Effects of Imiquimod on Hair Follicle Stem Cells and Hair Cycle Progression

Topical imiquimod (IMQ) application is widely used as a model for psoriasiform-like skin inflammation in mice. Although the effects on the epidermis are well characterized, it is unclear how IMQ affects hair follicles and cycling. Here we investigated how IMQ affects hair follicle stem cells and whether the timing of IMQ application influences the immune infiltrate. Our results show that IMQ application at mid and late telogen activated hair follicle stem cells leading to premature hair cycle entry (anagen), which was accompanied by massive infiltration of inflammatory macrophages and gamma delta T cells, whereas the number of the respective resident populations decreased. Interestingly, high resident macrophage numbers were present in Rag2−/− mice and were maintained after IMQ treatment explaining why IMQ-induced anagen was reduced. This could be rescued after macrophage depletion suggesting that resident macrophages inhibit whereas inflammatory infiltrating macrophages stimulate hair follicle stem cell activation. The expression of the anagen-inhibiting factor BMP-4 was reduced by IMQ treatment as well as the activating factors Wnt showing that IMQ-induced hair follicle stem cell activation occurs by a Wnt-independent mechanism involving inflammatory cytokines such as CCL2 and TNF-α. On the basis of our findings, we recommend conducting experiments with IMQ during mid and late telogen as the biggest differences in immune cell composition are observed

Myeloid STAT3 promotes formation of colitis-associated colorectal cancer in mice

Myeloid cells lacking STAT3 promote antitumor responses of NK and T cells but it is unknown if this crosstalk affects development of autochthonous tumors. We deleted STAT3 in murine myeloid cells (STAT3(Δm)) and examined the effect on the development of autochthonous colorectal cancers (CRCs). Formation of Azoxymethane/Dextransulfate (AOM/DSS)-induced CRCs was strongly suppressed in STAT3(Δm) mice. Gene expression profiling showed strong activation of T cells in the stroma of STAT3(Δm) CRCs. Moreover, STAT3(Δm) host mice were better able to control the growth of transplanted MC38 colorectal tumor cells which are known to be killed in a T cell-dependent manner. These data suggest that myeloid cells lacking STAT3 control formation of CRCs mainly via cross activation of T cells. Interestingly, the few CRCs that formed in STAT3(Δm) mice displayed enhanced stromalization but appeared normal in size indicating that they have acquired ways to escape enhanced tumor surveillance. We found that CRCs in STAT3(Δm) mice consistently activate STAT3 signaling which is implicated in immune evasion and might be a target to prevent tumor relapse

EGFR Controls Hair Shaft Differentiation in a p53-Independent Manner

Biological Sciences; Cell Biology; Developmental Biology; Stem Cells ResearchSCOPUS: ar.jinfo:eu-repo/semantics/publishe

Imiquimod clears tumors in mice independent of adaptive immunity by converting pDCs into tumor-killing effector cells

Imiquimod is a synthetic compound with antitumor properties; a 5% cream formulation is successfully used to treat skin tumors. The antitumor effect of imiquimod is multifactorial, although its ability to modulate immune responses by triggering TLR7/8 is thought to be key. Among the immune cells suggested to be involved are plasmacytoid DCs (pDCs). However, a direct contribution of pDCs to tumor killing in vivo and the mechanism of their recruitment to imiquimod-treated sites have never been demonstrated. Using a mouse model of melanoma, we have now demonstrated that pDCs can directly clear tumors without the need for the adaptive immune system. Topical imiquimod treatment led to TLR7-dependent and IFN-α/β receptor 1–dependent (IFNAR1-dependent) upregulation of expression of the chemokine CCL2 in mast cells. This was essential to induce skin inflammation and for the recruitment of pDCs to the skin. The recruited pDCs were CD8α+ and induced tumor regression in a TLR7/MyD88- and IFNAR1-dependent manner. Lack of TLR7 and IFNAR1 or depletion of pDCs or CD8α+ cells from tumor-bearing mice completely abolished the effect of imiquimod. TLR7 was essential for imiquimod-stimulated pDCs to produce IFN-α/β, which led to TRAIL and granzyme B secretion by pDCs via IFNAR1 signaling. Blocking these cytolytic molecules impaired pDC-mediated tumor killing. Our results demonstrate that imiquimod treatment leads to CCL2-dependent recruitment of pDCs and their transformation into a subset of killer DCs able to directly eliminate tumor cells

TNFα shedding and epidermal inflammation are controlled by Jun proteins

Inducible epidermal deletion of JunB and c-Jun in adult mice causes a psoriasis-like inflammatory skin disease. Increased levels of the proinflammatory cytokine TNFα play a major role in this phenotype. Here we define the underlying molecular mechanism using genetic mouse models. We show that Jun proteins control TNFα shedding in the epidermis by direct transcriptional activation of tissue inhibitor of metalloproteinase-3 (TIMP-3), an inhibitor of the TNFα-converting enzyme (TACE). TIMP-3 is down-regulated and TACE activity is specifically increased, leading to massive, cell-autonomous TNFα shedding upon loss of both JunB and c-Jun. Consequently, a prominent TNFα-dependent cytokine cascade is initiated in the epidermis, inducing severe skin inflammation and perinatal death of newborns from exhaustion of energy reservoirs such as glycogen and lipids. Importantly, this metabolic “cachectic” phenotype can be genetically rescued in a TNFR1-deficient background or by epidermis-specific re-expression of TIMP-3. These findings reveal that Jun proteins are essential physiological regulators of TNFα shedding by controlling the TIMP-3/TACE pathway. This novel mechanism describing how Jun proteins control skin inflammation offers potential targets for the treatment of skin pathologies associated with increased TNFα levels

