Molecular bases of dominant negative and loss of function mutations at the murine c-kit/white spotting locus: W37, Wv, W41 and W

Functional roles of interstitial cells of Cajal in the GI tract of rats

Interstitial cells of Cajal (ICC) are distributed through the gastrointestinal (GI) tract, but the functional role of these cells comes primarily from studies of mice. Whether the functions of ICC are similar in larger animals is largely speculative. We investigated whether the Kit mutation in Ws/Ws rats had consequences on ICC populations in the stomach, small intestine, and colon and whether loss of ICC resulted in functional defects similar to Kit mutations in mice. Immunohistochemical labeling with c-KIT or ANO1 antibodies revealed loss of intramuscular ICC (ICC-IM) and reduced myenteric ICC (ICC-MY) in the stomachs of Ws/Ws mutants. Disruption of ICC-MY networks but not ICC within the deep muscular plexus (ICC-DMP) was observed in the small intestine. ICC in the proximal colon was reduced, but no population was absent. ICC loss in the stomach caused loss of spontaneous transient depolarizations, reduced pacemaker activity, and reduced responses to cholinergic and nitrergic nerve stimulation. Loss of ICC-MY in the small intestine resulted in abnormal pacemaker activity, but neural responses appeared to be normal. In the proximal colon, tonic inhibition due to ongoing nitrergic neural inputs was reduced, spontaneous spike complexes were less rhythmic, and nitrergic neural responses were reduced. Apamin-sensitive inhibitory neural responses were retained throughout the GI tract. In summary, Ws/Ws rats have lesions in ICC and functional deficits similar to, but not identical to, Kit mutant mice. These larger animals with more robust GI muscles may be useful for investigations into the role of ICC in normal and abnormal GI motility.NEW & NOTEWORTHY The physiological roles of interstitial cells of Cajal (ICC) throughout the gastrointestinal (GI) tract have been derived predominantly from studies of mice. We sought to determine whether reduction in ICC in the rat, a commonly used animal for studies of GI motor functions, leads to functional deficits. Ws/Ws rats display reduced ICC leading to a disruption in pacemaker activity and neuroeffector responses. Our results provide additional evidence for the functions of ICC in the GI tract.

Understanding erythroid physiology and pathology in humanized mice: A closer look

Erythropoiesis, the process of red blood cell (RBC) development from haematopoietic stem cells, is crucial in haematology research due to its intricate regulation and implications in various pathologies such as anaemia and haemoglobinopathies. Humanized mice, created by introducing human cells or tissues into immunodeficient mice, offer a promising avenue in vivo approach. However, challenges persist in fully replicating human erythropoiesis in these models, particularly in generating mature human RBCs capable of sustained circulation. This review discusses the differences between human and mouse erythropoiesis, recent progress made using refined humanized mouse models for studying human erythropoiesis and erythropoietic disorders, the challenges that impede a faithful mimicking of human phenotypes in these mice and recommendations for future research improvements. Despite progress being made, enhancing the translational potential of humanized mouse models for human erythropoiesis research remains a priority.

The history of cytokines and growth factors development

The discovery and development of cytokines and growth factors represent transformative events in modern medicine, spanning from early observations of immune mediators to current therapeutic applications. This review chronicles the historical progression from the initial identification of permeability factors in 1926 to contemporary engineered cytokine therapeutics. Key milestones include the discovery of interferon (1957), the characterization of colony-stimulating factors, and the development of recombinant proteins in the 1980s. The field has evolved from basic understanding of immune communication to sophisticated therapeutic interventions, including targeted inhibitors and engineered cell therapies. While significant advances have been made in treating various diseases through cytokine modulation, challenges remain in managing pleiotropic effects and optimizing delivery systems. Recent innovations in bioengineering and cell therapy suggest promising directions for future therapeutic applications.

Conditional heterozygous loss of kit receptor tyrosine kinase in neural crest cell lineage is associated with midline cleft lip and bifid nose deformity

OBJECTIVES

The receptor tyrosine kinase Kit is expressed in cells derived from the trunk neural crest (NC), such as melanocytes; however, its role in cranial NC cell development is not fully understood.

METHODS

We investigated the effects of the heterozygous loss of Kit in NC cells during embryonic development by mating Kit2lox/+ mice with Wnt1-Cre mice to produce Wnt1-Cre; Kit2lox/+ embryos. In addition, Wnt1-Cre mice were mated with Rosa26R-yellow fluorescent protein (YFP) mice to visualize the tissue regions expressing Cre recombinase. Histological studies of the craniofacial regions of these mice were performed using samples from embryonic day (E) 12.5 and postnatal day (P) 1. Cellular apoptosis and proliferation were both analyzed through the immunostaining of tissue sections collected on E13.5 and E14.5 using anti-cleaved caspase 3 (CC3) to detect apoptosis and anti-Ki67 to detect proliferation. Cells from YFP-positive tissue regions of the facial areas of Wnt1-Cre; Kit+/+; Rosa26R-YFP embryos and Wnt1-Cre; Kit2lox/+; Rosa26R-YFP embryos collected on E12.5 and E15.5 were cultured and evaluated for cell proliferation.

RESULTS

Compared with control littermates, Wnt1-Cre; Kit2lox/+ embryos exhibited midline cleft lip and bifid nose deformities. Substantial early (P1) postnatal lethality was observed in Wnt1-Cre; Kit2lox/+ mice, with none surviving to 3 weeks of age. YFP-positive cells from the maxillary regions of Wnt1-Cre; Kit2lox/+; Rosa26R-YFP embryos exhibited defective cell growth and self-renewal in vitro.

CONCLUSION

Conditional heterozygous loss of Kit in Wnt1-Cre; Kit2lox/+ embryos is associated with craniofacial dysplasia and exhibit defective NC development in vitro and in vivo.

AMH regulates a mosaic population of AMHR2-positive cells in the ovarian surface epithelium

The function and homeostasis of the mammalian ovary depend on complex paracrine interactions between multiple cell types. Using primary mouse tissues and isolated cells, we showed in vitro that ovarian follicles secrete factor(s) that suppresses the growth of ovarian epithelial cells in culture. Most of the growth suppressive activity was accounted for by Anti-Mullerian Hormone/Mullerian Inhibitory Substance (AMH/MIS) secreted by granulosa cells of the follicles, as determined by immune depletion experiments. Additionally, conditioned medium from granulosa cells from wild-type control, but not AMH knockout, suppressed epithelial cell growth. Tracing of the AMH-regulated cells using AMHR2 (AMH receptor 2)-Cre:ROSA26 mutant mice indicated the presence of populations of AMHR2-positive epithelial cells on the ovarian surface and oviduct epithelia. Cells isolated from the mutant mice indicated that a subpopulation of cells marked by AMHR2-Cre:ROSA26 accounted for most cell growth and expansion in ovarian surface epithelial cells, and the AMHR2 lineage-derived cells were regulated by AMH in vitro; whereas, fewer AMHR2-Cre:ROSA26-marked cells accounted for oviduct epithelial cell outgrowth. The results reveal a paracrine pathway in maintaining follicle-epithelial homeostasis in the ovary and support a subpopulation of AMHR2 lineage marked epithelial cells as ovarian epithelial stem/progenitor cells with higher proliferative potential regulatable by follicle-secreted AMH.

Epigenetic Phenomenon of Paramutation in Plants and Animals

The phenomenon of paramutation describes the interaction between two alleles, in which one allele initiates inherited epigenetic conversion of another allele without affecting the DNA sequence. Epigenetic transformations due to paramutation are accompanied by the change in DNA and/or histone methylation patterns, affecting gene expression. Studies of paramutation in plants and animals have identified small non-coding RNAs as the main effector molecules required for the initiation of epigenetic changes in gene loci. Due to the fact that small non-coding RNAs can be transmitted across generations, the paramutation effect can be inherited and maintained in a population. In this review, we will systematically analyze examples of paramutation in different living systems described so far, highlighting common and different molecular and genetic aspects of paramutation between organisms, and considering the role of this phenomenon in evolution.

