Metabolic dysregulation and adipose tissue fibrosis: role of collagen VI. Mol Cell Biol. 2009;29:1575-1591. [PMID: 19114551 DOI: 10.1128/mcb.01300-08]

Identification of potential hub genes associated with skin wound healing based on time course bioinformatic analyses

Background

The skin is the largest organ of the body and has multiple functions. Wounds remain a significant healthcare problem due to the large number of traumatic and pathophysiological conditions patients suffer.

Methods

Gene expression profiles of 37 biopsies collected from patients undergoing split-thickness skin grafts at five different time points were downloaded from two datasets (GSE28914 and GSE50425) in the Gene Expression Omnibus (GEO) database. Principal component analysis (PCA) was applied to classify samples into different phases. Subsequently, differentially expressed genes (DEGs) analysis, Gene Ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway functional enrichment analyses were performed, and protein–protein interaction (PPI) networks created for each phase. Furthermore, based on the results of the PPI, hub genes in each phase were identified by molecular complex detection combined with the ClueGO algorithm.

Results

Using principal component analysis, the collected samples were divided into four phases, namely intact phase, acute wound phase, inflammatory and proliferation phase, and remodeling phase. Intact samples were used as control group. In the acute wound phase, a total of 1 upregulated and 100 downregulated DEGs were identified. Tyrosinase (TYR), tyrosinase Related Protein 1 (TYRP1) and dopachrome tautomerase (DCT) were considered as hub genes and enriched in tyrosine metabolism which dominate the process of melanogenesis. In the inflammatory and proliferation phase, a total of 85 upregulated and 164 downregulated DEGs were identified. CHEK1, CCNB1 and CDK1 were considered as hub genes and enriched in cell cycle and P53 signaling pathway. In the remodeling phase, a total of 121 upregulated and 49 downregulated DEGs were identified. COL4A1, COL4A2, and COL6A1 were considered as hub genes and enriched in protein digestion and absorption, and ECM-receptor interaction.

Conclusion

This comprehensive bioinformatic re-analysis of GEO data provides new insights into the molecular pathogenesis of wound healing and the potential identification of therapeutic targets for the treatment of wounds.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12893-021-01298-w.

Towards an understanding of the mechanoreciprocity process in adipocytes and its perturbation with aging

Adipose tissue (AT) is a complex organ, with multiple functions that are essential for maintaining metabolic health. A feature of AT is its capability to expand in response to physiological challenges, such as pregnancy and aging, and during chronic states of positive energy balance occurring throughout life. AT grows through adipogenesis and/or an increase in the size of existing adipocytes. One process that is required for healthy AT growth is the remodeling of the extracellular matrix (ECM), which is a necessary step to restore mechanical homeostasis and maintain tissue integrity and functionality. While the relationship between mechanobiology and adipogenesis is now well recognized, less is known about the role of adipocyte mechanosignaling pathways in AT growth. In this review article, we first summarize evidence linking ECM remodelling to AT expansion and how its perturbation is associated to a metabolically unhealthy phenotype. Subsequently, we highlight findings suggesting that molecules involved in the dynamic, bidirectional process (mechanoreciprocity) enabling adipocytes to sense changes in the mechanical properties of the ECM are interconnected to pathways regulating lipid metabolism. Finally, we discuss processes through which aging may influence the ability of adipocytes to appropriately respond to alterations in ECM composition.

