Myeloid and dendritic cells enhance therapeutics-induced cytokine release syndrome features in humanized BRGSF-HIS preclinical model.

Objectives: Despite their efficacy, some immunotherapies have been shown to induce immune-related adverse events, including the potentially life-threatening cytokine release syndrome (CRS), calling for reliable and translational preclinical models to predict potential safety issues and investigate their rescue. Here, we tested the reliability of humanized BRGSF mice for the assessment of therapeutics-induced CRS features in preclinical settings. Methods: BRGSF mice reconstituted with human umbilical cord blood CD34+ cells (BRGSF-CBC) were injected with anti-CD3 antibody (OKT3), anti-CD3/CD19 bispecific T-cell engager Blinatumomab, or VISTA-targeting antibody. Human myeloid and dendritic cells' contribution was investigated in hFlt3L-boosted BRGSF-CBC mice. OKT3 treatment was also tested in human PBMC-reconstituted BRGSF mice (BRGSF-PBMC). Cytokine release, immune cell distribution, and clinical signs were followed. Results: OKT3 injection in BRGSF-CBC mice induced hallmark features of CRS, specifically inflammatory cytokines release, modifications of immune cell distribution and activation, body weight loss, and temperature drop. hFlt3L-boosted BRGSF-CBC mice displayed enhanced CRS features, revealing a significant role of myeloid and dendritic cells in this process. Clinical CRS-managing treatment Infliximab efficiently attenuated OKT3-induced toxicity. Comparison of OKT3 treatment's effect on BRGSF-CBC and BRGSF-PBMC mice showed broadened CRS features in BRGSF-CBC mice. CRS-associated features were also observed in hFlt3L-boosted BRGSF-CBC mice upon treatment with other T-cell or myeloid-targeting compounds. Conclusions: These data show that BRGSF-CBC mice represent a relevant model for the preclinical assessment of CRS and CRS-managing therapies. They also confirm a significant role of myeloid and dendritic cells in CRS development and exhibit the versatility of this model for therapeutics-induced safety assessment.

Two birds with one stone: human SIRPα nanobodies for functional modulation and in vivo imaging of myeloid cells.

Signal-regulatory protein α (SIRPα) expressed by myeloid cells is of particular interest for therapeutic strategies targeting the interaction between SIRPα and the "don't eat me" ligand CD47 and as a marker to monitor macrophage infiltration into tumor lesions. To address both approaches, we developed a set of novel human SIRPα (hSIRPα)-specific nanobodies (Nbs). We identified high-affinity Nbs targeting the hSIRPα/hCD47 interface, thereby enhancing antibody-dependent cellular phagocytosis. For non-invasive in vivo imaging, we chose S36 Nb as a non-modulating binder. By quantitative positron emission tomography in novel hSIRPα/hCD47 knock-in mice, we demonstrated the applicability of 64Cu-hSIRPα-S36 Nb to visualize tumor infiltration of myeloid cells. We envision that the hSIRPα-Nbs presented in this study have potential as versatile theranostic probes, including novel myeloid-specific checkpoint inhibitors for combinatorial treatment approaches and for in vivo stratification and monitoring of individual responses during cancer immunotherapies.

Corticosterone inhibits GAS6 to govern hair follicle stem-cell quiescence.

Chronic, sustained exposure to stressors can profoundly affect tissue homeostasis, although the mechanisms by which these changes occur are largely unknown. Here we report that the stress hormone corticosterone-which is derived from the adrenal gland and is the rodent equivalent of cortisol in humans-regulates hair follicle stem cell (HFSC) quiescence and hair growth in mice. In the absence of systemic corticosterone, HFSCs enter substantially more rounds of the regeneration cycle throughout life. Conversely, under chronic stress, increased levels of corticosterone prolong HFSC quiescence and maintain hair follicles in an extended resting phase. Mechanistically, corticosterone acts on the dermal papillae to suppress the expression of Gas6, a gene that encodes the secreted factor growth arrest specific 6. Restoring Gas6 expression overcomes the stress-induced inhibition of HFSC activation and hair growth. Our work identifies corticosterone as a systemic inhibitor of HFSC activity through its effect on the niche, and demonstrates that the removal of such inhibition drives HFSCs into frequent regeneration cycles, with no observable defects in the long-term.

