Collagen Stiffness and Architecture Regulate Fibrotic Gene Expression in Engineered Adipose Tissue

Unilocular adipocyte and lipid tracer for immunofluorescent images

Adipose tissue is a highly dynamic endocrine organ that serves as the body's primary energy reservoir through the storage and mobilization of lipids. Adipocyte cellular size has been recognized as an indicator of cellular status; hypertrophic adipocytes are more prone to insulin resistance and the secretion of pro-inflammatory cytokines. Thus, the size and number of lipids is important to consider both in the clinic with a biopsy and when developing disease models and regenerative tissue constructs. Tools available to analyze adipocyte size are finely tuned for hematoxylin-eosin images and tend to be challenged by confocal derived z-stack images which contain intensity gradients. Therefore, ImageJ manual analysis is the commonly utilized tool to measure these images. With there being heterogeneity in different researcher's analytical approach when conducted manually, the MATLAB script, PixCell, was developed to reduce the subjectivity and time involved in adipocyte size analysis. Given its stepwise thresholding and masking steps, PixCell retains on average a >80% accuracy when tested on excised human adipose tissue, adipocyte-laden collagen gels, and lipoaspirate seeded silk scaffolds. PixCell is able to consistently detect and measure lipids within regions of varying pixel intensities. This makes PixCell an appealing tool for use in both the clinical and pre-clinical setting, while greatly enhancing and streamlining the user experience of analyzing lipid sizes.

Mechanisms of assembly and remodelling of the extracellular matrix

The extracellular matrix (ECM) is the complex meshwork of proteins and glycans that forms the scaffold that surrounds and supports cells. It exerts key roles in all aspects of metazoan physiology, from conferring physical and mechanical properties on tissues and organs to modulating cellular processes such as proliferation, differentiation and migration. Understanding the mechanisms that orchestrate the assembly of the ECM scaffold is thus crucial to understand ECM functions in health and disease. This Review discusses novel insights into the compositional diversity of matrisome components and the mechanisms that lead to tissue-specific assemblies and architectures tailored to support specific functions. The Review then highlights recently discovered mechanisms, including post-translational modifications and metabolic pathways such as amino acid availability and the circadian clock, that modulate ECM secretion, assembly and remodelling in homeostasis and human diseases. Last, the Review explores the potential of 'matritherapies', that is, strategies to normalize ECM composition and architecture to achieve a therapeutic benefit.

Mapping biological influences on the human plasma proteome beyond the genome

Broad-capture proteomic platforms now enable simultaneous assessment of thousands of plasma proteins, but most of these are not actively secreted and their origins are largely unknown. Here we integrate genomic with deep phenomic information to identify modifiable and non-modifiable factors associated with 4,775 plasma proteins in ~8,000 mostly healthy individuals. We create a data-driven map of biological influences on the human plasma proteome and demonstrate segregation of proteins into clusters based on major explanatory factors. For over a third (N = 1,575) of protein targets, joint genetic and non-genetic factors explain 10-77% of the variation in plasma (median 19.88%, interquartile range 14.01-31.09%), independent of technical factors (median 2.48%, interquartile range 0.78-6.41%). Together with genetically anchored causal inference methods, our map highlights potential causal associations between modifiable risk factors and plasma proteins for hundreds of protein-disease associations, for example, COL6A3, which possibly mediates the association between reduced kidney function and cardiovascular disease. We provide a map of biological and technical influences on the human plasma proteome to help contextualize findings from proteomic studies.

A Preliminary Study on Factors That Drive Patient Variability in Human Subcutaneous Adipose Tissues

