Dynamic expression pattern of neuro-oncological ventral antigen 1 (Nova1) in the rat brain after focal cerebral ischemia/reperfusion insults

17β-estradiol regulates the RNA-binding protein Nova1, which then regulates the alternative splicing of estrogen receptor β in the aging female rat brain

Alternative RNA splicing results in the translation of diverse protein products arising from a common nucleotide sequence. These alternative protein products are often functional and can have widely divergent actions from the canonical protein. Studies in humans and other vertebrate animals have demonstrated that alternative splicing events increase with advanced age, sometimes resulting in pathological consequences. Menopause represents a critical transition for women, where the beneficial effects of estrogens are no longer evident; therefore, factors underlying increased pathological conditions in women are confounded by the dual factors of aging and declining estrogens. Estrogen receptors (ERs) are subject to alternative splicing, the spliced variants increase following menopause, and they fail to efficiently activate estrogen-dependent signaling pathways. However, the factors that regulate the alternative splicing of ERs remain unknown. We demonstrate novel evidence supporting a potential biological feedback loop where 17β-estradiol regulates the RNA-binding protein Nova1, which, in turn, regulates the alternative splicing of ERβ. These data increase our understanding of ER alternative splicing and could have potential implications for women taking hormone replacement therapy after menopause.

Nova1 mediates resistance of rat pheochromocytoma cells to hypoxia-induced apoptosis via the Bax/Bcl-2/caspase-3 pathway

Neuro-oncological ventral antigen 1 (Nova1) is a well known brain-specific splicing factor. Several studies have identified Nova1 as a regulatory protein at the top of a hierarchical network. However, the function of Nova1 during hypoxia remains poorly understood. This study aimed to investigate the protective effect of Nova1 against cell hypoxia and to further explore the Bax/Bcl-2/caspase-3 pathway as a potential mechanism. During hypoxia, the survival rate of pheochromocytoma PC12 cells was gradually decreased and the apoptosis rate was gradually increased, peaking at 48 h of hypoxia. At 48 h after transfection of PC12 cells with pCMV-Myc-Nova1, the expression of Nova1 was significantly increased, with wide distribution in the cytoplasm and nucleus. Moreover, the survival rate was significantly increased and the apoptosis rate was significantly decreased. Additionally, the mRNA and protein expression levels of Bax and caspase-3 were significantly increased in the pCMV-Myc group and significantly decreased in the pCMV-Myc-Nova1 group, whereas that of Bcl-2 was significantly decreased in the pCMV-Myc group and significantly increased in the pCMV-Myc-Nova1 group. This study indicated that Nova1 could be linked to resistance to the hypoxia-induced apoptosis of PC12 cells via the Bax/Bcl-2/caspase-3 pathway, and this finding may be of significance for exploring novel mechanisms of hypoxia and the treatment of hypoxia-associated diseases.

Neuro-oncological ventral antigen 1 (NOVA1): Implications in neurological diseases and cancers

Neuro-oncological ventral antigen 1 (NOVA1) is a RNA-binding protein that interacts with RNA containing repeats of the YCAY sequence. This protein is a brain-specific splicing factor regulating neuronal alternative splicing. It has been increasingly recognized as an important contributor to neurological disorders and carcinogenesis. In this review, we summarize the biological functions and pathological roles of NOVA1. The clinical implications of NOVA1 will also be discussed.

Proteomic Analysis of Mouse Cortex Postsynaptic Density following Neonatal Brain Hypoxia-Ischemia

Proteomics of the synapses and postsynaptic densities (PSDs) have provided a deep understanding of protein composition and signal networks in the adult brain, which underlie neuronal plasticity and neurodegenerative or psychiatric disorders. However, there is a paucity of knowledge about the architecture and organization of PSDs in the immature brain, and how it is modified by brain injury in an early developing stage. Mass spectrometry (MS)-based proteomic analysis was performed on PSDs prepared from cortices of postnatal day 9 naïve mice or pups which had suffered hypoxic-ischemic (HI) brain injury. 512 proteins of different functional groups were identified from PSDs collected 1 h after HI injury, among which 60 have not been reported previously. Seven newly identified proteins involved in neural development were highlighted. HI injury increased the yield of PSDs at early time points upon reperfusion, and multiple proteins were recruited into PSDs following the insult. Quantitative analysis was performed using spectral counting, and proteins whose relative expression was more than 50% up- or downregulated compared to the sham animals 1 h after HI insult were reported. Validation with Western blotting demonstrated changes in expression and phosphorylation of the N-methyl-D-aspartate receptor, activation of a series of postsynaptic protein kinases and dysregulation of scaffold and adaptor proteins in response to neonatal HI insult. This work, along with other recent studies of synaptic protein profiling in the immature brain, builds a foundation for future investigation on the molecular mechanisms underlying developing plasticity. Furthermore, it provides insights into the biochemical changes of PSDs following early brain hypoxia-ischemia, which is helpful for understanding not only the injury mechanisms, but also the process of repair or replenishment of neuronal circuits during recovery from brain damage.

