Organ-on-a-chip systems possess a promising future as drug screening assays and as testbeds for disease modeling in the context of both single-organ systems and multi-organ-chips. Although it ...comprises approximately one fourth of the body weight of a healthy human, an organ frequently overlooked in this context is white adipose tissue (WAT). WAT-on-a-chip systems are required to create safety profiles of a large number of drugs due to their interactions with adipose tissue and other organs
via
paracrine signals, fatty acid release, and drug levels through sequestration. We report a WAT-on-a-chip system with a footprint of less than 1 mm
2
consisting of a separate media channel and WAT chamber connected
via
small micropores. Analogous to the
in vivo
blood circulation, convective transport is thereby confined to the vasculature-like structures and the tissues protected from shear stresses. Numerical and analytical modeling revealed that the flow rates in the WAT chambers are less than 1/100 of the input flow rate. Using optimized injection parameters, we were able to inject pre-adipocytes, which subsequently formed adipose tissue featuring fully functional lipid metabolism. The physiologically relevant microfluidic environment of the WAT-chip supported long term culture of the functional adipose tissue for more than two weeks. Due to its physiological, highly controlled, and computationally predictable character, the system has the potential to be a powerful tool for the study of adipose tissue associated diseases such as obesity and type 2 diabetes.
Organs-on-a-chip possess a promising future as drug screening assays and testbeds for disease modeling in the context of both single-organ systems and multi-organ-chips.
The discovery and generation of effective therapeutics to combat disease lies at the heart of biomedical research. Preclinical studies form the foundation of potential disease treatments, guiding ...their journey from scientific discovery to impactful patient outcomes. However, over the past two decades, preclinical research has been frequently plagued by the failure to replicate consistent results, costing an estimated $28 billion USD per year. Potential therapeutics from preclinical studies entering phase I trials only had a 10.4% approval rate between 2003 and 2014 and an even lower 6% to 7% rate between 2011 and 2017. The disappointing reality of promising preclinical findings that fail to translate into effective therapies has raised serious concerns within the scientific community. The cause of this failure is potentially elucidated in a 2015 retrospective analysis of four large biotech companies that showed the most common causes of termination in phase I and II clinical trials since 2003 are the lack of efficacy (60% of all trials) and toxicity (30%). Given these insights and the emergence of advanced technologies that enable large-cohort, in vitro human testing, a pressing need to reassess our approaches to studying human diseases exists. Such changes are vital to facilitating the development of lifesaving therapeutics that can extend both health span and life span by more efficiently.
Impaired white adipose tissue (WAT) function has been recognized as a critical early event in obesity‐driven disorders, but high buoyancy, fragility, and heterogeneity of primary adipocytes have ...largely prevented their use in drug discovery efforts highlighting the need for human stem cell‐based approaches. Here, human stem cells are utilized to derive metabolically functional 3D adipose tissue (iADIPO) in a microphysiological system (MPS). Surprisingly, previously reported WAT differentiation approaches create insulin resistant WAT ill‐suited for type‐2 diabetes mellitus drug discovery. Using three independent insulin sensitivity assays, i.e., glucose and fatty acid uptake and suppression of lipolysis, as the functional readouts new differentiation conditions yielding hormonally responsive iADIPO are derived. Through concomitant optimization of an iADIPO‐MPS, it is abled to obtain WAT with more unilocular and significantly larger (≈40%) lipid droplets compared to iADIPO in 2D culture, increased insulin responsiveness of glucose uptake (≈2–3 fold), fatty acid uptake (≈3–6 fold), and ≈40% suppressing of stimulated lipolysis giving a dynamic range that is competent to current in vivo and ex vivo models, allowing to identify both insulin sensitizers and desensitizers.
This study uses human stem cells to derive metabolically functional 3D adipose tissue in a microphysiological system. Through concomitant optimization, the adipose system shows mostly unilocular and significantly larger lipid droplets, increased insulin responsiveness of glucose uptake, fatty acid uptake, and suppressing of stimulated lipolysis compared to 2D culture, providing a good dynamic range to identify insulin sensitizers and desensitizers.
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BFBNIB, FZAB, GIS, IJS, KILJ, NLZOH, NUK, OILJ, SAZU, SBCE, SBMB, UL, UM, UPUK
Exercise confers protection against obesity, type 2 diabetes and other cardiometabolic diseases
. However, the molecular and cellular mechanisms that mediate the metabolic benefits of physical ...activity remain unclear
. Here we show that exercise stimulates the production of N-lactoyl-phenylalanine (Lac-Phe), a blood-borne signalling metabolite that suppresses feeding and obesity. The biosynthesis of Lac-Phe from lactate and phenylalanine occurs in CNDP2
cells, including macrophages, monocytes and other immune and epithelial cells localized to diverse organs. In diet-induced obese mice, pharmacological-mediated increases in Lac-Phe reduces food intake without affecting movement or energy expenditure. Chronic administration of Lac-Phe decreases adiposity and body weight and improves glucose homeostasis. Conversely, genetic ablation of Lac-Phe biosynthesis in mice increases food intake and obesity following exercise training. Last, large activity-inducible increases in circulating Lac-Phe are also observed in humans and racehorses, establishing this metabolite as a molecular effector associated with physical activity across multiple activity modalities and mammalian species. These data define a conserved exercise-inducible metabolite that controls food intake and influences systemic energy balance.