Adipose tissue is a dynamic regulatory organ that has profound effects on the overall health of patients. Unfortunately, inconsistencies in human adipose tissues are extensive and multifactorial, including large variability in cellular sizes, lipid content, inflammation, extracellular matrix components, mechanics, and cytokines secreted. Given the high human variability, and since much of what is known about adipose tissue is from animal models, we sought to establish correlations and patterns between biological, mechanical, and epidemiological properties of human adipose tissues. To do this, twenty-six independent variables were cataloged for twenty patients, which included patient demographics and factors that drive health, obesity, and fibrosis. A factorial analysis for mixed data (FAMD) was used to analyze patterns in the dataset (with BMI > 25), and a correlation matrix was used to identify interactions between quantitative variables. Vascular endothelial growth factor A (VEGFA) and actin alpha 2, smooth muscle (ACTA2) gene expression were the highest loadings in the first two dimensions of the FAMD. The number of adipocytes was also a key driver of patient-related differences, where a decrease in the density of adipocytes was associated with aging. Aging was also correlated with a decrease in overall lipid percentage of subcutaneous tissue, with lipid deposition being favored extracellularly, an increase in transforming growth factor-β1 (TGFβ1), and an increase in M1 macrophage polarization. An important finding was that self-identified race contributed to variance between patients in this study, where Black patients had significantly lower gene expression levels of TGFβ1 and ACTA2. This finding supports the urgent need to account for patient ancestry in biomedical research to develop better therapeutic strategies for all patients. Another important finding was that TGFβ induced factor homeobox 1 (TGIF1), an understudied signaling molecule, which is highly correlated with leptin signaling, was correlated with metabolic inflammation. Furthermore, this study draws attention to what we define as "extracellular lipid droplets", which were consistently found in collagen-rich regions of the obese adipose tissues evaluated here. Reduced levels of TGIF1 were correlated with higher numbers of extracellular lipid droplets and an inability to suppress fibrotic changes in adipose tissue. Finally, this study indicated that M1 and M2 macrophage markers were correlated with each other and leptin in patients with a BMI > 25. This finding supports growing evidence that macrophage polarization in obesity involves a complex, interconnecting network system rather than a full switch in activation patterns from M2 to M1 with increasing body mass. Overall, this study reinforces key findings in animal studies and identifies important areas for future research, where human and animal studies are divergent. Understanding key drivers of human patient variability is required to unravel the complex metabolic health of unique patients.

Mechanobiology in Metabolic Dysfunction-Associated Steatotic Liver Disease and Obesity

With the ongoing obesity epidemic, the prevalence of metabolic dysfunction-associated steatotic liver disease (MASLD) is expected to rise and necessitates a greater understanding of how the disease proceeds from benign excess lipid in hepatocytes to liver fibrosis and eventually to liver cancer. MASLD is caused, at least in part, by hepatocytes' storage of free fatty acids (FAs) that dysfunctional adipocytes are no longer able to store, and therefore, MASLD is a disease that involves both the liver and adipose tissues. The disease progression is not only facilitated by biochemical signals, but also by mechanical cues such as the increase in stiffness often seen with fibrotic fatty livers. The change in stiffness and accumulation of excess lipid droplets impact the ability of a cell to mechanosense and mechanotranduce, which perpetuates the disease. A mechanosensitive protein that is largely unexplored and could serve as a potential therapeutic target is the intermediate filament vimentin. In this review, we briefly summarize the recent research on hepatocyte and adipocyte mechanobiology and provide a synopsis of studies on the varied, and sometimes contradictory, roles of vimentin. This review is intended to benefit and encourage future studies on hepatocyte and adipocyte mechanobiology in the context of MASLD and obesity.

Combined effects of matrix stiffness and obesity-associated signaling directs progressive phenotype in PANC-1 pancreatic cancer cells in vitro

