Growth Hormone and the Human Hair Follicle

Abstract

Ever since the discoveries that human hair follicles (HFs) display the functional peripheral equivalent of the hypothalamic-pituitary-adrenal axis, exhibit elements of the hypothalamic-pituitary-thyroid axis, and even generate melatonin and prolactin, human hair research has proven to be a treasure chest for the exploration of neurohormone functions. However, growth hormone (GH), one of the dominant neurohormones of human neuroendocrine physiology, remains to be fully explored in this context. This is interesting since it has long been appreciated clinically that excessive GH serum levels induce distinct human skin pathology. Acromegaly, or GH excess, is associated with hypertrichosis, excessive androgen-independent growth of body hair, and hirsutism in females, while dysfunctional GH receptor-mediated signaling (Laron syndrome) is associated with alopecia and prominent HF defects. The outer root sheath keratinocytes have recently been shown to express functional GH receptors. Furthermore, and contrary to its name, recombinant human GH is known to inhibit female human scalp HFs’ growth ex vivo, likely via stimulating the expression of the catagen-inducing growth factor, TGF-β2. These limited available data encourage one to systematically explore the largely uncharted role of GH in human HF biology to uncover nonclassical functions of this core neurohormone in human skin physiology.

Evaluation of the Safety and Effectiveness of Nutritional Supplements for Treating Hair Loss

“…Insulin growth factor-1 (IGF-1) plays an important role in hair follicle development and in the hair growth cycle . Modulated by growth hormone, deficiencies in either IGF-1 and/or growth hormone have been associated with several causes and types of hair loss, including alopecia and TE …”

Skin manifestations and submacroscopical features of acromegaly: A case‐control study using dermoscopy and high‐frequency ultrasound

“…Furthermore, on skin biopsies, the size of sweat gland acini and the density of innervation to the sweat glands have been proved to be greater in acromegaly, implying the trophic effect of GH on sweat glands and/or the associated nerves to promote sweat production resulting in hyperhidrosis such as wet hands, back and forehead 24 . Thirdly, in the case of GH excess, as in acromegaly, both IGF‐1, an anagen promoter, and transforming growth factor‐β (TGF‐β), a catagen promoter are upregulated, with the unexplained interplay of androgens and GH, clinically leading to the hypertrichosis and hirsutism in females 25 . These mechanisms together cause the greasy, sweaty and hairy skin in acromegalic patients.…”

“…24 Thirdly, in the case of GH excess, as in acromegaly, both IGF-1, an anagen promoter, and transforming growth factor-β (TGF-β), a catagen promoter are upregulated, with the unexplained interplay of androgens and GH, clinically leading to the hypertrichosis and hirsutism in females. 25 These mechanisms together cause the greasy, sweaty and hairy skin in acromegalic patients.…”

Acanthosis Nigricans: Pointer of Endocrine Entities

“…Patients present a variety of skin manifestations, including IR-mediated skin features, specific lesions related to secondary DM, and dermatologic hallmarks of syndromic acromegaly as seen in multiple endocrine neoplasia type 1 or McCune-Albright syndrome [ 154 , 155 ]. Although the proliferation of dermal fibroblasts is attributed to the increased levels of GH, IGF-1 is responsible for the proliferation of epidermal keratinocytes [ 156 , 157 ]. However, we did not identify any studies particularly addressing the issue of AN in acromegaly.…”