Fibroblasts can condense a hydrated collagen lattice to a tissue-like structure 1/28th the area of the starting gel in 24 hr. The rate of the process can be regulated by varying the protein content of the lattice, the cell number, or the con- centration of an inhibitor such as Colcemid. Fibroblasts of high population doubling level propagated in vitro, which have left the cell cycle, can carry out the contraction at least as efficiently as cycling cells. The potential uses of the system as an immu- nologically tolerated "tissue" for wound hea ing and as a model for studying fibroblast function are discussed.

Production of a tissue-like structure by contraction of collagen lattices by human fibroblasts of different proliferative

Nearly 50 years ago, Chase published a review of hair cycling in which he detailed hair growth in the mouse and integrated hair biology with the biology of his day. In this review we have used Chas...

/pdf/controls-of-hair-follicle-cycling-2h0o2ckdy0.pdf

Controls of hair follicle cycling.

Summary
We have known for over 30 years that minoxidil stimulates hair growth, yet our understanding of its mechanism of action on the hair follicle is very limited. In animal studies, topical minoxidil shortens telogen, causing premature entry of resting hair follicles into anagen, and it probably has a similar action in humans. Minoxidil may also cause prolongation of anagen and increases hair follicle size. Orally administered minoxidil lowers blood pressure by relaxing vascular smooth muscle through the action of its sulphated metabolite, minoxidil sulphate, as an opener of sarcolemmal KATP channels. There is some evidence that the stimulatory effect of minoxidil on hair growth is also due to the opening of potassium channels by minoxidil sulphate, but this idea has been difficult to prove and to date there has been no clear demonstration that KATP channels are expressed in the hair follicle. A number of in vitro effects of minoxidil have been described in monocultures of various skin and hair follicle cell types including stimulation of cell proliferation, inhibition of collagen synthesis, and stimulation of vascular endothelial growth factor and prostaglandin synthesis. Some or all of these effects may be relevant to hair growth, but the application of results obtained in cell culture studies to the complex biology of the hair follicle is uncertain. In this article we review the current state of knowledge on the mode of action of minoxidil on hair growth and indicate lines of future research.

Minoxidil: mechanisms of action on hair growth

Despite more than a hundred years of professional hair research, and substantial recent progress in unravelling the molecular controls of hair follicle morphogenesis, the chronobiological control system that cyclically drives the hair follicle through dramatic remodelling processes between phases of growth (anagen), regression (catagen), and relative resting (telogen) have remained disappointingly obscure. In view of the vast literature that has become available over the past decades on numerous genetic, biochemical, cellular and pharmacological aspects of hair growth follicle control under physiological and pathological conditions, it is astounding how comparatively few researchers in the field have published theoretical concepts that explore how hair follicle cycling might be controlled. Since this question is at the very heart of basic and clinically applied hair biology, it deserves a much more systematic and serious public exploration, which the following contributions are designed to stimulate.

https://onlinelibrary.wiley.com/doi/pdf/10.1111/j.1600-0625.1999.tb00376.x

What controls hair follicle cycling

It is now more than 15 years since the molecular structures of the major prostanoid receptors were elucidated. Since then, substantial progress has been achieved with respect to distribution and function, signal transduction mechanisms, and the design of agonists and antagonists ( ). This review systematically details these advances. More recent developments in prostanoid receptor research are included. The DP2 receptor, also termed CRTH2, has little structural resemblance to DP1 and other receptors described in the original prostanoid receptor classification. DP2 receptors are more closely related to chemoattractant receptors. Prostanoid receptors have also been found to heterodimerize with other prostanoid receptor subtypes and nonprostanoids. This may extend signal transduction pathways and create new ligand recognition sites: prostacyclin/thromboxane A2 heterodimeric receptors for 8- epi -prostaglandin E2, wild-type/alternative (alt4) heterodimers for the prostaglandin FP receptor for bimatoprost and the prostamides. It is anticipated that the 15 years of research progress described herein will lead to novel therapeutic entities.

https://pharmrev.aspetjournals.org/content/pharmrev/63/3/471.full.pdf

International Union of Basic and Clinical Pharmacology. LXXXIII: Classification of Prostanoid Receptors, Updating 15 Years of Progress

