Expression of glycogen synthase and phosphofructokinase in muscle from Type 1 (insulin-dependent) diabetic patients before and after intensive insulin treatment

Abstract

SummaryThe aim of the present study was to determine whether short-term appropriate insulinization of Type i (insulin-dependent) diabetic patients in longterm poor glycaemic control (HbAlc > 9.5 %) was associated with an adaptive regulation of the activity and gene expression of key proteins in muscle glycogen storage and glycolysis: glycogen synthase and phosphofructokinase, respectively. In nine diabetic patients biopsies of quadriceps muscle were taken before and 24-h after intensified insulin therapy and compared to findings in eight control subjects. Subcutaneous injections of rapid acting insulin were given at 3-h intervals to improve glycaemic control in diabetic patients (fasting plasma glucose decreased from 20.8 + 0.8 to 8.7+0.8mmol/1 whereas fasting serum insulin increased from 59 + 8 to 173 + 3 pmol/1). Before intensified insulin therapy, analysis of muscle biopsies from diabetic patients showed a normal total glycogen synthase activity but a 48 % decrease (p --0.006) in glycogen synthase fractional velocity (0.1 mmol/1 glucose 6-phosphate) (FV01) and a 45 % increase (p = 0.01) in the half-maximal activation constant of glycogen synthase (A0.5). The activity of phosphofructokinase and the specific mRNA and immunoreactive protein levels of both glycogen synthase and phosphofructokinase were similar in the two groups. The 2.8-fold increase in serum insulin levels and the halving of the plasma glucose level for at least 15 h were associated with a normalization of glycogen synthase fractional activity (FV0.I) and of the half-maximal activation constant (A05) whereas the enzyme activity of phosphofructokinase and the mRNA and protein levels of both glycogen synthase and phosphofructokinase remained normal. In conclusion: 1) Reduced allosterical activation of glycogen synthase in muscle of Type 1 diabetic patients in poor metabolic control occurs in the presence of normal total activity as well as normal immunoreactive protein mass and mRNA level of glycogen synthase. 2) Changes in serum insulin within the physiological range play no role in the short-term regulation of glycogen synthase mRNA and protein abundance in muscle from Type I diabetic patients. [Diabetologia (1994) 37: 82-90]

Acute regulation by insulin of phosphatidylinositol-3-kinase, Rad, Glut 4, and lipoprotein lipase mRNA levels in human muscle.

“…The absence of alterations of GS and PFK-1 mRNAs in the presence of physiological levels of hyperinsulinemia has already been reported (8,10,11). The lack of change in the presence of high insulin concentrations suggests that the expression of these genes is not regulated by insulin.…”

“…The expression of the protein Ras associated to diabetes (Rad) 1 was enhanced (6) and the expression of hexokinase II (7) and glycogen synthase (GS) (8) was decreased in patients with non-insulindependent diabetes mellitus (NIDDM). On the other hand, the expression of the genes coding Glut 4 (9) and 6-phosphofructo-1-kinase (PFK-1) (8) seemed unaltered in obese or NIDDM patients, and intensive insulin treatment did not modify the expression of the genes for GS and PFK-1 in type I diabetic subjects (10). Using the euglycemic hyperinsulinic glucose clamp, a method that allows the individual effect of insulin to be studied, it was found that Glut 4, GS, and hexokinase I mRNA levels were unaltered in normal muscle; whereas, hexokinase II mRNA increased three times in response to insulin (11).…”

Altered energetic properties in skeletal muscle of men with well-controlled insulin-dependent (type 1) diabetes

“…Prior studies of diabetic muscle properties have typically selected patients without carefully screening for activity (23,42) or included active patients with "no more than two exercise sessions weekly on a regular basis" (19). We chose to closely match patients to control subjects to eliminate any bias due to activity and used a sample size similar to that in other studies of muscle properties in types 1 and 2 patients (42,45,47). This matching permitted us to take into account the role of chronic activity level in the variation in the energetic properties of a muscle.…”

“…Assays of a key glycolytic enzyme, phosphofructokinase, showed no difference between type 1 diabetic patients and control subjects (45). However, measurements during exercise provide evidence that the lower oxidative and higher glycolytic fluxes found in obesity and type 2 diabetes are also common to type 1 diabetes; specifically, V O 2 max is reduced (34) and blood lactate levels are elevated (48) in exercising type 1 patients compared with age-and activity-matched control subjects.…”

Acquired Defects of Glycogen Synthase Activity in Cultured Human Skeletal Muscle Cells: Influence of High Glucose and Insulin Levels

“…Defects in this enzyme can significantly alter the intracellular routing and metabolism of glucose and contribute to insulin resistance in muscle tissue. Individuals with obesity and those with type II and type I diabetes and in poor metabolic control often exhibit insulin resistance (4,5) that is associated with impaired GS activity and reduced rates of glycogen synthesis in skeletal muscle (2,(5)(6)(7)(8)(9)(10)(11)(12). While these abnormalities may have an underlying genetic basis in obesity and type II diabetes (13,14), recent evidence indicates that there are likely to be acquired components of insulin resistance in these conditions as well (15,16).…”