Edwige Roy

Abrogation of ICOS/ICOS ligand costimulation in NOD mice results in autoimmune deviation toward the neuromuscular system

NOD mice spontaneously develop insulin‐dependent diabetes around 10–40 wk of age. Numerous immune gene variants contribute to the autoimmune process. However, genes that direct the autoimmune response toward β cells remain ill defined. In this study, we provide evidence that the Icos and Icosl genes contribute to the diabetes process. Protection from diabetes in ICOS−/− and ICOSL−/− NOD mice was unexpectedly associated with the development of an autoimmune disorder of the neuro‐muscular system, characterized by myositis, sensory ganglionitis and, to a reduced extent, inflammatory infiltrates in the CNS. This syndrome was reproduced upon adoptive transfer of CD4+ and CD8+ T cells from diseased donors to naïve NOD.scid recipients. Our data further show that protection from diabetes results from defective activation of autoimmune diabetogenic effector T cells in ICOS−/− NOD mice, whereas acceleration of diabetes in BDC2.5 ICOS−/− NOD mice is induced by a dominant defect in Treg. Taken together, our findings indicate that costimulation signals play a key role in regulating immune tolerance in peripheral tissues and that the ICOS/ICOSL costimulatory pathway influences the balance between Treg and diabetogenic effector T cells.

Distant Mesenchymal Progenitors Contribute to Skin Wound Healing and Produce Collagen: Evidence from a Murine Fetal Microchimerism Model

The contribution of distant and/or bone marrow-derived endogenous mesenchymal stem cells (MSC) to skin wounds is controversial. Bone marrow transplantation experiments employed to address this have been largely confounded by radiation-resistant host-derived MSC populations. Gestationally-acquired fetal MSC are known to engraft in maternal bone marrow in all pregnancies and persist for decades. These fetal cells home to damaged maternal tissues, mirroring endogenous stem cell behavior. We used fetal microchimerism as a tool to investigate the natural homing and engraftment of distant MSC to skin wounds. Post-partum wild-type mothers that had delivered transgenic pups expressing luciferase under the collagen type I-promoter were wounded. In vivo bioluminescence imaging (BLI) was then used to track recruitment of fetal cells expressing this mesenchymal marker over 14 days of healing. Fetal cells were detected in 9/43 animals using BLI (Fisher exact p = 0.01 versus 1/43 controls). These collagen type I-expressing fetal cells were specifically recruited to maternal wounds in the initial phases of healing, peaking on day 1 (n = 43, p<0.01). This was confirmed by detection of Y-chromosome+ve fetal cells that displayed fibroblast-like morphology. Histological analyses of day 7 wounds revealed vimentin-expressing fetal cells in dermal tissue. Our results demonstrate the participation of distant mesenchymal cells in skin wounds. These data imply that endogenous MSC populations are likely recruited from bone marrow to wounds to participate in healing.

Nck adaptors are positive regulators of the size and sensitivity of the T-cell repertoire

The size and sensitivity of the T-cell repertoire governs the effectiveness of immune responses against invading pathogens. Both are modulated by T-cell receptor (TCR) activity through molecular mechanisms, which remain unclear. Here, we provide genetic evidence that the SH2/SH3 domain containing proteins Nck lower the threshold of T-cell responsiveness. The hallmarks of Nck deletion were T-cell lymphopenia and hyporeactivity to TCR-mediated stimulation. In the absence of the Nck adaptors, peripheral T cells expressing a TCR with low avidity for self-antigens were strongly reduced, whereas an overall impairment of T-cell activation by weak antigenic stimulation was observed. Mechanistically, Nck deletion resulted in a significant decrease in calcium mobilization and ERK phosphorylation upon TCR engagement. Taken together, our findings unveil a crucial role for the Nck adaptors in shaping the T-cell repertoire to ensure maximal antigenic coverage and optimal T cell excitability.

Transgenic Flash Mice for In Vivo Quantitative Monitoring of Canonical Wnt Signaling to Track Hair Follicle Cycle Dynamics

Hair follicles (HFs) upon development enter a lifelong cycle of growth, regression, and resting. These phases have been extensively studied at the cellular and molecular levels for individual HFs. However, HFs group into domains with coordinated cycling strongly influenced by their environment. These macroscopic hair domains have been difficult to study and can be influenced by physiological or pathological conditions, such as pregnancy or skin wounds. To robustly address this issue, we generated a mouse model for quantitative monitoring of β-catenin activity reflecting HF cycle dynamics macroscopically by using live bioluminescence imaging. These mice allowed live tracking of HF cycles and development, and highlighted hair regenerative patterns known to occur through macro-environmental cues, including initiation events, propagating anagen and border stability, and allowed refinement of a mechanistic mathematical model that integrates epidermal cell population dynamics into an excitable reaction-diffusion model. HF cycling could be studied in situations of pregnancy, wound healing, hair plucking, as well as in response to cyclosporine or Wnt3a stimulation. In conclusion, we developed a model for analysis of HF cycling at the macroscopic level that will allow refined analysis of hair cycle kinetics as well as its propagation dynamics.

