Effect of adenovirus-mediated expression of Sonic hedgehog gene on hair regrowth in mice with chemotherapy-induced alopecia

Hair Growth-Promoting Effects of Rosehip (Rosa canina L.) Seed Oil in C57BL/6 Mice

Rosehip (Rosa canina L.) seeds, a by-product of the food processing industry, contain various bioactive compounds that have potential cosmetic and pharmacological applications. Rosehip seed oil (RHSO) has been shown to exert therapeutic effects in skin disorders, but its role in promoting hair growth remains unknown. In this study, we aimed to elucidate the hair growth-promoting activity of RHSO and the related mechanisms of action. The depleted dorsal skin of telogenic C57BL/6 mice was topically treated with RHSO for 21 days, and the extent of hair regrowth was assessed. The results indicated that RHSO stimulated hair growth by inducing the early transition of hair follicles from telogen to anagen phase. Histological analysis revealed significant increases in hair follicle density, hair bulb size, and skin thickness. RHSO treatment also upregulated the expression of hair growth-associated genes, including β-catenin, phospho-glycogen synthase kinase-3 beta, Sonic hedgehog, smoothened, cyclin D1, cyclin E, and insulin like growth factor 1. These findings suggest that RHSO stimulates hair growth and may show promise as a preventive and/or therapeutic agent for hair loss.

DNA Methylation Mediates lncRNA2919 Regulation of Hair Follicle Regeneration

Hair follicles (HFs) are organs that periodically regenerate during the growth and development of mammals. Long non-coding RNAs (lncRNAs) are non-coding RNAs with crucial roles in many biological processes. Our previous study identified that lncRNA2919 is highly expressed in catagen during the HF cycle. In this study, the in vivo rabbit model was established using intradermal injection of adenovirus-mediated lncRNA2919. The results showed that lncRNA2919 decreased HF depth and density and contributed to HF regrowth, thereby indicating that lncRNA2919 plays a negative role in HF regeneration. Moreover, methylation levels of the lncRNA2919 promoter at different HF cycle stages were detected through bisulfite sequencing. The key CpG site that negatively correlates with lncRNA2919 expression during the HF cycle was identified. 5-Aza-dc-induced demethylation upregulated lncRNA2919 expression, and the core promoter region of lncRNA2919 was verified on the basis of luciferase activity. Furthermore, we found that DNA methylation could prevent the binding of EGR1 to the lncRNA2919 promoter region, thereby affecting the transcriptional expression of lncRNA2919. Collectively, DNA methylation inhibits the transcriptional expression of lncRNA2919, which plays a vital role in the HF cycle and HF regrowth. These findings contribute to the basic theory of epigenetics in HF biology and provide references for further research in HF disease treatment and animal wool production.

Exploring the effects of Chinese herbal ingredients on the signaling pathway of alopecia and the screening of effective Chinese herbal compounds

ETHNOPHARMACOLOGICAL RELEVANCE

alopecia is a hair disorder that can add a significant medical and psychological burden to patients. Currently, the FDA-approved drugs for the treatment of androgenetic alopecia (AGA) are minoxidil and finasteride and immunosuppressives are therapeutic options for alopecia areata (AA), but the objective adverse effects and high cost of these treatments reduce patient compliance and thus the effectiveness of the drugs. Traditional Chinese medicine (TCM) has good efficacy, a high safety profile and low treatment costs, but its mechanism of action is still not fully understood. The use of signaling pathways to modulate hair loss is a major direction in the study of the pathogenesis and pharmacology of alopecia.

AIM OF THE STUDY

This review aims to collect the results of experimental studies related to alopecia, to screen previously documented combinations of herbs claimed to be effective based on the herbs and their constituent compounds used in the identified studies, and to uncover other useful information that we hope will better guide the clinical application and scientific research of drug combinations or individual herbs for the treatment of alopecia.