Therapeutic modulation of KIT ligand in melanocytic disorders with implications for mast cell diseases

KIT ligand and its associated receptor KIT serve as a master regulatory system for both melanocytes and mast cells controlling survival, migration, proliferation and activation. Blockade of this pathway results in cell depletion, while overactivation leads to mastocytosis or melanoma. Expression defects are associated with pigmentary and mast cell disorders. KIT ligand regulation is complex but efficient targeting of this system would be of significant benefit to those suffering from melanocytic or mast cell disorders. Herein, we review the known associations of this pathway with cutaneous diseases and the regulators of this system both in skin and in the more well-studied germ cell system. Exogenous agents modulating this pathway will also be presented. Ultimately, we will review potential therapeutic opportunities to help our patients with melanocytic and mast cell disease processes potentially including vitiligo, hair greying, melasma, urticaria, mastocytosis and melanoma.

Anaphylactic degranulation by mast cells requires the mobilization of inflammasome components

The inflammasome components NLRP3 and ASC are cytosolic proteins, which upon sensing endotoxins or danger cues, form multimeric complexes to process interleukin (IL)-1β for secretion. Here we found that antigen (Ag)-triggered degranulation of IgE-sensitized mast cells (MCs) was mediated by NLRP3 and ASC. IgE-Ag stimulated NEK7 and Pyk2 kinases in MCs to induce the deposition of NLRP3 and ASC on granules and form a distinct protein complex (granulosome) that chaperoned the granules to the cell surface. MCs deficient in NLRP3 or ASC did not form granulosomes, degranulated poorly in vitro and did not evoke systemic anaphylaxis in mice. IgE-Ag-triggered anaphylaxis was prevented by an NLRP3 inhibitor. In endotoxin-primed MCs, pro-IL-1β was rapidly packaged into granules after IgE-Ag stimulation and processed within granule remnants by proteases after degranulation, causing lethal anaphylaxis in mice. During IgE-Ag-mediated degranulation of endotoxin-primed MCs, granulosomes promoted degranulation, combined with exteriorization and processing of IL-1β, resulting in severe inflammation.

A novel Kit mutant rat enables hematopoietic stem cell engraftment without irradiation

Hematopoietic stem cell (HSC) transplantation is extensively studied in mouse models, but their limited scale presents challenges for effective engraftment and comprehensive evaluations. Rats, owing to their larger size and anatomical similarity to humans, offer a promising alternative. In this study, we establish a rat model with the KitV834M mutation, mirroring KitW41 mice often used in KIT signaling and HSC research. KitV834M rats are viable and fertile, displaying anemia and mast cell depletion similar to KitW41 mice. The colony-forming unit assay revealed that the KitV834M mutation leads to reduced proliferation and loss of or decreased pluripotency of hematopoietic stem and progenitor cells (HSPCs), resulting in diminished competitive repopulating capacity of KitV834M HSPCs in competitive transplantation assays. Importantly, KitV834M rats support donor rat-HSC engraftment without irradiation. Leveraging the larger scale of this rat model enhances our understanding of HSC biology and transplantation dynamics, potentially advancing our knowledge in this field.

Loss of Dicer in Newborn Melanocytes Leads to Premature Hair Graying and Changes in Integrin Expression

Premature hair graying occurs owing to the depletion of melanocyte stem cells in the hair follicle, which can be accelerated by stress caused by genetic or environmental factors. However, the connection between stress and melanocyte stem cell loss is not fully understood. MicroRNAs are molecules that control gene expression by regulating mRNA stability and translation and are produced by the enzyme Dicer, which is repressed under stress. In this study, using 2 mouse genetic models and human and mouse cell lines, we found that the inactivation of Dicer in melanocytes leads to misplacement of these cells within the hair follicle, resulting in a lack of melanin transfer to keratinocytes in the growing hair and the exhaustion of the melanocyte stem cell pool. We also show that miR-92b, which regulates ItgaV mRNA and protein levels, plays a role in altering melanocyte migration. Overall, our findings suggest that the Dicer-miR92b-ItgaV pathway serves as a major signaling pathway linking stress to premature hair greying.

Mast Cells in Cardiac Remodeling: Focus on the Right Ventricle

In response to various stressors, cardiac chambers undergo structural remodeling. Long-term exposure of the right ventricle (RV) to pressure or volume overload leads to its maladaptive remodeling, associated with RV failure and increased mortality. While left ventricular adverse remodeling is well understood and therapeutic options are available or emerging, RV remodeling remains underexplored, and no specific therapies are currently available. Accumulating evidence implicates the role of mast cells in RV remodeling. Mast cells produce and release numerous inflammatory mediators, growth factors and proteases that can adversely affect cardiac cells, thus contributing to cardiac remodeling. Recent experimental findings suggest that mast cells might represent a potential therapeutic target. This review examines the role of mast cells in cardiac remodeling, with a specific focus on RV remodeling, and explores the potential efficacy of therapeutic interventions targeting mast cells to mitigate adverse RV remodeling.

Distinct mast cell subpopulations within and around lymphatic vessels regulate lymph flow and progression of inflammatory-erosive arthritis in TNF-transgenic mice

Objective

Inflammatory-erosive arthritis is exacerbated by dysfunction of joint-draining popliteal lymphatic vessels (PLVs). Synovial mast cells are known to be pro-inflammatory in rheumatoid arthritis (RA). In other settings they have anti-inflammatory and tissue reparative effects. Herein, we elucidate the role of mast cells on PLV function and inflammatory-erosive arthritis in tumor necrosis factor transgenic (TNF-tg) mice that exhibit defects in PLVs commensurate with disease progression.

Methods

Whole mount immunofluorescent microscopy, toluidine blue stained histology, scanning electron microscopy, and in silico bioinformatics were performed to phenotype and quantify PLV mast cells. Ankle bone volumes were assessed by μCT, while corresponding histology quantified synovitis and osteoclasts. Near-infrared indocyanine green imaging measured lymphatic clearance as an outcome of PLV draining function. Effects of genetic MC depletion were assessed via comparison of 4.5-month-old WT, TNF-tg, MC deficient KitW-sh/W-sh (cKit-/-), and TNF-tg x cKit-/- mice. Pharmacological inhibition of mast cells was assessed by treating TNF-tg mice with placebo or cromolyn sodium (3.15mg/kg/day) for 3-weeks.

Results

PLVs are surrounded by MCT+/MCPT1+/MCPT4+ mast cells whose numbers are increased 2.8-fold in TNF-tg mice. The percentage of peri-vascular degranulating mast cells was inversely correlated with ICG clearance. A population of MCT+/MCPT1-/MCPT4- mast cells were embedded within the PLV structure. In silico single-cell RNA-seq (scRNAseq) analyses identified a population of PLV-associated mast cells (marker genes: Mcpt4, Cma1, Cpa3, Tpsb2, Kit, Fcer1a & Gata2) with enhanced TGFβ-related signaling that are phenotypically distinct from known MC subsets in the Mouse Cell Atlas. cKit-/- mice have greater lymphatic defects than TNF-tg mice with exacerbation of lymphatic dysfunction and inflammatory-erosive arthritis in TNF-tg x cKit-/- vs. TNF-Tg mice. Cromolyn sodium therapy stabilized PLV mast cells, increased TNF-induced bone loss, synovitis, and osteoclasts, and decreased ICG clearance.

Conclusions

Mast cells are required for normal lymphatic function. Genetic ablation and pharmacological inhibition of mast cells exacerbates TNF-induced inflammatory-erosive arthritis with decreased lymphatic clearance. Together, these findings support an inflammatory role of activated/degranulated peri-PLV mast cells during arthritic progression, and a homeostatic role of intra-PLV mast cells, in which loss of the latter dominantly exacerbates arthritis secondary to defects in joint-draining lymphatics, warranting investigation into specific cellular mechanisms.

Physiological and regenerative functions of sterile-α motif protein-14 in hematopoiesis

Sterile α-motif domain-14 (Samd14) protein expression increases the regenerative capacity of the erythroid system. Samd14 is transcriptionally upregulated and promotes cell signaling via the receptor tyrosine kinase Kit in a critical window of acute erythroid regeneration. We generated a hematopoietic-specific conditional Samd14 knockout mouse model (Samd14-CKO) to study the role of Samd14 in hematopoiesis. The Samd14-CKO mouse was viable and exhibited no steady-state hematopoietic phenotype. Samd14-CKO mice were hypersensitive to 5-fluorouracil, resulting in more severe anemia during recovery and impaired erythroid progenitor colony formation. Ex vivo, Samd14-CKO hematopoietic progenitors were defective in their ability to form mast cells. Samd14-CKO mast cells exhibited altered Kit/stem cell factor (SCF), IL-3/IL-3R signaling, and less granularity than Samd14-FL/FL cells. Our findings indicate that Samd14 promotes both erythroid and mast cell functions. The Samd14-CKO mouse phenotype exhibits striking similarities to the KitW/W-v mice, which carry Kit mutations resulting in reduced tyrosine kinase-dependent signaling, causing mast cell and erythroid abnormalities. The Samd14-CKO mouse model is a new tool for studying hematologic pathologies involving Kit signaling.

