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Male pattern hair loss (MPHL), also referred to as male androgenetic alopecia (AGA) is the most common type of non‐scarring progressive hair loss, with 80% of men suffering from this condition in their lifetime. In MPHL, the hair line recedes to a specific part of the scalp which cannot be accurately predicted. Hair is lost from the front, vertex, and the crown, yet temporal and occipital follicles remain. The visual effect of hair loss is due to hair follicle miniaturisation, where terminal hair follicles become dimensionally smaller. Miniaturisation is also characterised by a shortening of the growth phase of the hair cycle (anagen), and a prolongation of the dormant phase (kenogen). Together, these changes result in the production of thinner and shorter hair fibres, referred to as miniaturised or vellus hairs. It remains unclear why miniaturisation occurs in this specific pattern, with frontal follicles being susceptible while occipital follicles remain in a terminal state. One main factor we believe to be at play, which will be discussed in this viewpoint, is the developmental origin of the skin and hair follicle dermis on different regions of the scalp. [ABSTRACT FROM AUTHOR]

Introduction and aims Androgenetic alopecia (AGA) is defined by hair loss from the frontal, parietal and vertex regions of the scalp; however, occipital follicles are spared. Hair follicles in AGA undergo miniaturization, which is the transition of terminal follicles into vellus follicles. Similarly with age, the diameter of the hair shaft decreases with loss of pigmentation, which is also seen in miniaturized follicles. To investigate whether frontal follicles have accelerated ageing compared with occipital follicles, we looked at methylation levels of genes associated with ageing. As the thickness and pigmentation of hair fibre are influenced by the dermal papilla (DP), we conducted microarray analysis of frontal and occipital DP to establish whether accelerated ageing of follicles is driven by DP. Methods The biological age of frontal and occipital follicles was calculated using methylation status of ELOVL2, ASPA, EDARADD and PDE4C (n = 3). For microarray analysis, DP was microdissected from the frontal (FDP) and occipital (ODP) follicles from patients undergoing hair transplantation surgeries to treat AGA (n = 4). Results Frontal follicles were found to have significantly higher biological age compared with patient-matched occipital follicles suggesting accelerated ageing of follicles in AGA. Transcriptomic analysis revealed significant increase in expression of several genes in FDP and notably EGR1 , HSPB1 , DNAJB1 and APOD, which have been shown to be upregulated in the DP of aged mice compared with young mice. We found downregulation of TRPS1 in FDP, which represses EGR1. Mutations in TRPS1 underlie trichorhinophalangeal syndrome which is associated with vellus-type hair. Conclusions Our transcriptional and molecular analysis revealed that FDP and frontal follicles have an advanced biological age relative to ODP. This increased age is also reflected in the transcriptional signature of FDP. We hypothesize that these changes are in part due to regulation of signalling by the transcriptional repressor TRPS1 , whose expression is decreased in FDP. [ABSTRACT FROM AUTHOR]

The human hair follicle (HF) exhibits peripheral clock activity, with knock-down of clock genes (BMAL1 and PER1) prolonging active hair growth (anagen) and increasing pigmentation. Similarly, thyroid hormones prolong anagen and stimulate pigmentation in cultured human HFs. In addition they are recognized as key regulators of the central clock that controls circadian rhythmicity. Therefore, we asked whether thyroxine (T4) also influences peripheral clock activity in the human HF. Over 24 hours we found a significant reduction in protein levels of BMAL1 and PER1, with their transcript levels also decreasing significantly. Furthermore, while all clock genes maintained their rhythmicity in both the control and T4 treated HFs, there was a significant reduction in the amplitude of BMAL1 and PER1 in T4 (100 nM) treated HFs. Accompanying this, cell-cycle progression marker Cyclin D1 was also assessed appearing to show an induced circadian rhythmicity by T4 however, this was not significant. Contrary to short term cultures, after 6 days, transcript and/or protein levels of all core clock genes (BMAL1, PER1, clock, CRY1, CRY2) were up-regulated in T4 treated HFs. BMAL1 and PER1 mRNA was also up-regulated in the HF bulge, the location of HF epithelial stem cells. Together this provides the first direct evidence that T4 modulates the expression of the peripheral molecular clock. Thus, patients with thyroid dysfunction may also show a disordered peripheral clock, which raises the possibility that short term, pulsatile treatment with T4 might permit one to modulate circadian activity in peripheral tissues as a target to treat clock-related disease. [ABSTRACT FROM AUTHOR]

