Hair Follicle Neogenesis Research Articles

Wound-induced hair follicle neogenesis: a new perspective on hair follicles regeneration in adult mammals

To explore the research progress of the cell sources and related signaling pathways of the wound-induced hair follicle neogenesis (WIHN) in recent years. The literature related to WIHN in recent years was reviewed, and the cell sources and molecular mechanism were summarized and discussed. Current research shows that WIHN is a rare regeneration phenomenon in the skin of adult mammals, with multiple cell origins, both hair follicle stem cells and epithelial stem cells around the wound. Its molecular mechanism is complicated, which is regulated by many signaling pathways. Besides, the process is closely related to the immune response, the immunocytes and their related cytokines provide suitable conditions for this process. There are still many unsolved problems on the cellular origins and molecular mechanisms of the WIHN. Further study on the mechanisms will enhance the understanding of adult mammals' hair follicle regeneration and may provide new strategy for functional healing of the human skin.

Major Improvement in Wound Healing Through Pharmacologic Mobilization of Stem Cells in Severely Diabetic Rats.

Current therapeutic strategies for diabetic foot ulcer (DFU) have focused on developing topical healing agents, but few agents have controlled prospective data to support their effectiveness in promoting wound healing. We tested a stem cell mobilizing therapy for DFU using a combination of AMD3100 and low-dose FK506 (tacrolimus) (AF) in streptozocin-induced type 1 diabetic (T1DM) rats and type 2 diabetic Goto-Kakizaki (GK) rats that had developed peripheral artery disease and neuropathy. Here, we show that the time for healing back wounds in T1DM rats was reduced from 27 to 19 days, and the foot wound healing time was reduced from 25 to 20 days by treatment with AF (subcutaneously, every other day). Similarly, in GK rats treated with AF, the healing time on back wounds was reduced from 26 to 21 days. Further, this shortened healing time was accompanied by reduced scar and by regeneration of hair follicles. We found that AF therapy mobilized and recruited bone marrow-derived CD133+ and CD34+ endothelial progenitor cells and Ym1/2+ M2 macrophages into the wound sites, associated with enhanced capillary and hair follicle neogenesis. Moreover, AF therapy improved microcirculation in diabetic and neuropathic feet in GK rats. This study provides a novel systemic therapy for healing DFU.

Sustained release of inhibitor from bionic scaffolds for wound healing and functional regeneration.

Small molecules play remarkable roles in promoting tissue regeneration, but are limited by their burst release. Small molecules such as deferoxamine (DFO) have been released slowly from silk hydrogels and stimulated angiogenesis and wound healing, but failed to achieve functional recovery of skin. Various bioactive molecules are required to create a suitable niche for better skin regeneration by controlling their release behaviors. Herein, a small molecule SB216763, a GSK-3 inhibitor, was loaded on silk fibroin nanofibers (SNF), and then mixed with chitosan (CS) to prepare the small molecule-loaded composite bionic scaffolds (CSNF-SB). Given the interaction of SNF and SB216763, the sustained release of SB216763 for more than 21 days was achieved for SNF and CSNF-SB composite scaffolds. Compared to drug-free CSNF scaffolds, CSNF-SB showed better cell adhesion and proliferation capacity, suggesting bioactivity. The upregulated expression of β-catenin in fibroblasts in vitro revealed that the released small molecules maintained their function in composite scaffolds. Quicker and better wound healing was realized with the drug-loaded scaffolds, which was significantly superior to that treated with drug-free scaffolds. Unlike the DFO-loaded silk hydrogel system, hair follicle neogenesis was also found in the drug-loaded-scaffold treatment wounds, demonstrating functional recovery. Therefore, silk nanofibers as versatile carriers for different small bioactive molecules could be used to fabricate scaffolds with optimized niches and then achieve functional recovery of tissues. The small molecule-loaded bionic scaffolds have a promising future in skin tissue regeneration.

