SMALL RNA AS ANTIAGING COSMECEUTICALS 461 transfective expression of miR-Hyal in mouse skin (67% reduction) without any crossover off-target effect. SMALL RNA IN HAIR CARE COSMECEUTICALS The most common types of hair growth disorders are caused by aberrant hair follicle (HF) cycling. One such disorder is androgenetic alopecia, characterized by a shortening of the anagen phase and prolongation of telogen combined with miniaturization of HF (71). An- drogens, which play a key role in androgenetic alopecia, have been identifi ed in people with this condition. Studies demonstrated that variations in the androgen receptor gene led to increased activity of androgen receptors in HFs. As a result, current pharmacological thera- pies for hair disorders include a range of antiandrogens that block the intracellular androgen receptors (72). A promising line of studies has been completed by Kerner and colleagues who proposed modulating androgen receptor expression with RNAi for hair and skin ther- apy (29,30). It becomes clear that RNAi technology could be applied for treating androge- netic alopecia to modulate genes that are involved in hair loss in a highly specifi c manner. Alopecia areata is also an autoimmune disease affecting HFs, resulting in hair loss. This was thought to be triggered by a collapse of immune privilege. Nakamura et al. suggested an involvement predominantly by Th1 cells in alopecia lesions (31). Therefore, they es- tablished a gene therapy experiment in an alopecia areata C3H/HeJ mouse model focus- ing on Tbx21 gene that plays a key role in Th1 cell development. Topical application of siRNAs conjugated to a delivering vehicle was found to result in a knockdown of the Tbx21 gene and have a positive effect on symptoms of alopecia in C3H/HeJ mice, which in turn led to restoring of hair growth. miRNAs, which play a critical role in skin morphogenesis, were also reported to be involved in regulation of HFs development and cycling, however, neither their expression nor their roles has been characterized yet (73). Recently, an investigation showed that the expression of miR-31 was markedly increased during anagen and decreased during catagen and telogen. Administration of an antisense miR-31 inhibitor into mouse skin during the early and mid- anagen phases of hair cycle resulted in accelerated anagen development and altered differen- tiation of hair matrix keratinocytes and hair shaft formation. Both in vitro and in vivo data suggested that miR-31 regulated negatively the expression of Fgf10, Krt16, Krt17, Dlx3 genes as well as some keratin genes (32). Thus, by targeting a number of growth regulatory molecules and cytoskeletal proteins, miR-31 could be involved in establishing an optimal balance of gene expression in HF required for its proper growth and hair fi ber formation. SMALL RNA IN STEM CELL-BASED COSMECEUTICALS Reversal of cellular senescence would be an important function of antiaging cosmeceuti- cals, thus many attempts have been undertaken to infl uence cellular senescence. The stem cell extract is known to have regenerative properties because of containing many cytokines and growth factors, which offers promising potential for preventing skin aging (74). However, there are ethical difficulties regarding the use of human embryonic stem cells (hESCs). One way to circumvent the issues is by the generation of pluripotent cells

JOURNAL OF COSMETIC SCIENCE 462 directly from donor’s own cells. Induced pluripotent stem cells (iPSCs) are cells that were originally from adult tissues, but have been forced to produce proteins that are thought to be essential for the pluripotency of hESCs. By making cells express embryonic stem cell proteins, such as Oct4, Sox2, Klf4, and c-Myc, iPSCs exhibited the essential charac- teristics of hESCs as confi rmed by morphological and other molecular criteria (75). miRNAs have been identifi ed to play a critical role in the maintenance and renewal of hESCs. Recently, several investigations showed that a small noncoding RNA, called miR-302, can replace all previously defi ned proteins to reprogram human and mouse somatic cells to ESC-like iPSCs (76–78). It is demonstrated that miR-302 functions as a gene silencer and simultaneously downregulates multiple key epigenetic regulators, in- cluding lysine-specifi c histone demethylases 1 and 2 (LSD1/2), DNA (cytosine-5-) -meth- yltransferase 1 (DNMT1), and methyl-CpG binding proteins 1 and 2 (MECP1/2), which subsequently triggers the activation of stem cell factors Oct4 and Sox2 to complete the reprogramming process (33). The functions of miR-302 have provided a convenient means to control both quantity and quality of iPSCs, opening up a new avenue to application of stem cell facial. On the basis of RNAi technology to reprogram skin cells into stem cells, essential elements will be extracted for production of innovative cosmetic ingredient. CHALLENGES IN TRANSDERMAL DELIVERY OF SMALL RNA A variety of methods for delivery of RNA through skin have been demonstrated how- ever, effective patient-friendly delivery remains a major challenge to clinical utility of small RNA cosmeceuticals. In general, a topical application of cosmetic formulations requires a successful delivery of active ingredients through lipid barrier of skin to reach targeted lower layers without causing any irritation (79). However, it is diffi cult to intro- duce small RNA into skin by conventional methods. The obstacles lie in the highly lipo- philic nature and barrier function of uppermost layer of skin, the stratum corneum, for instance, which restrict or prevent hydrophilic, high molecular weight and charged mol- ecules such as RNAs from permeating into the dermis (80). MICROPORATION TECHNOLOGY To deliver successfully hydrophilic drugs or macromolecular agents of interest such as small RNA, many research groups and pharmaceutical companies have paid a great atten- tion to the use of microporation methods and devices (80). In summary, microporation techniques include typically iontophoresis (81), electroporation (82), sonophoresis (83), and microneedle (84). They share a common goal of enhancing permeability through a biological membrane by creating transient aqueous transport pathways of micron dimen- sions across the membrane (80). NANOTECHNOLOGY Recently, much of ongoing research is focused on the use of nanotechnology to aid non- invasive transdermal delivery of novel small RNA therapeutics. Some progress toward