title: The arrector pili muscle, the bridge between the follicular stem cell niche and the interfollicular epidermis.
abstract: Proximally, the arrector pili muscle (APM) attaches to the follicular stem cell niche in the bulge, but its distal properties are comparatively unclear. In this work, a novel method employing an F-actin probe, phalloidin, was employed to visualize the APM anatomy. Phalloidin staining of the APM was validated by comparison with conventional antibodies/stains and by generating three-dimensional reconstructions. The proximal attachment of the APM to the bulge in 8 patients with androgenic alopecia was studied using Masson's trichrome stain. Phalloidin visualized extensive branching of the APM. The distal end of the human APM exhibits a unique "C"-shaped structure connecting to the dermal-epidermal junction. The proximal APM attachment was observed to be lost or extremely miniaturized in androgenic alopecia. The unique shape, location, and attachment sites of the APM suggest a significant role for this muscle in maintaining follicular integrity. Proximally, the APM encircles the follicular unit and only attaches to the primary hair follicle in the bulge; this attachment is lost in irreversible hair loss. The APM exhibits an arborized morphology as it ascends toward the epidermis, and anchors to the basement membrane.
authors.affiliation: Department of Dermatology, School of Medicine, Health and Dentistry, University of Melbourne, Melbourne, VIC, Australia. torkamani_niloufar@yahoo.com.|Epworth Hospital, Dermatology Research Centre, Melbourne, VIC, Australia. torkamani_niloufar@yahoo.com.|Dermatology Lab, Epworth Research Institute, 185-187 Hoddle Street, Richmond, VIC, 3121, Australia. torkamani_niloufar@yahoo.com.
authors.forename: Niloufar
authors.identifier: http://orcid.org/0000-0001-6259-8675
authors.initials: N
authors.lastname: Torkamani
authors.affiliation: Department of Dermatology, School of Medicine, Health and Dentistry, University of Melbourne, Melbourne, VIC, Australia.|Epworth Hospital, Dermatology Research Centre, Melbourne, VIC, Australia.
authors.forename: Nicholas
authors.initials: N
authors.lastname: Rufaut
authors.affiliation: Department of Dermatology, School of Medicine, Health and Dentistry, University of Melbourne, Melbourne, VIC, Australia.|Epworth Hospital, Dermatology Research Centre, Melbourne, VIC, Australia.
authors.forename: Leslie
authors.initials: L
authors.lastname: Jones
authors.affiliation: Department of Dermatology, School of Medicine, Health and Dentistry, University of Melbourne, Melbourne, VIC, Australia.|Epworth Hospital, Dermatology Research Centre, Melbourne, VIC, Australia.
authors.forename: Rodney
authors.initials: R
authors.lastname: Sinclair
mesh_terms: D000199:Actins; D000505:Alopecia / Q000473:pathology; D000715:Anatomy / Q000379:methods*; D001485:Basement Membrane / Q000033:anatomy & histology / Q000473:pathology; D004817:Epidermis / Q000033:anatomy & histology* / Q000473:pathology; D018859:Hair Follicle / Q000033:anatomy & histology* / Q000166:cytology* / Q000473:pathology; D006801:Humans; D009130:Muscle, Smooth / Q000033:anatomy & histology* / Q000473:pathology; D010590:Phalloidine; D012535:Scalp / Q000033:anatomy & histology* / Q000166:cytology / Q000473:pathology; D013194:Staining and Labeling; D055153:Stem Cell Niche
chemical_list: D000199:Actins; D010590:Phalloidine
keywords: Arrector pili muscle; Phalloidin; Stemcells