The contribution of the arrector pili muscle and sebaceous glands to the follicular unit structure

Assessment of the anti-hair loss potential of Camellia japonica fruit shell extract in vitro

OBJECTIVE

Hair loss is caused by various factors. Impacts of these factors are often overlapped and intensified. Currently, mitigation of hair loss is being studied by proliferating dermal papilla cells (DPCs) and inhibiting deleterious factors such as dihydrotestosterone (DHT) and oxidative stress on hair growth. Camellia japonica (C. japonica) fruit shell is a discarded part. Its biological activity remains to be elucidated. In this study, we investigated the capacity of C. japonica fruit shell extract (CJFSE) for hair loss mitigation.

METHODS

MTT assay, spheroid culture and quantitative RT-PCR were performed to observe the proliferative effect of CJFSE on hair follicle dermal papilla cells (HFDPCs). Effects of CJFSE on DHT-induced hair loss were confirmed by Dkk-1 ELISA, β-galactosidase (β-gal) and 5α-reductase activity assay. In addition, effects of CJFSE on oxidative stress were confirmed through DPPH and ROS production assays.

RESULTS

CJFSE increased the proliferation and spheroid size of HFDPCs. Expression levels of VEGF-A, Wnt-1, c-Myc and Cyclin D1 were upregulated by CJFSE. CJFSE also suppressed 5α-reductase activity and DHT-induced decrease in cell proliferation, Dkk-1 secretion and β-gal activity. Moreover, CJFSE showed DPPH scavenging activity and ameliorated hydrogen peroxide-induced ROS production and β-gal activity. Finally, gallic acid and protocatechuic acid were observed in CJFSE through HPLC analysis.

CONCLUSION

CJFSE has the potential to alleviate hair loss by promoting hair cell growth and suppressing effects of DHT and oxidative stress on hair.

The combination of hair follicle-specific marker LHX2 and co-expressed marker can distinguish between sweat gland placodes and hair placodes in rat

Eccrine sweat gland (ESG) and hair follicle (HF) are different skin appendages but share many common development characteristics. Although the morphology of adult ESG and HF is obviously different, it is difficult to distinguish ESG placodes from HFs placodes morphologically. To study the fate determination of ESG and HF, specific antigen markers for ESG placodes and HF placodes must be found first to distinguish them. In the study, we detected the expression of commonly used keratins 4, 5, 7-10, 12, 14, 15, 17-20, 27 and 73, and the reported ESG and HF specific markers, P-cadherin, Lymphoid enhancer factor 1 (LEF1), LIM Homeobox gene 2 (LHX2), Na⁺/K⁺-ATPase (NKA) and Na⁺-K⁺-2Cl^- cotransporter 1 (NKCC1) in ESG and HF placodes by single-immunofluorescence staining and double-immunofluorescence staining. To further verify the results of immunofluorescence staining, Western blot (WB) was used to detect the differential antigen and some co-expressed antigens of ESG and HF placodes. The results showed that both ESG and HF placodes expressed K4/5/14/1517/18, P-cadherin and LEF1, neither expressed K7/8/9/10/12/19/20/27/73, NKA or NKCC1. HF placodes specifically expressed LHX2. Combination of LHX2 and co-expressed antigen K14, can distinguish ESG placodes from HF placodes. We conclude that LHX2 is a specific marker for HF placodes, and ESG placodes and HF placodes can be distinguished by double immunofluorescence staining of the specific marker LHX2 and the co-expressed markers, such as K4, K5, K14, K15, K17, K18, P-cadherin and LEF1.

Alopecias in humans: biology, pathomechanisms and emerging therapies

BACKGROUND

The hair follicle is a complete mini-organ with a complex biology. Recent discoveries have shed light on the pathogenesis and genetic basis of a number of hair loss conditions, offering novel treatment alternatives.

OBJECTIVE

To explore the biology and physiology of hair growth, the pathomechanism behind alopecias and emerging therapies.

CONCLUSION AND CLINICAL IMPORTANCE

Hair growth is influenced by numerous physiological moderators. Greater understanding of the biology and physiology of the hair follicle and the pathomechanisms of hair disease facilitates development of targeted treatments. Sublingual minoxidil is a promising therapy in humans where optimised drug delivery enhances efficacy and reduces systemic adverse effects. Janice kinase inhibitors, which disrupt the inflammatory cascade, help maintain the hair follicle, preserve immune privilege, and regrow hair in alopecia areata. As the pathomechanisms of other forms of alopecia become better understood, new targeted therapies with greater efficacy will emerge.

