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

1,25-(OH)2D3 promotes hair growth by inhibiting NLRP3/IL-1β and HIF-1α/IL-1β signaling pathways

Vitamin D is a crucial vitamin that participates in various biological processes through the Vitamin D Receptor (VDR). While there are studies suggesting that VDR might regulate hair growth through ligand-independent mechanisms, the efficacy of Vitamin D in treating hair loss disorders has also been reported. Here, through in vivo experiments in mice, in vitro organ culture of hair follicles, and cellular-level investigations, we demonstrate that 1,25-(OH)2D3 promotes mouse hair regeneration, prolongs the hair follicle anagen, and enhances the proliferation and migration capabilities of dermal papilla cells and outer root sheath keratinocytes in a VDR-dependent manner. Transcriptome analysis of VDR-knockout mouse skin reveals the involvement of HIF-1α, NLRP3, and IL-1β in these processes. Finally, we confirm that 1,25-(OH)2D3 can counteract the inhibitory effects of DHT on hair growth. These findings suggest that 1,25-(OH)2D3 has a positive impact on hair growth and may serve as a potential therapeutic agent for androgenetic alopecia (AGA).

In vitro hair growth-promoting effect of Lgr5-binding octapeptide in human primary hair cells

BACKGROUND

Hair loss occurs due to various biological and environmental causes, which can have psychosocial consequences. The Wnt/β-catenin signaling is well-known for its role in hair growth and regeneration, as it induces the proliferation and differentiation of hair cells. When the leucine-rich G protein-coupled receptor 5 (Lgr5) interacts with the R-spondins, the frizzled receptor (FZD), a Wnt receptor, becomes stabilized, resulting in an increased β-catenin activity.

AIM

We investigated whether the octapeptide that binds to Lgr5 enhances proliferation and differentiation of human primary hair cells through the activation of Wnt/β-catenin signaling.

METHODS

The binding affinity of the octapeptide to Lgr5 was evaluated using surface plasmon resonance (SPR). We confirmed changes in proliferation and related factors like β-catenin activation and growth factors (GFs) expression in human hair follicle dermal papilla cells (HHFDPCs). Additionally, we observed the proliferation and the expression of differentiation markers in human hair follicle outer root sheath cells (HHFORSCs), human hair follicle germinal matrix cells (HHFGMCs), and human hair follicle stem cells (HHFSCs). We used three-dimensional HHFDPC spheroid culture treated with dihydrotestosterone (DHT) to create in vitro conditions that mimic androgenetic alopecia, and we studied the effects of octapeptide on Wnt expression and HHFSC differentiation.

RESULTS

The binding of the octapeptide to Lgr5 was confirmed using SPR analysis. In HHFDPCs, treatment with octapeptide resulted in a concentration-dependent increase in proliferation. We also observed increased nuclear translocation of β-catenin and increased expression of its downstream targets. HHFDPCs treated with octapeptide exhibited increased expression of growth factors and phosphorylation of Akt and ERK. In addition, we confirmed that octapeptide increased proliferation and induced differentiation in HHFORSCs, HHFGMCs, and HHFSCs. Under the HHFDPC spheroid culture conditions, we found that octapeptide restored the inhibition of Wnt-5a and Wnt-10b expressions by DHT. In HHFSCs treated with HHFDPC spheroid culture media, we observed that octapeptide recovered the inhibition of differentiation by DHT.

CONCLUSION

We found that octapeptides activated the Wnt/β-catenin signaling and induced the proliferation and differentiation of human primary hair cells by acting as an exogenous ligand for Lgr5. In addition, octapeptides recovered inhibited hair regeneration characters by DHT in androgenetic alopecia-mimic in vitro model. These findings suggest that octapeptides may be a promising therapeutic option for treating hair loss.

Establishment and characterization of matched immortalized human frontal and occipital scalp dermal papilla cell lines from androgenetic alopecia

Androgenetic alopecia (AGA), also known as male pattern baldness, is a common hair loss condition influenced by genetic and hormonal factors. Variations in gene expression and androgen responsiveness have been observed between the frontal and occipital regions of AGA patients. However, obtaining and cultivating frontal hair follicles is challenging. Therefore, no matched frontal and occipital dermal papilla (DP) cell lines have been reported yet. This study aimed to establish matched immortalized human frontal and occipital scalp DP cell lines from AGA patients. Simian virus 40 large T antigen (SV40T-Ag) and human telomerase reverse transcriptase (hTERT) were introduced into primary human DP cells. The obtained cell lines were characterized by assessing their gene expression patterns, androgen receptor (AR) levels, and the presence of 5-alpha reductase (5αR). Additionally, we examined their response to dihydrotestosterone (DHT) and evaluated cell viability. The conditioned medium from the frontal DP cell line inhibited human hair follicle growth, leading to reduced keratinocyte proliferation and increased apoptosis. Furthermore, when the cells were cultured in a 3D environment mimicking in vivo conditions, the 3D cultured frontal DP cell line exhibited weaker sphere aggregation than the occipital DP cell line due to the increased expression of matrix metalloproteinase 1 (MMP1), MMP3, and MMP9. Additionally, the expression of DP signature genes was inhibited in the 3D cultured frontal DP cell line. These matched frontal and occipital DP cell lines hold significant potential as valuable resources for research on hair loss. Their establishment allows us to investigate the differences between frontal and occipital DP cells, contributing to a better understanding of the molecular mechanisms underlying AGA. Furthermore, these cell lines may be valuable for developing targeted therapeutic approaches for hair loss conditions.

Establishment and functional characterization of immortalized rabbit dermal papilla cell lines

Hair follicle (HF) undergo periodic growth and development in mammals, which regulated by dermal papilla cells (DPCs) are reported to play an important role in HF morphogenesis and development. However, primary DPCs have low proliferative activity, age quickly, and fresh cell isolation is both time-consuming and laborious. In this study, we introduced the SV40 large T antigen (SV40T) into dissociated early passage rabbit vibrissae DPCs with lentiviral vectors and established seven immortalized DPC lines (R-1, R-2, R-3, R-4, R-5, R-6 and R-7). These cell lines displayed early passage morphology and high alkaline phosphatase activity. RT-PCR and immunofluorescence staining showed that all the immortalized cell lines expressed the DPC markers (α-SMA, IGF1, ALPL, FGF2, BMP2 and TGFβ2), but α-SMA was only expressed well in R-3, R-4, and R-7. Furthermore, it was found that R-7 was the only line to survive beyond 50 passages. Compared to melanoma cells, R-7 did not undergo malignant transformation. Karyotyping and cell growth viability analysis illustrated that the R-7 cell line preserved the basic characteristics of primary DPCs. The R-7 DPCs established have potential application for future hair research. The study provides the theoretical basis in the cell research of HF growth and development.