Collagen VI as a driver and disease biomarker in human fibrosis

Fibrosis of visceral organs such as the lungs, heart, kidneys and liver remains a major cause of morbidity and mortality and is also associated with many other disorders, including cancer and metabolic disease. In this review, we focus upon the microfibrillar collagen VI, which is present in the extracellular matrix (ECM) of most tissues. However, expression is elevated in numerous fibrotic conditions, such as idiopathic pulmonary disease (IPF), and chronic liver and kidney diseases. Collagen VI is composed of three subunits α1, α2 and α3, which can be replaced with alternate chains of α4, α5 or α6. The C-terminal globular domain (C5) of collagen VI α3 can be proteolytically cleaved to form a biologically active fragment termed endotrophin, which has been shown to actively drive fibrosis, inflammation and insulin resistance. Tissue biopsies have long been considered the gold standard for diagnosis and monitoring of progression of fibrotic disease. The identification of neoantigens from enzymatically processed collagen chains have revolutionised the biomarker field, allowing rapid diagnosis and evaluation of prognosis of numerous fibrotic conditions, as well as providing valuable clinical trial endpoint determinants. Collagen VI chain fragments such as endotrophin (PRO-C6), C6M and C6Mα3 are emerging as important biomarkers for fibrotic conditions.

Association of Omental Adipocyte Hypertrophy and Fibrosis with Human Obesity and Type 2 Diabetes

OBJECTIVE

Morphological alterations including adipocyte hypertrophy and fibrosis deposition are important surrogate markers of visceral adipose tissue function, but the relationships between these morphological changes and type 2 diabetes mellitus (T2DM) and impaired insulin sensitivity are poorly defined.

METHODS

Omental adipose tissue was obtained from 66 individuals with obesity but without T2DM (OB group), 93 individuals with both obesity and T2DM (T2DM group), and 15 individuals with normal BMI and normal glucose tolerance (NGT group). Adipocyte diameter and volume were measured through pathological section analysis. Pericellular and perilobular fibrosis was determined through picrosirius red staining and immunochemistry, while fibrosis-related genes were tested through gene expression and hydroxyproline content.

RESULTS

Compared with the NGT and OB groups, individuals from the T2DM group displayed increased adipocyte diameter and volume levels. Increased adipocyte size (diameter and volume) was positively associated with hyperglycemia and insulin resistance and inversely correlated with insulin sensitivity (using the Matsuda whole-body insulin sensitivity index assessment of insulin sensitivity) and β-cell function (disposition index 30 and disposition index 120). The fibrosis levels of the OB group were the highest out of the three groups, whereas the fibrosis levels of T2DM individuals were lower than the OB group but higher than the NGT group. Although fibrosis was negatively correlated with T2DM, fibrosis deposition was not remarkably associated with impaired systemic insulin sensitivity and glucose metabolism.

CONCLUSIONS

Compared with fibrosis deposition, adipocyte hypertrophy is more closely associated with T2DM and impaired systemic insulin sensitivity.

Mammary gland adipocytes in lactation cycle, obesity and breast cancer

The mammary gland (MG) is an exocrine gland present in female mammals responsible for the production and secretion of milk during the process of lactation. It is mainly composed by epithelial cells and adipocytes. Among the features that make the MG unique there are 1) its highly plastic properties displayed during pregnancy, lactation and involution (all steps belonging to the lactation cycle) and 2) its requirement to grow in close association with adipocytes which are absolutely necessary to ensure MG's proper development at puberty and remodeling during the lactation cycle. Although MG adipocytes play such a critical role for the gland development, most of the studies have focused on its epithelial component only, leaving the role of the neighboring adipocytes largely unexplored. In this review we aim to describe evidences regarding MG's adipocytes role and properties in physiologic conditions (gland development and lactation cycle), obesity and breast cancer, emphasizing the existing gaps in the literature which deserve further investigation.

The cellular and functional complexity of thermogenic fat

Brown and beige adipocytes are mitochondria-enriched cells capable of dissipating energy in the form of heat. These thermogenic fat cells were originally considered to function solely in heat generation through the action of the mitochondrial protein uncoupling protein 1 (UCP1). In recent years, significant advances have been made in our understanding of the ontogeny, bioenergetics and physiological functions of thermogenic fat. Distinct subtypes of thermogenic adipocytes have been identified with unique developmental origins, which have been increasingly dissected in cellular and molecular detail. Moreover, several UCP1-independent thermogenic mechanisms have been described, expanding the role of these cells in energy homeostasis. Recent studies have also delineated roles for these cells beyond the regulation of thermogenesis, including as dynamic secretory cells and as a metabolic sink. This Review presents our current understanding of thermogenic adipocytes with an emphasis on their development, biological functions and roles in systemic physiology.

