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

Identification of immune microenvironment changes, immune-related pathways and genes in male androgenetic alopecia

BACKGROUND

Although androgenetic alopecia (AGA) is classified as a non-inflammatory alopecia, histological evidence of microinflammation has long been recognized. However, changes in the immune microenvironment, immune-related pathways and the expression of immune-related genes (IRGs) involved in AGA remain unclear.

METHODS

The microarray gene expression data (GSE36169) from patients with male AGA were analyzed. gene set enrichment analysis (GSEA) among statistically changed genes was done. Kyoto Encyclopedia of Genes and Genomes and Gene Ontology analyses among differentially expressed genes were performed. differentially expressed genes were screened to identify IRGs based on the ImmPort database. The cytohubba-MCC plugin of Cytoscape was applied to screen hub immune genes. The infiltration levels of 28 immune cells were quantified adopting single-sample GSEA (ssGSEA) algorithm. The microarray gene expression data (GSE90594) of male AGA was analyzed to validate hub IRGs genes and differential infiltrated immune cells.

RESULTS

The ssGSEA revealed γδT cell, central memory CD8+ T cell, mast cell, immature B cell, activated CD8+ T cell, effector memory CD4+ T cell, eosinophil and neutrophil were significantly increased infiltration in the bald scalp. GSEA showed statistically changed genes were most enriched in immune related pathways, including innate immune system, adaptive immune system, cytokine signaling, interferon-γ signaling, interferon signaling and interleukins signaling. The 4 hub IRGs, including matrix metallopeptidase 9, protein tyrosine phosphatase receptor type C, bone morphogenetic protein 2, and thrombospondin 1, were enriched in the pathways of allograft rejection, coagulation and interferon-γ response.

CONCLUSION

In summary, we proposed that the increase in γδ T cells, central memory CD8+ T cells, activated CD8+ T cell as well as the infiltration of mast cells contributed to immune microenvironment changes in male AGA. The 4 hub IRGs may be involved in the development and progression of hair loss in male AGA through interferon-γ signal pathways.

Injury-induced interleukin-1 alpha promotes Lgr5 hair follicle stem cells de novo regeneration and proliferation via regulating regenerative microenvironment in mice

BACKGROUND

The hair follicles (HFs) are barely regenerated after loss in injuries in mammals as well as in human beings. Recent studies have shown that the regenerative ability of HFs is age-related; however, the relationship between this phenomenon and the stem cell niche remains unclear. This study aimed to find a key secretory protein that promotes the HFs regeneration in the regenerative microenvironment.

METHODS

To explore why age affects HFs de novo regeneration, we established an age-dependent HFs regeneration model in leucine-rich repeat G protein-coupled receptor 5 (Lgr5) + /mTmG mice. Proteins in tissue fluids were analyzed by high-throughput sequencing. The role and mechanism of candidate proteins in HFs de novo regeneration and hair follicle stem cells (HFSCs) activation were investigated through in vivo experiments. The effects of candidate proteins on skin cell populations were investigated by cellular experiments.

RESULTS

Mice under 3-week-old (3W) could regenerate HFs and Lgr5 HFSCs, which were highly correlated with the immune cells, cytokines, IL-17 signaling pathway, and IL-1α level in the regeneration microenvironment. Additionally, IL-1α injection induced de novo regeneration of HFs and Lgr5 HFSCs in 3W mouse model with a 5 mm wound, as well as promoted activation and proliferation of Lgr5 HFSCs in 7-week-old (7W) mice without wound. Dexamethasone and TEMPOL inhibited the effects of IL-1α. Moreover, IL-1α increased skin thickness and promoted the proliferation of human epidermal keratinocyte line (HaCaT) and skin-derived precursors (SKPs) in vivo and in vitro, respectively.

CONCLUSIONS

In conclusion, injury-induced IL-1α promotes HFs regeneration by modulating inflammatory cells and oxidative stress-induced Lgr5 HFSCs regeneration as well as promoting skin cell populations proliferation. This study uncovers the underlying molecular mechanisms enabling HFs de novo regeneration in an age-dependent model.

