Human Skin Derived Epidermal Melanocytes.pdf

Human skin-derived epidermal melanocytes are responsible for UV protection and skin color. Much investigation has focused on its dermatological applications, pigmentation disorders, and melanoma treatment. Scientists are exploring the signaling pathways behind physiological processes and disease pathogenesis. Current understanding reveals that changes in even the small steps in the pathways can have pathological formation. Therefore, much research is underway to delineate pathways and develop therapeutics.

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Human Skin Derived Epidermal Melanocytes:
Architects of Skin Pigmentation

Human skin-derived epidermal melanocytes are responsible for UV protection and skin color. Much
investigation has focused on its dermatological applications, pigmentation disorders, and melanoma
treatment. Scientists are exploring the signaling pathways behind physiological processes and
disease pathogenesis. Current understanding reveals that changes in even the small steps in the
pathways can have pathological formation. Therefore, much research is underway to delineate
pathways and develop therapeutics.
Human Skin Derived Epidermal Melanocytes
Human Skin-derived Epidermal Melanocytes in Adult tissues are melanin-producing cells in the skin
epidermis and hair follicles. Melanocytes are also present in the retina, adipocytes, heart, ears, and
neurons. However, they differ from epidermal cells in their embryonic origins. Although melanocytes
from hair and skin have similarities, they are also distinct in their cell composition and response.
They are oval fusiform-shaped cells with dendritic morphology. They are smaller than keratinocytes
and contain melanosomes in their cytoplasm. Melanosomes are melanin-producing organelles. They
are identified by their specific protein expression of tyrosinase (TYR), microphthalmia transcription
factor (MITF), tyrosine-related proteins (TYRP1, TYRP2), etc.
Origin of Melanocytes
Neural crest cells belonging to the ectoderm germ layer differentiate in later stages into
melanocytes. Among neural crest cells, the cranial cells form the dermis of the head, whereas the
trunk cells develop the skin epidermis in other regions. The dorsal population of trunk neural crest
cells forms skin melanocytes, but recent studies have indicated that ventral cell populations also

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differentiate into these cells. Schwann cells originating from ventral trunk cells have shown
differentiation into melanocytes in vitro in a melanocyte culture medium. The difference in the
molecular composition of dermal and epidermal melanocytes supports the claim that these cells
arise from two different cell populations. Neural crest cells differentiate into melanocyte precursors-
melanoblasts. Melanoblasts then proliferate and migrate to the tissue to transform into
melanocytes, requiring Wnt signaling.
Functions of Melanocytes
The primary function of Human Epidermal Melanocytes in adults is the production of melanin that
imparts color to the skin and shields it from UV radiation. These cells form two types of melanin
pigment- eumelanin, which has a photoprotective effect, and pheomelanin, which generates
oxidative stress. Therefore, high amounts of pheomelanin increase the susceptibility to skin cancer.
These cells also participate in immunological function by expressing HLA molecules, presenting
antigens to immune cells, and releasing inflammatory mediators such as IL6, TGF-β, IL10, α-MSH,
eicosanoids, NO, etc. They participate in complex cross-talk with skin cells—keratinocytes and
dermal fibroblasts. Both secrete several factors, such as bFGF, NGF, SCF, NRG1, etc., that regulate
melanocyte proliferation, mobility, shape, and pigmentation.
The disruption in melanocyte function can result in hypopigmentation disorders such as vitiligo,
oculocutaneous albinism, or hyperpigmentation disorders like lentigo senilis.
Isolation of Melanocytes
The isolation procedure begins with the extraction of a thin section of skin. Its overnight incubation
results in the separation of epidermal and dermal layers. Trypsin-EDTA digestion of the epidermis
yields two cell populations- keratinocytes and melanocytes. Both can be cultivated in the tissue
culture dish. Within a week, melanocytes appear in the culture and can be detached from the
culture dish by low-concentration trypsin-EDTA while keeping keratinocytes adhered to the dish.
The melanocytes can be cultured afterward in a keratinocyte growth medium containing 0.2 mM
calcium chloride. Further media supplementation can include bFGF, α-MSH, insulin, and
triiodothyronine. Some papers suggest low pH for the maintenance of these cells to reduce melanin
synthesis and generation of its toxic intermediates for the promotion of cell growth. Furthermore,
the addition of factors like stem cell factor, endothelin-1, cholera toxin, etc., can also improve cell
survival and maintenance in culture.
Melanocyte Regulation
MITF is the master regulator of melanocyte survival, proliferation, and melanin synthesis. It triggers
the expression of melanin-producing enzymes and melanosome-related proteins. Mutations in MITF
are linked to melanoma. MITF is, in turn, regulated by proopiomelanocortin (POMC) and opsin (OPN)
signaling. In response to UV exposure, keratinocytes and melanocytes secrete high levels of a
neuropeptide-POMC. POMC cleavage forms α-MSH that bonds to melanocortin-1 receptor (MC1R)
on melanocytes, forming cAMP that triggers MITF expression. OPN are light-sensitive GPCRs on
keratinocytes and melanocytes that, upon activation, induce the transcription of TYR, TYRP1, and
TYRP2 by cAMP, MAPK, and PKC signaling pathways.