Humanized mouse models for inherited thrombocytopenia studies

Inherited thrombocytopenia (IT) is a group of hereditary disorders characterized by a reduced platelet count as the main clinical manifestation, and often with abnormal platelet function, which can subsequently lead to impaired hemostasis. In the past decades, humanized mouse models (HMMs), that are mice engrafted with human cells or genes, have been widely used in different research areas including immunology, oncology, and virology. With advances of the development of immunodeficient mice, the engraftment, and reconstitution of functional human platelets in HMM permit studies of occurrence and development of platelet disorders including IT and treatment strategies. This article mainly reviews the development of humanized mice models, the construction methods, research status, and problems of using humanized mice for the in vivo study of human thrombopoiesis.

Intracytoplasmic sperm injection induces transgenerational abnormalities in mice

In vitro fertilization (IVF) and intracytoplasmic sperm injection (ICSI) are 2 major assisted reproductive techniques (ARTs) used widely to treat infertility. Recently, spermatogonial transplantation emerged as a new ART to restore fertility to young patients with cancer after cancer therapy. To examine the influence of germ cell manipulation on behavior of offspring, we produced F1 offspring by a combination of two ARTs, spermatogonial transplantation and ICSI. When these animals were compared with F1 offspring produced by ICSI using fresh wild-type sperm, not only spermatogonial transplantation-ICSI mice but also ICSI-only control mice exhibited behavioral abnormalities, which persisted in the F2 generation. Furthermore, although these F1 offspring appeared normal, F2 offspring produced by IVF using F1 sperm and wild-type oocytes showed various types of congenital abnormalities, including anophthalmia, hydrocephalus, and missing limbs. Therefore, ARTs can induce morphological and functional defects in mice, some of which become evident only after germline transmission.

Chemically defined cytokine-free expansion of human haematopoietic stem cells

Haematopoietic stem cells (HSCs) are a rare cell type that reconstitute the entire blood and immune systems after transplantation and can be used as a curative cell therapy for a variety of haematological diseases1,2. However, the low number of HSCs in the body makes both biological analyses and clinical application difficult, and the limited extent to which human HSCs can be expanded ex vivo remains a substantial barrier to the wider and safer therapeutic use of HSC transplantation3. Although various reagents have been tested in attempts to stimulate the expansion of human HSCs, cytokines have long been thought to be essential for supporting HSCs ex vivo4. Here we report the establishment of a culture system that allows the long-term ex vivo expansion of human HSCs, achieved through the complete replacement of exogenous cytokines and albumin with chemical agonists and a caprolactam-based polymer. A phosphoinositide 3-kinase activator, in combination with a thrombopoietin-receptor agonist and the pyrimidoindole derivative UM171, were sufficient to stimulate the expansion of umbilical cord blood HSCs that are capable of serial engraftment in xenotransplantation assays. Ex vivo HSC expansion was further supported by split-clone transplantation assays and single-cell RNA-sequencing analysis. Our chemically defined expansion culture system will help to advance clinical HSC therapies.

Intravital Microscopy for Hematopoietic Studies

The bone marrow (BM) is home to numerous cell types arising from hematopoietic stem cells (HSCs) and nonhematopoietic mesenchymal stem cells, as well as stromal cell components. Together they form the BM microenvironment or HSC niche. HSCs critically depend on signaling from these niches to function and survive in the long term. Significant advances in imaging technologies over the past decade have permitted the study of the BM microenvironment in mice, particularly with the development of intravital microscopy (IVM), which provides a powerful method to study these cells in vivo and in real time. Still, there is a lot to be learnt about the interactions of individual HSCs with their environment - at steady state and under various stresses - and whether specific niches exist for distinct developing hematopoietic lineages. Here, we describe our protocol and techniques used to visualize transplanted HSCs in the mouse calvarium, using combined confocal and two-photon IVM.

Parental mutations influence wild-type offspring via transcriptional adaptation

Transgenerational epigenetic inheritance (TEI) is mostly discussed in the context of physiological or environmental factors. Here, we show intergenerational and transgenerational inheritance of transcriptional adaptation (TA), a process whereby mutant messenger RNA (mRNA) degradation affects gene expression, in nematodes and zebrafish. Wild-type offspring of animals heterozygous for mRNA-destabilizing alleles display increased expression of adapting genes. Notably, offspring of animals heterozygous for nontranscribing alleles do not display this response. Germline-specific mutations are sufficient to induce TA in wild-type offspring, indicating that, at least for some genes, mutations in somatic tissues are not necessary for this process. Microinjecting total RNA from germ cells of TA-displaying heterozygous zebrafish can trigger TA in wild-type embryos and in their progeny, suggesting a model whereby mutant mRNAs in the germline trigger a TA response that can be epigenetically inherited. In sum, this previously unidentified mode of TEI reveals a means by which parental mutations can modulate the offspring's transcriptome.

Xenotransplantation of Human Spermatogonia Into Various Mouse Recipient Models

Spermatogonial stem cells are the foundation of continuous spermatogenesis in adult mammals. Xenograft models have been established to define human SSCs, mostly using infertile and immune-deficient mice as the recipients for human germ cell transplantation. However, it is time-consuming to prepare such recipients using irradiation or chemotherapeutic agents, and this approach may also introduce confounding factors when residual endogenous germ cells recover in transplanted recipients. It remains to be determined whether immune-competent genetically infertile mice can be suitable recipients for xenotransplantation. In this study, we observed similar engraftment efficiencies when using spermatogonia from human biopsied testes across immune-deficient nude mice, immune-competent ICR mice, and genetically infertile Kit w/w-v mice, suggesting minimal immunological rejection from immune-competent mouse recipients upon xenotransplantation of human germ cells. More importantly, we derived EpCAM negative and TNAP positive spermatogonia-like cells (SLCs) from human pluripotent stem cells (PSCs), which highly expressed spermatogonial markers including PLZF, INTERGRINα6, TKTL1, CD90, and DRMT3. We found that upon transplantation, these SLCs proliferated and colonized at the basal membrane of seminiferous tubules in testes of both immune-deficient nude mice and Kit w/w-v mice, though complete spermatogenesis would likely require supporting human signaling factors and microenvironment. Taken together, our study functionally defined the cell identity of PSC-derived SLCs, and supported xenotransplantation using genetically infertile recipients as a convenient model for functionally evaluating spermatogonia derived from different species.

Mast Cells in the Mammalian Testis and Epididymis-Animal Models and Detection Methods

Mast cells (MCs) are an evolutionary well-conserved type of cells, mediating and modulating allergic responses in innate immunity and tissue remodeling after chronic inflammation. Among other tissues, they inhabit both the testis and epididymis. In the testis, MCs usually appear in the interstitial compartment in humans, but not in other standard experimental models, like rats and mice. MCs seem to be responsible for testicular tissue fibrosis in different causes of infertility. Although experimental animal models follow the effect on MC activation or penetration to the interstitial tissue like in humans to some extent, there is an inconsistency in the available literature regarding experimental design, animal strain, and detection methods used. This comprehensive review offers an insight into the literature on MCs in mammalian testes and epididymides. We aimed to find the most suitable model for research on MC and offer recommendations for future experimental designs. When using in vivo animal models, tunica albuginea incorporation and standard histological assessment need to be included. Domesticated boar strains kept in modified controlled conditions exhibit the highest similarity to the MC distribution in the human testis. 3D testicular models are promising but need further fine-tuning to become a valid model for MC investigation.

