Emerging interactions between skin stem cells and their niches

Sphingolipid metabolism orchestrates establishment of the hair follicle stem cell compartment

Sphingolipids serve as building blocks of membranes to ensure subcellular compartmentalization and facilitate intercellular communication. How cell type-specific lipid compositions are achieved and what is their functional significance in tissue morphogenesis and maintenance has remained unclear. Here, we identify a stem cell-specific role for ceramide synthase 4 (CerS4) in orchestrating fate decisions in skin epidermis. Deletion of CerS4 prevents the proper development of the adult hair follicle bulge stem cell (HFSC) compartment due to altered differentiation trajectories. Mechanistically, HFSC differentiation defects arise from an imbalance of key ceramides and their derivate sphingolipids, resulting in hyperactivation of noncanonical Wnt signaling. This impaired HFSC compartment establishment leads to disruption of hair follicle architecture and skin barrier function, ultimately triggering a T helper cell 2-dominated immune infiltration resembling human atopic dermatitis. This work uncovers a fundamental role for a cell state-specific sphingolipid profile in stem cell homeostasis and in maintaining an intact skin barrier.

Hair regrowth in alopecia areata and re-pigmentation in vitiligo in response to treatment: Commonalities and differences

Both alopecia areata (AA) and vitiligo share common pathogenesis involving, interferon-γ (IFN-γ) and interleukin-15 (IL-15) signalling pathways that activate cytotoxic CD8+ T lymphocytes. These shared mechanisms may explain why both diseases respond to currently available treatments (e.g. topical/systemic corticosteroid) and emerging treatment modalities. As compared with the speed of re-pigmentation in vitiligo lesions, the regeneration of pigmented terminal hair follicles in AA lesions appears fast in response to treatments targeting the inhibition of the Janus kinases (JAKs) and other kinases. We summarize the commonalities and differences between AA and vitiligo focusing on the treatment modalities, followed by recent findings associated with hair follicle stem cells (HFSC) in hair bulge (HBg) and melanocyte stem cells (McSC) in HBg and hair germ (HGm). We then discuss how HFSC and HGm-McSC are involved in the initiation of anagen phase, followed by pigmented terminal hair regrowth in the recovering AA lesions in association with immunology. We also discuss how HBg-McSC contribute to the migration of fully dendritic mature melanocytes into interfollicular epidermis and the equal distribution of melanin in recovering vitiligo lesions. Finally, we present four hypotheses to elucidate the delayed distribution of melanin by mature melanocytes in depigmented vitiligo lesions from the aspects of stem cell biology, as compared with quick hair recovery in AA: (1) McSC are less abundant than HFSC. (2) McSC require a long travel, whereas HFSC reside close to hair regeneration trigger point. (3) Keratinocyte scaffold to accept melanin is not well preserved, whereas scaffold for hair regrowth is well preserved. (4) Inhibitors targeting JAKs and other kinases have less direct effects on melanocyte proliferation and differentiation in vitiligo than hair regrowth in AA. Our review provides an overview of treatment modalities and bridges the gap between scientific advancement and clinical practice in AA and vitiligo management.

Bioengineering strategies for regeneration of skin integrity: A literature review

Objective

The skin is a complex organ that includes various stem cell populations. Current approaches for non-healing skin defects are sometimes inadequate and many attempts have been made to regenerate skin integrity. The aim of this review is to bridge the gap between basic research and clinical application of skin integrity regeneration.

Methods

A literature search was carried out in PubMed using combinations of the keywords "skin integrity", "tissue-engineered skin", "bioengineered skin", and "skin regeneration". Articles published from 1968 to 2023 reporting evidence from in vivo and in vitro skin regeneration experiments were included.

Results

These articles showed that stem cells can be differentiated into normal skin cells, including keratinocytes, and are a significant source of skin organoids, which are useful for investigating skin biology; and that emerging direct reprogramming methods have great potential to regenerate skin from the wounded skin surface.

Conclusion

Recent advances in skin regeneration will facilitate further advancement of both basic and clinical research in skin biology.

BMP4 regulates differentiation of nestin-positive stem cells into melanocytes

Hair follicle (HF) development and pigmentation are complex processes governed by various signaling pathways, such as TGF-β and FGF signaling pathways. Nestin + (neural crest like) stem cells are also expressed in HF stem cells, particularly in the bulge and dermal papilla region. However, the specific role and differentiation potential of these Nestin-positive cells within the HF remain unclear, especially regarding their contribution to melanocyte formation and hair pigmentation. Bone morphogenetic protein 4 (BMP4), members of the TGFβ family, has been implicated in regulating HF growth, coloration, and related cellular behaviors. Its role in directing Nestin-positive cells toward a melanocytic lineage has yet to be fully explored. In this study, mouse HF organoids were constructed and shown to be an ideal model for studying HF growth and development in vitro. Using this model as a basis, we demonstrated that BMP4 controls HF coloration as well as its length, number, and even size. Furthermore, Nestin-positive cells in the HF-especially those in the bulge region-differentiate into melanocytes, which produce the pigments that give HF its color under BMP4 stimulation. The resulting increase in pigmentation within the mouse HF organoids underscores that BMP4 has a major regulatory role in the formation of melanocytes from Nestin-positive stem cells. This research provides insights into the cellular mechanisms underlying hair pigmentation and suggests potential therapeutic applications for pigmentation disorders.

Intermittent fasting triggers interorgan communication to suppress hair follicle regeneration

Intermittent fasting has gained global popularity for its potential health benefits, although its impact on somatic stem cells and tissue biology remains elusive. Here, we report that commonly used intermittent fasting regimens inhibit hair follicle regeneration by selectively inducing apoptosis in activated hair follicle stem cells (HFSCs). This effect is independent of calorie reduction, circadian rhythm alterations, or the mTORC1 cellular nutrient-sensing mechanism. Instead, fasting activates crosstalk between adrenal glands and dermal adipocytes in the skin, triggering the rapid release of free fatty acids into the niche, which in turn disrupts the normal metabolism of HFSCs and elevates their cellular reactive oxygen species levels, causing oxidative damage and apoptosis. A randomized clinical trial (NCT05800730) indicates that intermittent fasting inhibits human hair growth. Our study uncovers an inhibitory effect of intermittent fasting on tissue regeneration and identifies interorgan communication that eliminates activated HFSCs and halts tissue regeneration during periods of unstable nutrient supply.

Deciphering normal and cancer stem cell niches by spatial transcriptomics: opportunities and challenges

Cancer stem cells (CSCs) often exhibit stem-like attributes that depend on an intricate stemness-promoting cellular ecosystem within their niche. The interplay between CSCs and their niche has been implicated in tumor heterogeneity and therapeutic resistance. Normal stem cells (NSCs) and CSCs share stemness features and common microenvironmental components, displaying significant phenotypic and functional plasticity. Investigating these properties across diverse organs during normal development and tumorigenesis is of paramount research interest and translational potential. Advancements in next-generation sequencing (NGS), single-cell transcriptomics, and spatial transcriptomics have ushered in a new era in cancer research, providing high-resolution and comprehensive molecular maps of diseased tissues. Various spatial technologies, with their unique ability to measure the location and molecular profile of a cell within tissue, have enabled studies on intratumoral architecture and cellular cross-talk within the specific niches. Moreover, delineation of spatial patterns for niche-specific properties such as hypoxia, glucose deprivation, and other microenvironmental remodeling are revealed through multilevel spatial sequencing. This tremendous progress in technology has also been paired with the advent of computational tools to mitigate technology-specific bottlenecks. Here we discuss how different spatial technologies are used to identify NSCs and CSCs, as well as their associated niches. Additionally, by exploring related public data sets, we review the current challenges in characterizing such niches, which are often hindered by technological limitations, and the computational solutions used to address them.

