Proteomic Analysis of Hearts from Akita Mice Suggests That Increases in Soluble Epoxide Hydrolase and Antioxidative Programming Are Key Changes in Early Stages of Diabetic Cardiomyopathy

Cardiovascular disease is the leading cause of diabetic morbidity
with more than 10% of type 1 diabetes mellitus (T1DM) patients dying
before they are 40 years old. This study utilized Akita mice, a murine
model with T1DM progression analogous to that of humans. Diabetic
cardiomyopathy in Akita mice presents as cardiac atrophy and diastolic
impairment at 3 months of age, but we observed cardiac atrophy in
hearts from recently diabetic mice (5 weeks old). Hearts from 5 week
old mice were analyzed with a rigorous label-free quantitative proteomic
approach to identify proteins that may play a critical role in the
early pathophysiology of diabetic cardiomyopathy. Eleven proteins
were differentially expressed in diabetic hearts: products of GANC, PLEKHN1, COL1A1, GSTK1, ATP1A3, RAP1A, ACADS, EEF1A1, HRC, EPHX2, and PKP2 (gene names). These proteins
are active in cellular defense, metabolism, insulin signaling, and
calcium handling. Further analysis of Akita hearts using biochemical
assays showed that the cellular defenses against oxidative stress
were increased, including antioxidant capacity (2–3-fold) and
glutathione levels (20%). Immunoblots of five and twelve week old
Akita heart homogenates showed 30% and 145% increases in expression
of soluble epoxide hydrolase (sEH (gene name EPHX2)), respectively, and an approximate 100% increase in sEH was seen
in gastrocnemius tissue of 12 week old Akita mice. In contrast, 12
week old Akita livers showed no change in sEH expression. Our results
suggest that increases in sEH and antioxidative programming are key
factors in the development of type 1 diabetic cardiomyopathy in Akita
mice and reveal several other proteins whose expression may be important
in this complex pathophysiology.