Follicle Abnormalities Research Articles

Transglutaminase 3: The Involvement in Epithelial Differentiation and Cancer.

Transglutaminases (TGMs) contribute to the formation of rigid, insoluble macromolecular complexes, which are essential for the epidermis and hair follicles to perform protective and barrier functions against the environment. During differentiation, epidermal keratinocytes undergo structural alterations being transformed into cornified cells, which constitute a highly tough outermost layer of the epidermis, the stratum corneum. Similar processes occur during the hardening of the hair follicle and the hair shaft, which is provided by the enzymatic cross-linking of the structural proteins and keratin intermediate filaments. TGM3, also known as epidermal TGM, is one of the pivotal enzymes responsible for the formation of protein polymers in the epidermis and the hair follicle. Numerous studies have shown that TGM3 is extensively involved in epidermal and hair follicle physiology and pathology. However, the roles of TGM3, its substrates, and its importance for the integument system are not fully understood. Here, we summarize the main advances that have recently been achieved in TGM3 analyses in skin and hair follicle biology and also in understanding the functional role of TGM3 in human tumor pathology as well as the reliability of its prognostic clinical usage as a cancer diagnosis biomarker. This review also focuses on human and murine hair follicle abnormalities connected with TGM3 mutations.

Mechanisms regulating follicle selection in ruminants: lessons learned from multiple ovulation models.

Selection of a single dominant follicle from a cohort of growing follicles is a unique biological process, a key step in female reproductive function in monovular species, and lies at the core of reproductive technologies in cattle. Follicle growth and the number of follicles that ovulate are regulated by precise endocrine, paracrine, and autocrine mechanisms. Most of our current understanding about follicle selection focuses on the role of FSH, LH, and the IGF family in follicle growth and selection of the dominant follicle. However, more recently the role of members of the TGF-ß family has been highlighted, particularly in high fecundity genotypes in sheep. Intercellular signaling between the oocyte and granulosa cells (GC) regulates proliferation and differentiation due to actions of bone morphogenetic protein 15 (BMP15) and growth and differentiation factor 9 (GDF9) within the follicle. Mutations that either knockout or reduce the activity of BMP15 or GDF9 have been found to increase ovulation rate in heterozygotes and generally cause severe follicle abnormalities in homozygotes. A mutation in the intracellular kinase domain of the BMPR1B receptor (Booroola fecundity gene) increases ovulation rate in heterozygotes with further increases in ovulation in homozygotes. The physiological mechanisms linking these mutations to increased ovulation rates are still not well defined. A recently identified high fecundity bovine genotype, Trio, causes increased expression of SMAD6, an intracellular inhibitor of the BMP15/GDF9 signalling pathways. This bovine model has provided insights into the mechanisms associated with selection of multiple dominant follicles and multiple ovulations in carriers of fecundity alleles. The present review focuses on the mechanisms involved in follicle selection in ruminants with a special emphasis on the contribution made by multiple ovulation models in both cattle and sheep. The evaluation of multiple ovulation models in ruminants has allowed us to construct a new physiological model that relates changes in the BMP15/GDF9 signalling pathways to the physiological changes that result in selection of multiple dominant follicles. This model is characterized by acquisition of dominance at a smaller follicle size but at a similar time in the follicular wave with multiple follicles acquiring dominance in a hierarchal sequence, delaying FSH suppression and, thus allowing additional follicles to continue to grow and acquire dominance.

Dermoscopic patterns of common facial inflammatory skin diseases

Several common inflammatory dermatoses, such as rosacea, seborrheic dermatitis (SD), discoid lupus erythematosus (DLE) and granulomatous skin diseases manifest as erythematous macules or plaques on the facial skin. Although clinical examination represents the cornerstone of diagnosis, the broad variety of clinical features and uncommon presentations of these diseases may cause at times diagnostic and therapeutic uncertainty. Dermoscopy, in addition to its well-documented value in evaluation of skin tumours, is continuously gaining appreciation also in the field of general dermatology. To describe and compare the dermoscopic patterns of common facial inflammatory skin diseases including SD, erythematotelangiectatic rosacea (ER), sarcoidosis, lupus vulgaris (LV), DLE and granuloma faciale (GF). Dermoscopic images of lesions from patients with histopathologically confirmed diagnosis of SD, ER, sarcoidosis, LV, DLE or GF were retrospectively evaluated for the presence of several criteria. Selection of the dermoscopic variables included in the evaluation process was based on the data available in the literature and on our preliminary observations. One hundred and fifteen dermoscopic images were included in the study. SD was dermoscopically characterized by dotted vessels and yellow scales, whereas ER was typified by a characteristic pattern of vascular polygons. Sarcoidosis and LV very commonly exhibited orange-yellowish areas and linear branching vessels. Features related to follicle abnormalities and linear branching vessels were the most common dermoscopic criteria of DLE and GF. This study provides new insights into the dermoscopic variability in common facial inflammatory dermatoses.