Assessing the Contribution of Relative Macrophage Frequencies to Subcutaneous Adipose Tissue

Background: Macrophages play an important role in regulating adipose tissue function, while their frequencies in adipose tissue vary between individuals. Adipose tissue infiltration by high frequencies of macrophages has been linked to changes in adipokine levels and low-grade inflammation, frequently associated with the progression of obesity. The objective of this project was to assess the contribution of relative macrophage frequencies to the overall subcutaneous adipose tissue gene expression using publicly available datasets.

Methods: Seven publicly available microarray gene expression datasets from human subcutaneous adipose tissue biopsies (n = 519) were used together with TissueDecoder to determine the adipose tissue cell-type composition of each sample. We divided the subjects in four groups based on their relative macrophage frequencies. Differential gene expression analysis between the high and low relative macrophage frequencies groups was performed, adjusting for sex and study. Finally, biological processes were identified using pathway enrichment and network analysis.

Results: We observed lower frequencies of adipocytes and higher frequencies of adipose stem cells in individuals characterized by high macrophage frequencies. We additionally studied whether, within subcutaneous adipose tissue, interindividual differences in the relative frequencies of macrophages were reflected in transcriptional differences in metabolic and inflammatory pathways. Adipose tissue of individuals with high macrophage frequencies had a higher expression of genes involved in complement activation, chemotaxis, focal adhesion, and oxidative stress. Similarly, we observed a lower expression of genes involved in lipid metabolism, fatty acid synthesis, and oxidation and mitochondrial respiration.

Conclusion: We present an approach that combines publicly available subcutaneous adipose tissue gene expression datasets with a deconvolution algorithm to calculate subcutaneous adipose tissue cell-type composition. The results showed the expected increased inflammation gene expression profile accompanied by decreased gene expression in pathways related to lipid metabolism and mitochondrial respiration in subcutaneous adipose tissue in individuals characterized by high macrophage frequencies. This approach demonstrates the hidden strength of reusing publicly available data to gain cell-type-specific insights into adipose tissue function.

Putting ATM to BED: How Adipose Tissue Macrophages Are Affected by Bariatric Surgery, Exercise, and Dietary Fatty Acids

With increasing adiposity in obesity, adipose tissue macrophages contribute to adipose tissue malfunction and increased circulating proinflammatory cytokines. The chronic low-grade inflammation that occurs in obesity ultimately gives rise to a state of metainflammation that increases the risk of metabolic disease. To date, only lifestyle and surgical interventions have been shown to be somewhat effective at reversing the negative consequences of obesity and restoring adipose tissue homeostasis. Exercise, dietary interventions, and bariatric surgery result in immunomodulation, and for some individuals their effects are significant with or without weight loss. Robust evidence suggests that these interventions reduce chronic inflammation, in part, by affecting macrophage infiltration and promoting a phenotypic switch from the M1- to M2-like macrophages. The purpose of this review is to discuss the impact of dietary fatty acids, exercise, and bariatric surgery on cellular characteristics affecting adipose tissue macrophage presence and phenotypes in obesity.

