Involvement of the neuronal phosphotyrosine signal adaptor N-Shc in kainic acid-induced epileptiform activity

Positive Association of Human SHC3 Gene with Schizophrenia in a Northeast Chinese Han Population

OBJECTIVE

Schizophrenia is one of the most devastating neuropsychiatric disorders. Genetic epidemiological studies have confirmed that schizophrenia is a genetic disease. Genes promoting neurodevelopment may be potential candidates for schizophrenia. As an adaptor linking a number of tyrosine kinase receptors in multiple intracellular signaling cascades, Src homology 2 domain containing transforming protein 3 (SHC3) is a member of the Shc-like adaptor protein family, and expressed predominantly in the mature neurons of the central nervous system (CNS). In the present study, we aimed to investigate the association of SHC3 and schizophrenia.

METHODS

An independent case-control association study was performed in a sample including 710 schizophrenia patients and 1314 healthy controls from a Northeast Chinese Han population.

RESULTS

The allelic and genotypic association analyses showed that four SNPs in SHC3 significantly associated with schizophrenia (rs2316280, rs4877041, rs944485 and rs7021743). The haplotype composing of these four SNPs also showed significantly individual and global association with schizophrenia.

CONCLUSION

Our present results suggest SHC3 as a susceptibility gene for schizophrenia.

Neuroprotection from Excitotoxic Injury by Local Administration of Lipid Emulsion into the Brain of Rats

Lipid emulsion was recently shown to attenuate cell death caused by excitotoxic conditions in the heart. There are key similarities between neurons and cardiomyocytes, such as excitability and conductibility, which yield vulnerability to excitotoxic conditions. However, systematic investigations on the protective effects of lipid emulsion in the central nervous system are still lacking. This study aimed to determine the neuroprotective effects of lipid emulsion in an in vivo rat model of kainic acid-induced excitotoxicity through intrahippocampal microinjections. Kainic acid and/or lipid emulsion-injected rats were subjected to the passive avoidance test and elevated plus maze for behavioral assessment. Rats were sacrificed at 24 h and 72 h after kainic acid injections for molecular study, including immunoblotting and qPCR. Brains were also cryosectioned for morphological analysis through cresyl violet staining and Fluorojade-C staining. Anxiety and memory functions were significantly preserved in 1% lipid emulsion-treated rats. Lipid emulsion was dose-dependent on the protein expression of β-catenin and the phosphorylation of GSK3-β and Akt. Wnt1 mRNA expression was elevated in lipid emulsion-treated rats compared to the vehicle. Neurodegeneration was significantly reduced mainly in the CA1 region with increased cell survival. Our results suggest that lipid emulsion has neuroprotective effects against excitotoxic conditions in the brain and may provide new insight into its potential therapeutic utility.

Trkb-IP3 Pathway Mediating Neuroprotection in Rat Hippocampal Neuronal Cell Culture Following Induction of Kainic Acid

Background

Following brain injury, development of hippocampal sclerosis often led to the temporal lobe epilepsy which is sometimes resistant to common anti-epileptic drugs. Cellular and molecular changes underlying epileptogenesis in animal models were studied, however, the underlying mechanisms of kainic acid (KA) mediated neuronal damage in rat hippocampal neuron cell culture alone has not been elucidated yet.

Methods

Embryonic day 18 (E-18) rat hippocampus neurons were cultured with poly-L-lysine coated glass coverslips. Following optimisation, KA (0.5 μM), a chemoconvulsant agent, was administered at three different time-points (30, 60 and 90 min) to induce seizure in rat hippocampal neuronal cell culture. We examined cell viability, neurite outgrowth density and immunoreactivity of the hippocampus neuron culture by measuring brain derived neurotrophic factor (BDNF), γ-amino butyric acid A (GABA_A) subunit α-1 (GABRA1), tyrosine receptor kinase B (TrkB), and inositol trisphosphate receptor (IP₃R/IP3) levels.

Results

The results revealed significantly decreased and increased immunoreactivity changes in TrkB (a BDNF receptor) and IP₃R, respectively, at 60 min time point.

Conclusion

The current findings suggest that TrkB and IP3 could have a neuroprotective role which could be a potential pharmacological target for anti-epilepsy drugs.

[Functional roles of phosphotyrosine adaptor Shc in the brain]

Adaptor molecules (adaptor proteins) have indispensable roles in cellular signaling, essential for cellular proliferation, development and metabolism. Shc (Src homology and collagen homology)-family molecule is a group of adaptor molecules, and indicated to be involved in intracellular phosphotyrosine signaling. Shc family has 4 subtypes, ShcA-ShcD, and there are long and short isoforms in ShcA and ShcC whereas ShcB and ShcD have short isoform only. There are three domains conserved in all Shc-family isoforms: phosphotyrosine-binding (PTB) domain, collagen-homology 1 (CH1) domain and Src-homology 2 (SH2) domain, from the N-terminal to C-terminal. PTB and SH2 domains recognize and bind to phosphotyrosine in other molecules, and CH1 domain is recognized and bind to SH2 domain in Grb2, an adaptor molecule, when the tyrosine residues in the domain are phosphorylated. Expression of ShcA is observed in all tissues except for brain in adult animals, although ShcA mRNA is detected in brain during embryonic days. On the other hand, in adult brain, expressions of ShcB, ShcC, and ShcD are observed. Analysis of single knockout mice (ShcA (neuron specific), ShcB, ShcC) and double knockout mice for ShcB and C indicated essential roles of Shc-family molecules in proliferation and survival of cells in various brain regions as well as synaptic plasticity and higher brain functions such as learning and memory. Studies on multiple-knockout mice of Shc-family molecules may further clarify possible involvements of Shc family in physiological and pathophysiological functions in brain.