Adipocyte Glucocorticoid Receptor Deficiency Attenuates Aging- and HFD-Induced Obesity and Impairs the Feeding-Fasting Transition

The role of oxidative stress, glucocorticoid receptor and ARMC5 in lipid metabolism

Lipid metabolism includes lipogenesis, lipolysis, and cholesterol metabolism and it exerts a wide range of biological effects. We previously found novel roles of adipocyte oxidative stress in diet-induced obesity, adipocyte glucocorticoid receptor in Cushing syndrome, and ARMC5 in adrenocortical cells. Using genetically modified mice in which oxidative stress was eliminated or augmented specifically in adipose tissues, we have been able to elucidate that obesity-induced oxidative stress inhibited healthy adipose expansion and ameliorated insulin sensitivity. Using adipocyte-specific glucocorticoid receptor knockout mice, we found that glucocorticoids also inhibited healthy adipose expansion and decreased insulin sensitivity. This was partly due to the transcriptional upregulation of ATGL. We identified ARMC5 as a novel ubiquitin E3 ligase of full-length SREBF, a master regulator of lipid metabolism. In adrenocortical cells, ARMC5 suppresses SREBF2 activity, and loss of ARMC5 may lead to cholesterol accumulation and the development of primary bilateral macronodular adrenal hyperplasia.

Stress increases sperm respiration and motility in mice and men

Semen quality and fertility has declined over the last 50 years, corresponding to ever-increasing environmental stressors. However, the cellular mechanisms involved and their impact on sperm functions remain unknown. In a repeated sampling human cohort study, we identify a significant effect of prior perceived stress to increase sperm motility 2-3 months following stress, timing that expands upon our previous studies revealing significant stress-associated changes in sperm RNA important for fertility. We mechanistically examine this post-stress timing in mice using an in vitro stress model in the epididymal epithelial cells responsible for sperm maturation and find 7282 differentially H3K27me3 bound DNA regions involving genes critical for mitochondrial and metabolic pathways. Further, prior stress exposure significantly changes the composition and size of epithelial cell-secreted extracellular vesicles that when incubated with mouse sperm, increase mitochondrial respiration and sperm motility, adding to our prior work showing impacts on embryo development. Together, these studies identify a time-dependent, translational signaling pathway that communicates stress experience to sperm, ultimately affecting reproductive functions.

Deficiency of glucocorticoid receptor in bone marrow adipocytes has mild effects on bone and hematopoiesis but does not influence expansion of marrow adiposity with caloric restriction

Introduction

Unlike white adipose tissue depots, bone marrow adipose tissue (BMAT) expands during caloric restriction (CR). Although mechanisms for BMAT expansion remain unclear, prior research suggested an intermediary role for increased circulating glucocorticoids.

Methods

In this study, we utilized a recently described mouse model (BMAd-Cre) to exclusively target bone marrow adipocytes (BMAds) for elimination of the glucocorticoid receptor (GR) (i.e. Nr3c1) whilst maintaining GR expression in other adipose depots.

Results

Mice lacking GR in BMAds (BMAd-Nr3c1 -/-) and control mice (BMAd-Nr3c1 +/+) were fed ad libitum or placed on a 30% CR diet for six weeks. On a normal chow diet, tibiae of female BMAd-Nr3c1-/- mice had slightly elevated proximal trabecular metaphyseal bone volume fraction and thickness. Both control and BMAd-Nr3c1-/- mice had increased circulating glucocorticoids and elevated numbers of BMAds in the proximal tibia following CR. However, no significant differences in trabecular and cortical bone were observed, and quantification with osmium tetroxide and μCT revealed no difference in BMAT accumulation between control or BMAd-Nr3c1 -/- mice. Differences in BMAd size were not observed between BMAd-Nr3c1-/- and control mice. Interestingly, BMAd-Nr3c1-/- mice had decreased circulating white blood cell counts 4 h into the light cycle.

Discussion

In conclusion, our data suggest that eliminating GR from BMAd has minor effects on bone and hematopoiesis, and does not impair BMAT accumulation during CR.

Effects of glucocorticoids on adipose tissue plasticity

Glucocorticoids (GCs) play an important role in metabolic adaptation, regulating carbohydrate-lipid homeostasis and the immune system. Because they also have anti-inflammatory and immunosuppressive properties, synthetic analogues of GCs have been developed and are widely used in the treatment of chronic inflammatory conditions and in organ transplantation. GCs are among the most commonly prescribed drugs in the world. However, long term and high GC doses can cause side effects such as GC-induced diabetes and lipodystrophy. In recent years, a large number of independent studies have reported the effects of constitutive and adipocyte-specific deletion of the GC receptor (GR) in mice under different diets and treatments, resulting in contrasting phenotypes. To avoid potential compensatory mechanisms associated with the constitutive adipocyte GR silencing during adipose tissue development, our team has generated an inducible mouse model of GR deletion specifically in the adipocyte (AdipoGR-KO). Using this mouse model, we were able to demonstrate the critical role of the adipocyte GR in GC-induced metabolic changes. Indeed, under conditions of hypercorticism, AdipoGR-KO mice showed an improvement in glucose tolerance and insulin sensitivity, as well as in lipid profile, despite a massive increase in adiposity. This result is explained by a densification of adipose tissue vascularization, highlighting the repressive role of adipocyte GR in the healthy expansion of this tissue. Our work has largely contributed to the demonstration of the important role of the adipocyte GR in the physiology and pathophysiology of the adipose tissue and its impact on energy homeostasis.

Adipocyte Glucocorticoid Receptor Activation With High Glucocorticoid Doses Impairs Healthy Adipose Tissue Expansion by Repressing Angiogenesis

In humans, glucocorticoids (GCs) are commonly prescribed because of their anti-inflammatory and immunosuppressive properties. However, high doses of GCs often lead to side effects, including diabetes and lipodystrophy. We recently reported that adipocyte glucocorticoid receptor (GR)-deficient (AdipoGR-KO) mice under corticosterone (CORT) treatment exhibited a massive adipose tissue (AT) expansion associated with a paradoxical improvement of metabolic health compared with control mice. However, whether GR may control adipose development remains unclear. Here, we show a specific induction of hypoxia-inducible factor 1α (HIF-1α) and proangiogenic vascular endothelial growth factor A (VEGFA) expression in GR-deficient adipocytes of AdipoGR-KO mice compared with control mice, together with an increased adipose vascular network, as assessed by three-dimensional imaging. GR activation reduced HIF-1α recruitment to the Vegfa promoter resulting from Hif-1α downregulation at the transcriptional and posttranslational levels. Importantly, in CORT-treated AdipoGR-KO mice, the blockade of VEGFA by a soluble decoy receptor prevented AT expansion and the healthy metabolic phenotype. Finally, in subcutaneous AT from patients with Cushing syndrome, higher VEGFA expression was associated with a better metabolic profile. Collectively, these results highlight that adipocyte GR negatively controls AT expansion and metabolic health through the downregulation of the major angiogenic effector VEGFA and inhibition of vascular network development.

ARTICLE HIGHLIGHTS

Lipidomics for diagnosis and prognosis of pulmonary hypertension

Background

Pulmonary hypertension (PH) poses a significant health threat with high morbidity and mortality, necessitating improved diagnostic tools for enhanced management. Current biomarkers for PH lack functionality and comprehensive diagnostic and prognostic capabilities. Therefore, there is a critical need to develop biomarkers that address these gaps in PH diagnostics and prognosis.

