Establishment of a Novel Mouse Model for Soft Tissue Expansion

Activating autophagy promotes skin regeneration induced by mechanical stretch during tissue expansion

Background

Tissue expansion, a technique in which skin regeneration is induced by mechanical stretch stimuli, is commonly used for tissue repair and reconstruction. In this study, we aimed to monitor the autophagy levels of expanded skin after the application of expansion stimuli and explore the effect of autophagy modulation on skin regeneration.

Methods

A rat scalp expansion model was established to provide a stable expanded skin response to mechanical stretch. Autophagy levels at different time points (6, 12, 24, 48 and 72 h after the last expansion) were detected via western blotting. The effect of autophagy regulation on skin regeneration during tissue expansion was evaluated via skin expansion efficiency assessment, western blotting, immunofluorescence staining, TUNEL staining and laser Doppler blood flow imaging.

Results

The autophagic flux reached its highest level 48 h after tissue expansion. Activating autophagy by rapamycin increased the area of expanded skin as well as the thicknesses of epidermis and dermis. Furthermore, activating autophagy accelerated skin regeneration during tissue expansion by enhancing the proliferation of cells and the number of epidermal basal and hair follicle stem cells, reducing apoptosis, improving angiogenesis, and promoting collagen synthesis and growth factor secretion. Conversely, the regenerative effects were reversed when autophagy was blocked.

Conclusions

Autophagy modulation may be a promising therapeutic strategy for improving the efficiency of tissue expansion and preventing the incidence of the complication of skin necrosis.

The Dynamic Changes in Skin Thickness of Forehead during Tissue Expansion

In addition to providing extra flap size, the tissue expansion process also brings changes in flap thickness. This study aims to identify the changes in the forehead flap thickness during the tissue expansion period. Patients undergoing forehead expander embedment from September 2021 to September 2022 were included. The thickness of the forehead skin and subcutaneous tissue were measured with ultrasound before and 1, 2, 3, and 4 months after expansion. Twelve patients were included. The average expansion period was 4.6 months, and the mean expansion volume was 657.1 mL. The thickness of skin and subcutaneous tissue in the central forehead changed from 1.09 ± 0.06 to 0.63 ± 0.05 mm and from 2.53 ± 0.25 to 0.71 ± 0.09 mm, respectively. In the left frontotemporal region, skin and subcutaneous tissue thickness changed from 1.03 ± 0.05 to 0.52 ± 0.05 mm and 2.02 ± 0.21 to 0.62 ± 0.08 mm. On the right side, skin and subcutaneous tissue thickness changed from 1.01 ± 0.05 to 0.50 ± 0.04 mm and 2.06 ± 0.21 to 0.50 ± 0.05 mm. This study measured the dynamic changes in the thickness of the forehead flap during expansion. The thickness of the forehead flap decreased the fastest in the first 2 months of expansion, and the changes in skin and subcutaneous thickness slowed down in the third and fourth months and tended to a minimum value. Additionally, the thickness of subcutaneous tissue decreased greater in magnitude than the dermal tissue.

Montelukast Attenuates Retraction of Expanded Flap by Inhibiting Capsule Formation around Silicone Expander through TGF-β1 Signaling

BACKGROUND

Tissue expansion has tremendous applications in plastic surgery, but flap retraction provides insufficient tissue for use. Inspired by the use of montelukast to suppress capsular contracture, the authors investigated the effects of montelukast on capsule formation around the expander and retraction of the expanded scalp of the rat.

METHODS

Thirty-six male Sprague-Dawley rats were randomly divided into control and montelukast groups. In each group, 12 expanded flaps with or without capsules were harvested for histologic and molecular analysis; the six remaining expanded flaps were transferred to repair defects. Myofibroblast and transforming growth factor-β1 expression in the capsule was determined using immunofluorescence. Capsule ultrastructure was observed using transmission electron microscopy. Related protein expression in the capsules was detected using Western blot analysis.

RESULTS

A comparison of control and montelukast groups revealed that areas of the harvested expanded flaps with capsules were greater (2.04 ± 0.11 cm 2 versus 2.42 ± 0.12 cm 2 , respectively; P = 0.04); the retraction rate decreased (41.3% ± 2.16% versus 28.13% ± 2.17%, respectively; P < 0.01). However, the increased areas and decreased retraction disappeared after capsule removal. The number of myofibroblasts declined. Thin, sparse collagen fibers were observed in the capsules. The expression of COL1, COL3, TGF-β1, EGR1, and phosphorylated ERK1/2 in the capsules decreased. Furthermore, the recipient area repaired by the transferred expanded flap was increased from 4.25 ± 0.39 cm 2 to 6.58 ± 0.31 cm 2 ( P < 0.01).

