Exploring the role of autophagy in psoriasis pathogenesis: Insights into sustained inflammation and dysfunctional keratinocyte differentiation

Psoriasis is a common and prevalent chronic papulosquamous cutaneous disorder characterized by sustained inflammation, uncontrolled keratinocyte proliferation, dysfunctional differentiation, and angiogenesis. Autophagy, an intracellular catabolic process, can be induced in response to nutrient stress. It entails the degradation of cellular constituents through the lysosomal machinery, and its association with psoriasis has been well-documented. Nevertheless, there remains a notable dearth of research concerning the involvement of autophagy in the pathogenesis of psoriasis within human skin. This review provides a comprehensive overview of autophagy in psoriasis pathogenesis, focusing on its involvement in two key pathological manifestations: sustained inflammation and uncontrolled keratinocyte proliferation and differentiation. Additionally, it discusses potential avenues for disease management.

Interferon-Alpha Induces Psoriatic Inflammation in Mice by Phosphorylating FOXO3

Psoriasis is a chronic, immune-mediated inflammatory skin disease characterized by epidermal thickening and inflammatory cell infiltration. Excessive proliferation of keratinocytes and resistance to apoptosis lead to thickening of the epidermis. Plasmacytoid dendritic cells are involved in the occurrence of psoriasis mainly by secreting interferon-alpha (IFN-α). IFN-α is a glycoprotein with antiviral, antitumor, and immunomodulatory effects, but its role in psoriasis remains unclear. In this investigation, a mild psoriatic phenotype was observed in mice upon topical application of IFN-α cream, and the inflammation was exacerbated when combined with imiquimod (IMQ). Immunohistochemical analyses demonstrated that IFN-α induces psoriatic inflammation in mice by stimulating phosphorylation of forkhead box O3, consistent with the involvement of this protein in cell proliferation, apoptosis, and inflammation. Our results suggested that topical IFN-α caused psoriatic inflammation and that the psoriatic inflammation was exacerbated by the combination of IFN-α and IMQ, possibly due to the dysfunction of forkhead box O3.

Oxymatrine ameliorates imiquimod-induced psoriasis pruritus and inflammation through inhibiting heat shock protein 90 and heat shock protein 60 expression in keratinocytes

In this work, we aimed to investigate whether oxymatrine exerts its anti-pruritic and anti-inflammatory efficacy in the imiquimod-induced psoriasis mice and the related mechanism. We established the psoriasis model by applying the imiquimod ointment topically and oxymatrine was injected intraperitoneally as the treatment. The behavior and skin morphology results indicated that oxymatrine inhibits imiquimod-induced pruritus alleviating keratinization of skin and inflammatory infiltration. Moreover, we examined the expression of various indicators and found heat shock protein (HSP) 90 and 60 upregulated in model group, which were reversed in oxymatrine treated groups. Molecular docking and the studies in vivo confirmed that HSP90 and HSP60 participate in the inhibitory effect of oxymatrine on the phenotypes of psoriasis mice. Mechanically, immunofluorescence staining demonstrated that oxymatrine-induced downregulation of HSP90 and HSP60 was mainly in keratinocytes. In vitro results showed that oxymatrine decreases the expression of HSP90 and HSP60 upregulated by TNF-α and IFN-γ in HaCaTs cells and the siRNA mediated HSP90 and HSP60 silencing reverses inflammation inhibited by oxymatrine. Taken together, these results indicate that oxymatrine relieves psoriasis pruritic and inflammation by inhibiting the expression of HSP90 and HSP60 in keratinocytes through MAPK signaling pathway.