Recent Trends in Macromolecule-Based Approaches for Hair Loss Treatment

Macromolecules are large, complex molecules composed of smaller subunits known as monomers. The four primary categories of macromolecules found in living organisms are carbohydrates, lipids, proteins, and nucleic acids; they also encompass a broad range of natural and synthetic polymers. Recent studies have shown that biologically active macromolecules can help regenerate hair, providing a potential solution for current hair regeneration therapies. This review examines the latest developments in the use of macromolecules for the treatment of hair loss. The fundamental principles of hair follicle (HF) morphogenesis, hair shaft (HS) development, hair cycle regulation, and alopecia have been introduced. Microneedle (MN) and nanoparticle (NP) delivery systems are innovative treatments for hair loss. Additionally, the application of macromolecule-based tissue-engineered scaffolds for the in vitro and in vivo neogenesis of HFs is discussed. Furthermore, a new research direction is explored wherein artificial skin platforms are adopted as a promising screening method for hair loss treatment drugs. Through these multifaceted approaches, promising aspects of macromolecules for future hair loss treatments are identified.

iPSC-based approach for human hair follicle regeneration

Hair follicles (HFs) are a multifunctional structure involved in physical protection, thermoregulation, sensational detection, and wound healing. Formation and cycling of HFs require dynamic interaction between different cell types of the follicles. Although the processes have been well studied, the generation of human functional HFs with a normal cycling pattern for clinical utilization has yet to be achieved. Recently, human pluripotent stem cells (hPSCs) serve as an unlimited cell source for generating various types of cells including cells of the HFs. In this review, HF morphogenesis and cycling, different cell sources used for HF regeneration, and potential strategies for HF bioengineering using induced pluripotent stem cells (iPSCs) are depicted. Challenges and perspectives toward the therapeutic use of bioengineered HFs for hair loss disorder are also discussed.

Scalable and high-throughput production of an injectable platelet-rich plasma (PRP)/cell-laden microcarrier/hydrogel composite system for hair follicle tissue engineering

Background

Tissue engineering of hair follicles (HFs) has enormous potential for hair loss treatment. However, certain challenges remain, including weakening of the dermal papilla cell (DPC) viability, proliferation, and HF inducibility, as well as the associated inefficient and tedious preparation process required to generate extracellular matrix (ECM)-mimicking substrates for biomolecules or cells. Herein, we utilized gelatin methacryloyl (GelMA) and chitosan hydrogels to prepare scalable, monodispersed, and diameter-controllable interpenetrating network GelMA/chitosan-microcarriers (IGMs) loaded with platelet-rich plasma (PRP) and seeded with DPCs, on a high-throughput microfluidic chip.

Results

The ECM-mimicking hydrogels used for IGMs exhibited surface nano-topography and high porosity. Mass production of IGMs with distinct and precise diameters was achieved by adjusting the oil and aqueous phase flow rate ratio. Moreover, IGMs exhibited appropriate swelling and sustained growth factor release to facilitate a relatively long hair growth phase. DPCs seeded on PRP-loaded IGMs exhibited good viability (> 90%), adhesion, spreading, and proliferative properties (1.2-fold greater than control group). Importantly, PRP-loaded IGMs presented a higher hair inducibility of DPCs in vitro compared to the control and IGMs group (p < 0.05). Furthermore, DPC/PRP-laden IGMs were effectively mixed with epidermal cell (EPC)-laden GelMA to form a PRP-loaded DPC/EPC co-cultured hydrogel system (DECHS), which was subcutaneously injected into the hypodermis of nude mice. The PRP-loaded DECHS generated significantly more HFs (~ 35 per site) and novel vessels (~ 12 per site) than the other groups (p < 0.05 for each).

Conclusion

Taken together, these results illustrate that, based on high-throughput microfluidics, we obtained scalable and controllable production of ECM-mimicking IGMs and DECHS, which simulate an effective micro- and macro-environment to promote DPC bioactivity and hair regeneration, thus representing a potential new strategy for HF tissue engineering.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12951-022-01671-8.

Unlocking the Potential of Induced Pluripotent Stem Cells for Wound Healing: The Next Frontier of Regenerative Medicine

Significance: Nonhealing wounds are a significant burden for the health care system all over the world. Existing treatment options are not enough to promote healing, highlighting the urgent need for improved therapies. In addition, the current advancements in tissue-engineered skin constructs and stem cell-based therapies are facing significant hurdles due to the absence of a renewable source of functional cells. Recent Advances: Induced pluripotent stem cell technology (iPSC) is emerging as a novel tool to develop the next generation of personalized medicine for the treatment of chronic wounds. The iPSC provides unlimited access to various skin cells to generate complex personalized three-dimensional skin constructs for disease modeling and autologous grafts. Furthermore, the iPSC-based therapies can target distinct wound healing phases and have shown accelerating wound closure by enhancing angiogenesis, cell migration, tissue regeneration, and modulating inflammation. Critical Issues: Since the last decade, iPSC has been revolutionizing the field of wound healing and skin tissue engineering. Despite the current progress, safety and heterogeneity among iPSC lines are still major hurdles in addition to the lack of large animal studies. These challenges need to be addressed before translating an iPSC-based therapy to the clinic. Future Directions: Future considerations should be given to performing large animal studies to check the safety and efficiency of iPSC-based therapy in a wound healing setup. Furthermore, strategies should be developed to overcome variation between hiPSC lines, develop an efficient manufacturing process for iPSC-derived products, and generate complex skin constructs with vasculature and skin appendages.

Adaptive multi‐degree‐of‐freedom in situ bioprinting robot for hair‐follicle‐inclusive skin repair: A preliminary study conducted in mice

Skin acts as an essential barrier, protecting organisms from their environment. For skin trauma caused by accidental injuries, rapid healing, personalization, and functionality are vital requirements in clinical, which are the bottlenecks hindering the translation of skin repair from benchside to bedside. Herein, we described a novel design and a proof‐of‐concept demonstration of an adaptive bioprinting robot to proceed rapid in situ bioprinting on a full‐thickness excisional wound in mice. The three‐dimensional (3D) scanning and closed‐loop visual system integrated in the robot and the multi‐degree‐of‐freedom mechanism provide immediate, precise, and complete wound coverage through stereotactic bioprinting, which hits the key requirements of rapid‐healing and personalization in skin repair. Combined with the robot, epidermal stem cells and skin‐derived precursors isolated from neonatal mice mixed with Matrigel were directly printed into the injured area to replicate the skin structure. Excisional wounds after bioprinting showed complete wound healing and functional skin tissue regeneration that closely resembling native skin, including epidermis, dermis, blood vessels, hair follicles and sebaceous glands etc. This study provides an effective strategy for skin repair through the combination of the novel robot and a bioactive bioink, and has a promising clinical translational potential for further applications.