Hair Transplantation: Basic Overview

Modern hair restoration surgery is based on a technique known as follicular unit transplantation in which follicular units (FUs) are the exclusive structures used as hair grafts. In Part 1 of this two-part review, we describe how the techniques employed in hair transplantation have evolved into their present forms. Anatomic concepts of specific relevance for dermatologists are discussed, including the distribution and ex-vivo morphology of scalp FUs. Male androgenetic alopecia and female pattern hair loss are the most common reasons for hair loss consultations with dermatologists and will be the primary focus of this review. However, as not all hair disorders are suitable for transplantation, this review will also describe which scalp conditions are amenable to surgery and which are not. In addition, guidelines are provided to help dermatologists better define good or bad candidates for hair transplantation. Finally, other conditions for which hair transplantation surgery is indicated are reviewed.

Progress in studies of epidermal stem cells and their application in skin tissue engineering

The epidermis, which is the outermost layer of mammalian skin, provides an essential barrier that is essential for maintenance of life. The epidermis is a stratified epithelium, which is maintained by the proliferation of epidermal stem cells (EPSCs) at the basal layer of the epidermis. As a unique cell population characterized by self-renewal and differentiation capabilities, EPSCs ensure the maintenance of adult skin homeostasis and participate in repair of the epidermis after injury. Recently, the utilization of EPSCs for wound healing and tissue regeneration has been attracting increased attention from researchers. In addition, the advances in tissue engineering have increased the interest in applying EPSCs in tissue-engineered scaffolds to further reconstitute injured tissues. In this review, we introduce research developments related to EPSCs, including methods recently used in the culture and enrichment of EPSCs, as well as advanced tools to study EPSCs. The function and mechanism of the EPSC-dermal units in the development and homeostasis of the skin are also summarized. Finally, the potential applications of EPSCs in skin tissue engineering are discussed.

Adipose Infiltration of the Dermis, Involving the Arrector Pili Muscle, and Dermal Displacement of Eccrine Sweat Coils: New Histologic Observations in Frontal Fibrosing Alopecia

BACKGROUND

Frontal fibrosing alopecia (FFA) is an irreversible scarring alopecia, and its incidence has reached epidemic size. Immune privilege collapse of the bulge and epithelial mesenchymal transition play a role in the pathogenesis. We have noted adipose tissue in the dermis in several specimens from FFA.

OBJECTIVE

Our primary objective was to verify the presence of adipose tissue at the isthmus level in biopsies from FFA. Additional objectives included the presence of deep inflammation and position of the sweat coils.

METHODS

Eighty-three histologic specimens of FFA diagnosed at the Dermatopathology Laboratory at the Department of Dermatology, University of Miami, within 3 years were evaluated retrospectively. All biopsies were bisected horizontally and assessed at several levels. Sixty biopsies from androgenetic alopecia served as controls. Statistical analysis was performed using the χ test. A P value of 0.05 or less was considered significant.

RESULTS

Sixty specimens met the inclusion criteria for optimal quality and classic diagnostic features. Seventy percent demonstrated fat tissue infiltration at the isthmus level as clusters of cells or small globules versus 23% of the controls. The fat infiltration in the arrector pili muscle (APM) was present in 55% versus 15% of the controls, and the sweat coils were positioned in the reticular dermis in 43% versus 1.7% of the controls. All results were statistically significant (P < 0.0001). When accounting for the simultaneous presence of any of these 3 variables, 30% of the FFA cases had triple positivity, 61.7% had double positivity, and 75% had at least 1 positive variable versus 0%, 15%, and 10%, respectively, of the controls.

CONCLUSION

New histologic findings in FFA involve the presence of adipose tissue in the dermis. We believe that the close interaction of the hair follicles and the APM with the adipose tissue may play a role in APM degeneration and in epithelial mesenchymal transition.

