A dual Ucp1 reporter mouse model for imaging and quantitation of brown and brite fat recruitment

Amphiphilic cytokine traps remodel marrow adipose tissue for hematopoietic microenvironment amelioration

Hematopoietic stem cell transplantation (HSCT) is extensively employed in the treatment of hematological malignancies but is markedly constrained by the paucity of hematopoietic stem/progenitor cells (HSPCs). Recent studies have found that marrow adipose tissue (MAT) acts on hematopoiesis through complicated mechanisms. Therefore, the osteo-organoids fabricated in vivo using biomaterials loaded with recombinant human bone morphogenetic protein 2 (rhBMP-2) have been used as models of MAT for our research. To obtain sufficient amounts of therapeutic HSPCs and healthy MAT, we have developed amphiphilic chitosan (AC)-gelatin as carriers of rhBMP-2 to the regulate type conversion of adipose tissue and trap hematopoietic growth factors. Unlike medicine interventions or cell therapies, the traps based on AC not only attenuate the occupancy of adipocytes within the hematopoietic microenvironment while preserving stem cell factor concentrations, but also improve marrow metabolism by promoting MAT browning. In conclusion, this approach increases the proportion of HSPCs in osteo-organoids, and optimizes the composition and metabolic status of MAT. These findings furnish an experimental basis for regulating hematopoiesis in vivo through materials that promote the development of autologous HSPCs. Additionally, this approach presents a theoretical model of rapid adipogenesis for the study of adipose-related pathologies and potential pharmacological targets.

Gene expression and characterization of clonally derived murine embryonic brown and brite adipocytes

White adipocytes store energy, while brown and brite adipocytes release heat via nonshivering thermogenesis. In this study, we characterized two murine embryonic clonal preadipocyte lines, EB5 and EB7, each displaying unique gene marker expression profiles. EB5 cells differentiate into brown adipocytes, whereas EB7 cells into brite (also known as beige) adipocytes. To draw a comprehensive comparison, we contrasted the gene expression patterns, adipogenic capacity, as well as carbohydrate and lipid metabolism of these cells to that of F442A, a well-known white preadipocyte and adipocyte model. We found that commitment to differentiation in both EB5 and EB7 cells can be induced by 3-Isobutyl-1-methylxanthine/dexamethasone (Mix/Dex) and staurosporine/dexamethasone (St/Dex) treatments. Additionally, the administration of rosiglitazone significantly enhances the brown and brite adipocyte phenotypes. Our data also reveal the involvement of a series of genes in the transcriptional cascade guiding adipogenesis, pinpointing GSK3β as a critical regulator for both EB5 and EB7 adipogenesis. In a developmental context, we observe that, akin to brown fat progenitors, brite fat progenitors make their appearance in murine development by 11-12 days of gestation or potentially earlier. This result contributes to our understanding of adipocyte lineage specification during embryonic development. In conclusion, EB5 and EB7 cell lines are valuable for research into adipocyte biology, providing insights into the differentiation and development of brown and beige adipocytes. Furthermore, they could be useful for the characterization of drugs targeting energy balance for the treatment of obesity and metabolic diseases.

Uncoupling protein 1-driven Cre (Ucp1-Cre) is expressed in the epithelial cells of mammary glands and various non-adipose tissues

OBJECTIVE

Uncoupling protein 1 (UCP1), a mitochondrial protein responsible for nonshivering thermogenesis in adipose tissue, serves as a distinct marker for thermogenic brown and beige adipocytes. Ucp1-Cre mice are thus widely used to genetically manipulate these thermogenic adipocytes. However, evidence suggests that UCP1 may also be expressed in non-adipocyte cell types. In this study, we investigated the presence of UCP1 expression in different mouse tissues that have not been previously reported.

METHODS

We employed Ucp1-Cre mice crossed with Cre-inducible transgenic reporter Nuclear tagging and Translating Ribosome Affinity Purification (NuTRAP) mice to investigate Ucp1-Cre expression in various tissues of adult female mice and developing embryos. Tamoxifen-inducible Ucp1-CreERT2 mice crossed with NuTRAP mice were used to assess active Ucp1 expression in adult mice. Immunostaining, RNA analysis, and single-cell/nucleus RNA-seq (sc/snRNA-seq) data analysis were performed to determine the expression of endogenous UCP1 and Ucp1-Cre-driven reporter expression. We also investigated the impact of UCP1 deficiency on mammary gland development and function using Ucp1-knockout (KO) mice.

RESULTS

Ucp1-Cre expression was observed in the mammary glands within the inguinal white adipose tissue of female Ucp1-Cre; NuTRAP mice. Ucp1-Cre was activated during embryonic development in various tissues, including mammary glands, as well as in the brain, kidneys, eyes, and ears, specifically in epithelial cells in these organs. However, Ucp1-CreERT2 showed no or only partial activation in these tissues of adult mice, indicating the potential for low or transient expression of endogenous Ucp1. While sc/snRNA-seq data suggest potential expression of UCP1 in mammary epithelial cells in adult mice and humans, Ucp1-KO female mice displayed normal mammary gland development and function.

CONCLUSIONS

Our findings reveal widespread Ucp1-Cre expression in various non-adipose tissue types, starting during early development. These results highlight the importance of exercising caution when interpreting data and devising experiments involving Ucp1-Cre mice.

Development and expansion of intramuscular adipose tissue is not dependent on UCP-1-lineage cells in mice

Accumulation of adipose tissue within and outside of skeletal muscle is associated with orthopedic injury and metabolic disease, where it is thought to impede muscle function. The close juxtaposition between this adipose and myofibers has led to hypotheses that paracrine interactions between the two regulate local physiology. Recent work suggests that intramuscular adipose tissue (IMAT) may have features of beige or brown fat, indicated by the expression of uncoupling protein-1 (UCP-1). However, this is contested by other studies. Clarification of this point is needed to inform our understanding of the relationship between IMAT and muscle health. To achieve this, we examined the effects of constitutive UCP-1+ cell ablation (UCP1-DTA) on IMAT development and homeostasis. IMAT developed normally in UCP1-DTA mice, with no significant differences in quantity compared with wild-type littermates. Likewise, IMAT accumulation in response to glycerol-induced injury was similar between genotypes, with no significant differences in adipocyte size, quantity, or dispersion. This suggests that neither physiological nor pathological IMAT express UCP-1 and that the development of IMAT does not depend on UCP-1 lineage cells. In response to β3-adrenergic stimulation, we find minor, localized UCP-1 positivity in wildtype IMAT, but the bulk of the adipocytes are unresponsive. In contrast, two depots of muscle-adjacent (epi-muscular) adipose tissue have reduced mass in UCP1-DTA mice and UCP-1 positivity in wildtype littermates, comparable to traditional beige and brown adipose depots. Taken together this evidence strongly supports a white adipose phenotype for mouse IMAT and a brown/beige phenotype for some adipose outside the muscle boundary.

