Desmogleins 1 and 3 in the companion layer anchor mouse anagen hair to the follicle

Anchorage of the hair to its follicle is of paramount importance for survival of rodents in the wild, and is aberrant in some human alopecias. Little is understood about the mechanisms responsible for hair shaft anchorage. Desmoglein (Dsg)3-/- (knockout) mice lose hair during telogen, but their anagen hairs remain anchored to the follicle. We hypothesized that Dsg1 compensates for the loss of Dsg3 in the anagen hair follicles of these Dsg3-/- mice. Consistent with this hypothesis, we found Dsg1 and Dsg3 expression overlapping in the companion layer. To functionally address this hypothesis, we used exfoliative toxin A (ETA) to inactivate Dsg1 in Dsg3-/- mice. Four hours after injection of ETA, Dsg3-/- mice, but not Dsg3+/+ or Dsg3+/- mice, showed striking loss of anagen hair, which was confirmed and quantitated by gentle tape stripping. Histology of the skin of these mice as well as of the tape-stripped hair showed separation between the outer root sheath and inner root sheath of the hair follicle, at the plane of the companion layer. Immunostaining for trichohyalin and K6, which highlights the companion layer, in skin and stripped hair confirmed the plane of separation. Labeling of proliferating cells with bromodeoxyuridine demonstrated that the matrix keratinocytes responsible for producing the hair shaft were below the split and remained in the follicle after loss of the anagen hair. These findings demonstrate the importance of the companion layer, and particularly the Dsg1 and Dsg3 in this layer, in anchoring the anagen hair to the follicle.     

Functional anatomy of the hair follicle: The Secondary Hair Germ

The secondary hair germ (SHG)—a transitory structure in the lower portion of the mouse telogen hair follicle (HF)—is directly involved in anagen induction and eventual HF regrowth. Some crucial aspects of SHG functioning and ontogenetic relations with other HF parts, however, remain undefined. According to recent evidence (in contrast to previous bulge‐centric views), the SHG is the primary target of anagen‐inducing signalling and a source of both the outer root sheath (ORS) and ascending HF layers during the initial (morphogenetic) anagen subphase. The SHG is comprised of two functionally distinct cell populations. Its lower portion (originating from lower HF cells that survived catagen) forms all ascending HF layers, while the upper SHG (formed by bulge‐derived cells) builds up the ORS. The predetermination of SHG cells to a specific morphogenetic fate contradicts their attribution to the “stem cell” category and supports SHG designation as a “germinative” or a “founder” cell population. The mechanisms of this predetermination driving transition of the SHG from “refractory” to the “competent” state during the telogen remain unknown. Functionally, the SHG serves as a barrier, protecting the quiescent bulge stem cell niche from the extensive follicular papilla/SHG signalling milieu. The formation of the SHG is a prerequisite for efficient “precommitment” of these cells and provides for easier sensing and a faster response to anagen‐inducing signals. In general, the formation of the SHG is an evolutionary adaptation, which allowed the ancestors of modern Muridae to acquire a specific, highly synchronized pattern of hair cycling.     

Trichohyalin: presence in the granular layer and stratum corneum of normal human epidermis.

Trichohyalin, a protein contained in granules in the cells of the hair-follicle inner root sheath and in the medulla of the hair shaft, has been purified previously from sheep hair bulbs and is also a major protein of filiform papillae of tongue epithelium. Polyclonal affinity-purified antibodies and a monoclonal antibody raised to purified pig tongue trichohyalin both stained the inner root sheath of hair follicles and the medulla of hair fibers and identified human trichohyalin as a single 220-kDa band on immunoblots of human hair bulb proteins. These antibodies were used to examine human epidermis by immunofluorescence and immunoblotting. The antibodies decorate granules in cells in the granular layer and stratum corneum of non-hair-bearing human skin, and immunoblots identify a protein in epidermis comigrating with trichohyalin from human hair and human tongue epithelium. Absorption of antibody to trichohyalin on a trichohyalin affinity column abrogated staining of the epidermis and the bands on the immunoblots. Trypsin-separated epidermis contained 220 and 160 kDa bands identified as trichohyalin, but epidermis shaved from skin and quickly frozen showed only a single 220-kDa band, indicating that the 160-kDa protein was generated by proteolysis. Double immunofluorescence for trichohyalin and filaggrin showed that some cells containing filaggrin also contain trichohyalin. These studies show that trichohyalin is not limited to hair and tongue but is present in isolated cells in the granular layer and stratum corneum of normal epidermis.     

