Primary infection enhances neutrophil-mediated host defense by educating HSPCs.

Hematopoietic stem and progenitor cells (HSPCs) can give rise to all kinds of immune cells including neutrophils. Neutrophils are the first line of defense in the innate immune system with a short lifespan, due to which it is well-accepted that neutrophils have no immune memory. However, recent reports showed that the changes in HSPCs induced by primary stimulation could last a long time, which contributes to enhancing response to subsequent infection by generating more monocytes or macrophages equipped with stronger anti-bacterial function. Here, we used the reinfection mice model to reveal that primary infection could improve neutrophil-mediated host defense by training neutrophil progenitors in mammals, providing a new idea to enhance neutrophil number and improve neutrophil functions, which is pretty pivotal for patients with compromised or disordered immunity.

HDAC6 deacetylates IDH1 to promote the homeostasis of hematopoietic stem and progenitor cells.

Hematopoietic stem and progenitor cells (HSPCs) are cells mainly present in the bone marrow and capable of forming mature blood cells. However, the epigenetic mechanisms governing the homeostasis of HSPCs remain elusive. Here, we demonstrate an important role for histone deacetylase 6 (HDAC6) in regulating this process. Our data show that the percentage of HSPCs in Hdac6 knockout mice is lower than in wild-type mice due to decreased HSPC proliferation. HDAC6 interacts with isocitrate dehydrogenase 1 (IDH1) and deacetylates IDH1 at lysine 233. The deacetylation of IDH1 inhibits its catalytic activity and thereby decreases the 5-hydroxymethylcytosine level of ten-eleven translocation 2 (TET2) target genes, changing gene expression patterns to promote the proliferation of HSPCs. These findings uncover a role for HDAC6 and IDH1 in regulating the homeostasis of HSPCs and may have implications for the treatment of hematological diseases.

Heat-inactivated Escherichia coli promotes hematopoietic regeneration after irradiation with IL-1ß.

BACKGROUND AIMS: Hematopoietic stem and progenitor cells (HSPCs) are known to produce short-lived mature blood cells via proliferation and differentiation in a process that depends partially on regulatory cytokines from the bone marrow (BM) microenvironment. Delayed BM recovery after tremendous damage to the hematopoietic system can lead to neutropenia, anemia, thrombopenia and even death. However, efficiently promote BM recovery is still a big problem to be solved. Here, the authors aim to use heat-inactivated Escherichia coli (HIEC) to enhance BM recovery and further to find out the potential mechanism. METHODS: X-rad was used to establish HIEC/IL-1ß-induced radioprotection model. Single-cell RNA sequencing, RT-PCR, and western blotting were performed to detect the expression of IL-1R1 on HSPCs. Flow cytometry and automated hematology analyzer were used to analyze the percentage and absolute number of different populations of hematopoietic cells. The effects of IL-1ß on HSPCs were studied using in vivo and in vitro experiments. RESULTS: HIEC/IL-1ß pre-treatment can significantly increase the survival rate of lethally irradiated mice, and these mice showed better hematopoietic regeneration compared with control group. IL-1R was expressed on HSPCs, and IL-1ß could directly function on HSPCs to promote the proliferation and differentiation of HSPCs, and inhibit the apoptosis of HSPCs. CONCLUSIONS: HIEC pre-treatment can rescue lethally irradiated mice by promoting hematopoietic recovery via IL-1ß/IL-1R1 signaling, which can promote the proliferation of HSPCs by enhancing the cell cycle and attenuating the apoptosis of HSPCs.

Inflammasome-mediated GSDMD activation facilitates escape of Candida albicans from macrophages.

Candida albicans is the most common cause of fungal sepsis. Inhibition of inflammasome activity confers resistance to polymicrobial and LPS-induced sepsis; however, inflammasome signaling appears to protect against C. albicans infection, so inflammasome inhibitors are not clinically useful for candidiasis. Here we show disruption of GSDMD, a known inflammasome target and key pyroptotic cell death mediator, paradoxically alleviates candidiasis, improving outcomes and survival of Candida-infected mice. Mechanistically, C. albicans hijacked the canonical inflammasome-GSDMD axis-mediated pyroptosis to promote their escape from macrophages, deploying hyphae and candidalysin, a pore-forming toxin expressed by hyphae. GSDMD inhibition alleviated candidiasis by preventing C. albicans escape from macrophages while maintaining inflammasome-dependent but GSDMD-independent IL-1ß production for anti-fungal host defenses. This study demonstrates key functions for GSDMD in Candida's escape from host immunity in vitro and in vivo and suggests that GSDMD may be a potential therapeutic target in C. albicans-induced sepsis.

Single-cell transcriptome profiling reveals neutrophil heterogeneity in homeostasis and infection.

The full neutrophil heterogeneity and differentiation landscape remains incompletely characterized. Here, we profiled >25,000 differentiating and mature mouse neutrophils using single-cell RNA sequencing to provide a comprehensive transcriptional landscape of neutrophil maturation, function and fate decision in their steady state and during bacterial infection. Eight neutrophil populations were defined by distinct molecular signatures. The three mature peripheral blood neutrophil subsets arise from distinct maturing bone marrow neutrophil subsets. Driven by both known and uncharacterized transcription factors, neutrophils gradually acquire microbicidal capability as they traverse the transcriptional landscape, representing an evolved mechanism for fine-tuned regulation of an effective but balanced neutrophil response. Bacterial infection reprograms the genetic architecture of neutrophil populations, alters dynamic transitions between subpopulations and primes neutrophils for augmented functionality without affecting overall heterogeneity. In summary, these data establish a reference model and general framework for studying neutrophil-related disease mechanisms, biomarkers and therapeutic targets at single-cell resolution.

