Emergency granulopoiesis is the enhanced and accelerated production of granulocytes that occurs during acute infection. The contribution of hematopoietic stem cells (HSCs) to this process was ...reported; however, how HSCs participate in emergency granulopoiesis remains elusive. Here, using a mouse model of emergency granulopoiesis we observe transcriptional changes in HSCs as early as 4 h after lipopolysaccharide (LPS) administration. We observe that the HSC identity is changed towards a myeloid‐biased HSC and show that CD201 is enriched in lymphoid‐biased HSCs. While CD201 expression under steady‐state conditions reveals a lymphoid bias, under emergency granulopoiesis loss of CD201 marks the lymphoid‐to‐myeloid transcriptional switch. Mechanistically, we determine that lymphoid‐biased CD201+ HSCs act as a first response during emergency granulopoiesis due to direct sensing of LPS by TLR4 and downstream activation of NF‐κΒ signaling. The myeloid‐biased CD201− HSC population responds indirectly during an acute infection by sensing G‐CSF, increasing STAT3 phosphorylation, and upregulating LAP/LAP* C/EBPβ isoforms. In conclusion, HSC subpopulations support early phases of emergency granulopoiesis due to their transcriptional rewiring from a lymphoid‐biased to myeloid‐biased population and thus establishing alternative paths to supply elevated numbers of granulocytes.
Synopsis
Emergency granulopoiesis is the enhanced and accelerated production of granulocytes during acute infection. Here, using a mouse model of emergency granulopoiesis we provide cellular and molecular insights into the regulation of emergency granulopoiesis at the level of hematopoietic stem cells (HSCs).
Single‐cell transcriptomics reveals that HSCs respond to emergency granulopoiesis shortly after infection by transcriptionally rewiring specific subpopulations.
The cell surface marker CD201 allows the separation of HSCs to distinct lineages.
During emergency granulopoiesis, HSCs compromise the lymphoid output and favor the myeloid production.
CD201+ and CD201− HSCs sense acute infection by using distinct receptors and signaling pathways ultimately employing distinct isoforms of the transcription factor C/EBPβ.
A mouse model of emergency granulopoiesis provides insight into the role of hematopoietic stem cells in the enhanced and accelerated production of granulocytes that occurs during acute infection.
Chronic inflammation represents a major threat to human health since long‐term systemic inflammation is known to affect distinct tissues and organs. Recently, solid evidence demonstrated that chronic ...inflammation affects hematopoiesis; however, how chronic inflammation affects hematopoietic stem cells (HSCs) on the mechanistic level is poorly understood. Here, we employ a mouse model of chronic multifocal osteomyelitis (CMO) to assess the effects of a spontaneously developed inflammatory condition on HSCs. We demonstrate that hematopoietic and nonhematopoietic compartments in CMO BM contribute to HSC expansion and impair their function. Remarkably, our results suggest that the typical features of murine multifocal osteomyelitis and the HSC phenotype are mechanistically decoupled. We show that the CMO environment imprints a myeloid gene signature and imposes a pro‐inflammatory profile on HSCs. We identify IL‐6 and the Jak/Stat3 signaling pathway as critical mediators. However, while IL‐6 and Stat3 blockage reduce HSC numbers in CMO mice, only inhibition of Stat3 activity significantly rescues their fitness. Our data emphasize the detrimental effects of chronic inflammation on stem cell function, opening new venues for treatment.
Synopsis
Chronic inflammation induces HSC expansion and reduces HSC fitness by hyperactivating the IL‐6/Jak/Stat3 signaling pathway. These effects of chronic inflammation on HSCs are mitigated upon inhibition of Stat3.
CMO mice, suffering from sterile chronic inflammation, exhibit an expansion of the HSC pool and a reduction of HSC fitness.
The CMO environment imprints a myeloid gene signature and imposes a pro‐inflammatory profile in HSCs.
Inactivation of the IL‐1β/MyD88 pathway in CMO mice is not sufficient to prevent defects in the HSC compartment.
IL‐6 and Jak/Stat3 signaling mediate HSC alterations in CMO mice and inhibition of Stat3 activity rescues HSC function.
Chronic inflammation induces HSC expansion and reduces HSC fitness by hyperactivating the IL‐6/Jak/Stat3 signaling pathway. These effects of chronic inflammation on HSCs are mitigated upon inhibition of Stat3.