MATERIALS AND METHODS

We have reviewed experimental studies to determine the methods used and the mechanisms of action of the herbs and constituent compounds. The following keywords were searched in databases, including PubMed, EMBASE, CNKI and CSTJ." Medicinal plants" "Chinese herbal medicine", "hair loss", " alopecia", "androgenetic alopecia" and " alopecia areata ". We also collected combinations of drugs from books approved by various schools for screening.

RESULTS

Using known combinations of compounds within herbal medicine to match the documented combinations, 34 topical combinations and 74 oral combinations were identified, and among the 108 herbal combinations screened Angelica, Rehmannia glutinosaLigusticum chuanxiong hort, Radix Rehmanniae, etc. The number of occurrences was very high, and the association with vascular drugs was also found to be very close.

CONCLUSIONS

This review further elucidates the therapeutic mechanisms of the compounds within the herbal components associated with alopecia and screens for other combinations that may be dominated by this component for the treatment of alopecia, uncovering compounds from other drugs that may be key factors in the treatment of alopecia. This improvement will provide a better quality of evidence for the effectiveness of herbs and compounds used to treat alopecia.

Red ginseng oil promotes hair growth and protects skin against UVC radiation

Background

A wide range of environmental factors, such as diseases, nutritional deficiencies, ageing, hormonal imbalances, stress, and ultraviolet (UV) radiation, may affect the structure and function of the skin that covers the entire surface of the human body. In this study, we investigated roles of red ginseng oil (RGO) in enhancing skin functions, including hair growth and skin protection, using mouse models.

Methods

For hair growth experiment, shaved dorsal skins of C57BL/6 mice were topically applied with vehicle, RGO, RGO's major compounds, or minoxidil for consecutive 21 days and skin tissues were examined the hair growth promoting capacity. For skin protection experiment, SKH-1 hairless mice were topically applied with vehicle or RGO twice a day for three days prior to exposure to UVC radiation at 20 kJ/cm². Skin tissues were collected to evaluate skin protective effects of RGO.

Results

Topical application of RGO to C57BL/6 mice effectively promoted hair regeneration by inducing early telogen-to-anagen transition and significantly increasing the density and bulb diameter of hair follicles. Major compounds, including linoleic acids and β-sitosterol, contributed to RGO-promoted hair growth. Treatment with RGO as well as its major components upregulated expression of hair growth–related proteins. Furthermore, in SKH-1 hairless mice, RGO had a protective effect against UVC-induced skin damage by inhibiting inflammation and apoptosis, as well as inducing cytoprotective systems.

Conclusion

These data suggest that RGO may be a potent agent for improving skin health and thereby preventing and/or treating hair loss and protecting skin against UV radiation.

A randomized controlled clinical study of acupuncture therapy for Seborrheic alopecia in young and middle ages: Study protocol clinical trial (SPIRIT compliant)

INTRODUCTION

Seborrheic alopecia (SA) has clinical manifestations, duration of disease, and priorities. In the current situation where there are many and complicated clinical treatments, Western medicine treatment can delay and control the development of the disease and promote hair regeneration. However, some patients may aggravate symptoms after taking the drug, and the condition is easy to repeat after stopping the drug. Acupuncture is an important method for non-surgical treatment of SA, and it has various methods, low side effects, high safety, and simple and economical. Therefore, we will use a clinical randomized controlled study to explore the effect of acupuncture on SA, and provide a new idea and reference for the treatment of this disease.

METHODS/DESIGN

We will select 60 patients diagnosed with SA. They will be randomly divided into intervention group and control groups. The control group will be given conventional treatment measures. The intervention group will receive acupuncture. Efficacy will be evaluated by comparing the skin lesion score and dermatological quality of life index before and after treatment.

DISCUSSION

This trial may provide evidence regarding the clinical effectiveness, safety, and cost-effectiveness of acupuncture for patients with SA.

TRIAL REGISTRATION NUMBER

CTR2000030430.