Circadian Rhythms of Skin Surface Lipids and Physiological Parameters in Healthy Chinese Women Reveals Circadian Changes in Skin Barrier Function

BACKGROUND

Circadian rhythms are driven by the biological clock, an endogenous oscillator that generates approximately 24 h cycles in mammals. The circadian regulation of the lipid metabolism plays a crucial role in overall metabolic health. An analysis of the correlation between the skin's physiological parameters and skin lipids can provide a better insight into the rhythmic changes in skin condition.

OBJECTIVES

The aim was to reveal how skin surface lipids (SSLs) participate in the regulation of circadian rhythms in the skin and the importance of the circadian oscillation of facial lipid molecules in maintaining epidermal homeostasis.

METHODS

Changes in SSLs were assessed using UPLC-QTOF-MS. The skin's physiological parameters were quantified using non-invasive instruments. Multivariate data analysis was employed to evaluate the differences.

RESULTS

Both skin surface lipids and physiological parameters exhibited certain circadian variation patterns. Four major lipid classes (fatty acids, glycerophospholipids, prenol lipids, saccharolipids) exhibited circadian rhythmic trends, with seven lipid subclasses contributing most significantly to the overall patterns observed. Among the physiological parameters assessed, sebum secretion, transepidermal water loss, moisture measurement value, and skin surface temperature exhibited sinusoidal circadian rhythms. Further analysis revealed significant correlations between fatty acids and saccharolipids with moisture measurement values, and between glycerolipids and pH value. In addition, lipids closely associated with the barrier such as unsaturated fatty acids and ceramide chain lengths correlated significantly with moisture measurement values.

CONCLUSIONS

Through correlation analysis, the study elucidates the influence of diurnal fluctuations in skin surface lipids on skin barrier function. These findings hold significant implications for understanding skin barrier impairment associated with circadian rhythm disruptions.

Comprehensive analysis of skin growth-related hub genes and microenvironment characterization in a mouse expanded skin model

Background

Mechanical stretch-mediated tissue expansion is effective for obtaining extra skin and soft tissue required for the repair of defects or reconstruction of surface organs. Understanding the cellular and molecular mechanisms and identifying hub genes and key cell types associated with skin expansion could help predict the success of skin growth during expansion procedures.

Methods

We analyzed murine chip sequencing data and single-cell sequencing data available from the Gene Expression Omnibus database. Based on the differentially expressed and epithelial-mesenchymal transition-related genes, random forest and protein-protein interaction network analysis identified hub genes for predicting skin regeneration in tissue expansion. The fate of the cell subpopulations, expression of hub genes in different cell types, and their communication were also assessed.

Results

Five genes, integrin beta 5 (Itgb5), tropomyosin 1 (Tpm1), secreted frizzled-related protein-1 (Sfrp1), Notch1, and insulin-like growth factor binding protein 2 (Igfbp2), were identified as having the greatest impact on prediction accuracy. These hub genes were primarily enriched in the Notch and phosphoinositide 3-kinase-AKT pathways. Immune cell infiltration analysis further revealed that mast cell infiltration was significantly higher in the expanded skin group than that in the control group. According to single-cell data, the interactions between epithelial cells, stem cells, and other cell types were higher in the expanded skin group than those in the control group. Moreover, Tpm1, Sfrp1, and Notch1 were highly expressed in all epithelial and stem cell subgroups.

Conclusions

The hub genes, Notch1, Tpm1 and Sfrp1, and their associated signaling pathways such as Notch and Wnt signaling and functions in key cell subsets highlight prospective therapeutic strategies to enhance skin growth under mechanical expansion. Moreover, mast cell activation and infiltration may trigger immune responses in the expanded skin, which requires further investigation.

Epidermal stem cells: Interplay with the skin microenvironment during wound healing

Skin undergoes everyday turnover while often challenged by injuries. The wound healing process in the skin is a dynamic sequence of events that involves various cell types and signaling pathways. Epidermal stem cells (EpdSCs), the tissue-resident stem cells in the skin tissue, are at the center of this complicated process due to their special ability to self-renew and differentiate. During this process, EpdSCs interact actively with the tissue microenvironment, which is essential for proper re-epithelialization and skin barrier restoration. This review describes the intricate interplays between EpdSCs and various components of their surroundings, including extracellular matrix/fibroblasts, vasculature/endothelial cells, and immune cells, as well as their roles in tissue repair.

Recovering skin-nerve interaction by nanoscale metal-organic framework for diabetic ulcers healing

Skin-nerve interaction plays an important role in promoting wound healing. However, in diabetic ulcers (DUs), the diabetic periphery neuropathy and excessive levels of reactive oxygen species (ROS) block skin-nerve interaction and further impede the DUs healing. Herein, we developed a nanoscale metal-organic framework loaded with nerve growth factor (NGF/Ce-UiO-66, denoted NGF/CU) for the treatment of DUs. The Ce-UiO-66 (CU) was applied as an antioxidant to scavenge ROS and reduce the inflammatory response while the NGF aided in the recovery of cutaneous nerves to further promote DUs healing. Both in vitro and in vivo experiments revealed the effective ability of NGF/CU for DUs healing. Subsequent RNA sequencing analysis revealed the mechanism that NGF/CU can improve wound healing by inhibiting the NF-κB signaling pathway and recovering the neuroendocrine system of the skin. This strategy of nerve regulation will provide more ideas for the treatment of DUs and other organ injuries.

A single-center clinical trial evaluating topical propranolol for preventing stress-induced hair loss

There is currently a lack of pathological research on the hair loss caused by stress, and there is no effective treatment available. It has been previously reported that stress can cause sympathetic nerve activation and release of norepinephrine, which binds to beta-2 adrenergic receptors and causes a series of chemical reactions. Propranolol, as a beta-2 adrenergic receptors blocker, competitively antagonizes the effects of norepinephrine. We initiated a single-center clinical trial with a self-controlled approach to assess the effectiveness of topical applied hydrochloride salt of propranolol solution in preventing stress-induced hair loss in humans. A total of 20 volunteers were enrolled. 14 out of 20 volunteers experienced a significant reduction in the number of hair loss (p < .05) after using hydrochloride salt of propranolol solution. No local adverse reactions were found. This study showed hydrochloride salt of propranolol solution may alleviate stress-induced alopecia to a certain extent, which provides clues for the development of pharmaceutical interventions for the treatment of stress-induced alopecia.