CONCLUSION

Montelukast attenuates retraction of the expanded flap by inhibiting capsule formation through suppressing transforming growth factor-β1 signaling.

CLINICAL RELEVANCE STATEMENT

This study provides novel insights into a method for increasing the area of the expanded flap.

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.

The Immediate Contraction of the Expanded Forehead Flap

INTRODUCTION

Flaps contract immediately after harvest, which added difficulty to flap design. This study aims to investigate the immediate contraction rate of the expanded forehead flap used in nasal reconstruction.

METHODS

Patients undergoing nasal reconstruction with expanded forehead flaps from September 2021 to January 2023 were included. Objective measurements of the pedicle width, maximum width, maximum length, and flap size of the expanded forehead flap before and after harvest were conducted.

RESULTS

Fourteen patients, including 9 males and 5 females, were included. The average expansion period was 4.6 months, and the mean injection volume was 658.6 ml. The average retraction rate of pedicle width, maximum width, maximum length, and size of the flap after harvest were 16.15%, 30.26%, 26.86%, and 50.89%, respectively.

CONCLUSION

This study presents the contraction rate of the expanded forehead flap used for nasal reconstruction. The data from the measurement will help surgeons to design the expanded forehead flap.

LEVEL OF EVIDENCE

Level-Level IV.

Looking into the Skin in Health and Disease: From Microscopy Imaging Techniques to Molecular Analysis

The skin is a complex organ that includes a wide variety of tissue types with different embryological origins [...].

Mechanical Stretch Induced Skin Regeneration: Molecular and Cellular Mechanism in Skin Soft Tissue Expansion

Skin soft tissue expansion is one of the most basic and commonly used techniques in plastic surgery to obtain excess skin for a variety of medical uses. However, skin soft tissue expansion is faced with many problems, such as long treatment process, poor skin quality, high retraction rate, and complications. Therefore, a deeper understanding of the mechanisms of skin soft tissue expansion is needed. The key to skin soft tissue expansion lies in the mechanical stretch applied to the skin by an inflatable expander. Mechanical stimulation activates multiple signaling pathways through cellular adhesion molecules and regulates gene expression profiles in cells. Meanwhile, various types of cells contribute to skin expansion, including keratinocytes, dermal fibroblasts, and mesenchymal stem cells, which are also regulated by mechanical stretch. This article reviews the molecular and cellular mechanisms of skin regeneration induced by mechanical stretch during skin soft tissue expansion.

Mechanical stretching can modify the papillary dermis pattern and papillary fibroblast characteristics during skin regeneration

Clinical application of mechanical stretching is a reconstructive method for skin repair. Although studies have reported dermal fibroblast heterogeneity, whether stretching affects individual fibroblast subpopulations equally remains unclear. Here, we show the changes in dermal structure and papillary fibroblast (Fp) in regenerated human skin. Exhausted skin regeneration caused dermal-epidermal junction (DEJ) flattening, papillary dermis thinning, and an increase in the type III collagen (COL3)/type I collagen (COL1) ratio with upregulated hallmarks of aging. Well-regenerated skin displayed a notable increase in the Fp population. Consistent changes were observed in the rat expansion model. Moreover, we found that TGFβ1 expression was especially increased in skin showing good regeneration. Activation of the TGFβ1/Smad2/3 pathway improved exhausted skin regeneration and resulted in increased collagen content and Fp proliferation, while pharmacological inhibition of TGFβ1 action impacted well-regenerated skin. Short-term mechanical stretching that promoted skin regeneration enhanced Fp proliferation, extracellular matrix (ECM) synthesis, and increased TGFβ1 expression, leading to good regeneration. Conversely, long-term stretching induced premature Fp senescence, leading to poor regeneration. This work shows the mechanism of mechanical stretching in well skin regeneration that enhances Fp proliferation and ECM synthesis via the TGFβ1/Smad2/3 pathway, and highlights a crucial role of Fps in stretching-induced skin regeneration.

Transcriptome Profiling Reveals Important Transcription Factors and Biological Processes in Skin Regeneration Mediated by Mechanical Stretch

Background: Mechanical stretch is utilized to promote skin regeneration during tissue expansion for reconstructive surgery. Although mechanical stretch induces characteristic morphological changes in the skin, the biological processes and molecular mechanisms involved in mechanically induced skin regeneration are not well elucidated.