Chemotherapy-Induced Hair Loss: The Use of Biomarkers for Predicting Alopecic Severity and Treatment Efficacy

Damage to hair follicles following exposure to toxic chemotherapeutics can cause substantial hair loss, commonly known as chemotherapy-induced alopecia (CIA). Preventive therapies remain limited; however, recent advances in the use of scalp cooling technologies have proved successful in preventing or reducing hair loss in some patients. Further improvements in scalp cooling efficacy and/or development of novel treatments to prevent chemotherapy-induced hair loss are required. To achieve this, post-chemotherapy assessment of hair follicle damage markers, with and without scalp cooling, would provide invaluable mechanistic and prognostic information. At present, the availability of such data is extremely limited. This article describes the potential utility of a combination of biomarkers in assessing drug-induced alopecia and the protective potential of existing or new treatments. A greater understanding of the precise mechanisms of anti-CIA therapies through biomarker analysis would enhance the rationale, use, and development of such treatments.

Hedgehog stimulates hair follicle neogenesis by creating inductive dermis during murine skin wound healing

Mammalian wounds typically heal by fibrotic repair without hair follicle (HF) regeneration. Fibrosis and regeneration are currently considered the opposite end of wound healing. This study sought to determine if scar could be remodeled to promote healing with HF regeneration. Here, we identify that activation of the Sonic hedgehog (Shh) pathway reinstalls a regenerative dermal niche, called dermal papilla, which is required and sufficient for HF neogenesis (HFN). Epidermal Shh overexpression or constitutive Smoothened dermal activation results in extensive HFN in wounds that otherwise end in scarring. While long-term Wnt activation is associated with fibrosis, Shh signal activation in Wnt active cells promotes the dermal papilla fate in scarring wounds. These studies demonstrate that mechanisms of scarring and regeneration are not distant from one another and that wound repair can be redirected to promote regeneration following injury by modifying a key dermal signal.

On wounding, scar formation in mammals arises causing no hair follicle regeneration, but it is unclear if scarring precludes regeneration. Here, the authors show that if Sonic hedgehog signaling is activated in the wound, an inductive dermal niche forms, enabling regeneration and hair follicle formation.

Hair-Growth Potential of Ginseng and Its Major Metabolites: A Review on Its Molecular Mechanisms

The functional aspect of scalp hair is not only to protect from solar radiation and heat/cold exposure but also to contribute to one's appearance and personality. Progressive hair loss has a cosmetic and social impact. Hair undergoes three stages of hair cycle: the anagen, catagen, and telogen phases. Through cyclical loss and new-hair growth, the number of hairs remains relatively constant. A variety of factors, such as hormones, nutritional status, and exposure to radiations, environmental toxicants, and medications, may affect hair growth. Androgens are the most important of these factors that cause androgenic alopecia. Other forms of hair loss include immunogenic hair loss, that is, alopecia areata. Although a number of therapies, such as finasteride and minoxidil, are approved medications, and a few others (e.g., tofacitinib) are in progress, a wide variety of structurally diverse classes of phytochemicals, including those present in ginseng, have demonstrated hair growth-promoting effects in a large number of preclinical studies. The purpose of this review is to focus on the potential of ginseng and its metabolites on the prevention of hair loss and its underlying mechanisms.

Hair Regenerative Mechanisms of Red Ginseng Oil and Its Major Components in the Testosterone-Induced Delay of Anagen Entry in C57BL/6 Mice

Hair loss (alopecia) is a universal problem for numerous people in the world. The present study was conducted to investigate the effects of red ginseng oil (RGO) and its major components on hair re-growth using testosterone (TES)-induced delay of anagen entry in C57BL/6 mice and their mechanisms of action. Seven-week-old C57BL/6 mice were daily treated with TES for 1 h prior to topical application of 10% RGO, 1% linoleic acid (LA), 1% β-sitosterol (SITOS), or 1% bicyclo(10.1.0)tridec-1-ene (BICYCLO) once a day for 28 days. Hair regenerative capacity was significantly restored by treatment of RGO and its major compounds in the TES-treated mice. Histological analysis showed that RGO along with LA and SITOS but not BICYCLO promoted hair growth through early inducing anagen phase that was delayed by TES in mice. Treatment of mice with RGO, LA, or SITOS up-regulated Wnt/β-catenin and Shh/Gli pathways-mediated expression of genes such as β-catenin, Lef-1, Sonic hedgehog, Smoothened, Gli-1, Cyclin D1, and Cyclin E in the TES-treated mice. In addition, RGO and its major components reduced the protein level of TGF-β but enhanced the expression of anti-apoptotic protein Bcl-2. These results suggest that RGO is a potent novel therapeutic natural product for treatment of androgenic alopecia possibly through hair re-growth activity of its major components such as LA and SITOS.

