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.

Background: 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.

Methods: 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.

Results: 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.

Conclusions: 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.