Endothelial angiogenic activity and adipose angiogenesis is controlled by extracellular matrix protein TGFBI

Several studies have suggested that extracellular matrix (ECM) remodeling and the microenvironment are tightly associated with adipogenesis and adipose angiogenesis. In the present study, we demonstrated that transforming growth factor-beta induced (TGFBI) suppresses angiogenesis stimulated by adipocyte-conditioned medium (Ad-CM), both in vitro and in vivo. TGFBI knockout (KO) mice exhibited increased numbers of blood vessels in adipose tissue, and blood vessels from these mice showed enhanced infiltration into Matrigel containing Ad-CM. The treatment of Ad-CM-stimulated SVEC-10 endothelial cells with TGFBI protein reduced migration and tube-forming activity. TGFBI protein suppressed the activation of the Src and extracellular signaling-related kinase signaling pathways of these SVEC-10 endothelial cells. Our findings indicated that TGFBI inhibited adipose angiogenesis by suppressing the activation of Src and ERK signaling pathways, possibly because of the stimulation of the angiogenic activity of endothelial cells.

Comparative Transcriptome Profiling of Cold Exposure and β3-AR Agonist CL316,243-Induced Browning of White Fat

Beige adipocytes are newly identified thermogenic-poised adipocytes that could be activated by cold or β3-adrenergic receptor (β3-AR) signaling and offer therapeutic potential for treating obesity and metabolic diseases. Here we applied RNA-sequencing analysis in the beige fat of mice under cold exposure or β3-AR agonist CL316,243 (CL) treatment to provide a comparative and comprehensive analysis for the similarity and heterogeneity of these two stimulants. Importantly, via KEGG analysis, we found that cold and CL commonly induced oxidative phosphorylation. Meanwhile, cold increased glycerolipid and amino acids metabolism while CL treatment triggered a broader spectrum of metabolic responses including carbohydrate metabolism. Besides, cold or CL treatment featured greater heterogeneity in downregulated gene programs. Of note, the top changed genes in each category were confirmed by qPCR analysis. Overall, our analysis provided a better understanding of the heterogeneity of differential models for beige adipocytes activation and a possible clue for optimizing β3-AR agonists in the future.

Aging adipose: Depot location dictates age-associated expansion and dysfunction

Adipose tissue has a variety of diverse functions that maintain energy homeostasis. In conditions of excess energy availability, adipose tissue increases its lipid storage and communicates the nutritional abundance to various organs in the body. In conditions of energy depletion, such as fasting, cold exposure, or prolonged exercise, triglycerides stored in adipose tissue are released as free fatty acids to support the shift to catabolic metabolism. These diverse functions of storage, communication, and energy homeostasis are shared between numerous adipose depots including subcutaneous, visceral, brown, beige, intramuscular, marrow, and dermal adipose tissue. As organisms age, the cellular composition of these depots shifts to facilitate increased inflammatory cell infiltration, decreased vasculature, and increased adipocyte quantity and lipid droplet size. The purpose of this review is to give a comprehensive overview of the molecular and cellular changes that occur in various aged adipose depots and discuss their impact on physiology. The molecular signature of aged adipose leads to higher prevalence of metabolic disease in aged populations including type 2 diabetes, cardiovascular disease, Alzheimer's disease, and certain types of cancer.

Adipose tissue fibrosis assessed by high resolution ex vivo MRI as a hallmark of tissue alteration in morbid obesity

To determine whether magnetic resonance imaging (MRI) when used in an optimal ex vivo setting can help detecting and quantifying the 3D fibrosis fraction in human subcutaneous adipose tissue (SAT) samples, as compared to histology. This prospective observational study was approved by our institutional review board 3D MRI acquisitions were performed at 4.0 T (Bruker) on XX human SAT samples (around 1 cm3) collected from biopsy in morbidly obese patients. Such acquisitions included saturation-recovery T1 mapping (spatial resolution: 200 µm, acquisition time: ~16 minutes) and DIXON imaging (spatial resolution: 200 µm, acquisition time: ~20 minutes). After MRI, histological quantification of fibrosis was performed using picrosirius staining. T1 maps were clustered based on a k-means algorithm allowing quantification of fibrosis within the adipose tissue and percentage of fibrosis over the entire sample volume was calculated. Fat maps were computed from DIXON in-phase and out-of-phase images. The 3D MRI fibrosis percentage within the SAT samples were comprised between 6% and 15%. Excellent correlations and levels of agreement were observed between single slice MRI and histology (r=0.9, P=0.08) and between 3D MRI and histology in terms fibrosis percentages within SAT samples (r=0.9, P=0.01). High Field ex vivo MRI was able to quantify fibrosis in human SAT samples with high agreement with histology and moreover to provide 3D SAT fibrosis quantification avoiding histological sampling errors.

