Wnt5a/β-catenin signaling drives calcium-induced differentiation of human primary keratinocytes

Convergence of Calcium Channel Regulation and Mechanotransduction in Skeletal Regenerative Biomaterial Design

Cells are known to perceive their microenvironment through extracellular and intracellular mechanical signals. Upon sensing mechanical stimuli, cells can initiate various downstream signaling pathways that are vital to regulating proliferation, growth, and homeostasis. One such physiologic activity modulated by mechanical stimuli is osteogenic differentiation. The process of osteogenic mechanotransduction is regulated by numerous calcium ion channels-including channels coupled to cilia, mechanosensitive and voltage-sensitive channels, and channels associated with the endoplasmic reticulum. Evidence suggests these channels are implicated in osteogenic pathways such as the YAP/TAZ and canonical Wnt pathways. This review aims to describe the involvement of calcium channels in regulating osteogenic differentiation in response to mechanical loading and characterize the fashion in which those channels directly or indirectly mediate this process. The mechanotransduction pathway is a promising target for the development of regenerative materials for clinical applications due to its independence from exogenous growth factor supplementation. As such, also described are examples of osteogenic biomaterial strategies that involve the discussed calcium ion channels, calcium-dependent cellular structures, or calcium ion-regulating cellular features. Understanding the distinct ways calcium channels and signaling regulate these processes may uncover potential targets for advancing biomaterials with regenerative osteogenic capabilities.

Protective effect of Saussurea involucrata polysaccharide against skin dryness induced by ultraviolet radiation

Background: Exposure to ultraviolet B (UVB) radiation can damage the epidermis barrier function and eventually result in skin dryness. At present, little work is being devoted to skin dryness. Searching for active ingredients that can protect the skin against UVB-induced dryness will have scientific significance. Methods: Saussurea involucrata polysaccharide (SIP) has been shown to have significant antioxidant and anti-photodamage effects on the skin following UVB irradiation. To evaluate the effect of SIP on UVB-induced skin dryness ex vivo, SIP-containing hydrogel was applied in a mouse model following exposure to UVB and the levels of histopathological changes, DNA damage, inflammation, keratinocyte differentiation, lipid content were then evaluated. The underlying mechanisms of SIP to protect the cells against UVB induced-dryness were determined in HaCaT cells. Results: SIP was found to lower UVB-induced oxidative stress and DNA damage while increasing keratinocyte differentiation and lipid production. Western blot analysis of UVB-irradiated skin tissue revealed a significant increase in peroxisome proliferator-activated receptor-α (PPAR-α) levels, indicating that the underlying mechanism may be related to PPAR-α signaling pathway activation. Conclusions: By activating the PPAR-α pathway, SIP could alleviate UVB-induced oxidative stress and inhibit the inflammatory response, regulate proliferation and differentiation of keratinocytes, and mitigate lipid synthesis disorder. These findings could provide candidate active ingredients with relatively clear mechanistic actions for the development of skin sunscreen moisturizers.

Phospholipase C-γ1 potentially facilitates subcellular localization of activated β-catenin, p-β-catenin(S552), during bovine herpesvirus 1 productive infection in MDBK cells

Bovine herpesvirus 1 (BoHV-1) is a significant risk factor for the bovine respiratory disease complex (BRDC), a severe disease causing great economic losses to the cattle industry worldwide. Previous studies have reported that both phospholipase C-γ1 (PLC-γ1) and β-catenin are activated during BoHV-1 infection for efficient replication. However, the interplay between PLC-γ1 and β-catenin as a consequence of virus infection remains to be elucidated. Here, we reported that PLC-γ1 interacted with β-catenin, which was enhanced following virus infection. PLC-γ1-specific inhibitor, U73122, significantly reduced the mRNA levels of β-catenin in BoHV-1-infected cells; however, the steady-state protein levels were not affected due to the virus infection. Interestingly, the treatment of virus-infected cells with U73122 reduced the accumulation of activated β-catenin [p-β-catenin(S552)] in fractions of the cytoplasmic membrane as that observed with the treatment of methyl-β-cyclodextrin (MβCD), which can disrupt cytoplasmic membrane structure via sequestering cholesterol. Nucleus accumulation of p-β-catenin(S552) was increased following U73122 treatment in virus-infected cells. In addition, the association of p-β-catenin(S552) with cytoplasmic membrane induced by the virus infection was significantly disrupted by the treatment of U73122 and MβCD. These data indicated that the PLC-γ1 signaling is potentially involved in the regulation of β-catenin signaling stimulated by BoHV-1 infection partially via affecting the subcellular localization of p-β-catenin(S552).

