Guanine nucleotide exchange factor RABGEF1 regulates keratinocyte-intrinsic signaling to maintain skin homeostasis

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Abstract

Epidermal keratinocytes form a structural and immune barrier that is essential for skin homeostasis. However, the mechanisms that regulate epidermal barrier function are incompletely understood. Here we have found that keratinocyte-specific deletion of the gene encoding RAB guanine nucleotide exchange factor 1 (RABGEF1, also known as RABEX-5) severely impairs epidermal barrier function in mice and induces an allergic cutaneous and systemic phenotype. RABGEF1-deficient keratinocytes exhibited aberrant activation of the intrinsic IL-1R/MYD88/NF-κB signaling pathway and MYD88-dependent abnormalities in expression of structural proteins that contribute to skin barrier function. Moreover, ablation of MYD88 signaling in RABGEF1-deficient keratinocytes or deletion of Il1r1 restored skin homeostasis and prevented development of skin inflammation. We further demonstrated that epidermal RABGEF1 expression is reduced in skin lesions of humans diagnosed with either atopic dermatitis or allergic contact dermatitis as well as in an inducible mouse model of allergic dermatitis. Our findings reveal a key role for RABGEF1 in dampening keratinocyte-intrinsic MYD88 signaling and sustaining epidermal barrier function in mice, and suggest that dysregulation of RABGEF1 expression may contribute to epidermal barrier dysfunction in allergic skin disorders in mice and humans. Thus, RABGEF1-mediated regulation of IL-1R/MYD88 signaling might represent a potential therapeutic target.

Authors

Thomas Marichal, Nicolas Gaudenzio, Sophie El Abbas, Riccardo Sibilano, Oliwia Zurek, Philipp Starkl, Laurent L. Reber, Dimitri Pirottin, Jinah Kim, Pierre Chambon, Axel Roers, Nadine Antoine, Yuko Kawakami, Toshiaki Kawakami, Fabrice Bureau, See-Ying Tam, Mindy Tsai, Stephen J. Galli

Store-operated Ca²⁺ entry regulates Ca²⁺-activated chloride channels and eccrine sweat gland function

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Abstract

Eccrine sweat glands are essential for sweating and thermoregulation in humans. Loss-of-function mutations in the Ca²⁺ release–activated Ca²⁺ (CRAC) channel genes ORAI1 and STIM1 abolish store-operated Ca²⁺ entry (SOCE), and patients with these CRAC channel mutations suffer from anhidrosis and hyperthermia at high ambient temperatures. Here we have shown that CRAC channel–deficient patients and mice with ectodermal tissue–specific deletion of Orai1 (Orai1^K14Cre) or Stim1 and Stim2 (Stim1/2^K14Cre) failed to sweat despite normal sweat gland development. SOCE was absent in agonist-stimulated sweat glands from Orai1^K14Cre and Stim1/2^K14Cre mice and human sweat gland cells lacking ORAI1 or STIM1 expression. In Orai1^K14Cre mice, abolishment of SOCE was associated with impaired chloride secretion by primary murine sweat glands. In human sweat gland cells, SOCE mediated by ORAI1 was necessary for agonist-induced chloride secretion and activation of the Ca²⁺-activated chloride channel (CaCC) anoctamin 1 (ANO1, also known as TMEM16A). By contrast, expression of TMEM16A, the water channel aquaporin 5 (AQP5), and other regulators of sweat gland function was normal in the absence of SOCE. Our findings demonstrate that Ca²⁺ influx via store-operated CRAC channels is essential for CaCC activation, chloride secretion, and sweat production in humans and mice.

Authors

Axel R. Concepcion, Martin Vaeth, Larry E. Wagner II, Miriam Eckstein, Lee Hecht, Jun Yang, David Crottes, Maximilian Seidl, Hyosup P. Shin, Carl Weidinger, Scott Cameron, Stuart E. Turvey, Thomas Issekutz, Isabelle Meyts, Rodrigo S. Lacruz, Mario Cuk, David I. Yule, Stefan Feske

