Existence of Trichohyalin-Keratohyalin Hybrid Granules: Co-Localization of Two Major Intermediate Filament-Associated Proteins in Non-Follicular Epithelia

The study revealed that trichohyalin, a protein previously thought to be exclusive to hair follicles, was also expressed in non-follicular, keratinizing, stratified epithelia, such as the filiform papillae of the tongue and nail matrix epithelia. It formed hybrid granules with filaggrin, another intermediate filament-associated protein, in these tissues. Trichohyalin was absent in normal trunk and scalp epidermis but present in certain hyperplastic skin diseases. The findings suggested that trichohyalin was not limited to hair follicle cells but was associated with filaggrin in various normal and pathological epithelia, potentially playing a role in aggregating intermediate filaments containing keratins K6 and K16.