Epidermal ET-1 signal induces activation of resting hair follicles by upregulating the PI3K/AKT pathway in the dermis

The prevalence of alopecia has increased recently. Hair loss is often accompanied by the resting phase of hair follicles (HFs). Dermal papilla (DP) plays a crucial role in HF development, growth, and regeneration. Activating DP can revive resting HFs. Augmenting WNT/β-catenin signaling stimulates HF growth. However, the factors responsible for activating resting HFs effectively are unclear. In this study, we investigated epidermal cytokines that can activate resting HFs effectively. We overexpressed β-catenin in both in vivo and in vitro models to observe its effects on resting HFs. Then, we screened potential epidermal cytokines from GEO DATASETs and assessed their functions using mice models and skin-derived precursors (SKPs). Finally, we explored the molecular mechanism underlying the action of the identified cytokine. The results showed that activation of WNT/β-catenin in the epidermis prompted telogen-anagen transition. Keratinocytes infected with Ctnnb1-overexpressing lentivirus enhanced SKP expansion. Subsequently, we identified endothelin 1 (ET-1) expressed higher in hair-growing epidermis and induced the proliferation of DP cells and activates telogen-phase HFs in vivo. Moreover, ET-1 promotes the proliferation and stemness of SKPs. Western blot analysis and in vivo experiments revealed that ET-1 induces the transition from telogen-to-anagen phase by upregulating the PI3K/AKT pathway. These findings highlight the potential of ET-1 as a promising cytokine for HF activation and the treatment of hair loss.

Injectable and biofunctionalized fibrin hydrogels co-embedded with stem cells induce hair follicle genesis

Fibrin-based hydrogels have been widely used in various tissue engineering because of their biocompatibility, biodegradability, tunable mechanical characteristics and nanofibrous structural properties. However, their ability to support stem cells for hair follicle neogenesis is unclear. In this study, we investigated the effect of fibrin hydrogels in supporting skin-derived precursors (SKPs) in hair follicle neogenesis. Our results showed that SKPs in fibrin hydrogels with high cell viability and proliferation, the stemness of SKPs could be maintained, and the expression of hair induction signature genes such as akp2 and nestin was enhanced. Moreover, hair follicle reconstruction experiments showed de novo hair genesis in mice and the hairs persisted for a long time without teratoma formation. More importantly, the blood vessels and sebaceous glands were also regenerated. Our study demonstrated that fibrin hydrogels are promising in hair follicle regeneration and have potential application in clinical settings for alopecia and wound healing.

Facilitation of mouse skin-derived precursor growth and yield by optimizing plating density

Multiple methodologies have been reported to facilitate skin-derived precursor (SKP) growth, but the impact of plating density on SKP growth has not been studied. To determine the optimal plating density, we used six plating densities and two types of flasks for mouse SKP (mSKP) culture. On the 14th day, the number, diameter, and viability of mSKP spheres were compared by morphological assessment and cell counting kit 8, and we found the optimal plating density was 2.5 × 10⁵–5 × 10⁵ cells/mL. In addition, we investigated the correlation between the SKP spheres and the adherent cell colonies in the serum-free culture system. We treated the adherent cell colonies with two culture conditions and characterized the cells generated from two conditions by immunocytochemistry and induced differentiation, respectively. The results elucidated that the adherent cell colonies differentiated into either mSKPs or dermal mesenchymal stem cells under appropriate culture conditions. In conclusion, mSKP spheres differentiated from the adherent cell colonies. The optimal plating density significantly promoted and advanced the proliferation of adherent cell colonies, which optimized mSKP growth and yield. The adherent cell colonies possessed the capacity of differentiating into different types of cells under appropriate culture conditions.

Amphiregulin promotes hair regeneration of skin-derived precursors via the PI3K and MAPK pathways

Objectives

There are significant clinical challenges associated with alopecia treatment, including poor efficiency of related drugs and insufficient hair follicles (HFs) for transplantation. Skin‐derived precursors (SKPs) exhibit great potential as stem cell‐based therapies for hair regeneration; however, the proliferation and hair‐inducing capacity of SKPs gradually decrease during culturing.

Materials and Methods

We describe a 3D co‐culture system accompanied by kyoto encyclopaedia of genes and genomes and gene ontology enrichment analyses to determine the key factors and pathways that enhance SKP stemness and verified using alkaline phosphatase assays, Ki‐67 staining, HF reconstitution, Western blot and immunofluorescence staining. The upregulated genes were confirmed utilizing corresponding recombinant protein or small‐interfering RNA silencing in vitro, as well as the evaluation of telogen‐to‐anagen transition and HF reconstitution in vivo.

