EpCAM (CD326) Regulates Intestinal Epithelial Integrity and Stem Cells via Rho-Associated Kinase

Humans with biallelic inactivating mutations in Epithelial Cell Adhesion Molecule (EpCAM) develop congenital tufting enteropathy (CTE). To gain mechanistic insights regarding EpCAM function in this disorder, we prepared intestinal epithelial cell (IEC) organoids and spheroids. IEC organoids and spheroids were generated from ROSA-CreERT2 EpCAMfl/fl mice. Proliferation, tight junctions, cell polarity and epithelial integrity were assessed in tamoxifen-induced EpCAM-deficient organoids via confocal immunofluorescence microscopy and Western blotting. Olfm4-expressing stem cells were assessed in IEC cells in vitro and in vivo via fluorescence in situ hybridization. To determine if existing drugs could ameliorate effects of EpCAM deficiency in IEC cells, a variety of pharmacologic inhibitors were screened. Deletion of EpCAM resulted in increased apoptosis and attenuated growth of organoids and spheroids. Selected claudins were destabilized and epithelial integrity was severely compromised. Epithelial integrity was improved by treatment with Rho-associated coiled-coil kinase (ROCK) inhibitors without restoration of claudin expression. Correspondingly, enhanced phosphorylation of myosin light chain, a serine/threonine ROCK substrate, was observed in EpCAM-deficient organoids. Strikingly, frequencies of Olfm4-expressing stem cells in EpCAM-deficient IEC cells in vitro and in vivo were decreased. Treatment with ROCK inhibitors increased numbers of stem cells in EpCAM-deficient organoids and spheroids. Thus, EpCAM regulates intestinal epithelial homeostasis via a signaling pathway that includes ROCK.

Amelioration of Congenital Tufting Enteropathy in EpCAM (TROP1)-Deficient Mice via Heterotopic Expression of TROP2 in Intestinal Epithelial Cells

TROP1 (EpCAM) and TROP2 are homologous cell surface proteins that are widely expressed, and often co-expressed, in developing and adult epithelia. Various functions have been ascribed to EpCAM and TROP2, but responsible mechanisms are incompletely characterized and functional equivalence has not been examined. Adult intestinal epithelial cells (IEC) express high levels of EpCAM, while TROP2 is not expressed. EpCAM deficiency causes congenital tufting enteropathy (CTE) in humans and a corresponding lethal condition in mice. We expressed TROP2 and EpCAM in the IEC of EpCAM-deficient mice utilizing a villin promoter to assess EpCAM and TROP2 function. Expression of EpCAM or TROP2 in the IEC of EpCAM knockout mice prevented CTE. TROP2 rescue (T2R) mice were smaller than controls, while EpCAM rescue (EpR) mice were not. Abnormalities were observed in the diameters and histology of T2R small intestine, and Paneth and stem cell markers were decreased. T2R mice also exhibited enlarged mesenteric lymph nodes, enhanced permeability to 4 kDa FITC-dextran and increased sensitivity to detergent-induced colitis, consistent with compromised barrier function. Studies of IEC organoids and spheroids revealed that stem cell function was also compromised in T2R mice. We conclude that EpCAM and TROP2 exhibit functional redundancy, but they are not equivalent.

Matriptase Cleaves EpCAM and TROP2 in Keratinocytes, Destabilizing Both Proteins and Associated Claudins

The homologs EpCAM and TROP2, which both interact with claudin-1 and claudin-7, are frequently coexpressed in epithelia including skin. Intestine uniquely expresses high levels of EpCAM but not TROP2. We previously identified EpCAM as a substrate of the membrane-anchored protease matriptase and linked HAI-2, matriptase, EpCAM and claudin-7 in a pathway that is pivotal for intestinal epithelial cells (IEC) homeostasis. Herein, we reveal that TROP2 is also a matriptase substrate. Matriptase cleaved TROP2 when purified recombinant proteins were mixed in vitro. TROP2, like EpCAM, was also cleaved after co-transfection of matriptase in 293T cells. Neither EpCAM nor TROP2 cleavage was promoted by protease-disabled matriptase or matriptase that harbored the ichthyosis-associated G827R mutation. We confirmed that EpCAM and TROP2 are both expressed in skin and detected cleavage of these proteins in human keratinocytes (HaCaT cells) after the physiologic inhibition of matriptase by HAI proteins was relieved by siRNA knockdown. Knockdown of EpCAM or TROP2 individually had only small effects on claudin-1 and claudin-7 levels, whereas elimination of both markedly diminished claudin levels. HAI-1 knockdown promoted EpCAM and TROP2 cleavage accompanied by reductions in claudins, whereas HAI-2 knockdown had little impact. Double knockdown of HAI-1 and HAI-2 induced nearly complete cleavage of EpCAM and TROP2 and drastic reductions of claudins. These effects were eliminated by concurrent matriptase knockdown. Decreases in claudin levels were also diminished by the lysosomal inhibitor chloroquine and cleaved EpCAM/TROP2 fragments accumulated preferentially. We demonstrate that TROP2 and EpCAM exhibit redundancies with regard to regulation of claudin metabolism and that an HAI, matriptase, EpCAM and claudin pathway analogous to what we described in IECs exists in keratinocytes. This study may offer insights into the mechanistic basis for matriptase dysregulation-induced ichthyosis.

