Androgen-induced delay of hair growth in the golden Syrian hamster

Gender-Difference in Hair Length as Revealed by Crispr-Based Production of Long-Haired Mice with Dysfunctional FGF5 Mutations

Fibroblast growth factor 5 (FGF5) is an important molecule required for the transition from anagen to catagen phase of the mammalian hair cycle. We previously reported that Syrian hamsters harboring a 1-bp deletion in the Fgf5 gene exhibit excessive hair growth in males. Herein, we generated Fgf5 mutant mice using genome editing via oviductal nucleic acid delivery (GONAD)/improved GONAD (i-GONAD), an in vivo genome editing system used to target early embryos present in the oviductal lumen, to study gender differences in hair length in mutant mice. The two lines (Fgf5go-malc), one with a 2-bp deletion (c.552_553del) and the other with a 1-bp insertion (c.552_553insA) in exon 3 of Fgf5, were successfully established. Each mutation was predicted to disrupt a part of the FGF domain through frameshift mutation (p.Glu184ValfsX128 or p.Glu184ArgfsX128). Fgf5go-malc1 mice had heterogeneously distributed longer hairs than wild-type mice (C57BL/6J). Notably, this change was more evident in males than in females (p < 0.0001). Immunohistochemical analysis revealed the presence of FGF5 protein in the dermal papilla and outer root sheath of the hair follicles from C57BL/6J and Fgf5go-malc1 mice. Histological analysis revealed that the prolonged anagen phase might be the cause of accelerated hair growth in Fgf5go-malc1 mice.

Dihydrotestosterone-induced hair regrowth inhibition by activating androgen receptor in C57BL6 mice simulates androgenetic alopecia

Androgenic alopecia (AGA), also known as male pattern baldness, is one of the most common hair loss diseases worldwide. The main treatments of AGA include hair transplant surgery, oral medicines, and LDL laser irradiation, although no treatment to date can fully cure this disease. Animal models play important roles in the exploration of potential mechanisms of disease development and in assessing novel treatments. The present study describes androgen receptor (AR) in C57BL/6 mouse hair follicles that can be activated by dihydrotestosterone (DHT) and translocate to the nucleus. This led to the design of a mouse model of androgen-induced AGA in vivo and in vitro. DHT was found to induce early hair regression, hair miniaturization, hair density loss, and changes in hair morphology in male C57BL/6 mice. These effects of DHT could be partly reversed by the AR antagonist bicalutamide. DHT had similar effects in an ex vivo model of hair loss. Evaluation of histology, organ culture, and protein expression could explain the mechanism by which DHT delayed hair regrowth.

Evaluating hair growth promoting effects of candidate substance: A review of research methods

Androgenetic alopecia (AGA) is the most common form of hair loss disorder. As the prevalence of AGA rises, the demand for AGA treatments is rising accordingly, prompting research to identify therapeutic candidates to treat AGA. Because AGA is caused by crosstalk among multiple hair follicle (HF) cell components, understanding the effects of candidate molecules on HF cells is essential to determining therapeutic candidates for treatment. To date, research has centered on HF dermal papilla and outer root sheath cells and has indicated that the hair growth effects of candidate substances may be mediated via alterations in several signaling pathways and signature genes in these HF cells. In more integrative evaluations, the HF unit is used as an ex vivo organ culture model to verify the effects of therapeutic candidates. Animal models have also been used to evaluate the effects of candidate substances. The main outcomes used to evaluate the effects of candidate substances are 1) changes in HF growth rates in vitro, 2) anagen induction capabilities, and 3) the effects of androgen modulation. This article reviews a series of methods used to evaluate the hair growth-promoting effects of candidate substances, providing an overview of cell assays, organs, and animal models used in AGA research in order to facilitate AGA research moving forward.

Tetrahydroxystilbene Glucoside Effectively Prevents Apoptosis Induced Hair Loss

The effect of Polygonum multiflorum against hair loss has been widely recognized. 2,3,5,4′-Tetrahydroxystilbene-2-O-β-D-glucoside (TSG) is the main component of Polygonum multiflorum; however, its role in hair regeneration has not been established. To evaluate the hair growth-promoting activity of TSG, depilated C57BL/6J mice were topically treated with normal saline, TSG, Pifithrin-α, Minoxidil for 2 weeks. In this study, we identified that p53, Caspase-3, Active Caspase-3, and Caspase-9 were obviously upregulated in the skin of human and mice with hair loss by western blot analysis. Depilated mice treated with TSG showed markedly hair regrowth. TUNEL⁺ cells were also reduced in mice with TSG. These changes were accompanied with inhibition of Fas, p53, Bax, Active Caspase-3, and Procaspase-9 activities. These results demonstrated that TSG exerts great hair regrowth effect on hair loss, which was probably mediated by inhibition of p53, Fas, and Bax induced apoptosis.

