A Short-Term High-Fat Diet Improved the Survival of Fat Grafts in Mice by Promoting Macrophage Infiltration and Angiogenesis

Postoperative Intermittent Fasting Improves Outcome of Autologous Fat Grafting in Mice

BACKGROUND

Autologous fat grafting confronts challenges of inconsistent retention and complications. Intermittent fasting (IF), an emerging dietary management strategy, shows potential in tissue repair and fat metabolism, and yet to know in fat grafting.

OBJECTIVES

The aim of this study is to address the impact of 16:8 IF on the outcome of fat grafting in mice.

METHODS

Male C57BL/6 mice were randomly assigned to postoperative IF regimen group (n = 24) and ad libitum group with unrestricted feeding (n = 24). For postoperative IF group, animals were put on a feeding schedule with 8 hours of unrestricted access to standard diet per day followed by 16-h fasting period after fat grafting. Fat grafts were harvested at 2, 4 and 12 weeks postoperatively. We addressed the mass retention and graft quality through weighting and ultrasound examination. Histological remodeling of fat grafts was evaluated by Masson staining and immunofluorescence staining.

RESULTS

In comparison with unrestricted feeding, postoperative IF strategies improved the mass retention of fat grafts, and optimized the outcomes characterized by enhanced adipogenesis, accelerated revascularization, facilitated M2 macrophage infiltration as well as reduced fibrosis and oil cyst formation.

CONCLUSION

Postoperative IF improved the retention and outcomes of fat grafting in mice, and could be suggested as a dietary intervention strategy after fat grafting clinically.

NO LEVEL ASSIGNED

This journal requires that authors assign a level of evidence to each submission to which Evidence-Based Medicine rankings are applicable. This excludes Review Articles, Book Reviews, and manuscripts that concern Basic Science, Animal Studies, Cadaver Studies, and Experimental Studies. For a full description of these Evidence-Based Medicine ratings, please refer to the Table of Contents or the online Instructions to Authors www.springer.com/00266 .

Crosstalk Between H-Type Vascular Endothelial Cells and Macrophages: A Potential Regulator of Bone Homeostasis

The crosstalk between H-type endothelial cells (ECs) and macrophages is critical for maintaining angiogenesis and osteogenesis in bone homeostasis. As core components of type H vessels, ECs respond to various pro-angiogenic signals, forming specialized vascular structures characterized by high expression of platelet-endothelial cell adhesion molecule-1 (CD31) and endothelial mucin (EMCN), thereby facilitating angiogenesis-osteogenesis coupling during bone formation. Macrophages, as key immune cells in the perivascular region, are primarily classified into the classically activated pro-inflammatory M1 phenotype and the selectively activated anti-inflammatory M2 phenotype, thereby performing dual functions in regulating local tissue homeostasis and innate immunity. In recent years, the complex crosstalk between type H vessel ECs and macrophages has garnered significant interest in the context of bone-related diseases. Orderly regulation of angiogenesis and bone immunity provides a new direction for preventing bone metabolic disorders such as osteoporosis and osteoarthritis. However, their interactions in bone homeostasis remain insufficiently understood, with limited clinical data available. This review comprehensively examines the intricate interactions between type H vessel ECs and macrophages with diverse phenotypes, and Insights into the signaling pathways that regulate their crosstalk, focusing on their roles in angiogenesis and osteogenesis. Furthermore, the review discusses recent interventions targeting this crosstalk and the challenges that remain. These insights may offer new perspectives on bone homeostasis and provide a theoretical foundation for developing novel therapeutic strategies.

Adipose stem cells regulate lipid metabolism by upregulating mitochondrial fatty acid β-oxidation in macrophages to improve the retention rate of transplanted fat

BACKGROUND

At present, fat transplantation is widely used in the plastic surgery industry, but the long-term preservation rate of transplanted fat decreases because of complications such as oil cysts due to the inability in macrophages to metabolize absorption. In cell-assisted lipotransfer technology, adipose-derived stem cells (ASCs) can influence the inflammatory response of grafts through the immunoregulation in macrophages, and the lipid metabolism in macrophages plays an important role in this process. Therefore, we hypothesized ASCs could improve the retention rate of fat grafts by regulating the progress of lipid metabolism in macrophages.

METHODS

We established fat transplantation and ASC-assisted fat transplantation model in C57BL/6 mice in vivo, and bone marrow-derived macrophages cocultured with apoptotic adipocytes were treated with or without ASCs in vitro. Graft retention, tissue structure, fibrosis, macrophage phenotype transformation, lipid deposition, mitochondrial morphology, oxygen consumption rate (OCR), fatty acid β-oxidation (FAO) level, and ATP production were assessed. Additionally, fat transplantation and ASC-assisted fat transplantation model was treated with etomoxir which inhibits mitochondrial FAO. Macrophages pretreated with etomoxir were co-cultured with apoptotic adipocytes and treated with or without ASCs. The method aboved was used for detection and verification.

RESULTS

In vivo, ASC-assisted fat transplantation improved macrophage mitochondrial expression and FAO level, promoted the early transformation of M2 macrophages, reduced the long-term lipid deposition of macrophages, and improved the retention rate of fat grafts. In vitro, ASCs up-regulated the level of mitochondrial FAO, OCR and ATP production in macrophages, reduced lipid deposition of macrophages and promoted M2 macrophages polarization by paracine function. The ability of ASCs in group pretreated with etomoxir to reduce the foaming of macrophages, promote the transformation to M2 macrophages, and improve the retention rate of fat transplantation was weakened.