Whole-Mount Adult Ear Skin Imaging Reveals Defective Neuro-Vascular Branching Morphogenesis in Obese and Type 2 Diabetic Mouse Models

Obesity and type 2 diabetes are frequently associated with peripheral neuropathy. Though there are multiple methods for diagnosis and analysis of morphological changes of peripheral nerves and blood vessels, three-dimensional high-resolution imaging is necessary to appreciate the pathogenesis with an anatomically recognizable branching morphogenesis and patterning. Here we established a novel technique for whole-mount imaging of adult mouse ear skin to visualize branching morphogenesis and patterning of peripheral nerves and blood vessels. Whole-mount immunostaining of adult mouse ear skin showed that peripheral sensory and sympathetic nerves align with large-diameter blood vessels. Diet-induced obesity (DIO) mice exhibit defective vascular smooth muscle cells (VSMCs) coverage, while there is no significant change in the amount of peripheral nerves. The leptin receptor-deficient db/db mice, a severe obese and type 2 diabetic mouse model, exhibit defective VSMC coverage and a large increase in the amount of smaller-diameter nerve bundles with myelin sheath and unmyelinated nerve fibers. Interestingly, an increase in the amount of myeloid immune cells was observed in the DIO but not db/db mouse skin. These data suggest that our whole-mount imaging method enables us to investigate the neuro-vascular and neuro-immune phenotypes in the animal models of obesity and diabetes.

DLX3-Dependent STAT3 Signaling in Keratinocytes Regulates Skin Immune Homeostasis

Epidermal-specific deletion of the homeobox transcription regulator DLX3 disrupts keratinocyte differentiation and results in an IL-17-linked psoriasis-like skin inflammation. To identify the epidermal initiating signals produced by DLX3-null keratinocytes, we performed acute deletion of DLX3 in adult epidermis using a tamoxifen-inducible Krt14-cre/ERT system. K14CreERT;DLX3^fl/fl skin exhibited dysregulated expression of differentiation-associated genes, upregulation of proinflammatory cytokines, and accumulation of Langerhans cells and macrophages within 3 days of tamoxifen-induced DLX3 ablation. We also observed increased accumulation of IL-17A-secreting Vγ4 γδ T cells and heightened levels of IL-17 and IL-36 family of cytokines starting 1 week after DLX3 deletion. Interestingly, transcriptome profiling of K14CreERT;DLX3^fl/fl epidermis at 3 days identified activated STAT3 as a transcriptional regulator and revealed differential expression of STAT3 signaling-related genes. Furthermore, activation of STAT3 was strongly increased in K14CreERT;DLX3^fl/fl skin, and topical treatment with an inhibitor of STAT3 activation attenuated the immune phenotype. RNA-seq analysis of vehicle and STAT3 inhibitor treated K14CreERT;DLX3^fl/fl skin identified differentially expressed genes associated with inhibition of leukocyte infiltration. Collectively, our results show that DLX3 is a critical regulator of STAT3 signaling network that maintains skin homeostasis.

Matriptase-mediated cleavage of EpCAM destabilizes claudins and dysregulates intestinal epithelial homeostasis

Congenital tufting enteropathy (CTE) is a severe autosomal recessive human diarrheal disorder with characteristic intestinal epithelial dysplasia. CTE can be caused by mutations in genes encoding EpCAM, a putative adhesion molecule, and HAI-2, a cell surface protease inhibitor. A similar phenotype occurs in mice whose intestinal epithelial cells (IECs) fail to express the tight junction-associated protein claudin-7. EpCAM stabilizes claudin-7 in IECs, and HAI-2 regulates the cell surface serine protease matriptase, a known modifier of intestinal epithelial physiology. Therefore, we hypothesized that HAI-2, matriptase, EpCAM, and claudin-7 were functionally linked. Herein we have demonstrated that active matriptase cleaves EpCAM after Arg80 and that loss of HAI-2 in IECs led to unrestrained matriptase activity and efficient cleavage of EpCAM. Cleavage of EpCAM decreased its ability to associate with claudin-7 and targeted it for internalization and lysosomal degradation in conjunction with claudin-7. CTE-associated HAI-2 mutant proteins exhibited reduced ability to inhibit matriptase and also failed to efficiently stabilize claudin-7 in IECs. These results identify EpCAM as a substrate of matriptase and link HAI-2, matriptase, EpCAM, and claudin-7 in a functionally important pathway that causes disease when it is dysregulated.