Bacteria Induce Skin Regeneration Via Il-1β Signaling

Environmental factors that enhance regeneration are largely unknown. We hypothesized that skin bacteria modulate regeneration. Here, we assessed low, medium, and high levels of bacterial burden in wound healing and Wound Induced Hair follicle Neogenesis (WIHN), a rare adult organogenesis model (Ito et al., 2007; Plikus et al., 2017). WIHN levels and stem cell markers indeed correlated with bacterial counts, being lowest in germ free (GF), intermediate in conventional specific pathogen free (SPF), and highest even in mice infected with pathogenic Staphylococcus aureus. We identified IL-1β and keratinocyte-dependent IL-1R-MyD88 signaling as necessary and sufficient for bacteria to promote regeneration. Finally, in a small clinical trial, we found that a topical broad-spectrum antibiotic slowed skin wound healing. These results demonstrate a novel role for IL-1β to control morphogenesis and counter conventional notions that infection inhibits regeneration with a need for full sterility of small wounds.

Induction of hair follicle neogenesis with cultured mouse dermal papilla cells in de novo regenerated skin tissues.

De novo skin regeneration with human keratinocytes amplified in culture is a life-saving procedure for patients with extensive skin loss and chronic wounds. It also provides a valuable platform for gene function and therapeutic assessments. Nevertheless, tissues generated in this manner lack hair follicles that are important for skin homeostasis, barrier function, and repair. In this study, we generated skin tissues with human keratinocytes combined with dermal papilla (DP) cells isolated from mouse whisker hair. For this, cultured keratinocytes and mouse DP (mDP) cells were mixed at 10:1 ratio and seeded onto devitalized human dermal matrix derived from surgically discarded human abdominoplasty skin. After 1week in submerged culture, the cell/matrix composites were grafted onto the skin wound beds of immunocompromised NSG.SCID mice. Histological analysis of 6-week-old skin grafts showed that tissues generated with the addition of mDP cells contained Sox2-positive dermal condensates and well-differentiated folliculoid structures that express human keratinocyte markers. These results indicate that cultured mDP cells can induce hair follicle neogenesis in the de novo regenerated skin tissues. Our method offers a new experimental system for mechanistic studies of hair follicle morphogenesis and tissue regeneration and provides insights to solving an important clinical challenge in generation of fully functional skin with a limited source of donor cells.

Characterization of human dermal sheath cells reveals CD36-expressing perivascular cells associated with capillary blood vessel formation in hair follicles

Dermal sheath (DS) is located at the outermost border of hair follicles, comprising the connective tissue sheath of these follicles; DS cells are known to contribute to hair cycling and follicle neogenesis. However, the mechanisms by which DS cells contribute to hair formation are currently unclear. We investigated the global transcriptional profile of human DS cells in early passaged culture, compared with those of human dermal papilla cells (DP cells) and dermal fibroblasts. Vascular related genes were highly expressed in DS cells, and expression of the multi-ligand receptor, CD36, was significantly higher in DS cells than in DP cells. Further analyses with whole-mount imaging technique showed that dense networks of blood capillaries were formed in the DS of human anagen hair follicles, whereas regression of blood capillaries was observed in telogen and catagen hair follicles. We found that CD36-expressing cells were present in populations of DS cells, but were rarely observed in populations of DP cells and fibroblasts. Furthermore, our results indicated that CD36-expressing DS cells may participate in angiogenesis. Therefore, we concluded that CD36-expressing DS cells may modulate blood capillaries in hair follicles, in association with hair cycling.

