Deficiency of lymphatic ERG and FLI1 in systemic sclerosis is associated with rarefaction of skin blood and lymphatic vasculature

ERG and FLI1 are important regulators of angiogenesis, but their role in lymphatic vasculature is less known. The goal of this study was to determine the role of ERG and FLI1 in postnatal lymphangiogenesis and their involvement in SSc lymphatic system defects. IF were used to detect ERG and FLI1 in SSc and healthy controls (HC) skin biopsies. Human lymphatic endothelial cells (LECs) were used in cell culture experiments. Transcriptional and chromatin analysis of ERG or FLI1 silenced LECs was performed using microarrays and ATAC-seq, respectively. Effects of ERG and FLI1 deficiency on in vitro tubulogenesis was examined using Matrigel assay. Erg and Fli1 endothelial specific knockouts (ErgCKO and Fli1CKO) and lymphatic specific knockouts (ProxErgCKO and ProxFli1CKO) were generated to examine vessel regeneration. ERG and FLI1 protein levels were reduced in blood and lymphatic vasculature in SSc skin biopsies. ERG and FLI1 were shown to regulate genes involved in lymphatic vessel specification, including VEGFR3/FLT4, LYVE-1, and PROX1, and this effect was, at least in part, due to chromatin remodeling. ERG/FLT4 pathway regulated in vitro tubulogenesis in LECs. Deficiency of Erg and Fli1 impaired function of blood and lymphatic vessel during wound healing. ERG and FLI1 are essential regulators of blood and lymphatic vessel regeneration. Deficiency of ERG and FLI1 in SSc endothelial cells, may contribute to rarefaction of blood and lymphatic vasculature in SSc patients. Microarray analysis was performed at The Boston University Microarray Core Facility. Affymetrix CEL files were normalized to produce gene-level expression values using the implementation of the Robust Multiarray Average (RMA) in the affy package (version 1.36.1) included within in the Bioconductor software suite (version 2.12) and an Entrez Gene-specific probe set mapping from BrainArray (version 16.0.0). RLE and NUSE quality metrics were computed using the affy PLM Bioconductor package (version 1.34.0). All microarray analyses were performed using the R environment for statistical computing (version 2.15.1).