Project description:MicroRNAs (miRNAs) are evolutionary conserved, non-coding, gene regulatory RNA molecules found in both plants and animals and amongst almost every cell and tissue type. They are about 22 nucleotides long and are involved in silencing of mRNA through sequence specific binding to the 3’ untranslated region (UTR) of the mRNA subsequently causing translational repression and/or will promote the degradation of protein-coding mRNA. Specifically, the miRNA family, mir-146 a/b, has been previously found to be involved in the regulation of the innate immune response by functioning as a negative regulator to help fine-tune the immune response. Microglial cells are the macrophage of the brain participating as major players of the innate immune response. During prion disease, no immune response is mounted against PrPSc possibly due to its similarity to host PrPc and thus, the host immune response would be suppressed and tightly regulated. Therefore, an increased expression of mir-146 by microglial cells during prion disease may function as one of these negative regulators. Our objective of this experiment is to use DNA microarrays to investigate the gene regulation of mir-146 previously found upregulated in our studies of mouse brain tissue specifically in microglial cells during prion disease with the aim of having a better understanding of prion pathobiology and a potential target for therapeutic intervention. Mir-146 expression was confirmed via in situ analysis of brain tissue and was further investigated in a microglial murine cell line (EOC 13.31). To mimic mir-146 upregulation during prion disease, mir-146 a & b were overexpressed in EOCs using a lipid based reverse transfection system. Furthermore, endogeneous mir-146 was knocked down as another method to help confirm the mRNA targets affected by mir-146. Simultaneously, another experiment was performed for the investigation of its involvement in the innate immune response by stimulating the EOCs with differing concentrations of LPS from E.coli (055:B5). Total RNA was collected and prepared at several timepoints and the levels of expression of both mir-146 a & b was tested via qRT-PCR. The RNA collected from the EOCs from each condition were used as target material for dual-color, competitive hybridization to Agilent whole mouse genome 4x44K oligo arrays. All the significant targets found on the mircorarrays were compared against the various conditions to find a consensus of affected mir-146 mRNA targets.

Project description:Prion diseases typically have long pre-clinical incubation periods during which time the infectious prion particle and infectivity steadily propagate in the brain. Abnormal neuritic sprouting and synaptic deficits are apparent during pre-clinical disease, however, gross neuronal loss is not detected until the onset of the clinical phase. The molecular events that accompany early neuronal damage and ultimately conclude with neuronal death remain obscure. In this study, we used laser capture microdissection to isolate hippocampal CA1 neurons and then determined their pre-clinical transcriptional response during infection. We found that gene expression within these neurons is dynamic and characterized by distinct phases of activity. A major cluster of genes is altered during pre-clinical disease after which expression either returns to basal levels, or alternatively undergoes a direct reversal during clinical disease. Strikingly, we show that this cluster contains a signature highly reminiscent of synaptic N-methyl-D-aspartic acid (NMDA) receptor signaling and the activation of neuroprotective pathways. Additionally, genes involved in neuronal projection and dendrite development were also altered throughout the disease, culminating in a general decline of gene expression for synaptic proteins. Similarly, deregulated miRNAs such as miR-132-3p, miR-124a-3p, miR-16-5p, miR-26a-5p, miR-29a-3p and miR-140-5p follow concomitant patterns of expression. This is the first in depth genomic study describing the pre-clinical response of hippocampal neurons to early prion replication. Our findings suggest that prion replication results in the persistent stimulation of a programmed response, at least in part mediated by synaptic NMDA receptor activity that initially promotes cell survival and neurite remodelling. However, this response is terminated prior to the onset of clinical symptoms in the infected hippocampus, seemingly pointing to a critical juncture in the disease. Manipulation of these early neuroprotective pathways may redress the balance between degeneration and survival, providing a potential inroad for treatment. The CA1 hippocampal region was dissected out using LCM and RNA was extracted from these samples. In total, 6 different time points were screened for both RNA and miRNA expression levels in prion infected and control animals. Gene expression profiles from 6 time points (n M-bM-^IM-% 2) were determined using whole mouse 4x44K arrays. We successfully validated a subset of candidate genes that were deregulated during early prion disease. We performed a similar assessment of temporal miRNAs expression levels throughout the infection using the TLDA platform which was further validated by individual real-time PCR assays. In parallel, immunoctyochemistry was used to characterize the cellular presence of astrocytes, microglial and neurons in the CA1 region throughout the disease which correlated well with both mRNA and miRNA expression profiles. Staining for the PrPRes and neuronal toxicity levels was also performed to determine the spatial and temporal PrPRes deposition and assess the level of neuronal death that occurs in the hippocampus, respectively. Using bioinformatic methods, potential pathways that were implicated by our data to be deregulated during early prion disease were presented while potential miRNA regulation of some of these candidate genes implicated in these pathways was also included.

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Mus musculus

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