M2 macrophage-derived exosomes induce angiogenesis and increase skin flap survival through HIF1AN/HIF-1α/VEGFA control.

BACKGROUND: Skin flap transplantation is a routine strategy in plastic and reconstructive surgery for skin-soft tissue defects. Recent research has shown that M2 macrophages have the potential for pro-angiogenesis during tissue healing. METHODS: In our research, we extracted the exosomes from M2 macrophages(M2-exo) and applied the exosomes in the model of skin flap transplantation. The flap survival area was measured, and the choke vessels were assessed by morphological observation. Hematoxylin and eosin (H&E) staining and Immunohistochemistry were applied to assess the neovascularization. The effect of M2-exo on the function of Human umbilical vein endothelial cells (HUVECs) was also investigated. We also administrated 2-methoxyestradiol (2-ME2, an inhibitor of HIF-1α) to explore the underlying mechanism. We tested the effects of M2-Exo on the proliferation of HUVECs through CCK8 assay and EdU staining assay. RESULTS: The survival area and number of micro-vessels in the skin flaps were increased in the M2-exo group. Besides, the dilation rate of choke vessels was also enhanced in the M2-exo group. Additionally, compared with the control group, M2-exo could accelerate the proliferation, migration and tube formation of HUVECs in vitro. Furthermore, the expression of the pro-angiogenesis factors, HIF-1α and VEGFA, were overexpressed with the treatment of the M2-exo. The expression of HIF1AN protein level was decreased in the M2-exo group. Finally, treatment with HIF-1α inhibitor reverses the pro-survival effect of M2-exo on skin flaps by interfering with the HIF1AN/HIF-1α/VEGFA signaling pathway. CONCLUSION: This study showed that M2-exosomes promote skin flap survival by enhancing angiogenesis, with HIF1AN/HIF-1α/VEGFA playing a crucial role in this process.

Hypoxic mesenchymal stem cell-derived exosomes promote the survival of skin flaps after ischaemia-reperfusion injury via mTOR/ULK1/FUNDC1 pathways.

Flap necrosis, the most prevalent postoperative complication of reconstructive surgery, is significantly associated with ischaemia-reperfusion injury. Recent research indicates that exosomes derived from bone marrow mesenchymal stem cells (BMSCs) hold potential therapeutic applications in several diseases. Traditionally, BMSCs are cultured under normoxic conditions, a setting that diverges from their physiological hypoxic environment in vivo. Consequently, we propose a method involving the hypoxic preconditioning of BMSCs, aimed at exploring the function and the specific mechanisms of their exosomes in ischaemia-reperfusion skin flaps. This study constructed a 3 × 6 cm2 caudal superficial epigastric skin flap model and subjected it to ischaemic conditions for 6 h. Our findings reveal that exosomes from hypoxia-pretreated BMSCs significantly promoted flap survival, decrease MCP-1, IL-1ß, and IL-6 levels in ischaemia-reperfusion injured flap, and reduce oxidative stress injury and apoptosis. Moreover, results indicated that Hypo-Exo provides protection to vascular endothelial cells from ischaemia-reperfusion injury both in vivo and in vitro. Through high-throughput sequencing and bioinformatics analysis, we further compared the differential miRNA expression profiles between Hypo-Exo and normoxic exosomes. Results display the enrichment of several pathways, including autophagy and mTOR. We have also elucidated a mechanism wherein Hypo-Exo promotes the survival of ischaemia-reperfusion injured flaps. This mechanism involves carrying large amounts of miR-421-3p, which target and regulate mTOR, thereby upregulating the expression of phosphorylated ULK1 and FUNDC1, and subsequently further activating autophagy. In summary, hypoxic preconditioning constitutes an effective and promising method for optimizing the therapeutic effects of BMSC-derived exosomes in the treatment of flap ischaemia-reperfusion injury.

Individualized design of thoracodorsal artery perforator chimeric flap for customized reconstruction of complex three-dimensional defects in the extremities.

BACKGROUND: It was always challenging to accurately and effectively reconstruct the complicated defects with three-dimensional tissue deficits in the extremities. Muscle-chimeric perforator flap is an excellent choice for repairing those complicated wound. However, problems like donor-site morbidity and time-consuming intramuscular dissection still exist. This purpose of this study was to present a novel design of the thoracodorsal artery perforator (TDAP) chimeric flap for the customized reconstruction of complex three-dimensional tissue defects in the extremities. METHODS: From January 2012 to June 2020, 17 patients with complex three-dimensional deficits in the extremities were retrospectively analyzed. All patients in this series underwent extremity reconstruction using latissimus dorsi (LD)-chimeric TDAP flap. Three different types of LD-chimeric TDAP flaps were performed. RESULTS: A total of seventeen TDAP chimeric flaps were successfully harvested for the reconstruction of those complex three-dimensional defects in extremities. Among them, Design Type A flaps were used in 6 cases, Design Type B flaps were performed in 7 cases, and Design Type C flaps were used in the remaining 4 cases. The sizes of the skin paddles ranged from 6 cm × 3 cm to 24 cm × 11 cm. Meanwhile, the sizes of the muscle segments ranged from 3 cm × 4 cm to 33 cm × 4 cm. All the flaps survived. Nevertheless, one case required re-exploration owing to venous congestion. Moreover, the primary closure of the donor site was successfully achieved in all patients, and the mean follow-up time was 15.8 months. Most of the cases displayed satisfactory contour. CONCLUSION: The LD-chimeric TDAP flap is available for the reconstruction of complicated defects with three-dimensional tissue deficits in the extremities. It provided a flexible design for customized coverage of complex soft tissue defects with limited donor site morbidity.

