The severity of the ischemic insult promotes differential activation of the endoplasmic reticulum stress pathways

VITTONE L.; SALAS MA; BECERRA R,; SAID M; SILVESTRI MA; MARIANGELO JI; MUNDIÑA-WEILENMANN C;; ESOIN F; ROMAN B

Ciudad Autonoma de Buenos Aires

Congreso; Reunión Conjunta de Sociedades de Biociencias; 2017

SAFIS

Restoration of coronary flow after an ischemic event rescues the heart from further damage. However, reperfusion can cause different deleterious effects. After brief ischemic periods, reversible contractile dysfunction and arrhythmias occurred while irreversible damage with cell death appeared following a prolonged ischemia. Ischemia and Reperfusion (I/R), among several other pathological entities, challenge the endoplasmic reticulum (ER) protein folding capacity, leading to a condition known as ER stress. The adaptive response to ER stress is the unfolded protein response (UPR) and comprises three signaling pathways which lead to different effects: 1) ATF6 induces the transcription of XBP1 and GRP78 (the main ER chaperone that promotes protein folding); 2) IRE1 produces the splicing of XBP1 (sXBP1) which also increases GRP78 expression and 3) PERK attenuates protein synthesis. If ER stress is severe or prolonged, PERK and IRE1 may result in cell death: PERK promotes the expression of the pro-apoptotic protein CHOP and IRE1 the activation of the pro-apoptotic proteins caspase12. The aim of this work was to study the characteristics of the UPR associated to a reversible (I/Rrev) or irreversible (I/Rirrev) I/R damage. Isolated perfused rat hearts were subjected to I/R injury (20min/30min, I/Rrev) or (30min/60min, I/Rirrev). At the end of R mRNA expression of GRP78, total XBP1, sXBP1, CHOP and GAPDH as a housekeeping gene (real time qRT-PCR) were assessed. Expression of caspase-12 (Westernblot) and apoptosis (TUNEL assay) were also evaluated.The levels of mRNA of GRP78 and sXBP1 increased in both I/R protocols with respect to control hearts (datos I/Rrev, I/Rirrev xx fold change respectively, n=7-10, p>0.05). Conversely, the mRNA levels of XBP1 and CHOP only increased in I/Rirrev (datos). Under this latter condition the activation of caspase12 and apoptosis were detected. These results indicate that UPR is effectively triggered in I/R, however the pattern of ER response varies depending on the severity of the I/R insult. After a prolonged ischemic insult, the ER response may play a deleterious role contributing to apoptosis cell death.