Dlx3 is a crucial regulator of hair follicle differentiation and cycling

Dlx homeobox transcription factors regulate epidermal, neural and osteogenic cellular differentiation. Here, we demonstrate the central role of Dlx3 as a crucial transcriptional regulator of hair formation and regeneration. The selective ablation of Dlx3 in the epidermis results in complete alopecia owing to failure of the hair shaft and inner root sheath to form, which is caused by the abnormal differentiation of the cortex. Significantly, we elucidate the regulatory cascade that positions Dlx3 downstream of Wnt signaling and as an upstream regulator of other transcription factors that regulate hair follicle differentiation, such as Hoxc13 and Gata3. Colocalization of phospho-Smad1/5/8 and Dlx3 is consistent with a regulatory role for BMP signaling to Dlx3 during hair morphogenesis. Importantly, mutant catagen follicles undergo delayed regression and display persistent proliferation. Moreover, ablation of Dlx3 expression in the telogen bulge stem cells is associated with a loss of BMP signaling, precluding re-initiation of the hair follicle growth cycle. Taken together with hair follicle abnormalities in humans with Tricho-Dento-Osseous (TDO) syndrome, an autosomal dominant ectodermal dysplasia linked to mutations in the DLX3 gene, our results establish that Dlx3 is essential for hair morphogenesis, differentiation and cycling programs.

Smad4-dependent desmoglein-4 expression contributes to hair follicle integrity

We have previously shown that keratinocyte-specific deletion of Smad4, a TGFβ/Activin/BMP signaling mediator, results in a progressive alopecia. To further assess the molecular mechanisms of Smad4 loss-mediated alopecia, we examined expression levels of key molecules associated with hair follicle differentiation in Smad4-deleted skin. Among them, Desmoglein 4 (Dsg4) was down-regulated in Smad4-deleted skin prior to the onset of hair follicle abnormalities with gradual depletion coinciding with hair follicle degeneration. Chromatin immunoprecipitation (ChIP) assay showed that Smad4, together with the BMP mediators Smad1 and Smad5, but not the TGFβ/Activin mediators Smad2 or Smad3, bound to the Smad Binding Element (SBE) of the Dsg4 promoter. A Dsg4 reporter assay revealed that Smad4 was required for the maximal transactivation of Dsg4 in cooperation with Smad1 and Smad5. Mutating the SBE of the Dsg4 promoter abrogated Smad4 transactivation of Dsg4. Furthermore, BMP ligands, but not ligands of TGFβ and Activin, induced endogenous Dsg4 expression. Our data demonstrate that in the presence of Smad4, BMP signaling participated in transcriptional regulation of Dsg4. Thus, Smad4 loss-associated Dsg4 depletion contributed, at least in part, to hair follicles degeneration in Smad4 deficient skin.

The targeted overexpression of a Claudin mutant in the epidermis of transgenic mice elicits striking epidermal and hair follicle abnormalities

Skin is one of the largest organs of the body, and is formed during development through a highly orchestrated process involving mesenchymal-epithelial interactions, cell commitment, and terminal differentiation. It protects against microorganism invasion and UV irradiation, inhibits water loss, regulates body temperature, and is an important part of the immune system. Using transgenic mouse technology, we have demonstrated that Claudin (Cldn)-containing tight junctions (TJs) are intricately involved in cell signaling during epidermal differentiation and that an epidermal suprabasal overexpression of Cldn6 results in a perturbed epidermal terminal differentiation program with distinct phenotypic abnormalities. To delineate the role of the Cldn cytoplasmic tail domain in epidermal differentiation, we engineered transgenic mice targeting the overexpression of a Cldn6 cytoplasmic tail-truncation mutant in the epidermis. Transgenic mice were characterized by a lethal barrier dysfunction in addition to the existence of hyperproliferative squamous invaginations/cysts replacing hair follicles. Immunohistochemical analysis revealed an epidermal cytoplasmic accumulation of Cldn6, Cldn11, Cldn12, and Cldn18, downregulation of Cldn1 and aberrant expression of various classical markers of epidermal differentiation; namely the basal keratins as well as K1, involucrin, loricrin, and filaggrin. Collectively these studies suggest an important role for Cldns in epidermal/hair follicle differentiation programs likely involving cross talk to signaling pathways (e.g., Notch) directing cell fate selection and differentiation.