Melatonin Promotes the Development of Secondary Hair Follicles in Adult Cashmere Goats by Activating the Keap1-Nrf2 Signaling Pathway and Inhibiting the Inflammatory Transcription Factors NFκB and AP-1

Exogenous melatonin (MT) has been used to promote the growth of secondary hair follicles and improve cashmere fiber quality, but the specific cellular-level mechanisms involved are unclear. This study was carried out to investigate the effect of MT on the development of secondary hair follicles and on cashmere fiber quality in cashmere goats. The results showed that MT improved secondary follicle numbers and function as well as enhanced cashmere fiber quality and yield. The MT-treated goat groups had high secondary-to-primary ratios (S:P) for hair follicles, greater in the elderly group (p < 0.05). Antioxidant capacities of secondary hair follicles improved fiber quality and yield in comparison with control groups (p < 0.05/0.01). Levels of reactive oxygen and nitrogen species (ROS, RNS) and malondialdehyde (MDA) were lowered (p < 0.05/0.01) by MT. There was significant upregulation of antioxidant genes (for SOD-3; GPX-1; NFE2L2) and the protein of nuclear factor (Nrf2), and downregulation of the Keap1 protein. There were significant differences in the expression of genes for secretory senescence-associated phenotype (SASP) cytokines (IL-1β, IL-6, MMP-9, MMP-27, CCL-21, CXCL-12, CXCL-14, TIMP-1,2,3) plus their protein of key transcription factors, nuclear factor kappa B (NFκB) and activator protein-1 (AP-1), in comparison with the controls. We concluded that MT could enhance antioxidant capacity and reduce ROS and RNS levels of secondary hair follicles through the Keap1-Nrf2 pathway in adult cashmere goats. Furthermore, MT reduced the expression of the SASP cytokines genes by inhibiting the protein of NFκB and AP-1 in the secondary hair follicles in older cashmere goats, thus delaying skin aging, improving follicle survival, and increasing the number of secondary hair follicles. Collectively, these effects of exogenous MT enhanced the quality and yield of cashmere fibers, especially at 5-7 years old.

Local and Systemic Expression Pattern of MMP-2 and MMP-9 in Complex Regional Pain Syndrome

Matrix metalloproteinases (MMP)-2 and MMP-9 play important roles in inflammation as well as in pain processes. For this reason, we compared the concentrations of these enzymes in skin and serum of patients with complex regional pain syndrome (CRPS), other pain diseases and healthy subjects. We analyzed ipsi- and contralateral skin biopsies of 18 CRPS patients, as well as in 10 pain controls and 9 healthy subjects. Serum samples were analyzed from 20 CRPS, 17 pain controls and 17 healthy subjects. All samples were analyzed with ELISA. Concentrations were then compared to clinical data as well as to quantitative sensory testing data.MMP-2 was increased in both ipsi- and contralateral skin biopsies of CRPS patients compared to healthy subjects. While low ipsilateral MMP-2 was associated with trophic changes, contralateral MMP-2 inversely correlated with the CRPS severity. MMP-9 was also locally increased in ipsilateral CRPS skin, and higher ipsi- and contralateral MMP-9 levels correlated with CRPS severity. We conclude that MMP-2 and MMP-9 are differently expressed depending on the clinical phenotype in CRPS. PERSPECTIVE: This article describes an upregulation of MMPs in CRPS and pain controls and shows different expression of MMP-2 and -9 depending on clinical phenotype in CRPS. These results provide evidence that MMP-2 and -9 play a key role in CRPS pathophysiology.

Low-Level Light Therapy Downregulates Scalp Inflammatory Biomarkers in Men With Androgenetic Alopecia and Boosts Minoxidil 2% to Bring a Sustainable Hair Regrowth Activity

BACKGROUND AND OBJECTIVES

Low-level light therapies using visible to infrared light are known to activate several cellular functions, such as adenosine triphosphate and nitric oxide synthesis. However, few clinical observations report its biological consequences for skin and scalp homeostasis. Since scalp inflammation was recognized as a potential physiological obstacle to the efficacy of the reference hair regrowth drug Minoxidil in vivo and since perifollicular inflammation is the hallmark of about 50%-70% follicular units in androgenetic alopecia, we decided to investigate whether the anti-inflammatory activity of LLLT/GentleWaves® device were assigned to L'Oréal by Light BioScience L.L.C., Virginia Beach, VA (US) could enhance hair regrowth activity of Minoxidil.