Recombinant filaggrin-2 improves skin barrier function and attenuates ultraviolet B (UVB) irradiation-induced epidermal barrier disruption

The integrity of the skin barrier is essential for maintaining skin health, with the stratum corneum and filaggrin 2 (FLG-2) playing a key role. FLG-2 deficiency or mutation has been linked to diseases such as atopic dermatitis, while external stressors such as ultraviolet B (UVB) radiation further damage the epidermal barrier. This study investigated the effects of recombinant filaggrin (rFLG) on skin barrier function and UVB induced epidermal destruction. Cell experiments showed that 10 μg/mL of rFLG could increase the mobility of HaCaT cells from 20 % to 42 %, increase the epithelial resistance (TEER) value by about 2 times, and up-regulate the tight junction associated protein by about 2 times. In mouse models of UVB-induced epidermal barrier destruction, rFLG at concentrations of 0.5, 1, and 2 mg/mL showed effective cell uptake and skin penetration, alleviating erythema, and reducing skin thickness in mice by 1.5-3 times. Among them, 2 mg/mL of rFLG treatment restored the expression of tight junction proteins (LOR, ZO-1, and caspase-14), reduced collagen degradation, and reduced oxidative stress by normalizing serum hydroxyproline and superoxide dismutase levels. In addition, 2 mg/mL of rFLG inhibited UVB-induced upregulation of matrix metalloproteinases (MMP-3 and MMP-9) and reduced pro-inflammatory factors (IL-10, IL-1α, IL-6, and TNF-α) and apoptotic markers (P38, Bax, and Bcl-2) to normal levels. These findings suggested that rFLG effectively enhanced skin barrier integrity and mitigated UVB-induced epidermal barrier destruction, highlighting its potential as a therapeutic agent for diseases associated with skin barrier dysfunction.

An in-depth review of the dermal toxicity of T-2 toxin: Clinical symptoms, injury mechanisms, and treatment approach

T-2 toxin, a notable mycotoxin derived from the Fusarium genus, possesses significant heat and ultraviolet radiation resilience, making its elimination from food or feed sources a challenging task. T-2 toxin can be rapidly absorbed from inhalation dust particles, ingest food and skin contact. T-2 toxin has skin toxicity, which can cause varying degrees of structural and functional damage to the skin tissue depending on the type of animal, age, and dose of toxin. Skin contact is not a prerequisite for T-2 toxin to exert skin toxicity, T-2 toxin can also cause skin damage when ingested through the digestive tract. The core dermal toxic molecular mechanism of T-2 toxin is oxidative damage and inflammatory reaction. Some physical methods and chemical methods were used to remove T-2 toxin from the surface of the skin, to have a certain mitigating effect on dermal toxicity caused by T-2 toxin. Grasping T-2 toxin's skin toxicity mechanism is vital for creating effective prevention and treatments. This paper summarizes the comprehensive date from in vitro and in vivo studies, highlighting the molecular mechanism of skin damage by T-2 toxin and current treatment strategies, to provide reference for further research on the skin toxicity of T-2 toxin.

AIMP1-Derived Peptide Secreted from Hair Follicle Stem Cells Promotes Hair Growth by Activating Dermal Papilla Cells

Hair follicle stem cells (HFSCs) and dermal papilla cells (DPCs) are crucial in the biogenesis and maintenance of hair follicles (HFs). This study demonstrated that a fragment derived from aminoacyl-tRNA synthetase-interacting multifunctional protein1 (AIMP1) secreted from HFSCs activated DPCs and maintained HF homeostasis. A histological analysis revealed that AIMP1 levels in HF decreased with hair loss. Hair regrowth in AIMP1-induced mice was faster than in non-induced mice. Deletion mapping revealed 41 amino acids (TN41, aa 6-46) as the active region of AIMP1. The N-terminal peptide fragment of AIMP1 generated by MMP1 was secreted from Wnt-treated HFSCs to activate DPCs. TN41 activated Akt and ERK, increased β-catenin, and enhanced DPC activation. TN41 promoted hair shaft elongation in cultured human HFs and improved the hair-inducing activity of cultured DPC spheroids. Our findings suggest that the AIMP1 fragment secreted from HFSCs stimulates active hair regrowth through activating DPCs.

Dermal Papilla Cells: From Basic Research to Translational Applications

As an appendage of the skin, hair protects against ultraviolet radiation and mechanical damage and regulates body temperature. It also reflects an individual's health status and serves as an important method of expressing personality. Hair loss and graying are significant psychosocial burdens for many people. Hair is produced from hair follicles, which are exclusively controlled by the dermal papilla (DP) at their base. The dermal papilla cells (DPCs) comprise a cluster of specialized mesenchymal cells that induce the formation of hair follicles during early embryonic development through interaction with epithelial precursor cells. They continue to regulate the growth cycle, color, size, and type of hair after the hair follicle matures by secreting various factors. DPCs possess stem cell characteristics and can be cultured and expanded in vitro. DPCs express numerous stemness-related factors, enabling them to be reprogrammed into induced pluripotent stem cells (iPSCs) using only two, or even one, Yamanaka factor. DPCs are an important source of skin-derived precursors (SKPs). When combined with epithelial stem cells, they can reconstitute skin and hair follicles, participating in the regeneration of the dermis, including the DP and dermal sheath. When implanted between the epidermis and dermis, DPCs can induce the formation of new hair follicles on hairless skin. Subcutaneous injection of DPCs and their exosomes can promote hair growth. This review summarizes the in vivo functions of the DP; highlights the potential of DPCs in cell therapy, particularly for the treatment of hair loss; and discusses the challenges and recent advances in the field, from basic research to translational applications.

The sensory nerve regulates stem cell homeostasis through Wnt5a signaling

Increasing evidence indicates that nerves play a significant role in regulating stem cell homeostasis and developmental processes. To explore the impact of nerves on epithelial stem cell homeostasis during tooth development, the regulation of sensory nerves on stem cell homeostasis was investigated using a rat model of incisor development. Impaired mineralization, decreased enamel thickness, and fractured enamel rods of the incisor were observed after denervation. qPCR and histological staining revealed that the expression of enamel-related factors ameloblastin (AMBN), kallikrein-4, amelogenin (Amelx), collagen type XVII (col17a), and enamelin were decreased in the incisor enamel of rats with sensory nerve injure. The decreased expression of Wnt5a in ameloblasts was coupled with the downregulation of calcium ion-related calmodulin kinase II. These results implicate that the sensory nerves are essential in stem cell homeostasis for enamel mineralization and development.

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).

Epidermal stem cells: skin surveillance and clinical perspective

The skin epidermis is continually influenced by a myriad of internal and external elements. At its basal layer reside epidermal stem cells, which fuels epidermal renovation and hair regeneration with powerful self-renewal ability, as well as keeping diverse signals that direct their activity under surveillance with quick response. The importance of epidermal stem cells in wound healing and immune-related skin conditions has been increasingly recognized, and their potential for clinical applications is attracting attention. In this review, we delve into recent advancements and the various physiological and psychological factors that govern distinct epidermal stem cell populations, including psychological stress, mechanical forces, chronic aging, and circadian rhythm, as well as providing an overview of current methodological approaches. Furthermore, we discuss the pathogenic role of epidermal stem cells in immune-related skin disorders and their potential clinical applications.

