**Figure 5.** **Serum deprivation up-regulates αklotho expression in MDCK cells.** (**A**) Arithmetic mean ± SEM of αklotho transcript levels relative to *TBP* in MDCK cells incubated for 24 h with or without 5% fetal bovine serum (FBS; *n* = 5; *paired t*-test). (**B**, **C**) Arithmetic mean ± SEM of MDCK cell viability (**B**) or number (**C**) upon incubation with or without 5% FBS for 24 h (**B**: *n* = 4, *one-sample t*-test; **C**: *n* = 6, *one-sample t*-test). (**D**) Rate of apoptosis and necrosis of MDCK cells cultured with or without 5% FBS for 24 h (*n* = 6, *one-sample t* test). (**E**) Arithmetic mean ± SEM of αklotho transcript levels relative to *TBP* in NRK-52E cells incubated for 24 h with or without 5% newborn calf serum (NBCS) (*n* = 8, *paired t-*test). (**F**, **G**) Arithmetic mean ± SEM of NRK-52E cell viability (**F**) or number (**G**) upon incubation with or without 5% NBCS for 24 h (**F**: *n* = 5, *one-sample t*-test; **G**: *n* = 4, *one-sample t*-test). (**H**) Rate of apoptotis and necrosis of NRK-52E cells cultured with or without 5% NBCS for 24 h (*n* = 5, *one-sample Wilcoxon* test). ^{*}*p* < 0.05, ^{**}*p* < 0.01 indicates significant difference from control cells; Abbreviations: a. u.: arbitrary units; ctr: control.