A natural canine homologue of alopecia areata in humans

Background Alopecia areata (AA) is suspected to be an autoimmune disease directed preferentially against hair follicles (HF) affecting both humans and various mammalian species. Recently, two rodent models of AA were described, namely the ageing C3H/HeJ mouse and the DEBR rat. Despite several case reports of canine AA in the literature, there has been no systematic assessment of the disease in these companion animals, and it is also not known whether dogs with AA could be useful as an outbred homologue of this disease in humans. Objectives To evaluate the clinical, histopathological and immunopathological features of 25 dogs with AA and compare these data with those found in the human disease. Patients/methods Twenty‐five client‐owned dogs exhibiting macroscopic alopecia with peri‐ or intrabulbar lymphocytic infiltrates were selected for study. Biopsies and sera were obtained and assessed by histopathology, direct immunofluorescence of immunoreactant deposition, immunohistochemistry for lymphocyte markers, indirect immunofluorescence and immunoblotting analysis of circulating serum IgG, selective immunoprecipitation of HF proteins by serum IgG, and passive transfer of purified canine IgG into naïve C57BL/10 mice. Results Clinical signs including alopecia, skin hyperpigmentation and leucotrichia usually developed during adulthood and were first seen on the face, followed by the forehead, ears and legs. Spontaneous remission of alopecia occurred in 60% of dogs and regrowing hair shafts were often non‐pigmented. Histological examination of skin biopsy specimens revealed peri‐ and intrabulbar mononuclear cell infiltrates affecting almost exclusively anagen HF. Direct immunofluorescence analysis detected HF‐specific IgG in 73% of dogs, while indirect immunofluorescence revealed circulating IgG autoantibodies to the HF inner and outer root sheaths, matrix and precortex. Immunoblotting analysis revealed IgG reactivity to proteins in the 45–60 kDa molecular weight range and with a 200–220 kDa doublet. The latter was identified as trichohyalin by selective immunoprecipitation. Purified HF‐reactive IgG, pooled from AA‐affected dogs, was injected intradermally to the anagen skin of naïve mice where it was associated with the local retention of HFs in an extended telogen phase in AA‐treated skin compared with that seen in controls. Conclusions These findings are very similar to those reported for human AA patients; therefore, they support the consideration of dogs with AA as a useful homologue for the study of the pathogenesis of this common autoimmune disease of humans.     

Human scalp skin and hair follicles express neurotrophin-3 and its high-affinity receptor tyrosine kinase C, and show hair cycle-dependent alterations in expression

BACKGROUND: Neurotrophin (NT)-3 and its high-affinity receptor tyrosine kinase C (Trk C) are essential for nervous system development. These members of the NT family are also involved in murine hair morphogenesis and cycling. However, their role in human hair follicle (HF) biology remains to be elucidated. OBJECTIVES: To explore the role of NTs in human skin and HF biology. METHODS: The immunoreactivity (IR) of NT-3 and Trk C was studied in human scalp skin and HFs by immunofluorescent and light microscopic immunohistology. Skin biopsies were obtained from normal human scalp containing mainly anagen VI HFs from women (age 53-57 years) undergoing elective plastic surgery. RESULTS: Both NT-3 and Trk C showed prominent, yet distinct, IR patterns in human scalp anagen HFs (anagen VI), whereas they were weakly expressed in catagen and increased again in telogen HFs. Within HF compartments, NT-3 IR was prominent in the outer root sheath, inner root sheath, dermal papilla and connective tissue sheath. Trk C IR was prominent in all HF epithelial and mesenchymal compartments. Outside the HF, both NT-3 and Trk C showed prominent IR in the epidermis, sebaceous glands and sweat glands. CONCLUSIONS: These observations provide the first indication that NT-3 and Trk C are expressed in human scalp skin and HFs, and suggest that Trk C-mediated signalling is involved not only in murine but also in human HF biology. They may be useful in determining therapeutic strategies for the treatment of hair cycle and skin-related disorders.     