The role of HR-HPV integration in the progression of premalignant lesions into different cancer types

High-risk human papillomavirus (HR-HPV) is associated with the development of different types of cancer, such as cervical, head and neck (including oral, laryngeal, and oropharyngeal), vulvar, vaginal, penile, and anal cancers. The progression of premalignant lesions to cancer depends on factors associated with the host cell and the different epithelia infected by HPV, such as basal cells of the flat epithelium and the cells of the squamocolumnar transformation zone (STZ) found in the uterine cervix and the anal canal, which is rich in heparan sulfate proteoglycans and integrin-like receptors. On the other hand, factors associated with the viral genotype, infection with multiple viruses, viral load, viral persistence, and type of integration determine the viral breakage pattern and the sites at which the virus integrates into the host cell genome (introns, exons, intergenic regions), inducing the loss of function of tumor suppressor genes and increasing oncogene expression. This review describes the role of viral integration and the molecular mechanisms induced by HR-HPV in different types of tissues. The purpose of this review is to identify the common factors associated with the role of integration events in the progression of premalignant lesions in different types of cancer.

scHolography: a computational method for single-cell spatial neighborhood reconstruction and analysis

Spatial transcriptomics has transformed our ability to study tissue complexity. However, it remains challenging to accurately dissect tissue organization at single-cell resolution. Here we introduce scHolography, a machine learning-based method designed to reconstruct single-cell spatial neighborhoods and facilitate 3D tissue visualization using spatial and single-cell RNA sequencing data. scHolography employs a high-dimensional transcriptome-to-space projection that infers spatial relationships among cells, defining spatial neighborhoods and enhancing analyses of cell-cell communication. When applied to both human and mouse datasets, scHolography enables quantitative assessments of spatial cell neighborhoods, cell-cell interactions, and tumor-immune microenvironment. Together, scHolography offers a robust computational framework for elucidating 3D tissue organization and analyzing spatial dynamics at the cellular level.

Improving dermal fibroblast-to-epidermis communications and aging wound repair through extracellular vesicle-mediated delivery of Gstm2 mRNA

Skin aging is characterized by the disruption of skin homeostasis and impaired skin injury repair. Treatment of aging skin has long been limited by the unclear intervention targets and delivery techniques. Engineering extracellular vesicles (EVs) as an upgraded version of natural EVs holds great potential in regenerative medicine. In this study, we found that the expression of the critical antioxidant and detoxification gene Gstm2 was significantly reduced in aging skin. Thus, we constructed the skin primary fibroblasts-derived EVs encapsulating Gstm2 mRNA (EVsGstm2), and found that EVsGstm2 could significantly improve skin homeostasis and accelerate wound healing in aged mice. Mechanistically, we found that EVsGstm2 alleviated oxidative stress damage of aging dermal fibroblasts by modulating mitochondrial oxidative phosphorylation, and promoted dermal fibroblasts to regulate skin epidermal cell function by paracrine secretion of Nascent Polypeptide-Associated Complex Alpha subunit (NACA). Furthermore, we confirmed that NACA is a novel skin epidermal cell protective molecule that regulates skin epidermal cell turnover through the ROS-ERK-ETS-Cyclin D pathway. Our findings demonstrate the feasibility and efficacy of EVs-mediated delivery of Gstm2 for aged skin treatment and unveil novel roles of GSTM2 and NACA for improving aging skin.

A new G3BP1-GFP reporter system for assessing skin toxicity by real-time monitoring of stress granules in vitro

The skin, the organ with the largest surface area in the body, is the most susceptible to chemical exposure from the external environment. In this study, we aimed to establish an in vitro skin toxicity monitoring system that utilizes the mechanism of stress granule (SG) formation induced by various cellular stresses. In HaCaT cells, a keratinocyte cell line that comprises the human skin, a green fluorescent protein (GFP) was knocked in at the C-terminal genomic locus of Ras GTPase-activating protein-binding protein 1 (G3BP1), a representative component of SGs. The G3BP1-GFP knock-in HaCaT cells and wild-type (WT) HaCaT cells formed SGs containing G3BP1-GFP upon exposure to arsenite and household chemicals, such as bisphenol A (BPA) and benzalkonium chloride (BAC), in real-time. In addition, the exposure of G3BP1-GFP knock-in HaCaT cells to BPA and BAC promoted the phosphorylation of eukaryotic initiation factor 2 alpha and protein kinase R-like endoplasmic reticulum kinase, which are cell signaling factors involved in SG formation, similar to WT HaCaT cells. In conclusion, this novel G3BP1-GFP knock-in human skin cell system can monitor SG formation in real-time and be utilized to assess skin toxicity to various substances.

Role of umbilical cord mesenchymal stromal cells in skin rejuvenation

Aging is the main cause of many degenerative diseases. The skin is the largest and the most intuitive organ that reflects the aging of the body. Under the interaction of endogenous and exogenous factors, there are cumulative changes in the structure, function, and appearance of the skin, which are characterized by decreased synthesis of collagen and elastin, increased wrinkles, relaxation, pigmentation, and other aging characteristics. skin aging is inevitable, but it can be delayed. The successful isolation of mesenchymal stromal cells (MSC) in 1991 has greatly promoted the progress of cell therapy in human diseases. The International Society for Cellular Therapy (ISCT) points out that the MSC is a kind of pluripotent progenitor cells that have self-renewal ability (limited) in vitro and the potential for mesenchymal cell differentiation. This review mainly introduces the role of perinatal umbilical cord-derived MSC(UC-MSC) in the field of skin rejuvenation. An in-depth and systematic understanding of the mechanism of UC-MSCs against skin aging is of great significance for the early realization of the clinical transformation of UC-MSCs. This paper summarized the characteristics of skin aging and summarized the mechanism of UC-MSCs in skin rejuvenation reported in recent years. In order to provide a reference for further research of UC-MSCs to delay skin aging.

Split-Thickness Skin and Dermal Pixel Grafts Can Be Expanded up to 500 Times to Re-Epithelialize a Full-Thickness Burn Wound

Objective: Autologous skin transplantation is limited by donor site availability for patients with extensive burns. The objective of this study was to demonstrate the feasibility and efficacy of split-thickness skin (STS) and dermal pixel grafts (PG) in the treatment of burns. Approach: The study was divided into three arms of validation, expansion, and combination that all followed the same study design. Sixteen deep partial-thickness burns were created on the dorsum of anesthetized pigs. Three days postinjury the burns were debrided and grafted with STS and dermal PGs. The PGs were prepared by harvesting two skin grafts (split-thickness skin graft [STSG] and dermal graft) from the same donor site going down in depth. The grafts were minced to 0.3 × 0.3 × 0.3 mm PGs and suspended in a small volume of hydrogel. Healing was monitored for 6, 10, 14, or 28 days. In the validation study the PGs at 1:2 expansion ratio were transplanted and compared with STSG and untreated controls. The expansion study investigated the maximum expansion potential of the PGs and the combination of the benefits of transplanting STS and dermal PGs together. Results: The validation study showed that when STS and dermal PGs were transplanted in a 1:2 ratio they fully re-epithelialized the wounds in 14 days. The expansion study demonstrated that using expansion ratios up to 1:500 the wounds were re-epithelialized by day 28. The combination study showed that there was no additional benefit to use STS and dermal PGs together. Innovation: Pixel grafting provides expansion ratios greater than conventional STSG. The possibility to harvest both STS and dermal PGs from the same donor area further reduces the need for healthy skin. Conclusion: STSG and dermal grafts can be minced to PGs with preserved viability and expanded up to 500 times to re-epithelialize a wound.

