Hair shaft elongation, follicle growth, and spontaneous regression in long-term, gelatin sponge-supported histoculture of human scalp skin

Comparison of "Dimensionality" of Cancer Cell Culture in Gelfoam® Histoculture and Matrigel

Cell and tissue culture can be performed on different substrates such as on plastic, in Matrigel™, and on Gelfoam^®, a sponge matrix. Each of these substrates consists of a very different surface, ranging from hard and inflexible, a gel, and a sponge-matrix, respectively. Folkman and Moscona found that cell shape was tightly coupled to proper gene expression. The flexibility of a substrate is important for cells to maintain their optimal shape. Human osteosarcoma cells, stably expressing a fusion protein of a_v integrin, and green fluorescent protein (GFP), grew as a simple monolayer without any structure formation on the surface of a plastic dish. When the osteosarcoma cells were cultured within Matrigel, the cancer cells formed colonies but no other structures. When the cancer cells were seeded on Gelfoam^®, the cells formed 3-dimensional tissue-like structures. These results indicate that Gelfoam^® histoculture, unlike Matrigel™ culture, is true 3-dimensional.

Nestin-Expressing Hair-Follicle-Associated Pluripotent (HAP) Stem Cells Promote Whisker Sensory-Nerve Growth in Long-Term 3D-Gelfoam® Histoculture

Mouse whiskers containing hair-follicle-associated pluripotent (HAP) stem cells, from nestin-driven green fluorescent protein (ND-GFP) transgenic mice, were placed in 3D histoculture supported by Gelfoam(®). β-III tubulin-positive fibers, consisting of ND-GFP-expressing HAP stem cells, extended up to 500 mm from the whisker nerve stump in histoculture. The growing fibers had growth cones on their tips expressing F-actin indicating they were growing axons. The growing whisker sensory nerve was highly enriched in ND-GFP HAP stem cells which appeared to play a major role in its elongation and interaction with other nerves placed in 3D culture, including the sciatic nerve, the trigeminal nerve, and the trigeminal nerve ganglion. The results suggested that a major function of HAP stem cells in the hair follicle is for growth of the hair follicle sensory nerve.

3D Sponge-Matrix Histoculture: An Overview

Three-dimensional cell culture and tissue culture (histoculture) is much more in vivo-like than 2D culture on plastic. Three-dimensional culture allows investigation of crucial events in tumor biology such as drug response, proliferation and cell cycle progression, cancer cell migration, invasion, metastasis, immune response, and antigen expression that mimic in vivo conditions. Three-dimensional sponge-matrix histoculture maintains the in vivo phenotype, including the formation of differentiated structures of normal and malignant tissues, perhaps due to cells maintaining their natural shape in a sponge-gel matrix such as Gelfoam^®. Sponge-matrix histoculture can also support normal tissues and their function including antibody-producing lymphoid tissue that allows efficient HIV infection, hair-growing skin, excised hair follicles that grow hair, pluripotent stem cells that form nerves, and much more.

Hair-Shaft Growth in Gelfoam® Histoculture of Skin and Isolated Hair Follicles

Human scalp skin with abundant hair follicles in various stages of the hair growth cycle was histocultured for up to 40 days on Gelfoam^® at the air/liquid interface. The anagen hair follicles within the histoculture scalp skin produced growing hair shafts. Hair follicles could continue their cycle in histoculture; for example, apparent spontaneous catagen induction was observed both histologically and by the actual regression of the hair follicle. In addition, vellus follicles were shown to be viable at day 40 after initiation of culture. Follicle keratinocytes continued to incorporate [³H]thymidine for up to several weeks after shaft elongation had ceased. Intensive hair growth was observed in the pieces of shaved mouse skin histocultured on Gelfoam^®. Isolated human and mouse hair follicles also produced growing hair shafts. By day 63 in histoculture of mouse hair follicles, the number of hair follicle-associated pluripotent (HAP) stem cells increased significantly and the follicles were intact. Gelfoam^® histoculture of skin demonstrated that the hair follicle cells are the most sensitive to doxorubicin which prevented hair growth, thereby mimicking chemotherapy-induced alopecia in Gelfoam^® histoculture.

Efficacy of a Cell-Cycle Decoying Killer Adenovirus on 3-D Gelfoam®-Histoculture and Tumor-Sphere Models of Chemo-Resistant Stomach Carcinomatosis Visualized by FUCCI Imaging

