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.

Effects of EGFR-TKI on epidermal melanin unit integrity: Therapeutic implications for hypopigmented skin disorders.

Epidermal melanin unit integrity is crucial for skin homeostasis and pigmentation. Epidermal growth factor (EGF) receptor (EGFR) is a pivotal player in cell growth, wound healing, and maintaining skin homeostasis. However, its influence on skin pigmentation is relatively unexplored. This study investigates the impact and underlying mechanisms of EGFR inhibitors on skin pigmentation. We evaluated EGF and EGFR expression in various skin cells using quantitative real-time PCR, Western blot, and immunofluorescence. EGF and EGFR were predominantly expressed in epidermal keratinocytes, and treatment with the EGFR tyrosine kinase inhibitors (EGFR-TKIs) gefitinib and PD153035 significantly increased stem cell factor (SCF) and endothelin-1 (ET-1) expression in cultured keratinocytes. Enhanced melanocyte migration and proliferation were observed in co-culture, as evidenced by time-lapse live imaging and single-cell tracking assays. Furthermore, topical application of gefitinib to guinea pig dorsal skin induced increased pigmentation and demonstrated efficacy in mitigating rhododendrol-induced leukoderma. Suppression of EGF signaling indirectly enhanced skin pigmentation by upregulating SCF and ET-1 in epidermal keratinocytes. This novel mechanism highlights the pivotal role of EGF signaling in regulating skin pigmentation, and topical EGFR-TKI therapy at an appropriate dose may be a promising approach for depigmentation disorder management.

SCF/C-kit drives spermatogenesis disorder induced by abscopal effects of cranial irradiation in mice.

Cranial radiotherapy is a major treatment for leukemia and brain tumors. Our previous study found abscopal effects of cranial irradiation could cause spermatogenesis disorder in mice. However, the exact mechanisms are not yet fully understood. In the study, adult male C57BL/6 mice were administrated with 20 Gy X-ray cranial irradiation (5 Gy per day for 4 days consecutively) and sacrificed at 1, 2 and 4 weeks. Tandem Mass Tag (TMT) quantitative proteomics of testis was combined with bioinformatics analysis to identify key molecules and signal pathways related to spermatogenesis at 4 weeks after cranial irradiation. GO analysis showed that spermatogenesis was closely related to oxidative stress and inflammation. Severe oxidative stress occurred in testis, serum and brain, while serious inflammation also occurred in testis and serum. Additionally, the sex hormones related to hypothalamic-pituitary-gonadal (HPG) axis were disrupted. PI3K/Akt pathway was activated in testis, which upstream molecule SCF/C-Kit was significantly elevated. Furthermore, the proliferation and differentiation ability of spermatogonial stem cells (SSCs) were altered. These findings suggest that cranial irradiation can cause spermatogenesis disorder through brain-blood-testicular cascade oxidative stress, inflammation and the secretory dysfunction of HPG axis, and SCF/C-kit drive this process through activating PI3K/Akt pathway.

Stem cell factor and cKIT modulate endothelial glycolysis in hypoxia.

AIMS: In hypoxia, endothelial cells (ECs) proliferate, migrate, and form new vasculature in a process called angiogenesis. Recent studies have suggested that ECs rely on glycolysis to meet metabolic needs for angiogenesis in ischaemic tissues, and several studies have investigated the molecular mechanisms integrating angiogenesis and endothelial metabolism. Here, we investigated the role of stem cell factor (SCF) and its receptor, cKIT, in regulating endothelial glycolysis during hypoxia-driven angiogenesis. METHODS AND RESULTS: SCF and cKIT signalling increased the glucose uptake, lactate production, and glycolysis in human ECs under hypoxia. Mechanistically, SCF and cKIT signalling enhanced the expression of genes encoding glucose transporter 1 (GLUT1) and glycolytic enzymes via Akt- and ERK1/2-dependent increased translation of hypoxia inducible factor 1A (HIF1A). In hypoxic conditions, reduction of glycolysis and HIF-1α expression using chemical inhibitors significantly reduced the SCF-induced in vitro angiogenesis in human ECs. Compared with normal mice, mice with oxygen-induced retinopathy (OIR), characterized by ischaemia-driven pathological retinal neovascularization, displayed increased levels of SCF, cKIT, HIF-1α, GLUT1, and glycolytic enzymes in the retina. Moreover, cKIT-positive neovessels in the retina of mice with OIR showed elevated expression of GLUT1 and glycolytic enzymes. Further, blocking SCF and cKIT signalling using anti-SCF neutralizing IgG and cKIT mutant mice significantly reduced the expression of HIF-1α, GLUT1, and glycolytic enzymes and decreased the pathological neovascularization in the retina of mice with OIR. CONCLUSION: We demonstrated that SCF and cKIT signalling regulate angiogenesis by controlling endothelial glycolysis in hypoxia and elucidated the SCF/cKIT/HIF-1α axis as a novel metabolic regulation pathway during hypoxia-driven pathological angiogenesis.

