USP28 Serves as a Key Suppressor of Mitochondrial Morphofunctional Defects and Cardiac Dysfunction in the Diabetic Heart.

BACKGROUND: The majority of people with diabetes are susceptible to cardiac dysfunction and heart failure, and conventional drug therapy cannot correct diabetic cardiomyopathy progression. Herein, we assessed the potential role and therapeutic value of USP28 (ubiquitin-specific protease 28) on the metabolic vulnerability of diabetic cardiomyopathy. METHODS: The type 2 diabetes mouse model was established using db/db leptin receptor-deficient mice and high-fat diet/streptozotocin-induced mice. Cardiac-specific knockout of USP28 in the db/db background mice was generated by crossbreeding db/m and Myh6-Cre+/USP28fl/fl mice. Recombinant adeno-associated virus serotype 9 carrying USP28 under cardiac troponin T promoter was injected into db/db mice. High glucose plus palmitic acid-incubated neonatal rat ventricular myocytes and human induced pluripotent stem cell-derived cardiomyocytes were used to imitate diabetic cardiomyopathy in vitro. The molecular mechanism was explored through RNA sequencing, immunoprecipitation and mass spectrometry analysis, protein pull-down, chromatin immunoprecipitation sequencing, and chromatin immunoprecipitation assay. RESULTS: Microarray profiling of the UPS (ubiquitin-proteasome system) on the basis of db/db mouse hearts and diabetic patients' hearts demonstrated that the diabetic ventricle presented a significant reduction in USP28 expression. Diabetic Myh6-Cre+/USP28fl/fl mice exhibited more severe progressive cardiac dysfunction, lipid accumulation, and mitochondrial disarrangement, compared with their controls. On the other hand, USP28 overexpression improved systolic and diastolic dysfunction and ameliorated cardiac hypertrophy and fibrosis in the diabetic heart. Adeno-associated virus serotype 9-USP28 diabetic mice also exhibited less lipid storage, reduced reactive oxygen species formation, and mitochondrial impairment in heart tissues than adeno-associated virus serotype 9-null diabetic mice. As a result, USP28 overexpression attenuated cardiac remodeling and dysfunction, lipid accumulation, and mitochondrial impairment in high-fat diet/streptozotocin-induced type 2 diabetes mice. These results were also confirmed in neonatal rat ventricular myocytes and human induced pluripotent stem cell-derived cardiomyocytes. RNA sequencing, immunoprecipitation and mass spectrometry analysis, chromatin immunoprecipitation assays, chromatin immunoprecipitation sequencing, and protein pull-down assay mechanistically revealed that USP28 directly interacted with PPARα (peroxisome proliferator-activated receptor α), deubiquitinating and stabilizing PPARα (Lys152) to promote Mfn2 (mitofusin 2) transcription, thereby impeding mitochondrial morphofunctional defects. However, such cardioprotective benefits of USP28 were largely abrogated in db/db mice with PPARα deletion and conditional loss-of-function of Mfn2. CONCLUSIONS: Our findings provide a USP28-modulated mitochondria homeostasis mechanism that involves the PPARα-Mfn2 axis in diabetic hearts, suggesting that USP28 activation or adeno-associated virus therapy targeting USP28 represents a potential therapeutic strategy for diabetic cardiomyopathy.

Restricted Boltzmann Machines Implemented by Spin-Orbit Torque Magnetic Tunnel Junctions.

Artificial intelligence has surged forward with the advent of generative models, which rely heavily on stochastic computing architectures enhanced by true random number generators with adjustable sampling probabilities. In this study, we develop spin-orbit torque magnetic tunnel junctions (SOT-MTJs), investigating their sigmoid-style switching probability as a function of the driving voltage. This feature proves to be ideally suited for stochastic computing algorithms such as the restricted Boltzmann machines (RBM) prevalent in pretraining processes. We exploit SOT-MTJs as both stochastic samplers and network nodes for RBMs, enabling the implementation of RBM-based neural networks to achieve recognition tasks for both handwritten and spoken digits. Moreover, we further harness the weights derived from the preceding image and speech training processes to facilitate cross-modal learning from speech to image generation. Our results clearly demonstrate that these SOT-MTJs are promising candidates for the development of hardware accelerators tailored for Boltzmann neural networks and other stochastic computing architectures.