Metformin induces M2 polarization via AMPK/PGC-1α/PPAR-γ pathway to improve peripheral nerve regeneration.

OBJECTIVES: Investigating the effect of metformin on peripheral nerve regeneration and the molecular mechanism. METHODS: In this study, a rat model of sciatic nerve injury and an inflammatory bone marrow-derived macrophage (BMDM) cell model were established. We assessed the sensory and motor function of the hind limbs four weeks after sciatic nerve injury, immunofluorescence was used to detect axonal regeneration and myelin formation, as well as local macrophage subtypes. We investigated the polarizing effect of metformin on inflammatory macrophages, and western blotting was applied to detect the molecular mechanisms behind it. RESULTS: Metformin treatment accelerated functional recovery, axon regeneration and remyelination, and promoted M2 macrophage polarization. In vivo, metformin transformed pro-inflammatory macrophages into pro-regeneration M2 macrophages. Protein expression levels of phosphorylated AMP-activated protein kinase (p-AMPK), proliferator-activated receptor-γ co-activator 1α (PGC-1α), and peroxisome proliferator-activated receptor-γ (PPAR-γ) increased upon metformin treatment. Moreover, inhibition of AMPK abolished the effects of metformin treatment on M2 polarization. CONCLUSION: Metformin promoted M2 macrophage polarization by activating the AMPK/PGC-1α/PPAR-γ signaling axis, thereby promoting peripheral nerve regeneration.

Variations in deep iliac circumflex artery perforator chimeric flap design for single-stage customized-reconstruction of composite bone and soft-tissue defect.

BACKGROUND: The deep iliac circumflex artery (DICA) perforator (DICAP) chimeric flap is a valuable treatment strategy for single-stage reconstruction of composite bone and soft-tissue defects in upper and lower extremities. However, its utilization rate remains low owing to anatomical variations that lead to challenges when identifying and dissecting perforators. METHODS: A comprehensive anatomical investigation was conducted on the DICA system by injecting lead oxide into 12 fresh cadavers following a standardized procedure. From January 2008 to December 2020, 30 patients with composite bone and soft-tissue defects received reconstruction surgery with DICAP chimeric flap. One of the four specified surgical techniques was used to create a modified DICAP chimeric flap for the patients based on the size, shape, and location of the defect. RESULTS: Two branching patterns of DICA, transverse and ascending branches, were observed, and the former gave off the osteomusculocutaneous perforators and terminal musculocutaneous perforators. Thirty DICAP chimeric flaps were elevated successfully. The size of the skin paddles measured from 9 × 4.5 cm to 22 × 9 cm, and the bone components ranged from 3 × 2.5 × 1.5 cm to 6 × 3.5 × 2 cm. All flaps survived successfully after the operation, and all patients achieved primary closure of the donor sites. No patient encountered the fracture of transferred iliac segments. The mean bone union time was 5.5 months (ranging from 4 to 8 months). CONCLUSION: The DICA system is a suitable source for harvesting the DICAP chimeric flap to reconstruct composite bone and soft-tissue defects. It provides a flexible design for individualized coverage of such defects with limited donor-site morbidity.

Itaconic acid induces angiogenesis and suppresses apoptosis via Nrf2/autophagy to prolong the survival of multi-territory perforator flaps.

Background: Perforator flaps are widely used in hand microsurgery to reconstruct and repair soft tissue injuries. However, ischemia and subsequent ischemia-reperfusion injury may cause distal necrosis of the flap. Itaconic acid (IA) is a modulator of macrophage function, which exerts anti-inflammatory effects in macrophage activation. Methods: The necrotic area of the flap was detected by measuring the flap temperature with an infrared thermometer. Flap cell apoptosis was detected by TUNEL staining and Western blot analysis of the apoptosis-associated proteins Bcl-2 and Bax. HE staining was used to detect angiogenesis of the skin flaps. CD31 was detected to identify positive vascular expression, and the survival of choke vessels in different areas of the skin flap was assessed by arteriography. In addition, Western blot was performed to quantify the expressions of VEGF, Nrf2, LC3II, SQSTM1, and CTSD. Results: Itaconic acid raises VEGF protein levels in skin flaps and the number of CD31-positive vessels. The skin flaps in the IA treatment group exhibited higher neovascularization and less necrosis than those in the control group. The results of TUNEL staining and Western blot revealed that Itaconic acid attenuated apoptosis in the ischemic area of flap. The combination of itaconic acid and Nrf2 inhibitor ML385 reversed this beneficial effect. The results revealed that itaconic acid attenuated apoptosis, enhanced angiogenesis, and enhanced autophagy. Conclusion: In summary, our findings indicate that itaconic acid might be an effective treatment to reduce flap necrosis. Additionally, this study identified a novel mechanism for the effects of itaconic acid on flap survival.