MFG-E8 Drives Melanoma Growth by Stimulating Mesenchymal Stromal Cell-Induced Angiogenesis and M2 Polarization of Tumor-Associated Macrophages

Secretion of the powerful angiogenic factor MFG-E8 by pericytes can bypass the therapeutic effects of anti-VEGF therapy, but the mechanisms by which MFG-E8 acts are not fully understood. In this study, we investigated how this factor acts to promote the growth of melanomas that express it. We found that mouse bone marrow-derived mesenchymal stromal cells (MSC) expressed a substantial amount of MFG-E8. To assess its expression from this cell type, we implanted melanoma cells and MSC derived from wild type (WT) or MFG-E8 deficient [knockout (KO)] into mice and monitored tumor growth. Tumor growth and M2 macrophages were each attenuated in subjects coimplanted with KO-MSC compared with WT-MSC. In both xenograft tumors and clinical specimens of melanoma, we found that MFG-E8 expression was heightened near blood vessels where MSC could be found. Through in vitro assays, we confirmed that WT-MSC-conditioned medium was more potent at inducing M2 macrophage polarization, compared with KO-MSC-conditioned medium. VEGF and ET-1 expression in KO-MSC was significantly lower than in WT-MSC, correlating in vivo with reduced tumor growth and numbers of pericytes and M2 macrophages within tumors. Overall, our results suggested that MFG-E8 acts at two levels, by increasing VEGF and ET-1 expression in MSC and by enhancing M2 polarization of macrophages, to increase tumor angiogenesis. Cancer Res; 76(14); 4283-92. ©2016 AACR.

EpCAM Expressed by Murine Epidermal Langerhans Cells Modulates Immunization to an Epicutaneously Applied Protein Antigen

Langerhans cells (LCs) induce type 2 antibodies reactive with protein antigens that are applied to murine skin in the absence of adjuvant after extending their dendrites through tight junctions to acquire antigens and migrating to regional lymph nodes. In response to contact sensitizers, epithelial cell adhesion molecule (EpCAM) on LCs promotes LC dendrite mobility and LC migration. In epithelial cells, EpCAM regulates expression and distribution of selected tight junctions-associated claudins. To determine if EpCAM regulates claudins in LC and immune responses to externally applied proteins, we studied conditional knockout mice with EpCAM-deficient LCs. Although LC claudin-1 levels were dramatically reduced in the absence of EpCAM, conditional knockout mice with EpCAM-deficient LCs and control LC dendrites docked with epidermal tight junctions with equal efficiencies and ingested surface proteins. Topical immunization of conditional knockout mice with EpCAM-deficient LCs with ovalbumin led to increased induction of type 2 Ova-specific antibodies and enhanced proliferation of ovalbumin-reactive T cells associated with increased accumulation of LCs in lymph nodes. These results suggest that, in the absence of strong adjuvants, EpCAM-deficient LCs exhibit increased migration to regional lymph nodes. EpCAM appears to differentially regulate LC mobility/migration in the setting of limited inflammation as compared with the intense inflammation triggered by contact sensitizers.

Milk Fat Globule-Epidermal Growth Factor 8 (MFG-E8) Is a Novel Anti-inflammatory Factor in Rheumatoid Arthritis in Mice and Humans

Milk fat globule-epidermal growth factor 8 (MFG-E8) is an anti-inflammatory glycoprotein that mediates the clearance of apoptotic cells and is implicated in the pathogenesis of autoimmune and inflammatory diseases. Because MFG-E8 also controls bone metabolism, we investigated its role in rheumatoid arthritis (RA), focusing on inflammation and joint destruction. The regulation of MFG-E8 by inflammation was assessed in vitro using osteoblasts, in arthritic mice and in patients with RA. K/BxN serum transfer arthritis (STA) was applied to MFG-E8 knock-out mice to assess its role in the pathogenesis of arthritis. Stimulation of osteoblasts with lipopolysaccharide (LPS) and tumor necrosis factor (TNF)-α downregulated the expression of MFG-E8 by 30% to 35%. MFG-E8-deficient osteoblasts responded to LPS with a stronger production of pro-inflammatory cytokines. In vivo, MFG-E8 mRNA levels were 52% lower in the paws of collagen-induced arthritic (CIA) mice and 24% to 42% lower in the serum of arthritic mice using two different arthritis models (CIA and STA). Similarly, patients with RA (n = 93) had lower serum concentrations of MFG-E8 (-17%) compared with healthy controls (n = 140). In a subgroup of patients who had a moderate to high disease activity (n = 21), serum concentrations of MFG-E8 rose after complete or partial remission had been achieved (+67%). Finally, MFG-E8-deficient mice subjected to STA exhibited a stronger disease burden, an increased number of neutrophils in the joints, and a more extensive local and systemic bone loss. This was accompanied by an increased activation of osteoclasts and a suppression of osteoblast function in MFG-E8-deficient mice. Thus, MFG-E8 is a protective factor in the pathogenesis of RA and subsequent bone loss. Whether MFG-E8 qualifies as a novel biomarker or therapeutic target for the treatment of RA is worth addressing in further studies.

