Calpastatin overexpression decreases calpain activity in aged mice. Western blots and quantitative PCR have been performed by using kidney cortex extracts from 2-months old (2mo) and 2 years old (2 yr) wild type (WT) and CalpTG (TG) mice. There was no significant difference of calpain 1 expression in WT and CalpTG mice at 2 months or 2 years at the protein level (A,B, n = 6/group) or at the RNA level (C, n = 6/group). Similarly, calpain 2 expression did not differ significantly between the 2 groups at the protein level (D,E, n = 6/group) or at the mRNA level (F, n = 6/group). As expected and previously described, only CalpTG mice expressed the transgenic rabbit calpastatin (G, n = 6/group). Mouse calpastatin mRNA expression did not differ among the different groups (H, n = 6/group). Calpain activity was measured by the ratio of the 145 kDa specific breakdown product of spectrin A by calpains, indexed to the intact spectrin. Calpains activity was similar at 2 months but significantly decreased in 2-years old CalpTG mice in comparison to aged WT mice (I,J, *p < 0.05, n = 6/group).