Exercise-induced gene expression changes in the rat spinal cord

Abstract

There is growing evidence that exercise benefits recovery of neuromuscular function from spinal cord injury (SCI). However, the effect of exercise on gene expression in the spinal cord is poorly understood. We used oligonucleotide microarrays to compare thoracic and lumbar regions of spinal cord of either exercising (voluntary wheel running for 21 days) or sedentary rats. The expression data were filtered using statistical tests for significance, and K-means clustering was then used to segregate lists of significantly changed genes into sets based upon expression patterns across all experimental groups. Levels of brain-derived neurotrophic factor (BDNF) protein were also measured after voluntary exercise, across different regions of the spinal cord. BDNF mRNA increased with voluntary exercise, as has been previously shown for other forms of exercise, contributed to by increases in both exon I and exon III. The exercise-induced gene expression changes identified by microarray analysis are consistent with increases in pathways promoting neuronal health, signaling, remodeling, cellular transport, and development of oligodendrocytes. Taken together these data suggest cellular pathways through which exercise may promote recovery in the SCI population.

Figure 1

K-Means clustering of 110 probe sets identified as significantly changed by either Dchip or CyberT. Probe sets are clustered into nine groups based upon expression patterns across all conditions. Normalized intensity of expression values is shown on the y-axis. The tissue condition is indicated on the x-axis: from left to right, lumbar sedentary (LS), lumbar exercising (LE), thoracic sedentary (TS), thoracic exercising (TE). Probe sets identified as significantly changed in the lumbar region are in gray, those changed in the thoracic region are in black, and the three probe sets changed in both lumbar and thoracic are broken lines.

Figure 2

RT-PCR analysis of select transcripts in the thoracic region (A) and lumbar region (B) and of the rat spinal cord. Analysis of both the entire experimental group (N = 8 and N = 6 for thoracic and lumbar samples, respectively) or the high runner samples used for microarray analysis (N = 4 and N = 3 for thoracic and lumbar, respectively) are shown. *p < 0.05. Values are normalized to 100% of sedentary control and represented as percentage of control gene expression. Error bars represent ±SE.

Figure 3

BDNF protein levels in different regions of the rat spinal cord with exercise. BDNF protein levels are normalized to total protein levels for each region of the spinal cord. Error bars represent ±SE. Conditions are sedentary (open bars), 5 days of exercise (hashed bars), and 21 days of exercise (solid bars). *p < 0.05.