Is the dermal papilla a primary target in alopecia areata?

Alopecia areata: a review of disease pathogenesis

BACKGROUND

Alopecia areata is a disorder that results in nonscarring hair loss. The psychological impact can be significant, leading to feelings of depression and social isolation. Objectives In this article, we seek to review the pathophysiological mechanisms proposed in recent years in a narrative fashion.

METHODS

We searched MEDLINE and Scopus for articles related to alopecia areata, with a particular emphasis on its pathogenesis.

RESULTS

The main theory of alopecia areata pathogenesis is that it is an autoimmune phenomenon resulting from a disruption in hair follicle immune privilege. What causes this breakdown is an issue of debate. Some believe that a stressed hair follicle environment triggers antigen presentation, while others blame a dysregulation in the central immune system entangling the follicles. Evidence for the latter theory is provided by animal studies, as well investigations around the AIRE gene. Different immune-cell lines including plasmacytoid dendritic cells, natural killer cells and T cells, along with key molecules such as interferon-γ, interleukin-15, MICA and NKG2D, have been identified as contributing to the autoimmune process.

CONCLUSIONS

Alopecia areata remains incurable, although it has been studied for years. Available treatment options at best are beneficial for milder cases, and the rate of relapse is high. Understanding the exact mechanisms of hair loss in alopecia areata is therefore of utmost importance to help identify potential therapeutic targets.

Keratinocytic vascular endothelial growth factor as a novel biomarker for pathological skin condition

Skin is an emerging target tissue in pharmaceutical and cosmetic science. Safety assessment for dermal toxicity is a critical step for development of topically applicable pharmaceutical agents and ingredients in cosmetics. Urgent needs exist to set up toxicity testing methods for dermal safety, and identification of novel biomarkers for pathological cutaneous alteration is highly required. Here we will discuss if vascular endothelial growth factor (VEGF) has a potential as a biomarker for dermal impairment. Experimental and clinical evidences for induction of keratinocytic VEGF under pathological conditions will be reviewed.

The use of dermal papilla cells in studies of normal and abnormal hair follicle biology

The mesenchyme-derived dermal papilla plays a major regulatory role in the complex cell biology of the hair follicle. The ability to culture dermal papilla cells from a range of species and particularly a range of normal and disordered human hair follicles has enabled the development of a powerful new model system for investigating hair follicle biology. Already these studies have reinforced the importance of dermal papilla cells in initiating new follicle growth and in androgen action in human hair follicles. The retention of hair growth inducing capabilities and characteristics that reflect their in vivo responsiveness to androgens in culture means that they offer a potentially useful approach despite significant drawbacks in working with the cells themselves. Further studies using dermal papilla cells may well elucidate key molecules involved in hair biology in health and disease and, thereby, lead to better therapeutic regimens.