Reduced cell cohesiveness of outgrowths from eccrine sweat glands delays wound closure in elderly skin

Human skin heals more slowly in aged vs. young adults, but the mechanism for this delay is unclear. In humans, eccrine sweat glands (ESGs) and hair follicles underlying wounds generate cohesive keratinocyte outgrowths that expand to form the new epidermis. Here, we compared the re‐epithelialization of partial‐thickness wounds created on the forearm of healthy young (< 40 yo) and aged (> 70 yo) adults. Our results confirm that the outgrowth of cells from ESGs is a major feature of repair in young skin. Strikingly, in aged skin, although ESG density is unaltered, less than 50% of the ESGs generate epithelial outgrowths during repair (vs. 100% in young). Surprisingly, aging does not alter the wound‐induced proliferation response in hair follicles or ESGs. Instead, there is an overall reduced cohesiveness of keratinocytes in aged skin. Reduced cell–cell cohesiveness was most obvious in ESG‐derived outgrowths that, when present, were surrounded by unconnected cells in the scab overlaying aged wounds. Reduced cell–cell contact persisted during the repair process, with increased intercellular spacing and reduced number of desmosomes. Together, reduced outgrowths of ESG (i) reduce the initial number of cells participating in epidermal repair, (ii) delay wound closure, and (iii) lead to a thinner repaired epidermis in aged vs. young skin. Failure to form cohesive ESG outgrowths may reflect impaired interactions of keratinocytes with the damaged ECM in aged skin. Our findings provide a framework to better understand the mediators of delayed re‐epithelialization in aging and further support the importance of ESGs for the repair of human wounds.

Destruction of the arrector pili muscle and fat infiltration in androgenic alopecia

BACKGROUND

Androgenic alopecia (AGA) is the most common hair loss condition in men and women. Hair loss is caused by follicle miniaturization, which is largely irreversible beyond a certain degree of follicular regression. In contrast, hair loss in telogen effluvium (TE) is readily reversible. The arrector pili muscle (APM) connects the follicle to the surrounding skin.

OBJECTIVES

To compare histopathological features of the APM in AGA and TE.

METHODS

Archival blocks of 4-mm scalp punch biopsies from eight patients with AGA and five with TE were obtained. New 4-mm biopsies from five normal cases were used as controls. Serial 7-μm sections were stained with a modified Masson's trichrome stain. 'Reconstruct' software was used to construct and evaluate three-dimensional images of the follicle and APM.

RESULTS

The APM degenerated and was replaced by adipose tissue in all AGA specimens. Remnants of the APM remained attached to the hair follicle. There was no fat in the normal skin specimens. Fat was seen in two of five TE specimens but could be attributed to these patients also showing evidence of AGA. Quantitative analysis showed that muscle volume decreased and fat volume increased significantly (P < 0·05) in AGA compared with controls.

CONCLUSIONS

APM degeneration and replacement with fat in AGA has not previously been described. The underlying mechanism remains to be determined. However, we speculate that this phenomenon might be related to depletion of stem or progenitor cells from the follicle mesenchyme, explaining why AGA is treatment resistant.

Beyond goosebumps: does the arrector pili muscle have a role in hair loss?

The arrector pili muscle (APM) consists of a small band of smooth muscle that connects the hair follicle to the connective tissue of the basement membrane. The APM mediates thermoregulation by contracting to increase air-trapping, but was thought to be vestigial in humans. The APM attaches proximally to the hair follicle at the bulge, a known stem cell niche. Recent studies have been directed toward this muscle's possible role in maintaining the follicular integrity and stability. This review summarizes APM anatomy and physiology and then discusses the relationship between the follicular unit and the APM. The potential role of the APM in hair loss disorders is also described, and a model explaining APM changes in hair loss is proposed.

Miniaturized Hairs Maintain Contact with the Arrector Pili Muscle in Alopecia Areata but not in Androgenetic Alopecia: A Model for Reversible Miniaturization and Potential for Hair Regrowth

BACKGROUND

Hair follicle miniaturization is the hallmark of male pattern hair loss (MPHL), female pattern hair loss (FPHL), and alopecia areata (AA). AA has the potential for complete hair regrowth and reversal of miniaturization. MPHL and FPHL are either irreversible or show only partial regrowth and minimal reversal of miniaturization.

HYPOTHESIS

The arrector pili muscle (APM) attachment to the hair follicle bulge, a recognized repository of stem cells may be necessary for reversal of hair follicle miniaturization.

MATERIALS AND METHODS

Sequential histological sections from MPHL, FPHL, AA, and telogen effluvium were used to create three-dimensional images to compare the relationship between the APM and bulge.

RESULTS

In AA, contact was maintained between the APM and the bulge of miniaturized follicles while in MPHL and FPHL contact was lost.

DISCUSSION

Contact between the APM and the bulge in AA may be required for reversal of hair follicle miniaturization. Maintenance of contact between miniaturized follicles in AA could explain the complete hair regrowth while loss of contact between the APM and the bulge in MPHL and FPHL may explain why the hair loss is largely irreversible. This loss of contact may reflect changes in stem cell biology that also underlie irreversible miniaturization.