Methods

To address this need, we employed a comprehensive metabolomics analysis in 233 blood based samples coupled with machine learning analysis. For functional insights, human pulmonary arteries (PA) of idiopathic pulmonary arterial hypertension (PAH) lungs were investigated and the effect of extrinsic FFAs on human PA endothelial and smooth muscle cells was tested in vitro.

Results

PA of idiopathic PAH lungs showed lipid accumulation and altered expression of lipid homeostasis-related genes. In PA smooth muscle cells, extrinsic FFAs caused excessive proliferation and endothelial barrier dysfunction in PA endothelial cells, both hallmarks of PAH.In the training cohort of 74 PH patients, 30 disease controls without PH, and 65 healthy controls, diagnostic and prognostic markers were identified and subsequently validated in an independent cohort. Exploratory analysis showed a highly impacted metabolome in PH patients and machine learning confirmed a high diagnostic potential. Fully explainable specific free fatty acid (FFA)/lipid-ratios were derived, providing exceptional diagnostic accuracy with an area under the curve (AUC) of 0.89 in the training and 0.90 in the validation cohort, outperforming machine learning results. These ratios were also prognostic and complemented established clinical prognostic PAH scores (FPHR4p and COMPERA2.0), significantly increasing their hazard ratios (HR) from 2.5 and 3.4 to 4.2 and 6.1, respectively.

Conclusion

In conclusion, our research confirms the significance of lipidomic alterations in PH, introducing innovative diagnostic and prognostic biomarkers. These findings may have the potential to reshape PH management strategies.

Adipocyte Glucocorticoid Receptor Inhibits Immune Regulatory Genes to Maintain Immune Cell Homeostasis in Adipose Tissue

Glucocorticoids acting via the glucocorticoid receptors (GR) are key regulators of metabolism and the stress response. However, uncontrolled or excessive GR signaling adversely affects adipose tissue, including endocrine, immune, and metabolic functions. Inflammation of the adipose tissue promotes systemic metabolic dysfunction; however, the molecular mechanisms underlying the role of adipocyte GR in regulating genes associated with adipose tissue inflammation are poorly understood. We performed in vivo studies using adipocyte-specific GR knockout mice in conjunction with in vitro studies to understand the contribution of adipocyte GR in regulating adipose tissue immune homeostasis. Our findings show that adipocyte-specific GR signaling regulates adipokines at both mRNA and plasma levels and immune regulatory (Coch, Pdcd1, Cemip, and Cxcr2) mRNA gene expression, which affects myeloid immune cell presence in white adipose tissue. We found that, in adipocytes, GR directly influences Cxcr2. This chemokine receptor promotes immune cell migration, indirectly affecting Pdcd1 and Cemip gene expression in nonadipocyte or stromal cells. Our findings suggest that GR adipocyte signaling suppresses inflammatory signals, maintaining immune homeostasis. We also found that GR signaling in adipose tissue in response to stress is sexually dimorphic. Understanding the molecular relationship between GR signaling and adipose tissue inflammation could help develop potential targets to improve local and systemic inflammation, insulin sensitivity, and metabolic health.

Social Isolation and Breast Cancer

Although the role of life stressors in breast cancer remains unclear, social isolation is consistently associated with increased breast cancer risk and mortality. Social isolation can be defined as loneliness or an absence of perceived social connections. In female mice and rats, social isolation is mimicked by housing animals 1 per cage. Social isolation causes many biological changes, of which an increase in inflammatory markers and disruptions in mitochondrial and cellular metabolism are commonly reported. It is not clear how the 2 traditional stress-induced pathways, namely, the hypothalamic-pituitary-adrenocortical axis (HPA), resulting in a release of glucocorticoids from the adrenal cortex, and autonomic nervous system (ANS), resulting in a release of catecholamines from the adrenal medulla and postganglionic neurons, could explain the increased breast cancer risk in socially isolated individuals. For instance, glucocorticoid receptor activation in estrogen receptor positive breast cancer cells inhibits their proliferation, and activation of β-adrenergic receptor in immature immune cells promotes their differentiation toward antitumorigenic T cells. However, activation of HPA and ANS pathways may cause a disruption in the brain-gut-microbiome axis, resulting in gut dysbiosis. Gut dysbiosis, in turn, leads to an alteration in the production of bacterial metabolites, such as short chain fatty acids, causing a systemic low-grade inflammation and inducing dysfunction in mitochondrial and cellular metabolism. A possible causal link between social isolation-induced increased breast cancer risk and mortality and gut dysbiosis should be investigated, as it offers new tools to prevent breast cancer.

Acute Deletion of the Glucocorticoid Receptor in Hepatocytes Disrupts Postprandial Lipid Metabolism in Male Mice

Hepatic lipid metabolism is highly dynamic, and disruption of several circadian transcriptional regulators results in hepatic steatosis. This includes genetic disruption of the glucocorticoid receptor (GR) as the liver develops. To address the functional role of GR in the adult liver, we used an acute hepatocyte-specific GR knockout model to study temporal hepatic lipid metabolism governed by GR at several preprandial and postprandial circadian timepoints. Lipidomics analysis revealed significant temporal lipid metabolism, where GR disruption results in impaired regulation of specific triglycerides, nonesterified fatty acids, and sphingolipids. This correlates with increased number and size of lipid droplets and mildly reduced mitochondrial respiration, most noticeably in the postprandial phase. Proteomics and transcriptomics analyses suggest that dysregulated lipid metabolism originates from pronounced induced expression of enzymes involved in fatty acid synthesis, β-oxidation, and sphingolipid metabolism. Integration of GR cistromic data suggests that induced gene expression is a result of regulatory actions secondary to direct GR effects on gene transcription.

Inherited stress resiliency prevents the development of metabolic alterations in diet-induced obese mice

OBJECTIVE

Chronic stress promotes obesity and metabolic comorbidities. The ability of individuals to cope with stress may serve as an important parameter in the development of obesity-related metabolic outcomes. The aim of this study was to clarify whether differences in stress response affect metabolic health under obesity.

METHODS

The study was performed in a selectively bred mouse model of social dominance (Dom) and submissiveness (Sub), which exhibit stress resilience or vulnerability, respectively. Mice were given a high-fat diet (HFD) or standard diet, followed by physiological, histological, and molecular analyses.

RESULTS

The HFD caused hyperleptinemia, glucose intolerance, insulin resistance, steatosis of the liver and pancreas, and brown adipose tissue whitening in Sub mice, whereas Dom mice were protected from these consequences of the HFD. The HFD increased circulating levels of interleukin (IL)-1β and induced the expression of proinflammatory genes in the liver and in epididymal white adipose tissue of Sub mice, with no changes in Dom mice. The Cox2 inhibitor celecoxib (15 mg/kg/d) reduced serum IL-1β, improved glucose tolerance and insulin sensitivity, and prevented hepatic and brown adipose tissue whitening in HFD-fed Sub mice.

CONCLUSIONS

The extent of stress resiliency is associated with inflammation and contributes to population heterogeneity in the development of healthy or unhealthy obesity.

Glucocorticoid activation of anti-inflammatory macrophages protects against insulin resistance

Insulin resistance (IR) during obesity is linked to adipose tissue macrophage (ATM)-driven inflammation of adipose tissue. Whether anti-inflammatory glucocorticoids (GCs) at physiological levels modulate IR is unclear. Here, we report that deletion of the GC receptor (GR) in myeloid cells, including macrophages in mice, aggravates obesity-related IR by enhancing adipose tissue inflammation due to decreased anti-inflammatory ATM leading to exaggerated adipose tissue lipolysis and severe hepatic steatosis. In contrast, GR deletion in Kupffer cells alone does not alter IR. Co-culture experiments show that the absence of GR in macrophages directly causes reduced phospho-AKT and glucose uptake in adipocytes, suggesting an important function of GR in ATM. GR-deficient macrophages are refractory to alternative ATM-inducing IL-4 signaling, due to reduced STAT6 chromatin loading and diminished anti-inflammatory enhancer activation. We demonstrate that GR has an important function in macrophages during obesity by limiting adipose tissue inflammation and lipolysis to promote insulin sensitivity.

