Thrombospondin-1 promotes fibro-adipogenic stromal expansion and contractile dysfunction of the diaphragm in obesity.

Pulmonary disorders impact 40% to 80% of individuals with obesity. Respiratory muscle dysfunction is linked to these conditions; however, its pathophysiology remains largely undefined. Mice subjected to diet-induced obesity (DIO) develop diaphragmatic weakness. Increased intra-diaphragmatic adiposity and extracellular matrix (ECM) content correlate with reductions in contractile force. Thrombospondin-1 (THBS1) is an obesity-associated matricellular protein linked with muscular damage in genetic myopathies. THBS1 induces proliferation of fibro-adipogenic progenitors (FAPs) - mesenchymal cells that differentiate into adipocytes and fibroblasts. We hypothesized that THBS1 drives FAP-mediated diaphragm remodeling and contractile dysfunction in DIO. We tested this by comparing the effects of dietary challenge on diaphragms of wild-type (WT) and Thbs1 knockout (Thbs1-/-) mice. Bulk and single-cell transcriptomics demonstrated DIO-induced stromal expansion in WT diaphragms. Diaphragm FAPs displayed upregulation of ECM and TGF ß-related expression signatures and augmentation of a Thy1-expressing sub-population previously linked to type 2 diabetes. Despite similar weight gain, Thbs1-/- mice were protected from these transcriptomic changes and from obesity-induced increases in diaphragm adiposity and ECM deposition. Unlike WT controls, Thbs1-/- diaphragms maintained normal contractile force and motion after DIO challenge. These findings establish THBS1 as a necessary mediator of diaphragm stromal remodeling and contractile dysfunction in overnutrition and a potential therapeutic target in obesity-associated respiratory dysfunction.

3D engineered scaffold for large-scale Vigil immunotherapy production.

Previously, we reported successful cellular expansion of a murine colorectal carcinoma cell line (CT-26) using a three-dimensional (3D) engineered extracellular matrix (EECM) fibrillar scaffold structure. CCL-247 were grown over a limited time period of 8 days on 3D EECM or tissue culture polystyrene (TCPS). Cells were then assayed for growth, electroporation efficiency and Vigil manufacturing release criteria. Using EECM scaffolds, we report an expansion of CCL-247 (HCT116), a colorectal carcinoma cell line, from a starting concentration of 2.45 × 105 cells to 1.9 × 106 cells per scaffold. Following expansion, 3D EECM-derived cells were assessed based on clinical release criteria of the Vigil manufacturing process utilized for Phase IIb trial operation with the FDA. 3D EECM-derived cells passed all Vigil manufacturing release criteria including cytokine expression. Here, we demonstrate successful Vigil product manufacture achieving the specifications necessary for the clinical trial product release of Vigil treatment. Our results confirm that 3D EECM can be utilized for the expansion of human cancer cell CCL-247, justifying further clinical development involving human tissue sample manufacturing including core needle biopsy and minimal ascites samples.

Early B-cell transcription factor-2 defect as a novel cause of lipodystrophy: disruption of the adipose tissue character and integrity.

We report a novel cause of partial lipodystrophy associated with early B cell factor 2 (EBF2) nonsense variant (EBF2 8:26033143 C>A, c.493G>T, p.E165X) in a patient with an atypical form of partial lipodystrophy. The patient presented with progressive adipose tissue loss and metabolic deterioration at pre-pubertal age. In vitro and in vivo disease modeling demonstrates that the EBF2 variant impairs adipogenesis, causing excess accumulation of undifferentiated CD34+ cells, extracellular matrix proteins, and inflammatory myeloid cells in subcutaneous adipose tissues. Thus, this EBF2 p.E165X variant disrupts adipose tissue structure and function, leading to the development of partial lipodystrophy syndrome.

Safety and effectiveness of metabolic surgery in older Japanese patients.