Kit Ligand and Kit receptor tyrosine kinase sustain synaptic inhibition of Purkinje cells.

The cell-type-specific expression of ligand/receptor and cell-adhesion molecules is a fundamental mechanism through which neurons regulate connectivity. Here, we determine a functional relevance of the long-established mutually exclusive expression of the receptor tyrosine kinase Kit and the trans-membrane protein Kit Ligand by discrete populations of neurons in the mammalian brain. Kit is enriched in molecular layer interneurons (MLIs) of the cerebellar cortex (i.e., stellate and basket cells), while cerebellar Kit Ligand is selectively expressed by a target of their inhibition, Purkinje cells (PCs). By in vivo genetic manipulation spanning embryonic development through adulthood, we demonstrate that PC Kit Ligand and MLI Kit are required for, and capable of driving changes in, the inhibition of PCs. Collectively, these works in mice demonstrate that the Kit Ligand/Kit receptor dyad sustains mammalian central synapse function and suggest a rationale for the affiliation of Kit mutation with neurodevelopmental disorders.

PGR-KITLG signaling drives a tumor-mast cell regulatory feedback to modulate apoptosis of breast cancer cells.

The immune microenvironment constructed by tumor-infiltrating immune cells and the molecular phenotype defined by hormone receptors (HRs) have been implicated as decisive factors in the regulation of breast cancer (BC) progression. Here, we found that the infiltration of mast cells (MCs) informed impaired prognoses in HR(+) BC but predicted improved prognoses in HR(-) BC. However, molecular features of MCs in different BC remain unclear. We next discovered that HR(-) BC cells were prone to apoptosis under the stimulation of MCs, whereas HR(+) BC cells exerted anti-apoptotic effects. Mechanistically, in HR(+) BC, the KIT ligand (KITLG), a major mast cell growth factor in recruiting and activating MCs, could be transcriptionally upregulated by the progesterone receptor (PGR), and elevate the production of MC-derived granulin (GRN). GRN attenuates TNFα-induced apoptosis in BC cells by competitively binding to TNFR1. Furthermore, disruption of PGR-KITLG signaling by knocking down PGR or using the specific KITLG-cKIT inhibitor iSCK03 potently enhanced the sensitivity of HR(+) BC cells to MC-induced apoptosis and exerted anti-tumor activity. Collectively, these results demonstrate that PGR-KITLG signaling in BC cells preferentially induces GRN expression in MCs to exert anti-apoptotic effects, with potential value in developing precision medicine approaches for diagnosis and treatment.

Glycoprotein hormone subunit alpha 2 (GPHA2): A pituitary stem cell-expressed gene associated with NOTCH2 signaling.

NOTCH2 is expressed in pituitary stem cells and is necessary for stem cell maintenance, proliferation, and differentiation. However, the pathways NOTCH2 engages to affect pituitary development remain unclear. In this study, we hypothesized that glycoprotein hormone subunit A2 (GPHA2), a corneal stem cell factor and ligand for the thyroid stimulating hormone receptor (TSHR), is downstream of NOTCH2 signaling. We found Gpha2 is expressed in quiescent pituitary stem cells by RNAscope in situ hybridization and scRNA seq. In Notch2 conditional knockout pituitaries, Gpha2 mRNA is reduced compared with control littermates. We then investigated the possible functions of GPHA2. Pituitaries treated with a GPHA2 peptide do not have a change in proliferation. However, in dissociated adult pituitary cells, GPHA2 increased pCREB expression and this induction was reversed by co-treatment with a TSHR inhibitor. These data suggest GPHA2 is a NOTCH2 related stem cell factor that activates TSHR signaling, potentially impacting pituitary development.