A mouse model of androgenetic alopecia

Androgenetic alopecia (AGA), commonly known as male pattern baldness, is a form of hair loss that occurs in both males and females. Although the exact cause of AGA is not known, it is associated with genetic predisposition through traits related to androgen synthesis/metabolism and androgen signaling mediated by the androgen receptor (AR). Current therapies for AGA show limited efficacy and are often associated with undesirable side effects. A major hurdle to developing new therapies for AGA is the lack of small animal models to support drug discovery research. Here, we report the first rodent model of AGA. Previous work demonstrating that the interaction between androgen-bound AR and beta-catenin can inhibit Wnt signaling led us to test the hypothesis that expression of AR in hair follicle cells could interfere with hair growth in an androgen-dependent manner. Transgenic mice overexpressing human AR in the skin under control of the keratin 5 promoter were generated. Keratin 5-human AR transgenic mice exposed to high levels of 5alpha-dihydrotestosterone showed delayed hair regeneration, mimicking the AGA scalp. This effect is AR mediated, because treatment with the AR antagonist hydroxyflutamide inhibited the effect of dihydrotestosterone on hair growth. These results support the hypothesis that androgen-mediated hair loss is AR dependent and suggest that AR and beta-catenin mediate this effect. These mice can now be used to test new therapeutic agents for the treatment of AGA, accelerating the drug discovery process.

Photoperiodic and hormonal influences on fur density and regrowth in two hamster species

Temperate and boreal mammals undergo seasonal changes in pelage that facilitate thermoregulation in winter and summer. We investigated photoperiodic influences on pelage characteristics of male Siberian and Syrian hamsters. Fur density (mg fur/cm2 skin) was measured by weighing the shavings of fur patches removed from the dorsal and ventral surfaces of hamsters maintained in long days (LDs) or transferred to short days (SDs). Patches were reshaved 3 wk later to assess fur regrowth (mg regrown fur/cm2 skin). Fur density was greater in SD than in LD Siberian hamsters after 11 wk of differential phototreatment. The onset of increased fur density in SDs was accompanied by a transient increase in fur regrowth (11-14 wk on the dorsal surface and 7-10 and 11-14 wk on the ventral surface), suggestive of a seasonal molting process. Fur density, body mass, and pelage color of Siberian hamsters returned to values characteristic of LD males after a similar duration of prolonged (>27 wk) SD treatment and appear to be regulated by a similar or common interval-timing mechanism. In Syrian hamsters, dorsal fur density, fur regrowth, and hair lengths were greater in SD than in LD males. Castration increased and testosterone (T) treatment decreased dorsal and ventral fur regrowth in LD and SD hamsters, but the effects of T manipulations on fur density were limited to a decrease in dorsal fur density after T treatment. Decreased circulating T in SDs likely contributes to the seasonal molt of male hamsters by increasing the rate of fur growth during the transition to the winter pelage.

Controls of hair follicle cycling

Nearly 50 years ago, Chase published a review of hair cycling in which he detailed hair growth in the mouse and integrated hair biology with the biology of his day. In this review we have used Chase as our model and tried to put the adult hair follicle growth cycle in perspective. We have tried to sketch the adult hair follicle cycle, as we know it today and what needs to be known. Above all, we hope that this work will serve as an introduction to basic biologists who are looking for a defined biological system that illustrates many of the challenges of modern biology: cell differentiation, epithelial-mesenchymal interactions, stem cell biology, pattern formation, apoptosis, cell and organ growth cycles, and pigmentation. The most important theme in studying the cycling hair follicle is that the follicle is a regenerating system. By traversing the phases of the cycle (growth, regression, resting, shedding, then growth again), the follicle demonstrates the unusual ability to completely regenerate itself. The basis for this regeneration rests in the unique follicular epithelial and mesenchymal components and their interactions. Recently, some of the molecular signals making up these interactions have been defined. They involve gene families also found in other regenerating systems such as fibroblast growth factor, transforming growth factor-beta, Wnt pathway, Sonic hedgehog, neurotrophins, and homeobox. For the immediate future, our challenge is to define the molecular basis for hair follicle growth control, to regenerate a mature hair follicle in vitro from defined populations, and to offer real solutions to our patients' problems.