Adipose Tissue Analysis Toolkit (ATAT) for automated analysis of adipocyte size and extracellular matrix in white adipose tissue.

OBJECTIVE: The pathological expansion of white adipose tissue (WAT) in obesity involves adipocyte hypertrophy accompanied by expansion of the collagen-rich pericellular extracellular matrix (ECM) and development of crown-like structures (CLS). Traditionally, WAT morphology is assessed through immunohistochemical analysis of WAT sections. However, manual analysis of large histological sections is time-consuming, and the available digital tools for analyzing adipocyte size and pericellular ECM are limited. To address this gap, the authors developed the Adipose Tissue Analysis Toolkit (ATAT), an ImageJ plugin facilitating analysis of adipocyte size, WAT ECM, and CLS. METHODS AND RESULTS: ATAT utilizes local and image-level differentials in pixel intensity to independently threshold image background, distinguishing adipocyte-free tissue without user input. It accurately captures adipocytes in histological sections stained with common dyes and automates the analysis of adipocyte cross-sectional area, total-field, and localized region-of-interest ECM. ATAT allows fully automated batch analysis of histological images using default or user-defined adipocyte detection parameters. CONCLUSIONS: ATAT provides several advantages over existing WAT image analysis tools, enabling high-throughput analyses of adipocyte-specific parameters and facilitating the assessment of ECM changes associated with WAT remodeling due to weight changes and other pathophysiological alterations that affect WAT function.

Downregulation of the kidney glucagon receptor, essential for renal function and systemic homeostasis, contributes to chronic kidney disease.

The glucagon receptor (GCGR) in the kidney is expressed in nephron tubules. In humans and animal models with chronic kidney disease, renal GCGR expression is reduced. However, the role of kidney GCGR in normal renal function and in disease development has not been addressed. Here, we examined its role by analyzing mice with constitutive or conditional kidney-specific loss of the Gcgr. Adult renal Gcgr knockout mice exhibit metabolic dysregulation and a functional impairment of the kidneys. These mice exhibit hyperaminoacidemia associated with reduced kidney glucose output, oxidative stress, enhanced inflammasome activity, and excess lipid accumulation in the kidney. Upon a lipid challenge, they display maladaptive responses with acute hypertriglyceridemia and chronic proinflammatory and profibrotic activation. In aged mice, kidney Gcgr ablation elicits widespread renal deposition of collagen and fibronectin, indicative of fibrosis. Taken together, our findings demonstrate an essential role of the renal GCGR in normal kidney metabolic and homeostatic functions. Importantly, mice deficient for kidney Gcgr recapitulate some of the key pathophysiological features of chronic kidney disease.

Leptin Reduction as a Required Component for Weight Loss.

Partial leptin reduction can induce significant weight loss, while weight loss contributes to partial leptin reduction. The cause-and-effect relationship between leptin reduction and weight loss remains to be further elucidated. Here, we show that FGF21 and the glucagon-like peptide 1 receptor (GLP-1R) agonist liraglutide rapidly induced a reduction in leptin. This leptin reduction contributed to the beneficial effects of GLP-1R agonism in metabolic health, as transgenically maintaining leptin levels during treatment partially curtailed the beneficial effects seen with these agonists. Moreover, a higher degree of leptin reduction during treatment, induced by including a leptin neutralizing antibody with either FGF21 or liraglutide, synergistically induced greater weight loss and better glucose tolerance in diet-induced obese mice. Furthermore, upon cessation of either liraglutide or FGF21 treatment, the expected immediate weight regain was observed, associated with a rapid increase in circulating leptin levels. Prevention of this leptin surge with leptin neutralizing antibodies slowed down weight gain and preserved better glucose tolerance. Mechanistically, a significant reduction in leptin induced a higher degree of leptin sensitivity in hypothalamic neurons. Our observations support a model that postulates that a reduction of leptin levels is a necessary prerequisite for substantial weight loss, and partial leptin reduction is a viable strategy to treat obesity and its associated insulin resistance.

