# Hyperbaric oxygen pretreatment on endothelial cell injury via heat shock factor 1 in decompression sickness

## TL;DR

Hyperbaric oxygen pretreatment protects blood vessel cells from injury in decompression sickness by activating a specific stress response pathway.

## Contribution

The study identifies the ROS/AKT/HSF-1 pathway as a novel mechanism through which hyperbaric oxygen pretreatment protects endothelial cells from decompression sickness.

## Key findings

- Hyperbaric oxygen increases HSF-1 activation and heat shock proteins HSP27 and HSP40.
- HSF-1 inhibition reverses the protective effects of hyperbaric oxygen in both cell and animal models.
- ROS and AKT signaling are critical for HSF-1 activation in this protective mechanism.

## Abstract

This study investigated the protective role and mechanisms of hyperbaric oxygen (HBO) pretreatment in enhancing vascular endothelial cell (VEC) resistance to bubble-induced injury by focusing on heat shock factor 1 (HSF-1) to prevent decompression sickness (DCS).

Primary cultured rat pulmonary microvascular endothelial cells (PMVECs) and Sprague–Dawley rats were used as experimental models. Western blot analysis was performed to examine the activation patterns of HSF-1 and the expression of downstream proteins after HBO exposure. Specific inhibitors were used to delineate the signaling pathways involved in HSF-1 activation. At peak protein expression time points, a cellular bubble-induced injury model and a rat DCS model were established. The functional roles of HSF-1 and its downstream proteins in protection against HBO were evaluated using specific inhibitors and siRNAs.

HBO significantly enhanced the nuclear translocation of HSF-1 and upregulated the expression of downstream heat shock proteins 27 and 40 in PMVECs and lung tissues, peaking at 12 and 18 h after HBO exposure, respectively. The reactive oxygen species (ROS) levels and phosphorylation of ERK1/2, P38 MAPK, and AKT were markedly elevated after HBO exposure. AKT inhibition substantially suppressed HSF-1 activation, whereas ERK1/2 and P38 MAPK inhibition had no effect. ROS scavenging with Mito-Tempo reduced AKT phosphorylation and HSF-1 activation. Bubble-induced injury significantly decreased the viability of PMVECs and increased the levels of endothelial microparticles, inflammatory cytokines, and endothelial injury markers in culture media. HBO pretreatment ameliorated these pathological changes, which were reversed by HSF-1, HSP27, or HSP40 inhibition. In DCS rats, HBO pretreatment decreased lung wet-to-dry ratios, histopathological scores, serum inflammatory cytokines, endothelial microparticles, and endothelial injury markers. These benefits were reversed by the HSF-1 inhibitor KRIBB11.

HBO pretreatment enhanced VEC resistance to bubble injury and mitigated DCS-related damage in rats via HSP27 and HSP40 expression upregulated by the ROS/AKT/HSF-1 signaling pathway.