Topical retinoic acid alters the expression of cellular retinoic acid-binding protein-I and cellular retinoic acid-binding protein-II in non-lesional but not lesional psoriatic skin

Predictive role of vitamin A serum concentration in psoriatic patients treated with IL-17 inhibitors to prevent skin and systemic fungal infections

The use of biological drugs in psoriasis is replacing traditional therapies due to their specific mechanism and limited side effects. However, the use of Interleukin 17 inhibitors and the modification of its cytokine pathway could favor the risk of fungal infections. All-trans retinoic acid is an active metabolite of vitamin A with anti-inflammatory and immunoregulatory properties through its capacity to stimulate both innate and adaptive immunity and to its effects on proliferation, differentiation and apoptosis in a variety of immune cells. Furthermore, it has been recently discovered that All-trans retinoic acid has a direct fungistatic effect against Candida and Aspergillus Fumigatus. On the basis of these new insights, in the current review, we suggest that the evaluation of serum level of All-trans retinoic acid or vitamin A should be considered as a predictive marker for the development of fungal infections among psoriatic patients treated with Interleukin 17 inhibitors. In clinical practice, vitamin A test could be added in the routine hospital diagnostic management for a better selection of psoriatic patients eligible to Interleukin 17 inhibitors.

Cellular retinoic acid binding protein-II expression and its potential role in skin aging

Skin aging is an intricate biological process consisting of intrinsic and extrinsic alterations of epidermal and dermal structures. Retinoids play an important role in epidermal cell growth and differentiation and are beneficial to counteract skin aging. Cellular retinoic acid binding protein-II (CRABP-II) selectively binds all trans-retinoic acid, the most active retinoid metabolite, contributing to regulate intracytoplasmic retinoid trafficking and keratinocyte differentiation. Immunohistochemistry revealed a reduced epidermal and dermal CRABP-II expression in aged human and mouse skin. To better clarify the role of CRABP-II, we investigated age-related skin changes in CRABP-II knock-out mice. We documented an early reduction of keratinocyte layers, proliferation and differentiation rate, dermal and hypodermal thickness, pilosebaceous units and dermal vascularity in CRABP-II knock-out compared with wild-type mice. Ultrastructural investigation documented reduced number and secretion of epidermal lamellar bodies in CRABP-II knock-out compared with wild-type mice. Cultured CRABP-II knock-out-derived dermal fibroblasts proliferated less and showed reduced levels of TGF-β signal-related genes, Col1A1, Col1A2, and increased MMP2 transcripts compared with those from wild-type. Our data strongly support the hypothesis that a reduction of CRABP-II expression accelerates and promotes skin aging, and suggest CRABP-II as a novel target to improve the efficacy of retinoid-mediated anti-aging therapies.

Retinol and vitamin A metabolites accumulate through RBP4 and STRA6 changes in a psoriasis murine model

Background

Psoriasis is a common chronic inflammatory skin disease that features the abnormal proliferation of keratinocytes. This proliferation could partly result from disturbances in vitamin A metabolism. Changes in psoriasis patients of the levels of retinol-binding protein 4 (RBP4), a carrier of retinol (vitamin A); transmembrane protein stimulated by retinoic acid 6 (STRA6); and other retinol metabolic molecules have not yet been fully established. Therefore, we investigated vitamin A-related proteins in mice with imiquimod (IMQ)-induced psoriasis.

Methods

Thirty mice were divided into four study groups: two groups underwent IMQ application for 3 or 6 days (groups A and B, respectively), and two groups underwent Vaseline application for 3 or 6 days (groups C and D, respectively). Blood and skin samples from both lesional and non-lesional areas of the mice were analyzed using enzyme-linked immunosorbent assays, hematoxylin and eosin staining, immunochemistry, real-time reverse transcription polymerase chain reaction, and RNA sequencing.