Results

The 3D co‐culture system revealed that epidermal stem cells and adipose‐derived stem cells enhanced SKP proliferation and HF regeneration capacity by amphiregulin (AREG), with the promoted stemness allowing SKPs to gain an earlier telogen‐to‐anagen transition and high‐efficiency HF reconstitution. By contrast, inhibitors of the phosphoinositide 3‐kinase (PI3K) and mitogen‐activated protein kinase (MAPK) pathways downstream of AREG signalling resulted in diametrically opposite activities.

Conclusions

By exploiting a 3D co‐culture model, we determined that AREG promoted SKP stemness by enhancing both proliferation and hair‐inducing capacity through the PI3K and MAPK pathways. These findings suggest AREG therapy as a potentially promising approach for treating alopecia.

Photobiomodulation therapy for hair regeneration: A synergetic activation of β-CATENIN in hair follicle stem cells by ROS and paracrine WNTs

Photobiomodulation therapy (PBMT) has shown encouraging results in the treatment of hair loss. However, the mechanism by which PBMT controls cell behavior to coordinate hair cycle is unclear. Here, PBMT is found to drive quiescent hair follicle stem cell (HFSC) activation and alleviate hair follicle atrophy. Mechanistically, PBMT triggers a new hair cycle by upregulating β-CATENIN expression in HFSCs. Loss of β-Catenin (Ctnnb1) in HFSCs blocked PBMT-induced hair regeneration. Additionally, we show PBMT-induced reactive oxygen species (ROS) activate the PI3K/AKT/GSK-3β signaling pathway to inhibit proteasome degradation of β-CATENIN in HFSCs. Furthermore, PBMT promotes the expression and secretion of WNTs in skin-derived precursors (SKPs) to further activate the β-CATENIN signal in HFSCs. By contrast, eliminating ROS or inhibiting WNT secretion attenuates the activation of HFSCs triggered by PBMT. Collectively, our work suggests that PBMT promotes hair regeneration through synergetic activation of β-CATENIN in HFSCs by ROS and paracrine WNTs by SKPs.

Long-Term Observation and Sequencing Analysis of SKPs-Derived Corneal Endothelial Cell-Like Cells for Treating Corneal Endothelial Dysfunction

Corneal endothelial dysfunction is a principal cause of visual deficiency. Corneal transplantation is the most effective treatment for corneal endothelial dysfunction. However, a severe shortage of available donor corneas or human corneal endothelial cells (HCECs) remains a global challenge. Previously, we acquired corneal endothelial cell-like cells (CEC-like cells) derived from human skin-derived precursors (SKPs). CEC-like cells were injected into rabbit and monkey corneal endothelial dysfunction models and exerted excellent therapeutic effect. In this study, we prolonged the clinical observation in the monkey experiment for 2 years. Polymerase chain reaction (PCR) and DNA sequencing were carried out to confirm the existence of CEC-like cells. Histological examinations were carried out to show the corneal morphology. Further transcriptome sequencing was also carried out on HCEC, CEC-like cells before transplantation and after transplantation. We found that the monkeys cornea remained transparent and normal thickness. The total endothelial cell density decreased gradually, but tended to be stable and remained in a normal range during 2-year observation. The CEC-like cells persist during observation and could adapt to the microenvironment after transplantation. The gene expression pattern of CEC-like cells was similar to HCEC and changed slightly after transplantation. In conclusion, this study presented a brand-new insight into CEC-like cells and further provided a promising prospect of cell-based therapy for corneal endothelial dysfunction. The renewable cell source, novel derivation method and simple treatment strategy may be clinically applied in regenerative medicine in the future.

Intracarotid Transplantation of Skin-Derived Precursor Schwann Cells Promotes Functional Recovery After Acute Ischemic Stroke in Rats

Purpose: Skin-derived Precursor Schwann cells (SKP-SCs) have been reported to provide neuroprotection for the injured and dysmyelinated nervous system. However, little is known about SKP-SCs on acute ischemic stroke (AIS). We aimed to explore the efficacy and the potential mechanism of action of SKP-SCs on AIS in a rat ischemic stroke model.