Hyperleptinemia contributes to antipsychotic drug-associated obesity and metabolic disorders.

Despite their high degree of effectiveness in the management of psychiatric conditions, exposure to antipsychotic drugs, including olanzapine and risperidone, is frequently associated with substantial weight gain and the development of diabetes. Even before weight gain, a rapid rise in circulating leptin concentrations can be observed in most patients taking antipsychotic drugs. To date, the contribution of this hyperleptinemia to weight gain and metabolic deterioration has not been defined. Here, with an established mouse model that recapitulates antipsychotic drug-induced obesity and insulin resistance, we not only confirm that hyperleptinemia occurs before weight gain but also demonstrate that hyperleptinemia contributes directly to the development of obesity and associated metabolic disorders. By suppressing the rise in leptin through the use of a monoclonal leptin-neutralizing antibody, we effectively prevented weight gain, restored glucose tolerance, and preserved adipose tissue and liver function in antipsychotic drug-treated mice. Mechanistically, suppressing excess leptin resolved local tissue and systemic inflammation typically associated with antipsychotic drug treatment. We conclude that hyperleptinemia is a key contributor to antipsychotic drug-associated weight gain and metabolic deterioration. Leptin suppression may be an effective approach to reducing the undesirable side effects of antipsychotic drugs.

Adipose Tissue Analysis Toolkit (ATAT) for Automated Analysis of Adipocyte Size and Extracellular Matrix in White Adipose Tissue.

Objective: The pathological expansion of white adipose tissue (WAT) in obesity involves adipocyte hypertrophy accompanied by expansion of collagen-rich pericellular extracellular matrix (ECM) and the development of crown-like structures (CLS). Traditionally, WAT morphology is assessed through immunohistochemical analysis of WAT sections. However, manual analysis of large histological sections is time-consuming, and available digital tools for analyzing adipocyte size and pericellular ECM are limited. To address this gap, we developed the Adipose Tissue Analysis Toolkit (ATAT), an ImageJ plugin facilitating analysis of adipocyte size, WAT ECM and CLS. Methods and Results: ATAT utilizes local and image-level differentials in pixel intensity to independently threshold background, distinguishing adipocyte-free tissue without user input. It accurately captures adipocytes in histological sections stained with common dyes and automates the analysis of adipocyte cross-sectional area, total-field, and localized region-of-interest ECM. ATAT allows fully automated batch analysis of histological images using default or user-defined adipocyte detection parameters. Conclusions: ATAT provides several advantages over existing WAT image analysis tools, enabling high-throughput analyses of adipocyte-specific parameters and facilitating the assessment of ECM changes associated with WAT remodeling due to weight changes and other pathophysiological alterations that affect WAT function. Study Importance Questions: What is already known about this subject?: The manual analysis of large WAT histological sections is very time-consuming, while digital tools for the analysis of WAT are limited.What are the new findings in your manuscript?: - ATAT enables fully automated analysis of batches of histological images using either default or user-defined adipocyte detection parameters- ATAT allows high-throughput analyses of adipocyte-specific parameters and pericellular extracellular matrix- ATAT enables the assessment of fibrotic changes associated with WAT remodeling and crown-like structuresHow might your results change the direction of research or the focus of clinical practice?: - ATAT is designed to work with histological sections and digital images obtained using a slide scanner or a microscope.- This tool will help basic and clinical researchers to conduct automated analyses of adipose tissue histological sections.

Adipocyte mesenchymal transition contributes to mammary tumor progression.

