Serially Transplanted Nonpericytic CD146(-) Adipose Stromal/Stem Cells in Silk Bioscaffolds Regenerate Adipose Tissue In Vivo

Development of a new biomaterial based on cashew tree gum (Anarcadium occidentale L.) enriched with hydroxyapatite and evaluation of cytotoxicity in adipose-derived stem cell cultures

Cashew tree gum is a polysaccharide material highly available in the Northeast region of Brazil. It has been explored for biocompatibility with human tissues. This research aimed to describe the synthesis and characterization of cashew gum/hydroxyapatite scaffold and evaluate the possible cytotoxicity in murine adipo-derived stem cells (ADSCs) cultures. ADSCs of the subcutaneous fat tissue of Wistar rats were collected, isolated, expanded, differentiated into three strains, and characterized immunophenotypically. The scaffolds were synthesized through chemical precipitation, lyophilized and characterized through scanning electron microscopy (SEM), infrared spectroscopy (FTIR), X-ray diffraction (XRD), thermal analysis (TG and DTG), and mechanical testing. The scaffold presented a crystalline structure and pores with an average diameter of 94.45 ± 50.57 μm. By mechanical tests, the compressive force and modulus of elasticity were like the cancellous bone. The isolated adipose-derived stem cells (ADSCs) presented fibroblast morphology, adhesion capacity to plastic, differentiation in osteogenic, adipogenic and chondrogenic lineages, positive expression for the CD105 and CD90 markers and negative expression for the CD45 and CD14 markers. The MTT test showed increased cell viability, and the biomaterial showed a high level of hemocompatibility (<5 %). This study allowed the development of a new scaffold for future surgical applicability in tissue regeneration.

Dipeptidyl peptidase-4 cell surface expression marks an abundant adipose stem/progenitor cell population with high stemness in human white adipose tissue

The capacity of adipose stem/progenitor cells (ASCs) to undergo self-renewal and differentiation is crucial for adipose tissue homoeostasis, regeneration and expansion. However, the heterogeneous ASC populations of the adipose lineage constituting adipose tissue are not precisely known. In the present study, we demonstrate that cell surface expression of dipeptidyl peptidase-4 (DPP4)/cluster of differentiation 26 (CD26) subdivides the DLK1^-/CD34⁺/CD45^-/CD31^- ASC pool of human white adipose tissues (WATs) into two large populations. Ex vivo, DPP4⁺ ASCs possess higher self-renewal and proliferation capacity and lesser adipocyte differentiation potential than DDP4^- ASCs. The knock-down of DPP4 in ASC leads to significantly reduced proliferation and self-renewal capacity, while adipogenic differentiation is increased. Ectopic overexpression of DPP4 strongly inhibits adipogenesis. Moreover, in whole mount stainings of human subcutaneous (s)WAT, we detect DPP4 in CD34⁺ ASC located in the vascular stroma surrounding small blood vessels and in mature adipocytes. We conclude that DPP4 is a functional marker for an abundant ASC population in human WAT with high proliferation and self-renewal potential and low adipogenic differentiation capacity.

CD146 expression regulates osteochondrogenic differentiation of human adipose-derived stem cells

Tissue engineering aims to develop innovative approaches to repair tissue defects. The use of adipose-derived stem cells (ASCs) in tissue regeneration was extensively investigated for osteochondrogenesis. Among the ASC population, ASCs expressing the CD146 were demonstrated to be multipotent and considered as perivascular stem cells, although the functional role of CD146 expression in these cells remains unclear. Herein, we investigated the influence of CD146 expression on osteochondrogenic differentiation of ASCs. Our results showed that, in two-dimensional culture systems, sorted CD146⁺ ASCs proliferated less and displayed higher adipogenic and chondrogenic potential than CD146^- ASCs. The latter demonstrated a higher osteogenic capacity. Besides this, CD146⁺ ASCs in three-dimensional Matrigel/endothelial growth medium (EGM) cultures showed the highest angiogenic capability. When cultured in three-dimensional collagen scaffolds, CD146⁺ ASCs showed a spontaneous chondrogenic differentiation, further enhanced by the EGM medium's addition. Finally, CD146^- ASCs seeded on hexafluoroisopropanol silk scaffolds displayed a greater spontaneous osteogenetic capacity. Altogether, these findings demonstrated a functional and relevant influence of CD146 expression in ASC properties and osteochondrogenic commitment. Exploiting the combination of specific differentiation properties of ASC subpopulations and appropriate culture systems could represent a promising strategy to improve the efficacy of new regenerative therapies.

