p75 neurotrophin receptor mediates apoptosis in transit-amplifying cells and its overexpression restores cell death in psoriatic keratinocytes

Role of stress in skin diseases: A neuroendocrine-immune interaction view

Psychological stress is a crucial factor in the development of many skin diseases, and the stigma caused by skin disorders may further increase the psychological burden, forming a vicious cycle of psychological stress leading to skin diseases. Therefore, understanding the relationship between stress and skin diseases is necessary. The skin, as the vital interface with the external environment, possesses its own complex immune system, and the neuroendocrine system plays a central role in the stress response of the body. Stress-induced alterations in the immune system can also disrupt the delicate balance of immune cells and inflammatory mediators in the skin, leading to immune dysregulation and increased susceptibility to various skin diseases. Stress can also affect the skin barrier function, impair wound healing, and promote the release of pro-inflammatory cytokines, thereby exacerbating existing skin diseases such as psoriasis, atopic dermatitis, acne, and urticaria. In the present review, we explored the intricate relationship between stress and skin diseases from a neuroendocrine-immune interaction perspective. We explored the occurrence and development of skin diseases in the context of stress, the stress models for skin diseases, the impact of stress on skin function and diseases, and relevant epidemiological studies and clinical trials. Understanding the relationship between stress and skin diseases from a neuroendocrine-immune interaction perspective provides a comprehensive framework for targeted interventions and new insights into the diagnosis and treatment of skin diseases.

The link between psoriasis and other diseases based on epidemiological and genetic analyses

Psoriasis is a chronic disease, which is associated with numerous genetic and environmental factors. The high prevalence of psoriasis worldwide (2-3% of the general population) and its various comorbidities lead to research on its pathogenesis. The aim of this article is to describe the current state of knowledge on the potential links between psoriasis and other diseases, such as inflammatory bowel diseases, uveitis, arthritis, hypertension, metabolic syndrome, diabetes mellitus, atherosclerosis, fatty liver disease, dyslipidaemia, sleep apnoea, celiac disease, lymphoma, erectile dysfunction, Parkinson's disease, osteoporosis, chronic obstructive pulmonary disease, psychiatric disorders and substance use. Further research in this area may lead to better treatment options in the future.

CD271 activation prevents low to high-risk progression of cutaneous squamous cell carcinoma and improves therapy outcomes

BACKGROUND

Cutaneous squamous cell carcinoma (cSCC) is the second most prevalent form of skin cancer, showing a rapid increasing incidence worldwide. Although most cSCC can be cured by surgery, a sizeable number of cases are diagnosed at advanced stages, with local invasion and distant metastatic lesions. In the skin, neurotrophins (NTs) and their receptors (CD271 and Trk) form a complex network regulating epidermal homeostasis. Recently, several works suggested a significant implication of NT receptors in cancer. However, CD271 functions in epithelial tumors are controversial and its precise role in cSCC is still to be defined.

METHODS

Spheroids from cSCC patients with low-risk (In situ or Well-Differentiated cSCC) or high-risk tumors (Moderately/Poorly Differentiated cSCC), were established to explore histological features, proliferation, invasion abilities, and molecular pathways modulated in response to CD271 overexpression or activation in vitro. The effect of CD271 activities on the response to therapeutics was also investigated. The impact on the metastatic process and inflammation was explored in vivo and in vitro, by using zebrafish xenograft and 2D/3D models.

RESULTS

Our data proved that CD271 is upregulated in Well-Differentiated tumors as compared to the more aggressive Moderately/Poorly Differentiated cSCC, both in vivo and in vitro. We demonstrated that CD271 activities reduce proliferation and malignancy marker expression in patient-derived cSCC spheroids at each tumor grade, by increasing neoplastic cell differentiation. CD271 overexpression significantly increases cSCC spheroid mass density, while it reduces their weight and diameter, and promotes a major fold-enrichment in differentiation and keratinization genes. Moreover, both CD271 overexpression and activation decrease cSCC cell invasiveness in vitro. A significant inhibition of the metastatic process by CD271 was observed in a newly established zebrafish cSCC model. We found that the recruitment of leucocytes by CD271-overexpressing cells directly correlates with tumor killing and this finding was further highlighted by monocyte infiltration in a THP-1-SCC13 3D model. Finally, CD271 activity synergizes with Trk receptor inhibition, by reducing spheroid viability, and significantly improves the outcome of photodynamic therapy (PTD) or chemotherapy in spheroids and zebrafish.

CONCLUSION

Our study provides evidence that CD271 could prevent the switch between low to high-risk cSCC tumors. Because CD271 contributes to maintaining active differentiative paths and favors the response to therapies, it might be a promising target for future pharmaceutical development.

Extracellular serine empowers epidermal proliferation and psoriasis-like symptoms

The contribution of nutrient availability to control epidermal cell proliferation, inflammation, and hyperproliferative diseases remains unknown. Here, we studied extracellular serine and serine/glycine metabolism using human keratinocytes, human skin biopsies, and a mouse model of psoriasis-like disease. We focused on a metabolic enzyme, serine hydroxymethyltransferase (SHMT), that converts serine into glycine and tetrahydrofolate-bound one‑carbon units to support cell growth. We found that keratinocytes are both serine and glycine auxotrophs. Metabolomic profiling and hypoxanthine supplementation indicated that SHMT silencing/inhibition reduced cell growth through purine depletion, leading to nucleotide loss. In addition, topical application of an SHMT inhibitor suppressed both keratinocyte proliferation and inflammation in the imiquimod model and resulted in a decrease in psoriasis-associated gene expression. In conclusion, our study highlights SHMT2 activity and serine/glycine availability as an important metabolic hub controlling both keratinocyte proliferation and inflammatory cell expansion in psoriasis and holds promise for additional approaches to treat skin diseases.

Emerging roles of keratinocytes in nociceptive transduction and regulation

Keratinocytes are the predominant block-building cells in the epidermis. Emerging evidence has elucidated the roles of keratinocytes in a wide range of pathophysiological processes including cutaneous nociception, pruritus, and inflammation. Intraepidermal free nerve endings are entirely enwrapped within the gutters of keratinocyte cytoplasm and form en passant synaptic-like contacts with keratinocytes. Keratinocytes can detect thermal, mechanical, and chemical stimuli through transient receptor potential ion channels and other sensory receptors. The activated keratinocytes elicit calcium influx and release ATP, which binds to P2 receptors on free nerve endings and excites sensory neurons. This process is modulated by the endogenous opioid system and endothelin. Keratinocytes also express neurotransmitter receptors of adrenaline, acetylcholine, glutamate, and γ-aminobutyric acid, which are involved in regulating the activation and migration, of keratinocytes. Furthermore, keratinocytes serve as both sources and targets of neurotrophic factors, pro-inflammatory cytokines, and neuropeptides. The autocrine and/or paracrine mechanisms of these mediators create a bidirectional feedback loop that amplifies neuroinflammation and contributes to peripheral sensitization.