PBX1 Attenuates Hair Follicle-Derived Mesenchymal Stem Cell Senescence and Apoptosis by Alleviating Reactive Oxygen Species-Mediated DNA Damage Instead of Enhancing DNA Damage Repair

Tissues and organs undergo structural deterioration and functional decline during aging. DNA damage is considered a major cause of stem cell senescence. Although stem cells develop sophisticated DNA repair systems, when the intrinsic and extrinsic insults exceed the DNA repair capacity, cellular senescence, and age-related diseases inevitably occur. Therefore, the prevention and alleviation of DNA damage is an alternative to DNA repair in attenuating stem cell senescence and preventing age-related diseases. Pre-B-cell leukaemia homeobox 1 (PBX1) participates in maintaining the pluripotency of human embryonic and haematopoietic stem cells. Our recent studies showed that PBX1 promotes hair follicle-derived mesenchymal stem cell (HF-MSC) proliferation, decreases cellular senescence and apoptosis, and enhances induced pluripotent stem cell generation. Whether PBX1 attenuates HF-MSC senescence and apoptosis by alleviating DNA damage or by enhancing DNA repair remains unknown. In this study, we aimed to determine the effects of PBX1 on the intrinsic ROS or extrinsic H₂O₂-induced cellular senescence of HF-MSCs. To this end, we generated HF-MSCs overexpressing either PBX1, or poly (ADP-ribose) polymerase 1, or both. Our results showed that PBX1 overexpression attenuates HF-MSC senescence and apoptosis by alleviating reactive oxygen species (ROS)-mediated DNA damage instead of enhancing DNA repair. This is the first study to report that PBX1 attenuates stem cell senescence and apoptosis by alleviating DNA damage. It provides new insight into the mechanism of stem cell senescence and lays the foundation for the development of strategies for age-related disease prevention and treatment, and in particular, hair follicle repair and regeneration.

HaCaT‑conditioned medium supplemented with the small molecule inhibitors SB431542 and CHIR99021 and the growth factor PDGF‑AA prevents the dedifferentiation of dermal papilla cells in vitro

Hair loss, including alopecia, is a common and distressing problem for men and women, and as a result, there is considerable interest in developing treatments that can prevent or reverse hair loss. Dermal papillae closely interact with epidermal cells and play a key role during hair follicle induction and hair morphogenesis. As dermal papilla cells (DPCs) lose their hair‑inducing ability in monolayer cultures in vitro, it is difficult to obtain de novo hair follicle structures following DPC transplantation in vivo. The present study aimed to explore culture conditions to maintain DPC characteristics using conditioned media (CM) from the supernatant of cultured HaCaT keratinocyte cells supplemented with other components. Initially, it was observed that during passaging of in vitro monolayer DPC cultures, the Wnt/β‑catenin pathway was repressed, while the TGF‑β/Smad pathway was activated, and that HaCaT cells cultivated in 1% fetal bovine serum had higher levels of expression of Wnt3a and Wnt10b compared with normal keratinocytes. Culturing of high‑passage (P7) DPCs in CM from HaCaT cells (HaCaT‑CM) actively stimulated cell proliferation and maintained Sox2 and Versican expression levels. Supplementation of HaCaT‑CM with SB431542 (SB, a TGF‑β receptor inhibitor), CHIR99021, (CHIR, a GSK3α/β inhibitor and activator of Wnt signaling) and platelet‑derived growth factor (PDGF)‑AA further increased the expression levels of Sox2, Versican and alkaline phosphatase (ALP) in P7 DPCs. Three‑dimensional culture of P7 DPCs using hanging drop cultures in HaCaT‑CM supplemented with SB, CHIR and PDGF‑AA resulted in larger cell aggregates and a further significant upregulation of Sox2, ALP and Versican expression levels. Taken together, these findings demonstrated that HaCaT‑CM supplemented with SB, CHIR and PDGF‑AA may preserve the hair‑inducing ability of high‑passage DPCs and may therefore be useful in reconstructing new hair follicles in vivo.

Interfollicular epidermal stem-like cells for the recreation of the hair follicle epithelial compartment

BACKGROUND

Hair follicle (HF) development and growth are dependent on epithelial-mesenchymal interactions (EMIs). Dermal papilla (DP) cells are recognized as the key inductive mesenchymal player, but the ideal source of receptive keratinocytes for human HF regeneration is yet to be defined. We herein investigated whether human interfollicular epidermal keratinocytes with stem-like features (EpSlKCs), characterized by a α6bri/CD71dim expression, can replace human hair follicular keratinocytes (HHFKCs) for the recreation of the HF epithelium and respective EMIs.

METHODS

The α6bri/CD71dim cellular fraction was selected from the whole interfollicular keratinocyte population through fluorescence-activated cell sorting and directly compared with follicular keratinocytes in terms of their proliferative capacity and phenotype. The crosstalk with DP cells was studied in an indirect co-culture system, and EpSlKC hair forming capacity tested in a hair reconstitution assay when combined with DP cells.

RESULTS

EpSlKCs exhibited a phenotypic profile similar to follicular keratinocytes and were capable of increasing DP cell proliferation and, for short co-culture times, the number of alkaline phosphatase-active cells, suggesting an improvement of their inductivity. Moreover, the recreation of immature HFs and sebaceous glands was observed after EpSlKC and DP cell co-grafting in nude mice.

CONCLUSIONS

Our results suggest that EpSlKCs are akin to follicular keratinocytes and can crosstalk with DP cells, contributing to HF morphogenesis in vivo, thus representing an attractive epithelial cell source for hair regeneration strategies.

Towards developing an organotypic model for the preclinical study and manipulation of human hair matrix-dermal papilla interactions

Organ culture of microdissected scalp hair follicles (HFs) has become the gold standard for human ex vivo hair research; however, availability is becoming very limited. Although various simplistic “HF-equivalent” in vitro models have been developed to overcome this limitation, they often fail to sufficiently mimic the complex cell–cell and cell–matrix interactions between epithelial and mesenchymal cell populations that underlie the specific growth processes occurring in a native HF. Here, we have attempted to overcome these limitations by developing a novel human hair research model that combines dermal papilla (DP) fibroblasts, cultured as 3-dimensional (3D) spheroids (DPS), with plucked anagen hair shafts (HS). We show that DPS express HF inductivity markers, such as alkaline phosphatase (ALP), versican and noggin, while plucked HSs retain substantial remnants of the anagen hair matrix. When cultured together, DPS adhere to and surround the plucked HS (HS-DPS), and significantly enhance HS expression of the differentiation marker keratin-85 (K85; p < 0.0001), while simultaneously decreasing the percentage of TUNEL + cells in the proximal HS (p = 0.0508). This simple model may offer a physiologically relevant first step toward evaluating HF differentiation in the human anagen hair matrix.