Loss of milk fat globule-epidermal growth factor 8 (MFG-E8) in mice leads to low bone mass and accelerates ovariectomy-associated bone loss by increasing osteoclastogenesis

Milk fat globule-epidermal growth factor 8 (MFG-E8) is a glycoprotein that controls the engulfment of apoptotic cells and exerts inflammation-modulatory effects. Recently, it has been implicated in osteoclastogenesis and the pathogenesis of inflammatory periodontal bone loss, but its role in physiological bone homeostasis is still not well defined. Here, we evaluated the influence of MFG-E8 on osteoblasts and osteoclasts and its impact on bone remodeling in healthy and ovariectomized mice as a model for post-menopausal osteoporosis. Total and trabecular bone mineral densities at the lumbar spine in 6-week-old MFG-E8 KO mice were reduced by 11% (p < 0.05) and 17% (p < 0.01), respectively, as compared to wild-type (WT) mice. Accordingly, serum levels of the bone formation marker P1NP were decreased by 37% (p < 0.01) in MFG-E8 KO mice as were the ex vivo mineralization capacity and expression of osteoblast genes (Runx2, alkaline phosphatase, osteocalcin) in MFG-E8 KO osteoblasts. In contrast, serum bone resorption markers CTX1 and TRAP5b were increased by 30% and 60% (p < 0.05), respectively, in MFG-E8 KO mice. Furthermore, bone marrow macrophages from MFG-E8-KO mice differentiated more effectively into osteoclasts, as compared to WT cells. MFG-E8-deficient osteoclasts displayed increased bone resorption ex vivo, which could be reversed by the presence of recombinant MFG-E8. To determine the significance of the enhanced osteoclastogenesis in MFG-E8 KO mice, we performed an ovariectomy, which is associated with bone loss due to increased osteoclast activity. Indeed, MFG-E8 KO mice lost 12% more trabecular bone density than WT mice after ovariectomy. Together, these data indicate that MFG-E8 controls steady-state and pathological bone turnover and may therefore represent a new target gene in the treatment of bone diseases.

Mushrooming insights into skin dendritic cell physiology

Mechanisms responsible for protective immunity against epicutaneous Candida infections are incompletely characterized. In this issue of Immunity, Kashem et al. demonstrate that different Candida life forms engage selected skin dendritic cell subsets in distinct compartments, resulting in qualitatively different immune responses.

TSLP expression: analysis with a ZsGreen TSLP reporter mouse

Thymic stromal lymphopoietin (TSLP) is a type I cytokine that plays a central role in induction of allergic inflammatory responses. Its principal targets have been reported to be dendritic cells and/or CD4 T cells; epithelial cells are a principal source. We report in this study the development of a reporter mouse (TSLP-ZsG) in which a ZsGreen (ZsG)-encoding construct has been inserted by recombineering into a bacterial artificial chromosome immediately at the translation initiating ATG of TSLP. The expression of ZsG by mice transgenic for the recombinant BAC appears to be a faithful surrogate for TSLP expression, particularly in keratinocytes and medullary thymic epithelial cells. Limited ZsG and TSLP mRNA was observed in bone marrow-derived mast cells, basophils, and dendritic cells. Using the TSLP-ZsG reporter mouse, we show that TNF-α and IL-4/IL-13 are potent inducers of TSLP expression by keratinocytes and that local activation of Th2 and Th1 cells induces keratinocyte TSLP expression. We suggest that the capacity of TSLP to both induce Th2 differentiation and to be induced by activated Th2 cells raises the possibility that TSLP may be involved in a positive feedback loop to enhance allergic inflammatory conditions.

