The genomic response of the ipsilateral and contralateral cortex to stroke in aged rats

Abstract

Aged rats recover poorly after unilateral stroke, whereas young rats recover readily possibly with the help from the contralateral, healthy hemisphere. In this study we asked whether anomalous, age-related changes in the transcriptional activity in the brains of aged rats could be one underlying factor contributing to reduced functional recovery. We analysed gene expression in the periinfarct and contralateral areas of 3-month- and 18-month-old Sprague Dawley rats. Our experimental end-points were cDNA arrays containing genes related to hypoxia signalling, DNA damage and apoptosis, cellular response to injury, axonal damage and re-growth, cell lineage differentiation, dendritogenesis and neurogenesis. The major transcriptional events observed were: (i) Early up-regulation of DNA damage and down-regulation of anti-apoptosis-related genes in the periinfarct region of aged rats after stroke; (ii) Impaired neurogenesis in the periinfarct area, especially in aged rats; (iii) Impaired neurogenesis in the contralateral (unlesioned) hemisphere of both young and aged rats at all times after stroke and (iv) Marked up-regulation, in aged rats, of genes associated with inflammation and scar formation. These results were confirmed with quantitative real-time PCR. We conclude that reduced transcriptional activity in the healthy, contralateral hemisphere of aged rats in conjunction with an early up-regulation of DNA damage-related genes and pro-apoptotic genes and down-regulation of axono- and neurogenesis in the periinfarct area are likely to account for poor neurorehabilitation after stroke in old rats.

Fig. 1

Diagram shows the number of up- and down-regulated genes in young and aged rat brain. The genes showing both up- and down-regulation during their time course are included in a separate circle.

Fig. 2

Time course of changes in the numbers of up- and down-regulated genes in post ischaemic brain. The numbers of genes up- and down-regulated more than 1.5-fold in the periinfarct (A) or contralateral area (B) at two time-points of young or aged rats were presented in the form of bar graphs. Stem cell, hypoxia signalling pathway and apoptosis-related genes are presented as black, empty and grey boxes, respectively.

Fig. 3

Validation of altered stem cell-related gene expression by realtime quantitative PCR. Selected genes identified from the macroarray analysis were further confirmed by real-time PCR. The expression profiles are presented in the form of column graphs. The numbers on the vertical axis represent the average fold change. The horizontal axis denotes the post stroke time-points. pi, periinfart; cl, contralateral; 3d, after stroke day 3; 14d, after stroke day 14.

Fig. 4

Validation of altered hypoxia signalling pathway-related gene expression by real-time quantitative PCR. Selected genes identified from the macroarray analysis were further confirmed by real-time PCR. The expression profiles are presented in the form of column graphs. The numbers on the vertical axis represent the average fold change. The horizontal axis denotes the post stroke time-points. pi, periinfart; cl, contralateral; 3d, after stroke day 3; 14d, after stroke day 14.

Fig. 5

Validation of altered apoptosis-related gene expression by realtime quantitative PCR. The selected genes identified from the microarray analysis were further confirmed by real-time PCR. The expression profiles are presented in the form of column graphs. The numbers on the vertical axis represent the average fold change. The horizontal axis denotes the after stroke time-points. pi, periinfart; cl, contralateral; 3d, after stroke day 3; 14d, after stroke day 14.

Fig. 6

Overview of major genetic events in the ipsilateral hemisphere tentatively associated with functional recovery of the after stroke in young and aged rats.

Fig. 7

Overview of major genetic events in the contralateral hemisphere tentatively associated with functional recovery of the after stroke in young and aged rats.