Lipolytic function of adipocyte/endothelial cocultures

3D bioprinted white adipose model for in vitro study of cancer-associated cachexia induced adipose tissue remodeling

Cancer-associated cachexia (CAC) is a complex metabolic and behavioral syndrome with multiple manifestations that involve systemic inflammation, weight loss, and adipose lipolysis. It impacts the quality of life of patients and is the direct cause of death in 20-30% of cancer patients. The severity of fat loss and adipose tissue remodeling negatively correlate with patients' survival outcomes. To address the mechanism of fat loss and design potential approaches to prevent the process, it will be essential to understand CAC pathophysiology through white adipose tissue models. In the present study, an engineered human white adipose tissue (eWAT) model based on three-dimensional (3D) bioprinting was developed and treated with pancreatic cancer cell-conditioned medium (CM) to mimic the status of CAC in vitro. We found that the CM treatment significantly increased the lipolysis and accumulation of the extracellular matrix (ECM). The 3D eWATs were further vascularized to study the influence of vascularization on lipolysis and CAC progression, which was largely unknown. Results demonstrated that CM treatment improved the angiogenesis of vascularized eWATs (veWATs), and veWATs demonstrated decreased glycerol release but increased Ucp1 expression, compared to eWATs. Many unique inflammatory cytokines (IL-8, CXCL-1, GM-CSF, etc) from the CM were detected and supposed to contribute to eWAT lipolysis, Ucp1 up-regulation, and ECM development. In response to CM treatment, eWATs also secreted inflammatory adipokines related to the metastatic ability of cancer, muscle atrophy, and vascularization (NGAL, CD54, IGFBP-2, etc). Our work demonstrated that the eWAT is a robust model for studying cachectic fat loss and the accompanying remodeling of adipose tissue. It is therefore a useful tool for future research exploring CAC physiologies and developing potential therapies.

Adipose-derived cells: building blocks of three-dimensional microphysiological systems

Microphysiological systems (MPS) created with human-derived cells and biomaterial scaffolds offer a potential in vitro alternative to in vivo animal models. The adoption of three-dimensional MPS models has economic, ethical, regulatory, and scientific implications for the fields of regenerative medicine, metabolism/obesity, oncology, and pharmaceutical drug discovery. Key opinion leaders acknowledge that MPS tools are uniquely positioned to aid in the objective to reduce, refine, and eventually replace animal experimentation while improving the accuracy of the finding's clinical translation. Adipose tissue has proven to be an accessible and available source of human-derived stromal vascular fraction (SVF) cells, a heterogeneous population available at point of care, and adipose-derived stromal/stem cells, a relatively homogeneous population requiring plastic adherence and culture expansion of the SVF cells. The adipose-derived stromal/stem cells or SVF cells, in combination with human tissue or synthetic biomaterial scaffolds, can be maintained for extended culture periods as three-dimensional MPS models under angiogenic, stromal, adipogenic, or osteogenic conditions. This review highlights recent literature relating to the versatile use of adipose-derived cells as fundamental components of three-dimensional MPS models for discovery research and development. In this context, it compares the merits and limitations of the adipose-derived stromal/stem cells relative to SVF cell models and considers the likely directions that this emerging field of scientific discovery will take in the near future.

Mechanical Memory Impairs Adipose-Derived Stem Cell (ASC) Adipogenic Capacity After Long-Term In Vitro Expansion

Introduction

Adipose derived stem cells (ASCs) hold great promise for clinical applications such as soft tissue regeneration and for in vitro tissue models and are notably easy to derive in large numbers. Specifically, ASCs provide an advantage for in vitro models of adipose tissue, where they can be employed as tissue specific cells and for patient specific models. However, ASC in vitro expansion may unintentionally reduce adipogenic capacity due to the stiffness of tissue culture plastic (TCPS).

Methods

Here, we expanded freshly isolated ASCs on soft and stiff substrates for 4 passages before adipogenic differentiation. At the last passage we swapped the substrate from stiff to soft, or soft to stiff to determine if short term exposure to a different substrate altered adipogenic capacity.