Targeting heat shock protein 47 alleviated doxorubicin-induced cardiotoxicity and remodeling in mice through suppression of the NLRP3 inflammasome.

AIM: Doxorubicin-induced cardiotoxicity (DIC) is an increasing problem, occurring in many cancer patients receiving anthracycline chemotherapy, ultimately leading to heart failure (HF). Unfortunately, DIC remains difficult to manage due to an ignorance regarding pathophysiological mechanisms. Our work aimed to evaluate the role of HSP47 in doxorubicin-induced HF, and to explore the molecular mechanisms. METHODS AND RESULTS: Mice were exposed to multi-intraperitoneal injection of doxorubicin (DOX, 4mg/kg/week, for 6 weeks continuously) to produce DIC. HSP47 expression was significantly upregulated in serum and in heart tissue in DOX-treated mice and in isolated cardiomyocytes. Mice with cardiac-specific HSP47 overexpression and knockdown were generated using recombinant adeno-associated virus (rAVV9) injection. Importantly, cardiac-specific HSP47 overexpression exacerbated cardiac dysfunction in DIC, while HSP47 knockdown prevented DOX-induced cardiac dysfunction, cardiac atrophy and fibrosis in vivo and in vitro. Mechanistically, we identified that HSP47 directly interacted with IRE1α in cardiomyocytes. Furthermore, we provided powerful evidence that HSP47-IRE1α complex promoted TXNIP/NLRP3 inflammasome and reinforced USP1-mediated NLRP3 ubiquitination. Moreover, NLRP3 deficiency in vivo conspicuously abolished HSP47-mediated cardiac atrophy and fibrogenesis under DOX condition. CONCLUSION: HSP47 was highly expressed in serum and cardiac tissue after doxorubicin administration. HSP47 contributed to long-term anthracycline chemotherapy-associated cardiac dysfunction in an NLRP3-dependent manner. HSP47 therefore represents a plausible target for future therapy of doxorubicin-induced HF.

Steering the Reaction Pathway of CO2 Electroreduction by Tuning the Coordination Number of Copper Catalysts.

Cu-based catalysts are optimal for the electroreduction of CO2 to generate hydrocarbon products. However, controlling product distribution remains a challenging topic. The theoretical investigations have revealed that the coordination number (CN) of Cu considerably influences the adsorption energy of *CO intermediates, thereby affecting the reaction pathway. Cu catalysts with different CNs were fabricated by reducing CuO precursors via cyclic voltammetry (Cyc-Cu), potentiostatic electrolysis (Pot-Cu), and pulsed electrolysis (Pul-Cu), respectively. High-CN Cu catalysts predominantly generate C2+ products, while low-CN Cu favors CH4 production. For instance, over the high-CN Pot-Cu, C2+ is the main product, with the Faradaic efficiency (FE) reaching 82.5% and a partial current density (j) of 514.3 mA cm-2. Conversely, the low-CN Pul(3)-Cu favors the production of CH4, achieving the highest FECH4 value of 56.7% with a jCH4 value of 234.4 mA cm-2. In situ X-ray absorption spectroscopy and Raman spectroscopy studies further confirm the different *CO adsorptions over Cu catalysts with different CN, thereby directing the reaction pathway of the CO2RR.

Highly Efficient Electrosynthesis of Glycine over an Atomically Dispersed Iron Catalyst.