Aim: According to the current guidelines in Japan, the upper age limit for bariatric and metabolic surgery is 65 y. This study aimed to examine the appropriateness of this upper age limit. Methods: Using the database maintained by the Japanese Society for Treatment of Obesity, we conducted an analysis of patients in two age groups: those aged <65 y and those aged ≥65 y. Our analysis focused on postoperative weight loss, improvement in comorbidities, and frequency of perioperative complications. Results: A total of 2885 patients aged <65 y (mean, 43.9 ± 9.5 y) with a preoperative body mass index of 42.4 ± 8.1 kg/m2, while 56 aged ≥65 y (mean, 67.3 ± 3.2 y; maximum, 78 y) with a preoperative body mass index of 40.5 ± 6.6 kg/m2. Patients aged ≥65 y had a higher rate of dyslipidemia and hypertension. The rates of reoperation, surgical complications, and postoperative complications did not differ between the age groups. Both groups achieved significant weight loss postoperatively, and no differences in the improvement of comorbidities were noted. After adjusting the covariate balance via propensity score matching, no age-related differences in perioperative and postoperative complications were observed. Conclusion: Metabolic surgery is safe and effective for older patients with clinically severe obesity. Weight loss was less in patients aged ≥65 y, but the percentage of total weight loss did not differ between the groups.

Thrombospondin-1 promotes fibro-adipogenic stromal expansion and contractile dysfunction of the diaphragm in obesity.

Pulmonary disorders impact 40-80% of individuals with obesity. Respiratory muscle dysfunction is linked to these conditions; however, its pathophysiology remains largely undefined. Mice subjected to diet-induced obesity (DIO) develop diaphragmatic weakness. Increased intra-diaphragmatic adiposity and extracellular matrix (ECM) content correlate with reductions in contractile force. Thrombospondin-1 (THBS1) is an obesity-associated matricellular protein linked with muscular damage in genetic myopathies. THBS1 induces proliferation of fibro-adipogenic progenitors (FAPs)-mesenchymal cells that differentiate into adipocytes and fibroblasts. We hypothesized that THBS1 drives FAP-mediated diaphragm remodeling and contractile dysfunction in DIO. We tested this by comparing effects of dietary challenge on diaphragms of wild-type (WT) and Thbs1 knockout ( Thbs1 -/- ) mice. Bulk and single-cell transcriptomics demonstrated DIO-induced stromal expansion in WT diaphragms. Diaphragm FAPs displayed upregulation of ECM and TGFß-related expression signatures, and augmentation of a Thy1 -expressing sub-population previously linked to type 2 diabetes. Despite similar weight gain, Thbs1 -/- mice were protected from these transcriptomic changes, and from obesity-induced increases in diaphragm adiposity and ECM deposition. Unlike WT controls, Thbs1 -/- diaphragms maintained normal contractile force and motion after DIO challenge. These findings establish THBS1 as a necessary mediator of diaphragm stromal remodeling and contractile dysfunction in overnutrition, and potential therapeutic target in obesity-associated respiratory dysfunction.

Monolithically 3D-Printed Microfluidics with Embedded µTesla Pump.

Microfluidics has earned a reputation for providing numerous transformative but disconnected devices and techniques. Active research seeks to address this challenge by integrating microfluidic components, including embedded miniature pumps. However, a significant portion of existing microfluidic integration relies on the time-consuming manual fabrication that introduces device variations. We put forward a framework for solving this disconnect by combining new pumping mechanics and 3D printing to demonstrate several novel, integrated and wirelessly driven microfluidics. First, we characterized the simplicity and performance of printed microfluidics with a minimum feature size of 100 µm. Next, we integrated a microtesla (µTesla) pump to provide non-pulsatile flow with reduced shear stress on beta cells cultured on-chip. Lastly, the integration of radio frequency (RF) device and a hobby-grade brushless motor completed a self-enclosed platform that can be remotely controlled without wires. Our study shows how new physics and 3D printing approaches not only provide better integration but also enable novel cell-based studies to advance microfluidic research.

Fibro-Adipogenic Remodeling of the Diaphragm in Obesity-Associated Respiratory Dysfunction.

Respiratory dysfunction is a common complication of obesity, conferring cardiovascular morbidity and increased mortality and often necessitating mechanical ventilatory support. While impaired lung expansion in the setting of increased adipose mass and reduced central response to hypercapnia have been implicated as pathophysiological drivers, the impact of obesity on respiratory muscles-in particular, the diaphragm-has not been investigated in detail. Here, we demonstrate that chronic high-fat diet (HFD) feeding impairs diaphragm muscle function, as assessed in vivo by ultrasonography and ex vivo by measurement of contractile force. During an HFD time course, progressive adipose tissue expansion and collagen deposition within the diaphragm parallel contractile deficits. Moreover, intradiaphragmatic fibro-adipogenic progenitors (FAPs) proliferate with long-term HFD feeding while giving rise to adipocytes and type I collagen-depositing fibroblasts. Thrombospondin 1 (THBS1), a circulating adipokine, increases with obesity and induces FAP proliferation. These findings suggest a novel role for FAP-mediated fibro-adipogenic diaphragm remodeling in obesity-associated respiratory dysfunction.