Sensing the oxygen and temperature in the adipose tissues - who's sensing what?

Adipose tissues, composed of various cell types, including adipocytes, endothelial cells, neurons, and immune cells, are organs that are exposed to dynamic environmental challenges. During diet-induced obesity, white adipose tissues experience hypoxia due to adipocyte hypertrophy and dysfunctional vasculature. Under these conditions, cells in white adipose tissues activate hypoxia-inducible factor (HIF), a transcription factor that activates signaling pathways involved in metabolism, angiogenesis, and survival/apoptosis to adapt to such an environment. Exposure to cold or activation of the β-adrenergic receptor (through catecholamines or chemicals) leads to heat generation, mainly in brown adipose tissues through activating uncoupling protein 1 (UCP1), a proton uncoupler in the inner membrane of the mitochondria. White adipose tissues can undergo a similar process under this condition, a phenomenon known as 'browning' of white adipose tissues or 'beige adipocytes'. While UCP1 expression has largely been confined to adipocytes, HIF can be expressed in many types of cells. To dissect the role of HIF in specific types of cells during diet-induced obesity, researchers have generated tissue-specific knockout (KO) mice targeting HIF pathways, and many studies have commonly revealed that intact HIF-1 signaling in adipocytes and adipose tissue macrophages exacerbates tissue inflammation and insulin resistance. In this review, we highlight some of the key findings obtained from these transgenic mice, including Ucp1 KO mice and other models targeting the HIF pathway in adipocytes, macrophages, or endothelial cells, to decipher their roles in diet-induced obesity.

Uncoupling protein 1-driven Cre (Ucp1-Cre) is expressed in the epithelial cells of mammary glands and various non-adipose tissues

Objective

Uncoupling protein 1 (UCP1), a mitochondrial protein responsible for nonshivering thermogenesis in adipose tissue, serves as a distinct marker for thermogenic brown and beige adipocytes. Ucp1-Cre mice are thus widely used to genetically manipulate these thermogenic adipocytes. However, evidence suggests that UCP1 may also be expressed in non-adipocyte cell types. In this study, we investigated the presence of UCP1 expression in different mouse tissues that have not been previously reported.

Methods

We employed Ucp1-Cre mice crossed with Cre-inducible transgenic reporter Nuclear tagging and Translating Ribosome Affinity Purification (NuTRAP) mice, to investigate Ucp1-Cre expression in various tissues of adult female mice and developing embryos. Tamoxifen-inducible Ucp1-CreERT2 mice crossed with NuTRAP mice were used to assess active UCP1 expression. Immunostaining, RNA analysis, and single-cell/nucleus RNA-seq (sc/snRNA-seq) data analysis were performed to determine the expression of endogenous UCP1 and Ucp1-Cre-driven reporter expression. We also investigated the impact of UCP1 deficiency on mammary gland development and function using Ucp1-knockout (KO) mice.

Results

Ucp1-Cre expression was observed in the mammary glands within the inguinal white adipose tissue of female Ucp1-Cre; NuTRAP mice. However, endogenous Ucp1 was not actively expressed as Ucp1-CreERT2 failed to induce the reporter expression in the mammary glands. Ucp1-Cre was activated during embryonic development in various tissues, including mammary glands, as well as in the brain, kidneys, eyes, and ears, specifically in epithelial cells in these organs. While sc/snRNA-seq data suggest potential expression of UCP1 in mammary epithelial cells in adult mice and humans, Ucp1-KO female mice displayed normal mammary gland development and function.

Conclusions

Our findings reveal widespread Ucp1-Cre expression in various non-adipose tissue types, starting during early development. These results highlight the importance of exercising caution when interpreting data and devising experiments involving Ucp1-Cre mice.

The widely used Ucp1-CreEvdr transgene elicits complex developmental and metabolic phenotypes

Bacterial artificial chromosome transgenic models, including most Cre-recombinases, enable potent interrogation of gene function in vivo but require rigorous validation as limitations emerge. Due to its high relevance to metabolic studies, we performed comprehensive analysis of the Ucp1-CreEvdr line which is widely used for brown fat research. Hemizygotes exhibited major brown and white fat transcriptomic dysregulation, indicating potential altered tissue function. Ucp1-CreEvdr homozygotes also show high mortality, growth defects, and craniofacial abnormalities. Mapping the transgene insertion site revealed insertion in chromosome 1 accompanied by large genomic alterations disrupting several genes expressed in a range of tissues. Notably, Ucp1-CreEvdr transgene retains an extra Ucp1 gene copy that may be highly expressed under high thermogenic burden. Our multi-faceted analysis highlights a complex phenotype arising from the presence of the Ucp1-CreEvdr transgene independently of the intended genetic manipulations. Overall, comprehensive validation of transgenic mice is imperative to maximize discovery while mitigating unexpected, off-target effects.

Salt-inducible kinase inhibition promotes the adipocyte thermogenic program and adipose tissue browning

OBJECTIVE

Norepinephrine stimulates the adipose tissue thermogenic program through a β-adrenergic receptor (βAR)-cyclic adenosine monophosphate (cAMP)-protein kinase A (PKA) signaling cascade. We discovered that a noncanonical activation of the mechanistic target of rapamycin complex 1 (mTORC1) by PKA is required for the βAR-stimulation of adipose tissue browning. However, the downstream events triggered by PKA-phosphorylated mTORC1 activation that drive this thermogenic response are not well understood.

