Identification of the Transgene Integration Site and Host Genome Changes in MRP8-Cre/ires-EGFP Transgenic Mice by Targeted Locus Amplification

Transgene Mapping in Animals: What to Choose?

The phenomenal progress in biotechnology and genomics is both inspiring and overwhelming-a classic curse of choice, particularly when it comes to selecting methods for mapping transgene DNA integration sites. Transgene localization remains a crucial task for the validation of transgenic mouse or other animal models generated by pronuclear microinjection. Due to the inherently random nature of DNA integration, reliable characterization of the insertion site is essential. Over the years, a vast number of mapping methods have been developed, and new approaches continue to emerge, making the choice of the most suitable technique increasingly complex. Factors such as cost, required reagents, and the nature of the generated data require careful consideration. In this review, we provide a structured overview of current transgene mapping techniques, which we have broadly classified into three categories: classic PCR-based methods (such as inverse PCR and TAIL-PCR), next-generation sequencing with target enrichment, and long-read sequencing platforms (PacBio and Oxford Nanopore). To aid in decision-making, we include a comparative table summarizing approximate costs for the methods. While each approach has its own advantages and limitations, we highlight our top four recommended methods, which we believe offer the best balance of cost-effectiveness, reliability, and simplicity for identifying transgene integration sites.

The need for Cre-loci controls in conditional mouse experiments: Mrp8-cre transgene predisposes mice to antibody-induced arthritis

The Cre/loxP system is extensively utilized to pinpoint gene functions in specific cell types or developmental stages, typically without major disturbance to the host's genome. However, we found that the random insertion of the Mrp8-cre transgene significantly promotes the host's innate immune response. This effect is characterized by elevated susceptibility to cartilage antibody-induced arthritis, likely due to interference with genes near the insertion site. These findings underscore the potential biological disturbances caused by random transgene integration, and the necessity for stringent control strategies to avoid biased interpretations when using Cre-conditional strains.

GM-CSF-mediated epithelial-immune cell cross-talk orchestrates pulmonary immunity to Aspergillus fumigatus

Aspergillus fumigatus causes life-threatening mold pneumonia in immunocompromised patients, particularly in those with quantitative or qualitative defects in neutrophils. Whereas innate immune cell cross-talk licenses neutrophil antifungal activity in the lung, the role of epithelial cells in this process is unknown. Here, we find that surfactant protein C (SPC)-expressing lung epithelial cells integrate infection-induced interleukin-1 and type III interferon signaling to produce granulocyte-macrophage colony-stimulating factor (GM-CSF) preferentially at local sites of fungal infection and neutrophil influx. Using in vivo models that distinguish the role of GM-CSF during acute infection from its homeostatic function in alveolar macrophage survival and surfactant catabolism, we demonstrate that epithelial-derived GM-CSF increases the accumulation and fungicidal activity of GM-CSF-responsive neutrophils, which is essential for host survival. Our findings establish SPC+ epithelial cells as a central player in regulating the quality and strength of neutrophil-dependent immunity against inhaled mold pathogens.

Comprehensive analysis of myeloid reporter mice

Macrophages are a pivotal cell type within the synovial lining and sub-lining of the joint, playing a crucial role in maintaining homeostasis of synovium. Although fate-mapping techniques have been employed to differentiate synovial macrophages from other synovial myeloid cells, no comprehensive study has yet been conducted within the mouse synovial macrophage compartment. In this study, we present, for the first time, lineage tracing results from 18 myeloid-specific fate-mapping models in mouse peripheral blood (PB) and synovial tissue. The identification of synovial macrophages and monocyte-lineage cells through flow cytometry was further validated using cellular indexing of transcriptomes and epitopes by sequencing (CITE-seq) datasets. These findings provide a valuable methodological tool for researchers to select appropriate models for studying the function of synovial myeloid cells and serve as a reference for investigations in other tissue types.

Periodontitis-related myocardial fibrosis by expansion of collagen-producing SiglecF+ neutrophils

BACKGROUNDS AND AIMS

Patients with periodontitis (PD) are prone to developing myocardial infarction (MI), yet the prognosis and mechanisms remain unclear. Given the presumed close association of neutrophils with both conditions, this study aims to elucidate the roles of neutrophils in mediating the interaction between PD and MI.

METHODS

Three prospective cohorts and PD + MI mouse model were investigated to assess the effects of PD on MI prognosis. Single-cell-RNA sequencing and genome-wide association study were employed to identify the neutrophil subtype involved. To characterize the function of SiglecF+ neutrophils, bone marrow transplantation, Edu-pulse chasing, lineage tracing, and collagen contraction assay were utilized. Adoptive neutrophil transfer, conditional Siglecf knockout and lipid nanoparticles facilitating local SiglecF+ neutrophils depletion was harnessed to explore the roles of SiglecF+ neutrophils in MI repair.

RESULTS

Persisting but not short-term PD upset MI prognosis (cardiac fibrosis and function) in human and mice. Bone marrow neutrophils of PD were intrinsically skewed toward longer-lived SiglecF+ neutrophil differentiation, a subtype that was converted by GMCSF or TGFβ in PPARγ-dependent manner. SiglecF+ neutrophils were expanded in infarcted PD heart where they deposit collagen and activate fibroblasts to instigate excessive fibrosis. SiglecF+ neutrophil depletion was efficacious for mitigating fibrosis.