Potential Applications and Perspectives of Humanized Mouse Models

As medical and pharmacological technology advances, new and complex modalities of disease treatment that are more personalized and targeted are being developed. Often these modalities must be validated in the presence of critical components of the human biological system. Given the incongruencies between murine and human biology, as well as the human-tropism of certain drugs and pathogens, the selection of animal models that accurately recapitulate the intricacies of the human biological system becomes more salient for disease modeling and preclinical testing. Immunodeficient mice engrafted with functional human tissues (so-called humanized mice), which allow for the study of physiologically relevant disease mechanisms, have thus become an integral aspect of biomedical research. This review discusses the recent advancements and applications of humanized mouse models on human immune system and liver humanization in modeling human diseases, as well as how they can facilitate translational medicine.

Mast Cell–Tumor Interactions: Molecular Mechanisms of Recruitment, Intratumoral Communication and Potential Therapeutic Targets for Tumor Growth

Mast cells (MCs) are tissue-resident immune cells that are important players in diseases associated with chronic inflammation such as cancer. Since MCs can infiltrate solid tumors and promote or limit tumor growth, a possible polarization of MCs to pro-tumoral or anti-tumoral phenotypes has been proposed and remains as a challenging research field. Here, we review the recent evidence regarding the complex relationship between MCs and tumor cells. In particular, we consider: (1) the multifaceted role of MCs on tumor growth suggested by histological analysis of tumor biopsies and studies performed in MC-deficient animal models; (2) the signaling pathways triggered by tumor-derived chemotactic mediators and bioactive lipids that promote MC migration and modulate their function inside tumors; (3) the possible phenotypic changes on MCs triggered by prevalent conditions in the tumor microenvironment (TME) such as hypoxia; (4) the signaling pathways that specifically lead to the production of angiogenic factors, mainly VEGF; and (5) the possible role of MCs on tumor fibrosis and metastasis. Finally, we discuss the novel literature on the molecular mechanisms potentially related to phenotypic changes that MCs undergo into the TME and some therapeutic strategies targeting MC activation to limit tumor growth.

Dopamine signaling regulates hematopoietic stem and progenitor cell function

Hematopoietic stem and progenitor cell (HSPC) function in bone marrow (BM) is controlled by stroma-derived signals, but the identity and interplay of these signals remain incompletely understood. Here, we show that sympathetic nerve-derived dopamine directly controls HSPC behavior through D2-subfamily dopamine receptors. Blockade of dopamine synthesis as well as pharmacological or genetic inactivation of D2-subfamily dopamine receptors lead to reduced HSPC frequency, inhibition of proliferation and low BM transplantation efficiency. Conversely, treatment with a D2-type receptor agonist increases BM regeneration and transplantation efficiency. Mechanistically, dopamine controls expression of the kinase Lck, which, in turn, regulates mitogen-activated protein kinase-mediated signaling triggered by stem cell factor in HSPCs. Our work reveals critical functional roles of dopamine in HSPCs, which may open up new therapeutic options for improved BM transplantation and other conditions requiring the rapid expansion of HSPCs.

Building the Next Generation of Humanized Hemato-Lymphoid System Mice

Since the late 1980s, mice have been repopulated with human hematopoietic cells to study the fundamental biology of human hematopoiesis and immunity, as well as a broad range of human diseases in vivo. Multiple mouse recipient strains have been developed and protocols optimized to efficiently generate these “humanized” mice. Here, we review three guiding principles that have been applied to the development of the currently available models: (1) establishing tolerance of the mouse host for the human graft; (2) opening hematopoietic niches so that they can be occupied by human cells; and (3) providing necessary support for human hematopoiesis. We then discuss four remaining challenges: (1) human hematopoietic lineages that poorly develop in mice; (2) limited antigen-specific adaptive immunity; (3) absent tolerance of the human immune system for its mouse host; and (4) sub-functional interactions between human immune effectors and target mouse tissues. While major advances are still needed, the current models can already be used to answer specific, clinically-relevant questions and hopefully inform the development of new, life-saving therapies.

Sirolimus augments hematopoietic stem and progenitor cell regeneration following hematopoietic insults

The role of mammalian target of rapamycin and its suppressor sirolimus in the regulation of hematopoietic stem and progenitor cells (HSPCs) is controversial. We show here that sirolimus enhanced regeneration of HSPCs in mice exposed to sublethal total body irradiation (TBI) and other regenerative stressors. Sorted Lin^- CD150⁺ bone marrow cells from sirolimus-treated TBI mice had increased expression of c-Kit and other hematopoietic genes. HSPCs from sirolimus-treated TBI mice were functionally competent when tested by competitive engraftment in vivo. Postradiation regeneration of HSPCs in mice treated with sirolimus was accompanied by decreased γ-H2AX levels detected by flow cytometry and increased expression of DNA repair genes by quantitative polymerase chain reaction. Reduction of cell death and DNA damage post-radiation by sirolimus was associated with enhanced clearance of cellular reactive oxygen species (ROS) in HSPCs. Increased HSPC recovery with sirolimus was also observed in mice injected with hematoxic agents, busulfan and 5-fluorouracil. In contrast, sirolimus showed no effect on HSPCs in normal mice at steady state, but stimulated HSPC expansion in mice carrying the Wv mutation at the c-Kit locus. In human to mouse xenotransplantation, sirolimus enhanced engraftment of irradiated human CD34⁺ cells. In summary, our results are consistent with sirolimus' acceleration of HSPC recovery in response to hematopoietic stress, associated with reduced DNA damage and ROS. Sirolimus might have clinical application for the treatment and prevention of hematopoietic injury.

Anti-CD117 immunotherapy to eliminate hematopoietic and leukemia stem cells

Precise replacement of diseased or dysfunctional organs is the goal of regenerative medicine and has appeared to be a distant goal for a long time. In the field of hematopoietic stem cell transplantation, this goal is now becoming tangible as gene-editing technologies and novel conditioning agents are entering the clinical arena. Targeted immunologic depletion of hematopoietic stem cells (HSCs), which are at the very root of the hematopoietic system, will enable more selective and potentially more effective hematopoietic stem cell transplantation in patients with hematological diseases. In contrast to current conditioning regimes based on ionizing radiation and chemotherapy, immunologic conditioning will spare mature hematopoietic cells and cause substantially less inflammation and unspecific collateral damage to other organs. Biological agents that target the stem cell antigen CD117 are the frontrunners for this purpose and have exhibited preclinical activity in depletion of healthy HSCs. The value of anti-CD117 antibodies as conditioning agents is currently being evaluated in early clinical trials. Whereas mild, antibody-based immunologic conditioning concepts might be appropriate for benign hematological disorders in which incomplete replacement of diseased cells is sufficient, higher efficacy will be required for treatment and elimination of hematologic stem cell malignancies such as acute myeloid leukemia and myelodysplastic syndrome. Antibody-drug conjugates, bispecific T-cell engaging and activating antibodies (TEAs), or chimeric antigen receptor (CAR) T cells might offer increased efficacy compared with naked antibodies and yet higher tolerability and safety compared with current genotoxic conditioning approaches. Here, we summarize the current state regarding immunologic conditioning concepts for the treatment of HSC disorders and outline potential future developments.

Bone Marrow Endothelial Cells Take Up Blood-Borne Immune Complexes via Fcγ Receptor IIb2 in an Erythropoietin-Dependent Manner

Immune complexes (ICs) in blood are efficiently removed mainly by liver reticuloendothelial systems consisting of sinusoidal endothelial cells and Kupffer cells expressing FcγR. The bone marrow (BM) also has sinusoidal vasculatures, and sinusoidal BM endothelial cells (BMECs) bear unique function, including hematopoietic niches and traffic regulation of hematopoietic cells. In this study, we found that sinusoidal BMECs express FcγRIIb2, which is markedly increased in anemic conditions or by the administration of erythropoietin (Epo) in healthy mice. BMECs expressed Epo receptor (EpoR), and the Epo-induced increase in FcγRIIb2 expression was abolished in Epor^-/- ::HG1-Epor transgenic mice, which lack EpoR in BMECs except for BM erythroblasts, suggesting the effect was directly mediated via EpoR on BMECs. Further, although BMECs hardly captured i.v.-injected soluble ICs in healthy mice, Epo administration induced a remarkable increase in the uptake of ICs in a FcγRIIb-dependent manner. Enhancement of the IC incorporation capacity by Epo was also observed in cultured BMECs in vitro, suggesting the direct effect of Epo on BMECs. Moreover, we found that i.v.-injected ICs in Epo-treated mice were more rapidly removed from the circulation than in PBS-treated mice. These results reveal a novel function of BMECs to efficiently remove circulating blood-borne ICs in an FcγRIIb2-mediated manner.

