FGF2 disruption enhances thermogenesis in brown and beige fat to protect against adiposity and hepatic steatosis

Adipocyte-derived shed Syndecan-4 suppresses lipolysis contributing to impaired adipose tissue browning and adaptive thermogenesis

Lipolysis in white adipose tissue (WAT) provides fatty acids as energy substrates for thermogenesis to increase energy expenditure. Syndecan-4 (Sdc4) is a transmembrane proteoglycan bearing heparan sulfate chains. Although single nucleotide polymorphisms (SNPs) of the Sdc4 gene have been identified linking to metabolic syndromes, its specific function in adipose tissue remains obscure. Here, we show that Sdc4 serves as a regulator of lipid metabolism and adaptive thermogenesis. Sdc4 expression and shedding are elevated in the white adipose tissue (WAT) of diet-induced obese mice. Adipocyte-specific deletion of Sdc4 promotes lipolysis and WAT browning, thereby raising whole-body energy expenditure to protect against diet-induced obesity. Mechanistically, fibroblast growth factor 2 (FGF2) is a paracrine factor that maintains energy homeostasis. Elevated shed Sdc4 concentrates and delivers FGF2 to fibroblast growth factor receptor 1 (FGFR1) on adipocytes, which in turn suppresses lipolysis by reducing hormone-sensitive lipase (HSL) activity, thus exaggerating adipose tissue dysfunction upon high-fat diet induction. Sdc4-deficient adipocytes show higher lipolytic and thermogenic capacity by enhancing HSL phosphorylation and UCP1 expression. Overall, our study reveals that adipocyte-derived shed Sdc4 is a novel suppressor of lipolysis, contributing to decreased energy expenditure, thus exaggerating obesity. Targeting shed Sdc4 is a potential therapeutic strategy for obesity.

Discovery of novel obesity genes through cross-ancestry analysis

Gene discoveries in obesity have largely relied on homogeneous populations, limiting their generalizability across ancestries. We performed a gene-based rare variant association study of BMI on 839,110 individuals from six ancestries across two population-scale biobanks. A cross-ancestry meta-analysis identified 13 genes, including five novel ones: YLPM1 , RIF1 , GIGYF1 , SLC5A3 , and GRM7 , that conferred about three-fold risk for severe obesity, were expressed in the brain and adipose tissue, and were linked to obesity traits such as body-fat percentage. While YLPM1 , MC4R, and SLTM showed consistent effects, GRM7 and APBA1 showed significant ancestral heterogeneity. Polygenic risk additively increased obesity penetrance, and phenome-wide studies identified additional associations, including YLPM1 with altered mental status. These genes also influenced cardiometabolic comorbidities, including GIGYF1 and SLTM towards type 2 diabetes with or without BMI as a mediator, and altered levels of plasma proteins, such as LECT2 and NCAN, which in turn affected BMI. Our findings provide insights into the genetic basis of obesity and its related comorbidities across ancestries and ascertainments.

Single-nucleus transcriptomes reveal the underlying mechanisms of dynamic whitening in thermogenic adipose tissue in goats

BACKGROUND

Thermogenic adipose tissue, both beige and brown, experiences whitening as animals are exposed to warmth and age, but the potential mechanisms are not fully understood. In this study, we employed single-nucleus RNA-seq to construct a cell atlas during whitening progression and identified the characteristics of thermogenic adipocytes.

RESULTS

Our histological studies and bulk transcriptome gene expression analysis confirmed that both perirenal and omental adipose tissues (pAT and oAT) exhibited progressive whitening in goats. Compared to the classic brown adipocytes in mice, goat thermogenic adipocytes were more closely related in gene expression patterns to human beige adipocytes, which was also confirmed by adipocyte type- and lineage-specific marker expression analysis. Furthermore, trajectory analysis revealed beige- and white-like adipocytes deriving from a common origin, coexisting and undergoing the transdifferentiation. In addition, differences in gene expression profiles and cell communication patterns (e.g., FGF and CALCR signaling) between oAT and pAT suggested a lower thermogenic capacity of oAT than that of pAT.