CONCLUSIONS

This study demonstrated that long-lasting PD-aggravated MI prognosis by expanding scar-associated SiglecF+ neutrophils into the heart and highlighted the clinical relevance of oral health examination for treating MI in a holistic fashion.

Neutrophil-specific Shp1 loss results in lethal pulmonary hemorrhage in mouse models of acute lung injury

Acute respiratory distress syndrome (ARDS) is associated with significant morbidity and mortality, and neutrophils are critical to its pathogenesis. Neutrophil activation is closely regulated by inhibitory tyrosine phosphatases including Src homology region 2 domain-containing phosphatase-1 (Shp1). Here, we report that loss of neutrophil Shp1 in mice produced hyperinflammation and lethal pulmonary hemorrhage in sterile inflammation and pathogen-induced models of acute lung injury (ALI) through a Syk kinase-dependent mechanism. We observed large intravascular neutrophil clusters, perivascular inflammation, and excessive neutrophil extracellular traps in neutrophil-specific Shp1-KO mice, suggesting an underlying mechanism for the observed pulmonary hemorrhage. Targeted immunomodulation through the administration of a Shp1 activator (SC43) reduced agonist-induced reactive oxygen species in vitro and ameliorated ALI-induced alveolar neutrophilia and NETs in vivo. We propose that the pharmacologic activation of Shp1 has the potential to fine tune neutrophil hyperinflammation that is central to the pathogenesis of ARDS.

LIFR regulates cholesterol-driven bidirectional hepatocyte-neutrophil cross-talk to promote liver regeneration

Liver regeneration is under metabolic and immune regulation. Despite increasing recognition of the involvement of neutrophils in regeneration, it is unclear how the liver signals to the bone marrow to release neutrophils after injury and how reparative neutrophils signal to hepatocytes to reenter the cell cycle. Here we report that loss of the liver tumour suppressor Lifr in mouse hepatocytes impairs, whereas overexpression of leukaemia inhibitory factor receptor (LIFR) promotes liver repair and regeneration after partial hepatectomy or toxic injury. In response to physical or chemical damage to the liver, LIFR from hepatocytes promotes the secretion of cholesterol and CXCL1 in a STAT3-dependent manner, leading to the efflux of bone marrow neutrophils to the circulation and damaged liver. Cholesterol, via its receptor ERRα, stimulates neutrophils to secrete hepatocyte growth factor to accelerate hepatocyte proliferation. Altogether, our findings reveal a LIFR-STAT3-CXCL1-CXCR2 axis and a LIFR-STAT3-cholesterol-ERRα-hepatocyte growth factor axis that form bidirectional hepatocyte-neutrophil cross-talk to repair and regenerate the liver.

Neutrophil Granulopoiesis Optimized Through Ex Vivo Expansion of Hematopoietic Progenitors in Engineered 3D Gelatin Methacrylate Hydrogels

Neutrophils are the first line of defense of the innate immune system. In response to methicillin-resistant Staphylococcus aureus infection in the skin, hematopoietic stem, and progenitor cells (HSPCs) traffic to wounds and undergo extramedullary granulopoiesis, producing neutrophils necessary to resolve the infection. This prompted the engineering of a gelatin methacrylate (GelMA) hydrogel that encapsulates HSPCs within a matrix amenable to subcutaneous delivery. The authors study the influence of hydrogel mechanical properties to produce an artificial niche for granulocyte-monocyte progenitors (GMPs) to efficiently expand into functional neutrophils that can populate infected tissue. Lin-cKIT+ HSPCs, harvested from fluorescent neutrophil reporter mice, are encapsulated in GelMA hydrogels of varying polymer concentration and UV-crosslinked to produce HSPC-laden gels of specific stiffness and mesh sizes. Softer 5% GelMA gels yield the most viable progenitors and effective cell-matrix interactions. Compared to suspension culture, 5% GelMA results in a twofold expansion of mature neutrophils that retain antimicrobial functions including degranulation, phagocytosis, and ROS production. When implanted dermally in C57BL/6J mice, luciferase-expressing neutrophils expanded in GelMA hydrogels are visualized at the site of implantation for over 5 days. They demonstrate the potential of GelMA hydrogels for delivering HSPCs directly to the site of skin infection to promote local granulopoiesis.

Dusp6 deficiency attenuates neutrophil-mediated cardiac damage in the acute inflammatory phase of myocardial infarction

Dual-specificity phosphatase 6 (DUSP6) serves a specific and conserved function on the dephosphorylation of extracellular signal-regulated kinase 1/2 (ERK1/2). We previously identified Dusp6 as a regenerative repressor during zebrafish heart regeneration, therefore we propose to investigate the role of this repressor in mammalian cardiac repair. Utilizing a rat strain harboring Dusp6 nonsense mutation, rat neutrophil-cardiomyocyte co-culture, bone marrow transplanted rats and neutrophil-specific Dusp6 knockout mice, we find that Dusp6 deficiency improves cardiac outcomes by predominantly attenuating neutrophil-mediated myocardial damage in acute inflammatory phase after myocardial infarction. Mechanistically, Dusp6 is transcriptionally activated by p38-C/EBPβ signaling and acts as an effector for maintaining p-p38 activity by down-regulating pERK and p38-targeting phosphatases DUSP1/DUSP16. Our findings provide robust animal models and novel insights for neutrophil-mediated cardiac damage and demonstrate the potential of DUSP6 as a therapeutic target for post-MI cardiac remodeling and other relevant inflammatory diseases.