Approaches for Regenerative Healing of Cutaneous Wound with an Emphasis on Strategies Activating the Wnt/β-Catenin Pathway

Significance: In adult mammals, spontaneous repair of a cutaneous wound occurs slowly and leaves a scar with skin adnexa deficiencies. To accelerate cutaneous wound-healing rates and avoid scar formation, current studies have focused on regenerative therapies. Recent Advances: Emerging therapeutics for regenerative wound healing often focus on the use of growth factors and stem cells. However, these therapeutic approaches have limited routine clinical use due to high costs and technical requirements. Critical Issue: Understanding the molecular mechanisms involved in the signaling pathways for cutaneous wound healing and neogenic synthesis of the skin components is important for identification of novel targets for the development of regenerative wound-healing agents. Future Directions: The Wnt/β-catenin pathway is a well-known key player for enhancement of the overall healing process involving tissue regeneration via crosstalk with other signaling pathways. Strategies that activate the Wnt/β-catenin pathway via modulation of the pathway-controlling regulatory factors could provide effective therapeutic approaches for regenerative wound healing.

A Beginner's Introduction to Skin Stem Cells and Wound Healing

The primary function of the skin is that of a physical barrier against the environment and diverse pathogens; therefore, its integrity is essential for survival. Skin regeneration depends on multiple stem cell compartments within the epidermis, which, despite their different transcriptional and proliferative capacity, as well as different anatomical location, fall under the general term of skin stem cells (SSCs). Skin wounds can normally heal without problem; however, some diseases or extensive damage may delay or prevent healing. Non-healing wounds represent a serious and life-threatening scenario that may require advanced therapeutic strategies. In this regard, increased focus has been directed at SSCs and their role in wound healing, although emerging therapeutical approaches are considering the use of other stem cells instead, such as mesenchymal stem cells (MSCs). Given its extensive and broad nature, this review supplies newcomers with an introduction to SSCs, wound healing, and therapeutic strategies for skin regeneration, thus familiarizing the reader with the subject in preparation for future in depth reading.

Oat β-glucan ameliorates epidermal barrier disruption by upregulating the expression of CaSR through dectin-1-mediated ERK and p38 signaling pathways

The integrity of the epidermal barrier and the maintenance of barrier homeostasis depend on the dynamic balance between the proliferation and differentiation of keratinocytes. Calcium (Ca²⁺) plays a crucial role in maintaining a balance of these two processes as well as in the formation of an epidermal permeability barrier. In this study, we showed that topical application of oat β-glucan (OG) could ameliorate epidermal hyperplasia and accelerate the recovery of the epidermal barrier by promoting epidermal differentiation. Mechanistic studies revealed a positive interaction between OG and the dectin-1 receptor, and this interaction could lead to an upregulated expression of the calcium-sensing receptor (CaSR) via activation of the downstream ERK and p38 pathways. This consequently increased the sensitivity of keratinocytes to extracellular Ca²⁺ under the condition of calcium loss following the disruption of the epidermal barrier, resulting in the maintenance of normal keratinocyte differentiation in the epidermis, and ultimately promoting the recovery of the epidermal barrier. These findings clearly demonstrated the healing effect of OG on a physically damaged epidermal barrier. Thus, OG could be considered a valuable component in the development of skin repair agents.

Calcium-Sensing Receptor Participates in High Glucose-Induced EndMT in Primary Human Aortic Endothelial Cells

Objective

Previous studies have shown that high glucose (HG) induces endothelial cell (EC) damage via endothelial-to-mesenchymal transition (EndMT). Although the underlying mechanisms are still unclear, recent studies have demonstrated the role of calcium-sensing receptor (CaSR) in mediating EC damage. Therefore, the aim of our study was to investigate whether CaSR mediates HG-induced EndMT and to determine the underlying mechanism.