Results

Expansion on stiff substrates reduced adipogenic capacity by 50% which was not rescued by swapping to a soft substrate for the last passage. Stiff substrates had greater nuclear area and gene expression of nesprin-2, a protein that mediates the tension of the nuclear envelope by tethering it to the actin cytoskeleton. Upon swapping to a soft substrate, the nuclear area was reduced but nesprin-2 levels did not fully recover, which differentially regulated cell commitment transcriptional factors.

Conclusion

Therefore, in vitro expansion on stiff substrates must be carefully considered when the end-goal of the expansion is for adipose tissue or soft tissue applications.

Hypoxia induces stress fiber formation in adipocytes in the early stage of obesity

In obese adipose tissue (AT), hypertrophic expansion of adipocytes is not matched by new vessel formation, leading to AT hypoxia. As a result, hypoxia inducible factor-1⍺ (HIF-1⍺) accumulates in adipocytes inducing a transcriptional program that upregulates profibrotic genes and biosynthetic enzymes such as lysyl oxidase (LOX) synthesis. This excess synthesis and crosslinking of extracellular matrix (ECM) components cause AT fibrosis. Although fibrosis is a hallmark of obese AT, the role of fibroblasts, cells known to regulate fibrosis in other fibrosis-prone tissues, is not well studied. Here we have developed an in vitro model of AT to study adipocyte-fibroblast crosstalk in a hypoxic environment. Further, this in vitro model was used to investigate the effect of hypoxia on adipocyte mechanical properties via ras homolog gene family member A (RhoA)/Rho-associated coiled-coil kinases (ROCK) signaling pathways. We confirmed that hypoxia creates a diseased phenotype by inhibiting adipocyte maturation and inducing actin stress fiber formation facilitated by myocardin-related transcription factor A (MRTF-A/MKL1) nuclear translocation. This work presents new potential therapeutic targets for obesity by improving adipocyte maturation and limiting mechanical stress in obese AT.

Endothelial cell crosstalk improves browning but hinders white adipocyte maturation in 3D engineered adipose tissue

Central to the development of adipose tissue (AT) engineered models is the supporting vasculature. It is a key part of AT function and long-term maintenance, but the crosstalk between adipocytes and endothelial cells is not well understood. Here, we directly co-culture the two cell types at varying ratios in a 3D Type I collagen gel. Constructs were evaluated for adipocyte maturation and function and vascular network organization. Further, these constructs were treated with forskolin, a beta-adrenergic agonist, to stimulate lipolysis and browning. Adipocytes in co-cultures were found to be less mature than an adipocyte-only control, shown by smaller lipid droplets and downregulation of key adipocyte-related genes. The most extensive vascular network formation was found in the 1:1 co-culture, supported by vascular endothelial growth factor (VEGF) upregulation. After forskolin treatment, the presence of endothelial cells was shown to upregulate PPAR coactivator 1 alpha (PGC-1α) and leptin, but not uncoupling protein 1 (UCP1), suggesting a specific crosstalk that enhances early stages of browning.

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.

Engineering of microscale vascularized fat that responds to perfusion with lipoactive hormones

Current methods to treat large soft-tissue defects mainly rely on autologous transfer of adipocutaneous flaps, a method that is often limited by donor site availability. Engineered vascularized adipose tissues can potentially be a viable and readily accessible substitute to autologous flaps. In this study, we engineered a small-scale adipose tissue with pre-patterned vasculature that enables immediate perfusion. Vessels formed after one day of perfusion and displayed barrier function after three days of perfusion. Under constant perfusion, adipose tissues remained viable and responded to lipoactive hormones insulin and epinephrine with lipid accumulation and loss, respectively. Adipocyte growth correlated inversely with distance away from the feeding vessel, as predicted by a Krogh-type model.