Cancer cell plasticity, stem cell factors, and therapy resistance: how are they linked?

Cellular plasticity can occur naturally in an organism and is considered an adapting mechanism during the developmental stage. However, abnormal cellular plasticity is observed in different diseased conditions, including cancer. Cancer cell plasticity triggers the stimuli of epithelial-mesenchymal transition (EMT), abnormal epigenetic changes, expression of stem cell factors and implicated signaling pathways, etc., and helps in the maintenance of CSC phenotype. Conversely, CSC maintains the cancer cell plasticity, EMT, and epigenetic plasticity. EMT contributes to increased cell migration and greater diversity within tumors, while epigenetic changes, stem cell factors (OCT4, NANOG, and SOX2), and various signaling pathways allow cancer cells to maintain various phenotypes, giving rise to intra- and inter-tumoral heterogeneity. The intricate relationships between cancer cell plasticity and stem cell factors help the tumor cells adopt drug-tolerant states, evade senescence, and successfully acquire drug resistance with treatment dismissal. Inhibiting molecules/signaling pathways involved in promoting CSCs, cellular plasticity, EMT, and epigenetic plasticity might be helpful for successful cancer therapy management. This review discussed the role of cellular plasticity, EMT, and stem cell factors in tumor initiation, progression, reprogramming, and therapy resistance. Finally, we discussed how the intervention in this axis will help better manage cancers and improve patient survivability.

Stem cell-derived paracrine factors by modulated reactive oxygen species to enhance cancer immunotherapy.

Herein, we present an approach for manipulating paracrine factors and signaling pathways in adipose-derived stem cells (ADSCs) to achieve highly effective tumor immunotherapy. Our method involves precise control of reactive oxygen species concentration using the CD90-maleimide-pluronic F68-chlorin e6 conjugate (CPFC) to create ACPFC, which is then attached to ADSCs through the CD90 receptor-specific interaction. By regulating the irradiated laser power, ACPFC promotes signaling pathways such as cascade-3, VEGFR2, α2ß1, C3AR1, CR1-4, and C5AR1, leading to the secretion of various inflammatory cytokines such as IFN-γ, TGF-ß, and IL-6, while inhibiting AKT, ERK, NFkB, PAR1, and PAR3/4 signaling pathways to reduce the secretion of cell growth factors like TIMP-1, TIMP-2, VEGF, Ang-2, FGF-2, and HGF. When ACPFC is injected intravenously into a tumor animal model, it autonomously targets and accumulates at the tumor site, and upon laser irradiation, it generates various anti-inflammatory factors while reducing angiogenesis growth factors. The resulting antitumor response recruits CD3+CD8+ cytotoxic T cells and CD3+CD4+ helper T cells into the tumor and spleen, leading to highly effective melanoma and pancreatic tumor treatment in mice. Our technology for regulating stem cell paracrine factors holds significant promise for the treatment of various diseases.

Differentiation of human primary testicular cells in the presence of SCF using the organoid culture system.