The microfollicle: a model of the human hair follicle for in vitro studies

Access to complex in vitro models that recapitulate the unique markers and cell-cell interactions of the hair follicle is rather limited. Creation of scalable, affordable, and relevant in vitro systems which can provide predictive screens of cosmetic ingredients and therapeutic actives for hair health would be highly valued. In this study, we explore the features of the microfollicle, a human hair follicle organoid model based on the spatio-temporally defined co-culture of primary cells. The microfollicle provides a 3D differentiation platform for outer root sheath keratinocytes, dermal papilla fibroblasts, and melanocytes, via epidermal-mesenchymal-neuroectodermal cross-talk. For assay applications, microfollicle cultures were adapted to 96-well plates suitable for medium-throughput testing up to 21 days, and characterized for their spatial and lineage markers. The microfollicles showed hair-specific keratin expression in both early and late stages of cultivation. The gene expression profile of microfollicles was also compared with human clinical biopsy samples in response to the benchmark hair-growth compound, minoxidil. The gene expression changes in microfollicles showed up to 75% overlap with the corresponding gene expression signature observed in the clinical study. Based on our results, the cultivation of the microfollicle appears to be a practical tool for generating testable insights for hair follicle development and offers a complex model for pre-clinical substance testing.

Knockdown of FOXA2 Impairs Hair-Inductive Activity of Cultured Human Follicular Keratinocytes

Reciprocal interactions between hair-inductive dermal cells and epidermal cells are essential for de novo genesis of hair follicles. Recent studies have shown that outer root sheath (ORS) follicular keratinocytes can be expanded in vitro, but the cultured cells often lose receptivity to hair-inducing dermal signals. In this study, we first investigated whether the hair-inductive activity (trichogenicity) of cultured human ORS follicular keratinocytes was correlated with the cultivation period. ORS follicular keratinocytes from the scalp were cultured for 3, 4, 5, or 6 weeks and were then implanted into nude mice along with freshly isolated neonatal mouse dermal cells. We observed that the trichogenicity of the implanted ORS cells was inversely correlated with their cultivation period. These initial findings prompted us to investigate the differentially expressed genes between the short-term (20 days) and long-term (42 days) cultured ORS cells, trichogenic and non-trichogenic, respectively, by microarray analysis. We found that forkhead box protein A2 (FOXA2) was the most up-regulated transcription factor in the trichogenic ORS cells. Thus, we investigated whether the trichogenicity of the cells was affected by FOXA2 expression. We found a significant decrease in the number of induced hair follicles when the ORS cells were transfected with a FOXA2 small interfering RNA versus control small interfering RNA. Taken together, our data strongly suggest that FOXA2 significantly influences the trichogenicity of human ORS cells.

Altered FGF expression profile in human scalp-derived fibroblasts upon WNT activation: implication of their role to provide folliculogenetic microenvironment

Background

Hair follicle (HF) formation and growth are sustained by epithelial-mesenchymal interaction via growth factors and cytokines. Pivotal roles of FGFs on HF regeneration and neogenesis have been reported mainly in rodent models. FGF expression is regulated by upstream pathways, represented by canonical WNT signaling; however, how FGFs influence on human folliculogenesis remains elusive. The aim of this study is to assess if human scalp-derived fibroblasts (sFBs) are able to modulate their FGF expression profile in response to WNT activation and to evaluate the influence of WNT-activated or suppressed FGFs on folliculogenesis.

Methods

Dermal papilla cells (DPCs), dermal sheath cells (DSCs), and sFBs were isolated from the human scalp and cultured independently. The gene expression profile of FGFs in DPCs, DSCs, and sFBs and the influence of WNT activator, CHIR99021, on FGF expression pattern in sFBs were evaluated by reverse transcription polymerase chain reaction, which were confirmed at protein level by western blotting analysis. The changes in the expression of DPC or keratinocyte (KC) biomarkers under the presence of FGF7 or 9 were examined in both single and co-culture assay of DPCs and/or KCs. The influence of FGF 7 and FGF 9 on hair morphogenesis and growth was analyzed in vivo using mouse chamber assay.

Results

In single culture, sFBs were distinguished from DPCs and DSCs by relatively high expression of FGF5 and FGF18, potential inducers of hair cycle retardation or catagen phase. In WNT-activated state, sFBs downregulated FGF7 while upregulating FGF9, a positive regulator of HF morphogenesis, FGF16 and FGF20 belonging to the same FGF subfamily. In addition, CHIR99021, a WNT activator, dose-dependently modulated FGF7 and 9 expression to be folliculogenic. Altered expressions of FGF7 and FGF9 by CHIR99021 were confirmed at protein level. Supplementation of FGF9 to cultured DPCs resulted in upregulation of representative DP biomarkers and this tendency was sustained, when DPCs were co-cultured with KCs. In mouse chamber assay, FGF9 increased both the number and the diameter of newly formed HFs, while FGF7 decreased HF diameter.

Conclusion

The results implied that sFBs support HF formation by modulating regional FGF expression profile responding to WNT activation.

Nanoscale microenvironment engineering based on layer-by-layer self-assembly to regulate hair follicle stem cell fate for regenerative medicine

Hair regenerative medicine, a promising strategy for the treatment of hair loss, will likely involve the transplantation of autologous hair follicular stem cells (HFSCs) and dermal papilla cells (DPCs) into regions of hair loss. Cyclic hair regeneration results from the periodic partial activation of HFSCs. However, previous studies have not successfully achieved large-scale HFSC expansion in vitro without the use of feeder cells, with a lack of research focused on regulating HFSC fate for hair follicular (HF) regeneration. Hence, an emerging focus in regenerative medicine is the reconstruction of natural extracellular matrix (ECM) regulatory characteristics using biomaterials to generate cellular microenvironments for expanding stem cells and directing their fate for tissue regeneration.

Methods: HFSCs were coated with gelatin and alginate using layer-by-layer (LbL) self-assembly technology to construct biomimetic ECM for HFSCs; after which transforming growth factor (TGF)-β2 was loaded into the coating layer, which served as a sustained-release signal molecule to regulate the fate of HFSCs both in vitro and in vivo. In vitro experiments (cell culture and siRNA) were employed to investigate the molecular mechanisms involved and in vivo implantation was carried out to evaluate hair induction efficiency.

Results: Nanoscale biomimetic ECM was constructed for individual HFSCs, which allowed for the stable amplification of HFSCs and maintenance of their stem cell properties. TGF-β2 loading into the coating layer induced transformation of CD34⁺ stem cells into highly proliferating Lgr5⁺ stem cells, similar to the partial activation of HFSCs in HF regeneration. Thus, LbL coating and TGF-β2 loading partially reconstructed the quiescent and activated states, respectively, of stem cells during HF regeneration, thereby mimicking the microenvironment that regulates stem cell fate for tissue regeneration during HF cycling. Improved HF regeneration was achieved when the two HFSC states were co-transplanted with neonatal mouse dermal cells into nude mice.

Conclusion: This study provides novel methods for the construction of stem cell microenvironments and experimental models of HF regeneration for the treatment of hair loss.

Comparative study between follicular unit transplantation with intact and non-intact hair bulb in treatment for stable vitiligo

OBJECTIVE

To compare the cosmetic efficacy of the transplantation of follicles with intact and non-intact hair bulbs in the treatment for vitiligo.