Short-term post-implantation dynamics of in vitro engineered human microvascularized adipose tissues

Engineered adipose tissues are developed for their use as substitutes for tissue replacement in reconstructive surgery. To ensure a timely perfusion of the grafted substitutes, different strategies can be used such as the incorporation of an endothelial component. In this study, we engineered human adipose tissue substitutes comprising of functional adipocytes as well as a natural extracellular matrix using the self-assembly approach, without the use of exogenous scaffolding elements. Human microvascular endothelial cells (hMVECs) were incorporated during tissue production in vitro and we hypothesized that their presence would favor the early connection with the host vascular network translating into functional enhancement after implantation into nude mice in comparison to the substitutes that were not enriched in hMVECs. In vitro, no significant differences were observed between the substitutes in terms of histological aspects. After implantation, both groups presented numerous adipocytes and an abundant matrix in addition to the presence of host capillaries within the grafts. The substitutes thickness and volume were not significantly different between groups over the short-term time course of 14 days (d). For the microvascularized adipose tissues, human CD31 staining revealed a human capillary network connecting with the host microvasculature as early as 3 d after grafting. The detection of murine red blood cells within human CD31+ structures confirmed the functionality of the human capillary network. By analyzing the extent of the global vascularization achieved, a tendency towards increased total capillary network surface and volume was revealed for prevascularized tissues over 14 d. Therefore, applying this strategy on thicker reconstructed adipose tissues with rate-limiting oxygen diffusion might procure added benefits and prove useful to provide voluminous substitutes for patients suffering from adipose tissue loss or defects.

Elucidating the role of plexin D1 in body fat distribution and susceptibility to metabolic disease using a zebrafish model system

Non-communicable diseases (NCDs) such as cardiovascular disease, diabetes and cancer were responsible for 68% of all deaths worldwide in 2012. The regional distribution of lipid deposited within adipose tissue (AT) - so called body fat distribution (BFD) - is a strong risk factor for NCDs. BFD is highly heritable; however, the genetic basis of BFD is almost entirely unknown. Genome-wide association studies have identified several loci associated with BFD, including at Plexin D1 (PLXND1) - a gene known to modulate angiogenesis. We recently demonstrated that zebrafish homozygous for a null mutation in plxnd1 had a reduced capacity to store lipid in visceral AT (VAT) leading to altered BFD. Moreover, we found that type V collagens were upregulated in plxnd1 mutants, and mediated the inhibitory effect of Plxnd1 on VAT growth. These results strengthen evidence that Plxnd1 influences BFD in human populations, and validate zebrafish as a model to study BFD. However, many pertinent questions remain unanswered. Here we outline potential Plxnd1 mechanisms of action in AT, and describe the genetic architecture at human PLXND1 that is associated with BFD and NCD susceptibility.

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 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.

Understanding the effects of mature adipocytes and endothelial cells on fatty acid metabolism and vascular tone in physiological fatty tissue for vascularized adipose tissue engineering

Engineering of large vascularized adipose tissue constructs is still a challenge for the treatment of extensive high-graded burns or the replacement of tissue after tumor removal. Communication between mature adipocytes and endothelial cells is important for homeostasis and the maintenance of adipose tissue mass but, to date, is mainly neglected in tissue engineering strategies. Thus, new co-culture strategies are needed to integrate adipocytes and endothelial cells successfully into a functional construct. This review focuses on the cross-talk of mature adipocytes and endothelial cells and considers their influence on fatty acid metabolism and vascular tone. In addition, the properties and challenges with regard to these two cell types for vascularized tissue engineering are highlighted.

Opportunities and challenges in three-dimensional brown adipogenesis of stem cells

The formation of brown adipose tissue (BAT) via brown adipogenesis has become a notable process due to its ability to expend energy as heat with implications in the treatment of metabolic disorders and obesity. With the advent of complexity within white adipose tissue (WAT) along with inducible brown adipocytes (also known as brite and beige), there has been a surge in deciphering adipocyte biology as well as in vivo adipogenic microenvironments. A therapeutic outcome would benefit from understanding early events in brown adipogenesis, which can be accomplished by studying cellular differentiation. Pluripotent stem cells are an efficient model for differentiation and have been directed towards both white adipogenic and brown adipogenic lineages. The stem cell microenvironment greatly contributes to terminal cell fate and as such, has been mimicked extensively by various polymers including those that can form 3D hydrogel constructs capable of biochemical and/or mechanical modifications and modulations. Using bioengineering approaches towards the creation of 3D cell culture arrangements is more beneficial than traditional 2D culture in that it better recapitulates the native tissue biochemically and biomechanically. In addition, such an approach could potentially protect the tissue formed from necrosis and allow for more efficient implantation. In this review, we highlight the promise of brown adipocytes with a focus on brown adipogenic differentiation of stem cells using bioengineering approaches, along with potential challenges and opportunities that arise when considering the energy expenditure of BAT for prospective therapeutics.