METHODS

We used a proteomic approach of Stable Isotope Labeling by/with Amino acids in Cell culture (SILAC) to characterize the global protein phosphorylation profile in brown adipocytes treated with the βAR agonist. We identified salt-inducible kinase 3 (SIK3) as a candidate mTORC1 substrate and further tested the effect of SIK3 deficiency or SIK inhibition on the thermogenic gene expression program in brown adipocytes and in mouse adipose tissue.

RESULTS

SIK3 interacts with RAPTOR, the defining component of the mTORC1 complex, and is phosphorylated at Ser884 in a rapamycin-sensitive manner. Pharmacological SIK inhibition by a pan-SIK inhibitor (HG-9-91-01) in brown adipocytes increases basal Ucp1 gene expression and restores its expression upon blockade of either mTORC1 or PKA. Short-hairpin RNA (shRNA) knockdown of Sik3 augments, while overexpression of SIK3 suppresses, Ucp1 gene expression in brown adipocytes. The regulatory PKA phosphorylation domain of SIK3 is essential for its inhibition. CRISPR-mediated Sik3 deletion in brown adipocytes increases type IIa histone deacetylase (HDAC) activity and enhances the expression of genes involved in thermogenesis such as Ucp1, Pgc1α, and mitochondrial OXPHOS complex protein. We further show that HDAC4 interacts with PGC1α after βAR stimulation and reduces lysine acetylation in PGC1α. Finally, a SIK inhibitor well-tolerated in vivo (YKL-05-099) can stimulate the expression of thermogenesis-related genes and browning of mouse subcutaneous adipose tissue.

CONCLUSIONS

Taken together, our data reveal that SIK3, with the possible contribution of other SIKs, functions as a phosphorylation switch for β-adrenergic activation to drive the adipose tissue thermogenic program and indicates that more work to understand the role of the SIKs is warranted. Our findings also suggest that maneuvers targeting SIKs could be beneficial for obesity and related cardiometabolic disease.

Application and trend of bioluminescence imaging in metabolic syndrome research

Bioluminescence imaging is a non-invasive technology used to visualize physiological processes in animals and is useful for studying the dynamics of metabolic syndrome. Metabolic syndrome is a broad spectrum of diseases which are rapidly increasing in prevalence, and is closely associated with obesity, type 2 diabetes, nonalcoholic fatty liver disease, and circadian rhythm disorder. To better serve metabolic syndrome research, researchers have established a variety of animal models expressing luciferase, while also committing to finding more suitable luciferase promoters and developing more efficient luciferase-luciferin systems. In this review, we systematically summarize the applications of different models for bioluminescence imaging in the study of metabolic syndrome.

Use of CIDEA Reporter Mouse Model for Screening Thermogenic Fat-Activating Drugs

Excessive fat accumulation is a risk factor for metabolic diseases. Activating non-shivering thermogenesis in adipose tissue increases energy expenditure and potentially reverses obesity-related metabolic dysfunctions. While brown/beige adipocytes specialize in non-shivering thermogenesis and catabolic lipid metabolism, thermogenic stimuli and pharmacological intervention can induce the recruitment and metabolic activation of these cell types in adipose tissue. Thus, these adipocytes are attractive therapeutic targets to combat obesity, and there is an increasing need for efficient screening strategies for thermogenic drugs. Cell death-inducing DNA fragmentation factor-like effector A (CIDEA) is a well-known marker of the thermogenic capacity of brown and beige adipocytes. We recently developed a CIDEA reporter mouse model that expresses multicistronic mRNAs encoding CIDEA, luciferase 2, and tdTomato proteins under endogenous Cidea promoter control. Here, we introduce the CIDEA reporter model system as a tool for in vitro and in vivo screening of drug candidate molecules with thermogenic effects and provide a detailed protocol to monitor CIDEA reporter expression.

Human Umbilical Vein Endothelial Cells Survive on the Ischemic TCA Cycle under Lethal Ischemic Conditions

It is generally believed that vascular endothelial cells (VECs) rely on glycolysis instead of the tricarboxylic acid (TCA) cycle under both normoxic and hypoxic conditions. However, the metabolic pattern of human umbilical vein endothelial cells (HUVECs) under extreme ischemia (hypoxia and nutrient deprivation) needs to be elucidated. We initiated a lethal ischemic model of HUVECs, performed proteomics and bioinformatics, and verified the metabolic pattern shift of HUVECs. Ischemic HUVECs displayed extensive aerobic respiration, including upregulation of the TCA cycle and mitochondrial respiratory chain in mitochondria and downregulation of glycolysis in cytoplasm. The TCA cycle was enhanced while the cell viability was decreased through the citrate synthase pathway when substrates of the TCA cycle (acetate and/or pyruvate) were added and vice versa when inhibitors of the TCA cycle (palmitoyl-CoA and/or avidin) were applied. The inconsistency of the TCA cycle level and cell viability suggested that the extensive TCA cycle can keep cells alive yet generate toxic substances that reduce cell viability. The data revealed that HUVECs depend on “ischemic TCA cycle” instead of glycolysis to keep cells alive under lethal ischemic conditions, but consideration must be given to relieve cell injury.

Downregulation of peripheral lipopolysaccharide binding protein impacts on perigonadal adipose tissue only in female mice

BACKGROUND AND AIMS

The sexual dimorphism in fat-mass distribution and circulating leptin and insulin levels is well known, influencing the progression of obesity-associated metabolic disease. Here, we aimed to investigate the possible role of lipopolysaccharide-binding protein (LBP) in this sexual dimorphism.

METHODS

The relationship between plasma LBP and fat mass was evaluated in 145 subjects. The effects of Lbp downregulation, using lipid encapsulated unlocked nucleomonomer agent containing chemically modified-siRNA delivery system, were evaluated in mice.

RESULTS

Plasma LBP levels were associated with fat mass and leptin levels in women with obesity, but not in men with obesity. In mice, plasma LBP downregulation led to reduced weight, fat mass and leptin gain after a high-fat and high-sucrose diet (HFHS) in females, in parallel to increased expression of adipogenic and thermogenic genes in visceral adipose tissue. This was not observed in males. Plasma LBP downregulation avoided the increase in serum LPS levels in HFHS-fed male and female mice. Serum LPS levels were positively correlated with body weight and fat mass gain, and negatively with markers of adipose tissue function only in female mice. The sexually dimorphic effects were replicated in mice with established obesity. Of note, LBP downregulation led to recovery of estrogen receptor alpha (Esr1) mRNA levels in females but not in males.