An overview on congenital alopecia in domestic animals

Alopecia, that is, lack of hair in any quantity, is a frequent complaint of pet owners. Although mostly acquired, rare congenital forms of alopecia exist that are associated with abnormalities in hair follicle morphogenesis. Congenital alopecias can result in changes in quality or quantity of hair follicles and the hair fibres produced by them. They vary in terms of clinical presentation and mode of inheritance. Histopathology is usually needed in order to differentiate between a reduced number of otherwise normal hair follicles and qualitative hair follicle abnormalities. Although our understanding of the molecular mechanisms that drive hair follicle morphogenesis in mice and humans has significantly increased during the last decade, still very little is known about congenital alopecias in domestic animals. Because of their rarity and the general lack of knowledge about their pathophysiology, classification of congenital alopecias in domestic animals is still unsatisfactory. This article reviews hair follicle morphogenesis and its most important molecular mechanisms, and it discusses the various forms of congenital alopecia occurring in domestic animals that have been described in the literature, differentiating between hair follicle aplasia, hair follicle dysplasia (i.e. defects associated with hair follicle development and defects associated with hair shaft formation), and neuroectodermal dysplasias, the latter involving the hair follicle pigmentary system.

Injections of osteoprotegerin and PMA delay tooth eruption

Tooth eruption requires alveolar bone resorption that is regulated by the dental follicle. This is reflected by the fact that failures of eruption often can be traced to either osteoclast deficiencies or to dental follicle abnormalities. To achieve maximal osteoclastogenesis and subsequent alveolar bone resorption for eruption, we have hypothesized that a reduction in gene expression of osteoprotegerin (OPG) in the follicle of the first mandibular molar of the rat at Day 3 is needed. To determine if OPG affects eruption, postnatal rats were injected with varying concentrations of OPG from Days 1-9 postnatally. Such studies indicated that the eruption time of the first mandibular molar was significantly delayed by 1 day or more as a result of OPG injection. Injection of phorbolmyristate acetate (PMA), an activator of protein kinase C (PKC) that in turn upregulates OPG expression, also delayed eruption by 1 day. PMA was only injected from Days 1-4 such that PKC-alpha would be increased and activated. Previous studies had shown that PKC-alpha gene expression is downregulated at the time (Day 3) that OPG expression is downregulated. In this study, using reverse transcription polymerase chain reaction techniques to examine OPG gene expression showed that PMA injection increased OPG gene expression in the dental follicle at Day 3 as compared to the controls. Thus, either injecting OPG or enhancing its expression in the follicle at Day 3 by injecting PMA delays the time of tooth eruption. Consequently, regulation of OPG production by the dental follicle likely affects the alveolar bone resorption needed for tooth eruption.

P‐41 Psychogenic alopecia by fur‐plucking in a family of seal‐point Siamese cats: three cases

Three seal‐point Siamese cats (phenotype = SIA n), from the same line of breeding, displayed fur‐plucking of the dorsum. Feline psychogenic alopecia is an anxiety neurosis. In these cats, fur‐plucking is an excessive grooming behaviour leading to fur hyperpigmentation. The first case was a 3‐year‐old intact female that had been fur‐plucking from 6 months of age. She was the offspring of the mating of a lilac‐point male (SIA a) and a SIA n female. The cat was treated with depomedrol and Viacutan® without effect. The second case was a 3‐year‐old castrated male that had been fur‐plucking from 9 months of age. He was treated with megestrol acetate with moderate effect. The third case was a 1‐year‐old intact female that had been fur‐plucking from 6 months of age and was the offspring of the first case and a male chocolate point (SIA b). She was treated with depomedrol and Viacutan® without effect. None of the littermates with other phenotypes (4 SIA a) had dermatological complaints. All affected cats underwent a full evaluation including dermatophyte testing (negative), ectoparasite tests (negative) and intradermal tests (negative). An 8‐week food elimination trial followed by a 3‐week challenge had no effect. Histopathology revealed a mild mononuclear superficial perivascular dermatitis and perifolliculitis. There were no morphological hair or hair follicle abnormalities. A diagnosis of feline psychogenic alopecia was made on the basis of exclusion. The finding of feline psychogenic alopecia in three closely related cats suggests that the disorder may be hereditary or have an inherited component. Funding: Kruuse A/S Denmark.

