M. T. Quintana1, J. He3, M. S. Willis3, W. E. Stansfield2 1University Of North Carolina At Chapel Hill,Department Of Surgery,Chapel Hill, NC, USA 2University of Toronto,Department Of Surgery, Division Of Cardiovascular Surgery,Toronto, Ontario, Canada 3University Of North Carolina At Chapel Hill,Department Of Pathology & Laboratory Medicine,Chapel Hill, NC, USA
Introduction:
Diabetic cardiomyopathy is characterized by structural and functional alterations leading to cardiac hypertrophy and heart failure. Alterations include metabolic disturbances in energy metabolism, increased lipid oxidation, intramyocardial triglyceride accumulation, and reduced glucose oxidation. These metabolic changes are regulated in part by peroxisome proliferator activating receptor (PPAR) signaling and subsequent changes in fatty acid metabolism. We recently identified that mice lacking ubiquitin ligase Muscle RING Finger 3 (MuRF3-/-) have increased cardiac PPAR-β activity in vivo. We hypothesized that challenging MuRF3-/- mice with a high-fat diet, where lipids act as PPAR ligands, would enhance the severity of diabetic cardiomyopathy.
Methods:
MuRF3-/- mice and strain-matched controls were fed a standard chow or high-fat diet for 26 weeks. Body weight, serum insulin, serum glucose, and fasting cholesterol and triglyceride levels were measured every two weeks and echocardiography was performed every three weeks. CPT1b, a key regulator of fatty acid metabolism downstream of PPAR-β in the diabetic cardiomyopathy pathway, was evaluated with real-time PCR.
Results:
MuRF3-/- mice have less circulating glucose after 26 weeks on high-fat diet (HFD) as compared to strain matched controls (168.8±6.2 vs. 240.2±15.5 mg/dL, P<0.05) and increased fasting circulating insulin levels relative to controls (4.7±0.3 vs. 3.4±0.2 ng/ml, P<0.05). Knockout mice do not show differences in fasting total cholesterol compared to wild-type mice at baseline (167±7.0 vs. 141±15.5 mg/dL, P=0.21) or 26 weeks HFD (162±24.3 vs. 151±8.0 mg/dL, P=0.65). There are no differences in serum triglyceride levels between knockout or wild-type mice at baseline (118±11.0 vs. 101±4.3 mg/dL, P=0.16) or after 26 weeks HFD (126±13.7 vs. 131±5.2 mg/dL, P=0.72). By echocardiography, MuRF3-/- mice have profoundly depressed fractional shortening (FS) at 6 weeks HFD compared to wild-type mice (43.6±6.1% vs. 49.2±3.5%, P<0.05). Wild-type mice do not display systolic dysfunction until 26 weeks HFD (FS 43.6±1.8 %). CPT1b mRNA expression is increased in MuRF3-/- mice (ΔΔct 3.57±1.1 in MuRF3-/- vs. 1.00±0.2 in controls, P<0.05).
Conclusion:
Mice lacking MuRF3 demonstrate exaggerated cardiomyopathy in the presence of high-fat diet. Increased PPAR-β activity, as well as increased CPT1b, are known contributors to diabetic cardiomyopathy. Taken together, these findings help corroborate a novel role for MuRF3 in protecting against the development of diabetic cardiomyopathy.