Bidirectional Association Between Psoriasis and Obesity: Benefits and Risks

Psoriasis is a chronic, immune-mediated inflammatory skin disease that is associated with several comorbidities such as obesity. This study was designed to estimate the possibility of utilizing psoriasin, nestin, keratin-16 (Krt16), and interleukin-21 (IL-21) as biochemical markers of psoriasis, to correlate these candidate psoriatic markers with biomarkers of obesity [body mass index (BMI), leptin, and resistin], and to elucidate the bidirectional association between obesity and psoriasis. Blood samples were collected from all participants (n = 108) who were classified according to their BMI into 4 groups: healthy control, obese, psoriatic, and obese psoriatic group. Plasma psoriasin, nestin, Krt16, IL-21, leptin, and resistin were estimated for all subjects. Psoriasin, nestin, Krt16, IL-21, leptin, and resistin were significantly elevated in psoriatic and obese psoriatic groups. However, only leptin, resistin, IL-21, and Krt16 were significantly increased in the obese group compared with the control group. Leptin and resistin showed significant positive correlations with psoriasis area and severity index score, psoriasin, nestin, Krt16, and IL-21. Cutoff values for psoriasin, nestin, Krt16, and IL-21 were 187.5 ng/mL, 1825 pg/mL, 33.1 ng/mL, and 128.6 ng/L, respectively. In conclusion, psoriasin, nestin, Krt16, and IL-21 can be utilized as biochemical markers of psoriasis; these psoriatic markers are significantly positively correlated with obesity biomarkers, and obesity can be considered a risk factor and/or consequence of psoriasis.

Constitutive Autophagy and Nucleophagy during Epidermal Differentiation

Epidermal keratinocytes migrate through the epidermis up to the granular layer where, on terminal differentiation, they progressively lose organelles and convert into anucleate cells or corneocytes. Our report explores the role of autophagy in ensuring epidermal function providing the first comprehensive profile of autophagy marker expression in developing epidermis. We show that autophagy is constitutively active in the epidermal granular layer where by electron microscopy we identified double-membrane autophagosomes. We demonstrate that differentiating keratinocytes undergo a selective form of nucleophagy characterized by accumulation of microtubule-associated protein light chain 3/lysosomal-associated membrane protein 2/p62 positive autolysosomes. These perinuclear vesicles displayed positivity for histone interacting protein, heterochromatin protein 1α, and localize in proximity with Lamin A and B1 accumulation, whereas in newborn mice and adult human skin, we report LC3 puncta coincident with misshaped nuclei within the granular layer. This process relies on autophagy integrity as confirmed by lack of nucleophagy in differentiating keratinocytes depleted from WD repeat domain phosphoinositide interacting 1 or Unc-51 like autophagy activating kinase 1. Final validation into a skin disease model showed that impaired autophagy contributes to the pathogenesis of psoriasis. Lack of LC3 expression in psoriatic skin lesions correlates with parakeratosis and deregulated expression or location of most of the autophagic markers. Our findings may have implications and improve treatment options for patients with epidermal barrier defects.

Analysis of epithelial-mesenchymal transition markers in psoriatic epidermal keratinocytes

Psoriasis is similar to endpoints of epithelial–mesenchymal transition (EMT), a process of epithelial cells transformed into fibroblast-like cells. The molecular epithelial and mesenchymal markers were analysed in psoriatic keratinocytes. No obvious alteration of epithelial markers E-cadherin (E-cad), keratin 10 (K10), K14 and K16 was detected in psoriatic keratinocytes. However, significantly increased expression of Vim, FN, plasminogen activator inhibitor 1 (PAI-1) and Slug was seen. IL-17A and IL-13 at 50 ng ml⁻¹ strongly decreased expression of K10, Vim and FN. TGF-β1 at 50 ng ml⁻¹ promoted the production of N-cad, Vim, FN and PAI-1. Slug was decreased by dexamethasone (Dex), but E-cad was upregulated by Dex. Silencing of ERK partially increased E-cad and K16, but remarkably inhibited K14, FN, Vim, β-catenin, Slug and α5 integrin. Moreover, inhibition of Rho and GSK3 by their inhibitors Y27632 and SB216763, respectively, strongly raised E-cad, β-catenin and Slug. Dex decreased Y27632-mediated increase of β-catenin. Dex at 2.0 µM inhibited SB216763-regulated E-cad, β-catenin and slug. In conclusion, EMT in psoriatic keratinocytes may be defined as an intermediate phenotype of type 2 EMT. ERK, Rho and GSK3 play active roles in the process of EMT in psoriatic keratinocytes.