STUDY DESIGN/MATERIALS AND METHODS

We conducted a first experimental clinical study on 64 men with androgenetic alopecia using LLLT/GentleWaves®, 590-nm predominant wavelength 70 seconds, specifically pulsed once per day, for 3 days, and we performed a whole-genome analysis of treated scalp biopsies. In a second clinical study, including 135 alopecic volunteers, we evaluated the hair regrowth activity in response to the upgraded LLLT/GentleWaves® device and Minoxidil.

RESULTS

In the first clinical study, whole-genome analysis of treated scalp biopsies showed downregulation of scalp inflammatory biomarkers, such as AP1/FOSB messenger RNA (mRNA) and mir21, together with the disappearance of CD69 mRNA, specific to scalp-infiltrating T cells of about 50% of the studied volunteers prior to the LLLT/GentleWaves® treatment. In the second clinical study, we observed that LLLT/GentleWaves® was able to boost the hair regrowth activity of a Minoxidil 2% lotion to the extent of the highest concentration (5%) in terms of efficacy, number of responders, and perceived performance.

CONCLUSIONS

Altogether, these observations suggest the potential benefit of LLLT/GentleWaves® as a noninvasive adjunctive technology for skin and scalp conditions, where a mild perifollicular inflammation is involved. Lasers Surg. Med. 2021. Copyright © 2021 Wiley Periodicals LLC.

Expression of matrix metalloproteinases and tissue inhibitor of matrix metalloproteinases in the hair cycle

According to the growth state of hair follicles, the hair cycle is divided into the anagen, catagen and telogen phases. A number of biological factors have been shown to synchronize with the hair cycle. As an important component of the hair follicle, the extracellular matrix is regulated by matrix metalloproteinases (MMPs) and their inhibitors (tissue inhibitor of matrix metalloproteinases; TIMPs). It has been reported that MMP-2, MMP-9 and TIMP-1 are associated with the hair cycle; however, their expression levels during the hair cycle have not been fully elucidated. Reverse transcription-polymerase chain reaction and ELISA analysis in the present study demonstrated that, during the hair cycle in mice, mRNA and protein expression levels of MMP-2 and MMP-9 were elevated in the anagen phase, and decreased during the catagen and telogen phases. Furthermore, SDS-PAGE gelatin zymography demonstrated that their activities fluctuated in the hair cycle. Additionally, it was observed that the mRNA and protein expression levels of TIMP-1 and TIMP-2 were negatively correlated with MMP-9 and MMP-2, respectively. Immunohistochemical examination demonstrated that MMP-2 and TIMP-2 were present in all structures of the hair follicle. However, MMP-9 and TIMP-1 were locally expressed in certain areas of the hair follicle, such as in the sebaceous gland at the anagen, catagen and telogen phases, and in the inner root sheath at the catagen phase. These results suggested that MMP-2 and MMP-9 may serve an important role in the hair growth cycle.

Collagenase IV plays an important role in regulating hair cycle by inducing VEGF, IGF-1, and TGF-β expression

Background

It has been reported that collagenases (matrix metalloproteinase 2 [MMP-2] and matrix metalloproteinase 9 [MMP-9]) are associated with hair cycle, whereas the mechanism of the association is largely unknown.

Methods

The mice were randomly allocated into four groups: saline, and 5, 10, and 15 nM SB-3CT. Immunohistochemical analysis was employed to examine MMP-2 and MMP-9 protein. Real-time polymerase chain reaction and enzyme-linked immunosorbent assay were performed to determine mRNA and protein levels of VEGF, IGF-1, TGF-β, and GAPDH. Growing hair follicles from anagen phase III–IV were scored based on hematoxylin and eosin staining. Hair regrowth was also evaluated.

Results

Results showed that mRNA expressions of enzymes changed with a peak at late anagen and a trough at telogen after depilation. Immunostaining showed that the highest expression of MMP-2 was more than that of MMP-9, and the highest expression of enzymes changed during anagen. The localizations of MMP-2 changed from dermal papilla, keratinocyte strand, out of root sheath, and basal plate at early anagen, to hair bulb, inner root sheath, and outer root sheath at late anagen. The localization of MMP-9 changed from partial keratinocyte to dermal papilla at early anagen and to outer root sheath at late anagen. VEGF, IGF-1, and TGF-β have been shown to regulate hair growth. We found mRNA and protein expressions of VEGF and IGF-1 fluctuated with a peak at anagen and a decrease at catagen to telogen. In contrast, mRNA and protein expressions of TGF-β changed with highest and lowest levels at anagen and telogen, respectively. With selective inhibitor of collagenase IV, SB-3CT, mice showed significant suppressed hair growth and decreased expression of VEGF, IGF-1, and TGF-β. The MMPs agonist also significantly increased expression of VEGF, IGF-1, and TGF-β. Meanwhile, SB-3CT treatment significantly suppressed hair growth.