Balding causes widespread psychological distress but is poorly controlled. The commonest treatment, minoxidil, was originally an antihypertensive drug that promoted unwanted hair. We hypothesized that another serendipitous discovery, increased eyelash growth side-effects of prostamide F2α-related eyedrops for glaucoma, may be relevant for scalp alopecias. Eyelash hairs and follicles are highly specialized and remain unaffected by androgens that inhibit scalp follicles and stimulate many others. Therefore, we investigated whether non-eyelash follicles could respond to bimatoprost, a prostamide F2α analog recently licensed for eyelash hypotrichosis. Bimatoprost, at pharmacologically selective concentrations, increased hair synthesis in scalp follicle organ culture and advanced mouse pelage hair regrowth in vivo compared to vehicle alone. A prostamide receptor antagonist blocked isolated follicle growth, confirming a direct, receptor-mediated mechanism within follicles; RT-PCR analysis identified 3 relevant receptor genes in scalp follicles in vivo. Receptors were located in the key follicle regulator, the dermal papilla, by analyzing individual follicular structures and immunohistochemistry. Thus, bimatoprost stimulates human scalp follicles in culture and rodent pelage follicles in vivo, mirroring eyelash behavior, and scalp follicles contain bimatoprost-sensitive prostamide receptors in vivo. This highlights a new follicular signaling system and confirms that bimatoprost offers a novel, low-risk therapeutic approach for scalp alopecias. [ABSTRACT FROM AUTHOR]

Highlights from the article: Hair follicles (HFs) are sensitive to xenobiotic damage, which can ultimately lead to hair loss such as in chemotherapy-induced alopecia (CIA) [[1]]. Human hair follicles (HFs) were cultured for 30 min with ABC transporter inhibitors verapamil (100 M, ABCB1) followed by the addition of 30 M 4HC for 48h or 1 M Doxorubicin for 1h followed by a 48h washout.

Androgenetic alopecia (AGA), a hereditary disorder that involves the progressive thinning of hair in a defined pattern, is driven by androgens. The hair follicle dermal papilla (DP) expresses androgen receptors (AR) and plays an important role in the control of normal hair growth. In AGA, it has been proposed that the inhibitory actions of androgens are mediated via the DP although the molecular nature of these interactions is poorly understood. To investigate mechanisms of AGA, we cultured DP cells (DPC) from balding and non-balding scalp and confirmed previous reports that balding DPC grow slower in vitro than non-balding DPC. Loss of proliferative capacity of balding DPC was associated with changes in cell morphology, expression of senescence-associated β-galactosidase, as well as decreased expression of proliferating cell nuclear antigen and Bmi-1; upregulation of p16INK4a/pRb and nuclear expression of markers of oxidative stress and DNA damage including heat shock protein-27, super oxide dismutase catalase, ataxia-telangiectasia-mutated kinase (ATM), and ATM- and Rad3-related protein. Premature senescence of balding DPC in vitro in association with expression of p16INK4a/pRB suggests that balding DPC are sensitive to environmental stress and identifies alternative pathways that could lead to novel therapeutic strategies for treatment of AGA.Journal of Investigative Dermatology (2008) 128, 1088–1094. doi:10.1038/sj.jid.5701147; published online 8 November 2007 [ABSTRACT FROM AUTHOR]

A letter to the editor is presented which discusses the effect of thymic peptides in the stimulation of hair follicle growth in human.