Regulation of osteoclast homeostasis and inflammatory bone loss by MFG-E8

The glycoprotein milk fat globule-epidermal growth factor factor 8 (MFG-E8) is expressed in several tissues and mediates diverse homeostatic functions. However, whether it plays a role in bone homeostasis has not been established. In this study, we show for the first time, to our knowledge, that osteoclasts express and are regulated by MFG-E8. Bone marrow-derived osteoclast precursors from MFG-E8-deficient (Mfge8(-/-)) mice underwent increased receptor activator of NF-κB ligand-induced osteoclastogenesis, leading to enhanced resorption pit formation compared with wild-type controls. Consistently, exogenously added MFG-E8 inhibited receptor activator of NF-κB ligand-induced osteoclastogenesis from mouse or human osteoclast precursors. Upon induction of experimental periodontitis, an oral inflammatory disease characterized by loss of bone support of the dentition, Mfge8(-/-) mice exhibited higher numbers of osteoclasts and more bone loss than did wild-type controls. Accordingly, local microinjection of anti-MFG-E8 mAb exacerbated periodontal bone loss in wild-type mice. Conversely, microinjection of MFG-E8 inhibited bone loss in experimental mouse periodontitis. In comparison with wild-type controls, Mfge8(-/-) mice also experienced >60% more naturally occurring chronic periodontal bone loss. In conclusion, MFG-E8 is a novel homeostatic regulator of osteoclasts that could be exploited therapeutically to treat periodontitis and perhaps other immunological disorders associated with inflammatory bone loss.

MFG-E8 regulates angiogenesis in cutaneous wound healing

Our research group recently demonstrated that pericytes are major sources of the secreted glycoprotein and integrin ligand lactadherin (MFG-E8) in B16 melanoma tumors, and that MFG-E8 promotes angiogenesis via enhanced PDGF-PDGFRβ signaling mediated by integrin-growth factor receptor crosstalk. However, sources of MFG-E8 and its possible roles in skin physiology are not well characterized. The objective of this study was to characterize the involvement of MFG-E8 in skin wound healing. In the dermis of normal murine and human skin, accumulations of MFG-E8 were found around CD31(+) blood vessels, and MFG-E8 colocalized with PDGFRβ(+), αSMA(+), and NG2(+) pericytes. MFG-E8 protein and mRNA levels were elevated in the dermis during full-thickness wound healing in mice. MFG-E8 was diffusely present in granulation tissue and was localized around blood vessels. Wound healing was delayed in MFG-E8 knockout mice, compared with the wild type, and myofibroblast and vessel numbers in wound areas were significantly reduced in knockout mice. Inhibition of MFG-E8 production with siRNA attenuated the formation of capillary-like structures in vitro. Expression of MFG-E8 in fibrous human granulation tissue with scant blood vessels was less than that in granulation tissue with many blood vessels. These findings suggest that MFG-E8 promotes cutaneous wound healing by enhancing angiogenesis.

Epithelial cell adhesion molecule (EpCAM) regulates claudin dynamics and tight junctions

Epithelial cell adhesion molecule (EpCAM) (CD326) is a surface glycoprotein expressed by invasive carcinomas and some epithelia. Herein, we report that EpCAM regulates the composition and function of tight junctions (TJ). EpCAM accumulated on the lateral interfaces of human colon carcinoma and normal intestinal epithelial cells but did not co-localize with TJ. Knockdown of EpCAM in T84 and Caco-2 cells using shRNAs led to changes in morphology and adhesiveness. TJ formed readily after EpCAM knockdown; the acquisition of trans-epithelial electroresistance was enhanced, and TJ showed increased resistance to disruption by calcium chelation. Preparative immunoprecipitation demonstrated that EpCAM bound tightly to claudin-7. Co-immunoprecipitation documented associations of EpCAM with claudin-7 and claudin-1 but not claudin-2 or claudin-4. Claudin-1 associated with claudin-7 in co-transfection experiments, and claudin-7 was required for association of claudin-1 with EpCAM. EpCAM knockdown resulted in decreases in claudin-7 and claudin-1 proteins that were reversed with lysosome inhibitors. Immunofluorescence microscopy revealed that claudin-7 and claudin-1 continually trafficked into lysosomes. Although EpCAM knockdown decreased claudin-1 and claudin-7 protein levels overall, accumulations of claudin-1 and claudin-7 in TJ increased. Physical interactions between EpCAM and claudins were required for claudin stabilization. These findings suggest that EpCAM modulates adhesion and TJ function by regulating intracellular localization and degradation of selected claudins.

