Reduced inflammation has a potential relationship with the maintenance of cardiac and mitochondrial function after cold preservation in hibernators

Background Longer heart preservation method for heart transplantation is crucial for enabling transport to more distant regions, increasing matching opportunities. Hibernators experience low body temperatures and reduced heart rates during hibernation, similar to cold preservation, yet their hearts function normally upon arousal. This suggests that hibernators' hearts have a strong tolerance to low temperatures. A recent study suggests that mitochondria-related genes are differentially expressed in the hearts of ground squirrels during hibernation and arousal. However, whether mitochondrial function plays a role in their strong cold tolerance remains unclear. Purpose This study aims to clarify the relationship between mitochondrial function maintenance and cold preservation tolerance in hamsters (hibernators) and rats (non-hibernators). Additionally, we investigated the mechanisms underlying mitochondrial function maintenance and cold preservation tolerance using RNA sequencing (RNA-seq). Methods 6-month-old Syrian hamsters (n=8) and SD rats (n=8) were used. After euthanasia, hearts were excised and infused with Celsior and preserved on ice in the same solution for 24 hours. Following cold ischemia, the hearts were reperfused for 1 hour at 37°C using a Langendorff perfusion system. LV function was assessed by rate pressure product (RPP). Myocardial tissue samples were collected before (0 h) and after preservation (24 h), and post-reperfusion (25 h). Mitochondrial function (O2 consumption rate, respiratory control ratio (RCR), and H2O2 generation) was evaluated using Oxygraph-2k. RNA-seq was performed using heart tissues and analyzed by RNAseq Chef, with qRT-PCR used to validation. Statistical analysis was conducted using t-tests, one-way and two-way ANOVA (post-hoc: Tukey). The correlation between RPP and RCR was analyzed using by the Pearson test. Results Hamsters showed better cardiac function after reperfusion than rats. The RCR, a parameter of intrinsic mitochondrial respiratory capacity, was significantly higher in hamsters compared to rats. In rats, RCR remained decreased after cold storage, whereas in hamsters, it decreased after cold preservation but showed a tendency to recover after reperfusion. The RCR at 25 h had a strong correlation with RPP. RNA-seq results revealed a upregulation of inflammation-related genes in rats, while these genes minimally changed in hamsters. Similarly, qRT-PCR results showed that inflammatory marker expressions were higher after reperfusion than before in rats. Conclusions Hamsters showed better cardiac mitochondrial function than rats. Inflammatory markers were increased after reperfusion in rats. This suggests a potential relationship between maintenance of mitochondrial function and reduced inflammation in cold preservation. The effects of inflammation inhibitors in rats need to be investigated in the future to further clarify this relationship.