Wheat germ agglutinin as a counterstain for immunofluorescence studies of equine hoof lamellae

Equine laminitis is a common, painful, debilitating condition of the hoof that is a leading cause of disability in horses, often necessitating euthanasia. The equine hoof represents an extreme evolutionary adaptation of an epidermal structure homologous to the human or murine nail units. Immunohistochemistry is frequently utilized in the study of the pathophysiology of laminitis. The complex, multilayered, extensively interdigitated epidermal-dermal lamellar interface renders precise interpretation of immunofluorescence localization difficult, especially when effective technique and reagents render non-reactive tissues completely dark. Fluorescent-conjugated wheat germ agglutinin (WGA) selectively labels dermal extracellular matrix fibres and epidermal cell membranes in tissue sections of horse hoof lamellae, is compatible with indirect immunofluorescence and augments interpretation of indirect immunofluorescence antigen localization. The current report details the use of WGA as a rapid, simple, economical counterstain for immunofluorescence studies of the equine hoof and may have application to other complex epidermal tissue structures.

Novel nanosome delivery system combined with siRNA targeting the antimicrobial gene DFB4: a new approach for psoriasis management?

In a recently published issue of the journal, Bracke et al. demonstrate an impressive improvement in psoriasiform features in allogeneic human skin grafts transplanted onto immune-deficient mice. This improvement was achieved using a novel nanosome (SECosome) as a vehicle for delivering topically applied siRNA to human epidermis. Targeting the gene DFB4 with this delivery system, they prevented translation of the antimicrobial peptide, human β defensin-2(hBD2), thus normalizing the psoriasiform epidermal phenotype of siRNA/SECosome-treated human skin grafts. This study encourages the exploration of topical gene silencing strategies in dermatology and refocuses our attention on both, the role of hBD2 in psoriasis pathogenesis and the thorny question which animal model reflects human psoriasis most faithfully.

Development of TAP, a non-invasive test for qualitative and quantitative measurements of biomarkers from the skin surface

Background

The skin proteome contains valuable information on skin condition, but also on how skin may evolve in time and may respond to treatments. Despite the potential of measuring regulatory-, effector- and structural proteins in the skin for biomarker applications in clinical dermatology and skin care, convenient diagnostic tools are lacking. The aim of the present study was to develop a highly versatile and non-invasive diagnostic tool for multiplex measurements of protein biomarkers from the surface of skin.

Results

The Transdermal Analyses Patch (TAP) is a novel molecular diagnostic tool that has been developed to capture biomarkers directly from skin, which are quantitatively analyzed in spot-ELISA assays. Optimisation of protocols for TAP production and biomarker analyses makes TAP measurements highly specific and reproducible. In measurements of interleukin-1α (IL-1α), IL-1 receptor antagonist (IL-1RA) and human β-defensin (hBD-1) from healthy skin, TAP appears far more sensitive than skin lavage-based methods using ELISA. No side-effects were observed using TAP on human skin.

Conclusion

TAP is a practical and valuable new skin diagnostic tool for measuring protein-based biomarkers from skin, which is convenient to use for operators, with minimal burden for patients.

Reduction of inflammatory slan (6-sulfo LacNAc) dendritic cells in psoriatic skin of patients treated with etanercept