Vitamin A resolves lineage plasticity to orchestrate stem cell lineage choices

Lineage plasticity-a state of dual fate expression-is required to release stem cells from their niche constraints and redirect them to tissue compartments where they are most needed. In this work, we found that without resolving lineage plasticity, skin stem cells cannot effectively generate each lineage in vitro nor regrow hair and repair wounded epidermis in vivo. A small-molecule screen unearthed retinoic acid as a critical regulator. Combining high-throughput approaches, cell culture, and in vivo mouse genetics, we dissected its roles in tissue regeneration. We found that retinoic acid is made locally in hair follicle stem cell niches, where its levels determine identity and usage. Our findings have therapeutic implications for hair growth as well as chronic wounds and cancers, where lineage plasticity is unresolved.

Epithelial stem cells and niches in lung alveolar regeneration and diseases

Alveoli serve as the functional units of the lungs, responsible for the critical task of blood-gas exchange. Comprising type I (AT1) and type II (AT2) cells, the alveolar epithelium is continuously subject to external aggressors like pathogens and airborne particles. As such, preserving lung function requires both the homeostatic renewal and reparative regeneration of this epithelial layer. Dysfunctions in these processes contribute to various lung diseases. Recent research has pinpointed specific cell subgroups that act as potential stem or progenitor cells for the alveolar epithelium during both homeostasis and regeneration. Additionally, endothelial cells, fibroblasts, and immune cells synergistically establish a nurturing microenvironment-or "niche"-that modulates these epithelial stem cells. This review aims to consolidate the latest findings on the identities of these stem cells and the components of their niche, as well as the molecular mechanisms that govern them. Additionally, this article highlights diseases that arise due to perturbations in stem cell-niche interactions. We also discuss recent technical innovations that have catalyzed these discoveries. Specifically, this review underscores the heterogeneity, plasticity, and dynamic regulation of these stem cell-niche systems. It is our aspiration that a deeper understanding of the fundamental cellular and molecular mechanisms underlying alveolar homeostasis and regeneration will open avenues for identifying novel therapeutic targets for conditions such as chronic obstructive pulmonary disease (COPD), fibrosis, coronavirus disease 2019 (COVID-19), and lung cancer.

Recent progress in hair follicle stem cell markers and their regulatory roles

Hair follicle stem cells (HFSCs) in the bulge are a multipotent adult stem cell population. They can periodically give rise to new HFs and even regenerate the epidermis and sebaceous glands during wound healing. An increasing number of biomarkers have been used to isolate, label, and trace HFSCs in recent years. Considering more detailed data from single-cell transcriptomics technology, we mainly focus on the important HFSC molecular markers and their regulatory roles in this review.

Hair follicle stem cells promote epidermal regeneration under expanded condition

Skin soft tissue expansion is the process of obtaining excess skin mixed with skin development, wound healing, and mechanical stretching. Previous studies have reported that tissue expansion significantly induces epidermal proliferation throughout the skin. However, the mechanisms underlying epidermal regeneration during skin soft tissue expansion are yet to be clarified. Hair follicle stem cells (HFSCs) have been recognized as a promising approach for epidermal regeneration. This study examines HFSC-related epidermal regeneration mechanisms under expanded condition and proposes a potential method for its cellular and molecular regulation.

Cellular senescence and wound healing in aged and diabetic skin

Cellular senescence is a biological mechanism that prevents abnormal cell proliferation during tissue repair, and it is often accompanied by the secretion of various factors, such as cytokines and chemokines, known as the senescence-associated secretory phenotype (SASP). SASP-mediated cell-to-cell communication promotes tissue repair, regeneration, and development. However, senescent cells can accumulate abnormally at injury sites, leading to excessive inflammation, tissue dysfunction, and intractable wounds. The effects of cellular senescence on skin wound healing can be both beneficial and detrimental, depending on the condition. Here, we reviewed the functional differences in cellular senescence that emerge during wound healing, chronic inflammation, and skin aging. We also review the latest mechanisms of wound healing in the epidermis, dermis, and subcutaneous fat, with a focus on cellular senescence, chronic inflammation, and tissue regeneration. Finally, we discuss the potential clinical applications of promoting and inhibiting cellular senescence to maximize benefits and minimize detrimental effects.

Deciphering the molecular mechanisms of stem cell dynamics in hair follicle regeneration

Hair follicles, which are connected to sebaceous glands in the skin, undergo cyclic periods of regeneration, degeneration, and rest throughout adult life in mammals. The crucial function of hair follicle stem cells is to maintain these hair growth cycles. Another vital aspect is the activity of melanocyte stem cells, which differentiate into melanin-producing melanocytes, contributing to skin and hair pigmentation. Sebaceous gland stem cells also have a pivotal role in maintaining the skin barrier by regenerating mature sebocytes. These stem cells are maintained in a specialized microenvironment or niche and are regulated by internal and external signals, determining their dynamic behaviors in homeostasis and hair follicle regeneration. The activity of these stem cells is tightly controlled by various factors secreted by the niche components around the hair follicles, as well as immune-mediated damage signals, aging, metabolic status, and stress. In this study, we review these diverse stem cell regulatory and related molecular mechanisms of hair regeneration and disease conditions. Molecular insights would provide new perspectives on the disease mechanisms as well as hair and skin disorder treatment.

SOX family transcription factors as therapeutic targets in wound healing: A comprehensive review

The SOX family plays a vital role in determining the fate of cells and has garnered attention in the fields of cancer research and regenerative medicine. It also shows promise in the study of wound healing, as it actively participates in the healing processes of various tissues such as skin, fractures, tendons, and the cornea. However, our understanding of the mechanisms behind the SOX family's involvement in wound healing is limited compared to its role in cancer. Gaining insight into its role, distribution, interaction with other factors, and modifications in traumatized tissues could provide valuable new knowledge about wound healing. Based on current research, SOX2, SOX7, and SOX9 are the most promising members of the SOX family for future interventions in wound healing. SOX2 and SOX9 promote the renewal of cells, while SOX7 enhances the microvascular environment. The SOX family holds significant potential for advancing wound healing research. This article provides a comprehensive review of the latest research advancements and therapeutic tools related to the SOX family in wound healing, as well as the potential benefits and challenges of targeting the SOX family for wound treatment.

