Transcriptional changes in the brains of cattle orally infected with the bovine spongiform encephalopathy agent precede detection of infectivity

Abstract

Bovine spongiform encephalopathy (BSE) is a fatal, transmissible, neurodegenerative disease of cattle. BSE can be transmitted experimentally between cattle through the oral route, and in this study, brain tissue samples from animals at different time points postinoculation were analyzed for changes in gene expression. The aims of this study were to identify differentially regulated genes during the progression of BSE using microarray-based gene expression profiling and to understand the effect of prion pathogenesis on gene expression. A total of 114 genes were found to be differentially regulated over the time course of the infection, and many of these 114 genes encode proteins involved in immune response, apoptosis, cell adhesion, stress response, and transcription. This study also revealed a broad correlation between gene expression profiles and the progression of BSE in cattle. At 21 months postinoculation, the largest number of differentially regulated genes was detected, suggesting that there are many pathogenic processes in the animal brain even prior to the detection of infectivity in the central nervous systems of these orally infected cattle. Moreover, evidence is presented to suggest that it is possible to predict the infectious status of animals using the expression profiles from this study.

FIG. 1.

Condition tree of clustering analysis for BSE time course samples. The analysis was performed by GeneSpring using all 24,128 genes (probe sets) on Affymetrix bovine microarray GeneChips. Similarity was measured using the Spearman correlation with a value of 1 for the separation ratio and a value if 0.001 for the minimum distance to merge similar branches. Three positive-control animals (Positive-1, -2, and -3) and three negative-control animals (Negative-1, -2, and -3) were used in the study. 21m-2, sample from 21 mpi from animal 2.

FIG. 2.

Gene expression profiles of T-cell receptor gamma variable 3-1 (a), proteasome 26S subunit (b), a gene similar to 14-3-3 protein theta (c), a gene similar to metalloprotease 1 (d), nuclear receptor (NR1H3) (e), T-cell receptor delta chain variable region (f), acetylcholine receptor (nicotinic, beta 4) (g), and a gene similar to glycine dehydrogenase during the progression of BSE (h). neg, negative control; pos, positive control; 6m, 6 mpi.

FIG. 3.

Relative levels of expression of Arg2, BOLA-DMA, IGTA4, IGTB5, COL9A1, and GSTA2 during the progression of BSE. The graphs of quantitative RT-PCR and microarrays are shown side by side for comparison. The time points are 6 mpi (6m), 21 mpi (21m), 27 mpi (27m), 36 mpi (36m), and 39 mpi (39m). neg, negative control; pos, positive control.

FIG. 4.

Condition trees of clustering analysis. The analysis was performed by GeneSpring using 205 genes found by ANOVA analysis. The individual samples were grouped by time point. Similarity was measured using the standard correlation with a value of 1 for the separation ratio and a value of 0.001 for the minimum distance to merge similar branches. Each colored bar represents a gene, and the color represents the level of expression. The relative levels of expression are displayed in different colors: red, 5; orange, 2; yellow, 1; dark yellow, 0.7; dark blue, 0.4; and blue, 0.1. (a) Samples taken from negative controls, samples taken from animals at 6 mpi, 21 mpi, 27 mpi, 36 mpi, and 39 mpi, and samples taken from positive controls. (b) Samples taken from negative controls and positive controls and samples taken from animals at 6 mpi and 45 mpi.