A Novel Epithelial Keratin, hK6irs1, Is Expressed Differentially in All Layers of the Inner Root Sheath, Including Specialized Huxley Cells of the Human Hair Follicle

The study characterized a novel human epithelial keratin, hK6irs1, which was expressed in all layers of the inner root sheath (IRS) of the human hair follicle, including specialized Huxley cells. This keratin was the human equivalent of the mouse keratin mK6irs and showed high sequence identity with other keratins. The expression of hK6irs1 began in the lowermost bulb region and was associated with the onset of terminal differentiation in the Henle and Huxley layers. Specialized Huxley cells, or Flügelzellen, developed extensions that connected with the companion layer, suggesting a role in maintaining structural integrity. The study provided insights into hair follicle biology and proposed that IRS keratins might be linked to hair disorders like loose anagen hair syndrome and certain forms of alopecia.