METHODS

The single-hair follicle units with intact hair bulbs and un-intact hair bulbs were transplanted into the skin of vitiligo. The diameters of regrowing hair shafts and repigmentation of implanted follicles were detected analyzed by dermatoscopy (Beining BN-PFMF Skin and Hair Visualizer).

RESULTS

The survival rates of follicles with intact and non-intact hair bulbs were 60.00% and 50.62%, respectively. The average diameters of hair shafts and repigmentation of the two groups were 92.83 ± 7.26 µm vs 55.86 ± 2.64 µm (p < .05), 2.62 ± 0.13 mm vs 2.63 ± 0.17 mm (p > .05), respectively.

CONCLUSION

Single follicle transplantation was an alternative effective choice for the treatment of vitiligo. The skin implanted with follicle with non-intact hair bulb was less hairy.

Effects of platelet-rich plasma on in vitro hair follicle germ preparation for hair regenerative medicine

Hair regenerative medicine is a promising approach for the treatment of hair loss and involves the transplantation of follicular stem cells into bald spots to regenerate hair. Various approaches have been investigated to engineer tissue grafts for use in hair regenerative medicine. Tissue-like three-dimensional aggregates, such as bioengineered hair follicle germs (HFGs), have shown great promise for hair regeneration, with normal tissue morphology and hair cycles. However, these approaches have not yet been applied in clinical settings, and further studies are needed to improve hair generation efficiency. The biological molecules in in vivo microenvironments around HFGs may provide cues for the in vitro preparation of HFGs with higher trichogenic functionalities. Activated platelet-rich plasma releasate (PRPr) is an autologous source of signaling molecules including growth factors and cytokines. In this study, we investigated the effects of PRPr on the preparation of HFGs in vitro. The presence of PRPr did not hinder the spontaneous formation of dumbbell-like HFGs from a suspension of embryonic skin-derived epithelial and mesenchymal cells in a custom-designed HFG culture plate. HFGs prepared with PRPr displayed greater levels of follicular gene expression compared to those prepared in the absence of PRPr. Moreover, the hair regeneration ability upon intracutaneous transplantation was significantly improved in the presence of PRPr. These results suggest that PRPr is beneficial for engineering HFGs for autologous hair regenerative medicine.

Hair Regeneration Potential of Human Dermal Sheath Cells Cultured Under Physiological Oxygen

We investigated the effect of oxygen tension on the proliferation and hair-inductive capacity of human dermal papilla cells (DPCs) and dermal sheath cells (DSCs). DPCs and DSCs were separately obtained from human hair follicles and each cultured under atmospheric/hyperoxic (20% O₂), physiological/normoxic (6% O₂), or hypoxic (1% O₂) conditions. Proliferation of DPCs and DSCs was highest under normoxia. Compared with hyperoxia, hypoxia inhibited proliferation of DPCs, but enhanced that of DSCs. In DPCs, hypoxia downregulated the expression of hair-inductive capacity-related genes, including BMP4, LEF1, SOX2, and VCAN. In DSCs, both normoxia and hypoxia upregulated SOX2 expression, whereas hypoxia downregulated BMP4 expression. Microarray analysis revealed that normoxia increased the expression of pluripotency-related genes, including SPRY, NR0B1, MSX2, IFITM1, and DAZL, compared with hyperoxia. In an in vivo hair follicle reconstitution assay, cultured DPCs and DSCs were transplanted with newborn mouse epidermal keratinocytes into nude mice using a chamber method. In this experiment, normoxia resulted in the most efficient induction of DPC hair follicles, whereas hypoxia caused the most efficient induction and maturation of DSC hair follicles. These results suggest that application of physiological/hypoxic oxygen tension to cultured human DSCs enhances proliferation and maintenance of hair inductivity for skin engineering and clinical applications. Impact statement Dermal sheath cells (DSCs) and dermal papilla cells (DPCs) are useful cell sources for cell-based regenerative therapy. This is the first report to describe that low-oxygen conditions are better for DSCs. Normoxic and hypoxic culture of DSCs is beneficial for expanding these hair follicular cells and advancing development of cell-based therapy for both wound healing and hair regeneration. The current study supports that optimized oxygen tension can be applied to use expanded human DPCs and DSCs for skin engineering and clinical applications.

LncRNA-PCAT1 maintains characteristics of dermal papilla cells and promotes hair follicle regeneration by regulating miR-329/Wnt10b axis

BACKGROUND

The failure of hair follicle regeneration is the major cause of alopecia, which is a highly prevalent disease worldwide. Dermal papilla (DP) cells play important role in the regulation of hair follicle regeneration. However, the molecular mechanism of how dermal papilla cells direct follicle regeneration is still to be elucidated.

METHODS

In vitro DP 3D culturing and in vivo nude mice DP sphere implanted models were used to examine the molecular regulation of DP cells and follicle regeneration. qRT-PCR and Western blotting were used to detect gene and protein expression, respectively. Immunofluorescence was used to detect the expression level of Wnt10b, Ki-67 and β-catenin. Luciferase assay was used to examine the relationship among PCAT1, miR-329 and Wnt10b. ALP activity was measured by ELISA. H&E staining was used to measure follicle growth in skin tissues.

RESULTS

Up-regulation of PCAT1 and Wnt10b, however, down-regulation of miR-329 were found in the in vitro 3D dermal papilla. Bioinformatics analysis and luciferase assays demonstrated that PCAT1 promoted Wnt10b expression by sponging miR-329. Knockdown of PCAT1 suppressed the proliferation and activity, as well as ALP and other DP markers of DP cells by targeting miR-329. Knockdown of PCAT1 regulated miR-329/Wnt10b axis to attenuate β-catenin expression and nucleus translocation to inhibit Wnt/β-catenin signaling. Furthermore, knockdown of PCAT1 suppressed DP sphere induced follicle regeneration and hair growth in nude mice.

CONCLUSION

PCAT1 maintains characteristics of DP cells by targeting miR-329 to activating Wnt/β-catenin signaling pathway, thereby promoting hair follicle regeneration.

Tissue engineering strategies for human hair follicle regeneration: How far from a hairy goal?

The demand for an efficient therapy for alopecia disease has fueled the hair research field in recent decades. However, despite significant improvements in the knowledge of key processes of hair follicle biology such as genesis and cycling, translation into hair follicle replacement therapies has not occurred. Great expectation has been recently put on hair follicle bioengineering, which is based on the development of fully functional hair follicles with cycling activity from an expanded population of hair‐inductive (trichogenic) cells. Most bioengineering approaches focus on in vitro reconstruction of folliculogenesis by manipulating key regulatory molecular/physical features of hair follicle growth/cycling in vivo. Despite their great potential, no cell‐based product is clinically available for hair regeneration therapy to date. This is mainly due to demanding issues that still hinder the functionality of cultured human hair cells. The present review comprehensively compares emergent strategies using different cell sources and tissue engineering approaches, aiming to successfully achieve a clinical cure for hair loss. The hurdles of these strategies are discussed, as well as the future directions to overcome the obstacles and fulfill the promise of a “hairy” feat.