A new technique for quantitative analysis of hair loss in mice using grayscale analysis

Alopecia is a common form of hair loss which can occur in many different conditions, including male-pattern hair loss, polycystic ovarian syndrome, and alopecia areata. Alopecia can also occur as a side effect of chemotherapy in cancer patients. In this study, our goal was to develop a consistent and reliable method to quantify hair loss in mice, which will allow investigators to accurately assess and compare new therapeutic approaches for these various forms of alopecia. The method utilizes a standard gel imager to obtain and process images of mice, measuring the light absorption, which occurs in rough proportion to the amount of black (or gray) hair on the mouse. Data that has been quantified in this fashion can then be analyzed using standard statistical techniques (i.e., ANOVA, T-test). This methodology was tested in mouse models of chemotherapy-induced alopecia, alopecia areata and alopecia from waxing. In this report, the detailed protocol is presented for performing these measurements, including validation data from C57BL/6 and C3H/HeJ strains of mice. This new technique offers a number of advantages, including relative simplicity of application, reliance on equipment which is readily available in most research laboratories, and applying an objective, quantitative assessment which is more robust than subjective evaluations. Improvements in quantification of hair growth in mice will improve study of alopecia models and facilitate evaluation of promising new therapies in preclinical studies.

Treatment and prevention of chemotherapy-induced alopecia with PTH-CBD, a collagen-targeted parathyroid hormone analog, in a non-depilated mouse model

Alopecia is a psychologically devastating complication of chemotherapy for which there is currently no effective therapy. PTH-CBD is a collagen-targeted parathyroid hormone analog that has shown promise as a therapy for alopecia disorders. This study compared the efficacy of prophylactic versus therapeutic administration of PTH-CBD in chemotherapy-induced alopecia using a mouse model that mimics the cyclic chemotherapy dosing used clinically. C57BL/6J mice were treated with a single subcutaneous injection of PTH-CBD (320 mcg/kg) or vehicle control before or after hair loss developing from three courses of cyclophosphamide chemotherapy (50-150 mg/kg/week). Mice receiving chemotherapy alone developed hair loss and depigmentation over 6-12 months. Mice pretreated with PTH-CBD did not develop these changes and maintained a normal-appearing coat. Mice treated with PTH-CBD after development of hair loss showed a partial recovery. Observations of hair loss were confirmed quantitatively by gray scale analysis. Histological examination showed that in mice receiving chemotherapy alone, there were small, dystrophic hair follicles mostly in the catagen phase. Mice receiving PTH-CBD before chemotherapy showed a mix of normal-appearing telogen and anagen hair follicles with no evidence of dystrophy. Mice receiving PTH-CBD therapy after chemotherapy showed intermediate histological features. PTH-CBD was effective in both the prevention and the treatment of chemotherapy-induced alopecia in mice, but pretreatment appears to result in a better cosmetic outcome. PTH-CBD shows promise as an agent in the prevention of this complication of chemotherapy and improving the quality of life for cancer patients.