Wound Microbiota and Its Impact on Wound Healing

Wound healing is a complex process influenced by age, systemic conditions, and local factors. The wound microbiota's crucial role in this process is gaining recognition. This concise review outlines wound microbiota impacts on healing, emphasizing distinct phases like hemostasis, inflammation, and cell proliferation. Inflammatory responses, orchestrated by growth factors and cytokines, recruit neutrophils and monocytes to eliminate pathogens and debris. Notably, microbiota alterations relate to changes in wound healing dynamics. Commensal bacteria influence immune responses, keratinocyte growth, and blood vessel development. For instance, Staphylococcus epidermidis aids keratinocyte progression, while Staphylococcus aureus colonization impedes healing. Other bacteria like Group A Streptococcus spp. And Pseudomonas affect wound healing as well. Clinical applications of microbiota-based wound care are promising, with probiotics and specific bacteria like Acinetobacter baumannii aiding tissue repair through molecule secretion. Understanding microbiota influence on wound healing offers therapeutic avenues. Tailored approaches, including probiotics, prebiotics, and antibiotics, can manipulate the microbiota to enhance immune modulation, tissue repair, and inflammation control. Despite progress, critical questions linger. Determining the ideal microbiota composition for optimal wound healing, elucidating precise influence mechanisms, devising effective manipulation strategies, and comprehending the intricate interplay between the microbiota, host, and other factors require further exploration.

In Vitro Three-Dimensional (3D) Models for Melanoma Immunotherapy

Melanoma is responsible for the majority of skin cancer-related fatalities. Immune checkpoint inhibitor (ICI) treatments have revolutionized the management of the disease by significantly increasing patient survival rates. However, a considerable number of tumors treated with these drugs fail to respond or may develop resistance over time. Tumor growth and its response to therapies are critically influenced by the tumor microenvironment (TME); it directly supports cancer cell growth and influences the behavior of surrounding immune cells, which can become tumor-permissive, thereby rendering immunotherapies ineffective. Ex vivo modeling of melanomas and their response to treatment could significantly advance our understanding and predictions of therapy outcomes. Efforts have been directed toward developing reliable models that accurately mimic melanoma in its appropriate tissue environment, including tumor organoids, bioprinted tissue constructs, and microfluidic devices. However, incorporating and modeling the melanoma TME and immune component remains a significant challenge. Here, we review recent literature regarding the generation of in vitro 3D models of normal skin and melanoma and the approaches used to incorporate the immune compartment in such models. We discuss how these constructs could be combined and used to test immunotherapies and elucidate treatment resistance mechanisms. The development of 3D in vitro melanoma models that faithfully replicate the complexity of the TME and its interaction with the immune system will provide us with the technical tools to better understand ICI resistance and increase its efficacy, thereby improving personalized melanoma therapy.

The frontline of alternatives to animal testing: novel in vitro skin model application in drug development and evaluation

The FDA Modernization Act 2.0 has brought nonclinical drug evaluation into a new era. In vitro models are widely used and play an important role in modern drug development and evaluation, including early candidate drug screening and preclinical drug efficacy and toxicity assessment. Driven by regulatory steering and facilitated by well-defined physiology, novel in vitro skin models are emerging rapidly, becoming the most advanced area in alternative testing research. The revolutionary technologies bring us many in vitro skin models, either laboratory-developed or commercially available, which were all built to emulate the structure of the natural skin to recapitulate the skin's physiological function and particular skin pathology. During the model development, how to achieve balance among complexity, accessibility, capability, and cost-effectiveness remains the core challenge for researchers. This review attempts to introduce the existing in vitro skin models, align them on different dimensions, such as structural complexity, functional maturity, and screening throughput, and provide an update on their current application in various scenarios within the scope of chemical testing and drug development, including testing in genotoxicity, phototoxicity, skin sensitization, corrosion/irritation. Overall, the review will summarize a general strategy for in vitro skin model to enhance future model invention, application, and translation in drug development and evaluation.

The Roles of WNT Signaling Pathways in Skin Development and Mechanical-Stretch-Induced Skin Regeneration

The WNT signaling pathway plays a critical role in a variety of biological processes, including development, adult tissue homeostasis maintenance, and stem cell regulation. Variations in skin conditions can influence the expression of the WNT signaling pathway. In light of the above, a deeper understanding of the specific mechanisms of the WNT signaling pathway in different physiological and pathological states of the skin holds the potential to significantly advance clinical treatments of skin-related diseases. In this review, we present a comprehensive analysis of the molecular and cellular mechanisms of the WNT signaling pathway in skin development, wound healing, and mechanical stretching. Our review sheds new light on the crucial role of the WNT signaling pathway in the regulation of skin physiology and pathology.

Cell Cultures as a Versatile Tool in the Research and Treatment of Autoimmune Connective Tissue Diseases

Cell cultures are an important part of the research and treatment of autoimmune connective tissue diseases. By culturing the various cell types involved in ACTDs, researchers are able to broaden the knowledge about these diseases that, in the near future, may lead to finding cures. Fibroblast cultures and chondrocyte cultures allow scientists to study the behavior, physiology and intracellular interactions of these cells. This helps in understanding the underlying mechanisms of ACTDs, including inflammation, immune dysregulation and tissue damage. Through the analysis of gene expression patterns, surface proteins and cytokine profiles in peripheral blood mononuclear cell cultures and endothelial cell cultures researchers can identify potential biomarkers that can help in diagnosing, monitoring disease activity and predicting patient's response to treatment. Moreover, cell culturing of mesenchymal stem cells and skin modelling in ACTD research and treatment help to evaluate the effects of potential drugs or therapeutics on specific cell types relevant to the disease. Culturing cells in 3D allows us to assess safety, efficacy and the mechanisms of action, thereby aiding in the screening of potential drug candidates and the development of novel therapies. Nowadays, personalized medicine is increasingly mentioned as a future way of dealing with complex diseases such as ACTD. By culturing cells from individual patients and studying patient-specific cells, researchers can gain insights into the unique characteristics of the patient's disease, identify personalized treatment targets, and develop tailored therapeutic strategies for better outcomes. Cell culturing can help in the evaluation of the effects of these therapies on patient-specific cell populations, as well as in predicting overall treatment response. By analyzing changes in response or behavior of patient-derived cells to a treatment, researchers can assess the response effectiveness to specific therapies, thus enabling more informed treatment decisions. This literature review was created as a form of guidance for researchers and clinicians, and it was written with the use of the NCBI database.

Tissue Biology: In Search of a New Paradigm

Animal tissues are made up of multiple cell types that are increasingly well-characterized, yet our understanding of the core principles that govern tissue organization is still incomplete. This is in part because many observable tissue characteristics, such as cellular composition and spatial patterns, are emergent properties, and as such, they cannot be explained through the knowledge of individual cells alone. Here we propose a complex systems theory perspective to address this fundamental gap in our understanding of tissue biology. We introduce the concept of cell categories, which is based on cell relations rather than cell identity. Based on these notions we then discuss common principles of tissue modularity, introducing compositional, structural, and functional tissue modules. Cell diversity and cell relations provide a basis for a new perspective on the underlying principles of tissue organization in health and disease.