HIF2A-LOX Pathway Promotes Fibrotic Tissue Remodeling in Thyroid-Associated Orbitopathy.

Thyroid-associated orbitopathy (TAO) is a disfiguring periocular connective tissue disease associated with autoimmune thyroid disorders. It is a potentially blinding condition, for which no effective pharmacological treatment has been established. Despite a suggested role played by autoimmune thyrotropin receptor activation in the pathogenesis of TAO, the cellular and molecular events contributing to the fibrotic and inflammatory disease process of TAO are not fully defined. By developing a three-dimensional organoid culture of human orbital fibroblasts (OFs), we sought to determine the molecular mechanism underlying the fibrotic disease process of TAO. In this ex vivo model, we have demonstrated that hypoxia-inducible factor (HIF) 2α (HIF2A), but not its paralog HIF1A, accelerates extracellular matrix (ECM) deposition by inducing a collagen-cross-linking enzyme, lysyl oxidase (LOX). Inhibiting HIF2A and LOX with short hairpin RNA or small molecular antagonists effectively ameliorated fibrotic disease process within TAO organoids. Conversely, the overexpression of a constitutively active HIF2A in mouse OFs was sufficient to initiate LOX-dependent fibrotic tissue remodeling in OF organoids. Consistent with these findings, HIF2A and LOX were highly expressed in human TAO tissues paralleling excess ECM deposition. We propose that the HIF2A-LOX pathway can be a potential therapeutic target for the prevention and treatment of TAO.

Transcription factor 21 (TCF21) promotes proinflammatory interleukin 6 expression and extracellular matrix remodeling in visceral adipose stem cells.

The visceral (VIS) and subcutaneous (SQ) fat pads are developmentally distinct white adipose tissue depots and contribute differently to inflammation and insulin resistance associated with obesity. The basic helix-loop-helix transcriptional regulator, transcription factor 21 (TCF21), is a marker gene for white adipose tissues and is abundantly expressed in VIS-derived adipose stem cells (ASCs), but not in SQ-derived ASCs. However, TCF21's role in regulating fat depot-specific gene expression and function is incompletely understood. Here, using siRNA-mediated Tcf21 knockdowns and lentiviral gene transfer of TCF21 in mouse ASCs, we demonstrate that TCF21 is required for the VIS ASC-specific expression of interleukin 6 (IL6), a key cytokine that contributes to the proinflammatory nature of VIS depots. Concurrently, TCF21 promotes MMP-dependent collagen degradation and type IV collagen deposition through the regulation of the extracellular matrix (ECM) modifiers, matrix metalloproteinase (MMP) 2, MMP13, and tissue inhibitor of MMP1 (TIMP1), as well as collagen type IV α1 chain (COL4A1) in VIS ASCs. We also found that although IL6 mediates the expression of Mmp13 and Timp1 in VIS ASCs, the TCF21-dependent expression of Mmp2 and Col4a1 is IL6-independent. These results suggest that TCF21 contributes to the proinflammatory environment in VIS fat depots and to active ECM remodeling of these depots by regulating IL6 expression and MMP-dependent ECM remodeling in a spatiotemporally coordinated manner.

Membrane-Tethered Metalloproteinase Expressed by Vascular Smooth Muscle Cells Limits the Progression of Proliferative Atherosclerotic Lesions.