Applications of flow cytometry sorting in the pharmaceutical industry: A review

The article reviews applications of flow cytometry sorting in manufacturing of pharmaceuticals. Flow cytometry sorting is an extremely powerful tool for monitoring, screening and separating single cells based on any property that can be measured by flow cytometry. Different applications of flow cytometry sorting are classified into groups and discussed in separate sections as follows: (a) isolation of cell types, (b) high throughput screening, (c) cell surface display, (d) droplet fluorescent-activated cell sorting (FACS). Future opportunities are identified including: (a) sorting of particular fractions of the cell population based on a property of interest for generating inoculum that will result in improved outcomes of cell cultures and (b) the use of population balance models in combination with FACS to design and optimize cell cultures.

Quiescence, Stemness and Adipogenic Differentiation Capacity in Human DLK1-/CD34+/CD24+ Adipose Stem/Progenitor Cells

We explore the status of quiescence, stemness and adipogenic differentiation capacity in adipose stem/progenitor cells (ASCs) ex vivo, immediately after isolation from human subcutaneous white adipose tissue, by sorting the stromal vascular fraction into cell-surface DLK1⁺/CD34⁻, DLK1⁺/CD34^dim and DLK1⁻/CD34⁺ cells. We demonstrate that DLK1⁻/CD34⁺ cells, the only population exhibiting proliferative and adipogenic capacity, express ex vivo the bonafide quiescence markers p21^Cip1, p27^Kip1 and p57^Kip2 but neither proliferation markers nor the senescence marker p16^Ink4a. The pluripotency markers NANOG, SOX2 and OCT4 are barely detectable in ex vivo ASCs while the somatic stemness factors, c-MYC and KLF4 and the early adipogenic factor C/EBPβ are highly expressed. Further sorting of ASCs into DLK1⁻/CD34⁺/CD24⁻ and DLK1⁻/CD34⁺/CD24⁺ fractions shows that KLF4 and c-MYC are higher expressed in DLK1⁻/CD34⁺/CD24⁺ cells correlating with higher colony formation capacity and considerably lower adipogenic activity. Proliferation capacity is similar in both populations. Next, we show that ASCs routinely isolated by plastic-adherence are DLK1⁻/CD34⁺/CD24⁺. Intriguingly, CD24 knock-down in these cells reduces proliferation and adipogenesis. In conclusion, DLK1⁻/CD34⁺ ASCs in human sWAT exist in a quiescent state, express high levels of somatic stemness factors and the early adipogenic transcription factor C/EBPβ but senescence and pluripotency markers are barely detectable. Moreover, our data indicate that CD24 is necessary for adequate ASC proliferation and adipogenesis and that stemness is higher and adipogenic capacity lower in DLK1⁻/CD34⁺/CD24⁺ relative to DLK1⁻/CD34⁺/CD24⁻ subpopulations.

Fat-On-A-Chip Models for Research and Discovery in Obesity and Its Metabolic Comorbidities

