The epithelial immune microenvironment (EIME) in atopic dermatitis and psoriasis.

The skin provides both a physical barrier and an immunologic barrier to external threats. The protective machinery of the skin has evolved to provide situation-specific responses to eliminate pathogens and to provide protection against physical dangers. Dysregulation of this machinery can give rise to the initiation and propagation of inflammatory loops in the epithelial microenvironment that result in inflammatory skin diseases in susceptible people. A defective barrier and microbial dysbiosis drive an interleukin 4 (IL-4) loop that underlies atopic dermatitis, while in psoriasis, disordered keratinocyte signaling and predisposition to type 17 responses drive a pathogenic IL-17 loop. Here we discuss the pathogenesis of atopic dermatitis and psoriasis in terms of the epithelial immune microenvironment-the microbiota, keratinocytes and sensory nerves-and the resulting inflammatory loops.

TRPV1-positive sensory nerves and neuropeptides are involved in epidermal barrier repair after tape stripping in mice.

BACKGROUND: The integumentary system of the skin serves as an exceptional protective barrier, with the stratum corneum situated at the forefront. This outermost layer is composed of keratinocytes that biosynthesize filaggrin (encoded by the gene Flg), a pivotal constituent in maintaining skin health. Nevertheless, the precise role of sensory nerves in restoration of the skin barrier after tape stripping-induced epidermal disruption, in contrast to the wound-healing process, remains a tantalizing enigma. OBJECTIVE: This study aimed to elucidate the cryptic role of sensory nerves in repair of the epidermal barrier following tape stripping-induced disruption. METHODS: Through the implementation of resiniferatoxin (RTX)-treated denervation mouse model, we investigated the kinetics of barrier repair after tape stripping and performed immunophenotyping and gene expression analysis in the skin or dorsal root ganglia (DRG) to identify potential neuropeptides. Furthermore, we assessed the functional impact of candidates on the recovery of murine keratinocytes and RTX-treated mice. RESULTS: Ablation of TRPV1-positive sensory nerve attenuated skin barrier recovery and sustained subcutaneous inflammation, coupled with elevated IL-6 level in ear homogenates after tape stripping. Expression of the keratinocyte differentiation marker Flg in the ear skin of RTX-treated mice was decreased compared with that in control mice. Through neuropeptide screening, we found that the downregulation of Flg by IL-6 was counteracted by somatostatin or octreotide (a chemically stable somatostatin analog). Furthermore, RTX-treated mice given octreotide exhibited a partial improvement in barrier recovery after tape stripping. CONCLUSION: Sensory neurons expressing TRPV1 play an indispensable role in restoring barrier function following epidermal injury. Our findings suggest the potential involvement of somatostatin in restoring epidermal repair after skin injury.

A ubiquitin-like protein encoded by the "noncoding" RNA TINCR promotes keratinocyte proliferation and wound healing.

Although long noncoding RNAs (lncRNAs) are transcripts that do not encode proteins by definition, some lncRNAs actually contain small open reading frames that are translated. TINCR (terminal differentiation-induced ncRNA) has been recognized as a lncRNA that contributes to keratinocyte differentiation. However, we here show that TINCR encodes a ubiquitin-like protein that is well conserved among species and whose expression was confirmed by the generation of mice harboring a FLAG epitope tag sequence in the endogenous open reading frame as well as by targeted proteomics. Forced expression of this protein promoted cell cycle progression in normal human epidermal keratinocytes, and mice lacking this protein manifested a delay in skin wound healing associated with attenuated cell cycle progression in keratinocytes. We termed this protein TINCR-encoded ubiquitin-like protein (TUBL), and our results reveal a role for TINCR in the regulation of keratinocyte proliferation and skin regeneration that is dependent on TUBL.

Real-world analysis of apalutamide-associated skin adverse events in Japanese patients with advanced prostate cancer: a multi-institutional study in the Chu-shikoku Japan Urological Consortium.