The V654A second-site KIT mutation increases tumor oncogenesis and STAT activation in a mouse model of gastrointestinal stromal tumor

Gastrointestinal stromal tumor (GIST) is the most common human sarcoma and arises in the gastrointestinal tract. Most GISTs are caused by activating mutations in the KIT receptor tyrosine kinase, such as the exon 11 KIT V559Δ mutation. The small molecule imatinib inhibits KIT and has been a mainstay of therapy in GIST. Unfortunately, imatinib-treated patients typically relapse, most often due to clonal emergence of the resistance-associated KIT V654A mutation. To determine the biologic impact of this second-site mutation in vivo, we created a mouse model with the corresponding V558Δ;V653A Kit double mutation restricted (a) spatially to ETV1⁺ cells, which include the interstitial cells of Cajal (ICCs) from which GISTs presumably originate, and (b) temporally through tamoxifen treatment after birth. This resulted in the first in vivo model of the most common second-site mutation associated with imatinib resistance in GIST and the first in vivo demonstration that cell-autonomous expression of mutant KIT in the ICC lineage leads to GIST. GISTs driven by the V558Δ;V653A Kit double mutation were resistant to imatinib, while cabozantinib was more effective in overcoming resistance than sunitinib. Compared to control mice with a single V558Δ Kit mutation, mice with a double V558Δ; V653A Kit mutation had increased tumor oncogenesis and associated KIT-dependent STAT activation. Our findings demonstrate that the biologic consequences of a second-site mutation in an oncogenic driver may include not only a mechanism for drug resistance, but changes in tumor oncogenic potential and differential activation of signaling pathways.

A role for glia maturation factor dependent activation of mast cells and microglia in MPTP induced dopamine loss and behavioural deficits in mice

The molecular mechanism mediating degeneration of nigrostriatal dopaminergic neurons in Parkinson's disease (PD) is not yet fully understood. Previously, we have shown the contribution of glia maturation factor (GMF), a proinflammatory protein in dopaminergic neurodegeneration mediated by activation of mast cells (MCs). In this study, methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP)-induced nigrostriatal neurodegeneration and astro-glial activations were determined by western blot and immunofluorescence techniques in wild type (WT) mice, MC-deficient (MC-KO) mice and GMF-deficient (GMF-KO) mice, with or without MC reconstitution before MPTP administration. We show that GMF-KO in the MCs reduces the synergistic effects of MC and Calpain1 (calcium-activated cysteine protease enzyme)-dependent dopaminergic neuronal loss that reduces motor behavioral impairments in MPTP-treated mouse. Administration of MPTP increase in calpain-mediated proteolysis in nigral dopaminergic neurons further resulting in motor decline in mice. We found that MPTP administered WT mice exhibits oxidative stress due to significant increases in the levels of malondialdehyde, superoxide dismutase and reduction in the levels of reduced glutathione and glutathione peroxidase activity as compared with both MC-KO and GMF-KO mice. The number of TH-positive neurons in the ventral tegmental area, substantia nigra and the fibers in the striatum were significantly reduced while granulocyte macrophage colony-stimulating factor (GM-CSF), MC-Tryptase, GFAP, IBA1, Calpain1 and intracellular adhesion molecule 1 expression were significantly increased in WT mice. Similarly, tyrosine hydroxylase, dopamine transporters and vesicular monoamine transporters 2 proteins expression were significantly reduced in the SN of MPTP treated WT mice. The motor behavior as analyzed by rotarod and hang test was significantly reduced in WT mice as compared with both the MC-KO and GMF-KO mice. We conclude that GMF-dependent MC activation enhances the detrimental effect of astro-glial activation-mediated oxidative stress and neuroinflammation in the midbrain, and its inhibition may slowdown the progression of PD.

Machine learning predicts putative hematopoietic stem cells within large single-cell transcriptomics data sets

Hematopoietic stem cells (HSCs) are an essential source and reservoir for normal hematopoiesis, and their function is compromised in many blood disorders. HSC research has benefitted from the recent development of single-cell molecular profiling technologies, where single-cell RNA sequencing (scRNA-seq) in particular has rapidly become an established method to profile HSCs and related hematopoietic populations. The classic definition of HSCs relies on transplantation assays, which have been used to validate HSC function for cell populations defined by flow cytometry. Flow cytometry information for single cells, however, is not available for many new high-throughput scRNA-seq methods, thus highlighting an urgent need for the establishment of alternative ways to pinpoint the likely HSCs within large scRNA-seq data sets. To address this, we tested a range of machine learning approaches and developed a tool, hscScore, to score single-cell transcriptomes from murine bone marrow based on their similarity to gene expression profiles of validated HSCs. We evaluated hscScore across scRNA-seq data from different laboratories, which allowed us to establish a robust method that functions across different technologies. To facilitate broad adoption of hscScore by the wider hematopoiesis community, we have made the trained model and example code freely available online. In summary, our method hscScore provides fast identification of mouse bone marrow HSCs from scRNA-seq measurements and represents a broadly useful tool for analysis of single-cell gene expression data.

Efficient generation of Knock-in/Knock-out marmoset embryo via CRISPR/Cas9 gene editing

Genetically modified nonhuman primates (NHP) are useful models for biomedical research. Gene editing technologies have enabled production of target-gene knock-out (KO) NHP models. Target-gene-KO/knock-in (KI) efficiency of CRISPR/Cas9 has not been extensively investigated in marmosets. In this study, optimum conditions for target gene modification efficacies of CRISPR/mRNA and CRISPR/nuclease in marmoset embryos were examined. CRISPR/nuclease was more effective than CRISPR/mRNA in avoiding mosaic genetic alteration. Furthermore, optimal conditions to generate KI marmoset embryos were investigated using CRISPR/Cas9 and 2 different lengths (36 nt and 100 nt) each of a sense or anti-sense single-strand oligonucleotide (ssODN). KIs were observed when CRISPR/nuclease and 36 nt sense or anti-sense ssODNs were injected into embryos. All embryos exhibited mosaic mutations with KI and KO, or imprecise KI, of c-kit. Although further improvement of KI strategies is required, these results indicated that CRISPR/Cas9 may be utilized to produce KO/KI marmosets via gene editing.

Restore natural fertility of Kitw/Kitwv mouse with nonobstructive azoospermia through gene editing on SSCs mediated by CRISPR-Cas9

Background

Male infertility is a serious social problem in modern society. Nonobstructive azoospermia (NOA) caused by germ cell gene defects is an important reason for male infertility, but effective clinical treatment for this disease has not been established.

Methods

We choose Kit^w/Kit^wv mouse as a research model and try to develop a new treatment strategy and “cure” its infertility. Mutant spermatogonial stem cells (SSCs) were isolated from one single unilateral testis of a 14-day-old Kit^w/Kit^wv mouse and propagated in vitro. The C to T point mutation on Kit^wv site of these SSCs was corrected through CRISPR-Cas9-mediated homology-directed repair (HDR) in vitro. Then, the repaired SSCs were screened out, proliferated, and transplanted into the remaining testis, and complete spermatogenesis was established in the recipient testis.

Results

Healthy offsprings with wild type Kit gene or Kit^w mutation were obtained through natural mating 4 months after SSC transplantation.

Conclusion

In this study, we established an effective new treatment strategy for NOA caused by germ cell gene defects through a combination of SSC isolation, CRISPR-Cas9-mediated gene editing, and SSC transplantation, which brought hope for these NOA patients to restore their natural fertility.