Concise review: understanding clonal dynamics in homeostasis and injury through multicolor lineage tracing

Lineage tracing is an essential tool to study stem cell fate. Although traditional lineage tracing techniques have considerably advanced our understanding of stem cell behavior, they pose significant limitations for identification and longitudinal tracking of the progeny of individual stem cells, to compare their behaviors. This is of importance given the well‐established heterogeneity among stem cells both in terms of potentialities and proliferative capacities. The recent development of multicolor genetic reporters addressable to specific cell populations largely overcomes these issues. These new “rainbow” technologies provide increased resolution in clonal identification and offer the possibility to study the relative distribution, contacts, tiled arrangement, and competitive interactions among cells or groups of cells of the same type. Stem Cells 2014;32:3046–3054

Bimodal behaviour of interfollicular epidermal progenitors regulated by hair follicle position and cycling

Interfollicular epidermal (IFE) homeostasis is a major physiological process allowing maintenance of the skin barrier function. Despite progress in our understanding of stem cell populations in different hair follicle compartments, cellular mechanisms of IFE maintenance, in particular, whether a hierarchy of progenitors exists within this compartment, have remained controversial. We here used multicolour lineage tracing with Brainbow transgenic labels activated in the epidermis to track individual keratinocyte clones. Two modes of clonal progression could be observed in the adult murine dorsal skin. Clones attached to hair follicles showed rapid increase in size during the growth phase of the hair cycle. On the other hand, clones distant from hair follicles were slow cycling, but could be mobilized by a proliferative stimulus. Reinforced by mathematical modelling, these data support a model where progenitor cycling characteristics are differentially regulated in areas surrounding or away from growing hair follicles. Thus, while IFE progenitors follow a non‐hierarchical mode of development, spatiotemporal control by their environment can change their potentialities, with far‐reaching implications for epidermal homeostasis, wound repair and cancer development.

Biphasic recruitment of microchimeric fetal mesenchymal cells in fibrosis following acute kidney injury

Fetal microchimeric cells (FMCs) enter the maternal circulation and persist in tissue for decades. They have capacity to home to injured maternal tissue and differentiate along that tissues lineage. This raises the question of the origin(s) of cells transferred to the mother during pregnancy. FMCs with a mesenchymal phenotype have been documented in several studies, which makes mesenchymal stem cells an attractive explanation for their broad plasticity. Here we assessed the recruitment and mesenchymal lineage contribution of FMCs in response to acute kidney fibrosis induced by aristolochic acid injection. Serial in vivo bioluminescence imaging revealed a biphasic recruitment of active collagen-producing FMCs during the repair process of injured kidney in post-partum wild-type mothers that had delivered transgenic pups expressing luciferase under the collagen type I-promoter. The presence of FMCs long-term post injury (day 60) was associated with profibrotic molecules (TGF-β/CTGF), serum urea levels, and collagen deposition. Immunostaining confirmed FMCs at short term (day 15) using post-partum wild-type mothers that had delivered green fluorescent protein-positive pups and suggested a mainly hematopoietic phenotype. We conclude that there is biphasic recruitment to, and activity of, FMCs at the injury site. Moreover, we identified five types of FMC, implicating them all in the reparative process at different stages of induced renal interstitial fibrosis.

A multicolour unbiased model to determine the Epidermal cell fate: localization and study of the epidermal stem cell niche

S | Epidermal Structure and Function

Genetic variation in the mitogen-activated protein kinase/extracellular signal-regulated kinase pathway affects contact hypersensitivity responses

Using a genetic resource that enables rapid mapping of genes for complex traits, we demonstrate dramatic diversity between murine strains in response to immune challenge. We identified several candidate genes that point to the MAPK/ERK pathway as a key modulator of this process.

Past stem cells and finally in transit: SLC1A3 instructs skin niche coupling

During postnatal growth of the skin and homeostatic hair cycling, different proliferative compartments contribute to tissue expansion and establishment of a functional epidermis. A new study by Reichenbach et al ( ) reports coordinated proliferation of three distinct epithelial stem cell niches and a role for glutamate transporter Slc1a3 in synchronisation of activated stem and progenitor cells.