Role of glucocorticoid receptor (GR) in white adipose tissue beiging

AIM

Glucocorticoids (GCs) play a crucial role in energy homeostasis including white adipose tissue function; however, chronic GC excess is detrimental to mammals' health. White hypertrophic adiposity is a main factor for neuroendocrine-metabolic dysfunctions in monosodium L-glutamate (MSG)-damaged hypercorticosteronemic rat. Nevertheless, little is known about the receptor path in endogenous GC impact on white adipose tissue-resident precursor cells to bring them into beige lineage. Thus, our aim was to explore whether transient/chronic endogenous hypercorticosteronemia affects browning capacity in white adipose tissue pads from MSG rats during development.

MAIN METHODS

Control and MSG male rats aged 30 and 90 days were 7-day exposed to cold conditions in order to stimulate wet white epidydimal adipose tissue (wEAT) beiging capacity. This procedure was also replicated in adrenalectomized rats.

KEY FINDINGS

Data indicated that whereas epidydimal white adipose tissue pads from prepubertal hypercorticosteronemic rats retained full expression of GR/MR genes resulting in a drastic reduction in wEAT beiging capacity, conversely, chronic hypercorticosteronemic adult MSG rats developed down-regulation of corticoid genes (and reduced GR cytosolic mediators) in wEAT pads and consequently partially restored local beiging capacity. Finally, wEAT pads from adrenalectomized rats revealed up-regulation of GR gene accompanied by full local beiging capacity.

SIGNIFICANCE

This study strongly supports a GR-dependent inhibitory effect of GC excess on white adipose tissue browning, an issue strongly supporting a key role of GR in the non-shivering thermogenic process. As a consequence, normalizing the GC milieu could be a relevant factor to handle dysmetabolism in white hyperadipose phenotypes.

Ectopic lipid metabolism in anterior pituitary dysfunction

Over the past decades, adapted lifestyle and dietary habits in industrialized countries have led to a progress of obesity and associated metabolic disorders. Concomitant insulin resistance and derangements in lipid metabolism foster the deposition of excess lipids in organs and tissues with limited capacity of physiologic lipid storage. In organs pivotal for systemic metabolic homeostasis, this ectopic lipid content disturbs metabolic action, thereby promotes the progression of metabolic disease, and inherits a risk for cardiometabolic complications. Pituitary hormone syndromes are commonly associated with metabolic diseases. However, the impact on subcutaneous, visceral, and ectopic fat stores between disorders and their underlying hormonal axes is rather different, and the underlying pathophysiological pathways remain largely unknown. Pituitary disorders might influence ectopic lipid deposition indirectly by modulating lipid metabolism and insulin sensitivity, but also directly by organ specific hormonal effects on energy metabolism. In this review, we aim to I) provide information about the impact of pituitary disorders on ectopic fat stores, II) and to present up-to-date knowledge on potential pathophysiological mechanisms of hormone action in ectopic lipid metabolism.

11β-HSD as a New Target in Pharmacotherapy of Metabolic Diseases

Glucocorticoids (GCs), which are secreted by the adrenal cortex, are important regulators in the metabolism of carbohydrates, lipids, and proteins. For the proper functioning of the body, strict control of their release is necessary, as increased GCs levels may contribute to the development of obesity, type 2 diabetes mellitus, hypertension, cardiovascular diseases, and other pathological conditions contributing to the development of metabolic syndrome. 11β-hydroxysteroid dehydrogenase type I (11β-HSD1) locally controls the availability of the active glucocorticoid, namely cortisol and corticosterone, for the glucocorticoid receptor. Therefore, the participation of 11β-HSD1 in the development of metabolic diseases makes both this enzyme and its inhibitors attractive targets in the pharmacotherapy of the above-mentioned diseases.

Differential In Vitro Effects of SGLT2 Inhibitors on Mitochondrial Oxidative Phosphorylation, Glucose Uptake and Cell Metabolism

(1) The cardio-reno-metabolic benefits of the SGLT2 inhibitors canagliflozin (cana), dapagliflozin (dapa), ertugliflozin (ertu), and empagliflozin (empa) have been demonstrated, but it remains unclear whether they exert different off-target effects influencing clinical profiles. (2) We aimed to investigate the effects of SGLT2 inhibitors on mitochondrial function, cellular glucose-uptake (GU), and metabolic pathways in human-umbilical-vein endothelial cells (HUVECs). (3) At 100 µM (supra-pharmacological concentration), cana decreased ECAR by 45% and inhibited GU (IC5o: 14 µM). At 100 µM and 10 µM (pharmacological concentration), cana increased the ADP/ATP ratio, whereas dapa and ertu (3, 10 µM, about 10× the pharmacological concentration) showed no effect. Cana (100 µM) decreased the oxygen consumption rate (OCR) by 60%, while dapa decreased it by 7%, and ertu and empa (all 100 µM) had no significant effect. Cana (100 µM) inhibited GLUT1, but did not significantly affect GLUTs’ expression levels. Cana (100 µM) treatment reduced glycolysis, elevated the amino acids supplying the tricarboxylic-acid cycle, and significantly increased purine/pyrimidine-pathway metabolites, in contrast to dapa (3 µM) and ertu (10 µM). (4) The results confirmed cana´s inhibition of mitochondrial activity and GU at supra-pharmacological and pharmacological concentrations, whereas the dapa, ertu, and empa did not show effects even at supra-pharmacological concentrations. At supra-pharmacological concentrations, cana (but not dapa or ertu) affected multiple cellular pathways and inhibited GLUT1.

A macrophage-hepatocyte glucocorticoid receptor axis coordinates fasting ketogenesis

Fasting metabolism and immunity are tightly linked; however, it is largely unknown how immune cells contribute to metabolic homeostasis during fasting in healthy subjects. Here, we combined cell-type-resolved genomics and computational approaches to map crosstalk between hepatocytes and liver macrophages during fasting. We identified the glucocorticoid receptor (GR) as a key driver of fasting-induced reprogramming of the macrophage secretome including fasting-suppressed cytokines and showed that lack of macrophage GR impaired induction of ketogenesis during fasting as well as endotoxemia. Mechanistically, macrophage GR suppressed the expression of tumor necrosis factor (TNF) and promoted nuclear translocation of hepatocyte GR to activate a fat oxidation/ketogenesis-related gene program, cooperatively induced by GR and peroxisome proliferator-activated receptor alpha (PPARα) in hepatocytes. Together, our results demonstrate how resident liver macrophages directly influence ketogenesis in hepatocytes, thereby also outlining a strategy by which the immune system can set the metabolic tone during inflammatory disease and infection.

Glucocorticoids coordinate macrophage metabolism through the regulation of the tricarboxylic acid cycle

OBJECTIVES

Glucocorticoids (GCs) are one of the most widely prescribed anti-inflammatory drugs. By acting through their cognate receptor, the glucocorticoid receptor (GR), GCs downregulate the expression of pro-inflammatory genes and upregulate the expression of anti-inflammatory genes. Metabolic pathways have recently been identified as key parts of both the inflammatory activation and anti-inflammatory polarization of macrophages, immune cells responsible for acute inflammation and tissue repair. It is currently unknown whether GCs control macrophage metabolism, and if so, to what extent metabolic regulation by GCs confers anti-inflammatory activity.