Isolation of an "Early" Transit Amplifying Keratinocyte Population in Human Epidermis: A Role for the Low Affinity Neurotrophin Receptor CD271

In the interfollicular epidermis (IFE), stem cells (KSC) generate transit amplifying (TA) cells that, after symmetric divisions, produce differentiating daughters. Here, we isolated and characterized the highly proliferative interfollicular epidermal basal cell population "early" TA (ETA) cells, based on their capacity to adhere to type IV collagen. Proliferation and colony-forming efficiency in ETA cells are lower than in KSC but higher than in "late" TA (LTA). Stemness, proliferation, and differentiation markers confirmed that ETA cells display a unique phenotype. Skin reconstructs derived from ETA cells present different features (epidermal thickness, Ki67, and Survivin expression), as compared to skin equivalents generated from either KSC or LTA cells. The low-affinity neurotrophin receptor CD271, which regulates the KSC to TA cell transition in the human epidermis through an on/off switch control mechanism, is predominantly expressed in ETA cells. Skin equivalents generated from siRNA CD271 ETA cells display a more proliferative and less differentiated phenotype, as compared to mock-derived reconstructs. Consistently, CD271 overexpression in LTA cells generates a more proliferative skin equivalent than mock LTA cells. Finally, the CD271 level declines with cellular senescence, while it induces a delay in p16INK4 expression. We conclude that ETA cells represent the first KSC progenitor with exclusive features. CD271 identifies and modulates ETA cells, thus participating in the early differentiation and regenerative capacity of the human epidermis.

Electroacupuncture promotes apoptosis and inhibits axonogenesis by activating p75 neurotrophin receptor for triple-negative breast xenograft in mice

PURPOSE

The aim of this study was to investigate the anti-tumor effect of electroacupuncture (EA) on mice bearing breast tumors by regulating p75 neurotrophin receptor (p75NTR) and remodelling intratumoral innervation.

METHODS

Female BALB/c mice were implanted with 4T1 breast tumor cells to establish a murine mammary cancer model. Tumor volume and weight were measured to evaluate tumor growth. Cell apoptosis was assessed by TUNEL assay. The relative expression of p75NTR, TrkA, TrkB, NGF and proNGF were detected by immunohistochemistry. Neurotransmitter and neurotrophin were detected by enzyme-linked immunosorbent assay. Intratumoral innervation was confirmed by β3-tubulin and TH labeling immunohistochemistry. The antagonist TAT-Pep5 was employed to determine if the effects of EA on tumor growth and cell apoptosis were mediated by p75NTR.

RESULTS

Peritumoral EA alleviated tumor growth especially after 14 days of intervention. Apoptosis index in the tumor tissue was obviously decreased after EA. Meanwhile, EA intervention significantly upregulated the expression of p75NTR and proNGF, along with a decline in the tumor growth and an increase in the cell apoptosis. Besides, EA reduced local sympathetic innervation and downregulated sympathetic neurotransmitter NE level in the local tumor. Furthermore, p75NTR antagonist alleviated EA-mediated cell apoptosis and intratumoral innervation.

CONCLUSIONS

One mechanism of EA intervention for alleviating tumor progression is mediated by p75NTR to promote apoptosis and decrease intratumoral axonogenesis in the tumor microenvironment.

Roles Played by Stress-Induced Pathways in Driving Ethnic Heterogeneity for Inflammatory Skin Diseases

Immune-mediated skin conditions (IMSCs) are a diverse group of autoimmune diseases associated with significant disease burden. Atopic dermatitis and psoriasis are among the most common IMSCs in the United States and have disproportionate impact on racial and ethnic minorities. African American patients are more likely to develop atopic dermatitis compared to their European American counterparts; and despite lower prevalence of psoriasis among this group, African American patients can suffer from more extensive disease involvement, significant post-inflammatory changes, and a decreased quality of life. While recent studies have been focused on understanding the heterogeneity underlying disease mechanisms and genetic factors at play, little emphasis has been put on the effect of psychosocial or psychological stress on immune pathways, and how these factors contribute to differences in clinical severity, prevalence, and treatment response across ethnic groups. In this review, we explore the heterogeneity of atopic dermatitis and psoriasis between African American and European American patients by summarizing epidemiological studies, addressing potential molecular and environmental factors, with a focus on the intersection between stress and inflammatory pathways.

Serum Cholesteryl Ester Transfer Protein (CETP) and Sortilin (SORT) in Patients with Psoriasis with Relation to Systemic Treatment

Psoriasis is a common inflammatory skin disease, which is tightly associated with metabolic disorders. Cholesteryl ester transfer protein (CETP) and sortilin (SORT) are molecules engaged in lipid metabolism of proatherogenic properties. They have been hardly ever studied in psoriasis before. Serum CETP and SORT concentrations were measured in 33 patients with plaque-type psoriasis before and after 12 weeks of treatment with methotrexate or acitretin. There was no significant difference in CEPT and SORT serum concentrations between patients and controls. Positive correlations between CETP after the treatment with acitretin and activity of transaminases (R = 0.65, R = 0.56, respectively) were noted. CETP was positively related with triglycerides (R = 0.49), glucose (R = 0.54) and CRP (R = 0.64) before the treatment with methotrexate, which all disappeared afterwards. Systemic therapy with methotrexate caused normalization of SORT concentration. There was significant correlation between SORT and WBC (p < 0.01) and CRP (p < 0.05). CETP and SORT cannot be used as individual biomarkers. Nevertheless, they show some interesting relations with other parameters. Increased concentration of CETP perhaps could investigated as a marker of liver side effects of acitretin treatment in psoriatics. SORT could be considered as a new indicator of metabolically induced inflammation in psoriasis. Methotrexate may be preferred in patients with high SORT concentrations. Further studies are needed to establish their exact role in psoriatic patients.

The concept of intrinsic versus extrinsic apoptosis

Regulated cell death is a vital and dynamic process in multicellular organisms that maintains tissue homeostasis and eliminates potentially dangerous cells. Apoptosis, one of the better-known forms of regulated cell death, is activated when cell-surface death receptors like Fas are engaged by their ligands (the extrinsic pathway) or when BCL-2-family pro-apoptotic proteins cause the permeabilization of the mitochondrial outer membrane (the intrinsic pathway). Both the intrinsic and extrinsic pathways of apoptosis lead to the activation of a family of proteases, the caspases, which are responsible for the final cell demise in the so-called execution phase of apoptosis. In this review, I will first discuss the most common types of regulated cell death on a morphological basis. I will then consider in detail the molecular pathways of intrinsic and extrinsic apoptosis, discussing how they are activated in response to specific stimuli and are sometimes overlapping. In-depth knowledge of the cellular mechanisms of apoptosis is becoming more and more important not only in the field of cellular and molecular biology but also for its translational potential in several pathologies, including neurodegeneration and cancer.

Psychological Stress, Mast Cells, and Psoriasis-Is There Any Relationship?

