M1/M2 Macrophages Play Different Roles in Adipogenic Differentiation of PDGFRα+ Preadipocytes In Vitro

Combination of Supramicrosurgical Lymphatico-Venular Anastomosis (sLVA) and Lymph-Sparing Liposuction in Treating Cancer-Related Lymphedema: Rationale for a Regional One-Stage Approach

Objective: Cancer-related lymphedema represents a potential complication of cancer treatment. The aim of this study is to evaluate the effectiveness of the combination of lymphatico-venular anastomosis and liposuction in the treatment of secondary lymphedema. Methods: We present a retrospective analysis of patients affected by cancer-related unilateral limb lymphedema. Inclusion criteria included previous neoplastic pathology with the consequent development of unilateral limb lymphedema, while the exclusion criteria included the presence of comorbidities and the persistence of cancer, as well as previous lymphatic surgery. The outcomes to be included were a reduction in the limb volume and lymphangitis rate, and an improvement in the quality of life. Patients' data were assessed before surgery and 1 year after surgery. Perioperative management included clinical and ultrasonographical evaluations. Under local anesthesia, lymphatico-venular anastomosis with the supramicrosurgical technique and the liposuction of the affected limb was performed in the same surgical session. Results: A total of 24 patients were enrolled in the study. One year after the surgery, an average volume reduction of 37.9% was registered (p = 0.0000000596). The lymphangitis rate decreased after surgery from 4.67 to 0.95 per year (p = 0.000007899). The quality-of-life score improved from 68.7 to 16 according to the LLIS scale. Conclusions: The combination of LVA and liposuction represents a valid strategy for treating cancer-related lymphedema, ensuring stable results over time. In addition, it can be performed under local anesthesia, resulting in being minimally invasive and well-tolerated by patients. This paper reports on the short-term efficacy of this combined technique.

LncRNA U90926 is dispensable for the development of obesity-associated phenotypes in vivo

Obesity is a global health problem characterized by excessive fat accumulation, driven by adipogenesis and lipid accumulation. Long non-coding RNAs (lncRNAs) have recently been implicated in regulating adipogenesis and adipose tissue function. Mouse lncRNA U90926 was previously identified as a repressor of in vitro adipogenesis in 3T3-L1 preadipocytes. Consequently, we hypothesized that, in vivo, U90926 may repress adipogenesis, and hence its deletion would increase weight gain and adiposity. We tested the hypothesis by applying U90926-deficient (U9-KO) mice to a high-throughput phenotyping pipeline. Compared with WT, U9-KO mice showed no major differences across a wide range of behavioral, neurological, and other physiological parameters. In mice fed a standard diet, we have found no differences in obesity-related phenotypes, including weight gain, fat mass, and plasma concentrations of glucose, insulin, triglycerides, and free fatty acids, in U9-KO mice compared to WT. U90926 deficiency lacked a major effect on white adipose tissue morphology and gene expression profile. Furthermore, in mice fed a high-fat diet, we found increased expression of U90926 in adipose tissue stromal vascular cell fraction, yet observed no effect of U90926 deficiency on weight gain, fat mass, adipogenesis marker expression, and immune cell infiltration into the adipose tissue. These data suggest that the U90926 lacks an essential role in obesity-related phenotypes and adipose tissue biology in vivo.

The Evolving Function of Vasculature and Pro-angiogenic Therapy in Fat Grafting

Autologous fat grating is a widely-accepted method to correct soft tissue deficiency. Although fat transplantation shows excellent biocompatibility and simple applicability, the relatively low retention rate caused by fat necrosis is still a challenge. The vasculature is integral after fat grafting, serving multiple crucial functions. Rapid and effective angiogenesis within grafts is essential for supplying oxygen necessary for adipocytes' survival. It facilitates the influx of inflammatory cells to remove necrotic adipocytes and aids in the delivery of regenerative cells for adipose tissue regeneration in fat grafts. The vasculature also provides a niche for interaction between adipose progenitor cells and vascular progenitor cells, enhancing angiogenesis and adipogenesis in grafts. Various methods, such as enriching grafts with diverse pro-angiogenic cells or utilizing cell-free approaches, have been employed to enhance angiogenesis. Beige and dedifferentiated adipocytes in grafts could increase vessel density. This review aims to outline the function of vasculature in fat grafting and discuss different cell or cell-free approaches that can enhance angiogenesis following fat grafting.

