What’s new in hair — April 2017 | Dr. Claire A. Higgins
Cell. 2017 Apr 20;169(3):483-496.e13. doi: 10.1016/j.cell.2017.03.038. Epub 2017 Apr 13.
In the anagen hair follicle, transit amplifying cells (TACs) of the hair matrix differentiate giving rise to 7 lineages of the follicle (medulla, hair cortex, hair cuticle, cuticle, huxley’s and henles layers of the inner root sheath, and the companion layer) during anagen. In this paper by Yang et al, they perform singe cell RNA sequencing of murine hair follicles, and define the pathways along which TAC embark, in order to differentiate into these 7 epithelial lineages of the follicle. They show that TAC are spatially organised, and primed to divide asymmetrically relative to the basement membrane to give rise to the different epithelial lineages. Intriguingly, the authors also performed single cell RNA sequencing on dermal papilla cells, and identified 4 sub compartments. Within these, there is a BMP gradient, with effectors and inhibitors of BMP signalling at opposite poles of the dermal papilla. Genes such as Wnt10b are also located in the compartment of the DP adjacent to the TAC which become two of the layers of the inner root sheath. The authors propose that these dermal papilla compartment act as 4 micro niches, which confer lineage specificity in an ordered manner to the adjacent TACs.
Exp Dermatol. 2017 Apr 28. doi: 10.1111/exd.13373. [Epub ahead of print] Review.
Female pattern hair loss (FPHL) is the most common form of hair loss in women, and it increases in prevalence with age. The pathology of the disease is almost identical to male pattern hair loss (MPL) in that there is a reduction in the duration of anagen, and an increased duration of telogen in affected follicles. As a consequence, FPHL and MPL are often grouped together under the androgenic alopecia category. Despite this, FPHL and MPL have distinct patterning; FPHL is mainly characterised by a diffuse reduction of hair in the mid and frontal scalp, while MPL is characterised by deep recession of the frontal hairline and vertex balding. In this review article, Redler et al summarise the current results of genetic studies into FPHL, and introduce some of the hypotheses explaining susceptibility. They highlight that none of the published genetic studies have shown clear overlap of susceptibility loci between MPL and FPHL. While the pathology of the disease may be identical, and androgens may be involved in some FPHL cases, the data from these genetic studies clearly suggests that there are several non-androgenic mechanisms which contribute to FPHL. Going forward, having a better understanding the aetiology of FPHL will hopefully lead to the development of targeted treatments for FPHL.
As a carrier-transporter for hair follicle reconstitution, platelet-rich plasma promotes proliferation and induction of mouse dermal papilla cells
Sci Rep. 2017 Apr 25;7(1):1125. doi: 10.1038/s41598-017-01105-8.
Platelet Rich Plasma (PRP) is quickly becoming a popular autologous treatment for hair loss. While the specific constituents of PRP remain to be elucidated, it is thought it contains a source of growth factors which promote dermal papilla proliferation upon injection. In this paper, Xiao et al assessed whether PRP could also affect dermal papilla inductivity. The authors cultured trichogenic mouse dermal papilla cells in normal growth medium, or medium containing 5% PRP. When these were implanted onto nude mice, significantly more hair follicles were induced by the cells cultured with 5% PRP, as compared to trichogenic mouse dermal papilla in normal growth medium. The authors also made PRP gels, to see whether PRP could act as a bioactive scaffold to promote hair growth. Mouse dermal papilla cells grown in these scaffolds were able to induce large numbers of hair follicles in a grafting assay. However, the mechanism by which PRP affects the hair inductive capacity of dermal papilla cells remains to be understood.
Genome-wide differential expression profiling of long non-coding RNAs in androgenetic alopecia in a Chinese male population
J Eur Acad Dermatol Venereol. 2017 Apr 17. doi: 10.1111/jdv.14278. [Epub ahead of print]
Long non coding RNAs (lncRNAs) are RNAs that are more than 200 nucleotides in length, yet have no protein coding capability. Instead, these are regulatory RNAs, with key roles in transcription, post-transcriptional processing and chromatin remodelling. In this study, Bao et al performed microarrays to assess the levels of lncRNAs in androgenic alopecia (AGA). They compared scalp from areas affected by androgenic AGA, and unaffected scalp regions, identifying 2143 differentially expressed lncRNAs. LncRNAs can also be associated with genes, and this was the case for one of the most differentially expressed lncRNAs identified in the study. CTD-2636A23.2, which was down regulated in AGA, is associated with HMGCS1. Intriguingly, HMGCS1 has a role in male gonad development, and so it is likely there is an androgenic link with the CTD-2636A23.2 and AGA. Further analysis of the differentially regulated lncRNAs may reveal biomarkers for AGA susceptibly, or potentially therapeutic targets for intervention.
Exp Dermatol. 2017 Apr 18. doi: 10.1111/exd.13368. [Epub ahead of print]
The two most studied compartments of the hair follicle are the mesenchymal dermal papilla, and the epithelial bulge. Interaction between the cells which reside in both these locations are critical for hair follicle growth and cycling. Thus, knowing how to selectively isolate cells from these compartments is a desirable technique in the hair research field. In this methods paper, Topouzi et al outline a step by step approach to isolate and culture dermal papilla cells from human hair follicles, highlighting common pitfalls and difficult steps in the micro dissection process. This paper will be useful for new researchers in the hair field, who wish to quickly acquire technical ability in dermal papilla micro dissection.
A new path in defining light parameters for hair growth: Discovery and modulation of photoreceptors in human hair follicle
Lasers Surg Med. 2017 Apr 18. doi: 10.1002/lsm.22673. [Epub ahead of print]
Light therapy, or photobiomodulation is quickly becoming a popular ‘natural’ treatment of skin conditions such as hair loss, psoriasis, and eczema. However, it seems that every trial uses different light wavelengths, or different light intensities, and it is difficult to identify the best conditions for treatment. In addition, it is not clearly understood why the skin and hair follicle are responsive to light. In this manuscript, Buscone et al sought to identify light receptors within the hair follicle to understand how the follicle is responsive to light. Specifically, they looked at opsin receptors, and found that while OPN2 and OPN3 are present in the follicle, OPN1, 4 and 5 are not. Using immunofluorescence to localise these receptors, they found OPN2 in the outer root sheath, and bulge region of the follicle, while OPN3 expression was found in the inner root sheath. Later, to assess the effect of light at two wave lengths on the hair follicle, they employed the Philpott model for hair growth. They found that while 3.2J/cm2 of 453nm light can significantly prolong anagen, 3.2J/cm2 of 689nm light had no effect on the follicle. These results are intriguing, and demonstrate that light in the blue region of the electromagnetic spectrum has the most prominent effect on the follicle.