Obesity is a leading risk factor of pancreatic ductal adenocarcinoma (PDAC) that contributes to poor disease prognosis and outcomes. Retrospective studies have identified this link, but interactions surrounding obesity and PDAC are still unclear. Research has shifted to contributions of fibrosis (desmoplasia) on malignancy, which involves increased deposition of collagens and other extracellular matrix (ECM) molecules and increased ECM crosslinking, all of which contribute to increased tissue stiffening. However, fibrotic stiffening is underrepresented as a model feature in current PDAC models. Fibrosis is shared between PDAC and obesity, and can be leveraged for in vitro model design, as current animal obesity models of PDAC are limited in their ability to isolate individual components of fibrosis to study cell behavior. In the current study, methacrylated type I collagen (PhotoCol®) was photo-crosslinked to pathological stiffness levels to recapitulate fibrotic ECM stiffening. PANC-1 cells were encapsulated within PhotoCol®, and the tumor-tissue constructs were prepared to represent normal (healthy) (~600 Pa) and pathological (~2000 Pa) tissues. Separately, human mesenchymal stem cells were differentiated into adipocytes representing lean (2D differentiation) and obese fat tissue (3D collagen matrix differentiation), and conditioned media was applied to PANC-1 tumor-tissue constructs. Conditioned media from obese adipocytes showed increased vimentin expression, a hallmark of invasiveness and progression, that was not seen after exposure to media from lean adipocytes or control media. Characterization of the obese adipocyte secretome suggested that some PANC-1 differences may arise from increased interleukin-8 and -10 compared to lean adipocytes. Additionally, high matrix stiffness associated induced an amoeboid morphology in PANC-1 cells that was not present at low stiffness. Amoeboid morphology is an accessory to epithelial-to-mesenchymal transition and is used to navigate complex ECM environments. This plasticity has greater implications for treatment efficacy of metastatic cancers. Overall, this work 1) highlights the importance of investigating PDAC-obesity interactions to study the effects on disease progression and persistence, 2) establishes PhotoCol® as a matrix material that can be leveraged to study amoeboid morphology and invasion in PDAC, and 3) emphasizes the importance of integrating both biophysical and biochemical interactions associated within both pathologies for in vitro PDAC models.

Geometry of adipocyte packing in subcutaneous tissue contributes to nonlinear tissue properties captured through a Gaussian process surrogate model

Subcutaneous tissue mechanical response is governed by the geometry and mechanical properties at the microscale and drives physiological and clinical processes such as drug delivery. Even though adipocyte packing is known to change with age, disease, and from one individual to another, the link between the geometry of the packing and the overall mechanical response of adipose tissue remains poorly understood. Here we create 1200 periodic representative volume elements (RVEs) that sample the possible space of Laguerre packings describing adipose tissue. RVE mechanics are modeled under tri-axial loading. Equilibrium configuration of RVEs is solved by minimizing an energetic potential that includes volume change contributions from adipocyte expansion, and area change contributions from collagen foam stretching. The resulting mechanical response across all RVE samples is interpolated with the aid of a Gaussian process (GP), revealing how the microscale geometry dictates the overall RVE mechanics. For example, increase in adipocyte size and increase in sphericity lead to adipose tissue softening. We showcase the use of the homogenized model in finite element simulations of drug injection by implementing a Blatz-Ko model, informed by the GP, as a custom material in the popular open-source package FEBio. These simulations show how microscale geometry can lead to vastly different injection dynamics even if the constituent parameters are held constant, highlighting the importance of characterizing individual's adipose tissue structure in the development of personalized therapies.

Injectable MSC Spheroid and Microgel Granular Composites for Engineering Tissue

Many cell types require direct cell-cell interactions for differentiation and function; yet, this can be challenging to incorporate into 3-dimensional (3D) structures for the engineering of tissues. Here, a new approach is introduced that combines aggregates of cells (spheroids) with similarly-sized hydrogel particles (microgels) to form granular composites that are injectable, undergo interparticle crosslinking via light for initial stabilization, permit cell-cell contacts for cell signaling, and allow spheroid fusion and growth. One area where this is important is in cartilage tissue engineering, as cell-cell contacts are crucial to chondrogenesis and are missing in many tissue engineering approaches. To address this, granular composites are developed from adult porcine mesenchymal stromal cell (MSC) spheroids and hyaluronic acid microgels and simulations and experimental analyses are used to establish the importance of initial MSC spheroid to microgel volume ratios to balance mechanical support with tissue growth. Long-term chondrogenic cultures of granular composites produce engineered cartilage tissue with extensive matrix deposition and mechanical properties within the range of cartilage, as well as integration with native tissue. Altogether, a new strategy of injectable granular composites is developed that leverages the benefits of cell-cell interactions through spheroids with the mechanical stabilization afforded with engineered hydrogels.