CONCLUSIONS

We constructed a cell atlas of goat pAT and oAT and descripted the characteristics of thermogenic adipocytes during whitening progression. Altogether, our results make a significant contribution to the molecular and cellular mechanisms behind the whitening of thermogenic adipocytes, and providing new insights into obesity prevention in humans and cold adaptation in animals.

Eye on the horizon: The metabolic landscape of the RPE in aging and disease

To meet the prodigious bioenergetic demands of the photoreceptors, glucose and other nutrients must traverse the retinal pigment epithelium (RPE), a polarised monolayer of cells that lie at the interface between the outer retina and the choroid, the principal vascular layer of the eye. Recent investigations have revealed a metabolic ecosystem in the outer retina where the photoreceptors and RPE engage in a complex exchange of sugars, amino acids, and other metabolites. Perturbation of this delicate metabolic balance has been identified in the aging retina, as well as in age-related macular degeneration (AMD), the leading cause of blindness in the Western world. Also common in the aging and diseased retina are elevated levels of cytokines, oxidative stress, advanced glycation end-products, increased growth factor signalling, and biomechanical stress - all of which have been associated with metabolic dysregulation in non-retinal cell types and tissues. Herein, we outline the role of these factors in retinal homeostasis, aging, and disease. We discuss their effects on glucose, mitochondrial, lipid, and amino acid metabolism in tissues and cell types outside the retina, highlighting the signalling pathways through which they induce these changes. Lastly, we discuss promising avenues for future research investigating the roles of these pathological conditions on retinal metabolism, potentially offering novel therapeutic approaches to combat age-related retinal disease.

Deciphering adipose development: Function, differentiation and regulation

The overdevelopment of adipose tissues, accompanied by excess lipid accumulation and energy storage, leads to adipose deposition and obesity. With the increasing incidence of obesity in recent years, obesity is becoming a major risk factor for human health, causing various relevant diseases (including hypertension, diabetes, osteoarthritis and cancers). Therefore, it is of significance to antagonize obesity to reduce the risk of obesity-related diseases. Excess lipid accumulation in adipose tissues is mediated by adipocyte hypertrophy (expansion of pre-existing adipocytes) or hyperplasia (increase of newly-formed adipocytes). It is necessary to prevent excessive accumulation of adipose tissues by controlling adipose development. Adipogenesis is exquisitely regulated by many factors in vivo and in vitro, including hormones, cytokines, gender and dietary components. The present review has concluded a comprehensive understanding of adipose development including its origin, classification, distribution, function, differentiation and molecular mechanisms underlying adipogenesis, which may provide potential therapeutic strategies for harnessing obesity without impairing adipose tissue function.

The Role of Exerkines in Obesity-Induced Disruption of Mitochondrial Homeostasis in Thermogenic Fat

There is a notable correlation between mitochondrial homeostasis and metabolic disruption. In this review, we report that obesity-induced disruption of mitochondrial homeostasis adversely affects lipid metabolism, adipocyte differentiation, oxidative capacity, inflammation, insulin sensitivity, and thermogenesis in thermogenic fat. Elevating mitochondrial homeostasis in thermogenic fat emerges as a promising avenue for developing treatments for metabolic diseases, including enhanced mitochondrial function, mitophagy, mitochondrial uncoupling, and mitochondrial biogenesis. The exerkines (e.g., myokines, adipokines, batokines) released during exercise have the potential to ameliorate mitochondrial homeostasis, improve glucose and lipid metabolism, and stimulate fat browning and thermogenesis as a defense against obesity-associated metabolic diseases. This comprehensive review focuses on the manifold benefits of exercise-induced exerkines, particularly emphasizing their influence on mitochondrial homeostasis and fat thermogenesis in the context of metabolic disorders associated with obesity.

