Calcium-Inducible MAPK/AP-1 Signaling Drives Semaphorin 3A Expression in Normal Human Epidermal Keratinocytes

PIEZO1 Promotes Odontoblast-Mediated Reactionary Dentinogenesis via SEMA3A

Located at the interface of the dentin-pulp complex, the odontoblasts are specialized cells responsible for dentin synthesis and nociceptive signal detection in response to external stimuli. Recent studies have shown that the mechanosensitive ion channel PIEZO1 is involved in bone formation and remodeling through the influx of calcium ions, and it is abundantly expressed in odontoblasts. However, the specific role of PIEZO1 in reactionary dentinogenesis and the underlying mechanisms remain elusive. In this study, we found intense PIEZO1 expression in the plasma membrane and cytoplasm of odontoblasts in healthy human third molars, mouse mandibular molars, and human odontoblast-like cells (hOBLCs). In hOBLCs, PIEZO1 positively regulated DSPP, DMP1, and COL1A1 expression through the Ca2+/PI3K-Akt/SEMA3A signaling pathway. In addition, exogenous SEMA3A supplementation effectively reversed reduced mineralization capacity in PIEZO1-knockdown hOBLCs. In vivo, Piezo1 expression peaked at day 7 and returned to baseline at day 21 in a wild-type mice dentin injury model, with Sema3a presenting a similar expression pattern. To investigate the specific role of PIEZO1 in odontoblast-mediated reactionary dentinogenesis, mice with a conditional knockout of Piezo1 in odontoblasts were generated, and no significant differences in teeth phenotypes were observed between the control and conditional knockout (cKO) mice. Nevertheless, cKO mice exhibited reduced reactionary dentin formation and decreased Sema3a and Dsp positive staining after dentin injury, indicating impaired dental pulp repair by odontoblasts. In summary, these findings suggest that PIEZO1 enhances the mineralization capacity of hOBLCs in vitro via the Ca2+/PI3K-Akt/SEMA3A signaling pathway and contributes to reactionary dentinogenesis in vivo.

Oat β-glucan repairs the epidermal barrier by upregulating the levels of epidermal differentiation, cell-cell junctions and lipids via Dectin-1

BACKGROUND AND PURPOSE

Oat β-glucan could ameliorate epidermal hyperplasia and accelerate epidermal barrier repair. Dectin-1 is one of the receptors of β-glucan and many biological functions of β-glucan are mediated by Dectin-1. Dectin-1 promotes wound healing through regulating the proliferation and migration of skin cells. Thus, this study aimed to investigate the role of oat β-glucan and Dectin-1 in epidermal barrier repair.

EXPERIMENTAL APPROACH

To investigate the role of Dectin-1 in the epidermal barrier, indicators associated with the recovery of a damaged epidermal barrier, including histopathological changes, keratinization, proliferation, apoptosis, differentiation, cell-cell junctions and lipid content were compared between WT and Dectin-1-/- mice. Further, the effect of oat β-glucan on the disruption of the epidermal barrier was also compared between WT and Dectin-1-/- mice.

KEY RESULTS

Dectin-1 deficiency resulted in delayed recovery and marked keratinization, as well as abnormal levels of keratinocyte differentiation, cell-cell junctions and lipid synthesis during the restoration of the epidermal barrier. Oat β-glucan significantly reduces epidermal hyperplasia, promotes epidermal differentiation, increases cell-cell junction expression, promotes lipid synthesis and ultimately accelerates the recovery of damaged epidermal barriers via Dectin-1. Oat β-glucan could promote CaS receptor expression and activate the PPAR-γ signalling pathway via Dectin-1.

CONCLUSION AND IMPLICATIONS

Oat β-glucan promote the recovery of damaged epidermal barriers through promoting epidermal differentiation, increasing the expression of cell-cell junctions and lipid synthesis through Dectin-1. Dectin-1 deficiency delay the recovery of epidermal barriers, which indicated that Dectin-1 may be a potential target in epidermal barrier repair.

