The use of adipose-derived stem cells as sheets for wound healing

Cellular therapies have shown immense promise in the treatment of nonhealing wounds. Cell sheets are an emerging strategy in tissue engineering, and these cell sheets are promising as a delivery method of mesenchymal stem cells to the wound bed. Cell sheet technology utilizes temperature dependent polymers to allow for lifting of cultured cells and extracellular matrix without the use of digestive enzymes. While mesenchymal stem cells (MSCs) have shown success in cell sheets for myocardial repair, examination of cell sheets in the field of wound healing has been limited. We previously developed a novel cell sheet composed of human adipose-derived stem cells (ASCs). Both single and triple layer cell sheets were examined in a full-thickness murine wound model. The treatment cell sheets were compared with untreated controls and analyzed at timepoints of 7, 14, 18 and 21 d. The ASC cell sheets showed increased healing at 7, 14 and 18 d, and this effect was increased in the triple layer cell sheet group. Future development of these cell sheets will focus on increasing angiogenesis in the wound bed, utilizing multiple cell types, and examining allogeneic cell sheets. Here we review our experiment, expand upon our future directions and discuss the potential of an off-the-shelf cell sheet. In the field of wound healing, such a cell sheet is both clinically and scientifically exciting.     

Fat depot-specific gene signature and ECM remodeling of Sca1high adipose-derived stem cells

Stem cell antigen-1 (Sca1 or Ly6A/E) is a cell surface marker that is widely expressed in mesenchymal stem cells, including adipose-derived stem cells (ASCs). We hypothesized that the fat depot-specific gene signature of Sca1^high ASCs may play the major role in defining adipose tissue function and extracellular matrix (ECM) remodeling in a depot-specific manner. Herein we aimed to characterize the unique gene signature and ECM remodeling of Sca1^high ASCs isolated from subcutaneous (inguinal) and visceral (epididymal) adipose tissues. Sca1^high ASCs are found in the adventitia and perivascular areas of adipose tissues. Sca1^high ASCs purified with magnetic-activated cell sorting (MACS) demonstrate dendrite or round shape with the higher expression of cytokines and chemokines (e.g., Il6, Cxcl1) and the lower expression of a glucose transporter (Glut1). Subcutaneous and visceral fat-derived Sca1^high ASCs particularly differ in the gene expressions of adhesion and ECM molecules. While the expression of the major membrane-type collagenase (MMP14) is comparable between the groups, the expressions of secreted collagenases (MMP8 and MMP13) are higher in visceral Sca1^high ASCs than in subcutaneous ASCs. Consistently, slow but focal MMP-dependent collagenolysis was observed with subcutaneous adipose tissue-derived vascular stromal cells, whereas rapid and bulk collagenolysis was observed with visceral adipose tissue-derived cells in MMP-dependent and -independent manners. These results suggest that the fat depot-specific gene signatures of ASCs may contribute to the distinct patterns of ECM remodeling and adipose function in different fat depots.     

Fabrication of functional three-dimensional tissues by stacking cell sheets in vitro

The fabrication of 3D tissues retaining the original functions of tissues/organs in vitro is crucial for optimal tissue engineering and regenerative medicine. The fabrication of 3D tissues also contributes to the establishment of in vitro tissue/organ models for drug screening. Our laboratory has developed a fabrication system for functional 3D tissues by stacking cell sheets of confluent cultured cells detached from a temperature-responsive culture dish. Here we describe the protocols for the fabrication of 3D tissues by cell sheet engineering. Three-dimensional cardiac tissues fabricated by stacking cardiac cell sheets pulsate spontaneously, synchronously and macroscopically. Via this protocol, it is also possible to fabricate other tissues, such as 3D tissue including capillary-like prevascular networks, from endothelial cells sandwiched between layered cell sheets. Cell sheet stacking technology promises to provide in vitro tissue/organ models and more effective therapies for curing tissue/organ failures.     