ERα-36 regulates progesterone receptor activity in breast cancer.

BACKGROUND: Alterations in estrogen and progesterone signaling, via their respective receptors, estrogen receptor alpha (ERα) and progesterone receptor (PR), respectively, are largely involved in the development of breast cancer (BC). The recent identification of ERα-36, a splice variant of ERα, has uncovered a new facet of this pathology. Although ERα-36 expression is associated with poor prognosis, metastasis development, and resistance to treatment, its predictive value has so far not been associated with a BC subtype and its mechanisms of action remain understudied. METHODS: To study ERα-36 expression in BC specimens, we performed immunochemical experiments. Next, the role of ERα-36 in progesterone signaling was investigated by generating KO clones using the CRISPR/CAS9 technology. PR signaling was also assessed by proximity ligation assay, Western blotting, RT-QPCR, and ChIP experiments. Finally, proliferation assays were performed with the IncuCyte technology and migration experiments using scratch assays. RESULTS: Here, we demonstrate that ERα-36 expression at the plasma membrane is correlated with a reduced disease-free survival in a cohort of 160 BC patients, particularly in PR-positive tumors, suggesting a crosstalk between ERα-36 and PR. Indeed, we show that ERα-36 interacts constitutively with PR in the nucleus of tumor cells. Moreover, it regulates PR expression and phosphorylation on key residues, impacting the biological effects of progesterone. CONCLUSIONS: ERα-36 is thus a regulator of PR signaling, interfering with its transcriptional activity and progesterone-induced anti-proliferative effects as well as migratory capacity. Hence, ERα-36 may constitute a new prognostic marker as well as a potential target in PR-positive BC.

Dermal Adipocyte Lipolysis and Myofibroblast Conversion Are Required for Efficient Skin Repair.

Mature adipocytes store fatty acids and are a common component of tissue stroma. Adipocyte function in regulating bone marrow, skin, muscle, and mammary gland biology is emerging, but the role of adipocyte-derived lipids in tissue homeostasis and repair is poorly understood. Here, we identify an essential role for adipocyte lipolysis in regulating inflammation and repair after injury in skin. Genetic mouse studies revealed that dermal adipocytes are necessary to initiate inflammation after injury and promote subsequent repair. We find through histological, ultrastructural, lipidomic, and genetic experiments in mice that adipocytes adjacent to skin injury initiate lipid release necessary for macrophage inflammation. Tamoxifen-inducible genetic lineage tracing of mature adipocytes and single-cell RNA sequencing revealed that dermal adipocytes alter their fate and generate ECM-producing myofibroblasts within wounds. Thus, adipocytes regulate multiple aspects of repair and may be therapeutic for inflammatory diseases and defective wound healing associated with aging and diabetes.

Unexpected genomic rearrangements at targeted loci associated with CRISPR/Cas9-mediated knock-in.

The CRISPR/Cas9 gene editing tool enables accessible and efficient modifications which (re)ignited molecular research in certain species. However, targeted integration of large DNA fragments using CRISPR/Cas9 can still be challenging in numerous models. To systematically compare CRISPR/Cas9's efficiency to classical homologous recombination (cHR) for insertion of large DNA fragments, we thoroughly performed and analyzed 221 experiments targeting 128 loci in mouse ES cells. Although both technologies proved efficient, CRISPR/Cas9 yielded significantly more positive clones as detected by overlapping PCRs. It also induced unexpected rearrangements around the targeted site, ultimately rendering CRISPR/Cas9 less efficient than cHR for the production of fully validated clones. These data show that CRISPR/Cas9-mediated recombination can induce complex long-range modifications at targeted loci, thus emphasizing the need for thorough characterization of any genetically modified material obtained through CRISPR-mediated gene editing before further functional studies or therapeutic use.

Signaling Networks among Stem Cell Precursors, Transit-Amplifying Progenitors, and their Niche in Developing Hair Follicles.

