The Role of Keratinocytes in Disorders of Pigmentation

• From the extremities of dendritic melanocytes, melanosomes are transfered to the neighbouring  keratinocytes. However, the mechanisms  implicated in this transfer are not well understood but involve an intimate contact between a melanocyte and a keratinocyte (in the epidermis). This in turn implies the presence of cell membrane proteins.
• The incapacity to do this explains the hypopigmentation seen in nevus depigmentosus and guttate leukoderma of Darier’s disease.
• Once the melanosomes are transferred to the surrounding keratinocytes, they aggregate in clusters (in light skin individuals) or in a unique intracellular mass (in individuals with darker skin). These units form an apical “lid” around the nucleus of keratinocytes, which enables DNA (Desoxyribonucleic Acid) to be shielded against damage (for example against Ultraviolet (UV) light- induced damage).
• The mechanisms involved in the cellular migration of the melonaphagosomes within the keratinocytes are unknown, but intermediary fibres (Keratin) would play a role. Mutations on the keratin genes 5 and 14 result in pigmentary disorders such as Dowling-Degos disease and pigmented and reticulate dermopathy.

Contributors:

Dr Christophe HSU – dermatologist. Geneva, Switzerland

Source of Information: Goh BK. The Science Behind Pigmentary Disorders.  NSC Dermatology Update 2012, Singapore