The research landscape on vascularized composite allografts: a bibliometric analysis (2002-2021).

OBJECTIVE: Vascularized composite allografts (VCAs) refer to the transplantation of multiple types of tissues during plastic and reconstructive surgery. Several publications have emerged in the field of VCA. However, there are no bibliometric studies on this topic. The aim was to multidimensionally analyze the knowledge base and hotspots in this subject. METHODS: We retrieved all publications related to VCA from the Web of Science Core Collection (WoSCC), published from 2002 to 2021. Next, scientometric analysis of different items was performed using various bibliometrics software to explore knowledge base, research hotspots, and advancement trends in this field. RESULTS: We included a total of 3,190 English articles from 2002 to 2021. The number of publications increased steadily annually. The United States produced the highest number of publications, followed by China. Most publications were from Harvard University, followed by Johns Hopkins University. The most authoritative academic journal was Plastic and Reconstructive Surgery. Transplantation occupied the first rank of co-cited journal list. Maria Z Siemionow may have the highest influence in the VCA field with the highest number of citations (n = 88) and co-cited references (n = 1252). Clinical studies on different allografts, immunosuppression, and tissue engineering were both the knowledge base and recent topics in VCA research. CONCLUSIONS: The first bibliometric study comprehensively summarized the trends and development of VCA research with steady growth over the past two decades. Currently, the most active topics are the clinical application of multiple allografts, immunosuppression strategies/therapies, and translation of tissue engineering to clinical practice.

Waveform-arranged multiple skin paddles: A novel design to reconstruct complex soft tissue defects of the extremities with a modified multi-lobed perforator flap.

BACKGROUND: Multi-lobed perforator flap was one of popular approaches for one-stage reconstruction of complex soft tissue defects because of its minimal donor-site morbidity. However, the area of skin island that can be harvested on the donor site is limited on the angiosome distribution, Moreover, large defects require more than the conventional skin island provided by a traditional multi-lobed perforator flap. For further extended skin paddles, this study presented a novel design of waveform-arranged skin paddles to elevated a modified multi-lobed perforator flap for the reconstruction of complex soft tissue defects in the extremities. METHODS: From March of 2015 to March of 2020, fifteen patients underwent complex soft tissue defects reconstruction with waveform-arranged multi-lobed perforator flaps. According the size, shape and localization of the defects, two strategies were performed to design this modified multi-lobed flap. RESULTS: A total of fifteen waveform-arranged multi-lobed perforator flaps were successfully harvested to reconstruct complex soft tissue defects of the extremities. Among of them, Waveform-arranged dual skin paddles perforator flap were performed in eleven cases, and the waveform-arranged tripaddle perforator flaps were used in four cases. All the flaps survived and no flap related complication was observed postoperatively. The donor sites were closed directly in all cases. The mean follow-up time was 15.6 months. Most of the cases showed satisfactory contour. CONCLUSION: The waveform design of multi-lobed perforator flap was an alternative approach for reconstruction of complex soft tissue defects; it can maximize the harvested skin area of the donor site to provide extended skin island.

HIF-1α Regulates Bone Homeostasis and Angiogenesis, Participating in the Occurrence of Bone Metabolic Diseases.

In the physiological condition, the skeletal system's bone resorption and formation are in dynamic balance, called bone homeostasis. However, bone homeostasis is destroyed under pathological conditions, leading to the occurrence of bone metabolism diseases. The expression of hypoxia-inducible factor-1α (HIF-1α) is regulated by oxygen concentration. It affects energy metabolism, which plays a vital role in preventing bone metabolic diseases. This review focuses on the HIF-1α pathway and describes in detail the possible mechanism of its involvement in the regulation of bone homeostasis and angiogenesis, as well as the current experimental studies on the use of HIF-1α in the prevention of bone metabolic diseases. HIF-1α/RANKL/Notch1 pathway bidirectionally regulates the differentiation of macrophages into osteoclasts under different conditions. In addition, HIF-1α is also regulated by many factors, including hypoxia, cofactor activity, non-coding RNA, trace elements, etc. As a pivotal pathway for coupling angiogenesis and osteogenesis, HIF-1α has been widely studied in bone metabolic diseases such as bone defect, osteoporosis, osteonecrosis of the femoral head, fracture, and nonunion. The wide application of biomaterials in bone metabolism also provides a reasonable basis for the experimental study of HIF-1α in preventing bone metabolic diseases.