Dawn-to-dusk dry fasting decreases circulating inflammatory cytokines in subjects with increased body mass index

BACKGROUND

The circadian rhythm involves numerous metabolic processes, including sleep/awakening, body temperature regulation, hormone secretion, hepatic function, cellular plasticity, and cytokine release (inflammation), that appear to have a dynamic relationship with all the processes above. Studies have linked various cytokines to the chronic state of low-grade inflammation and oxidative stress in obesity. Dawn-to-dusk dry fasting (DDDF) could alleviate the adverse effects of obesity by decreasing inflammation. This study examined the effects of DDDF on circulating inflammatory cytokines in subjects with increased body mass index (BMI).

METHODS

The current observational prospective study included adult subjects with a BMI equal to or greater than 25 kg/m2 who practiced the annual religious 30-day DDDF. Individuals with significant underlying medical conditions were excluded to limit confounding factors. All subjects were evaluated within two weeks before 30-day DDDF, within the fourth week of 30-day DDDF, and within two weeks after 30-day DDDF. Multiple cytokines and clinical health indicators were measured at each evaluation.

RESULTS

Thirteen subjects (10 men and three women) with a mean age of 32.9 years (SD = 9.7 years) and a mean BMI of 32 kg/m2 (SD = 4.6 kg/m2) were included. An overall associated decrease in the levels of multiple cytokines with DDDF was observed. A significant decrease in the mean interleukin 1 beta level was observed within the fourth week of 30-day DDDF (P = 0.045), which persisted even after the fasting period (P = 0.024). There was also a significant decrease in the mean levels of interleukin 15 (IL-15) (P = 0.014), interleukin 1 receptor antagonist (P = 0.041), macrophage-derived chemokine (MDC) (P = 0.013), and monokine induced by interferon gamma/chemokine (C-X-C motif) ligand 9 (P = 0.027) within the fourth week of 30-day DDDF and in the mean levels of fibroblast growth factor 2 (P = 0.010), interleukin 12 p40 subunit (P = 0.038), interleukin 22 (P = 0.025) and tumor necrosis factor alpha (P = 0.046) within two weeks after 30-DDDF. In terms of anthropometric parameters, there was a decrease in mean body weight (P = 0.032), BMI (P = 0.028), and hip circumference (P = 0.007) within the fourth week of 30-day DDDF and a decrease in mean weight (P = 0.026), BMI (P = 0.033) and hip circumference (P = 0.016) within two weeks after 30-day DDDF compared with the levels measured within two weeks before 30-day DDDF. Although there was no significant correlation between changes in weight and changes in circulating inflammatory cytokines, there was a significant positive correlation between changes in waist circumference and changes in specific inflammatory cytokines (e.g., IL-15, MDC, platelet-derived growth factor, soluble CD40L, vascular endothelial growth factor A) within the fourth week of 30-day DDDF and/or two weeks after 30-day DDDF. A significant decrease in mean average resting heart rate within the fourth week of 30-day DDDF was also observed (P = 0.023), and changes between average resting heart rate and changes in interleukin-8 levels within the fourth week of 30-day DDDF compared with baseline levels were positively correlated (r = 0.57, P = 0.042).

CONCLUSION

DDDF appears to be a unique and potent treatment to reduce low-grade chronic inflammation caused by obesity and visceral adiposity. Further studies with more extended follow-up periods are warranted to investigate the long-term anti-inflammatory benefits of DDDF in individuals with increased BMI.

FGFR1 Signaling Facilitates Obesity-Driven Pulmonary Outgrowth in Metastatic Breast Cancer