Conclusion

All these data suggest that the type IV collagenases, MMP-2 and MMP-9, play important roles in hair cycle, and this could be mediated by induced expression of VEGF, IGF-1, and TGF-β.

Matriptase expression and zymogen activation in human pilosebaceous unit

Studies of human genetic disorders and mouse models reveal the important roles of matriptase in hair growth. Here, we investigate matriptase expression and zymogen activation in hair follicles. We show: 1) layer-dependent distribution patterns, with much higher matriptase expression in cells of the outer root sheath and matrix cells of the hair bulb than in cells of the inner root sheath; 2) cycle-dependent expression patterns, with matriptase expressed in the anagen and catagen phases of the hair lifecycle, but not in the telogen phase; 3) reduced expression of the matriptase inhibitor, HAI-1, in the catagen phase, suggesting increased proteolytic activity in this phase; and 4) definitive matriptase zymogen activation patterns, with the highest matriptase activation observed in matrix cells and outer root sheath cells in the isthmus/bulge region. In sebaceous glands, matriptase is highly expressed in basal and ductal cells, with much lower expression in the differentiated, lipid-filled cells of the interior. We also show that matriptase potently activates hepatocyte growth factor (HGF) in vitro, and that the HGF receptor, c-Met, is co-expressed in those cells that express activated matriptase. Our observations suggest that the matriptase-HGF-c-MET pathway has the potential to be engaged, primarily in proliferative cells rather than terminally differentiated epithelial cells of the human pilosebaceous unit.

From buds to follicles: matrix metalloproteinases in developmental tissue remodeling during feather morphogenesis

Organogenesis involves a series of dynamic morphogenesis and remodeling processes. Since feathers exhibit complex forms, we have been using the feather as a model to analyze how molecular pathways and cellular events are used. While several major molecular pathways have been studied, the roles of matrix degrading proteases and inhibitors in feather morphogenesis are unknown. Here we addressed this knowledge gap by studying the temporal and spatial expression of proteases and inhibitors in developing feathers using mammalian antibodies that cross react with chicken proteins. We also investigated the effect of protease inhibitors on feather development employing an in vitro feather bud culture system. The results show that antibodies specific for mammalian MMP2 and TIMP2 stained positive in both feather epithelium and mesenchyme. The staining co-localized in structures of E10-E13 developing feathers. Interestingly, MMP2 and TIMP2 exhibited a complementary staining pattern in developing E15 and E20 feathers and in maturing feather filaments. Although they exhibited a slight delay in feather bud development, similar patterns of MMP2 and TIMP2 staining were observed in in vitro culture explants. The broad spectrum pharmacological inhibitors AG3340 and BB103 (MMP inhibitors) but not Aprotinin (a plasmin inhibitor) showed a reversible effect on epithelium invagination and feather bud elongation. TIMP2, a physiological inhibitor to MMPs, exhibited a similar effect. Markers of feather morphogenesis showed that MMP activity was required for both epithelium invagination and mesenchymal cell proliferation. Inhibition of MMP activity led to an overall delay in the expression of molecules that regulate either early feather bud growth and/or differentiation and thereby produced abnormal buds with incomplete follicle formation. This work demonstrates that MMPs and their inhibitors are not only important in injury repair, but also in development tissue remodeling as demonstrated here for the formation of feather follicles.