In blood, the transcription factor C/EBPa is essential for myeloid differentiation and has been implicated in regulating self-renewal of fetal liver haematopoietic stem cells (HSCs). However, its ...function in adult HSCs has remained unknown. Here, using an inducible knockout model we found that C/EBPa-deficient adult HSCs underwent a pronounced increase in number with enhanced proliferation, characteristics resembling fetal liver HSCs. Consistently, transcription profiling of C/EBPa-deficient HSCs revealed a gene expression program similar to fetal liver HSCs. Moreover, we observed that age-specific Cebpa expression correlated with its inhibitory effect on the HSC cell cycle. Mechanistically we identified N-Myc as a downstream target of C/EBPa, and loss of C/EBPa resulted in de-repression of N-Myc. Our data establish C/EBPa as a central determinant in the switch from fetal to adult HSCs.
WW domain binding protein 1‐like (WBP1L), also known as outcome predictor of acute leukaemia 1 (OPAL1), is a transmembrane adaptor protein, expression of which correlates with ETV6‐RUNX1 ...(t(12;21)(p13;q22)) translocation and favourable prognosis in childhood leukaemia. It has a broad expression pattern in haematopoietic and in non‐haematopoietic cells. However, its physiological function has been unknown. Here, we show that WBP1L negatively regulates signalling through a critical chemokine receptor CXCR4 in multiple leucocyte subsets and cell lines. We also show that WBP1L interacts with NEDD4‐family ubiquitin ligases and regulates CXCR4 ubiquitination and expression. Moreover, analysis of Wbp1l‐deficient mice revealed alterations in B cell development and enhanced efficiency of bone marrow cell transplantation. Collectively, our data show that WBP1L is a novel regulator of CXCR4 signalling and haematopoiesis.
DNA methylation was first described almost a century ago; however, the rules governing its establishment and maintenance remain elusive. Here we present data demonstrating that active transcription ...regulates levels of genomic methylation. We identify a novel RNA arising from the CEBPA gene locus that is critical in regulating the local DNA methylation profile. This RNA binds to DNMT1 and prevents CEBPA gene locus methylation. Deep sequencing of transcripts associated with DNMT1 combined with genome-scale methylation and expression profiling extend the generality of this finding to numerous gene loci. Collectively, these results delineate the nature of DNMT1-RNA interactions and suggest strategies for gene-selective demethylation of therapeutic targets in human diseases.
Mutation or epigenetic silencing of the transcription factor C/EBPα is observed in ∼10% of patients with acute myeloid leukemia (AML). In both cases, a common global gene expression profile is ...observed, but downstream targets relevant for leukemogenesis are not known. Here, we identify Sox4 as a direct target of C/EBPα whereby its expression is inversely correlated with C/EBPα activity. Downregulation of Sox4 abrogated increased self-renewal of leukemic cells and restored their differentiation. Gene expression profiles of leukemia-initiating cells (LICs) from both Sox4 overexpression and murine C/EBPα mutant AML models clustered together but differed from other types of AML. Our data demonstrate that Sox4 overexpression resulting from C/EBPα inactivation contributes to the development of leukemia with a distinct LIC phenotype.
•C/EBPα represses Sox4 transcription in a DNA-binding-dependent manner•SOX4 is overexpressed in human AML samples with mutated or silent CEBPA•Sox4 mediates leukemic outgrowth due to defective C/EBPα in murine and human models•LICs in Sox4- or mutated C/EBPα-driven AML models share a gene expression signature
MIR139 is a tumor suppressor and is commonly silenced in acute myeloid leukemia (AML). However, the tumor-suppressing activities of miR-139 and molecular mechanisms of MIR139-silencing remain largely ...unknown. Here, we studied the poorly prognostic MLL-AF9 fusion protein-expressing AML. We show that MLL-AF9 expression in hematopoietic precursors caused epigenetic silencing of MIR139, whereas overexpression of MIR139 inhibited in vitro and in vivo AML outgrowth. We identified novel miR-139 targets that mediate the tumor-suppressing activities of miR-139 in MLL-AF9 AML. We revealed that two enhancer regions control MIR139 expression and found that the polycomb repressive complex 2 (PRC2) downstream of MLL-AF9 epigenetically silenced MIR139 in AML. Finally, a genome-wide CRISPR-Cas9 knockout screen revealed RNA Polymerase 2 Subunit M (POLR2M) as a novel MIR139-regulatory factor. Our findings elucidate the molecular control of tumor suppressor MIR139 and reveal a role for POLR2M in the MIR139-silencing mechanism, downstream of MLL-AF9 and PRC2 in AML. In addition, we confirmed these findings in human AML cell lines with different oncogenic aberrations, suggesting that this is a more common oncogenic mechanism in AML. Our results may pave the way for new targeted therapy in AML.
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