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EMUNI, FIS, FZAB, GEOZS, GIS, IJS, IMTLJ, KILJ, KISLJ, MFDPS, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, SBMB, SBNM, UKNU, UL, UM, UPUK, VKSCE, ZAGLJ
The activation of brown/beige adipose tissue (BAT) metabolism and the induction of uncoupling protein 1 (UCP1) expression are essential for BAT-based strategies to improve metabolic homeostasis. ...Here, we demonstrate that BAT utilizes actomyosin machinery to generate tensional responses following adrenergic stimulation, similar to muscle tissues. The activation of actomyosin mechanics is critical for the acute induction of oxidative metabolism and uncoupled respiration in UCP1+ adipocytes. Moreover, we show that actomyosin-mediated elasticity regulates the thermogenic capacity of adipocytes via the mechanosensitive transcriptional co-activators YAP and TAZ, which are indispensable for normal BAT function. These biomechanical signaling mechanisms may inform future strategies to promote the expansion and activation of brown/beige adipocytes.
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•BAT adrenergic stimulation induces an actomyosin-based mechanical response•Modulation of actomyosin responses alters oxidative metabolism in adipocytes•Thermogenic gene expression in adipocytes is in part regulated by YAP/TAZ
Tharp et al. show that brown adipocytes engage tensional actomyosin machinery, similar to muscle tissues, following adrenergic stimulation to mediate the thermogenic program and normal BAT function. These effects are mechanistically mediated through the YAP/TAZ pathway and, on a broad level, highlight the importance of cellular mechanics for cell metabolism.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
Obesity-linked insulin resistance is a major precursor to the development of type 2 diabetes. Previous work has shown that phosphorylation of PPARγ (peroxisome proliferator-activated receptor γ) at ...serine 273 by cyclin-dependent kinase 5 (Cdk5) stimulates diabetogenic gene expression in adipose tissues. Inhibition of this modification is a key therapeutic mechanism for anti-diabetic drugs that bind PPARγ, such as the thiazolidinediones and PPARγ partial agonists or non-agonists. For a better understanding of the importance of this obesity-linked PPARγ phosphorylation, we created mice that ablated Cdk5 specifically in adipose tissues. These mice have both a paradoxical increase in PPARγ phosphorylation at serine 273 and worsened insulin resistance. Unbiased proteomic studies show that extracellular signal-regulated kinase (ERK) kinases are activated in these knockout animals. Here we show that ERK directly phosphorylates serine 273 of PPARγ in a robust manner and that Cdk5 suppresses ERKs through direct action on a novel site in MAP kinase/ERK kinase (MEK). Importantly, pharmacological inhibition of MEK and ERK markedly improves insulin resistance in both obese wild-type and ob/ob mice, and also completely reverses the deleterious effects of the Cdk5 ablation. These data show that an ERK/Cdk5 axis controls PPARγ function and suggest that MEK/ERK inhibitors may hold promise for the treatment of type 2 diabetes.
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IJS, KISLJ, NUK, SBMB, UL, UM, UPUK
Human genetics has been instrumental in identification of genetic variants linked to type 2 diabetes. Recently a rare, putative loss-of-function mutation in the orphan G-protein coupled receptor 151 ...(GPR151) was found to be associated with lower odds ratio for type 2 diabetes, but the mechanism behind this association has remained elusive. Here we show that Gpr151 is a fasting- and glucagon-responsive hepatic gene which regulates hepatic gluconeogenesis. Gpr151 ablation in mice leads to suppression of hepatic gluconeogenesis genes and reduced hepatic glucose production in response to pyruvate. Importantly, the restoration of hepatic Gpr151 levels in the Gpr151 knockout mice reverses the reduced hepatic glucose production. In this work, we establish a previously unknown role of Gpr151 in the liver that provides an explanation to the lowered type 2 diabetes risk in individuals with nonsynonymous mutations in GPR151.