The obesity epidemic and its associated comorbidities present a looming challenge to health care delivery throughout the world. Obesity is characterized as a sterile inflammatory process within adipose tissues leading to dysregulated secretion of bioactive adipokines such as adiponectin and leptin, as well as systemic metabolic dysfunction. The majority of current obesity research has focused primarily on preclinical animal models in vivo and two-dimensional cell culture models in vitro. Neither of these generalized approaches is optimal due to interspecies variability, insufficient accuracy with respect to predicting human outcomes, and failure to recapitulate the three-dimensional (3D) microenvironment. Consequently, there is a growing demand and need for more sophisticated microphysiological systems to reproduce more physiologically accurate human white and brown/beige adipose depots. To address this research need, human and murine cell lines and primary cultures are being combined with bioscaffolds to create functional 3D environments that are suitable for metabolically active adipose organoids in both static and perfusion bioreactor cultures. The development of these technologies will have considerable impact on the future pace of discovery for novel small molecules and biologics designed to prevent and treat metabolic syndrome and obesity in humans. Furthermore, when these adipose tissue models are integrated with other organ systems they will have applicability to obesity-related disorders such as diabetes, nonalcoholic fatty liver disease, and osteoarthritis. Impact statement The current review article summarizes the advances made within the organ-onchip field, as it pertains to adipose tissue models of obesity and obesity-related syndromes, such as diabetes, non-alcoholic fatty liver disease, and osteoarthritis. As humanized 3D adipose-derived constructs become more accessible to the research community, it is anticipated that they will accelerate and enhance the drug discovery pipeline for obesity, diabetes, and metabolic diseases by reducing the preclinical evaluation process and improving predictive accuracy. Such developments, applications, and usages of existing technologies can change the paradigm of personalized medicine and create substantial progress in our approach to modern medicine.

Characterization and Proteomic Analysis of Decellularized Adipose Tissue Hydrogels Derived from Lean and Overweight/Obese Human Donors

While decellularized adipose tissue (DAT) has potential as an "off-the-shelf" biomaterial product for regenerative medicine, it remains to be determined if donor-source body mass index (BMI) impacts the functionality of DAT. This study set out to comparatively characterize lean versus overweight/obese-donor derived DAT hydrogel based on proteome and to analyze their respective effects on adipose stromal/stem cell (ASC) viability, and differentiation in vitro. Decellularized adipose tissue from lean (lDAT) and overweight/obese (oDAT) donors is produced and characterized. Variability in the fibril microstructures is found, with dense fibrotic fiber clusters and large pore area uniquely present in the oDAT samples. Proteomic analysis reveals that lDAT contains a greater proportion of enriched extracellular proteins and a smaller proportion of enriched intracellular proteins relative to oDAT. Biocompatibility studies show that ASCs cultured in lDAT and oDAT hydrogels remain viable. The adipogenic and osteogenic differentiation capability of ASCs seeded in lDAT and oDAT hydrogels is confirmed by an upregulation in marker gene expression and phenotypic analysis. In conclusion, this study establishes that DAT hydrogels derived from lean and overweight/obese adipose donors present similar physicochemical profiles with some distinctive features while comparably supporting the viability and adipogenic differentiation of ASCs in vitro.

Biomaterials for breast reconstruction: Promises, advances, and challenges

Breast reconstruction is the opportunity that provides the chance of having breast after undergoing surgical removal of the breast tissue due to cancer-related surgery. However, this varies on the stage of the cancer diagnosis and the procedure undertaken. There are many regenerative medicine methods that provide several initiatives and direct solutions to problems such as the development of "bioactive tissue," which can regenerate adipose tissues with similar normal functions and structures. There have been several studies which have previously explored for the improvement of breast reconstruction including different variations of biomaterials, different fabrication and processing techniques, cells as well as growth factors which enable bioengineers and tissue engineers to reconstruct a suitable breast for patients with breast cancer. Many factors such as shape, proper volume, mechanical properties have been studies but very scattered with not adequate solution for existing patients worldwide. This review article aims to cover recent advances in the biomaterials, which can be used for reconstruction of breasts as well as looking at the various factors that might lead to individuals needing reconstruction and the materials that are available. The focus would be to look at the various biomaterials that are available to use for reconstruction, their properties, and their structural integrity.

Fat Graft Enrichment Strategies: A Systematic Review

BACKGROUND

Autologous fat grafting is a dynamic modality used in plastic surgery as an adjunct to improve functional and aesthetic form. However, current practices in fat grafting for soft-tissue augmentation are plagued by tremendous variability in long-term graft retention, resulting in suboptimal outcomes and repetitive procedures. This systematic review identifies and critically appraises the evidence for various enrichment strategies that can be used to augment and improve the viability of fat grafts.

METHODS

A comprehensive literature search of the Medline and PubMed databases was conducted for animal and human studies published through October of 2017 with multiple search terms related to adipose graft enrichment agents encompassing growth factors, platelet-rich plasma, adipose-derived and bone marrow stem cells, gene therapy, tissue engineering, and other strategies. Data on level of evidence, techniques, complications, and outcomes were collected.