PURPOSE: Development of organoids using human primary testicular cells has remained a challenge due to the complexity of the mammalian testicular cytoarchitecture and culture methods. In this study, we generated testicular organoids derived from human primary testicular cells. Then, we evaluated the effect of stem cell factor (SCF) on cell differentiation and apoptosis in the testicular organoid model. METHODS: The testicular cells were harvested from the three brain-dead donors. Human spermatogonial stem cells (SSCs) were characterized using immunocytochemistry (ICC), RT-PCR and flow cytometry. Testicular organoids were generated from primary testicular cells by hanging drop culture method and were cultured in three groups: control group, experimental group 1 (treated FSH and retinoic acid (RA)), and experimental group 2 (treated FSH, RA and SCF), for five weeks. We assessed the expression of SCP3 (Synaptonemal Complex Protein 3) as a meiotic gene, PRM2 (Protamine 2) as a post-meiotic marker and apoptotic genes of Bax (BCL2-Associated X Protein) and Bcl-2 (B-cell lymphoma 2), respectively by using RT-qPCR. In addition, we identified the expression of PRM2 by immunohistochemistry (IHC). RESULTS: Relative expression of SCP3, PRM2 and Bcl-2 were highest in group 2 after five weeks of culture. In contrast, BAX expression level was lower in experimental group 2 in comparison with other groups. IHC analyses indicated the highest expression of PRM2 as a postmeiotic marker in group 2 in comparison to 2D culture and control groups but not find significant differences between experimental group 1 and experimental group 2 groups. Morphological evaluations revealed that organoids are compact spherical structures and in the peripheral region composed of uncharacterized elongated fibroblast-like cells. CONCLUSION: Our findings revealed that the testicular organoid culture system promote the spermatogonial stem cell (SSC) differentiation, especially in presence of SCF. Developed organoids are capable of recapitulating many important properties of a stem cell niche.

Epigenetic histone modification by butyrate downregulates KIT and attenuates mast cell function.

Short-chain fatty acid butyrate is produced from the bacterial fermentation of indigestible fiber in the intestinal lumen, and it has been shown to attenuate lung inflammation in murine asthma models. Mast cells (MCs) are initiators of inflammatory response to allergens, and they play an important role in asthma. MC survival and proliferation is regulated by its growth factor stem cell factor (SCF), which acts through the receptor, KIT. It has previously been shown that butyrate attenuates the activation of MCs by allergen stimulation. However, how butyrate mechanistically influences SCF signalling to impact MC function remains unknown. Here, we report that butyrate treatment triggered the modification of MC histones via butyrylation and acetylation, and inhibition of histone deacetylase (HDAC) activity. Further, butyrate treatment caused downregulation of SCF receptor KIT and associated phosphorylation, leading to significant attenuation of SCF-mediated MC proliferation, and pro-inflammatory cytokine secretion. Mechanistically, butyrate inhibited MC function by suppressing KIT and downstream p38 and Erk phosphorylation, and it mediated these effects via modification of histones, acting as an HDAC inhibitor and not via its traditional GPR41 (FFAR3) or GPR43 (FFAR2) butyrate receptors. In agreement, the pharmacological inhibition of Class I HDAC (HDAC1/3) mirrored butyrate's effects, suggesting that butyrate impacts MC function by HDAC1/3 inhibition. Taken together, butyrate epigenetically modifies histones and downregulates the SCF/KIT/p38/Erk signalling axis, leading to the attenuation of MC function, validating its ability to suppress MC-mediated inflammation. Therefore, butyrate supplementations could offer a potential treatment strategy for allergy and asthma via epigenetic alterations in MCs.

Stem cell factor inhibition reduces Th2 inflammation and cellular infiltration in a mouse model of eosinophilic esophagitis.

Eosinophilic esophagitis (EoE) is a T helper (Th)2-mediated inflammatory disorder characterized endoscopically by eosinophilic infiltration leading to fibrosis of the esophagus. Stem cell factor (SCF), a multifunctional cytokine, is upregulated in several allergic diseases, including in patients with EoE. Mast cells and eosinophils express c-kit, the cell surface receptor for SCF, and have been found to play an important role in EoE. Therefore, we investigated whether blocking SCF represents a potential therapeutic approach for EoE. Esophageal inflammation was induced in mice using peanut allergen. In mice with experimental EoE, we found that SCF was upregulated in the esophageal tissue. In EoE mice injected with a polyclonal antibody specific for SCF, we observed a decrease in both mast cells and eosinophils by histological and flow cytometric analysis. Furthermore, Th2 cytokines in the esophagus were decreased in anti-SCF treated mice, as were levels of Th2 cytokines from lung-draining and esophageal lymph nodes. Serum levels of peanut-specific immunoglobulin E were reduced following treatment with anti-SCF. In Kitlf/f-Col1-Cre-ERT mice, which have SCF deleted primarily in myofibroblasts that develop in EoE, we observed similar results as the anti-SCF treated animals for inflammatory cell accumulation, cytokines, and histopathology. These results indicate that therapeutic treatments targeting SCF can reduce allergic inflammation in EoE.

