The mesenchymal component of hair follicle neogenesis: background, methods and molecular characterization

Human induced pluripotent stem cell-derived ectodermal precursor cells contribute to hair follicle morphogenesis in vivo

Well-orchestrated epithelial-mesenchymal interactions are crucial for hair follicle (HF) morphogenesis. In this study, ectodermal precursor cells (EPCs) with the capacity to cross talk with hair-inductive dermal cells were generated from human induced pluripotent stem cells (hiPSCs) and assessed for HF-forming ability in vivo. EPCs derived from three hiPSC lines generated with 4 or 3 factors (POU5F1, SOX2, KLF4 +/- MYC) mostly expressed keratin 18, a marker of epithelial progenitors. When cocultured with human dermal papilla (DP) cells, a 4 factor 201B7 hiPSC-EPC line upregulated follicular keratinocyte (KC) markers more significantly than normal human adult KCs (NHKCs) and other hiPSC-EPC lines. DP cells preferentially increased DP biomarker expression in response to this line. Interestingly, 201B7 hiPSCs were shown to be ectodermal/epithelial prone, and the derived EPCs were putatively in a wingless-type MMTV integration site family (WNT)-activated state. Importantly, co-transplantation of 201B7 hiPSC-EPCs, but not NHKCs, with trichogenic mice dermal cells into immunodeficient mice resulted in HF formation. Human HF stem cell markers were detected in reconstituted HFs; however, a low frequency of human-derived cells implied that hiPSC-EPCs contributed to HF morphogenesis via direct repopulation and non-cell autonomous activities. The current study suggests a, to our knowledge, previously unrecognized advantage of using hiPSCs to enhance epithelial-mesenchymal interactions in HF 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.

A specific combination of zeaxanthin, spermidine and rutin prevents apoptosis in human dermal papilla cells

Hair follicle (HF) regression is characterized by the activation of apoptosis in HF cells. Dermal papilla cells play a leading role in the regulation of HF development and cycling. Human follicular dermal papilla cells (HFDPC) were used to investigate the protective activities of rutin, sperimidine and zeaxanthine. HFDP cell incubation with staurosporine caused apoptosis, which was completely inhibited by exposure to rutin (2.2 μM), spermidine (1 μM) and zeaxanthin (80 μM). These agents were much less effective when applied as single compounds. Moreover, treatment preserved the expression of anti-apoptotic molecules such as Bcl-2, MAP-kinases and their phosphorylated forms. In conclusion, the investigated agents may represent an effective treatment for the prevention of apoptosis, one of the leading events involved in hair bulb regression.

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.

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

It is well known that dermal papilla cells (DPCs) play crucial roles in hair follicle induction. In this study, we examined whether Wnt/β-catenin activation results in maintenance of the hair-inducing ability of human DPCs. Expression of DPC marker genes was maintained under Wnt/β-catenin signalling stimulation by GSK-3β inhibition. Furthermore, human DPCs showed constant hair induction when transplanted with murine epidermal cell fraction. Alu-positive human DPCs were essentially detected adjacent to the reconstructing epidermal structure positive for P-cadherin immunoreactivity. The transplanted human DPCs were abundant in the surrounding dermal sheath portion of the fully regenerated hair follicles. These results support the importance of Wnt/β-catenin signalling in hair follicle induction. This study may provide valuable information to establish a culture method of human DPCs for cell-based therapy.