Stomach cancer carcinomatosis peritonitis (SCCP) is a recalcitrant disease. The goal of the present study was to establish an in vitro-in vivo-like imageable model of SCCP to develop cell-cycle-based therapeutics of SCCP. We established 3-D Gelfoam^® histoculture and tumor-sphere models of SCCP. FUCCI-expressing MKN-45 stomach cancer cells were transferred to express the fluorescence ubiquinized cell-cycle indicator (FUCCI). FUCCI-expressing MKN-45 cells formed spheres on agarose or on Gelfoam^® grew into tumor-like structures with G₀/G₁ cancer cells in the center and S/G₂ cancer cells located in the surface as indicated by FUCCI imaging when the cells fluoresced red or green, respectively. We treated FUCCI-expressing cancer cells forming SCCP tumors in Gelfoam^® histoculture with OBP-301, cisplatinum (CDDP), or paclitaxel. CDDP or paclitaxel killed only cycling cancer cells and were ineffective against G₁/G₂ MKN-45 cells in tumors growing on Gelfoam^®. In contrast, the telomerase-dependent adenovirus OBP-301 decoyed the MKN-45 cells in tumors on Gelfoam^® to cycle from G₀/G₁ phase to S/G₂ phase and reduced their viability. CDDP- or paclitaxel-treated MKN-45 tumors remained quiescent and did not change in size. In contrast, OB-301 reduced the size of the MKN-45 tumors on Gelfoam^®. We examined the cell cycle-related proteins using Western blotting. CDDP increased the expression of p53 and p21 indicating cell cycle arrest. In contrast, OBP-301 decreased the expression of p53 and p21 Furthermore, OBP-301 increased the expression of E2F and pAkt as further indication of cell cycle decoy. This 3-D Gelfoam^® histoculture and FUCCI imaging are powerful tools to discover effective therapy of SCCP such as OBP-301.

Protocols for Gelfoam(®) Histoculture of Hair-Shaft-Producing Mouse Whisker Follicles Containing Nestin-GFP-Expressing Hair-Follicle-Associated Pluripotent (HAP) Stem Cells for Long Time Periods

Gelfoam(®)-histocultured whisker follicles from nestin-driven-green fluorescent protein (ND-GFP) mice produced growing pigmented and unpigmented hair shafts. Hair-shaft length increased rapidly by day 4 and continued growing until at least day 12 after which the hair-shaft length was constant. By day 63 in histoculture, the number of ND-GFP hair follicle-associated pluripotent (HAP) stem cells increased significantly and the follicles were intact. Three-dimensional Gelfoam(®) histoculture of hair follicles can provide a very long-term period for evaluating novel agents to promote hair growth.

Putting the Human Hair Follicle Cycle on the Map

A detailed characterization of the normal (in situ) human hair follicle cycle, supplemented with expressional data on specific hair follicle markers, has been awaited by basic hair researchers and dermatologists. Combining this hair cycle guide, together with a thorough analysis of the human-on-mouse hair xenograft model, provides solid ground for examining human hair cycle biology and pathology and for hair cycle-related pharmacological testing.

Surface Tension Guided Hanging-Drop: Producing Controllable 3D Spheroid of High-Passaged Human Dermal Papilla Cells and Forming Inductive Microtissues for Hair-Follicle Regeneration

Human dermal papilla (DP) cells have been studied extensively when grown in the conventional monolayer. However, because of great deviation from the real in vivo three-dimensional (3D) environment, these two-dimensional (2D) grown cells tend to lose the hair-inducible capability during passaging. Hence, these 2D caused concerns have motivated the development of novel 3D culture techniques to produce cellular microtissues with suitable mimics. The hanging-drop approach is based on surface tension-based technique and the interaction between surface tension and gravity field that makes a convergence of liquid drops. This study used this technique in a converged drop to form cellular spheroids of dermal papilla cells. It leads to a controllable 3Dspheroid model for scalable fabrication of inductive DP microtissues. The optimal conditions for culturing high-passaged (P8) DP spheroids were determined first. Then, the morphological, histological and functional studies were performed. In addition, expressions of hair-inductive markers including alkaline phosphatase, α-smooth muscle actin and neural cell adhesion molecule were also analyzed by quantitative RT-PCR, immunostaining and immunoblotting. Finally, P8-DP microtissues were coimplanted with newborn mouse epidermal cells (EPCs) into nude mice. Our results indicated that the formation of 3D microtissues not only endowed P8-DP microtissues many similarities to primary DP, but also confer these microtissues an enhanced ability to induce hair-follicle (HF) neogenesis in vivo. This model provides a potential to elucidate the native biology of human DP, and also shows the promising for the controllable and scalable production of inductive DP cells applied in future follicle regeneration.

Extensive Hair-Shaft Elongation by Isolated Mouse Whisker Follicles in Very Long-Term Gelfoam® Histoculture

We have previously studied mouse whisker follicles in Gelfoam® histoculture to determine the role of nestin-expressing plutipotent stem cells, located within the follicle, in the growth of the follicular sensory nerve. Long-term Gelfoam® whisker histoculture enabled hair follicle nestin-expressing stem cells to promote the extensive elongation of the whisker sensory nerve, which contained axon fibers. Transgenic mice in which the nestin promoter drives green fluorescent protein (ND-GFP) were used as the source of the whiskers allowing imaging of the nestin-expressing stem cells as they formed the follicular sensory nerve. In the present report, we show that Gelfoam®-histocultured whisker follicles produced growing pigmented and unpigmented hair shafts. Hair-shaft length increased rapidly by day-4 and continued growing until at least day-12 after which the hair-shaft length was constant. By day-63 in histoculture, the number of ND-GFP hair follicle stem cells increased significantly and the follicles were intact. The present study shows that Gelfoam® histoculture can support extensive hair-shaft growth as well as hair follicle sensory-nerve growth from isolated hair follicles which were maintained over very long periods of time. Gelfoam® histoculture of hair follicles can provide a very long-term period for evaluating novel agents to promote hair growth.