Loss of endothelial membrane KIT ligand affects systemic KIT ligand levels but not bone marrow hematopoietic stem cells.

A critical regulatory role of hematopoietic stem cell (HSC) vascular niches in the bone marrow has been implicated to occur through endothelial niche cell expression of KIT ligand. However, endothelial-derived KIT ligand is expressed in both a soluble and membrane-bound form and not unique to bone marrow niches, and it is also systemically distributed through the circulatory system. Here, we confirm that upon deletion of both the soluble and membrane-bound forms of endothelial-derived KIT ligand, HSCs are reduced in mouse bone marrow. However, the deletion of endothelial-derived KIT ligand was also accompanied by reduced soluble KIT ligand levels in the blood, precluding any conclusion as to whether the reduction in HSC numbers reflects reduced endothelial expression of KIT ligand within HSC niches, elsewhere in the bone marrow, and/or systemic soluble KIT ligand produced by endothelial cells outside of the bone marrow. Notably, endothelial deletion, specifically of the membrane-bound form of KIT ligand, also reduced systemic levels of soluble KIT ligand, although with no effect on stem cell numbers, implicating an HSC regulatory role primarily of soluble rather than membrane KIT ligand expression in endothelial cells. In support of a role of systemic rather than local niche expression of soluble KIT ligand, HSCs were unaffected in KIT ligand deleted bones implanted into mice with normal systemic levels of soluble KIT ligand. Our findings highlight the need for more specific tools to unravel niche-specific roles of regulatory cues expressed in hematopoietic niche cells in the bone marrow.

Clorfl86/RHEX Is a Negative Regulator of SCF/KIT Signaling in Human Skin Mast Cells.

Mast cells (MCs) are key effector cells in allergic and inflammatory diseases, and the SCF/KIT axis regulates most aspects of the cells' biology. Using terminally differentiated skin MCs, we recently reported on proteome-wide phosphorylation changes initiated by KIT dimerization. C1orf186/RHEX was revealed as one of the proteins to become heavily phosphorylated. Its function in MCs is undefined and only some information is available for erythroblasts. Using public databases and our own data, we now report that RHEX exhibits highly restricted expression with a clear dominance in MCs. While expression is most pronounced in mature MCs, RHEX is also abundant in immature/transformed MC cell lines (HMC-1, LAD2), suggesting early expression with further increase during differentiation. Using RHEX-selective RNA interference, we reveal that RHEX unexpectedly acts as a negative regulator of SCF-supported skin MC survival. This finding is substantiated by RHEX's interference with KIT signal transduction, whereby ERK1/2 and p38 both were more strongly activated when RHEX was attenuated. Comparing RHEX and capicua (a recently identified repressor) revealed that each protein preferentially suppresses other signaling modules elicited by KIT. Induction of immediate-early genes strictly requires ERK1/2 in SCF-triggered MCs; we now demonstrate that RHEX diminution translates to this downstream event, and thereby enhances NR4A2, JUNB, and EGR1 induction. Collectively, our study reveals RHEX as a repressor of KIT signaling and function in MCs. As an abundant and selective lineage marker, RHEX may have various roles in the lineage, and the provided framework will enable future work on its involvement in other crucial processes.

Endothelial cell-derived stem cell factor promotes lipid accumulation through c-Kit-mediated increase of lipogenic enzymes in brown adipocytes.