Restoration of the intrinsic properties of human dermal papilla in vitro

The dermal papilla (DP) plays pivotal roles in hair follicle morphogenesis and cycling. However, characterization and/or propagation of human DPs have been unsatisfactory because of the lack of efficient isolation methods and the loss of innate characteristics in vitro. We hypothesized that culture conditions sustaining the intrinsic molecular signature of the human DP could facilitate expansion of functional DP cells. To test this, we first characterized the global gene expression profile of microdissected, non-cultured human DPs. We performed a 'two-step' microarray analysis to exclude the influence of unwanted contaminants in isolated DPs and successfully identified 118 human DP signature genes, including 38 genes listed in the mouse DP signature. The bioinformatics analysis of the DP gene list revealed that WNT, BMP and FGF signaling pathways were upregulated in intact DPs and addition of 6-bromoindirubin-3'-oxime, recombinant BMP2 and basic FGF to stimulate these respective signaling pathways resulted in maintained expression of in situ DP signature genes in primarily cultured human DP cells. More importantly, the exposure to these stimulants restored normally reduced DP biomarker expression in conventionally cultured DP cells. Cell growth was moderate in the newly developed culture medium. However, rapid DP cell expansion by conventional culture followed by the restoration by defined activators provided a sufficient number of DP cells that demonstrated characteristic DP activities in functional assays. The study reported here revealed previously unreported molecular mechanisms contributing to human DP properties and describes a useful technique for the investigation of human DP biology and hair follicle bioengineering.

Valproic acid induces hair regeneration in murine model and activates alkaline phosphatase activity in human dermal papilla cells

Background

Alopecia is the common hair loss problem that can affect many people. However, current therapies for treatment of alopecia are limited by low efficacy and potentially undesirable side effects. We have identified a new function for valproic acid (VPA), a GSK3β inhibitor that activates the Wnt/β-catenin pathway, to promote hair re-growth in vitro and in vivo.

Methodology/ Principal Findings

Topical application of VPA to male C3H mice critically stimulated hair re-growth and induced terminally differentiated epidermal markers such as filaggrin and loricrin, and the dermal papilla marker alkaline phosphatase (ALP). VPA induced ALP in human dermal papilla cells by up-regulating the Wnt/β-catenin pathway, whereas minoxidil (MNX), a drug commonly used to treat alopecia, did not significantly affect the Wnt/β-catenin pathway. VPA analogs and other GSK3β inhibitors that activate the Wnt/β-catenin pathway such as 4-phenyl butyric acid, LiCl, and BeCl₂ also exhibited hair growth-promoting activities in vivo. Importantly, VPA, but not MNX, successfully stimulate hair growth in the wounds of C3H mice.

Conclusions/ Significance

Our findings indicate that small molecules that activate the Wnt/β-catenin pathway, such as VPA, can potentially be developed as drugs to stimulate hair re-growth.

Isolation and characterization of stem cell-enriched human and canine hair follicle keratinocytes

The epithelial (keratinocyte) stem cells locating at the bulge region of hair follicles have been reported to possess high proliferative capacity in vitro and multipotency to repopulate hair follicles, sebaceous glands, and the epidermis, indicating the importance of those cells for the clinical applications including gene therapy and regenerative medicine. However, most of previous investigations adopted rodent bulge cells. The biological properties of human and rodent bulge cells have been reported to be distinct. Accordingly, it is crucial to directly isolate and characterize human bulge cells. However, the supply of human hair follicles for investigative purposes may be extremely limited in some situation. Dogs share analogous hair loss disorders with humans. Recent investigations have uncovered the biological similarities between canine bulge cells, suggesting that canine bulge cells are valuable substitute for the biological characterization of human bulge cells. Here, we provided the protocols for the isolation and characterization of human and canine hair follicle stem cell-enriched keratinocytes. Manual microdissection still represents the most commonly used technique to enrich bulge cells from human and canine hair follicles. Positive selection using a cell surface marker, CD200, should enable further enrichment of human bulge cells. Confirmation of successful isolation and molecular and cellular biological characterization of bulge cells are possible by real-time PCR and flow cytometry analyses described here. Colony-forming assay enables not only the evaluation of in vitro proliferative capacity but also the subcloning of holoclone keratinocytes, putative keratinocyte stem cells. Finally, hair reconstitution assay is available for the assessment of multipotency in vivo and sets a basis for tissue engineering of hair follicles.