Psoriasis vulgaris is a common inflammatory skin disease with still unknown pathogenesis. In recent years, genetic and environmental factors have been mentioned as the main causes. Among environmental factors, many researchers are trying to investigate the role of mental health and its importance in the development of many diseases. In the pathophysiology of psoriasis, the role of the interaction between the nervous, endocrine, and immune systems are often emphasized. So far, no one has clearly indicated where the pathological process begins. One of the hypotheses is that chronic stress influences the formation of hormonal changes (lowering the systemic cortisol level), which favors the processes of autoimmunity. In inflammatory skin conditions, mast cells (MCs) are localized close to blood vessels and peripheral nerves, where they probably play an important role in the response to environmental stimuli and emotional stress. They are usually connected with a fast immune response, not only in allergies but also a protective response to microbial antigens. Among many cells of the immune system, MCs have receptors for the hormones of the hypothalamic-pituitary-adrenal (HPA) axis on their surface. In this review, we will try to take a closer look at the role of MCs in the pathophysiology of psoriasis. This knowledge may give the opportunity to search for therapeutic solutions.

Leptin Receptor (rs1137101) and Brain-Derived Neurotrophic Factor (rs925946) Gene Variants Are Associated with Obesity in the Early- but Not in the Late-Onset Population of Hungarian Psoriatic Patients

Background: Psoriatic patients have considerably higher odds of being obese compared with the general population; however, the exact pathophysiological link between psoriasis and obesity needs to be elucidated. Methods: To investigate the association of psoriasis with established obesity-related gene variants, we conducted a population-based case-control study including 3541 subjects (574 psoriasis cases and 2967 controls from the general Hungarian population). Genotyping of 20 SNPs at ADIPOQ, BDNF, FTO, GNPDA2, LEPR, MC4R, NEGR1, NPY, PPARG, TMEM18, and UCP2 were determined, and differences in genotype and allele distributions were investigated. Multiple logistic regression analyses were implemented. Results: Analysis revealed an association between the G allele of the rs1137101 polymorphism (LEPR gene) and obesity risk (OR: 3.30 (1.45; 7.50), p = 0.004) in the early-onset group of psoriatic patients. Furthermore, the T allele of rs925946 polymorphism (BDNF gene) was also associated with increased risk of obesity in early-onset psoriasis (OR: 2.26 (1.24; 4.14), p = 0.008). Conclusions: Our results suggest that in psoriatic patients, there are prominent differences in the causes of obesity that should be accounted for, including not only environmental factors but also patient characteristics, such as the time of disease onset as well as genetic factors.

Proprotein Convertase Subtilisin/Kexin Type 9, Angiopoietin-Like Protein 8, Sortilin, and Cholesteryl Ester Transfer Protein-Friends of Foes for Psoriatic Patients at the Risk of Developing Cardiometabolic Syndrome?

Psoriasis is a systemic, immune-metabolic disease with strong genetic predispositions and autoimmune pathogenic traits. During psoriasis progression, a wide spectrum of comorbidities comes into play with the leading role of the cardio-metabolic syndrome (CMS) that occurs with the frequency of 30–50% amongst the psoriatic patients. Both conditions—psoriasis and CMS—have numerous common pathways, mainly related to proinflammatory pathways and cytokine profiles. Surprisingly, despite the years of research, the exact pathways linking the occurrence of CMS in the psoriasis population are still not fully understood. Recently published papers, both clinical and based on the basic science, shed new light into this relationship providing an insight into novel key-players proteins with plausible effects on above-mentioned interplay. Taking into account recent advances in this important medical matter, this review aims to discuss comprehensively the role of four proteins: proprotein convertase subtilisin/kexin type-9 (PSCK9), angiopoietin-like protein 8 (ANGPLT8), sortilin (SORT1), and cholesteryl ester transfer proteins (CEPT) as plausible links between psoriasis and CMS.

Role of bulge epidermal stem cells and TSLP signaling in psoriasis

Psoriasis is a common inflammatory skin disease involving a cross‐talk between epidermal and immune cells. The role of specific epidermal stem cell populations, including hair follicle stem cells (HF‐SCs) in psoriasis is not well defined. Here, we show reduced expression of c‐JUN and JUNB in bulge HF‐SCs in patients with scalp psoriasis. Using lineage tracing in mouse models of skin inflammation with inducible deletion of c‐Jun and JunB, we found that mutant bulge HF‐SCs initiate epidermal hyperplasia and skin inflammation. Mechanistically, thymic stromal lymphopoietin (TSLP) was identified in mutant cells as a paracrine factor stimulating proliferation of neighboring non‐mutant epidermal cells, while mutant inter‐follicular epidermal (IFE) cells are lost over time. Blocking TSLP in psoriasis‐like mice reduced skin inflammation and decreased epidermal proliferation, VEGFα expression, and STAT5 activation. These findings unravel distinct roles of HF‐SCs and IFE cells in inflammatory skin disease and provide novel mechanistic insights into epidermal cell interactions in inflammation.

Do DLX3 and CD271 Protect Human Keratinocytes from Squamous Tumor Development?

Well-regulated epidermal homeostasis depends on the function of different classes of factors, such as transcription regulators and receptors. Alterations in this homeostatic balance may lead to the development of cutaneous squamous tumorigenesis. The homeobox transcription factor DLX3 is determinant for a p53-dependent regulation of epidermal differentiation and modulates skin carcinogenesis. The maintenance of skin homeostasis also involves the action of neurotrophins (NTs) and their receptors, Trk and CD271. While Trk receptor overexpression is a hallmark of cancer, there are conflicting data on CD271 expression and function in cutaneous SCC (cSCC). Previous studies have reported NT receptors expression in head and neck SSC (HNSCC). We show that CD271 is expressed at low levels in primary cSCC cells and the number of CD271+ cells correlates with cell cohesion in SCC spheroids. In normal epidermis, CD271 is expressed in proliferative progenitor cells and DLX3 in terminally differentiated keratinocytes. Brain-derived neurotrophic factor (BDNF) and neurotrophin 3 (NT3) increase DLX3 expression. In the absence of a functional BDNF receptor TrkB in keratinocytes, we hypothesize that the BDNF-dependent DLX3 response could be mediated via CD271. Altogether, our results support a putative CD271-DLX3 connection in keratinocytes, which might be crucial to preventing squamous skin cancer.

Cold atmospheric plasma ameliorates imiquimod-induced psoriasiform dermatitis in mice by mediating antiproliferative effects

Psoriasis is a chronic hyperproliferative skin disease characterised by excessive growth of keratinocytes. Indeed, inducing keratinocyte apoptosis is a key mechanism responsible for psoriatic plaques clearance following some important existing therapies, which display pro-oxidant activity. Cold atmospheric plasma (CAP), acting as a tuneable source of reactive oxygen and nitrogen species (RONS), can controllably transfer RONS to the cellular environment, deliver antiproliferative RONS concentrations and exert antiproliferative and proapoptotic effects. This study was undertaken to evaluate the therapeutic potential of CAP in psoriasis. We used cell models of psoriasis-like inflammation by adding lipopolysaccharide (LPS) or tumour necrosis factor alpha (TNF-α) to HaCaT keratinocytes. Indirect plasma, plasma-activated medium (PAM), was administered to HaCaT cells. Atmospheric pressure plasma jet (APPJ) was applied directly to imiquimod (IMQ)-induced psoriasiform dermatitis in mice. The results showed that PAM induced an increase in intracellular ROS and caused keratinocyte apoptosis. Moreover, cells under inflammation showed lesser viability and larger apoptosis rate. With repeated administration of APPJ, psoriasiform lesions showed ameliorated morphological manifestation and reduced epidermal proliferation. Overall, this study supports that CAP holds good potential in psoriasis treatment.

