Olivier Gaillard

Human hair greying is linked to a specific depletion of hair follicle melanocytes affecting both the bulb and the outer root sheath

Background  Although hair greying is a very common phenomenon characterized by loss of pigment in the hair shaft, the events that cause and control natural hair whitening with age in humans are still unclear.

Thyroid hormone receptor β1 is expressed in the human hair follicle: THYROID HORMONE RECEPTOR β1 IN HUMAN HAIR

To understand better the mechanisms by which thyroid hormone can exert its effects on the hair follicle, we looked for the expression of members of the thyroid hormone receptor (TR) family in human hair follicles. Immunoreactive TRs were detected in both dermal and epithelial compartments of the human pilosebaceous unit. Using reverse transcriptase–polymerase chain reaction, we established that TRβ1 was the predominant form of TR expressed in the human hair follicle. In addition, we investigated the effects of 3,3′,5‐triiodo‐ l‐thyronine (T3) on the survival of human hair follicles in vitro, to understand the role of this thyroid hormone on hair follicle homeostasis. A physiological level of free T3 significantly enhanced human hair survival in vitro.

Human hair shape is programmed from the bulb

Background  Few biological data on curly hair follicles have been reported in the literature.

Expression of peroxisome proliferator activated receptors (PPARs) in human hair follicles and PPARα involvement in hair growth

Peroxisome proliferator-activated receptors (PPARs), which belong to the nuclear hormone receptor superfamily, have recently been described as potent key regulators of epidermal development. As 1,25-dihydroxyvitamin D3, retinoic acid and triiodothyronine are known to exert effects on skin and hair follicle growth through similar receptors, we decided to investigate both the expression pattern of the PPAR alpha, -delta and -gamma subtypes and their role in human hair follicles. Using reverse transcriptase-polymerase chain reaction and immunohistochemistry, we established that PPAR alpha, -delta and -gamma were expressed in both dermal and epithelial human hair follicle cells. Additionally, we evaluated the dose effect of clofibrate, a PPAR alpha ligand, on the survival of human hair follicles in culture. A beneficial effect was observed within a narrow range of concentrations.

Expression of NAD+ dependent 15-hydroxyprostaglandin dehydrogenase and protection of prostaglandins in human hair follicle

Abstract:  NAD+ dependent 15‐hydroxyprostaglandin dehydrogenate (15‐PGDH) catalyses oxidation of 15(S)‐hydroxyl group of prostaglandins and as a result inactivates their physiological potential. Positive effects of prostaglandins or prostaglandin analogues were reported on terminal hair, vellus hair or eyelash growth and a complex prostaglandin network was recently described in human hair follicle. In the present study, we showed that 15‐PGDH was expressed in human hair follicle mainly in melanocytes and keratinocytes, which brought us to consider this enzyme as a possible target to sustain local prostaglandin production. Using a recombinant enzymatic strategy, specific 15‐PGDH inhibitors were screened. We identified a thiazolidine dione derivative exhibiting efficacy on follicular outer root sheath keratinocytes, since it concomitantly decreased the production of deactivated 13,14 dihydro 15‐ketoprostaglandin F2α and sustained prostaglandin F2αin vitro production. In the context of recent interest in prostaglandins and prostaglandin analogues as hair regrowth agents, we postulated that the use of selected 15‐PGDH inhibitors could reinforce or prolong the effect of these physiological mediators on hair and skin.

Human hair follicle pigmentary unit as a direct target for modulators of melanogenesis, as studied by [14C]‐2‐Thiouracil incorporation

Abstract:  The purpose of this study was to evaluate human hair follicle melanogenic activity using the [14C]‐2‐thiouracil, which was known to incorporate into nascent melanins. Results obtained on pigmented, grey and non‐pigmented hair follicles demonstrated that [14C]‐2‐TU incorporation was restricted to the melanogenic compartment with a strong accumulation located around dermal papilla and within the fibre of pigmented hair follicles. Quantitative analysis of [14C]‐2‐TU incorporation showed a significant increase in pigmented hair follicles upon stimulation with 1 μm forskolin concomitant to an increase in tyrosinase levels. A strong significant decrease in [14C]‐2‐TU incorporation was noted, when hair follicles were incubated with the tyrosinase competitive inhibitor kojic acid (200 μm). Incubation with the MC1‐R agonist α‐MSH (0.2 μm) did not induce a significant stimulation of hair melanogenesis. The present model could thus represent a useful new tool to identify modulators of human hair pigmentation.

6-O glucose linoleate supports in vitro human hair growth and lipid synthesis

The hair follicle is a very active organ with a complex structure, which produces a hair fibre at a rate of 0.3 mm a day. Accordingly, the hair follicle is highly demanding in energy source, as the hair bulb matrix cells are endowed with one of the highest rates of proliferation in the human body. Moreover, recent data have shown the involvement of lipids in hair follicle function. As in vitro‐grown hair follicle keeps producing a hair fibre that closely resembles the natural hair fibre, we decided to use this model to investigate the role of a new of glucose linoleate derivative (6‐O‐linoleyl‐d‐glucose: 6‐O‐GL) as a lipid precursor and energy provider. Our results demonstrated that 6‐O‐GL was (i) quite stable and surprisingly resistant to oxidative degradation, and (ii) readily taken up and metabolized by the hair follicle into various lipids, namely neutral lipids, ceramides and polar lipids. Moreover, it supported hair follicle growth and survival in a glucose‐ and linoleic‐acid free medium. 6‐O‐GL thus appeared to be a bi‐functional nutrient, ensuring both proper fibre quality and production by the hair follicle.