TGFβ1 overexpression by keratinocytes alters skin dendritic cell homeostasis and enhances contact hypersensitivity

Overexpression of Transforming Growth Factor Beta1 (TGFβ1) in mouse epidermis causes cutaneous inflammation and keratinocyte hyperproliferation. Here, we examined acute effects of TGFβ1 overproduction by keratinocytes on skin dendritic cells (DCs). TGFβ1 induction for 2 and 4 days increased numbers and CD86 expression of B220+ plasmacytoid DCs (pDCs) and CD207+CD103+, CD207−CD103−CD11b+ and CD207−CD103−CD11b− dermal DCs (dDCs) in skin draining lymph nodes (SDLN). The dermis of TGFβ1-overexpressing mice had significantly more pDCs, CD207+CD103+ dDCs and CD207-CD11b+ dDCs in the absence of increased dermal proliferation. Application of dye, TRITC, in dibutylpthalate (DBP) solution after TGFβ1 induction increased the numbers of TRITC+CD207− dDCs in SDLN, and augmented TRITC/DBP-induced Langerhans cell (LC) migration 72 hrs post-TRITC treatment. Consistent with this, LC migration was increased in vitro by TGFβ1 overexpression in skin explants and by exogenous TGFβ1 in culture media. Transient TGFβ1 induction during DNFB sensitization increased contact hypersensitivity responses by 1.5-fold. Thus, elevated epidermal TGFβ1 alone is sufficient to alter homeostasis of multiple cutaneous DC subsets and enhance DC migration and immune responses to contact sensitizers. These results highlight a role for keratinocyte-derived TGFβ1 in DC trafficking and the initiation of skin inflammation.

Stress-induced production of chemokines by hair follicles regulates the trafficking of dendritic cells in skin

Langerhans cells (LCs) are epidermal dendritic cells with incompletely understood origins that associate with hair follicles for unknown reasons. Here we show that in response to external stress, mouse hair follicles recruited Gr-1(hi) monocyte-derived precursors of LCs whose epidermal entry was dependent on the chemokine receptors CCR2 and CCR6, whereas the chemokine receptor CCR8 inhibited the recruitment of LCs. Distinct hair-follicle regions had differences in their expression of ligands for CCR2 and CCR6. The isthmus expressed the chemokine CCL2; the infundibulum expressed the chemokine CCL20; and keratinocytes in the bulge produced the chemokine CCL8, which is the ligand for CCR8. Thus, distinct hair-follicle keratinocyte subpopulations promoted or inhibited repopulation with LCs via differences in chemokine production, a feature also noted in humans. Pre-LCs failed to enter hairless skin in mice or humans, which establishes hair follicles as portals for LCs.

Epidermal Langerhans cells tune skin reactivity to contact allergens

Allergic contact dermatitis is a common disorder that has fascinated dermatologists and immunologists for decades. Extensive studies of contact sensitivity reactions in mice established a mechanistic paradigm that has been revisited in recent years, and the involvement of Langerhans cells (LCs), a population of epidermal dendritic cells, in immune responses to epicutaneously applied antigens has been questioned. In this issue of the JCI, Gomez de Agüero et al. describe an elegant series of experiments that implicate LCs in tolerance induction, positioning these cells as key regulators of immunologic barrier function.

Potentiation of platelet-derived growth factor receptor-β signaling mediated by integrin-associated MFG-E8

OBJECTIVE

Pericytes/pericyte precursors produce milk fat globule-associated protein with epidermal growth factor and factor VIII-like domains (MFG-E8) in vivo, and this α(v) integrin ligand enhances angiogenesis in tumors and in oxygen-induced retinopathy in mice. Inhibition of MFG-E8 production or function attenuates platelet-derived growth factor-BB (PDGF-BB)-induced migration of pericyte/pericyte precursor-like 10T1/2 cells in vitro. Herein, we describe mechanisms by which MFG-E8 modulates PDGF-BB:PDGF receptor β (PDGFRβ) signaling in 10T1/2 cells.

METHODS AND RESULTS

Small interfering RNA depletion of MFG-E8 from 10T1/2 cells or antibody inhibition of MFG-E8 action enhanced PDGF-BB-dependent degradation of PDGFRβ and attenuated signaling. Coimmunoprecipitation revealed transient association of MFG-E8 with PDGFRβ in PDGF-BB-treated 10T1/2 cells and reduced PDGFRβ-focal adhesion kinase association in MFG-E8-depleted cells. Confocal microscopy demonstrated that MFG-E8 binding to 10T1/2 cells was RGD motif and α(v) dependent but PDGF-BB treatment independent, whereas colocalization of MFG-E8 with PDGFRβ was enhanced by PDGF-BB. Ubiquitination of PDGFRβ was also increased in MFG-E8 small interfering RNA-transfected cells.

CONCLUSION

Integrin α(v)-bound MFG-E8 associates with PDGFRβ and focal adhesion kinase after PDGF-BB treatment, results in cell surface retention of PDGFRβ, delays receptor degradation, potentiates downstream signaling, and enhances migration of 10T1/2 cells. MFG-E8 may promote angiogenesis, in part, via cell autonomous actions on pericytes or pericyte precursors that result in enhanced PDGF-BB:PDGFRβ signaling mediated via integrin-growth factor receptor cross-talk.

