Myocardial SSAT induction via AMPK signaling and its implication for ischemic injury.

Spermidine/spermine N-1-acetyl-transferase (SSAT) is a catabolic enzyme that participates in polyamine metabolism. SSAT has been reported to be induced in some organs subjected to ischemia-reperfusion, but its induction mechanism has not been clarified, and little is known about SSAT regulation by ischemia per se. We induced regional ischemia of rat heart by coronary ligation and found that SSAT expression increased in ischemic myocardium. In neonatal rat cardiomyocytes and HEK293 cells, SSAT was up-regulated at the transcriptional step primarily by ATP depletion rather than oxygen deprivation. Moreover, an AMPK inhibitor compound C and AMPKalpha1-silencing RNAs attenuated the SSAT induction by ATP depletion, and an AMPK activator AICAR induced SSAT expression even without ATP depletion. When SSAT was suppressed using siRNA, the caspase activities and Bax/Bcl-2 ratios further increased in ATP depletion. These results suggest that myocardial SSAT is induced by AMPK signaling and function as a cardioprotectant under ATP-depleted conditions.