METHODS

Using transcriptomic and metabolomic profiling of macrophages, we identified GC-controlled pathways involved in metabolism, especially in mitochondrial function.

RESULTS

Metabolic analyses revealed that GCs repress glycolysis in inflammatory myeloid cells and promote tricarboxylic acid (TCA) cycle flux, promoting succinate metabolism and preventing intracellular accumulation of succinate. Inhibition of ATP synthase attenuated GC-induced transcriptional changes, likely through stalling of TCA cycle anaplerosis. We further identified a glycolytic regulatory transcription factor, HIF1α, as regulated by GCs, and as a key regulator of GC responsiveness during inflammatory challenge.

CONCLUSIONS

Our findings link metabolism to gene regulation by GCs in macrophages.

The Glucocorticoid Receptor in Osterix-Expressing Cells Regulates Bone Mass, Bone Marrow Adipose Tissue, and Systemic Metabolism in Female Mice During Aging

Hallmarks of aging-associated osteoporosis include bone loss, bone marrow adipose tissue (BMAT) expansion, and impaired osteoblast function. Endogenous glucocorticoid levels increase with age, and elevated glucocorticoid signaling, associated with chronic stress and dysregulated metabolism, can have a deleterious effect on bone mass. Canonical glucocorticoid signaling through the glucocorticoid receptor (GR) was recently investigated as a mediator of osteoporosis during the stress of chronic caloric restriction. To address the role of the GR in an aging-associated osteoporotic phenotype, the current study utilized female GR conditional knockout (GR-CKO; GR^fl/fl :Osx-Cre+) mice and control littermates on the C57BL/6 background aged to 21 months and studied in comparison to young (3- and 6-month-old) mice. GR deficiency in Osx-expressing cells led to low bone mass and BMAT accumulation that persisted with aging. Surprisingly, however, GR-CKO mice also exhibited alterations in muscle mass (reduced % lean mass and soleus fiber size), accompanied by reduced voluntary physical activity, and also exhibited higher whole-body metabolic rate and elevated blood pressure. Moreover, increased lipid storage was observed in GR-CKO osteoblastic cultures in a glucocorticoid-dependent fashion despite genetic deletion of the GR, and could be reversed via pharmacological inhibition of the mineralocorticoid receptor (MR). These findings provide evidence of a role for the GR (and possibly the MR) in facilitating healthy bone maintenance with aging in females. The effects of GR-deficient bone on whole-body physiology also demonstrate the importance of bone as an endocrine organ and suggest evidence for compensatory mechanisms that facilitate glucocorticoid signaling in the absence of osteoblastic GR function; these represent new avenues of research that may improve understanding of glucocorticoid signaling in bone toward the development of novel osteogenic agents. © 2021 American Society for Bone and Mineral Research (ASBMR).

Metabolic profiling of attached and detached metformin and 2-deoxy-D-glucose treated breast cancer cells reveals adaptive changes in metabolome of detached cells

Anchorage-independent growth of cancer cells in vitro is correlated to metastasis formation in vivo. Metformin use is associated with decreased breast cancer incidence and currently evaluated in cancer clinical trials. The combined treatment with metformin and 2-deoxy-D-glucose (2DG) in vitro induces detachment of viable MDA-MB-231 breast cancer cells that retain their proliferation capacity. This might be important for cell detachment from primary tumors, but the metabolic changes involved are unknown. We performed LC/MS metabolic profiling on separated attached and detached MDA-MB-231 cells treated with metformin and/or 2DG. High 2DG and metformin plus 2DG altered the metabolic profile similarly to metformin, inferring that metabolic changes are necessary but not sufficient while the specific effects of 2DG are crucial for detachment. Detached cells had higher NADPH levels and lower fatty acids and glutamine levels compared to attached cells, supporting the role of AMPK activation and reductive carboxylation in supporting anchorage-independent survival. Surprisingly, the metabolic profile of detached cells was closer to untreated control cells than attached treated cells, suggesting detachment might help cells adapt to energy stress. Metformin treated cells had higher fatty and amino acid levels with lower purine nucleotide levels, which is relevant for understanding the anticancer mechanisms of metformin.

Glucocorticoid/Adiponectin Axis Mediates Full Activation of Cold-Induced Beige Fat Thermogenesis

Glucocorticoids (GCs), a class of corticosteroids produced by the adrenal cortex in response to stress, exert obesity-promoting effects. Although adaptive thermogenesis has been considered an effective approach to counteract obesity, whether GCs play a role in regulating cold stress-induced thermogenesis remains incompletely understood. Here, we show that the circulating levels of stress hormone corticosterone (GC in rodents) were significantly elevated, whereas the levels of adiponectin, an adipokine that was linked to cold-induced adaptive thermogenesis, were decreased 48 h post cold exposure. The administration of a glucocorticoid hydrocortisone downregulated adiponectin protein and mRNA levels in both WAT and white adipocytes, and upregulated thermogenic gene expression in inguinal fat. In contrast, mifepristone, a glucocorticoid receptor antagonist, enhanced adiponectin expression and suppressed energy expenditure in vivo. Mechanistically, hydrocortisone suppressed adiponectin expression by antagonizing PPARγ in differentiated 3T3-L1 adipocytes. Ultimately, adiponectin deficiency restored mifepristone-decreased oxygen consumption and suppressed the expression of thermogenic genes in inguinal fat. Taken together, our study reveals that the GCs/adiponectin axis is a key regulator of beige fat thermogenesis in response to acute cold stress.

Genomic and Non-Genomic Actions of Glucocorticoids on Adipose Tissue Lipid Metabolism

Glucocorticoids (GCs) are hormones that aid the body under stress by regulating glucose and free fatty acids. GCs maintain energy homeostasis in multiple tissues, including those in the liver and skeletal muscle, white adipose tissue (WAT), and brown adipose tissue (BAT). WAT stores energy as triglycerides, while BAT uses fatty acids for heat generation. The multiple genomic and non-genomic pathways in GC signaling vary with exposure duration, location (adipose tissue depot), and species. Genomic effects occur directly through the cytosolic GC receptor (GR), regulating the expression of proteins related to lipid metabolism, such as ATGL and HSL. Non-genomic effects act through mechanisms often independent of the cytosolic GR and happen shortly after GC exposure. Studying the effects of GCs on adipose tissue breakdown and generation (lipolysis and adipogenesis) leads to insights for treatment of adipose-related diseases, such as obesity, coronary disease, and cancer, but has led to controversy among researchers, largely due to the complexity of the process. This paper reviews the recent literature on the genomic and non-genomic effects of GCs on WAT and BAT lipolysis and proposes research to address the many gaps in knowledge related to GC activity and its effects on disease.

A guide to changing paradigms of glucocorticoid receptor function-a model system for genome regulation and physiology

The glucocorticoid receptor (GR) is a bona fide ligand-regulated transcription factor. Cloned in the 80s, the GR has become one of the best-studied and clinically most relevant members of the nuclear receptor superfamily. Cooperative activity of GR with other transcription factors and a plethora of coregulators contribute to the tissue- and context-specific response toward the endogenous and pharmacological glucocorticoids (GCs). Furthermore, nontranscriptional activities in the cytoplasm are emerging as an additional function of GR. Over the past 40 years, the concepts of GR mechanisms of action had been constantly changing. Different methodologies in the pregenomic and genomic era of molecular biological research and recent cutting-edge technology in single-cell and single-molecule analysis are steadily evolving the views, how the GR in particular and transcriptional regulation in general act in physiological and pathological processes. In addition to the development of technologies for GR analysis, the use of model organisms provides insights how the GR in vivo executes GC action in tissue homeostasis, inflammation, and energy metabolism. The model organisms, namely the mouse, but also rats, zebrafish, and recently fruit flies carrying mutations of the GR became a major driving force to analyze the molecular function of GR in disease models. This guide provides an overview of the exciting research and paradigm shifts in the GR field from past to present with a focus on GR transcription factor networks, GR DNA-binding and single-cell analysis, and model systems.

