Franny Jongbloed

28 CHAPTER 2 Figure 2. Kidney function of male and female mice after undergoing 37 and 60 minutes of bilateral renal IRI, respectively, preceded by 3-day fasting or ad libitum feeding. (A) Serum urea levels are significantly lower in fasted males and females on day 2 after renal IRI. (B) Serum creatinine levels show no significant differences between fasted and ad libitum fed mice. M=male, F=female, Adlib=ad libitum fed. Δ=no standard deviation is shown as only two animals comprised this group. As time after IRI might influence the severity of the pathological changes, four fasted male mice were sacrificed at POD7 and histology was compared withmice that died due to kidney failure. The tubular necrosis score of these four sacrificed mice was identical to that of the mice sacrificed at day 28 (median score 1), showing a similar contrast with the mice that died due to kidney failure, indicative of an acute protective effect of the diet. The amount of tubular regeneration is scored between 0 and 4 with 4 as the strongest regenerative response. Mice found dead or moribund scored a median pathology score for tubular regeneration of 0.5 and 0, respectively, and the fasted mice had a median score of 3.5, including mice sacrificed at POD7 and at later time-points ( P< 0.0001) (Figure 3B). When subdivided by gender and diet group, fasted male and female mice showed significantly less necrosis ( P= 0.0018 and P= 0.0035, respectively) and significantly more regeneration ( P= 0.0089 and 0.0036, respectively) compared to the AL fed groups (Figures 3 C/D). Representative images of the pathological lesions observed in the different groups are shown in Figure 4. Gene expression profiles in kidneys show overlap between young and aged male mice in response to fasting Firstly, gene expression profiles were compared between kidneys of ad libitum fed and three days fasted aged male mice (without renal IRI) by whole-genome mRNA microarray analysis. The total number of probe sets differentially regulated was assessed. In total, 854 out of 45,141 probe sets were significantly differentially regulated (FDR ≤ 5%) in the fasted aged mice with a fold change ≥ 1.5. Of these 854 probe sets, 454 probe sets were upregulated and 400 downregulated (Figure 5A). Secondly, since fasting was shown to confer resistance to IRI in young-lean male mice 9 , we performed a similar mRNA analysis in kidneys