The innermost cell layer of the outer root sheath is positive with Ki-67

Production of progenitor cells from primary human epithelial cell monolayer cultures

Primary keratinocytes derived from human epidermis are widely used in tissue engineering and regenerative medicine. An important aspect in clinical applications is the preservation of human skin keratinocyte stem cells. However, it is difficult to expand the number of human skin keratinocyte stem cells, which are undifferentiated and highly proliferative in culture by using standard cell culture methods. It is even more difficult to identify them, since universal specific markers for human skin keratinocyte stem cells have not been identified. In this paper, we show a method to produce a large number of primary progenitor human skin keratinocytes by using our novel culture techniques. Primary human skin keratinocyte monolayers are cultured using twice the volume of medium without serum and lacking essential fatty acids. Once the cells reach 70-80% confluence, they begin to float up into the overlying medium and are called "epithelial pop-up keratinocytes (ePUKs)" allowing the cells to be passaged without the use of trypsin. We analyzed the properties of ePUKs by cell size, cell viability, immunocytofluorescence biomarker staining, and cell cycle phase distribution by fluorescence-activated cell sorting (FACS). Our results showed that these ePUKs appear to be progenitor epithelial cells, which are small in size, undifferentiated, and have a high proliferative capacity. We believe that ePUKs are suitable for use in medical applications requiring a large number of primary human progenitor skin keratinocytes.

Potential involvement of the stem cell factor receptor c-kit in alopecia areata and androgenetic alopecia: histopathological, immunohistochemical, and semiquantitative investigations

Alopecia areata (AAR) and androgenetic alopecia (AGA) are two major forms of alopecia based on altered hair growth condition. In general, the cell cycle is regulated by several mechanisms including the stem cell factor/c-kit signaling. To assess a role for stem cell activity in alopecia, we performed histopathological, immunohistochemical, and semiquantitative analyses of c-kit as well as Ki-67 in scalp biopsy specimens obtained from 14 patients with AAR, 18 patients with AGA, and 6 age-matched control subjects, using the specific antibodies. Formalin-fixed, paraffin-embedded skin sections were examined. Immunoreactivities for Ki-67 and c-kit were localized in keratinocytes and melanocytes in the outermost layer of hair follicles. The mean length of hair follicles was significantly shorter in the AAR and AGA groups than in the control group. The mean number of Ki-67-immunoreactive cells per follicle was significantly reduced in the AAR and AGA groups as compared with the control group. The mean number of c-kit-immunoreactive cells per follicle was significantly increased in the AAR and AGA groups as compared with the control group. Our results indicate that c-kit is upregulated in the hair follicle cells in these forms of alopecia, and suggest that the upregulation reflects a negative feedback mechanism in response to possible downregulation of the ligand stem cell factor.

Effect of caffeine and testosterone on the proliferation of human hair follicles in vitro

BACKGROUND

Androgenetic alopecia (AGA) is a common problem in men of all ages, affecting approximately 50% at 50 years of age. The underlying cause is an androgen-dependent miniaturization of genetically predetermined hair follicles. Here, the hair organ culture model was used to investigate the effects of testosterone and caffeine; the latter being a promising candidate for hair growth stimulation.

METHODS

Hair follicles from 14 biopsies, taken from the vertex areas from male AGA patients, were cultivated for 120-192 h in vitro with normal William's E medium (control) or William's E medium containing different concentrations of testosterone and/or caffeine. Hair shaft elongation was measured daily and at the end of cultivation, cryosections of follicles were stained with Ki-67 to evaluate the degree and localization of keratinocyte proliferation.

RESULTS

Significant growth suppression was found in hair follicles treated with 5 microg/ml testosterone. This was counteracted by caffeine in concentrations of 0.001% and 0.005%. Moreover, caffeine alone led to a significant stimulation of hair follicle growth. These results were confirmed immunohistochemically by Ki-67 staining.

CONCLUSIONS

Androgen-dependent growth inhibition of ex vivo hair follicles from patients suffering from AGA was present in the human hair organ culture model, a constellation which may serve for future studies to screen new substances against androgen-dependent hair loss. Caffeine was identified as a stimulator of human hair growth in vitro; a fact which may have important clinical impact in the management of AGA.