CONCLUSION

LBP seems to exert a negative feedback on ERα-mediated estrogen action, impacting on genes involved in thermogenesis. The known decreased estrogen action and negative effects of metabolic endotoxemia may be targeted through LBP downregulation.

The armadillo-repeat containing X-linked protein 3, ARMCX3, is a negative regulator of the browning of adipose tissue associated with obesity

OBJECTIVES

To determine the role of armadillo repeat-containing X-linked protein 3 (ARMCX3) in the thermogenic plasticity of adipose tissue.

METHODS

Adipose tissues were characterized in Armcx3-KO male mice. Armcx3 gene expression was analyzed in adipose tissue from mice exposed to thermogenic inducers (cold, β3-adenergic stimulus) and in differentiating brown and beige cells in culture. Analyses encompassed circulating metabolite and hormonal profiling, tissue characterization, histology, gene expression patterns, and immunoblot assays. Armcx3 gene expression was assessed in subcutaneous adipose tissue from lean individuals and individuals with obesity and was correlated with expression of marker genes of adipose browning. The effects of adenoviral-mediated overexpression of ARMCX3 on differentiating brown adipocyte gene expression and respiratory activity were determined.

RESULTS

Male mice lacking ARMCX3 showed significant induction of white adipose tissue browning. In humans, ARMCX3 expression in subcutaneous adipose tissue was inversely correlated with the expression of marker genes of thermogenic activity, including CIDEA, mitochondrial transcripts, and creatine kinase-B. Armcx3 expression in adipose tissues was repressed by thermogenic activation (cold or β3-adrenergic stimulation) and was upregulated by obesity in mice and humans. Experimentally-induced increases in Armcx3 caused down-regulation of thermogenesis-related genes and reduced mitochondrial oxidative activity of adipocytes in culture, whereas siRNA-mediated Armcx3 knocking-down enhanced expression of thermogenesis-related genes.

CONCLUSION

ARMCX3 is a novel player in the control of thermogenic adipose tissue plasticity that acts to repress acquisition of the browning phenotype and shows a direct association with indicators of obesity in mice and humans.

Susceptibility to diet-induced obesity at thermoneutral conditions is independent of UCP1

Activation of uncoupling protein 1 (UCP1) in brown adipose tissue (BAT) upon cold stimulation leads to substantial increase in energy expenditure to defend body temperature. Increases in energy expenditure after a high-caloric food intake, termed diet-induced thermogenesis, are also attributed to BAT. These properties render BAT a potential target to combat diet-induced obesity. However, studies investigating the role of UCP1 to protect against diet-induced obesity are controversial and rely on the phenotyping of a single constitutive UCP1-knockout model. To address this issue, we generated a novel UCP1-knockout model by Cre-mediated deletion of exon 2 in the UCP1 gene. We studied the effect of constitutive UCP1 knockout on metabolism and the development of diet-induced obesity. UCP1 knockout and wild-type mice were housed at 30°C and fed a control diet for 4 wk followed by 8 wk of high-fat diet. Body weight and food intake were monitored continuously over the course of the study, and indirect calorimetry was used to determine energy expenditure during both feeding periods. Based on Western blot analysis, thermal imaging and noradrenaline test, we confirmed the lack of functional UCP1 in knockout mice. However, body weight gain, food intake, and energy expenditure were not affected by loss of UCP1 function during both feeding periods. We introduce a novel UCP1-KO mouse enabling the generation of conditional UCP1-knockout mice to scrutinize the contribution of UCP1 to energy metabolism in different cell types or life stages. Our results demonstrate that UCP1 does not protect against diet-induced obesity at thermoneutrality.NEW & NOTEWORTHY We provide evidence that the abundance of UCP1 does not influence energy metabolism at thermoneutrality studying a novel Cre-mediated UCP1-KO mouse model. This model will be a foundation for a better understanding of the contribution of UCP1 in different cell types or life stages to energy metabolism.

White, beige and brown adipose tissue: structure, function, specific features and possibility formation and divergence in pigs

Introduction. Traditionally, mammalian adipose tissue is divided into white (white adipose tissue – WAT) and brown (brown adipose tissue – BAT). While the functions of WAT are well known as the triglyceride depot, the role of BAT in mammalian physiology has been under close investigation. The first description of the role of BAT in maintaining thermogenesis dates back to 1961. This article offers a review of structural and functional specificity of white, beige and brown adipose tissue. Results and discussion. The differences and descriptions of adipocytes and their impact on the maintenance of the main functions of the mammalian body are described in this manuscript. In particular, thermogenesis, stress response, obesity, type II diabetes. In addition to WAT and BAT, an intermediate form was also detected in the body – beige fat (BeAT or Brite). The opposite opinions regarding the presence of three types of adipose tissue in the human and animal bodies are presented. Studies on the identification of uncoupling proteins 1 and 3 and their role in the transformation of white fat into beige/brown are considered. Basically, the data on the factors of endogenous and exogenous nature on their formation are given on the example of the human body. Conclusion. With an abundance of publications on the keywords: “white, brown fat”, these studies, in the overwhelming majority, are devoted to the role of these fats in the formation of human thermogenesis, the assessment of the impact on obesity. Pigs have also been suggested to lack functional BAT, which is a major cause of neonatal death in the swine industry, therefore the focus on investigating role of different types of adipose tissue in pigs seems very promising in order to understand whether there is a compensating mechanism of thermogenesis.

Conditional gene targeting using UCP1-Cre mice directly targets the central nervous system beyond thermogenic adipose tissues

Objective

Uncoupling protein 1 (UCP1) is a mitochondrial protein critical for adaptive thermogenesis in adipose tissues, and it is typically believed to be restricted to thermogenic adipose tissues. UCP1-Cre transgenic mice are utilized in numerous studies to provide “brown adipose-specific” conditional gene targeting. Here, we examined the distribution of Cre and UCP1 throughout the body in UCP1-Cre reporter mice.

Methods

UCP1-Cre mice crossed to Ai14-tdTomato and Ai9-tdTomato reporter mice were used to explore the tissue distribution of Cre recombinase and Ucp1 mRNA in various tissues. UCP1-Cre mice were independently infected with either a Cre-dependent PHP.eB-tdTomato virus or a Cre-dependent AAV-tdTomato virus to determine whether and where UCP1 is actively expressed in the adult central nervous system. In situ analysis of the deposited single cell RNA sequencing data was used to evaluate Ucp1 expression in the hypothalamus.