Expression of HLA-DR by anagen hair follicles in alopecia areata

The expression of HLA-DR within hair follicles in alopecia areata was studied using an immunoperoxidase method. Scalp biopsies were taken from 12 patients with alopecia areata and from 6 normal control subjects. Frozen sections were stained with a panel of 4 anti-HLA-DR monoclonal antibodies, Leu 2, Leu 3, Leu 4, and T6 antibodies. The expression of DR in normal hair follicles and in most anagen follicles from nonlesional alopecia skin was confined to dendritic cells which were sparse below the level of the arrector pilorum insertion. Of the 37 anagen follicles examined in lesional skin, 25 displayed staining for DR on epithelial cells in the precortical matrix and presumptive cortex. Six follicles showed DR staining in other epithelial compartments, the lower bulb matrix, inner root sheath, and outer root sheath. Infiltration of the hair bulb matrix by T cells was seen in the majority of follicles where epithelial cells were DR+. The aberrant expression of DR antigens by hair follicle epithelium provides direct evidence that immune mechanisms are operating in the pathogenesis of alopecia areata. In a previous study of alopecia areata we found evidence of cell injury confined to the precortical matrix and presumptive cortex in lesional anagen follicles. The relative restriction of epithelial DR expression to the same site suggests that this region of the follicle is of fundamental importance in the disease process.     

Injury modifies the fate of hair follicle dermal stem cell progeny in a hair cycle‐dependent manner

The dermal papilla (DP) is one of two principal mesenchymal compartments of the hair follicle (HF). We previously reported that a population of HF dermal stem cells (hfDSCs) function to regenerate the dermal sheath (DS), but intriguingly also contribute new cells to the adult DP at the onset of anagen hair growth to maintain normal cycling of HFs and support the production of large hair fibres. Here, we asked whether injury altered the behaviour of hfDSCs and their progeny in order to support wound‐induced hair growth (WIHG) and if the response was modulated by hair cycle stage. αSMACreER^T2:ROSA^YFP mice received tamoxifen to label the DS, including hfDSCs. Full‐thickness excisions were made on the dorsal skin during various stages of the hair cycle. The skin was harvested at the subsequent anagen. Interestingly, there was an increase in the magnitude of recruitment of hfDSC progeny into the DP after injury compared to follicles entering natural second anagen. This bias towards a DP fate only occurred when a wound was induced during certain stages of the HC. In summary, injury modifies the fate of hfDSCs progeny, biasing them towards recruitment into the DP, with the hair cycle stage also influencing this response.     

Characterization of hair follicle antigens targeted by the anti-hair follicle immune response

Alopecia areata is a common disfiguring hair loss disorder that primarily affects the hair follicle as it enters the prolonged growth phase called anagen. The last few years have yielded an explosion of more rigorously obtained data on the etiology and pathogenesis of this disorder. While a consensus is rapidly building in support of an autoimmune pathogenesis, there are still several enigmatic issues to be resolved. These include the possibility that alopecia areata is really a multientity disorder with causes that are multifactorial. This will have important implications for the research scientist's search for the jigsaw puzzle's largest missing piece--the identification of the target autoantigen(s). There is now much evidence that autoimmune diseases with both T and B cell components have shared target autoantigens/epitopes. It is likely that alopecia areata is similar, as there is now very strong evidence for the generation of autoantibodies as well as autoreactive T cells to hair follicles in the pathogenesis of this disease. The following brief review outlines the progress we have made over the last five to ten years in the characterization of hair follicle antigens targeted by antibodies in alopecia areata. Results of these studies now show that the elicitation of antibodies to hair follicle-specific proteins is a highly conserved phenomenon in all affected species studied to date. Candidate autoantigens that have been identified include the 44/46 kDa hair-specific keratin (expressed in the precortical zone of anagen hair follicles) and trichohyalin (an important intermediate filament-associated protein) expressed in the inner root sheath of the growing hair follicle. Moreover, there is evidence that anti-hair follicle antibodies are modulated during the disease process, can occur before clinically detectable hair loss, and may be reduced in titer during successful treatment. Preliminary data from passive transfer experiments suggest that in some species these antibodies may disrupt hair cycling. We are currently applying a more molecular approach (e.g., cDNA library screening) to identify hair follicle antigens truly associated with the onset of the disorder.     