The calcium-binding protein calretinin is a marker of the companion cell layer of the human hair follicle

BACKGROUND

Ultrastructural studies of the hair follicle show that the outer root sheath (ORS) does not consist of a homogeneous cell population. The innermost cell layer of the ORS, also called the companion layer, is a single cell layer closely associated with the Henle layer of the inner root sheath.

OBJECTIVES

To describe the immunohistochemical expression of calretinin, a calcium-binding protein, in the human hair follicle.

METHODS

Immunohistochemical studies using two different antisera to calretinin were performed in paraffin-embedded and in frozen scalp specimens using standard techniques.

RESULTS

Calretinin immunostaining was consistently and specifically found in the companion cell layer of hair follicles.

CONCLUSIONS

These findings provide further evidence to support the notion that the companion layer is not only morphologically, but also immunohistochemically, different from the other cells of the ORS.

Controls of hair follicle cycling

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 Chase as our model and tried to put the adult hair follicle growth cycle in perspective. We have tried to sketch the adult hair follicle cycle, as we know it today and what needs to be known. Above all, we hope that this work will serve as an introduction to basic biologists who are looking for a defined biological system that illustrates many of the challenges of modern biology: cell differentiation, epithelial-mesenchymal interactions, stem cell biology, pattern formation, apoptosis, cell and organ growth cycles, and pigmentation. The most important theme in studying the cycling hair follicle is that the follicle is a regenerating system. By traversing the phases of the cycle (growth, regression, resting, shedding, then growth again), the follicle demonstrates the unusual ability to completely regenerate itself. The basis for this regeneration rests in the unique follicular epithelial and mesenchymal components and their interactions. Recently, some of the molecular signals making up these interactions have been defined. They involve gene families also found in other regenerating systems such as fibroblast growth factor, transforming growth factor-beta, Wnt pathway, Sonic hedgehog, neurotrophins, and homeobox. For the immediate future, our challenge is to define the molecular basis for hair follicle growth control, to regenerate a mature hair follicle in vitro from defined populations, and to offer real solutions to our patients' problems.

Serpins in the human hair follicle

Proteinases and their inhibitors are very likely to function as mediators or regulators of the hair growth cycle. Very little information is currently available, however, regarding the specific inhibitors present in human hair follicles at defined stages of their growth cycle. In this study we have analyzed two proteinase inhibitors, plasminogen activator inhibitor type 2 and protease nexin 1, in human hair follicles using in situ hybridization and/or immunohistochemistry. Protease nexin 1 mRNA was found only in the mesenchymal population of the hair follicle, i.e., the follicular papilla cells, during the anagen but not the catagen phase. In contrast, plasminogen activator inhibitor type 2 was localized to several epithelial populations in the follicle: the more differentiated cells of the infundibulum; the companion layer in anagen follicles; and the single layer of outer root sheath cells directly abutting the club hair in telogen follicles. At least some of the plasminogen activator inhibitor type 2 in human follicles appears to be in the relaxed form, as evidenced by strong staining with an antibody that is specific for this form of the inhibitor. This suggests that plasminogen activator inhibitor type 2 interacts with and is cleaved by an endogenous follicular proteinase and supports a constitutive role for this inhibitor in human follicular epithelia.

Association of p63 with proliferative potential in normal and neoplastic human keratinocytes

p63, a recently identified member of the p53 gene family, encodes multiple products with transactivating, death-inducing, and dominant-negative activities. We show that in normal human epidermis, in hair follicles, and in stratified epidermal cultures, p63 protein is principally restricted to cells with high proliferative potential and is absent from the cells that are undergoing terminal differentiation. In normal human epidermis and in hair follicles, basal cells with abundant p63 are interspersed with cells with little or no p63. Whenever p63 mRNA is present, it encodes mainly truncated, potentially dominant-negative isotypes. In squamous cell carcinomas, the number of cells containing p63 and their distribution depends on the degree of anaplasia. In highly differentiated tumors, p63 is confined to a ring of basal-like cells surrounding, but at a distance from, centers of terminal differentiation. In less differentiated tumors, most cells contain p63 and their distribution is chaotic with respect to centers of terminal differentiation. p63 appears to be a valuable diagnostic marker for anaplastic keratinocytes.

