The RNA m^(6)A demethylase ALKBH5 drives emergency granulopoiesis and neutrophil mobilization by upregulating G-CSFR expression

Emergency granulopoiesis and neutrophil mobilization that can be triggered by granulocyte colony-stimulating factor(G-CSF)through its receptor G-CSFR are essential for antibacterial innate defense.However,the epigenetic modifiers crucial for intrinsically regulating G-CSFR expression and the antibacterial response of neutrophils remain largely unclear.N6-methyladenosine(m^(6)A)RNA modification and the related demethylase alkB homolog 5(ALKBH5)are key epigenetic regulators of immunity and inflammation,but their roles in neutrophil production and mobilization are still unknown.We used cecal ligation and puncture(CLP)-induced polymicrobial sepsis to model systemic bacterial infection,and we report that ALKBH5 is required for emergency granulopoiesis and neutrophil mobilization.ALKBH5 depletion significantly impaired the production of immature neutrophils in the bone marrow of septic mice.In addition,Alkbh5-deficient septic mice exhibited higher retention of mature neutrophils in the bone marrow and defective neutrophil release into the circulation,which led to fewer neutrophils at the infection site than in their wild-type littermates.During bacterial infection,ALKBH5 imprinted production-and mobilization-promoting transcriptome signatures in both mouse and human neutrophils.Mechanistically,ALKBH5 erased m^(6)A methylation on the CSF3R mRNA to increase the mRNA stability and protein expression of G-CSFR,consequently upregulating cell surface G-CSFR expression and downstream STAT3 signaling in neutrophils.The RIP-qPCR results confirmed the direct binding of ALKBH5 to the CSF3R mRNA,and the binding strength declined upon bacterial infection,accounting for the decrease in G-CSFR expression on bacteria-infected neutrophils.Considering these results collectively,we define a new role of ALKBH5 in intrinsically driving neutrophil production and mobilization through m^(6)A demethylation-dependent posttranscriptional regulation,indicating that m^(6)A RNA modification in neutrophils is a potential target for treating bacterial infections and neutropenia.

TL1A and IL-18 synergy promotes GM-CSF-dependent thymic granulopoiesis in mice

Acute systemic inflammation critically alters the function of the immune system,often promoting myelopoiesis at the expense of lymphopoiesis.In the thymus,systemic inflammation results in acute thymic atrophy and,consequently,impaired T-lymphopoiesis.The mechanism by which systemic inflammation impacts the thymus beyond suppressing T-cell development is still unclear.Here,we describe how the synergism between TL1A and IL-18 suppresses T-lymphopoiesis to promote thymic myelopoiesis.The protein levels of these two cytokines were elevated in the thymus during viral-induced thymus atrophy infection with murine cytomegalovirus(MCMV)or pneumonia virus of mice(PVM).In vivo administration of TL1A and IL-18 induced acute thymic atrophy,while thymic neutrophils expanded.Fate mapping with Ms4a3-Cre mice demonstrated that thymic neutrophils emerge from thymic granulocyte-monocyte progenitors(GMPs),while Rag1-Cre fate mapping revealed a common developmental path with lymphocytes.These effects could be modeled ex vivo using neonatal thymic organ cultures(NTOCs),where TL1A and IL-18 synergistically enhanced neutrophil production and egress.NOTCH blockade by the LY411575 inhibitor increased the number of neutrophils in the culture,indicating that NOTCH restricted steady-state thymic granulopoiesis.To promote myelopoiesis,TL1A,and IL-18 synergistically increased GM-CSF levels in the NTOC,which was mainly produced by thymic ILC1s.In support,TL1A-and IL-18-induced granulopoiesis was completely prevented in NTOCs derived from Csf2rb-/-mice and by GM-CSFR antibody blockade,revealing that GM-CSF is the essential factor driving thymic granulopoiesis.Taken together,our findings reveal that TL1A and IL-18 synergism induce acute thymus atrophy while promoting extramedullary thymic granulopoiesis in a NOTCH and GM-CSF-controlled manner.

Identification of target genes of transcription factor CEBPB in acute promyelocytic leukemia cells induced by all-trans retinoic acid

Objective:To indentify target genes of transcription factor CCA AT enhancer-binding protein P(CEBPB) in acute proinyelocytie leukemia cells induced by all-tram retinoie acid.Methods: A new strategy for high—throughput identification of direct target genes was established by combining chromatin immunoprecipitation(ChIP) with in vitro selection.Then,106 potential CKBPB binding fragments from the genome of the all-trans retinoie acid(ATRA)-treated NB4 cells were identified.Results:Of them,82 were mapped in proximity to known or previously predicted genes;7 were randomly picked up for further confirmation by ChlP-PCR and 3 genes (CALM,1TPR2 and 0RM2) were found to be specificaUy up-regulated in the ATRA-treated NB4 cells,indicating that they might lie the down-stream target genes of ATKA.Conclusions:Our results provided new insight into the mechanisms of ATRA-induced granulocytic differentiation.

Another look at the life of a neutrophil

Neutrophils are considered as the privates of the innate immune system. They are born in the bone marrow, migrate to the tissues where they kill putative intruders. After their job they are quickly removed from the battlefield by macrophages. This view of a predetermined pathway fitted nicely in their short lifespan of 5 h. However, recent studies indicated that their lifespan was in the order of several days. Recently, it became clear that neutrophils have functions beyond killing of pathogens. The reported half-life of 5 h is hardly compatible with those functions. Moreover, the organism actively invests in rescuing primed neutrophils from clearance by the body. It appears that their half-life is highly dependent on the method used to measure their life span. Here, we discuss the literature and show that neutrophils compartmentalize which could explain partially the differences reported for their lifespan. Moreover, the methodology to label neutrophils ex-vivo could have similar deteriorating effects on their lifespan as found for transfused red blood cells.