Use of human intra-tissue stem/progenitor cells and induced pluripotent stem cells for hair follicle regeneration

Background

The hair follicle (HF) is a unique miniorgan, which self-renews for a lifetime. Stem cell populations of multiple lineages reside within human HF and enable its regeneration. In addition to resident HF stem/progenitor cells (HFSPCs), the cells with similar biological properties can be induced from human-induced pluripotent stem cells (hiPSCs). As approaches to regenerate HF by combining HF-derived cells have been established in rodents and a huge demand exists to treat hair loss diseases, attempts have been made to bioengineer human HF using HFSPCs or hiPSCs.

Main body of the abstract

The aim of this review is to comprehensively summarize the strategies to regenerate human HF using HFSPCs or hiPSCs. HF morphogenesis and regeneration are enabled by well-orchestrated epithelial-mesenchymal interactions (EMIs). In rodents, various combinations of keratinocytes with mesenchymal (dermal) cells with trichogenic capacity, which were transplanted into in vivo environment, have successfully generated HF structures. The regeneration efficiency was higher, when epithelial or dermal HFSPCs were adopted. The success in HF formation most likely depended on high receptivity to trichogenic dermal signals and/or potent hair inductive capacity of HFSPCs. In theory, the use of epithelial HFSPCs in the bulge area and dermal papilla cells, their precursor cells in the dermal sheath, or trichogenic neonatal dermal cells should elicit intense EMI sufficient for HF formation. However, technical hurdles, represented by the limitation in starting materials and the loss of intrinsic properties during in vitro expansion, hamper the stable reconstitution of human HFs with this approach. Several strategies, including the amelioration of culture condition or compartmentalization of cells to strengthen EMI, can be conceived to overcome this obstacle. Obviously, use of hiPSCs can resolve the shortage of the materials once reliable protocols to induce wanted HFSPC subsets have been developed, which is in progress. Taking advantage of their pluripotency, hiPSCs may facilitate previously unthinkable approaches to regenerate human HFs, for instance, via bioengineering of 3D integumentary organ system, which can also be applied for the treatment of other diseases.

Short conclusion

Further development of methodologies to reproduce bona fide EMI in HF formation is indispensable. However, human HFSPCs and hiPSCs hold promise as materials for human HF regeneration.

Serenoa repens and N-acetyl glucosamine/milk proteins complex differentially affect the paracrine communication between endothelial and follicle dermal papilla cells

Current treatments for hair follicle (HF) disruption are based on 5-α reductase inhibitors and prostaglandin modulators. Botanicals and nutraceutical compounds interfere with hair loss or stimulate its partial regrowth. Here, we used in vitro cocultures to investigate the activity of Serenoa repens ( SR) and N-acetyl glucosamine + milk proteins (NAG/Lac) on the paracrine interactions between human microvascular endothelial cells (HMVEC) and HF dermal papilla cells (FDPC). Both SR and NAG/Lac-induced endothelial tubulogenesis were enhanced by FDPC. SR promoted proliferation of both the cell types, while NAG/Lac was effective on endothelium. Vascular endothelial growth factor production, enhanced by SR, was further augmented by FDPC. In FDPC 5-α reductase-II and β-catenin expressions were modified by SR and less by NAG/Lac, with no additional effect by HMVEC. SR and NAG/Lac prevented lipid peroxidation, whereas NAG/Lac was effective on interleukin 1β production. Finally, SR and NAG/Lac differentially affected HMVEC permeability and tight junction proteins content. These data provide a mechanistic background for the potential use of these compounds as promoters of HF vascularization.

Impact of substrate stiffness on dermal papilla aggregates in microgels

Interaction between cells and the extracellular environment plays a vital role in cellular development. The mechanical property of a 3-dimensional (3D) culture can be modified to mimic in vivo conditions. Dermal papilla (DP) cells are shown to gradually lose their inductivity in hair cycle development in a 2-dimensional culture. They are shown to partially restore their inductivity when transferred into a 3D microenvironment. In this study, a microarray fabricated from three different concentrations of poly-ethylene-glycol-diacrylate 3500, namely 5%, 10% and 15% w/v, yielded increasing substrate stiffness. The impact of varying substrate stiffness was tested for DP cell viability, attachment, and selected hair inductive markers. DP aggregates were shown to be viable and exhibited greater spreading with increasing substrate stiffness. Moreover, DP aggregates cultured on a softer substrate showed a greater fold change of gene and protein expressions than those cultured on a harder substrate.

Restoration of hair-inductive activity of cultured human follicular keratinocytes by co-culturing with dermal papilla cells

Hair follicle outer root sheath (ORS) cells can be expanded in vitro, but often lose receptivity to hair-inducing dermal signals. Recent studies have shown hair-inductive activity (trichogenicity) can be restored in rat ORS cells expanded with a fibroblast feeder by co-culturing with rat vibrissae dermal papilla (DP) cells. In this study, we investigated whether the trichogenicity of human ORS cells can be restored by co-culturing with human DP cells. ORS cells from human scalp hair follicles were cultured independently or with DP cells for 5 days and implanted into nude mice alongside freshly isolated neonatal mouse dermal cells. Although there was no hair induction when monocultured ORS cells were implanted, it was observed in co-cultured ORS cells. We also observed differential regulation of a number of genes in ORS cells co-cultured with DP cells compared to monocultured ORS cells as examined by microarray. Taken together, our data strongly suggest that human DP cells restore the trichogenicity of co-cultured ORS cells by influencing ORS gene expression through paracrine factors.

Engineering the niche for hair regeneration - A critical review

Recent progress in hair follicle regeneration and alopecia treatment necessitates revisiting the concepts and approaches. In this sense, there is a need for shedding light on the clinical and surgical therapies benefitting from nanobiomedicine. From this perspective, this review attempts to recognize requirements upon which new hair therapies are grounded; to underline shortcomings and opportunities associated with recent advanced strategies for hair regeneration; and most critically to look over hair regeneration from nanomaterials and pluripotent stem cell standpoint. It is noteworthy that nanotechnology is able to illuminate a novel path for reprogramming cells and controlled differentiation to achieve the desired performance. Undoubtedly, this strategy needs further advancement and a lot of critical questions have yet to be answered. Herein, we introduce the salient features, the hurdles that must be overcome, the hopes, and practical constraints to engineer stem cell niches for hair follicle regeneration.

Establishment and characterization of five immortalized human scalp dermal papilla cell lines

Dermal papilla (DP) regulates the growth and cycling of hair follicles. Cultured DP cells are useful for the study of their role in relation to hair growth and regeneration. However, cultivation of human DP cells is tedious and difficult. In addition, cultured DP cells possess a relatively short replicative life span, requiring immortalized human DP cell lines. We previously established an immortalized human DP cell line, SV40T-hTERT-DPC, by introducing human telomerase reverse transcriptase (hTERT) gene into the transformed cell line, SV40T-DPC. In this study, we co-transfected the simian virus 40 large T antigen (SV40T-Ag) and hTERT into DP cells from scalp hair follicles from a male with androgenetic alopecia and established five immortalized DP cell lines and named KNU-101, KNU-102, KNU-103, KNU-201 and KNU-202. We then evaluated tumorigenicity, expression of DP markers, responses to androgen, Wnt3a and BMP4, and expression of DP signature genes. These cell lines displayed early passage morphology and maintained responses to androgen, Wnt and BMP. Furthermore, these cell lines expressed DP markers and DP signature genes. KNU cell lines established in this study are potentially useful sources for hair research.

