Project description:Over-expression of wild type PrP in skeletal muscles is sufficient to cause a primary myopathy with no signs of peripheral neuropathy, possibly due to accumulation of a cytotoxic truncated form of PrP and/or PrP aggregation. In this study we used DNA microarrays to identify 1499 transcripts that are temporally deregulated concomitant with inducible PrPC over-expression in the skeletal muscles of transgenic mice. Examination using microarrays revealed a transcriptional profile with both similarities and differences to previously investigated models of myopathies. Down-regulation of genes coding for the myofibrillar proteins MYH2, MYH6, MYH7, MYL2, MYL3 and up-regulation of lysosomal genes CTSS, CTSD, CTSZ, DPEP2, HEXA, HEXB and LAMP1 coincide with the observed myopathy and lysosome accumulation on over-expression of PrPC. Down-regulation of the MEF2C gene, a key regulatory transcriptional factor muscle development and remodeling of adult muscles in response to physiologic and pathologic signals, may contribute to the centrally placed nuclei in the skeletal muscles. Significantly, up-regulation of genes involved in p53 signaling and the induction of p53 protein, suggest a central role for this molecule in the myopathy. Several p53-regulated genes involved in cell cycle arrest (CDNK1A, GADD45a and GADD45b) and apoptosis (BAK1, PMAIP1, BBC3, and BAX) are induced. We suggest that PrPC over-expression in skeletal muscles, possibly in response to accumulation of a cytotoxic truncated form of PrP, causes a primary myopathy involving the induction of p53-dependent pathways. Wild type (WT), PrP-null (KO), and Tg(HQK) mice were fed food pellets either lacking or containing 6g doxycycline (Dox)/kg food to induce PrPC expression. Skeletal muscles from the quadriceps of hind legs were removed at day 0, 4, 7, 14, 30 and 60 days following administration of Dox. Total RNA was isolated from these tissues for use in subsequent microarray analysis. Mouse gene expression was analysed by two-colour microarray experiments using an inhouse manufactured 16K mouse cDNA microarray. Age matched reference mice (WT) and experimental (KO and HQK) Alexa Flour labeled aRNA were used in each competitive hybridization. Each sample was labeled individually with both Alexa Fluor 555 and 647 for subsequent dye-swapped hybridizations to account for intensity bias. 3 individual mice from each experimental group at each time point were individually processed for separate microarrays. We used the program EDGE to identify genes that were differentially expressed in mouse skeletal muscle in either transgenic HQK mice over expressing PrP, or PrP knock out (KO) mice after administration of Dox. We used a P value cut-off of 0.05 as the criteria of selection of significantly differentially expressed genes.

Project description:A key event in the pathogenic process of prion diseases is the conversion of the cellular prion protein (PrPC) to an abnormal and protease-resistant isoform (PrPSc). Mice lacking PrP are resistant to prion infection, and down-regulation of PrPC during prion infection prevents neuronal loss and the progression to clinical disease. These results are suggestive of the potential beneficial effect of silencing PrPC during prion diseases. However, the silencing of a protein that is widely expressed throughout the CNS could be detrimental to brain homeostasis. The physiological role of PrPC remains still unclear, but several putative functions have been proposed. Among these, several lines of evidence support PrPC function in neuronal development and maintenance. To assess the influence of PrPC on gene expression profile during development in the mouse brain, we undertook a microarray analysis by using RNA isolated from the hippocampus, at two different developmental stages: newborn (4-day-old) and adult (3-month-old) mice, both from Prnp+/+ and Prnp0/0 animals. The comparison of the different datasets allowed us to identify “commonly” co-regulated genes and “uniquely” de-regulated genes during postnatal development in these animal models. The lack of PrPC during neuronal development affected several biological pathways, among which the most representative were cell signaling, cell-cell communication and transduction process. In addition, the absence of PrPC influenced genes involved in calcium homeostasis, nervous system development, synaptic transmission and cell adhesion. There was only a moderate alteration of the gene expression profile during neuronal development in the animal models we studied. PrPC deficiency does not lead to a dramatic alteration of gene expression profile, and produces moderate altered gene expression levels from young to adult animals. Thus, our results may provide additional support to silencing endogenous PrPC levels as a therapeutic approach to prion diseases.

Project description:A key event in the pathogenic process of prion diseases is the conversion of the cellular prion protein (PrPC) to an abnormal and protease-resistant isoform (PrPSc). Mice lacking PrP are resistant to prion infection, and down-regulation of PrPC during prion infection prevents neuronal loss and the progression to clinical disease. These results are suggestive of the potential beneficial effect of silencing PrPC during prion diseases. However, the silencing of a protein that is widely expressed throughout the CNS could be detrimental to brain homeostasis. The physiological role of PrPC remains still unclear, but several putative functions have been proposed. Among these, several lines of evidence support PrPC function in neuronal development and maintenance. To assess the influence of PrPC on gene expression profile during development in the mouse brain, we undertook a microarray analysis by using RNA isolated from the hippocampus, at two different developmental stages: newborn (4-day-old) and adult (3-month-old) mice, both from Prnp+/+ and Prnp0/0 animals. The comparison of the different datasets allowed us to identify “commonly” co-regulated genes and “uniquely” de-regulated genes during postnatal development in these animal models. The lack of PrPC during neuronal development affected several biological pathways, among which the most representative were cell signaling, cell-cell communication and transduction process. In addition, the absence of PrPC influenced genes involved in calcium homeostasis, nervous system development, synaptic transmission and cell adhesion. There was only a moderate alteration of the gene expression profile during neuronal development in the animal models we studied. PrPC deficiency does not lead to a dramatic alteration of gene expression profile, and produces moderate altered gene expression levels from young to adult animals. Thus, our results may provide additional support to silencing endogenous PrPC levels as a therapeutic approach to prion diseases. To analyze the influence of PrPC expression on CNS gene expression profile during development, we investigated WT PrPC (Prnp+/+) and Prnp0/0 mice at two different developmental stages: in neonatal animals (postnatal day 4, P4) and in adult animals (3 months old). For each developmental stage, hippocampi of 3 (pups) or 4 (adult) animals were dissected immediately after animal sacrifice and promptly processed for RNA extraction and purification, for a total of 14 samples.

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Inducible expression of PrPC in mouse skeletal muscles results in myopathy characterized by changes in gene expression

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