Results

As expected, Ucp1 expression was detected in both brown and inguinal adipose tissues. Ucp1 expression was also detected in the kidney, adrenal glands, thymus, and hypothalamus. Consistent with detectable Ucp1 expression, tdTomato expression was also observed in brown adipose tissue, inguinal white adipose tissue, kidney, adrenal glands, and hypothalamus of both male and female UCP1-Cre; Ai14-tdTomato and UCP1-Cre; Ai9-tdTomato mice by fluorescent imaging and qPCR. Critically, expression of tdTomato, and thus UCP1, within the central nervous system was observed in regions of the brain critical for the regulation of energy homeostasis, including the ventromedial hypothalamus (VMH).

Conclusions

TdTomato expression in UCP1-Cre; tdTomato mice is not restricted to thermogenic adipose tissues. TdTomato was also expressed in the kidneys, adrenal glands, and throughout the brain, including brain regions and cell types that are critical for multiple aspects of central regulation of energy homeostasis. Collectively, these data have important implications for the utility of UCP1-Cre mice as genetic tools to investigate gene function specifically in brown adipose tissue.

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UCP1-Cre transgenic mice express Cre in tissues beyond thermogenic adipose tissues.

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UCP1-Cre; tdTomato reporter mice show that Cre is also expressed throughout the brain, kidney, and adrenal glands.

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Ucp1 mRNA is actively expressed in the central nervous system of adult mice.

Multi-Aspect Optoacoustic Imaging of Breast Tumors under Chemotherapy with Exogenous and Endogenous Contrasts: Focus on Apoptosis and Hypoxia

Breast cancer is a complex tumor type involving many biological processes. Most chemotherapeutic agents exert their antitumoral effects by rapid induction of apoptosis. Another main feature of breast cancer is hypoxia, which may drive malignant progression and confer resistance to various forms of therapy. Thus, multi-aspect imaging of both tumor apoptosis and oxygenation in vivo would be of enormous value for the effective evaluation of therapy response. Herein, we demonstrate the capability of a hybrid imaging modality known as multispectral optoacoustic tomography (MSOT) to provide high-resolution, simultaneous imaging of tumor apoptosis and oxygenation, based on both the exogenous contrast of an apoptosis-targeting dye and the endogenous contrast of hemoglobin. MSOT imaging was applied on mice bearing orthotopic 4T1 breast tumors before and following treatment with doxorubicin. Apoptosis was monitored over time by imaging the distribution of xPLORE-APOFL750©, a highly sensitive poly-caspase binding apoptotic probe, within the tumors. Oxygenation was monitored by tracking the distribution of oxy- and deoxygenated hemoglobin within the same tumor areas. Doxorubicin treatment induced an increase in apoptosis-depending optoacoustic signal of xPLORE-APOFL750© at 24 h after treatment. Furthermore, our results showed spatial correspondence between xPLORE-APO750© and deoxygenated hemoglobin. In vivo apoptotic status of the tumor tissue was independently verified by ex vivo fluorescence analysis. Overall, our results provide a rationale for the use of MSOT as an effective tool for simultaneously investigating various aspects of tumor pathophysiology and potential effects of therapeutic regimes based on both endogenous and exogenous molecular contrasts.

Mouse model of the adipose organ: the heterogeneous anatomical characteristics

Adipose tissue plays a pivotal role in energy storage, hormone secretion, and temperature control. Mammalian adipose tissue is largely divided into white adipose tissue and brown adipose tissue, although recent studies have discovered the existence of beige adipocytes. Adipose tissues are widespread over the whole body and each location shows distinctive metabolic features. Mice are used as a representative experimental model system in metabolic studies due to their numerous advantages. Importantly, the adipose tissues of experimental animals and humans are not perfectly matched, and each adipose tissue exhibits both similar and specific characteristics. Nevertheless, the diversity and characteristics of mouse adipose tissue have not yet been comprehensively summarized. This review summarizes diverse information about the different types of adipose tissue being studied in mouse models. The types and characteristics of adipocytes were described, and each adipose tissue was classified by type, and features such as its distribution, origin, differences from humans, and metabolic characteristics were described. In particular, the distribution of widely studied adipose tissues was illustrated so that researchers can comprehensively grasp its location. Also, the adipose tissues misused or confusingly used among researchers were described. This review will provide researchers with comprehensive information and cautions needed to study adipose tissues in mouse models.

Development of CIDEA reporter mouse model and its application for screening thermogenic drugs

Cell death-inducing DNA fragmentation factor-like effector A (CIDEA) is a lipid droplet-associated protein and is a known marker of the thermogenic capacity of brown/beige adipocytes. To monitor the expression of CIDEA in live mice in a non-invasive manner, we generated CIDEA reporter mice expressing multicistronic mRNAs encoding CIDEA, luciferase 2, and tdTomato proteins under the control of the Cidea promoter. The expression level of endogenous CIDEA protein in adipose tissue was not affected by the expression of polycistronic reporters. The two CIDEA reporters, luciferase 2 and tdTomato, correctly reflected CIDEA protein levels. Importantly, luciferase activity was induced by cold exposure and the treatment with β3-adrenergic receptor agonist CL316,243 in interscapular and inguinal adipose tissue, which was detectable by in vivo bioluminescence imaging. We further evaluated the effects of candidate brown adipogenic agents using this CIDEA reporter system and demonstrated a positive correlation between drug-induced luciferase activity and thermogenic gene expression levels both in vitro and in vivo. Collectively, we established a dual CIDEA reporter mouse model in which fluorescence and luminescence signals correctly reflect CIDEA expression, and therefore, suggested that this reporter system can be used to evaluate the thermogenic efficacy of candidate molecules.