Cell differentiation in human anagen hair and hair follicles studied with anti-hair keratin monoclonal antibodies

By a hybridoma technique using BALB/c mice and Sp2/0-Ag14 mouse myeloma cells, monoclonal antibodies against hair fibrous proteins (HFP) were produced. Two monoclonal antibodies, designated as HKN-5 and HKN-7, were chosen. Either HFP or epidermal fibrous proteins (EFP) were electrophoretically separated on polyacrylamide gels with sodium dodecyl sulfate. By immunoblot analyses, HKN-5 and HKN-7 decorated the electrophoretic bands of HFP but not those of EFP. Immunohistochemically, these monoclonal antibodies stained the medulla, cortex, cuticle, and inner root sheath in the keratogenous zone of anagen hairs, but not hair matrix cells. HKN-5 further reacted with the innermost cells (IMC) of the outer root sheath; these cells formed a single cell layer located outside of the Henle's layer. HKN-7 did not react with the outer root sheath including the IMC. Neither monoclonal antibody reacted with any other skin components or any tissues of other organs examined. Ultrastructurally, the IMC of the outer root sheath showed a unique cell differentiation forming an independent cell layer. It is suggested that the cells in the medulla, cortex, cuticle, and inner root sheath of anagen hair and hair follicles possess a similar keratin expression and that the IMC of the outer root sheath display a unique keratin expression and their own cell differentiation, resulting in 2 types of keratinization of the outer root sheath; keratinization of IMC and trichilemmal keratinization.     

PDGF isoforms induce and maintain anagen phase of murine hair follicles

BACKGROUND: It is known that platelet-derived growth factor (PDGF) receptors are expressed in hair follicle (HF) epithelium. OBJECTIVES: The aim of the present study was to clarify the effects of PDGF-AA and -BB on the cyclic growth of HFs. METHODS: PDGF-AA or -BB was injected into the dorsal skin of C3H mice during the second telogen phase once daily for five consecutive days, or PDGF-AA or -BB dissolved in hyaluronic acid was injected only once. In order to confirm the effects of different PDGF isoforms, anti-PDGF-AA antibody or anti-PDGF-BB antibody was injected just after each injection of PDGF-AA or -BB. In addition, anti-PDGF antibodies were injected into the skin of C3H mice during the second anagen phase once daily for 5 days. We studied expression of signaling molecules in the skin where anagen phase had been induced by PDGF injection by real-time RT-PCR. RESULTS: Both PDGF-AA and -BB injection experiments immediately induced the anagen phase of the hair growth cycle at the injection sites. The induction of anagen was interfered by anti-PDGF antibody treatment. Real-time RT-PCR using extracted RNA from the PDGF injected sites of skin samples showed upregulated expression of HF differentiation-related key signaling molecules, Sonic hedgehog (Shh), Lef-1 and Wnt5a. CONCLUSIONS: These results indicate that both PDGF-AA and -BB are involved in the induction and maintenance of the anagen phase in the mouse hair cycle. Local application of PDGF-AA and -BB might therefore prove to be an effective treatment option for alopecia associated with early catagen induction and elongated telogen phase.     