RESULTS

A total of 1382 articles were identified, of which 147 met inclusion criteria. The majority of enrichment strategies demonstrated positive benefit for fat graft survival, particularly with growth factors and adipose-derived stem cell enrichment. Platelet-rich plasma and adipose-derived stem cells had the strongest evidence to support efficacy in human studies and may demonstrate a dose-dependent effect.

CONCLUSIONS

Improved understanding of enrichment strategies contributing to fat graft survival can help to optimize safety and outcomes. Controlled clinical studies are lacking, and future studies should examine factors influencing graft survival through controlled clinical trials in order to establish safety and to obtain consistent outcomes.

Human Adipose Derived Cells in Two- and Three-Dimensional Cultures: Functional Validation of an In Vitro Fat Construct

Obesity, defined as a body mass index of 30 kg/m² or above, has increased considerably in incidence and frequency within the United States and globally. Associated comorbidities including cardiovascular disease, type 2 diabetes mellitus, metabolic syndrome, and nonalcoholic fatty liver disease have led to a focus on the mechanisms promoting the prevention and treatment of obesity. Commonly utilized in vitro models employ human or mouse preadipocyte cell lines in a 2-dimensional (2D) format. Due to the structural, biochemical, and biological limitations of these models, increased attention has been placed on "organ on a chip" technologies for a 3-dimensional (3D) culture. Herein, we describe a method employing cryopreserved primary human stromal vascular fraction (SVF) cells and a human blood product-derived biological scaffold to create a 3D adipose depot in vitro. The "fat-on-chip" 3D cultures have been validated relative to 2D cultures based on proliferation, flow cytometry, adipogenic differentiation, confocal microscopy/immunofluorescence, and functional assays (adipokine secretion, glucose uptake, and lipolysis). Thus, the in vitro culture system demonstrates the critical characteristics required for a humanized 3D white adipose tissue (WAT) model.

Human Adipose-Derived Hydrogel Characterization Based on In Vitro ASC Biocompatibility and Differentiation

Hydrogels serve as three-dimensional scaffolds whose composition can be customized to allow attachment and proliferation of several different cell types. Extracellular matrix-derived hydrogels are considered close replicates of the tissue microenvironment. They can serve as scaffolds for in vitro tissue engineering and are a useful tool to study cell-scaffold interaction. The aim of the present study was to analyze the effect of adipose-derived stromal/stem cells (ASCs) and decellularized adipose tissue-derived (DAT) hydrogel interaction on ASC morphology, proliferation, differentiation, and DAT hydrogel microstructure. First, the ASCs were characterized using flow cytometry, adipogenic/osteogenic differentiation, colony-forming unit fibroblast assay and doubling time. The viability and proliferation assays showed that ASCs seeded in DAT hydrogel at different concentrations and cultured for 21 days remained viable and displayed proliferation. ASCs were seeded on DAT hydrogel and cultured in stromal, adipogenic, or osteogenic media for 14 or 28 days. The analysis of adipogenic differentiation demonstrated the upregulation of adipogenic marker genes and accumulation of oil droplets in the cells. Osteogenic differentiation demonstrated the upregulation of osteogenic marker genes and mineral deposition in the DAT hydrogel. The analysis of DAT hydrogel fiber metrics revealed that ASC seeding, and differentiation altered both the diameter and arrangement of fibers in the matrix. Matrix metalloproteinase-2 (MMP-2) activity was assessed to determine the possible mechanism for DAT hydrogel remodeling. MMP-2 activity was observed in all ASC seeded samples, with the osteogenic samples displaying the highest MMP-2 activity. These findings indicate that DAT hydrogel is a cytocompatible scaffold that supports the adipogenic and osteogenic differentiation of ASCs. Furthermore, the attachment of ASCs and differentiation along adipogenic and osteogenic lineages remodels the microstructure of DAT hydrogel.