TGFβ signaling regulates lipogenesis in human sebaceous glands cells

Background

Sebaceous glands are components of the skin essential for its normal lubrication by the production of sebum. This contributes to skin health and more importantly is crucial for the skin barrier function. A mechanistic understanding of sebaceous gland cells growth and differentiation has lagged behind that for keratinocytes, partly because of a lack of an in vitro model that can be used for experimental manipulation.

Methods

We have developed an in vitro culture model to isolate and grow primary human sebocytes without transformation that display functional characteristics of sebocytes. We used this novel method to probe the effect of Transforming Growth Factor β (TGFβ) signaling on sebocyte differentiation, by examining the expression of genes involved in lipogenesis upon treatment with TGFβ1. We also repressed TGFβ signaling through knockdown of the TGFβ Receptor II to address if the effect of TGFβ activation is mediated via canonical Smad signal transduction.

Results

We find that activation of the TGFβ signaling pathway is necessary and sufficient for maintaining sebocytes in an undifferentiated state. The presence of TGFβ ligand triggered decreased expression in genes required for the production of characteristics sebaceous lipids and for sebocyte differentiation such as FADS2 and PPARγ, thereby decreasing lipid accumulation through the TGFβ RII-Smad2 dependent pathway.

Conclusion

TGFβ signaling plays an essential role in sebaceous gland regulation by maintaining sebocytes in an undifferentiated state. This data was generated using a novel method for human sebocyte culture, which is likely to prove generally useful in investigations of sebaceous gland growth and differentiation. These findings open a new paradigm in human skin biology with important implications for skin therapies.

The basement membrane of hair follicle stem cells is a muscle cell niche

The hair follicle bulge in the epidermis associates with the arrector pili muscle (APM) that is responsible for piloerection ("goosebumps"). We show that stem cells in the bulge deposit nephronectin into the underlying basement membrane, thus regulating the adhesion of mesenchymal cells expressing the nephronectin receptor, α8β1 integrin, to the bulge. Nephronectin induces α8 integrin-positive mesenchymal cells to upregulate smooth muscle markers. In nephronectin knockout mice, fewer arrector pili muscles form in the skin, and they attach to the follicle above the bulge, where there is compensatory upregulation of the nephronectin family member EGFL6. Deletion of α8 integrin also abolishes selective APM anchorage to the bulge. Nephronectin is a Wnt target; epidermal β-catenin activation upregulates epidermal nephronectin and dermal α8 integrin expression. Thus, bulge stem cells, via nephronectin expression, create a smooth muscle cell niche and act as tendon cells for the APM. Our results reveal a functional role for basement membrane heterogeneity in tissue patterning. PAPERCLIP:

A study of the secretion mechanism of the sebaceous gland using three-dimensional reconstruction to examine the morphological relationship between the sebaceous gland and the arrector pili muscle in the follicular unit

BACKGROUND

New models of the structural relationship between the arrector pili (AP) muscle and the sebaceous gland (SG) have been proposed recently.

OBJECTIVES

The purpose of the present study was to establish the actual morphological relationship between components of the follicular unit (FU) including the hair follicles, AP muscle and SG using 3D reconstruction of serially sectioned specimens so as to expand previous explanations of the secretory mechanism of the SG and to suggest other possible mechanisms based on newly proposed model.

METHODS

Scalp skin specimens were processed using routine histological procedures, with serially sectioned tissue slides being stained with Masson's trichrome. 'Reconstruct' software was used to align, assemble and reconstruct the sections, with observations of the 3D-reconstructed FU [including hair follicles (HFs), AP muscle and SG].

RESULTS

Fifty FUs were reconstructed. The AP muscle was curved and concave as it supported the basal portion of the sebaceous lobules in the perifolliculum. Sebaceous lobules were located between the AP muscle and HFs (angular area) and some sebaceous lobules located in the opposite (counter-angular) area.

CONCLUSIONS

We propose that the concave part of the AP muscle pushes up the basal portion of the sebaceous lobule between the HFs and AP muscle during AP muscle contraction and hair erection. In addition, the sebaceous lobule located at the counter-angular position is squeezed by the HF during AP muscle relaxation and hair repositioning. Combined with the previous mechanism of SG secretion, this newly established mechanism based on the 3D structure of the FU will improve our understanding of AP muscle function and SG secretion.