Studying Metabolic Abnormalities in the Costello Syndrome HRAS G12V Mouse Model: Isolation of Mouse Embryonic Fibroblasts and Their In Vitro Adipocyte Differentiation

Costello syndrome (CS), characterized by a developmental delay and a failure to thrive, is also associated with an impaired lipid and energy metabolism. White adipose tissue is a central sensor of whole-body energy homeostasis, and HRAS hyperactivation may affect adipocyte differentiation and mature adipocyte homeostasis. An extremely useful tool for delineating in vitro intrinsic cellular signaling leading to metabolic alterations during adipogenesis is mouse embryonic fibroblasts, known to differentiate into adipocytes in response to adipogenesis-stimulating factors. Here, we describe in detail the isolation and maintenance of CS HRAS G12V mouse embryonic fibroblasts, their differentiation into adipocytes, and an assessment of adipocyte differentiation.

Mesoporous silica coated CeO2 nanozymes with combined lipid-lowering and antioxidant activity induce long-term improvement of the metabolic profile in obese Zucker rats

Obesity is one of the most important public health problems that is associated with an array of metabolic disorders linked to cardiovascular disease, stroke, type 2 diabetes, and cancer. A sustained therapeutic approach to stop the escalating prevalence of obesity and its associated metabolic comorbidities remains elusive. Herein, we developed a novel nanocomposite based on mesoporous silica coated cerium oxide (CeO₂) nanozymes that reduce the circulating levels of fatty acids and remarkably improve the metabolic phenotype in a model of obese Zucker rats five weeks after its administration. Lipidomic and gene expression analyses showed an amelioration of the hyperlipidemia and of the hepatic and adipose metabolic dysregulations, which was associated with a down-regulation of the hepatic PI3K/mTOR/AKT pathway and a reduction of the M1 proinflammatory cytokine TNF-α. In addition, the coating of the CeO₂ maximized its cell antioxidant protective effects and minimized non-hepatic biodistribution. The one-pot synthesis method for the nanocomposite fabrication is implemented entirely in aqueous solution, room temperature and open atmosphere conditions, favoring scalability and offering a safe and translatable lipid-lowering and antioxidant nanomedicine to treat metabolic comorbidities associated with obesity. This approach may be further applied to address other metabolic disorders related to hyperlipidemia, low-grade inflammation and oxidative stress.

A physiological glucocorticoid rhythm is an important regulator of brown adipose tissue function

Objective

Brown adipose tissue (BAT) displays a strong circadian rhythm in metabolic activity, but it is unclear how this rhythm is regulated. As circulating levels of corticosterone coincide with the rhythm of triglyceride-derived fatty acid (FA) uptake by BAT, we investigated whether corticosterone regulates BAT circadian rhythm.

Methods

Corticosterone levels were flattened by implanting mice with subcutaneous corticosterone-releasing pellets, resulting in constant circulating corticosterone levels.

Results

Flattened corticosterone rhythm caused a complete loss of circadian rhythm in triglyceride-derived fatty acid uptake by BAT. This effect was independent of glucocorticoid receptor expression in (brown) adipocytes and was not caused by deregulation of clock gene expression or overexposure to glucocorticoids, but rather seemed mediated by reduced sympathetic innervation of BAT. In a mouse model of hyperlipidemia and metabolic syndrome, long-term experimental flattening of corticosterone − and thus rhythm in BAT function − resulted in adiposity.

Conclusions

This study highlights that a physiological rhythm in glucocorticoids is an important regulator of BAT function and essential for the maintenance of metabolic health.

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Flattening of corticosterone rhythm blunts circadian activity of brown adipose tissue.

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Disturbed corticosterone rhythm − rather than overexposure− is responsible for blunted brown adipose tissue activity.

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The metabolic effect of flattened corticosterone levels is independent of adipocyte glucocorticoid receptor expression.

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Long-term flattening of corticosterone levels results in increased adiposity in a female mouse model for metabolic syndrome.

Obesity-induced excess of 17-hydroxyprogesterone promotes hyperglycemia through activation of glucocorticoid receptor

Type 2 diabetes mellitus (T2DM) has become an expanding global public health problem. Although the glucocorticoid receptor (GR) is an important regulator of glucose metabolism, the relationship between circulating glucocorticoids (GCs) and the features of T2DM remains controversial. Here, we show that 17-hydroxyprogesterone (17-OHP), an intermediate steroid in the biosynthetic pathway that converts cholesterol to cortisol, binds to and stimulates the transcriptional activity of GR. Hepatic 17-OHP concentrations are increased in diabetic mice and patients due to aberrantly increased expression of Cyp17A1. Systemic administration of 17-OHP or overexpression of Cyp17A1 in the livers of lean mice promoted the pathogenesis of hyperglycemia and insulin resistance, whereas knockdown of Cyp17A1 abrogated metabolic disorders in obese mice. Therefore, our results identify a Cyp17A1/17-OHP/GR-dependent pathway in the liver that mediates obesity-induced hyperglycemia, suggesting that selectively targeting hepatic Cyp17A1 may provide a therapeutic avenue for treating T2DM.

Molecular Mechanisms of Glucocorticoid-Induced Insulin Resistance

Glucocorticoids (GCs) are steroids secreted by the adrenal cortex under the hypothalamic-pituitary-adrenal axis control, one of the major neuro-endocrine systems of the organism. These hormones are involved in tissue repair, immune stability, and metabolic processes, such as the regulation of carbohydrate, lipid, and protein metabolism. Globally, GCs are presented as ‘flight and fight’ hormones and, in that purpose, they are catabolic hormones required to mobilize storage to provide energy for the organism. If acute GC secretion allows fast metabolic adaptations to respond to danger, stress, or metabolic imbalance, long-term GC exposure arising from treatment or Cushing’s syndrome, progressively leads to insulin resistance and, in fine, cardiometabolic disorders. In this review, we briefly summarize the pharmacological actions of GC and metabolic dysregulations observed in patients exposed to an excess of GCs. Next, we describe in detail the molecular mechanisms underlying GC-induced insulin resistance in adipose tissue, liver, muscle, and to a lesser extent in gut, bone, and brain, mainly identified by numerous studies performed in animal models. Finally, we present the paradoxical effects of GCs on beta cell mass and insulin secretion by the pancreas with a specific focus on the direct and indirect (through insulin-sensitive organs) effects of GCs. Overall, a better knowledge of the specific action of GCs on several organs and their molecular targets may help foster the understanding of GCs’ side effects and design new drugs that possess therapeutic benefits without metabolic adverse effects.

Stress, glucocorticoid signaling pathway, and metabolic disorders

BACKGROUND AND AIMS

Glucocorticoids and the GR serve as an essential molecular mediator of stress and different physiologic processes. This review summarizes main findings from studies on the role of the GC/GR signaling in the modulation of genes for nutrient processing by the different organs involved in metabolic diseases.

METHODS

Descriptive review of relevant papers known to the author was conducted.

RESULTS

Several high-throughput screenings in the past 15 years have identified potential GR DNA-binding regions in different cell types with genes that are annotated to be important for the control of metabolism. Transcriptional regulation of these GC-responsive genes provides links between the hypothalamic-pituitary-adrenal axis (HPA) and systemic energy homeostasis in both physiological and pathophysiological states. Future studies must reconsider the use of agonist, the utilization of animal models of stress and metabolic disorders, and validation in humans.