Comparative proteomic analyses of human adipose extracellular matrices decellularized using alternative procedures

Decellularized human adipose tissue has potential clinical utility as a processed biological scaffold for soft tissue cosmesis, grafting, and reconstruction. Adipose tissue decellularization has been accomplished using enzymatic-, detergent-, and/or solvent-based methods. To examine the hypothesis that distinct decellularization processes may yield scaffolds with differing compositions, the current study employed mass spectrometry to compare the proteomes of human adipose-derived matrices generated through three independent methods combining enzymatic-, detergent-, and/or solvent-based steps. In addition to protein content, bioscaffolds were evaluated for deoxyribose nucleic acid depletion, extracellular matrix composition, and physical structure using optical density, histochemical staining, and scanning electron microscopy. Mass spectrometry based proteomic analyses identified 25 proteins (having at least two peptide sequences detected) in the scaffolds generated with an enzymatic approach, 143 with the detergent approach, and 102 with the solvent approach, as compared to 155 detected in unprocessed native human fat. Immunohistochemical detection confirmed the presence of the structural proteins actin, collagen type VI, fibrillin, laminin, and vimentin. Subsequent in vivo analysis of the predominantly enzymatic- and detergent-based decellularized scaffolds following subcutaneous implantation in GFP⁺ transgenic mice demonstrated that the matrices generated with both approaches supported the ingrowth of host-derived adipocyte progenitors and vasculature in a time dependent manner. Together, these results determine that decellularization methods influence the protein composition of adipose tissue-derived bioscaffolds. © 2018 Wiley Periodicals, Inc. J Biomed Mater Res Part A: 106A:2481-2493, 2018.

A Novel, Sterilized Microvascular Tissue Product Improves Healing in a Murine Pressure Ulcer Model

Background:

Processed microvascular tissue (PMVT), a human structural allograft, is derived from lyophilized human tissue containing microcirculatory cellular components. Since PMVT serves as a source of extracellular matrix (ECM), growth factors, cytokines, and chemokines modulating angiogenesis, inflammation, apoptosis, and endogenous cell recruitment, we hypothesized its application would accelerate wound regeneration in a validated pressure ulcer (PU) model developed in C57BL/6 mice using two 24-hour cycles of skin ischemia/reperfusion created by placement and removal of external magnets.

Methods:

Two identical PU injuries (n = 50 female mice) were treated with (a) topical particulate PMVT, (b) injected rehydrated PMVT, or (c) saline control injection, and assessed daily for closure rates, scab formation/removal, and temperature. A baseline control cohort (n = 5) was euthanized at day 0 and treatment group cohorts (n = 5) were killed at 3, 7, or 14 days postinjury. The PU injuries were collagenase-digested for flow cytometric analysis of inflammatory, reparative, and stem cell frequencies and analyzed by hematoxylin and eosin (H&E) histology and immunofluorescence.

Results:

PMVT-accelerated wound closure, most notably, topical PMVT significantly increased mean closure from d5 (13% versus -9%) through d13 (92% versus 38%) compared with phosphate-buffered saline (PBS) controls (P < 0.05). PMVT also hastened scab formation/removal, significantly accelerated disappearance of inflammatory myeloid (CD11b+) cells while upregulating α-smooth muscle actin, vascular endothelial growth factor A, and placental growth factor and raised skin temperature surrounding the PU site, consistent with increased blood flow.

Conclusions:

These results indicate that PMVT has potential as an advanced treatment for restoring normal tissue function in ischemic wounds and merits clinical study.

Bone Marrow Adipocyte Developmental Origin and Biology

PURPOSE OF REVIEW

This review explores how the relationships between bone marrow adipose tissue (BMAT) adipogenesis with advancing age, obesity, and/or bone diseases (osteopenia or osteoporosis) contribute to mechanisms underlying musculoskeletal pathophysiology.

RECENT FINDINGS

Recent studies have re-defined adipose tissue as a dynamic, vital organ with functions extending beyond its historic identity restricted solely to that of an energy reservoir or sink. "State of the art" methodologies provide novel insights into the developmental origin, physiology, and function of different adipose tissue depots. These include genetic tracking of adipose progenitors, viral vectors application, and sophisticated non-invasive imaging modalities. While constricted within the rigid bone cavity, BMAT vigorously contributes to local and systemic metabolic processes including hematopoiesis, osteogenesis, and energy metabolism and undergoes dynamic changes as a function of age, diet, bone topography, or sex. These insights will impact future research and therapies relating to osteoporosis.

