Cooperative ETS transcription factors are required for lymphatic endothelial cell integrity and resilience.

Lymphatics maintain fluid homeostasis, immune surveillance, and tissue integrity. Here, we identified the E26 transformation-specific transcription factors Erg and Fli1 as essential cooperative regulators of lymphatic integrity and function. Using inducible lymphatic endothelial cell-specific deletion in mice, we demonstrated that combined loss of Erg and Fli1 in adults results in fatal lymphatic failure, including chylothorax, chylous ascites, and impaired lymphatic drainage. Single-cell transcriptomic analysis revealed that loss of Erg and Fli1 causes disrupted lymphatic heterogeneity and dysregulation of key lymphatic genes, including valve-specific gene profiles. Erg and Fli1 coordinated lymphatic-immune crosstalk by transcriptionally regulating C-C motif chemokine ligand 21, which mediates DC trafficking. Erg or Fli1 loss also induced proinflammatory and prothrombotic gene expression, further contributing to lymphatic dysfunction. During embryonic development, the codeletion led to lymphatic mispatterning and loss of valve-initiating lymphatic endothelial cell clusters. The impact of loss of Erg and Fli1 function on lymphatic development in mice is consistent with FOXC2 mutations in lymphedema-distichiasis syndrome or ERG gene variants underlying primary lymphedema in humans. Moreover, Erg and Fli1 were required for regenerative lymphangiogenesis and lymphatic repair following injury in adults. Our findings establish Erg and Fli1 as core transcriptional regulators of lymphatic identity, integrity, and function.