Adenovirus-mediated Wnt5a expression inhibits the telogen-to-anagen transition of hair follicles in mice

The canonical Wnt/β-catenin pathway plays an important role in hair cycle induction. Wnt5a is a non-canonical Wnt family member that generally antagonizes canonical Wnt signaling in other systems. In hair follicles, Wnt5a and canonical Wnt are both expressed in cells in the telogen stage. Wnt5a has been shown to be critical for controlling hair cell fate. However, the role that Wnt5a plays in the transition from the telogen to anagen stage is unknown. In this study, using whole-mount in situ hybridization, we show that Wnt5a is produced by several other cell types, excluding dermal papilla cells, throughout the hair cycle. For example, Wnt5a is expressed in bulge and secondary hair germ cells in the telogen stage. Our studies focused on the depilated 8-week-old mouse as a synchronized model of hair growth. Interestingly, overexpression of adenovirus Wnt5a in the dorsal skin of mice led to the elongation of the telogen stage and inhibition of the initiation of the anagen stage. However, following an extended period of time, four pelage hair types grew from hairless skin that was induced by Wnt5a, and the structure of these new hair shafts was normal. Using microarray analysis and quantitative arrays, we showed that the expression of β-catenin and some target genes of canonical Wnt signaling decreased after Wnt5a treatment. These data demonstrate that Wnt5a may inhibit the telogen stage to maintain a quiescent state of the hair follicle.

Biology of human hair: know your hair to control it

Hair can be engineered at different levels--its structure and surface--through modification of its constituent molecules, in particular proteins, but also the hair follicle (HF) can be genetically altered, in particular with the advent of siRNA-based applications. General aspects of hair biology are reviewed, as well as the most recent contributions to understanding hair pigmentation and the regulation of hair development. Focus will also be placed on the techniques developed specifically for delivering compounds of varying chemical nature to the HF, indicating methods for genetic/biochemical modulation of HF components for the treatment of hair diseases. Finally, hair fiber structure and chemical characteristics will be discussed as targets for keratin surface functionalization.

Prevention of chemotherapy-induced alopecia by the anti-death FNK protein

Many anticancer drugs attack rapidly dividing cells, including not only malignant cells but also hair follicle cells, and induce alopecia. Chemotherapy-induced alopecia (CIA) is an emotionally distressing side effect of cancer chemotherapy. There is currently no useful preventive therapy for CIA. We have previously constructed anti-death rFNK protein from rat Bcl-x(L) by site-directed mutagenesis to strengthen cytoprotective activity. When fused to the protein transduction domain (PTD) of HIV/Tat, the fusion protein PTD (TAT)-rFNK successfully entered cells from the outside in vitro and in vivo to exhibit anti-death activity against apoptosis and necrosis. Here, we show that topical application of FNK protected against CIA in a newborn rat model. The protective activity against hair-loss was observed in 30-1000 nM TAT-rFNK administrative groups in a dose-dependent manner. Furthermore, a human version of FNK (hFNK) fused to other PTD peptides exhibited a protective ability. These results suggest that PTD-FNK possesses protective activity against CIA and is not restricted to a sequence of PTD peptides or species of FNK. Thus, PTD-FNK represents potential to develop a useful method for preventing CIA in cancer patients.

Cutaneous gene therapy

Possibilities of using the skin for somatic gene therapy have been investigated for more than 20 years. Strategies have included both direct gene transfer into the skin and indirect gene transfer utilizing cultured cells as an intermediate step for gene manipulation. Viral as well as nonviral vectors have been used, and both gene addition and gene editing have been performed. Although cutaneous gene therapy has now begun translating into clinical medicine (as seen by the first clinical gene therapy project of an inherited skin disorder) further developments are still required.

Investigational medications in the treatment of alopecia

Androgenetic alopecia (hereditary thinning) is the most common cause of hair loss in both men and women. Chemotherapy-induced alopecia is another distressing cause of hair loss. With a better understanding of follicular biology and the signals responsible for hair growth and regression, targeted therapies for hair loss are being investigated. This review summarises investigational medications for androgenetic and chemotherapy-induced alopecia that are in preclinical stages or later.

Useful plants of dermatology. VIII. The false hellebore (Veratrum californicum)

Plants have and continue to provide medicine with an abundance of pharmacologically interesting and useful chemicals. In recent years, cyclopamine, a steroidal alkaloid isolated from Veratrum californicum, has been instrumental in dissecting the sonic hedgehog pathway. This brief report outlines cyclopamine's discovery with discussion of its potential application to clinical dermatology.