Adipose-Derived Stem Cells in Novel Approaches to Breast Reconstruction: Their Suitability for Tissue Engineering and Oncological Safety

Adipose-derived stem cells (ADSCs) are rapidly becoming the gold standard cell source for tissue engineering strategies and hold great potential for novel breast reconstruction strategies. However, their use in patients with breast cancer is controversial and their oncological safety, particularly in relation to local disease recurrence, has been questioned. In vitro, in vivo, and clinical studies using ADSCs report conflicting data on their suitability for adipose tissue regeneration in patients with cancer. This review aims to provide an overview of the potential role for ADSCs in breast reconstruction and to examine the evidence relating to the oncologic safety of their use in patients with breast cancer.

Adipose tissue-derived stromal vascular fraction in regenerative medicine: a brief review on biology and translation

Adipose/fat tissue provides an abundant source of stromal vascular fraction (SVF) cells for immediate administration and can also give rise to a substantial number of cultured, multipotent adipose-derived stromal cells (ADSCs). Recently, both SVF and ADSCs have gained wide-ranging translational significance in regenerative medicine. Initially used for cosmetic breast enhancement, this mode of treatment has found use in many diseases involving immune disorders, tissue degeneration, and ischaemic conditions. In this review, we try to address several important aspects of this field, outlining the biology, technology, translation, and challenges related to SVF- and ADSC-based therapies. Starting from the basics of SVF and ADSC isolation, we touch upon recently developed technologies, addressing elements of novel methods and devices under development for point-of-care isolation of SVF. Characterisation of SVF cells and ADSCs is also an evolving area and we look into unusual expression of CD34 antigen as an interesting marker for such purposes. Based on reports involving different cells of the SVF, we draw a potential mode of action, focussing on angiogenesis since it involves multiple cells, unlike immunomodulation which is governed predominantly by ADSCs. We have looked into the latest research, experimental therapies, and clinical trials which are utilising SVF/ADSCs in conditions such as multiple sclerosis, Crohn’s disease, peripheral neuropathy, osteoarthritis, diabetic foot ulcer, and so forth. However, problems have arisen with regards to the lack of proper regulatory guidelines for such therapies and, since the introduction of US Food and Drug Administration draft guidelines and the Reliable and Effective Growth for Regenerative Health Options that Improve Wellness (REGROW) Act, the debate became more public with regards to safe and efficacious use of these cells.

CD146 (MCAM) in human cs-DLK1-/cs-CD34+ adipose stromal/progenitor cells

To precisely characterize CD146 in adipose stromal/progenitor cells (ASCs) we sorted the stromal vascular faction (SVF) of human abdominal subcutaneous white adipose tissue (sWAT) according to cell surface (cs) expression of CD146, DLK1 and CD34. This test identified three main SVF cell populations: ~50% cs-DLK1^-/cs-CD34⁺/cs-CD146^- ASCs, ~7.5% cs-DLK1⁺/cs-CD34^dim/+/cs-CD146⁺ and ~7.5% cs-DLK1⁺/cs-CD34^dim/+/cs-CD146^- cells. All cells contained intracellular CD146. Whole mount fluorescent IHC staining of small vessels detected CD146⁺ endothelial cells (CD31⁺/CD34⁺/CD146⁺) and pericytes (CD31^-/CD34^-/CD146⁺ ASCs). The cells in the outer adventitial layer showed the typical ASC morphology, were strongly CD34⁺ and contained low amounts of intracellular CD146 protein (CD31^-/CD34⁺/CD146⁺). Additionally, we detected wavy CD34^-/CD146⁺ and CD34^dim/CD146⁺ cells. CD34^dim/CD146⁺ cells were slightly more bulky than CD34^-/CD146⁺ cells. Both CD34^-/CD146⁺ and CD34^dim/CD146⁺ cells were detached from the inner pericyte layer and protruded into the outer adventitial layer. Cultured early passage ASCs contained low levels of CD146 mRNA, which was expressed in two different splicing variants, at a relatively high amount of the CD146-long form and at a relatively low amount of the CD146-short form. ASCs contained low levels of CD146 protein, which consisted predominantly long form and a small amount of short form. The CD146 protein was highly stable, and the majority of the protein was localized in the Golgi apparatus. In conclusion, the present study contributes to a better understanding of the spatial localization of CD34⁺/CD146⁺ and CD34^-/CD146⁺ cells in the adipose niche of sWAT and identifies CD146 as intracellular protein in cs-DLK1^-/cs-CD34⁺/cs-CD146^- ASCs.