Glycine is a nonessential amino acid that plays a vital role in various biological activities. However, the conventional synthesis of glycine requires sophisticated procedures or toxic feedstocks. Herein, we report an electrochemical pathway for glycine synthesis via the reductive coupling of oxalic acid and nitrate or nitrogen oxides over atomically dispersed Fe-N-C catalysts. A glycine selectivity of 70.7% is achieved over Fe-N-C-700 at -1.0 V versus RHE. Synergy between the FeN3C structure and pyrrolic nitrogen in Fe-N-C-700 facilitates the reduction of oxalic acid to glyoxylic acid, which is crucial for producing glyoxylic acid oxime and glycine, and the FeN3C structure could reduce the energy barrier of *HOOCCH2NH2 intermediate formation thus accelerating the glyoxylic acid oxime conversion to glycine. This new synthesis approach for value-added chemicals using simple carbon and nitrogen sources could provide sustainable routes for organonitrogen compound production.

Abnormal Degraded Tapetum 1 (ADT1) is required for tapetal cell death and pollen development in rice.

The timely degradation of tapetum, the innermost somatic anther cell layer in flowering plants, is critical for pollen development. Although several genes involved in tapetum development have been characterized, the molecular mechanisms underlying tapetum degeneration remain elusive. Here, we showed that mutation in Abnormal Degraded Tapetum 1 (ADT1) resulted in overaccumulation of Reactive Oxygen Species (ROS) and abnormal anther development, causing earlier tapetum Programmed Cell Death (PCD) and pollen abortion. ADT1 encodes a nuclear membrane localized protein, which is strongly expressed in the developing microspores and tapetal cells during early anther development. Moreover, ADT1 could interact with metallothionein MT2b, which was related to ROS scavenging and cell death regulation. These findings indicate that ADT1 is required for proper timing of tapetum PCD by regulating ROS homeostasis, expanding our understanding of the regulatory network of male reproductive development in rice.

Switching Reaction Pathways of CO2 Electroreduction by Modulating Cations in the Electrochemical Double Layer.

Tuning the selectivity of CO2 electroreduction reaction (CO2RR) solely by changing electrolyte is a very attractive topic. In this study, we conducted CO2RR in different aqueous electrolytes over bulk metal electrodes. It was discovered that controlled CO2RR could be achieved by modulating cations in the electrochemical double layer. Specifically, ionic liquid cations in the electrolyte significantly inhibits the hydrogen evolution reaction (HER), while yielding high Faraday efficiencies toward CO (FECO) or formate (FEformate) depending on the alkali metal cations. For example, the product could be switched from CO (FECO=97.3 %) to formate (FEformate=93.5 %) by changing the electrolyte from 0.1 M KBr-0.5 M 1-octyl-3-methylimidazolium bromide (OmimBr) to 0.1 M CsBr-0.5 M OmimBr aqueous solutions over pristine Cu foil electrode. In situ spectroscopy and theoretical calculations reveal that the ordered structure generated by the assembly of Omim+ under an applied negative potential alters the hydrogen bonding structure of the interfacial water, thereby inhibiting the HER. The difference in selectivity in the presence of different cations is attributed to the hydrogen bonding effect caused by Omim+, which alters the solvated structure of the alkali metal cations and thus affects the stabilization of intermediates of different pathways.

Selective Electrochemical Oxidation of Benzylic C-H to Benzylic Alcohols with the Aid of Imidazolium Radical Mediators.

Selective oxidation of benzylic C-H to benzylic alcohols is a well-known challenge in the chemical community since benzylic C-H is more prone to be overoxidized to benzylic ketones. In this work, we report the highly selective electro-oxidation of benzylic C-H to benzylic alcohols in an undivided cell in ionic liquid-based solution. As an example, the selectivity toward xanthydrol could be as high as 95.7% at complete conversion of xanthene, a typical benzylic C-H compound, on gram-scale in imidazolium bromide/H2O/DMF. Mechanism investigation reveals that the imidazolium radical generated in situ participants in a proton-coupled electron transfer process and low-barrier hydrogen bonds stabilize the reaction intermediates, together steering the redox equilibrium, favoring benzylic alcohols over benzylic ketones.