Application of mesenchymal stem cells for anti-senescence and clinical challenges

Senescence is a hot topic nowadays, which shows the accumulation of senescent cells and inflammatory factors, leading to the occurrence of various senescence-related diseases. Although some methods have been identified to partly delay senescence, such as strengthening exercise, restricting diet, and some drugs, these only slow down the process of senescence and cannot fundamentally delay or even reverse senescence. Stem cell-based therapy is expected to be a potential effective way to alleviate or cure senescence-related disorders in the coming future. Mesenchymal stromal cells (MSCs) are the most widely used cell type in treating various diseases due to their potentials of self-replication and multidirectional differentiation, paracrine action, and immunoregulatory effects. Some biological characteristics of MSCs can be well targeted at the pathological features of aging. Therefore, MSC-based therapy is also a promising strategy to combat senescence-related diseases. Here we review the recent progresses of MSC-based therapies in the research of age-related diseases and the challenges in clinical application, proving further insight and reference for broad application prospects of MSCs in effectively combating senesce in the future.

Ccrl2-centred immune-related lncRNA-mRNA co-expression network revealed the local skin immune activation mechanism of moxibustion on adjuvant arthritis mice

BACKGROUND

Moxibustion is an important external therapy of traditional medicine that operates on some acupoints on the skin and is usually used for immune-related diseases. However, whether the immune function of the skin, especially the immune-related lncRNAs, contributes to the mechanism of moxibustion remains unclear.

METHODS

Adjuvant arthritis (AA) was induced by injection of Complete Freund's adjuvant (CFA) into the right hind paw of mice. Moxibustion was administered on the Zusanli (ST36) acupoint for 3 weeks. The alteration of foot volume and cytokine concentration in serum was used to evaluate the anti-inflammation effect of moxibustion. CD83 expression in the local skin of ST36 was measured by immunofluorescence staining. Transcriptome RNA sequencing (RNA-seq) and lncRNA-mRNA network analysis were performed to construct a moxibustion-induced Immune-related lncRNA-mRNA co-expression network. qRT-PCR was used to validate the RNA-seq data.

RESULTS

Moxibustion at ST36 relieved the foot swelling, decreased the TNF-α and IL-1β concentrations in serum, and obviously increased the CD83 expression at the local skin of ST36. A total of 548 differentially expressed lncRNAs and 520 linked mRNAs were screened out. The significantly and predominately enriched Go term was inflammatory and immune response, and the main pathways related to inflammatory and immune responses include Toll-like receptor, cytokine-cytokine receptor, and MAPK signaling. The immune-related lncRNA-mRNA co-expression network showed 88 lncRNAs and 36 mRNAs, and Ccrl2 is the central hub of this network.

CONCLUSION

Local immune activation is significantly triggered by moxibustion in ST36 of AA mice. The Ccrl2-centered immune-related lncRNA-mRNA co-expression network would be a promising target for decoding the mechanism of moxibustion for immune-related diseases.

mTOR signaling in hair follicle and hair diseases: recent progress

Mammalian target of rapamycin (mTOR) signaling pathway is a major regulator of cell proliferation and metabolism, playing significant roles in proliferation, apoptosis, inflammation, and illness. More and more evidences showed that the mTOR signaling pathway affects hair follicle circulation and maintains the stability of hair follicle stem cells. mTOR signaling may be a critical cog in Vitamin D receptor (VDR) deficiency-mediated hair follicle damage and degeneration and related alopecia disorders. This review examines the function of mTOR signaling in hair follicles and hair diseases, and talks about the underlying molecular mechanisms that mTOR signaling regulates.

Skin substitutes as treatment for chronic wounds: current and future directions

Chronic wounds such as diabetic foot ulcers and venous leg ulcers place a significant burden on the healthcare system and in some cases, have 5-year mortality rates comparable to cancer. They negatively impact patients' quality of life due to pain, odor, decreased mobility, and social isolation. Skin substitutes are an advanced therapy recommended for wounds that fail to show decrease in size with standard care. The choice of substitute used should be based on evidence, which often differs based on wound etiology. There are more than 75 skin substitutes currently available, and that number is rising. In this review, we discuss current management and future directions of chronic wounds while providing a review of available randomized control trial data for various skin substitutes.

An innervated skin 3D in vitro model for dermatological research

A 3D in vitro model of innervated skin would be a useful tool in dermatological research to study the effect of different chemicals and compounds on the sensory properties of skin. Current innervated skin models are limited in composition and often composed of ex vivo skin explants and/or animal-derived material. In this study, our aim was to develop a human innervated skin model with a better biomimicry composition for in vitro research. Fibrin hydrogel and aligned electrospun fibers of poly(ethylene oxide terephthalate)/poly(butylene terephthalate) (PEOT/PBT) were used as a scaffold to generate the 3D in vitro model. The skin component was made of primary human keratinocytes and primary human fibroblasts, while the neuronal component was composed of iPSC-derived sensory neurons. Our results showed that the dermal component consisted of fibroblasts and synthesized collagen. The epidermal component was characterized by the expression of keratins 10 and 14, and involucrin. Finally, sensory neurons extended axons throughout the scaffold and reached the epidermis. Treating the model with a capsaicin solution for 30 min, which was performed as a proof of concept test for sensitization studies, resulted into partial depletion of substance P and tubulin β3. This model could be used for studying skin-neuron interactions and cutaneous toxicity.

Supplementary Information

The online version contains supplementary material available at 10.1007/s44164-022-00021-0.

Three-Dimensional Cell Cultures: The Bridge between In Vitro and In Vivo Models

Although historically, the traditional bidimensional in vitro cell system has been widely used in research, providing much fundamental information regarding cellular functions and signaling pathways as well as nuclear activities, the simplicity of this system does not fully reflect the heterogeneity and complexity of the in vivo systems. From this arises the need to use animals for experimental research and in vivo testing. Nevertheless, animal use in experimentation presents various aspects of complexity, such as ethical issues, which led Russell and Burch in 1959 to formulate the 3R (Replacement, Reduction, and Refinement) principle, underlying the urgent need to introduce non-animal-based methods in research. Considering this, three-dimensional (3D) models emerged in the scientific community as a bridge between in vitro and in vivo models, allowing for the achievement of cell differentiation and complexity while avoiding the use of animals in experimental research. The purpose of this review is to provide a general overview of the most common methods to establish 3D cell culture and to discuss their promising applications. Three-dimensional cell cultures have been employed as models to study both organ physiology and diseases; moreover, they represent a valuable tool for studying many aspects of cancer. Finally, the possibility of using 3D models for drug screening and regenerative medicine paves the way for the development of new therapeutic opportunities for many diseases.

A systematic review of natural products for skin applications: Targeting inflammation, wound healing, and photo-aging

BACKGROUND

Every day the skin is constantly exposed to several harmful factors that induce oxidative stress. When the cells are incapable to maintain the balance between antioxidant defenses and reactive oxygen species, the skin no longer can keep its integrity and homeostasis. Chronic inflammation, premature skin aging, tissue damage, and immunosuppression are possible consequences induced by sustained exposure to environmental and endogenous reactive oxygen species. Skin immune and non-immune cells together with the microbiome are essential to efficiently trigger skin immune responses to stress. For this reason, an ever-increasing demand for novel molecules capable of modulating immune functions in the skin has risen the level of their development, particularly in the field of natural product-derived molecules.