Methods: Adult male Sprague–Dawley rats were subjected to a middle cerebral artery occlusion (MCAO) for 1.5 h on Day 0 and subsequently received an intracarotid injection of 2 × 10⁶ green fluorescent protein (GFP) -labeled SKP-SCs or phosphate buffered saline (PBS) during reperfusion. Neurological function was assessed by behavioral tests on Days 1, 4, 7, 14, and 28. In a satellite cohort, rat brains were harvested and infarct volume was measured with 2,3,5-triphenyltetrazolium chloride (TTC) staining on Days 1 and 7, and migration and survival of SKP-SCs in the brain were traced by monitoring green fluorescence at 6 and12 h on Day 0, and on Days 1, 4, 7, 14, and 28. Histopathology and immunofluorescence staining were used to analyze the morphology, survival and apoptosis of neurons. Additionally, in an in vitro SKP-SC co-culture model using fetal rat primary cortical neurons underwent oxygen glucose deprivation/reoxygenation (OGD/R), Western blot was used to detect the expression of apoptosis indicators including activated caspase-3, Bax, and Bcl-2. TUNEL staining was used to count apoptotic cells.

Results: Intracarotid transplantation of SKP-SCs effectively migrated to the periinfarct area and survived for at least 4 weeks. Transplanted SKP-SCs inhibited neuronal apoptosis, reduced infarct volume, and improved neurological recovery in the MCAO rats. Moreover, in vitro data showed that SKP-SCs treatment inhibited OGD/R-induced neuronal apoptosis and promoted survival of the cultured primary cortical neurons.

Conclusions: Intracarotid transplantation of SKP-SCs promoted functional recovery in the rat AIS model and possesses the potential to be further developed as a novel therapy to treat ischemic stroke in humans.

Transplantation of Skin Precursor-Derived Schwann Cells Yields Better Locomotor Outcomes and Reduces Bladder Pathology in Rats with Chronic Spinal Cord Injury

Cell transplantation for spinal cord injury (SCI) has largely been studied in sub-acute settings within 1–2 weeks of injury. In contrast, here we transplanted skin-derived precursors differentiated into Schwann cells (SKP-SCs) into the contused rat spinal cord 8 weeks post-injury (wpi). Twenty-one weeks later (29 wpi), SKP-SCs were found to have survived transplantation, integrated with host tissue, and mitigated the formation of a dense glial scar. Furthermore, transplanted SKP-SCs filled much of the lesion sites and greatly enhanced the presence of endogenous SCs, which myelinated thousands of sprouting/spared host axons in and around the injury site. In addition, SKP-SC transplantation improved locomotor outcomes and decreased pathological thickening of bladder wall. To date, functional improvements have very rarely been observed with cell transplantation beyond the sub-acute stage of injury. Hence, these findings indicate that skin-derived SCs are a promising candidate cell type for the treatment of chronic SCI.

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SKP-SCs injected 8 weeks after SCI survive long-term and integrate with host tissue

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SKP-SC transplants boosted the presence of endogenous SCs in the chronic SCI site

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Treated spinal cords showed enhanced growth and SC myelination of axons

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Treated rats displayed better locomotor outcomes with reduced bladder pathologies

Multipotentiality of skin-derived precursors: application to the regeneration of skin and other tissues

Skin-derived precursors (SKPs) have been described as multipotent dermal precursors. Here, we provide a review of the breadth and depth of scientific literature and studies regarding SKPs, accounting for a large number of scientific publications. Interestingly, these progenitors can be isolated from embryonic and adult skin, as well as from a population of dermal cells cultured in vitro in monolayer. Gathering information from different authors, this review explores different aspects of the SKP theme, such as the potential distinct origins of SKPs in rodents and in humans, and also their ability to differentiate in vitro and in vivo into multiple lineages of different progeny. This remarkable capacity makes SKPs an interesting endogenous source of precursors to explore in the framework of experimental and therapeutic applications in different domains. SKPs are not only involved in the skin's dermal maintenance and support as well as wound healing, but also in hair follicle morphogenesis. This review points out the interests of future researches on SKPs for innovative perspectives that may be helpful in many different types of scientific and medical domains.

Protective effect of skin-derived precursors on photoaging in nude mice

OBJECTIVES

Currently, innovative methods to prevent photoaging are needed. Skin-derived precursors (SKP) have been shown to play a crucial role in resisting UVB-induced apoptosis in vitro. The objective of this study was to explore the effect of SKP on preventing skin photoaging in vivo.

METHODS

Skin-derived precursors from neonatal BALB/c mice were isolated, identified and intradermally transplanted with a PKH26 label to track their survival. These were then injected at different concentrations into the buttock dermis of nude mice at 2-weekly intervals before UV irradiation. Photographs, assessment of live skin surface, histology with quantitative real-time polymerase chain reaction and immunohistochemistry were used to evaluate the impact of SKP on wrinkles and other relevant indicators of skin photoaging.