CONCLUSION

This review recapitulates the significant role of the GC/GR signaling in molecular metabolic control and metabolic disorders. Potential future research focus and optimizations have also been identified.

Regulation of thermogenic adipocytes during fasting and cold

Cold exposure activates brown and brown-like adipocytes that dissipate large amounts of glucose and fatty acids via uncoupling protein 1 (UCP1) to drive non-shivering thermogenesis (NST). Evidence for the existence of these thermogenic adipocytes in adult humans gave rise to a renaissance in research on brown adipose tissue, establishing it as linchpin of energy homeostasis and metabolic health. Besides low ambient temperature, shortage or excess of food affect thermoregulation. Upon high caloric meals thermogenic adipocytes burn excess calories and maintain energy balance. In contrast, in conditions of nutrient deprivation, counter-regulatory mechanisms prevent thermogenic adipocytes from "wasting" energy substrates that need to be conserved. In this review, we discuss cell-autonomous mechanisms, metabolites, and hormones that modify NST in response to nutrient fluctuations. In particular, we focus on how thermogenic adipocytes balance thermogenesis with systemic energy homeostasis during fasting periods.

Natural constituents from food sources as therapeutic agents for obesity and metabolic diseases targeting adipose tissue inflammation

Adipose tissue, an endocrine and paracrine organ, plays critical roles in the regulation of whole-body metabolic homeostasis. Obesity is accompanied with a chronic low-grade inflammation status in adipose tissue, which disrupts its endocrine function and results in metabolic derangements, such as type 2 diabetes. Dietary bioactive components, such as flavonoids, polyphenols and unsaturated fatty acids from fruits and vegetables, have been widely revealed to alleviate both systemic and adipose tissue inflammation, and improve metabolic disorders. Remarkably, some dietary bioactive components mitigate the inflammatory response in adipocytes, macrophages, and other immune cells, and modulate the crosstalk between adipocytes and macrophages or other immune cells, in adipose tissue. Epidemiological and preclinical studies related to these substances have indicated beneficial effects on adipose tissue inflammation. The main purpose of this review is to provide a comprehensive and up-to-date state of knowledge on dietary components targeting adipose tissue inflammation and their underlying mechanisms. These natural products have great potential to be developed as functional food or lead compounds for treating and/or preventing metabolic disorders.

Role of Mineralocorticoid Receptor in Adipogenesis and Obesity in Male Mice

Increased visceral adiposity and hyperglycemia, 2 characteristics of metabolic syndrome, are also present in conditions of excess glucocorticoids (GCs). GCs are hormones thought to act primarily via the glucocorticoid receptor (GR). GCs are commonly prescribed for inflammatory disorders, yet their use is limited due to many adverse metabolic side effects. In addition to GR, GCs also bind the mineralocorticoid receptor (MR), but there are many conflicting studies about the exact role of MR in metabolic disease. Using MR knockout mice (MRKO), we find that both white and brown adipose depots form normally when compared with wild-type mice at P5. We created mice with adipocyte-specific deletion of MR (FMRKO) to better understand the role of MR in metabolic dysfunction. Treatment of mice with excess GCs for 4 weeks, via corticosterone in drinking water, induced increased fat mass and glucose intolerance to similar levels in FMRKO and floxed control mice. Separately, when fed a high-fat diet for 16 weeks, FMRKO mice had reduced body weight, fat mass, and hepatic steatosis, relative to floxed control mice. Decreased adiposity likely resulted from increased energy expenditure since food intake was not different. RNA sequencing analysis revealed decreased enrichment of genes associated with adipogenesis in inguinal white adipose of FMRKO mice. Differentiation of mouse embryonic fibroblasts (MEFs) showed modestly impaired adipogenesis in MRKO MEFs compared with wild type, but this was rescued upon the addition of peroxisome proliferator-activated receptor gamma (PPARγ) agonist or PPARγ overexpression. Collectively, these studies provide further evidence supporting the potential value of MR as a therapeutic target for conditions associated with metabolic syndrome.

Correlation among body composition and metabolic regulation in a male mouse model of Cushing's syndrome

Glucocorticoids play a critical role in the regulation of homeostasis, including metabolism. In patients with Cushing's syndrome, chronic glucocorticoid excess disrupts physiological internal milieu, resulting in central obesity, muscle atrophy, fatty liver, and insulin resistance. However, the relationship among various metabolic effects of glucocorticoids remains unknown. In the present study, we studied a male mouse model of Cushing's syndrome and indicated that glucocorticoid excess alters metabolic phenotype and body composition involving possible communication among skeletal muscle, liver, and adipose tissue.

Endogenous Glucocorticoid Signaling in the Regulation of Bone and Marrow Adiposity: Lessons from Metabolism and Cross Talk in Other Tissues

PURPOSE OF REVIEW

The development of adiposity in the bone marrow, known as marrow adipose tissue (MAT), is often associated with musculoskeletal frailty. Glucocorticoids, which are a key component of the biological response to stress, affect both bone and MAT. These molecules signal through receptors such as the glucocorticoid receptor (GR), but the role of the GR in regulation of MAT is not yet clear from previous studies. The purpose of this review is to establish and determine the role of GR-mediated signaling in marrow adiposity by comparing and contrasting what is known against other energy-storing tissues like adipose tissue, liver, and muscle, to provide better insight into the regulation of MAT during times of metabolic stress (e.g., dietary challenges, aging).

RECENT FINDINGS

GR-mediated glucocorticoid signaling is critical for proper storage and utilization of lipids in cells such as adipocytes and hepatocytes and proteolysis in muscle, impacting whole-body composition, energy utilization, and homeostasis through a complex network of tissue cross talk between these systems. Loss of GR signaling in bone promotes increased MAT and decreased bone mass. GR-mediated signaling in the liver, adipose tissue, and muscle is critical for whole-body energy and metabolic homeostasis, and both similarities and differences in GR-mediated GC signaling in MAT as compared with these tissues are readily apparent. It is clear that GC-induced pathways work together through these tissues to affect systemic biology, and understanding the role of bone in these patterns of tissue cross talk may lead to a better understanding of MAT-bone biology that improves treatment strategies for frailty-associated diseases.

The glucocorticoid receptor in brown adipocytes is dispensable for control of energy homeostasis

Aberrant activity of the glucocorticoid (GC)/glucocorticoid receptor (GR) endocrine system has been linked to obesity-related metabolic dysfunction. Traditionally, the GC/GR axis has been believed to play a crucial role in adipose tissue formation and function in both, white (WAT) and brown adipose tissue (BAT). While recent studies have challenged this notion for WAT, the contribution of GC/GR signaling to BAT-dependent energy homeostasis remained unknown. Here, we have generated and characterized a BAT-specific GR-knockout mouse (GRBATKO ), for the first time allowing to genetically interrogate the metabolic impact of BAT-GR. The HPA axis in GRBATKO mice was intact, as was the ability of mice to adapt to cold. BAT-GR was dispensable for the adaptation to fasting-feeding cycles and the development of diet-induced obesity. In obesity, glucose and lipid metabolism, insulin sensitivity, and food intake remained unchanged, aligning with the absence of changes in thermogenic gene expression. Together, we demonstrate that the GR in UCP1-positive BAT adipocytes plays a negligible role in systemic metabolism and BAT function, thereby opposing a long-standing paradigm in the field.