Decellularized adipose matrix provides an inductive microenvironment for stem cells in tissue regeneration

Stem cells play a key role in tissue regeneration due to their self-renewal and multidirectional differentiation, which are continuously regulated by signals from the extracellular matrix (ECM) microenvironment. Therefore, the unique biological and physical characteristics of the ECM are important determinants of stem cell behavior. Although the acellular ECM of specific tissues and organs (such as the skin, heart, cartilage, and lung) can mimic the natural microenvironment required for stem cell differentiation, the lack of donor sources restricts their development. With the rapid development of adipose tissue engineering, decellularized adipose matrix (DAM) has attracted much attention due to its wide range of sources and good regeneration capacity. Protocols for DAM preparation involve various physical, chemical, and biological methods. Different combinations of these methods may have different impacts on the structure and composition of DAM, which in turn interfere with the growth and differentiation of stem cells. This is a narrative review about DAM. We summarize the methods for decellularizing and sterilizing adipose tissue, and the impact of these methods on the biological and physical properties of DAM. In addition, we also analyze the application of different forms of DAM with or without stem cells in tissue regeneration (such as adipose tissue), repair (such as wounds, cartilage, bone, and nerves), in vitro bionic systems, clinical trials, and other disease research.     

Culture on Tissue‐Specific Coatings Derived from α‐Amylase‐Digested Decellularized Adipose Tissue Enhances the Proliferation and Adipogenic Differentiation of Human Adipose‐Derived Stromal Cells

While extracellular matrix (ECM)‐derived coatings have the potential to direct the response of cell populations in culture, there is a need to investigate the effects of ECM sourcing and processing on substrate bioactivity. To develop improved cell culture models for studying adipogenesis, the current study examines the proliferation and adipogenic differentiation of human adipose‐derived stem/stromal cells (ASCs) on a range of ECM‐derived coatings. Human decellularized adipose tissue (DAT) and commercially available bovine tendon collagen (COL) are digested with α‐amylase or pepsin to prepare the coatings. Physical characterization demonstrates that α‐amylase digestion generates softer, thicker, and more stable coatings, with a fibrous tissue‐like ultrastructure that is lost in the pepsin‐digested thin films. ASCs cultured on the α‐amylase‐digested ECM have a more spindle‐shaped morphology, and proliferation is significantly enhanced on the α‐amylase‐digested DAT coatings. Further, the α‐amylase‐digested DAT provides a more pro‐adipogenic microenvironment, based on higher levels of adipogenic gene expression, glycerol‐3‐phosphate dehydrogenase (GPDH) enzyme activity, and perilipin staining. Overall, this study supports α‐amylase digestion as a new approach for generating bioactive ECM‐derived coatings, and demonstrates tissue‐specific bioactivity using adipose‐derived ECM to enhance ASC proliferation and adipogenic differentiation.     

Construction and characterization of osteogenic and vascular endothelial cell sheets from rat adipose-derived mesenchymal stem cells

In this study, adipose-derived mesenchymal stem cells (ADSCs) were isolated from adipose tissues of rats. Flow cytometry identification showed that ADSCs of passage 3 highly expressed CD29 and CD44, but hardly expressed CD31 and CD45. Adipogenic, osteogenic, and chondrogenic differentiation were confirmed by the results of oil red O staining, alkaline phosphatase (ALP), and alcian blue staining, respectively. ADSCs at a density of 1 × 10⁶/cm² were cultured in the osteogenic medium and the osteogenic cell sheets could be obtained after 14 d. The cell sheets were positive with von kossa staining. The transmission electron microscopy (TEM) result showed that needle-like calcium salt crystals were deposited on the ECM. These results suggested that the osteogenic cell sheets may have potential osteogenesis ability. ADSCs at a density of 1 × 10⁶/cm² were cultured in the endothelial cell growth medium-2 and the endothelial cell sheets can be formed after 16 d of culture. The TEM image confirmed that the Weibel-Palade corpuscle was seen in the cells. The expression of CD31 was positive, suggesting that the endothelial cell sheets may have a strong ability to form blood vessels. In this study, two types of cell sheets with the potential abilities of osteogenesis and blood vessels formation were obtained by induced culture of ADSCs in vitro, which lays a foundation to build vascularized tissue engineered bone for the therapy of bone defects.     

Effect of different cell sheet ECM microenvironment on the formation of vascular network

The repair and reconstruction of large bone defects remains as a significant clinical challenge mainly due to the insufficient vascularization. The prefabrication of vascular network based on cell sheet technique brings a promising potential for sufficient vascularization due to rich extracellular matrix (ECM) of cell sheets. However, the effect of different cell sheet ECM micro-environment on the formation of a vascular network has not been well understood. Here our goal is to study the effect of different cell sheets on the formation of a vascular network. First we cultured human bone marrow mesenchymal stem cells (hBMSCs) under two culture conditions to obtain osteogenic differentiated cell sheet (ODCS) and undifferentiated cell sheet (UDCS), respectively. Then the human umbilical vein endothelial cells (HUVECs) were seeded onto the surface of the two sheets at different seeding densities to fabricate pre-vascularized cell sheets. Our results indicated that the two sheets facilitated the alignment of HUVECs and promoted the formation of vascular networks. Quantitative analysis showed that the number of networks in ODCS was higher than that in the UDCS. The ECM of the two sheets was remodeled and rearranged during the tubulogenesis process. Furthermore, results showed that the optimal seeding density of HUVECs was 5 × 10⁴ cell/cm². In summary, these results suggest that the vascularized ODCS has a promising potential to construct pre-vascularized tissue for bone repair.     