Methods: A male rat scalp expansion model was established and the important biological processes related to mechanical stretch-induced skin regeneration were identified using Gene Ontology (GO) analysis, Kyoto Encyclopedia of Genes and Genomes (KEGG) analysis, and gene set enrichment analysis (GSEA). Analysis was also conducted by constructing a protein–protein interaction (PPI) network, identifying key modules and hub genes, determining transcription factor (TF)-mRNA regulatory relationships, and confirming the expression pattern of the TFs and hub genes.

Results: We identified nine robust hub genes (CXCL1, NEB, ACTN3, MYOZ1, ACTA1, TNNT3, PYGM, AMPD1, and CKM) that may serve as key molecules in skin growth. These genes were determined to be involved in several important biological processes, including keratinocyte differentiation, cytoskeleton reorganization, chemokine signaling pathway, glycogen metabolism, and voltage-gated ion channel activity. The potentially significant pathways, including the glucagon signaling pathway, the Wnt signaling pathway, and cytokine–cytokine receptor interaction, were distinguished. In addition, we identified six TFs (LEF1, TCF7, HMGA1, TFAP2C, FOSL1, and ELF5) and constructed regulatory TF–mRNA interaction networks.

Conclusion: This study generated a comprehensive overview of the gene networks underlying mechanically induced skin regeneration. The functions of these key genes and the pathways in which they participate may reveal new aspects of skin regeneration under mechanical strain. Furthermore, the identified TF regulators can be used as potential candidates for clinical therapeutics for skin pretreatment before reconstructive surgery.

Secreted PEDF modulates fibroblast collagen synthesis through M1 macrophage polarization under expanded condition

Tissue expansion is widely used to obtain new skin tissue for repairing defects in the clinical practice of plastic surgery. One major complication can be dermal thinning during expansion, which usually leads to skin rupture. Collagen synthesis can determine dermal thickness and can be influenced by macrophage polarization during expansion. The aim of the study was to test whether pigment epithelium-derived factor (PEDF) could be a modulator of collagen synthesis in fibroblasts by regulating macrophage polarization during skin expansion. Our results showed that PEDF mRNA expression was increased in expanded human and mouse epidermis. PEDF protein levels were elevated in the subcutaneous exudates of a rat skin expansion model. Increased PEDF mRNA expression was accompanied by dermal thinning during a three-week expansion protocol. Subcutaneous injection of PEDF in vivo further resulted in dermal thinning and cell number increase of M1 macrophage in the expanded skin. PEDF also promoted macrophage polarization in vitro to the M1 subtype under hypoxic conditions. PEDF did not influence collagen gene expression in fibroblasts directly, but attenuated collagen synthesis in a macrophage-mediated manner. Additionally, blockage of PEDF receptors on macrophages with inhibitors rescued collagen synthesis in fibroblasts. Our research demonstrated PEDF elevation in expanded skin leads to dermal thinning through M1 macrophage-mediated collagen synthesis inhibition in fibroblasts. Our results could form a basis for the development of novel strategies to improve skin integrity in expanded skin by using PEDF.

Hair follicle bulge-derived stem cells promote tissue regeneration during skin expansion

Skin expansion is widely used in reconstructive surgery to obtain supplemental and optimal skin. Enhancing the regenerative capacity of expanded skin is therefore of great interest. Hair follicle bulge-derived stem cells (HFBSCs) located in hair follicle bulges are closely associated with skin; HFBSC transplantation could promote cutaneous wound repair. However, the effects of transplanted HFBSCs on skin regeneration during expansion remain unclear. The aim of the study was to reveal the potential effects of transplanted HFBSCs in the expanded skin and explore its mechanism. Our results showed higher skin area, tissue weight, epidermal thickness, dermal thickness, proliferating cell count, collagen content, microcirculatory blood flow, blood vessels, and lower retraction ratios were observed in HFBSC-injected rats compared to uninjected controls. Moreover, the transplanted HFBSCs directly contributed to tissue regeneration by differentiating into vascular endothelial cells, epidermal cells, and the outer root sheath cells of hair follicle. Higher expression of EGF, VEGF, bFGF, and TGF-β were observed in HFBSC-injected rats. Our research demonstrated the transplanted HFBSCs could promote skin regeneration by differentiating into various types of skin related cells and by up-regulating the expression of growth factors. Our results could form a basis for the development of novel strategies to enhance regeneration in expanded skin by using HFBSCs.