Wntless regulates lipogenic gene expression in adipocytes and protects against diet-induced metabolic dysfunction

Phospholipid isotope tracing suggests β-catenin-driven suppression of phosphatidylcholine metabolism in hepatocellular carcinoma

Activating mutations in the CTNNB1 gene encoding β-catenin are among the most frequently observed oncogenic alterations in hepatocellular carcinoma (HCC). Profound alterations in lipid metabolism, including increases in fatty acid oxidation and transformation of the phospholipidome, occur in HCC with CTNNB1 mutations, but it is unclear what mechanisms give rise to these changes. We employed untargeted lipidomics and targeted isotope tracing to measure phospholipid synthesis activity in an inducible human liver cell line expressing mutant β-catenin, as well as in transgenic zebrafish with activated β-catenin-driven HCC. In both models, activated β-catenin expression was associated with large changes in the lipidome including conserved increases in acylcarnitines and ceramides and decreases in triglycerides. Lipid isotope tracing analysis in human cells revealed a reduction in phosphatidylcholine (PC) production rates as assayed by choline incorporation. We developed lipid isotope tracing analysis for zebrafish tumors and observed reductions in phosphatidylcholine synthesis by both the CDP-choline and PEMT pathways. The observed changes in the β-catenin-driven HCC phospholipidome suggest that zebrafish can recapitulate conserved features of HCC lipid metabolism and may serve as a model for identifying future HCC-specific lipid metabolic targets.

Impaired Remodeling of White Adipose Tissue in Obesity and Aging: From Defective Adipogenesis to Adipose Organ Dysfunction

The adipose organ adapts and responds to internal and environmental stimuli by remodeling both its cellular and extracellular components. Under conditions of energy surplus, the subcutaneous white adipose tissue (WAT) is capable of expanding through the enlargement of existing adipocytes (hypertrophy), followed by de novo adipogenesis (hyperplasia), which is impaired in hypertrophic obesity. However, an impaired hyperplastic response may result from various defects in adipogenesis, leading to different WAT features and metabolic consequences, as discussed here by reviewing the results of the studies in animal models with either overexpression or knockdown of the main molecular regulators of the two steps of the adipogenesis process. Moreover, impaired WAT remodeling with aging has been associated with various age-related conditions and reduced lifespan expectancy. Here, we delve into the latest advancements in comprehending the molecular and cellular processes underlying age-related changes in WAT function, their involvement in common aging pathologies, and their potential as therapeutic targets to influence both the health of elderly people and longevity. Overall, this review aims to encourage research on the mechanisms of WAT maladaptation common to conditions of both excessive and insufficient fat tissue. The goal is to devise adipocyte-targeted therapies that are effective against both obesity- and age-related disorders.

Activation of GFRAL+ neurons induces hypothermia and glucoregulatory responses associated with nausea and torpor

GFRAL-expressing neurons actuate aversion and nausea, are targets for obesity treatment, and may mediate metformin effects by long-term GDF15-GFRAL agonism. Whether GFRAL+ neurons acutely regulate glucose and energy homeostasis is, however, underexplored. Here, we report that cell-specific activation of GFRAL+ neurons using a variety of techniques causes a torpor-like state, including hypothermia, the release of stress hormones, a shift from glucose to lipid oxidation, and impaired insulin sensitivity, glucose tolerance, and skeletal muscle glucose uptake but augmented glucose uptake in visceral fat. Metabolomic analysis of blood and transcriptomics of muscle and fat indicate alterations in ketogenesis, insulin signaling, adipose tissue differentiation and mitogenesis, and energy fluxes. Our findings indicate that acute GFRAL+ neuron activation induces endocrine and gluco- and thermoregulatory responses associated with nausea and torpor. While chronic activation of GFRAL signaling promotes weight loss in obesity, these results show that acute activation of GFRAL+ neurons causes hypothermia and hyperglycemia.

Fabrication of a three-dimensional bone marrow niche-like acute myeloid Leukemia disease model by an automated and controlled process using a robotic multicellular bioprinting system

BACKGROUND

Acute myeloid leukemia (AML) is a hematological malignancy that remains a therapeutic challenge due to the high incidence of disease relapse. To better understand resistance mechanisms and identify novel therapies, robust preclinical models mimicking the bone marrow (BM) microenvironment are needed. This study aimed to achieve an automated fabrication process of a three-dimensional (3D) AML disease model that recapitulates the 3D spatial structure of the BM microenvironment and applies to drug screening and investigational studies.

