Macrophages Undergo M1-to-M2 Transition in Adipose Tissue Regeneration in a Rat Tissue Engineering Model

Research Progress on the Immunogenicity and Regeneration of Acellular Adipose Matrix: A Mini Review

Acellular adipose matrix (AAM) has received increasing attention for soft tissue reconstruction, due to its abundant source, high long-term retention rate and in vivo adipogenic induction ability. However, the current decellularization methods inevitably affect native extracellular matrix (ECM) properties, and the residual antigens can trigger adverse immune reactions after transplantation. The behavior of host inflammatory cells mainly decides the regeneration of AAM after transplantation. In this review, recent knowledge of inflammatory cells for acellular matrix regeneration will be discussed. These advancements will inform further development of AAM products with better properties.

Methoxy polyethylene glycol modification promotes adipogenesis by inducing the production of regulatory T cells in xenogeneic acellular adipose matrix

Acellular adipose matrix (AAM) has emerged as an important biomaterial for adipose tissue regeneration. Current decellularization methods damage the bioactive components of the extracellular matrix (ECM), and the residual immunogenic antigens may induce adverse immune responses. Here, we adopted a modified decellularization method which can protect more bioactive components with less immune reaction by methoxy polyethylene glycol (mPEG). Then, we determined the adipogenic mechanisms of mPEG-modified AAM after xenogeneic transplantation. AAM transplantation caused significantly lesser adipogenesis in the wild-type group than in the immune-deficient group. The mPEG-modified AAM showed significantly lower immunogenicity and higher adipogenesis than the AAM alone after xenogeneic transplantation. Furthermore, mPEG modification increased regulatory T (Treg) cell numbers in the AAM grafts, which in turn enhanced the M2/M1 macrophage ratio by secreting IL-10, IL-13, and TGF-β1. These findings suggest that mPEG modification effectively reduces the immunogenicity of xenogeneic AAM and promotes adipogenesis in the AAM grafts. Hence, mPEG-modified AAM can serve as an ideal biomaterial for xenogeneic adipose tissue engineering.

Roles of Perivascular Adipose Tissue in Hypertension and Atherosclerosis

Significance: Perivascular adipose tissue (PVAT), which is present surrounding most blood vessels, from the aorta to the microvasculature of the dermis, is mainly composed of fat cells, fibroblasts, stem cells, mast cells, and nerve cells. Although the PVAT is objectively present, its physiological and pathological significance has long been ignored. Recent Advances: PVAT was considered as a supporting component of blood vessels and a protective cushion to the vessel wall from the neighboring tissues during relaxation and contraction. Nonetheless, further extensive research found that PVAT actively regulates blood vessel tone through PVAT-derived vasoactive factors, including both relaxing and contracting factors. In addition, PVAT contributes to atherosclerosis through paracrine secretion of a large number of bioactive factors such as adipokines and cytokines. Thereby, PVAT regulates the functions of blood vessels through various mechanisms operating directly on PVAT or on the underlying vessel layers, including vascular smooth muscle cells (VSMCs) and endothelial cells (ECs). Critical Issues: PVAT is a unique adipose tissue that plays an essential role in maintaining the vascular structure and regulating vascular function and homeostasis. This review focuses on recent updates on the various PVAT roles in hypertension and atherosclerosis. Future Directions: Future studies should further investigate the actual contribution of alterations in PVAT metabolism to the overall systemic outcomes of cardiovascular disease, which remains largely unknown. In addition, the messengers and underlying mechanisms responsible for the crosstalk between PVAT and ECs and VSMCs in the vascular wall should be systematically addressed, as well as the contributions of PVAT aging to vascular dysfunction.

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.

The pathogenic importance of CCL21 and CCR7 in rheumatoid arthritis

Innate and adaptive immunity regulate the inflammatory and erosive phenotypes observed in rheumatoid arthritis (RA) patients. Hence, identifying novel pathways that participate in different stages of RA pathology will provide valuable insights concerning the mechanistic behavior of different joint leukocytes and the strategy to restrain their activity. Recent findings have revealed that CCL21 poses as a risk factor for RA and expression of its receptor, CCR7, on circulating monocytes is representative of the patient's disease activity score. Expression of CCR7 was found to be the hallmark of RA synovial fluid (SF) M1 macrophages (MФs) and its levels were potentiated in response to M1 mediating factors and curtailed by M2 mediators in naïve MФs. Intriguingly, although both CCR7 ligands, CCL19 and CCL21, are elevated in RA specimens, only CCL21 was predominately responsible for CCR7's pathological manifestation of RA. Unique subset of MФs differentiated in response to CCL21 stimulation, exhibited upregulation in Th17-polarizing monokines. Moreover, CCL21-activated monokines were capable of differentiating naïve T cells into joint Th17 cells, which also partook in RA osteoclastogenesis. Finally, to conserve chronic inflammation, SF CCL21 amplified RA neovascularization directly and indirectly by promoting RA FLS and MΦs to secrete proangiogenic factors, VEGF and IL-17. This review aims to shed light on the broad pathogenic impact of CCL21, linking immunostimulatory MФs with Th17 cells, while concurrently advancing RA bone destruction and neovascularization.