Leishmania exploits host cAMP/EPAC/calcineurin signaling to induce an IL-33-mediated anti-inflammatory environment for the establishment of infection

Host anti-inflammatory responses are critical for the progression of visceral leishmaniasis, and the pleiotropic cytokine interleukin (IL)-33 was found to be upregulated in infection. Here, we documented that IL-33 induction is a consequence of elevated cAMP-mediated exchange protein activated by cAMP (EPAC)/calcineurin-dependent signaling and essential for the sustenance of infection. Leishmania donovani-infected macrophages showed upregulation of IL-33 and its neutralization resulted in decreased parasite survival and increased inflammatory responses. Infection-induced cAMP was involved in IL-33 production and of its downstream effectors PKA and EPAC, only the latter was responsible for elevated IL-33 level. EPAC initiated Rap-dependent phospholipase C activation, which triggered the release of intracellular calcium followed by calcium/calmodulin complex formation. Screening of calmodulin-dependent enzymes affirmed involvement of the phosphatase calcineurin in cAMP/EPAC/calcium/calmodulin signaling-induced IL-33 production and parasite survival. Activated calcineurin ensured nuclear localization of the transcription factors, nuclear factor of activated T cell 1 and hypoxia-inducible factor 1 alpha required for IL-33 transcription, and we further confirmed this by chromatin immunoprecipitation assay. Administering specific inhibitors of nuclear factor of activated T cell 1 and hypoxia-inducible factor 1 alpha in BALB/c mouse model of visceral leishmaniasis decreased liver and spleen parasite burden along with reduction in IL-33 level. Splenocyte supernatants of inhibitor-treated infected mice further documented an increase in tumor necrosis factor alpha and IL-12 level with simultaneous decrease of IL-10, thereby indicating an overall disease-escalating effect of IL-33. Thus, this study demonstrates that cAMP/EPAC/calcineurin signaling is crucial for the activation of IL-33 and in effect creates anti-inflammatory responses, essential for infection.

Unraveling the Mechanisms Involved in the Beneficial Effects of Magnesium Treatment on Skin Wound Healing

The skin wound healing process consists of hemostatic, inflammatory, proliferative, and maturation phases, with a complex cellular response by multiple cell types in the epidermis, dermis, and immune system. Magnesium is a mineral essential for life, and although magnesium treatment promotes cutaneous wound healing, the molecular mechanism and timing of action of the healing process are unknown. This study, using human epidermal-derived HaCaT cells and human normal epidermal keratinocyte cells, was performed to investigate the mechanism involved in the effect of magnesium on wound healing. The expression levels of epidermal differentiation-promoting factors were reduced by MgCl2, suggesting an inhibitory effect on epidermal differentiation in the remodeling stage of the late wound healing process. On the other hand, MgCl2 treatment increased the expression of matrix metalloproteinase-7 (MMP7), a cell migration-promoting factor, and enhanced cell migration via the MEK/ERK pathway activation. The enhancement of cell migration by MgCl2 was inhibited by MMP7 knockdown, suggesting that MgCl2 enhances cell migration which is mediated by increased MMP7 expression. Our results revealed that MgCl2 inhibits epidermal differentiation but promotes cell migration, suggesting that applying magnesium to the early wound healing process could be beneficial.

The Involvement of Semaphorins in the Pathogenesis of Skin Diseases

Semaphorins belong to a group of membrane and secretory proteins that act as ligands for several receptor families and are involved in modulating cell signaling pathways. They bind multimeric receptor complexes on the cell membrane to exert their effects and initiate unique intracellular signal transduction cascades. These proteins can influence several processes that are very important for cell function, such as cell division and differentiation. Semaphorins are involved in cell migration, apoptosis, cell adhesion, aggregation, and numerous immune processes due to their immunoregulatory effects. Semaphorins are expressed in keratinocytes, which is why they have become a target for studies on the pathogenesis of skin diseases. Most studies to date on the role of semaphorins in the pathogenesis of skin diseases have been carried out in cellular or animal models, and there are few clinical studies evaluating the role of semaphorins in the pathogenesis and therapy of skin diseases. In this narrative review, we summarized the current state of knowledge on the role of semaphorins in the pathogenesis of skin diseases and their potential importance as targets for therapy. We also tried to present the key findings and weaknesses of previous research in this field. The novelty of this article lies in the comprehensive presentation of the role of semaphorins in the pathogenesis of skin diseases, including the results of studies on cell cultures and animal models, elucidating the mechanisms and signaling pathways through which semaphorins affect the development of skin diseases, as well as on the presentation of the results of existing clinical trials evaluating the role of semaphorins in the pathogenesis of skin diseases, and as potential therapeutic targets.