Establishment and characterization of an immortalized human dermal papilla cell line

Establishment of immortalized human dermal papilla cells (DPCs) retaining the characteristics of DPCs would be a great help for hair researchers. We recently established a simian virus 40T (SV40T)-transformed human DP cell line (SV40TDPC). However, the cell line senesced around passage 25 and ceased proliferation. In this study, we introduced the human telomerase reverse transcriptase (hTERT) gene into SV40T-DPC and established an immortalized human DP cell line. The cell line, SV40T-hTERT-DPC, did not induce tumors when inoculated into nude mice. SV40T-hTERT-DPC maintained morphology of early passage DPCs, expressed markers of DPCs, and retained responses to Wnt/β-catenin and bone morphogenic protein (BMP) signaling pathways known to be required for hair-inducing activity of DPCs. The data strongly suggest that SV40T-hTERT-DPC retains many characteristics of human DPCs in vivo without malignant transformation.

Sphere formation restores and confers hair-inducing capacity in cultured mesenchymal cells

Interactions between epithelial and dermal cells are essential for hair follicle morphogenesis and maintenance. In experimental trials of hair regeneration, isolated dermal cells have been shown to possess hair-inducing capacity. However, dermal cells lose this potential immediately after cultivation. Sphere-forming multipotent cells derived from the dermis possess hair-inducing capacity. These previous findings raise the question of whether hair-inducing capacity depends on the identity as dermal cells or the process of sphere formation. To address this issue, we compared the in vitro and in vivo characteristics of two-dimensionally cultured or thereafter sphere formation-induced dermal and lung mesenchymal cells. We show that sphere-forming mesenchymal cells exhibited higher expression of Wnt signalling genes. Sphere-forming cells but not two-dimensionally cultured cells possessed in vivo hair-inducing capacity. These data suggest that various mesenchymal cells attain hair-inducing capacity through the process of sphere formation.

Molecular biological and immunohistological characterization of canine dermal papilla cells and the evaluation of culture conditions

The dermal papilla (DP) plays pivotal roles in hair follicle morphogenesis and cycling. However, our understanding of the biology of the canine DP is extremely limited. The aim of this study was to elucidate molecular biological and immunohistochemical characteristics of canine DP cells and determine appropriate conditions for in vitro expansion. Histological investigation revealed that the canine DP expressed biomarkers of human and rodent DP, including alkaline phosphatase (ALP) and versican. When microdissected, canine DP, but not fibroblasts, strongly expressed the DP-related genes for alkaline phosphatase, Wnt inhibitory factor 1 and lymphoid enhancer-binding factor 1, confirming successful isolation. The growth rate of isolated canine DP cells was moderate in conventional culture conditions for rodent and human DP; however, AmnioMAX-C100 complete medium allowed more efficient cultivation. Dermal papilla marker gene expression was maintained in early passage cultured DP cells, but gradually lost after the third passage. Approaches to mimic the in vivo DP environment in culture, such as supplementation of keratinocyte-conditioned medium or use of extracellular matrix-coated dishes, moderately ameliorated loss of DP gene expression in canine DP cells. It is possible that constituent factors in AmnioMAX may influence culture. These findings suggested that further refinements of culture conditions may enable DP cell expansion without impairing intrinsic properties and, importantly, demonstrated that AmnioMAX-cultured early passage canine DP cells partly maintained the biological characteristics of in vivo canine DP cells. This study provides crucial information necessary for further optimization of culture conditions of canine DP.

Mature hair follicles generated from dissociated cells: a universal mechanism of folliculoneogenesis

The hair follicle is considered to be a model system for studying organogenesis. In our initial study using mouse cells (Zheng et al., 2005) we found that new hair follicle formation always starts from an epithelial platform: the epidermal cells aggregate, the aggregates encyst, and from the periphery of the cysts, centrifugally, hair buds, pegs, and follicles form. In this report, we extend our initial study to four distantly related mammals: opossum, rat, dog and human. We find that in these four species, plus mouse, the most trichogenic cells are found in the earliest stages of hair follicle development and that the cellular mechanism of new hair follicle formation starting from dissociated cells is largely the same. These studies suggest that there is essentially one way by which dissociated mammalian skin cells form a new hair follicle in vivo and that this mechanism has been highly conserved.