The hair follicle (HF) is a complex miniorgan that serves as an ideal model system to study stem cell (SC) interactions with the niche during growth and regeneration. Dermal papilla (DP) cells are required for SC activation during the adult hair cycle, but signal exchange between niche and SC precursors/transit-amplifying cell (TAC) progenitors that regulates HF morphogenetic growth is largely unknown. Here we use six transgenic reporters to isolate 14 major skin and HF cell populations. With next-generation RNA sequencing, we characterize their transcriptomes and define unique molecular signatures. SC precursors, TACs, and the DP niche express a plethora of ligands and receptors. Signaling interaction network analysis reveals a bird's-eye view of pathways implicated in epithelial-mesenchymal interactions. Using a systematic tissue-wide approach, this work provides a comprehensive platform, linked to an interactive online database, to identify and further explore the SC/TAC/niche crosstalk regulating HF growth.

An Integrated Transcriptome Atlas of Embryonic Hair Follicle Progenitors, Their Niche, and the Developing Skin.

Defining the unique molecular features of progenitors and their niche requires a genome-wide, whole-tissue approach with cellular resolution. Here, we co-isolate embryonic hair follicle (HF) placode and dermal condensate cells, precursors of adult HF stem cells and the dermal papilla/sheath niche, along with lineage-related keratinocytes and fibroblasts, Schwann cells, melanocytes, and a population inclusive of all remaining skin cells. With next-generation RNA sequencing, we define gene expression patterns in the context of the entire embryonic skin, and through transcriptome cross-comparisons, we uncover hundreds of enriched genes in cell-type-specific signatures. Axon guidance signaling and many other pathway genes are enriched in multiple signatures, implicating these factors in driving the large-scale cellular rearrangements necessary for HF formation. Finally, we share all data in an interactive, searchable companion website. Our study provides an overarching view of signaling within the entire embryonic skin and captures a molecular snapshot of HF progenitors and their niche.

PDGF signalling in the dermis and in dermal condensates is dispensable for hair follicle induction and formation.

Embryonic hair follicle (HF) induction and formation is dependent on signalling crosstalk between the dermis and specialized dermal condensates on the mesenchymal side and epidermal cells and incipient placodes on the epithelial side, but the precise nature and succession of signals remain unclear. Platelet-derived growth factor (PDGF) signalling is involved in the development of several organs and the maintenance of adult tissues, including HF regeneration in the hair cycle. As both PDGF receptors, PDGFRα and PDGFRß, are expressed in embryonic dermis and dermal condensates, we explored in this study the role of PDGF signalling in HF induction and formation in the developing skin mesenchyme. We conditionally ablated both PDGF receptors with Tbx18(Cre) in early dermal condensates before follicle formation, and with Prx1-Cre broadly in the ventral dermis prior to HF induction. In both PDGFR double mutants, HF induction and formation ensued normally, and the pattern of HF formation and HF numbers were unaffected. These data demonstrate that mesenchymal PDGF signalling, either in the specialized niche or broadly in the dermis, is dispensable for HF induction and formation.

Cxcr4 is transiently expressed in both epithelial and mesenchymal compartments of nascent hair follicles but is not required for follicle formation.

Hair follicle (HF) morphogenesis relies on the coordinated exchange of signals between mesenchymal and epithelial compartments of embryonic skin. Chemokine receptor Cxcr4 expression was recently identified in dermal condensates (DCs) of nascent HFs, but its role in promoting HF morphogenesis remains unknown. Our analyses confirmed Cxcr4 expression in condensate cells, and additionally revealed transient Cxcr4 expression in incipient epithelial hair placodes. Placodal Cxcr4 appeared prior to detection in DCs, representing a switch of expression between epithelial and mesenchymal compartments. To explore the functional role of this receptor in both compartments for early HF formation, we conditionally ablated Cxcr4 with condensate-targeting Tbx18(cre) knock-in and epidermis-targeting Krt14-cre transgenic mice. Conditional knockouts for both crosses were viable throughout embryogenesis and into adulthood. Morphological and biochemical marker analyses revealed comparable numbers of HFs forming in knockout embryos compared to wild-type littermate controls in both cases, suggesting that neither dermal nor epithelial Cxcr4 expression is required for early HF morphogenesis. We conclude that Cxcr4 expression and chemokine signaling through this receptor in embryonic mouse skin is dispensable for HF formation.

Adult stem cell niches: cellular and molecular components.

