Transforming growth factor β1 signaling links extracellular matrix remodeling to intracellular lipogenesis upon physiological feeding events

Lipid-associated macrophages reshape BAT cell identity in obesity

Obesity and type 2 diabetes cause a loss in brown adipose tissue (BAT) activity, but the molecular mechanisms that drive BAT cell remodeling remain largely unexplored. Using a multilayered approach, we comprehensively mapped a reorganization in BAT cells. We uncovered a subset of macrophages as lipid-associated macrophages (LAMs), which were massively increased in genetic and dietary model of BAT expansion. LAMs participate in this scenario by capturing extracellular vesicles carrying damaged lipids and mitochondria released from metabolically stressed brown adipocytes. CD36 scavenger receptor drove LAM phenotype, and CD36-deficient LAMs were able to increase brown fat genes in adipocytes. LAMs released transforming growth factor β1 (TGF-β1), which promoted the loss of brown adipocyte identity through aldehyde dehydrogenase 1 family member A1 (Aldh1a1) induction. These findings unfold cell dynamic changes in BAT during obesity and identify LAMs as key responders to tissue metabolic stress and drivers of loss of brown adipocyte identity.

A Novel TGFβ Receptor Inhibitor, IPW-5371, Prevents Diet-induced Hepatic Steatosis and Insulin Resistance in Irradiated Mice

As the number of cancer survivors increases and the risk of accidental radiation exposure rises, there is a pressing need to characterize the delayed effects of radiation exposure and develop medical countermeasures. Radiation has been shown to damage adipose progenitor cells and increase liver fibrosis, such that it predisposes patients to developing metabolic-associated fatty liver disease (MAFLD) and insulin resistance. The risk of developing these conditions is compounded by the global rise of diets rich in carbohydrates and fats. Radiation persistently increases the signaling cascade of transforming growth factor β (TGFβ), leading to heightened fibrosis as characteristic of the delayed effects of radiation exposure. We investigate here a potential radiation medical countermeasure, IPW-5371, a small molecule inhibitor of TGFβRI kinase (ALK5). We found that mice exposed to sub-lethal whole-body irradiation and chronic Western diet consumption but treated with IPW-5371 had a similar body weight, food consumption, and fat mass compared to control mice exposed to radiation. The IPW-5371 treated mice maintained lower fibrosis and fat accumulation in the liver, were more responsive to insulin and had lower circulating triglycerides and better muscle endurance. Future studies are needed to verify the improvement by IPW-5371 on the structure and function of other metabolically active tissues such as adipose and skeletal muscle, but these data demonstrate that IPW-5371 protects liver and whole-body health in rodents exposed to radiation and a Western diet, and there may be promise in using IPW-5371 to prevent the development of MAFLD.

M2 macrophage-derived TGF-β induces age-associated loss of adipogenesis through progenitor cell senescence

OBJECTIVES

Adipose tissue is an endocrine and energy storage organ composed of several different cell types, including mature adipocytes, stromal cells, endothelial cells, and a variety of immune cells. Adipose tissue aging contributes to the pathogenesis of metabolic dysfunction and is likely induced by crosstalk between adipose progenitor cells (APCs) and immune cells, but the underlying molecular mechanisms remain largely unknown. In this study, we revealed the biological role of p16high senescent APCs, and investigated the crosstalk between each cell type in the aged white adipose tissue.

METHODS

We performed the single-cell RNA sequencing (scRNA-seq) analysis on the p16high adipose cells sorted from aged p16-CreERT2/Rosa26-LSL-tdTomato mice. We also performed the time serial analysis on the age-dependent bulk RNA-seq datasets of human and mouse white adipose tissues to infer the transcriptome alteration of adipogenic potential within aging.

RESULTS

We show that M2 macrophage-derived TGF-β induces APCs senescence which impairs adipogenesis in vivo. p16high senescent APCs increase with age and show loss of adipogenic potential. The ligand-receptor interaction analysis reveals that M2 macrophages are the donors for TGF-β and the senescent APCs are the recipients. Indeed, treatment of APCs with TGF-β1 induces senescent phenotypes through mitochondrial ROS-mediated DNA damage in vitro. TGF-β1 injection into gonadal white adipose tissue (gWAT) suppresses adipogenic potential and induces fibrotic genes as well as p16 in APCs. A gWAT atrophy is observed in cancer cachexia by APCs senescence, whose induction appeared to be independent of TGF-β induction.

CONCLUSIONS

Our results suggest that M2 macrophage-derived TGF-β induces age-related lipodystrophy by APCs senescence. The TGF-β treatment induced DNA damage, mitochondrial ROS, and finally cellular senescence in APCs.

Single-nuclei RNA Profiling Reveals Disruption of Adipokine and Inflammatory Signaling in Adipose Tissue of Burn Patients

OBJECTIVE

We conducted a large-scale investigation of the systemic and adipose tissue-specific alterations in a clinical population of burn patients to identify factors that may influence hypermetabolism.