Fascia Promotes Adipose Tissue Regeneration by Improving Early Macrophage Infiltration after Fat Grafting in a Mouse Model

BACKGROUND

Low early macrophage fat graft infiltration (within a week of surgery) hinders tissue regeneration, suggesting that macrophages play a vital role in early angiogenesis and adipogenesis. However, the source of macrophages during this period is unclear.

METHOD

C57BL/6 mice were split into fascial removal (FR) group and control groups (CG). Mice had a piece of back fascia removed in the FR group, which was immediately replaced in the CG, and inguinal fat injected into the transplantation site of both groups. Separately, fascia was harvested from green fluorescent protein-expressing mice and transplanted into C57BL/6 mice for tracing macrophage infiltration after fat grafting.

RESULTS

The number of capillaries in the FR group was lower than that in the CG at days 3 ( P < 0.01) and 7 ( P < 0.05). Moreover, the number of small adipocytes in the FR group was lower than in the CG on days 3, 7, and 14 (all P < 0.05), and the relative expression of several adipogenic proteins was significantly lower in the FR group than in the CG on days 14 and 30. The timeline of macrophage infiltration was consistent with angiogenesis and adipogenesis. The number of macrophages in the FR group was significantly lower than in the CG at days 3 and 7 ( P < 0.05), and there were more fascia-derived macrophages than circulation-derived macrophages infiltrated into fat grafts within 7 days. Finally, the graft retention was lower in the FR group than the CG at day 90 ( P < 0.05).

CONCLUSION

In the early stage after fat grafting, fascial macrophage infiltration initiates tissue regeneration, thereby improving graft retention by promoting angiogenesis and adipogenesis.

CLINICAL RELEVANCE STATEMENT

In the clinic, injecting fat close to the fascia may increase fat retention. Fascia is widespread and self-regenerating, which may be a promising alternative source of local macrophages, with implications for tissue-engineering therapies such as correction of soft-tissue defects and breast reconstruction.

Recent Developments in Extracellular Matrix Remodeling for Fat Grafting

Remodeling of the extracellular matrix (ECM), which provides structural and biochemical support for surrounding cells, is vital for adipose tissue regeneration after autologous fat grafting. Rapid and high-quality ECM remodeling can improve the retention rate after fat grafting by promoting neovascularization, regulating stem cells differentiation, and suppressing chronic inflammation. The degradation and deposition of ECM are regulated by various factors, including hypoxia, blood supply, inflammation, and stem cells. By contrast, ECM remodeling alters these regulatory factors, resulting in a dynamic relationship between them. Although researchers have attempted to identify the cellular sources of factors associated with tissue regeneration and regulation of the microenvironment, the factors and mechanisms that affect adipose tissue ECM remodeling remain incompletely understood. This review describes the process of adipose ECM remodeling after grafting and summarizes the factors that affect ECM reconstruction. Also, this review provides an overview of the clinical methods to avoid poor ECM remodeling. These findings may provide new ideas for improving the retention of adipose tissue after fat transplantation.

Browning of White Adipocytes in Fat Grafts Associated With Higher Level of Necrosis and Type 2 Macrophage Recruitment

BACKGROUND

Induced browning adipocytes were assumed less viable and more prone to necrosis for their hypermetabolic property. A previous study showed that browning of adipocytes was more evident in fat grafts with necrosis in humans.

OBJECTIVES

The authors aimed to estimate whether fat transfer-induced browning biogenesis was associated with necrosis and its potential inflammation mechanisms in murine models.