Generation of spatiotemporal vortices in nonlinear photonic crystals.

Spatiotemporal vortices (STOVs) are a new, to the best of our knowledge, type of structured light in which the optical phase circulates in space-time. In this work, we propose to generate STOVs via second harmonic generation in lithium niobate nonlinear photonic crystals (NPCs) with a linearly chirped Gaussian pulse as the fundamental wave. The structural function of the NPC is derived by the inverse design method. Numerical simulations of the intensity and phase profiles of the generated second harmonic waves are performed with both the amplitude-phase-modulated and the simplified binary-phase-modulated NPCs. We anticipate our study will be valuable for the experimental generation and manipulation of STOVs in NPCs.

Application of QSAR for investigation on coagulation mechanisms of textile wastewater.

Coagulation is an effective preliminary treatment process for textile wastewater. In order to evaluate the effectiveness of the coagulation process, we performed quantitative structure activity relationship (QSAR) analyses with total organic carbon (TOC) removal rates (Rexp) as an index by three different coagulants (AlCl3, FeCl3, and MgCl2). The experimental results showed that the average Rexp of the three coagulants was 39.12% ± 2.60%, 51.60% ± 2.88%, and 49.95% ± 3.17%. Subsequently, 42 molecular descriptors of dye molecules were calculated by quantitative calculation softwares Gaussian 09, Material Studio 7.0, and Multiwfn 3.7, and then QSAR models were constructed by a multiple linear regression (MLR) method for the three coagulation systems. The developed QSAR models demonstrated excellent stability, robustness, and predictability with values of R2 = 0.7677, 0.8015, and 0.7035, Q2INT = 0.6067, 0.7026, and 0.5898, Q2EXT = 0.5505, 0.5076, and 0.5697, respectively. Based on the analysis of quantum parameters, the coagulation mechanism for AlCl3, FeCl3 is primarily electrostatic adsorption as well as hydrogen bonding, while MgCl2 coagulates dyes mainly by electrostatic adsorption. This study provides an assessment of the removal rules and a feasible method for predicting dye removal rates in AlCl3, FeCl3, and MgCl2 coagulation process.

QSAR model and mechanism research on color removal efficiency of dying wastewater by FeCl3 coagulation.

Coagulation is the most widely used method in the treatment of printing and dying wastewater. To better understand the relationship between the coagulation effect and dye molecular structures, quantitative structure activity relationship (QSAR) analyses were performed to elucidate the factors affecting the coagulation in ferric chloride (FeCl3) coagulation process. First, the coagulation experiments on 38 dye molecules were conducted to determine their color removal rates (Rexp) by FeCl3 under different pH conditions (i.e., pH = 4 and 10). The results showed that the average Rexp of dyes were 41.36% ± 2.40% at pH value of 4 and 55.70% ± 2.83% at pH value of 10. Subsequently, a multiple linear regression (MLR) method was used to construct QSAR models based on Rexp and 42 molecular parameters calculated by Gaussian 09, Materials Studio 7.0 and Multiwfn. The developed QSAR models exhibited excellent stability, reliability, and robustness with values of R2 = 0.7950, 0.8170, Q2INT = 0.6401, 0.7382, Q2EXT = 0.5168, 0.5441, at pH values of 4 and 10, respectively. Through analysis of quantum parameter values, electrostatic adsorption and hydrogen bonding adsorption were primarily responsible for the coagulation process. Therefore, this study could be useful in providing critical information for evaluating the removal efficiency and a feasible way to predict the removal rate of dyes by FeCl3 when no coagulation experiments were conducted.

HIF-1α Negatively Regulates Irisin Expression Which Involves in Muscle Atrophy Induced by Hypoxia.

