Hair-inducing ability of human dermal papilla cells cultured under Wnt/β-catenin signalling activation

Epidermal stem cells and skin tissue engineering in hair follicle regeneration

The reconstitution of a fully organized and functional hair follicle from dissociated cells propagated under defined tissue culture conditions is a challenge still pending in tissue engineering. The loss of hair follicles caused by injuries or pathologies such as alopecia not only affects the patients' psychological well-being, but also endangers certain inherent functions of the skin. It is then of great interest to find different strategies aiming to regenerate or neogenerate the hair follicle under conditions proper of an adult individual. Based upon current knowledge on the epithelial and dermal cells and their interactions during the embryonic hair generation and adult hair cycling, many researchers have tried to obtain mature hair follicles using different strategies and approaches depending on the causes of hair loss. This review summarizes current advances in the different experimental strategies to regenerate or neogenerate hair follicles, with emphasis on those involving neogenesis of hair follicles in adult individuals using isolated cells and tissue engineering. Most of these experiments were performed using rodent cells, particularly from embryonic or newborn origin. However, no successful strategy to generate human hair follicles from adult cells has yet been reported. This review identifies several issues that should be considered to achieve this objective. Perhaps the most important challenge is to provide three-dimensional culture conditions mimicking the structure of living tissue. Improving culture conditions that allow the expansion of specific cells while protecting their inductive properties, as well as methods for selecting populations of epithelial stem cells, should give us the necessary tools to overcome the difficulties that constrain human hair follicle neogenesis. An analysis of patent trends shows that the number of patent applications aimed at hair follicle regeneration and neogenesis has been increasing during the last decade. This field is attractive not only to academic researchers but also to the companies that own almost half of the patents in this field.

A model system to analyse the ability of human keratinocytes to form hair follicles

Earlier studies showed that dermal cells lose trichogenic capacity with passage, but studies on the effect of keratinocyte passage on human hair follicle neogenesis and graft quality have been hampered by the lack of a suitable model system. We recently documented human hair follicle neogenesis in grafted dermal-epidermal composites, and in the present study, we determined the effects of keratinocyte passage on hair follicle neogenesis. Dermal equivalents were made with cultured human dermal papilla cells and were overlaid with either primary or passaged human keratinocytes to form dermal-epidermal composites; these were then grafted onto immunodeficient mice. Superior hair follicle neogenesis was observed using early keratinocyte cultures. Characteristics such as formation of hair shafts and sebaceous glands, presence of hair follicles with features of anagen or telogen follicles, and reproducible hair and skin function parameters make this model a tool to study human hair follicle neogenesis and development.

A review of adipocyte lineage cells and dermal papilla cells in hair follicle regeneration

Alopecia is an exceedingly prevalent problem effecting men and women of all ages. The standard of care for alopecia involves either transplanting existing hair follicles to bald areas or attempting to stimulate existing follicles with topical and/or oral medication. Yet, these treatment options are fraught with problems of cost, side effects, and, most importantly, inadequate long-term hair coverage. Innovative cell-based therapies have focused on the dermal papilla cell as a way to grow new hair in previously bald areas. However, despite this attention, many obstacles exist, including retention of dermal papilla inducing ability and maintenance of dermal papilla productivity after several passages of culture. The use of adipocyte lineage cells, including adipose-derived stem cells, has shown promise as a cell-based solution to regulate hair regeneration and may help in maintaining or increasing dermal papilla cells inducing hair ability. In this review, we highlight recent advances in the understanding of the cellular contribution and regulation of dermal papilla cells and summarize adipocyte lineage cells in hair regeneration.

Mycophenolate antagonizes IFN-γ-induced catagen-like changes via β-catenin activation in human dermal papilla cells and hair follicles

Recently, various immunosuppressant drugs have been shown to induce hair growth in normal hair as well as in alopecia areata and androgenic alopecia; however, the responsible mechanism has not yet been fully elucidated. In this study, we investigate the influence of mycophenolate (MPA), an immunosuppressant, on the proliferation of human dermal papilla cells (hDPCs) and on the growth of human hair follicles following catagen induction with interferon (IFN)-γ. IFN-γ was found to reduce β-catenin, an activator of hair follicle growth, and activate glycogen synthase kinase (GSK)-3β, and enhance expression of the Wnt inhibitor DKK-1 and catagen inducer transforming growth factor (TGF)-β2. IFN-γ inhibited expression of ALP and other dermal papillar cells (DPCs) markers such as Axin2, IGF-1, and FGF 7 and 10. MPA increased β-catenin in IFN-γ-treated hDPCs leading to its nuclear accumulation via inhibition of GSK3β and reduction of DKK-1. Furthermore, MPA significantly increased expression of ALP and other DPC marker genes but inhibited expression of TGF-β2. Therefore, we demonstrate for the first time that IFN-γ induces catagen-like changes in hDPCs and in hair follicles via inhibition of Wnt/β-catenin signaling, and that MPA stabilizes β-catenin by inhibiting GSK3β leading to increased β-catenin target gene and DP signature gene expression, which may, in part, counteract IFN-γ-induced catagen in hDPCs.