UCP1 expression in the mouse adrenal gland is not upregulated by thermogenic conditions

The uncoupling protein 1 (UCP1) gene is known to be highly expressed in brown adipose tissue (BAT) that functions in thermogenesis. It has been shown that UCP1 mRNA is localized to the mouse adrenal gland, but its significance remains elusive. To explore how UCP1 expression in the adrenal gland is regulated, we generated a reporter knock-in mouse in which the GFP gene was inserted into the UCP1 locus using CRISPR-Cas9 system. Firstly, we confirmed by Western blot analysis UCP1-driven GFP protein expression in interscapular BAT of the knock-in mice kept at 4 °C. Immunohistochemistry showed that GFP protein was detected in the adrenal gland of the knock-in mice. More intense GFP expression was observed in the adrenal medulla than in the cortex of the reporter mice irrespectively of cold exposure. Immunohistochemistry using anti-UCP1 antibody, as well as Western blot analysis verified UCP1 protein expression in the wild-type adrenal medulla. These results suggest that the mouse adrenal gland is a novel organ expressing UCP1 protein and its expression is not upregulated by cold exposure.

Fibroblast growth factor induced Ucp1 expression in preadipocytes requires PGE2 biosynthesis and glycolytic flux

High uncoupling protein 1 (Ucp1) expression is a characteristic of differentiated brown adipocytes and is linked to adipogenic differentiation. Paracrine fibroblast growth factor 8b (FGF8b) strongly induces Ucp1 transcription in white adipocytes independent of adipogenesis. Here, we report that FGF8b and other paracrine FGFs act on brown and white preadipocytes to upregulate Ucp1 expression via a FGFR1-MEK1/2-ERK1/2 axis, independent of adipogenesis. Transcriptomic analysis revealed an upregulation of prostaglandin biosynthesis and glycolysis upon Fgf8b treatment of preadipocytes. Oxylipin measurement by LC-MS/MS in FGF8b conditioned media identified prostaglandin E₂ as a putative mediator of FGF8b induced Ucp1 transcription. RNA interference and pharmacological inhibition of the prostaglandin E₂ biosynthetic pathway confirmed that PGE2 is causally involved in the control over Ucp1 transcription. Importantly, impairment of or failure to induce glycolytic flux blunted the induction of Ucp1, even in the presence of PGE₂ . Lastly, a screening of transcription factors identified Nrf1 and Hes1 as required regulators of FGF8b induced Ucp1 expression. Thus, we conclude that paracrine FGFs co-regulate prostaglandin and glucose metabolism to induce Ucp1 expression in a Nrf1/Hes1-dependent manner in preadipocytes, revealing a novel regulatory network in control of Ucp1 expression in a formerly unrecognized cell type.

Brown Adipose Tissue in Breast Cancer Evaluated by [18F] FDG-PET/CT

PURPOSE

Recently brown adipose tissue (BAT) activation has been proposed to have a possible role in breast cancer. The aim of this study was to evaluate BAT activation in patients with breast cancer and its relationship with molecular characteristics of tumor.

PROCEDURES

The study group comprised 79 patients with histologically proven ductal breast carcinoma (51 ± 13 years). Data on distribution, intensity (SUVmax), and total metabolic activity (TMA) of BAT were obtained from [¹⁸F] FDG-PET/CT. Clinical and biochemical data were obtained from the database.

RESULTS

BAT activation was present in 12 of the 79 patients (15.2 %). Patients with BAT activation were younger and had a lower body mass index (BMI) (p < 0.05 and p < 0.0005, respectively) and showed less frequently metastasis (p < 0.05). No significant differences were found in estrogen receptor (ER), progesterone receptor (PgR), Ki67, grade, and in molecular subtypes. In patients younger than 55 years and with a BMI < 26, no significant differences were observed between patients with and without BAT activation. In the 12 patients with BAT activation, a significant inverse correlation was observed between TMA and BMI (r = - 0.64, p < 0.05). TMA and SUVmax were higher in grade 2 than in grade 3 patients. No significant differences were found in both TMA and SUVmax between patients with and without lymph node metastases. A significant difference in both TMA and SUVmax was observed among different molecular types, with luminal B patients showing higher values.

CONCLUSIONS

In conclusion, the present study suggests a relation between BAT activation and positive known prognostic factor in breast cancer, such as intermediate tumor grade and luminal B cancer type.

Phenotypic Discovery of SB1501, an Anti-obesity Agent, through Modulating Mitochondrial Activity

Obesity has become a pandemic that threatens the quality of life and discovering novel therapeutic agents that can reverse obesity and obesity-related metabolic disorders are necessary. Here, we aimed to identify new anti-obesity agents using a phenotype-based approach. We performed image-based high-content screening with a fluorogenic bioprobe (SF44), which visualizes cellular lipid droplets (LDs), to identify initial hit compounds. A structure-activity relationship study led us to yield a bioactive compound SB1501, which reduces cellular LDs in 3T3-L1 adipocytes without cytotoxicity. SB1501 induced the expression of gene products that regulate mitochondrial biogenesis and fatty acid oxidation in 3T3-L1 adipocytes. Daily treatment with SB1501 improved the metabolic states of db/db mice by reducing body fat mass, adipose tissue mass, food intake, and increasing glucose tolerance. The anti-obesity effect of SB1501 may result from perturbation of the PGC-1α-UCP1 regulatory axis in inguinal white adipose tissue and brown adipose tissue. These data suggest the therapeutic potential of SB1501 as an anti-obesity agent via modulating mitochondrial activities.

Uncoupling protein-1 expression does not protect mice from diet-induced obesity

We studied the metabolic phenotype of a novel Ucp1-LUC-iRFP713 knock-in reporter gene mouse model originally generated to monitor endogenous Ucp1 gene expression. Both reporter mice and reporter cells reliably reflected Ucp1 gene expression in vivo and in vitro. We here report an unexpected reduction in UCP1 content in homozygous knock-in (KI) reporter mice. As a result, the thermogenic capacity of KI mice stimulated by norepinephrine was largely blunted, making them more sensitive to an acute cold exposure. In return, these reporter mice with reduced UCP1 expression enabled us to investigate the physiological role of UCP1 in the prevention of weight gain. We observed no substantial differences in body mass across the three genotypes, irrespective of the type of diet or the ambient temperature, possibly due to the insufficient UCP1 activation. Indeed, activation of UCP1 by daily injection of the selective β₃-adrenergic receptor agonist CL316,243 resulted in significantly greater reduction of body weight in wild-type mice than in KI mice. Taken together, we conclude that the intact expression of UCP1 is essential for cold-induced thermogenesis but the presence of UCP1 per se does not protect mice from diet-induced obesity.NEW & NOTEWORTHY To study the functional role of UCP1-dependent brown adipose tissue thermogenesis for energy balance, new animal models are needed. By metabolic phenotyping of a novel mouse model with low UCP1 levels in brown fat, we demonstrate that the susceptibility to diet-induced obesity is not increased despite impaired cold-induced thermogenic capacity. Brown fat requires pharmacological activation to promote negative energy balance in diet-induced obese mice.