METHODS

To build this model, we investigated a unique class of tetramer peptides with an innate ability to self-assemble into stable hydrogel. An automated robotic bioprinting process was established to fabricate a 3D BM (niche-like) multicellular AML disease model comprised of leukemia cells and the BM's stromal and endothelial cellular fractions. In addition, monoculture and dual-culture models were also fabricated. Leukemia cell compatibility, functionalities (in vitro and in vivo), and drug assessment studies using our model were performed. In addition, RNAseq and gene expression analysis using TaqMan arrays were also performed on 3D cultured stromal cells and primary leukemia cells.

RESULTS

The selected peptide hydrogel formed a highly porous network of nanofibers with mechanical properties similar to the BM extracellular matrix. The robotic bioprinter and the novel quadruple coaxial nozzle enabled the automated fabrication of a 3D BM niche-like AML disease model with controlled deposition of multiple cell types into the model. This model supported the viability and growth of primary leukemic, endothelial, and stromal cells and recapitulated cell-cell and cell-ECM interactions. In addition, AML cells in our model possessed quiescent characteristics with improved chemoresistance attributes, resembling more the native conditions as indicated by our in vivo results. Moreover, the whole transcriptome data demonstrated the effect of 3D culture on enhancing BM niche cell characteristics. We identified molecular pathways upregulated in AML cells in our 3D model that might contribute to AML drug resistance and disease relapse.

CONCLUSIONS

Our results demonstrate the importance of developing 3D biomimicry models that closely recapitulate the in vivo conditions to gain deeper insights into drug resistance mechanisms and novel therapy development. These models can also improve personalized medicine by testing patient-specific treatments.

Phospholipid isotope tracing reveals β-catenin-driven suppression of phosphatidylcholine metabolism in hepatocellular carcinoma

Background and Aims

Activating mutations in the CTNNB1 gene encoding β-catenin are among the most frequently observed oncogenic alterations in hepatocellular carcinoma (HCC). HCC with CTNNB1 mutations show profound alterations in lipid metabolism including increases in fatty acid oxidation and transformation of the phospholipidome, but it is unclear how these changes arise and whether they contribute to the oncogenic program in HCC.

Methods

We employed untargeted lipidomics and targeted isotope tracing to quantify phospholipid production fluxes in an inducible human liver cell line expressing mutant β-catenin, as well as in transgenic zebrafish with activated β-catenin-driven HCC.

Results

In both models, activated β-catenin expression was associated with large changes in the lipidome including conserved increases in acylcarnitines and ceramides and decreases in triglycerides. Lipid flux analysis in human cells revealed a large reduction in phosphatidylcholine (PC) production rates as assayed by choline tracer incorporation. We developed isotope tracing lipid flux analysis for zebrafish and observed similar reductions in phosphatidylcholine synthesis flux accomplished by sex-specific mechanisms.

Conclusions

The integration of isotope tracing with lipid abundances highlights specific lipid class transformations downstream of β-catenin signaling in HCC and suggests future HCC-specific lipid metabolic targets.

Antibodies to sclerostin or G-CSF receptor partially eliminate bone or marrow adipocyte loss, respectively, following vertical sleeve gastrectomy

Vertical sleeve gastrectomy (VSG), the most utilized bariatric procedure in clinical practice, greatly reduces body weight and improves a variety of metabolic disorders. However, one of its long-term complications is bone loss and increased risk of fracture. Elevated circulating sclerostin (SOST) and granulocyte-colony stimulating factor (G-CSF) concentrations have been considered as potential contributors to VSG-associated bone loss. To test these possibilities, we administrated antibodies to SOST or G-CSF receptor and investigated alterations to bone and marrow niche following VSG. Neutralizing either SOST or G-CSF receptor did not alter beneficial effects of VSG on adiposity and hepatic steatosis, and anti-SOST treatment provided a further improvement to glucose tolerance. SOST antibodies partially reduced trabecular and cortical bone loss following VSG by increasing bone formation, whereas G-CSF receptor antibodies had no effects on bone mass. The expansion in myeloid cellularity and reductions in bone marrow adiposity seen with VSG were partially eliminated by treatment with Anti-G-CSF receptor. Taken together, these experiments demonstrate that antibodies to SOST or G-CSF receptor may act through independent mechanisms to partially block effects of VSG on bone loss or marrow niche cells, respectively.

