Abstract 15057: Activation of the E3 ligase Cbl by Neutrophil Cathepsin G Impairs Insulin Receptor Signaling in Cardiomyocyte Degeneration
Background: Inflammation is a key component of systemic insulin resistance, which is a hallmark of diabetic cardiomyopathy. The molecular mechanisms that link inflammation to impaired insulin receptor (IR) signaling in the heart are not well understood. We have shown previously that neutrophil derived protease cathepsin G (Cat.G) induced activation of Cbl, a E3 ubiquitin ligase that targets receptor tyrosine kinase signaling, resulting in their ubiquitination and down-regulation. We hypothesized that Cat.G impairs IR signaling through Cbl activation in cardiomyocytes.
Results: Hearts from diabetic mice (24 weeks high-fat diet-fed mice) show increased neutrophil infiltration and Cat.G activity, along with an increase in myocyte death. Immunoprecitpitation and western blot studies show impaired IR signaling that was associated with an increase in IR interaction with Cbl. We assessed next whether Cbl activation was involved in IR signaling downregulation and myocyte apoptosis secondary to exposure of Cat.G. Acute stimulation with Cat.G (5 min to 30 min) induced IR tyrosine phosphorylation along with its interaction with Cbl. However, chronic stimulation with Cat.G (1-4hrs) increased both IR ubiquitination and degradation. Inhibition of the ubiquitin proteasome system, with MG132 or lactacystin, or adenoviral expression of dominant negative mutant Cbl significantly reduced IR degradation induced by Cat.G. In contrast, adenoviral expression of wild type Cbl enhanced IR ubiquitination and degradation in response to Cat.G. Restoration of IR signaling, by adenoviral expression of IR, attenuated IR downstream signaling downregulation, myofibril degeneration and myocyte apoptosis induced by Cat.G.
Conclusions: These data suggest that activation of neutrophil derived proteases is a positive regulator of IR signaling downregulation and may play a role in myofibril degeneration and myocyte apoptosis during the development of DCM.
- © 2013 by American Heart Association, Inc.