RESULTS

SKP exhibited a sphere-like structure and could survive for at least 2 weeks after intradermal transplantation. A large dose of SKP transplantation (10⁵ SKP +UV) at 2-weekly intervals were able to ameliorate coarse UV-induced wrinkles. Moreover, the skin smoothness value, dermal thickness and collagen percentage were significantly increased in mice that received a large dose of SKP (10⁵ SKP +UV). UV radiation induced the mRNA expression of MMP-13 and decreased the mRNA and protein expression of TβRII, but these effects were diminished by SKP transplantation. The transplantation of SKP could increase the mRNA of TIMP-1.

CONCLUSIONS

We found that transplanted SKP exert a beneficial impact on preventing UV-induced wrinkles in vivo, suggesting that SKP transplantation is a promising candidate for preventing photoaging.

BC-Box Motif-Mediated Neuronal Differentiation of Somatic Stem Cells

Von Hippel-Lindau tumor suppressor protein (pVHL) functions to induce neuronal differentiation of neural stem/progenitor cells (NSCs) and skin-derived precursors (SKPs). Here we identified a neuronal differentiation domain (NDD) in pVHL. Neuronal differentiation of SKPs was induced by intracellular delivery of a peptide composed of the amino-acid sequences encoded by the NDD. Neuronal differentiation mediated by the NDD was caused by the binding between it and elongin C followed by Janus kinase-2 (JAK2) ubiquitination of JAK2 and inhibition of the JAK2/the signal transducer and activator of transcription-3(STAT)3 pathway. The NDD in pVHL contained the BC-box motif ((A,P,S,T)LXXX (A,C) XXX(A,I,L,V)) corresponding to the binding site of elongin C. Therefore, we proposed that other BC-box proteins might also contain an NDD; and subsequently also identified in them an NDD containing the amino-acid sequence encoded by the BC-box motif in BC-box proteins. Furthermore, we showed that different NDD peptide-delivered cells differentiated into different kinds of neuron-like cells. That is, dopaminergic neuron-like cells, cholinergic neuron-like cells, GABAnergic neuron-like cells or rhodopsin-positive neuron-like cells were induced by different NDD peptides. These novel findings might contribute to the development of a new method for promoting neuronal differentiation and shed further light on the mechanism of neuronal differentiation of somatic stem cells.

Schwann Cells in the Ventral Dermis Do Not Derive from Myf5-Expressing Precursors

The embryonic origin of lineage precursors of the trunk dermis is somewhat controversial. Precursor cells traced by Myf5 and Twist2 (Dermo1) promoter activation (i.e., cells of presumed dermomyotomal lineage) have been reported to generate Schwann cells. On the other hand, abundant data demonstrate that dermal Schwann cells derive from the neural crest. This is relevant because dermal precursors give rise to neural lineages, and multilineage differentiation potential qualifies them as adult stem cells. However, it is currently unclear whether neural lineages arise from dedifferentiated Schwann cells instead of mesodermally derived dermal precursor cells. To clarify these discrepancies, we traced SOX2⁺ adult dermal precursor cells by two independent Myf5 lineage tracing strains. We demonstrate that dermal Schwann cells do not belong to the Myf5⁺ cell lineage, indicating that previous tracing data reflected aberrant cre recombinase expression and that bona fide Myf5⁺ dermal precursors cannot transdifferentiate to neural lineages in physiological conditions.

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Adult Myf5-cre^Sor mice aberrantly trace dermal Schwann cells (dSCs)

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Dedifferentiated, SOX2⁺ dSCs are the neural-competent precursors in the dermis

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These findings cast doubt on the multipotency of adult skin-derived precursors

Skin-derived precursors possess the ability of differentiation into the epidermal progeny and accelerate burn wound healing

Skin-derived precursors (SKPs) are remnants of the embryonic neural crest stem cells that reside in the dermis until adulthood. Although they possess a wide range of differentiation potentials, their differentiation into keratinocyte-like cells and their roles in skin wound healing are obscure. The present study aimed to investigate the differentiation of SKPs into keratinocyte-like cells and evaluate their role in healing of third degree burn wounds. To this aim, SKPs were differentiated into keratinocyte-like cells on tissue culture plate and collagen-chitosan scaffold prepared by freeze-drying. Their differentiation capability was detected by real-time RT-PCR and immunofluorescence. Thereafter, they were cultured on scaffold and implanted in a rat model of burn wound. Histopathological and immunohistochemical analyses were employed to examine the reconstituted skin. The research findings revealed that SKPs were able to differentiate along the epidermal lineage and this ability can be enhanced on a suitable scaffold. Additionally, the results indicated that SKPs apparently promoted wound healing process and accelerate its transition from proliferating stage to maturational phase, especially if they were differentiated into keratinocyte-like cells. Regarding the results, it is concluded that SKPs are able to differentiate into keratinocyte-like cells, particularly when they are cultured on collagen-chitosan scaffold. Moreover, they can regenerate epidermal and dermal layers including thick collagen bundles, possibly through differentiation into keratinocyte-like cells.