Exogenous connective tissue growth factor preserves the hair-inductive ability of human dermal papilla cells

Connective tissue growth factor influences human dermal papilla cells' hair inductive ability through several signaling pathways.

The dermal papilla: an instructive niche for epithelial stem and progenitor cells in development and regeneration of the hair follicle

The dermal papilla (DP) of the hair follicle is both a chemical and physical niche for epithelial progenitor cells that regenerate the cycling portion of the hair follicle and generate the hair shaft. Here, we review experiments that revealed the importance of the DP in regulating the characteristics of the hair shaft and frequency of hair follicle regeneration. More recent work showed that the size of this niche is dynamic and actively regulated and reduction in DP cell number per follicle is sufficient to cause hair thinning and loss. The formation of the DP during follicle neogenesis provides a context to contemplate the mechanisms that maintain DP size and the potential to exploit these processes for hair preservation or restoration.

Treatment of MSCs with Wnt1a-conditioned medium activates DP cells and promotes hair follicle regrowth

Hair loss (alopecia) is a common problem for people. The dermal papilla is the key signaling center that regulates hair growth and it engage in crosstalk with the microenvironment, including Wnt signaling and stem cells. In this study, we explored the effects of bone marrow mesenchymal stem cell overexpression of Wnt1a on mouse hair follicle regeneration. Wnt-CM accelerated hair follicle progression from telogen to anagen and enhanced the ALP expression in the DP area. Moreover, the hair induction-related genes were upregulated, as demonstrated by qRT-PCR. Wnt-CM treatment restored and increased DP cell expression of genes downregulated by dihydrotestosterone treatment, as demonstrated by qRT-PCR assays. Our study reveals that BM-MSC-generated Wnt1a promotes the DP's ability to induce hair cycling and regeneration.

Controllable production of transplantable adult human high-passage dermal papilla spheroids using 3D matrigel culture

We have succeeded in culturing human dermal papilla (DP) cell spheroids and developed a three-dimensional (3D) Matrigel (basement membrane matrix) culture technique that can enhance and restore DP cells unique characteristics in vitro. When 1 × 10(4) DP cells were cultured on the 96-well plates precoated with Matrigel for 5 days, both passage 2 and passage 8 DP cells formed spheroidal microtissues with a diameter of 150-250 μm in an aggregative and proliferative manner. We transferred and recultured these DP spheroids onto commercial plates. Cells within DP spheres could disaggregate and migrate out, which was similar to primary DP. Moreover, we examined the expression of several genes and proteins associated with hair follicle inductivity of DP cells, such as NCAM, Versican, and α-smooth muscle actin, and confirmed that their expression level was elevated in the spheres compared with the dissociated DP cells. To examine the hair-inducing ability of DP spheres, hair germinal matrix cells (HGMCs) and DP spheres were mixed and cultured on Matrigel. Unlike the dissociated DP cells and HGMCs cocultured in two dimensions, HGMCs can differentiate into hair-like fibers under the induction of the DP spheres made from the high-passage cells (passage 8) in vitro. We are the first to show that passage 3 human HGMCs differentiate into hair-like fibers in the presence of human DP spheroids. These results suggest that the 3D Matrigel culture technique is an ideal culture model for forming DP spheroids and that sphere formation partially models the intact DP, resulting in hair induction, even by high-passage DP cells.

Wnt5a attenuates Wnt/β-catenin signalling in human dermal papilla cells

Findings of recent studies have demonstrated modulation of Wnt/β-catenin signalling by Wnt5a, which is highly expressed in hair follicular dermal papilla (DP) in vivo. Here, we investigated the question of whether Wnt5a can affect canonical Wnt/β-catenin signalling in DP cells. Treatment with Wnt5a resulted in attenuation of Wnt3a-mediated elevation of β-catenin signalling, which was increased by Wnt5a siRNA transfection in cultured DP cells, as examined by reporter assay. In addition, treatment with Wnt5a resulted in repressed Wnt3a-mediated expression of Axin2, EP2 and LEF1 in cultured DP cells, whereas Wnt5a siRNA transfection resulted in increased Wnt3a-mediated expression of the genes in isolated DPs of cultured hair follicles. Moreover, treatment with Wnt5a resulted in attenuation of Wnt3a-mediated accumulation of β-catenin in the nucleus in DP cells. Our data strongly suggest that Wnt5a acts as an autocrine factor and attenuates canonical Wnt signalling pathway in human DP cells.

