Increased c-Fos protein in the brains of scrapie-infected SAMP8, SAMR1, AKR and C57BL mice

Noise exposure immediately activates cochlear mitogen-activated protein kinase signaling

Noise-induced hearing loss (NIHL) is a major public health issue worldwide. Uncovering the early molecular events associated with NIHL would reveal mechanisms leading to the hearing loss. Our aim is to investigate the immediate molecular responses after different levels of noise exposure and identify the common and distinct pathways that mediate NIHL. Previous work showed mice exposed to 116 decibels sound pressure level (dB SPL) broadband noise for 1 h had greater threshold shifts than the mice exposed to 110 dB SPL broadband noise, hence we used these two noise levels in this study. Groups of 4-8-week-old CBA/CaJ mice were exposed to no noise (control) or to broadband noise for 1 h, followed by transcriptome analysis of total cochlear RNA isolated immediately after noise exposure. Previously identified and novel genes were found in all data sets. Following exposure to noise at 116 dB SPL, the earliest responses included up-regulation of 243 genes and down-regulation of 61 genes, while a similar exposure at 110 dB SPL up-regulated 155 genes and down-regulated 221 genes. Bioinformatics analysis indicated that mitogen-activated protein kinase (MAPK) signaling was the major pathway in both levels of noise exposure. Nevertheless, both qualitative and quantitative differences were noticed in some MAPK signaling genes, after exposure to different noise levels. Cacna1b , Cacna1g , and Pla2g6 , related to calcium signaling were down-regulated after 110 dB SPL exposure, while the fold increase in the expression of Fos was relatively lower than what was observed after 116 dB SPL exposure. These subtle variations provide insight on the factors that may contribute to the differences in NIHL despite the activation of a common pathway.

CREB-dependent gene regulation by prion protein: impact on MMP-9 and beta-dystroglycan

Corruption of the normal function of the cellular prion protein (PrP(C)) by the scrapie isoform (PrP(Sc)) emerges as a critical causal event in Transmissible Spongiform Encaphalopathies (TSE) pathogenesis. However, PrP(C) physiological role remains unclear. By exploiting the properties of the 1C11 neuroectodermal cell line, able to convert into 1C11(5-HT) serotonergic or 1C11(NE) noradrenergic neuronal cells, we assigned a signaling function to PrP(C). Here, we establish that antibody-mediated PrP(C) ligation promotes the recruitment of the cAMP responsive element binding protein (CREB) transcription factor downstream from the MAPK ERK1/2, in 1C11 precursor cells and their 1C11(5-HT) and 1C11(NE) neuronal progenies. Whatever the differentiation state of 1C11 cells, the PrP(C)-dependent CREB activation triggers Egr-1 and c-fos transcription, two immediate early genes that relay CREB's role in cell survival and proliferation as well as in neuronal plasticity. Furthermore, in 1C11-derived neuronal cells, we draw a link between the PrP(C)-CREB coupling and a transcriptional regulation of the metalloproteinase MMP-9 and its inhibitor TIMP-1, which play pivotal roles in neuronal pathophysiology. Finally, the PrP(C)-dependent control on MMP-9 impacts on the processing of the transmembrane protein, beta-dystroglycan. Taken together, our data define molecular mechanisms that likely mirror PrP(C) ubiquitous contribution to cytoprotection and its involvement in neuronal plasticity.

Expression of transcription factors CREB and c-Fos in the brains of terminal Creutzfeldt-Jakob disease cases

Expression levels and localization of transcription factors cAMP response element binding protein (CREB(1) and CREB(2)) and c-Fos, as well as levels of up-stream mitogen-activated protein kinases/extracellular signal-regulated kinases (ERK-1 and ERK-2) and p38 kinase, were examined in the brains (frontal cortex) of eleven cases with Creutzfeldt-Jakob disease (CJD) and five age-matched controls. Preserved expression levels of ERK-1-P, ERK-2-P and p38-P were observed in CJD. However, significantly reduced levels, as revealed by gel electrophoresis and Western blotting, and reduced numbers of immunoreactive nuclei, as seen by immunohistochemistry, to CREB, CREB-P, c-Fos and c-Fos-P were found in CJD when compared with controls. These observations point to exhausted CREB and c-Fos brain responses, in spite of preserved up-stream signaling kinases, thus favoring cell death in terminal stages of CJD.

Identification of up-regulated genes by array analysis in scrapie-infected mouse brains

The major neuropathological features of the transmissible spongiform encephalopathies (TSEs) are well documented, however, the underlying molecular events are poorly defined. We have applied cDNA expression arrays and quantitative RT-PCR to the study of gene expression in the brain, and more specifically in the hippocampus, of the well-characterized ME7/CV mouse model of scrapie. The number of genes showing consistent, scrapie-associated changes in expression was limited, and was primarily restricted to glial-associated genes. Increased expression of genes encoding glial fibrillary acidic protein, vimentin, complement component 1q (alpha and beta polypeptides), cathepsin D, clusterin and cystatin C was evident in the hippocampus from 170 days after inoculation (dpi), with expression increasing thereafter to terminal disease (225-235 dpi). Elevation of gene expression preceded clinical disease by approximately 30 days, and coincided with a 20-day period in the ME7/CV model during which 50% of the CA1 hippocampal neurones are lost. Increased expression of cystatin C, an inhibitor of lysosomal cysteine proteases, is a novel finding in the context of TSE neuropathology and was confirmed by Western analysis and immunocytochemistry.