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Melanosome Formation
Melanosome formation occurs in four stages (Fig 1). In stage 1, they are similar to endosomes in
expressing endosomal markers and showing a spherical morphology. They lack the protein for
melanin synthesis. In stage 2, they become elongated with the accumulation of matrix fibrils. This
stage also exhibits the presence of melanin synthesis enzymes. In stage 3, their morphology
becomes elliptical, and melanin production begins, conferring brown color to melanosomes. At stage
4, melanin covers the fibrils, imparting black color to the organelles and completing the melanosome
formation.
Research has suggested that protein trafficking pathways into melanosomes occur via vesicle
trafficking from early to maturing melanosomes, from the Golgi apparatus, and through microtubule
transport. Mutation in the delivery proteins leads to several disorders, thus demonstrating the
significance of the trafficking process.

Figure 1. Stages of melanosome formation. (Source- PMID:27589732)
Melanosome Transport
Skin epidermal melanocytes transfer melanin granules into keratinocytes through their dendritic
processes. Within the filopodia of dendritic processes, pigment globules encapsulate several
melanosomes. After the uptake of melanosomes by keratinocytes, the membrane of globules
degrades, and melanosomes accumulate near the nucleus. Although this transfer mechanism is still
under investigation, present data alludes to the following different hypotheses for the transport of
melanosomes to keratinocytes (Fig 2):
 Keratinocytes phagocytose dendritic processes containing melanosomes.
 Direct transfer of melanosomes by fusion of membranes of keratinocytes and dendritic
process.
 Dendritic processes shed melanosome globules. Keratinocyte microvilli capture and absorb
them via the protease-activated receptor 2 pathway.
 Melanosomes are released from cells by exocytosis, followed by their uptake into
keratinocytes by endocytosis.

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Figure 2. Transport of melanosomes from dendritic processes of melanocytes to keratinocytes.
(Source-PMID: 37511054)
Melanogenesis
Melanogenesis or melanin synthesis is a key pathway in melanocytes. The generation of both
eumelanin and pheomelanin begins with the conversion of tyrosine into dihydroxyphenylalanine
(DOPA) by tyrosine hydroxylase and subsequent formation of dopaquinone from DOPA by TYR. In
the absence of cysteine, TYRP1 and TYRP2 convert dopaquinone into eumelanin by a multi-step
pathway. Eumelanin exists in brown and black colors, and their ratio defines skin color. Cysteine
shifts the reactions towards the formation of pheomelanin, which imparts a red color to hair.
pH of melanosomes plays a key role in melanogenesis. Low pH is crucial for fibril formation during
melanosome maturation, whereas pH between 6-7 is essential for the TYR activity. The pH is
controlled by membrane transporters such as v-ATPase, OCA2, TPC2, and SLC45A2. Mutation or
polymorphisms in these transporters can cause pigment variations.
Product-Related Queries, Or Partnership Inquiries
Melanocytes in Research
Scientists employ melanocytes to develop therapeutics for pigmentation disorders and melanoma.
Studies have shown poor response to cancer therapy in melanin-rich melanoma, suggesting
inhibition of melanogenesis for better outcomes. Gene editing of TYR has demonstrated
improvements in pigmentary disorders. The developmental process of melanocytes is still a subject
of investigation. Drug screening on these cells aids in the selection of suitable drug candidates.
Research is ongoing to explore pathways for cellular processes such as melanosome biogenesis,
melanogenesis, and melanosome transport for drug discovery.
Conclusion
Melanocyte pathway aberrations can drive pathological disorders. There is still much to learn about
these cells, and further research can unravel their signaling. Their connection to pigmentation and
cancer has stimulated a great deal of investigation. Since there is currently no proven cure for
pigmentary illnesses, more research on these cells is necessary. Kosheeka offers human skin
epidermal melanocytes from adults to advance research in this field. Our team follows GMP
guidelines to ensure cell consistency and reproducibility in results.

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FAQs
Q- What are melanocytes?
They are melanin-producing cells found primarily in skin and hair, as well as in the ears, neurons,
heart, retina, and other tissues.
Q- What are the functions of melanocytes?
The functions of these cells include melanin synthesis for UV protection, cytokine secretion, HLA
molecule expression, antigen presentation, and interaction with other skin cells.
Q- What are melanosomes?
These are organelles that contain melanin synthesis enzymes. They transport to keratinocytes and
accumulate near their nucleus for pigmentation.
Q- How does pH affect melanin synthesis?
Melanosome formation requires low pH in the early stages. In the later stages, the tyrosinase
enzyme acts at pH 6.8 to synthesize melanin.