Spontaneous alopecia areata-like hair loss in one congenic and seven inbred laboratory mouse strains

Alopecia areata (AA) research has been hampered by the lack of suitable animal models for use in experimental procedures. AA-like hair loss has been observed in several species, including dogs, cats, horses, cattle, and nonhuman primates; however, these examples are isolated cases in outbred species of large size, limiting their use in AA research. Inbred rodent strains are ideal research models. C3H/HeJ mice can develop spontaneous AA-like hair loss and have previously been advanced as a suitable experimental model. The search for additional mouse strains with AA-like hair loss has continued. Nonscarring, inflammatory, spontaneously reversible hair loss has been observed in individual mice from several inbred mouse strains. Aside from C3H/HeJ mice, an AA-like phenotype has been observed in the substrain C3H/HeJBir, with an expression frequency of 5%. Up to 10% of individuals in an A/J mouse colony have been confirmed to develop patchy AA-like hair loss. Isolated examples of AA have also been identified in C3H/HeN/J mice, C3H/OuJ mice, HRS/J+/hr heterozygous normal mice, CBA/CaHN-Btk(xid)/J mice, and BALB.2R-H2h2/Lil mice, each with a colony frequency of less than 1%. BALB.2R-H2h2/Lil mice may also have severe nail defects. AA is regarded as rare in nonhuman species; however, nonscarring inflammatory based alopecia has been identified in several mouse strains. These examples may represent different subtypes of the heterogeneous AA phenotype. Pathologic and genetic analysis of different AA affected mouse strains may contribute to understanding AA pathogenesis and elucidating susceptibility genes.     

Comprehensive analysis of FGF and FGFR expression in skin: FGF18 is highly expressed in hair follicles and capable of inducing anagen from telogen stage hair follicles

We quantified the mRNA expression of all 22 fibroblast growth factor family members (FGF) and their four receptors (FGFR) in adult mouse full-thickness skin at various stages of the hair growth cycle. We found that in addition to mRNA encoding FGF previously identified in skin (FGF1, 2, 5, 7, 10, 13, and 22), FGF18 mRNA was also strongly expressed. Expression of these FGF varied throughout hair growth cycle: mRNA expression of FGF18 and 13 peaked at telogen; FGF7 and 10 at anagen V; and FGF5 and 22 at anagen VI. In situ hybridization revealed that FGF18 mRNA is mainly expressed in the anagen inner root sheath and telogen bulge of hair follicles. In culture, FGF18 stimulated DNA synthesis in human dermal fibroblasts, dermal papilla cells, epidermal keratinocytes and vascular endothelial cells. When FGF18 was administered subcutaneously to mice in a uniform telogen state, anagen hair growth was observed. Our findings suggest that FGF18 is important for the regulation of hair growth and the maintenance of skin in adult mice.     

Peptidylarginine deiminase isoforms are differentially expressed in the anagen hair follicles and other human skin appendages

Peptidylarginine deiminases (PAD) catalyze the conversion of arginine residues to citrullines. Five isoforms are known that present distinct tissue locations. In the epidermis, like in the skin, only PAD1, 2, and 3 are expressed. Their pattern of expression in skin appendages is not known. Here, confocal microscopy analysis using highly specific antibodies demonstrated that PAD1 and 3 are expressed in human anagen hair follicles, PAD1 and 2, in arrector pili muscles and sweat glands, whereas no PAD were detected in sebaceous glands. PAD1 was detected in the cuticle and the Huxley layer of the inner root sheath (IRS), and in the companion layer. PAD3 was localized in the medulla, and in the three layers of the IRS. Using anti-modified citrulline antibodies, we also showed that deiminated proteins appeared in the lower part of the IRS, first in the Henle layer, then in the cuticle, and finally in the Huxley layer. Our data demonstrate that PAD3 is the enzyme that deiminates trichohyalin in the medulla and the Henle layer, indicate that PAD1 and 3 are involved in the hair follicle program of differentiation, and suggest a role for PAD1 and 2 in the physiology of sweat glands and arrector pili muscles.     

