Disruption of the VEGFR3–HSPG2 induces lymphatic reflux dysfunction and sepsis

The lymphatic system plays a central role in fluid transport and immune regulation, yet its contribution to sepsis remains incompletely understood. Analysis of more than 500,000 individuals from the UK Biobank reveals that lymphatic system disorders and genetic variants in FLT4 (VEGFR3) are strongly associated with increased sepsis risk. Single-cell RNA sequencing further shows a marked reduction of VEGFR3^high lymphatic endothelial cells during sepsis. LEC-specific deletion of VEGFR3 impairs lymphatic reflux without disrupting vessel architecture, leading to barrier failure, systemic inflammation, bacterial dissemination, and sepsis. Mechanistically, VEGFR3 sustains lymphatic glycocalyx integrity by promoting SOX18-dependent HSPG2 transcription and heparan sulfate biosynthesis. Consistently, LEC-specific HSPG2 knockdown or pharmacological inhibition of SOX18 phenocopies VEGFR3 deficiency, whereas heparan sulfate supplementation alleviates sepsis-like pathology. Moreover, HSPG2 genetic variants are significantly associated with both lymphatic disorders and sepsis. Collectively, these findings identify lymphatic reflux dysfunction as a pathogenic determinant of sepsis and establish disruption of the VEGFR3–SOX18–HSPG2–heparan sulfate axis as an active driver of disease.