Obesity is associated with increased cancer incidence and progression. However, the relationship between adiposity and cancer remains poorly understood at the mechanistic level. Here, we report that adipocytes from tumor-invasive mammary fat undergo de-differentiation to fibroblast-like precursor cells during tumor progression and integrate into the tumor microenvironment. Single-cell sequencing reveals that these de-differentiated adipocytes lose their original identities and transform into multiple cell types, including myofibroblast- and macrophage-like cells, with their characteristic features involved in immune response, inflammation, and extracellular matrix remodeling. The de-differentiated cells are metabolically distinct from tumor-associated fibroblasts but exhibit comparable effects on tumor cell proliferation. Inducing de-differentiation by Xbp1s overexpression promotes tumor progression despite lower adiposity. In contrast, promoting lipid-storage capacity in adipocytes through MitoNEET overexpression curbs tumor growth despite greater adiposity. Collectively, the metabolic interplay between tumor cells and adipocytes induces adipocyte mesenchymal transition and contributes to reconfigure the stroma into a more tumor-friendly microenvironment.

Activating Connexin43 gap junctions primes adipose tissue for therapeutic intervention.

Adipose tissue is a promising target for treating obesity and metabolic diseases. However, pharmacological agents usually fail to effectively engage adipocytes due to their extraordinarily large size and insufficient vascularization, especially in obese subjects. We have previously shown that during cold exposure, connexin43 (Cx43) gap junctions are induced and activated to connect neighboring adipocytes to share limited sympathetic neuronal input amongst multiple cells. We reason the same mechanism may be leveraged to improve the efficacy of various pharmacological agents that target adipose tissue. Using an adipose tissue-specific Cx43 overexpression mouse model, we demonstrate effectiveness in connecting adipocytes to augment metabolic efficacy of the ß 3-adrenergic receptor agonist Mirabegron and FGF21. Additionally, combing those molecules with the Cx43 gap junction channel activator danegaptide shows a similar enhanced efficacy. In light of these findings, we propose a model in which connecting adipocytes via Cx43 gap junction channels primes adipose tissue to pharmacological agents designed to engage it. Thus, Cx43 gap junction activators hold great potential for combination with additional agents targeting adipose tissue.

Mitochondrial regulation and white adipose tissue homeostasis.

The important role of mitochondria in the regulation of white adipose tissue (WAT) remodeling and energy balance is increasingly appreciated. The remarkable heterogeneity of the adipose tissue stroma provides a cellular basis to enable adipose tissue plasticity in response to various metabolic stimuli. Regulating mitochondrial function at the cellular level in adipocytes, in adipose progenitor cells (APCs), and in adipose tissue macrophages (ATMs) has a profound impact on adipose homeostasis. Moreover, mitochondria facilitate the cell-to-cell communication within WAT, as well as the crosstalk with other organs, such as the liver, the heart, and the pancreas. A better understanding of mitochondrial regulation in the diverse adipose tissue cell types allows us to develop more specific and efficient approaches to improve adipose function and achieve improvements in overall metabolic health.

Cannabinoid receptor 1 signaling in hepatocytes and stellate cells does not contribute to NAFLD.

The endocannabinoid system regulates appetite and energy expenditure and inhibitors of cannabinoid receptor 1 (CB-1) induce weight loss with improvement in components of the metabolic syndrome. While CB-1 blockage in brain is responsible for weight loss, many of the metabolic benefits associated with CB-1 blockade have been attributed to inhibition of CB-1 signaling in the periphery. As a result, there has been interest in developing a peripherally restricted CB-1 inhibitor for the treatment of nonalcoholic fatty liver disease (NAFLD) that would lack the unwanted centrally mediated side effects. Here, we produced mice that lacked CB-1 in hepatocytes or stellate cells to determine if CB-1 signaling contributes to the development of NAFLD or liver fibrosis. Deletion of CB-1 in hepatocytes did not alter the development of NAFLD in mice fed a high-sucrose diet (HSD) or a high-fat diet (HFD). Similarly, deletion of CB-1 specifically in stellate cells also did not prevent the development of NAFLD in mice fed the HFD, nor did it protect mice from carbon tetrachloride-induced fibrosis. Combined, these studies do not support a direct role for hepatocyte or stellate cell CB-1 signaling in the development of NAFLD or liver fibrosis.

