Pro-survival and pro-apoptotic mechanisms triggered by endoplasmic reticulum stress in the ischemic-reperfused myocardium

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

Mar del Plata

Congreso; Reunión conjunta SAI SAFIS SAIC; 2018

Sociedad Argentina de Investigación Clínica, Sociedad Argentina de Fisiología

Myocardial ischemia/reperfusion (I/R) produces a wide spectrum of pathophysiological alterations depending on the duration of ischemia. When ischemia is brief, I/R causes reversible contractile dysfunction and arrhythmias (stunned heart) and when it is prolonged, I/R leads to cell death. Severe I/R challenges the endoplasmic reticulum (ER) protein folding capacity, leading to ER stress, however there is still a gap for its occurrence in the stunned heart. ER stress response (UPR) comprises three pathways: 1) ATF6 induces transcription of XBP1 and GRP78 (main ER chaperone); 2) IRE1alpha produces spliced XBP1 (sXBP1) increasing GRP78 expression and also leads to apoptosis through JNK and caspase-12 activation; 3) PERK attenuates protein synthesis via eIF2alpha phosphorylation and promotes CHOP expression, a pro-apoptotic protein. Under mild stress, upregulation of ER chaperones restores ER homeostasis and enhances survival. The severe stress switches UPR to pro-apoptotic signals and cell death. Our aim was to study the presence of UPR in the stunned heart. Isolated perfused rat hearts were subjected to reversible (20/30min) or irreversible (30/60min) I/R. mRNA expression of ER stress markers (qRT-PCR) and proteins of early UPR response (Western blot) were assessed. Myocardial damage was evaluated by lactate dehydrogenase (LDH) release and apoptosis (TUNEL assay). While GRP78, XBP1 and sXBP1 mRNA levels significantly increased in both I/R protocols vs. non-ischemic hearts (Ctrl), CHOP mRNA only increased in irreversible I/R (1.86±0.10 fold change n=13, p