STAT3-Induced Gli1 Promotes the Differentiation and Maturation of Myelofibrosis Fibrocytes

Abstract

Myelofibrosis (MF) is characterized by constitutive activation of the Janus kinase (JAK)-signal transducer and activator of transcription (STAT) pathway and progressive bone marrow (BM) fibrosis. We previously found that the BM fibrosis in MF is induced by clonal monocyte-derived fibrocytes. However, whether or how the JAK-STAT pathway affects MF fibrocyte differentiation and maturation has not been elucidated. A recent study suggested that the transcription factor glioma-associated oncogene homolog 1 (Gli1) plays a significant role in the induction of BM fibrosis in MF (Schneider et al. Cell Stem Cell 2017). We have recently found that MF BM fibrocytes express high levels of Gli1 both in situ and in vitro (ASH 2018: Abstract 1793). Therefore, we sought to determine whether Gli1 affects the differentiation and maturation of MF fibrocytes and whether Gli1 expression is induced by the constitutively activated JAK-STAT pathway. To test our hypothesis, we first cultured normal donor and MF patients' BM CD14+ monocytes in fibrocyte differentiation-supporting medium and then transfected them using Gli1-siRNA. After 14 days we quantitated the number of mature fibrocytes using F-actin and DAPI staining. We found that the numbers of BM monocyte-derived fibrocytes in cultures containing Gli1-siRNA were significantly lower compared to mock-transfected cells. To study downstream effects of Gli1 silencing, we transfected mature fibrocytes with Gli1-siRNA and found that the expression of G…