Immune and Non-immune Interactions in the Pathogenesis of Androgenetic Alopecia

Abstract

Androgenetic alopecia (AGA), a leading cause of progressive hair loss, affects up to 50% of males aged 50 years, causing significant psychological burden. Current treatments, such as anti-androgen drugs and minoxidil, show heterogeneous effects, even with long-term application. Meanwhile, the large-scale adoption of other adjuvant therapies has been slow, partly due to insufficient mechanistic evidence. A major barrier to developing better treatment for AGA is the incomplete understanding of its pathogenesis. The predominant academic consensus is that AGA is caused by abnormal expression of androgens and their receptors in individuals with a genetic predisposition. Emerging evidence suggests the contributing role of factors such as immune responses, oxidative stress, and microbiome changes, which were not previously given due consideration. Immune-mediated inflammation and oxidative stress disrupt hair follicles' function and damage the perifollicular niche, while scalp dysbiosis influences local metabolism and destabilizes the local microenvironment. These interconnected mechanisms collectively contribute to AGA pathogenesis. These additional aspects enhance our current understanding and confound the conventional paradigm, bridging the gap in developing holistic solutions for AGA. In this review, we gather existing evidence to discuss various etiopathogenetic factors involved in AGA and their possible interconnections, aiming to lay the groundwork for the future identification of therapeutic targets and drug development. Additionally, we summarize the advantages and disadvantages of AGA research models, ranging from cells and tissues to animals, to provide a solid basis for more effective mechanistic studies.

Keywords: AR; EDAR2; PAX1; Alopecia; Androgen; Androgenetic alopecia; Estrogen; Follicle miniaturization; Pattern hair loss.