Pericyte-derived MFG-E8 regulates pathologic angiogenesis

OBJECTIVE

MFG-E8 (also called lactadherin and SED1) is a secreted glycoprotein that has been previously implicated in enhancement of vascular endothelial growth factor-dependent angiogenesis. Major sources of MFG-E8 in vivo and precise mechanisms of MFG-E8 action remain undetermined. The objective of this study was to identify important sources of MFG-E8 in vivo and further elucidate the role(s) of MFG-E8 in the regulation of angiogenesis.

METHODS AND RESULTS

We used knockout mice and anti-MFG-E8 antibodies to study MFG-E8 function in vivo. In melanomas and in retinas of mice with oxygen-induced retinopathy, MFG-E8 colocalized with pericytes rather than endothelial cells, and platelet-derived growth factor receptor β+ pericytes/pericyte precursors purified from tumors contained large amounts of MFG-E8 mRNA. Tumor- and retinopathy-associated angiogenesis was diminished in MFG-E8 knockout mice, and pericyte coverage of neovessels was reduced. Inhibition of MFG-E8 production by 10T1/2 cells (surrogate pericyte/pericyte precursors) using small interfering RNAs and short hairpin RNAs, or inhibition of MFG-E8 action with some anti-MFG-E8 antibodies, selectively attenuated migration in vitro. Significantly, the anti-MFG-E8 antibodies that inhibited 10T1/2 cell migration in vitro also inhibited pathological angiogenesis in vivo.

CONCLUSIONS

These studies strongly implicate MFG-E8 in pericyte/pericyte precursor function and indicate that MFG-E8-directed therapeutics may merit further development.

Protective T cell immunity in mice following protein-TLR7/8 agonist-conjugate immunization requires aggregation, type I IFN, and multiple DC subsets

The success of a non-live vaccine requires improved formulation and adjuvant selection to generate robust T cell immunity following immunization. Here, using protein linked to a TLR7/8 agonist (conjugate vaccine), we investigated the functional properties of vaccine formulation, the cytokines, and the DC subsets required to induce protective multifunctional T cell immunity in vivo. The conjugate vaccine required aggregation of the protein to elicit potent Th1 CD4+ and CD8+ T cell responses. Remarkably, the conjugate vaccine, through aggregation of the protein and activation of TLR7 in vivo, led to an influx of migratory DCs to the LN and increased antigen uptake by several resident and migratory DC subsets, with the latter effect strongly influenced by vaccine-induced type I IFN. Ex vivo migratory CD8-DEC205+CD103-CD326- langerin-negative dermal DCs were as potent in cross-presenting antigen to naive CD8+ T cells as CD11c+CD8+ DCs. Moreover, these cells also influenced Th1 CD4+ T cell priming. In summary, we propose a model in which broad-based T cell-mediated responses upon vaccination can be maximized by codelivery of aggregated protein and TLR7/8 agonist, which together promote optimal antigen acquisition and presentation by multiple DC subsets in the context of critical proinflammatory cytokines.

IL-1 signalling is dispensable for protective immunity in Leishmania-resistant mice

Leishmaniasis is a parasitic disease affecting ∼12 million people. Control of infection (e.g. in C57BL/6 mice) results from IL-12-dependent production of IFNγ by Th1/Tc1 cells. In contrast, BALB/c mice succumb to infection because of preferential Th2-type cytokine induction. Infected dendritic cells (DC) represent important sources of IL-12. Genetically determined differences in DC IL-1α/β production contribute to disease outcome. Whereas the course of disease was not dramatically altered in IL-1RI(-/-) mice, local administration of IL-1α to infected C57BL/6 mice improved disease outcome. To definitively elucidate the involvement of IL-1 in immunity against leishmaniasis, we now utilized IL-1α/β-double-deficient C57BL/6 mice. C57BL/6 mice are believed to be a good surrogate model for human, self limited cutaneous leishmaniasis (CL). Leishmania major-infected IL-1α/β(-/-) mice were resistant to experimental CL comparable to controls. In addition, DC-based vaccination against leishmaniasis in C57BL/6 mice was independent of IL-1. Thus, in Leishmania-resistant C57BL/6 mice, IL-1 signalling is dispensable for protection.