Dendritic cells maintain dermal adipose–derived stromal cells in skin fibrosis

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Abstract

Scleroderma is a group of skin-fibrosing diseases for which there are no effective treatments. A feature of the skin fibrosis typical of scleroderma is atrophy of the dermal white adipose tissue (DWAT). Adipose tissue contains adipose-derived mesenchymal stromal cells (ADSCs) that have regenerative and reparative functions; however, whether DWAT atrophy in fibrosis is accompanied by ADSC loss is poorly understood, as are the mechanisms that might maintain ADSC survival in fibrotic skin. Here, we have shown that DWAT ADSC numbers were reduced, likely because of cell death, in 2 murine models of scleroderma skin fibrosis. The remaining ADSCs showed a partial dependence on dendritic cells (DCs) for survival. Lymphotoxin β (LTβ) expression in DCs maintained ADSC survival in fibrotic skin by activating an LTβ receptor/β₁ integrin (LTβR/β₁ integrin) pathway on ADSCs. Stimulation of LTβR augmented the engraftment of therapeutically injected ADSCs, which was associated with reductions in skin fibrosis and improved skin function. These findings provide insight into the effects of skin fibrosis on DWAT ADSCs, identify a DC-ADSC survival axis in fibrotic skin, and suggest an approach for improving mesenchymal stromal cell therapy in scleroderma and other diseases.

Authors

Jennifer J. Chia, Tong Zhu, Susan Chyou, Dragos C. Dasoveanu, Camila Carballo, Sha Tian, Cynthia M. Magro, Scott Rodeo, Robert F. Spiera, Nancy H. Ruddle, Timothy E. McGraw, Jeffrey L. Browning, Robert Lafyatis, Jessica K. Gordon, Theresa T. Lu

RAC1 activation drives pathologic interactions between the epidermis and immune cells

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Abstract

Interactions between the epidermis and the immune system govern epidermal tissue homeostasis. These epidermis-immune interactions are altered in the inflammatory disease psoriasis; however, the pathways that underlie this aberrant immune response are not well understood. Here, we determined that Ras-related C3 botulinum toxin substrate 1 (RAC1) is a key mediator of epidermal dysfunction. RAC1 activation was consistently elevated in psoriatic epidermis and primary psoriatic human keratinocytes (PHKCs) exposed to psoriasis-related stimuli, but not in skin from patients with basal or squamous cell carcinoma. Expression of a constitutively active form of RAC1 (RAC^V12) in mice resulted in the development of lesions similar to those of human psoriasis that required the presence of an intact immune system. RAC1^V12-expressing mice and human psoriatic skin showed similar RAC1-dependent signaling as well as transcriptional overlap of differentially expressed epidermal and immune pathways. Coculture of PHKCs with immunocytes resulted in the upregulation of RAC1-dependent proinflammatory cytokines, an effect that was reproduced by overexpressing RAC1 in normal human keratinocytes. In keratinocytes, modulating RAC1 activity altered differentiation, proliferation, and inflammatory pathways, including STAT3, NFκB, and zinc finger protein 750 (ZNF750). Finally, RAC1 inhibition in xenografts composed of human PHKCs and immunocytes abolished psoriasiform hyperplasia and inflammation in vivo. These studies implicate RAC1 as a potential therapeutic target for psoriasis and as a key orchestrator of pathologic epidermis-immune interactions.

Authors

Mårten C.G. Winge, Bungo Ohyama, Clara N. Dey, Lisa M. Boxer, Wei Li, Nazanin Ehsani-Chimeh, Allison K. Truong, Diane Wu, April W. Armstrong, Teruhiko Makino, Matthew Davidson, Daniela Starcevic, Andreas Kislat, Ngon T. Nguyen, Takashi Hashimoto, Bernard Homey, Paul A. Khavari, Maria Bradley, Elizabeth A. Waterman, M. Peter Marinkovich

Oxidative stress and dysfunctional NRF2 underlie pachyonychia congenita phenotypes

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Abstract

Palmoplantar keratoderma (PPK) are debilitating lesions that arise in individuals with pachyonychia congenita (PC) and feature upregulation of danger-associated molecular patterns and skin barrier regulators. The defining features of PC-associated PPK are reproduced in mice null for keratin 16 (Krt16), which is commonly mutated in PC patients. Here, we have shown that PPK onset is preceded by oxidative stress in footpad skin of Krt16^–/– mice and correlates with an inability of keratinocytes to sustain nuclear factor erythroid–derived 2 related factor 2–dependent (NRF2-dependent) synthesis of the cellular antioxidant glutathione (GSH). Additionally, examination of plantar skin biopsies from individuals with PC confirmed the presence of high levels of hypophosphorylated NRF2 in lesional tissue. In Krt16^–/– mice, genetic ablation of Nrf2 worsened spontaneous skin lesions and accelerated PPK development in footpad skin. Hypoactivity of NRF2 in Krt16^–/– footpad skin correlated with decreased levels or activity of upstream NRF2 activators, including PKCδ, receptor for activated C kinase 1 (RACK1), and p21. Topical application of the NRF2 activator sulforaphane to the footpad of Krt16^–/– mice prevented the development of PPK and normalized redox balance via regeneration of GSH from existing cellular pools. Together, these findings point to oxidative stress and dysfunctional NRF2 as contributors to PPK pathogenesis, identify K16 as a regulator of NRF2 activation, and suggest that pharmacological activation of NRF2 should be further explored for PC treatment.

