c-Myc expression in human anagen hair follicles

The expression and role of c-Myc in mouse hair follicle morphogenesis and cycling

Although the function of c-Myc has been clarified in many tissues, until now its expression and role in hair follicle morphogenesis and the hair cycle remains unknown. In this study we detected c-Myc expression pattern in the process of mouse hair follicle development and normal cycle. We found that during hair follicle morphogenesis, the stage-specific expression of c-Myc was detected in mouse skin and was predominantly localized to the hair follicle epithelium. c-Myc expression was also consistently found in mouse skin throughout the hair follicle cycle. Through the in vivo injection of c-Myc inhibitory peptide and c-Myc expression plasmid, we also investigated the direct effects of c-Myc on the hair follicle structures during the hair follicle cycle. Our results showed that c-Myc inhibitory peptide significantly restrained the development of anagen hair follicles, while the injection of plasmid DNA encoding c-Myc in vivo clearly promoted anagen development. Our data indicate that c-Myc may play an important role in the proliferation and differentiation of the hair follicle keratinocytes during hair follicle development. c-Myc also was shown to participate in the regulation of the mouse hair growth cycle and could promote the proliferation of the hair matrix keratinocytes as well as the differentiation of the inner root sheath.

Differential expression of stem-cell-associated markers in human hair follicle epithelial cells

Several putative biomarkers have been suggested for identifying murine follicular stem cells; however, human hair follicles have a different pattern of biomarker expression, and follicular stem cell isolation methods have not been established. To isolate a stem cell population applicable to clinical settings, we conducted a comprehensive survey of the expression of stem-cell-associated (K15, CD200, CD34, and CD271) and other biomarkers (K1, K14, CD29, and CD49f) in immunohistological sections of the human epidermis and follicular outer root sheath (ORS). We also examined freshly isolated and cultured epidermal or follicular cells with single- and multicolor flow cytometry or immunocytochemistry. After sorting cells by CD200, CD34, and forward scatter (FSC) values (cell size), colony-forming assays were performed. We found that biomarkers were differentially expressed in the epidermis and ORS. Basal bulge cells were mainly K15+CD200+CD34(-)CD271(-), and suprabasal cells were K15(-)CD200+CD34(-)CD271(-). We categorized follicular cells into nine subpopulations according to biomarker expression profiles. The CD200+CD34(-) bulge cells had much higher colony-forming abilities than the CD34+ population, and were divided into two subpopulations: a CD200+CD34(-)FSC(high) (K15-rich, basal) and a CD200+CD34(-)FSC(low) (K15-poor, suprabasal) population. The former formed fewer but larger-sized colonies than the latter. Follicular epithelial cell cultivation resulted in loss of K15, CD200, CD34, and CD271 expression, but maintenance of K14, CD29, and CD49f expression. We found that the bulge contained two populations with different localizations, cell sizes, and colony-forming abilities. We showed that K15, CD200, CD34, and CD271 were useful biomarkers for characterizing freshly isolated human follicular epithelial cells in diverse stages of differentiation.

Properties and histochemical application of a novel antibody against trichohyalin granules

We obtained an antibody, anti-inner root sheath cells antibody (anti-IRSC Ab), that reacted with the inner root sheath (IRS) cells especially trichohyalin granules (THG). In order to compare the properties of anti-IRSC Ab and AE15, which is a specific monoclonal antibody against THG, histochemical and biochemical examinations were performed. In vivo localization with anti-IRSC Ab and AE15 indicated that both antibodies reacted with THG, but anti-IRSC Ab reacted with THG in the suprabulbar region of the Huxley layer, whereas AE15 reacted with THG in the suprabulbar region and upper bulbar portion of the Huxley layer, as shown by immunohistochemical and immunoelectron microscopic analyses. The results of immunoblot analysis showed that anti-IRSC Ab reacted with a protein spot at 45 kDa, pI 6.5, but AE15 reacted with high molecular weight proteins at pI 5.5. Furthermore, anti-IRSC Ab reacted with specimens of squamous cell carcinoma (SCC) but did not react with those of basal cell carcinoma (BCC). In contrast, AE15 reacted with neither SCC nor BCC. These findings suggest that anti-IRSC Ab and AE 15 recognized different component proteins in THG, and therefore indicated that THG, like as keratohyalin granules, might consist of several proteins. It is the novel finding that the anti-IRSC Ab positive substance in THG in the normal hair and SCC cells.