Valproic acid promotes human hair growth in in vitro culture model

BACKGROUND

β-Catenin, the transducer of Wnt signaling, is critical for the development and growth of hair follicles. In the absence of Wnt signals, cytoplasmic β-catenin is phosphorylated by glycogen synthase kinase (GSK)-3 and then degraded. Therefore, inhibition of GSK-3 may enhance hair growth via β-catenin stabilization. Valproic acid is an anticonvulsant and a mood-stabilizing drug that has been used for decades. Recently, valproic acid was reported to inhibit GSK-3β in neuronal cells, but its effect on human hair follicles remains unknown.

OBJECTIVES

To determine the effect of VPA on human hair growth.

METHODS

We investigated the effect of VPA on cultured human dermal papilla cells and outer root sheath cells and on an in vitro culture of human hair follicles, which were obtained from scalp skin samples of healthy volunteers. Anagen induction by valproic acid was evaluated using C57BL/6 mice model.

RESULTS

Valproic acid not only enhanced the viability of human dermal papilla cells and outer root sheath cells but also promoted elongation of the hair shaft and reduced catagen transition of human hair follicles in organ culture model. Valproic acid treatment of human dermal papilla cells led to increased β-catenin levels and nuclear accumulation and inhibition of GSK-3β by phosphorylation. In addition, valproic acid treatment accelerated the induction of anagen hair in 7-week-old female C57BL/6 mice.

CONCLUSIONS

Valproic acid enhanced human hair growth by increasing β-catenin and therefore may serve as an alternative therapeutic option for alopecia.

Strategies to enhance epithelial-mesenchymal interactions for human hair follicle bioengineering

Hair follicle morphogenesis and regeneration depend on intensive but well-orchestrated interactions between epithelial and mesenchymal components. Accordingly, the enhancement of this crosstalk represents a promising approach to achieve successful bioengineering of human hair follicles. The present article summarizes the techniques, both currently available and potentially feasible, to promote epithelial-mesenchymal interactions (EMIs) necessary for human hair follicle regeneration. The strategies include the preparation of epithelial components with high receptivity to trichogenic dermal signals and/or mesenchymal cell populations with potent hair inductive capacity. In this regard, bulge epithelial stem cells, keratinocytes predisposed to hair follicle fate or keratinocyte precursor cells with plasticity may provide favorable epithelial cell populations. Dermal papilla cells sustaining intrinsic hair inductive capacity, putative dermal papilla precursor cells in the dermal sheath/neonatal dermis or trichogenic dermal cells derived from undifferentiated stem/progenitor cells are promising candidates as hair inductive dermal cells. The most established protocol for in vivo hair follicle reconstitution is co-grafting of epithelial and mesenchymal components into immunodeficient mice. In theory, combination of individually optimized cellular components of respective lineages should elicit most intensive EMIs to form hair follicles. Still, EMIs can be further ameliorated by the modulation of non-cell autonomous conditions, including cell compartmentalization to replicate the positional relationship in vivo and humanization of host environment by preparing human stromal bed. These approaches may not always synergistically intensify EMIs, however, step-by-step investigation probing optimal combinations should maximally enhance EMIs to achieve successful human hair follicle bioengineering.

Lef1 contributes to the differentiation of bulge stem cells by nuclear translocation and cross-talk with the Notch signaling pathway

Lymphoid enhancer binding factor-1 (Lef1) is an essential regulatory protein in the Wnt signal pathway, which controls cell growth and differentiation. Investigators in the field of skin biology have confirmed that multipotent bulge stem cells (BSCs) are responsible for hair follicle development and regeneration. However, the role of Lef1 remains poorly understood. In this study, we investigated the pattern of Lef1 expression at different stages of the hair growth cycle. Lef1 was strongly expressed during anagen but attenuated in both catagen- and telogen-phase hair follicles in vivo. When stem cells were induced to differentiate toward a hair fate in a co-culture system, Lef1 was notably up-regulated and accumulated in the nucleus, appearing to activate the target protein c-myc and jagged1. Simultaneously, the Wnt and Notch signaling pathways were co-activated, as confirmed by the increased expression of β-catenin and notch1. Plasmids expressing Lef1 and ΔNLef1, a construct in which the β-catenin-binding domain of Lef1 was deleted, were used to evaluate the effects of Lef1 on stem cell differentiation. Lef1 overexpression promoted bulge stem cell differentiation toward a hair fate, which was accompanied by the subsequent migration of β-catenin into the nucleus, whereas no changes were observed in the control group. Taken together, our results demonstrate that Lef1 plays an important role in bulge stem cell differentiation, promoting β-catenin translocation into the nucleus, activating downstream signaling molecules, eventually causing hair follicle bulge stem cells to adopt the hair fate.