A new model for the morphology of the arrector pili muscle in the follicular unit based on three-dimensional reconstruction

In the classic model of the arrector pili (AP) muscle, each hair follicle is independently associated with a single AP muscle. Recently, new models have been proposed based on interpretations of serial histological cross-sectional images. The purpose of this study was to confirm the morphology of the AP muscle in relation to the follicular unit (FU) using quantitative three-dimensional (3D) reconstruction of serially sectioned images. Skin samples were obtained from the parietal region of the scalp, and processed using routine histological procedures. The serially sectioned slides were stained with Masson's trichrome. All the hairs and hair follicles of the FU exhibited some degree of slanting, with the single AP muscle slanted in the same direction. The distal portion of the AP muscle was divided into branches, as in a bronchial tree. There was branching in the single AP muscle present in the FU, and it was inserted into all the hair follicles of the FU either tightly or loosely. We suggest that the classic anatomy of the AP muscle must be modified with this new model, now confirmed by computer-based 3D reconstruction.

Nothing but skin and bone

Skin and bone - what comes to mind at hearing this phrase? While certainly a metaphor for disease, it also defines two very different tissues, one a flexible and contiguous outer covering, the other a morphologically diverse hard tissue distributed at over 200 sites in the body. As the accompanying series of Reviews highlights, these tissues are indeed diverse, but there are also surprising similarities. Skin is the interface between the internal organs and the environment, and as such plays a crucial role in the body's defense mechanism. The skin and its many appendages are responsible for functions as diverse as epidermal barrier and defense, immune surveillance, UV protection, thermoregulation, sweating, lubrication, pigmentation, the sensations of pain and touch, and, importantly, the protection of various stem cell niches in the skin. Bone serves a number of purposes: it provides protection for vital organs, a lever for locomotion, a reservoir for calcium, and the site of adult hematopoiesis. The tissue is composed of osteoblasts, osteoclasts, and their individual precursors plus a complex mixture of mesenchymal, myeloid, and lymphoid cells in the marrow space. Finally, the endothelial microenvironment provides nutrition and is a conduit for the influx and emigration of cells that impact bone biology in several important ways. This Review series guides the reader through these various facets of 2 diverse, yet interdependent, tissues.

Myogenic differentiation of dermal papilla cells from bovine skin

Cells from the dermal papilla and dermal sheath of hair follicles exhibit pronounced plasticity in vitro, being capable of adopting fat, bone, hematopoietic, and nerve cell phenotypes. In this study, we show that bovine dermal papilla cells (DPC) are also capable of undergoing skeletal muscle differentiation. DiI labeled DPC incorporated into myotubes when co-cultured with differentiating C(2)C(12) myoblasts. Bovine-specific PCR assays showed that the muscle markers MyoD and myogenin were up-regulated, confirming that the DPC had adopted a myogenic gene expression program. Nine clonal lines of DPC underwent both adipogenic and myogenic differentiation, demonstrating the multipotency of individual cells. Primary populations of both DPC and extra-follicular dermal fibroblasts were also capable of both adipogenic and myogenic differentiation. However, on myogenic differentiation, cells derived from dermal papillae expressed higher levels of myogenin than primary fibroblasts derived from extra-follicular dermis, suggesting that papilla cells undergo myogenesis more efficiently. This result shows that populations of fibroblastic cells derived from different anatomical sites within the skin are not equivalent with respect to their plasticity. Cultured DPC and dermal fibroblasts both expressed Pax3, a marker for the dermomyotome which represents a common embryological origin of muscle and dermis. Quantitative PCR showed that Pax3 expression levels before myogenic induction correlated with myogenin expression levels after myogenesis. These results suggest that a degree of dedifferentiation may underlie the plasticity of dermal cells in vitro, and that this plasticity may be predicted, at least in part, by levels of Pax3 expression.

Multiunit arrector pili muscular structure as a variation observed by using computer-based three-dimensional reconstruction

The arrector pili (AP) muscle was recently suggested to comprise one AP muscular unit inserted into all the hair follicles contained within the follicular unit (FU). This study investigated the presence of variations in AP muscular units associated with the FUs. Human cadaver scalp skin specimens were serially sectioned and stained with Masson's trichrome. Three-dimensional reconstructions of the serially sectioned images were analyzed on a computer, which revealed two types of variation in 20 FUs, one of which was the multiunit AP muscular structure, in which the AP muscular unit was inserted into two or more FUs.