Franny Jongbloed

92 CHAPTER 4 Figure 4. Relative S6 phosphorylation signals in kidney after various diet interventions. The ratio of phosphorylated S6 over total S6 was significantly lower after three days of fasting compared to its control diet. All other dietary interventions showed a large variation in phosphorylation levels that did not reach statistical significance. Although the beneficial effects of both long-term and short-term DR have been acknowledged, the mechanisms underlying DR are still subject of investigation. Various pathways, factors and genes have been proposed to play a central role in the protective effects 27 , but attempts to validate these yielded conflicting results 28-31 . We produced extensive expression datasets of diets proven to be either protective or not protective against renal IRI. Gene expression profiles of the non-protective CHO-free diet showed a considerable overlap with gene expression profiles of protective diets, namely three days of fasting, two weeks 30% DR and 3-days of protein-free diet (Figure 3). A PCA plot demonstrated the partial different directionality of gene expression in the CHO-free diet compared to the other dietary interventions. The 3-day 30% DR diet also showed considerable overlap with the protective diets, mainly with two weeks 30% DR, and a partially different but also partially overlapping directionality in response. These findings could either indicate that overlapping probe sets and pathways are not involved in the induction of protection against renal IRI, or that theymay require additional changes in other probe sets to induce this effect. Particularly, the striking similarity between three days and two weeks 30% DR suggests that three days is sufficient to activate a transcriptomic response which is not yet sufficient to induce phenotypical protection. In addition, the non-protective fat-free diet showed strong