Methods

Bioinformatics analysis of microarray profiles (GSE30780) and protein-protein interaction (PPI) analyses were performed to select the hub genes. As for in vitro research, the human aortic ECs (HAECs) were exposed to HG to induce EndMT. The expression of CaSR and β-catenin was determined, as well as their effects on EndMT (endothelial marker CD31, mesenchymal marker FSP1, and α-SMA).

Results

The bioinformatics analysis indicated CaSR was significantly increased in HG-treated HAECs and was one of the hub genes. The in vitro results showed that HG significantly inhibited the expression of CD31 and increased FSP1 and α-SMA in a concentration- and time-dependent manner. Moreover, CaSR was increased in HAECs after HG treatment. The CaSR antagonist attenuated HG-induced expression of EndMT-related markers. Furthermore, HG treatment increased the nuclear translocation of β-catenin in HAECs. In contrast, blocking the nuclear translocation of β-catenin by DKK1 could attenuate HG-induced EndMT (increased the protein expression of CD31 by 30% and decreased the protein expression of FSP1 by 15% and α-SMA by 25%). CaSR siRNA further inhibited the HG-induced nuclear translocation of β-catenin in HAECs.

Conclusion

Our research demonstrated that HG-induced EndMT in HAECs might be mediated by CaSR and the downstream nuclear translocation of β-catenin.

C3a and Its Receptor C3aR Are Detectable in Normal Human Epidermal Keratinocytes and Are Differentially Regulated via TLR3 and LL37

To study the molecular interplay between TLRs and complement representing ancient danger-sensing mechanisms, we examined the regulation of the C3a/anaphylatoxin C3a receptor (C3aR) axis in normal human epidermal keratinocytes (NHEKs) by treatment with different TLR ligands. Protein staining followed by flow cytometry revealed highly constitutive intracellular expression levels of the C3aR in NHEKs. Stimulation with Poly I:C up-regulated C3aR mRNA and intra- and extracellular expression in NHEKs which showed functional relevance by up-regulating CXCL10 and down-regulating C3 expression in response to C3a. mRNA and protein levels of C3 and protease cathepsin L (CTSL) that can cleave C3 were up-regulated by the TLR3 ligand Poly I:C. Enhanced intracellular expression levels of the biologically active C3 fragment (C3a), in response to TLR3 stimulation were also detectable in NHEKs. Cathelicidin antimicrobial peptide LL-37 potentiated Poly I:C-induced C3aR, C3, and CTSL up-regulation. In conclusion, we point to a role of TLR3 to promote up-regulation of C3aR, C3, and CTSL expression levels and generation of C3a. Our data provide evidence that local generation and activation of complement components as described for T cells or myeloid cells represent a scenario which may take place in a similar way in NHEKs.

Insight Into the Function of RIPK4 in Keratinocyte Differentiation and Carcinogenesis

The receptor-interacting protein kinase 4 (RIPK4), a member of the RIPK family, was originally described as an interaction partner of protein kinase C (PKC) β and PKCδ. RIPK4 is identified as a key regulator of keratinocyte differentiation, cutaneous inflammation, and cutaneous wound repair. The mechanism by which RIPK4 integrates upstream signals to initiate specific responses remains elusive. Previous studies have indicated that RIPK4 can regulate several signaling pathways, including the NF-κB, Wnt/β-catenin, and RAF/MEK/ERK pathways. Furthermore, RIPK4-related biological signaling pathways interact with each other to form a complex network. Mounting evidence suggests that RIPK4 is aberrantly expressed in various kinds of cancers. In several types of squamous cell carcinoma (SCC), the mutations that drive aggressive SCC have been found in RIPK4. In addition, the function of RIPK4 in carcinogenesis is probably tissue-specific, since RIPK4 can play a dual role as both a tumor promoter and a tumor suppressor in different tumor types. Therefore, RIPK4 may represent as an independent prognostic factor and a promising novel therapeutic target, which can be used to identify the risks of patients and guide personalized treatments. In future, RIPK4-interacting pathways and precise molecular targets need to be investigated in order to further elucidate the mechanisms underlying epidermal differentiation and carcinogenesis.