Noncoding dsRNA induces retinoic acid synthesis to stimulate hair follicle regeneration via TLR3

How developmental programs reactivate in regeneration is a fundamental question in biology. We addressed this question through the study of Wound Induced Hair follicle Neogenesis (WIHN), an adult organogenesis model where stem cells regenerate de novo hair follicles following deep wounding. The exact mechanism is uncertain. Here we show that self-noncoding dsRNA activates the anti-viral receptor toll like receptor 3 (TLR3) to induce intrinsic retinoic acid (RA) synthesis in a pattern that predicts new hair follicle formation after wounding in mice. Additionally, in humans, rejuvenation lasers induce gene expression signatures for dsRNA and RA, with measurable increases in intrinsic RA synthesis. These results demonstrate a potent stimulus for RA synthesis by non-coding dsRNA, relevant to their broad functions in development and immunity.

639-P: Pharmacological Mobilization and Recruitment of Bone Marrow Stem Cells Accelerates Diabetic Wound Healing in Rats with Diabetic Complications

Introduction: The lifetime incidence of foot ulcers has been estimated to be 19% to 34% among persons with diabetes. Diabetic wound healing(DWH) remains a challenge. Given the promising role of stem cells in wound healing, the current study proposed to improve DWH by mobilizing and recruiting bone marrow stem cells pharmacologically with combination of AMD3100 and low-dose FK506 (AF) in rats. Methods: T2 GK rats and STZ induced T1DM SD rats were used. To determine the role of bone marrow stem cells, bone marrow from GFP tg Lewis were transplanted into wt Lewis rats and T1 rats were induced by STZ injection at 2 months following bone marrow transplantation. Full-thickness wounds were created in the dorsal skin or in the foot skin at 6 weeks after STZ injection or GK rats at 4 month old. Wounded rats were divided into two experimental groups and received saline or a combination of AMD3100 (1mg/kg) and FK506 (0.1mg/kg) immediately after wounding and every 2 days until complete healing. Results: At the time of wounding, all animals developed peripheral artery disease and neuropathy. The back wound healing time was reduced from 27 to 19 days and the foot wound healing time was reduced from 25 to 20 days in T1DM rats treated with AF. Similarly, the back wound healing time was reduced from 26(S) to 21(AF) days in GK rats. Equally important, healing was accompanied by reduced scar and regeneration of hair follicles. Searching for the mechanisms, we found that AF therapy mobilized bone marrow stem cells to peripheral blood and recruited bone marrow-derived CD31+CD133+ endothelial progenitor cells, CD34+ stem cells and Ym1/2+ M2 macrophages into the wound sites and enhanced capillary and hair follicle neogenesis. Conclusion: Combination of AMD3100 and low-dose FK506 results in better and faster healing of diabetic wounds in rats with diabetic peripheral artery disease and neuropathy. Our findings offer a significant therapeutic approach to healing of DFU. Disclosure L. Qi: None. A.R. Ahmadi: None. J. Huang: None. Q. Lin: None. M. Chen: None. H. Kuwabara: None. K. Iwasaki: None. J. Burdick: None. Z. Sun: None.

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

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

Exosomes derived from human dermal papilla cells promote hair growth in cultured human hair follicles and augment the hair‐inductive capacity of cultured dermal papilla spheres

Dermal papillae (DP) play key roles in hair growth and regeneration by regulating follicular cell activity. Owing to the established roles of exosomes (Exos) in the regulation of cell functions, we investigated whether DP-derived Exos, especially those from three-dimensional (3D)-cultured DP cells, affect hair growth, cycling and regeneration. Exos derived from 3D DP (3D DP-Exos) promoted the proliferation of DP cells and outer root sheath (ORS) cells and increased the expression of growth factors (IGF-1, KGF and HGF) in DP cells. 3D DP-Exo treatment also increased hair shaft elongation in cultured human hair follicles. In addition, local injections of 3D DP-Exos induced anagen from telogen and also prolonged anagen in mice. Moreover, Exo treatment in human DP spheres augmented hair follicle neogenesis when the DP spheres were implanted with mouse epidermal cells. Similar results were obtained using Exos derived from 2D-cultured DP cells (2D DP-Exo). Collectively, our data strongly suggest that Exos derived from DP cells promote hair growth and hair regeneration by regulating the activity of follicular dermal and epidermal cells; accordingly, these findings have implications for the development of therapeutic strategies for hair loss.