BACKGROUND

Previous research has identified chronic disturbances in adipose tissue inflammation, lipolysis, and browning, which may drive the perpetuation of hypermetabolism following the severe adrenergic stress of a burn injury. Given that adipose tissue is thought to be a central node in the regulation of systemic metabolism, we believe that systematically delineating the pathologic role of adipose tissue postburn, will lead to the identification of novel interventions to mitigate morbidity and mortality from severe burns.

METHODS

This was a single-institution cohort study, which obtained plasma and subcutaneous adipose tissue samples from severely burn adult patients over various time points during acute hospitalization. Whole-body clinical, metabolic, and inflammatory mediators were assessed in plasma, while genetic analyses through RT-qPCR and single-nuclei RNA sequencing were conducted in adipose tissue.

RESULTS

Systemic inflammation and adrenergic stress increase IL-6 signaling, lipolysis, browning, and adipokine dysfunction in the adipose tissue of adult burn patients, which may further propagate the long-term hypermetabolic response. Moreover, using single-nuclei RNA sequencing, we provide the first comprehensive characterization of alterations in the adipose tissue microenvironment occurring at acute and chronic stages postburn.

CONCLUSION

We provide novel insight toward the effect of burns on adipokine release, inflammatory signaling pathways, and adipose heterogeneity over the trajectory of acute and chronic stages.

Uremic Toxin-Induced Exosome-like Extracellular Vesicles Contain Enhanced Levels of Sulfated Glycosaminoglycans which Facilitate the Interaction with Very Small Superparamagnetic Iron Oxide Particles

Uremic toxins exert pathophysiological effects on cells and tissues, such as the generation of a pro-calcifying subtype of exosome-like extracellular vesicles (EVs) in vascular cells. Little is known about the effects of the toxins on the surface structure of EVs. Thus, we studied the effects of uremic toxins on the abundance of sulfated glycosaminoglycans (GAGs) in EVs, and the implications for binding of ligands such as very small superparamagnetic iron oxide particles (VSOPs) which could be of relevance for radiological EV-imaging. Vascular cells were treated with the uremic toxins NaH2PO4 and a mixture of urea and indoxyl sulfate. Uremia in rats was induced by adenine feeding. EVs were isolated from culture supernatants and plasma of rats. By proton T1-relaxometry, magnetic particle spectroscopy, and analysis of genes, proteins, and GAG-contents, we analyzed the roles of GAGs in the ligand binding of EVs. By influencing GAG-associated genes in host cells, uremic toxins induced higher GAG contents in EVs, particularly of sulfated chondroitin sulfate and heparan sulfate chains. EVs with high GAG content interacted stronger with VSOPs compared to control ones. This was confirmed by experiments with GAG-depleted EVs from genetically modified CHO cells and with uremic rat-derived EVs. Mechanistically, uremic toxin-induced PI3K/AKT-signaling and expression of the sulfate transporter SLC26A2 in host cells contributed to high GAG contents in EVs. In conclusion, uremic conditions induce enhanced GAG contents in EVs, which entails a stronger interaction with VSOPs. VSOPs might be suitable for radiological imaging of EVs rich in GAGs.

GPS2-mediated regulation of the adipocyte secretome modulates adipose tissue remodeling at the onset of diet-induced obesity

OBJECTIVE

Dysfunctional, unhealthy expansion of white adipose tissue due to excess dietary intake is a process at the root of obesity and Type 2 Diabetes development. The objective of this study is to contribute to a better understanding of the underlying mechanism(s) regulating the early stages of adipose tissue expansion and adaptation to dietary stress due to an acute, high-fat diet (HFD) challenge, with a focus on the communication between adipocytes and other stromal cells.

METHODS

We profiled the early response to high-fat diet exposure in wildtype and adipocyte-specific GPS2-KO (GPS2-AKO) mice at the cellular, tissue and organismal level. A multi-pronged approach was employed to disentangle the complex cellular interactions dictating tissue remodeling, via single-cell RNA sequencing and FACS profiling of the stromal fraction, and semi-quantitative proteomics of the adipocyte-derived exosomal cargo after 5 weeks of HFD feeding.

RESULTS

Our results indicate that loss of GPS2 in mature adipocytes leads to impaired adaptation to the metabolic stress imposed by HFD feeding. GPS2-AKO mice are significantly more inflamed, insulin resistant, and obese, compared to the WT counterparts. At the cellular level, lack of GPS2 in adipocytes impacts upon other stromal populations, with both the eWAT and scWAT depots exhibiting changes in the immune and non-immune compartments that contribute to an increase in inflammatory and anti-adipogenic cell types. Our studies also revealed that adipocyte to stromal cell communication is facilitated by exosomes, and that transcriptional rewiring of the exosomal cargo is crucial for tissue remodeling. Loss of GPS2 results in increased expression of secreted factors promoting a TGFβ-driven fibrotic microenvironment favoring unhealthy tissue remodeling and expansion.

