Three-dimensional co-culture of BM-MSCs and eccrine sweat gland cells in Matrigel promotes transdifferentiation of BM-MSCs

Advances and applications of biomimetic biomaterials for endogenous skin regeneration

Endogenous regeneration is becoming an increasingly important strategy for wound healing as it facilitates skin's own regenerative potential for self-healing, thereby avoiding the risks of immune rejection and exogenous infection. However, currently applied biomaterials for inducing endogenous skin regeneration are simplistic in their structure and function, lacking the ability to accurately mimic the intricate tissue structure and regulate the disordered microenvironment. Novel biomimetic biomaterials with precise structure, chemical composition, and biophysical properties offer a promising avenue for achieving perfect endogenous skin regeneration. Here, we outline the recent advances in biomimetic materials induced endogenous skin regeneration from the aspects of structural and functional mimicry, physiological process regulation, and biophysical property design. Furthermore, novel techniques including in situ reprograming, flexible electronic skin, artificial intelligence, single-cell sequencing, and spatial transcriptomics, which have potential to contribute to the development of biomimetic biomaterials are highlighted. Finally, the prospects and challenges of further research and application of biomimetic biomaterials are discussed. This review provides reference to address the clinical problems of rapid and high-quality skin regeneration.

Biomaterial-based mechanical regulation facilitates scarless wound healing with functional skin appendage regeneration

Scar formation resulting from burns or severe trauma can significantly compromise the structural integrity of skin and lead to permanent loss of skin appendages, ultimately impairing its normal physiological function. Accumulating evidence underscores the potential of targeted modulation of mechanical cues to enhance skin regeneration, promoting scarless repair by influencing the extracellular microenvironment and driving the phenotypic transitions. The field of skin repair and skin appendage regeneration has witnessed remarkable advancements in the utilization of biomaterials with distinct physical properties. However, a comprehensive understanding of the underlying mechanisms remains somewhat elusive, limiting the broader application of these innovations. In this review, we present two promising biomaterial-based mechanical approaches aimed at bolstering the regenerative capacity of compromised skin. The first approach involves leveraging biomaterials with specific biophysical properties to create an optimal scarless environment that supports cellular activities essential for regeneration. The second approach centers on harnessing mechanical forces exerted by biomaterials to enhance cellular plasticity, facilitating efficient cellular reprogramming and, consequently, promoting the regeneration of skin appendages. In summary, the manipulation of mechanical cues using biomaterial-based strategies holds significant promise as a supplementary approach for achieving scarless wound healing, coupled with the restoration of multiple skin appendage functions.

Epidermal and dermal cells from adult rat eccrine sweat gland-containing skin can reconstruct the three-dimensional structure of eccrine sweat glands

BACKGROUND

Previously, we have demonstrated that eccrine sweat gland cells (ESGCs) can reconstruct the three-dimensional (3D) structure of eccrine sweat glands (ESGs). However, there is still a need to explore source cells capable of regenerating ESG to address the issue of ESG regeneration in ESGC-deficient conditions, such as severe burns.

METHODS

The epidermal cells and dermal cells in adult rat ventral foot skin (ESG-bearing) were isolated. The isolated single epidermal cells and dermal cells were mixed with Matrigel, and then the mixture was implanted into the axillary/inguinal fat pads of nude mice. Five weeks after implantation, the Matrigel plugs were harvested and the morphology and differentiation of the cells were examined by H&E staining and fluorescent immunohistochemical staining for ESG markers, such as Na+ -K+ -2Cl- cotransporter 1 (NKCC1), Na+ -K+ -ATPase (NKA), Foxa1 and K14.

RESULTS

The epidermal cells and dermal cells of adult rat ventral foot skin can reconstruct 3D structure and express specific markers of ESGs in skin, such as NKCC1, NKA and Foxa1, indicating the ESG-phenotypic differentiation of the 3D structures. Double immunofluorescence staining showed that some 3D structures expressed both the myoepithelial cell marker alpha-SMA and the common marker K14 of duct cells and myoepithelial cells, while some 3D structures expressed only K14, indicating that ESG-like 3D structures differentiated into duct-like and secretory coiled cells.