Dermal dendritic cells (DCs) play a central role in the immunopathology of psoriasis. We previously identified slanDCs as pro-inflammatory TNF-α, IL-23- and IL-12-producing DCs in human blood and as prominent inflammatory dermal TNF-α secreting and CD11c-positive DC subset in psoriasis. Here, we ask for the effects of TNF-α-inhibition on inflammatory slanDCs in skin and blood of 10 patients with psoriasis during 24 weeks of treatment with etanercept. Treatment with etanercept reduced the frequency of dermal slanDCs but did not induce apoptosis as determined by lack of increased active caspase-3-expression. In parallel, we found increased frequencies of slanDCs in blood which expressed lower levels of HLA-DR. Stimulating slanDCs isolated from the blood of healthy donors in vitro induced a strong production of IL-1β, IL-6, IL-23 and IL-12p70. This capacity was efficiently reduced in the presence of etanercept, thereby indicating that TNF-α is an autocrine stimulus for maturation and pro-inflammatory cytokine production of slanDCs. In vivo, we noticed that treatment with etanercept did reduce the number of dermal slanDCs in parallel to the overall expression of TNF-α and IL-23p19. However, successful treatment did not down-regulated the percentage of dermal slanDCs that stained positive for TNF-α and IL-23p19 indicating that remaining slanDCs kept their pro-inflammatory capacity. This study provides novel insights into the immune regulatory properties of etanercept at the level of inflammatory slanDCs in vivo in skin and blood as well as in vitro.

Thyrotropin-releasing hormone (TRH) promotes wound re-epithelialisation in frog and human skin

There remains a critical need for new therapeutics that promote wound healing in patients suffering from chronic skin wounds. This is, in part, due to a shortage of simple, physiologically and clinically relevant test systems for investigating candidate agents. The skin of amphibians possesses a remarkable regenerative capacity, which remains insufficiently explored for clinical purposes. Combining comparative biology with a translational medicine approach, we report the development and application of a simple ex vivo frog (Xenopus tropicalis) skin organ culture system that permits exploration of the effects of amphibian skin-derived agents on re-epithelialisation in both frog and human skin. Using this amphibian model, we identify thyrotropin-releasing hormone (TRH) as a novel stimulant of epidermal regeneration. Moving to a complementary human ex vivo wounded skin assay, we demonstrate that the effects of TRH are conserved across the amphibian-mammalian divide: TRH stimulates wound closure and formation of neo-epidermis in organ-cultured human skin, accompanied by increased keratinocyte proliferation and wound healing-associated differentiation (cytokeratin 6 expression). Thus, TRH represents a novel, clinically relevant neuroendocrine wound repair promoter that deserves further exploration. These complementary frog and human skin ex vivo assays encourage a comparative biology approach in future wound healing research so as to facilitate the rapid identification and preclinical testing of novel, evolutionarily conserved, and clinically relevant wound healing promoters.

A novel control of human keratin expression: cannabinoid receptor 1-mediated signaling down-regulates the expression of keratins K6 and K16 in human keratinocytes in vitro and in situ

Cannabinoid receptors (CB) are expressed throughout human skin epithelium. CB1 activation inhibits human hair growth and decreases proliferation of epidermal keratinocytes. Since psoriasis is a chronic hyperproliferative, inflammatory skin disease, it is conceivable that the therapeutic modulation of CB signaling, which can inhibit both proliferation and inflammation, could win a place in future psoriasis management. Given that psoriasis is characterized by up-regulation of keratins K6 and K16, we have investigated whether CB1 stimulation modulates their expression in human epidermis. Treatment of organ-cultured human skin with the CB1-specific agonist, arachidonoyl-chloro-ethanolamide (ACEA), decreased K6 and K16 staining intensity in situ. At the gene and protein levels, ACEA also decreased K6 expression of cultured HaCaT keratinocytes, which show some similarities to psoriatic keratinocytes. These effects were partly antagonized by the CB1-specific antagonist, AM251. While CB1-mediated signaling also significantly inhibited human epidermal keratinocyte proliferation in situ, as shown by K6/Ki-67-double immunofluorescence, the inhibitory effect of ACEA on K6 expression in situ was independent of its anti-proliferative effect. Given recent appreciation of the role of K6 as a functionally important protein that regulates epithelial wound healing in mice, it is conceivable that the novel CB1-mediated regulation of keratin 6/16 revealed here also is relevant to wound healing. Taken together, our results suggest that cannabinoids and their receptors constitute a novel, clinically relevant control element of human K6 and K16 expression.