Authors

Michelle L. Kerns, Jill M.C. Hakim, Rosemary G. Lu, Yajuan Guo, Andreas Berroth, Roger L. Kaspar, Pierre A. Coulombe

Hyperactivation of JAK1 tyrosine kinase induces stepwise, progressive pruritic dermatitis

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Abstract

Skin homeostasis is maintained by the continuous proliferation and differentiation of epidermal cells. The skin forms a strong but flexible barrier against microorganisms as well as physical and chemical insults; however, the physiological mechanisms that maintain this barrier are not fully understood. Here, we have described a mutant mouse that spontaneously develops pruritic dermatitis as the result of an initial defect in skin homeostasis that is followed by induction of a Th2-biased immune response. These mice harbor a mutation that results in a single aa substitution in the JAK1 tyrosine kinase that results in hyperactivation, thereby leading to skin serine protease overexpression and disruption of skin barrier function. Accordingly, treatment with an ointment to maintain normal skin barrier function protected mutant mice from dermatitis onset. Pharmacological inhibition of JAK1 also delayed disease onset. Together, these findings indicate that JAK1-mediated signaling cascades in skin regulate the expression of proteases associated with the maintenance of skin barrier function and demonstrate that perturbation of these pathways can lead to the development of spontaneous pruritic dermatitis.

Authors

Takuwa Yasuda, Toshiyuki Fukada, Keigo Nishida, Manabu Nakayama, Masashi Matsuda, Ikuo Miura, Teruki Dainichi, Shinji Fukuda, Kenji Kabashima, Shinji Nakaoka, Bum-Ho Bin, Masato Kubo, Hiroshi Ohno, Takanori Hasegawa, Osamu Ohara, Haruhiko Koseki, Shigeharu Wakana, Hisahiro Yoshida

A GRHL3-regulated repair pathway suppresses immune-mediated epidermal hyperplasia

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Abstract

Dermal infiltration of T cells is an important step in the onset and progression of immune-mediated skin diseases such as psoriasis; however, it is not known whether epidermal factors play a primary role in the development of these diseases. Here, we determined that the prodifferentiation transcription factor grainyhead-like 3 (GRHL3), which is essential during epidermal development, is dispensable for adult skin homeostasis, but required for barrier repair after adult epidermal injury. Consistent with activation of a GRHL3-regulated repair pathway in psoriasis, we found that GRHL3 is upregulated in lesional skin and binds known epidermal differentiation gene targets. Using an imiquimod-induced model of immune-mediated epidermal hyperplasia, we found that mice lacking GRHL3 have an exacerbated epidermal damage response, greater sensitivity to disease induction, delayed resolution of epidermal lesions, and resistance to anti–IL-22 therapy compared with WT animals. ChIP-Seq and gene expression profiling of murine skin revealed that while GRHL3 regulates differentiation pathways both during development and during repair from immune-mediated damage, it targets distinct sets of genes in the 2 processes. In particular, GRHL3 suppressed a number of alarmin and other proinflammatory genes after immune injury. This study identifies a GRHL3-regulated epidermal barrier repair pathway that suppresses disease initiation and helps resolve existing lesions in immune-mediated epidermal hyperplasia.

Authors

William M. Gordon, Michael D. Zeller, Rachel H. Klein, William R. Swindell, Hsiang Ho, Francisco Espetia, Johann E. Gudjonsson, Pierre F. Baldi, Bogi Andersen