Mesenchymal stem cell-secreted extracellular vesicles carrying TGF-β1 up-regulate miR-132 and promote mouse M2 macrophage polarization

The effects of mesenchymal stem cells (MSCs) on different types of diseases are controversial, and the inner mechanisms remain unknown, which retards the utilization of MSCs in disease therapy. In this study, we aimed to elucidate the mechanisms of MSCs-extracellular vesicles (EVs) carrying transforming growth factor-beta 1 (TGF-β1) in M2 polarization in mouse macrophages via the microRNA-132 (miR-132)/E3 ubiquitin ligase myc binding protein 2 (Mycbp2)/tuberous sclerosis complex 2 (TSC2) axis. Mouse MSCs were isolated for adipogenic and osteogenic induction, followed by co-culture with mouse macrophages RAW264.7. Besides, mouse macrophages RAW264.7 were co-cultured with MSCs-EVs in vitro, where the proportion of macrophages and inflammation were detected by flow cytometry and ELISA. The experimental data revealed that MSCs-EVs promoted M2 polarization of macrophages, and elevated interleukin (IL)-10 expression and inhibited levels of IL-1β, tumour necrosis factor (TNF)-α and IL-6. MSC-EV-treated macrophages RAW264.7 increased TGF-β1 expression, thus elevating miR-132 expression. MiR-132 directly bound to Mycbp2, as confirmed by luciferase activity assay. Meanwhile, E3 ubiquitin ligase Mycbp2 could ubiquitinate TSC2 protein. Furthermore, silencing TGF-β1 inhibited M2 polarization of MSC-EV-treated macrophages. Taken conjointly, this study provides evidence reporting that MSC-secreted EVs carry TGF-β1 to promote M2 polarization of macrophages via modulation of the miR-132/Mycbp2/TSC2 axis.

Rationale for the design of 3D-printable bioresorbable tissue-engineering chambers to promote the growth of adipose tissue

Tissue engineering chambers (TECs) bring great hope in regenerative medicine as they allow the growth of adipose tissue for soft tissue reconstruction. To date, a wide range of TEC prototypes are available with different conceptions and volumes. Here, we addressed the influence of TEC design on fat flap growth in vivo as well as the possibility of using bioresorbable polymers for optimum TEC conception. In rats, adipose tissue growth is quicker under perforated TEC printed in polylactic acid than non-perforated ones (growth difference 3 to 5 times greater within 90 days). Histological analysis reveals the presence of viable adipocytes under a moderate (less than 15% of the flap volume) fibrous capsule infiltrated with CD68⁺ inflammatory cells. CD31-positive vascular cells are more abundant at the peripheral zone than in the central part of the fat flap. Cells in the TEC exhibit a specific metabolic profile of functional adipocytes identified by ¹H-NMR. Regardless of the percentage of TEC porosity, the presence of a flat base allowed the growth of a larger fat volume (p < 0.05) as evidenced by MRI images. In pigs, bioresorbable TEC in poly[1,4-dioxane-2,5-dione] (polyglycolic acid) PURASORB PGS allows fat flap growth up to 75 000 mm³ at day 90, (corresponding to more than a 140% volume increase) while at the same time the TEC is largely resorbed. No systemic inflammatory response was observed. Histologically, the expansion of adipose tissue resulted mainly from an increase in the number of adipocytes rather than cell hypertrophy. Adipose tissue is surrounded by perfused blood vessels and encased in a thin fibrous connective tissue containing patches of CD163⁺ inflammatory cells. Our large preclinical evaluation defined the appropriate design for 3D-printable bioresorbable TECs and thus opens perspectives for further clinical applications.

In vivo tissue engineering of an adipose tissue flap using fat grafts and Adipogel