Scalable production of controllable dermal papilla spheroids on PVA surfaces and the effects of spheroid size on hair follicle regeneration

Organ size and numbers are vital issues in bioengineering for hair follicle (HF) regeneration. Murine HF dermal papilla (DP) cells are able to induce HF neogenesis when transplanted as aggregates. However, how the preparation of murine and human DP aggregates affects HF inductivity and the size of regenerated HF is yet to be determined. Here we report a scalable method for production of controllable human and rat DP spheroids in general labs for reproducible experiments. Compared with more hydrophobic polyethylene and poly(ethylene-co-vinyl alcohol), DP cells are poorly adhesive to hydrophilic polyvinyl alcohol (PVA). Seeded in PVA-coated 96-welled commercial PCR tube arrays, DP cells quickly aggregate into single spheroids with progressive compaction. Varying seeded cell numbers and culture periods enables us to control the size and cell number of the spheroids. The spheroids obtained have high viability and preserve DP characters. A proof of principle experiment was conducted to examine the size effect on the efficiency and efficacy of HF regeneration. We found that both human and rat DP spheroids are able to induce HF neogenesis and larger DP spheroids exhibit higher HF inductivity. However, the average diameter of regenerated hair fiber did not significantly change with the increasing size of transplanted DP spheroids. The result suggests that an appropriate size of DP spheroid is essential for HF inductivity, but its size cannot be directly translated to a thicker regenerated hair. Our results also have implications on the efficiency and efficacy in the regeneration of other epithelial organs.

Morphogenesis of chimeric hair follicles in engineered skin substitutes with human keratinocytes and murine dermal papilla cells

Engineered skin substitutes (ESS) have been used successfully to treat life-threatening burns, but lack cutaneous appendages. To address this deficiency, dermal constructs were prepared using collagen-glycosaminoglycan scaffolds populated with murine dermal papilla cells expressing green fluorescent protein (mDPC-GFP), human dermal papilla cells (hDPC) and/or human fibroblasts (hF). Subsequently, human epidermal keratinocytes (hK) or hK genetically modified to overexpress stabilized β-catenin (hK') were used to prepare ESS epithelium. After 10 days incubation at air-liquid interface, ESS were grafted to athymic mice and were evaluated for 6 weeks. Neofollicles were observed in ESS containing mDPC-GFP, but not hDPC or hF, independent of whether or not the hK were genetically modified. Based on detection of GFP fluorescence, mDPC were localized to the dermal papillae of the well-defined follicular structures of grafted ESS. In addition, statistically significant increases in LEF1, WNT10A and WNT10B were found in ESS with neofollicles. These results demonstrate a model for generation of chimeric hair in ESS.

Epithelial Wnt ligand secretion is required for adult hair follicle growth and regeneration

β-Catenin, a key transducer molecule of Wnt signaling, is required for adult hair follicle growth and regeneration. However, the cellular source of Wnt ligands required for Wnt/β-catenin activation during anagen induction is unknown. In this study, we genetically deleted Wntless (Wls), a gene required for Wnt ligand secretion by Wnt-producing cells, specifically in the hair follicle epithelium during telogen phase. We show that epithelial Wnt ligands are required for anagen, as loss of Wls in the follicular epithelium resulted in a profound hair cycle arrest. Both the follicular epithelium and dermal papilla showed markedly decreased Wnt/β-catenin signaling during anagen induction compared with control hair follicles. Surprisingly, hair follicle stem cells that are responsible for hair regeneration maintained expression of stem cell markers but exhibited significantly reduced proliferation. Finally, we demonstrate that epidermal Wnt ligands are critical for adult wound-induced de novo hair formation. Collectively, these data show that Wnt ligands secreted by the hair follicle epithelium are required for adult hair follicle regeneration and provide new insight into potential cellular targets for the treatment of hair disorders such as alopecia.