Immunohistochemical investigation of the different developmental stages of trichofolliculoma with special reference to the Merkel cell

The morphologic features of trichofolliculoma are variable, reminiscent of the anagen, catagen, and telogen phases of a normal hair follicle in its cycle. We recently described an early, fully developed stage and late stages of trichofolliculoma. Using immunohistochemical examination, we sought to demonstrate hyperplasia of Merkel cells in all three stages of trichofolliculoma. We found this to be the most striking in small lesions of the late stage. The distribution of the Merkel cells in several stages of trichofolliculoma coincided with the known arrangement of normal follicular Merkel cells during the follicular cycle. However, antibodies against neurofilaments failed to detect innervated Merkel cells, in contrast to normal follicular Merkel cells. Antibodies against Ki67 did not reveal proliferative Merkel cells in any of the trichofolliculomas, but for unknown reasons, a distinct cytoplasmic staining of Merkel cell processes sometimes occurred. Nuclear Ki67 was strongly expressed in the nuclei of follicular keratinocytes of the fully developed trichofollicullomas, whereas those at a late stage showed a markedly decreased staining pattern. Our finding of Merkel cells in all trichofolliculomas underlines their classification as hamartomas with follicular differentiation. Hyperplasia of Merkel cells, even in trichofolliculomas at a late stage, as regressing lesions might implicate hitherto unknown regulatory functions of this neuroendocrine cell.

Analysis of apoptotic cell death in human hair follicles in vivo and in vitro

We analyzed changes of growth and apoptotic cell death in human hair follicles. In anagen hair follicles, terminal deoxynucleotidyltransferase-mediated deoxyuridine triphosphate-biotin nick labeling-positive cells were observed in the keratogenous zone of the upper bulb matrix, the inner root sheath, and the companion layer of the outer root sheath. DNA ladder formation was also detected in anagen hair follicles. In catagen hair follicles, the lower bulb matrix cells around the dermal papilla and the outer layer cells of the outer root sheath became strongly positive, showing that apoptosis in catagen hair is distinct from that in anagen hair. We also confirmed the mRNA expression of four caspases (caspase-1, caspase-3, caspase-4, and caspase-7) in anagen hair follicles by reverse transcriptase-polymerase chain reaction and in situ hybridization. When human anagen hair follicles were cultured in the presence of transforming growth factor-beta or tumor necrosis factor-alpha in the serum-free medium, transforming growth factor-beta but not tumor necrosis factor-alpha induced catagen-like morphologic changes, which were indistinguishable from normal catagen hair follicles. Tumor necrosis factor-alpha, however, strongly inhibited the elongation of the hair shaft in a dose-dependent manner, accompanied by abnormal morphology and increased cell death in the bulb matrix cells. Our results suggest that apoptosis in hair follicles involves two different types. One is related to the terminal differentiation of follicular epithelial cells in anagen hair. The other occurs as a major driving force to eliminate the distinct portion of epithelial components in catagen hair. Furthermore, this study strongly indicates that the transforming growth factor-beta pathway is involved in the induction of catagen phase in human hair cycle.

A novel human type II cytokeratin, K6hf, specifically expressed in the companion layer of the hair follicle

In an attempt to identify new members of the human type II hair keratin family by means of 3'- and 5'-RACE methods and cDNA from anagen hair follicles, we detected a sequence that encoded a hitherto unknown type II cytokeratin. The novel cytokeratin comprises 251 amino acids and exhibits the highest sequence homology with K5. Comparative one- and two-dimensional western blots of keratins from anagen hair bulbs, containing or not containing the outer and inner root sheaths (ORS/IRS), and from footsole epidermis with an antibody against the new cytokeratin, revealed its comigration with K6 and its expression in the ORS/IRS complex. We have therefore named the new cytokeratin K6hf, to distinguish it from the various K6 isoforms and to indicate its expression in the hair follicle. Both in situ hybridization with a K6hf-specific cRNA probe and indirect immunofluorescence with the K6hf antibody showed that K6hf is exclusively expressed in the so-called "companion layer" of the hair follicle, a single layered band of flat and vertically oriented cells between the cuboidal ORS cells and the IRS that stretches from the lowermost bulb region to the isthmus of the follicle. Concomitant K17 and K16 expression studies showed that besides suprabasal ORS cells, these cytokeratins are sequentially expressed subsequent to K6hf in companion cells above the hair bulb. Our study confirms the view of a vertically oriented companion layer differentiation. The clearly delayed K17 and K16 expression relative to that of K6hf in companion cells most probably excludes these keratins as possible type I partners of K6hf and suggests the existence of a still unknown type I partner of its own. Thus, not only morphologically but also biochemically, the companion layer is different from the ORS and can therefore be regarded as an independent histologic compartment of the hair follicle.