3-dimensional tissue is formed from cancer cells in vitro on Gelfoam®, but not on Matrigel™

Cell and tissue culture can be performed on different substrates such as on plastic, in Matrigel™, and on Gelfoam(®), a sponge matrix. Each of these substrates consists of a very different surface, ranging from hard and inflexible, a gel, and a sponge-matrix, respectively. Folkman and Moscona found that cell shape was tightly coupled to DNA synthesis and cell growth. Therefore, the flexibility of a substrate is important for cells to maintain their optimal shape. Human osteosarcoma cells, stably expressing a fusion protein of α(v) integrin and green fluorescent protein (GFP), grew as a simple monolayer without any structure formation on the surface of a plastic dish. When the osteosarcoma cells were cultured within Matrigel™, the cancer cells formed colonies but no other structures. When the cancer cells were seeded on Gelfoam(®), the cells formed three-dimensional tissue-like structures. The behavior of 143B osteosarcoma cells on Gelfoam(®) in culture is remarkably different from those of these cells in monolayer culture or in Matrigel™. Tissue-like structures were observed only in Gelfoam(®) culture. The data in this report suggest a flexible structural substrate such as Gelfoam(®) provides a more in vivo-like culture condition than monolayer culture or Matrigel(TM) and that Matrigel(TM) does not result in actual three-dimensional culture.

Invading cancer cells are predominantly in G0/G1 resulting in chemoresistance demonstrated by real-time FUCCI imaging

Invasive cancer cells are a critical target in order to prevent metastasis. In the present report, we demonstrate real-time visualization of cell cycle kinetics of invading cancer cells in 3-dimensional (3D) Gelfoam® histoculture, which is in vivo-like. A fluorescence ubiquitination cell cycle indicator (FUCCI) whereby G0/G1 cells express a red fluorescent protein and S/G2/M cells express a green fluorescent protein was used to determine the cell cycle position of invading and non-invading cells. With FUCCI 3D confocal imaging, we observed that cancer cells in G0/G1 phase in Gelfoam® histoculture migrated more rapidly and further than cancer cells in S/G2/M phases. Cancer cells ceased migrating when they entered S/G2/M phases and restarted migrating after cell division when the cells re-entered G0/G1. Migrating cancer cells also were resistant to cytotoxic chemotherapy, since they were preponderantly in G0/G1, where cytotoxic chemotherapy is not effective. The results of the present report suggest that novel therapy targeting G0/G1 cancer cells should be developed to prevent metastasis.

The role of hair follicle nestin-expressing stem cells during whisker sensory-nerve growth in long-term 3D culture

We have previously reported that nestin-expressing hair follicle stem cells can differentiate into neurons, Schwann cells, and other cell types. In the present study, vibrissa hair follicles, including their sensory nerve stump, were excised from transgenic mice in which the nestin promoter drives green fluorescent protein (ND-GFP mice), and were placed in 3D histoculture supported by Gelfoam®. β-III tubulin-positive fibers, consisting of ND-GFP-expressing cells, extended up to 500 µm from the whisker nerve stump in histoculture. The growing fibers had growth cones on their tips expressing F-actin. These findings indicate that β-III tubulin-positive fibers elongating from the whisker follicle sensory nerve stump were growing axons. The growing whisker sensory nerve was highly enriched in ND-GFP cells which appeared to play a major role in its elongation and interaction with other nerves in 3D culture, including the sciatic nerve, the trigeminal nerve, and the trigeminal nerve ganglion. The results of the present report suggest a major function of the nestin-expressing stem cells in the hair follicle is for growth of the follicle sensory nerve.

Mimicking hair disorders by genetic manipulation of organ-cultured human hair follicles

Human hair follicles can be dissected out of scalp skin and cultured in vitro in defined growth medium. Hair follicle organ cultures have previously been used to investigate the molecular and cellular mechanisms through which various factors regulate the maintenance and cycling of adult hair follicles. In this issue, Samuelov et al. transfected organ-cultured human hair follicles with siRNA nucleotides and suppressed the expression of the endogenous P-cadherin gene in follicular keratinocytes. Knocking down the expression of P-cadherin in hair follicles in vitro recapitulated the hair follicle phenotype observed in patients with hypotrichosis with juvenile macular dystrophy (HJMD) and enabled the authors to establish a cause-effect relationship between loss of P-cadherin and suppression of the canonical Wnt signaling pathway and upregulation of TGFβ2 during development of the hair abnormalities observed in HJMD patients.