Exposure to high altitude environment leads to skeletal muscle atrophy. As a hormone secreted by skeletal muscles after exercise, irisin contributes to promoting muscle regeneration and ameliorating skeletal muscle atrophy, but its role in hypoxia-induced skeletal muscle atrophy is still unclear. Our results showed that 4 w of hypoxia exposure significantly reduced body weight and gastrocnemius muscle mass of mice, as well as grip strength and the duration time of treadmill exercise. Hypoxic treatment increased HIF-1α expression and decreased both the circulation level of irisin and its precursor protein FNDC5 expression in skeletal muscle. In in vitro, CoCl2-induced chemical hypoxia and 1% O2 ambient hypoxia both reduced FNDC5, along with the increase in HIF-1α. Moreover, the decline in the area and diameter of myotubes caused by hypoxia were rescued by inhibiting HIF-1α via YC-1. Collectively, our research indicated that FNDC5/irisin was negatively regulated by HIF-1α and could participate in the regulation of muscle atrophy caused by hypoxia.

Stable Lead-Free Tin Halide Perovskite with Operational Stability >1200 h by Suppressing Tin(II) Oxidation.

Sn-based perovskites are the most promising alternative materials for Pb-based perovskites to address the toxicity problem of lead. However, the development of SnII -based perovskites has been hindered by their extreme instability. Here, we synthesized efficient and stable lead-free Cs4 SnBr6 perovskite by using SnF2 as tin source instead of easily oxidized SnBr2 . The SnF2 configures a fluorine-rich environment, which can not only suppress the oxidation of Sn2+ in the synthesis, but also construct chemically stable Sn-F coordination to hinder the electron transfer from Sn2+ to oxygen within the long-term operation process. The SnF2 -derived Cs4 SnBr6 perovskite shows a high photoluminescence quantum yield of 62.8 %, and excellent stability against oxygen, moisture, and light radiation for 1200 h, representing one of the most stable lead-free perovskites. The results pave a new pathway to enhance the optical properties and stability of lead-free perovskite for high-performance light emitters.

Boosting electrochemical nitrogen reduction reaction performance of two-dimensional Mo porphyrin monolayers via turning the coordination environment.

Designing atomically dispersed metal catalysts for the nitrogen reduction reaction (NRR) is an effective approach to achieve better energy conversion efficiencies. In this study, we designed a series of single molybdenum (Mo) atom-anchored porous two-dimensional Mo porphyrin (2D Mo-Pp) monolayers modified by B, C, O, P and S as efficient NRR catalysts to improve the catalytic performance. We introduced two key parameters, θ (pz orbital filling of heteroatoms) and φ (Bader charge of central Mo atoms). It shows that θ and φ play important roles in nitrogen absorption by analyzing the regression models. In particular, the theoretical results suggested that the 2D Mo-Pp monolayer modified by B has an ultralow limiting potential of 0.35 V and can suppress the hydrogen evolution reaction, making the 2D Mo-Pp monolayer modified by B a promising NRR electrocatalyst with high efficiency and selectivity. This work provides insights into the rational design of the elaborate structure of single-atom catalysts with tunable electrocatalytic activities.

Mutations in inherited fibrinogen disorders correlated with clinical features in the Chinese population.

Two probands with unknown reasons for low fibrinogen activity were considered to investigate the association between mutations in inherited fibrinogen disorders (IFDs) and clinical features in the Chinese population. A routine coagulation test was conducted on a Sysmex CS5100 coagulation analyzer, and Sanger sequencing was employed to analyze mutations. A PubMed database search through May 2020 was performed to identify relevant studies regarding the congenital fibrinogen disorder epidemic in China. A common heterozygous missense mutation (c.1233G > A p.Arg35His), a novel heterozygous mutation (c.2014T > C p.Trp672Arg), and a novel homozygous mutation (c.16A > G p.Ile6Val) in the FGA gene were identified in two probands with dysfibrinogenemia. The global coagulation screening assay can distinguish four types of IFD, especially a ratio of Fib:Ag/Fib:C equal to 1.5, which can distinguish patients with hypofibrinogenemia from those with hypodysfibrinogenemia. A total of 81 mutations from 76 probands in 45 IFD families have been reported in the Chinese population. Arg35 in FGA and Arg301 in FGG were responsible for IFD in more than half of patients in the Chinese population. It is possible to distinguish four types of IFD by using a global coagulation screening assay. Mutations in FGA, FGB and FGG occur in different functional regions, and Arg changes account for more than 70% of patients with IFD in the Chinese population, especially Arg-Cys, which may be associated with severe clinical symptoms.