The role of Evi/Wntless in exporting Wnt proteins

Intercellular communication by Wnt proteins governs many essential processes during development, tissue homeostasis and disease in all metazoans. Many context-dependent effects are initiated in the Wnt-producing cells and depend on the export of lipidated Wnt proteins. Although much focus has been on understanding intracellular Wnt signal transduction, the cellular machinery responsible for Wnt secretion became better understood only recently. After lipid modification by the acyl-transferase Porcupine, Wnt proteins bind their dedicated cargo protein Evi/Wntless for transport and secretion. Evi/Wntless and Porcupine are conserved transmembrane proteins, and their 3D structures were recently determined. In this Review, we summarise studies and structural data highlighting how Wnts are transported from the ER to the plasma membrane, and the role of SNX3-retromer during the recycling of its cargo receptor Evi/Wntless. We also describe the regulation of Wnt export through a post-translational mechanism and review the importance of Wnt secretion for organ development and cancer, and as a future biomarker.

Signaling pathways in obesity: mechanisms and therapeutic interventions

Obesity is a complex, chronic disease and global public health challenge. Characterized by excessive fat accumulation in the body, obesity sharply increases the risk of several diseases, such as type 2 diabetes, cardiovascular disease, and nonalcoholic fatty liver disease, and is linked to lower life expectancy. Although lifestyle intervention (diet and exercise) has remarkable effects on weight management, achieving long-term success at weight loss is extremely challenging, and the prevalence of obesity continues to rise worldwide. Over the past decades, the pathophysiology of obesity has been extensively investigated, and an increasing number of signal transduction pathways have been implicated in obesity, making it possible to fight obesity in a more effective and precise way. In this review, we summarize recent advances in the pathogenesis of obesity from both experimental and clinical studies, focusing on signaling pathways and their roles in the regulation of food intake, glucose homeostasis, adipogenesis, thermogenesis, and chronic inflammation. We also discuss the current anti-obesity drugs, as well as weight loss compounds in clinical trials, that target these signals. The evolving knowledge of signaling transduction may shed light on the future direction of obesity research, as we move into a new era of precision medicine.

TCF7L2 plays a complex role in human adipose progenitor biology, which might contribute to genetic susceptibility to type 2 diabetes

INTRODUCTION

Non-coding genetic variation at TCF7L2 is the strongest genetic determinant of type 2 diabetes (T2D) risk in humans. TCF7L2 encodes a transcription factor mediating the nuclear effects of WNT signaling in adipose tissue (AT). In vivo studies in transgenic mice have highlighted important roles for TCF7L2 in adipose tissue biology and systemic metabolism.

OBJECTIVE

To map the expression of TCF7L2 in human AT, examine its role in human adipose cell biology in vitro, and investigate the effects of the fine-mapped T2D-risk allele at rs7903146 on AT morphology and TCF7L2 expression.

METHODS

Ex vivo gene expression studies of TCF7L2 in whole and fractionated human AT. In vitro TCF7L2 gain- and/or loss-of-function studies in primary and immortalized human adipose progenitor cells (APCs) and mature adipocytes (mADs). AT phenotyping of rs7903146 T2D-risk variant carriers and matched controls.

RESULTS

Adipose progenitors (APs) exhibited the highest TCF7L2 mRNA abundance compared to mature adipocytes and adipose-derived endothelial cells. Obesity was associated with reduced TCF7L2 transcript levels in whole subcutaneous abdominal AT but paradoxically increased expression in APs. In functional studies, TCF7L2 knockdown (KD) in abdominal APs led to dose-dependent activation of WNT/β-catenin signaling, impaired proliferation and dose-dependent effects on adipogenesis. Whilst partial KD enhanced adipocyte differentiation, near-total KD impaired lipid accumulation and adipogenic gene expression. Over-expression of TCF7L2 accelerated adipogenesis. In contrast, TCF7L2-KD in gluteal APs dose-dependently enhanced lipid accumulation. Transcriptome-wide profiling revealed that TCF7L2 might modulate multiple aspects of AP biology including extracellular matrix secretion, immune signaling and apoptosis. The T2D-risk allele at rs7903146 was associated with reduced AP TCF7L2 expression and enhanced AT insulin sensitivity.

CONCLUSIONS

TCF7L2 plays a complex role in AP biology and has both dose- and depot-dependent effects on adipogenesis. In addition to regulating pancreatic insulin secretion, genetic variation at TCF7L2 might also influence T2D risk by modulating AP function.

