MicroRNAs (miRNAs) have been shown to play important roles in both brain development and the regulation of adult neural cell functions. However, a systematic analysis of brain miRNA functions has been hindered by a lack of comprehensive information regarding the distribution of miRNAs in neuronal versus glial cells. To address this issue, we performed microarray analyses of miRNA expression in the four principal cell types of the CNS (neurons, astrocytes, oligodendrocytes, and microglia) using primary cultures from postnatal d 1 rat cortex. These analyses revealed that neural miRNA expression is highly cell-type specific, with 116 of the 351 miRNAs examined being differentially expressed fivefold or more across the four cell types. We also demonstrate that individual neuron-enriched or neuron-diminished RNAs had a significant impact on the specification of neuronal phenotype: overexpression of the neuron-enriched miRNAs miR-376a and miR-434 increased the differentiation of neural stem cells into neurons, whereas the opposite effect was observed for the glia-enriched miRNAs miR-223, miR-146a, miR-19, and miR-32. In addition, glia-enriched miRNAs were shown to inhibit aberrant glial expression of neuronal proteins and phenotypes, as exemplified by miR-146a, which inhibited neuroligin 1-dependent synaptogenesis. This study identifies new nervous system functions of specific miRNAs, reveals the global extent to which the brain may use differential miRNA expression to regulate neural cell-type-specific phenotypes, and provides an important data resource that defines the compartmentalization of brain miRNAs across different cell types.

Background: Cellular miRNAs play an important role in the regulation of gene expression in eukaryotes. Recently, miRNAs have also been shown to be able to target and inhibit viral gene expression. Computational predictions revealed earlier that the HIV-1 genome includes regions that may be potentially targeted by human miRNAs. Here we report the functionality of predicted miR-29a target site in the HIV-1 nef gene. Results: We find that the human miRNAs hsa-miR-29a and 29b are expressed in human peripheral blood mononuclear cells. Expression of a luciferase reporter bearing the nef miR-29a target site was decreased compared to the luciferase construct without the target site. Locked nucleic acid modified anti-miRNAs targeted against hsa-miR-29a and 29b specifically reversed the inhibitory effect mediated by cellular miRNAs on the target site. Ectopic expression of the miRNA results in repression of the target Nef protein and reduction of virus levels. Conclusion: Our results show that the cellular miRNA hsa-miR29a downregulates the expression of Nef protein and interferes with HIV-1 replication.

MicroRNAs (miRNAs) are a new class of 18–23 nucleotide long non-coding RNAs that play critical roles in a wide spectrum of biological processes. Recent reports also throw light into the role of microRNAs as critical effectors in the intricate host-pathogen interaction networks. Evidence suggests that both virus and hosts encode microRNAs. The exclusive dependence of viruses on the host cellular machinery for their propagation and survival also make them highly susceptible to the vagaries of the cellular environment like small RNA mediated interference. It also gives the virus an opportunity to fight and/or modulate the host to suite its needs. Thus the range of interactions possible through miRNA-mRNA cross-talk at the host-pathogen interface is large. These interactions can be further fine-tuned in the host by changes in gene expression, mutations and polymorphisms. In the pathogen, the high rate of mutations adds to the complexity of the interaction network. Though evidence regarding microRNA mediated cross-talk in viral infections is just emerging, it offers an immense opportunity not only to understand the intricacies of host-pathogen interactions, and possible explanations to viral tropism, latency and oncogenesis, but also to develop novel biomarkers and therapeutics.

Several microRNAs have been implicated in neurogenesis, neuronal differentiation, neurodevelopment, and memory. Development of miRNA-based therapeutics, however, needs tools for effective miRNA modulation, tissue-specific delivery, and in vivo evidence of functional effects following the knockdown of miRNA. Expression of miR-29a is reduced in patients and animal models of several neurodegenerative disorders, including Alzheimer's disease, Huntington's disease, and spinocerebellar ataxias. The temporal expression pattern of miR-29b during development also correlates with its protective role in neuronal survival. Here, we report the cellular and behavioral effect of in vivo, brain-specific knockdown of miR-29. We delivered specific anti-miRNAs to the mouse brain using a neurotropic peptide, thus overcoming the blood-brain-barrier and restricting the effect of knockdown to the neuronal cells. Large regions of the hippocampus and cerebellum showed massive cell death, reiterating the role of miR-29 in neuronal survival. The mice showed characteristic features of ataxia, including reduced step length. However, the apoptotic targets of miR-29, such as Puma, Bim, Bak, or Bace1, failed to show expected levels of up-regulation in mice, following knockdown of miR-29. In contrast, another miR-29 target, voltage-dependent anion channel1 (VDAC1), was found to be induced several fold in the hippocampus, cerebellum, and cortex of mice following miRNA knockdown. Partial restoration of apoptosis was achieved by down-regulation of VDAC1 in miR-29 knockdown cells. Our study suggests that regulation of VDAC1 expression by miR-29 is an important determinant of neuronal cell survival in the brain. Loss of miR-29 results in dysregulation of VDAC1, neuronal cell death, and an ataxic phenotype.