Survival of dormant, disseminated breast cancer cells contributes to tumor relapse and metastasis. Women with a body mass index greater than 35 have an increased risk of developing metastatic recurrence. Herein, we investigated the effect of diet-induced obesity (DIO) on primary tumor growth and metastatic progression using both metastatic and systemically dormant mouse models of breast cancer. This approach led to increased PT growth and pulmonary metastasis. We developed a novel protocol to induce obesity in Balb/c mice by combining dietary and hormonal interventions with a thermoneutral housing strategy. In contrast to standard housing conditions, ovariectomized Balb/c mice fed a high-fat diet under thermoneutral conditions became obese over a period of 10 weeks, resulting in a 250% gain in fat mass. Obese mice injected with the D2.OR model developed macroscopic pulmonary nodules compared with the dormant phenotype of these cells in mice fed a control diet. Analysis of the serum from obese Balb/c mice revealed increased levels of FGF2 as compared with lean mice. We demonstrate that serum from obese animals, exogenous FGF stimulation, or constitutive stimulation through autocrine and paracrine FGF2 is sufficient to break dormancy and drive pulmonary outgrowth. Blockade of FGFR signaling or specific depletion of FGFR1 prevented obesity-associated outgrowth of the D2.OR model.

IMPLICATIONS

Overall, this study developed a novel DIO model that allowed for demonstration of FGF2:FGFR1 signaling as a key molecular mechanism connecting obesity to breakage of systemic tumor dormancy and metastatic progression.

Adipose Tissue-Derived Products May Present Inflammatory Properties That Affect Chondrocytes and Synoviocytes from Patients with Knee Osteoarthritis

Adipose tissue-derived cell-based injectable therapies have been demonstrated to have disease-modifying effects on joint tissues in preclinical studies on animal osteoarthritis (OA) models, but clinical results are heterogeneous and not always satisfactory. The aim of this study was to investigate the influence of adipose tissue properties on the therapeutic effects of the adipose-derived product in an in vitro OA setting. Micro-fragmented adipose tissue (MF-AT) samples were obtained from 21 OA patients (mean age 51.7 ± 11.8 years, mean BMI 25.7 ± 4.1 kg/m2). The analysis of the MF-AT supernatant was performed to analyze the release of inflammatory factors. The effects of MF-AT inflammatory factors were investigated on chondrocytes and synoviocytes gene expression levels. Patients' characteristics were analyzed to explore their influence on MF-AT inflammatory molecules and on the MF-AT effects on the gene expression of chondrocytes and synoviocytes. The study results demonstrated that adipose tissue-derived products may present inflammatory properties that influence the therapeutic potential for OA treatment, with products with a higher pro-inflammatory profile stimulating a higher expression of genes related to a more inflamed and catabolic phenotype. A higher pro-inflammatory cytokine pattern and a higher pro-inflammatory effect were found in adipose tissue-derived products obtained from OA patients with higher BMI.

Cold Stress Induced Liver Injury of Mice through Activated NLRP3/Caspase-1/GSDMD Pyroptosis Signaling Pathway

The body needs to generate heat to ensure basic life activities when exposed to cold temperatures. The liver, as the largest glycogen storage organ in the body and main heat-producing organ at rest, may play a role in chronic cold exposure. Recent studies suggested that pyroptosis plays a crucial role in liver diseases. However, the role of pyroptosis in cold stress-induced liver injury is not clear. Hence, in this study, we attempted to investigate the effects of chronic cold exposure on liver function, apoptosis, oxidative stress and inflammation in mice by establishing a mouse model of chronic cold exposure, and to investigate whether pyroptosis pathways are involved in the process of chronic cold exposure. In vivo, our results show that inflammatory cell infiltration and other pathological changes in liver cells and the activity of liver enzyme evidently increased in the serum and liver of cold-exposed mice, suggesting cold stress may result in liver injury. Remarkably, increased expression of heat shock protein 70 (HSP70) and HSP90 proteins proved the cold stress model is successfully constructed. Then, elevated levels of apoptosis, inflammation, oxidative stress and pyroptosis related proteins and mRNAs, such as cysteinyl aspartate specific proteinase-3 (Caspase-3), inducible nitric oxide synthase (iNOS), nuclear factor erythroid2-related factor 2 (Nrf2) and gasdermins D (GSDMD), confirmed that cold exposure activated apoptosis, oxidative stress and pyroptosis, and released inflammation cytokines. Meanwhile, in vitro, we got similar results as in vivo. Further, adding an NLR family pyrin domain containing 3 (NLRP3) inhibitors found that suppression expression of NLRP3 results in the essential proteins of pyroptosis and antioxidant evidently reduced, and adding GSDMD inhibitor found that suppression expression of GSDMD accompanies with the level of Nrf2 and heme oxygenase-1 (HO-1) obviously reduced. In summary, these findings provide a new understanding of the underlying mechanisms of the cold stress response, which can inform the development of new strategies to combat the effects of hypothermia.