Identification and Transcriptional Analysis of Zinc Finger-Homeodomain (ZF-HD) Family Genes in Cucumber.

Zinc finger-homeodomain (ZF-HD) proteins encode a family of plant-specific transcription factors that play essential roles in regulating plant growth and development as well as responses to abiotic/biotic stresses by activating or repressing the target genes. In this study, genome-wide characterization and expression profiling of the ZF-HD gene family in cucumber (Cucumis sativus) were performed for the first time. By using bioinformatics approaches, a total of 13 ZF-HD genes (designated as CsMIF1-CsMIF3 and CsZHD1-CsZHD10) were identified in the cucumber genome, which were unevenly distributed on six chromosomes. According to the phylogenetic analysis of cucumber and other species, they were divided into two distinct families, MINI ZINC FINGER (MIF) and zinc finger-homeodomain (ZHD), and the ZHD family was further divided into six subfamilies (ZHDI-ZHDVI). CsZF-HD members were mostly conserved in each subfamily with minor variations in motif distribution, and gene structure analysis showed that the CsZF-HD genes had only one intron or no intron at all. Expression analysis showed that most CsZF-HD genes had tissue-specific expression patterns, and some of them exhibited highly variable expression during fruit development. qRT-PCR results indicated that the selected CsZF-HD genes were responsive to drought stress, and some of them were differentially expressed in response to the inoculation of powdery mildew (PM) and downy mildew (DM) based on publicly available RNA-seq data. The results lay the foundation for further functional analysis of the ZF-HD genes and explore their potential application to the improvement of stress tolerance in cucumber.

Establishment of a Novel Mouse Model for Soft Tissue Expansion.

BACKGROUND: Despite its increasing use, not much is known about tissue expansion, and its complication rates are significantly high. Thus, there is an urgent need to establish a stable animal model to overcome the limitations and complications of tissue expansion. Although the mouse model has shown several advantages in the in-depth studies, an appropriate mouse expansion model has rarely been reported, likely because of its loose skin. MATERIALS AND METHODS: A micro expander was designed and implanted under the scalp of a mouse (expanded group); sterilized saline was regularly injected into the expander. In sham-operated mice (control group), a silicone sheet was implanted under the scalp. Skin samples were collected 5 wk after surgery. Histologic changes including epidermal and dermal thickness and collagen fiber arrangement were analyzed. In addition, vascular density and cell proliferation ratio were determined. An ultrastructural analysis was also performed. RESULTS: With the application of the expansion device, the skin became tight and showed area enlargement. The epidermal thickness of the expanded skin increased significantly (P < 0.01), whereas the thickness of the dermis decreased significantly (P < 0.05) as compared with the control skin. Masson staining demonstrated that collagen bundles were arranged more compactly in the expanded skin (P < 0.05) than in the controls. Furthermore, more proliferating cells (P < 0.05) and blood vessels (P < 0.01) were observed. Transmission electron microscopy showed that the fibers of expanded skin were stretched and broken into bundles of various diameters, with abundant active fibroblasts. CONCLUSIONS: A reliable mouse model of scalp skin expansion was successfully established, which may be a promising tool for in-depth studies on skin soft tissue expansion.

Strain effects on Co,N co-decorated graphyne catalysts for overall water splitting electrocatalysis.