The spatiotemporal expression and mineralization regulation of p75 neurotrophin receptor in the early tooth development

OBJECTIVE

The aim of this study was to investigate the spatiotemporal expression and potential role of p75NTR in tooth morphogenesis and tissue mineralization.

MATERIALS AND METHODS

The dynamic morphology of the four stages (from the beginning of E12.5 d, then E13.5 d and E15.5 d, to the end of E18.5 d) was observed, and the expressions of p75NTR and Runx2 were traced. The ectomesenchymal stem cells (EMSCs) were harvested in vitro, and the biological characteristics were observed. Moreover, the mineralization capability of EMSCs was evaluated. The relations between p75NTR and ALP, Col-1 and Runx2 were investigated.

RESULTS

The morphologic results showed that the dental lamina appeared at E12.5 d, the bud stage at E13.5 d, the cap stage at E15.5 d and the bell stage at E18.5 d. p75NTR and Runx2 showed the similar expression pattern. EMSCs from the four stages showed no significant difference in proliferation. But the positive rate of p75NTR in the E12.5 d cells was significantly lower than that in the other three stages (P < 0.05). Moreover, the higher positive rate of p75NTR the cells were, the stronger mineralization capability they showed. p75NTR was well positively correlated with the mineralization-related markers ALP, Col-1 and Runx2, which increased gradually with the mature of dental germs.

CONCLUSION

p75NTR might play an important role in the regulation of tooth morphogenesis, especially dental hard tissue formation.

The role of TrkA in the promoting wounding-healing effect of CD271 on epidermal stem cells

CD271, a receptor of nerve growth factor (NGF), affects the biological properties of epidermal stem cells (eSCs) which are essential for skin wound closure. Tropomyosin-receptor kinase A (TrkA), another receptor of NGF, combined with CD271 has been involved with nervous system and skin keratinocytes. However, the exact role of TrkA combined with CD271 in eSCs during skin wound closure is still unclear. This study aimed to reveal the role of TrkA in the promoting wounding-healing effect of CD271 on eSCs. We obtained CD271-vo (over-expression of CD271) eSCs by lentiviral infection. K252a was used to inhibit TrkA expression. Full-thickness skin mouse wound closure model (5 mm in diameter) was used to detect the ability of CD271 over-expressed/TrkA-deficient during wound healing. The biological characteristics of eSCs and their proliferation and apoptosis were detected using immunohistochemistry and western blot. The expressions of protein kinase B (pAkt)/Akt, phosphorylated extracellular-signal-related kinase (pERK)/ERK1/2, and c-Jun N-terminal kinase (pJNK)/JNK were also detected by western blot. We found that over-expression of CD271 promoted the biological functions of eSCs. Interestingly, over-expression of CD271 in the absence of TrkA neither promoted eSCs' migration and proliferation nor promoted wound healing in a mouse model. In addition, we observed the reduced expression of pAkt/Akt and pERK/ERK1/2 following TrkA inhibition in vitro. Our studies demonstrated that the role of TrkA in the promoting wounding-healing effect of CD271 on eSCs.

Rapamycin-induced autophagy protects proximal tubular renal cells against proteinuric damage through the transcriptional activation of the nerve growth factor receptor NGFR

Experimental evidence demonstrated that macroautophagy/autophagy exerts a crucial role in maintain renal cellular homeostasis and represents a protective mechanism against renal injuries. Interestingly, it has been demonstrated that in the human proximal tubular renal cell line, HK-2, the MTOR inhibitor rapamycin enhanced autophagy and mitigated the apoptosis damage induced by urinary protein overload. However, the underlying molecular mechanism has not yet been elucidated. In our study we demonstrated, for the first time, that in HK-2 cells, the exposure to low doses of rapamycin transactivated the NGFR promoter, leading to autophagic activation. Indeed, we observed that in HK-2 cells silenced for the NGFR gene, the rapamycin-induced autophagic process was prevented, as the upregulation of the proautophagic markers, BECN1, as well as LC3-II, and the autophagic vacuoles evaluated by transmission electron microscopy, were not found. Concomitantly, using a series of deletion constructs of the NGFR promoter we found that the EGR1 transcription factor was responsible for the rapamycin-mediated transactivation of the NGFR promoter. Finally, our results provided evidence that the cotreatment with rapamycin plus albumin further enhanced autophagy via NGFR activation, reducing the proapoptotic events promoted by albumin alone. This effect was prevented in HK-2 cells silenced for the NGFR gene or pretreated with the MTOR activator, MHY1485. Taken together, our results describe a novel molecular mechanism by which rapamycin-induced autophagy, mitigates the tubular renal damage caused by proteinuria, suggesting that the use of low doses of rapamycin could represent a new therapeutic strategy to counteract the tubule-interstitial injury observed in patients affected by proteinuric nephropathies, avoiding the side effects of high doses of rapamycin.

The neurotrophin Neuritin1 (cpg15) is involved in melanoma migration, attachment independent growth, and vascular mimicry

The neurotrophin Neuritin1 (NRN1; cpg15) belongs to the candidate plasticity gene (CPG) family and is expressed in postmitotic-differentiating neurons of the developmental nervous system and neuronal structures associated with plasticity in the brain of human adult.Our newest findings document that NRN1 deregulation could contribute also to disease development and have impact on malignant melanoma. Our analyses displayed the over-expression of NRN1 in melanoma in vitro and in vivo, shown by immunohistochemistry and qRT-PCR on microdissected melanoma tissue; furthermore, soluble NRN1 was detectable in tissue culture supernatant and serum of melanoma patients.To investigate the role of NRN1 in melanoma we performed knockdown, over-expression and recombinant-NRN1-treatment experiments affiliated by functional assays. Our results show that migration, attachment independent growth and vasculogenesis were affected after manipulation of NRN1 on endogenous and extrinsic level. Interestingly, high NRN1 serum levels correlate with low MIA serum levels (< 10ng/ml). Therefore, we speculate that NRN1 could be a marker for early melanoma stages, in particular.In summary, we detected an overexpression of NRN1 in melanoma patient. In functional cell culture experiments we found a correlation between NRN1 expression and the cancerous behavior of melanoma cells.

Cd271 mediates proliferation and differentiation of epidermal stem cells to support cutaneous burn wound healing

Burn wounds can significantly reduce the quality of life of patients with respect to their physiology and psychology and can even threaten their lives. Many treatments have been proposed, including stem cell therapy but no effective method can as yet cure such damage. Our study highlights the role of Cd271 in epidermal stem cells (eSC) during the healing of burn wounds. The expression of Cd271 increases together with burn wound healing. Injection of Cd271-over-expressing eSC into wounds promotes the healing rate in a mouse burn model. Over-expression of Cd271 enhances the abilities of eSC with regard to their differentiation, proliferation and migration and even their resistance to apoptosis in vitro. These results are in accordance with a hypothesis suggesting that Cd271 promotes the healing of skin burn wounds by improving the potential of eSC for differentiation, proliferation and migration. Our findings shed light on the role of Cd271 in wound healing and may provide new therapeutic approaches for curing burn wounds of the skin.