Discovery and functional assessment of a novel adipocyte population driven by intracellular Wnt/β-catenin signaling in mammals

Wnt/β-catenin signaling has been well established as a potent inhibitor of adipogenesis. Here, we identified a population of adipocytes that exhibit persistent activity of Wnt/β-catenin signaling, as revealed by the Tcf/Lef-GFP reporter allele, in embryonic and adult mouse fat depots, named as Wnt⁺ adipocytes. We showed that this β-catenin-mediated signaling activation in these cells is Wnt ligand- and receptor-independent but relies on AKT/mTOR pathway and is essential for cell survival. Such adipocytes are distinct from classical ones in transcriptomic and genomic signatures and can be induced from various sources of mesenchymal stromal cells including human cells. Genetic lineage-tracing and targeted cell ablation studies revealed that these adipocytes convert into beige adipocytes directly and are also required for beige fat recruitment under thermal challenge, demonstrating both cell autonomous and non-cell autonomous roles in adaptive thermogenesis. Furthermore, mice bearing targeted ablation of these adipocytes exhibited glucose intolerance, while mice receiving exogenously supplied such cells manifested enhanced glucose utilization. Our studies uncover a unique adipocyte population in regulating beiging in adipose tissues and systemic glucose homeostasis.

Simple oligonucleotide-based multiplexing of single-cell chromatin accessibility

Microdroplet single-cell ATAC-seq is widely used to measure chromatin accessibility, however, highly scalable and simple sample multiplexing procedures are not available. Here, we present a transposome-assisted single nucleus barcoding approach for ATAC-seq (SNuBar-ATAC) that utilizes a single oligonucleotide adaptor for multiplexing samples during the existing tagmentation step and does not require a pre-labeling procedure. The accuracy and scalability of SNuBar-ATAC was evaluated using cell line mixture experiments. We applied SNuBar-ATAC to investigate treatment-induced chromatin accessibility dynamics by multiplexing 28 mice with lung tumors that received different combinations of chemo, radiation, and targeted immunotherapy. We also applied SNuBar-ATAC to study spatial epigenetic heterogeneity by multiplexing 32 regions from a human breast tissue. Additionally, we show that SNuBar can multiplex single cell ATAC and RNA multiomic assays in cell lines and human breast tissue samples. Our data show that SNuBar is a highly accurate, easy-to-use, and scalable system for multiplexing scATAC-seq and scATAC and RNA co-assay experiments.

Wnt Signaling: From Mesenchymal Cell Fate to Lipogenesis and Other Mature Adipocyte Functions

Wnt signaling is an ancient and evolutionarily conserved pathway with fundamental roles in the development of adipose tissues. Roles of this pathway in mesenchymal stem cell fate determination and differentiation have been extensively studied. Indeed, canonical Wnt signaling is a significant endogenous inhibitor of adipogenesis and promoter of other cell fates, including osteogenesis, chondrogenesis, and myogenesis. However, emerging genetic evidence in both humans and mice suggests central roles for Wnt signaling in body fat distribution, obesity, and metabolic dysfunction. Herein, we highlight recent studies that have begun to unravel the contributions of various Wnt pathway members to critical adipocyte functions, including carbohydrate and lipid metabolism. We further explore compelling evidence of complex and coordinated interactions between adipocytes and other cell types within adipose tissues, including stromal, immune, and endothelial cells. Given the evolutionary conservation and ubiquitous cellular distribution of this pathway, uncovering the contributions of Wnt signaling to cell metabolism has exciting implications for therapeutic intervention in widespread pathologic states, including obesity, diabetes, and cancers.

Obesity-induced changes in human islet G protein-coupled receptor expression: Implications for metabolic regulation

G protein-coupled receptors (GPCRs) are a large family of cell surface receptors that are the targets for many different classes of pharmacotherapy. The islets of Langerhans are central to appropriate glucose homeostasis through their secretion of insulin, and islet function can be modified by ligands acting at the large number of GPCRs that islets express. The human islet GPCRome is not a static entity, but one that is altered under pathophysiological conditions and, in this review, we have compared expression of GPCR mRNAs in human islets obtained from normal weight range donors, and those with a weight range classified as obese. We have also considered the likely outcomes on islet function that the altered GPCR expression status confers and the possible impact that adipokines, secreted from expanded fat depots, could have at those GPCRs showing altered expression in obesity.