CONCLUSION

Epidermal and dermal cells from adult ESG-bearing skin can be used as a cell source for ESG regeneration.

Eccrine Sweat Gland and Its Regeneration: Current Status and Future Directions

Eccrine sweat glands (ESGs) play an important role in temperature regulation by secreting sweat. Insufficiency or dysfunction of ESGs in a hot environment or during exercise can lead to hyperthermia, heat exhaustion, heatstroke, and even death, but the ability of ESGs to repair and regenerate themselves is very weak and limited. Repairing the damaged ESGs and regenerating the lost or dysfunctional ESGs poses a challenge for dermatologists and bum surgeons. To promote and accelerate research on the repair and regeneration of ESGs, we summarized the development, structure and function of ESGs, and current strategies to repair and regenerate ESGs based on stem cells, scaffolds, and possible signaling pathways involved.

Biochemical and structural cues of 3D-printed matrix synergistically direct MSC differentiation for functional sweat gland regeneration

Mesenchymal stem cells (MSCs) encapsulation by three-dimensionally (3D) printed matrices were believed to provide a biomimetic microenvironment to drive differentiation into tissue-specific progeny, which made them a great therapeutic potential for regenerative medicine. Despite this potential, the underlying mechanisms of controlling cell fate in 3D microenvironments remained relatively unexplored. Here, we bioprinted a sweat gland (SG)-like matrix to direct the conversion of MSC into functional SGs and facilitated SGs recovery in mice. By extracellular matrix differential protein expression analysis, we identified that CTHRC1 was a critical biochemical regulator for SG specification. Our findings showed that Hmox1 could respond to the 3D structure activation and also be involved in MSC differentiation. Using inhibition and activation assay, CTHRC1 and Hmox1 synergistically boosted SG gene expression profile. Together, these findings indicated that biochemical and structural cues served as two critical impacts of 3D-printed matrix on MSC fate decision into the glandular lineage and functional SG recovery.

TNF-α suppresses sweat gland differentiation of MSCs by reducing FTO-mediated m6A-demethylation of Nanog mRNA

An effect of inhibition of tumor necrosis factor-α (TNF-α) on differentiation of mesenchymal stromal cells (MSCs) has been demonstrated, but the exact mechanisms that govern MSCs differentiation remain to be further elucidated. Here, we show that TNF-α inhibits the differentiation of MSCs to sweat glands in a specific sweat gland-inducing environment, accompanied with reduced expression of Nanog, a core pluripotency factor. We elucidated that fat mass and obesity-associated protein (FTO)-mediated m⁶A demethylation is involved in the regulation of MSCs differentiation potential. Exposure of MSCs to TNF-α reduced expression of FTO, which demethylated Nanog mRNA. Reduced expression of FTO increased Nanog mRNA methylation, decreased Nanog mRNA and protein expression, and significantly inhibited MSCs capacity for differentiation to sweat gland cells. Our finding is the first to elucidate the functional importance of m⁶A modification in MSCs, providing new insights that the microenvironment can regulate the multipotency of MSCs at the post-transcriptional level. Moreover, to maintain differentiation capacity of MSCs by regulating m⁶A modification suggested a novel potential therapeutic target for stem cell-mediated regenerative medicine.

Direct reprogramming of epidermal cells toward sweat gland-like cells by defined factors

Several studies have reported inducing adult cells into sweat gland-like cells; however, slow transition and low efficiency limit the potential for cell-based treatment. Here, we show that overexpression of the transcription factor FoxC1 was sufficient to reprogram epidermal cells to induced functional sweat gland-like cells (iSGCs). The iSGCs expressing secreting-related genes, had a global gene expression profile between fetal SGCs (P5) and adult SGCs (P28). Moreover, iSGCs transplanted into the burn mice model facilitated wound repair and sweat gland regeneration. We further demonstrated that the Foxc1 upregulated BMP5 transcription and BMP5 is responsible for the cell-type transition. Collectively, this study shows that lineage reprogramming of epidermal cells into iSGCs provides an excellent cell source and a promising regenerative strategy for anhidrosis and hypohidrosis.