Spontaneous hair follicle germ (HFG) formation in vitro, enabling the large-scale production of HFGs for regenerative medicine

Hair follicle morphogenesis is triggered by reciprocal interactions between hair follicle germ (HFG) epithelial and mesenchymal layers. Here, we developed a method for large-scale preparation of HFGs in vitro via self-organization of cells. We mixed mouse epidermal and mouse/human mesenchymal cells in suspension and seeded them in microwells of a custom-designed array plate. Over a 3-day culture period, cells initially formed a randomly distributed single cell aggregate and then spatially separated from each other, exhibiting typical HFG morphological features. These self-sorted hair follicle germs (ssHFGs) were shown to be capable of efficient hair-follicle and shaft generation upon intracutaneous transplantation into the backs of nude mice. This finding facilitated the large-scale preparation of approximately 5000 ssHFGs in a microwell-array chip made of oxygen-permeable silicone. We demonstrated that the integrity of the oxygen supply through the bottom of the silicone chip was crucial to enabling both ssHFG formation and subsequent hair shaft generation. Finally, spatially aligned ssHFGs on the chip were encapsulated into a hydrogel and simultaneously transplanted into the back skin of nude mice to preserve their intervening spaces, resulting in spatially aligned hair follicle generation. This simple ssHFG preparation approach is a promising strategy for improving current hair-regenerative medicine techniques.

Unlocking the vital role of host cells in hair follicle reconstruction by semi-permeable capsules

Organ regeneration is becoming a promising choice for many patients; however, many details about the mechanisms underlying organ regeneration remain unknown. As regenerative organs, hair follicles offer a good model to study the mechanisms associated with regenerative medicine. The relevant studies have mainly focused on donor cells, and there are no systematic studies involving the effect of host factors on hair follicle reconstruction. Thus, we intend to explore the effect of host cells on hair follicle reconstruction. Epidermal and dermal cells from red fluorescent protein (RFP) transgenic newborn mice were injected into green fluorescent protein (GFP) transgenic mice. In addition, we wrapped the mixed dermal and epidermal cells from GFP transgenic and RFP transgenic mice by the Cell-in-a-Box kit to form "capsules," so that the cells within would be isolated from host cells. These capsules were cultured in vitro and transplanted in vivo. Fully developed reconstructed hair follicles were observed after the injection of mixed cells. These reconstructed follicles mainly consisted of donor cells, as well as a small number of host cells. The encapsulated cells gradually aggregated into cell spheres in vitro without apparent differentiation towards hair follicles. With respect to the transplanted capsules, concentric circle structures were observed, but no hair follicles or hair shafts formed. When the concentric circle structures were transplanted in vivo, mature hair follicles were observed 30 days later. Host cells were found in the reconstructed hair follicles. Thus, we conclude that host cells participate in the process of hair follicle reconstruction, and they play a vital role in the process, especially for the maturation of reconstructed hair follicles. Furthermore, we established a special hair follicle reconstruction system with the help of capsules: transplant cells were isolated from host, but other factors from host could exchange with cells inside.

As a carrier-transporter for hair follicle reconstitution, platelet-rich plasma promotes proliferation and induction of mouse dermal papilla cells

Morphogenesis of hair follicles during development and in hair reconstitution assays involves complex interactions between epithelial cells and dermal papilla cells (DPCs). DPCs may be a source of cells for hair regeneration in alopecia patients. Reconstitution of engineered hair follicles requires in vitro culture of trichogenic cells, a three-dimensional scaffolds, and biomolecular signals. However, DPCs tend to lose their biological activity when cultured as trichogenic cells, and scaffolds currently used for hair follicle regeneration lack biological efficiency and biocompatibility. Platelet-rich plasma (PRP) gel forms a three-dimensional scaffold that can release endogenous growth factors, is mitogenic for a variety of cell types and is used in model tissue repair and regeneration systems. We found that 5% activated PRP significantly enhanced cell proliferation and hair-inductive capability of mouse and human DPCs in vitro and promoted mouse hair follicle formation in vivo. PRP also formed a three-dimensional gel after activation. We used PRP gel as a scaffold to form many de novo hair follicles on a plane surface, showing it to be candidate bioactive scaffold capable of releasing endogenous growth factors for cell-based hair follicle regeneration.

Various Types of Minor Trauma to Hair Follicles During Follicular Unit Extraction for Hair Transplantation

BACKGROUND

When performing follicular unit extraction (FUE), various types of minor hair follicle trauma unapparent during follicular unit strip surgery are likely to occur. However, no studies have examined such damage.

METHODS

In total, 100 grafts were randomly selected from each of 42 patients who underwent FUE with a 1-mm-diameter sharp punch. A ×5.5 magnifying loupe and a ×60 magnifying binocular microscope were used. The transection rate (TR), paring, fractures of and damage to the dermal papilla (DP) areas, and hair bulb partial injury were assessed.

RESULTS

Observation with the magnifying loupe revealed an average TR of 7.40%, and 4.31, 1.90, 1.52, and 0.43 hair follicles per 100 grafts exhibited paring, fracture, DP partial injury, and hair bulb partial injury, respectively. An average of 9.21 telogen hairs were observed. Microscopic examination revealed a TR of 6.34%, and 9.07, 1.95, 0.79, and 1.24 hair follicles per 100 grafts exhibited paring, fracture, DP injury, and hair bulb partial injury, respectively. An average of 16.62 telogen hairs were observed.

CONCLUSIONS

Various types of minor hair follicle damage occur during FUE as shown by loupe and microscopic examination of the grafts. Especially paring and hair bulb injury were more apparent under microscopic examination. These minor hair follicle injuries should be considered when choosing operative method or surgical techniques.

Hair Follicle Generation by Injections of Adult Human Follicular Epithelial and Dermal Papilla Cells into Nude Mice

Objective

Dermal papilla and hair epithelial stem cells regulate hair formation and the growth cycle. Damage to or loss of these cells can cause hair loss. Although several studies claim to reconstitute hairs using rodent cells in an animal model, additional research is needed to develop a stable human hair follicle reconstitution protocol. In this study, we have evaluated hair induction by injecting adult cultured human dermal papilla cells and a mixture of hair epithelial and dermal papilla cells in a mouse model.

