The Biology and Genomics of Human Hair Follicles: A Focus on Androgenetic Alopecia

Androgenetic Alopecia (AGA), a common hair-loss disorder, is influenced by aging, genetics, and lifestyle factors. It is characterized by the progressive miniaturization of hair follicles, leading to their transformation into vellus and atrophy. The study reviews the functional anatomy of hair follicles and the cell signaling events that play a role in follicle cycling. It also discusses the pathology of AGA and the known molecular mechanisms underlying this condition. The study highlights the importance of understanding the molecular and genetic mechanisms of AGA, given its high prevalence and potential comorbidities such as coronary heart disease, hypertension, hyperinsulinemia, obesity, and prostatic cancer. The authors suggest that a more comprehensive understanding of AGA at the molecular level is needed, and that studying AGA using a multi-omics approach could help resolve the unknowns that still remain. The document also discusses the biology and genomics of human hair follicles, with a focus on AGA. It results from a progressive shortening of the anagen phase, leading to miniaturization of the hair follicles and eventual atrophy. In AGA, genetically predisposed hair follicles transform from large thick pigmented hairs to barely visible depigmented hairs. The document also discusses the role of androgens in AGA. Androgens increase the size of hair follicles in androgen-sensitive areas but have a detrimental effect on genetically predisposed hair follicles, promoting their miniaturization. Individuals with genetic predisposition exhibit hair follicle cells with a higher density of androgen receptors and an increased activity of 5α-reductase type 2, leading to hair cycle disruption. The document also mentions that disruption in hair follicle stem cell activation has been demonstrated in AGA pathogenesis. Furthermore, the document discusses the role of inflammation in the pathogenesis of AGA, with evidence of infiltration of inflammatory cells into the bulge where the hair follicle stem cells reside.