For decades, plastic surgeons have spent considerable effort exploring anatomical regions for free flap design. More recently, tissue-engineering approaches have been utilised in an attempt to grow transplantable tissue flaps in vivo. The aim of this study was to engineer a fat flap with a vascular pedicle by combining autologous fat grafts and a novel acellular hydrogel (Adipogel) in an established tissue-engineering model comprising a chamber and blood vessel loop. An arteriovenous loop was created in the rat groin from the femoral vessels and positioned inside a perforated polycarbonate chamber. In Group 1, the chamber contained minced, centrifuged autologous fat; in Group 2, Adipogel was added to the graft; and in Group 3, Adipogel alone was used. Constructs were histologically examined at 6 and 12 weeks. In all groups, new tissue was generated. Adipocytes, although appearing viable in the graft at the time of insertion, were predominantly nonviable at 6 weeks. However, by 12 weeks, new fat had formed in all groups and was significantly greater in the combined fat/Adipogel group. No significant difference was seen in final construct total volume or construct neovascularisation between the groups. This study demonstrated that a pedicled adipose flap can be generated in rats by combining a blood vessel loop, an adipogenic hydrogel, and a lipoaspirate equivalent. Success appears to be based on adipogenesis rather than on adipocyte survival, and consistent with our previous work, this adipogenesis occurred subsequent to graft death and remodelling. The regenerative process was significantly enhanced in the presence of Adipogel.

Injectable Allograft Adipose Matrix Supports Adipogenic Tissue Remodeling in the Nude Mouse and Human

Supplemental Digital Content is available in the text.

Background:

Adipose tissue reaches cellular stasis after puberty, leaving adipocytes unable to significantly expand or renew under normal physiologic conditions. This is problematic in progressive lipodystrophies, in instances of scarring, and in soft-tissue damage resulting from lumpectomy and traumatic deformities, because adipose tissue will not self-renew once damaged. This yields significant clinical necessity for an off-the-shelf de novo soft-tissue replacement mechanism.

Methods:

A process comprising separate steps of removing lipid and cellular materials from adipose tissue has been developed, creating an ambient temperature-stable allograft adipose matrix. Growth factors and matrix proteins relevant to angiogenesis and adipogenesis were identified by enzyme-linked immunosorbent assay and immunohistochemistry, and subcutaneous soft-tissue integration of the allograft adipose matrix was investigated in vivo in both the athymic mouse and the dorsum of the human wrist.

Results:

Allograft adipose matrix maintained structural components and endogenous growth factors. In vitro, adipose-derived stem cells cultured on allograft adipose matrix underwent adipogenesis in the absence of media-based cues. In vivo, animal modeling showed vasculature formation followed by perilipin A–positive tissue segments. Allograft adipose matrix maintained soft-tissue volume in the dorsal wrist in a 4-month investigation with no severe adverse events, becoming palpably consistent with subcutaneous adipose.

Conclusions:

Subcutaneous implantation of allograft adipose matrix laden with retained angiogenic and adipogenic factors served as an inductive scaffold for sustaining adipogenesis. Tissue incorporation assessed histologically from both the subcutaneous injection site of the athymic nude mouse over 6 months and human dorsal wrist presented adipocyte morphology residing within the injected scaffold.

Macrophage populations show an M1-to-M2 transition in an experimental model of coronal pulp tissue engineering with mesenchymal stem cells

AIM

To assess M1/M2 macrophage phenotypes in a coronal pulp regeneration model in rats, under the hypothesis that there are dynamic M1/M2 phenotype changes during the different stages of the pulp regeneration.

METHODOLOGY

The maxillary first molars of Wistar rats were pulpotomized, and biodegradable hydrogel-made scaffolds carrying rat bone marrow mesenchymal stem cells were implanted in the pulp chamber. After 3, 7 and 14 days, samples were processed for (i) histological analysis and double immunoperoxidase staining for CD68 (a general macrophage marker) and one of either CCR7 (an M1 marker), CD163 (an M2 marker) or CD206 (an M2 marker); (ii) real-time PCR for AIF1 (an M1 marker), CD163, CD206, IL-10 and TNF-α mRNA expression; and (iii) Western blotting for the detection of CD68, CCR7 and CD206 proteins.

RESULTS

Histological analysis of the implanted region revealed sparse cellular distribution at 3 days, pulp-like tissue with a thin dentine bridge-like structure at 7 days, and dentine bridge-like mineralized tissue formation and resorption of most scaffolds at 14 days. CCR7+ macrophages had the highest density at 3 days, and then significantly decreased until 14 days (P < 0.05). In contrast, M2 marker (CD163 or CD206) expressing macrophages had the lowest density at 3 days and significantly increased until 14 days (P < 0.05). AIF1 and TNF-α mRNA levels, and CD68 and CCR7 protein levels were highest at 3 days. CD163 and CD206 mRNA levels, and CD206 protein levels increased with time and showed the highest at 14 days. IL-10 mRNA was highest at 3 days, decreased at 7 days and increased at 14 days.

CONCLUSIONS

Macrophages in the regenerating pulp tissue underwent a distinct transition from M1-dominant to M2-dominant, suggesting that the M1-to-M2 transition of macrophages plays an important role in creating a favourable microenvironment necessary for pulp tissue regeneration.

