GLI1 Activates Pro-fibrotic Pathways in Myelofibrosis Fibrocytes

Authors

Taghi Manshouri
Ivo Veletic
Ping Li
C Cameron Yin
Sean M Post
Srdan Verstovsek
Zeev Estrov

Publication Date

5-20-2022

Journal

Cell Death Discovery

Abstract

Bone marrow (BM) fibrosis was thought to be induced exclusively by mesenchymal stromal cells (MSCs). However, we and others found that neoplastic fibrocytes induce BM fibrosis in myelofibrosis (MF). Because glioma-associated oncogene-1 (GLI1), an effector of the Hedgehog pathway, plays a role in the induction of BM fibrosis, we wondered whether GLI1 affects fibrocyte-induced BM fibrosis in MF. Multiplexed fluorescence immunohistochemistry analysis of MF patients' BM detected high levels of GLI1 in MF fibrocytes compared to MSCs or normal fibrocytes. Immunostaining, RNA in situ hybridization, gene expression analysis, and western immunoblotting detected high levels of GLI1 and GLI1-induced matrix metalloproteases (MMP) 2 and 9 in MF patients BM-derived cultured fibrocytes. Similarly, MF patients' BM-derived GLI1+ fibrocytes were found in BMs and spleens of MF xenograft mice. GLI1 silencing reduced the levels of MMP2/9, phosphorylated SMAD2/3, and procollagen-I, and knockdown or inhibition of GLI1 decreased fibrocyte formation and induced apoptosis of both fibrocytes and fibrocyte progenitors. Because Janus kinase (JAK)2-induced STAT3 is constitutively activated in MF and because STAT3 induces GLI1 expression, we sought to determine whether STAT3 activates GLI1 in MF fibrocytes. Imaging analysis detected phosphotyrosine STAT3 in MF patients' BM fibrocytes, and transfection of fibrocytes with STAT3-siRNA or treatment with a JAK1/2 inhibitor ruxolitinib reduced GLI1 and MMP2/9 levels. Chromatin immunoprecipitation and a luciferase assay revealed that STAT3 induced the expression of the GLI1 gene in both MF BM fibrocytes and fibrocyte progenitors. Together, our data suggest that STAT3-activated GLI1 contributes to the induction of BM fibrosis in MF.

Keywords

Animals, Fibrosis, Hedgehog Proteins, Humans, Matrix Metalloproteinase 2, Matrix Metalloproteinase 9, Mice, Primary Myelofibrosis, STAT3 Transcription Factor, Zinc Finger Protein GLI1

DOI

10.1038/s41419-022-04932-4

PMID

35595725

PMCID

PMC9122946

PubMedCentral® Posted Date

5-20-2022

PubMedCentral® Full Text Version

Post-print

Published Open-Access

yes