Androgenetic alopecia: new insights into the pathogenesis and mechanism of hair loss

Abstract

The hair follicle is a complete mini-organ that lends itself as a model for investigation of a variety of complex biological phenomena, including stem cell biology, organ regeneration and cloning. The arrector pili muscle inserts into the hair follicle at the level of the bulge- the epithelial stem cell niche. The arrector pili muscle has been previously thought to be merely a bystander and not to have an active role in hair disease.Computer generated 3D reconstructions of the arrector pili muscle have helped explain why women with androgenetic alopecia (AGA) experience diffuse hair loss rather than the patterned baldness seen in men. Loss of attachment between the bulge stem cell population and the arrector pili muscle also explains why miniaturization is irreversible in AGA but not alopecia areata.A new model for the progression of AGA is presented.

Induction of Hair Keratins Expression by an Annurca Apple-Based Nutraceutical Formulation in Human Follicular Cells

“…Abnormalities in keratinization lead to the thinning of the fibers, anticipating hair loss. In the case of androgenic alopecia, one of the most common cause of patterned hair loss, pathogenesis has been partially elucidated and proven to involve an altered metabolism of testosterone with an increased activity of the type II isoform of the 5-α reductase enzyme (5AR) [35]. Finasteride, the only United States Federal Drug administration (FDA)-approved oral agent for the treatment of hair loss, is a specific inhibitor of 5AR type II isoform, while Minoxidil, the other FDA-approved agent, acts topically as a potassium channel opener, increasing vascularization of the hair bulb [36,37].…”

The usefulness of dermoscopy in canine pattern alopecia: a descriptive study

“…19 In humans, androgenetic alopecia is considered an inherited condition caused by a genetically determined hair follicle sensitivity to the effects of dihydrotestosterone, with the result of a gradual shortening of anagen phase and a prolongation of kenogen phase. [20][21][22][23][24] Increased concentrations of both 5-α reductase isoenzyme and androgen receptor have been detected in the balding scalp, suggesting that such changes contribute to hair loss. 25 To date, the pathogenesis of canine pattern alopecia is not known and the involvement of an abnormality in hair follicle hormonal receptor is still debated.…”

The Role of Finasteride in the Management of Androgenetic Alopecia in Male: A Narrative Review

“…[1][2][3] The occurrence varies by age and ethnicities, with White having higher prevalence compared to Asian and African-American 2 It is exhibited by the developed loss of hair on the scalp in a characteristic distribution, with the front scalp, middle scalp, temporal scalp and vertex of scalp being the most common affected areas. [3][4][5] AGA is commonly classified by using the modified Norwood-Hamilton scale, which is a detailed classification system used worldwide. 4 The severity is classified into Type I to VII, with increasing severity of hair thinning in the temples and vertex progressing to the entire top of scalp.…”

“…4 The pathogenesis of AGA is shortening of a hair growing phase which dictates the hair length coined as anagen phase. 5 This phase typically last 2 to 6 years with majority of the follicles in the normal scalp undergoing this phase. 1 Shortened anagen phase causes follicular miniaturization in which the newly grown hair shaft is shorter and thinner.…”