BACKGROUND: Apalutamide-associated skin adverse events are more common in the Japanese than in the global population. However, limited clinical data have hampered further understanding. This real-world study investigated the clinical characteristics of skin adverse events in patients with advanced prostate cancer. METHODS: We retrospectively reviewed 119 patient records from 16 institutions in Japan. Skin adverse events were graded according to the Common Terminology Criteria for Adverse Events (v5.0). The incidence and characteristics of skin adverse events (along with the clinical risk factors for their incidence, worsening, and recurrence) were evaluated. RESULTS: Fifty-five patients (46.2%) experienced skin adverse events. The median times to the incidence and remission of skin adverse events were 62 and 30 days, respectively. Grade 3 skin adverse events were observed in 15 patients (12.6%). The median time from the first incidence to apalutamide interruption was significantly longer in patients with progression to grade 3 skin adverse events than in those without such a progression (8 vs. 0 days, p = 0.005). Skin adverse events were observed in 45.2% of patients who resumed apalutamide treatment (median treatment interruption time: 31.5 days). Sixteen patients (13.4%) permanently discontinued apalutamide due to skin adverse events. No significant clinical risk factors for the incidence, worsening and recurrence of apalutamide-associated skin adverse events were observed. CONCLUSIONS: Nearly half of the Japanese patients in this study experienced skin adverse events following apalutamide administration. The time to apalutamide discontinuation after the incidence of skin adverse events was positively correlated with the worsening of these events.

PD-L1 on mast cells suppresses effector CD8+ T-cell activation in the skin in murine contact hypersensitivity.

BACKGROUND: The programmed cell death-1 (PD-1)/programmed death ligand 1 (PD-L1) pathway is known to inhibit the activation of effector CD8+ T cells. However, just how this regulatory pathway is involved in the pathophysiology of CD8+ T-cell-mediated inflammatory skin diseases remains unclear. OBJECTIVE: Our aim was to elucidate the mechanisms by which the PD-1/PD-L1 pathway exerts its regulatory roles in CD8+ T-cell-mediated cutaneous immune responses. METHODS: PD-L1-deficient (Pdl1-/-) mice were used for the murine contact hypersensitivity model. Inflammatory responses such as IFN-γ production from CD8+ T cells in the skin was evaluated by flow cytometry. RESULTS: Compared with wild-type mice, Pdl1-/- mice exhibited exacerbated ear swelling and increased numbers of IFN-γ+ CD8+ T cells in the skin. Adoptive T-cell transfer experiments revealed the involvement of the PD-1/PD-L1 pathway in the elicitation phase of contact hypersensitivity. Bone marrow chimera experiments showed that PD-L1 on radioresistant cells was responsible for this regulatory pathway. Flow cytometric analysis revealed that among the radioresistant cells in the skin, PD-L1 was most highly expressed on mast cells (MCs) before and after elicitation. Administration of anti-PD-L1 blocking antibody during the elicitation phase significantly enhanced ear swelling responses and increased the number of IFN-γ+CD8+ T cells in the skin of wild-type mice, whereas no significant effects were observed in MC-deficient (WBB6F1/J-KitW/KitW-v/J and C57BL/6-KitW-sh/W-sh) mice. The high level of expression of PD-L1 on human skin MCs was confirmed by database analysis and immunohistochemical analysis. CONCLUSION: PD-L1 on MCs negatively regulates CD8+ T-cell activation in the skin.

Prolonged high-intensity exercise induces fluctuating immune responses to herpes simplex virus infection via glucocorticoids.

BACKGROUND: Epidemiologic studies have yielded conflicting results regarding the influence of a single bout of prolonged high-intensity exercise on viral infection. OBJECTIVE: We sought to learn whether prolonged high-intensity exercise either exacerbates or ameliorates herpes simplex virus type 2 (HSV-2) infection according to the interval between virus exposure and exercise. METHODS: Mice were intravaginally infected with HSV-2 and exposed to run on the treadmill. RESULTS: Prolonged high-intensity exercise 17 hours after infection impaired the clearance of HSV-2, while exercise 8 hours after infection enhanced the clearance of HSV-2. These impaired or enhanced immune responses were related to a transient decrease or increase in the number of blood-circulating plasmacytoid dendritic cells. Exercise-induced glucocorticoids transiently decreased the number of circulating plasmacytoid dendritic cells by facilitating their homing to the bone marrow via the CXCL12-CXCR4 axis, which led to their subsequent increase in the blood. CONCLUSION: A single bout of prolonged high-intensity exercise can be either deleterious or beneficial to antiviral immunity.

