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.
Coactivator-associated arginine methyltransferase I (CARM1; PRMT4) regulates gene expression by multiple mechanisms including methylation of histones and coactivation of steroid receptor ...transcription. Mice lacking CARM1 are small, fail to breathe and die shortly after birth, demonstrating the crucial role of CARM1 in development. In adults, CARM1 is overexpressed in human grade-III breast tumors and prostate adenocarcinomas, and knockdown of CARM1 inhibits proliferation of breast and prostate cancer cell lines. Based on these observations, we hypothesized that loss of CARM1 in mouse embryos would inhibit pulmonary cell proliferation, resulting in respiratory distress. By contrast, we report here that loss of CARM1 results in hyperproliferation of pulmonary epithelial cells during embryonic development. The lungs of newborn mice lacking CARM1 have substantially reduced airspace compared with their wild-type littermates. In the absence of CARM1, alveolar type II cells show increased proliferation. Electron microscopic analyses demonstrate that lungs from mice lacking CARM1 have immature alveolar type II cells and an absence of alveolar type I cells. Gene expression analysis reveals a dysregulation of cell cycle genes and markers of differentiation in the Carm1 knockout lung. Furthermore, there is an overlap in gene expression in the Carm1 knockout and the glucocorticoid receptor knockout lung, suggesting that hyperproliferation and lack of maturation of the alveolar cells are at least in part caused by attenuation of glucocorticoid-mediated signaling. These results demonstrate for the first time that CARM1 inhibits pulmonary cell proliferation and is required for proper differentiation of alveolar cells.
The Ets transcription factor PU.1 is essential for inducing the differentiation of monocytes, macrophages, and B cells in fetal liver and adult bone marrow. PU.1 controls hematopoietic ...differentiation through physical interactions with other transcription factors, such as C/EBPα and the AP-1 family member c-Jun. We found that PU.1 recruits c-Jun to promoters without the AP-1 binding sites. To address the functional importance of this interaction, we generated PU.1 point mutants that do not bind c-Jun while maintaining normal DNA binding affinity. These mutants lost the ability to transactivate a target reporter that requires a physical PU.1-c-Jun interaction, and did not induce monocyte/macrophage differentiation of PU.1-deficient cells. Knock-in mice carrying these point mutations displayed an almost complete block in hematopoiesis and perinatal lethality. While the PU.1 mutants were expressed in hematopoietic stem and early progenitor cells, myeloid differentiation was severely blocked, leading to an almost complete loss of mature hematopoietic cells. Differentiation into mature macrophages could be restored by expressing PU.1 mutant fused to c-Jun, demonstrating that a physical PU.1-c-Jun interaction is crucial for the transactivation of PU.1 target genes required for myeloid commitment and normal PU.1 function in vivo during macrophage differentiation.
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