Active thermogenesis in the brown adipose tissue (BAT) facilitating the utilization of lipids and glucose is critical for maintaining body temperature and reducing metabolic diseases, whereas inactive BAT accumulates lipids in brown adipocytes (BAs), leading to BAT whitening. Although cellular crosstalk between endothelial cells (ECs) and adipocytes is essential for the transport and utilization of fatty acid in BAs, the angiocrine roles of ECs mediating this crosstalk remain poorly understood. Using single-nucleus RNA sequencing and knock-out male mice, we demonstrate that stem cell factor (SCF) derived from ECs upregulates gene expressions and protein levels of the enzymes for de novo lipogenesis, and promotes lipid accumulation by activating c-Kit in BAs. In the early phase of lipid accumulation induced by denervation or thermoneutrality, transiently expressed c-Kit on BAs increases the protein levels of the lipogenic enzymes via PI3K and AKT signaling. EC-specific SCF deletion and BA-specific c-Kit deletion attenuate the induction of the lipogenic enzymes and suppress the enlargement of lipid droplets in BAs after denervation or thermoneutrality in male mice. These data provide insight into SCF/c-Kit signaling as a regulator that promotes lipid accumulation through the increase of lipogenic enzymes in BAT when thermogenesis is inhibited.

JNK signaling during IL-3-mediated differentiation contributes to the c-kit-potentiated allergic inflammatory capacity of mast cells.

Mast cells are leukocytes that mediate various aspects of immunity and drive allergic hypersensitivity pathologies. Mast cells differentiate from hematopoietic progenitor cells in a manner that is largely IL-3 dependent. However, molecular mechanisms, including the signaling pathways that control this process, have yet to be thoroughly investigated. Here, we examine the role of the ubiquitous and critical mitogen-activated protein kinase signaling pathway due to its position downstream of the IL-3 receptor. Hematopoietic progenitor cells were harvested from the bone marrow of C57BL/6 mice and differentiated to bone marrow-derived mast cells in the presence of IL-3 and mitogen-activated protein kinase inhibitors. Inhibition of the JNK node of the mitogen-activated protein kinase pathway induced the most comprehensive changes to the mature mast cell phenotype. Bone marrow-derived mast cells differentiated during impaired JNK signaling expressed impaired c-kit levels on the mast cell surface, first detected at week 3 of differentiation. Following 1 wk of inhibitor withdrawal and subsequent stimulation of IgE-sensitized FcεRI receptors with allergen (TNP-BSA) and c-kit receptors with stem cell factor, JNK-inhibited bone marrow-derived mast cells exhibited impediments in early-phase mediator release through degranulation (80% of control), as well as late-phase secretion of CCL1, CCL2, CCL3, TNF, and IL-6. Experiments with dual stimulation conditions (TNP-BSA + stem cell factor or TNP-BSA alone) showed that impediments in mediator secretion were found to be mechanistically linked to reduced c-kit surface levels. This study is the first to implicate JNK activity in IL-3-mediated mast cell differentiation and also identifies development as a critical and functionally determinative period.

SCF/c-Kit-activated signaling and angiogenesis require Gαi1 and Gαi3.

The stem cell factor (SCF) binds to c-Kit in endothelial cells, thus activating downstream signaling and angiogenesis. Herein, we examined the role of G protein subunit alpha inhibitory (Gαi) proteins in this process. In MEFs and HUVECs, Gαi1/3 was associated with SCF-activated c-Kit, promoting c-Kit endocytosis, and binding of key adaptor proteins, subsequently transducing downstream signaling. SCF-induced Akt-mTOR and Erk activation was robustly attenuated by Gαi1/3 silencing or knockout (KO), or due to dominant negative mutations but was strengthened substantially following ectopic overexpression of Gαi1/3. SCF-induced HUVEC proliferation, migration, and capillary tube formation were suppressed after Gαi1/3 silencing or KO, or due to dominant negative mutations. In vivo, endothelial knockdown of Gαi1/3 by intravitreous injection of endothelial-specific shRNA adeno-associated virus (AAV) potently reduced SCF-induced signaling and retinal angiogenesis in mice. Moreover, mRNA and protein expressions of SCF increased significantly in the retinal tissues of streptozotocin-induced diabetic retinopathy (DR) mice. SCF silencing, through intravitreous injection of SCF shRNA AAV, inhibited pathological retinal angiogenesis and degeneration of retinal ganglion cells in DR mice. Finally, the expression of SCF and c-Kit increased in proliferative retinal tissues of human patients with proliferative DR. Taken together, Gαi1/3 mediate SCF/c-Kit-activated signaling and angiogenesis.