Exercise and Adipose Tissue Immunity: Outrunning Inflammation

Chronic inflammation is considered a precipitating factor and possibly an underlying cause of many noncommunicable diseases, including cardiovascular disease, metabolic diseases, and some cancers. Obesity, which manifests in more than 650 million people worldwide, is the most common chronic inflammatory condition, with visceral adiposity thought to be the major inflammatory hub that links obesity and chronic disease. Adipose tissue (AT) inflammation is triggered or heightened in large part by (1) accelerated immune cell recruitment, (2) reshaping of the AT stromal-immuno landscape (e.g., immune cells, endothelial cells, fibroblasts, adipocyte progenitors), and (3) perturbed AT immune cell function. Exercise, along with diet management, is a cornerstone in promoting weight loss and preventing weight regain. This review focuses on evidence that increased physical activity reduces AT inflammation caused by hypercaloric diets or genetic obesity. The precise cell types and mechanisms responsible for the therapeutic effects of exercise on AT inflammation remain poorly understood. This review summarizes what is known about obesity-induced AT inflammation and immunomodulation and highlights mechanisms by which aerobic exercise combats inflammation by remodeling the AT immune landscape. Furthermore, key areas are highlighted that require future exploration and novel discoveries into the burgeoning field of how the biology of exercise affects AT immunity.

Adipocyte-Derived Versican and Macrophage-Derived Biglycan Control Adipose Tissue Inflammation in Obesity

Obesity is characterized by adipose tissue inflammation. Because proteoglycans regulate inflammation, here we investigate their role in adipose tissue inflammation in obesity. We find that adipose tissue versican and biglycan increase in obesity. Versican is produced mainly by adipocytes and biglycan by adipose tissue macrophages. Both proteoglycans are also present in adipose tissue from obese human subjects undergoing gastric bypass surgery. Deletion of adipocyte-specific versican or macrophage-specific biglycan in mice reduces macrophage accumulation and chemokine and cytokine expression, although only adipocyte-specific versican deletion leads to sustained improvement in glucose tolerance. Macrophage-derived biglycan activates inflammatory genes in adipocytes. Versican expression increases in cultured adipocytes exposed to excess glucose, and adipocyte-conditioned medium stimulates inflammation in resident peritoneal macrophages, in part because of a versican breakdown product, versikine. These findings provide insights into the role of adipocyte- and macrophage-derived proteoglycans in adipose tissue inflammation in obesity.

SIRT1 promotes lipid metabolism and mitochondrial biogenesis in adipocytes and coordinates adipogenesis by targeting key enzymatic pathways

The NAD+-dependent deacetylase SIRT1 controls key metabolic functions by deacetylating target proteins and strategies that promote SIRT1 function such as SIRT1 overexpression or NAD+ boosters alleviate metabolic complications. We previously reported that SIRT1-depletion in 3T3-L1 preadipocytes led to C-Myc activation, adipocyte hyperplasia, and dysregulated adipocyte metabolism. Here, we characterized SIRT1-depleted adipocytes by quantitative mass spectrometry-based proteomics, gene-expression and biochemical analyses, and mitochondrial studies. We found that SIRT1 promoted mitochondrial biogenesis and respiration in adipocytes and expression of molecules like leptin, adiponectin, matrix metalloproteinases, lipocalin 2, and thyroid responsive protein was SIRT1-dependent. Independent validation of the proteomics dataset uncovered SIRT1-dependence of SREBF1c and PPARα signaling in adipocytes. SIRT1 promoted nicotinamide mononucleotide acetyltransferase 2 (NMNAT2) expression during 3T3-L1 differentiation and constitutively repressed NMNAT1 and 3 levels. Supplementing preadipocytes with the NAD+ booster nicotinamide mononucleotide (NMN) during differentiation increased expression levels of leptin, SIRT1, and PGC-1α and its transcriptional targets, and reduced levels of pro-fibrotic collagens (Col6A1 and Col6A3) in a SIRT1-dependent manner. Investigating the metabolic impact of the functional interaction of SIRT1 with SREBF1c and PPARα and insights into how NAD+ metabolism modulates adipocyte function could potentially lead to new avenues in developing therapeutics for obesity complications.

