Genetically Induced Moderate Inhibition of the Proteasome in Cardiomyocytes Exacerbates Myocardial Ischemia-Reperfusion Injury in Mice
Rationale: Both cardiomyocyte-restricted proteasome functional enhancement and pharmacological proteasome inhibition (PSMI) were shown to attenuate myocardial ischemia/reperfusion (I/R) injury. The role of cardiac proteasome dysfunction during I/R and the perspective to diminish I/R injury by manipulating proteasome function remain unclear.
Objective: We sought to determine proteasome adequacy in I/R hearts, create a mouse model of cardiomyocyte-restricted PSMI (CR-PSMI), and test CR-PSMI impact on I/R injury.
Methods and Results: Myocardial I/R were modeled by ligation (30min) and subsequent release of the left anterior descending artery in mice overexpressing GFPdgn, a validated surrogate proteasome substrate. At 24h of reperfusion, myocardial proteasome activities were significantly lower while total ubiquitin conjugates and GFPdgn protein levels were markedly higher in all regions of the I/R hearts than the sham controls, indicative of proteasome functional insufficiency. CR-PSMI in intact mice was achieved by transgenic (tg) overexpression of a peptidase-disabled mouse β5 subunit (T60A-β5) driven by an attenuated mouse mhc6 promoter. Overexpressed T60A-β5 can replace endogenous β5 and inhibits proteasome chymotrypsin-like activities in the heart. Mice with moderate CR-PSMI showed no abnormalities at the baseline but displayed markedly more pronounced structural and functional damage during I/R, compared with non-tg littermates. The exacerbation of I/R injury by moderate CR-PSMI was associated with significant increases in the protein level of PTEN and protein kinase Cδ; (PKCδ), decreased Akt activation, and reduced PKCϵ.
Conclusions: Myocardial I/R causes proteasome functional insufficiency in cardiomyocytes and moderate CR-PSMI augments PTEN and PKCδ, suppresses Akt and PKCϵ, increases cardiomyocyte apoptosis, and aggravates I/R injury in mice.
- Received April 7, 2012.
- Accepted June 26, 2012.
- Copyright © 2012, American Heart Association