Results

IMQ-treated mice developed erythema, scales, and skin thickening. Compared with the control groups, IMQ-treated groups had the following changes: 1) interleukin (IL)-17A, IL-23, and tumor necrosis factor (TNF)-α levels were raised significantly in both serum and lesional skin (all p < 0.001); 2) retinol levels in lesional skin increased slightly (p = 0.364), but no change was evident in serum retinol levels; 3) STRA6 was upregulated in both lesional skin (p = 0.021) and serum (p = 0.034); 4) RBP4 levels were elevated in serum (p = 0.042), but exhibited only an increasing trend (p = 0.273) in lesional skin; and 5) proteins and enzymes that mediate retinoic acid formation and transformation were upregulated in lesional skin.

Conclusions

As the demand for vitamin A in psoriatic mice increased, retinol underwent relocation from the circulation to target tissues. RBP4, STRA6, and the transformation from retinol to retinoic acid were upregulated, which may be part of the mechanism of psoriasis skin lesion formation. We propose that a positive feedback mechanism was formed that maintained the severity of psoriasis.

Cellular Retinoic-Acid Binding Protein 2 in Solid Tumor

The retinoic acid (RA) signaling pathway is crucial for many biological processes. The RA transporter, Cellular Retinoic-Acid Binding Protein 2 (CRABP2), is abnormally expressed in various tumor types. CRABP2 presents significant effects on tumorous behaviors and functions, including cell proliferation, apoptosis, invasion, migration, metastasis, and angiogenesis. The tumorigenesis mechanism of CRABP2, as both suppressor and promotor, is complicated, therefore, there remains the need for further investigation. Elucidating the regulating mechanisms in a specific stage of the tumor could facilitate CRABP2 to be a biomarker in cancer diagnosis and prognosis. Besides, clarifying the pathways of CRABP2 in cancer development will contribute to the gene-targeted therapy. In this review, we summarized the expression, distribution, and mechanism of CRABP2 in solid tumors. Illuminating the CRABP2 signaling pathway may benefit understanding the retinoid signaling pathway, providing a useful biomarker for future clinical trials.

Expression and potential role of cellular retinol binding protein I in psoriasis

Psoriasis is a diffuse chronic skin disorder characterized from accelerated epidermal turnover and inflammatory cell infiltrate. Retinoids influence keratinocyte proliferation and differentiation as well as inflammatory response. Cellular retinol binding protein (CRBPI) regulates intracellular vitamin A bioavailability and contributes to maintain skin homeostasis. The aim of present study was to investigate the expression of CRBPI and its role in the pathogenesis of skin psoriasis. Immunohistochemistry revealed more diffuse and increased CRBPI expression in all epidermal layers of human psoriatic lesions except in the stratum corneum. An imiquimod-induced psoriatic-like model documented the increase of skin lesional area and severity index score as well as of the severity of microscopic features as parakeratosis, papillomatosis and spongiosis in CRBPI-knockout compared to wild-type mice, associated to the increased keratinocyte CK17 and Ki-67 expression and the reduction of CK1, CRABPII and RXRα. Gene array of imiquimod-induced psoriatic skin documented the greater up-regulation of EGF/PDGF-related genes and down-regulation of EGR1 and pro-inflammatory IL-related genes in CRBPI-knockout compared to wild-type mice. Finally, CRBPI transfection in HaCaT cells increased AKT and NF-κB-related genes and proteins and down-regulated IL-2, IL-6 and IL-8 pro-inflammatory signalling. Although not recognized as a psoriatic susceptibility gene in our cohort of patients, the present data strongly supported the potential role of CRBPI to sustain keratinocyte proliferation and differentiation and to counteract pro-inflammatory genes expression in psoriatic lesions.

Retinoic Acid promotes interleukin-4 plasmid-dimethylsulfoxide topical transdermal delivery for treatment of psoriasis

Background

Psoriasis is an autoimmune disease that is caused by a shift in the Th1/Th2 balance toward Th1-dominant immunity. It has been established as an effective treatment to counteract psoriasis by subcutaneous injection of recombinant interleukin (IL)-4, and IL-4 gene therapy by topical transdermal penetration has shown its antipsoriatic effect in mice. Retinoic acid (RA) and dimethylsulfoxide can increase the efficiency of gene transfection in the topical transdermal delivery system.