Limited activation of the intrinsic apoptotic pathway plays a main role in amyloid-β-induced apoptosis without eliciting the activation of the extrinsic apoptotic pathway

Amyloid-β (Aβ), a main pathogenic factor of Alzheimer's disease (AD), induces apoptosis accompanied by caspase activation. However, limited caspase activation and the suppression of the intrinsic apoptotic pathway (IAPW) are frequently observed upon Aβ treatment. In this study, we investigated whether these suppressive effects of Aβ can be overcome; we also examined the death-related pathways. Single treatments of cells with Aβ42 for up to 48 h barely induced caspase activation. In cells treated with Aβ42 twice for 2 h followed by 22 h (2+22 h) or for longer durations, the apoptotic protease activating factor-1 (Apaf-1) apoptosome was formed and caspases-3 and -9 were activated to a certain extent, suggesting the activation of the IAPW. However, the Aβ42-induced activation of the IAPW differed from that induced by treatment with other agents, such as staurosporine (STS) in that lower amounts of cytochrome c were released from the mitochondria, the majority of procaspase-9 in the Apaf-1 complex was not processed and caspase-3 was activated to a lesser extent in the peptide-treated cells. Thus, it seemed that the IAPW was not fully activated by Aβ42. The 30- and 41/43-kDa fragments derived from procaspase-8 were detected, which appear to be produced through the IAPW without death-inducing signaling-complex (DISC) formation, a key feature of the extrinsic apoptotic pathway (EAPW). Bid cleavage was observed only after caspase-3 activity reached its maximal levels, suggesting that the cleavage may contribute in a limited capacity to the amplification process of the IAPW in the Aβ-treated cells. Taken together, our data suggest that the IAPW, albeit functional only to a limited extent, plays a major role in Aβ42-induced apoptosis without the EAPW.

p75 Neurotrophin Receptor in the Skin: Beyond Its Neurotrophic Function

p75 neurotrophin receptor (p75^NTR), also known as CD271, is the low-affinity receptor that, together with the tyrosine kinase receptor tropomyosin-receptor kinase (Trk), mediate neurotrophin (NT) functions. Beside their classic role in skin innervation, NT and their receptors constitute a complex cutaneous network associated with a number of autocrine and paracrine activities. In this context, the role of p75^NTR is becoming more and more important. This review will focus on the intriguing functions of p75^NTR in healthy and diseased skin. First, p75^NTR counterbalances the proliferative and survival activities of its cognate receptor Trk by inducing keratinocyte apoptosis. In addition, p75^NTR identifies an early transit-amplifying (TA) keratinocyte population and plays a critical role in keratinocyte stem cell transition to its progeny as well as in epidermal differentiation. p75^NTR is absent in psoriatic TA cells, thus rendering these cells resistant to apoptosis. On the other hand, p75^NTR infection restores NT-induced apoptosis in psoriatic keratinocytes. Taken together, these results provide evidence for a critical role of p75^NTR in epidermal homeostasis, while its lack may account for the TA defect in psoriasis. While the issue of p75^NTR as a marker of melanoma initiating cells is still to be solved, there is strong evidence that downregulation of this receptor is a precondition to melanoma invasion and metastasis in vitro and in vivo. All in all, this review points to p75^NTR as a major actor in both physiologic and pathologic conditions at the skin level.

p75 neurotrophin receptor regulates differential mineralization of rat ectomesenchymal stem cells

OBJECTIVES

The aim of this study was to investigate whether p75NTR (p75 neurotrophin receptor) regulates differential mineralization capacity of rEMSCs (rat ectomesenchymal stem cells) and underlying mechanisms associated with Mage-D1 (melanoma-associated antigens-D1).

MATERIALS AND METHODS

Immunohistochemical staining of p75NTR in developing tooth germs was performed on E12.5d (embryonic 12.5 days) and E19.5d (embryonic 19.5 days). E12.5d EMSCs and E19.5d EMSCs were isolated in the same pregnant Sprague-Dawley rats from embryonic maxillofacial processes and tooth germs. p75NTR small-interfering RNA, p75NTR overexpression plasmid, Mage-D1 small-interfering RNA and recombined rat NGF were used to transfect cells.

RESULTS

p75NTR was expressed in epithelial-mesenchymal interaction areas at E12.5d and E19.5d tooth germ development stages. E19.5d EMSCs had higher p75NTR expression levels and differential mineralization capacity but lower levels of cell proliferation. Under induction by mineralized culture medium, the potential of differential mineralization had identical trends in regulation of p75NTR in EMSCs; Mage-D1 did not fluctuate and TrkA was not expressed. Binding of p75NTR and Mage-D1 were detected. Mage-D1 knockdown significantly down-regulated expression of related genes, which NGF could not rescue.

CONCLUSION

p75NTR participated in tooth germ development stages and mediated differential mineralization of EMSCs. p75NTR played a critical role in regulating the potential of differential mineralization of EMSCs. Mage-D1 seemed to act as a bridge in the underlying mechanism of effects of p75NTR.

Stress-related skin disorders

Emerging research has suggested that the skin is not only a target of organismal distress but also an active participant of the stress response through production of local "HPA axis" components, peripheral nerve endings, and resident skin cells, including keratinocytes, mast cells, and immune/immune accessory cells. There are also bidirectional communication pathways between the brain and the skin, which play significant roles in integrating these interactions. In this review, we summarize the intricate relations between stress and several skin conditions. We have tried to identify the underlying mechanisms that link stress to the common dermatoses according to the latest scientific findings.

Expression of Nerve Growth Factor (NGF), TrkA, and p75(NTR) in Developing Human Fetal Teeth

Nerve growth factor (NGF) is important for the development and the differentiation of neuronal and non-neuronal cells. NGF binds to specific low- and high-affinity cell surface receptors, respectively, p75^NTR and TrkA. In the present study, we examined by immunohistochemistry the expression patterns of the NGF, p75^NTR, and TrkA proteins during human fetal tooth development, in order to better understand the mode of NGF signaling action in dental tissues. The results obtained show that these molecules are expressed in a wide range of dental cells of both epithelial and mesenchymal origin during early stages of odontogenesis, as well as in nerve fibers that surround the developing tooth germs. At more advanced developmental stages, NGF and TrkA are localized in differentiated cells with secretory capacities such as preameloblasts/ameloblasts secreting enamel matrix and odontoblasts secreting dentine matrix. In contrast, p75^NTR expression is absent from these secretory cells and restricted in proliferating cells of the dental epithelium. The temporospatial distribution of NGF and p75^NTR in fetal human teeth is similar, but not identical, with that observed previously in the developing rodent teeth, thus indicating that the genetic information is well-conserved during evolution. The expression patterns of NGF, p75^NTR, and TrkA during odontogenesis suggest regulatory roles for NGF signaling in proliferation and differentiation of epithelial and mesenchymal cells, as well as in attraction and sprouting of nerve fibers within dental tissues.

