Ca2+-independent alterations in diastolic sarcomere length and relaxation kinetics in a mouse model of lipotoxic diabetic cardiomyopathy.
Previous studies demonstrated increased fatty acid uptake and metabolism in MHC-FATP transgenic mice that overexpress fatty acid transport protein (FATP)1 in the heart under the control of the alpha-myosin heavy chain (alpha-MHC) promoter. Doppler tissue imaging and hemodynamic measurements revealed diastolic dysfunction, in the absence of changes in systolic function. The experiments here directly test the hypothesis that the diastolic dysfunction in MHC-FATP mice reflects impaired ventricular myocyte contractile function. In vitro imaging of isolated adult MHC-FATP ventricular myocytes revealed that mean diastolic sarcomere length is significantly (P<0.01) shorter than in wild-type (WT) cells (1.79+/-0.01 versus 1.84+/-0.01 microm). In addition, the relaxation rate (dL/dt) is significantly (P<0.05) slower in MHC-FATP than WT myocytes (1.58+/-0.09 versus 1.92+/-0.13 microm/s), whereas both fractional shortening and contraction rates are not different. Application of 40 mmol/L 2,3-butadionemonoxime (a nonspecific ATPase inhibitor that relaxes actin-myosin interactions) increased diastolic sarcomere length in both WT and MHC-FATP myocytes to the same length, suggesting that MHC-FATP myocytes are partially activated at rest. Direct measurements of intracellular Ca(2+) revealed that diastolic [Ca(2+)](i) is unchanged in MHC-FATP myocytes and the rate of calcium removal is unexpectedly faster in MHC-FATP than WT myocytes. Moreover, diastolic sarcomere length in MHC-FATP and WT myocytes was unaffected by removal of extracellular Ca(2+) or by buffering of intracellular Ca(2+) with the Ca(2+) chelator BAPTA (100 micromol/L), indicating that elevated intracellular Ca(2+) does not underlie impaired diastolic function in MHC-FATP ventricular myocytes. Functional assessment of skinned myocytes, however, revealed that myofilament Ca(2+) sensitivity is markedly increased in MHC-FATP, compared with WT, ventricular cells. In addition, biochemical experiments demonstrated increased expression of the beta-MHC isoform in MHC-FATP, compared with WT ventricles, which likely contributes to the slower relaxation rate observed in MHC-FATP myocytes. Collectively, these data demonstrate that derangements in lipid metabolism in MHC-FATP ventricles, which are similar to those observed in the diabetic heart, result in impaired diastolic function that primarily reflects changes in myofilament function, rather than altered Ca(2+) cycling.
Flagg
Thomas P
TP
Department of Molecular Biology and Pharmacology, Washington University School of Medicine, St Louis, MO 63110, USA.
Cazorla
Olivier
O
Remedi
Maria S
MS
Haim
Todd E
TE
Tones
Michael A
MA
Bahinski
Anthony
A
Numann
Randal E
RE
Kovacs
Attila
A
Schaffer
Jean E
JE
Nichols
Colin G
CG
Nerbonne
Jeanne M
JM
D000818:Animals; D002118:Calcium / Q000502:physiology; D002614:Chelating Agents / Q000494:pharmacology; D048909:Diabetes Complications / Q000473:pathology / Q000503:physiopathology*; D003931:Diacetyl / Q000031:analogs & derivatives / Q000494:pharmacology; D003971:Diastole; D004195:Disease Models, Animal; D004533:Egtazic Acid / Q000031:analogs & derivatives / Q000494:pharmacology; D050612:Fatty Acid Transport Proteins / Q000235:genetics / Q000502:physiology*; D005227:Fatty Acids / Q000378:metabolism*; D054144:Heart Failure, Diastolic / Q000473:pathology / Q000503:physiopathology*; D006352:Heart Ventricles / Q000473:pathology; D007537:Isometric Contraction; D051379:Mice; D008822:Mice, Transgenic; D009200:Myocardial Contraction; D009206:Myocardium / Q000378:metabolism; D032383:Myocytes, Cardiac / Q000187:drug effects / Q000502:physiology* / Q000648:ultrastructure; D018995:Myosin Heavy Chains / Q000096:biosynthesis / Q000235:genetics; D011993:Recombinant Fusion Proteins / Q000502:physiology; D012518:Sarcomeres / Q000187:drug effects / Q000648:ultrastructure*
D002614:Chelating Agents; D050612:Fatty Acid Transport Proteins; D005227:Fatty Acids; D011993:Recombinant Fusion Proteins; C493569:Slc27a1 protein, mouse; C004717:diacetylmonoxime; D004533:Egtazic Acid; D018995:Myosin Heavy Chains; C025603:1,2-bis(2-aminophenoxy)ethane-N,N,N',N'-tetraacetic acid; D003931:Diacetyl; D002118:Calcium