Matrisomal components involved in regenerative wound healing in axolotl and Acomys: implications for biomaterial development

Achieving regeneration in humans has been a long-standing goal of many researchers. Whereas amphibians like the axolotl (Ambystoma mexicanum) are capable of regenerating whole organs and even limbs, most mammals heal their wounds via fibrotic scarring. Recently, the African spiny mouse (Acomys sp.) has been shown to be injury resistant and capable of regenerating several tissue types. A major focal point of research with Acomys has been the identification of drivers of regeneration. In this search, the matrisome components related to the extracellular matrix (ECM) are often overlooked. In this review, we compare Acomys and axolotl skin wound healing and blastema-mediated regeneration by examining their wound healing responses and comparing the expression pattern of matrisome genes, including glycosaminoglycan (GAG) related genes. The goal of this review is to identify matrisome genes that are upregulated during regeneration and could be potential candidates for inclusion in pro-regenerative biomaterials. Research papers describing transcriptomic or proteomic coverage of either skin regeneration or blastema formation in Acomys and axolotl were selected. Matrisome and GAG related genes were extracted from each dataset and the resulting lists of genes were compared. In our analysis, we found several genes that were consistently upregulated, suggesting possible involvement in regenerative processes. Most of the components have been implicated in regulation of cell behavior, extracellular matrix remodeling and wound healing. Incorporation of such pro-regenerative factors into biomaterials may help to shift pro-fibrotic processes to regenerative responses in treated wounds.

Transcriptome analysis of mRNAs, lncRNAs, and miRNAs in the skeletal muscle of Tibetan chickens at different developmental stages

Introduction: As a valuable genetic resource, native birds can contribute to the sustainable development of animal production. Tibetan chickens, known for their special flavor, are one of the important local poultry breeds in the Qinghai-Tibet Plateau. However, Tibetan chickens have a slow growth rate and poor carcass traits compared with broilers. Although most of the research on Tibetan chickens focused on their hypoxic adaptation, there were fewer studies related to skeletal muscle development. Methods: Here, we performed the transcriptional sequencing of leg muscles from Tibetan chicken embryos at E (embryonic)10, E14, and E18. Results: In total, 1,600, 4,610, and 2,166 DE (differentially expressed) mRNAs, 210, 573, and 234 DE lncRNAs (long non-coding RNAs), and 52, 137, and 33 DE miRNAs (microRNAs) were detected between E10 and E14, E10 and E18, and E14 and E18, respectively. Functional prediction showed several DE mRNAs and the target mRNAs of DE lncRNAs and DE miRNAs were significantly enriched in sarcomere organization, actin cytoskeleton organization, myofibril, muscle fiber development, and other terms and pathways related to muscle growth and development. Finally, a lncRNA-miRNA-mRNA ceRNA (competing endogenous RNA) network associated with muscle growth and development, which contained 6 DE lncRNAs, 13 DE miRNAs, and 50 DE mRNAs, was constructed based on the screened DE RNAs by Gene Ontology (GO) enrichment. These DE RNAs may play a critical regulatory role in the skeletal muscle development of chickens. Discussion: The results provide a genomic resource for mRNAs, lncRNAs, and miRNAs potentially involved in the skeletal muscle development of chickens, which lay the foundation for further studies of the molecular mechanisms underlying skeletal muscle growth and development in Tibetan chickens.

Aptamer Nanoconstructs Crossing Human Blood-Brain Barrier Discovered via Microphysiological System-Based SELEX Technology