MicroRNA-mediated regulation of BM-MSCs differentiation into sweat gland-like cells: targeting NF-κB

Sweat gland regeneration is important for patients with an extensive deep burn injury. In previous study, we reported that bone marrow-mesenchymal stem cells (BM-MSCs) could differentiate into sweat gland-like cells (SGLCs), but the underlying molecular mechanism remains unclear. Recently, microRNAs (miRNAs or miRs) are reported to manipulate many biological processes. However, whether the process of MSCs differentiation into sweat gland cells (SGCs) is regulated by miRNAs has not been reported. In this study, BM-MSCs were induced into SGLCs by co-culturing with SGCs. Differential expressions of miRNAs between BM-MSC and SGLCs were determined through miRNAs microarray and 68 miRNAs were found significantly changed in miRNA profile including hsa-miR-138-5p. Bioinformatics analysis showed that hsa-miR-138-5p targeted a group of nuclear factor-κB (NF-κB) related genes which play an important role in skin appendage development. As expected, hsa-miR-138-5p inhibitor transfected into BM-MSCs partly mimicked the effects of co-culture and increased the number of SGLCs by increasing the expression of NF-κB related genes. These results suggest that hsa-miR-138-5p and NF-κB are involved in the regulation of BM-MSCs differentiation into SGLCs. This study may also offer a new approach to yield SGCs for burn patients.

Time course of differentiation of different cell types in 3D-reconstructed eccrine sweat glands

Epidermal basal cells invaginate into the dermis to form sweat ducts, which then grow downwards further to form secretory coils during the ontogenesis of eccrine sweat glands, but the time course of differentiation of different cell types in 3D-reconstructed eccrine sweat glands remain unclear. In this study, secretory cell-specific marker K7, clear secretory cell-specific marker CA II, dark secretory cell-specific marker GCDFP-15, myoepithelial cell-specific marker α-SMA, inner duct cell-specific marker S100P and outer duct cell-specific marker S100A2 were detected by immunofluorescence staining. The results showed that S100P and S100A2 were first detected at 2 weeks post implantation, K7 and α-SMA at 3 weeks, and GCDFP-15 and CA II at 4 weeks. The differentiation of ducts preceded secretory coils in 3D-reconstructed eccrine sweat glands. After 8 weeks post implantation, the distribution of these markers in 3D-reconstructed eccrine sweat glands was similar to that in native ones, and the percentage of the 3D-reconstructed glands expressing these markers maintained steady. We conclude that although the 3D-reconstructed and native eccrine sweat glands originated from different cells, the differentiation of different cell types in 3D-reconstructed eccrine sweat glands parallels the sequence observed during embryonic development.

Effects of Simvastatin on the Viability and Secretion of Vascular Endothelial Growth Factor of Cell Spheroids Cultured in Growth Media

PURPOSE

This study evaluates the effects of simvastatin on the morphology, viability, secretion of vascular endothelial growth factor (VEGF) and expression of stemness markers and messenger RNA of cell spheroids cultured in growth media.

MATERIALS AND METHODS

Three-dimensional cell spheroids with stem cells and osteoblast-like cells were fabricated using concave, silicon, elastomer-based microwells in the presence of simvastatin at concentrations of 1 and 10 μM. Qualitative cellular viability was determined with a confocal microscope, and quantitative cellular viability was evaluated using a Cell Counting Kit-8 assay. The expression of stem cell surface markers was tested, and a quantitative real-time polymerase chain reaction was performed to evaluate the expression of collagen I and Runx2.

RESULTS

The cell spheroids were well formed in the microwells, but the addition of simvastatin produced significant changes in the morphology of spheroids. No significant changes in cellular viability were noted with the addition of simvastatin on day 1, but the addition of simvastatin significantly decreased cellular viability on day 5. The addition of simvastatin significantly increased the secretion of VEGF. The expression of the CD90 surface marker was seen regardless of whether simvastatin was added. The addition of simvastatin significantly decreased the expression of collagen I.