Adipocyte iron levels impinge on a fat-gut crosstalk to regulate intestinal lipid absorption and mediate protection from obesity.

Iron overload is positively associated with diabetes risk. However, the role of iron in adipose tissue remains incompletely understood. Here, we report that transferrin-receptor-1-mediated iron uptake is differentially required for distinct subtypes of adipocytes. Notably, adipocyte-specific transferrin receptor 1 deficiency substantially protects mice from high-fat-diet-induced metabolic disorders. Mechanistically, low cellular iron levels have a positive impact on the health of the white adipose tissue and can restrict lipid absorption from the intestine through modulation of vesicular transport in enterocytes following high-fat diet feeding. Specific reduction of adipocyte iron by AAV-mediated overexpression of the iron exporter Ferroportin1 in adult mice effectively mimics these protective effects. In summary, our studies highlight an important role of adipocyte iron in the maintenance of systemic metabolism through an adipocyte-enterocyte axis, offering an additional level of control over caloric influx into the system after feeding by regulating intestinal lipid absorption.

Adiponectin preserves metabolic fitness during aging.

Adiponectin is essential for the regulation of tissue substrate utilization and systemic insulin sensitivity. Clinical studies have suggested a positive association of circulating adiponectin with healthspan and lifespan. However, the direct effects of adiponectin on promoting healthspan and lifespan remain unexplored. Here, we are using an adiponectin null mouse and a transgenic adiponectin overexpression model. We directly assessed the effects of circulating adiponectin on the aging process and found that adiponectin null mice display exacerbated age-related glucose and lipid metabolism disorders. Moreover, adiponectin null mice have a significantly shortened lifespan on both chow and high-fat diet. In contrast, a transgenic mouse model with elevated circulating adiponectin levels has a dramatically improved systemic insulin sensitivity, reduced age-related tissue inflammation and fibrosis, and a prolonged healthspan and median lifespan. These results support a role of adiponectin as an essential regulator for healthspan and lifespan.

Dermal adipocytes contribute to the metabolic regulation of dermal fibroblasts.

Dermal fibroblasts are an essential population of skin cells. They are not only responsible for synthesis and remodelling of the extracellular matrix of the dermis, but also communicate with other skin cells via autocrine and paracrine interactions. Skin-associated dermal adipocytes reside below the reticular dermis. Strong lipolysis is observed during the regression of dermal adipocytes. However, the nature of the local intercellular crosstalk in which lipids released by dermal adipocytes affecting the metabolism of adjacent skin fibroblasts has not yet been examined. With the use of a series of novel mouse models that allow us to manipulate adipocytes, we demonstrate that dermal adipocytes can modulate the structure of the dermis through regulating extracellular matrix production in dermal fibroblasts. Fatty acids released by dermal adipocytes are involved in this process. Our observations offer new in vivo insights into the role of dermal adipocyte-derived lipids in influencing metabolism of adjacent local cells in the skin through a paracrine effect in the microenvironment of the dermal adipocyte.

The ER stress-autophagy axis: implications for cognitive dysfunction in diabetes mellitus.

Unfolded protein response (UPR) often coordinates with autophagy to maintain cellular proteostasis. Disturbance of proteostasis correlates with diseases including diabetes and neurological complications. In a recent article in Clinical Science, Kong et al. highlighted the critical role of endoplasmic reticulum (ER) stress-autophagy axis in maintaining cognitive functions and provided pharmacological evidence with respect to cognitive improvements in a diabetic mouse model. These novel findings present new insights into the pathological mechanisms and therapeutic implications with the ER stress modulators in diabetes-related cognitive dysfunction.

Suppressing adipocyte inflammation promotes insulin resistance in mice.

