Transcriptome analysis reveals altered cholesterol metabolism during the neurodegeneration in mouse scrapie model

Abstract

To identify the dynamic transcriptional alterations in CNS during the development of prion disease, brains of scrapieinfected mice and age-matched, mock-inoculated controls were analyzed immediately before inoculation and at different time points post-inoculation using Affymetrix microarray technique. A total of 449 probe sets, representing 430 genes, showed differential expression between scrapie-and mockinoculated mice over the time course. These genes could be separated into two clusters according to expression patterns: the genes in cluster 1 demonstrated lower mRNA levels in scrapie-infected brains when compared with mock-inoculated brains, whereas genes in cluster 2 showed higher mRNA levels in scrapie-infected brains. Functional analysis of differentially expressed genes revealed the most severely affected biological process: cholesterol metabolism. The expression patterns of the cholesterol-related genes indicated an inhibited cholesterol synthesis in the diseased brains. Conspicuously, a number of cluster 1 genes, including some of cholesterol-related genes, showed not only decreasing mRNA levels in scrapie-infected brains but also increasing mRNA levels in mock-inoculated brains with increasing age. Quantitative RT-PCR analysis of some cholesterol-related genes in untreated mice suggested that changes of the examined genes observed in mock-inoculated brains are mainly age related. This finding indicated a link between agerelated genes and scrapie-associated neurodegeneration. Keywords: age-related gene, cholesterol metabolism, microarray, neurodegeneration, prion disease, scrapie. Prion diseases or transmissible spongiform encephalopathies (TSEs) are a class of fatal neurodegenerative diseases which occur in humans and various animal species. The prevalent forms of prion diseases are Creutzfeldt-Jakob disease (CJD) in humans, bovine spongiform encephalopathy in cattle and scrapie in sheep and goats. The neuropathology of prion diseases is characterized by generation and deposition of a misfolded, protease-resistant isoform (PrP Sc ) of a normal host protein, the prion protein (PrP C ), as well as by gliosis, vacuolation or spongiform degeneration, and neuronal cell death (Kretzschmar et al. 1996). So far, a number of experimental models for TSE have been established in animals. A widely used model is infecting mice with mouseadapted scrapie strains, which results in clinical signs and neuropathology associated with prion disease. The incubation interval (the time between inoculation and terminal disease) and the neuropathology depend on the genetic background of the hosts and the inoculated scrapie strains (Bruce 2003).In previous studies, microarray techniques were applied to study the global gene expression alterations in brains of scrapie-infected, terminally diseased mice (Riemer et al. 2004;Xiang et al. 2004) and in brains of post-mortem human CJD patients (Xiang et al. 2005). In brains of infected mice at terminal stages (TS), the up-regulation of genes Received November 17, 2006; revised...

Transcriptional Changes in the Brains of Cattle Orally Infected with the Bovine Spongiform Encephalopathy Agent Precede Detection of Infectivity

“…Furthermore, in a recent systems biology study based on gene expression changes in mice with scrapie, mRNA levels of C1qa/b and C3ar1 reflecting activation of microglia and astrocytes are among the first detectable expression changes (10 weeks postinfection) and precede, e.g., clinical signs by many weeks (16). Not only are our results consistent with early changes of gene expression in mice infected with the TSE agent (16,36), they are also consistent with the behavioral changes in the early stages of prion infection in mice (9,10,20). Prion-infected mice have shown significant inability to discriminate a novel object from 7 week postinoculation compared with healthy mice (20).…”

“…At 36 mpi, the expression of NR1H3 reached its lowest level (Ϫ4.7-fold of the negative controls). This might be linked to the downregulation of cholesterol synthesis similar to the findings in mice with scrapie (36). The nuclear oxysterol receptors liver X receptor-alpha [LXRalpha (NR1H3)] and LXRbeta (NR1H2) regulate genes involved in cholesterol homeostasis in a coordinate manner.…”

“…The genes differentially regulated during development of BSE were then compared with genes that have been reported to be associated with prion diseases in other studies. Seven of these genes were found in this study: MHC-II (30), nicotinic beta 4 acetylcholine receptor (22), S100 calcium-binding protein (36), arginase (26), proteasome 26S subunit (17), 14-3-3 protein (18), and flotillin-1 (23) ( Table 1). Many other genes have been found to be differentially regulated by other microarray studies using mice with scrapie.…”

“…The correlation between BSE pathogenesis and the transcriptional activities of genes is however not explored in any detail. Gene expression profiling studies of mice with scrapie have shown that these studies can provide valuable insights in the possible pathomechanisms of the disease (5,25,27,29,36,37).…”

Dendritic Pathology in Prion Disease Starts at the Synaptic Spine

“…Because blocking the function of DRMs by reducing the levels of cholesterol or sphingomyelin in cultured neurons is known to induce the formation of varicosities and the elimination of synaptic spines (Hering et al, 2003), it may be tempting to speculate that the occurrence of varicosities in scrapie may be related to the accumulation of PrP Sc in DRMs. In support of this hypothesis, cDNA microarray studies identified several differentially expressed genes related to cholesterol synthesis during the presymptomatic phase of prion disease (Xiang et al, 2007;Skinner et al, 2006). Additional studies will have to prove whether alterations in the cholesterol synthesis or DRM function, because of PrP Sc accumulation, represents the primary cause of varicosity emergence and subsequent spine loss in prion disease.…”