Imaging atherosclerotic plaques by targeting Galectin-3 and activated macrophages using (89Zr)-DFO- Galectin3-F(ab')2 mAb

Rationale: The high expression of Galectin-3 (Gal3) in macrophages of atherosclerotic plaques suggests its participation in atherosclerosis pathogenesis, and raises the possibility to use it as a target to image disease severity in vivo. Here, we explored the feasibility of tracking atherosclerosis by targeting Gal3 expression in plaques of apolipoprotein E knockout (ApoE-KO) mice via PET imaging. Methods: Targeting of Gal3 in M0-, M1- and M2 (M2a/M2c)-polarized macrophages was assessed in vitro using a Gal3-F(ab')₂ mAb labeled with AlexaFluor®488 and ⁸⁹Zr- desferrioxamine-thioureyl-phenyl-isothiocyanate (DFO). To visualize plaques in vivo, ApoE-KO mice were injected i.v. with ⁸⁹Zr-DFO-Gal3-F(ab')₂ mAb and imaged via PET/CT 48 h post injection. Whole length aortas harvested from euthanized mice were processed for Sudan-IV staining, autoradiography, and immunostaining for Gal3, CD68 and α-SMA expression. To confirm accumulation of the tracer in plaques, ApoE-KO mice were injected i.v. with Cy5.5-Gal3-F(ab')₂ mAb, euthanized 48 h post injection, followed by cryosections of the body and acquisition of fluorescent images. To explore the clinical potential of this imaging modality, immunostaining for Gal3, CD68 and α-SMA expression were carried out in human plaques. Single cell RNA sequencing (scRNA-Seq) analyses were performed to measure LGALS3 (i.e. a synonym for Gal3) gene expression in each macrophage of several subtypes present in murine or human plaques. Results: Preferential binding to M2 macrophages was observed with both AlexaFluor®488-Gal3-F(ab')₂ and ⁸⁹Zr-DFO-Gal3-F(ab')₂ mAbs. Focal and specific ⁸⁹Zr-DFO-Gal3-F(ab')₂ mAb uptake was detected in plaques of ApoE-KO mice by PET/CT. Autoradiography and immunohistochemical analyses of aortas confirmed the expression of Gal3 within plaques mainly in macrophages. Moreover, a specific fluorescent signal was visualized within the lesions of vascular structures burdened by plaques in mice. Gal3 expression in human plaques showed similar Gal3 expression patterns when compared to their murine counterparts. Conclusions: Our data reveal that ⁸⁹Zr-DFO-Gal3-F(ab')₂ mAb PET/CT is a potentially novel tool to image atherosclerotic plaques at different stages of development, allowing knowledge-based tailored individual intervention in clinically significant disease.

Caffeic and Chlorogenic Acids Synergistically Activate Browning Program in Human Adipocytes: Implications of AMPK- and PPAR-Mediated Pathways

Caffeic acid (CA) and chlorogenic acid (CGA) are phenolic compounds claimed to be responsible for the metabolic effects of coffee and tea consumption. Along with their structural similarities, they share common mechanisms such as activation of the AMP-activated protein kinase (AMPK) signaling. The present study aimed to investigate the anti-obesity potential of CA and CGA as co-treatment in human adipocytes. The molecular interactions of CA and CGA with key adipogenic transcription factors were simulated through an in silico molecular docking approach. The expression levels of white and brown adipocyte markers, as well as genes related to lipid metabolism, were analyzed by real-time quantitative PCR and Western blot analyses. Mechanistically, the CA/CGA combination induced lipolysis, upregulated AMPK and browning gene expression and downregulated peroxisome proliferator-activated receptor γ (PPARγ) at both transcriptional and protein levels. The gene expression profiles of the CA/CGA-co-treated adipocytes strongly resembled brown-like signatures. Major pathways identified included the AMPK- and PPAR-related signaling pathways. Collectively, these findings indicated that CA/CGA co-stimulation exerted a browning-inducing potential superior to that of either compound used alone which merits implementation in obesity management. Further, the obtained data provide additional insights on how CA and CGA modify adipocyte function, differentiation and lipid metabolism.

Systems-Genetics-Based Inference of a Core Regulatory Network Underlying White Fat Browning

Recruitment of brite/beige cells, known as browning of white adipose tissue (WAT), is an efficient way to turn an energy-storing organ into an energy-dissipating one and may therefore be of therapeutic value in combating obesity. However, a comprehensive understanding of the regulatory mechanisms mediating WAT browning is still lacking. Here, we exploit the large natural variation in WAT browning propensity between inbred mouse strains to gain an inclusive view of the core regulatory network coordinating this cellular process. Combining comparative transcriptomics, perturbation-based validations, and gene network analyses, we present a comprehensive gene regulatory network of inguinal WAT browning, revealing up to four distinct regulatory modules with key roles for uncovered transcriptional factors, while also providing deep insights into the genetic architecture of brite adipogenesis. The presented findings therefore greatly increase our understanding of the molecular drivers mediating the intriguing cellular heterogeneity and plasticity of adipose tissue.

The colorful versatility of adipocytes: white-to-brown transdifferentiation and its therapeutic potential in humans

Brown and brite adipocytes contribute to energy expenditure through nonshivering thermogenesis. Though these cell types are thought to arise primarily from the de novo differentiation of precursor cells, their abundance is also controlled through the transdifferentiation of mature white adipocytes. Here, we review recent advances in our understanding of the regulation of white-to-brown transdifferentiation, as well as the conversion of brown and brite adipocytes to dormant, white-like fat cells. Converting mature white adipocytes into brite cells or reactivating dormant brown and brite adipocytes has emerged as a strategy to ameliorate human metabolic disorders. We analyze the evidence of learning from mice and how they translate to humans to ultimately scrutinize the relevance of this concept. Moreover, we estimate that converting a small percentage of existing white fat mass in obese subjects into active brite adipocytes could be sufficient to achieve meaningful benefits in metabolism. In conclusion, novel browning agents have to be identified before adipocyte transdifferentiation can be realized as a safe and efficacious therapy.