Pituitary adenylate cyclase-activating polypeptide promotes cutaneous dendritic cell functions in contact hypersensitivity.

BACKGROUND: Sensory nerves regulate cutaneous local inflammation indirectly through induction of pruritus and directly by acting on local immune cells. The underlying mechanisms for how sensory nerves influence cutaneous acquired immune responses remain to be clarified. OBJECTIVE: This study aimed to explore the effect of peripheral nerves on cutaneous immune cells in cutaneous acquired immune responses. METHODS: We analyzed contact hypersensitivity (CHS) responses as a murine model of delayed-type hypersensitivity in absence or presence of resiniferatoxin-induced sensory nerve denervation. We conducted ear thickness measurements, flow cytometric analyses, and mRNA expression analyses in CHS. RESULTS: CHS responses were attenuated in mice that were denervated during the sensitization phase of CHS. By screening neuropeptides, we found that pituitary adenylate cyclase-activating polypeptide (PACAP) mRNA expression was decreased in the dorsal root ganglia after denervation. Administration of PACAP restored attenuated CHS response in resiniferatoxin-treated mice, and pharmacological inhibition of PACAP suppressed CHS. Flow cytometric analysis of skin-draining lymph nodes showed that cutaneous dendritic cell migration and maturation were reduced in both denervated mice and PACAP antagonist-treated mice. The expression of chemokine receptors CCR7 and CXCR4 of dendritic cell s was enhanced by addition of PACAP in vitro. CONCLUSION: These findings indicate that a neuropeptide PACAP promotes the development of CHS responses by inducing cutaneous dendritic cell functions during the sensitization phase.

Percutaneous sensitization is limited by in situ inhibition of cutaneous dendritic cell migration through skin-resident regulatory T cells.

BACKGROUND: Percutaneous sensitization is associated with various allergic diseases, including asthma and food allergies. However, the immunologic mechanisms underlying how the skin regulates percutaneous sensitization are still unclear. OBJECTIVE: We aimed to investigate whether and how CD4+Foxp3+ regulatory T (Treg) cells residing in the skin regulate percutaneous sensitization in the skin. METHODS: Selective reduction of numbers of cutaneous Treg cells was achieved by means of intradermal injection of diphtheria toxin into the ear skin of Foxp3DTR mice, in which Treg cells specifically express the diphtheria toxin receptor fused with green fluorescent protein. RESULTS: Thirty percent to 40% of cutaneous Treg cells were capable of IL-10 production in both mice and human subjects. Selective reduction of cutaneous Treg cells at the sensitization site promoted migration of antigen-bearing dendritic cells (DCs) to the draining lymph nodes (dLNs). Accordingly, sensitization through the skin with reduced numbers of Treg cells led to enhanced antigen-specific immune responses in the dLNs, including both effector T-cell differentiation and T cell-dependent B-cell responses, such as the development of germinal center B cells expressing IgG1 and IgE. Furthermore, antigen-bearing cutaneous DC migration was enhanced in mice with IL-10 deficiency restricted to the cutaneous Treg cell compartment, suggesting an important role of cutaneous IL-10+ Treg cells in limiting percutaneous sensitization. Treg cells with a skin-homing phenotype in skin dLNs expressed high levels of IL-10, suggesting that they contribute to renewal and maintenance of the cutaneous IL-10+ Treg cell population. CONCLUSION: Skin-resident Treg cells limit percutaneous sensitization by suppressing antigen-bearing DC migration through in situ IL-10 production.

Cutaneous p38 mitogen-activated protein kinase activation triggers psoriatic dermatitis.