Specific roles for dendritic cell subsets during initiation and progression of psoriasis

Abstract Several subtypes of APCs are found in psoriasis patients, but their involvement in disease pathogenesis is poorly understood. Here, we investigated the contribution of Langerhans cells (LCs) and plasmacytoid DCs (pDCs) in psoriasis. In human psoriatic lesions and in a psoriasis mouse model (DKO* mice), LCs are severely reduced, whereas pDCs are increased. Depletion of pDCs in DKO* mice prior to psoriasis induction resulted in a milder phenotype, whereas depletion during active disease had no effect. In contrast, while depletion of Langerin‐expressing APCs before disease onset had no effect, depletion from diseased mice aggravated psoriasis symptoms. Disease aggravation was due to the absence of LCs, but not other Langerin‐expressing APCs. LCs derived from DKO* mice produced increased IL‐10 levels, suggesting an immunosuppressive function. Moreover, IL‐23 production was high in psoriatic mice and further increased in the absence of LCs. Conversely, pDC depletion resulted in reduced IL‐23 production, and therapeutic inhibition of IL‐23R signaling ameliorated disease symptoms. Therefore, LCs have an anti‐inflammatory role during active psoriatic disease, while pDCs exert an instigatory function during disease initiation

FAM3C/ILEI protein is elevated in psoriatic lesions and triggers psoriasiform hyperproliferation in mice

Abstract FAM3C/ILEI is an important cytokine for tumor progression and metastasis. However, its involvement in inflammation remains elusive. Here, we show that ILEI protein is highly expressed in psoriatic lesions. Inducible keratinocyte‐specific ILEI overexpression in mice (K5‐ILEIind) recapitulates many aspects of psoriasis following TPA challenge, primarily manifested by impaired epidermal differentiation and increased neutrophil recruitment. Mechanistically, ILEI triggers Erk and Akt signaling, which then activates STAT3 via Ser727 phosphorylation. Keratinocyte‐specific ILEI deletion ameliorates TPA‐induced skin inflammation. A transcriptomic ILEI signature obtained from the K5‐ILEIind model shows enrichment in several signaling pathways also found in psoriasis and identifies urokinase as a targetable enzyme to counteract ILEI activity. Pharmacological inhibition of urokinase in TPA‐induced K5‐ILEIind mice results in significant improvement of psoriasiform symptoms by reducing ILEI secretion. The ILEI signature distinguishes psoriasis from healthy skin with uPA ranking among the top “separator” genes. Our study identifies ILEI as a key driver in psoriasis, indicates the relevance of ILEI‐regulated genes for disease manifestation, and shows the clinical impact of ILEI and urokinase as novel potential therapeutic targets in psoriasis

Inducible overexpression of a FAM3C/ILEI transgene has pleiotropic effects with shortened life span, liver fibrosis and anemia in mice.

FAM3C/ILEI is an important factor in epithelial-to-mesenchymal transition (EMT) induction, tumor progression and metastasis. Overexpressed in many cancers, elevated ILEI levels and secretion correlate with poor patient survival. Although ILEI's causative role in invasive tumor growth and metastasis has been demonstrated in several cellular tumor models, there are no available transgenic mice to study these effects in the context of a complex organism. Here, we describe the generation and initial characterization of a Tet-ON inducible Fam3c/ILEI transgenic mouse strain. We find that ubiquitous induction of ILEI overexpression (R26-ILEIind) at weaning age leads to a shortened lifespan, reduced body weight and microcytic hypochromic anemia. The anemia was reversible at a young age within a week upon withdrawal of ILEI induction. Vav1-driven overexpression of the ILEIind transgene in all hematopoietic cells (Vav-ILEIind) did not render mice anemic or lower overall fitness, demonstrating that no intrinsic mechanisms of erythroid development were dysregulated by ILEI and that hematopoietic ILEI hyperfunction did not contribute to death. Reduced serum iron levels of R26-ILEIind mice were indicative for a malfunction in iron uptake or homeostasis. Accordingly, the liver, the main organ of iron metabolism, was severely affected in moribund ILEI overexpressing mice: increased alanine transaminase and aspartate aminotransferase levels indicated liver dysfunction, the liver was reduced in size, showed increased apoptosis, reduced cellular iron content, and had a fibrotic phenotype. These data indicate that high ILEI expression in the liver might reduce hepatoprotection and induce liver fibrosis, which leads to liver dysfunction, disturbed iron metabolism and eventually to death. Overall, we show here that the novel Tet-ON inducible Fam3c/ILEI transgenic mouse strain allows tissue specific timely controlled overexpression of ILEI and thus, will serve as a versatile tool to model the effect of elevated ILEI expression in diverse tissue entities and disease conditions, including cancer