Blood-brain barrier (BBB) remains one of the critical challenges in developing neurological therapeutics. Short single-stranded DNA/RNA nucleotides forming a three-dimensional structure, called aptamers, have received increasing attention as BBB shuttles for efficient brain drug delivery owing to their practical advantages over Trojan horse antibodies or peptides. Aptamers are typically obtained by combinatorial chemical technology, termed Systemic Evolution of Ligands by EXponential Enrichment (SELEX), against purified targets, living cells, or animal models. However, identifying reliable BBB-penetrating aptamers that perform efficiently under human physiological conditions has been challenging because of the poor physiological relevance in the conventional SELEX process. Here, we report a human BBB shuttle aptamer (hBS) identified using a human microphysiological system (MPS)-based SELEX (MPS-SELEX) method. A two-channel MPS lined with human brain microvascular endothelial cells (BMECs) interfaced with astrocytes and pericytes, recapitulating high-level barrier function of in vivo BBB, was exploited as a screening platform. The MPS-SELEX procedure enabled robust function-based screening of the hBS candidates, which was not achievable in traditional in vitro BBB models. The identified aptamer (hBS01) through five-round of MPS-SELEX exhibited high capability to transport protein cargoes across the human BBB via clathrin-mediated endocytosis and enhanced uptake efficiency in BMECs and brain cells. The enhanced targeting specificity of hBS01 was further validated both in vitro and in vivo, confirming its powerful brain accumulation efficiency. These findings demonstrate that MPS-SELEX has potential in the discovery of aptamers with high target specificity that can be widely utilized to boost the development of drug delivery strategies.

Collagen microgel to simulate the adipocyte microenvironment for in vitro research on obesity

Obesity is linked to adipose tissue dysfunction, a dynamic endocrine organ. Two-dimensional cultures present technical hurdles hampering their ability to follow individual or cell groups for metabolic disease research. Three-dimensional type I collagen microgels with embedded adipocytes have not been thoroughly investigated to evaluate adipogenic maintenance as instrument for studying metabolic disorders. We aimed to develop a novel tunable Col-I microgel simulating the adipocyte microenvironment to maintain differentiated cells with only insulin as in vitro model for obesity research. Adipocytes were cultured and encapsulated in collagen microgels at different concentrations (2, 3 and 4 mg/mL). Collagen microgels at 3 and 4 mg/mL were more stable after 8 days of culture. However, cell viability and metabolic activity were maintained at 2 and 3 mg/mL, respectively. Cell morphology, lipid mobilization and adipogenic gene expression demonstrated the maintenance of adipocyte phenotype in an in vitro microenvironment. We demonstrated the adequate stability and biocompatibility of the collagen microgel at 3 mg/mL. Cell and molecular analysis confirmed that adipocyte phenotype is maintained over time in the absence of adipogenic factors. These findings will help better understand and open new avenues for research on adipocyte metabolism and obesity. Insight box In the context of adipose tissue dysfunction research, new struggles have arisen owing to the difficulty of cellular maintenance in 2D cultures. Herein, we sought a novel approach using a 3D type I collagen-based biomaterial to adipocyte culture with only insulin. This component was tailored as a microgel in different concentrations to support the growth and survival of adipocytes. We demonstrate that adipocyte phenotype is maintained and key adipogenesis regulators and markers are over time. The cumulative results unveil the practical advantage of this microgel platform as an in vitro model to study adipocyte dysfunction and obesity.

Modeling lymphangiogenesis: Pairing in vitro and in vivo metrics

Lymphangiogenesis is the mechanism by which the lymphatic system develops and expands new vessels facilitating fluid drainage and immune cell trafficking. Models to study lymphangiogenesis are necessary for a better understanding of the underlying mechanisms and to identify or test new therapeutic agents that target lymphangiogenesis. Across the lymphatic literature, multiple models have been developed to study lymphangiogenesis in vitro and in vivo. In vitro, lymphangiogenesis can be modeled with varying complexity, from monolayers to hydrogels to explants, with common metrics for characterizing proliferation, migration, and sprouting of lymphatic endothelial cells (LECs) and vessels. In comparison, in vivo models of lymphangiogenesis often use genetically modified zebrafish and mice, with in situ mouse models in the ear, cornea, hind leg, and tail. In vivo metrics, such as activation of LECs, number of new lymphatic vessels, and sprouting, mirror those most used in vitro, with the addition of lymphatic vessel hyperplasia and drainage. The impacts of lymphangiogenesis vary by context of tissue and pathology. Therapeutic targeting of lymphangiogenesis can have paradoxical effects depending on the pathology including lymphedema, cancer, organ transplant, and inflammation. In this review, we describe and compare lymphangiogenic outcomes and metrics between in vitro and in vivo studies, specifically reviewing only those publications in which both testing formats are used. We find that in vitro studies correlate well with in vivo in wound healing and development, but not in the reproductive tract or the complex tumor microenvironment. Considerations for improving in vitro models are to increase complexity with perfusable microfluidic devices, co-cultures with tissue-specific support cells, the inclusion of fluid flow, and pairing in vitro models of differing complexities. We believe that these changes would strengthen the correlation between in vitro and in vivo outcomes, giving more insight into lymphangiogenesis in healthy and pathological states.