BACKGROUND: Psoriasis is a chronic inflammatory skin disease characterized by IL-17-mediated immune responses. p38 is known to be highly activated in the psoriatic epidermis; however, whether p38 is involved in the development of psoriasis is unclear. OBJECTIVE: We sought to demonstrate that activation of p38 mitogen-activated protein kinase is sufficient to induce psoriatic inflammation in mice and that cutaneous p38 activities are the topical therapeutic targets for psoriasis. METHODS: A p38 activator, anisomycin, was applied daily to murine skin. Transcriptomic analyses were performed to evaluate the similarities of the skin responses to those in human psoriasis and the existing animal model. BIRB796, a small-molecule inhibitor targeting p38 activities, was applied to the murine psoriatic models topically or to human psoriatic skin specimens ex vivo. RESULTS: Topical treatment with anisomycin induced key signatures in psoriasis, such as epidermal thickening, neutrophil infiltration, and gene expression of Il1a, Il1b, Il6, Il24, Cxcl1, Il23a, and Il17a, in treated murine skin. These responses were fully abrogated by topical treatment with BIRB796, and were reduced in IL-17A-deficient mice. Transcriptomic analyses demonstrated the similarities of anisomycin-induced dermatitis to human psoriasis and imiquimod-induced murine psoriatic dermatitis. Furthermore, BIRB796 targeting of p38 activities reduced expression of psoriasis-related genes in both human keratinocytes stimulated with recombinant IL-17A in vitro and psoriatic skin specimens ex vivo. CONCLUSION: Therefore our findings suggest that cutaneous p38 activation can be a key event in patients with psoriasis and a potential topical therapeutic target of a small molecule.

APOBEC3 regulates keratinocyte differentiation and expression of Notch3.

Apolipoprotein B mRNA editing enzyme, catalytic polypeptide-like (APOBEC) family consists of deaminases. Some isozymes of APOBEC3 are induced upon human papillomavirus infection or development of psoriasis skin lesions. However, the involvement of APOBEC3 in keratinocyte differentiation has not been addressed. We herein sought to evaluate the roles of APOBECs in mouse primary keratinocyte differentiation. We found that expression levels of APOBEC1 and APOBEC3 were increased during calcium-induced keratinocyte differentiation. Unexpectedly, however, the expression levels of keratinocyte differentiation markers keratin 1/10, involucrin, loricrin and filaggrin were higher in keratinocytes treated with APOBEC3 siRNAs than in those treated with control RNAs. In addition, the treatment of keratinocytes with APOBEC3 siRNAs increased the gene expression levels of Notch3, a master regulator of keratinocyte differentiation. Moreover, calcium-induced increase in Notch3 expression and keratinocyte differentiation were impaired by transfection with an APOBEC3 expression plasmid. Furthermore, co-treatment with Notch3 siRNAs reduced the APOBEC3 siRNA-mediated upregulation of Notch3 expression and in part attenuated the increased expression levels of keratinocyte differentiation markers. These results suggest that APOBEC3 is induced upon keratinocyte differentiation and negatively regulates the keratinocyte differentiation in part by its inhibitory role for Notch3 expression.

Inhibition of IL-17-committed T cells in a murine psoriasis model by a vitamin D analogue.

BACKGROUND: A better understanding of the means by which topical vitamin D analogues exert their therapeutic effect on psoriasis is of theoretical and practical importance. OBJECTIVE: We sought to clarify whether and how the topical vitamin D analogue calcipotriol (CAL) controls the IL-17A-mediated pathogenesis of murine psoriasis-like dermatitis in vivo. METHODS: Psoriasis-like dermatitis was induced by the topical application of an imiquimod (IMQ)-containing cream on the murine ear for 4 to 6 consecutive days. For topical CAL treatment, mice were treated daily with CAL solution on the ear before IMQ application. RESULTS: Mice treated topically with CAL exhibited much milder IMQ-induced psoriasis-like dermatitis compared with vehicle-treated mice, with impaired accumulation of IL-17A-committed T (T17) cells in the lesional skin. The IMQ-induced upregulation of Il12b and Il23a was marked in the epidermis and was abrogated by CAL application, suggesting CAL-mediated suppression of IL-23 expression. CAL inhibited Il12b and Il23a expression by Langerhans cells ex vivo stimulated with IMQ and CD40 cross-linking. Topical CAL also inhibited T17 cell expansion in the draining lymph nodes of IMQ-treated skin, implying a possible effect on T17 cell-mediated dermatitis at distant sites. In fact, topical CAL application on the IMQ-treated left ear resulted in amelioration of T17 cell accumulation and psoriasis-like dermatitis in the right ear subsequently treated with IMQ. CONCLUSION: Topical CAL can exert its antipsoriatic effect on CAL-treated lesions and, concomitantly, distant lesions by attenuating the T17 cell accumulation in both CAL-treated lesions and draining lymph nodes.

