Continuous short-term acclimation to moderate cold elicits cardioprotection in rats, and alters ß-adrenergic signaling and immune status.

Moderate cold acclimation (MCA) is a non-invasive intervention mitigating effects of various pathological conditions including myocardial infarction. We aim to determine the shortest cardioprotective regimen of MCA and the response of ß1/2/3-adrenoceptors (ß-AR), its downstream signaling, and inflammatory status, which play a role in cell-survival during myocardial infarction. Adult male Wistar rats were acclimated (9 °C, 1-3-10 days). Infarct size, echocardiography, western blotting, ELISA, mitochondrial respirometry, receptor binding assay, and quantitative immunofluorescence microscopy were carried out on left ventricular myocardium and brown adipose tissue (BAT). MultiPlex analysis of cytokines and chemokines in serum was accomplished. We found that short-term MCA reduced myocardial infarction, improved resistance of mitochondria to Ca2+-overload, and downregulated ß1-ARs. The ß2-ARs/protein kinase B/Akt were attenuated while ß3-ARs translocated on the T-tubular system suggesting its activation. Protein kinase G (PKG) translocated to sarcoplasmic reticulum and phosphorylation of AMPKThr172 increased after 10 days. Principal component analysis revealed a significant shift in cytokine/chemokine serum levels on day 10 of acclimation, which corresponds to maturation of BAT. In conclusion, short-term MCA increases heart resilience to ischemia without any negative side effects such as hypertension or hypertrophy. Cold-elicited cardioprotection is accompanied by ß1/2-AR desensitization, activation of the ß3-AR/PKG/AMPK pathways, and an immunomodulatory effect.

The cardioprotective effect persisting during recovery from cold acclimation is mediated by the ß2-adrenoceptor pathway and Akt activation.

The infarct size-limiting effect elicited by cold acclimation (CA) is accompanied by increased mitochondrial resistance and unaltered ß1-adrenergic receptor (AR) signaling persisting for 2 wk at room temperature. As the mechanism of CA-elicited cardioprotection is not fully understood, we examined the role of the salvage ß2-AR/Gi/Akt pathway. Male Wistar rats were exposed to CA (8°C, 5 wk), whereas the recovery group (CAR) was kept at 24°C for additional 2 wk. We show that the total number of myocardial ß-ARs in the left ventricular myocardium did not change after CA but decreased after CAR. We confirmed the infarct size-limiting effect in both CA and CAR groups. Acute administration of ß2-AR inhibitor ICI-118551 abolished the protective effect in the CAR group but had no effect in the control and CA groups. The inhibitory Giα1/2 and Giα3 proteins increased in the membrane fraction of the CAR group, and the phospho-Akt (Ser473)-to-Akt ratio also increased. Expression, phosphorylation, and mitochondrial location of the Akt target glycogen synthase kinase (GSK-3ß) were affected neither by CA nor by CAR. However, GSK-3ß translocated from the Z-disk to the H-zone after CA, and acquired its original location after CAR. Our data indicate that the cardioprotection observed after CAR is mediated by the ß2-AR/Gi pathway and Akt activation. Further studies are needed to unravel downstream targets of the central regulators of the CA process and the downstream targets of the Akt protein after CAR.NEW & NOTEWORTHY Cardioprotective effect of cold acclimation and that persisting for 2 wk after recovery engage in different mechanisms. The ß2-adrenoceptor/Gi pathway and Akt are involved only in the mechanism of infarct size-limiting effect occurring during the recovery phase. GSK-3ß translocated from the Z-line to the H-zone of sarcomeres by cold acclimation returns back to the original position after the recovery phase. The results provide new insights potentially useful for the development of cardiac therapies.