Generation of Spontaneous Tone by Gastrointestinal Sphincters

An important feature of the gastrointestinal (GI) muscularis externa is its ability to generate phasic contractile activity. However, in some GI regions, a more sustained contraction, referred to as "tone," also occurs. Sphincters are muscles oriented in an annular manner that raise intraluminal pressure, thereby reducing or blocking the movement of luminal contents from one compartment to another. Spontaneous tone generation is often a feature of these muscles. Four distinct smooth muscle sphincters are present in the GI tract: the lower esophageal sphincter (LES), the pyloric sphincter (PS), the ileocecal sphincter (ICS), and the internal anal sphincter (IAS). This chapter examines how tone generation contributes to the functional behavior of these sphincters. Historically, tone was attributed to contractile activity arising directly from the properties of the smooth muscle cells. However, there is increasing evidence that interstitial cells of Cajal (ICC) play a significant role in tone generation in GI muscles. Indeed, ICC are present in each of the sphincters listed above. In this chapter, we explore various mechanisms that may contribute to tone generation in sphincters including: (1) summation of asynchronous phasic activity, (2) partial tetanus, (3) window current, and (4) myofilament sensitization. Importantly, the first two mechanisms involve tone generation through summation of phasic events. Thus, the historical distinction between "phasic" versus "tonic" smooth muscles in the GI tract requires revision. As described in this chapter, it is clear that the unique functional role of each sphincter in the GI tract is accompanied by a unique combination of contractile mechanisms.

Undifferentiated spermatogonia regulate Cyp26b1 expression through NOTCH signaling and drive germ cell differentiation

Cytochrome P450 family 26 subfamily B member 1 (CYP26B1) regulates the concentration of all-trans retinoic acid (RA) and plays a key role in germ cell differentiation by controlling local distribution of RA. The mechanisms regulating Cyp26b1 expression in postnatal Sertoli cells, the main components of the stem cell niche, are so far unknown. During gonad development, expression of Cyp26b1 is maintained by Steroidogenic Factor 1 (SF-1) and Sex-Determining Region Y Box-9 (SOX9), which ensure that RA is degraded and germ cell differentiation is blocked. Here, we show that the NOTCH target Hairy/Enhancer-of-Split Related with YRPW Motif 1 (HEY1), a transcriptional repressor, regulates germ cell differentiation via direct binding to the Cyp26b1 promoter and thus inhibits its expression in Sertoli cells. Further, using in vivo germ cell ablation, we demonstrate that undifferentiated type A spermatogonia are the cells that activate NOTCH signaling in Sertoli cells through their expression of the NOTCH ligand JAGGED-1 (JAG1) at stage VIII of the seminiferous epithelium cycle, therefore mediating germ cell differentiation by a ligand concentration-dependent process. These data therefore provide more insights into the mechanisms of germ cell differentiation after birth and potentially explain the spatiotemporal RA pulses driving the transition between undifferentiated to differentiating spermatogonia.-Parekh, P. A., Garcia, T. X., Waheeb, R., Jain, V., Gandhi, P., Meistrich, M. L., Shetty, G., Hofmann, M.-C. Undifferentiated spermatogonia regulate Cyp26b1 expression through NOTCH signaling and drive germ cell differentiation.

Nitric oxide and its role as a non-adrenergic, non-cholinergic inhibitory neurotransmitter in the gastrointestinal tract

NO is a neurotransmitter released from enteric inhibitory neurons and responsible for modulating gastrointestinal (GI) motor behaviour. Enteric neurons express nNOS (NOS1) that associates with membranes of nerve varicosities. NO released from neurons binds to soluble guanylate cyclase in post-junctional cells to generate cGMP. cGMP-dependent protein kinase type 1 (PKG1) is a major mediator but perhaps not the only pathway involved in cGMP-mediated effects in GI muscles based on gene deletion studies. NOS1+ neurons form close contacts with smooth muscle cells (SMCs), interstitial cells of Cajal (ICC) and PDGFRα+ cells, and these cells are electrically coupled (SIP syncytium). Cell-specific gene deletion studies have shown that nitrergic responses are due to mechanisms in SMCs and ICC. Controversy exists about the ion channels and other post-junctional mechanisms that mediate nitrergic responses in GI muscles. Reduced nNOS expression in enteric inhibitory motor neurons and/or reduced connectivity between nNOS+ neurons and the SIP syncytium appear to be responsible for motor defects that develop in diabetes. An overproduction of NO in some inflammatory conditions also impairs normal GI motor activity. This review summarizes recent findings regarding the role of NO as an enteric inhibitory neurotransmitter. LINKED ARTICLES: This article is part of a themed section on Nitric Oxide 20 Years from the 1998 Nobel Prize. To view the other articles in this section visit http://onlinelibrary.wiley.com/doi/10.1111/bph.v176.2/issuetoc.

A single-cell hematopoietic landscape resolves 8 lineage trajectories and defects in Kit mutant mice

Hematopoietic stem and progenitor cells (HSPCs) maintain the adult blood system, and their dysregulation causes a multitude of diseases. However, the differentiation journeys toward specific hematopoietic lineages remain ill defined, and system-wide disease interpretation remains challenging. Here, we have profiled 44 802 mouse bone marrow HSPCs using single-cell RNA sequencing to provide a comprehensive transcriptional landscape with entry points to 8 different blood lineages (lymphoid, megakaryocyte, erythroid, neutrophil, monocyte, eosinophil, mast cell, and basophil progenitors). We identified a common basophil/mast cell bone marrow progenitor and characterized its molecular profile at the single-cell level. Transcriptional profiling of 13 815 HSPCs from the c-Kit mutant (W41/W41) mouse model revealed the absence of a distinct mast cell lineage entry point, together with global shifts in cell type abundance. Proliferative defects were accompanied by reduced Myc expression. Potential compensatory processes included upregulation of the integrated stress response pathway and downregulation of proapoptotic gene expression in erythroid progenitors, thus providing a template of how large-scale single-cell transcriptomic studies can bridge between molecular phenotypes and quantitative population changes.

The Role of Mast Cells in Autoimmune Bullous Dermatoses

Skin mast cells (MCs), a resident immune cell type with broad regulatory capacity, play an important role in sensing danger signals as well as in the control of the local immune response. It is conceivable to expect that skin MCs regulate autoimmune response and are thus involved in autoimmune diseases in the skin, e.g., autoimmune bullous dermatoses (AIBD). Therefore, exploring the role of MCs in AIBD will improve our understanding of the disease pathogenesis and the search for novel therapeutic targets. Previously, in clinical studies with AIBD, particularly bullous pemphigoid, patients' samples have demonstrated that MCs are likely involved in the development of the diseases. However, using MC-deficient mice, studies with mouse models of AIBD have obtained inconclusive or even discrepant results. Therefore, it is necessary to clarify the observed discrepancies and to elucidate the role of MCs in AIBD. Here, in this review, we aim to clarify discrepant findings and finally elucidate the role of MCs in AIBD by summarizing and discussing the findings in both clinical and experimental studies.

Mast Cells: Key Contributors to Cardiac Fibrosis

Historically, increased numbers of mast cells have been associated with fibrosis in numerous cardiac pathologies, implicating mast cells in the development of cardiac fibrosis. Subsequently, several approaches have been utilised to demonstrate a causal role for mast cells in animal models of cardiac fibrosis including mast cell stabilising compounds, rodents deficient in mast cells, and inhibition of the actions of mast cell-specific proteases such as chymase and tryptase. Whilst most evidence supports a pro-fibrotic role for mast cells, there is evidence that in some settings these cells can oppose fibrosis. A major gap in our current understanding of cardiac mast cell function is identification of the stimuli that activate these cells causing them to promote a pro-fibrotic environment. This review will present the evidence linking mast cells to cardiac fibrosis, as well as discuss the major questions that remain in understanding how mast cells contribute to cardiac fibrosis.

The gp130 Cytokine Interleukin-11 Regulates Engraftment of Vav1-/- Hematopoietic Stem and Progenitor Cells in Lethally Irradiated Recipients

During bone marrow transplantation, hematopoietic stem and progenitor cells (HSPCs) respond to signals from the hematopoietic microenvironment by coordinately activating molecular pathways through Rho GTPases, including Rac. We have previously shown that deletion of Vav1, a hematopoietic-specific activator of Rac, compromises engraftment of transplanted adult HSPCs without affecting steady-state hematopoiesis in adult animals. Here, we show that Vav1^-/- fetal HSPCs can appropriately seed hematopoietic tissues during ontogeny but cannot engraft into lethally irradiated recipients. We demonstrate that the engraftment defect of Vav1^-/- HSPCs is abrogated in the absence of irradiation and demonstrate that Vav1 is critical for the response of HSPCs to the proinflammatory cytokine interleukin-11 (IL-11) that is upregulated in the marrow of irradiated recipients. Vav1^-/- HSPCs display abnormal proliferative responses to IL-11 in vitro and dysregulated activation of pathways critical to engraftment of HSPCs. The engraftment of Vav1^-/- HSPCs can be partially rescued in irradiated recipients treated with an anti-IL-11 antibody. These data suggest that HSPCs may respond to different functional demands by selective usage of the IL-11-Vav-Rac pathway, contextualizing further the recent view that HSPCs capable of reconstituting the blood system following transplantation might be distinct from those supporting hematopoiesis during homeostatic conditions. Stem Cells 2018; 36:446-457.