OBJECTIVE: Obesity-induced insulin resistance is closely associated with chronic subclinical inflammation in white adipose tissue. However, the mechanistic involvement of adipocyte-derived inflammation under these disease conditions remains unclear. Our aim was to investigate the relative inflammation-related contributions of adipocytes and macrophages to insulin sensitivity. METHODS: RIDα/ß is an adenoviral protein complex that inhibits several inflammatory pathways, including TLR4, TNFα, and IL1ß signaling. We generated novel mouse models with adipocyte-specific and macrophage-specific doxycycline (dox)-inducible RIDα/ß-transgenic mice (RIDad and RIDmac mice, respectively). RESULTS: RIDα/ß induction significantly reduced LPS-stimulated inflammatory markers, such as Tnf, Il1b, and Saa3 in adipose tissues. Surprisingly, RIDad mice had elevated levels of postprandial glucose and insulin and exhibited glucose intolerance and insulin resistance, even under chow-fed conditions. Moreover, the RIDad mice displayed further insulin resistance under obesogenic (high-fat diet, HFD) conditions despite reduced weight gain. In addition, under pre-existing obese and inflamed conditions on an HFD, subsequent induction of RIDα/ß in RIDad mice reduced body weight gain, further exacerbating glucose tolerance, enhancing insulin resistance and fatty liver, and reducing adiponectin levels. This occurred despite effective suppression of the inflammatory pathways (including TNFα and IL1ß). In contrast, RIDmac mice, upon HFD feeding, displayed similar weight gain, comparable adiponectin levels, and insulin sensitivity, suggesting that the inflammatory properties of macrophages did not exert a negative impact on metabolic readouts. RIDα/ß expression and the ensuing suppression of inflammation in adipocytes enhanced adipose tissue fibrosis and reduced vascularization. CONCLUSION: Our novel findings further corroborate our previous observations suggesting that suppressing adipocyte inflammation impairs adipose tissue function and promotes insulin resistance, despite beneficial effects on weight gain.

Partial leptin deficiency confers resistance to diet-induced obesity in mice.

OBJECTIVE: Hyperleptinemia per se is sufficient to promote leptin resistance in the obese state. Leptin sensitivity can be restored by reducing circulating leptin levels within a physiologically healthy range and is a viable antiobesity and antidiabetic strategy. However, a previous study suggests that partial leptin deficiency favors diet-induced obesity and related metabolic disorders in mice, arguing that a lower leptin level may indeed promote diet-induced obesity and its associated metabolic disorders. Here, we aim to elucidate what the impact of partial leptin deficiency is on fat mass and insulin sensitivity. METHODS: We used two different mouse models of partial leptin deficiency: an adipocyte-specific congenital heterozygous leptin knockout mouse line (LepHZ) and the well-established whole body heterozygous leptin knockout mouse (OBHZ). The metabolic studies of OBHZ and LepHZ mice were performed both on normal carbohydrate-rich chow diet and on a high-fat diet (HFD). Male and female mice were included in the study to account for sex-specific differences. Body weight, food intake, glucose tolerance, and insulin tolerance were tested. Histology of adipose tissue and liver tissue allowed insights into adipose tissue inflammation and hepatic triglyceride content. Immunohistochemistry was paired with RT-PCR analysis for expression levels of inflammatory markers. RESULTS: Both OBHZ and LepHZ mice displayed reduced circulating leptin levels on the chow diet and HFD. On chow diet, male OBHZ and LepHZ mice showed elevated fat mass and body weight, while their glucose tolerance and insulin sensitivity remained unchanged. However, the inability in partially leptin-deficient mice to fully induce circulating leptin during the development of diet-induced obesity results in reduced food intake and leaner mice with lower body weight compared to their littermate controls. Importantly, a strong reduction of adipose tissue inflammation is observed along with improvements in insulin sensitivity and enhanced glucose tolerance. Additionally, partial leptin deficiency protects the mice from fatty liver and liver fibrosis. Chronically HFD-fed OBHZ and LepHZ mice remain more sensitive to exogenous leptin injection, as reflected by their reduced food intake upon an acute leptin treatment. CONCLUSION: In response to HFD feeding, the inability to upregulate leptin levels due to partial leptin deficiency protects mice from diet-induced obesity and metabolic dysregulation. Thus, in an obesogenic environment, maintaining lower leptin levels is highly beneficial for both obesity and diabetes management. Chronic leptin reduction represents a viable preventive strategy whose efficacy awaits clinical testing.

