Figure 4. Ubqln1-CKO impairs myocardial UPS performance without affecting proteasome peptidase activities at 3 weeks of age.

(A and B) Representative image (A) and pooled densitometry data (B) of Western blot analyses for the indicated proteins in ventricular myocardial samples. Tg GFPdgn was introduced into Ubqlin1-CKO and control background through mouse crossbreeding. (C–H) Myocardial proteasomal peptidase activity assays. Crude protein extracts from the ventricular myocardium of homozygous Ubqln1-CKO mice and littermate control (combining Ubqln1^fl/fl and heterozygous Ubqln1-CKO) mice as well as from a Tg mouse model of desmin-related cardiomyopathy serving as a positive control [(+)CTL] for the assays were assayed for their 20S and 26S proteasomal chymotrypsin-like (C and D), caspase-like (E and F), and trypsin-like (G and H) activities using specific fluorogenic substrates. The P values between control and Ubqln1-CKO groups were derived from 2-tailed unpaired t test with Welch’s correction. *P < 0.05; **P < 0.01; ***P < 0.005 vs. control and Ubqln1-CKO, Welch’s ANOVA followed by Tukey’s test for pair-wise comparison. Each dot and each lane in Western blot represents an independent mouse.