K25 (K25irs1), K26 (K25irs2), K27 (K25irs3), and K28 (K25irs4) Represent the Type I Inner Root Sheath Keratins of the Human Hair Follicle

July 2006 in “ Journal of Investigative Dermatology ”

Lutz Langbein, Michael A. Rogers, Silke Praetzel‐Wunder, Burkhard Helmke, Peter Schirmacher, Jürgen Schweizer

inner root sheath keratins K25 K26 K27 K28 K71 alopecia hair follicle IRS layers medulla IRS cuticle mutations hair loss baldness

TLDR K25, K27, and K28 are found in all inner root sheath layers of hair, while K26 is only in the cuticle.

The study investigated the expression patterns of type I inner root sheath (IRS) keratins K25 (K25irs1), K26 (K25irs2), K27 (K25irs3), and K28 (K25irs4) in the human hair follicle. It found that K25, K27, and K28 were expressed in all three IRS layers and the medulla, while K26 was restricted to the IRS cuticle. The research clarified the expression of these keratins, which were previously only partially characterized, and aligned their nomenclature with a new consensus system. The study also highlighted the critical role of K71 (K6irs1) in IRS integrity, noting that mutations in this keratin could significantly impact hair follicle function, as evidenced by severe alopecia and structural disturbances in mouse models with K71 mutations.

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