrequent. SCN2B-IR neuropil was detected in deep laminae of the subnucleus caudalis as well as in the subnuclei interpolaris, oralis and principalis. These findings suggest that SCN2B is expressed by various types of sensory neurons in the TG. There appears to be SCN2B-containing pathway in the TG and trigeminal sensory nuclei.

MicroRNA­449a regulates the progression of brain aging by targeting SCN2B in SAMP8 mice.

Our previous study demonstrated that the expression of sodium channel voltage­gated beta 2 (SCN2B) increased with aging in senescence­accelerated mouse prone 8 (SAMP8) mice, and was identified to be associated with a decline in learning and memory, while the underlying mechanism is unclear. In the present study, multiple differentially expressed miRNAs, which may be involved in the process of aging by regulating target genes, were identified in the prefrontal cortex and hippocampus of SAMP8 mice though miRNA microarray analysis. Using bioinformatics prediction, SCN2B was identified to be one of the potential target genes of miR­449a, which was downregulated in the hippocampus. Previous studies demonstrated that miR­449a is involved in the occurrence and progression of aging by regulating a variety of target genes. Therefore, it was hypothesized that miR­449a may be involved in the process of brain aging by targeting SCN2B. To verify this hypothesis, the following experiments were conducted: A reverse transcription­quantitative polymerase chain reaction assay revealed that the expression level of miR­449a was significantly decreased in the prefrontal cortex and hippocampus of 12­month old SAMP8 mice; a dual­luciferase reporter assay verified that miR­449a regulated SCN2B expression by binding to the 3'­UTR 'seed region'; an anti­Ago co­immunoprecipitation combined with Affymetrix microarray analyses demonstrated that the target mRNA highly enriched with Ago­miRNPs was confirmed to be SCN2B. Finally, overexpression of miR­449a or inhibition of SCN2B promoted the extension of hippocampal neurons in vitro. The results of the present study suggested that miR­449a was downregulated in the prefrontal cortex and hippocampus of SAMP8 mice and may regulate the process of brain aging by targeting SCN2B.

MicroRNA-9 induces defective trafficking of Nav1.1 and Nav1.2 by targeting Navß2 protein coding region in rat with chronic brain hypoperfusion.

BACKGROUND: Previous studies have demonstrated that the trafficking defects of Nav1.1/Nav1.2 are involved in the dementia pathophysiology. However, the detailed mechanisms are not fully understood. Moreover, whether the impaired miRNAs regulation linked to dementia is a key player in sodium channel trafficking disturbance remains unclear. The cognitive impairment induced by chronic cerebral ischemia through chronic brain hypoperfusion (CBH) is likely reason to precede dementia. Therefore, our goal in the present study was to examine the role of microRNA-9 (miR-9) in regulating Nav1.1/Nav1.2 trafficking under CBH generated by bilateral common carotid artery occlusion (2VO). RESULTS: The impairment of Nav1.1/Nav1.2 trafficking and decreased expression of Navß2 were found in the hippocampi and cortices of rats following CBH generated by bilateral 2VO. MiR-9 was increased in both the hippocampi and cortices of rats following CBH by qRT-PCR. Intriguingly, miR-9 suppressed, while AMO-miR-9 enhanced, the trafficking of Nav1.1/Nav1.2 from cytoplasm to cell membrane. Further study showed that overexpression of miR-9 inhibited the Navß2 expression by targeting on its coding sequence (CDS) domain by dual luciferase assay. However, binding-site mutation or miR-masks failed to influence Navß2 expression as well as Nav1.1/Nav1.2 trafficking process, indicating that Navß2 is a potential target for miR-9. Lentivirus-mediated miR-9 overexpression also inhibited Navß2 expression and elicited translocation deficits to cell membrane of Nav1.1/Nav1.2 in rats, whereas injection of lentivirus-mediated miR-9 knockdown could reverse the impaired trafficking of Nav1.1/Nav1.2 triggered by 2VO. CONCLUSIONS: We conclude that miR-9 may play a key role in regulating the process of Nav1.1/Nav1.2 trafficking via targeting on Navß2 protein in 2VO rats at post-transcriptional level, and inhibition of miR-9 may be a potentially valuable approach to prevent Nav1.1/Nav1.2 trafficking disturbance induced by CBH.