CONCLUSIONS

Adipocytes serve as an intercellular signaling hub, communicating with the stromal compartment via paracrine signaling. Our study highlights the importance of proper regulation of the 'secretome' released by energetically stressed adipocytes at the onset of obesity. Altered transcriptional regulation of factors secreted via adipocyte-derived exosomes (AdExos), in the absence of GPS2, contributes to the establishment of an anti-adipogenic, pro-fibrotic adipose tissue environment, and to hastened progression towards a metabolically dysfunctional phenotype.

Lipidomic Profile Analysis of Lung Tissues Revealed Lipointoxication in Pulmonary Veno-Occlusive Disease

Pulmonary veno-occlusive disease (PVOD) is a rare form of pulmonary arterial hypertension (PAH) occurring in a heritable form (hPVOD) due to biallelic inactivating mutations of EIF2AK4 (encoding GCN2, general control nonderepressible 2) or in a sporadic form in older age (sPVOD), following exposure to chemotherapy or organic solvents. In contrast to PAH, PVOD is characterized by a particular remodeling of the pulmonary venous system and the obliteration of small pulmonary veins by fibrous intimal thickening and patchy capillary proliferation. The pathobiological knowledge of PVOD is poor, explaining the absence of medical therapy for PVOD. Lung transplantation remains the only therapy for eligible PVOD patients. As we recently demonstrated, respiratory diseases, chronic obstructive pulmonary disease, or cystic fibrosis exhibit lipointoxication signatures characterized by excessive levels of saturated phospholipids contributing to the pathological features of these diseases, including endoplasmic reticulum stress, pro-inflammatory cytokines production, and bronchoconstriction. In this study, we investigated and compared the clinical data and lung lipid signature of control (10 patients), idiopathic PAH (7 patients), heritable PAH (9 BMPR2 mutations carriers), hPVOD (10 EIF2AK4 mutation carriers), and sPVOD (6 non-carriers) subjects. Mass spectrometry analyses demonstrated lung lipointoxication only in hPVOD patients, characterized by an increased abundance of saturated phosphatidylcholine (PC) at the expense of the polyunsaturated species in the lungs of hPVOD patients. The present data suggest that lipointoxication could be a potential player in the etiology of PVOD.

The regulation of adipocyte growth in white adipose tissue

Adipocytes can increase in volume up to a thousand-fold, storing excess calories as triacylglycerol in large lipid droplets. The dramatic morphological changes required of adipocytes demands extensive cytoskeletal remodeling, including lipid droplet and plasma membrane expansion. Cell growth-related signalling pathways are activated, stimulating the production of sufficient amino acids, functional lipids and nucleotides to meet the increasing cellular needs of lipid storage, metabolic activity and adipokine secretion. Continued expansion gives rise to enlarged (hypertrophic) adipocytes. This can result in a failure to maintain growth-related homeostasis and an inability to cope with excess nutrition or respond to stimuli efficiently, ultimately leading to metabolic dysfunction. We summarize recent studies which investigate the functional and cellular structure remodeling of hypertrophic adipocytes. How adipocytes adapt to an enlarged cell size and how this relates to cellular dysfunction are discussed. Understanding the healthy and pathological processes involved in adipocyte hypertrophy may shed light on new strategies for promoting healthy adipose tissue expansion.

Epigenetic Profiling in the Saliva of Obese Pregnant Women

Maternal obesity is associated with inflammation and oxidative stress, strongly impacting the intrauterine environment with detrimental consequences for both mother and offspring. The saliva is a non-invasive biofluid reflecting both local and systemic health status. This observational study aimed to profile the epigenetic signature in the saliva of Obese (OB) and Normal-Weight (NW) pregnant women. Sixteen NW and sixteen OB Caucasian women with singleton spontaneous pregnancies were enrolled. microRNAs were quantified by the OpenArray Platform. The promoter region methylation of Suppressor of Cytokine Signaling 3 (SOCS3) and Transforming Growth Factor Beta 1 (TGF-Beta1) was assessed by pyrosequencing. There were 754 microRNAs evaluated: 20 microRNAs resulted in being differentially expressed between OB and NW. microRNA pathway enrichment analysis showed a significant association with the TGF-Beta signaling pathway (miTALOS) and with fatty acids biosynthesis/metabolism, lysine degradation, and ECM–receptor interaction pathways (DIANA–miRPath). Both SOCS3 and TGF-Beta1 were significantly down-methylated in OB vs. NW. These results help to clarify impaired mechanisms involved in obesity and pave the way for the understanding of specific damaged pathways. The characterization of the epigenetic profile in saliva of pregnant women can represent a promising tool for the identification of obesity-related altered mechanisms and of possible biomarkers for early diagnosis and treatment of pregnancy-adverse conditions.