Regulation of blood-testis barrier assembly in vivo by germ cells

The assembly of the blood-testis barrier (BTB) during postnatal development is crucial to support meiosis. However, the role of germ cells in BTB assembly remains unclear. Herein, Kit^W/Kit^WV mice were used as a study model. These mice were infertile, failing to establish a functional BTB to support meiosis due to c-Kit mutation. Transplantation of undifferentiated spermatogonia derived from normal mice into the testis of Kit^W/Kit^WV mice triggered functional BTB assembly, displaying cyclic remodeling during the epithelial cycle. Also, transplanted germ cells were capable of inducing Leydig cell testosterone production, which could enhance the expression of integral membrane protein claudin 3 in Sertoli cells. Early spermatocytes were shown to play a vital role in directing BTB assembly by expressing claudin 3, which likely created a transient adhesion structure to mediate BTB and cytoskeleton assembly in adjacent Sertoli cells. In summary, the positive modulation of germ cells on somatic cell function provides useful information regarding somatic-germ cell interactions.-Li, X.-Y., Zhang, Y., Wang, X.-X., Jin, C., Wang, Y.-Q., Sun, T.-C., Li, J., Tang, J.-X., Batool, A., Deng, S.-L., Chen, S.-R., Cheng, C. Y., Liu, Y.-X. Regulation of blood-testis barrier assembly in vivo by germ cells.

Mast Cells Granular Contents Are Crucial for Deep Vein Thrombosis in Mice

RATIONALE

Deep vein thrombosis (DVT) and its complication pulmonary embolism have high morbidity reducing quality of life and leading to death. Cellular mechanisms of DVT initiation remain poorly understood.

OBJECTIVE

We sought to determine the role of mast cells (MCs) in DVT initiation and validate MCs as a potential target for DVT prevention.

METHODS AND RESULTS

In a mouse model, DVT was induced by partial ligation (stenosis) of the inferior vena cava. We demonstrated that 2 strains of mice deficient for MCs were completely protected from DVT. Adoptive transfer of in vitro differentiated MCs restored thrombosis. MCs were present in the venous wall, and the number of granule-containing MCs decreased with thrombosis. Pharmacological depletion of MCs granules or prevention of MC degranulation also reduced DVT. Basal plasma levels of von Willebrand factor and recruitment of platelets to the inferior vena cava wall after DVT induction were reduced in MC-deficient mice. Stenosis application increased plasma levels of soluble P-selectin in wild-type but not in MC-deficient mice. MC releasate elevated ICAM-1 (intercellular adhesion molecule-1) expression on HUVEC (human umbilical vein endothelial cells) in vitro. Topical application of compound 48/80, an MC secretagogue, or histamine, a Weibel-Palade body secretagogue from MCs, potentiated DVT in wild-type mice, and histamine restored thrombosis in MC-deficient animals.

CONCLUSIONS

MCs exacerbate DVT likely through endothelial activation and Weibel-Palade body release, which is, at least in part, mediated by histamine. Because MCs do not directly contribute to normal hemostasis, they can be considered potential targets for prevention of DVT in humans.

Influenza Infection in Mice Induces Accumulation of Lung Mast Cells through the Recruitment and Maturation of Mast Cell Progenitors

Mast cells (MCs) are powerful immune cells that mature in the peripheral tissues from bone marrow (BM)-derived mast cell progenitors (MCp). Accumulation of MCs in lung compartments where they are normally absent is thought to enhance symptoms in asthma. The enrichment of lung MCs is also observed in mice subjected to models of allergic airway inflammation. However, whether other types of lung inflammation trigger increased number of MCp, which give rise to MCs, is unknown. Here, mouse-adapted H1N1 influenza A was used as a model of respiratory virus infection. Intranasal administration of the virus induced expression of VCAM-1 on the lung vascular endothelium and an extensive increase in integrin β7^hi lung MCp. Experiments were performed to distinguish whether the influenza-induced increase in the number of lung MCp was triggered mainly by recruitment or in situ cell proliferation. A similar proportion of lung MCp from influenza-infected and PBS control mice were found to be in a proliferative state. Furthermore, BM chimeric mice were used in which the possibility of influenza-induced in situ cell proliferation of host MCp was prevented. Influenza infection in the chimeric mice induced a similar number of lung MCp as in normal mice. These experiments demonstrated that recruitment of MCp to the lung is the major mechanism behind the influenza-induced increase in lung MCp. Fifteen days post-infection, the influenza infection had elicited an immature MC population expressing intermediate levels of integrin β7, which was absent in controls. At the same time point, an increased number of toluidine blue⁺ MCs was detected in the upper central airways. When the inflammation was resolved, the MCs that accumulated in the lung upon influenza infection were gradually lost. In summary, our study reveals that influenza infection induces a transient accumulation of lung MCs through the recruitment and maturation of MCp. We speculate that temporary augmented numbers of lung MCs are a cause behind virus-induced exacerbations of MC-related lung diseases such as asthma.

ANO1 in intramuscular interstitial cells of Cajal plays a key role in the generation of slow waves and tone in the internal anal sphincter

KEY POINTS

The internal anal sphincter develops tone important for maintaining high anal pressure and continence. Controversy exists regarding the mechanisms underlying tone development. We examined the hypothesis that tone depends upon electrical slow waves (SWs) initiated in intramuscular interstitial cells of Cajal (ICC-IM) by activation of Ca²⁺ -activated Cl^- channels (ANO1, encoded by Ano1) and voltage-dependent L-type Ca²⁺ channels (Cav_L , encoded by Cacna1c). Measurement of membrane potential and contraction indicated that ANO1 and Cav_L have a central role in SW generation, phasic contractions and tone, independent of stretch. ANO1 expression was examined in wildtype and Ano1^/+egfp mice with immunohistochemical techniques. Ano1 and Cacna1c expression levels were examined by quantitative PCR in fluorescence-activated cell sorting. ICC-IM were the predominant cell type expressing ANO1 and the most likely candidate for SW generation. SWs in ICC-IM are proposed to conduct to smooth muscle where Ca²⁺ entry via Cav_L results in phasic activity that sums to produce tone.

ABSTRACT

The mechanism underlying tone generation in the internal anal sphincter (IAS) is controversial. We examined the hypothesis that tone depends upon generation of electrical slow waves (SWs) initiated in intramuscular interstitial cells of Cajal (ICC-IM) by activation of Ca²⁺ -activated Cl^- channels (encoded by Ano1) and voltage-dependent L-type Ca²⁺ channels (encoded by Cacna1c). Phasic contractions and tone in the IAS were nearly abolished by ANO1 and Cav_L antagonists. ANO1 antagonists also abolished SWs as well as transient depolarizations that persisted after addition of Cav_L antagonists. Tone development in the IAS did not require stretch of muscles, and the sensitivity of contraction to ANO1 antagonists was the same in stretched versus un-stretched muscles. ANO1 expression was examined in wildtype and Ano1^/+egfp mice with immunohistochemical techniques. Dual labelling revealed that ANO1 expression could be resolved in ICC but not smooth muscle cells (SMCs) in the IAS and rectum. Ano1, Cacna1c and Kit gene expression were the same in extracts of IAS and rectum muscles. In IAS cells isolated with fluorescence-activated cell sorting, Ano1 expression was 26.5-fold greater in ICC than in SMCs while Cacna1c expression was only 2-fold greater in SMCs than in ICC. These data support a central role for ANO1 and Cav_L in the generation of SWs and tone in the IAS. ICC-IM are the probable cellular candidate for ANO1 currents and SW generation. We propose that ANO1 and Cav_L collaborate to generate SWs in ICC-IM followed by conduction to adjacent SMCs where phasic calcium entry through Cav_L sums to produce tone.