Human female hair follicles are a direct, nonclassical target for thyroid-stimulating hormone

Pituitary thyroid-stimulating hormone (TSH) regulates thyroid hormone synthesis via receptors (TSH-R) expressed on thyroid epithelial cells. As the hair follicle (HF) is uniquely hormone-sensitive and, hypothyroidism with its associated, increased TSH serum levels clinically can lead to hair loss, we asked whether human HFs are a direct target for TSH. Here, we report that normal human scalp skin and microdissected human HFs express TSH-R mRNA. TSH-R-like immunoreactivity is limited to the mesenchymal skin compartments in situ. TSH may alter HF mesenchymal functions, as it upregulates alpha-smooth muscle actin expression in HF fibroblasts. TSH-R stimulation by its natural ligand in organ culture changes the expression of several genes of human scalp HFs (for example keratin K5), upregulates the transcription of classical TSH target genes and enhances cAMP production. Although the functional role of TSH in human HF biology awaits further dissection, these findings document that intracutaneous TSH-Rs are fully functional in situ and that HFs of female individuals are direct targets for nonclassical, extrathyroidal TSH bioregulation. This suggests that organ-cultured scalp HFs provide an instructive and physiologically relevant human model for exploring nonclassical functions of TSH, in and beyond the skin.

In vitro degradation of the inner root sheath in human hair follicles lacking sebaceous glands

BACKGROUND

Cultured hair follicles lacking sebaceous glands do not appear to degrade the inner root sheath (IRS), suggesting that the gland may be involved in this process.

OBJECTIVES

To examine this supposition in cultured hair follicles.

METHODS

Pilosebaceous units were isolated from hair follicles cultured in vitro, and IRS degradation was studied by histology.

RESULTS

When grown in culture, the fibres of follicles lacking sebaceous glands were encased in a layer of translucent tissue. During hair growth in vitro this tissue remained intact at the distal end of the follicle but disappeared further down towards the bulb and then reappeared towards the proximal end. Transection within the region lacking this tissue resulted in the release of a naked hair fibre and the production of hair with no attached tissue upon subsequent hair growth. The translucent tissue represented the IRS, thereby demonstrating that this tissue is indeed degraded in vitro. Histological comparison with freshly isolated pilosebaceous units indicated that IRS degradation in vitro strongly resembled the process that occurs in vivo.

CONCLUSIONS

These data suggest that the sebaceous gland does not itself participate in IRS degradation. Indeed, this phenomenon appears to be a function of the follicle itself and is probably intimately linked with the processes of cellular proliferation, differentiation and death that occur during hair biogenesis.

Human Scalp Dermal Papilla and Fibrous Sheath Cells have a different expression profile of Matrix Metalloproteinases in vitro when compared to Scalp Dermal Fibroblasts

The dermal papilla is a cluster of specialised mesenchymal cells at the bottom of the mammalian hair follicle, embedded in a loose extracellular matrix. These cells have the capability to induce and support hair growth via close epithelial-mesenchymal interactions with the keratinocytes surrounding the hair matrix. The extracellular matrix of the dermal papilla differs markedly from the interfollicular matrix and plays a key role in the maintenance of hair growth. In this study we investigated the expression pattern and activity of matrix metalloproteinases (MMP) and their tissue inhibitor in in vitro cultures of cells derived from scalp dermal papilla and fibrous sheath. Expression and activity of MMP-1, MMP-2, MMP-3, MMP-9, TIMP-1, TIMP-2 and MT1-MMP were analysed in those cells cultured in contact with one of the relevant protein component of the dermal matrix, collagen type I as well as in monolayer. Zymographic analysis showed activation of MMP-2 in all cells grown in three-dimensional collagen lattices whereas MMP-9 was activated only in three-dimensional collagen cultures of dermal fibroblasts and weakly in follicular cells. Expression of MMP-1, TIMP-1, TIMP-2 and MT1-MMP was similar in all cells, in both culture conditions, whereas expression of MMP-3 was absent in dermal papilla cells. In addition to a series of reported morphological and functional differences between dermal fibroblasts and the dermal mesenchyme-derived cells of the hair follicle, we reported differences in MMP expression in dermal papilla and fibrous sheath cells within the mesenchymal population of the hair follicle.