Enhanced Efficacy of Cholesterol-Minus Sonic Hedgehog in Postnatal Skin

The role of Sonic hedgehog (Shh) as a morphogen in diverse developmental settings depends on covalent addition of cholesterol. In this study, expression of Shh lacking cholesterol stimulated hair growth with greater efficacy than native Shh, suggesting that Shh acts as a chemokine rather than a morphogen in this postnatal role. Thus, a structural modification that renders a morphogen ineffective in developmental models may have distinct advantages for postnatal applications.

Tumour stem cells and drug resistance

The contribution of tumorigenic stem cells to haematopoietic cancers has been established for some time, and cells possessing stem-cell properties have been described in several solid tumours. Although chemotherapy kills most cells in a tumour, it is believed to leave tumour stem cells behind, which might be an important mechanism of resistance. For example, the ATP-binding cassette (ABC) drug transporters have been shown to protect cancer stem cells from chemotherapeutic agents. Gaining a better insight into the mechanisms of stem-cell resistance to chemotherapy might therefore lead to new therapeutic targets and better anticancer strategies.

Basal cell nevus syndrome

PURPOSE OF REVIEW

Basal cell nevus syndrome (BCNS), is a hereditary condition transmitted as an autosomal dominant trait exhibiting high penetrance and variable expressivity. Inherited or spontaneous mutations in the human homologue of the Drosophila patched gene underlie the disorder and in addition to tumor predisposition, are associated with a range of 'patterning' defects. Recent advances, with glimpses of possible therapies are emerging, but because of the wide-ranging nature of phenotypic expression and overlap with other syndromes, there is difficulty. Finally, because of the importance of PTCH and paralogous genes in many species other than humans, reports appear in a correspondingly wide range of journals, which makes 'keeping abreast' difficult.

RECENT FINDINGS

Progress has been achieved in understanding the role of Gli-1, 2, & 3 in development of 'sporadic' BCCs and BCNS. Expression of PTCH1 is now known to be regulated by alternative promoters and a single functional Gli-binding site. Expression of FOXE1 as a new transcriptional target of Gli2 has been demonstrated in human epidermis and BCCs. Finally, the discovery of Shh pathway inhibitors such as cyclopamine, a naturally occurring alkaloid and ornithine decarboxylase inhibition suggest possible interventional therapies.

SUMMARY

In BCNS, phenotype does not correlate with position of mutations within Patched, suggesting genetic makeup and environment modulate effects of premature protein truncation induced by PTCH mutation. These developmental abnormalities occur as a result of haplo-insufficiency in heterozygotes for the mutated gene, whereas neoplastic complications arise from a classical two-hit tumor suppressor gene model. Attention is therefore turning toward TP53 and PTCH associations.

Immunoprevention of basal cell carcinomas with recombinant hedgehog-interacting protein

Basal cell carcinomas (BCCs) are driven by abnormal hedgehog signaling and highly overexpress several hedgehog target genes. We report here our use of one of these target genes, hedgehog-interacting protein (Hip1), as a tumor-associated antigen for immunoprevention of BCCs in Ptch1^+/− mice treated with ionizing radiation. Hip1 mRNA is expressed in adult mouse tissues at levels considerably lower than those in BCCs. Immunization with either of two large recombinant Hip1 polypeptides was well tolerated in Ptch1^+/− mice, induced B and T cell responses detectable by enzyme-linked immunosorbent assay, Western blot, delayed type hypersensitivity, and enzyme-linked immunospot assay, and reduced the number of BCCs by 42% (P < 0.001) and 32% (P < 0.01), respectively. We conclude that immunization with proteins specifically up-regulated by hedgehog signaling may hold promise as a preventive option for patients such as those with the basal cell nevus syndrome who are destined to develop large numbers of BCCs.

