Distribution of constitutively expressed MEF-2A in adult rat and human nervous systems

Neuroglial Involvement in Abnormal Glutamate Transport in the Cochlear Nuclei of the Igf1 -/- Mouse

Insulin-like growth factor 1 (IGF-1) is a powerful regulator of synaptic activity and a deficit in this protein has a profound impact on neurotransmission, mostly on excitatory synapses in both the developing and mature auditory system. Adult Igf1^−/− mice are animal models for the study of human syndromic deafness; they show altered cochlear projection patterns into abnormally developed auditory neurons along with impaired glutamate uptake in the cochlear nuclei, phenomena that probably reflect disruptions in neuronal circuits. To determine the cellular mechanisms that might be involved in regulating excitatory synaptic plasticity in 4-month-old Igf1^−/− mice, modifications to neuroglia, astroglial glutamate transporters (GLTs) and metabotropic glutamate receptors (mGluRs) were assessed in the cochlear nuclei. The Igf1^−/− mice show significant decreases in IBA1 (an ionized calcium-binding adapter) and glial fibrillary acidic protein (GFAP) mRNA expression and protein accumulation, as well as dampened mGluR expression in conjunction with enhanced glutamate transporter 1 (GLT1) expression. By contrast, no differences were observed in the expression of glutamate aspartate transporter (GLAST) between these Igf1^−/− mice and their heterozygous or wildtype littermates. These observations suggest that congenital IGF-1 deficiency may lead to alterations in microglia and astrocytes, an upregulation of GLT1, and the downregulation of groups I, II and III mGluRs. Understanding the molecular, biochemical and morphological mechanisms underlying neuronal plasticity in a mouse model of hearing deficits will give us insight into new therapeutic strategies that could help to maintain or even improve residual hearing when human deafness is related to IGF-1 deficiency.

Stage 4S neuroblastoma tumors show a characteristic DNA methylation portrait

Stage 4S neuroblastoma (NB) is a special type of NB found in infants with metastases at diagnosis and is associated with an excellent outcome due to its remarkable capacity to undergo spontaneous regression. As genomics have not been able to explain this intriguing clinical presentation, we here aimed at profiling the DNA methylome of stage 4S NB to better understand this phenomenon. To this purpose, differential methylation analyses between International Neuroblastoma Staging System (INSS) stage 4S, stage 4 and stage 1/2 were performed, using methyl-CpG-binding domain (MBD) sequencing data of 14 stage 4S, 14 stage 4, and 13 stage 1/2 primary NB tumors (all MYCN non-amplified in order not to confound results). Stage 4S-specific hyper- and hypomethylated promoters were determined and further characterized for genomic localization and function by cytogenetic band enrichment, gene set enrichment, transcription factor target enrichment and differential RNA expression analyses. We show that specific chromosomal locations are enriched for stage 4S differentially methylated promoters and that stage 4S tumors show characteristic hypermethylation of specific subtelomeric promoters. Furthermore, genes involved in important oncogenic pathways, in neural crest development and differentiation, and in epigenetic processes are differentially methylated and expressed in stage 4S tumors. Based on these findings, we describe new biological mechanisms possibly contributing to the stage 4S-specific tumor biology and spontaneous regression. In conclusion, this study is the first to describe the highly characteristic stage 4S DNA methylome. These findings will open new avenues to further unravel the NB pathology in general and stage 4S disease specifically.

IGF-1 deficiency causes atrophic changes associated with upregulation of VGluT1 and downregulation of MEF2 transcription factors in the mouse cochlear nuclei

Insulin-like growth factor 1 (IGF-1) is a neurotrophic protein that plays a crucial role in modulating neuronal function and synaptic plasticity in the adult brain. Mice lacking the Igf1 gene exhibit profound deafness and multiple anomalies in the inner ear and spiral ganglion. An issue that remains unknown is whether, in addition to these peripheral abnormalities, IGF-1 deficiency also results in structural changes along the central auditory pathway that may contribute to an imbalance between excitation and inhibition, which might be reflected in abnormal auditory brainstem responses (ABR). To assess such a possibility, we evaluated the morphological and physiological alterations in the cochlear nucleus complex of the adult mouse. The expression and distribution of the vesicular glutamate transporter 1 (VGluT1) and the vesicular inhibitory transporter (VGAT), which were used as specific markers for labeling excitatory and inhibitory terminals, and the involvement of the activity-dependent myocyte enhancer factor 2 (MEF2) transcription factors in regulating excitatory synapses were assessed in a 4-month-old mouse model of IGF-1 deficiency and neurosensorial deafness (Igf1 (-/-) homozygous null mice). The results demonstrate decreases in the cochlear nucleus area and cell size along with cell loss in the cochlear nuclei of the deficient mouse. Additionally, our results demonstrate that there is upregulation of VGluT1, but not VGAT, immunostaining and downregulation of MEF2 transcription factors together with increased wave II amplitude in the ABR recording. Our observations provide evidence of an abnormal neuronal cytoarchitecture in the cochlear nuclei of Igf1 (-/-) null mice and suggest that the increased efficacy of glutamatergic synapses might be mediated by MEF2 transcription factors.

MEF-2 regulates activity-dependent spine loss in striatopallidal medium spiny neurons

Striatal dopamine depletion profoundly reduces the density of spines and corticostriatal glutamatergic synapses formed on D(2) dopamine receptor expressing striatopallidal medium spiny neurons, leaving D(1) receptor expressing striatonigral medium spiny neurons relatively intact. Because D(2) dopamine receptors diminish the excitability of striatopallidal MSNs, the pruning of synapses could be a form of homeostatic plasticity aimed at restoring activity into a preferred range. To characterize the homeostatic mechanisms controlling synapse density in striatal medium spiny neurons, striatum from transgenic mice expressing a D(2) receptor reporter construct was co-cultured with wild-type cerebral cortex. Sustained depolarization of these co-cultures induced a profound pruning of glutamatergic synapses and spines in striatopallidal medium spiny neurons. This pruning was dependent upon Ca(2+) entry through Cav1.2 L-type Ca(2+) channels, activation of the Ca(2+)-dependent protein phosphatase calcineurin and up-regulation of myocyte enhancer factor 2 (MEF2) transcriptional activity. Depolarization and MEF2 up-regulation increased the expression of two genes linked to synaptic remodeling-Nur77 and Arc. Taken together, these studies establish a translational framework within which striatal adaptations linked to the symptoms of Parkinson's disease can be explored.