Abnormal keratinocyte differentiation in the nasal planum of Labrador Retrievers with hereditary nasal parakeratosis (HNPK)

Hereditary nasal parakeratosis (HNPK) is an inherited disorder described in Labrador Retrievers and Greyhounds. It has been associated with breed-specific variants in the SUV39H2 gene encoding a histone 3 methyltransferase involved in epigenetic silencing. Formalin-fixed biopsies of the nasal planum of Labrador Retrievers were screened by immunofluorescence microscopy for the presence and distribution of epidermal proliferation and differentiation markers. Gene expression of these markers was further analysed using RNA sequencing (RNA-seq) and ultrastructural epidermal differences were investigated by electron microscopy. Differentiation of the nasal planum in the basal and suprabasal epidermal layers of HNPK-affected dogs (n = 6) was similar compared to control dogs (n = 6). In the upper epidermal layers, clear modifications were noticed. Loricrin protein was absent in HNPK-affected nasal planum sections in contrast to sections of the same location of control dogs. However, loricrin was present in the epidermis of paw pads and abdominal skin from HNPK dogs and healthy control dogs. The patterns of keratins K1, K10 and K14, were not markedly altered in the nasal planum of HNPK-affected dogs while the expression of the terminal differentiation marker involucrin appeared less regular. Based on RNA-seq, LOR and IVL expression levels were significantly decreased, while KRT1, KRT10 and KRT14 levels were up-regulated (log2fold-changes of 2.67, 3.19 and 1.71, respectively) in HNPK-affected nasal planum (n = 3) compared to control dogs (n = 3). Electron microscopical analysis revealed structural alterations in keratinocytes and stratum corneum, and disrupted keratinocyte adhesions and distended intercellular spaces in lesional samples (n = 3) compared to a sample of a healthy control dog (n = 1). Our findings demonstrate aberrant keratinocyte terminal differentiation of the nasal planum of HNPK-affected Labrador Retrievers and provide insights into biological consequences of this inactive SUV39H2 gene variant.

Fucoidan from Undaria pinnatifida Ameliorates Epidermal Barrier Disruption via Keratinocyte Differentiation and CaSR Level Regulation

The epidermal barrier acts as a line of defense against external agents as well as helps to maintain body homeostasis. The calcium concentration gradient across the epidermal barrier is closely related to the proliferation and differentiation of keratinocytes (KCs), and the regulation of these two processes is the key to the repair of epidermal barrier disruption. In the present study, we found that fucoidan from Undaria pinnatifida (UPF) could promote the repair of epidermal barrier disruption in mice. The mechanistic study demonstrated that UPF could promote HaCaT cell differentiation under low calcium condition by up-regulating the expression of calcium-sensing receptor (CaSR), which could then lead to the activation of the Catenin/PLCγ1 pathway. Further, UPF could increase the expression of CaSR through activate the ERK and p38 pathway. These findings reveal the molecular mechanism of UPF in the repair of the epidermal barrier and provide a basis for the development of UPF into an agent for the repair of epidermal barrier repair.

The pathological role of Wnt5a in psoriasis and psoriatic arthritis

Psoriasis (PsO) is a chronic inflammatory skin disease with both local and systemic components. PsO‐associated arthritis, known as psoriatic arthritis (PsA), develops in approximately 13%‐25% of PsO patients. Various factors associated with both PsO and PsA indicate that these conditions are part of a single disease. Identification of novel targets for the development of drugs to treat both PsO and PsA is desirable to provide more patient‐friendly treatment regimens. Such targets will likely represent ‘common checkpoints’ of inflammation, for example key components or transduction cascades of the signalling pathways involved. Emerging evidence supports involvement of the non‐canonical Wnt signalling pathways in the development of both PsO and PsA, especially the Wnt5a‐activated signalling cascades. These, together with interlinked factors, are crucial in the interactions among keratinocytes, immune cells and inflammatory factors in PsO, as well as among chondrocytes, osteoblasts and osteoclasts that trigger both subchondral bone remodelling and cartilage catabolism in PsA. This review focuses on the pathological role of Wnt5a signalling and its interaction with other interlinked pathways in both PsO and PsA, and also on the main challenges for future research, particularly with respect to molecules targeting Wnt signalling pathways for the treatment of PsO and PsA.