Alternate Day Fasting Improves Physiological and Molecular Markers of Aging in Healthy, Non-obese Humans

Caloric restriction and intermittent fasting are known to prolong life- and healthspan in model organisms, while their effects on humans are less well studied. In a randomized controlled trial study (ClinicalTrials.gov identifier: NCT02673515), we show that 4 weeks of strict alternate day fasting (ADF) improved markers of general health in healthy, middle-aged humans while causing a 37% calorie reduction on average. No adverse effects occurred even after >6 months. ADF improved cardiovascular markers, reduced fat mass (particularly the trunk fat), improving the fat-to-lean ratio, and increased β-hydroxybutyrate, even on non-fasting days. On fasting days, the pro-aging amino-acid methionine, among others, was periodically depleted, while polyunsaturated fatty acids were elevated. We found reduced levels sICAM-1 (an age-associated inflammatory marker), low-density lipoprotein, and the metabolic regulator triiodothyronine after long-term ADF. These results shed light on the physiological impact of ADF and supports its safety. ADF could eventually become a clinically relevant intervention.

Glucocorticoids and Brown Adipose Tissue: Do glucocorticoids really inhibit thermogenesis?

A reduction in the thermogenic activity of brown adipose tissue (BAT) is presently discussed as a possible determinant for the development of obesity in humans. One group of endogenous factors that could potentially affect BAT activity is the glucocorticoids (e.g. cortisol). We analyse here studies examining the effects of alterations in glucocorticoid signaling on BAT recruitment and thermogenic capacity. We find that irrespective of which manipulation of glucocorticoid signaling is examined, a seemingly homogeneous picture of lowered thermogenic capacity due to glucocorticoid stimulation is apparently obtained: e.g. lowered uncoupling protein 1 (UCP1) protein levels per mg protein, and an increased lipid accumulation in BAT. However, further analyses generally indicate that these effects result from a dilution effect rather than a true decrease in total capacity; the tissue may thus be said to be in a state of pseudo-atrophy. However, under conditions of very low physiological stimulation of BAT, glucocorticoids may truly inhibit Ucp1 gene expression and consequently lower total UCP1 protein levels, but the metabolic effects of this reduction are probably minor. It is thus unlikely that glucocorticoids affect organismal metabolism and induce the development of obesity through alterations of BAT activity.

The glucocorticoid receptor in osteoprogenitors regulates bone mass and marrow fat

Excess fat within bone marrow is associated with lower bone density. Metabolic stressors such as chronic caloric restriction (CR) can exacerbate marrow adiposity, and increased glucocorticoid signaling and adrenergic signaling are implicated in this phenotype. The current study tested the role of glucocorticoid signaling in CR-induced stress by conditionally deleting the glucocorticoid receptor (GR) in bone marrow osteoprogenitors (Osx1-Cre) of mice subjected to CR and ad libitum diets. Conditional knockout of the GR (GR-CKO) reduced cortical and trabecular bone mass as compared to wildtype (WT) mice under both ad libitum and CR conditions. No interaction was detected between genotype and diet, suggesting that the GR is not required for CR-induced skeletal changes. The lower bone mass in GR-CKO mice, and the further suppression of bone by CR, resulted from suppressed bone formation. Interestingly, treatment with the -adrenergic receptor antagonist propranolol mildly but selectively improved metrics of cortical bone mass in GR-CKO mice during CR, suggesting interaction between adrenergic and glucocorticoid signaling pathways that affects cortical bone. GR-CKO mice dramatically increased marrow fat under both ad libitum and CR-fed conditions, and surprisingly propranolol treatment was unable to rescue CR-induced marrow fat in either WT or GR-CKO mice. Additionally, serum corticosterone levels were selectively elevated in GR-CKO mice with CR, suggesting the possibility of bone-hypothalamus-pituitary-adrenal crosstalk during metabolic stress. This work highlights the complexities of glucocorticoid and β-adrenergic signaling in stress-induced changes in bone mass, and the importance of GR function in suppressing marrow adipogenesis while maintaining healthy bone mass.

Adipose glucocorticoid action influences whole-body metabolism via modulation of hepatic insulin action

The connection between adipose glucocorticoid action and whole-body metabolism is incompletely understood. Thus, we generated adipose tissue-specific glucocorticoid receptor-knockout (Ad-GcR-/-) mice to explore potential mechanisms. Ad-GcR-/- mice had a lower concentration of fasting plasma nonesterified fatty acids and less hepatic steatosis. This was associated with increased protein kinase B phosphorylation and increased hepatic glycogen synthesis after an oral glucose challenge. High-fat diet (HFD)-fed Ad-GcR-/- mice were protected against the development of hepatic steatosis and diacylglycerol-PKCε-induced impairments in hepatic insulin signaling. Under hyperinsulinemic-euglycemic conditions, hepatic insulin response was ∼10-fold higher in HFD-fed Ad-GcR-/- mice. Insulin-mediated suppression of adipose lipolysis was improved by 40% in Ad-GcR-/- mice. Adipose triglyceride lipase expression was decreased and insulin-mediated perilipin dephosphorylation was increased in Ad-GcR-/- mice. In metabolic cages, food intake decreased by 3 kcal/kg per hour in Ad-GcR-/- mice. Therefore, physiologic adipose glucocorticoid action appears to drive hepatic lipid accumulation during stressors such as fasting. The resultant hepatic insulin resistance prevents hepatic glycogen synthesis, preserving glucose for glucose-dependent organs. Absence of adipose glucocorticoid action attenuates HFD-induced hepatic insulin resistance; potential explanations for reduction in hepatic steatosis include reductions in adipose lipolysis and food intake.-Abulizi, A., Camporez, J.-P., Jurczak, M. J., Høyer, K. F., Zhang, D., Cline, G. W., Samuel, V. T., Shulman, G. I., Vatner, D. F. Adipose glucocorticoid action influences whole-body metabolism via modulation of hepatic insulin action.

Ectopic lipid deposition mediates insulin resistance in adipose specific 11β-hydroxysteroid dehydrogenase type 1 transgenic mice

CONTEXT

Excessive adipose glucocorticoid action is associated with insulin resistance, but the mechanisms linking adipose glucocorticoid action to insulin resistance are still debated. We hypothesized that insulin resistance from excess glucocorticoid action may be attributed in part to increased ectopic lipid deposition in liver.

METHODS

We tested this hypothesis in the adipose specific 11β-hydroxysteroid dehydrogenase-1 (HSD11B1) transgenic mouse, an established model of adipose glucocorticoid excess. Tissue specific insulin action was assessed by hyperinsulinemic-euglycemic clamps, hepatic lipid content was measured, hepatic insulin signaling was assessed by immunoblotting. The role of hepatic lipid content was further probed by administration of the functionally liver-targeted mitochondrial uncoupler, Controlled Release Mitochondrial Protonophore (CRMP).

FINDINGS

High fat diet fed HSD11B1 transgenic mice developed more severe hepatic insulin resistance than littermate controls (endogenous suppression of hepatic glucose production was reduced by 3.8-fold, P < 0.05); this was reflected by decreased insulin-stimulated hepatic insulin receptor kinase tyrosine phosphorylation and AKT serine phosphorylation. Hepatic insulin resistance was associated with a 53% increase (P < 0.05) in hepatic triglyceride content, a 73% increase in diacylglycerol content (P < 0.01), and a 66% increase in PKCε translocation (P < 0.05). Hepatic insulin resistance was prevented with administration of CRMP by reversal of hepatic steatosis and prevention of hepatic diacylglycerol accumulation and PKCε activation.

CONCLUSIONS

These findings are consistent with excess adipose glucocorticoid activity being a predisposing factor for the development of lipid (diacylglycerol-PKCε)-induced hepatic insulin resistance.

