Zhiguo Nie

Transcription factor MEF2C influences neural stem/progenitor cell differentiation and maturation in vivo

Emerging evidence suggests that myocyte enhancer factor 2 (MEF2) transcription factors act as effectors of neurogenesis in the brain, with MEF2C the predominant isoform in developing cerebrocortex. Here, we show that conditional knockout of Mef2c in nestin-expressing neural stem/progenitor cells (NSCs) impaired neuronal differentiation in vivo, resulting in aberrant compaction and smaller somal size. NSC proliferation and survival were not affected. Conditional null mice surviving to adulthood manifested more immature electrophysiological network properties and severe behavioral deficits reminiscent of Rett syndrome, an autism-related disorder. Our data support a crucial role for MEF2C in programming early neuronal differentiation and proper distribution within the layers of the neocortex.

μ-Opioid Receptors Modulate NMDA Receptor-Mediated Responses in Nucleus Accumbens Neurons

The nucleus accumbens (NAcc) may play a major role in opiate dependence, and central NMDA receptors are reported to influence opiate tolerance and dependence. Therefore, we investigated the effects of the selective μ-opioid receptor agonist [d-Ala2-N-Me-Phe4,Gly-ol5]-enkephalin (DAMGO) on membrane properties of rat NAcc neurons and on events mediated by NMDA and non-NMDA glutamate receptors, using intracellular recording in a brain slice preparation. Most NAcc neurons showed a marked inward rectification (correlated with Cs+- and Ba2+-sensitive inward relaxations) when hyperpolarized, as well as a slowly depolarizing ramp with positive current pulses. Superfusion of DAMGO did not alter membrane potential, input resistance, or the inward relaxations. In the presence of 6-cyano-7-nitroquinoxaline-2,3-dione (CNQX) used to block non-NMDA glutamate receptors and bicuculline to block GABAAreceptors, EPSPs evoked by local stimulation displayed characteristics of an NMDA component: (1) long duration, (2) voltage sensitivity, and (3) blockade by the NMDA receptor antagonistdl-2-amino-5-phosphonovaleric acid (d-APV). DAMGO (0.1–1 μm) significantly decreased both NMDA- and non-NMDA–EPSP amplitudes with reversal of this effect by naloxone and the μ-selective antagonist [Cys2-Tyr3-Orn5-Pen7]-somatostatinamide (CTOP). To assess a postsynaptic action of DAMGO, we superfused slices with tetrodotoxin and evoked inward currents by local application of glutamate agonists. Surprisingly, 0.1–1 μm DAMGO markedly enhanced the NMDA currents (with reversal by CTOP) but reduced the non-NMDA currents. At higher concentrations (5 μm), DAMGO reduced NMDA currents, but this effect was enhanced, not blocked, by CTOP. These results indicate a complex DAMGO modulation of the NMDA component of glutamatergic synaptic transmission in NAcc: μ receptor activation decreases NMDA–EPSP amplitudes presynaptically yet increases NMDA currents postsynaptically. These new data may provide a cellular mechanism for the previously reported role of NMDA receptors in opiate tolerance and dependence.

Presynaptic CRF1 Receptors Mediate the Ethanol Enhancement of GABAergic Transmission in the Mouse Central Amygdala

Corticotropin-releasing factor (CRF) is a 41-amino-acid neuropeptide involved in stress responses initiated from several brain areas, including the amygdala formation. Research shows a strong relationship between stress, brain CRF, and excessive alcohol consumption. Behavioral studies suggest that the central amygdala (CeA) is significantly involved in alcohol reward and dependence. We recently reported that the ethanol augmentation of GABAergic synaptic transmission in rat CeA involves CRF1 receptors, because both CRF and ethanol significantly enhanced the amplitude of evoked GABAergic inhibitory postsynaptic currents (IPSCs) in CeA neurons from wild-type (WT) and CRF2 knockout (KO) mice, but not in neurons of CRF1 KO mice. The present study extends these findings using selective CRF receptor ligands, gene KO models, and miniature IPSC (mIPSC) analysis to assess further a presynaptic role for the CRF receptors in mediating ethanol effects in the CeA. In whole-cell patch recordings of pharmacologically isolated GABAAergic IPSCs from slices of mouse CeA, both CRF and ethanol augmented evoked IPSCs in a concentration-dependent manner, with low EC50s. A CRF1 (but not CRF2) KO construct and the CRF1-selective nonpeptide antagonist NIH-3 (LWH-63) blocked the augmenting effect of both CRF and ethanol on evoked IPSCs. Furthermore, the new selective CRF1 agonist stressin1, but not the CRF2 agonist urocortin 3, also increased evoked IPSC amplitudes. Both CRF and ethanol decreased paired-pulse facilitation (PPF) of evoked IPSCs and significantly enhanced the frequency, but not the amplitude, of spontaneous miniature GABAergic mIPSCs in CeA neurons of WT mice, suggesting a presynaptic site of action. The PPF effect of ethanol was abolished in CeA neurons of CRF1 KO mice. The CRF1 antagonist NIH-3 blocked the CRF- and ethanol-induced enhancement of mIPSC frequency in CeA neurons. These data indicate that presynaptic CRF1 receptors play a critical role in permitting or mediating ethanol enhancement of GABAergic synaptic transmission in CeA, via increased vesicular GABA release, and thus may be a rational target for the treatment of alcohol abuse and alcoholism.