Techniques for the discovery and evaluation of drugs against alopecia

INTRODUCTION

Hair care, color and style play an important role in physical appearance and self-perception. Hair loss or alopecia is a common dermatological and affective disorder. Factors contributing to alopecia include genetic predisposition, hormonal factors, disease status, side effects of chemotherapeutic agents and stress. To keep pace with the demand for drugs for alopecia, attempts are being made to explore drugs with hair-growth-promotion activity. To explore and evaluate these, it is necessary to be familiar with the basics and the availability and suitability of techniques and experimental models of hair growth activity assessment.

AREAS COVERED

Basic and advanced techniques and models for assessing hair growth activity. A variety of pharmacological models of hair growth are reviewed. This review will help in selecting a suitable, relevant, inexpensive, easy and reliable model for hair growth assessment.

EXPERT OPINION

There is a need to identify the genes involved in hair follicle growth for the production of more effective animal models of the disorder. Standardization of pharmacological models will also be essential for better comparison and validation of results. Recently developed hair follicle organ culture models are a suitable, relevant and inexpensive alternative to traditional whole-animal pharmacological models and will, largely, replace whole-animal systems in the future.

A human folliculoid microsphere assay for exploring epithelial- mesenchymal interactions in the human hair follicle

The search for more effective drugs for the management of common hair growth disorders remains a top priority, both for clinical dermatology and industry. In this pilot study, we report a pragmatic organotypic assay for basic and applied hair research. The patented technique produces microdroplets, which generate human folliculoid microspheres (HFMs), consisting of human dermal papilla fibroblasts and outer root sheath keratinocytes within an extracellular matrix that simulates elements of the hair follicle mesenchyme. Studying a number of different markers (for example, proliferation, apoptosis, cytokeratin-6, versican), we show that these HFMs, cultured under well-defined conditions, retain several essential epithelial-mesenchymal interactions characteristic for human scalp hair follicle. Selected, recognized hair growth-modulatory agents modulate these parameters in a manner that suggests that HFMs allow the standardized preclinical assessment of test agents on relevant human hair growth markers under substantially simplified in vitro conditions that approximate the in vivo situation. Furthermore, we show by immunohistochemistry, reverse transcriptase-PCR, and DNA microarray techniques that HFMs also offer a useful discovery tool for the identification of target genes and their products for candidate hair drugs. HFM thus represent an instructive modern experimental and screening tool for basic and applied hair research in the human system.

Establishment and characteristics of Gottingen minipig skin in organ culture and monolayer cell culture: relevance to drug safety testing

Skin from Gottingen minipigs was used as a source of tissue for organ and cell culture and compared to human skin for growth conditions and sensitivity to irritants. Optimal organ culture conditions were determined, based on the preservation of the histological structure. These included serum-free, growth factor-free conditions with a calcium concentration of 1.5mM. Formulations in which the calcium concentration were low (0.075-0.15mM) failed to support tissue viability (even in the presence of dialyzed serum). Epidermal keratinocytes were grown from tissue explants and as single cells from enzyme-disrupted tissue. Optimal keratinocyte growth was achieved using a serum-free, growth factor-supplemented culture medium with a calcium concentration of 0.15mM. Fibroblasts were optimally grown from explant cultures using a medium with 1.5mM calcium and 10% fetal bovine serum. The conditions that were optimal for maintenance of intact pig skin, as well as for the isolated cells, are the same conditions that have been shown previously to be optimal for intact human skin and skin cells. In additional studies, pig skin keratinocytes and fibroblasts were exposed to a panel of contact irritants and contact sensitizers. Using growth inhibition as the response, the median effective dose values with each agent were very similar to the values previously determined for human epidermal keratinocytes and human dermal fibroblasts. Taken together, these data suggest that the skin from the Gottingen minipig can be used as a surrogate for human skin in ex vivo skin safety studies.

Towards the development of a simplified long-term organ culture method for human scalp skin and its appendages under serum-free conditions

Organ culture of human scalp skin is usually performed with serum-containing medium, which limits its analytical usefulness. Here we report that intact human scalp skin can be grown at the air/liquid interface in supplemented, serum-free William's E medium for more than 2 weeks. Active hair shaft growth was visible until day 16 and was significantly enhanced compared with minimum essential medium (MEM) + 10% fetal bovine serum (FBS). Moreover, William's E medium protected better against cell death than MEM + 10% FBS before day 12. Using quantitative immunochemistry, proliferating (Ki-67+) cells could still be observed in the epithelium of hair follicles even on day 17 of serum-free skin organ culture. The number of apoptotic (TUNEL+) cells in the skin epithelium rose steadily after day 5. Giemsa stains revealed mature skin mast cells even after 13 days in culture. The percentage of surviving hair follicles (mostly with catagen- or telogen-like morphology) gradually increased over time displaying mostly catagen hair follicles after 17 days of culture. Although epidermis and hair follicle epithelium showed increasing atrophy and degeneration, and their pigmentation decreased gradually over time, some long-term-surviving epithelial islands were found in association with remnants of follicular structures as late as on day 88. These preliminary data suggest that a very simple serum-free organ culture method allows prolonged human skin and hair follicle survival as well as some limited hair follicle cycling in intact skin for more than 2 weeks under well-defined experimental conditions. This pragmatic assay invites multiple uses, and may become a valuable tool for both skin and hair research.