Senescence of human skin-derived precursors regulated by Akt-FOXO3-p27(KIP¹)/p15(INK⁴b) signaling

Multipotent skin-derived precursors (SKPs) are dermal stem cells with the capacity to reconstitute the dermis and other tissues, such as muscles and the nervous system. Thus, the easily available human SKPs (hSKPs) hold great promises in regenerative medicine. However, long-term expansion is difficult for hSKPs in vitro. We previously demonstrated that hSKPs senesced quickly under routine culture conditions. To identify the underlying mechanisms so as to find an effective way to expand hSKPs, time-dependent microarray analysis of gene expression in hSKPs during in vitro culture was performed. We found that the senescence of hSKPs had a unique gene expression pattern that differs from reported typical senescence. Subsequent investigation ruled out the role of DNA damage and classical p53 and p16(INK4a) signaling in hSKP senescence. Examination of cyclin-dependent kinase inhibitors revealed the involvement of p15(INK4b) and p27(KIP1). Further exploration about upstream signals indicated the contribution of Akt hypo-activity and FOXO3 to hSKP senescence. Forced activation of Akt and knockdown of FOXO3, p15(INK4b) and p27(KIP1) effectively inhibited hSKP senescence and promoted hSKP proliferation. The unique senescent phenotype of human dermal stem cells and the role of Akt-FOXO3-p27(KIP1)/p15(INK4b) signaling in regulating hSKP senescence provide novel insights into the senescence and self-renewal regulation of adult stem cells. The present study also points out a way to propagate hSKPs in vitro so as to fulfill their promises in regenerative medicine.

Schwann cells originating from skin-derived precursors promote peripheral nerve regeneration in rats

Artificial guidance channels containing Schwann cells can promote the regeneration of injured peripheral nerve over long distances. However, primary Schwann cells are not suitable for autotransplantation. Under specific conditions, skin-derived progenitors can be induced to differentiate into Schwann cells. Therefore, adult rat dorsal skin (dermis)-derived progenitors were isolated and induced to differentiate with DMEM/F12 containing B27, neuregulin 1, and forskolin. Immunofluorescence staining and reverse transcription polymerase chain reaction (RT-PCR) confirmed that the resultant cells were indeed Schwann cells. Artificial guidance channels containing skin-derived progenitors, Schwann cells originating from skin-derived progenitors, or primary Schwann cells were used to bridge 5 mm sciatic nerve defects. Schwann cells originating from skin-derived progenitors significantly promoted sciatic nerve axonal regeneration. The significant recovery of injured rat sciatic nerve function after the transplantation of Schwann cells originating from skin-derived progenitors was confirmed by electromyogram. The therapeutic effect of Schwann cells originating from skin-derived progenitors was better than that of skin-derived progenitors. These findings indicate that Schwann cells originating from skin-derived precursors can promote peripheral nerve regeneration in rats.

Morphological and electrophysiological features of mature neurons in differentiated skin-derived precursor cells

In vitro modelling of neuronal pathologies is, in particular, demanding and a lot of efforts have been undertaken to differentiate skin derived precursor cells into neuronal cells. However, so far all attempts did not result in cells with functional features of neurons like the ability to generate action potentials or synaptic activity. Here, we report that simple modifications of the protocols result in neuronal cells that display action potentials and synaptic activity. We think that our observation is an important step to model individual neuronal pathologies in vitro.

Induction of Nestin-expressing Spheroids from Human Dermal Fibroblasts in a bFGF-dependent Manner

BACKGROUND AND OBJECTIVES

Neural stem/precursor cells are found in relatively inaccessible neurogenic regions of the adult brain, making them difficult to harvest for therapeutic purposes.

METHODS AND RESULTS

In this study, nestin-expressing spheroids were induced from primary cultures of newborn and adult foreskin-derived dermal fibroblasts using a novel, two-step induction method. Approximately 80% of dermal fibroblasts became nestin-expressing cells within 12 days. Nestin expression and spheroid-forming capacity were both blocked by removal of bFGF from the induction medium. The bFGF-induced, nestin-expressing spheroids possessed most of the features distinctive of skin-derived precursor cells.

CONCLUSIONS

Our findings support the possibility of inducing nestin-expressing spheroids from purified human dermal fibroblasts in a bFGF dependent manner. This is important because it may be impossible to induce spheroids from the small pool of residual neural crest-related precursor cells found in adults.