IL33-mediated NPM1 promotes fibroblast-to-myofibroblast transition via ERK/AP-1 signaling in silica-induced pulmonary fibrosis

Silicosis is a global occupational pulmonary disease due to the accumulation of silica dust in the lung. Lacking effective clinical drugs makes the treatment of this disease quite challenging in clinics largely because the pathogenic mechanisms remain obscure. Interleukin 33 (IL33), a pleiotropic cytokine, could promote wound healing and tissue repair via the receptor ST2. However, the mechanisms governing the involvement of IL33 in silicosis progression remain to be further explored. Here, we demonstrated that the IL33 levels in the lung sections were significantly overexpressed after bleomycin and silica treatment. Chromatin immunoprecipitation assay, knockdown, and reverse experiments were performed in lung fibroblasts to prove gene interaction following exogenous IL33 treatment or cocultured with silica-treated lung epithelial cells. Mechanistically, we illustrated that silica-stimulated lung epithelial cells secreted IL33 and further promoted the activation, proliferation, and migration of pulmonary fibroblasts by activating the ERK/AP-1/NPM1 signaling pathway in vitro. And more, treatment with NPM1 siRNA-loaded liposomes markedly protected mice from silica-induced pulmonary fibrosis in vivo. In conclusion, the involvement of NPM1 in the progression of silicosis is regulated by the IL33/ERK/AP-1 signaling axis, which is the potential therapeutic target candidate in developing novel antifibrotic strategies for pulmonary fibrosis.

Regulation of Semaphorin3A in the process of cutaneous wound healing

Semaphorin 3A (Sema3A) has been recognized as a crucial regulator of morphogenesis and homeostasis over a wide range of organ systems. However, its function in cutaneous wound healing is poorly understood. In our study, we demonstrated that Sema3A adenovirus plasmids transfection limited keratinocyte proliferation and decreased migrative capacity as assessed by in vitro wound healing assay. Sema3A transduction inhibited TGF-β1-mediated keratinocyte migration and EMT process. Besides, we applied mice with K14-Cre-mediated deletion of Sema3A and found that Sema3A depletion postponed wound closure with decreased re-epithelialization and matrix growth. Contrary to the results obtained with full-length Sema3A plasmids transfection, increased keratinocyte migration with recombinant Sema3A proteins resulted in quicker closure of the wounding area after a scratch. Further, exogenously applied recombinant Sema3A worked with EGF to maintain the activation of EGFR by interacting with NRP1 and thereby regulated the internalization of the EGFR-NRP1 complex. Taken together, these results indicated a paradoxical role of autonomous and non-autonomous Sema3A expression during wound healing. Combined administration of recombinant EGF and Sema3A proteins could accelerate the process of wound repair, thus providing promising treatment prospects in the future.

Semaphorin 3A: A potential target for prevention and treatment of nickel allergy

Metal allergy is one of the typical immune disorders encountered during the application of dental/medical materials and has a highly complex pathogenic mechanism. Semaphorin 3A (Sema3A), a member of the semaphorin family, is reported to be involved in various immune disorders. However, its role in metal allergy has not been clarified yet. Herein, we show that Sema3A expression was upregulated in nickel (Ni) allergy-induced mouse ear tissue and in NiCl₂-stimulated mouse keratinocytes. Moreover, Sema3A regulated tumor necrosis factor-alpha production and mitogen-activated protein kinase activation in keratinocytes. The specific deletion of Sema3A in keratinocytes did not affect immune cell infiltration but reduced edema and ear swelling; it also impeded Th1 responses to cause a slight alleviation in Ni allergy in mice. Our results demonstrate that Sema3A promotes the development of metal allergy and should be explored as a potential target for the prevention and treatment of metal allergy.