Desmocollin 1 expression and desmosomal remodeling during terminal differentiation of human anagen hair follicle: an electron microscopic study

The terminal differentiation (TD) program of keratinocytes of the human hair follicle (HF) occurs with specific temporal and spatial features in the various layers of the inner root sheath (IRS) and in the innermost layer of the outer root sheath (companion layer). This process is characterized by complex nuclear and cytoplasmic morphological changes, accompanied by profound modifications in intercellular junctions. As no correlation exists between the structure and the molecular composition of desmosomes during TD of the IRS/companion unit, the aim of our study was to investigate by transmission electron microscopy the remodeling of desmosomes in keratinizing cells of these compartments. By immunogold post embedding technique, we studied in anagen HFs the modulation of the synthesis of desmocollin 1 (Dsc1), a transmembrane glycoprotein specifically synthesized in the IRS and in the companion layer. Dsc1 immunoreactivity was actually confined to these compartments and tended to increase just before the level of TD, particularly in the Henle's layer and in the IRS cuticle. In Huxley's layer, the immunolabeling was patchy and in the companion layer Dsc1 synthesis was detected above the level of keratinization of Huxley's layer. In the whole IRS, concomitantly with TD, there was an abrupt and almost complete disappearance of Dsc1 synthesis. An asymmetric distribution of Dsc1 was noticed (i) between cells at different stages of differentiation and (ii) between cells belonging to layers with different spatial/temporal features of TD. Our results show that the ultrastructural modifications of desmosomes during TD of HF are paralleled by the modulation of the synthesis of desmocollin 1.

Evidence that Myc activation depletes the epidermal stem cell compartment by modulating adhesive interactions with the local microenvironment

Activation of Myc (c-Myc) causes epidermal cells to exit the stem cell compartment and differentiate into sebocytes and interfollicular epidermis at the expense of the hair lineages. To investigate how Myc exerts these effects we analysed the transcription of more than 10000 genes following Myc activation in the basal layer of mouse epidermis for 1 or 4 days. The major classes of induced genes were involved in synthesis and processing of RNA and proteins, in cell proliferation and in differentiation. More than 40% of the downregulated genes encoded cell adhesion and cytoskeleton proteins. Repression of these genes resulted in profound changes in the adhesive and motile behaviour of keratinocytes. Myc activation inhibited cell motility and wound healing, correlating with decreased expression of a large number of extracellular matrix proteins. Cell adhesion and spreading were also impaired, and this correlated with decreased expression of the alpha6beta4 integrin, decreased formation of hemidesmosomes and decreased assembly of the actomyosin cytoskeleton. We propose that Myc stimulates exit from the stem cell compartment by reducing adhesive interactions with the local microenvironment or niche, and that the failure of hair differentiation reflects an inability of keratinocytes to migrate along the outer root sheath to receive hair inductive stimuli.

Pattern of expression of c-Myc, Max and Bin1 in human anagen hair follicles

BACKGROUND

We recently reported the presence of c-Myc immunoreactivity in two distinct regions of the inner root sheath (IRS) of human anagen hair follicles; they corresponded to the regions where keratinocytes of Henle's and Huxley's layers enter the terminal differentiation phase that will lead to their exfoliation in the pilary canal. These regions were denoted lower (LR) ring and upper ring (UR).

OBJECTIVES

To extend these observations to other genes connected to c-Myc and specifically to Max and Bin1. Max is the best known heterodimeric partner of c-Myc, interacting with its C-terminal domain, and Bin1 is an adaptor protein interacting with its N-terminal domain.

METHODS

Human anagen hair follicles were processed for c-Myc, Max and Bin1 immunohistochemistry and immunofluorescence. The presence of different isoforms of Bin1 was evaluated by Western blot analysis.