BACKGROUND: The MMP (matrix metalloproteinase) family plays diverse and critical roles in directing vascular wall remodeling in atherosclerosis. Unlike secreted-type MMPs, a member of the membrane-type MMP family, MT1-MMP (membrane-type 1 MMP; MMP14), mediates pericellular extracellular matrix degradation that is indispensable for maintaining physiological extracellular matrix homeostasis. However, given the premature mortality exhibited by MT1-MMP-null mice, the potential role of the proteinase in atherogenesis remains elusive. We sought to determine the effects of both MT1-MMP heterozygosity and tissue-specific gene targeting on atherogenesis in APOE (apolipoprotein E)-null mice. METHODS AND RESULTS: MT1-MMP heterozygosity in the APOE-null background (Mmp14+/-Apoe-/- ) significantly promoted atherogenesis relative to Mmp14+/+Apoe-/- mice. Furthermore, the tissue-specific deletion of MT1-MMP from vascular smooth muscle cells (VSMCs) in SM22α-Cre(+)Mmp14F/FApoe-/- (VSMC-knockout) mice likewise increased the severity of atherosclerotic lesions. Although VSMC-knockout mice also developed progressive atherosclerotic aneurysms in their iliac arteries, macrophage- and adipose-specific MT1-MMP-knockout mice did not display this sensitized phenotype. In VSMC-knockout mice, atherosclerotic lesions were populated by hyperproliferating VSMCs (smooth muscle actin- and Ki67-double-positive cells) that were characterized by a proinflammatory gene expression profile. Finally, MT1-MMP-null VSMCs cultured in a 3-dimensional spheroid model system designed to mimic in vivo-like cell-cell and cell-extracellular matrix interactions, likewise displayed markedly increased proliferative potential. CONCLUSIONS: MT1-MMP expressed by VSMCs plays a key role in limiting the progression of atherosclerosis in APOE-null mice by regulating proliferative responses and inhibiting the deterioration of VSMC function in atherogenic vascular walls.

Designing 3-D Adipospheres for Quantitative Metabolic Study.

Quantitative assessment of adipose mitochondrial activity is critical for better understanding of adipose tissue function in obesity and diabetes. While the two-dimensional (2-D) tissue culture method has been sufficient to discover key molecules that regulate adipocyte differentiation and function, the method is insufficient to determine the role of extracellular matrix (ECM) molecules and their modifiers, such as matrix metalloproteinases (MMPs), in regulating adipocyte function in three-dimensional (3-D) in vivo-like microenvironments. By using a 3-D hanging drop tissue culture system, we are able to produce scalable 3-D adipospheres that are suitable for quantitative metabolic study in 3-D microenvironment.

Immunomagnetic Separation of Fat Depot-specific Sca1high Adipose-derived Stem Cells (ASCs).

The isolation of adipose-derived stem cells (ASCs) is an important method in the field of adipose tissue biology, adipogenesis, and extracellular matrix (ECM) remodeling. In vivo, ECM-rich environment consisting of fibrillar collagens provides a structural support to adipose tissues during the progression and regression of obesity. Physiological ECM remodeling mediated by matrix metalloproteinases (MMPs) plays a major role in regulating adipose tissue size and function(1,2). The loss of physiological collagenolytic ECM remodeling may lead to excessive collagen accumulation (tissue fibrosis), macrophage infiltration, and ultimately, a loss of metabolic homeostasis including insulin resistance(3,4). When a phenotypic change of the adipose tissue is observed in gene-targeted mouse models, isolating primary ASCs from fat depots for in vitro studies is an effective approach to define the role of the specific gene in regulating the function of ASCs. In the following, we define an immunomagnetic separation of Sca1(high) ASCs.

Adipose extracellular matrix remodelling in obesity and insulin resistance.

The extracellular matrix (ECM) of adipose tissues undergoes constant remodelling to allow adipocytes and their precursor cells to change cell shape and function in adaptation to nutritional cues. Abnormal accumulation of ECM components and their modifiers in adipose tissues has been recently demonstrated to cause obesity-associated insulin resistance, a hallmark of type 2 diabetes. Integrins and other ECM receptors (e.g. CD44) that are expressed in adipose tissues have been shown to regulate insulin sensitivity. It is well understood that a hypoxic response is observed in adipose tissue expansion during obesity progression and that hypoxic response accelerates fibrosis and inflammation in white adipose tissues. The expansion of adipose tissues should require angiogenesis; however, the excess deposition of ECM limits the angiogenic response of white adipose tissues in obesity. While recent studies have focused on the metabolic consequences and the mechanisms of adipose tissue expansion and remodelling, little attention has been paid to the role played by the interaction between peri-adipocyte ECM and their cognate cell surface receptors. This review will address what is currently known about the roles played by adipose ECM, their modifiers, and ECM receptors in obesity and insulin resistance. Understanding how excess ECM deposition in the adipose tissue deteriorates insulin sensitivity would provide us hints to develop a new therapeutic strategy for the treatment of insulin resistance and type 2 diabetes.