Anagen hair follicle repair: Timely regenerative attempts from plastic extra-bulge epithelial cells.

Anagen hair follicle repair (AHFR) is the regenerative scheme activated to restore the structure and hair growth following injuries to anagen hair follicles. Compared with telogen-to-anagen regeneration and hair follicle neogenesis, AHFR is a clinically important, yet relatively unexplored regenerative feature of hair follicles. Due to their highly proliferative character, germinative cells and matrix cells within hair bulbs are highly susceptible to injuries, such as chemotherapy and radiotherapy. Clinical and experimental observations suggest that damaged anagen hair follicles are able to repair themselves to resume anagen growth, bypassing premature catagen/telogen entry. Mechanistically, extra-bulge epithelial cells in the outer root sheath and the lower proximal cup are quickly mobilized for regeneration. These cells acquire stem cell-like properties, exhibiting high plasticity by breaking lineage restriction to regenerate all cell types in the lower segment of anagen hair follicles. Facilitating extra-bulge epithelial cells' mobilization ameliorates hair loss from chemo- and radiotherapy. On the other hand, quiescent bulge stem cells can also be activated, but only after more severe injuries and with slower activation dynamics. They show limited plasticity and regenerate part of the outer root sheath only. The dysrhythmic activation might render bulge stem cells susceptible to concomitant injuries due to their exit from quiescence.

Regeneration of rete ridges in Lanyu pig (Sus scrofa): Insights for human skin wound healing.

Rete ridges are important to the mechanical function of skin in animals with minimal hair, including humans. As mice do not exhibit rete ridges, the need for a quality animal model is pertinent. Here, we develop a Lanyu pig (Sus scrofa) full-thickness wound model to explore tissue regeneration because the architecture and function are similar to humans and inbred genetic variants are available. Full- and partial-thickness wounds were generated on the dorsum. Full-thickness wounds at post-wound day 57 exhibit severe scar with no signs of wound-induced hair follicle neogenesis. Wound contraction is greater in the anterior/posterior relative to the medial/lateral axis. In wound beds, K14+ cells increased while K10+ , p63+ and PCNA+ cells decreased compared to unwounded tissue. Epithelial β-catenin is unchanged. The wound bed expresses more ColI, less ColIII and no elastin. Rete ridges do not form after full-thickness wounding, but incompletely regenerate after partial-thickness wounding. An alkaline phosphatase (ALP)+ cell population, not associated with hair follicles, is present at the bottom of the rete ridge basal layer in pig and human unwounded skin. These K5+ /K10- /PCNA- /ALP+ epithelial cells are absent after full-thickness wounding but reappear after partial-thickness wounding, before invagination of new rete ridges. In summary, full-thickness wounding on the dorsum of Lanyu pigs results in scar formation and perturbed molecular expression while partial-thickness wounding permits limited rete ridge and papillary dermis regeneration. Future functional studies and further characterization will help contribute knowledge for the regenerative medicine field.

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

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

Skin-permeable liposome improved stability and permeability of bFGF against skin of mice with deep second degree scald to promote hair follicle neogenesis through inhibition of scar formation.

