Glutathione reverses early effects of glycation on myosin function

Abstract

Nonenzymatic glycosylation (glycation) has been recognized as an important posttranslational modification underlying alterations of structure and function of extracellular proteins during aging and diabetes. Intracellular proteins may also be affected by this modification, and glycation has been suggested to contribute to aging-related impairment in skeletal muscle function. Glycation is the chemical reaction of reducing sugars with primary amino groups resulting in the formation of irreversible advanced glycation end products. Glutathione is an abundant tripeptide in skeletal muscle. To understand the effect of glutathione on glycated myosin function, we used a single-fiber in vitro motility assay in which myosin is extracted from a single muscle fiber segment to propel fluorescent-labeled actin filaments. Myosin function responded to glucose exposure in a dose-dependent manner, i.e., motility speeds were reduced by 10, 34, and 90% of preincubation values after 30-min exposure to 1, 3, and 6 mM glucose, respectively. The 30-min 6 mM glucose incubation was followed by a 20-min 10 mM glutathione incubation. Glutathione treatment restored motility (0.98 ± 0.06 μm/s, n = 3; P < 0.001) after glucose exposure (0.10 ± 0.07 μm/s, n = 3), close to preincubation levels (1.12 ± 0.06 μm/s, n = 3). It is concluded that glucose modifies myosin function in a dose-dependent manner and that glutathione reverses the effect of glucose on myosin function.