Protection Against Chemotherapy-Induced Alopecia

PURPOSE

The goal is to provide an overview on the advances in protection against chemotherapy-induced alopecia (CIA).

MATERIALS AND METHODS

The four major parts of this review are (a) overview of the hair follicle biology, (b) characteristics of CIA, (c) state-of-the-art animal models of CIA, and (d) experimental approaches on protection against CIA.

RESULTS

The hair follicle represents an unintended target of cancer chemotherapy. CIA is a significant side effect that compromises the quality of life of patients. Overcoming CIA represents an area of unmet needs, especially for females and children. Significant progresses have been made in the last decade on the pathobiology of CIA. The pharmacological agents under evaluation include drug-specific antibodies, hair growth cycle modifiers, cytokines and growth factors, antioxidants, cell cycle or proliferation modifiers, and inhibitors of apoptosis. Their potential applications and limitations are discussed.

CONCLUSION

Multiple classes of agents with different action mechanisms have been evaluated in animal CIA models. Most of these protective agents have activity limited to a single chemotherapeutic agent. In comparison, calcitriol and cyclosporine A have broader spectrum of activity and can prevent against CIA by multiple chemotherapeutic agents. Among the three agents that have been evaluated in humans, AS101 and Minoxidil were able to reduce the severity or shorten the duration of CIA but could not prevent CIA.

The hair follicle and its stem cells as drug delivery targets

The hair follicle is a skin appendage with a complex structure containing many cell types that produce highly specialised proteins. The hair follicle is in a continuous cycle: anagen is the hair growth phase, catagen the involution phase and telogen is the resting phase. The follicle offers many potential therapeutic targets. Hoffman and colleagues have pioneered hair-follicle-specific targeting using liposomes to deliver small and large molecules, including genes. They have also pioneered ex vivo hair-follicle targeting with continued expression of the introduced gene following transplantation. Recently, it has been discovered that hair follicle stem cells are highly pluripotent and can form neurons, glial cells and other cell types, and this has suggested that hair follicle stem cells may serve as gene therapy targets for regenerative medicine.

Reorganization of hair follicles in human skin organ culture induced by cultured human follicle-derived cells

Studies of human hair follicle (HF) induction by follicle-derived cells have been limited due to a lack of suitable test systems. In this study, we established a skin organ culture system which supports HF formation by follicle-derived cells. Long-term skin organ cultures were set up from human retroauricular skin specimens and maintained in culture for up to 8 weeks. In vitro expanded human HF-derived cells from the dermal papilla (DP) and the outer root sheath (ORS) were injected together into the skin specimens and evaluated for their ability to induce reorganization of HFs. Macroscopic analysis of the cultured skin specimens demonstrated the growth of velus-like hair after 4 weeks in culture. Histologic evaluation of the cultured skin specimens after 8 weeks of culture revealed multiple miniaturized HFs with sebaceous glands. In addition, cell clusters of various differentiation stages could be demonstrated in serial sections of the cultured skin specimens. Labeling of HF-derived cells with the fluorescence dye CFDA-1 prior to injection suggested a de novo reorganization of HFs out of the injected cells. In conclusion, the study demonstrated HF formation by HF-derived cells in an in vitro skin organ culture model.

Hair follicles serve as local reservoirs of skin mast cell precursors

Several leukocyte populations normally reside in mouse skin, including Langerhans cells and gammadelta T cells in the epidermis and macrophage and mast cells in the dermis. Interestingly, these skin resident leukocytes are frequently identified within or around hair follicles (HFs), which are known to contain stem cell populations that can generate the epidermal architecture or give rise to the melanocyte lineage. Thus, we reasoned that HFs might serve as a local reservoir of the resident leukocyte populations in the skin. When vibrissal follicles of adult mice were cultured in the presence of stem cell factor (SCF), interleukin 3 (IL-3), IL-7, granulocyte-macrophage colony-stimulating factor, and Flt3 ligand, CD45+/lineage-/c-kit+/FcepsilonRI+ cells became detectable on the outgrowing fibroblasts in 10 days and expanded progressively thereafter. These HF-derived leukocytes showed characteristic features of connective tissue-type mast cells, including proliferative responsiveness to SCF, metachromatic granules, mRNA expression for mast cell proteases-1, -4, -5, and -6, and histamine release on ligation of surface IgE or stimulation with substance P or compound 48/80. These results, together with our findings that HFs contain c-kit+ cells and produce SCF mRNA and protein, suggest that HFs provide a unique microenvironment for local development of mast cells.