METHODS

Human subcutaneous adipose from thigh or abdomen of 5 patients via liposuction was injected in 100 µL or 500 µL (n = 20 per group) into the dorsal flank of 6- to 8-week-old female nude mice fed with normal chow diet and harvested after 2, 4, 8, and 12 weeks. Control groups did not receive any grafting procedures (sham operation), where lipoaspirates were analyzed immediately after harvest. Histology and electronic microscopy, immunological analyses of browning markers, necrosis marker, and type I/II macrophages markers in mice were performed.

RESULTS

Histology and electronic microscopy showed browning adipocytes in fat grafts with a higher level of necrosis (0.435 ± 0.017 pg/mL for cleaved caspase-3, **P < 0.01), IL-6 (749.0 ± 134.1 pg/mL,***P < 0.001) and infiltration of type 2 macrophage profiles in mice (twofold increase, *P < 0.05).

CONCLUSIONS

Browning of adipocytes induced by fat transfer in mice is in parallel with post-grafting necrotic levels associated with elevated interleukin-6 and activated type 2 macrophage profiles, which promote browning development.

Emerging Potential of Exosomes on Adipogenic Differentiation of Mesenchymal Stem Cells

The mesenchymal stem cells have multidirectional differentiation potential and can differentiate into adipocytes, osteoblasts, cartilage tissue, muscle cells and so on. The adipogenic differentiation of mesenchymal stem cells is of great significance for the construction of tissue-engineered fat and the treatment of soft tissue defects. Exosomes are nanoscale vesicles secreted by cells and widely exist in body fluids. They are mainly involved in cell communication processes and transferring cargo contents to recipient cells. In addition, exosomes can also promote tissue and organ regeneration. Recent studies have shown that various exosomes can influence the adipogenic differentiation of stem cells. In this review, the effects of exosomes on stem cell differentiation, especially on adipogenic differentiation, will be discussed, and the mechanisms and conclusions will be drawn. The main purpose of studying the role of these exosomes is to understand more comprehensively the influencing factors existing in the process of stem cell differentiation into adipocytes and provide a new idea in adipose tissue engineering research.

Effects of macrophage regulation on fat grafting survival: Improvement, mechanisms, and potential application-A review

BACKGROUND

Autologous fat grafting has become a popular tool in plastic surgery to solve soft tissue defects and achieve skin rejuvenation, but the volume loss after transplantation remains a disturbing problem. In recent years, some new strategies have improved the outcome to some extent, but the fat graft retention is still far from ideal, so there remains a wide development prospect in this field. Macrophages are closely related to the local microenvironment and tissue regeneration, and their role in fat grafting has been increasingly highlighted.

AIMS

This article was aimed to review the efficacy, possible mechanisms, and potential application of macrophage regulation on fat grafting, as well as concerns and future perspectives of this filed.

METHODS

A retrospective review of the published data was conducted.

RESULTS

Most studies indicated that up-regulating M2 macrophages during fat grafting would improve fat retention via promoting neovascularization. M2 macrophages could secrete several pro-angiogenic factors, accelerate extracellular matrix (ECM) remodeling, and directly function on endothelial cells to encourage vascular expansion. In addition, macrophages could influence the proliferation, apoptosis, and adipogenic differentiation of preadipocytes.

CONCLUSIONS

During autologous fat grafting, appropriately regulating macrophages may become a promising method to increase fat retention. Nevertheless, the M2 macrophage polarizing agents, treatment opportunity, and contraindications require further discussion. We hope our work could promote more in-depth studies in this field, and we are looking forward to a standard procedure for the macrophage therapy in clinical practice.

Blood Impairs Viability of Fat Grafts and Adipose Stem Cells: Importance of Washing in Fat Processing

BACKGROUND

Fat processing plays a pivotal role in graft survival. Each component of the blood in lipoaspirate affects fat survival in different ways, but the mechanisms are not clear.

OBJECTIVES

The aim of this study was to investigate, by various experimental methods, the effect of blood on the viability of fat grafts and adipose stem cells (ASCs).