Differential expression of nitric oxide synthases in human scalp epidermal and hair follicle pigmentary units: implications for regulation of melanogenesis

BACKGROUND: Nitric oxide (NO) is a ubiquitous gaseous lipophilic molecule generated from the conversion of L-arginine to L-citrulline by the NO synthases (NOSs). Ultraviolet radiation (UVR)-induced NO production appears to stimulate epidermal melanogenesis. However, given their relative protection from UVR, it is unclear whether NO plays a similar role in hair bulb melanocytes. OBJECTIVES: We aimed to identify the expression profiles of the NOS isoforms endothelial NOS (eNOS), neuronal NOS (nNOS) and inducible NOS (iNOS) and of phosphorylated eNOS and nitrotyrosine within the epidermal and follicular melanin units of normal human haired scalp during the hair growth cycle. METHODS: This study employed single and double immunohistochemical and immunofluorescence staining techniques using haired scalp from 10 healthy individuals (six women and four men). RESULTS: Melanocytes in the basal layer of the epidermis expressed eNOS, nNOS and nitrotyrosine. By contrast, melanogenically active melanocytes of the anagen hair bulb were wholly negative for these markers. However, other follicular melanocytes not actively involved in pigment production, including undifferentiated melanocytes located in the outer root sheath and melanocytes surviving the apoptosis-driven hair follicle (HF) regression during catagen/telogen, expressed eNOS, nNOS and nitrotyrosine. While iNOS was only weakly expressed in the basal layer of the human epidermis, it was highly expressed in keratinocytes of the inner root sheath (IRS), where it colocalized with trichohyalin, a differentiation-associated protein of the IRS that requires enzyme-catalysed conversion of arginine to citrulline. CONCLUSIONS: The NOS isoforms and nitrotyrosine are differentially expressed in different cutaneous melanocyte subpopulations. Results of this study suggest a possible role for eNOS, nNOS, iNOS and nitrotyrosine in melanocyte biology, particularly with respect to melanogenesis and melanocyte survival during HF regression. Another example of possible NO involvement in HF biology is the postsynthetic modification of trichohyalin in differentiating keratinocytes of the IRS. These results suggest that NO may influence several aspects of HF biology.     

Expression of decorin throughout the murine hair follicle cycle: hair cycle dependence and anagen phase prolongation

Decorin is a prototypical member of the small leucine‐rich proteoglycan (SLRP) family, which is involved in numerous biological processes. The role of decorin, as a representative SLRP, in hair follicle morphogenesis has not been elucidated. We present our initial findings on decorin expression patterns during induced murine hair follicle (HF) cycles. It was found that decorin expression is exclusively restricted to the epidermis, outer root sheath and sebaceous glands during the anagen phase, which correlates with the upregulation of decorin mRNA and protein expression in depilated murine dorsal skin. Furthermore, we used a functional approach to investigate the effects of recombinant human decorin (rhDecorin) via cutaneous injection into HFs at various murine hair cycle stages. The local injection of rhDecorin (100 μg/ml) into the hypodermis of depilated C57BL/6 mice at anagen delayed catagen progression. In contrast, rhDecorin injection during the telogen phase caused the premature onset of anagen, as demonstrated by the assessment of the following parameters: (i) hair shaft length, (ii) follicular bulbar diameter, (iii) hair follicle cycling score and (iv) follicular phase percentage. Taken together, our results suggest that decorin may modulate follicular cycling and morphogenesis. In addition, this study also provides insight into the molecular control mechanisms governing hair follicular epithelial–mesenchymal interactions.     

Immunohistochemical study on the keratin expression in generating rat hair tissues using anti-hair keratin monoclonal antibodies]