Alopecia in the horse - an overview.

Dr Stannard explains different forms of alopecia in the horse with emphasis on the hair follicle and its function in the production of hairs. Both normal and abnormal patterns of hair growth and shedding in the horse are reviewed. Overviews of several specific hair follicle abnormalities, both inflammatory and noninflammatory, are discussed in detail with their clinical relevance. Some of the clinical entities covered in this section (linear alopecia and alopecia areata) are caused by immunological attack against normal structures and could have been placed in Immunologic diseases. However, because the clinical presentation for these entities is alopecia, Dr Stannard chose to include them in his notes on alopecia. Other inclusions in this section include cutaneous bacterial infections (e.g. pastern folliculitis and dermatophilosis) as well as fungal infections of the hair (dermatophytosis).

Skin and hair follicle integrity is crucially dependent on β1 integrin expression on keratinocytes

beta 1 integrins are ubiquitously expressed receptors that mediate cell-cell and cell-extracellular matrix interactions. To analyze the function of beta1 integrin in skin we generated mice with a keratinocyte-restricted deletion of the beta 1 integrin gene using the cre-loxP system. Mutant mice developed severe hair loss due to a reduced proliferation of hair matrix cells and severe hair follicle abnormalities. Eventually, the malformed hair follicles were removed by infiltrating macrophages. The epidermis of the back skin became hyperthickened, the basal keratinocytes showed reduced expression of alpha 6 beta 4 integrin, and the number of hemidesmosomes decreased. Basement membrane components were atypically deposited and, at least in the case of laminin-5, improperly processed, leading to disruption of the basement membrane and blister formation at the dermal-epidermal junction. In contrast, the integrity of the basement membrane surrounding the beta 1-deficient hair follicle was not affected. Finally, the dermis became fibrotic. These results demonstrate an important role of beta 1 integrins in hair follicle morphogenesis, in the processing of basement membrane components, in the maintenance of some, but not all basement membranes, in keratinocyte differentiation and proliferation, and in the formation and/or maintenance of hemidesmosomes.

Conditional expression of the ErbB2 oncogene elicits reversible hyperplasia in stratified epithelia and up-regulation of TGFalpha expression in transgenic mice.

The ErbB2 receptor tyrosine kinase (RTK) is expressed in basal cells of squamous epithelia and the outer root sheath of hair follicles. We previously showed that constitutive expression of activated ErbB2 directed to these sites in the skin by the keratin 14 (K14) promoter produces prominent hair follicle abnormalities and striking skin hyperplasia in transgenic mice. However, perinatal lethality precluded the establishment of a transgenic line for analysis of ErbB2 function in adult animals. To investigate the significance of ErbB2 signaling in epithelial tissues during and post development, we developed a K14-rtTA/TetRE-ErbB2 'Tet-On' bitransgenic mouse system. These mice were normal until the ErbB2 transgene was induced by exposure to doxycycline (Dox). Prenatal induction resulted in perinatal death. Postnatally, ErbB2 transgene expression was observed at 4 h after the initiation of Dox, and reached a plateau at 24 h. Skin hyperplasia followed after 2 days and these changes reverted to normal upon Dox withdrawal. In adults, as in the neonates, prolonged ErbB2 induction caused prominent skin and hair follicle hyperplasias. Severe hyperplasias in the cornea, eye lids, tongue and esophagus were also observed. ErbB2 transgene induction was accompanied by increased expression of TGFalpha, a ligand of epidermal growth factor receptor (EGFR), and to a lesser extent, EGFR, further enhancing RTK signal transduction. We conclude that ErbB2 plays important roles in both development and maintenance of hair follicles and diverse squamous epithelia and that this ligand-inducible and tissue-specific 'Tet-On' transgenic mouse system provides a means to study transgenes with perinatal toxicity.