Cannabidiol exerts sebostatic and antiinflammatory effects on human sebocytes

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Abstract

The endocannabinoid system (ECS) regulates multiple physiological processes, including cutaneous cell growth and differentiation. Here, we explored the effects of the major nonpsychotropic phytocannabinoid of Cannabis sativa, (-)-cannabidiol (CBD), on human sebaceous gland function and determined that CBD behaves as a highly effective sebostatic agent. Administration of CBD to cultured human sebocytes and human skin organ culture inhibited the lipogenic actions of various compounds, including arachidonic acid and a combination of linoleic acid and testosterone, and suppressed sebocyte proliferation via the activation of transient receptor potential vanilloid-4 (TRPV4) ion channels. Activation of TRPV4 interfered with the prolipogenic ERK1/2 MAPK pathway and resulted in the downregulation of nuclear receptor interacting protein-1 (NRIP1), which influences glucose and lipid metabolism, thereby inhibiting sebocyte lipogenesis. CBD also exerted complex antiinflammatory actions that were coupled to A2a adenosine receptor-dependent upregulation of tribbles homolog 3 (TRIB3) and inhibition of the NF-κB signaling. Collectively, our findings suggest that, due to the combined lipostatic, antiproliferative, and antiinflammatory effects, CBD has potential as a promising therapeutic agent for the treatment of acne vulgaris.

Authors

Attila Oláh, Balázs I. Tóth, István Borbíró, Koji Sugawara, Attila G. Szöllõsi, Gabriella Czifra, Balázs Pál, Lídia Ambrus, Jennifer Kloepper, Emanuela Camera, Matteo Ludovici, Mauro Picardo, Thomas Voets, Christos C. Zouboulis, Ralf Paus, Tamás Bíró

Chronic itch development in sensory neurons requires BRAF signaling pathways

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Abstract

Chronic itch, or pruritus, is associated with a wide range of skin abnormalities. The mechanisms responsible for chronic itch induction and persistence remain unclear. We developed a mouse model in which a constitutively active form of the serine/threonine kinase BRAF was expressed in neurons gated by the sodium channel Nav1.8 (BRAF^Nav1.8 mice). We found that constitutive BRAF pathway activation in BRAF^Nav1.8 mice results in ectopic and enhanced expression of a cohort of itch-sensing genes, including gastrin-releasing peptide (GRP) and MAS-related GPCR member A3 (MRGPRA3), in nociceptors expressing transient receptor potential vanilloid 1 (TRPV1). BRAF^Nav1.8 mice showed de novo neuronal responsiveness to pruritogens, enhanced pruriceptor excitability, and heightened evoked and spontaneous scratching behavior. GRP receptor expression was increased in the spinal cord, indicating augmented coding capacity for itch subsequent to amplified pruriceptive inputs. Enhanced GRP expression and sustained ERK phosphorylation were observed in sensory neurons of mice with allergic contact dermatitis– or dry skin–elicited itch; however, spinal ERK activation was not required for maintaining central sensitization of itch. Inhibition of either BRAF or GRP signaling attenuated itch sensation in chronic itch mouse models. These data uncover RAF/MEK/ERK signaling as a key regulator that confers a subset of nociceptors with pruriceptive properties to initiate and maintain long-lasting itch sensation.

Authors

Zhong-Qiu Zhao, Fu-Quan Huo, Joseph Jeffry, Lori Hampton, Shadmehr Demehri, Seungil Kim, Xian-Yu Liu, Devin M. Barry, Li Wan, Zhong-Chun Liu, Hui Li, Ahu Turkoz, Kaijie Ma, Lynn A. Cornelius, Raphael Kopan, James F. Battey Jr., Jian Zhong, Zhou-Feng Chen

Retinoids activate the irritant receptor TRPV1 and produce sensory hypersensitivity

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Abstract

Retinoids are structurally related derivatives of vitamin A and are required for normal vision as well as cell proliferation and differentiation. Clinically, retinoids are effective in treating many skin disorders and cancers. Application of retinoids evokes substantial irritating side effects, including pain and inflammation; however, the precise mechanisms accounting for the sensory hypersensitivity are not understood. Here we show that both naturally occurring and synthetic retinoids activate recombinant or native transient receptor potential channel vanilloid subtype 1 (TRPV1), an irritant receptor for capsaicin, the pungent ingredient of chili peppers. In vivo, retinoids produced pain-related behaviors that were either eliminated or significantly reduced by genetic or pharmacological inhibition of TRPV1 function. These findings identify TRPV1 as an ionotropic receptor for retinoids and provide cellular and molecular insights into retinoid-evoked hypersensitivity. These findings also suggest that selective TRPV1 antagonists are potential therapeutic drugs for treating retinoid-induced sensory hypersensitivity.

Authors

Shijin Yin, Jialie Luo, Aihua Qian, Junhui Du, Qing Yang, Shentai Zhou, Weihua Yu, Guangwei Du, Richard B. Clark, Edgar T. Walters, Susan M. Carlton, Hongzhen Hu