CD271 Down-Regulation Promotes Melanoma Progression and Invasion in Three-Dimensional Models and in Zebrafish

CD271 is a neurotrophin receptor variably expressed in melanoma. Although contradictory data are reported on its role as a marker of tumor-initiating cells, little is known about its function in tumor progression. CD271 expression was higher in spheroids derived from freshly isolated cells of primary melanomas and in primary WM115 and WM793-B cell lines, and it decreased during progression to advanced stages in cells isolated from metastatic melanomas and in metastatic WM266-4 and 1205Lu cell lines. Moreover, CD271 was scarcely detected in the highly invasive spheroids (SKMEL28 and 1205Lu). CD271, originally expressed in the epidermis of skin reconstructs, disappeared when melanoma started to invade the dermis. SKMEL8 CD271(-) cells showed greater proliferation and invasiveness in vitro and were associated with a higher number of metastases in zebrafish compared with CD271(+) cells. CD271 silencing in WM115 induced a more aggressive phenotype in vitro and in vivo. On the contrary, CD271 overexpression in SKMEL28 cells reduced invasion in vitro, and CD271 overexpressing 1205Lu cells was associated with a lower percentage of metastases in zebrafish. A reduced cell-cell adhesion was also observed in the absence of CD271. Taken together, these results indicate that CD271 loss is critical for melanoma progression and metastasis.

Asymmetric stem-cell division ensures sustained keratinocyte hyperproliferation in psoriatic skin lesions

Excessive expansion of the transit-amplifying (TA) cell compartment is a distinct morphological characteristic of psoriatic epidermal hyperplasia. In order to examine the activation of basal stem cells and how they replenish such an enlarged compartment of TA cells in psoriatic epidermis, we utilized a BrdU labeling method to monitor mitotic stem cells in a mouse model of psoriasiform dermatitis, which was induced by imiquimod. Our results showed that perpendicular and parallel cell division characteristics of dividing stem cells existed in the inflamed epidermis. When we analyzed template‑DNA strand segregation in trypsin-dissociated human psoriatic keratinocytes using BrdU pulse-chase labeling, we found that the percentage of asymmetric segregation of BrdU was significantly increased in the cell pairs of psoriatic epidermal cells compared with normal epidermal cells. Furthermore, we also examined the effects of both interleukin (IL)-17A and IL-22 cytokines on the differentiation status of cultured human keratinocytes. The results indicated that both cytokines had synergistic effects on passage-one epidermal cell sheets derived from skin explants and also on cultured keratinocytes, were involved in the maintenance of the undifferentiated stem cell phenotype, and these results suggest an efficient mechanism for preventing the premature loss of basal stem-cell pools in the pro-inflammatory cytokine-enriched milieu of the psoriatic epidermis. Our findings suggest that inhibition of hyperactive stem cells represents a potential therapeutic target to combat recalcitrant epidermal hyperplasia in psoriasis.

Phosphodiesterase 4 in inflammatory diseases: Effects of apremilast in psoriatic blood and in dermal myofibroblasts through the PDE4/CD271 complex

Phosphodiesterases 4 (PDE4) act as proinflammatory enzymes via degradation of cAMP, whereas PDE4 inhibitors play an anti-inflammatory role in vitro and in vivo. In particular, apremilast has been recently approved for the treatment of psoriasis and psoriatic arthritis. However, little is known on the expression pattern of PDE4 in psoriasis. We report that PDE4B and PDE4D mRNA are overexpressed in peripheral blood mononuclear cells (PBMC) from psoriasis, as compared with normal controls, while apremilast reduces PBMC production of a number of pro-inflammatory cytokines and increases the levels of anti-inflammatory mediators. PDE4 expression is up-regulated in psoriatic dermis as compared with normal skin, with particular regard to fibroblasts. This is confirmed in vitro, where both dermal fibroblasts (DF) and, to a greater extent, myofibroblasts (DM) express all PDE4 isoforms at the mRNA and protein level. Because PDE4 interacts with the nerve growth factor (NGF) receptor CD271 in lung fibroblasts, we evaluated the relationship and function of PDE4 and CD271 in normal human skin fibroblasts. All PDE4 isoforms co-immunoprecipitate with CD271 in DM, while apremilast inhibits apoptosis induced by β-amyloid, a CD271 ligand, in DM. Furthermore, apremilast significantly reduces NGF- and transforming growth factor-β1 (TGF-β1)-induced fibroblast migration, and inhibits DF differentiation into DM mediated by NGF or TGF-β1. Finally, in DM, apremilast significantly reduces cAMP degradation induced by treatment with β-amyloid. Taken together, these results indicate that PDE4 play an important role in psoriasis. In addition, the study reveals that the PDE4/CD271 complex could be important in modulating fibroblast functions.

Distinction Between Cell Proliferation and Apoptosis Signals Regulated by Brain-Derived Neurotrophic Factor in Human Periodontal Ligament Cells and Gingival Epithelial Cells

Previously, we reported that brain-derived neurotrophic factor (BDNF) enhances periodontal tissue regeneration by inducing periodontal ligament cell proliferation in vivo. In addition, the down growth of gingival epithelial cells, which comprises a major obstacle to the regeneration, was not observed. However, the underlying molecular mechanism is still unclear. Therefore, this study aimed to investigate the effect of BDNF on cell proliferation and apoptosis in human periodontal ligament (HPL) cells and human gingival epithelial cells (OBA9 cells) and to explore the molecular mechanism in vitro. HPL cells dominantly expressed a BDNF receptor, TrkB, and BDNF increased cell proliferation and ERK phosphorylation. However, its proliferative effect was diminished by a MEK1/2 inhibitor (U0126) and TrkB siRNA transfection. Otherwise, OBA9 cells showed a higher expression level of p75, which is a pan-neurotrophin receptor, than that of HPL cells. BDNF facilitated not cell proliferation but cell apoptosis and JNK phosphorylation in OBA9 cells. A JNK inhibitor (SP600125) and p75 siRNA transfection attenuated the BDNF-induced cell apoptosis. Moreover, OBA9 cells pretreated with SP600125 or p75 siRNA showed cell proliferation by BDNF stimulation, though it was reduced by U0126 and TrkB siRNA. Interestingly, overexpression of p75 in HPL cells upregulated cell apoptosis and JNK phosphorylation by BDNF treatment. These results indicated that TrkB-ERK signaling regulates BDNF-induced cell proliferation, whereas p75-JNK signaling plays roles in cell apoptotic and cytostatic effect of BDNF. Overall, BDNF activates periodontal ligament cells proliferation and inhibits the gingival epithelial cells growth via the distinct pathway. J. Cell. Biochem. 117: 1543-1555, 2016. © 2015 Wiley Periodicals, Inc.

Nerve growth factor and proNGF simultaneously promote symmetric self-renewal, quiescence, and epithelial to mesenchymal transition to enlarge the breast cancer stem cell compartment

The discovery of cancer stem cells (CSCs) fundamentally advanced our understanding of the mechanisms governing breast cancer development. However, the stimuli that control breast CSC self-renewal and differentiation have still not been fully detailed. We previously showed that nerve growth factor (NGF) and its precursor proNGF can stimulate breast cancer cell growth and invasion in an autocrine manner. In this study, we investigated the effects of NGF and proNGF on the breast CSC compartment and found that NGF or proNGF enrich for CSCs in several breast cancer cell lines. This enrichment appeared to be achieved by increasing the number of symmetric divisions of quiescent/slow-proliferating CSCs. Interestingly, in vitro NGF pretreatment of MCF-7 luminal breast cancer cells promoted epithelial to mesenchymal transition in tumors of severe combined immunodeficient mice. Furthermore, p75(NTR), the common receptor for both neurotrophins and proneurotrophins, mediated breast CSC self-renewal by regulating the expression of pluripotency transcription factors. Our data indicate, for the first time, that the NGF/proNGF/p75(NTR) axis plays a critical role in regulating breast CSC self-renewal and plasticity.

