Abstract 1258: Proteasome β Subunit LMP-2 Is Required For Ischemic Preconditioning In Mouse Hearts
The ubiquitin-proteasome system plays an important role in many different cellular processes through degradation of specific proteins. Protein degradation is executed in the 20S proteasome, consisting of α and β subunits, and low molecular mass polypeptide 2 (LMP-2 or β1i) is one of the most active catalytic components of the proteasome. Ischemic preconditioning (IPC) activates cell signaling pathways and generates cardioprotection, but has not been previously linked to LMP-2 function. Here we examine whether LMP-2 is required for IPC cardioprotection. LMP-2 knockout mice (C57BL6 background) and wildtype C57BL6 mice were subjected to 30 minutes of ischemia (I-30) and 120 minutes of reperfusion (R-120) by occluding and reopening the left coronary artery with or without preceding IPC (I-10/R-5). At the end of experiment, infarct size was assessed by 1.5% triphenyltetrazolium chloride staining. IPC significantly decreased infarct size (IS), expressed as a percent of the area at risk (RA), in wildtype (WT) mice (CONWT/IPCWT = 47.0±5.0/22.8±3.6, n = 4. P < 0.01), but the protective effect of IPC was lost in LMP-2 knockout (KO) mice (CONKO/IPCKO = 51.8±3.1/45.8±6.9, n = 5. P > 0.05). Western blotting demonstrated that tissue level of PTEN (phosphatase and tensin homologue deleted on chromosome ten), a key protein phosphatase which negatively regulates activity of the survival kinase Akt, was significantly higher in LMP-2 knockout mice than wildtype mice, consistent with proteasomal regulation of PTEN. In conclusion, LMP-2 is necessary for IPC cardioprotection. Its action may be related to PTEN protein degradation.