Cutting edge: NF-κB p65 and c-Rel control epidermal development and immune homeostasis in the skin.

Psoriasis is an inflammatory skin disease in which activated immune cells and the proinflammatory cytokine TNF are well-known mediators of pathogenesis. The transcription factor NF-κB is a key regulator of TNF production and TNF-induced proinflammatory gene expression, and both the psoriatic transcriptome and genetic susceptibility further implicate NF-κB in psoriasis etiopathology. However, the role of NF-κB in psoriasis remains controversial. We analyzed the function of canonical NF-κB in the epidermis using CRE-mediated deletion of p65 and c-Rel in keratinocytes. In contrast to animals lacking p65 or c-Rel alone, mice lacking both subunits developed severe dermatitis after birth. Consistent with its partial histological similarity to human psoriasis, this condition could be prevented by anti-TNF treatment. Moreover, regulatory T cells in lesional skin played an important role in disease remission. Our results demonstrate that canonical NF-κB in keratinocytes is essential for the maintenance of skin immune homeostasis and is protective against spontaneous dermatitis.

The deubiquitinase activity of A20 is dispensable for NF-κB signaling.

A20 has been suggested to limit NF-κB activation by removing regulatory ubiquitin chains from ubiquitinated substrates. A20 is a ubiquitin-editing enzyme that removes K63-linked ubiquitin chains from adaptor proteins, such as RIP1, and then conjugates them to K48-linked polyubiquitin chains to trigger proteasomal degradation. To determine the role of the deubiquitinase function of A20 in downregulating NF-κB signaling, we have generated a knock-in mouse that lacks the deubiquitinase function of A20 (A20-OTU mice). These mice are normal and have no signs of inflammation, have normal proportions of B, T, dendritic, and myeloid cells, respond normally to LPS and TNF, and undergo normal NF-κB activation. Our results thus indicate that the deubiquitinase activity of A20 is dispensable for normal NF-κB signaling.

The Janus kinase inhibitor JTE-052 improves skin barrier function through suppressing signal transducer and activator of transcription 3 signaling.

BACKGROUND: Barrier disruption and the resulting continuous exposure to allergens are presumed to be responsible for the development of atopic dermatitis (AD). However, the mechanism through which skin barrier function is disrupted in patients with AD remains unclear. OBJECTIVES: Taking into account the fact that the TH2 milieu impairs keratinocyte terminal differentiation, we sought to clarify our hypothesis that the Janus kinase (JAK)-signal transducer and activator of transcription (STAT) pathway plays a critical role in skin barrier function and can be a therapeutic target for AD. METHODS: We analyzed the mechanism of keratinocyte differentiation using a microarray and small interfering RNA targeting STATs. We studied the effect of the JAK inhibitor JTE-052 on keratinocyte differentiation using the human skin equivalent model and normal human epidermal keratinocytes. We applied topical JAK inhibitor onto NC/Nga mice, dry skin model mice, and human skin grafted to immunocompromised mice. RESULTS: IL-4 and IL-13 downregulated genes involved in keratinocyte differentiation. STAT3 and STAT6 are involved in keratinocyte differentiation and chemokine production by keratinocytes, respectively. Topical application of the JAK inhibitor suppressed STAT3 activation and improved skin barrier function, permitting increases in levels of terminal differentiation proteins, such as filaggrin, and natural moisturizing factors in models of AD and dry skin and in human skin. CONCLUSION: STAT3 signaling is a key element that regulates keratinocyte differentiation. The JAK inhibitor can be a new therapeutic tool for the treatment of disrupted barrier function in patients with AD.