SMALL RNA AS ANTIAGING COSMECEUTICALS 459 and induced signifi cant reductions in levels of TYR, TYRP1, and MC1R. The use of silenc- ing MITF-siR led to signifi cant inhibition of melanin synthesis and melanoma cell apop- tosis. The results showed that, on treatment for 12 weeks, the patients treated with the MITF-siR cream were found to present signifi cantly lighter hyperpigmented facial lesions than before the treatment general improvement was fi rst noted after four weeks’ siRNA treatment. At the end of the treatment, clinical and colorimetric evaluations demon- strated 90.4% lightening of the siRNA-treated lesions toward normal skin color. The relative melanin contents in the lesions and adjacent normal skin after the treatment with the MITF-siR formulation were decreased by 26% and 7.4%, respectively. This treatment represents a safe and effective therapy for melasma, suggesting that siRNA-based agents could be developed for antiaging cosmeceuticals. In another study, tumor suppressor protein p53 has been demonstrated to promote UVB- induced skin pigmentation by stimulating transcription of a melanogenic cytokine, pro- opiomelanocortin (POMC), in keratinocytes (42). Analyses revealed increased expression and phosphorylation of p53 in the epidermis of hyperpigmented spots, accompanied by higher expression of melanogenic cytokines, including stem cell factor, endothelin-1, and POMC. The involvement of p53 in hyperpigmentation was also indicated by signifi - cantly higher expression of p53 transcriptional targets in the epidermis of hyperpig- mented spots. The in vivo data in UVB-exposed mouse skin showed that intradermal injection of p53-specifi c siRNA signifi cantly suppressed the expression of mRNAs and proteins encoding paracrine cytokines as well as melanogenic factors (7). This knockdown resulted in the inhibition of hyperpigmentation. Taken together, these data revealed the essential role played by p53 in hyperpigmentation of skin via regulation of paracrine- cytokine signaling, both in keratinocytes and melanocytes. SMALL RNA IN ANTIWRINKLE COSMECEUTICALS If aging skin were a Broadway production, then facial wrinkling would get top billing among the large cast of benign clinical signs appearing in the show (43). There are several types of facial wrinkles classifi ed with consideration to their location, pattern, histology, and etiology (44). Recent investigations showed that the dermis plays a decisive role, at least for skin aging caused by UV radiation. Exposure to UV radiation results in the ac- cumulation of damages to the mitochondrial DNA of dermal fi broblasts and thus an al- tered gene expression in the affected cells, which chronically drives both the dermal and epidermal aging process (45–48). Aged dermis has fragmented elastic fi bers, decreased collagen, and disproportionate types I and III collagens. This damage is attributed to several types of enzymes known as matrix metalloproteinases (MMPs) (49). Activation of MMPs can result in production of collagenase, elastase, gelatinase, and stromelysin (38,50). miRNAs, the most studied small noncoding RNAs, play an important role in many bio- logical processes by regulation of gene expression. Recently, miRNAs have been found to participate in the complex networks of cellular senescence and contribute to aging (51). Several investigations revealed that miR-29 members were upregulated in both elderly and senescence-model mice (52–54). Functional analysis showed that the transcriptional activation of miR-29 was triggered in response to DNA damage and occurred in a p53-dependent manner (55). The tumor suppressor p53 protects genome by promoting

JOURNAL OF COSMETIC SCIENCE 460 repairs of potentially carcinogenic lesions in DNA. Meanwhile, p53 eliminates or arrests proliferation of damaged or mutant cells by processes of apoptosis and cellular senescence (56). These studies implicated a delicate balance between the tumor-suppressing and age- promoting functions by p53 (57). Reduction of elastic fi bers and collagen protein is another essential factor in formation of wrinkles (58). Several investigations showed that overexpression of miR-29 repressed, whereas miR-29 inhibitors increased, levels of elastin mRNA and protein in vitro or in vivo (59,60). Indeed, miR-29 conserved seed sequences were found not only in tropoelas- tin but also in collagen (61). A number of reports have demonstrated that use of miR29 inhibitors could lead to increased levels of collagen (62,63). Other data also showed that oxLDL resulted in upregulation of miR-29b expression in a dose-dependent manner in vitro and subsequently increased levels in MMP-2/MMP-9 enzyme activities (64). Be- cause an increase in MMP activity has been linked to decreases in levels of collagen and elastin, a suitable strategy could be developed to manipulate the expression of miR-29 via an RNAi approach, by which this may offer a therapeutic opportunity against skin aging.*** Clinical studies demonstrated that there were signifi cantly higher levels of miR-29 in the skin from older donors compared to that from younger ones (27). Suppressing miR-29 by miR-29 antagonist was shown to lead to an increase in collagen, fi brillin, and elastin expression in skin fi broblast. Such fi nding could perhaps be used to develop highly effec- tive cosmetic solutions to reverse the process of skin aging (28). SMALL RNA IN MOISTURIZING COSMECEUTICALS With an adequate amount of water in the stratum corneum, the skin maintains its barrier function, feels soft and flexible, and looks smooth and healthy. Age, sun exposure, and dehydration are the main factors responsible for decreased skin elasticity (65). Moistur- izing cosmeceuticals have a beneficial effect on prevention and treatment of dry skin by enhancing natural functions of the skin. Hyaluronidase has recently drawn researchers’ attention. Hyaluronic acid is distributed in skin’s connective tissue and is one of the components in a water-retaining matrix. Hyaluroni- dase is a mucopolysaccharase that hydrolyzes glycosaminoglycans including hyaluronic acid. Thus, a reduction in the amount of hyaluronic acid by the hydrolysis could disable it from binding collagen and elastin molecules (66). This prevents formation and retention of new collagen and elastin and causes premature wrinkling and sagging (67). When a decrease in the level of hyaluronic acid occurs under such conditions as hyaluronidase activity is increased, moisture and tension of the skin are reduced (68). Therefore, hyaluronidase inhibitors are deemed useful cosmeceutical ingredients as they have antiaging effects on skin (69). Tan et al. reported that silencing of hyaluronidase gene Hyal by RNAi resulted in reduced degradation of extracellular matrix where hyaluronic acid was present (70). In a separate study, Lin et al. discussed a potential role of siRNA as a novel therapeutic agent for dry skin (22). They redesigned the seed sequence of mir-434-5p, which was found or consid- ered to be the only miRNA that targets both Tyr and Hyal genes in human, to form a highly matched region that binds to either TYR gene (miR-Tyr) or hyaluronidase gene (miR-Hyal). Interestingly, the targeted Hyal genes were knocked down specifi cally by