The mechanism by which FGF23/FGFR-1 activates NOX2-ROS in vascular endothelial cells in the context of severe heat stroke-induced acute lung injury

The high mortality rate of severe heat stroke is mainly related to multiple organ dysfunction syndrome (MODS), and respiratory failure caused by acute lung injury (ALI) is a significant factor in the development of MODS during the course of severe heat stroke. Previous research has demonstrated that severe heat stroke-induced acute lung injury (sHS-ALI) is associated with an increase in reactive oxygen species (ROS) in vascular endothelial cells (VECs), but the specific initiating factors and intermediate mechanisms involved are unclear.

In this study, the mRNA profiles of mouse lung tissues were analysed using high-throughput sequencing. Genome-wide knockout was performed using CRISPR-Cas9 technology to identify a cohort of differentially expressed genes that promote human umbilical vein endothelial cells survival after heat stress. The expression of key proteins [fibroblast growth factor 23 (FGF23), phosphorylated fibroblast growth factor receptor-1 (p-FGFR-1), FGFR-1, phosphorylated phospholipase C-γ2 (p-PLC-γ2), PLC-γ2, p–p47^phox, p67^phox, p22^phox, p40^phox, and nicotinamide adenine dinucleotide phosphate oxidase isoform 2 (NOX2)] involved in the FGF23/FGFR-1 mechanism was examined using western blotting and immunohistochemistry.

In this study, we first screened sHS-ALI target genes by cross-comparison in vivo and in vitro and found that FGF23 is the upstream promoter of sHS-ALI. Subsequent investigations involving the interference or inhibition of FGF23 expression revealed that FGF23 induced FGFR-1 Y766 phosphorylation during heat stress-induced VECs damage. In addition, FGF23 participated in NOX2 activation and ROS accumulation and was involved in the process of sHS-ALI. These findings indicated that the FGFR-1 Y766 site mutation strongly suppressed the production of p-PLC-γ2 and heat stress-induced NOX2-ROS activation in VECs. More importantly, mutation of the FGFR-1 Y766 phosphorylation site had no effect on FGF23 expression, and it was impossible to significantly induce the expression of p-PLC-γ2. Moreover, NOX2-ROS activation was inhibited, even in the presence of heat stress, the recombinant FGF23 protein, or combined stimulation.

This study confirmed that FGF23/FGFR1 signalling, as an upstream priming factor, mediated NOX2-ROS activation in VECs after heat stress, thus participating in the sHS-ALI process. FGFR-1 Y766 phosphorylation is essential for FGF23/FGFR-1 signalling activation in VECs, which is involved in sHS-ALI. These findings further clarify the mechanism underlying sHS-ALI and contribute to reducing the mortality and morbidity of severe heat stroke.