The innermost cells of the outer root sheath in human anagen hair follicles undergo specialized keratinization mediated by apoptosis

The innermost cell layer of the outer root sheath (IORS) is a special single cell layer located just outside Henle's layer. In situ end-labeling immunohistochemistry for apoptosis showed that labeled cells were most consistently located in the IORS from the suprabulbar portion to the infundibulum of anagen terminal hair follicles of the human scalp. Labeled cells were also sparsely scattered in the middle portion, including the bulge area of the outer root sheath of anagen hair, the regressing lower portion of catagen hair and the bulb of telogen hair. Ultrastructurally, the cells of the innermost layer underwent cellular degeneration through cytoplasmic vacuolization and nuclear pyknosis without keratohyalin production. These were compatible with the morphology of apoptotic cells. These findings confirmed that the innermost cell layer is different from other layers of the outer root sheath, not only by previously demonstrated criteria such as Ki67 immunostainability and characteristic ultrastructure but also by the mode of cell death.

Histochemistry of the human hair follicle

Immunohistochemistry of the human hair follicle is of increasing interest in hair research. The data on antigen distribution in the different epithelial and mesenchymal structures of this unique skin appendage are superfluous now. In the present chapter, I will concentrate on selected aspects related to hair follicle differentiation, epithelial-mesenchymal interactions, proliferation and metabolic activity. Hair diseases are common. Not unusually, hair growth and structure reflect systemic disturbances. Basic knowledge of hair anatomy and histochemistry is required for their rational evaluation. Immunohistochemistry is a valuable tool for microanatomy of the hair apparatus. It offers a link between the biochemical data and structural components of hair follicles, which may help to better understand physiology of hair growth and hair diseases.

Expression of a cell-cycle-associated nuclear antigen (MIB 1) in cholesteatoma and auditory meatal skin

Middle ear cholesteatoma is often invasive with consequent bone destruction. Inflammatory stimulation of the underlying connective tissue, as well as an autocrine mechanism, may be responsible for the dysregulation and abnormal proliferative features of the keratinocytes in cholesteatoma. Comparative investigations were performed to assess the epithelial cell kinetics of cholesteatoma and normal auditory meatal skin. Monoclonal antibody MIB 1 immunostaining (which recognizes a nuclear antigen expressed by dividing cells) was applied using the alkaline phosphatase antialkaline phosphatase immunolabeling method. Specimens of normal auditory meatal skin (n = 7) revealed an average MIB 1 score (quotient of the MIB 1-positive cells and the total number of cells) of 7.6 +/- 2.2%. Cholesteatoma samples (n = 13) showed an average MIB 1 score of 17.4 +/- 8.9% and a heterogeneity of proliferating epithelial areas. Epithelial cones growing toward the underlying stroma exhibited high mitotic activity. Statistically, the results of this study confirm a highly significant increase in the proliferation rate of cholesteatoma keratinocytes, which had an MIB 1 score that was 2.3 times higher than the score for keratinocytes of normal external auditory meatal skin.

