What’s new in hair — August 2016 | Dr. Claire A. Higgins
The arrector pili muscle, the bridge between the follicular stem cell niche and the interfollicular epidermis.
Anat Sci Int. 2016 Jul 29. doi:10.1007/s12565-016-0359-5
The arrector pili muscle (APM) is a smooth band of muscle that connects the skin dermis at its distal end, and the bulge region of the hair follicle at is proximal end. Previously, the Sinclair group demonstrated that loss of the APM is a morphological changes associated with androgenetic alopecia, but not alopecia areata. In this methods paper, Torkamani et al show that Phalloidin, an F-Actin probe, is highly sensitive to the APM, and consistently marks it along its entire length. 3D reconstructions of their staining in human skin revealed that the APM does not branch from a single point to connect to the dermal epidermal junction, but rather it only ever divides into two branches at a single point, and instead there are multiple branch points in close proximity. The authors hypothesise that the APM connection enables activation of bulge stem cells in the follicle, in response to wounding within the interfollicular epithelium.
JAAD Case Rep. 2016 Aug 1;2(4):298-300. doi: 10.1016/j.jdcr.2016.06.003.
Denosumab is a new drug approved by the FDA for treatment of postmenopausal women with osteoporosis. It is a monoclonal antibody to receptor activator of nuclear factor kappa β ligand (RANKL), an anti TNF agent, which suppresses osteoclast mediated bone reabsorption. In this case report by Lyakhovitsky et al, a 69 year old man with osteoporosis was given a 60mg subcutaneous dose of denosumab. Two weeks later he had developed patchy alopecia areata, and after two months he had alopecia universalis, despite having no history of alopecia in his family. The authors suggest two possible mechanisms by which denosumab may have triggered this onset of alopecia areata. Firstly, denosumab has similar homology to TNFα, and therefore may have resulted in an autoimmune reaction in the patient. RANKL, and its interaction with RANK play important roles in T cell and dendritic cell communication. Secondly, RANKL deficient mice have an impaired anagen initiation phase, suggesting that it is important for hair follicle cycling.
Epidemiology, clinical presentation and therapeutic approach in a multicenter series of dissecting cellulitis of the scalp.
J Eur Acad Dermatol Venereol. 2016 Aug 25. doi: 10.1111/jdv.13948.
Dissecting cellulitis of the scalp (DCS) is characterised by inflammatory nodules, abscesses and sinuses which lead to the progression of scarring alopecia. However, due to its rarity there are very few studies on patients diagnosed with DCS. In this report, Segurado-Miravalles et al describe a retrospective multicentre study across 4 Spanish hospitals that assessed 21 patients diagnosed with DCS. Interestingly, 81% of cases were male, 19% female, while 32.8 years was the average age of onset, ranging from 18-58. In 90% of patients, itching was associated with the development of alopecic patches. While a range of treatments were used across the different hospitals, the authors recommend a 30mg daily dose of isotretinoin as the first treatment of choice. Interestingly, they also postulate that there is a correlation with oily substance exposure and DCS; several of the patients in their study worked in mechanics, gas stations, or with buses, which are all careers that may frequently expose individuals to oil and grease.
Lasers Surg Med. 2016 Aug 9. doi: 10.1002/lsm.22570.
Laser therapy for hair removal is common practice in many clinics, however, treatment is often restricted to darkly pigmented hair fibers, where the melanin presents absorbs the laser energy. The eumelanin present in lighter hair does not absorb laser energy, and therefore laser therapy is often ineffective. In this manuscript, Shin et al assess photodynamic therapy as an alternate hair removal treatment for non-pigmented hair. They used BALB/c mice with white hair, and C57BL/6 mice with black hair (all in anagen), to test the efficacy of either photodynamic therapy or laser therapy. For photodynamic therapy, methyl aminolevulinate (MAL), a photo sensitising agent, was applied to skin for 4 hours, followed by 630nm LED irradiation. For laser therapy, an 800nm diode laser was used for irradiation. The authors found that with multiple (up to 7) sessions of photodynamic therapy, areas of permanent hair removal were observed in white mice. Comparatively, laser therapy was ineffective in white haired mice, while it worked well in black haired mice. Encouragingly, photodynamic therapy was also less effective in black haired mice. This suggests that while laser therapy is a suitable treatment for hair removal for dark hair fibers, photodynamic therapy may become a common treatment in the future for individuals with lighter hair colours. For effective photodynamic therapy, both the MAL, and the LED have to penetrate the whole depth of the follicle. While the 630nm laser can penetrate up to 5mm, the limiting factor in translating these murine studies to human skin will be the depth that MAL can penetrate.
JCI Insight. 2016; 1(13):e87146. Doi:10.1171/jci.insight.87146
Recently, the fat layer subjacent to the skin dermis was recognised as a distinct adipocyte depot from other fat depots within the body. In light of this, it was renamed dermal White Adipose Tissue (dWAT). In this paper, Kasza et al use an MRI based imaging technique to image all fat depots within the body, including dWAT. Using wild type mice, their imaging technique confirmed what hair biologists already know, that dWAT is at least 2 fold thicker in anagen sites versus telogen sites. However, using ob/ob mice (an obesity model), and wild type mice on a high fat diet, they found that dWAT accumulated with increasing body weight, showing a parallel with the accumulation of visceral fat. Interestingly, this demonstrates that fat depots in the body react similarly during obesity, despite their known heterogeneity.
Human Hair and the Impact of Cosmetic Procedures: A Review on Cleansing and Shape-Modulating Cosmetics
Cosmetics 2016; 3(3):26. doi:10.3390/cosmetics3030026
In this review by Cruz et al, the authors start by giving an overview of hair morphogenesis and cycling. They move through to discuss basic hair anatomy, reviewing the layers of the hair follicle, right down to the keratin tetramers from which the hair cortex is composed. They discuss the importance of different aspects of the follicle; for example, the outmost layer of the cuticle termed the epicuticle, contains 18-MEA and free lipids, which provide lubricity the hair and a first line of defence against environmental insults. The shape of these cuticle cells, and their arrangement adjacent to each other provides the hair with self-cleaning properties, although in this current day and age the accumulation of grease and dirt on the hair means it requires additional cleaning. The authors discuss the composition of different types of shampoos, conditioners, straightening and waving agents, the chemistry behind them, and how they interact with the hair fiber. This review is of interest to hair biologists, and cosmetic scientists alike, as understanding hair follicle biology and the structure of the hair fiber will no doubt aid the development of effective and safe hair care products.