Decellularized breast matrix as bioactive microenvironment for in vitro three-dimensional cancer culture

Breast cancer (BC) is a leading cause of cancer-related death in women with unsatisfactory survival rates. Advances in the understanding of the genetic basis of BC provide the opportunity to develop gene-based medicines capable of treating metastatic diseases. Here, we first demonstrated efficient tissue engineering approaches applied to normal breast and BC extracellular matrix (ECM) starting from decellularized human biopsies to generate a three-dimensional (3D) bioactive model with the sodium lauryl ether sulfate solution. The decellularized tissues maximized the genetic component removal from tissues and minimally injured ECM structures and native compositions by histology and ECM compositions analyses. Importantly, we proved that the 3D ECM retained tissues biological properties. We demonstrated that after 30 days of recellularization with MCF-7 cell (human breast adenocarcinoma cell line), the 3D cancer ECM induced an overexpression of epithelial–mesenchymal transition (EMT) and cancer proliferation. Meanwhile, normal ECM from the breast inhibited EMT and cell growth with the inducement of apoptosis. Given the biological activity preserved in the ECM after decellularization, we believe these approaches are powerful tools for future preclinical research for BC and breast development.     

Application of a cell sheet–polymer film complex with temperature sensitivity for increased mechanical strength and cell alignment capability

We have succeeded in fabricating a cell sheet–polymer film complex involving a temperature‐sensitive polymer that has enough mechanical strength that can be manipulated even by forceps. The polymer film can be removed by lowering the temperature after transplantation, demonstrating its potential use in regenerative medicine. Recently, tissue engineering involving cell sheets was developed, tissues being fabricated by layering of these cell sheets. This technique promises high density cell packing, which is important for native cell functions, and successful heart therapy using cardiac cell sheets has been reported. On the other hand, the fabrication of a large tissue using cell sheets is difficult because of fragility of the cell sheets. Here, we have developed a novel method in which cells are attached to a temperature‐sensitive poly‐N‐isopropylacrylamide film mixed with laminin and collagen IV, and report that the cell sheet–polymer film complex can be manipulated with forceps. A cell sheet can be removed from the polymer film by lowering the temperature after the manipulation. We have utilized this technique for the primary myocardium and fabricated a physiologically active multi‐layered cardiac cell sheet. By applying a micropattern to this polymer film, we have succeeded in making a skeletal muscle cell sheet in which myotubes are oriented in the desired direction. Overall, we showed that this method is useful for cell sheet manipulation, morphogenesis, and transplantation. Biotechnol. Bioeng. 2009;103: 370–377. © 2009 Wiley Periodicals, Inc.     

Isolation, characterization, and mesodermic differentiation of stem cells from adipose tissue of camel (Camelus dromedarius)

Adipose-derived stem cells are an attractive alternative as a source of stem cells that can easily be extracted from adipose tissue. Isolation, characterization, and multi-lineage differentiation of adipose-derived stem cells have been described for human and a number of other species. Here we aimed to isolate and characterize camel adipose-derived stromal cell frequency and growth characteristics and assess their adipogenic, osteogenic, and chondrogenic differentiation potential. Samples were obtained from five adult dromedary camels. Fat from abdominal deposits were obtained from each camel and adipose-derived stem cells were isolated by enzymatic digestion as previously reported elsewhere for adipose tissue. Cultures were kept until confluency and subsequently were subjected to differentiation protocols to evaluate adipogenic, osteogenic, and chondrogenic potential. The morphology of resultant camel adipose-derived stem cells appeared to be spindle-shaped fibroblastic morphology, and these cells retained their biological properties during in vitro expansion with no sign of abnormality in karyotype. Under inductive conditions, primary adipose-derived stem cells maintained their lineage differentiation potential into adipogenic, osteogenic, and chondrogenic lineages during subsequent passages. Our observation showed that like human lipoaspirate, camel adipose tissue also contain multi-potent cells and may represent an important stem cell source both for veterinary cell therapy and preclinical studies as well.     

