Type: Oral
Session: 602. Myeloid Oncogenesis: Basic: Mechanisms and Models of Myeloid Malignancy
Hematology Disease Topics & Pathways:
Fundamental Science, MDS
In order to determine how trisomy 8 affects hematopoiesis, we established a new trisomy 8 model by introducing a human chromosome 8 to mimic trisomy 8 in mouse ES cells. We succeeded in generating trisomy 8 chimeric mice and confirmed the mice showing emergence of hematopoiesis in fetal liver but significantly decreased the chimerism of trisomy 8 cells than the control mice. Wecompetitively transplanted trisomy 8 fetal liver cells at E14.5 into lethally-irradiated wild-type primary recipient mice, and moreover serial transplanted hematopoietic stem and progenitor cells (HSPCs) which isolated from the primary recipient mice. We found that trisomy 8 reduced the self-renewal capacity of HSPC and impeded the differentiation, but it was not sufficient to develop myeloid malignancies in mice.
To elucidate the molecular mechanism underlying the impaired hematopoiesis by trisomy 8, we performed RNA sequencing in HSCs isolated from the primary transplanted mice. Gene set enrichment analysis revealed that in comparison with the control HSCs, trisomy 8 HSCs had significantly positive enrichments in type I and type II interferon response genes, but also the canonical target genes of Runx1 and PU.1 TFs were positively enriched in trisomy 8 HSCs. In addition, ATAC-seq analysis revealed that trisomy 8 HSCs changed chromatin accessibility enriched with the binding motif of Runx TF, compared to control HSCs. Given the changes in chromatin accessibility in trisomy 8 HSC, we performed chromatin conformation capture sequencing (Hi-C) in HSPCs and found that trisomy 8 induced changes in chromatin structures such as topologically associating domain (TAD) and compartment A/B in the other chromosomes, which were partly associated with changes in transcription of genes.
Since the Runx1 gene is critical for HSC integrity and differentiation, and loss-of-function mutations of RUNX1 were often found in human myeloid malignancies with trisomy 8, we attempted to determine whether Runx1 deletion cancel the impaired self-renewal capacity of trisomy 8 HSC. We found that Runx1 deletion partially canceled the impaired repopulating capacity of trisomy 8 cells in recipient mice, suggesting the selective advantage of loss of function mutation of the RUNX1 gene in trisomy 8 mosaic people and patients with trisomy 8 MDS. Furthermore, as Janus kinase (JAK) and TANK-binding kinase 1 (TBK1) are critical for interferon signalling and activation of their downstream target genes, we revealed that the inhibition of either JAK or TBK function ameliorated trisomy 8-induced chromatin remodelling in HSCs. Overall, trisomy 8 changes chromatin structure and transcription of genes on other chromosomes in HSC accompanied with the malfunction of Runx1 TF, at least in part, due to the activation of interferon signaling, and results in the impaired hematopoiesis. We demonstrated that trisomy 8 creates the basis for transformation of MDS via remodeling chromatin structures in HSC.
Disclosures: No relevant conflicts of interest to declare.
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