Obesity-Associated ECM Remodeling in Cancer Progression

Adipose tissue, an energy storage and endocrine organ, is emerging as an essential player for ECM remodeling. Fibrosis is one of the hallmarks of obese adipose tissue, featuring excessive ECM deposition and enhanced collagen alignment. A variety of ECM components and ECM-related enzymes are produced by adipocytes and myofibroblasts in obese adipose tissue. Data from lineage-tracing models and a single-cell analysis indicate that adipocytes can transform or de-differentiate into myofibroblast/fibroblast-like cells. This de-differentiation process has been observed under normal tissue development and pathological conditions such as cutaneous fibrosis, wound healing, and cancer development. Accumulated evidence has demonstrated that adipocyte de-differentiation and myofibroblasts/fibroblasts play crucial roles in obesity-associated ECM remodeling and cancer progression. In this review, we summarize the recent progress in obesity-related ECM remodeling, the mechanism underlying adipocyte de-differentiation, and the function of obesity-associated ECM remodeling in cancer progression.

A three-dimensional human adipocyte model of fatty acid-induced obesity

Obesity prevalence has reached pandemic proportions, leaving individuals at high risk for the development of diseases such as cancer and type 2 diabetes. In obesity, to accommodate excess lipid storage, adipocytes become hypertrophic, which is associated with an increased pro-inflammatory cytokine secretion and dysfunction of metabolic processes such as insulin signaling and lipolysis. Targeting adipocyte dysfunction is an important strategy to prevent the development of obesity-associated disease. However, it is unclear how accurately animal models reflect human biology, and the long-term culture of human hypertrophic adipocytes in an in vitro 2D monolayer is challenging due to the buoyant nature of adipocytes. Here we describe the development of a human 3D in vitro disease model that recapitulates hallmarks of obese adipocyte dysfunction. First, primary human adipose-derived mesenchymal stromal cells are embedded in hydrogel, and infiltrated into a thin cellulose scaffold. The thin microtissue profile allows for efficient assembly and image-based analysis. After adipocyte differentiation, the scaffold is stimulated with oleic or palmitic acid to mimic caloric overload. Using functional assays, we demonstrated that this treatment induced important obese adipocyte characteristics such as a larger lipid droplet size, increased basal lipolysis, insulin resistance and a change in macrophage gene expression through adipocyte-conditioned media. This 3D disease model mimics physiologically relevant hallmarks of obese adipocytes, to enable investigations into the mechanisms by which dysfunctional adipocytes contribute to disease.

Autologous Human Immunocompetent White Adipose Tissue-on-Chip

Obesity and associated diseases, such as diabetes, have reached epidemic proportions globally. In this era of "diabesity", white adipose tissue (WAT) has become a target of high interest for therapeutic strategies. To gain insights into mechanisms of adipose (patho-)physiology, researchers traditionally relied on animal models. Leveraging Organ-on-Chip technology, a microphysiological in vitro model of human WAT is introduced: a tailored microfluidic platform featuring vasculature-like perfusion that integrates 3D tissues comprising all major WAT-associated cellular components (mature adipocytes, organotypic endothelial barriers, stromovascular cells including adipose tissue macrophages) in an autologous manner and recapitulates pivotal WAT functions, such as energy storage and mobilization as well as endocrine and immunomodulatory activities. A precisely controllable bottom-up approach enables the generation of a multitude of replicates per donor circumventing inter-donor variability issues and paving the way for personalized medicine. Moreover, it allows to adjust the model's degree of complexity via a flexible mix-and-match approach. This WAT-on-Chip system constitutes the first human-based, autologous, and immunocompetent in vitro adipose tissue model that recapitulates almost full tissue heterogeneity and can become a powerful tool for human-relevant research in the field of metabolism and its associated diseases as well as for compound testing and personalized- and precision medicine applications.