Lack of plakoglobin impairs integrity and wound healing in corneal epithelium in mice

We generated cornea-specific plakoglobin (Jup; junctional plakoglobin) knockout mice in order to investigate the function of plakoglobin on the maintenance of the homeostasis of corneal epithelium in mice. Cornea epithelium-specific conditional knockouts (Jup^CEΔ/CEΔ) (cKO) were obtained by breeding keratin12-Cre (Krt12-Cre) mice to Jup-floxed (Jup^f/f) mice. Light and transmission electron microscopic and immunohistochemical analyses were carried out to determine consequence of the loss of plakoglobin on maintaining corneal epithelium integrity under mechanical stress, e.g., brushing and wound healing. Immunohistochemistry analysis demonstrated that, although Jup ablation did not affect BrdU incorporation, basal cell-like cells labeled for keratin 14 were ectopically present in the supra-basal layer in mutant corneal epithelium, suggestive of altered cell differentiation. Plakoglobin-deficient epithelium exhibits increased fragility against mechanical intervention when compared to wild-type controls under identical treatment. Closure of an epithelial defect was significantly delayed in Jup^CEΔ/CEΔ epithelium. Our findings indicate that the lack of plakoglobin significantly affects corneal epithelium differentiation, as well as its structural integrity. Plakoglobin is essential to the maintenance of the structure of the corneal epithelium and its wound healing.

miRNA-203 Modulates Aldosterone Levels and Cell Proliferation by Targeting Wnt5a in Aldosterone-Producing Adenomas

CONTEXT

The aberrant expression or alternation of miRNA in the pathogenesis of aldosterone-producing adenomas (APAs) is still largely unknown.

OBJECTIVE

We investigated the role of miRNA-203 (screened from miRNA microarrays) and elucidated its effects on the Wnt/β-catenin pathway regarding aldosterone production and cell proliferation in APAs.

METHODS

miR-203 expression was upregulated or downregulated by transfecting miR-203 mimics or inhibitors into primary APA cells, the human adrenocortical cell line HAC15, and C57BL/6 mice. In vitro and biochemical data were correlated with the respective clinical parameters of APAs to evaluate their clinical importance.

RESULTS

The expression of miR-203 in human APA samples was significantly lower than that of peritumor adrenal samples. Tumoral miR-203 abundance correlated negatively with both plasma aldosterone level and tumor size in patients with APAs. miR-203 inhibitors increased aldosterone production and cell proliferation in HAC15 cells, and restoration of expression via miR-203 mimics showed decreased cell proliferation and aldosterone hypersecretion in APA cell cultures. In vivo selective inhibition of miR-203 via intra-adrenal injection of miR-203 inhibitors in mice led to a substantial increase in systolic blood pressure and plasma aldosterone levels. Additionally, the dual-luciferase reporter assay demonstrated that WNT5A is a direct target of miR-203. Furthermore, plasma Wnt5a levels in adrenal vein sampling were helpful in differentiating tumor localization, and preoperative plasma Wnt5a levels predicted the cure of hypertension after adrenalectomy.

CONCLUSION

We have demonstrated that attenuated miR-203 expression in APAs increases aldosterone production and the tumorigenesis of adrenal cells by activating the Wnt5a/β-catenin pathway.

Intracellular Calcium Determines the Adipogenic Differentiation Potential of Human Umbilical Cord Blood-Derived Mesenchymal Stem Cells via the Wnt5a/β-Catenin Signaling Pathway

Mesenchymal stem cells- (MSCs-) based therapies show different degrees of efficacies for the treatment of various diseases, including lipogenesis. We evaluated the adipogenic differentiation ability of human umbilical cord blood-derived MSCs (hUCB-MSCs) from different donors and examined the contribution of the intracellular calcium (Ca²⁺) level to this diversity. hUCB-MSCs treated with Ca²⁺ or the Ca²⁺ chelator BAPTA-AM increased and decreased adipogenic differentiation, respectively. Canonical Wnt5a/β-catenin expression decreased during adipogenic differentiation of hUCB-MSCs. Treatment with Wnt5a blocked the adipogenic differentiation of hUCB-MSCs and activated the Wnt pathway, with a decrease in the adipogenesis markers PPARγ and leptin, and reduced lipid vacuole-associated Oil red O activity. In contrast, inhibition of the Wnt pathway with dickkopf-1 and β-catenin small interfering RNA transfection promoted the adipogenic potential of hUCB-MSCs. Interestingly, the Ca²⁺-based system exhibited a synergic effect on adipogenic potential through the Wnt5a/β-catenin pathway. Our data suggest that the variable adipogenic differentiation potential of hUCB-MSCs from different lots is due to variation in the intracellular Ca²⁺ level, which can be used as a marker to predict hUCB-MSCs selection for lipogenesis therapy. Overall, these results demonstrate that exogenous calcium treatment enhanced the adipogenic differentiation of hUCB-MSCs via negatively regulating the Wnt5a/β-catenin signaling pathway.