As stem cells (SCs) in adult organs continue to be identified and characterized, it becomes clear that their survival, quiescence, and activation depend on specific signals in their microenvironment, or niche. Although adult SCs of diverse tissues differ by their developmental origin, cycling activity, and regenerative capacity, there appear to be conserved similarities regarding the cellular and molecular components of the SC niche. Interestingly, many organs house both slow-cycling and fast-cycling SC populations, which rely on the coexistence of quiescent and inductive niches for proper regulation. In this review we present a general definition of adult SC niches in the most studied mammalian systems. We further focus on dissecting their cellular organization and on highlighting recently identified key molecular regulators. Finally, we detail the potential involvement of the SC niche in tissue degeneration, with a particular emphasis on aging and cancer.

Wnt/ß-catenin signaling in dermal condensates is required for hair follicle formation.

Broad dermal Wnt signaling is required for patterned induction of hair follicle placodes and subsequent Wnt signaling in placode stem cells is essential for induction of dermal condensates, cell clusters of precursors for the hair follicle dermal papilla (DP). Progression of hair follicle formation then requires coordinated signal exchange between dermal condensates and placode stem cells. However, it remains unknown whether continued Wnt signaling in DP precursor cells plays a role in this process, largely due to the long-standing inability to specifically target dermal condensates for gene ablation. Here we use the Tbx18(Cre) knockin mouse line to ablate the Wnt-responsive transcription factor ß-catenin specifically in these cells at E14.5 during the first wave of guard hair follicle formation. In the absence of ß-catenin, canonical Wnt signaling is effectively abolished in these cells. Sox2(+) dermal condensates initiate normally; however by E16.5 guard hair follicle numbers are strongly reduced and by E18.5 most whiskers and guard hair follicles are absent, suggesting that active Wnt signaling in dermal condensates is important for hair follicle formation to proceed after induction. To explore the molecular mechanisms by which Wnt signaling in dermal condensates regulates hair follicle formation, we analyze genome-wide the gene expression changes in embryonic ß-catenin null DP precursor cells. We find altered expression of several signaling pathway genes, including Fgfs and Activin, both previously implicated in hair follicle formation. In summary, these data reveal a functional role of Wnt signaling in DP precursors for embryonic hair follicle formation and identify Fgf and Activin signaling as potential effectors of Wnt signaling-regulated events.

Enpp2/Autotaxin in dermal papilla precursors is dispensable for hair follicle morphogenesis.

Systematic ablation of previously identified dermal papilla (DP) signature genes in embryonic DP precursors will reveal their functional roles during hair follicle morphogenesis. In this study, we validate Enpp2/Autotaxin as one of the highest expressed signature genes in postnatal DP, and demonstrate specific expression of this lysophosphatidic acid (LPA)-generating enzyme in embryonic dermal condensates. We further identify dermal and epidermal expression of several LPA receptors, suggesting that LPA signaling could contribute to follicle morphogenesis in both mesenchymal and epithelial compartments. We then use the recently characterized Cre-expressing Tbx18 knock-in line to conditionally ablate Enpp2 in embryonic DP precursors. Despite efficient gene knockout in embryonic day 14.5 (E14.5) dermal condensates, morphogenesis proceeds regularly with normal numbers, lengths, and sizes of all hair follicle types, suggesting that Enpp2 is not required for hair follicle formation. To interrogate DP signature gene expression, we finally isolate control and Enpp2-null DP precursors and identify the expression and upregulation of LIPH, an alternative LPA-producing enzyme, suggesting that this gene could functionally compensate for the absence of Enpp2. We conclude that future coablation of both LPA-producing enzymes or of several LPA receptors may reveal the functional role of LPA signaling during hair follicle morphogenesis.

Brief report: musashi1-eGFP mice, a new tool for differential isolation of the intestinal stem cell populations.