The matrix in focus: new directions in extracellular matrix research from the 2021 ASMB hybrid meeting

The extracellular matrix (ECM) is a complex assembly of macromolecules that provides both architectural support and molecular signals to cells and modulate their behaviors. Originally considered a passive mechanical structure, decades of research have since demonstrated how the ECM dynamically regulates a diverse set of cellular processes in development, homeostasis, and disease progression. In September 2021, the American Society for Matrix Biology (ASMB) organized a hybrid scientific meeting, integrating in-person and virtual formats, to discuss the latest developments in ECM research. Here, we highlight exciting scientific advances that emerged from the meeting including (1) the use of model systems for fundamental and translation ECM research, (2) ECM-targeting approaches as therapeutic modalities, (3) cell-ECM interactions, and (4) the ECM as a critical component of tissue engineering strategies. In addition, we discuss how the ASMB incorporated mentoring, career development, and diversity, equity, and inclusion initiatives in both virtual and in-person events. Finally, we reflect on the hybrid scientific conference format and how it will help the ASMB accomplish its mission moving forward.

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.

Single-Cell Microgels for Diagnostics and Therapeutics

Cell encapsulation within hydrogel droplets is transforming what is feasible in multiple fields of biomedical science such as tissue engineering and regenerative medicine, in vitro modeling, and cell-based therapies. Recent advances have allowed researchers to miniaturize material encapsulation complexes down to single-cell scales, where each complex, termed a single-cell microgel, contains only one cell surrounded by a hydrogel matrix while remaining <100 μm in size. With this achievement, studies requiring single-cell resolution are now possible, similar to those done using liquid droplet encapsulation. Of particular note, applications involving long-term in vitro cultures, modular bioinks, high-throughput screenings, and formation of 3D cellular microenvironments can be tuned independently to suit the needs of individual cells and experimental goals. In this progress report, an overview of established materials and techniques used to fabricate single-cell microgels, as well as insight into potential alternatives is provided. This focused review is concluded by discussing applications that have already benefited from single-cell microgel technologies, as well as prospective applications on the cusp of achieving important new capabilities.

Mechanics of 3D Cell-Hydrogel Interactions: Experiments, Models, and Mechanisms

Hydrogels are highly water-swollen molecular networks that are ideal platforms to create tissue mimetics owing to their vast and tunable properties. As such, hydrogels are promising cell-delivery vehicles for applications in tissue engineering and have also emerged as an important base for ex vivo models to study healthy and pathophysiological events in a carefully controlled three-dimensional environment. Cells are readily encapsulated in hydrogels resulting in a plethora of biochemical and mechanical communication mechanisms, which recapitulates the natural cell and extracellular matrix interaction in tissues. These interactions are complex, with multiple events that are invariably coupled and spanning multiple length and time scales. To study and identify the underlying mechanisms involved, an integrated experimental and computational approach is ideally needed. This review discusses the state of our knowledge on cell-hydrogel interactions, with a focus on mechanics and transport, and in this context, highlights recent advancements in experiments, mathematical and computational modeling. The review begins with a background on the thermodynamics and physics fundamentals that govern hydrogel mechanics and transport. The review focuses on two main classes of hydrogels, described as semiflexible polymer networks that represent physically cross-linked fibrous hydrogels and flexible polymer networks representing the chemically cross-linked synthetic and natural hydrogels. In this review, we highlight five main cell-hydrogel interactions that involve key cellular functions related to communication, mechanosensing, migration, growth, and tissue deposition and elaboration. For each of these cellular functions, recent experiments and the most up to date modeling strategies are discussed and then followed by a summary of how to tune hydrogel properties to achieve a desired functional cellular outcome. We conclude with a summary linking these advancements and make the case for the need to integrate experiments and modeling to advance our fundamental understanding of cell-matrix interactions that will ultimately help identify new therapeutic approaches and enable successful tissue engineering.