CONCLUSIONS

Based on these findings, the application of simvastatin clearly decreased the cellular viability of the cell spheroids made with stem cells and osteoblast-like cells but increased the secretion of VEGF by the cell spheroids.

Gene-activated matrix/bone marrow-derived mesenchymal stem cells constructs regenerate sweat glands-like structure in vivo

It is a significant challenge to regenerate full-thickness skin defects with sweat glands. Various skin substitutes have been developed to resolve this issue with minimal success. In this study, to yield a novel construct for in situ regeneration of sweat glands, the collagen-chitosan porous scaffold was combined with Lipofectamine 2000/pDNA-EGF complexes to obtain the gene-activated scaffold (GAS), which was then seeded with bone marrow-derived mesenchymal stem cells (BM-MSCs). The porous scaffold functionalized as a reservoir for the incorporated gene complexes which were released in a sustained manner. The seeded BM-MSCs were transfected in situ by the released complexes and specially differentiated into sweat gland cells in vitro under the induction of the expressed epidermal growth factor (EGF). Application in vivo of the GAS/BM-MSCs constructs on the full-thickness skin defects of SD rats confirmed that GAS/BM-MSCs could accelerate the wound healing process and induce the in situ regeneration of the full-thickness skin with sweat gland-like structures. Analyzed by immunohistochemical staining, RT-qPCR and Western-blotting, the levels of the major sweat gland markers such as carcino-embryonic antigen (CEA), cytokeratin 8 (CK8) and cytokeratin 14 (CK14) were all up-regulated, indicating that GAS/BM-MSCs can facilitate the regeneration of sweat glands-like structure in vivo.

Expression of S100A2 and S100P in human eccrine sweat glands and their application in differentiating secretory coil-like from duct-like structures in the 3D reconstituted eccrine sweat spheroids

Secretory coils and ducts are two components of eccrine sweat glands with different structures and functions. In our previous study, we combined keratins and α-SMA to distinguish between secretory coils and ducts. However, the key deficiency of the method was that none of the antibodies used was specific for ducts. In this study, we first examined the co-localization of K5/K7, α-SMA/K14, K7/S100P and α-SMA/S100A2 by double-immunofluorescence staining to confirm the localization of S100P and S100A2 in native human eccrine sweat glands, and second we identified secretory coil-like and duct-like structures in the 3D reconstituted eccrine sweat gland spheroids by double-immunofluorescence staining for K7/S100P and α-SMA/S100A2. In native human eccrine sweat glands, S100A2 immunoreactivity was confined to the outer layer and S100P to the inner layer of the duct. In 12-week Matrigel plugs containing eccrine sweat gland cells, double-immunofluorescence staining for K7/S100P and α-SMA/S100A2 could easily distinguish duct-like structures from secretory coil-like structures. We conclude that S100A2 and S100P can be used as specific duct markers in eccrine sweat glands, and combined use of S100P or S100A2 with keratins enables easy to distinction between secretory coils and ducts.

Evaluation of the shape, viability, stemness and osteogenic differentiation of cell spheroids formed from human gingiva-derived stem cells and osteoprecursor cells

The present study was performed to create stem cell spheroids from human gingiva-derived stem cells and osteoprecursor cells and to evaluate the maintenance of the stemness, the viability and osteogenic differentiation of the cell spheroids. Gingiva-derived stem cells were isolated, and a total of 6×105 stem cells and osteoprecursor cells were seeded into concave micromolds at various ratios. Gingiva-derived stem cells and/or osteoprecursor cells formed spheroids in concave microwells. The spheroids demonstrated a smaller diameter when the number of osteoprecursor cells seeded was lower. The majority of cells in the spheroids were identified to be live cells and the cell spheroids preserved viability throughout the experimental period. The cell spheroids, which contained stem cells, were positive for stem-cell markers. Cell spheroids in concave microwells demonstrated a statistically significant increase in alkaline phosphatase activity as time progressed (P<0.05). A statistically significant difference in phosphatase activity was observed in the stem cell alone group when compared with the osteoprecursor cell group at day 5 (P<0.05). Mineralized extracellular deposits were observed in each group after Alizarin Red S staining. Within the limits of the present study, cell spheroids from gingival cells and osteoprecursor cells maintained shape, viability, stemness and osteogenic differentiation potential.