Innate Immune Cells in the Adipose Tissue in Health and Metabolic Disease

Metabolic disorders, such as obesity, type 2 diabetes mellitus, and nonalcoholic fatty liver disease, are characterized by chronic low-grade tissue and systemic inflammation. During obesity, the adipose tissue undergoes immunometabolic and functional transformation. Adipose tissue inflammation is driven by innate and adaptive immune cells and instigates insulin resistance. Here, we discuss the role of innate immune cells, that is, macrophages, neutrophils, eosinophils, natural killer cells, innate lymphoid type 2 cells, dendritic cells, and mast cells, in the adipose tissue in the healthy (lean) and diseased (obese) state and describe how their function is shaped by the obesogenic microenvironment, and humoral, paracrine, and cellular interactions. Moreover, we particularly outline the role of hypoxia as a central regulator in adipose tissue inflammation. Finally, we discuss the long-lasting effects of adipose tissue inflammation and its potential reversibility through drugs, caloric restriction, or exercise training.

Viscoelastic characterization of diabetic and non-diabetic human adipose tissue

BACKGROUND

Obesity-induced chronic inflammation and fibrosis in adipose tissue contributes to the progression of type 2 diabetes mellitus (DM). While fibrosis is known to induce mechanical stiffening of numerous tissue types, it is unknown whether DM is associated with alterations in adipose tissue mechanical properties.

OBJECTIVE

The purpose of this study was to investigate whether DM is associated with differences in bulk viscoelastic properties of adipose tissue from diabetic (DM) and non-diabetic (NDM) obese subjects.

METHODS

Bulk shear rheology was performed on visceral (VAT) and subcutaneous (SAT) adipose tissue, collected from obese subjects undergoing elective bariatric surgery. Rheology was also performed on the remaining extracellular matrix (ECM) from decellularized VAT (VAT ECM). Linear mixed models were used to assess whether correlations existed between adipose tissue mechanical properties and DM status, sex, age, and body mass index (BMI).

RESULTS

DM was not associated with significant differences in adipose tissue viscoelastic properties for any of the tissue types investigated. Tissue type dependent differences were however detected, with VAT having significantly lower shear storage and loss moduli than SAT and VAT ECM independent of DM status.

CONCLUSION

Although DM is typically associated with adipose tissue fibrosis, it is not associated with differences in macroscopic adipose tissue mechanical properties.

Early Childhood Fat Tissue Changes-Adipocyte Morphometry, Collagen Deposition, and Expression of CD163+ Cells in Subcutaneous and Visceral Adipose Tissue of Male Children

