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.
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Arrector pili muscle
Smooth muscle α-actin
- ORS KC:
Outer root sheath keratinocytes
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The authors would like to thank A/Prof. Robert Kapsa and Dr. Anita Quigley of the Centre for Neuroscience and Neurology Research, St Vincent’s Hospital Melbourne, for providing access to laboratory facilities and technical assistance. Niloufar Torkamani was supported by a University of Melbourne International Research Scholarship, a John Hayden Scholarship, and an Alwyn Stewart Memorial Trust Fund Faculty of Medicine Research Scholarship (University of Melbourne).
This study was funded by a University of Melbourne International Research Scholarship, a John Hayden Scholarship, and an Alwyn Stewart Memorial Trust Fund Faculty of Medicine Research Scholarship (University of Melbourne).
Conflict of interest
The authors declare that they have no conflict of interest.
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Torkamani, N., Rufaut, N., Jones, L. et al. The arrector pili muscle, the bridge between the follicular stem cell niche and the interfollicular epidermis. Anat Sci Int 92, 151–158 (2017). https://doi.org/10.1007/s12565-016-0359-5
- Arrector pili muscle