Cell proliferation and differentiation during the three dimensional reconstitution of eccrine sweat glands

The aim of this study is to characterize the cell proliferation and proliferating cell types during three-dimensional reconstitution of eccrine sweat glands. Eccrine sweat gland cells suspended in Matrigel were injected subcutaneously into the inguinal regions of nude mice. At 1, 2, 4, 6, 8, 14, 21, 28, 35 and 42 days post-implantation, Matrigel plugs were immunostained for Ki67, to detect cycling cells, and the Ki67 labeling index at different time points was calculated. Three pairs of antibodies, Ki67/K7, Ki67/K14 and Ki67/α-SMA, were used to identify proliferating cell types in the plugs, on days 28, 35 and 42, by immunofluorescence double staining. The Ki67 labeling index on the first day of implantation was 30.53%, rapidly reached a peak value of 81.43% at 2 days post-implantation, and then decreased gradually to a low of 2.87% at 42 days. Double immunofluorescence staining showed that K14/Ki67 double-stained cells accounted for 80% of the Ki67-positive cells, whereas K7/Ki67 and α-SMA/Ki67 double-stained cells each accounted for 10% of the Ki67-positive population on days 28, 35, or 42 post-implantation. We conclude that eccrine sweat gland cells rapidly enter the cell cycle after implantation, but quickly show decreased cell proliferation and increased cell differentiation.

Foxa1 gene and protein in developing rat eccrine sweat glands

To investigate the development of eccrine sweat glands and the expression of Foxa1 genes and proteins in the course of development, the footpads from E15.5 to E21.5, P1-P12, P14, P21, P28 and P56 rats were subjected to immunofluorescence staining of FoxA1 and double immunofluorescence staining of K14/α-SMA, FoxA1/K7 and FoxA1/α-SMA, and were processed for Foxa1 gene detection by RT-qPCR. The results showed that rat eccrine sweat gland germs was first observed emerging from the basal layer of epidermis at E19.5, and then elongated downward into the dermis, forming straight ducts by E21.5. Early development of the secretory segments appeared at P1. The Foxa1 gene was not expressed in rat footpads until P2, but from P2 to P5, its expression up-regulated sharply, and thereafter maintained at a high level until adulthood. FoxA1 protein was first observed at P6 in eccrine sweat glands, four days after initial detection of Foxa1 gene transcripts. In skin, FoxA1-positive cells were present exclusively in secretory coils, with 95% being K7-positive secretory cells and 5% being α-SMA-positive myoepithelial cells. We conclude that Foxa1 can be used as a marker of eccrine sweat glands in skin and also as a marker of secretory coils, and Foxa1 is related to the development of secretory coils.

Human eccrine sweat gland cells reconstitute polarized spheroids when subcutaneously implanted with Matrigel in nude mice

Increasing evidence indicates that maintenance of cell polarity plays a pivotal role in the regulation of glandular homeostasis and function. We examine the markers for polarity at different time points to investigate the formation of cell polarity during 3D reconstitution of eccrine sweat glands. Mixtures of eccrine sweat gland cells and Matrigel were injected subcutaneously into the inguinal regions of nude mice. At 2, 3, 4, 5 and 6 weeks post-implantation, Matrigel plugs were removed and immunostained for basal collagen IV, lateral β-catenin, lateroapical ZO-1 and apical F-actin. The results showed that the cell polarity of the spheroids appeared in sequence. Formation of basal polarity was prior to lateral, apical and lateroapical polarity. Collagen IV was detected basally at 2 weeks, β-catenin laterally and ZO-1 lateroapically at 3 weeks, and F-actin apically at 4 weeks post-implantation. At week 5 and week 6, the localization and the positive percentage of collagen IV, β-catenin, ZO-1 or F-actin in spheroids was similar to that in native eccrine sweat glands. We conclude that the reconstituted 3D eccrine sweat glands are functional or potentially functional.