Disorder of the mevalonate pathway inhibits calcium-induced differentiation of keratinocytes

Mutation of genes encoding the enzymes of the mevalonate pathway cause a variety of diseases, including skin disorders. Mutation of four genes in this pathway, including mevalonate kinase, phosphomevalonate kinase, mevalonate diphosphate decarboxylase and farnesyl diphosphate synthase, have demonstrated to be responsible for porokeratosis (PK). However, the pathogenesis of PK remains unclear. In the present study, specific enzyme inhibitors of the mevalonate pathway, including pravastatin (PRA), alendronate (ALD), farnesyl transferase inhibitor (FTI‑277) and geranylgeranyl transferase inhibitor (GGTI‑298), were used to investigate the effect on differentiation of keratinocytes (KCs). Western blotting demonstrated that PRA, ALD, FTI‑277 or GGTI‑298 alone, or in combination, inhibited the expression level of calcium‑induced differentiation maker involucrin (INV) in KCs. ALD and PRA induced greater inhibition of INV compared with FTI‑277 and GGTI‑298 treatment. These inhibitors additionally influenced the expression levels of keratin1. Mechanistic studies revealed that treatment of cells with inhibitors decreased the expression levels of p53 and Notch1, and regulated activation of the mitogen activated protein kinase and phosphoinositide‑3‑kinase/protein kinase B signaling pathways. The results of the present study suggested that regulation of the mevalonate pathway may be necessary for differentiation of KCs, and the pathogenesis of disseminated superficial actinic PK.

Skin renewal activity of non-thermal plasma through the activation of β-catenin in keratinocytes

For recent years, devices that generate non-thermal plasma (NTP) have been introduced into the field of dermatology. Since NTP has demonstrated strong anti-pathogenic activity with safety of use, NTP was first applied to sterilize the skin surface to aid in the healing of various kinds of skin diseases. However, the effect of NTP on skin regeneration has not yet been fully explored. In this study, the effect of NTP on the growth of keratinocytes was tested using the HaCaT human keratinocyte cell line and HRM2 hairless mice. Treatment with NTP allowed confluent keratinocytes to escape from G1 cell cycle arrest and increased the proportion of cells in S and G2 phases. In particular, NTP treatment immediately dispersed E-cadherin-mediated cell-to-cell interactions, resulting in the translocation of β-catenin to the nucleus and leading to the enhanced transcription of target genes including c-MYC and cyclin D1. Moreover, repeated treatment of the mice with NTP also stimulated epidermal expansion by activating β-catenin in the epidermal cells. The symptoms of cellular DNA damage were not detected after NTP treatment. Taken together, these results demonstrate that NTP may be employed as a new type of skin regenerating device.

To Control Site-Specific Skin Gene Expression, Autocrine Mimics Paracrine Canonical Wnt Signaling and Is Activated Ectopically in Skin Disease

Despite similar components, the heterogeneity of skin characteristics across the human body is enormous. It is classically believed that site-specific fibroblasts in the dermis control postnatal skin identity by modulating the behavior of the surface-overlying keratinocytes in the epidermis. To begin testing this hypothesis, we characterized the gene expression differences between volar (ventral; palmoplantar) and nonvolar (dorsal) human skin. We show that KERATIN 9 (KRT9) is the most uniquely enriched transcript in volar skin, consistent with its etiology in genetic diseases of the palms and soles. In addition, ectopic KRT9 expression is selectively activated by volar fibroblasts. However, KRT9 expression occurs in the absence of all fibroblasts, although not to the maximal levels induced by fibroblasts. Through gain-of-function and loss-of-function experiments, we demonstrate that the mechanism is through overlapping paracrine or autocrine canonical WNT-β-catenin signaling in each respective context. Finally, as an in vivo example of ectopic expression of KRT9 independent of volar fibroblasts, we demonstrate that in the human skin disease lichen simplex chronicus, WNT5a and KRT9 are robustly activated outside of volar sites. These results highlight the complexities of site-specific gene expression and its disruption in skin disease.