Objective

We investigated whether RA could improve anti-psoriasis efficiency using IL-4 expression plasmid pORF-mIL-4 (pIL-4) via transdermal delivery system in K14-vascular endothelial growth (K14-VEGF) factor transgenic mice.

Methods

After pretreatment with RA, plasmid pIL-4 in 10% dimethylsulfoxide was applied to the ear skin by topical transdermal penetration. Hematoxylin- eosin staining and immunohistochemistry were performed with ear samples to evaluate anti-psoriasis efficiency in mice.

Results

The psoriasis pathological features were relieved and psoriasis-associated factors were significantly reduced.

Conclusion

Our results reveal that topical application of pIL-4 in dimethylsulfoxide by transdermal delivery with RA pretreatment can improve psoriasis significantly.

Evaluation of plasma vitamin A and E levels and tear film changes in patients with psoriasis vulgaris

Purpose

To evaluate whether alterations in plasma vitamin A and E levels in patients with psoriasis have an effect on tear film changes.

Methods

Sixty-two eyes of 31 patients with psoriasis vulgaris (Group A) and 74 eyes of 37 age- and gender-matched control subjects (Group B) were included in the study. Ocular and medical histories and dietary habits were obtained from each patient. The tear film break-up time (TBUT), the Schirmer 1 test results and plasma vitamin A and E levels were evaluated.

Results

The mean Schirmer 1 test score was 14.76 ± 6.12 mm/5 min in Group A and 15.69 ± 3.10 mm/5 min in Group B. The mean plasma levels of vitamins A and E in Groups A and B were 1.86 ± 0.62 µmol/L and 1.88 ± 0.65 µmol/L vs. 26.21 ± 5.13 µmol/L and 27.19 ± 8.89 µmol/L, respectively. The Schirmer 1 test results and plasma vitamin A and E levels were not found to be significantly different between the groups (p > 0.05). The mean TBUT was 9.94 ± 6.18 seconds in Group A and 14.47 ± 5.65 seconds in Group B, a significant difference (p < 0.05). No correlation existed between plasma vitamin A and E levels, TBUT or the severity and duration of the disease (p > 0.05).

Conclusions

Plasma vitamin A and E levels do not seem to be related to tear film changes in patients with psoriasis vulgaris.

Retinol dehydrogenase 10 but not retinol/sterol dehydrogenase(s) regulates the expression of retinoic acid-responsive genes in human transgenic skin raft culture

Retinoic acid is essential for skin growth and differentiation, and its concentration in skin is controlled tightly. In humans, four different members of the short-chain dehydrogenase/reductase (SDR) superfamily of proteins were proposed to catalyze the rate-limiting step in the biosynthesis of retinoic acid (the oxidation of retinol to retinaldehyde). Epidermis contains at least three of these enzymes, but their relative importance for retinoic acid biosynthesis and regulation of gene expression during growth and differentiation of epidermis is not known. Here, we investigated the effect of the four human SDRs on retinoic acid biosynthesis, and their impact on growth and differentiation of keratinocytes using organotypic skin raft culture model of human epidermis. The results of this study demonstrate that ectopic expression of retinol dehydrogenase 10 (RDH10, SDR16C4) in skin rafts dramatically increases proliferation and inhibits differentiation of keratinocytes, consistent with the increased steady-state levels of retinoic acid and activation of retinoic acid-inducible genes in RDH10 rafts. In contrast, SDRs with dual retinol/sterol substrate specificity, namely retinol dehydrogenase 4 (RoDH4, SDR9C8), RoDH-like 3α-hydroxysteroid dehydrogenase (RL-HSD, SDR9C6), and RDH-like SDR (RDHL, SDR9C4) do not affect the expression of retinoic acid-inducible genes but alter the expression levels of several components of extracellular matrix. These results reveal essential differences in the metabolic contribution of RDH10 versus retinol/sterol dehydrogenases to retinoic acid biosynthesis and provide the first evidence that non-retinoid metabolic products of retinol/sterol dehydrogenases affect gene expression in human epidermis.