Matrix metalloproteinase-19 expression in normal and diseased skin: dysregulation by epidermal proliferation

Most of the matrix metalloproteinases (MMP) are not expressed in normal intact skin but they are upregulated in inflamed or diseased skin. The recently cloned MMP-19 is one of the few MMP members that are also expressed in healthy epidermis. In this study, we found that MMP-19 is generally coexpressed with cytokeratin 14 that is confined to keratinocytes of the stratum basale. MMP-19 was also detected in hair follicles, sebaceous glands, and eccrine sweat glands. Its expression, however, changed in cutaneous diseases exhibiting increased alternations of epidermal proliferation, such as psoriasis, eczema, and tinea. In the affected area, MMP-19 was also found in suprabasal and spinous epidermal layers. We also studied the regulation of MMP-19 expression at the protein level, as well as by using a promoter assay. The constitutive expression of MMP-19 was upregulated with phorbol myristate acetate and downregulated with retinoic acid and dexamethasone. Tumor necrosis factor-alpha, interleukin (IL)-6, TGF-beta, IL-15, IL-8, and RANTES as well as the bacterial compounds lipopolysaccharide and lipoteichoic acid did not show any profound effect in HaCaT cells. In contrast, type IV and type I collagens upregulated MMP-19 significantly. The dysregulation of MMP-19 expression in epidermis suggests its possible involvement in the perpetuation of cutaneous infections and proliferative disorders such as psoriasis.

Epimorphin acts to induce hair follicle anagen in C57BL/6 mice

Epimorphin is a mesenchymal morphogen that has been shown to mediate epithelial-mesenchymal signaling interactions in various organs. We now show that epimorphin functions in hair follicle morphogenesis; using a novel ex vivo organ culture assay, we define a mechanism for epimorphin signaling that may provide insight into general developmental processes. We found that epimorphin was produced by follicular mesenchymal cells and bound selectively to follicular epithelial cells, and that treatment with recombinant epimorphin could stimulate procession of hair follicles from telogen (resting stage) to anagen (growing stage). Based on analyses of epimorphin proteolytic digests that suggested a smaller peptide might be able to substitute for the full-length epimorphin molecule, we determined that pep7, a 10-amino acid peptide, was capable of inducing telogen-to-anagen transition both in the culture assay and in the mouse. That pep7 showed maximal activity only when modified with specific sulfhydryl-reactive reagents suggested that a particular structural conformation of the peptide was essential for activity; molecular dynamics studies were pursued to investigate the active peptide structure. These findings define a previously unknown morphogenic process in the hair follicle that may have applications to many other organs.

Protease-Activated Receptor-1 (Thrombin Receptor) Is Expressed in Mesenchymal Portions of Human Hair Follicle

Protease nexin-1, a serine protease inhibitor, is expressed specifically in the dermal papilla (DP) of anagen hair follicles and is suggested to be one of the modulators of the cyclic growth of hair follicles. Accumulating evidence has shown that protease nexin-1 plays its biologic role by inhibiting thrombin action in various systems other than the hair follicle. Thrombin has various physiologic functions including blood coagulation cascade, mostly via activation of protease-activated receptors (PAR). In this study, we investigated the expression of PAR mRNA using RT-PCR in dissected human hair follicles. We showed that PAR-1 mRNA was expressed specifically in the mesenchymal portions, including DP and connective tissue sheath, of anagen hair follicles. Furthermore, immunoreactivity for PAR-1 was detected in the DP and lower portion of connective tissue sheath in the anagen and catagen phases and in the DP of telogen hair follicles. Because only a pharmacologic level (100 nM) of thrombin significantly stimulated cell proliferation and DNA synthesis of the cultured dermal papilla cells, thrombin does not seem to have a mitogenic effect on dermal papilla cells physiologically. These results raise the possibility that thrombin is involved in the cyclic hair growth through its receptor of PAR-1.

Hair keratin pattern in human hair follicles grown in vitro

The keratin family includes epithelial (soft) keratins and hair (hard) keratins, and can be divided into acidic type I and basic to neutral type II subfamilies. Recently, nine type I and six type II hair keratin genes have been characterized through the screening of a human PAC library. The expression of these genes in the hair follicle was determined in vivo and a combined catalog of acidic and basic hair keratins was established. In this study, we investigated the expression and localization of most of the human hair keratin members of both types in human hair grown in vitro. We show that in vitro growth of hair follicles for 10 days in complete William's E culture medium did not alter the expression pattern of hair keratins. Similarly to the in vivo situation, each hair keratin was localized in precise and discrete compartments of the follicle, ranging from the matrix to the upper cortex and/or the hair cuticle. This study shows that the increase in length of in vitro grown follicles was accompanied by the proper hair shaft keratinization process. It also shows that hair follicle integrity was maintained in vitro, both in terms of gross morphology and molecular organization despite the complexity of the keratin expression pattern.