Decreased brain-derived neurotrophic factor plasma levels in psoriasis patients

Brain-derived neurotrophic factor (BDNF) is associated with neuroplasticity and synaptic strength, and is decreased in conditions associated with chronic stress. Nevertheless, BDNF has not yet been investigated in psoriasis, a chronic inflammatory systemic disease that is exacerbated by stress. Therefore, our aim was to determine BDNF plasma levels in psoriasis patients and healthy controls. Adult patients (n=94) presenting with psoriasis for at least 1 year were enrolled, and age- and gender-matched with healthy controls (n=307) from the Brazilian Longitudinal Study of Adult Health (ELSA-Brasil). Participants had neither a previous history of coronary artery disease nor current episode of major depression. BDNF plasma levels were determined using the Promega ELISA kit. A general linear model was used to compare BDNF levels in psoriasis patients and controls, with age, gender, systolic blood pressure, serum fasting glucose, blood lipid levels, triglycerides, smoking status, and body mass index examined. After adjusting for clinical and demographic variables, significantly decreased BNDF plasma levels were observed in psoriasis patients (P=0.01) (estimated marginal means of 3922 pg/mL; 95%CI=2660-5135) compared with controls (5788 pg/mL; 95%CI=5185-6442). Similar BDNF levels were found in both mild and severe cases of psoriasis. Our finding, that BDNF is decreased in psoriasis, supports the concept of a brain-skin connection in psoriasis. Further studies should determine if BDNF is increased after specific psoriasis treatments, and associated with different disease stages.

NOD-Like Receptor Signaling in Cholesteatoma

Background. Cholesteatoma is a destructive process of the middle ear resulting in erosion of the surrounding bony structures with consequent hearing loss, vestibular dysfunction, facial paralysis, or intracranial complications. The etiopathogenesis of cholesteatoma is controversial but is associated with recurrent ear infections. The role of intracellular innate immune receptors, the NOD-like receptors, and their associated signaling networks was investigated in cholesteatoma, since mutations in NOD-like receptor-related genes have been implicated in other chronic inflammatory disorders. Results. The expression of NOD2 mRNA and protein was significantly induced in cholesteatoma compared to the external auditory canal skin, mainly located in the epithelial layer of cholesteatoma. Microarray analysis showed significant upregulation for NOD2, not for NOD1, TLR2, or TLR4 in cholesteatoma. Moreover, regulation of genes in an interaction network of the NOD-adaptor molecule RIPK2 was detected. In addition to NOD2, NLRC4, and PYCARD, the downstream molecules IRAK1 and antiapoptotic regulator CFLAR showed significant upregulation, whereas SMAD3, a proapoptotic inducer, was significantly downregulated. Finally, altered regulation of inflammatory target genes of NOD signaling was detected. Conclusions. These results indicate that the interaction of innate immune signaling mediated by NLRs and their downstream target molecules is involved in the etiopathogenesis and growth of cholesteatoma.

CD271 mediates stem cells to early progeny transition in human epidermis

CD271 is the low-affinity neurotrophin (p75NTR) receptor that belongs to the tumor necrosis factor receptor superfamily. Because in human epidermis, CD271 is predominantly expressed in transit-amplifying (TA) cells, we evaluated the role of this receptor in keratinocyte differentiation and in the transition from keratinocyte stem cells (KSCs) to progeny. Calcium induced an upregulation of CD271 in subconfluent keratinocytes, which was prevented by CD271 small interfering RNA. Furthermore, CD271 overexpression provoked the switch of KSCs to TA cells, whereas silencing CD271 induced TA cells to revert to a KSC phenotype, as shown by the expression of β1-integrin and by the increased clonogenic ability. CD271(+) keratinocytes sorted from freshly isolated TA cells expressed more survivin and keratin 15 (K15) compared with CD271(-) cells and displayed a higher proliferative capacity. Early differentiation markers and K15 were more expressed in the skin equivalent generated from CD271(+) TA than from those derived from CD271(-) TA cells. By contrast, late differentiation markers were more expressed in skin equivalents from CD271(-) than in reconstructs from CD271(+) TA cells. Finally, skin equivalents originated from CD271(-) TA cells displayed a psoriatic phenotype. These results indicate that CD271 is critical for keratinocyte differentiation and regulates the transition from KSCs to TA cells.

p75NTR is highly expressed in vestibular schwannomas and promotes cell survival by activating nuclear transcription factor κB

Vestibular schwannomas (VSs) arise from Schwann cells (SCs) and result from the loss of function of merlin, the protein product of the NF2 tumor suppressor gene. In contrast to non-neoplastic SCs, VS cells survive long-term in the absence of axons. We find that p75(NTR) is overexpressed in VSs compared with normal nerves, both at the transcript and protein level, similar to the response of non-neoplastic SCs following axotomy. Despite elevated p75(NTR) expression, VS cells are resistant to apoptosis due to treatment with proNGF, a high affinity ligand for p75(NTR) . Furthermore, treatment with proNGF protects VS cells from apoptosis due to c-Jun N-terminal kinase (JNK) inhibition indicating that p75(NTR) promotes VS cell survival. Treatment of VS cells with proNGF activated NF-κB while inhibition of JNK with SP600125 or siRNA-mediated knockdown reduced NF-κB activity. Significantly, proNGF also activated NF-κB in cultures treated with JNK inhibitors. Thus, JNK activity appears to be required for basal levels of NF-κB activity but not for proNGF-induced NF-κB activity. To confirm that the increase in NF-κB activity contributes to the prosurvival effect of proNGF, we infected VS cultures with Ad.IκB.SerS32/36A virus, which inhibits NF-κB activation. Compared with control virus, Ad.IκB.SerS32/36A significantly increased apoptosis including in VS cells treated with proNGF. Thus, in contrast to non-neoplastic SCs, p75(NTR) signaling provides a prosurvival response in VS cells by activating NF-κB independent of JNK. Such differences may contribute to the ability of VS cells to survive long-term in the absence of axons.

Role of p75 neurotrophin receptor in stem cell biology: more than just a marker

p75(NTR), the common receptor for both neurotrophins and proneurotrophins, has been widely studied because of its role in many tissues, including the nervous system. More recently, a close relationship between p75(NTR) expression and pluripotency has been described. p75(NTR) was shown to be expressed in various types of stem cells and has been used to prospectively isolate stem cells with different degrees of potency. Here, we give an overview of the current knowledge on p75(NTR) in stem cells, ranging from embryonic to adult stem cells, and cancer stem cells. In an attempt to address its potential role in the control of stem cell biology, the molecular mechanisms underlying p75(NTR) signaling in different models are also highlighted. p75(NTR)-mediated functions include survival, apoptosis, migration, and differentiation, and depend on cell type, (pro)neurotrophin binding, interacting transmembrane co-receptors expression, intracellular adaptor molecule availability, and post-translational modifications, such as regulated proteolytic processing. It is therefore conceivable that p75(NTR) can modulate cell-fate decisions through its highly ramified signaling pathways. Thus, elucidating the potential implications of p75(NTR) activity as well as the underlying molecular mechanisms of p75(NTR) will shed new light on the biology of both normal and cancer stem cells.