Top-down and bottom-up control of stress-coping

In this 30th anniversary issue review, we focus on the glucocorticoid modulation of limbic-prefrontocortical circuitry during stress-coping. This action of the stress hormone is mediated by mineralocorticoid receptors (MRs) and glucocorticoid receptors (GRs) that are co-expressed abundantly in these higher brain regions. Via both receptor types, the glucocorticoids demonstrate, in various contexts, rapid nongenomic and slower genomic actions that coordinate consecutive stages of information processing. MR-mediated action optimises stress-coping, whereas, in a complementary fashion, the memory storage of the selected coping strategy is promoted via GR. We highlight the involvement of adipose tissue in the allocation of energy resources to central regulation of stress reactions, point to still poorly understood neuronal ensembles in the prefrontal cortex that underlie cognitive flexibility critical for effective coping, and evaluate the role of cortisol as a pleiotropic regulator in vulnerability to, and treatment of, trauma-related psychiatric disorders.

Adipocyte Glucocorticoid Receptor Deficiency Promotes Adipose Tissue Expandability and Improves the Metabolic Profile Under Corticosterone Exposure

Widely used for their anti-inflammatory and immunosuppressive properties, glucocorticoids are nonetheless responsible for the development of diabetes and lipodystrophy. Despite an increasing number of studies focused on the adipocyte glucocorticoid receptor (GR), its precise role in the molecular mechanisms of these complications has not been elucidated. In keeping with this goal, we generated a conditional adipocyte-specific murine model of GR invalidation (AdipoGR knockout [KO] mice). Interestingly, when administered a corticosterone treatment to mimic hypercorticism conditions, AdipoGR-KO mice exhibited an improved glucose tolerance and insulin sensitivity. This was related to the adipose-specific activation of the insulin-signaling pathway, which contributed to fat mass expansion, as well as a shift toward an anti-inflammatory macrophage polarization in adipose tissue of AdipoGR-KO animals. Moreover, these mice were protected against ectopic lipid accumulation in the liver and displayed an improved lipid profile, contributing to their overall healthier phenotype. Altogether, our results indicate that adipocyte GR is a key factor of adipose tissue expansion and glucose and lipid metabolism control, which should be taken into account in the further design of adipocyte GR-selective modulators.

Impact of MR on mature adipocytes in high-fat/high-sucrose diet-induced obesity

Active glucocorticoid levels are elevated in the adipose tissue of obesity due to the enzyme 11 beta-hydroxysteroid dehydrogenase type 1. Glucocorticoids can bind and activate both glucocorticoid receptor (GR) and mineralocorticoid receptor (MR), and pharmacological blockades of MR prevent high-fat diet-induced obesity and glucose intolerance. To determine the significance of MR in adipocytes, we generated adipocyte-specific MR-knockout mice (AdipoMR-KO) and fed them high-fat/high-sucrose diet. We found that adipocyte-specific deletion of MR did not affect the body weight, fat weight, glucose tolerance or insulin sensitivity. While liver weight was slightly reduced in AdipoMR-KO, there were no significant differences in the mRNA expression levels of genes associated with lipogenesis, lipolysis, adipocytokines and oxidative stress in adipose tissues between the control and AdipoMR-KO mice. The results indicated that MR in mature adipocytes plays a minor role in the regulation of insulin resistance and inflammation in high-fat/high-sucrose diet-induced obese mice.

Glucocorticoid Receptor and Adipocyte Biology

Glucocorticoids are steroid hormones that play a key role in metabolic adaptations during stress, such as fasting and starvation, in order to maintain plasma glucose levels. Excess and chronic glucocorticoid exposure, however, causes metabolic syndrome including insulin resistance, dyslipidemia, and hyperglycemia. Studies in animal models of metabolic disorders frequently demonstrate that suppressing glucocorticoid signaling improves insulin sensitivity and metabolic profiles. Glucocorticoids convey their signals through an intracellular glucocorticoid receptor (GR), which is a transcriptional regulator. The adipocyte is one cell type that contributes to whole body metabolic homeostasis under the influence of GR. Glucocorticoids' functions on adipose tissues are complex. Depending on various physiological or pathophysiological states as well as distinct fat depots, glucocorticoids can either increase or decrease lipid storage in adipose tissues. In rodents, glucocorticoids have been shown to reduce the thermogenic activity of brown adipocytes. However, in human acute glucocorticoid exposure, glucocorticoids act to promote thermogenesis. In this article, we will review the recent studies on the mechanisms underlying the complex metabolic functions of GR in adipocytes. These include studies of the metabolic outcomes of adipocyte specific GR knockout mice and identification of novel GR primary target genes that mediate glucocorticoid action in adipocytes.

Glucocorticoid-Induced Metabolic Disturbances Are Exacerbated in Obese Male Mice

The purpose of this study was to determine the effects of glucocorticoid-induced metabolic dysfunction in the presence of diet-induced obesity. C57BL/6J adult male lean and diet-induced obese mice were given dexamethasone, and levels of hepatic steatosis, insulin resistance, and lipolysis were determined. Obese mice given dexamethasone had significant, synergistic effects on fasting glucose, insulin resistance, and markers of lipolysis, as well as hepatic steatosis. This was associated with synergistic transactivation of the lipolytic enzyme adipose triglyceride lipase. The combination of chronically elevated glucocorticoids and obesity leads to exacerbations in metabolic dysfunction. Our findings suggest lipolysis may be a key player in glucocorticoid-induced insulin resistance and fatty liver in individuals with obesity.

Glucocorticoid Signaling in Health and Disease: Insights From Tissue-Specific GR Knockout Mice

Glucocorticoids are adrenally produced hormones critically involved in development, general physiology, and control of inflammation. Since their discovery, glucocorticoids have been widely used to treat a variety of inflammatory conditions. However, high doses or prolonged use leads to a number of side effects throughout the body, which preclude their clinical utility. The primary actions of glucocorticoids are mediated by the glucocorticoid receptor (GR), a transcription factor that regulates many complex signaling pathways. Although GR is nearly ubiquitous throughout the body, glucocorticoids exhibit cell- and tissue-specific effects. For example, glucocorticoids stimulate glucose production in the liver, reduce glucose uptake in the skeletal muscle, and decrease insulin secretion from the pancreatic β-cells. Mouse models represent an important approach to understanding the dynamic functions of GR signaling in normal physiology, disease, and resistance. In the absence of a viable GR null model, gene-targeting techniques utilizing promoter-driven recombination have provided an opportunity to characterize the tissue-specific actions of GR. The aim of the present review is to describe the organ systems in which GR has been conditionally deleted and summarize the functions ascribed to glucocorticoid action in those tissues.

Fat-brain connections: Adipocyte glucocorticoid control of stress and metabolism

Glucocorticoids act via multiple mechanisms to mobilize energy for maintenance and restoration of homeostasis. In adipose tissue, glucocorticoids can promote lipolysis and facilitate adipocyte differentiation/growth, serving both energy-mobilizing and restorative processes during negative energy balance. Recent data suggest that adipose-dependent feedback may also be involved in regulation of stress responses. Adipocyte glucocorticoid receptor (GR) deletion causes increased HPA axis stress reactivity, due to a loss of negative feedback signals into the CNS. The fat-to-brain signal may be mediated by neuronal mechanisms, release of adipokines or increased lipolysis. The ability of adipose GRs to inhibit psychogenic as well as metabolic stress responses suggests that (1) feedback regulation of the HPA axis occurs across multiple bodily compartments, and (2) fat tissue integrates psychogenic stress signals. These studies support a link between stress biology and energy metabolism, a connection that has clear relevance for numerous disease states and their comorbidities.