Deciphering the functions of the hair follicle infundibulum in skin physiology and disease

Abstract

The infundibulum is the funnel-shaped, uppermost epithelial segment of the hair follicle. Thus, as the infundibulum represents a major interface zone of mammalian skin epithelium with the environment and harbors a rich residential microflora, it is not surprising that this area is endowed with a specialized immune system and innate immune defenses. Clinically, the infundibulum is quite important, as it becomes prominently involved in many skin diseases such as acne, infundibular folliculitis and cysts, hidradenitis suppurativa, keratosis pilaris, Fox-Fordyce disease, and a subtype of basal cell carcinoma. Nevertheless, the biology of the infundibulum is only poorly understood, and it remains largely unknown how exactly the infundibulum contributes to skin disease, and how it might be targeted effectively for treating important skin diseases. Several recent studies in mouse models have identified new potential infundibular markers, shed light upon infundibular development and homeostasis, identified infundibular epithelial stem cells, and have implicated the infundibulum in the pathogenesis of additional skin disorders. These recent insights encourage one to systematically re-visit the biology and pathology of the infundibulum, one of the most important, yet least-studied frontiers in mammalian epithelial physiology.

Urokinase Receptor Promotes Skin Tumor Formation by Preventing Epithelial Cell Activation of Notch1

“…However, no hair cycle defects were observed in uPAR (10,29). The epithelium of the infundibulum is continuous with the epidermis; thus, its cells regenerate the epidermis after wounding, injury, or proliferative stimuli (30). FACS analysis of K14-GFP-actin þ epidermal cells (Fig.…”

Resting no more: re‐defining telogen, the maintenance stage of the hair growth cycle

“…However, this is a misconception: the distal (upper) regions of the telogen HF epithelium immediately above the bulge, i.e. the infundibulum and the isthmus (Schneider & Paus, 2014), actually contain numerous proliferating cells throughout telogen, including during the extended second telogen in the mouse (Geyfman et al, 2012) (Fig. 1B).…”

“…The infundibulum, from the Latin word for funnel, is above the entry of the sebaceous duct and merges with the interfollicular epithelium (Schneider & Paus, 2014). The isthmus of the HF is the short region between the point of attachment of the arrector pili muscle and the entry of the sebaceous gland duct (Fig.…”

Hair Follicle Terminal Differentiation Is Orchestrated by Distinct Early and Late Matrix Progenitors

“…The hair on our skin is a mammalian innovation that serves numerous functions, including thermoregulation, sensation and protection against the environment (Blanpain and Fuchs, 2009; Schneider and Paus, 2014). Hair follicles, which house the differentiated cells of the hair shaft, are initially formed from placodes that condense throughout the epidermis during embryonic development (Biggs and Mikkola, 2014).…”