Long term perfusion system supporting adipogenesis

Adipose tissue engineered models are needed to enhance our understanding of disease mechanisms and for soft tissue regenerative strategies. Perfusion systems generate more physiologically relevant and sustainable adipose tissue models, however adipocytes have unique properties that make culturing them in a perfusion environment challenging. In this paper we describe the methods involved in the development of two perfusion culture systems (2D and 3D) to test their applicability for long term in vitro adipogenic cultures. It was hypothesized that a silk protein biomaterial scaffold would provide a 3D framework, in combination with perfusion flow, to generate a more physiologically relevant sustainable adipose tissue engineered model than 2D cell culture. Consistent with other studies evaluating 2D and 3D culture systems for adipogenesis we found that both systems successfully model adipogenesis, however 3D culture systems were more robust, providing the mechanical structure required to contain the large, fragile adipocytes that were lost in 2D perfused culture systems. 3D perfusion also stimulated greater lipogenesis and lipolysis and resulted in decreased secretion of LDH compared to 2D perfusion. Regardless of culture configuration (2D or 3D) greater glycerol was secreted with the increased nutritional supply provided by perfusion of fresh media. These results are promising for adipose tissue engineering applications including long term cultures for studying disease mechanisms and regenerative approaches, where both acute (days to weeks) and chronic (weeks to months) cultivation are critical for useful insight.

Independent evaluation of low-level laser therapy at 635 nm for non-invasive body contouring of the waist, hips, and thighs

INTRODUCTION

The non-invasive body-contouring segment continues to exhibit uninhibited growth, a trend that has provoked the emergence of numerous body-contouring devices. One particular device, low-level laser therapy at 635 nm (LLLT-635), has exhibited promising clinical results. We performed an independent, physician-led trial to evaluate the utility of LLLT-635 nm for non-invasive body contouring of the waist, hips, and thighs.

METHODS

Eighty-six participants were retrospectively assessed at an individual clinic in the United States. A multi-head laser device was administered every-other-day for 2 weeks. Each treatment consisted of 20 minutes of anterior and posterior treatment. Patients received concurrent treatment of the waist, hips, and bilateral thighs. Circumferential measurements were evaluated at baseline and one week following the 2-week treatment administration phase.

RESULTS

Compared with baseline, a statistically significant 2.99 in. (7.59 cm) mean loss was observed at the post-procedure evaluation point (P < 0.0001). When analyzed individually, the waist, hips, and thighs each reported a statistically significant reduction of -1.12, -0.769, and -1.17, respectively. Furthermore, linear regression analysis revealed a weak linear dependence (r = 0.179) between the reported weight and circumference change.

CONCLUSION

These data further validate the clinical efficacy and safety of LLLT at 635 nm.

A biomimetic physiological model for human adipose tissue by adipocytes and endothelial cell cocultures with spatially controlled distribution

An in vitro model that recapitulates the characteristics of native human adipose tissue would largely benefit pathology studies and therapy development. In this paper, we fabricated a physiological model composed of both human adipocytes and endothelial cells with spatially controlled distribution that biomimics the structure and composition of human adipose tissue. Detailed studies into the cell-cell interactions between the adipocytes and endothelial cells revealed a mutual-enhanced effect which resembles the in vivo routine. Furthermore, comparisons between planar coculture and model coculture demonstrated improved adipocyte function as well as endothelial cell proliferation under the same conditions. This research provided a reliable model for human adipose tissue development studies and potential obesity-related therapy development.

In vitro 3D full-thickness skin-equivalent tissue model using silk and collagen biomaterials

Current approaches to skin equivalents often only include the epidermis and dermis. Here, a full-thickness skin equivalent is described including epidermis, dermis, and hypodermis, that could serve as an in vitro model for studying skin biology or as a platform for consumer product testing. The construct is easy to handle and is maintained for >14 d while expressing physiological morphologies of the epidermis and dermis, seen by keratin 10, collagens I and IV expression. The skin equivalent produces glycerol and leptin, markers of adipose metabolism. This work serves as a foundation for understanding a few necessary factors needed to develop a stable, functional model of full-thickness skin.