Keratinocyte differentiation induced by calcium, phorbol ester or interferon-gamma elicits distinct changes in the retinoid signalling pathways

BACKGROUND

Retinoids influence keratinocyte proliferation and differentiation via binding to nuclear retinoic acid receptors (RARalpha, -gamma) and retinoid X receptor alpha (RXRalpha). The effect of keratinocyte differentiation on expression of nuclear retinoid receptors and on the conversion of retinol into retinoic acid has not been examined earlier in depth.

OBJECTIVES

Our aim was to examine the expression of retinoid receptors and a retinoid-regulated gene CRABPII, as well as the metabolism of exogenous [(3)H]retinol in cultured human keratinocytes induced to differentiate by exposure to either calcium, phorbol 12-myristate 13-acetate (PMA), or interferon-gamma (IFNgamma).

METHODS

Normal human keratinocytes were cultured and exposed to differentiation-inducing agents. The mRNA and protein expression of retinoid receptors were examined using real-time PCR and Western blot. [(3)H]Retinol uptake and metabolism was monitored by HPLC with on-line radioactivity detection.

RESULTS

In calcium-exposed cells, increased expression of RARgamma and RXRalpha, enhanced metabolism of [(3)H]retinol to 3,4-didehydro-RA (ddRA), and an induction of CRABPII mRNA and protein was noted. In contrast, treatment with PMA and IFNgamma reduced the RARgamma and RXRalpha protein expression (preventable by the proteasome inhibitor MG132), increased the accumulation of [(3)H]RA and/or [(3)H]ddRA in the cells, and changed the CRABPII transcription.

CONCLUSIONS

Retinoid signalling is profoundly altered upon differentiation of keratinocytes and the effects depend on how cellular differentiation is initiated.

Both all-trans retinoic acid and cytochrome P450 (CYP26) inhibitors affect the expression of vitamin A metabolizing enzymes and retinoid biomarkers in organotypic epidermis

The biosynthesis of retinoic acid (RA) from retinol is controlled by several enzymes, e.g. dehydrogenases (RalDH2, RoDH-4) and retinol-esterifying enzyme (LRAT), whereas its degradation mainly involves CYP26 enzymes. In keratinocytes, RA activates the nuclear retinoid-receptors inducing the transcription of many genes. Here, we examined the effects of RA and the CYP26 inhibitors, liarozole and talarozole, on retinoid metabolism and RA-regulated genes in organotypic epidermis. RA induced the expression of CYP26 enzymes already after 8 h, whereas LRAT exhibited a later response and peaked at 48 h, indicating a feedback induction of retinol esterification. In line with a reduced biosynthesis of RA from retinol after exogenous RA, the expression of RDH16 reduced 80% in response to exogenous RA. The mRNA expression of RA-regulated genes (KRT2, KRT4, CRABPII and HBEGF) was altered within 24 h after RA exposure. In contrast, the CYP26 inhibitors caused only minor effects, except for a clear-cut induction of CYP26A1 only when combined with minute amounts of exogenous RA. Cellular accumulation of exogenous [3H]RA was higher after talarozole than after liarozole, probably indicating a greater CYP26-inhibitory potency of the former drug. The present study shows that CYP26A1 expression is extremely sensitive to both exogenous RA and increased endogenous RA levels, i.e. due to CYP26 inhibition, and thus an excellent biomarker for retinoid signalling in organotypic epidermis.

