Trichohyalin: presence in the granular layer and stratum corneum of normal human epidermis

Trichohyalin, a protein contained in granules in the cells of the hair-follicle inner root sheath and in the medulla of the hair shaft, has been purified previously from sheep hair bulbs and is also a major protein of filiform papillae of tongue epithelium. Polyclonal affinity-purified antibodies and a monoclonal antibody raised to purified pig tongue trichohyalin both stained the inner root sheath of hair follicles and the medulla of hair fibers and identified human trichohyalin as a single 220-kDa band on immunoblots of human hair bulb proteins. These antibodies were used to examine human epidermis by immunofluorescence and immunoblotting. The antibodies decorate granules in cells in the granular layer and stratum corneum of non-hair-bearing human skin, and immunoblots identify a protein in epidermis comigrating with trichohyalin from human hair and human tongue epithelium. Absorption of antibody to trichohyalin on a trichohyalin affinity column abrogated staining of the epidermis and the bands on the immunoblots. Trypsin-separated epidermis contained 220 and 160 kDa bands identified as trichohyalin, but epidermis shaved from skin and quickly frozen showed only a single 220-kDa band, indicating that the 160-kDa protein was generated by proteolysis. Double immunofluorescence for trichohyalin and filaggrin showed that some cells containing filaggrin also contain trichohyalin. These studies show that trichohyalin is not limited to hair and tongue but is present in isolated cells in the granular layer and stratum corneum of normal epidermis.