UNFOLDED PROTEIN RESPONSE IN THE STUNNED HEART

MUNDIÑA-WEILENMANN C; SALAS M; MARIÁNGELO JIE; SAID M; ROMÁN B; VITTONE L; SILVESTRI A

New London, NH

Congreso; Gordon Research Conference Cardiac Regulatory Mechanisms; 2018

Gordon Research Conferences

Restoration of coronary flow after an ischemic event is mandatory in order to preserve cardiac function. However reperfusion itself may result in mechanical, electrical and/or viability alterations in excess to that produced by ischemia alone. The resulting tissue damage is named ischemia?reperfusion (I/R) injury and depends mainly on the duration of the ischemia. If the ischemic period is brief, I/R can cause reversible contractile dysfunction and arrhythmias (stunned heart) and in its severest form (prolonged ischemia) I/R can lead to cell death. I/R injury challenges the endoplasmic reticulum (ER) protein folding capacity, leading to ER stress. The cell response to ER stress is known as the unfolded protein response (UPR) and comprises three pathways which initiate both, adaptive and apoptotic signaling cascades: 1) ATF6 induces the transcription of XBP1 and GRP78 (the main ER chaperone); 2) IRE1 produces the splicing of XBP1 (sXBP1) which increases GRP78 expression and also leads to apoptosis via the activation of JNK and caspase-12 and 3) PERK attenuates protein synthesis and promotes the expression of the pro-apoptotic protein CHOP. There is consensus that under mild or moderate stress, upregulation of ER chaperones restores ER homeostasis and enhances survival. If the adaptive mechanisms of the UPR are not sufficient (prolonged or overwhelming protein folding stress) a switch to pro-apoptotic signals generates cell death contributing to the progression of the ischemic heart disease.The aims of this work were: 1) To study if UPR is triggered in the stunned heart (I/Rrev) and 2) To compare this response with the UPR associated to an irreversible I/R damage with cell death (I/Rirrev). Isolated perfused rat hearts were subjected to I/R (20/30min, I/Rrev or 30/60min, I/Rirrev). To characterize the UPR response, mRNA expression of GRP78, total XBP1, sXBP1 and CHOP were evaluated by real time qRT-PCR and the activation of caspase-12 and JNK were assessed by Western blot, all determinations being performed at the end of R. In order to evaluate myocardial damage, lactate dehydrogenase (LDH) release and apoptosis (TUNEL assay) were measured. mRNA levels of GRP78, XBP1 and sXBP1 significantly increased in both I/R protocols vs. non-ischemic hearts (Ctrl) (I/Rrev: 1.68±0.14; 1.26±0.07; 4.17±0.60; I/Rirrev: 1.69±0.12; 1.53±0.07; 2.73±0.22 fold change respectively, n=4-10, p