Improved Long-Term Volume Retention of Stromal Vascular Fraction Gel Grafting with Enhanced Angiogenesis and Adipogenesis

BACKGROUND

The apoptosis of mature adipocytes after fat grafting can result in chronic inflammation, absorption, and fibrosis, leading to unpredictable outcomes. Selective elimination of mature adipocytes may result in better outcomes and a different underlying retention mode. The authors previously developed a mature adipocyte-free product, stromal vascular fraction gel, derived from lipoaspirate, which eliminates adipocytes and preserves the stromal vascular fraction. This study investigated the retention and regeneration mode of stromal vascular fraction gel grafting.

METHODS

Nude mice were grafted with human-derived stromal vascular fraction gel or Coleman fat. Detailed cellular events over 3 months were investigated histologically and immunohistochemically.

RESULTS

The retention rate 90 days after grafting was significantly higher for stromal vascular fraction gel grafts than for standard Coleman fat (82 ± 15 percent versus 42 ± 9 percent; p < 0.05). Histologic analysis suggested that, unlike Coleman fat grafts, stromal vascular fraction gel grafts did not include significant necrotic areas. Moreover, although adipose tissue regeneration was found in grafts of both groups, rapid angiogenesis and macrophage infiltration were observed at a very early stage after stromal vascular fraction gel grafting. The presence of small preadipocytes with multiple intracellular lipid droplets in stromal vascular fraction gel grafts on day 3 also suggested very early adipogenesis. Although some of the cells in the stromal vascular fraction survived in stromal vascular fraction gel grafts, most of the newly formed adipose tissue was host-derived.

CONCLUSION

Stromal vascular fraction gel has a high long-term retention rate and a unique adipose regeneration mode, involving prompt inflammation and infiltration of immune cells, stimulating rapid angiogenesis and inducing host cell-mediated adipogenesis.

Adipose Tissue Formation Utilizing Fat Flap Distraction Technique

Co-regulation between adipocytes and supporting vasculature is considered an important process in adipose tissue generation. The objective of this study was to evaluate the mechanical and biological effects of a distraction technique on adipose tissue formation and maintenance. Based on the hypothesis that fat flaps gradually receding from each other can develop an adipose tissue construct, perforated polycarbonate syringe-shaped chambers were implanted in a rabbit model. Latency (1 week) and distraction (3 weeks) periods were followed by a consolidation period in the experimental groups (4, 8, and 12 weeks). In the distraction group, the volume of fat pad gradually increased up to 16 weeks. A transition zone was observed at 8 weeks, indicating the initiation of tissue generation. Histomorphologic analysis showed adipose and collagen connective tissue at 8 weeks. At 16 weeks, the relative composition was altered significantly. Adipose components occupied most of the tissue, and connective tissue was reduced. Blood vessels with endothelial lining were noted adjacent to adipocyte clusters, as well as in inter-adipocyte areas. The vessels had increased in number and were evenly distributed by 16 weeks. Our distraction technique produced more balanced adipose tissue generation than a non-distraction method, with co-development of adipose and vascular tissues.

Artificial Organs 2016: A Year in Review

In this Editor's Review, articles published in 2016 are organized by category and briefly summarized. We aim to provide a brief reflection of the currently available worldwide knowledge that is intended to advance and better human life while providing insight for continued application of technologies and methods of organ Replacement, Recovery, and Regeneration. As the official journal of The International Federation for Artificial Organs, The International Faculty for Artificial Organs, the International Society for Mechanical Circulatory Support, the International Society for Pediatric Mechanical Cardiopulmonary Support, and the Vienna International Workshop on Functional Electrical Stimulation, Artificial Organs continues in the original mission of its founders "to foster communications in the field of artificial organs on an international level." Artificial Organs continues to publish developments and clinical applications of artificial organ technologies in this broad and expanding field of organ Replacement, Recovery, and Regeneration from all over the world. We were pleased to publish our second Virtual Issue in April 2016 on "Tissue Engineering in Bone" by Professor Tsuyoshi Takato. Our first was published in 2011 titled "Intra-Aortic Balloon Pumping" by Dr. Ashraf Khir. Other peer-reviewed Special Issues this year included contributions from the 11th International Conference on Pediatric Mechanical Circulatory Support Systems and Pediatric Cardiopulmonary Perfusion edited by Dr. Akif Ündar and selections from the 23rd Congress of the International Society for Rotary Blood Pumps edited by Dr. Bojan Biocina. We take this time also to express our gratitude to our authors for offering their work to this journal. We offer our very special thanks to our reviewers who give so generously of time and expertise to review, critique, and especially provide meaningful suggestions to the author's work whether eventually accepted or rejected. Without these excellent and dedicated reviewers the quality expected from such a journal could not be possible. We also express our special thanks to our Publisher, John Wiley & Sons for their expert attention and support in the production and marketing of Artificial Organs. We look forward to reporting further advances in the coming years.