Partial Deficiency of Zfp217 Resists High-Fat Diet-Induced Obesity by Increasing Energy Metabolism in Mice

Obesity-induced adipose tissue dysfunction and disorders of glycolipid metabolism have become a worldwide research priority. Zfp217 plays a crucial role in adipogenesis of 3T3-L1 preadipocytes, but about its functions in animal models are not yet clear. To explore the role of Zfp217 in high-fat diet (HFD)-induced obese mice, global Zfp217 heterozygous knockout (Zfp217^+/−) mice were constructed. Zfp217^+/− mice and Zfp217^+/+ mice fed a normal chow diet (NC) did not differ significantly in weight gain, percent body fat mass, glucose tolerance, or insulin sensitivity. When challenged with HFD, Zfp217^+/− mice had less weight gain than Zfp217^+/+ mice. Histological observations revealed that Zfp217^+/− mice fed a high-fat diet had much smaller white adipocytes in inguinal white adipose tissue (iWAT). Zfp217^+/− mice had improved metabolic profiles, including improved glucose tolerance, enhanced insulin sensitivity, and increased energy expenditure compared to the Zfp217^+/+ mice under HFD. We found that adipogenesis-related genes were increased and metabolic thermogenesis-related genes were decreased in the iWAT of HFD-fed Zfp217^+/+ mice compared to Zfp217^+/− mice. In addition, adipogenesis was markedly reduced in mouse embryonic fibroblasts (MEFs) from Zfp217-deleted mice. Together, these data indicate that Zfp217 is a regulator of energy metabolism and it is likely to provide novel insight into treatment for obesity.

The crosstalk of hedgehog, PI3K and Wnt pathways in diabetes

Hyperglycaemia causes pancreatic β-cells to release insulin that then attaches to a specific expression of receptor isoform and reverses high glucose concentrations. It is well known that insulin is capable of initiating insulin-receptor substrate (IRS)/phosphatidylinositol 3-kinase (PI3K)/protein kinase B (PKB) signaling pathways in target cells; such as liver, adipose tissues, and muscles. However, recent discoveries indicate that many other pathways, such as the Hedgehog (Hh) and growth factor-stimulating Wingless-related integration (Wnt) signaling pathways; are activated in hyperglycaemia as well. Although these two pathways are traditionally thought to have a decisive role in cellular growth and differentiation only, recent reports show that they are involved in regulating cellular homeostasis and energy balance. While insulin-activated IRS/PI3K/PKB pathway cascades are primarily known to reduce glucose production, it was recently discovered to increase the Hh signaling pathway's stability, thereby activating the PI3K/PKB/mammalian target of rapamycin complex 2 (mTORC2) signaling pathway. The Hh signaling pathway not only plays a role in lipid metabolism, insulin sensitivity, inflammatory response, diabetes-related complications, but crosstalks with the Wnt signaling pathway resulting in improved insulin sensitivity and decrease inflammatory response in diabetes.

Effects of normobaric cyclic hypoxia exposure on mesenchymal stem-cell differentiation-pilot study on bone parameters in elderly

BACKGROUND

Mesenchymal stem cells (MSC) of bone marrow are the progenitor of osteoblasts and adipocytes. MSC tend to differentiate into adipocytes, instead of osteoblasts, with aging. This favors the loss of bone mass and development of osteoporosis. Hypoxia induces hypoxia inducible factor 1α gene encoding transcription factor, which regulates the expression of genes related to energy metabolism and angiogenesis. That allows a better adaptation to low O2 conditions. Sustained hypoxia has negative effects on bone metabolism, favoring bone resorption. Yet, surprisingly, cyclic hypoxia (CH), short times of hypoxia followed by long times in normoxia, can modulate MSC differentiation and improve bone health in aging.

AIM

To evaluate the CH effect on MSC differentiation, and whether it improves bone mineral density in elderly.

METHODS

MSC cultures were induced to differentiate into osteoblasts or adipocytes, in CH (3% O2 for 1, 2 or 4 h, 4 d a week). Extracellular-matrix mineralization and lipid-droplet formation were studied in MSC induced to differentiate into osteoblast or adipocytes, respectively. In addition, gene expression of marker genes, for osteogenesis or adipogenesis, have been quantified by quantitative real time polymerase chain reaction. The in vivo studies with elderly (> 75 years old; n = 10) were carried out in a hypoxia chamber, simulating an altitude of 2500 m above sea level, or in normoxia, for 18 wk (36 CH sessions of 16 min each). Percentages of fat mass and bone mineral density from whole body, trunk and right proximal femur (femoral, femoral neck and trochanter) were assessed, using dual-energy X-ray absorptiometry.