The thiazolidinediones (TZDs) are ligands of PPARγ that improve insulin sensitivity, but their use is limited by significant side effects. Recently, we demonstrated a mechanism wherein TZDs improve ...insulin sensitivity distinct from receptor agonism and adipogenesis: reversal of obesity-linked phosphorylation of PPARγ at serine 273. However, the role of this modification hasn’t been tested genetically. Here we demonstrate that mice encoding an allele of PPARγ that cannot be phosphorylated at S273 are protected from insulin resistance, without exhibiting differences in body weight or TZD-associated side effects. Indeed, hyperinsulinemic-euglycemic clamp experiments confirm insulin sensitivity. RNA-seq in these mice reveals reduced expression of Gdf3, a BMP family member. Ectopic expression of Gdf3 is sufficient to induce insulin resistance in lean, healthy mice. We find Gdf3 inhibits BMP signaling and insulin signaling in vitro. Together, these results highlight the diabetogenic role of PPARγ S273 phosphorylation and focus attention on a putative target, Gdf3.
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•Blocking PPARγ S273 phosphorylation protects mice from insulin resistance in obesity•These mice do not show the side effects associated with TZD-based PPARγ agonism•These mice have reduced expression of Gdf3 mainly in macrophages•Gdf3 is sufficient to cause impaired glucose homeostasis in vivo and in vitro
Hall et al. show that mice lacking phosphorylation at serine 273 of PPARγ are protected from developing insulin resistance in response to high-fat-diet feeding, associated with dramatically reduced levels of Gdf3. Gdf3 in turn is sufficient to cause impaired insulin signaling both in vitro and in vivo.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
Coenzyme Q (CoQ) is essential for mitochondrial respiration and required for thermogenic activity in brown adipose tissues (BAT). CoQ deficiency leads to a wide range of pathological manifestations, ...but mechanistic consequences of CoQ deficiency in specific tissues, such as BAT, remain poorly understood. Here, we show that pharmacological or genetic CoQ deficiency in BAT leads to stress signals causing accumulation of cytosolic mitochondrial RNAs and activation of the eIF2α kinase PKR, resulting in activation of the integrated stress response (ISR) with suppression of UCP1 but induction of FGF21 expression. Strikingly, despite diminished UCP1 levels, BAT CoQ deficiency displays increased whole-body metabolic rates at room temperature and thermoneutrality resulting in decreased weight gain on high-fat diets (HFD). In line with enhanced metabolic rates, BAT and inguinal white adipose tissue (iWAT) interorgan crosstalk caused increased browning of iWAT in BAT-specific CoQ deficient animals. This mitohormesis-like effect depends on the ATF4-FGF21 axis and BAT-secreted FGF21, revealing an unexpected role for CoQ in the modulation of whole-body energy expenditure with wide-ranging implications for primary and secondary CoQ deficiencies.
Synopsis
How changes in levels of mitochondrial electron transport chain component coenzyme Q (CoQ) affects systemic metabolism remains poorly understood. Here CoQ deficiency in brown adipose tissue (BAT) is shown to activate mitochondrial stress signaling, white adipose tissue browning and whole-body respiration.
Depletion of CoQ in BAT triggers the mitochondrial unfolded protein response and integrated stress response.
BAT CoQ deficiency results in cytosolic accumulation of mitochondrial RNA, leading to PKR activation, ATF4 induction and, as a result, UCP1 suppression.
FGF21 secretion from CoQ-deficient BAT influences whole-body metabolism, culminating in the metabolic remodeling of inguinal white adipose tissue.
The ATF4-FGF21 axis in BAT elicits mitohormetic protective responses in peripheral tissues and metabolic adaptation to BAT CoQ deficiency.
Adipose tissue browning and enhanced whole-body respiration are systemic consequences of coenzyme Q depletion and resulting mitochondrial stress signaling.
Oxysterols are oxidized derivatives of cholesterol that play regulatory roles in lipid biosynthesis and homeostasis. How oxysterol signaling coordinates different lipid classes such as sterols and ...triglycerides remains incompletely understood. Here, we show that 4β-hydroxycholesterol (HC) (4β-HC), a liver and serum abundant oxysterol of poorly defined functions, is a potent and selective inducer of the master lipogenic transcription factor, SREBP1c, but not the related steroidogenic transcription factor SREBP2. By correlating tracing of lipid synthesis with lipogenic gene expression profiling, we found that 4β-HC acts as a putative agonist for the liver X receptor (LXR), a sterol sensor and transcriptional regulator previously linked to SREBP1c activation. Unique among the oxysterol agonists of the LXR, 4β-HC induced expression of the lipogenic program downstream of SREBP1c and triggered de novo lipogenesis both in primary hepatocytes and in the mouse liver. In addition, 4β-HC acted in parallel to insulin-PI3K–dependent signaling to stimulate triglyceride synthesis and lipid-droplet accumulation. Thus, 4β-HC is an endogenous regulator of de novo lipogenesis through the LXR-SREBP1c axis.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
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