Characterization of Lef-1 promoter segments that facilitate inductive developmental expression in skin

Lymphoid Enhancer Factor 1 (Lef-1) is an important developmental transcription factor required for the inductive formation of several epithelial-derived organs including hair follicles. Inductive expression of Lef-1 mRNA is tightly regulated during embryo development, suggesting the involvement of a highly regulated promoter. In vitro analysis of the Lef-1 gene has demonstrated the existence of at least two spatially distinct promoters with multiple transcriptional start sites that are responsive to the canonical Wnt/beta-catenin pathway. Regions of the Lef-1 promoter required for inductive regulation in vivo, however, have yet to be determined. To this end, we utilized LacZ-reporter transgenic mice to define segments of the human Lef-1 promoter capable of reproducing mesenchymal- or epithelial-restricted transcriptional patterns of Lef-1 expression during hair and vibrissa follicle development. These studies have revealed that a 110 bp Wnt/beta-catenin-responsive element, contained within a minimal 2.5 kb Lef-1 promoter, plays an important role in regulating mesenchymal, and potentially epithelial, expression during follicle development in mouse embryos. This 2.5 kb Lef-1 promoter also demonstrated inductive mesenchymal expression during postnatal anagen stage hair-follicle cycling. Additionally, analysis of Lef-1 promoter expression revealed previously uncharacterized regions of endogenous Lef-1 expression seen in the sebaceous glands of vibrissa and hair follicles in transgenic lines harboring the minimal Lef-1 promoter and additional intronic sequences. In summary, these studies have begun to dissect the transcriptional diversity of the human Lef-1 promoter during the hair/vibrissa follicle and sebaceous gland formation.

Gene delivery to the hair follicle

Skin and appendages such as hair follicles are attractive candidates for gene therapy targets because they are easily accessible and can be removed and genetically manipulated in culture. Hair follicles are of special interest because our understanding of hair follicle biology and pathophysiology has progressed significantly in recent years, and we now have a much better understanding of how genes, encoding transcription factors, growth factors, and cytokines regulate both hair follicle development and the cycles of hair follicle growth (anagen, catagen, and telogen) (Cotsarelis and Millar, 2001; Millar, 2002). Also important is the characterization of an increasing number of genetic mutations that affect hair growth and can result in hair loss (Cotsarelis and Millar, 2001). Gene therapy could be used to introduce genes that manipulate hair follicle growth and cycling or that replace the mutated defective gene with a normal wild-type gene. As our understanding of the polygenic basis for a number of alopecias improves, gene-based therapies might also be designed to provide more promising treatments than current palliative therapies for hair loss. This review will describe some of the recent progress in gene delivery to hair follicles and discuss examples of how gene delivery can cause phenotypic changes in hair follicles.

Pathways and consequences: Hedgehog signaling in human disease

Signaling pathways that play a fundamental role during development are turning out to underlie many disease states when misregulated. Here, we review some of the recent findings in the Hedgehog (Hh) pathway and the role it plays in different human diseases. We present a summary of the diseases that result from the inactivation or inappropriate activation of the Hh pathway. The human phenotypes generally fit the findings in model organisms and help to identify some potential targets for therapy.

Keratinocyte stem cells: a commentary

For many years it has been widely accepted that stem cells play a crucial role in adult tissue maintenance. The concept that the renewing tissues of the body contain a small subcompartment of self-maintaining stem cells, upon which the entire tissue is dependent, is also now accepted as applicable to all renewing tissues. Gene therapy and tissue engineering are driving considerable interest in the clinical application of such hierarchically organized cellular compartments. Recent initial observations have provided a tantalizing insight into the large pluripotency of these cells. Indeed, scientists are now beginning to talk about the possible totipotency of some adult tissue stem cells. Such work is currently phenomenologic, but analysis of data derived from genomics and proteomics, identifying the crucial control signals involved, will soon provide a further impetus to stem cell biology with far reaching applications. The epidermis with its relatively simple structure, ease of accessibility, and the ability to grow its cells in vitro is one obvious target tissue for testing stem cell manipulation theories. It is crucial, however, that the normal keratinocyte stem cell is thoroughly characterized prior to attempting to manipulate its pluripotency. This commentary assesses the data generated to date and critically discusses the conclusions that have been drawn. Our current level of understanding, or lack of understanding, of the keratinocyte stem cell is reviewed.