The intestinal epithelium self-renews rapidly and continuously throughout life, due to the presence of crypt stem cells. Two pools of these cells have been identified in the small intestine, which differ in position ("+4" or the bottom of the crypts), expression of specific markers (Bmi1/mTert or Lgr5/Ascl2), and cell cycle characteristics. Interestingly, the RNA-binding protein Musashi1 is expressed in both populations and therefore a potential marker for both stem cell types. In order to locate, isolate, and study Musashi1-expressing cells within the intestinal epithelium, we generated transgenic mice expressing GFP fluorescent protein under the control of a 7-kb Msi1 promoter. The expression pattern of GFP in the intestinal crypts of both small and large intestines completely overlapped that of Musashi1, validating our model. By using fluorescence-activated cell sorting, cellular, and molecular analyses, we showed that GFP-positive Msi1-expressing cells are divided into two major pools corresponding to the Lgr5- and mTert-expressing stem cells. Interestingly, monitoring the cell cycle activity of the two sorted populations reveals that they are both actively cycling, although differences in cell cycle length were confirmed. Altogether, our new reporter mouse model based upon Musashi1 expression is a useful tool to isolate and study stem cells of the intestinal epithelium. Moreover, these mice uniquely enable the concomitant study of two pools of intestinal stem cells within the same animal model.

Tbx18 targets dermal condensates for labeling, isolation, and gene ablation during embryonic hair follicle formation.

How cell fate decisions of stem and progenitor cells are regulated by their microenvironment or niche is a central question in stem cell and regenerative biology. Although functional analysis of hair follicle epithelial stem cells by gene targeting is well established, the molecular and genetic characterization of the dermal counterpart during embryonic morphogenesis has been lacking because of the absence of cell type-specific drivers. Here, we report that T-box transcription factor Tbx18 specifically marks dermal papilla (DP) precursor cells during embryonic hair follicle morphogenesis. With Tbx18(LacZ), Tbx18(H2BGFP), and Tbx18(Cre) knock-in mouse models, we demonstrate LacZ and H2BGFP (nuclear green fluorescent protein) expression and Cre activity in dermal condensates of nascent first-wave hair follicles at E14.5. As Tbx18 expression becomes more widespread throughout the dermis at later developmental stages, we use tamoxifen-inducible Cre-expressing mice, Tbx18(MerCreMer), to exclusively target DP precursor cells and their progeny. Finally, we ablate Tbx18 in full knockout mice, but find no perturbations in hair follicle formation, suggesting that Tbx18 is dispensable for normal DP function. In summary, our study establishes Tbx18 as a genetic driver to target for the first time embryonic DP precursors for labeling, isolation, and gene ablation that will greatly enhance investigations into their molecular functions during hair follicle morphogenesis.

Sox2 in the dermal papilla niche controls hair growth by fine-tuning BMP signaling in differentiating hair shaft progenitors.

How dermal papilla (DP) niche cells regulate hair follicle progenitors to control hair growth remains unclear. Using Tbx18(Cre) to target embryonic DP precursors, we ablate the transcription factor Sox2 early and efficiently, resulting in diminished hair shaft outgrowth. We find that DP niche expression of Sox2 controls the migration speed of differentiating hair shaft progenitors. Transcriptional profiling of Sox2 null DPs reveals increased Bmp6 and decreased BMP inhibitor Sostdc1, a direct Sox2 transcriptional target. Subsequently, we identify upregulated BMP signaling in knockout hair shaft progenitors and demonstrate that Bmp6 inhibits cell migration, an effect that can be attenuated by Sostdc1. A shorter and Sox2-negative hair type lacks Sostdc1 in the DP and shows reduced migration and increased BMP activity of hair shaft progenitors. Collectively, our data identify Sox2 as a key regulator of hair growth that controls progenitor migration by fine-tuning BMP-mediated mesenchymal-epithelial crosstalk.

p38 Inhibition ameliorates skin and skull abnormalities in Fgfr2 Beare-Stevenson mice.

Beare-Stevenson cutis gyrata syndrome (BSS) is a human genetic disorder characterized by skin and skull abnormalities. BSS is caused by mutations in the FGF receptor 2 (FGFR2), but the molecular mechanisms that induce skin and skull abnormalities are unclear. We developed a mouse model of BSS harboring a FGFR2 Y394C mutation and identified p38 MAPK as an important signaling pathway mediating these abnormalities. Fgfr2+/Y394C mice exhibited epidermal hyperplasia and premature closure of cranial sutures (craniosynostosis) due to abnormal cell proliferation and differentiation. We found ligand-independent phosphorylation of FGFR2 and activation of p38 signaling in mutant skin and calvarial tissues. Treating Fgfr2+/Y394C mice with a p38 kinase inhibitor attenuated skin abnormalities by reversing cell proliferation and differentiation to near normal levels. This study reveals the pleiotropic effects of the FGFR2 Y394C mutation evidenced by cutis gyrata, acanthosis nigricans, and craniosynostosis and provides a useful model for investigating the molecular mechanisms of skin and skull development. The demonstration of a pathogenic role for p38 activation may lead to the development of therapeutic strategies for BSS and related conditions, such as acanthosis nigricans or craniosynostosis.