De novo formation and ultra-structural characterization of a fiber-producing human hair follicle equivalent in vitro

Across many tissues and organs, the ability to create an organoid, the smallest functional unit of an organ, in vitro is the key both to tissue engineering and preclinical testing regimes. The hair follicle is an organoid that has been much studied based on its ability to grow quickly and to regenerate after trauma. But hair follicle formation in vitro has been elusive. Replacing hair lost due to pattern baldness or more severe alopecia, including that induced by chemotherapy, remains a significant unmet medical need. By carefully analyzing and recapitulating the growth conditions of hair follicle formation, we recreated human hair follicles in tissue culture that were capable of producing hair. Our microfollicles contained all relevant cell types and their structure and orientation resembled in some ways excised hair follicle specimens from human skin. This finding offers a new window onto hair follicle development. Having a robust culture system for hair follicles is an important step towards improved hair regeneration as well as to an understanding of how marketed drugs or drug candidates, including cancer chemotherapy, will affect this important organ.

Canine follicle stem cell candidates reside in the bulge and share characteristic features with human bulge cells

The hair follicle bulge has attracted great interest as a stem cell repository. Previous studies have focused on rodent or human bulge stem cells, and our understanding of those in other species is limited. In this study, we attempted to localize and characterize stem cell candidates in canine hair follicles. The canine skin xenografting study located label-retaining cells in the outer root sheath around the insertion point of the arrector pili muscle, where the immunoreactivity of human bulge markers, keratin 15 and follistatin, were detected. Canine bulge cell-enriched keratinocytes up-regulated human bulge biomarkers CD200 and DIO2, and conserved key cell regulators of bulge stem cells, such as SOX9 and LHX2. Importantly, canine bulge-derived keratinocytes were highly proliferative in vitro and, when combined with trichogenic dermal cells, reconstituted pilosebaceous structures as well as the epidermis in vivo. Successful detection of canine specific DNA sequences suggested that the regenerated tissue was of canine origin. In addition, canine specific bulge cell and sebocyte lineage markers were expressed in reconstituted pilosebaceous units, implying the multipotency of canine bulge cells. Our findings demonstrate a unique strategy utilizing canine bulge cells to investigate human stem cell biology and intractable hair disorders that involve the bulge region.

High-throughput reconstitution of epithelial-mesenchymal interaction in folliculoid microtissues by biomaterial-facilitated self-assembly of dissociated heterotypic adult cells

The aim of this study was to develop a method for efficient production of folliculoid keratinocyte-dermal papilla (DP) microtissues to facilitate epithelial-mesenchymal interaction. The behavior of DP cells and adult keratinocytes from hairless skin on poly(ethylene-co-vinyl alcohol) (EVAL) surface was investigated. Keratinocytes, poorly adherent both to substrate and between homotypic cells, become suspended disperse cells after homotypic cell seeding. Seeded simultaneously, keratinocytes and DP cells are able to aggregate into spheroidal microtissues. Dynamical analysis shows that DP cells act as a carrier in the process due to the heterotypic intercellular adhesion. DP cells attach faster to EVAL and start to aggregate. Keratinocytes adhere to DP cells and are then carried by DP cells to form initial hybrid aggregates. Due to the high motility of DP cells, these hybrid aggregates move collectively as clusters and merge into larger spheroids which subsequently detach from the substratum and can be easily collected. Compared with random cell distribution in spheroids generated in hanging drops, these hybrid spheroids have a preferential compartmented core-shell structure: an aggregated DP cell core surrounded by a keratinocyte shell. In addition to ameliorated DP signature gene expression, keratinocytes show down-regulated epidermal terminal differentiation and enhanced follicular differentiation. Functionally, these microtissues are able to grow hairs in vivo. This work sheds light on the complex effects and dynamics of cell-cell and cell-substratum interaction in the patterning of heterotypic cells into tissue forms and is of potential to be applied to mass generation of other epithelial organ primordia in vitro.