3D Adipose Tissue Culture Links the Organotypic Microenvironment to Improved Adipogenesis

Obesity and type 2 diabetes are strongly associated with adipose tissue dysfunction and impaired adipogenesis. Understanding the molecular underpinnings that control adipogenesis is thus of fundamental importance for the development of novel therapeutics against metabolic disorders. However, translational approaches are hampered as current models do not accurately recapitulate adipogenesis. Here, a scaffold-free versatile 3D adipocyte culture platform with chemically defined conditions is presented in which primary human preadipocytes accurately recapitulate adipogenesis. Following differentiation, multi-omics profiling and functional tests demonstrate that 3D adipocyte cultures feature mature molecular and cellular phenotypes similar to freshly isolated mature adipocytes. Spheroids exhibit physiologically relevant gene expression signatures with 4704 differentially expressed genes compared to conventional 2D cultures (false discovery rate < 0.05), including the concerted expression of factors shaping the adipogenic niche. Furthermore, lipid profiles of >1000 lipid species closely resemble patterns of the corresponding isogenic mature adipocytes in vivo (R2 = 0.97). Integration of multi-omics signatures with analyses of the activity profiles of 503 transcription factors using global promoter motif inference reveals a complex signaling network, involving YAP, Hedgehog, and TGFβ signaling, that links the organotypic microenvironment in 3D culture to the activation and reinforcement of PPARγ and CEBP activity resulting in improved adipogenesis.

Co-evolution of matrisome and adaptive adhesion dynamics drives ovarian cancer chemoresistance

Due to its dynamic nature, the evolution of cancer cell-extracellular matrix (ECM) crosstalk, critically affecting metastasis and treatment resistance, remains elusive. Our results show that platinum-chemotherapy itself enhances resistance by progressively changing the cancer cell-intrinsic adhesion signaling and cell-surrounding ECM. Examining ovarian high-grade serous carcinoma (HGSC) transcriptome and histology, we describe the fibrotic ECM heterogeneity at primary tumors and distinct metastatic sites, prior and after chemotherapy. Using cell models from systematic ECM screen to collagen-based 2D and 3D cultures, we demonstrate that both specific ECM substrates and stiffness increase resistance to platinum-mediated, apoptosis-inducing DNA damage via FAK and β1 integrin-pMLC-YAP signaling. Among such substrates around metastatic HGSCs, COL6 was upregulated by chemotherapy and enhanced the resistance of relapse, but not treatment-naïve, HGSC organoids. These results identify matrix adhesion as an adaptive response, driving HGSC aggressiveness via co-evolving ECM composition and sensing, suggesting stromal and tumor strategies for ECM pathway targeting.

Modeling Adipogenesis: Current and Future Perspective

Adipose tissue is contemplated as a dynamic organ that plays key roles in the human body. Adipogenesis is the process by which adipocytes develop from adipose-derived stem cells to form the adipose tissue. Adipose-derived stem cells' differentiation serves well beyond the simple goal of producing new adipocytes. Indeed, with the current immense biotechnological advances, the most critical role of adipose-derived stem cells remains their tremendous potential in the field of regenerative medicine. This review focuses on examining the physiological importance of adipogenesis, the current approaches that are employed to model this tightly controlled phenomenon, and the crucial role of adipogenesis in elucidating the pathophysiology and potential treatment modalities of human diseases. The future of adipogenesis is centered around its crucial role in regenerative and personalized medicine.

Adipose Tissue Fibrosis: Mechanisms, Models, and Importance

Increases in adipocyte volume and tissue mass due to obesity can result in inflammation, further dysregulation in adipose tissue function, and eventually adipose tissue fibrosis. Like other fibrotic diseases, adipose tissue fibrosis is the accumulation and increased production of extracellular matrix (ECM) proteins. Adipose tissue fibrosis has been linked to decreased insulin sensitivity, poor bariatric surgery outcomes, and difficulty in weight loss. With the rising rates of obesity, it is important to create accurate models for adipose tissue fibrosis to gain mechanistic insights and develop targeted treatments. This article discusses recent research in modeling adipose tissue fibrosis using in vivo and in vitro (2D and 3D) methods with considerations for biomaterial selections. Additionally, this article outlines the importance of adipose tissue in treating other fibrotic diseases and methods used to detect and characterize adipose tissue fibrosis.