Regulation of TrkB receptor tyrosine kinase and its internalization by neuronal activity and Ca2+ influx

Internalization of the neurotrophin–Trk receptor complex is critical for many aspects of neurotrophin functions. The mechanisms governing the internalization process are unknown. Here, we report that neuronal activity facilitates the internalization of the receptor for brain-derived neurotrophic factor, TrkB, by potentiating its tyrosine kinase activity. Using three independent approaches, we show that electric stimulation of hippocampal neurons markedly enhances TrkB internalization. Electric stimulation also potentiates TrkB tyrosine kinase activity. The activity-dependent enhancement of TrkB internalization and its tyrosine kinase requires Ca2+ influx through N-methyl-d-aspartate receptors and Ca2+ channels. Inhibition of internalization had no effect on TrkB kinase, but inhibition of TrkB kinase prevents the modulation of TrkB internalization, suggesting a critical role of the tyrosine kinase in the activity-dependent receptor endocytosis. These results demonstrate an activity- and Ca2+-dependent modulation of TrkB tyrosine kinase and its internalization, and they provide new insights into the cell biology of tyrosine kinase receptors

Analysis of effects of laryngopharyngeal reflux disease and proton pump inhibitor treatment on Eustachian tube function in patients with obstructive sleep apnea hypopnea

Objective: This study aims to explore the effects of laryngopharyngeal reflux disease (LPRD) and proton pump inhibitor (PPI) treatment on Eustachian tube function in patients with obstructive sleep apnea (OSA). Methods: The Eustachian tube score-7 (ETS-7) was observed before and after PPI treatment in the control group, OSA only group, and OSA + LPRD group. Results: Age, sex, smoking history, and drinking history showed no differences among 3 groups (P &gt; .05). The body mass index (BMI) in the control group was lower than that in other groups (P &lt; .017). Before PPI treatment, the abnormality rate of ETS-7 in the OSA + LPRD group statistically differed from that in the control group and the OSA only group (P &lt; .017). After PPI treatment, the abnormality rate of ETS-7 in the OSA + LPRD group exhibited no significant differences compared with that in the control group and the OSA only group (P &gt; .017), and it declined remarkably compared with that before PPI treatment (75% vs 35%, χ2 = 13.334, P = .001). Moreover, the multivariate analysis revealed that only LPRD had an independent correlation with the abnormality of ETS-7 (OR = 1.245, 95% CI: 1.759–6.861, P = .000). Conclusion: In view of its high incidence in OSA patients, LPRD may be a considerable factor for the high incidence of abnormality rate of ETS-7 in OSA patients, and PPI therapy is of significant value in improving Eustachian tube function in OSA patients with LPRD. </jats:p

Segregation of Nogo66 receptors into lipid rafts in rat brain and inhibition of Nogo66 signaling by cholesterol depletion

AbstractNogoA, a myelin-associated component, inhibits neurite outgrowth. Nogo66, a portion of NogoA, binds to Nogo66 receptor (NgR) and induces the inhibitory signaling. LINGO-1 and p75 neurotrophin receptor (p75), the low-affinity nerve growth factor receptor, are also required for NogoA signaling. However, signaling mechanisms downstream to Nogo receptor remain poorly understood. Here, we observed that NgR and p75 were colocalized in low-density membrane raft fractions derived from forebrains and cerebella as well as from cerebellar granule cells. NgR interacted with p75 in lipid rafts. In addition, disruption of lipid rafts by β-methylcyclodextrin, a cholesterol-binding reagent, reduced the Nogo66 signaling. Our results suggest an important role of lipid rafts in facilitating the interaction between NgRs and provide insight into mechanisms underlying the inhibition of neurite outgrowth by NogoA

The sphingosine-1-phosphate analogue, FTY-720, promotes the proliferation of embryonic neural stem cells, enhances hippocampal neurogenesis and learning and memory abilities in adult mice

BACKGROUND AND PURPOSE: Fingolimod (FTY‐720) is the first oral therapeutic drug approved for the relapsing–remitting forms of multiple sclerosis. Neural stem cells (NSCs) are capable of continuous self‐renewal and differentiation. The dentate gyrus of the hippocampus in the adult mammalian brain contains a population of NSCs and is one of the regions where neurogenesis takes place. FTY‐720 has been shown to have neuroprotective effects in several model systems, so we investigated the direct effects of FTY‐720 on NSCs and adult neurogenesis. EXPERIMENTAL APPROACHES: We assessed the effects of FTY‐720 on the proliferation and differentiation of cultured embryonic hippocampal NSCs using the 5‐bromo‐2‐deoxyuridine incorporation assay, the neurosphere formation assay and western blot analysis. Receptor selective agonists and antagonists were used to identify the mechanisms involved. Neurogenesis in the hippocampus of C57BL/6 mice was also assessed by immunohistochemistry. The Morris water maze and fear conditioning tests were used to detect the learning and memory abilities of mice. KEY RESULTS: FTY‐720 promoted the proliferation of embryonic hippocampal NSCs probably via the activation of ERK signalling, G(i/o) proteins and S1P(1) receptors. However, FTY‐720 did not affect the differentiation of cultured hippocampal NSCs. In vivo, chronic treatment with FTY‐720 promoted hippocampal neurogenesis in adult C57BL/6 mice and enhanced their learning and memory abilities. CONCLUSIONS AND IMPLICATIONS: Our results suggest a new target for the activation of NSCs and provide an insight into the therapeutic effects of FTY‐720 in neuropsychiatric disorders, neurodegenerative diseases and age‐related cognitive decline where hippocampal neurogenesis is compromised

Inhibition of Histone Deacetylase 3 (HDAC3) Mediates Ischemic Preconditioning and Protects Cortical Neurons against Ischemia in Rats

Brain ischemic preconditioning (PC) provides vital insights into the endogenous protection against stroke. Genomic and epigenetic responses to PC condition the brain into a state of ischemic tolerance. Notably, PC induces the elevation of histone acetylation, consistent with evidence that histone deacetylase (HDAC) inhibitors protect the brain from ischemic injury. However, less is known about the specific roles of HDACs in this process. HDAC3 has been implicated in several neurodegenerative conditions. Deletion of HDAC3 confers protection against neurotoxicity and neuronal injury. Here, we hypothesized that inhibition of HDAC3 may contribute to the neuronal survival elicited by PC. To address this notion, PC and transient middle cerebral artery occlusion (MCAO) were conducted in Sprague-Dawley rats. Additionally, primary cultured cortical neurons were used to identify the modulators and effectors of HDAC3 involved in PC. We found that nuclear localization of HDAC3 was significantly reduced following PC in vivo and in vitro. Treatment with the HDAC3-specific inhibitor, RGFP966, mimicked the neuroprotective effects of PC 24 h and 7 d after MCAO, causing a reduced infarct volume and less Fluoro-Jade C staining. Improved functional outcomes were observed in the neurological score and rotarod test. We further showed that attenuated recruitment of HDAC3 to promoter regions following PC potentiates transcriptional initiation of genes including Hspa1a, Bcl2l1, and Prdx2, which may underlie the mechanism of protection. In addition, PC-activated calpains were implicated in the cleavage of HDAC3. Pretreatment with calpeptin blockaded the attenuated nuclear distribution of HDAC3 and the protective effect of PC in vivo. Collectively, these results demonstrate that the inhibition of HDAC3 preconditions the brain against ischemic insults, indicating a new approach to evoke endogenous protection against stroke