Ethanol-related alterations in gene expression patterns in the developing murine hippocampus

It is well known that consuming alcohol prior to and during pregnancy can cause harm to the developing fetus. Fetal alcohol spectrum disorder is a term commonly used to describe a range of disabilities that may arise from prenatal alcohol exposure such as fetal alcohol syndrome, partial fetal alcohol syndrome, alcohol-related neurodevelopmental disorders, and alcohol-related birth defects. Here, we report that maternal binge alcohol consumption alters several important genes that are involved in nervous system development in the mouse hippocampus at embryonic day 18. Microarray analysis revealed that Nova1, Ntng1, Gal, Neurog2, Neurod2, and Fezf2 gene expressions are altered in the fetal hippocampus. Pathway analysis also revealed the association of the calcium signaling pathway in addition to other pathways with the differentially expressed genes during early brain development. Alteration of such important genes and dynamics of the signaling pathways may cause neurodevelopmental disorders. Our findings offer insight into the molecular mechanism involved in neurodevelopmental disorders associated with alcohol-related defects.

Up-regulation of brain-enriched miR-107 promotes excitatory neurotoxicity through down-regulation of glutamate transporter-1 expression following ischaemic stroke

Recent studies have uncovered that accumulation of glutamate after ischaemic stroke is closely associated with the down-regulation of glutamate transporter-1 (GLT-1) expression, suggesting that GLT-1 expression critically controls glutamate accumulation and the abnormal glutamate transport-elicited neuronal cell excitotoxicity in patients with ischaemic stroke. However, it remains unknown how GLT-1 expression is regulated under ischaemic stroke conditions. In the present study, we screened the expression of nine brain-specific or brain-enriched miRNAs in a focal cerebral ischaemia/reperfusion (I/R) injury rat model, which showed glutamate accumulation and down-regulated GLT-1 expression as expected, and revealed that the miR-107 level was elevated in both brain tissue and plasma in the model. Next, we examined the functional relationship of miR-107 with GLT-1 expression in a nerve cell hypoxia/reoxygenation (H/R) injury model. H/R treatment increased apoptosis of the nerve cells concomitant with glutamate accumulation, miR-107 elevation and suppressed GLT-1 expression, mimicking our in vivo findings in the cerebral I/R injury rat model in vitro. Co-treating the cells with an miR-107 inhibitor blocked all of the effects, demonstrating that miR-107 functions to inhibit GLT-1 expression and elevate glutamate accumulation. To extend these animal and cell-based studies to clinical patients, we measured the plasma levels of miR-107 and glutamate, and observed that both miR-107 and glutamate were elevated in patients with ischaemic stroke. On the basis of these observations, we conclude that elevated miR-107 expression after ischaemic stroke accounts, at least partially, for glutamate accumulation through suppression of GLT-1 expression. Our findings also highlight that the plasma level of miR-107 may serve as a novel biomarker for monitoring excitotoxicity in patients with ischaemic stroke.

MiR-181b-5p downregulates NOVA1 to suppress proliferation, migration and invasion and promote apoptosis in astrocytoma

MicroRNAs (miRNAs) are small, short noncoding RNAs that modulate the expression of numerous genes by targeting their mRNA. Numerous abnormal miRNA expression patterns are observed in various human malignancies, and certain miRNAs can act as oncogenes or tumor suppressors. Astrocytoma, the most common neuroepithelial cancer, represents the majority of malignant brain tumors in humans. In our previous studies, we found that the downregulation of miR-181b-5p in astrocytomas is associated with a poor prognosis. The aim of the present study was to investigate the functional role of miR-181b-5p and its possible target genes. miR-181b-5p was significantly downregulated in astrocytoma specimens, and the reduced expression of miR-181b-5p was inversely correlated with the clinical stage. The ectopic expression of miR-181b-5p inhibited proliferation, migration and invasion and induced apoptosis in astrocytoma cancer cells in vitro. The NOVA1 (neuro-oncological ventral antigen 1) gene was further identified as a novel direct target of miR-181b-5p. Specifically, miR-181b-5p bound directly to the 3'-untranslated region (UTR) of NOVA1 and suppressed its expression. In clinical specimens, NOVA1 was overexpressed, and its protein levels were inversely correlated with miR-181b-5p expression. Furthermore, the changing level of NOVA1 was significantly associated with a poor survival outcome. Similar to restoring miR-181b-5p expression, downregulating NOVA1 inhibited cell growth, migration and invasion. Overexpression of NOVA1 reversed the inhibitory effects of miR-181b-5p. Our results indicate that miR-181b-5p is a tumor suppressor in astrocytoma that inhibits tumor progression by targeting NOVA1. These findings suggest that miR-181b-5p may serve as a novel therapeutic target for astrocytoma.