CONCLUSIONS

ASCs increased the retention rate of transplanted fat by upregulating mitochondrial FAO to promote M2 polaration in macrophages. In addition, ASCs up-regulate mitochondrial FAO by paracrine effect to reduce foam cells formation and promote M2 transformation in macrophages in vitro.

Inflammation-mediated metabolic regulation in adipose tissue

Chronic inflammation of adipose tissue is a prominent characteristic of many metabolic diseases. Lipid metabolism in adipose tissue is consistently dysregulated during inflammation, which is characterized by substantial infiltration by proinflammatory cells and high cytokine concentrations. Adipose tissue inflammation is caused by a variety of endogenous factors, such as mitochondrial dysfunction, reactive oxygen species (ROS) production, endoplasmic reticulum (ER) stress, cellular senescence, ceramides biosynthesis and mediators of lipopolysaccharides (LPS) signaling. Additionally, the gut microbiota also plays a crucial role in regulating adipose tissue inflammation. Essentially, adipose tissue inflammation arises from an imbalance in adipocyte metabolism and the regulation of immune cells. Specific inflammatory signals, including nuclear factor-κB (NF-κB) signaling, inflammasome signaling and inflammation-mediated autophagy, have been shown to be involved in the metabolic regulation. The pathogenesis of metabolic diseases characterized by chronic inflammation (obesity, insulin resistance, atherosclerosis and nonalcoholic fatty liver disease [NAFLD]) and recent research regarding potential therapeutic targets for these conditions are also discussed in this review.

Lipolysis inhibition improves the survival of fat grafts through ameliorating lipotoxicity and inflammation

Fat grafting is a promising technique for correcting soft tissue abnormalities, but oil cyst formation and graft fibrosis frequently impede the therapeutic benefit of fat grafting. The lipolysis of released oil droplets after grafting may make the inflammation and fibrosis in the grafts worse; therefore, by regulating adipose triglyceride lipase (ATGL) via Atglistatin (ATG) and Forskolin (FSK), we investigated the impact of lipolysis on fat grafts in this study. After being removed from the mice and chopped into small pieces, the subcutaneous fat from wild-type C57BL/6J mice was placed in three different solutions for two hours: serum-free cell culture medium, culture medium+FSK (50 μM), and culture medium+ATG (100 μM). Following centrifugation to remove water and free oil droplets, 0.3 mL of the fat particles per mouse was subcutaneously injected into the back of mice. Additionally, the subcutaneous fat grafting area was immediately injected with PBS (control group), ATG (30 mg/kg), and FSK (15 mg/kg) following fat transplantation. Detailed cellular events after grafting were investigated by histological staining, real-time polymerase chain reaction, immunohistochemistry/immunofluorescent staining, and quantification. Two weeks after grafting, grafts treated with ATG showed lower expression of ATGL and decreased mRNA levels of TNFα and IL-6. In contrast, grafts treated with ATG showed elevated expression levels of IL-4 and IL-13 compared to the control grafts. In addition, fewer apoptotic cells and oil cysts were observed in ATG grafts. Meanwhile, a higher CD206+/CD68+ ratio of macrophages and more CD31+ vascular endothelial cells existed in the 2-month ATG grafts. In comparison to the control, ATG treatment improved the volume retention of grafts, and decreased graft fibrosis and oil cyst formation. By preventing oil droplet lipolysis, pharmacological suppression of ATGL shielded adipocytes from lipotoxicity following grafting. Additionally, ATG ameliorated the apoptosis and inflammation brought on by adipocyte death and oil droplet lipolysis in grafted fat. These all indicate that lipolysis inhibition improved transplanted fat survival and decreased the development of oil cysts and graft fibrosis, offering a potential postoperative pharmacological intervention for bettering fat grafting.

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.

Quality and Vitality of Autologous Fat Grafts Harvested by Different Techniques: A Clinical Comparison Study

BACKGROUND

Unpredictable outcomes with autologous fat grafting due to reabsorption processes present a major challenge for healthcare providers and patients. A higher number of viable adipocytes is considered to result in a higher volume being retained. Although various adverse factors have been extensively researched, other potential parameters have been less investigated or even neglected.

OBJECTIVE

The aim of this study was to investigate the harvesting process of adipose tissue as the primary cause of cell damage and to determine the risk factors associated with low cell survival.

METHODS

Thirty-nine male and female subjects undergoing planned elective liposuction or abdominoplasty were enrolled. Forty-seven lipoaspirates harvested by different liposuction techniques were analyzed. RNA isolation and real-time polymerase chain reaction was performed to elucidate differences in the expression of various adipocyte markers. Furthermore, scanning electron microscopy was performed on various samples to determine the cell damage caused by the different techniques.

RESULTS

A statistically significant lower expression of peroxisome proliferator-activated receptor γ was detected in subjects with a higher BMI. A trend towards a lower expression of perilipin 1 in lipoaspirates harvested by a super wet + ultrasound technique, compared with dry and super wet techniques, was shown. The lowest level of cell damage determined from scanning electron microscopy images was in lipoaspirates harvested by the super wet + ultrasound technique, and this level was statistically significantly different from those obtained by the 2 other techniques.

CONCLUSIONS

Optimization of the outcome in autologous fat grafting may be feasible by targeting and optimizing the harvesting process as a main risk factor for impaired adipocyte viability. Ultrasound-assisted liposuction might be considered a suitable harvesting technique.

LEVEL OF EVIDENCE: 5