Development of a Three-Dimensional Adipose Tissue Model for Studying Embryonic Exposures to Obesogenic Chemicals

Obesity is a rising issue especially in the United States that can lead to heart problems, type II diabetes, and respiratory problems. Since the 1970s, obesity rates in the United States have more than doubled in adults and children. Recent evidence suggests that exposure to certain chemicals, termed "obesogens," in utero may alter metabolic processes, predisposing individuals to weight gain. There is a need to develop a three-dimensional human tissue system that is able to model the effects of obesogens in vitro in order to better understand the impact of obesogens on early development. Human embryonic-derived stem cells in three-dimensional collagen embedded silk scaffolds were exposed to three different obesogens: Bisphenol A (BPA), Bisphenol S (BPS), and Tributyltin (TBT). The exposed tissues accumulated triglycerides and increased expression of adipogenic genes (Perilipin (PLIN1), peroxisome proliferator-activated receptor gamma (PPARy), fatty acid binding protein 4 (FABP4)) compared to equivalent control cultures with no obesogen exposure. These cultures were also compared to human adult stem cell cultures, which did not respond the same upon addition of obesogens. These results demonstrate the successful development of a representative tissue model of in utero obesogen exposures. This tissue system could be used to determine mechanisms of action of current obesogens and to screen other potential obesogens.

The gene expression profile of non-cultured, highly purified human adipose tissue pericytes: Transcriptomic evidence that pericytes are stem cells in human adipose tissue

Pericytes (PCs) are a subset of perivascular cells that can give rise to mesenchymal stromal cells (MSCs) when culture-expanded, and are postulated to give rise to MSC-like cells during tissue repair in vivo. PCs have been suggested to behave as stem cells (SCs) in situ in animal models, although evidence for this role in humans is lacking. Here, we analyzed the transcriptomes of highly purified, non-cultured adipose tissue (AT)-derived PCs (ATPCs) to detect gene expression changes that occur as they acquire MSC characteristics in vitro, and evaluated the hypothesis that human ATPCs exhibit a gene expression profile compatible with an AT SC phenotype. The results showed ATPCs are non-proliferative and express genes characteristic not only of PCs, but also of AT stem/progenitor cells. Additional analyses defined a gene expression signature for ATPCs, and revealed putative novel ATPC markers. Almost all AT stem/progenitor cell genes differentially expressed by ATPCs were not expressed by ATMSCs or culture-expanded ATPCs. Genes expressed by ATMSCs but not by ATPCs were also identified. These findings strengthen the hypothesis that PCs are SCs in vascularized tissues, highlight gene expression changes they undergo as they assume an MSC phenotype, and provide new insights into PC biology.

The Use of Silk as a Scaffold for Mature, Sustainable Unilocular Adipose 3D Tissue Engineered Systems

There is a critical need for monitoring physiologically relevant, sustainable, human adipose tissues in vitro to gain new insights into metabolic diseases. To support long-term culture, a 3D silk scaffold assisted culture system is developed that maintains mature unilocular adipocytes ex vivo in coculture with preadipocytes, endothelial cells, and smooth muscle cells obtained from small volumes of liquefied adipose samples. Without the silk scaffold, adipose tissue explants cannot be sustained in long-term culture (3 months) due to their fragility. Adjustments to media components are used to tune lipid metabolism and proliferation, in addition to responsiveness to an inflammatory stimulus. Interestingly, patient specific responses to TNFα stimulation are observed, providing a proof-of-concept translational technique for patient specific disease modeling in the future. In summary, this novel 3D scaffold assisted approach is required for establishing physiologically relevant, sustainable, human adipose tissue systems from small volumes of lipoaspirate, making this methodology of great value to studies of metabolism, adipokine-driven diseases, and other diseases where the roles of adipocytes are only now becoming uncovered.