Myocyte Enhancer Factor 2C as a Neurogenic and Antiapoptotic Transcription Factor in Murine Embryonic Stem Cells

Cell-based therapies require a reliable source of cells that can be easily grown, undergo directed differentiation, and remain viable after transplantation. Here, we generated stably transformed murine ES (embryonic stem) cells that express a constitutively active form of myocyte enhancer factor 2C (MEF2CA). MEF2C has been implicated as a calcium-dependent transcription factor that enhances survival and affects synapse formation of neurons as well as differentiation of cardiomyocytes. We now report that expression of MEF2CA, both in vitro and in vivo, under regulation of the nestin enhancer effectively produces “neuronal” progenitor cells that differentiate into a virtually pure population of neurons. Histological, electrophysiological, and behavioral analyses demonstrate that MEF2C-directed neuronal progenitor cells transplanted into a mouse model of cerebral ischemia can successfully differentiate into functioning neurons and ameliorate stroke-induced behavioral deficits.

Reduced NMDAR1 expression in the Sp4 hypomorphic mouse may contribute to endophenotypes of human psychiatric disorders

The reduced expression of the Sp4 gene in Sp4 hypomorphic mice resulted in subtle vacuolization in the hippocampus as well as deficits in sensorimotor gating and contextual memory, putative endophenotypes for schizophrenia and other psychiatric disorders. In this study, we examined both spatial learning/memory and hippocampal long-term potentiation (LTP) of Sp4 hypomorphic mice. Impaired spatial learning/memory and markedly reduced LTP were found. To corroborate the functional studies, the expression of N-methyl-D-aspartate (NMDA) glutamate receptors was investigated with both western blot and immunohistochemical analyses. The reduced expression of the Sp4 gene decreased the level of the NR1 subunit of NMDA receptors in Sp4 hypomorphic mice. In human, SP4 gene was found to be deleted sporadically in schizophrenia patients, corroborating evidence that polymorphisms of human SP4 gene are associated with schizophrenia and other psychiatric disorders. Impaired NMDA neurotransmission has been implicated in several human psychiatric disorders. As yet, it remains unclear how mutations of candidate susceptibility genes for these disorders may contribute to the disruption of NMDA neurotransmission. Sp4 hypomorphic mice could therefore serve as a genetic model to investigate impaired NMDA functions resulting from loss-of-function mutations of human SP4 gene in schizophrenia and/or other psychiatric disorders. Furthermore, aberrant expression of additional genes, besides NMDAR1, likely also contributes to the behavioral abnormalities in Sp4 hypomorphic mice. Thus, further investigation of the Sp4 pathway may provide novel insights in our understanding of a variety of neuropsychiatric disorders.

A Metabotropic Hypothesis for Ethanol Sensitivity of GABAergic and Glutamatergic Central Synapses

This chapter will address the sensitivity of ligand-gated ion channels to ethanol and show that such ethanol sensitivity (or lack of sensitivity) is not invariable for any given neuron. In fact, bringing together several pieces of electrophysiological and pharmacological data leads us to put forward a hypothesis that the ethanol sensitivity of ligand- gated ion channels is regulated by ‘metabotropic’ systems defined in the generic sense: that is, by receptor-activated, G-protein-linked, non-ionotropic, energetic mechanisms. This hypothesis might provide an explanation for the variability of ethanol-transmitter interactions seen in various laboratories.

Autistic Phenotype from MEF2C Knockout Cells

In their Research Article (“Identifying autism loci and genes by tracing recent shared ancestry,” 11 July 2008, p. [218][1]), E. M. Morrow et al. showed that gene expression associated with autism-spectrum disorders (ASD) is controlled by MEF2 transcription factors and hypothesized that autistic