Thrombospondin 1 as a novel biological marker of obesity and metabolic syndrome.

CONTEXT: Thrombospondin 1 (THBS1 or TSP-1) is an adipose-derived matricellular protein, which has recently been highlighted as a potential mediator of insulin resistance and adipose inflammation in obesity. OBJECTIVE: In this study, we aimed to determine the clinical significance of THBS1 as a novel biological marker of visceral obesity, metabolic syndrome, and diabetes. METHODS: The THBS1 mRNA level was quantified with real-time PCR in human adipose tissues obtained from 16 non-obese subjects. The relationships between serum THBS1 level and obesity/diabetes traits as well as the diagnostic components of metabolic syndrome were assessed in 164 normal-weight or overweight/obese subjects (78 males and 86 females; mean age, 50.4; mean BMI, 29.8) with analysis of covariance (ANCOVA) and regression analyses. RESULTS: THBS1 was predominantly expressed in visceral adipose tissues relative to subcutaneous adipose tissues (P<0.001). The visceral THBS1 expression was positively associated with the body mass index (BMI; γs=0.54, P=0.033). ANCOVA demonstrated that the THBS1 level is associated with abdominal obesity (P<0.001), hyperglycemia (P=0.02), and hypertension (P=0.04). Multivariable regression analysis suggested an association between serum THBS1 and fasting plasma glucose levels. The associations between serum THBS1 levels and obesity/diabetes traits were found preferentially in women (BMI, γs=0.30, P=0.05; FPG, γs=0.26, P=0.016). Subanalyses demonstrated that the association with obesity traits was predominantly found in premenopausal women (BMI, γs=0.41, P=0.007), whereas the association with diabetes traits was predominant in postmenopausal women (HbA1c, γs=0.38, P=0.01). During medical weight reduction treatment, the change in the serum THBS1 level was associated with the change in BMI and HbA1c in pre- and postmenopausal women, respectively. CONCLUSIONS: Serum THBS1 is a useful biological marker of obesity and metabolic syndrome in Japanese subjects, particularly in women. THBS1 may act as a critical circulating factor that couples obesity with metabolic syndrome and diabetes in humans.

The exocyst complex regulates free fatty acid uptake by adipocytes.

The exocyst is an octameric molecular complex that drives vesicle trafficking in adipocytes, a rate-limiting step in insulin-dependent glucose uptake. This study assessed the role of the exocyst complex in regulating free fatty acid (FFA) uptake by adipocytes. Upon differentiating into adipocytes, 3T3-L1 cells acquire the ability to incorporate extracellular FFAs in an insulin-dependent manner. A kinetic assay using fluoresceinated FFA (C12 dodecanoic acid) uptake allows the real-time monitoring of FFA internalization by adipocytes. The insulin-dependent uptake of C12 dodecanoic acid by 3T3-L1 adipocytes is mediated by Akt and phosphatidylinositol 3 (PI3)-kinase. Gene silencing of the exocyst components Exo70 and Sec8 significantly reduced insulin-dependent FFA uptake by adipocytes. Consistent with the roles played by Exo70 and Sec8 in FFA uptake, mCherry-tagged Exo70 and HA-tagged Sec8 partially colocalize with lipid droplets within adipocytes, suggesting their active roles in the development of lipid droplets. Tubulin polymerization was also found to regulate FFA uptake in collaboration with the exocyst complex. This study demonstrates a novel role played by the exocyst complex in the regulation of FFA uptake by adipocytes.

Fat depot-specific gene signature and ECM remodeling of Sca1(high) adipose-derived stem cells.

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

3-D adipocyte differentiation and peri-adipocyte collagen turnover.

