Temperature is an abiotic variable that regulates the functioning of life. The vascular tree is instrumental in the distribution of heat throughout the whole body, but the consequences of temperature changes on vascular cells remain largely unexplored. We investigated the response developed by ECs to fever (37°C – 40°C).

Microarray transcriptomic profiles were obtained from Human Coronary Artery ECs (HCAECs) cultured at 37°C or 40°C during 6h. The expression of thermosensitive genes was confirmed by RT-q-PCR in cells grown under static and laminar flowconditions. Key signaling pathways and upstream regulators predicted for each generic temperature were identified using ingenuity pathway analysis (IPA) and confirmed at the protein level using mechanistic approaches including reporter assays andinhibitors.

Under both static and laminar flow conditions, HCAECs set up a heat shock response involving HSF1 pathway and upregulation of HSPs. Moderate hyperthermia also activated the unfolded protein response (UPR), with IRE1alpha activation leading to theXBP1 splicing, synthesis of XBP1 and increase of specific genes. Unexpected activation of mTORC1 pathway in HCAECs was also observed as confirmed with rapamycin (mTORC1-specific inhibitor) which partially reversed the effect of temperature.

Beyond activation of classical adaptative pathways such as HSF1, HCAECs subjected to moderate hyperthermia switch on additional signaling pathways (UPR and mTORC1) and activate specific genes that might collectively help cells to survive understress conditions. This study unravels the mechanism through which the endothelium detects and reacts to intravascular temperature variations which may be at play during febrile hyperthermic episodes and/or at local inflammatory foci.