Bacteria-Induced Acute Inflammation Does Not Reduce the Long-Term Reconstitution Capacity of Bone Marrow Hematopoietic Stem Cells.

Pathogen-initiated chronic inflammation or autoimmune diseases accelerate proliferation and promote differentiation of hematopoietic stem cells (HSCs) but simultaneously reduce reconstitution capacity. Nevertheless, the effect of acute infection and inflammation on functional HSCs is still largely unknown. Here we found that acute infection elicited by heat-inactivated Escherichia coli (HIEC) expanded bone marrow lineage-negative (Lin)- stem-cell antigen 1 (Sca-1)+cKit+ (LSK) cell population, leading to reduced frequency of functional HSCs in LSK population. However, the total number of BM phenotypic HSCs (Flk2-CD48-CD150+ LSK cells) was not altered in HIEC-challenged mice. Additionally, the reconstitution capacity of the total BM between infected and uninfected mice was similar by both the competitive repopulation assay and measurement of functional HSCs by limiting dilution. Thus, occasionally occurring acute inflammation, which is critical for host defenses, is unlikely to affect HSC self-renewal and maintenance of long-term reconstitution capacity. During acute bacterial infection and inflammation, the hematopoietic system can replenish hematopoietic cells consumed in the innate inflammatory response by accelerating hematopoietic stem and progenitor cell proliferation, but preserving functional HSCs in the BM.

The role of CXCR2 in acute inflammatory responses and its antagonists as anti-inflammatory therapeutics.

PURPOSE OF REVIEW: CXCR2 is key stimulant of immune cell migration and recruitment, especially of neutrophils. Alleviating excessive neutrophil accumulation and infiltration could prevent prolonged tissue damage in inflammatory disorders. This review focuses on recent advances in our understanding of the role of CXCR2 in regulating neutrophil migration and the use of CXCR2 antagonists for therapeutic benefit in inflammatory disorders. RECENT FINDINGS: Recent studies have provided new insights into how CXCR2 signaling regulates hematopoietic cell mobilization and function in both health and disease. We also summarize several CXCR2 regulatory mechanisms during infection and inflammation such as via Wip1, T-bet, P-selectin glycoprotein ligand-1, granulocyte-colony-stimulating factor, and microbiome. Moreover, we provide an update of studies investigating CXCR2 blockade in the laboratory and in clinical trials. SUMMARY: Neutrophil homeostasis, migration, and recruitment must be precisely regulated. The CXCR2 signaling pathway is a potential target for modifying neutrophil dynamics in inflammatory disorders. We discuss the recent clinical use of CXCR2 antagonists for controlling inflammation.

Proteinase 3 Limits the Number of Hematopoietic Stem and Progenitor Cells in Murine Bone Marrow.

Hematopoietic stem and progenitor cells (HSPCs) undergo self-renewal and differentiation to guarantee a constant supply of short-lived blood cells. Both intrinsic and extrinsic factors determine HSPC fate, but the underlying mechanisms remain elusive. Here, we report that Proteinase 3 (PR3), a serine protease mainly confined to granulocytes, is also expressed in HSPCs. PR3 deficiency intrinsically suppressed cleavage and activation of caspase-3, leading to expansion of the bone marrow (BM) HSPC population due to decreased apoptosis. PR3-deficient HSPCs outcompete the long-term reconstitution potential of wild-type counterparts. Collectively, our results establish PR3 as a physiological regulator of HSPC numbers. PR3 inhibition is a potential therapeutic target to accelerate and increase the efficiency of BM reconstitution during transplantation.

The treatment of Terrien marginal degeneration using lamellar keratoplasty with dried corneosclera.

PURPOSE: To treat the Terrien marginal degeneration using lamellar keratoplasty with dried corneosclera and evaluate the clinical effect of this operation. METHODS: The study included 78 cases with Terrien marginal degeneration who underwent the lamellar keratoplasty with dried corneosclera. Among them, 48 cases in experiment I group and 30 cases in experiment II group underwent lamellar keratoplasty with glycerin-preserved corneosclera and anhydrous calcium chloride-storeded corneosclera respectively. All the patients were followed-up from 6 months to 10 years. The control group consisted of 38 cases with Terrien marginal degeneration electively undergoing lamellar keratoplasty with fresh corneosclera simultaneously. RESULTS: The area of the corneal thinning was mended and the eyeball was saved. The corneal astigmatism of the patients was corrected obviously. The patient's vision was improved significantly. No recurrence and rejection were observed after the operation. There is no significant difference between the experiment group (experiment I group or experiment II group) and control group. (P > 0.05), despite longer duration of postoperative corneal edema in experiment group. CONCLUSIONS: The lamellar keratoplasty with dried corneosclera for treatment of Terrien marginal degeneration is a safe and effective operation. It is an alternative to lamellar keratoplasty with fresh corneosclera for treatment of Terrien marginal degeneration. It is suitable to be popularized in the local hospital of our country.