Triiodothyronine Prevents Cardiac Ischemia/Reperfusion Mitochondrial Impairment and Cell Loss by Regulating miR30a/p53 Axis

Abstract

Mitochondrial dysfunctions critically affect cardiomyocyte survival during ischemia/reperfusion (I/R) injury. In this scenario p53 activates multiple signaling pathways that impair cardiac mitochondria and promote cell death. p53 is a validated target of miR-30 whose levels fall under ischemic conditions. Although triiodothyronine (T3) rescues post-ischemic mitochondrial activity and cell viability, no data are available on its role in the modulation of p53 signaling in I/R. Here we test the hypothesis that early T3 supplementation in rats inhibits the post I/R activation of p53 pro-death cascade through the maintenance of miRNA 30a expression. In our model, T3 infusion improves the recovery of post-ischemic cardiac performance. At the molecular level, the beneficial effect of T3 is associated with restored levels of miR-30a expression in the area at risk (AAR) that correspond to p53 mRNA downregulation. The concomitant decrease in p53 protein content reduces Bax expression and limits mitochondrial membrane depolarization resulting in preserved mitochondrial function and decreased apoptosis and necrosis extent in the AAR. Also in primary cardiomyocyte culture of neonatal rats, T3 prevents both miR-30a downregulation and p53 raise induced by hypoxia. The regulatory effect of T3 is greatly suppressed by miR-30a knockdown. Overall these data suggest a new mechanism of T3-mediated cardioprotection that is targeted to mitochondria and acts, at least in part, through the regulation of miR-30a/p53 axis.

Early and Short-term Triiodothyronine Supplementation Prevents Adverse Postischemic Cardiac Remodeling: Role of Transforming Growth Factor-β1 and Antifibrotic miRNA Signaling

“…Cardiac I/R was induced by 30-min occlusion of the left descending coronary artery (LAD) followed by unrestrained reperfusion in adult male Wistar rats weighing 385 ± 9 g, using a procedure described in detail elsewhere (31). ECG recordings were continuously acquired at a 2-kHz sampling rate (ML135 PowerLab/8SP equipped with ML135 Dual Bio Amp and MLA0112 ECG Lead Switch Box, ADI Instruments) during surgery up to 60 min after LAD occlusion.…”

“…On the basis of previous experiences (31,34,35), the homogeneity in the experimental groups was guaranteed by adopting the two following inclusion criteria: (a) severity score of ventricular arrhythmias occurring 5-20 min after coronary occlusion within the score rank 3 and (b) the development of Low-T3S 24 h after I/R (I/R-L group).…”

“…The latter defines the framework of the preclinical Low-T3S model (31). In any event, a subset of analyses were also performed in I/R rats that, in spite of arrhythmic score comparable to the I/R-L group, did not develop the Low-T3S (I/R euthyroid group [I/R-Eu]) (Supplementary Table S1).…”

“…No further death event was observed after the allocation to groups over the experimental period. Twenty-four hours after surgery, the surviving rats that developed Low-T3S were randomly assigned to receive a 48-h subcutaneous infusion of 6 μg/kg/d T3 (I/R-L+T3, n = 18) or T3 vehicle solution (I/R-L, n = 18) with an osmotic minipump (Alzet, model 2002) implanted in the interscapular space for constant drug administration, as previously described (31). A group of sham-operated rats was treated with constant infusion of T3 vehicle solution and used as control (Sham group, n = 12).…”

Thyroid hormones and the heart

“…T 3 modulates directly or via microRNA small molecules the mitochondrial function, biogenesis and quality through multiple regulation loops including reperfusion injury signaling kinase (RISK) and tumor suppressor protein p53. T 3 prevents the hypoxia mediated increase in p53 which occurs after myocardial infarction and promotes apoptosis, mitochondrial dysfunction and progression to heart failure [8]. The clinical relevance of thyroid hormones protection is currently tested in the ''Acute and long-term effects of thyroid hormone replacement therapy in patients with ST-Elevation Myocardial Infarction (STEMI) and borderline/reduced triiodothyronine levels'' (THiRST) study.…”