RESULTS

CH (4 h of hypoxic exposure) inhibited extracellular matrix mineralization and lipid-droplet formation in MSC induced to differentiate into osteoblasts or adipocytes, respectively. However, both parameters were not significantly affected by the other shorter hypoxia times assessed. The longest periods of hypoxia downregulated the expression of genes related to extracellular matrix formation, in MSC induced to differentiate into osteoblasts. Interestingly, osteocalcin (associated to energy metabolism) was upregulated. Vascular endothelial growth factor an expression and low-density lipoprotein receptor related protein 5/6/dickkopf Wnt signaling pathway inhibitor 1 (associated to Wnt/β-catenin pathway activation) increased in osteoblasts. Yet, they decreased in adipocytes after CH treatments, mainly with the longest hypoxia times. However, the same CH treatments increased the osteoprotegerin/receptor activator for nuclear factor kappa B ligand ratio in both cell types. An increase in total bone mineral density was observed in elderly people exposed to CH, but not in specific regions. The percentage of fat did not vary between groups.

CONCLUSION

CH may have positive effects on bone health in the elderly, due to its possible inhibitory effect on bone resorption, by increasing the osteoprotegerin / receptor activator for nuclear factor kappa B ligand ratio.

Stearoyl-CoA desaturase 5 (SCD5), a Δ-9 fatty acyl desaturase in search of a function

A large body of research has demonstrated that human stearoyl-CoA desaturase 1 (SCD1), a universally expressed fatty acid Δ9-desaturase that converts saturated fatty acids (SFA) into monounsaturated fatty acids (MUFA), is a central regulator of metabolic and signaling pathways involved in cell proliferation, differentiation, and survival. Unlike SCD1, stearoyl-CoA desaturase 5 (SCD5), a second SCD isoform found in a variety of vertebrates, including humans, has received considerably less attention but new information on the catalytic properties, regulation and biological functions of this enzyme has begun to emerge. This review will examine the new evidence that supports key metabolic and biological roles for SCD5, as well as the potential implication of this desaturase in the mechanisms of human diseases.

Wnt/β-catenin signaling regulates adipose tissue lipogenesis and adipocyte-specific loss is rigorously defended by neighboring stromal-vascular cells

OBJECTIVE

Canonical Wnt/β-catenin signaling is a well-studied endogenous regulator of mesenchymal cell fate determination, promoting osteoblastogenesis and inhibiting adipogenesis. However, emerging genetic evidence in humans links a number of Wnt pathway members to body fat distribution, obesity, and metabolic dysfunction, suggesting that this pathway also functions in adipocytes. Recent studies in mice have uncovered compelling evidence that the Wnt signaling pathway plays important roles in adipocyte metabolism, particularly under obesogenic conditions. However, complexities in Wnt signaling and differences in experimental models and approaches have thus far limited our understanding of its specific roles in this context.

METHODS

To investigate roles of the canonical Wnt pathway in the regulation of adipocyte metabolism, we generated adipocyte-specific β-catenin (β-cat) knockout mouse and cultured cell models. We used RNA sequencing, ChIP sequencing, and molecular approaches to assess expression of Wnt targets and lipogenic genes. We then used functional assays to evaluate effects of β-catenin deficiency on adipocyte metabolism, including lipid and carbohydrate handling. In mice maintained on normal chow and high-fat diets, we assessed the cellular and functional consequences of adipocyte-specific β-catenin deletion on adipose tissues and systemic metabolism.

RESULTS

We report that in adipocytes, the canonical Wnt/β-catenin pathway regulates de novo lipogenesis (DNL) and fatty acid monounsaturation. Further, β-catenin mediates effects of Wnt signaling on lipid metabolism in part by transcriptional regulation of Mlxipl and Srebf1. Intriguingly, adipocyte-specific loss of β-catenin is sensed and defended by CD45^-/CD31^- stromal cells to maintain tissue-wide Wnt signaling homeostasis in chow-fed mice. With long-term high-fat diet, this compensatory mechanism is overridden, revealing that β-catenin deletion promotes resistance to diet-induced obesity and adipocyte hypertrophy and subsequent protection from metabolic dysfunction.

CONCLUSIONS

Taken together, our studies demonstrate that Wnt signaling in adipocytes is required for lipogenic gene expression, de novo lipogenesis, and lipid desaturation. In addition, adipose tissues rigorously defend Wnt signaling homeostasis under standard nutritional conditions, such that stromal-vascular cells sense and compensate for adipocyte-specific loss. These findings underscore the critical importance of this pathway in adipocyte lipid metabolism and adipose tissue function.