Dynamic regulation of retinoic acid-binding proteins in developing, adult and neoplastic skin reveals roles for beta-catenin and Notch signalling

Retinoic acid (RA) signalling is essential for epidermal differentiation; however, the mechanisms by which it acts are largely unexplored. Partitioning of RA between different nuclear receptors is regulated by RA-binding proteins. We show that cellular RA-binding proteins CRABP1 and CRABP2 and the fatty acid-binding protein FABP5 are dynamically expressed during skin development and in adult tissue. CRABP1 is expressed in embryonic dermis and in the stroma of skin tumours, but confined to the hair follicle dermal papilla in normal postnatal skin. CRABP2 and FABP5 are expressed in the differentiating cells of sebaceous gland, interfollicular epidermis and hair follicles, with FABP5 being a prominent marker of sebaceous glands and anagen follicle bulbs. All three proteins are upregulated in response to RA treatment or Notch activation and are negatively regulated by Wnt/beta-catenin signalling. Ectopic follicles induced by beta-catenin arise from areas of the sebaceous gland that have lost CRABP2 and FABP5; conversely, inhibition of hair follicle formation by N-terminally truncated Lef1 results in upregulation of CRABP2 and FABP5. Our findings demonstrate that there is dynamic regulation of RA signalling in different regions of the skin and provide evidence for interactions between the RA, beta-catenin and Notch pathways.

Transient activation of FOXN1 in keratinocytes induces a transcriptional programme that promotes terminal differentiation: contrasting roles of FOXN1 and Akt

The forkhead transcription factor FOXN1 is required for normal cutaneous and thymic epithelial development. Mutations in FOXN1 give rise to the nude phenotype in mice, rats and man. However, the genes that are regulated by FOXN1 are unknown. To investigate FOXN1 function we expressed an inducible form of the protein, FOXN1ER, that is activated by 4-hydroxytamoxifen in primary human epidermal keratinocytes. Transient activation of FOXN1 decreased the proportion of keratinocytes that formed actively growing clones attributable to stem cell founders and increased the number of abortive clones, without inducing apoptosis. Within 24 hours the majority of cells had initiated terminal differentiation, as assessed by involucrin expression. We performed a cDNA microarray experiment to analyse changes in the transcription of approximately 6000 genes. Following FOXN1 activation we detected increases of two fold or greater in the RNA levels of over 30 genes. Genes promoting growth arrest, survival and differentiation featured prominently and markers of early events in keratinocyte differentiation were also detected. Since one of the induced genes was Akt we investigated whether Akt played a role in terminal differentiation. Activation of PI 3-kinase but not Akt was necessary for FOXN1-induced differentiation. In reconstituted epidermis FOXN1 promoted early stages of terminal differentiation whereas Akt activation was sufficient to induce late stages, including formation of the cornified layers. These results establish a role for FOXN1 in initiation of terminal differentiation and implicate Akt in subsequent events.

Vitamin A and infancy. Biochemical, functional, and clinical aspects

Vitamin A is a very intriguing natural compound. The molecule not only has a complex array of physiological functions, but also represents the precursor of promising and powerful new pharmacological agents. Although several aspects of human retinol metabolism, including absorption and tissue delivery, have been clarified, the type and amounts of vitamin A derivatives that are intracellularly produced remain quite elusive. In addition, their precise function and targets still need to be identified. Retinoic acids, undoubtedly, play a major role in explaining activities of retinol, but, recently, a large number of physiological functions have been attributed to different retinoids and to vitamin A itself. One of the primary roles this vitamin plays is in embryogenesis. Almost all steps in organogenesis are controlled by retinoic acids, thus suggesting that retinol is necessary for proper development of embryonic tissues. These considerations point to the dramatic importance of a sufficient intake of vitamin A and explain the consequences if intake of retinol is deficient. However, hypervitaminosis A also has a number of remarkable negative consequences, which, in same cases, could be fatal. Thus, the use of large doses of retinol in the treatment of some human diseases and the use of megavitamin therapy for certain chronic disorders as well as the growing tendency toward vitamin faddism should alert physicians to the possibility of vitamin overdose.