Peri-adipocyte extracellular matrix (ECM) remodeling is a key biological process observed during adipose tissue development and expansion. The genetic loss of a pericellular collagenase, MMP14 (also known as MT1-MMP), renders mice lipodystrophic with the accumulation of undigested collagen fibers in adipose tissues. MMP14 is not necessary for adipocyte differentiation (adipogenesis) per se under a conventional two-dimensional (2-D) culture condition; however, MMP14 plays a critical role in adipogenesis in vivo. The role of MMP14 in adipogenesis and adipocyte gene expression was uncovered in vitro only when tested within a three-dimensional (3-D) collagen gel, which recapitulated the in vivo ECM-rich environment. Studying adipogenesis in 3-D may serve as an effective experimental approach to bridge gaps in our understanding of in vivo adipocyte biology. Moreover, by assessing the content of collagen family members and their rate of degradation in adipose tissues, we should be able to better define the role of dynamic ECM remodeling in the pathogenesis of obesity and diabetes.

Thrombospondin 1 mediates high-fat diet-induced muscle fibrosis and insulin resistance in male mice.

Thrombospondin 1 (THBS1 or TSP-1) is a circulating glycoprotein highly expressed in hypertrophic visceral adipose tissues of humans and mice. High-fat diet (HFD) feeding induces the robust increase of circulating THBS1 in the early stages of HFD challenge. The loss of Thbs1 protects male mice from diet-induced weight gain and adipocyte hypertrophy. Hyperinsulinemic euglycemic clamp study has demonstrated that Thbs1-null mice are protected from HFD-induced insulin resistance. Tissue-specific glucose uptake study has revealed that the insulin-sensitive phenotype of Thbs1-null mice is mostly mediated by skeletal muscles. Further assessments of the muscle phenotype using RNA sequencing, quantitative PCR, and histological studies have demonstrated that Thbs1-null skeletal muscles are protected from the HFD-dependent induction of Col3a1 and Col6a1, coupled with a new collagen deposition. At the same time, the Thbs1-null mice display a better circadian rhythm and higher amplitude of energy expenditure with a browning phenotype in sc adipose tissues. These results suggest that THBS1, which circulates in response to a HFD, may induce insulin resistance and fibrotic tissue damage in skeletal muscles as well as the de-browning of sc adipose tissues in the early stages of a HFD challenge. Our study may shed new light on the pathogenic role played by a circulating extracellular matrix protein in the cross talk between adipose tissues and skeletal muscles during obesity progression.

On being the right size: scaling effects in designing a human-on-a-chip.

Developing a human-on-a-chip by connecting multiple model organ systems would provide an intermediate screen for therapeutic efficacy and toxic side effects of drugs prior to conducting expensive clinical trials. However, correctly designing individual organs and scaling them relative to each other to make a functional microscale human analog is challenging, and a generalized approach has yet to be identified. In this work, we demonstrate the importance of rational design of both the individual organ and its relationship with other organs, using a simple two-compartment system simulating insulin-dependent glucose uptake in adipose tissues. We demonstrate that inter-organ scaling laws depend on both the number of cells and the spatial arrangement of those cells within the microfabricated construct. We then propose a simple and novel inter-organ 'metabolically supported functional scaling' approach predicated on maintaining in vivo cellular basal metabolic rates by limiting resources available to cells on the chip. This approach leverages findings from allometric scaling models in mammals that limited resources in vivo prompt cells to behave differently than in resource-rich in vitro cultures. Although applying scaling laws directly to tissues can result in systems that would be quite challenging to implement, engineering workarounds may be used to circumvent these scaling issues. Specific workarounds discussed include the limited oxygen carrying capacity of cell culture media when used as a blood substitute and the ability to engineer non-physiological structures to augment organ function, to create the transport-accessible, yet resource-limited environment necessary for cells to mimic in vivo functionality. Furthermore, designing the structure of individual tissues in each organ compartment may be a useful strategy to bypass scaling concerns at the inter-organ level.

Peri-adipocyte ECM remodeling in obesity and adipose tissue fibrosis.

Adipocytes differentiate and function in environments rich in extracellular matrix (ECM) proteins. The phenotypes of genetically modified mice have aided in recognizing the importance of ECM proteins and their modifiers, e.g., proteinases, in the regulation of obesity and metabolism. Most of the molecular mechanisms through which ECM proteins and modifiers regulate adipogenesis or adipocyte function have not been fully defined. Adipose tissue fibrosis may be a factor that links obesity to diabetes or cardiovascular disease risk in conjunction with tissue inflammation. Defining the molecular mechanisms through which the ECM environment regulates adipogenesis and adipocyte function should provide us with a better understanding of the disease link between obesity and diabetes or cardiovascular diseases.