Excessive deposition of extracellular matrix (ECM) usually resulted in scar formation during wound healing, which caused skin dysfunction, such as hair loss. Basic fibroblast growth factor (bFGF) was very helpful for promoting hair follicle neogenesis and regulating the remodeling of ECM during wound healing. Because of its poor stability in wound fluids and low permeability against the dense wound scar, the repairing quality of bFGF on wound was hindered largely in clinical practice. To overcome these drawbacks, herein, a novel liposome with silk fibroin hydrogel core (bFGF-SF-LIP) was firstly prepared to stabilize bFGF, followed by insertion of laurocapam, a permeation enhancer, into the liposomal membrane to construct a skin-permeable liposome (SP-bFGF-SF-LIP). The encapsulated efficiency of bFGF was reaching to nearly 90% when ratio of drug/lipids above 1:300, and it activity was not compromised by laurocapam. SP-bFGF-SF-LIP exhibited a hydrodynamic diameter of 103.3 nm and Zeta potential of -2.31 mV. The stability of the encapsulated bFGF in wound fluid was obviously enhanced. After 24 h of incubation with wound fluid containing MMP-9, the remaining bFGF was as high as 65.4 ± 0.5% for SP-bFGF-SF-LIP, while only 2.1 ± 0.2% of free bFGF was remained. The skin-permeability of bFGF was significantly enhanced by SP-bFGF-SF-LIP and most of the encapsulated bFGF penetrated into the dermis. After treatment with SP-bFGF-SF-LIP, the morphology of hair follicle at wound zone was obviously improved and the hair regrew on the deep second scald mice model. The therapeutic mechanism was highly associated with inhibiting scar formation and promoting vascular growth in dermis. Conclusively, SP-bFGF-SF-LIP may a potential option to improve wound healing with high-quality.

Embryonic-Like Regenerative Phenomenon: Wound-Induced Hair Follicle Neogenesis

Wound-induced hair follicle neogenesis (WIHN) is a regenerative phenomenon that occurs widely in the skin of adult mammalians. A fully functional follicle can regenerate in the center of a full-thickness wound with a large enough size. The cellular origin of this process is similar to embryonic process. Many growth and development-related pathways are involved in WIHN. Studying WIHN can deeply explore the mechanism of biological growth, development and regeneration, and can identify new treatments for hair-related disorders. Our review aims to enlighten future study by summarizing the clinical manifestation of WIHN, as well as the cellular and molecular mechanism of WIHN in recent studies.

1434 Role of fibroblast DPP4 in wound healing, scarring and regeneration

Wounding results in inflammation, synthesis and remodeling of granulation tissue with extracellular matrix deposition and scar-formation which might reduce function of affected areas representing a challenging medical problem. During development and even in the presence of inflammation skin repair is scarless until fibroblasts become lineage-committed and express DPP4. The exact functions of this molecule remain unknown. It is hypothesized that through its peptidase activity DPP4 is able to modulate the microenvironment around fibroblasts at specific time points during wound healing and repair and thus determine the fate and function of these cells and others. We performed in vivo experiments applying 1.5x1.5 cm full-thickness wounds on the back of mice and analyzed gene and protein expression on sorted fibroblasts and tissue sections. We can show that DPP4 is expressed and upregulated in early stages of wounding but then reduced at the moment Wnt-activity and fibrogenic differentiation occurs suggesting a regulatory role for DPP in the scar formation process but also for Wnt pathway which is crucial for tissue regeneration. Blocking DPP4 early upon wounding results in abolishment of “wound induced hair follicle neogenesis (WIHN)” and increased dermal thickness while lack of DPP4-activity at later stages results in increased WIHN, a hallmark of regenerative repair. Our data suggests a crucial role for DPP4 for scarring and WIHN and further investigations might help elucidate the molecular mechanisms involved in supporting the wound healing functions of dermal fibroblast and inducing their scar-forming activities, which might help identifying targets for improving skin-regeneration.

