Understanding the roles of ERG and FLI1 in lymphatic development and maintenance

Abstract

Lymphatic vasculature is crucial for body homeostasis maintenance by regulating interstitial tissue fluid uptake, immune surveillance, and lipid absorption. However, the mechanisms underlying lymphatic vessel integrity maintenance and lymphangiogenesis are still elusive. ERG and FLI1 are members of the ETS transcription factor family which has a variable role in hematopoiesis and vasculogenesis. The role and mechanism of ERG and FLI1 in blood vasculature have been the subject of investigation for a long time. But in lymphatics, nothing has been known about their role and underlying mechanisms. In this study, we examined the roles of ERG and FLI1 in lymphatic development and maintenance. The depletion of both ERG/FLI1 results in lethality due to chylothorax with functional disorders of the valve. During the developmental process, ERG/FLI1 double knockout inhibits lymphatic proliferation and valve formation. However, interestingly ERG and FLI1 single knockout respectively only show mild or no phenotypes. To understand the underlying mechanism, single-cell RNA sequencing was conducted and revealed the relation of calcineurin-NFAT signaling. Nfatc1 is a downstream transcription factor of Foxc2 and Connexin37, regulating lymphatic valve formation by calcium reflux. The loss of ERG and FLI1 downregulates the expression of NFATC1 in LEC. Using ChiP-PCR we identified ERG binds to the NFATC1 promoter region. Our results suggest that a novel mechanism of ERG/FLI1 regulation of NFATC1 during valve development and maintenance, and contribute to potential targets for therapeutic intervention.