The biological functions and signaling mechanisms of the p75 neurotrophin receptor

The p75 neurotrophin receptor (p75(NTR)) regulates a wide range of cellular functions, including programmed cell death, axonal growth and degeneration, cell proliferation, myelination, and synaptic plasticity. The multiplicity of cellular functions governed by the receptor arises from the variety of ligands and co-receptors which associate with p75(NTR) and regulate its signaling. P75(NTR) promotes survival through interactions with Trk receptors, inhibits axonal regeneration via partnerships with Nogo receptor (Nogo-R) and Lingo-1, and promotes apoptosis through association with Sortilin. Signals downstream of these interactions are further modulated through regulated intramembrane proteolysis (RIP) of p75(NTR) and by interactions with numerous cytosolic partners. In this chapter, we discuss the intricate signaling mechanisms of p75(NTR), emphasizing how these signals are differentially regulated to mediate these diverse cellular functions.

Deciphering proneurotrophin actions

Like most growth factors, neurotrophins are initially synthesized as precursors that are cleaved to release C-terminal mature forms. The well-characterized mature neurotrophins bind to Trk receptors to initiate survival and differentiative responses. More recently, the precursor forms or proneurotrophins have been found to act as distinct ligands by binding to an unrelated receptor complex consisting of the p75 neurotrophin receptor (p75) and sortilin to initiate cell death. Induction of proNGF and p75 has been observed in preclinical injury models and in pathological states in the central nervous system, and strategies that block the proNGF/p75 interaction are effective in limiting neuronal apoptosis. In contrast, the mechanisms that regulate expression of other proneurotrophins, including proBDNF and proNT-3, are less well understood. Here, recent findings on the biological actions, regulation of expression, and pathophysiological effects of proneurotrophins will be reviewed.

miR-24 affects hair follicle morphogenesis targeting Tcf-3

During embryonic development, hair follicles (HFs) develop from an epidermal–mesenchymal cross talk between the ectoderm progenitor layer and the underlying dermis. Epidermal stem cell activation represents a crucial point both for HF morphogenesis and for hair regeneration. miR-24 is an anti-proliferative microRNA (miRNA), which is induced during differentiation of several cellular systems including the epidermis. Here, we show that miR-24 is expressed in the HF and has a role in hair morphogenesis. We generated transgenic mice ectopically expressing miR-24 under the K5 promoter. The K5::miR-24 animals display a marked defect in HF morphogenesis, with thinning of hair coat and altered HF structure. Expression of miR-24 alters the normal process of hair keratinocyte differentiation, leading to altered expression of differentiation markers. MiR-24 directly represses the hair keratinocyte stemness regulator Tcf-3. These results support the notion that microRNAs, and among them miR-24, have an important role in postnatal epidermal homeostasis.

Exposure to nerve growth factor worsens nephrotoxic effect induced by Cyclosporine A in HK-2 cells

Nerve growth factor is a neurotrophin that promotes cell growth, differentiation, survival and death through two different receptors: TrkA^NTR and p75^NTR. Nerve growth factor serum concentrations increase during many inflammatory and autoimmune diseases, glomerulonephritis, chronic kidney disease, end-stage renal disease and, particularly, in renal transplant. Considering that nerve growth factor exerts beneficial effects in the treatment of major central and peripheral neurodegenerative diseases, skin and corneal ulcers, we asked whether nerve growth factor could also exert a role in Cyclosporine A-induced graft nephrotoxicity. Our hypothesis was raised from basic evidence indicating that Cyclosporine A-inhibition of calcineurin-NFAT pathway increases nerve growth factor expression levels. Therefore, we investigated the involvement of nerve growth factor and its receptors in the damage exerted by Cyclosporine A in tubular renal cells, HK-2. Our results showed that in HK-2 cells combined treatment with Cyclosporine A + nerve growth factor induced a significant reduction in cell vitality concomitant with a down-regulation of Cyclin D1 and up-regulation of p21 levels respect to cells treated with Cyclosporine A alone. Moreover functional experiments showed that the co-treatment significantly up-regulated human p21promoter activity by involvement of the Sp1 transcription factor, whose nuclear content was negatively regulated by activated NFATc1. In addition we observed that the combined exposure to Cyclosporine A + nerve growth factor promoted an up-regulation of p75 ^NTR and its target genes, p53 and BAD leading to the activation of intrinsic apoptosis. Finally, the chemical inhibition of p75^NTR down-regulated the intrinsic apoptotic signal. We describe two new mechanisms by which nerve growth factor promotes growth arrest and apoptosis in tubular renal cells exposed to Cyclosporine A.

Expression of nuclear survivin in normal skin and squamous cell carcinoma: a possible role in tumour invasion

Background:

Survivin is detected in few adult normal cells and it is highly expressed in cancer. Nuclear survivin facilitates cell cycle entry, whereas the mitochondrial pool protects cells from apoptosis. Survivin is overexpressed in keratinocyte stem cells (KSCs) and protects them from apoptosis.

Methods:

As KSCs are at the origin of squamous cell carcinoma (SCC), we evaluated survivin expression in normal and cancerous skin in vivo by immunohistochemistry and western blotting. HaCaT cells overexpressing survivin and wound-healing assay are used. Analysis of variance and Student's T-tests are used for statistical analysis.

Results:

Survivin is localised in both the cytoplasm and nucleus of normal adult and young keratinocytes. Nuclear survivin is detected in one every 10 of 11 basal keratinocytes. When present in suprabasal cells, nuclear survivin is coexpressed with K10 but not with K15 or p75-neurotrophin receptor (p75NTR), a transit amplifying cell marker. Nuclear, but not cytoplasmic, survivin expression markedly increases in actinic keratosis and in SCC in situ, as compared with normal epidermis, and it is highest in poorly differentiated SCC. In SCC tumours, nuclear survivin-positive cells are mainly K10/p75NTR-negative and K15-positive. In poorly differentiated tumours, survivin mostly localises in the deep infiltrating areas. When overexpressed in keratinocytes, survivin increases cell migration.

Conclusion:

High survivin expression and the subcellular localisation of survivin correlate with keratinocyte differentiation and are associated with undifferentiated and more invasive SCC phenotype.

Role of neuropeptides, neurotrophins, and neurohormones in skin wound healing

Due to the close interactions between the skin and peripheral nervous system, there is increasing evidence that the cutaneous innervation is an important modulator of the normal wound healing process. The communication between sensory neurons and skin cells involves a variety of molecules (neuropeptides, neurohormones, and neurotrophins) and their specific receptors expressed by both neuronal and nonneuronal skin cells. It is well established that neurotransmitters and nerve growth factors released in skin have immunoregulatory roles and can exert mitogenic actions; they could also influence the functions of the different skin cell types during the wound healing process.