Exercise training does not correct abnormal cardiac glycogen accumulation in the db/db mouse model of type 2 diabetes.

Shearer J, Ross KD, Hughey CC, Johnsen VL, Hittel DS, Severson DL
Am J Physiol Endocrinol Metab. 2011 301 (1): E31-9

PMID: 21386062 · DOI:10.1152/ajpendo.00525.2010

Substrate imbalance is a well-recognized feature of diabetic cardiomyopathy. Insulin resistance effectively limits carbohydrate oxidation, resulting in abnormal cardiac glycogen accumulation. Aims of the present study were to 1) characterize the role of glycogen-associated proteins involved in excessive glycogen accumulation in type 2 diabetic hearts and 2) determine if exercise training can attenuate abnormal cardiac glycogen accumulation. Control (db(+)) and genetically diabetic (db/db) C57BL/KsJ-lepr(db)/lepr(db) mice were subjected to sedentary or treadmill exercise regimens. Exercise training consisted of high-intensity/short-duration (10 days) and low-intensity/long-duration (6 wk) protocols. Glycogen levels were elevated by 35-50% in db/db hearts. Exercise training further increased (2- to 3-fold) glycogen levels in db/db hearts. Analysis of soluble and insoluble glycogen pools revealed no differential accumulation of one glycogen subspecies. Phosphorylation (Ser(640)) of glycogen synthase, an indicator of enzymatic fractional activity, was greater in db/db mice subjected to sedentary and exercise regimens. Elevated glycogen levels were accompanied by decreased phosphorylation (Thr(172)) of 5'-AMP-activated kinase and phosphorylation (Ser(79)) of its downstream substrate acetyl-CoA carboxylase. Glycogen concentration was not associated with increases in other glycogen-associated proteins, including malin and laforin. Novel observations show that exercise training does not correct diabetes-induced elevations in cardiac glycogen but, rather, precipitates further accumulation.

MeSH Terms (14)

Animals Body Weight Diabetes Mellitus, Experimental Diabetes Mellitus, Type 2 Diabetic Cardiomyopathies Exercise Therapy Glycogen Glycogen Storage Disease Type IIb Mice Mice, Inbred C57BL Mice, Transgenic Myocardium Physical Conditioning, Animal Receptors, Leptin

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