Transformation of primary murine peritoneal mast cells by constitutive KIT activation is accompanied by loss of Cdkn2a/Arf expression.

Mast cells (MCs) are immune cells of the myeloid lineage distributed in tissues throughout the body. Phenotypically, they are a heterogeneous group characterized by different protease repertoires stored in secretory granules and differential presence of receptors. To adequately address aspects of MC biology either primary MCs isolated from human or mouse tissue or different human MC lines, like HMC-1.1 and -1.2, or rodent MC lines like L138.8A or RBL-2H3 are frequently used. Nevertheless, cellular systems to study MC functions are very limited. We have generated a murine connective tissue-like MC line, termed PMC-306, derived from primary peritoneal MCs (PMCs), which spontaneously transformed. We analyzed PMC-306 cells regarding MC surface receptor expression, effector functions and respective signaling pathways, and found that the cells reacted very similar to primary wildtype (WT) PMCs. In this regard, stimulation with MAS-related G-protein-coupled receptor member B2 (MRGPRB2) ligands induced respective signaling and effector functions. Furthermore, PMC-306 cells revealed significantly accelerated cell cycle progression, which however was still dependent on interleukine 3 (IL-3) and stem cell factor (SCF). Phenotypically, PMC-306 cells adopted an immature connective tissue-like MCs appearance. The observation of cellular transformation was accompanied by the loss of Cdkn2a and Arf expression, which are both described as critical cell cycle regulators. The loss of Cdkn2a and Arf expression could be mimicked in primary bone marrow-derived mast cells (BMMCs) by sustained SCF supplementation strongly arguing for an involvement of KIT activation in the regulation of Cdkn2a/Arf expression. Hence, this new cell line might be a useful tool to study further aspects of PMC function and to address tumorigenic processes associated with MC leukemia.

Lung-specific MCEMP1 functions as an adaptor for KIT to promote SCF-mediated mast cell proliferation.

Lung mast cells are important in host defense, and excessive proliferation or activation of these cells can cause chronic inflammatory disorders like asthma. Two parallel pathways induced by KIT-stem cell factor (SCF) and FcεRI-immunoglobulin E interactions are critical for the proliferation and activation of mast cells, respectively. Here, we report that mast cell-expressed membrane protein1 (MCEMP1), a lung-specific surface protein, functions as an adaptor for KIT, which promotes SCF-mediated mast cell proliferation. MCEMP1 elicits intracellular signaling through its cytoplasmic immunoreceptor tyrosine-based activation motif and forms a complex with KIT to enhance its autophosphorylation and activation. Consequently, MCEMP1 deficiency impairs SCF-induced peritoneal mast cell proliferation in vitro and lung mast cell expansion in vivo. Mcemp1-deficient mice exhibit reduced airway inflammation and lung impairment in chronic asthma mouse models. This study shows lung-specific MCEMP1 as an adaptor for KIT to facilitate SCF-mediated mast cell proliferation.

Sertoli cells are the source of stem cell factor for spermatogenesis.

Several cell types have been proposed to create the required microenvironment for spermatogenesis. However, expression patterns of the key growth factors produced by these somatic cells have not been systematically studied and no such factor has been conditionally deleted from its primary source(s), raising the question of which cell type(s) are the physiological sources of these growth factors. Here, using single-cell RNA sequencing and a series of fluorescent reporter mice, we found that stem cell factor (Scf), one of the essential growth factors for spermatogenesis, was broadly expressed in testicular stromal cells, including Sertoli, endothelial, Leydig, smooth muscle and Tcf21-CreER+ stromal cells. Both undifferentiated and differentiating spermatogonia were associated with Scf-expressing Sertoli cells in the seminiferous tubule. Conditional deletion of Scf from Sertoli cells, but not any other Scf-expressing cells, blocked the differentiation of spermatogonia, leading to complete male infertility. Conditional overexpression of Scf in Sertoli cells, but not endothelial cells, significantly increased spermatogenesis. Our data reveal the importance of anatomical localization for Sertoli cells in regulating spermatogenesis and that SCF produced specifically by Sertoli cells is essential for spermatogenesis.