In vitro oxidant stress causes preferential loss of IRS proteins in rat skeletal muscle.

Abstract

Oxidant stress, the imbalance of oxidant production and the antioxidant defenses in the cell, can impair the functionality of elements of the insulin signaling pathway that regulates glucose metabolism in skeletal muscle. In this context context, the primary purpose of the present investigation was to characterize the effects of shorter‐term (2 hr) and longer‐term (4 hr) oxidative stress on protein expression of critical insulin signaling elements in skeletal muscle. Soleus muscles from insulin‐sensitive lean Zucker rats were exposed in vitro to an oxidant stress (60–90 μM H2O2 produced by glucose oxidase) for 2 or 4 hr. The oxidant stress reduced (p<0.05) insulin‐stimulated glucose transport activity after shorter‐term (50%) or longer‐term (53%) exposure. Moreover, the diminution of insulin action in the presence of the oxidant stress after 4 hr was associated with decreased protein levels of the primary insulin receptor substrate (IRS) isoforms expressed in mammalian skeletal muscle, IRS‐1 (59%) and IRS‐2 (33%). In contrast, this longer‐term oxidant stress did not alter the protein expression of IR‐β, PI3‐kinase, Akt, and GSK‐3. In addition, the stress‐activated p38 mitogen‐activated protein kinase (p38 MAPK) was activated after both 2 hr and 4 hr of oxidant exposure. The selective p38 MAPK inhibitor (10 μM A304000) prevented a significant portion (40%) of the oxidant stress‐induced loss of IRS‐1, but not IRS‐2, protein in skeletal muscle.