Upregulation of myocardial 11 S-activated proteasome in experimental hyperglycemia

This study examined the hypothesis that the ubiquitin proteasome system (UPS) degrades proteins damaged by exposure to hyperglycemia. Experimental hyperglycemia was induced in male rats by treatment with streptozotocin. After 30 days, echocardiography confirmed the presence of cardiomyopathy as ejection fraction, fractional shortening, and diastolic function (E/A ratio) were decreased, and chamber diameter was increased in hyperglycemic animals. Proteasome non-ATP-dependent chymotryptic activity was increased over 2-fold in hyperglycemic hearts, but the ATP-dependent activity was decreased and levels of ubiquitinated proteins were increased. Protein levels of the PA28 alpha of the 11 S-activator ring were increased by 128% and the PA28 beta subunit increased by 58% in the hyperglycemic hearts. The alpha 3 subunit of the 20S-proteasome was increased by 82% while the catalytic beta 5 subunit was increased by 68% in hyperglycemic hearts. Protein oxidation as indicated by protein carbonyls was significantly higher in hyperglycemic hearts. These studies support the conclusion that the UPS becomes dysfunctional during long term hyperglycemia. However, 11 S-activated proteasome was increased suggesting a response to oxidative protein damage and a potential role for this form of the proteasome in a cardiac pathophysiology. (C) 2008 Published by Elsevier Inc.