PURPOSE

In this review, we explore different classes of molecules that showed evidence in modulate skin immune responses, as well as their target receptors and signaling pathways. Moreover, we describe the role of polyphenols, polysaccharides, fatty acids, peptides, and probiotics as possible treatments for skin conditions, including wound healing, infection, inflammation, allergies, and premature skin aging.

METHODS

Literature was searched, analyzed, and collected using databases, including PubMed, Science Direct, and Google Scholar. The search terms used included "Skin", "wound healing", "natural products", "skin microbiome", "immunomodulation", "anti-inflammatory", "antioxidant", "infection", "UV radiation", "polyphenols", "polysaccharides", "fatty acids", "plant oils", "peptides", "antimicrobial peptides", "probiotics", "atopic dermatitis", "psoriasis", "auto-immunity", "dry skin", "aging", etc., and several combinations of these keywords.

RESULTS

Natural products offer different solutions as possible treatments for several skin conditions. Significant antioxidant and anti-inflammatory activities were reported, followed by the ability to modulate immune functions in the skin. Several membrane-bound immune receptors in the skin recognize diverse types of natural-derived molecules, promoting different immune responses that can improve skin conditions.

CONCLUSION

Despite the increasing progress in drug discovery, several limiting factors need future clarification. Understanding the safety, biological activities, and precise mechanisms of action is a priority as well as the characterization of the active compounds responsible for that. This review provides directions for future studies in the development of new molecules with important pharmaceutical and cosmeceutical value.

Single-cell profiling reveals a potent role of quercetin in promoting hair regeneration

Hair loss affects millions of people at some time in their life, and safe and efficient treatments for hair loss are a significant unmet medical need. We report that topical delivery of quercetin (Que) stimulates resting hair follicles to grow with rapid follicular keratinocyte proliferation and replenishes perifollicular microvasculature in mice. We construct dynamic single-cell transcriptome landscape over the course of hair regrowth and find that Que treatment stimulates the differentiation trajectory in the hair follicles and induces an angiogenic signature in dermal endothelial cells by activating HIF-1α in endothelial cells. Skin administration of a HIF-1α agonist partially recapitulates the pro-angiogenesis and hair-growing effects of Que. Together, these findings provide a molecular understanding for the efficacy of Que in hair regrowth, which underscores the translational potential of targeting the hair follicle niche as a strategy for regenerative medicine, and suggest a route of pharmacological intervention that may promote hair regrowth.

Targeting lymphoid-derived IL-17 signaling to delay skin aging

Skin aging is characterized by structural and functional changes that contribute to age-associated frailty. This probably depends on synergy between alterations in the local niche and stem cell-intrinsic changes, underscored by proinflammatory microenvironments that drive pleotropic changes. The nature of these age-associated inflammatory cues, or how they affect tissue aging, is unknown. Based on single-cell RNA sequencing of the dermal compartment of mouse skin, we show a skew towards an IL-17-expressing phenotype of T helper cells, γδ T cells and innate lymphoid cells in aged skin. Importantly, in vivo blockade of IL-17 signaling during aging reduces the proinflammatory state of the skin, delaying the appearance of age-related traits. Mechanistically, aberrant IL-17 signals through NF-κB in epidermal cells to impair homeostatic functions while promoting an inflammatory state. Our results indicate that aged skin shows signs of chronic inflammation and that increased IL-17 signaling could be targeted to prevent age-associated skin ailments.

Different priming strategies improve distinct therapeutic capabilities of mesenchymal stromal/stem cells: Potential implications for their clinical use

Mesenchymal stromal/stem cells (MSCs) have shown significant therapeutic potential, and have therefore been extensively investigated in preclinical studies of regenerative medicine. However, while MSCs have been shown to be safe as a cellular treatment, they have usually been therapeutically ineffective in human diseases. In fact, in many clinical trials it has been shown that MSCs have moderate or poor efficacy. This inefficacy appears to be ascribable primarily to the heterogeneity of MSCs. Recently, specific priming strategies have been used to improve the therapeutic properties of MSCs. In this review, we explore the literature on the principal priming approaches used to enhance the preclinical inefficacy of MSCs. We found that different priming strategies have been used to direct the therapeutic effects of MSCs toward specific pathological processes. Particularly, while hypoxic priming can be used primarily for the treatment of acute diseases, inflammatory cytokines can be used mainly to prime MSCs in order to treat chronic immune-related disorders. The shift in approach from regeneration to inflammation implies, in MSCs, a shift in the production of functional factors that stimulate regenerative or anti-inflammatory pathways. The opportunity to fine-tune the therapeutic properties of MSCs through different priming strategies could conceivably pave the way for optimizing their therapeutic potential.

Optimization of Surface-Engineered Micropatterns on Bacterial Cellulose for Guided Scar-Free Skin Wound Healing

Bacterial cellulose (BC) has been widely used in tissue engineering due to its unique spatial structure and suitable biological properties. In this study, a small biologically active Arginine-Glycine-Aspartic acid-Serine (RGDS) tetrapeptide was incorporated on the porous BC surface followed by a low-energy CO₂ laser etching operation. As a result, different micropatterns were established on the BC surface with RGDS only anchored on the raised platform surface of the micropatterned BC (MPBC). Material characterization showed that all micropatterned structures exhibited platforms with a width of ~150 μm and grooves with a width of ~100 μm and a depth of ~300 μm, which displayed distinct hydrophilic and hydrophobic properties. The resulting RGDS-MPBC could hold the material integrity, as well as the microstructure morphology under a humid environment. In-vitro and in-vivo assays on cell migration, collagen deposition, and histological analysis revealed that micropatterns led to significant impacts on wound healing progress compared to the BC without surface-engineered micropatterns. Specifically, the basket-woven micropattern etched on the BC surface exhibited the optimal wound healing outcome with the presence of fewer macrophages and the least scar formation. This study further addresses the potential of adopting surface micropatterning strategies to promote skin wounds towards scar-free outcomes.

Immune-Epithelial Cross Talk in Regeneration and Repair

The epithelial tissues that line our body, such as the skin and gut, have remarkable regenerative prowess and continually renew throughout our lifetimes. Owing to their barrier function, these tissues have also evolved sophisticated repair mechanisms to swiftly heal and limit the penetration of harmful agents following injury. Researchers now appreciate that epithelial regeneration and repair are not autonomous processes but rely on a dynamic cross talk with immunity. A wealth of clinical and experimental data point to the functional coupling of reparative and inflammatory responses as two sides of the same coin. Here we bring to the fore the immunological signals that underlie homeostatic epithelial regeneration and restitution following damage. We review our current understanding of how immune cells contribute to distinct phases of repair. When unchecked, immune-mediated repair programs are co-opted to fuel epithelial pathologies such as cancer, psoriasis, and inflammatory bowel diseases. Thus, understanding the reparative functions of immunity may advance therapeutic innovation in regenerative medicine and epithelial inflammatory diseases.