Clinical studies in humans strongly support a link between
insulin resistance and non-ischaemic
heart failure. The occurrence of a specific
insulin-resistant
cardiomyopathy, independent of vascular abnormalities, is now recognized. The progression of cardiac pathology linked with
insulin resistance is poorly understood. Cardiac
insulin resistance is characterized by reduced availability of sarcolemmal Glut-4 transporters and consequent lower
glucose uptake. A shift away from glycolysis towards
fatty acid oxidation for
ATP supply is apparent and is associated with myocardial oxidative stress. Reliance of cardiomyocyte excitation-contraction coupling on glycolytically derived
ATP supply potentially renders cardiac function vulnerable to the metabolic remodelling adaptations observed in diabetes development. Findings from Glut-4-knockout mice demonstrate that cardiomyocytes with extreme
glucose uptake deficiency exhibit
cardiac hypertrophy and marked excitation-contraction coupling abnormalities characterized by reduced sarcolemmal Ca(2+) influx and sarcoplasmic reticulum Ca(2+) uptake. The 'milder' phenotype
fructose-fed mouse model of
type 2 diabetes does not show evidence of
cardiac hypertrophy, but cardiomyocyte loss linked with autophagic activation is evident.
Fructose feeding induces a marked reduction in intracellular Ca(2+) availability with myofilament adaptation to preserve contractile function in this setting. The cardiac metabolic adaptations of two load-independent models of diabetes, namely the Glut-4-deficient mouse and the
fructose-fed mouse are contrasted. The role of autophagy in diabetic cardiopathology is evaluated and anomalies of type 1 versus type 2 diabetic autophagic responses are highlighted.