Comparison of two methods for determining human adipose cell size

The mean cell sizes of specimens of human adipose tissue were determined on sectioned slices according to the method described by Sj?str?m et al. (J. Lipid Res. 1971. 12: 521-530) and on adipocytes isolated after treatment of the tissue with collagenase. The average mean cell sizes from 11 biopsy specimens were 94.4 and 94.0 micro m, respectively (r = 0.964; P(t(b)) < 0.001; y = 0.90x + 9.74), for the two methods. There was no indication of an increased rupture of isolated large human adipose cells. Thus, with precautions (freshly siliconized glassware and omitting the centrifugation of the isolated cells), the collagenase method may be used for metabolic as well as morphologic studies of human adipose tissue.     

Morphologic and functional study of a human insulin-secreting cell line

Monolayer cell cultures were obtained from a human insulinoma (HIN) after collagenase digestion. HIN cells were initially plated on extracellular matrix (ECM) secreted by bovine corneal endothelial cells. Capsular integrity from cell clusters quickly interrupted and cell began to migrate as adhesive sheets onto ECM. After 2 months on ECM cell attachment and proliferation occurred on plastic allowing cloning of cells by limiting dilution. 9 clones were successfully cultured for 7 months with 20 subsequent passages. Immunoreactivity for insulin by indirect immunofluorescence typical secretory granules by electron microscopy and stable amounts of immunoreactive insulin in culture media suggest that HIN cells are beta cell related. One clone HIN D8 when challenged for half an hour with either 30 mM glucose, 1 mM isobutyl Methylxanthine 4 mM Tolbutamide, 10(-6) M glucagon responded respectively with a 1.5, 2, 3 and 1.5 fold increase in insulin output. Population doubling time of HIN D8 was 42 hrs. Establishment of such insulin secreting cell lines provides a valuable tool for diabetes research.     

Effects of GSK3 inhibitors on in vitro expansion and differentiation of human adipose-derived stem cells into adipocytes

Background  

Multipotent stem cells exist within adipose tissue throughout life. An abnormal recruitment of these adipose precursor cells could participate to hyperplasia of adipose tissue observed in severe obesity or to hypoplasia of adipose tissue observed in lipodystrophy. Therefore, pharmacological molecules that control the pool of stem cells in adipose tissue are of great interest. Glycogen Synthase Kinase (GSK) 3 has been previously described as involved in differentiation of preadipose cells and might be a potential therapeutic target to modulate proliferation and differentiation of adipocyte precursors. However, the impact of GSK3 inhibition on human adipose-derived stem cells remained to be investigated. The aim of this study was to investigate GSK3 as a possible target for pharmacological inhibition of stem cell adipogenesis. To reach this goal, we studied the effects of pharmacological inhibitors of GSK3, i.e. lithium chloride (LiCl) and BIO on proliferation and adipocyte differentiation of multipotent stem cells derived from human adipose tissue.     

Engineering a bilayered hydrogel to control ASC differentiation

Natural polymers over the years have gained more importance because of their host biocompatibility and ability to interact with cells in vitro and in vivo. An area of research that holds promise in regenerative medicine is the combinatorial use of novel biomaterials and stem cells. A fundamental strategy in the field of tissue engineering is the use of three-dimensional scaffold (e.g., decellularized extracellular matrix, hydrogels, micro/nano particles) for directing cell function. This technology has evolved from the discovery that cells need a substrate upon which they can adhere, proliferate, and express their differentiated cellular phenotype and function. More recently, it has also been determined that cells not only use these substrates for adherence, but also interact and take cues from the matrix substrate (e.g., extracellular matrix, ECM). Therefore, the cells and scaffolds have a reciprocal connection that serves to control tissue development, organization, and ultimate function. Adipose-derived stem cells (ASCs) are mesenchymal, non-hematopoetic stem cells present in adipose tissue that can exhibit multi-lineage differentiation and serve as a readily available source of cells (i.e. pre-vascular endothelia and pericytes). Our hypothesis is that adipose-derived stem cells can be directed toward differing phenotypes simultaneously by simply co-culturing them in bilayered matrices. Our laboratory is focused on dermal wound healing. To this end, we created a single composite matrix from the natural biomaterials, fibrin, collagen, and chitosan that can mimic the characteristics and functions of a dermal-specific wound healing ECM environment.     