Effects of Human Mesenchymal Stem Cells Coculture on Calcium-Induced Differentiation of Normal Human Keratinocytes

The influence of mesenchymal stem cells (MSCs) on keratinocytes in altered microenvironments is poorly understood. Here, we cocultured umbilical cord blood-derived MSCs with normal human epidermal keratinocytes to evaluate their paracrine effect in the presence of high extracellular calcium (Ca²⁺ ) concentration. High Ca²⁺ environment to keratinocytes can disrupt normal skin barrier function due to abnormal/premature differentiation of keratinocytes. Surprisingly, we found that MSCs suppress both proliferation and differentiation of keratinocytes under a high Ca²⁺ environment in transforming growth factors β1 (TGFβ1)-dependent manner. Furthermore, we determined that MSCs can regulate the mitogen-activated protein kinases, phosphatidylinositol 3-kinase/protein kinase B, and protein kinase C pathways in Ca²⁺ -induced differentiated keratinocytes. Knockdown of TGFβ1 from MSCs results in decreased suppression of differentiation with significantly increased proliferation of keratinocytes compared with control MSCs. MSCs-derived TGFβ1 further induced growth inhibition of keratinocyte in high extracellular Ca²⁺ environment as analyzed by a decrease in DNA synthesis, accumulation of phosphorylated retinoblastoma protein, cdc2, and increased mRNA level of p21, and independent of TGFβ1/SMAD pathway. Taken together, we found that MSCs-derived TGFβ1 is a critical regulator of keratinocyte function, and involves multiple proximal signaling cascades. Stem Cells 2017;35:1592-1602.

The WNT-less wonder: WNT-independent β-catenin signaling

β-catenin is known as an Armadillo protein that regulates gene expression following WNT pathway activation. However, WNT-independent pathways also activate β-catenin. During the establishment of the melanocyte lineage, β-catenin plays an important role. In the context of physiopathology, β-catenin is activated genetically or transiently in various cancers, including melanoma, where it can be found in the nucleus of tumors. In this review, we discuss alternative pathways that activate β-catenin independent of WNTs and highlight what is known regarding these pathways in melanoma. We also discuss the role of β-catenin as a transcriptional regulator in various cell types, with emphasis on the different transcription factors it associates with independent of WNT induction. Finally, the role of WNT-independent β-catenin in melanocyte development and melanomagenesis is also discussed.

Upregulation of miR-203 and miR-210 affect growth and differentiation of keratinocytes after exposure to sulfur mustard in normoxia and hypoxia

Exposure of the skin to sulfur mustard (SM) results in long-term complications such as impaired tissue regeneration. Previous own studies in normal human epidermal keratinocytes (NHEK) treated with SM demonstrated reduced proliferation, premature differentiation and a restricted functionality of hypoxia-mediated signaling in the cells. Here, we investigated the involvement of microRNAs, miR-203 and miR-210, in these mechanisms. SM significantly upregulated the expression of miR-203 in NHEK when cultivated under normoxic and hypoxic conditions. SM had no effect on miR-210 under normoxia. However, miR-210 levels were greatly increased in NHEK when grown in hypoxia and further elevated upon exposure of the cells to SM. In normoxia and hypoxia, inhibition of miR-203 by transfection of NHEK with complementary oligonucleotides, anti-miR-203, attenuated the SM-induced impairment of metabolic activity and proliferation, and counteracted SM-promoted keratin-1 expression in these cells. Consistent ameliorating effects on dysregulated metabolic activity, proliferation and keratin-1 expression in SM-treated NHEK were obtained upon inhibition of miR-210 in these cells grown in hypoxia. Our findings provide evidence that miR-203 and miR-210 are key regulators in normal and SM-impaired keratinocyte functionality, and suggest potential usefulness of inhibitors against miR-203 and miR-210 for target-directed therapeutical intervention to improve re-epithelialization of SM-injured skin.