In vivo induction of hair growth by dermal cells isolated from hair follicles after extended organ culture

Successful hair follicle organ culture has been established for some time, but hair growth in vitro is limited and generally terminates prematurely in comparison with in vivo. The reasons why growth stops in culture are as yet unknown. In this investigation, adult rat vibrissa follicles for which growth in culture is limited to about 10 d, were maintained in vitro for a minimum of 20 d after the hair shaft stopped growing. The pattern of fiber growth and long-term follicle pathology reflected the initial hair cycle stage at the time of isolation. Furthermore, there was evidence that a group of follicles put into culture when in late anagen were attempting to cycle in vitro. Microscopy showed that, in spite of widespread pathologic changes to the follicle epithelium, dermal cells in the follicle showed remarkable resilience. Their viability was confirmed when primary cell cultures were established from isolated dermal tissue. These cells labeled positively for alpha-smooth muscle actin, an established marker of hair follicle dermal cell phenotype in vitro. Moreover, isolated dermal tissue induced hair growth when implanted into inactivated hair follicles in vivo. These data confirm that the cessation in hair growth is not due to a loss of the inductive capacity in the dermal component. Long-term organ culture may provide opportunities to investigate factors that are expressed or lost during hair growth cessation. In addition it may be possible to develop this method further to obtain a reliable and predictable model of hair follicle cycling in vitro.

Treatments for androgenetic alopecia and alopecia areata: current options and future prospects

Androgenetic alopecia and alopecia areata are common disorders of the hair follicle which may heavily influence self esteem and self image. Androgenetic alopecia is caused by the heightened sensitivity of scalp follicles to dihydro- testosterone whereas alopecia areata is induced by an autoimmune reaction. Current drug treatment approaches include the use of regrowth stimulators such as topical minoxidil and oral finasteride for androgenetic alopecia, as well as topical minoxidil, dithranol (anthralin), corticosteroids, contact sensitisers, and psoralen plus ultraviolet A irradiation (PUVA) therapy for alopecia areata. Combination regimens are also proposed. However, extreme cases of either type of alopecia do not generally respond well to these existing treatments. For this reason, new therapeutic strategies are directed towards both improving the targeting of existing agents, as well as the development of novel hypertrichotic modalities.

Controls of hair follicle cycling

Nearly 50 years ago, Chase published a review of hair cycling in which he detailed hair growth in the mouse and integrated hair biology with the biology of his day. In this review we have used Chase as our model and tried to put the adult hair follicle growth cycle in perspective. We have tried to sketch the adult hair follicle cycle, as we know it today and what needs to be known. Above all, we hope that this work will serve as an introduction to basic biologists who are looking for a defined biological system that illustrates many of the challenges of modern biology: cell differentiation, epithelial-mesenchymal interactions, stem cell biology, pattern formation, apoptosis, cell and organ growth cycles, and pigmentation. The most important theme in studying the cycling hair follicle is that the follicle is a regenerating system. By traversing the phases of the cycle (growth, regression, resting, shedding, then growth again), the follicle demonstrates the unusual ability to completely regenerate itself. The basis for this regeneration rests in the unique follicular epithelial and mesenchymal components and their interactions. Recently, some of the molecular signals making up these interactions have been defined. They involve gene families also found in other regenerating systems such as fibroblast growth factor, transforming growth factor-beta, Wnt pathway, Sonic hedgehog, neurotrophins, and homeobox. For the immediate future, our challenge is to define the molecular basis for hair follicle growth control, to regenerate a mature hair follicle in vitro from defined populations, and to offer real solutions to our patients' problems.

Cyclical changes in rat vibrissa follicles maintained In vitro

In mammals hair growth is cyclical; however, the factors that regulate the hair growth cycle are still poorly understood. The recent development of methods for culturing hair follicles in vitro has proved an important tool to investigate many aspects of the regulation of hair follicle growth. At present, however, these models are based on the culture of anagen hair follicles and have only partially been used to address the cyclical nature of hair growth. In this study we have made use of the fact that in rodents the hair growth cycle is synchronized, well characterized, and relatively short. We have isolated vibrissa follicles from 12 d old rats and confirmed by histology that these follicles are in the anagen stage of their first hair growth cycle. We have then maintained these follicles in vitro, on Gelfoam supports, for up to 23 d (35 d of age) and compared their histology with in vivo follicles from equivalent age littermates. We observed that 12 d old follicles maintained in vitro for up to 23 d show changes in morphology that suggest that cultured rat vibrissa follicles retain cyclical activity in vitro. Cyclical changes in hair follicle morphology were only seen in follicles maintained on gelfoam supports and moreover, hair follicle size appears to be a key feature in determining the ability of the follicle to cycle in vitro. All follicles that showed cyclical changes in vitro, however, appeared to remain blocked in pro-anagen. These data suggest that the vibrissa follicle is a in vitro good model system with which to investigate hair cycle control. J Invest Dermatol 115:1152-1155 2000

