# Inositol-Requiring Enzyme 1 pathway and autophagy drive sequential response of endothelial cells to febrile range hyperthermia

## TL;DR

The study shows how heart artery cells respond to fever-like temperatures by activating stress and recycling pathways, which could explain how fevers affect blood vessel health during infections.

## Contribution

The study identifies the IRE1α-autophagy pathway as a novel mechanism linking fever-range hyperthermia to endothelial dysfunction in coronary artery cells.

## Key findings

- Prolonged fever-range temperatures impair human coronary artery endothelial cell function and junction integrity.
- Hyperthermia activates the IRE1α pathway and autophagy, which degrade cell junctions and increase permeability.
- Pharmacological inhibition of IRE1α reduces autophagy and protects endothelial cell structure and function.

## Abstract

Fever is an evolutionarily conserved and adaptive response during infections. However, prolonged fever has numerous systemic metabolic and functional side effects. In the heart, prolonged fever associated with infection is linked to fatal adverse effects, particularly involving impaired coronary circulation. Yet, the direct relationship between elevated temperature and coronary microcirculation dysfunction, remains to be fully demonstrated. In this study, we aimed to explore the specific responses of human coronary artery endothelial cells (HCAECs) to fever-range hyperthermia.

HCAECs were cultured at either 37°C or 40°C for up to 24 hours. Transcriptomic and proteomic profiles were obtained through microarray and mass spectrometry after 6, 12, and 24 hours of exposure. Key signaling pathways, upstream regulators, and candidate mechanisms were identified and validated at the mRNA and protein levels using mechanistic approaches.

Prolonged hyperthermia compromised HCAEC function, evidenced by cell detachment, loss of junctions, and increased permeability. HCAECs rapidly activated the unfolded protein response (UPR), including IRE1α activation and XBP1 splicing. Additionally, autophagic flux was significantly elevated, participating in the degradation of junction proteins. Pharmacological inhibition of IRE1α reduced the autophagic burden, protected against cell detachment, and preserved junction integrity over time.

Our findings reveal that in response to fever-range hyperthermia, the IRE1α-autophagy axis regulates the survival and function of coronary endothelial cells. This mechanism could play a key role in modulating endothelial responses during infection and contribute to the pathological outcomes of fever. Furthermore, it may be relevant in local inflammatory conditions with elevated temperatures.