Characterization and assessment of hyperelastic and elastic properties of decellularized human adipose tissues

Decellularized adipose tissue (DAT) has shown potential as a regenerative scaffold for plastic and reconstructive surgery to augment or replace damaged or missing adipose tissue (e.g. following lumpectomy or mastectomy). The mechanical properties of soft tissue substitutes are of paramount importance in restoring the natural shape and appearance of the affected tissues, and mechanical mismatching can lead to unpredictable scar tissue formation and poor implant integration. The goal of this work was to assess the linear elastic and hyperelastic properties of decellularized human adipose tissue and compare them to those of normal breast adipose tissue. To assess the influence of the adipose depot source on the mechanical properties of the resultant decellularized scaffolds, we performed indentation tests on DAT samples sourced from adipose tissue isolated from the breast, subcutaneous abdominal region, omentum, pericardial depot and thymic remnant, and their corresponding force–displacement data were acquired. Elastic and hyperelastic parameters were estimated using inverse finite element algorithms. Subsequently, a simulation was conducted in which the estimated hyperelastic parameters were tested in a real human breast model under gravity loading in order to assess the suitability of the scaffolds for implantation. Results of these tests showed that in the human breast, the DAT would show similar deformability to that of native normal tissue. Using the measured hyperelastic parameters, we were able to assess whether DAT derived from different depots exhibited different intrinsic nonlinearities. Results showed that DAT sourced from varying regions of the body exhibited little intrinsic nonlinearity, with no statistically significant differences between the groups.     

Effect of cell size on lipid synthesis by human adipose tissue in vitro

When adipose tissue cells were incubated with collagenase for different periods of time, cell populations with different mean cell sizes were obtained from the same tissue sample. Lipid synthesis from glucose was studied as a function of adipose cell size and number. The incubations were performed in Parker medium 199, which is suitable for tissue culture of human adipose tissue. The results show that the larger cells of a specimen have a greater rate of lipid synthesis than the smaller cells of the same specimen. This is mainly due to an increase in the synthesis of glyceride-glycerol. Addition of insulin stimulated lipid synthesis. However, the larger adipose cells were less sensitive to the stimulating effect of insulin than the smaller cells.     

Stacked stem cell sheets enhance cell-matrix interactions

Cell sheet engineering has enabled the production of confluent cell sheets stacked together for use as a cardiac patch to increase cell survival rate and engraftment after transplantation, thereby providing a promising strategy for high density stem cell delivery for cardiac repair. One key challenge in using cell sheet technology is the difficulty of cell sheet handling due to its weak mechanical properties. A single-layer cell sheet is generally very fragile and tends to break or clump during harvest. Effective transfer and stacking methods are needed to move cell sheet technology into widespread clinical applications. In this study, we developed a simple and effective micropipette based method to aid cell sheet transfer and stacking. The cell viability after transfer was tested and multi-layer stem cell sheets were fabricated using the developed method. Furthermore, we examined the interactions between stacked stem cell sheets and fibrin matrix. Our results have shown that the preserved ECM associated with the detached cell sheet greatly facilitates its adherence to fibrin matrix and enhances the cell sheet-matrix interactions. Accelerated fibrin degradation caused by attached cell sheets was also observed.     

Engineering cartilage tissues with the shape of human nasal alar by using chondrocyte macroaggregate--Experiment study in rabbit model

Despite of progresses in tissue engineering based on cell/scaffold strategy, uneven cell distribution as well as tissue formation in the scaffold, limited cell seeding efficiency and inflammatory reaction triggered by the degradation of scaffold remain problems to be resolved. In this study, we proposed a novel cell-macroaggregate cultivation system, and explored a feasible strategy to construct three-dimensional cartilage tissue with shape of human nasal alar by using cell macroaggregate. Isolated chondrocytes was cultured at high density to form a monolayer chondrocyte sheet as well as expanded for seeding on the sheet to produce mechanically operable cell macroaggregate. Chondrocyte macroaggregates were then fabricated into transplants with shape of nasal alar by using Internal support or External scaffold techniques; results of in vivo chondrogenesis were investigated in immunocompetent animal. Chondrocyte macroaggregates presented long survival time and good viability; constructs fabricated using both techniques can develop into tissues with characteristic structure of native cartilage, glycosaminoglycans as well as type II collagen were highly produced in the ECM of engineered cartilages. By placing hyaluronan ester film as Internal support, the predetermined shape of the chondrocyte macroaggregate can be well maintained. In contrast, due to the poor mechanical stability of grafts fabricated in External scaffold group, obvious deformation occurred in harvested specimens. The experiment proved the usefulness of chondrocyte macroaggregate in cartilage regeneration, and provided a new strategy to engineer cartilage with special shape by using cell macroaggregate/biodegradable support.