RESULTS

Analysis of sections cut in several planes, including tangential, demonstrated the presence of a third ring of c-Myc-positive cells (intermediate ring; IR) in the cuticle of the IRS corresponding to the region where this thin layer undergoes keratinization. Max immunoreactivity was observed in the three layers of the IRS starting in the lower bulbar region and ending in each of them at the level of the corresponding c-Myc-positive ring. Bin1 immunoreactivity was clearly distinguished only in Huxley's layer and in the cuticle, starting in some cells below the UR and terminating at the level of the latter. The companion layer of the outer root sheath was also labelled up to the infundibular region. Max and Bin1 immunostaining were less consistently observed in other skin adnexae and in the epidermis.

CONCLUSIONS

The results indicate that the asynchronous differentiation along the axis of the hair follicle of the different layers of the IRS and of the companion layer involves the expression of different genes that are interrelated in the so-called 'Myc network'. The specific localization of c-Myc in the IRS only at the level of the discrete and limited regions of the three rings appears to be the hallmark of the switch from differentiation to terminal differentiation/cell deletion.

Identification of clustered cells in human hair follicle responsible for MMP-9 gelatinolytic activity: consequences for the regulation of hair growth

BACKGROUND

The control of human hair follicle growth and differentiation is dependent upon several well-identified factors, including androgens, cytokines, and growth factors. In humans, alopecia androgenetica is a common aging process thought to be regulated through complex genetic imbalances, which also involve several of these crucial identified factors (and probably others not yet characterized), alone or in combination. Among these factors, epidermal growth factor (EGF), as well as pro-inflammatory cytokines, play a pivotal role, as evidenced by their direct inhibitory effects on hair growth both in vitro and in vivo. Following such treatments, the in vitro growth of hair follicles was rapidly arrested and deleterious modifications of hair morphology were also observed.

AIM

Because these cytokines act, at least partly, through the induction of matrix metalloproteinases (MMP), and because tissue remodeling occurs during the hair cycle, we attempted to identify and localize MMP in the human pilosebaceous unit.

METHOD

We used zymography to observe human hair follicles in culture in vitro.

RESULTS

We observed that human hair follicles in culture in vitro mainly and almost exclusively produce MMP-2 and MMP-9 gelatinolytic activities. Furthermore, after stimulation with EGF, tumor necrosis factor-alpha (TNF-alpha), or interleukin-1alpha (IL-1alpha), MMP-9 production was strongly increased. Using immunohistochemistry, we then precisely localized MMP-9 in the lower part of the inner root sheath (Henle's layer) of control human anagen hair follicles.

CONCLUSIONS

Cytokine- and EGF-induced upregulation of MMP-9 in the lower epithelial compartment of the human hair bulb is a major mechanism through which hair follicle involution, observed in alopecia, may occur.

Contrasting localization of c-Myc with other Myc superfamily transcription factors in the human hair follicle and during the hair growth cycle

The mammalian hair follicle is a highly dynamic skin appendage that undergoes repeated cycles of growth and regression, involving closely co-ordinated regulation of cell proliferation, differentiation, and apoptosis. The Myc superfamily of transcription factors have been strongly implicated in the regulation of these processes in many tissues. Using immunohistochemistry, we have investigated the patterns of c-Myc, N-Myc, Max, and Mad1-4 expression at different stages of the human hair growth cycle. N-Myc, Max, Mad1, and Mad3 immunoreactivity was detected in the epidermis and the epithelium of both anagen and telogen hair follicles. Three distinct patterns of hair follicle c-Myc immunoreactivity were observed. In the infundibulum, c-Myc staining was predominantly in the basal layers, with little detectable immunoreactivity in the terminally differentiating suprabasal layers; this pattern was similar to that seen in the epidermis. In contrast, c-Myc expression in the follicle bulb was found both in the proliferating germinative epithelial cells and in the terminally differentiating matrix cells that give rise to the hair fiber. Finally, intense c-Myc immunoreactivity was detected in the bulge region of the outer root sheath. Using the C8/144B antibody as a bulge marker, we confirmed that c-Myc immunoreactivity in the outer root sheath correlates with the putative hair follicle stem cell compartment. c-Myc expression in the bulge was independent of the hair growth cycle stage. Our data suggest that Myc superfamily members serve different functions in separate epithelial compartments of the hair follicle and may play an important role in determining cell fate within the putative stem cell compartment.