Hippocampal metabolic proteins are modulated in voluntary and treadmill exercise rats

Systematic protein expression studies in the brain of exercising and sedentary animals have not been carried out so far and it was therefore decided to determine differences in metabolic protein levels in rat hippocampus of sedentary, voluntary and involuntary exercising rats by a proteomic approach. Aged, male Sprague-Dawley rats, 23 months old, were used for the study: the first group consisted of sedentary rats, the second of rats with voluntary exercise from five to 23 months and the third group was performing involuntary exercise on a treadmill from five to 23 months. Two-dimensional gel electrophoresis with subsequent mass spectrometrical identification of spots followed by quantification of spots was carried out. Identification of significantly differential proteins was validated by the determination of the corresponding enzyme activity. Five individual metabolic proteins showed differential protein levels in the three groups: mitochondrial precursors of ornithine aminotransferase, isocitrate dehydrogenase [NAD] subunit alpha, malate dehydrogenase, ubiquinol-cytochrome-c reductase complex core protein 1, and ubiquitin carboxyl-terminal hydrolase isozyme L1. The unambiguously identified metabolic proteins were mainly of mitochondrial localization and fit the expectations of altered mitochondrial activity in exercise. Reduced ubiquitin carboxyl-terminal hydrolase isoenzyme L1 levels in treadmill (forced) exercise show the involvement of the proteasomal pathway as a novel finding. These results not only form the basis for functional studies elucidating mechanisms and differences between voluntary and forced exercise in hippocampal metabolism but also highlight the most intriguing aspect that exercise is affecting the brain at the protein level.