Materials and Methods

In this experimental study, discarded human scalp skins were used to obtain dermal papilla and hair epithelial cells. After separation, cells were cultured and assessed for their characteristics. We randomly allocated 15 C57BL/6 nude mice into three groups that received injections in their dorsal skin. The first group received cultured dermal papilla cells, the second group received a mixture of cultured epithelial and dermal papilla cells, and the third group (control) received a placebo [phosphate-buffered saline (PBS-)].

Results

Histopathologic examination of the injection sites showed evidence of hair growth in samples that received cells compared with the control group. However, the group that received epithelial and dermal papilla cells had visible evidence of hair growth. PKH tracing confirmed the presence of transplanted cells in the new hair.

Conclusion

Our data showed that injection of a combination of adult human cultured dermal papilla and epithelial cells could induce hair growth in nude mice. This study emphasized that the combination of human adult cultured dermal papilla and epithelial cells could induce new hair in nude mice.

Induction of hair follicle dermal papilla cell properties in human induced pluripotent stem cell-derived multipotent LNGFR(+)THY-1(+) mesenchymal cells

The dermal papilla (DP) is a specialised mesenchymal component of the hair follicle (HF) that plays key roles in HF morphogenesis and regeneration. Current technical difficulties in preparing trichogenic human DP cells could be overcome by the use of highly proliferative and plastic human induced pluripotent stem cells (hiPSCs). In this study, hiPSCs were differentiated into induced mesenchymal cells (iMCs) with a bone marrow stromal cell phenotype. A highly proliferative and plastic LNGFR(+)THY-1(+) subset of iMCs was subsequently programmed using retinoic acid and DP cell activating culture medium to acquire DP properties. The resultant cells (induced DP-substituting cells [iDPSCs]) exhibited up-regulated DP markers, interacted with human keratinocytes to up-regulate HF related genes, and when co-grafted with human keratinocytes in vivo gave rise to fibre structures with a hair cuticle-like coat resembling the hair shaft, as confirmed by scanning electron microscope analysis. Furthermore, iDPSCs responded to the clinically used hair growth reagent, minoxidil sulfate, to up-regulate DP genes, further supporting that they were capable of, at least in part, reproducing DP properties. Thus, LNGFR(+)THY-1(+) iMCs may provide material for HF bioengineering and drug screening for hair diseases.

Human Hair Reconstruction: Close, But Yet So Far

Billions of dollars are annually invested in pharmaceutical industry and cosmetic sector with intent to develop new drugs and treatment strategies for alopecia. Because the hair looks an important characteristic of humans-an effective appendage in perception, expression of beauty, and preservation of self-esteem-the global market for hair loss treatment products is exponentially increasing. However, current methods to treat hair loss endure yet multiple challenges, such as unfavorable outcomes, nonpermanent and patient-dependent results, as well as unpredictable impacts, which limit their application. Over recent years, remarkable advances in the fields of regenerative medicine and hair tissue engineering have raised new hopes for introducing novel cell-based approaches to treat hair loss. Through cell-based approaches, it is possible to produce hair-like structures in the laboratory setting or manipulate cells in their native niche (in vivo lineage reprogramming) to reconstruct the hair follicle. However, challenging issues still exist with the functionality of cultured human hair cells, the proper selection of nonhair cell sources in cases of shortage of donor hair, and the development of defined culture conditions. Moreover, in the case of in vivo lineage reprogramming, selecting appropriate induction factors and their efficient delivery to guide resident cells into a hair fate-with the aim of reconstructing functional hair-still needs further explorations. In this study, we highlight recent advances and current challenges in hair loss treatment using cell-based approaches and provide novel insights for crucial steps, which must be taken into account to develop reproducible, safe, and efficient cell-based treatment.

Culture of Dermal Papilla Cells from Ovine Wool Follicles: An In Vitro Model for Papilla Size Determination

Common human balding or hair loss is driven by follicle miniaturization. Miniaturization is thought to be caused by a reduction in dermal papilla size. The molecular mechanisms that regulate papilla size are poorly understood, and their elucidation would benefit from a tractable experimental model. We have found that dermal papilla cells from sheep spontaneously aggregate in culture to form papilla-like structures. Here, we describe methods for microdissecting dermal papillae from wool follicles, for initiating and maintaining cultures of ovine papilla cells, and for using these cells in an in vitro assay to measure the effect of bioactive molecules on aggregate size.

Assembling Composite Dermal Papilla Spheres with Adipose-derived Stem Cells to Enhance Hair Follicle Induction

Intradermal adipose tissue plays an essential role for hair follicles (HFs) regeneration by regulating hair cycles. However, the effect of reconstruction of HFs and the involvement of adipose-related cells are poorly understood. We investigated assembly strategies for the interactions of dermal papilla (DP) cells with adipose-derived stem cells (ASCs) in promoting hair formation. DP cells lose DP traits during adherent culture, but preserved DP markers with a unified sphere diameter by seeding on chitosan-coated microenvironments. Next, ASCs isolated from rats were co-cultured with DP spheres by different assembling approaches to determine their interactions; a mixed sphere of ASCs with DP cells (MA-DPS), or a core-shell structure, outer ASCs shell and an inner DP core (CSA-DPS). CSA-DPS exhibited superior DP characteristics compared to MA-DPS. Conditional medium from ASCs, but not differentiated adipocytes, promoted DP markers and functional alkaline phosphatase activity from the DP cells. In vivo patch assay showed the core-shell assembling of CSA-DPS can reconstruct cellular arrangements and microenvironmental niches as dominated by PPARα signal in ASCs to induce the greater hair induction than MA-DPS or DP spheres alone. Therefore, the assembling of a core-shell sphere for DP with ASCs could reconstruct the HF cellular arrangement for hair formation. This paper set the groundwork for further evaluation of the input of other cell types.

Cytokine loaded layer-by-layer ultrathin matrices to deliver single dermal papilla cells for spot-by-spot hair follicle regeneration

Polymer nanocoated dermal papilla cells promoting hair regeneration.

Exploring the biology of the nail: An intriguing but less-investigated skin appendage

The nail is a highly keratinized structure covering the tip of the digit, and considered to have several important functions in our daily life. In recent years, as biological aspects of the nail organ have been characterized, we realize that the nail unit and the hair follicle share various biological and immunological features. In particular, development and homeostasis of the nail unit also requires intimate epithelial-mesenchymal interactions that involve signaling pathways such as Wnt. There is also a striking immunological resemblance between both appendages, since the nail matrix, like the anagen hair bulb and the bulge, was shown to present unique characteristics of an immune privileged site. On the other hand, considerable progress in identifying nail stem cells has succeeded in locating putative stem cell niches in the nail unit. In this context, it is intriguing that nail stem cells residing in the nail matrix were recently shown to possess the ability to organize the process leading to digit regeneration. Further elucidation of signaling pathways governing epithelial-mesenchymal interactions in the nail unit seems to be a key to develop a novel therapeutic tool to treat amputees using nail epithelium. However, it is at least certain that the nail unit has a promising potential for the future of regenerative medicine. This review explores the biology of the nail organ by focusing on intriguing knowledge gained from recent studies.

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.