The overexpression of the putative gut stem cell marker Musashi-1 induces tumorigenesis through Wnt and Notch activation.

The RNA-binding protein Musashi-1 (Msi1) has been proposed as a marker of intestinal epithelial stem cells. These cells are responsible for the continuous renewal of the intestinal epithelium. Although the function of Msi1 has been studied in several organs from different species and in mammalian cell lines, its function and molecular regulation in mouse intestinal epithelium progenitor cells are still undefined. We describe here that, in these cells, the expression of Msi1 is regulated by the canonical Wnt pathway, through a mechanism involving a functional Tcf/Lef binding site on its promoter. An in vitro study in intestinal epithelium primary cultures showed that Msi1 overexpression promotes progenitor proliferation and activates Wnt and Notch pathways. Moreover, Msi1-overexpressing cells exhibit tumorigenic properties in xenograft experiments. These data point to a positive feedback loop between Msi1 and Wnt in intestinal epithelial progenitors. They also suggest that Msi1 has oncogenic properties in these cells, probably through induction of both the Wnt and Notch pathways.

The frizzled-related sFRP2 gene is a target of thyroid hormone receptor alpha1 and activates beta-catenin signaling in mouse intestine.

The thyroid hormone receptor TRalpha1 regulates intestinal development and homeostasis by controlling epithelial proliferation in the crypts. This involves positive control of the Wnt/beta-catenin pathway. To further investigate the effect of thyroid hormone-TRalpha1 signaling on the intestinal epithelium proliferating compartment, we performed a comparative transcription profile analysis on laser microdissected crypt cells recovered from wild type animals with normal or perturbed hormonal status, as well as from TR knock-out mice. Statistical analysis and an in silico approach allowed us to identify 179 differentially regulated genes and to group them into organized functional networks. We focused on the "cell cycle/cell proliferation" network and, in particular, on the Frizzled-related protein sFRP2, whose expression was greatly increased in response to thyroid hormones. In vitro and in vivo analyses showed that the expression of sFRP2 is directly regulated by TRalpha1 and that it activates beta-catenin signaling via Frizzled receptors. Indeed, sFRP2 stabilizes beta-catenin, activates its target genes, and enhances cell proliferation. In conclusion, these new data, in conjunction with our previous results, indicate a complex interplay between TRalpha1 and components of the Wnt/beta-catenin pathway. Moreover, we describe in this study a novel mechanism of action of sFRP2, responsible for the activation of beta-catenin signaling.

The thyroid hormone receptor-alpha (TRalpha) gene encoding TRalpha1 controls deoxyribonucleic acid damage-induced tissue repair.

The thyroid hormone (TH) controls, via its nuclear receptor, TH receptor-alpha1 (TRalpha1), intestinal crypt cell proliferation in the mouse. In order to understand whether this receptor also plays a role in intestinal regeneration after DNA damage, we applied a protocol of gamma-ray irradiation and monitored cell proliferation and apoptosis at several time points. In wild-type mice, the dose of 8 Gy induced cell cycle arrest and apoptosis in intestinal crypts a few hours after irradiation. This phenomenon reverted 48 h after irradiation. TRalpha(0/0) mutant mice displayed a constant low level of proliferating cells and a high apoptosis rate during the period of study. At the molecular level, in TRalpha(0/0) animals we observed a delay in the p53 phosphorylation induced by DNA damage. In our search for the expression of the protein kinases responsible for p53 phosphorylation upon irradiation, we have focused on DNA-dependent protein kinase catalytic subunit (DNA-PKcs). The number of cells expressing DNA-PKcs in crypts remained high 48 h after irradiation, specifically in TRalpha mutants. Altogether, in TRalpha(0/0) animals the rate of apoptosis in crypt cells remained high, apparently due to an elevated number of cells still presenting DNA damage. In conclusion, the TRalpha gene plays a role in crypt cell homeostasis by regulating the rate of cell renewal and apoptosis induced by DNA damage.