METHODS

Blood and fat samples were obtained from 6 female patients undergoing aesthetic liposuction. For the in vivo experiment, we compared fat mixed with normal saline or various ratios of blood in nude mice. The samples were explanted at 2 and 8 weeks to evaluate the gross volume retention and histologic and immunohistochemical characteristics. For in vitro experiments, ASCs were pretreated with hemoglobin at different concentrations and for different times. We then assessed the proliferation, migration, adipogenesis, and reactive oxygen species production of ASCs.

RESULTS

Blood in the graft led to a decrease in graft viability, as evaluated by general observation and histologic and immunohistochemical morphology in vivo. In vitro experiments showed inhibited proliferation, migration, and adipogenesis, and increased reactive oxygen species production in ACSs, after hemoglobin treatment, suggesting impaired ASC viability.

CONCLUSIONS

This study suggests that blood impairs the viability of fat grafts and ASCs and provides evidence that washing to remove blood is important in fat processing.

BMPR2 promotes fatty acid oxidation and protects white adipocytes from cell death in mice

Adipocyte cell death is pathologically involved in both obesity and lipodystrophy. Inflammation and pro-inflammatory cytokines are generally regarded as inducers for adipocyte apoptosis, but whether some innate defects affect their susceptibility to cell death has not been extensively studied. Here, we found bone morphogenetic protein receptor type 2 (BMPR2) knockout adipocytes were prone to cell death, which involved both apoptosis and pyroptosis. BMPR2 deficiency in adipocytes inhibited phosphorylation of perilipin, a lipid-droplet-coating protein, and impaired lipolysis when stimulated by tumor necrosis factor (TNFα), which lead to failure of fatty acid oxidation and oxidative phosphorylation. In addition, impaired lipolysis was associated with mitochondria-mediated apoptosis and pyroptosis as well as elevated inflammation. These results suggest that BMPR2 is important for maintaining the functional integrity of adipocytes and their ability to survive when interacting with inflammatory factors, which may explain why adipocytes among individuals show discrepancy for death responses in inflammatory settings.

Exosomes derived from M0, M1 and M2 macrophages exert distinct influences on the proliferation and differentiation of mesenchymal stem cells

Background

Different phenotypes of macrophages (M0, M1 and M2 Mφs) have been demonstrated to play distinct roles in regulating mesenchymal stem cells in various in vitro and in vivo systems. Our previous study also found that cell-conditioned medium (CM) derived from M1 Mφs supported the proliferation and adipogenic differentiation of bone marrow mesenchymal stem cells (BMMSCs), whereas CM derived from either M0 or M2 Mφs showed an enhanced effect on cell osteogenic differentiation. However, the underlying mechanism remains incompletely elucidated. Exosomes, as key components of Mφ-derived CM, have received increasing attention. Therefore, it is possible that exosomes may modulate the effect of Mφ-derived CM on the property of BMMSCs. This hypothesis was tested in the present study.

Methods

In this study, RAW264.7 cells were induced toward M1 or M2 polarization with different cytokines, and exosomes were isolated from the unpolarized (M0) and polarized (M1 and M2) Mφs. Mouse BMMSCs were then cultured with normal complete medium or inductive medium supplemented with M0-Exos, M1-Exos or M2-Exos. Finally, the proliferation ability and the osteogenic, adipogenic and chondrogenic differentiation capacity of the BMMSCs were measured and analyzed.

Results

We found that only the medium containing M1-Exos, rather than M0-Exos or M2-Exos, supported cell proliferation and osteogenic and adipogenic differentiation. This was inconsistent with CM-based incubation. In addition, all three types of exosomes had a suppressive effect on chondrogenic differentiation.

Conclusion

Although our data demonstrated that exosomes and CM derived from the same phenotype of Mφs didn’t exert exactly the same cellular influences on the cocultured stem cells, it still confirmed the hypothesis that exosomes are key regulators during the modulation effect of Mφ-derived CM on BMMSC property.