Localization of ABCA12 from Golgi apparatus to lamellar granules in human upper epidermal keratinocytes.

[harlequin ichthyosis]

ABCA 12 is an ATP-binding cassette transporter and is thought to act as a transmembrane lipid transporter . We reported that deleterious ABCA 12 mutations cause a disturbance in lamellar granule (LG ) lipid transport in the epidermal granular layer keratinocytes , resulting in harlequin ichthyosis , a severe genodermatosis . Detailed localization of ABCA 12 in comparison with glucosylceramide and Golgi apparatus markers were studied in order to obtain clues to clarify the function (s ) of ABCA 12 in human skin . We performed double -labelling immunofluorescent staining using antibodies against ABCA 12 , glucosylceramide and two Golgi apparatus markers (TGN 46 and GM 130 ) in normal human skin and cultured keratinocytes . Immunogold electron microscopy for ABCA 12 and glucosylceramide was studied on postembedding and cryoultrathin sections of normal human skin . Confocal laser scanning microscopy demonstrated that ABCA 12 and glucosylceramide co -localized in the granular layer keratinocytes as well as in keratinocytes cultured in high Ca 2 + conditions through the Golgi apparatus to the cell periphery . Postembedding immunogold electron microscopy revealed that both ABCA 12 and glucosylceramide labellings were associated with the LG of the uppermost granular layer keratinocytes . Using cryoultramicrotomy , lamellar structures in the LG were more clearly observed , and ultrastructural localization of ABCA 12 and glucosylceramide was better demonstrated to LG in the uppermost granular layer cells . These results indicate that ABCA 12 plays an important role in lipid transport from the Golgi apparatus to LG in human granular layer keratinocytes .