Follicle abnormalities and fibre shedding in Merino weaners fed different levels of nutrition

A study was conducted to examine the relationship between fibre shedding and staple strength in Merino weaners genetically different in staple strength and fed different levels of nutrition. Fibre shedding at the point of break along the staple was estimated using 3 different techniques: (i) a subjective scoring system of wool follicle activity, based on their morphology in transverse skin sections; (ii) the number of fibres with club-ends after differential staining to identify remnants of the shed-follicle bulb; and (iii) changes in the number of fibres in the cross-section along individual staples. Irrespective of the technique used, the estimated proportion of shed fibres did not differ significantly between the sheep bred for sound and tender wool, but increased significantly (P < 0·05) in response to adverse nutritional conditions. Across all treatments, there was a significant (r2 = 0·63; P < 0·001) correlation between the proportion of shutdown follicles and the percentage decrease in the number of fibres in the staple cross-section, although the average difference between the techniques was 11·5%. Both techniques indicated that, on average, about 30% of the total follicle population became inactive and shed their fibre under the most adverse nutritional conditions, and that this was as high as 50–60% for some individual sheep. Neither of these techniques was closely correlated to the proportion of fibres with club-ends (r2 = 0·15 and 0·20, respectively; P < 0·01). The proportion of shutdown follicles and the percentage decrease in the number of fibres in the staple cross-section explained 54% and 52% of the variance in staple strength, respectively, compared with only 19% explained by the percentage of fibres with club-ends at the point of break. However, as fibre shedding failed to remove any variance in staple strength additional to that already attributed to along- and between-fibre changes in diameter, it is concluded that fibre shedding per se does not contribute significantly to nutritional-induced differences in staple strength.

Influence of dietary lysine content on wool follicle function in pre-ruminant lambs

SUMMARYWool follicles and fibres of pre-ruminant lambs abomasally fed isoenergetic diets with daily amounts of lysine ranging from 0·12 to 1·94 g/(kg live weight)0·75were examined by light and electron microscopy. In lambs which receivedca.0·9 g lysine/kg0·76daily, the follicles appeared normal, whereas in those which received less than 0·9 g lysine/kg0·75daily several follicle abnormalities developed and the percentages of follicles affected increased as the amount of lysine was decreased. These abnormalities included the formation of autophagic vacuoles (or apoptotic bodies) in follicle bulb cells, and retarded and incomplete keratinization of the wool fibres, which led to the kinking of fibres at the mid-dermal level and gross distortion and partial degradation of fibres in the distal parts of follicles with thickened outer root sheaths. Following the introduction of a low-lysine diet, autophagic vacuoles developed in most follicle bulbs within 24 h. Impaired keratinization and kinking of fibres were evident in increasing proportions of follicles after 2 days, and gross distortion of fibres after 3–4 days. When the lambs were returned to a diet with adequate lysine recovery of normal follicle structure followed a similar time pattern, except that gross distortion of fibres persisted in the distal parts of some follicles for longer than 1 week. In some lambs given more than 0·9 g lysine/kg0·75daily a small percentage of follicles had short keratogenous zones. Clumping of fibres, which occurred in the proximal parts of a small number of follicles, was unrelated to the amount of lysine in the diet.

Observations on the wool follicle abnormalities in Merino sheep exposed to prolonged wetting conducive to the development of fleece-rot

Groups of sheep found to be resistant and susceptible to fleece-rot following prolonged periods of natural and experimental rainfall were used in a preliminary study of the histopathological changes associated with the development of this condition. Wool follicle abnormalities affecting the growth of the wool fibre and inner root sheath were frequently observed. Weakened stretches of fibres, which appeared to result from impaired keratinization, were the sites of fibre breakage in the skin. Hypertrophic thickening and duplication of the inner root sheath occurred, and this material encased the proximal ends of broken fibres to form 'plugs'. The plugs grew vigorously in sheep that developed fleece-rot, apparently breaking the continuity of the skin as they emerged into the fleece. Fragments of plugs, broken wool fibres and exudate were present in fleece-rot bands along with cornified epithelial cells. Attempts to quantify the frequency of these abnormalities were complicated by marked variations in their horizontal and vertical distributions in the skin.

A survey of the follicle populations in a range of British breeds of sheep

Details are given of the S/P follicle ratios of a number of British breeds of sheep. These are discussed in relation to the figures of different authors for other breeds. Figures are given for the incidence of fibre shedding and follicle abnormalities, and evidence is presented which suggests that, at any rate in British breeds, follicles are formed after birth and it is suggested that the number formed may be roughly constant in all breeds. There is an appendix describing statistical treatment of the question of follicle competition.