Association of basonuclin with ability of keratinocytes to multiply and with absence of terminal differentiation

Basonuclin is a protein possessing three pairs of zinc fingers and a nuclear localization signal. Expression of the gene is largely confined to keratinocytes of stratified squamous epithelia and hair follicles. In the epidermis and in stratified epidermal cultures, basonuclin is present in the nuclei of cells in or close to the basal layer but not in the nuclei of cells in more superficial layers. The Ki-67 protein, a nuclear marker for any stage of the multiplication cycle is present in only a subclass of basonuclin-containing cells. In cultured keratinocytes, the disappearance of basonuclin mRNA is associated with loss of colony-forming ability and the appearance of mRNA for involucrin, a protein characteristic of terminal differentiation. In hair follicles, the largest reservoir of basonuclin-containing cells is the outer root sheath, which contains precursors of differentiated cells of the hair shaft and of the epidermis. Basonuclin is not a cell cycle marker but is likely instead to be a regulatory molecular whose presence in the keratinocyte is linked to the maintenance of proliferative capacity and prevention of terminal differentiation.

QBEND/10 (anti-CD34 antibody) in external root sheath cells and follicular tumors

The human hematopoietic progenitor cell antigen (CD34) is a cell surface protein expressed by human hematopoietic progenitor cells, vascular endothelium, and many mesenchymal tumors. Sections from six samples of normal skin and from 41 epithelial tumors of the skin were studied. Immunostaining of epithelial cells from the external root sheath below the attachment of the arrector pili muscle and above the matrix cells was noted in normal samples. Tumors derived from or differentiated toward cells of the outer sheath, especially trichilemmomas, were immunostained with QBEND/10 (anti-CD34 antibody), whereas other epithelial tumors studied were negative. CD34 could serve as a marker of outer sheath cell derivation and may well be of value in the distinction between trichilemmomas and other lesions with similar histopathological features.

Current topics of immunohistochemistry as applied to skin tumors

Suppressor oncogene p53 is expressed more frequently in the nodular portion than the superficial spreading portion of the same melanoma. PCNA expression follows the same pattern but it is strongly expressed already in the superficial spreading portion. CD34 is found to label dermatofibrosarcoma protuberans. There is the mixture of negative strands but the immunostains are predominantly positive in the three cases studied. Neurogenic tumors are reactive but the intensity of staining is only moderate. Fibrous histiocytoma, dermatofibroma and other fibrohistiocytic tumors are non-reactive. CD34 is expressed in the outer root sheath of hair follicle below the sebaceous gland level. A case of piloepidermal cyst is CD34 positive. CD34 is expressed in vascular endothelial cells; not only hemangiomas but also lymphangiosarcoma is CD34 positive. A case of indeterminate cell histiocytosis following scabies and superficial variant of clear cell sarcoma are discussed as examples of new entities.

Histochemistry of the human hair follicle with consideration of anagen phases I to VI

The hair follicle is composed of different epithelial layers under participation of mesenchymal and nerval factors. The present study is an attempt to localize differentiation and functional markers in the human hair follicle during anagen phases I to VI. Monoclonal antibody K 8.12 against keratins 13 and 16 showed an increasing reactivity with certain types of the follicle epithelia during anagen I to VI. Ki67 was expressed within the innermost layer of the outer hair root sheath. Scattered Ki67-positive matrix cells could be additionally identified during anagen V and VI but were absent in anagen I to IV. During anagen Merkel cells became more abundant in the bulbar area. Neuropeptide-like immunoreactivity expressed by bulbar (especially matrix) cells were evenly seen during the early anagen I and II. The findings are in favour of a neurohumoral modulatory role during anagen phases accompanied by an increase of expression of certain proliferation-associated antigens like keratin 16 and Ki67 among the complex epithelia of human hair follicles.

Histochemistry of the porcine pilosebaceous unit

The present study describes lectin and immunoreactivity in the pilosebaceous unit of porcine skin. Complex carbohydrates of mucin and biantennary Man/Gluc types were distributed among hair follicle epithelia (hair root sheaths, cuticula, shaft, and shaft matrix). Sebaceous glands expressed biantennary Man/Gluc carbohydrates and GalNAc residues. The expression of simple-type and epidermis-like keratins was confirmed by immunohistochemistry with monoclonal antibodies. Filaggrin-positive cells were found in the keratinizing zone of Henle's layer in anagen follicles. The innermost layer of the outer hair root sheath was stained with antibodies against the epidermal growth factor-receptor, keratin 10 and Ki67 antigen. The differences to humans were remarkably small.