Abstract 2046: Egr-1 promotes bone marrow fibrosis in primary myelofibrosis

Primary myelofibrosis (PMF) is a myeloproliferative neoplasm (MPN) characterized by JAK-STAT-activated proliferation of leukemia cells and progressive bone marrow fibrosis. However little is known about the bone marrow stromal cell (BMSC) intrinsic factors that work in concert with leukemia stem cells (LSCs) to promote fibrosis of the bone marrow in PMF. In this study we developed an in vitro model to simulate bone marrow fibrosis in PMF by exposing cultured BMSC, HS-5 cells to PMF-patient plasma. We observed that exposure of BMSCs to PMF plasma but not normal serum increased total cellular and mitochondrial reactive oxygen species (ROS), as well as Early growth response 1 (Egr-1) and its target gene expression in BMSCs. Egr-1 is a transcription factor that upregulates fibrosis-associated genes, and is acutely induced by numerous cytokines (e.g. TGF-β, PDGFα) that are elevated in PMF. Utilizing this model, we performed RNA sequencing of HS-5 cells exposed to PMF plasma. We observed that PMF plasma exposure alters pathways responsible for multiple DNA damage responses, G1/s cell cycle checkpoint regulation and protein homeostasis. Since PMF progression is associated with enhanced oxidative stress which induces both DNA damage and Egr-1 expression, we determined the effect of anti-oxidants on the induction Egr-1 and fibrosis associated genes in BMSCs following treatment with PMF plasma. We report that treatment with N-acetyl-cysteine (a ROS scavenger) and mitotempo (a mitochondrial ROS scavenger) abrogated the up-regulation of PMF plasma-induced fibrosis-associated genes in BMSCs. Additionally, knockdown of Egr-1 in BMSCs resulted in the down-regulation of collagen 1A1 and connective tissue growth factor (CTGF) following exposure to PMF plasma. These findings suggest that PMF plasma induces ROS and promotes the upregulation of pro-fibrotic genes in an Egr-1-dependent manner in PMF. Our studies suggest that inhibition of ROS and Egr-1-induced gene transcription could be used as a strategy to alleviate bone marrow fibrosis; a disease complication in PMF for which there are no approved therapies. Citation Format: Rekha M. Rao, Amar Kumar, Pratikkumar Vekaria, Abdulraheem Yacoub, Barry Skikne, Joseph McGuirk. Egr-1 promotes bone marrow fibrosis in primary myelofibrosis [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2019; 2019 Mar 29-Apr 3; Atlanta, GA. Philadelphia (PA): AACR; Cancer Res 2019;79(13 Suppl):Abstract nr 2