Semaphorin 3A is upregulated in keratinocytes upon nickel exposure, subsequently promoting Th1 cytokine responses and driving nickel allergic reactions.

Konjac Ceramide (kCer)-Mediated Signal Transduction of the Sema3A Pathway Promotes HaCaT Keratinocyte Differentiation

Simple Summary

Konjac ceramide (kCer) is a unique molecular species of plant-type ceramide, and is a potential Sema3A-like ligand of Nrp1. kCer suppresses histamine-stimulated cell migration of HaCaT keratinocytes. This effect of kCer is not due to histamine-activated GPCRs, but rather to Sema3A-Nrp1 receptor binding. The present study focused on the ability of kCer to induce cell differentiation, in addition to its anti-migratory effects. We demonstrated that the effects of kCer on cell migration and cell differentiation are perpetuated by a cascade of crosstalk between pathways downstream of Nrp1 and GPCR in HaCaT cells.

Abstract

Histamines suppress epidermal keratinocyte differentiation. Previously, we reported that konjac ceramide (kCer) suppresses histamine-stimulated cell migration of HaCaT keratinocytes. kCer specifically binds to Nrp1 and does not interact with histamine receptors. The signaling mechanism of kCer in HaCaT cells is also controlled by an intracellular signaling cascade activated by the Sema3A-Nrp1 pathway. In the present study, we demonstrated that kCer treatment induced HaCaT keratinocyte differentiation after migration of immature cells. kCer-induced HaCaT cell differentiation was accompanied by some features of keratinocyte differentiation markers. kCer induced activating phosphorylation of p38MAPK and c-Fos, which increased the protein levels of involucrin that was the latter differentiation marker. In addition, we demonstrated that the effects of both kCer and histamines are regulated by an intracellular mechanism of Rac1 activation/RhoA inhibition downstream of the Sema3A/Nrp1 receptor and histamine/GPCR pathways. In summary, the effects of kCer on cell migration and cell differentiation are regulated by cascade crosstalk between downstream Nrp1 and histamine-GPCR pathways in HaCaT cells.

Extract of Scutellaria baicalensis induces semaphorin 3A production in human epidermal keratinocytes

In a disease-state-dependent manner, the histamine-resistant itch in dry skin-based skin diseases such as atopic dermatitis (AD) and xerosis is mainly due to hyperinnervation in the epidermis. Semaphorin 3A (Sema3A) is a nerve repulsion factor expressed in keratinocytes and it suppresses nerve fiber elongation in the epidermis. Our previous studies have shown that Sema3A ointment inhibits epidermal hyperinnervation and scratching behavior and improves dermatitis scores in AD model mice. Therefore, we consider Sema3A as a key therapeutic target for improving histamine-resistant itch in AD and xerosis. This study was designed to screen a library of herbal plant extracts to discover compounds with potential to induce Sema3A in normal human epidermal keratinocytes (NHEKs) using a reporter gene assay, so that positive samples were found. Among the positive samples, only the extract of S. baicalensis was found to consistently increase Sema3A levels in cultured NHEKs in assays using quantitative real-time PCR and ELISA. In evaluation of reconstituted human epidermis models, the level of Sema3A protein in culture supernatants significantly increased by application of the extract of S. baicalensis. In addition, we investigated which components in the extract of S. baicalensis contributed to Sema3A induction and found that baicalin and baicalein markedly increased the relative luciferase activity, and that baicalein had higher induction activity than baicalin. Thus, these findings suggest that S. baicalensis extract and its compounds, baicalin and baicalein, may be promising candidates for improving histamine-resistant itch via the induction of Sema3A expression in epidermal keratinocytes.