Today, androgenetic alopecia (AGA) is considered to be an alteration of hair growth and/or a premature aging of the pilosebaceous unit with a multifactorial and even polygenic etiology.1 The fact that the success rate of treatment with either antihypertensive agents, or modulators of androgen metabolism, barely exceeds 30% means that other pathways may be envisioned. The implication of various activators of inflammation in the etiology of AGA has progressively and recently emerged from several independent studies.2–11 A fibroplasia of the dermal sheath, which surrounds the hair follicle, is now suspected to be a common terminal process resulting in theminiaturization and involution of the pilosebaceous unit in AGA.2–8 We review here several observations underlining the possible implication of a slow, silent, and painless process in AGA. Because we think that it should not be confused with a classical inflammatory process, we have called it microinflammation. An early study referred to an inflammatory infiltrate of mononuclear cells and lymphocytes in about 50% of the scalp samples studied.2 Another more recent study by Jaworsky et al.3 confirmed an inflammatory infiltrate of activated T cells and macrophages in the upper third of the hair follicles from transitional regions of alopecia (i.e. which are characterized by actively progressing alopecia). This study also reported the occurrence of a developing fibrosis of the perifollicular sheath, together with the degranulation of follicular adventitial mast cells. The miniaturization of the hair follicles was found to be associated with a deposit of so-called ‘‘collagen or connective tissue streamers’’ beneath the follicle,2,7 as well as a 2–2.5 times enlargement of the follicular dermal sheath composed of densely packed collagen bundles.3 This thickening of the dermal sheath in progression zones of AGA has also recently been observed in our laboratory using immunohistochemical staining (Fig. 1). Horizontal section studies of scalp biopsies indicate that the so-called perifollicular fibrosis is generally mild, consisting of loose, concentric layers of fibrotic collagen that must be distinguished from cicatricial alopecia.4 It is unclear whether or not the fibrosis seen in follicular streamers (stelae or fibrous tracts) is permanent and/or alters the downgrowth of anagen hair follicles. Only 55% of male pattern AGA patients with microinflammation had hair regrowth in response to minoxidil treatment, which was less than the 77% of patients with no signs of inflammation,4 suggesting that, to some extent, perifollicular microinflammation may account for some cases of male pattern AGA which do not respond to minoxidil.4 Another study on 412 patients (193 men and 219 women) confirmed the presence of a significant degree of inflammation and fibrosis in at least 37% of AGA cases.5 The upper location of the infiltrate near the infrainfundibulum2–7 clearly distinguishes AGA from alopecia areata (AA), the latter disease being characterized by infiltrates in the bulb and dermal papilla zone.12 The aim of this review is to determine the location and chronology of the microinflammation process within the complex pathophysiology of the human pilosebaceous unit in order to improve the possible approaches for the reduction or prevention of the development of AGA.

Androgenetic alopecia and microinflammation.

Activation of cytoprotective prostaglandin synthase-1 by minoxidil as a possible explanation for its hair growth-stimulating effect.

Prostaglandins regulate a wide number of physiological functions. Recently PGF(2alpha) analogue such as latanoprost was shown to have a real impact on hair regrowth. The aim of this study was to investigate and describe the expression profile in human hair follicle of prostaglandin metabolism key enzymes, i.e. carbonyl reductase-1 (CBR1), microsomal prostaglandin E synthase-1 (mPGES-1) and microsomal prostaglandin E synthase-2 (mPGES-2), cytosolic prostaglandin E synthase (cPGES), the aldoketoreductase AKR1C1 and the prostaglandin F synthase AKR1C3. Quantitative RT-PCR on plucked hair follicles revealed some sex-related differences, mPGES-2 and AKR1C3 expression levels being higher in women. Cell and hair follicle compartment specificity was investigated using Western blot, PGE(2) and PGF(2alpha) ELISA assays and immunohistochemistry. Most of the hair cell types were endowed with prostaglandin metabolism machinery and were thus able to produce PGE(2) and/or PGF(2alpha). The epithelial part of the hair bulb was identified by immunohistology and EIA assays as the main source of prostaglandin synthesis and interconversion. All these observations support the concept that prostaglandins might be involved in hair growth and differentiation control.

https://onlinelibrary.wiley.com/doi/pdf/10.1111/j.1600-0625.2007.00586.x

Prostaglandin metabolism in human hair follicle

Prostanoid pathway in hair follicle gained closer attention since trichogenic side-effects on hair growth has been observed concomitantly with prostaglandin F2α receptor (FP) agonist treatment of intraocular pressure. We thus investigated prostanoid receptor distribution in anagen hair follicle and different cell types from hair and skin. Using RT-PCR, Western blot and immunohistochemistry (IHC), we found that all receptors were present in hair follicle. This data shed new light on an underestimated complex network involved in hair growth control. Indeed most of these receptors showed a wide spectrum of expression in cultured cells and the whole hair follicle. Using IHC, we observed that expression of prostaglandin E2 receptors (EP2, EP3, EP4), prostaglandin D2 receptor (DP2), prostanoid thromboxane A2 receptor (TP) and to a lesser extent EP1 involved several hair follicle compartments. On the opposite, Prostaglandin I2 receptor (IP) and DP1 were more specifically expressed in hair cuticle layer and outer root sheath (ORS) basal layer, respectively. FP expression was essentially restricted to ORS companion layer and dermal papilla (DP). Although extracting a clear functional significance from this intricate network remains open challenge, FP labelling, i.e. could explain the biological effect of PGF2α on hair regrowth, by directly modulating DP function.

Prostanoid receptors in anagen human hair follicles

An O-acyl product derived from glucose which may be obtained by partial or total esterification of glucose and of vitamin F, comprising a mixture of esters, for example, monoesters, of glucose and of at least one acid chosen from linoleic acid, oleic acid, palmitic acid and stearic acid, compositions, for example, cosmetic and pharmaceutical compositions, comprising this novel derivative, and their use for improving the condition of head hair and/or other hairs, and, for example, for reducing and/or impeding the loss of head hair and/or other hairs, and/or for inducing and/or stimulating hair growth, as well as a process for preparing O-acyl derivatives mainly in position 6 of glucose, comprising preparing a mixed anhydride by reacting a carboxylic acid with a trimethylacetyl halide, followed by reacting said mixed anhydride formed with glucose.

Jean-François Michelet

Papers

Androgenetic alopecia and microinflammation.

Activation of cytoprotective prostaglandin synthase-1 by minoxidil as a possible explanation for its hair growth-stimulating effect.

Prostaglandin metabolism in human hair follicle

Prostanoid receptors in anagen human hair follicles

Derivative of glucose and of vitamin F, compositions comprising it, uses and preparation process