Melanogenese

Melanogenesis is the biological process by which melanin pigment is produced in specialized pigment-producing cells called melanocytes, primarily located in the epidermis and hair follicles. The pigment serves two main roles: giving color to skin, hair, and eyes, and providing protection against ultraviolet radiation by absorbing and dissipating UV light.

Biochemistry and pathways: Melanin synthesis occurs in melanosomes, organelles within melanocytes. The enzyme tyrosinase catalyzes the rate-limiting steps, converting the amino acid tyrosine to DOPA and then to dopaquinone. Tyrosinase-related proteins TYRP1 and TYRP2 (DCT) participate downstream. The pathway can produce two main types of melanin: eumelanin (brown/black) and pheomelanin (red/yellow); the relative balance determines individual coloration. Melanosomes mature through distinct stages and are trafficked along dendritic processes from melanocytes to neighboring keratinocytes, where pigment is distributed in the epidermis or hair shaft.

Regulation and factors: Melanogenesis is governed by genetic and environmental cues. The transcription factor MITF coordinates expression of melanogenic enzymes. Signaling pathways activated by ultraviolet exposure or hormonal signals—such as α-melanocyte-stimulating hormone (α-MSH) binding to the MC1R receptor—increase intracellular cAMP, upregulate MITF, and enhance enzyme activity. Additional factors include oxidative stress, cytokines, and nutritional status, all of which can influence pigment production and distribution.

Clinical and biological relevance: Variations in melanogenesis contribute to population differences in skin, hair, and eye color. Defects in the pathway cause conditions such as oculocutaneous albinism (often TYR or related gene mutations) with reduced or absent melanin. Other disorders involve hypopigmentation diseases, vitiligo (melanocyte loss), or hyperpigmentation phenomena like melasma.