Msx2 Supports Epidermal Competency during Wound-Induced Hair Follicle Neogenesis

Cutaneous wounds in adult mammals typically heal by scarring. However, large full-thickness wounds undergo wound-induced hair follicle neogenesis (WIHN), a form of regeneration. Here, we show that WIHN requires transient expression of epidermal Msx2 in two phases: the wound margin early and the wound center late. Msx2 expression is present in the migrating epithelium during early wound healing and then presents in the epithelium and mesenchyme later in the wound center. WIHN is abrogated in germline and epithelial-specific Msx2 mutant mice. Unlike the full-length Msx2 promoter, a minimal Msx2 promoter fails activation in the wound center, suggesting complex regulation of Msx2 expression. The Msx2 promoter binding sites include Tcf/Lef, Jun/Creb, Pax3, and three SMAD sites. However, basal epithelial-induced BMP suppression by noggin overexpression did not affect WIHN. We propose that Msx2 signaling is required for the epidermis to acquire spatiotemporal competence during WIHN. Topologically, hair regeneration dominates in the wound center, coinciding with late Msx2 expression. Together, these results suggest that intrinsic Msx2 expression supports epithelial competency during hair follicle neogenesis. This work provides insight into endogenous mechanisms modulating competency of adult epidermal progenitors for mammalian ectodermal appendage neogenesis, and offers the target Msx2 for future regeneration-promoting therapies.

Inducing hair follicle neogenesis with secreted proteins enriched in embryonic skin

Organ development is a sophisticated process of self-organization. However, despite growing understanding of the developmental mechanisms, little is known about how to reactivate them postnatally for regeneration. We found that treatment of adult non-hair fibroblasts with cell-free extract from embryonic skin conferred upon them the competency to regenerate hair follicles. Proteomics analysis identified three secreted proteins enriched in the embryonic skin, apolipoprotein-A1, galectin-1 and lumican that together were essential and sufficient to induce new hair follicles. These 3 proteins show a stage-specific co-enrichment in the perifolliculogenetic embryonic dermis. Mechanistically, exposure to embryonic skin extract or to the combination of the 3 proteins altered the gene expression to an inductive hair follicle dermal papilla fibroblast-like profile and activated Igf and Wnt signaling, which are crucial for the regeneration process. Therefore, a cocktail of organ-specific extracellular proteins from the embryonic environment can render adult cells competent to re-engage in developmental interactions for organ neogenesis. Identification of factors that recreate the extracellular context of respective developing tissues can become an important strategy to promote regeneration in adult organs.

PDGFA regulation of dermal adipocyte stem cells.

Adipose tissue is widely studied for its central role in regulating systemic metabolism and contribution to obesity-related diseases; however, skin resident dermal white adipose tissue (dWAT) also contributes to many aspects of skin function. Skin-resident mature adipocytes are thought to prevent hair growth activation through the secretion of BMP molecules (1). Furthermore, following S. aureus infection, adipose tissue in the skin expands and produces an antibacterial peptide (2). During wound healing, defects in adipogenesis can abrogate fibroblast recruitment into wound beds, leading to defects in extracellular matrix deposition and tissue repair (3). Migration of adipocyte precursors into the wounded area might also contribute to the mesenchymal repopulation of the wounded site (4) and in wounds where hair follicle neogenesis is observed fully functional adipocyte precursors are present (5). These findings highlight the breadth of the role of adipose tissue in the skin.

Targeting of CXXC5 by a Competing Peptide Stimulates Hair Regrowth and Wound-Induced Hair Neogenesis

The Wnt/β-catenin pathway has been implicated in hair follicle development and hair regeneration in adults. We discovered that CXXC-type zinc finger protein 5 (CXXC5) is a negative regulator of the Wnt/β-catenin pathway involved in hair regrowth and wound-induced hair follicle neogenesis via an interaction with Dishevelled. CXXC5 was upregulated in miniaturized hair follicles and arrector pili muscles in human balding scalps. The inhibitory effects of CXXC5 on alkaline phosphatase activity and cell proliferation were demonstrated using human hair follicle dermal papilla cells. Moreover, CXXC5-/- mice displayed accelerated hair regrowth, and treatment with valproic acid, a glycogen synthase kinase 3β inhibitor that activates the Wnt/β-catenin pathway, further induced hair regrowth in the CXXC5-/- mice. Disrupting the CXXC5-Dishevelled interaction with a competitor peptide activated the Wnt/β-catenin pathway and accelerated hair regrowth and wound-induced hair follicle neogenesis. Overall, these findings suggest that the CXXC5-Dishevelled interaction is a potential target for the treatment of hair loss.