Vaccination with TAT-antigen fusion protein induces protective, CD8(+) T cell-mediated immunity against Leishmania major

In murine leishmaniasis, healing is mediated by IFN-γ-producing CD4(+) and CD8(+) T cells. Thus, an efficacious vaccine should induce Th1 and Tc1 cells. Dendritic cells (DCs) pulsed with exogenous proteins primarily induce strong CD4-dependent immunity; induction of CD8 responses has proven to be difficult. We evaluated the immunogenicity of fusion proteins comprising the protein transduction domain of HIV-1 TAT and the Leishmania antigen LACK (Leishmania homolog of receptors for activated C kinase), as TAT-fusion proteins facilitate major histocompatibility complex class I-dependent antigen presentation. In vitro, TAT-LACK-pulsed DCs induced stronger proliferation of Leishmania-specific CD8(+) T cells compared with DCs incubated with LACK alone. Vaccination with TAT-LACK-pulsed DCs or fusion proteins plus adjuvant in vivo significantly improved disease outcome in Leishmania major-infected mice and was superior to vaccination with DCs treated with LACK alone. Vaccination with DC+TAT-LACK resulted in stronger proliferation of CD8(+) T cells when compared with immunization with DC+LACK. Upon depletion of CD4(+) or CD8(+) T cells, TAT-LACK-mediated protection was lost. TAT-LACK-pulsed IL-12p40-deficient DCs did not promote protection in vivo. In summary, these data show that TAT-fusion proteins are superior in activating Leishmania-specific Tc1 cells when compared with antigen alone and suggest that IL-12-dependent preferential induction of antigen-specific CD8(+) cells promotes significant protection against this important human pathogen.

Abnormal placental development and early embryonic lethality in EpCAM-null mice

BACKGROUND

EpCAM (CD326) is encoded by the tacstd1 gene and expressed by a variety of normal and malignant epithelial cells and some leukocytes. Results of previous in vitro experiments suggested that EpCAM is an intercellular adhesion molecule. EpCAM has been extensively studied as a potential tumor marker and immunotherapy target, and more recent studies suggest that EpCAM expression may be characteristic of cancer stem cells.

METHODOLOGY/PRINCIPAL FINDINGS

To gain insights into EpCAM function in vivo, we generated EpCAM -/- mice utilizing an embryonic stem cell line with a tacstd1 allele that had been disrupted. Gene trapping resulted in a protein comprised of the N-terminus of EpCAM encoded by 2 exons of the tacstd1 gene fused in frame to betageo. EpCAM +/- mice were viable and fertile and exhibited no obvious abnormalities. Examination of EpCAM +/- embryos revealed that betageo was expressed in several epithelial structures including developing ears (otocysts), eyes, branchial arches, gut, apical ectodermal ridges, lungs, pancreas, hair follicles and others. All EpCAM -/- mice died in utero by E12.5, and were small, developmentally delayed, and displayed prominent placental abnormalities. In developing placentas, EpCAM was expressed throughout the labyrinthine layer and by spongiotrophoblasts as well. Placentas of EpCAM -/- embryos were compact, with thin labyrinthine layers lacking prominent vascularity. Parietal trophoblast giant cells were also dramatically reduced in EpCAM -/- placentas.

CONCLUSION

EpCAM was required for differentiation or survival of parietal trophoblast giant cells, normal development of the placental labyrinth and establishment of a competent maternal-fetal circulation. The findings in EpCAM-reporter mice suggest involvement of this molecule in development of vital organs including the gut, kidneys, pancreas, lungs, eyes, and limbs.

IL-17 promotes progression of cutaneous leishmaniasis in susceptible mice

Resistance to leishmaniasis in C57BL/6 mice depends on Th1/Tc1 cells. BALB/c mice preferentially develop Th2 immunity and succumb to infection. We now assessed the role of IL-17 in cutaneous leishmaniasis. During the course of Leishmania major infection, BALB/c CD4 cells and neutrophils produced increased amounts of IL-17 as compared with cells from C57BL/6 mice. This increase was associated with significantly increased IL-23 release from L. major-infected BALB/c dendritic cells (DC), whereas IL-6 and TGF-beta1 production by BALB/c and C57BL/6 DC were comparable. Interestingly, lesion sizes in infected IL-17-deficient BALB/c mice were dramatically smaller and failed to progress as compared with those in control mice. Similar amounts of IL-4, IL-10, and IFN-gamma were produced by T cells from IL-17-deficient mice and control mice consistent with development of Th2-predominant immunity in all animals. Improved disease outcome was associated with decreased CXCL2-accumulation in lesion sites and decreased neutrophil immigration into lesions of infected IL-17-deficient mice confirming prior observations that enhanced neutrophil recruitment contributes to disease susceptibility in BALB/c mice. This study excludes an important facilitating role for IL-17 in Th1/Th2 development in L. major-infected BALB/c mice, and suggests that IL-23 production by L. major-infected DC maintains IL-17(+) cells that influence disease progression via regulation of neutrophil recruitment.