Human Skeletal Muscle Glyoxalase‐1 Protein Expression is Attenuated with Type 2 Diabetes

Abstract

INTRODUCTIONIndividuals with type 2 diabetes mellitus (T2DM) present with increased levels of advanced glycation endproducts (AGEs), which have been associated with progression and complications of the disease. AGEs are known to contribute to the disruption of insulin signaling in skeletal muscle and are primarily produced in vivo by the damaging glycolytic byproduct, methylglyoxal (MG). MG is effectively detoxified by the enzyme, glyoxalase‐1 (GLO1), whose protein expression has been previously shown to be inversely related to MG‐mediated protein‐damage and AGE formation. Despite the role of skeletal muscle insulin resistance in the pathogenesis of T2DM, GLO1 protein expression has not been fully elucidated in skeletal muscle. Additionally, the metabolic effects of insulin stimulation on GLO1 protein in human skeletal muscle has not been described.PURPOSETherefore, the purpose of this study was to examine skeletal muscle GLO1 protein content in individuals with T2DM compared to lean, healthy controls (LHC). Further, we sought to examine the effects of insulin stimulation on GLO1 protein expression through in vivo and in vitro approaches that included the hyperinsulinemic‐euglycemic clamp and primary human skeletal muscle cell culture experiments, respectively.METHODSSkeletal muscle biopsies from the vastus lateralis were obtained from 7 individuals with T2DM (age: 55 ± 4 yrs, BMI: 35.6 ± 2.4 kg/m2) and 10 LHCs (age: 27 ± 1 yrs, BMI: 22.3 ± 0.8 kg/m2) during basal and insulin stimulated states of the hyperinsulinemic (40mU/m2/min)‐euglycemic (5 mM) clamp. To further investigate the effect of insulin, primary human skeletal muscle cells were incubated with 300 pM insulin (a concentration similar to that experienced during the hyperinsulinemic‐euglycemic clamp) for 0, 30, and 180 mins. GLO1 protein content in human tissue and cell culture was assessed via western blot.RESULTSIndividuals with T2DM displayed a 5.6 fold reduction (p<0.0001) in GLO1 compared to LHC at baseline. Clamp‐induced hyperinsulinemia had no significant effect on GLO1 protein expression in either group (p>0.05). In cell culture, 30 minutes of insulin stimulation increased GLO1 protein expression by 37 % (p=0.0093). Interestingly, continued insulin stimulation for 180 mins returned GLO1 protein expression to levels comparable to baseline (0 min vs 180 min, p>0.05).CONCLUSIONThese data suggest that the skeletal muscle of T2DM may be susceptible to MG‐mediated protein damage and accumulation of AGEs. Further, prolonged exposure to hyperinsulinemia may attenuate early insulin mediated increases in GLO1 expression profiles. Further study is need to elucidate the exact mechanisms of these observations.