The fibroblast growth factor receptor antagonist SSR128129E inhibits fat accumulation via suppressing adipogenesis in mice

BACKGROUND

AS an allosteric inhibitor of fibroblast growth factor receptors (FGFRs), SSR128129E (SSR) extensively inhibits the fibroblast growth factor (FGF) signaling. Given the metabolic importance of FGFs and the global epidemic of obesity, we explored the effect of SSR on fat metabolism.

METHODS AND RESULTS

Three-week-old male mice were administered intragastrically with SSR (30 mg/kg/day) or PBS for 5 weeks. The effects of SSR on white and brown fat metabolism were investigated by respiratory metabolic monitoring, histological assessment and molecular analysis. Results indicated that SSR administration significantly reduced the body weight gain and the fat content of mice. SSR did not increase, but decreased the thermogenic capability of both brown and white fat. However, SSR markedly suppressed adipogenesis of adipose tissues. Further study demonstrated the involvement of ERK signaling in the action of SSR.

CONCLUSIONS

SSR may be a promising drug candidate for the prevention of obesity via suppressing adipogenesis. However, the influence of SSR on thermogenesis in humans should be further investigated before its clinical application.

Transcriptome Sequencing to Identify Important Genes and lncRNAs Regulating Abdominal Fat Deposition in Ducks

Simple Summary

Abdominal fat deposition affects the quality of duck meat and the feed conversion ratio. Here, we performed transcriptome sequencing of the abdominal adipose tissue of ducks with high and low abdominal fat rate by RNA sequencing, exploring the key regulatory genes and lncRNAs related to abdominal fat deposition. As a result, several candidate genes, lncRNAs, and pathways related to abdominal fat deposition in ducks were retrieved. This study lays the foundations for exploring molecular mechanisms underlying the regulation of abdominal fat deposition in ducks, providing a theoretical reference for breeding high-quality meat-producing ducks.

Abstract

Abdominal fat deposition is an important trait in meat-producing ducks. F2 generations of 304 Cherry Valley and Runzhou Crested White ducks were studied to identify genes and lncRNAs affecting abdominal fat deposition. RNA sequencing was used to study abdominal fat tissue of four ducks each with high or low abdominal fat rates. In all, 336 upregulated and 297 downregulated mRNAs, and 95 upregulated and 119 downregulated lncRNAs were identified. Target gene prediction of differentially expressed lncRNAs identified 602 genes that were further subjected to Gene Ontology and KEGG pathway analysis. The target genes were enriched in pathways associated with fat synthesis and metabolism and participated in biological processes, including Linoleic acid metabolism, lipid storage, and fat cell differentiation, indicating that these lncRNAs play an important role in abdominal fat deposition. PPAPA, FOXO3, FASN, PNPLA2, FKBP5, TCF7L2, BMP2, FGF2, LIFR, ZBTB16, SIRT, GYG2, NCOR1, and NR3C1 were involved in the regulation of abdominal fat deposition. PNPLA2, TCF7L2, FGF2, LIFR, BMP2, FKBP5, GYG2, and ZBTB16 were regulated by the lncRNAs TCONS_00038080, TCONS_0033547, TCONS_00066773, XR_001190174.3, XR_003492471.1, XR_003493494.1, XR_001192142.3, XR_002405656.2, XR_002401822.2, XR_003497063.1, and so on. This study lays foundations for exploring molecular mechanisms underlying the regulation of abdominal fat deposition in ducks and provides a theoretical basis for breeding high-quality meat-producing ducks.