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STAT3 protects hematopoietic stem cells from intrinsic interferon signaling and loss of long-term blood-forming activity

ABSTRACT: The transcriptional regulator signal transducer and activator of transcription 3 (STAT3) has a well-established anti-inflammatory function in mature myeloid cells. This role, however, has precluded an understanding of STAT3 function in hematopoietic stem and progenitor cells (HSPCs), as Stat3 deletion in the hematopoietic system induces systemic inflammation, which can impact HSPC activity. Thus, novel approaches to uncouple STAT3 function in HSPCs from the effects of systemic inflammation are needed. To address this, we established competitive mixed bone marrow (BM) chimeric mice with CreER-mediated conditional Stat3 deletion in 20% of the hematopoietic compartment. After confirming a lack of detectable inflammation in mice with Stat3-deficient BM, we found that, in contrast to Stat3-sufficient controls, Stat3-deficient HSPCs had impaired hematopoietic activity and failed to undergo expansion in BM. Single-cell RNA sequencing of Lin-ckit+Sca1+ (LSKs) BM cells revealed an altered transcriptional landscape in Stat3-deficient hematopoietic stem cells (HSCs) and multipotent progenitors, as evidenced by the intrinsic activation of cell cycle, stress response, and interferon signaling pathways. Consistent with their deregulation, Stat3-deficient LSKs accumulated γH2AX over time. Following secondary BM transplantation, Stat3-deficient HSPCs failed to reconstitute peripheral blood effectively, indicating a severe functional defect in the HSC compartment. Our results reveal essential roles for STAT3 in HSCs and suggest the potential for using targeted synthetic lethal approaches with STAT3 inhibition to remove defective or diseased HSPCs.

ORGANISM(S): Mus musculus

PROVIDER: GSE220466 | GEO | 2023/06/02

REPOSITORIES: GEO

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Project description:ETS Variant 6 (ETV6) encodes an essential transcriptional repressor abundantly expressed in hematopoietic stem and progenitor cells (HSPCs), where it is required for adult hematopoiesis. Heterozygous pathogenic germline ETV6 variants are associated with Thrombocytopenia 5 (T5), a poorly-understood genetic condition predisposing to thrombocytopenia and hematologic malignancies. To elucidate how germline ETV6 variants impact the HSPC compartment and contribute to disease, we generated a knock-in mouse harboring an Etv6R355X loss-of-function variant, which represents the mouse equivalent to the T5-associated variant ETV6R359X. All HSPC subpopulations are present in the bone marrow (BM) of Etv6R355X/+ mice under homeostatic conditions; however, these animals exhibit subtle shifts in the proportions and/or numbers of specific progenitor subtypes. To examine whether the Etv6R355X/+ mutation impacts HSPC function, we carried out serial competitive transplantation and observed that Etv6R355X/+ lineagesca1+cKit+ (LSK) cells exhibit significantly impaired reconstitution, with near complete failure to repopulate irradiated-recipients by the tertiary transplant. Mechanistic studies incorporating CUT&RUN, ATAC-Seq and Hi-C identify ETV6 binding at inflammatory gene loci, including those within the TNF pathway in Etv6+/+ HSPCs, the mouse BM-progenitor derived HPC5 cell line, and G-CSF-mobilized human CD34+ cells. Further, single-cell RNA sequencing of mouse LSK cells isolated six-weeks post-competitive transplantation reveals upregulation of inflammatory gene pathways. Corroborating these findings, we observe significantly increased production of TNF by Etv6R355X/+ versus Etv6+/+ HSPCs post-transplantation. From these studies, we conclude that ETV6 represses inflammatory response genes within HSPCs under conditions of hematopoietic stress, and that this mechanism may be critical to sustain HSPC function. Functionally, Etv6R355X/+ bone marrow (BM) cells exhibited reduced colony formation in later rounds of serial replating, while Etv6R355X/+ LSKs exhibited significantly impaired engraftment in serial competitive transplantation. RNA-seq of Etv6R355X/+ LSKs and/or sort-purified HSPCs revealed upregulation of genes associated with an active stem cell phenotype and pro-inflammatory signaling, including increased expression of the cytokine Tnf. CUT&RUN of Etv6+/+ LSKs and HPC5 hematopoietic progenitors showed that ETV6 binds to the Tnf locus at regions of open chromatin, while CUT&RUN of human CD34+ cells identified ETV6 targets enriched in TNF signaling. In line with these findings, Etv6R355X/+ HSPCs exhibited increased cell-cycling and TNF expression post-transplantation. Finally, genetic deletion of Tnf restored the serial replating capacity of Etv6R355X/+ BM cells.

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STAT3 protects hematopoietic stem cells from intrinsic interferon signaling and loss of long-term blood-forming activity

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