Abstract Body: Introduction: The impact of global ischemia and reperfusion on the brain has been extensively studied in animal models of cardiac arrest (CA) and resuscitation. Although therapeutic hypothermia has shown efficacy following the restoration of circulation, its underlying mechanisms remain incompletely understood. To gain insights into molecular pathways potentially effected by therapeutic hypothermia, we performed whole transcriptomic analysis using RNA sequencing to investigate differential gene expression in the hippocampus.

Methods: Male Sprague Dawley rats (Charles River Laboratories) with a weight between 400-800g were subjected to 8 minutes of ventricular fibrillation cardiac arrest (VFCA) and resuscitated with extracorporeal cardiopulmonary resuscitation (eCPR) (n=10). After return of spontaneous circulation, five animals were treated with hypothermic temperature control (33 ±0,5°C) for 12 hours (HT), and five animals where kept normothermic (NT). Sham animals (n=5) were subjected to the surgical procedures but underwent no cardiac arrest or eCPR. After 24 hours of survival, the hippocampus of one hemisphere was extracted, homogenized, and preserved in Trizol. Subsequently RNA libraries were prepared and analysed with Next Generation Sequencing. After preprocessing of reads and alignment to the rat genome, we applied DESeq to identify differentially expressed genes (DEGs) between groups. We considered DEGs with an adjusted p-value of <0.05 and log2 fold change > ± 1 as significantly deregulated.

Results: We found the largest number of DEGs between NT and sham (590 genes). In contrast, the HT vs sham group yielded 318 DEGs. Notably, only 62 DEGS were detected between NT and HT. Subsequent Gene Ontology (GO) analysis revealed similarly enriched pathways in both the HT vs sham and NT vs sham comparisons. Overlay analysis of common and unique DEGs identified 88 genes that were exclusively deregulated in response to HT, while 230 DEGs were commonly affected in both NT and HT conditions. Pathway analysis suggested that immune and apoptotic pathways were largely preserved among the 230 shared DEGs, whereas the HT-exclusive gene set showed upregulation of well-known neuroprotective genes.

Conclusion: Our findings suggest that HT does not alter the core pathological response to CA but selectively induces neuroprotective pathway, which may contribute to improved clinical outcome.