To investigate keratin expressions of generating rat hair tissues, monoclonal antibodies, HKN-2, 4, 5 and 6, were immunohistochemically applied on the skin specimens from 19-day-old rat fetus, newborn, 3-day-old and 7-day-old rats. In anagen hair tissues of 7-day-old rats, HKN-2 reacted with developing cells of the medulla, cortex, hair cuticle and inner and outer root sheaths. In the epidermis, HKN-2 reacted with spinous through horny cells. HKN-4 displayed a broad reactivity with all of the skin epithelial cells including hair tissue. These reactions were first seen in hair peg stage. HKN-2 and 4 first showed strong reactions with the innermost cell layer of the outer root sheath in anagen hair tissues of newborn rats. Reactivities by HKN-5 and 6 were localized in hair tissues in rats; however, HKN-5 showed no reaction with the innermost cell layer of the outer root sheath. HKN-5 and 6 showed no reaction with hair tissue before anagen. It is concluded that hair germ is different from epidermal basal cells in keratin expressions, that hair-specific keratins seem to be produced after the morphological differentiation of each layer, and that the innermost cell layer may differ from other outer root sheath since hair generation.     

Immunohistochemical distribution of aromatase and 3B-hydroxysteroid dehydrogenase in human hair follicle and sebaceous gland

Human hair follicles (HF) and sebaceous glands (SG) were assessed for the presence and distribution of the cytochrome P-450-aromatase (AR) and 3B-hydroxysteroid dehydrogenase (3B-HSD) enzymes. Immunohistochemical methods were used to examine both enzymes in male and female human skin specimens at various ages and different body sites. AR was found in the external root sheath of anagen, terminal HF, and in SG, whereas the 3B-HSD was found only in the SG. AR was rarely found in telogen HF. The expression of both enzymes, AR and 3B-HSD, did not vary with body site or sex. Localizing AR in the external root sheath of anagen HF suggests that AR may have a function in the HF cycle. We hypothesize that AR may be one of many enzymes or factors that play a role in the HF cycle by regulating the level of androgens formed locally, whereas 3B-HSD is localized in SG, converting weak androgen precursors to potent androgens, stimulating lipogenesis.     

Dynamic ultrastructural changes of the connective tissue sheath of human hair follicles during hair cycle

Summary Ultrastructural changes of the connective tissue sheath (CTS), including the hyaline membrane, of human hair follicles during the hair cycle, were studied in normal scalp skin specimens. In early anagen, the CTS was composed of a thin basal lamina and surrounding collagen tissue. The collagen tissue gradually thickened during the development of the hair and hair follicle. In mature anagen hair follicles, the collagen tissue was separated into three layers. The inner collagen layer, just outside the basal lamina, was thin and composed of collagen fibres running longitudinally parallel to the hair axis. The middle collagen layer was very thick with its collagen fibres running transversely against the hair axis and surrounding the inner hair tissue. Many fibroblasts were present among the collagen fibres in the middle layer, whereas the inner layer contained almost none. In the outer collagen layer, collagen fibres ran in various directions parallel to the outer surface of the outer root sheath cells. In late anagen, the basal lamina became very thick. In catagen, the basal lamine and the inner collagen layer became corrugated and showed oedematous change and degeneration. Surrounding fibroblasts showed active production of new collagen fibres, which seemed to fill the spaces left by the retraction of the hair follicle and hyaline membrane. These ultrastructural changes of the CTS show that there may be dynamic metabolic changes of the connective tissue around human hair follicles during the hair cycle.     

Intact hair follicle innervation is not essential for anagen induction and development

Abstract Neuropeptides produced, stored and secreted by the unusually dense sensory and autonomic innervation of hair follicles (HFs) can induce hair growth (anagen) and may be involved in hair growth control. To test the role of follicle innervation of HF cycling in vivo, we generated innervation-deficient HFs by unilateral surgical denervation of a defined region of back skin in C57BL/6 mice and assessed its effect on spontaneous and induced anagen development. Successful denervation was demonstrated by the absence of PGP 9.5+ or tyrosine hydroxylase+ nerves and nerve-associated neuropeptides (substance P, CGRP). By quantitative histomorphometry, no significant difference in spontaneous or cyclosporin A-induced anagen development could be detected between sham-operated control skin and denervated skin. Only after hair growth induction by depilation, a discrete, marginally significant retardation of anagen development was apparent in denervated HFs. Thus, even though cutaneous nerves may exert a minor modulatory role in depilation-induced hair growth, they are not essential for normal murine anagen development. Received: 4 March 1998