Characterization of a new tissue-engineered human skin equivalent with hair

We designed a new tissue-engineered skin equivalent in which complete pilosebaceous units were integrated. This model was produced exclusively from human fibroblasts and keratinocytes and did not contain any synthetic material. Fibroblasts were cultured for 35 d with ascorbic acid and formed a thick fibrous sheet in the culture dish. The dermal equivalent was composed of stacked fibroblast sheets and exhibited some ultrastructural organization found in normal connective tissues. Keratinocytes seeded on this tissue formed a stratified and cornified epidermis and expressed typical markers of differentiation (keratin 10, filaggrin, and transglutaminase). After 4 wk of culture, a continuous and ultrastructurally organized basement membrane was observed and associated with the expression of laminin and collagen IV and VII. Complete pilosebaceous units were obtained by thermolysin digestion and inserted in this skin equivalent in order to assess the role of the transfollicular route in percutaneous absorption. The presence of hair follicles abolished the lag-time observed during hydrocortisone diffusion and increased significantly its rate of penetration in comparison to the control (skin equivalent with sham hair insertion). Therefore, this new hairy human skin equivalent model allowed an experimental design in which the only variable was the presence of pilosebaceous units and provided new data confirming the importance of hair follicles in percutaneous absorption.

Denervation does not affect the growth of rat vibrissae

This study examines the hypothesis that neural factors influence the growth of rat vibrissae. We divided the vibrissae in rows alpha-delta, 1 and 2 and examined their regrowth during the first complete growth period in normal and nerve-lesioned rats. The lesions used were denervation through neonatal capsaicin treatment, surgical sympathecomy in adult rats, neurectomy of the mandibular and buccal branches of the facial nerve in adult rats or division of the infraorbital nerve in adult rats. Normal vibrissae developed a length of 51.1 mm and a diameter of 178 microm (row alpha-delta), 44.1 mm and 181 microm (row 1) and 33.2 mm and 165 microm (row 2). In all experimental groups the examined vibrissae developed a normal final length and proximal diameter. This indicates that local nerves do not influence vibrissal growth to any major extent.

Topical liposome targeting of dyes, melanins, genes, and proteins selectively to hair follicles

For therapeutic and cosmetic modification of hair, we have developed a hair-follicle-selective macromolecule and small molecule targeting system with topical application of phosphatidylcholine-based liposomes. Liposome-entrapped melanins, proteins, genes, and small-molecules have been selectively targeted to the hair follicle and hair shafts of mice. Liposomal delivery of these molecules is time dependent. Negligible amounts of delivered molecules enter the dermis, epidermis, or bloodstream thereby demonstrating selective follicle delivery. Naked molecules are trapped in the stratum corneum and are unable to enter the follicle. The potential of the hair-follicle liposome delivery system for therapeutic use for hair disease as well as for cosmesis has been demonstrated in 3-dimensional histoculture of hair-growing skin and mouse in vivo models. Topical liposome selective delivery to hair follicles has demonstrated the ability to color hair with melanin, the delivery of the active lac-Z gene to hair matrix cells and delivery of proteins as well. Liposome-targeting of molecules to hair follicles has also been achieved in human scalp in histoculture. Liposomes thus have high potential in selective hair follicle targeting of large and small molecules, including genes, opening the field of gene therapy and other molecular therapy of the hair process to restore hair growth, physiologically restore or alter hair pigment, and to prevent or accelerate hair loss.

Hair follicle elongation in organ culture of skin from newborn and adult mice

By means of skin organ culture, some biological characteristics of hair follicle elongation were examined. When skin sections from 6-day-old C3H mice were cultured, spontaneous elongation of hair follicles was maintained. Without insulin, hair follicle elongation was poorly maintained irrespective of the presence of serum at 20%. Insulin could be replaced by IGF-I at 100 ng/ml. During in vitro elongation of hair follicles, bromodeoxyuridine was incorporated into germinal epithelial cells around dermal papillae. Skin sections from 4-week-old C3H mice did not show hair follicle elongation in complete medium. However, when 0.5 mM minoxidil was added to the medium, concentration dependent thickening and elongation of hair follicles was observed. In contrast, in vitro elongation of newborn pelage hair follicles was not enhanced by minoxidil. These results suggest that this system with the use of skin sections from 4-week-old C3H mice would be a potential in vitro model of human androgenic alopecia in which the anagen phase is suppressed but the suppression is partially released by minoxidil.

Hair cycle stage of the mouse vibrissa follicle determines subsequent fiber growth and follicle behavior in vitro

The establishment of culture models representative of all aspects of in vivo hair follicle behavior is an important goal for theoretic and analytic studies. Rodent vibrissa follicles have regular, predictable, and relatively short growth cycles. In this investigation, we took advantage of these properties; we classified mouse vibrissa follicles according to different phases in the hair cycle and then compared fiber growth and morphologic changes in culture. Follicles isolated in the early phase of the growth cycle produced fine growing fibers with an average growth that exceeded 3 mm over 15 d. Even when hair growth had slowed or halted subsequently, histology showed that these follicles retained an anagen-like morphology. By contrast, follicles isolated toward the end of the growing cycle produced thicker fibers for much shorter periods, after which growth ceased and the fibers lifted up from the base of the follicle. Internally, these specimens resembled their telogen counterparts in situ. Follicles isolated in mid-growth demonstrated intermediate fiber growth characteristics. In organ culture, mouse vibrissa follicles therefore closely reflect their in vivo origin in growth characteristics and cycle timing. These data provide new opportunities for studying hair growth cycle mechanisms in vitro, but present a caveat for quantitative studies because there may be a greater growth cycle-related variation than has previously been assumed.