Pim1 kinase regulates c-Kit gene translation

Background

Receptor tyrosine kinase, c-Kit (CD117) plays a pivotal role in the maintenance and expansion of hematopoietic stem/progenitor cells (HSPCs). Additionally, over-expression and/or mutational activation of c-Kit have been implicated in numerous malignant diseases including acute myeloid leukemia. However, the translational regulation of c-Kit expression remains largely unknown.

Methods and results

We demonstrated that loss of Pim1 led to specific down-regulation of c-Kit expression in HSPCs of Pim1^−/− mice and Pim1^−/−2^−/−3^−/− triple knockout (TKO) mice, and resulted in attenuated ERK and STAT3 signaling in response to stimulation with stem cell factor. Transduction of c-Kit restored the defects in colony forming capacity seen in HSPCs from Pim1^−/− and TKO mice. Pharmacologic inhibition and genetic modification studies using human megakaryoblastic leukemia cells confirmed the regulation of c-Kit expression by Pim1 kinase: i.e., Pim1-specific shRNA knockdown down-regulated the expression of c-Kit whereas overexpression of Pim1 up-regulated the expression of c-Kit. Mechanistically, inhibition or knockout of Pim1 kinase did not affect the transcription of c-Kit gene. Pim1 kinase enhanced c-Kit ³⁵S methionine labeling and increased the incorporation of c-Kit mRNAs into the polysomes and monosomes, demonstrating that Pim1 kinase regulates c-Kit expression at the translational level.

Conclusions

Our study provides the first evidence that Pim1 regulates c-Kit gene translation and has important implications in hematopoietic stem cell transplantation and cancer treatment.

Follicle Depletion Provides a Permissive Environment for Ovarian Carcinogenesis

We modeled the etiology of postmenopausal biology on ovarian cancer risk using germ cell-deficient white-spotting variant (Wv) mice, incorporating oncogenic mutations. Ovarian cancer incidence is highest in peri- and postmenopausal women, and epidemiological studies have established the impact of reproductive factors on ovarian cancer risk. Menopause as a result of ovarian follicle depletion is thought to contribute to higher cancer risk. As a consequence of follicle depletion, female Wv mice develop ovarian tubular adenomas, a benign epithelial tumor corresponding to surface epithelial invaginations and papillomatosis frequently found in postmenopausal human ovaries. Lineage tracing using MISR2-Cre indicated that the tubular adenomas that developed in Wv mice were largely derived from the MISR2 lineage, which marked only a fraction of ovarian surface and oviduct epithelial cells in wild-type tissues. Deletion of p27, either heterozygous or homozygous, was able to convert the benign tubular adenomas into more proliferative tumors. Restricted deletion of p53 in Wv/Wv mice by either intrabursal injection of adenoviral Cre or inclusion of the MISR2-Cre transgene also resulted in augmented tumor growth. This finding suggests that follicle depletion provides a permissive ovarian environment for oncogenic transformation of epithelial cells, presenting a mechanism for the increased ovarian cancer risk in postmenopausal women.

Disruption of c-Kit Signaling in Kit(W-sh/W-sh) Growing Mice Increases Bone Turnover

c-Kit tyrosine kinase receptor has been identified as a regulator of bone homeostasis. The c-Kit loss-of-function mutations in WBB6F1/J-Kit^W/W-v mice result in low bone mass. However, these mice are sterile and it is unclear whether the observed skeletal phenotype is secondary to a sex hormone deficiency. In contrast, C57BL/6J-Kit^W-sh/^W-sh (W^sh/W^sh) mice, which carry an inversion mutation affecting the transcriptional regulatory elements of the c-Kit gene, are fertile. Here, we showed that W^sh/W^sh mice exhibited osteopenia with elevated bone resorption and bone formation at 6- and 9-week-old. The c-Kit W^sh mutation increased osteoclast differentiation, the number of committed osteoprogenitors, alkaline phosphatase activity and mineralization. c-Kit was expressed in both osteoclasts and osteoblasts, and c-Kit expression was decreased in W^sh/W^shosteoclasts, but not osteoblasts, suggesting an indirect effect of c-Kit on bone formation. Furthermore, the osteoclast-derived coupling factor Wnt10b mRNA was increased in W^sh/W^sh osteoclasts. Conditioned medium from W^sh/W^sh osteoclasts had elevated Wnt10b protein levels and induced increased alkaline phosphatase activity and mineralization in osteoblast cultures. Antagonizing Wnt10b signaling with DKK1 or Wnt10b antibody inhibited these effects. Our data suggest that c-Kit negatively regulates bone turnover, and disrupted c-Kit signaling couples increased bone resorption with bone formation through osteoclast-derived Wnt 10 b.

Enhanced Reconstitution of Human Erythropoiesis and Thrombopoiesis in an Immunodeficient Mouse Model with Kit(Wv) Mutations

In human-to-mouse xenograft models, reconstitution of human hematopoiesis is usually B-lymphoid dominant. Here we show that the introduction of homozygous Kit(Wv) mutations into C57BL/6.Rag2(null)Il2rg(null) mice with NOD-Sirpa (BRGS) strongly promoted human multi-lineage reconstitution. After xenotransplantation of human CD34(+)CD38(-) cord blood cells, these newly generated C57BL/6.Rag2(null)Il2rg(null)NOD-Sirpa Kit(Wv/Wv) (BRGSK(Wv/Wv)) mice showed significantly higher levels of human cell chimerism and long-term multi-lineage reconstitution compared with BRGS mice. Strikingly, this mouse displayed a robust reconstitution of human erythropoiesis and thrombopoiesis with terminal maturation in the bone marrow. Furthermore, depletion of host macrophages by clodronate administration resulted in the presence of human erythrocytes and platelets in the circulation. Thus, attenuation of mouse KIT signaling greatly enhances the multi-lineage differentiation of human hematopoietic stem and progenitor cells (HSPCs) in mouse bone marrow, presumably by outcompeting mouse HSPCs to occupy suitable microenvironments. The BRGSK(Wv/Wv) mouse model is a useful tool to study human multi-lineage hematopoiesis.

Multiple roles of NF1 in the melanocyte lineage

NF1 is a tumour suppressor gene, germline mutations of which lead to neurofibromatosis type 1 syndrome. Patients develop benign tumours from several types of cells including neural crest-derived cells. NF1 somatic mutations also occur in 15% of sporadic melanoma, a cancer originating from melanocytes. Evidence now suggests the involvement of NF1 mutations in melanoma resistance to targeted therapies. Although NF1 is ubiquitously expressed, genetic links between NF1 and genes involved in melanocyte biology have been described, implying the lineage-specific mechanisms. In this review, we summarize and discuss the latest advances related to the roles of NF1 in melanocyte biology and in cutaneous melanoma.

Mast cells and exosomes in hyperoxia-induced neonatal lung disease

Chronic lung disease of prematurity (CLD) is a frequent sequela of premature birth and oxygen toxicity is a major associated risk factor. Impaired alveolarization, scarring, and inflammation are hallmarks of CLD. Mast cell hyperplasia is a feature of CLD but the role of mast cells in its pathogenesis is unknown. We hypothesized that mast cell hyperplasia is a consequence of neonatal hyperoxia and contributes to CLD. Additionally, mast cell products may have diagnostic and prognostic value in preterm infants predisposed to CLD. To model CLD, neonatal wild-type and mast cell-deficient mice were placed in an O2 chamber delivering hyperoxic gas mixture [inspired O2 fraction (FiO2) of 0.8] (HO) for 2 wk and then returned to room air (RA) for an additional 3 wk. Age-matched controls were kept in RA (FiO2 of 0.21). Lungs from HO mice had increased numbers of mast cells, alveolar simplification and enlargement, and increased lung compliance. Mast cell deficiency proved protective by preserving air space integrity and lung compliance. The mast cell mediators β-hexosaminidase (β-hex), histamine, and elastase increased in the bronchoalveolar lavage fluid of HO wild-type mice. Tracheal aspirate fluids (TAs) from oxygenated and mechanically ventilated preterm infants were analyzed for mast cell products. In TAs from infants with confirmed cases of CLD, β-hex was elevated over time and correlated with FiO2. Mast cell exosomes were also present in the TAs. Collectively, these data show that mast cells play a significant role in hyperoxia-induced lung injury and their products could serve as potential biomarkers in evolving CLD.