Transcriptional changes in organoculture of full-thickness human skin following topical application of all-trans retinoic acid

One of the most studied classes of skin-targeted compounds is retinoids. All-trans retinoic acid (RA) also referred to as tretinoin, and its synthetic or natural derivatives (retinoids) affect epidermal growth and differentiation 1. Synthetic retinoids are today used widely in the treatment of psoriasis and other disorders of keratinization 2. Also, acne has been widely treated with various forms of natural and synthetic retinoids for more than 40 years 3. Later, retinoids has been used in the treatment for hyperpigmentation disorders such as post-inflammatory hyperpigmentation and melasma 4. Separate from the effect of retinoids in skin disease, Kligman and Willis were the first to introduce retinoids for use as antiphotoaging agents 5. After its application, the authors noticed improvement in skin depigmentation and rejuvenation 6. Today, retinoids are extensively used for this indication 7,8. Further studies have shown that RA's clinical effects include improvement in wrinkles, surface roughness, mottled pigmentation and skin appearance as a whole when used on photo-damaged skin 9–11. However, topical use of RA has also shown to develop erythema, scaling and burning/pruritus 12. Therefore, there is a constant thrive within the cosmetic industry to develop retinoid-like anti-ageing ingredients with significantly reduced side effects. At a cellular level, retinoids are known to modulate the proliferation and differentiation of epidermal keratinocytes 13,14,14,15 by binding to nuclear retinoic acid receptors (RARs) and 9-cis-retinoic acid receptors (RXRs), which results in upregulation or downregulation of the transcription of target genes 16. RA is the biologically active form of vitamin A (retinol). Endogenous production of RA by epidermal keratinocytes involves the uptake of preformed vitamin A from the surroundings followed by a series of metabolic activation steps involving retinol dehydrogenases (RDH1, RDH4, RDH10, RDH12 and DHRS9) and retinal dehydrogenases (RALDH1, RALDH2 and RALDH3) 17–19. DHRS9 specifically is encoding an enzyme that mediates conversion of retinol into RA. Whilst endogenously produced or exogenously applied, RA is transported through the cytoplasm by specific intracellular retinoic-binding proteins (CRABP2) 8. Once synthesized, the cellular levels of RA are controlled by several cytochrome P450-dependent enzymes (CYPs) – CYP26 A1, B1 and C1 – which metabolize RA into 4-hydroxy-RA, 4-oxo-RA and 18-OH-RA 20,21. CYP26B1 is known to be higher expressed than both CYP26A1 and CYP26C1 in human keratinocytes 19,22. Over the last quarter century, 532 genes have been validated to be regulated by RA 23. In some cases, this control is direct, driven by a liganded RAR:RXR heterodimer bound to a DNA response element; in others, it is indirect, reflecting the actions of intermediate transcription factors, non-classical associations of receptors with other proteins or even more distant mechanisms. Cell cultures have been studied extensively to characterize and prophesy the effect of retinoids on epidermal differentiation and growth 13,15,24–27. In addition, a selection of genes using RT-PCR has been studied in full-thickness skin treated with retinoids 28,29. Today, recent gene array techniques allow the characterization of the mRNA expression status of a large number of genes in cells or tissues after retinoid treatments with more than 170 studies conducted. Some studies using gene arrays have also been carried out on reconstructed epidermis and human epidermis in vivo 30. However, to our knowledge, gene array analysis following the treatment of RA on organoculture of full-thickness skin has not been investigated earlier. The aim of the present study was to determine whether it is possible to use an organoculture of full-thickness skin as a preclinical model to evaluate modulation of gene expression profile following topical application of a commercially available retinoid cream.