Whole hair follicle culture

In this article the authors have reviewed the historical background behind the organ culture of whole hair follicles. The methods developed by the authors and others for the isolation and whole organ maintenance of hair follicles from both human and other species are described. How whole organ models have been used to further understanding of the biology of the hair follicle and how they may be used in the future are discussed.

The feasibility of targeted selective gene therapy of the hair follicle

Loss of hair and hair colour is associated with ageing, and when it involves the scalp hair, it can be distressing to both sexes. Hair loss resulting from cancer chemotherapy is particularly distressing. However, safe, effective therapies directed to hair have only just started to be developed. The hair follicle is a complex skin appendage composed of epidermal and dermal tissue, with specialized keratinocytes, the hair matrix cells, forming the hair shaft. Specific therapy of the hair follicle depends on selective targeting of specific cells of the hair follicle. We have developed the histoculture of intact hair-growing skin on sponge-gel matrices. We have recently found in histocultured skin that liposomes can selectively target hair follicles to deliver both small and large molecules. That liposomes can target the hair follicle for delivery has been confirmed independently. Two decades ago we introduced the technique of entrapping DNA in liposomes for use in gene therapy. In this report we describe the selective targeting of the lacZ reporter gene to the hair follicles in mice after topical application of the gene entrapped in liposomes. These results demonstrate that highly selective, safe gene therapy for the hair process is feasible.

Confocal laser scanning microscopy: a new optical microscopic technique for applications in pathology and dermatology

Confocal laser scanning microscopy (CLSM) is a new optical microscopic technique, which offers significant advantages over conventional microscopy. CLSM is microscopy of optical sections. Light, which is emitted from regions other than the focal plane, is cut off by introducing a diaphragm in the beam path. The result is an optical "slice", which shows more details because the blurring from out of focus haze disappears. It has been repeatedly used in experimental, but also in diagnostic dermatopathology. The "in vivo" confocal microscopy, applied directly to the intact skin provides details of living cells in the superficial layers comparable to that of fixed and stained tissue. While the extent of its future applications is hard to predict, its potential for applications in dermatology appears enormous, particularly for studies of fixed or living tissues, where it is desirable to obtain clear images many micrometers below the surface of the tissue under examination.

Gelatin sponge-supported histoculture of human nasal mucosa

Considerable progress has recently been made in the understanding of airway inflammation by cell culture assays and in vivo provocation studies. Inasmuch as ethical considerations limit experimental work in humans, physiologically relevant in vitro models are required to better understand cellular and molecular tissue interactions in human nasal mucosa. Here we describe a human nasal mucosa culture model utilizing a simple gelatin sponge-supported histoculture system at the air-liquid interface. Viable mucosa was preserved for at least 48 h, as shown by morphology and immunohistochemical staining with Ki-67 as marker for proliferation. Pro-inflammatory mediators (kinins, histamine, thromboxane B2, prostaglandin F2 alpha, and substance P) are detectable in serum-containing as well as serum-free culture medium. Incubation with 10(-8) M substance P increases the number of degranulated mast cells after 48 h by 26% (P < 0.01). In this model, biochemical responses can be correlated with histologic alterations of the target tissue. Inflammatory parameters can be examined and compared in various patient groups and different stimulators/inhibitors. This culture method provides a valuable research tool for analyzing all compartments present in nasal mucosa under physiologically relevant conditions, and for studying complex interactions and responses of mucosal cell populations in their natural tissue environment.

Confocal microscopy of cells implanted into tissue blocks: cell migration in long-term histocultures

In three-dimensional tissues in vivo, cells find themselves in a unique, heterogeneous microenvironment among various cellular and noncellular elements. Cells are greatly affected by and contribute to their physical and chemical microenvironments. However, live cells are currently studied predominantly in homogeneous monolayer cultures where newly established contacts might be fundamentally different from contacts in vivo. Several systems have been suggested to simulate the three-dimensional environment of real tissue. In this report, we describe a new system for studying cell behavior inside real tissues in vitro. By fluorescently labeling mouse tumor cells, them implanting them into cultured tissue blocks (histocultures), we have observed cellular location and followed their locomotion, within tissues in vitro for days. We discuss the potential of the described system for studying different aspects of cell behavior in a nativelike microenvironment.

Different growth rates of pigmented and white hair in the beard: differentiation vs. proliferation?

A considerable difference in growth rates of pigmented and white anagen beard hair (0.47 mm/day vs. 1.12 mm/day, on average) was measured in three individuals over a 3-year period. Nuclear differentiation in the suprabulbar region of hair shafts revealed an earlier, and more intensive, condensation of chromatin in pigmented hair than in white hair. As other differences (diameter, presence or absence of medulla) between the two hair types could be excluded, the results suggest earlier terminal differentiation of pigmented hair compared with white hair.