A high-throughput screening platform for pigment regulating agents using pluripotent stem cell-derived melanocytes

Photoreactive Properties of Melanin Obtained from Human Induced Pluripotent Stem Cell-Derived Melanocytes

Although melanin is viewed as a natural sunscreen that protects pigmented cells against the adverse effects of solar radiation, recent studies have demonstrated that, under certain conditions, the pigment can actually contribute to light-induced oxidative damage of the cells. However, the main issue with such studies is finding natural pigments without photooxidative modifications. Recently, melanin obtained from melanocytes, generated from human induced pluripotent stem cells (hiPSC-Mel), was suggested as a promising source of the pigment without significant photooxidation. Although different studies have demonstrated the feasibility of the above-mentioned technique to obtain melanin-producing cells, no thorough analysis of the physicochemical properties of the pigment has been performed. To address this issue, we examined the key physicochemical parameters, including the aerobic photoreactivity of melanin isolated from hiPSC-Mel and compared them with those of melanin from other known sources of the pigment, such as bovine retinal pigment epithelium (bRPE) and phototype V (PT-V) hair. Electron paramagnetic resonance (EPR) spectroscopy, dynamic light scattering, UV-Vis absorption and HPLC analysis of melanin degradation products were used. The ability of the examined melanins to photogenerate reactive oxygen species was determined by employing EPR oximetry, EPR spin-trapping and time-resolved singlet oxygen phosphorescence. Although the results of such measurements demonstrated that melanin obtained from hiPSC-Mel exhibited the physicochemical properties typical for eumelanin, a contribution from pheomelanin with a substantial presence of benzothiazine subunits, was also evident. Importantly, the hiPSC-Mel pigment had significantly lower photoreactivity compared to bRPE melanin and PT-V hair melanin. Our findings indicate that hiPSC-Mel could be an excellent source of high-quality pigment for photoprotection studies.

Distinct melanocyte subpopulations defined by stochastic expression of proliferation or maturation programs enable a rapid and sustainable pigmentation response

The ultraviolet (UV) radiation triggers a pigmentation response in human skin, wherein, melanocytes rapidly activate divergent maturation and proliferation programs. Using single-cell sequencing, we demonstrate that these 2 programs are segregated in distinct subpopulations in melanocytes of human and zebrafish skin. The coexistence of these 2 cell states in cultured melanocytes suggests possible cell autonomy. Luria-Delbrück fluctuation test reveals that the initial establishment of these states is stochastic. Tracking of pigmenting cells ascertains that the stochastically acquired state is faithfully propagated in the progeny. A systemic approach combining single-cell multi-omics (RNA+ATAC) coupled to enhancer mapping with H3K27 acetylation successfully identified state-specific transcriptional networks. This comprehensive analysis led to the construction of a gene regulatory network (GRN) that under the influence of noise, establishes a bistable system of pigmentation and proliferation at the population level. This GRN recapitulates melanocyte behaviour in response to external cues that reinforce either of the states. Our work highlights that inherent stochasticity within melanocytes establishes dedicated states, and the mature state is sustained by selective enhancers mark through histone acetylation. While the initial cue triggers a proliferation response, the continued signal activates and maintains the pigmenting subpopulation via epigenetic imprinting. Thereby our study provides the basis of coexistence of distinct populations which ensures effective pigmentation response while preserving the self-renewal capacity.

Melanocytes in regenerative medicine applications and disease modeling

Melanocytes are dendritic cells localized in skin, eyes, hair follicles, ears, heart and central nervous system. They are characterized by the presence of melanosomes enriched in melanin which are responsible for skin, eye and hair pigmentation. They also have different functions in photoprotection, immunity and sound perception. Melanocyte dysfunction can cause pigmentary disorders, hearing and vision impairments or increased cancer susceptibility. This review focuses on the role of melanocytes in homeostasis and disease, before discussing their potential in regenerative medicine applications, such as for disease modeling, drug testing or therapy development using stem cell technologies, tissue engineering and extracellular vesicles.

7-desacetoxy-6,7-dehydrogedunin discovered by high-throughput screening system suppresses melanogenesis through ATP-P2X7 signaling inhibition

BACKGROUND

Hyperpigmented skin disorders such as melasma and lentigo are common photoaging diseases that cause cosmetic problems. The pigmentation is usually exacerbated by ultraviolet (UV) radiation, and various factors and pathways are involved in UV-mediated melanogenesis. Adenosine 5'-triphosphate (ATP), a well-known molecular unit of intracellular energy, is also regarded as a mediator of UV-mediated melanogenesis via the P2X7 purinergic receptor.

OBJECTIVE

To discover natural substances with an anti-melanogenic effect through inhibition of ATP-P2X7 axis by high-throughput screening (HTS).

METHODS

Among natural compounds provided by the Korea Chemical Bank, chemical compounds with a P2X7 inhibiting effect were screened through an HTS system. Then the selected compounds were verified for their anti-melanogenic effect after treating primary human epidermal melanocytes (PHEMs) with and without ATP. The expression of MITF, tyrosinase, and PMEL/gp100 was analyzed by Western blot, and melanin content was measured as 405 nm absorbance.

RESULTS

Among 962 natural compounds, 58 showed greater than 80% suppression of YO-PRO-1 fluorescence, representing P2X7 activity. Among them, considering cell viability, chemical stability, and availability, 7-desaxacetoxy-6,7-dehydrogedunin (7DG), a limonoid natural compound, was selected. The expression of MITF, tyrosinase, and PMEL/gp100; tyrosinase enzyme activity; and melanin content, which were increased by ATP treatment were abrogated by 7DG. Even when 7DG was treated in PHEMs without addition of ATP, tyrosinase expression and melanin content were significantly decreased. Hypopigmenting effect of 7DG was confirmed in ex vivo culture of human skins.

CONCLUSIONS

7DG has an anti-melanogenic effect through ATP-P2X7 pathway inhibition and could be a potential skin whitening material.