Non-invasive Reporter Gene Imaging of Cell Therapies, including T Cells and Stem Cells

Cell therapies represent a rapidly emerging class of new therapeutics. They are intended and developed for the treatment of some of the most prevalent human diseases, including cancer, diabetes, and for regenerative medicine. Currently, they are largely developed without precise assessment of their in vivo distribution, efficacy, or survival either clinically or preclinically. However, it would be highly beneficial for both preclinical cell therapy development and subsequent clinical use to assess these parameters in situ to enable enhancements in efficacy, applicability, and safety. Molecular imaging can be exploited to track cells non-invasively on the whole-body level and can enable monitoring for prolonged periods in a manner compatible with rapidly expanding cell types. In this review, we explain how in vivo imaging can aid the development and clinical translation of cell-based therapeutics. We describe the underlying principles governing non-invasive in vivo long-term cell tracking in the preclinical and clinical settings, including available imaging technologies, reporter genes, and imaging agents as well as pitfalls related to experimental design. Our emphasis is on adoptively transferred T cell and stem cell therapies.

Non-invasive in vivo imaging of UCP1 expression in live mice via near-infrared fluorescent protein iRFP720

Uncoupling protein 1 (UCP1) is a mitochondrial protein that is expressed in both brown and beige adipocytes. UCP1 uncouples the mitochondrial electron transport chain from ATP synthesis to produce heat via non-shivering thermogenesis. Due to their ability to dissipate energy as heat and ameliorate metabolic disorders, UCP1-expressing adipocytes are considered as a potential target for anti-obesity treatment. To monitor the expression of UCP1 in live mice in a non-invasive manner, we generated the Ucp1-iRFP720 knock-in (Ucp1-iRFP720 KI) mice, in which the gene encoding a near-infrared fluorescent protein iRFP720 is inserted into the Ucp1 gene locus. Using the heterozygous Ucp1-iRFP720 KI mice, we observed robust iRFP fluorescence in the interscapular region where brown adipose tissue is located. Moreover, the iRFP fluorescence was clearly observable in inguinal white adipose tissues in live mice administered with β3-adrenergic receptor agonist CL316,243. We also found that the homozygous Ucp1-iRFP720 KI mice, which are deficient in UCP1, displayed prominent iRFP fluorescence in the inguinal regions at the standard housing temperature. Consistent with this, the mice exhibited expanded populations of beige-like adipocytes in inguinal white adipose tissue, in which the Ucp1 promoter was dramatically activated. Thus, the Ucp1-iRFP720 KI mice provide a convenient model for non-invasive in vivo imaging of UCP1 expression in both brown and beige adipocytes in live mice.

Immunometabolic Links between Estrogen, Adipose Tissue and Female Reproductive Metabolism

The current knowledge of sex-dependent differences in adipose tissue biology remains in its infancy and is motivated in part by the desire to understand why menopause is linked to an increased risk of metabolic disease. However, the development and characterization of targeted genetically-modified rodent models are shedding new light on the physiological actions of sex hormones in healthy reproductive metabolism. In this review we consider the need for differentially regulating metabolic flexibility, energy balance, and immunity in a sex-dependent manner. We discuss the recent advances in our understanding of physiological roles of systemic estrogen in regulating sex-dependent adipose tissue distribution, form and function; and in sex-dependent healthy immune function. We also review the decline in protective properties of estrogen signaling in pathophysiological settings such as obesity-related metaflammation and metabolic disease. It is clear that the many physiological actions of estrogen on energy balance, immunity, and immunometabolism together with its dynamic regulation in females make it an excellent candidate for regulating metabolic flexibility in the context of reproductive metabolism.

Opposing Actions of Adrenocorticotropic Hormone and Glucocorticoids on UCP1-Mediated Respiration in Brown Adipocytes

Brown fat is a potential target in the treatment of metabolic disorders as recruitment and activation of this thermogenic organ increases energy expenditure and promotes satiation. A large variety of G-protein coupled receptors, known as classical drug targets in pharmacotherapy, is expressed in brown adipocytes. In the present study, we analyzed transcriptome data for the expression of these receptors to identify potential pathways for the recruitment and activation of thermogenic capacity in brown fat. Our analysis revealed 12 G_s-coupled receptors abundantly expressed in murine brown fat. We screened ligands for these receptors in brown adipocytes for their ability to stimulate UCP1-mediated respiration and Ucp1 gene expression. Adrenocorticotropic hormone (ACTH), a ligand for the melanocortin 2 receptor (MC2R), turned out to be the most potent activator of UCP1 whereas its capability to stimulate Ucp1 gene expression was comparably low. Adrenocorticotropic hormone is the glandotropic hormone of the endocrine hypothalamus–pituitary–adrenal-axis stimulating the release of glucocorticoids in response to stress. In primary brown adipocytes ACTH acutely increased the cellular respiration rate similar to isoproterenol, a β-adrenergic receptor agonist. The effect of ACTH on brown adipocyte respiration was mediated via the MC2R as confirmed by using an antagonist. Inhibitor-based studies revealed that ACTH-induced respiration was dependent on protein kinase A and lipolysis, compatible with a rise of intracellular cAMP in response to ACTH. Furthermore, it is dependent on UCP1, as cells from UCP1-knockout mice did not respond. Taken together, ACTH is a non-adrenergic activator of murine brown adipocytes, initiating the canonical adenylyl cyclase–cAMP–protein kinase A-lipolysis-UCP1 pathway, and thus a potential target for the recruitment and activation of thermogenic capacity. Based on these findings in primary cell culture, the physiological significance might be that cold-induced ACTH in concert with norepinephrine released from sympathetic nerves contributes to BAT thermogenesis. Notably, dexamethasone attenuated isoproterenol-induced respiration. This effect increased gradually with the duration of pretreatment. In vivo, glucocorticoid release triggered by ACTH might oppose beta-adrenergic stimulation of metabolic fuel combustion in BAT and limit stress-induced hyperthermia.