Lattice strain, either tensile or compressive, can fine-tune the electronic structure of surfaces via altering the distances between surface atoms, thereby modifying the catalytic activity of catalysts. Numerous examples of strain engineering have been applied to various electrocatalysts for both hydrogen evolution reaction (HER) and oxygen evolution reaction (OER), but strain-optimized 2D carbon-based single-atom electrocatalysts for catalyzing the overall water splitting reaction have received little attention. Here, we applied the lattice strain of Co,N co-decorated graphyne (Co@N1-GY) to directly optimize its catalytic activity for the overall water splitting reaction based on first-principles calculations. Our calculations suggest that compressive strain and tensile strain lead to less stability of Co@N1-GY and the distances between C and Co atoms increase linearly with the strain changing from compressive to tensile, thus linearly upshifting the p-band center of C atoms and the d-band center of Co atoms. In addition, biaxial strain has more remarkable effects on these properties than uniaxial strain. From compressive to tensile strain, the chemisorption of electrochemically generated intermediates in both HER and OER becomes weaker and weaker. A tensile strain of 0.5% on Co@N1-GY gives an ideal HER performance, while the OER reaches the minimum overpotential of 0.33 V under the biaxial tensile strain of 3%.

Early histological and ultrastructural changes in expanded murine scalp.

Tissue expansion has been widely used for plastic, reconstructive, and esthetic surgeries. A mouse scalp expansion model can effectively mimic the characteristics of human skin expansion. However, a detailed study of the histological features and ultrastructural characteristics of expanded scalp is lacking, especially early ultrastructural changes. Here, a mouse scalp expansion model was established and the expanded scalp samples were obtained on day 2 (group I) and 4 (group II) post final injection. Histological analysis revealed epidermal thickening, dermal thinning, subcutaneous fat thinning, and capsule formation in the expanded samples. Ultrastructural evaluation showed the presence of keratinocytes with numerous tonofibrils and damaged mitochondria, and several ruptured collagen fibers and increased number of active fibroblasts and myofibroblasts were observed in the dermis and capsules. Adipocyte dedifferentiation was detected in the expanded samples of both groups, but formation of autophagosomes was only detected in the dermal fibroblasts of group I. Thus, early changes in expanded tissue should be carefully monitored, as it may help avoid dermal thinning and promote expanded tissue regeneration.

Macrophages are necessary for skin regeneration during tissue expansion.

BACKGROUND: Tissue expansion is a procedure that promotes skin regeneration by mechanical stretch. During the stress and relaxation cycle, the skin undergoes a repeated microtrauma which triggers an immune response leading to the recruitment of macrophages to repair the damaged tissue. Macrophages have been found to be necessary for tissue repair and wound healing, but their effects on skin regeneration during mechanical stretch remain unclear. METHODS: The dynamic changes of macrophages in the rat skin tissues undergoing expansion were quantitatively determined by immunohistochemistry staining. The area of the expanded skin, skin thickness, dermal collagen density, cell proliferation and tissue vascularization were examined to determine the effects of macrophages on the expanding skin. The phenotypes of macrophages and the growth factors related to skin regeneration were also examined to evaluate the underlying mechanisms for the involvement of macrophages in skin regeneration. As a comparison, the tissue samples of expanding skin in which the macrophages were depleted by topically utilizing clodronate liposomes were also evaluated. RESULTS: The number of skin macrophages in skin maintained in the high level during the skin expansion compared to non-expanded skin. We found that a switch from an M1- to M2-dominant response during tissue expansion. After the macrophages were depleted, the skin regeneration was inhibited, as evidenced by a smaller expansion area, thinner skin layers and decreased cell proliferation rate, collagen synthesis and, skin vascularization. The secretion of epidermal growth factor (EGF), fibroblast growth factor (FGF), and vascular endothelial growth factor (VEGF) were decreased when macrophages were depleted. CONCLUSIONS: Our findings suggest that macrophages are necessary for skin regeneration during tissue expansion. Modulating inflammation may provide a key therapeutic strategy to promote skin growth under mechanical strain.