Abstract 15528: The Valosin-Containing Protein Provides a Novel Mechanism of Preconditioning in vivo
The valosin-containing protein (VCP) is an Akt-activating protein expressed in cancer cell lines, which activates the transcription factor NF-κB by promoting the ubiquitination and proteasome degradation of the NF-κB inhibitor IκBα, thereby promoting survival of cancer cells. However, the potential survival role of VCP in the heart remains unknown. Since active NF-κB increases the expression of the inducible nitric oxide synthase (iNOS), the mediator of the second window of preconditioning (SWOP), we tested the hypothesis that VCP may activate SWOP mechanisms via iNOS in a transgenic (TG) model of cardiac-specific VCP expression. VCP expression was detected in wild-type (WT) adult heart, where it co-precipitated with Akt. Three TG founder lines were obtained with over-expression of VCP from 4- to 7-fold. Increased iNOS expression was 2- to 8-fold among the three founder lines and was proportional to VCP expression (r=0.80, P<0.01). VCP TG mouse showed a 3-fold increase in Akt phosphorylation (Ser473) and in proteasome expression, and a 2-fold increase in proteasome activity and IκBα ubiquitination (all, P<0.05 vs WT). Cardiac function and myocyte size were unaffected. Both WT and TG mice were subjected to 45 min no-flow ischemia followed by 24h reperfusion. Infarct size was reduced by 60% in TG versus WT (P<0.01) despite similar area-at-risk, i.e., quantitatively similar to the protection by SWOP. Maximal protection was observed in the TG founder with 2-fold increase in iNOS expression, but was less (P<0.05) in founders with higher iNOS expression. In isolated cardiac myocytes, adeno-mediated VCP expression increased Akt phosphorylation, NF-κB DNA binding and iNOS expression, and reduced by 60% chelerythrine-induced apoptosis (all, P<0.05 versus LacZ). Protection against apoptosis was lost by pharmacological inhibition of Akt, upon silencing of the mammalian target of rapamycin complex-2 (mTORC2), responsible for phosphorylation of Akt on Ser473, and upon iNOS inhibition by aminoguanidine. Therefore, VCP activates a survival pathway sequentially involving Akt, NF-κB and iNOS, and stimulates proteasome degradation of IκBα, providing cardioprotection in vivo equivalent to SWOP and thereby representing a novel mechanism of preconditioning.
- © 2011 by American Heart Association, Inc.