The Insulin-like Growth Factor 1 Receptor Is Expressed by Epithelial Cells with Proliferative Potential in Human Epidermis and Skin Appendages: Correlation of Increased Expression with Epidermal Hyperplasia

The document reviewed the genomic organization and expression characteristics of human hair keratin genes, highlighting their role in hair follicle biology and hereditary disorders. It noted that research on human hair keratins lagged behind studies in other species. The review discussed the complex regulatory mechanisms of hair keratin expression and the differentiation of hair follicle compartments. It also addressed keratin-related pathologies, such as epidermolysis bullosa simplex and pachyonychia congenita, which affect the outer root sheath and nail beds, respectively. The study emphasized the need for further research to understand the molecular mechanisms governing hair follicle differentiation and keratin expression.

The study examined the expression of keratin K14 in human skin, particularly in the epidermis and hair follicles, using monospecific antisera and cRNA probes. It was found that K14 expression and filament organization differed significantly between the hair follicle and epidermis. In the outer root sheath (ORS) cells, which are mitotically active, K14 expression was low, and keratin filaments were fewer and more loosely organized compared to basal epidermal cells. As ORS cells differentiated, they increased K14 expression and formed denser keratin bundles. In contrast, matrix cells, which can differentiate into the inner root sheath, cuticle, and hair shaft, did not express K14 or form keratin filaments. Instead, they produced hair-specific keratins and dense filament bundles without inducing K14 expression. The study suggested that the patterns of K14 expression and filament organization in skin epithelial cells were linked to their pluripotency and highlighted the distinct differentiation programs of hair follicles compared to other stratified squamous epithelia.