The metabolic syndrome and signal transduction of gene expression.

Epidemiological studies have clearly shown that the so-called metabolic syndrome which is linked to insulin resistance and a reduced glucose utilization of muscle represents an important risk factor for cardiovascular disease. However, only little is known of the intracellular consequences of insulin resistance. An important feature of an altered substrate utilization is related to signal transduction of gene expression. For the example of myosin heavy chain expression, it is shown that metabolic signals exist which reflect the fuel flux and substrate utilization of the heart muscle cell. The signals were characterized in functional states of the heart associated with altered metabolic influences (fasting, diabetes, sucrose feeding, increased calorie intake, carnitine palmitoyltransferase inhibition). In the pressure-overloaded heart, metabolic interventions which are expected to increase glucose utilization (sucrose feeding, captopril treatment) have a pronounced effect. Although a link with gene expression remains to be established, it should be noted that the sarcoplasmic reticulum Ca(2+)-pump activity seems to be affected in a functionally comparable manner. It is concluded that metabolic signals alter the protein phenotype of heart muscle and it is expected that a deranged signal transduction affects, not only the heart, but also vascular muscle.