Partial Leptin Reduction as an Insulin Sensitization and Weight Loss Strategy.

The physiological role of leptin is thought to be a driving force to reduce food intake and increase energy expenditure. However, leptin therapies in the clinic have failed to effectively treat obesity, predominantly due to a phenomenon referred to as leptin resistance. The mechanisms linking obesity and the associated leptin resistance remain largely unclear. With various mouse models and a leptin neutralizing antibody, we demonstrated that hyperleptinemia is a driving force for metabolic disorders. A partial reduction of plasma leptin levels in the context of obesity restores hypothalamic leptin sensitivity and effectively reduces weight gain and enhances insulin sensitivity. These results highlight that a partial reduction in plasma leptin levels leads to improved leptin sensitivity, while pointing to a new avenue for therapeutic interventions in the treatment of obesity and its associated comorbidities.

Dermal adipose tissue has high plasticity and undergoes reversible dedifferentiation in mice.

Dermal adipose tissue (also known as dermal white adipose tissue and herein referred to as dWAT) has been the focus of much discussion in recent years. However, dWAT remains poorly characterized. The fate of the mature dermal adipocytes and the origin of the rapidly reappearing dermal adipocytes at different stages remain unclear. Here, we isolated dermal adipocytes and characterized dermal fat at the cellular and molecular level. Together with dWAT's dynamic responses to external stimuli, we established that dermal adipocytes are a distinct class of white adipocytes with high plasticity. By combining pulse-chase lineage tracing and single-cell RNA sequencing, we observed that mature dermal adipocytes undergo dedifferentiation and redifferentiation under physiological and pathophysiological conditions. Upon various challenges, the dedifferentiated cells proliferate and redifferentiate into adipocytes. In addition, manipulation of dWAT highlighted an important role for mature dermal adipocytes for hair cycling and wound healing. Altogether, these observations unravel a surprising plasticity of dermal adipocytes and provide an explanation for the dynamic changes in dWAT mass that occur under physiological and pathophysiological conditions, and highlight the important contributions of dWAT toward maintaining skin homeostasis.

Immunologic and endocrine functions of adipose tissue: implications for kidney disease.

Excess adiposity can induce adverse sequelae in multiple cell types and organ systems. The transition from the lean to the obese state is characterized by fundamental cellular changes at the level of the adipocyte. These changes affect the local microenvironment within the respective adipose tissue but can also affect nonadipose systems. Adipocytes within fat pads respond to chronic nutrient excess through hyperplasia or hypertrophy, which can differentially affect interorgan crosstalk between various adipose depots and other organs. This crosstalk is dependent on the unique ability of the adipocyte to coordinate metabolic adjustments throughout the body and to integrate responses to maintain metabolic homeostasis. These actions occur through the release of free fatty acids and metabolites during times of energy need - a process that is altered in the obese state. In addition, adipocytes release a wide array of signalling molecules, such as sphingolipids, as well as inflammatory and hormonal factors (adipokines) that are critical for interorgan crosstalk. The interactions of adipose tissue with the kidney - referred to as the adipo-renal axis - are important for normal kidney function as well as the response of the kidney to injury. Here, we discuss the mechanistic basis of this interorgan crosstalk, which clearly has great therapeutic potential given the increasing rates of chronic kidney disease secondary to obesity and type 2 diabetes mellitus.