Childhood obesity is a complex health problem, and not many studies have been done on adipose tissue remodeling in early childhood. The aim of this study was to examine extracellular matrix remodeling in the adipose tissue of healthy male children depending on their weight status. Subcutaneous and visceral adipose tissue was obtained from 45 otherwise healthy male children who underwent elective surgery for hernia repairs or orchidopexy. The children were divided into overweight/obese (n = 17) or normal weight groups (n = 28) depending on their body mass index (BMI) z-score. Serum was obtained for glucose, testosterone, triglyceride, total cholesterol, high-density lipoprotein (HDL), and low-density lipoprotein (LDL) measurements. Sections of adipose tissue were stained with hematoxylin and eosin to determine the adipocytes' surface area, and Masson's trichrome stain was used to detect the adipocytes' collagen content. Immunohistochemistry for CD163⁺ cells was also performed. The results showed that male children in the overweight group had higher serum triglyceride levels, greater adipocyte surface area and collagen content in their subcutaneous adipose tissue, more crown-like structures in fat tissues, and more CD163⁺ cells in their visceral adipose tissue than males in the normal weight group. In conclusion, in male children, obesity can lead to the hypertrophy of adipocytes, increased collagen deposition in subcutaneous adipose tissues, and changes in the polarization and accumulation of macrophages.

Potential of Nutraceutical Supplementation in the Modulation of White and Brown Fat Tissues in Obesity-Associated Disorders: Role of Inflammatory Signalling

The high incidence of obesity is associated with an increasing risk of several chronic diseases such as cardiovascular disease, type 2 diabetes and non-alcoholic fatty liver disease (NAFLD). Sustained obesity is characterized by a chronic and unsolved inflammation of adipose tissue, which leads to a greater expression of proinflammatory adipokines, excessive lipid storage and adipogenesis. The purpose of this review is to clarify how inflammatory mediators act during adipose tissue dysfunction in the development of insulin resistance and all obesity-associated diseases. In particular, we focused our attention on the role of inflammatory signaling in brown adipose tissue (BAT) thermogenic activity and the browning of white adipose tissue (WAT), which represent a relevant component of adipose alterations during obesity. Furthermore, we reported the most recent evidence in the literature on nutraceutical supplementation in the management of the adipose inflammatory state, and in particular on their potential effect on common inflammatory mediators and pathways, responsible for WAT and BAT dysfunction. Although further research is needed to demonstrate that targeting pro-inflammatory mediators improves adipose tissue dysfunction and activates thermogenesis in BAT and WAT browning during obesity, polyphenols supplementation could represent an innovative therapeutic strategy to prevent progression of obesity and obesity-related metabolic diseases.

Transcriptome analysis identifies signaling pathways related to meat quality in broiler chickens - the extracellular matrix (ECM) receptor interaction signaling pathway

Meat quality characteristics, including juiciness, flavor, and tenderness, can be mostly attributed to the total muscle fat content, intramuscular fat (IMF), and the composition of its fatty acids, which are regulated by the balance between lipid uptake, transport, synthesis, and subsequent metabolism, involving many genes and pathways. However, the detailed molecular mechanisms remain unclear. The purpose of this study was to identify the key signaling pathways related to chicken meat quality, and to provide help for improving chicken meat quality. The present study reports the RNA-sequencing analysis of pectorales and crureus of the Zhuanghe dagu chicken and the Arbor Acres Broiler chicken (AA chicken). We identified certain differentially expressed genes that affect IMF deposition, such as EHHADH, TECRL, NDUFAB1, PCCB, and HIBCH, which were upregulated in Zhuanghe dagu chicken , and GCDH, TPI1, ABHD13, PSMC1, MYST2, and FBXO11, which were upregulated in AA chickens. Pathway analysis using the Kyoto Encyclopedia of Genes and Genomes indicated that the extracellular matrix (ECM)–receptor interaction pathway is co-enriched in both tissues, and forms a sub-pathway of other enriched pathways. Intriguingly, the ECM–receptor interaction pathway genes are regulated differently in different gene pools. Collagens, which are main ECM constituents, and laminin and integrin β1 transmembrane receptors were significantly downregulated in both tissues of the AA chicken. The results showed that the ECM-receptor interaction pathway affect the quality of chicken meat by affecting the metabolism of intramuscular adipocytes. Further investigation of this signaling pathway will be helpful to the improvement of chicken meat quality.

RNA decay in processing bodies is indispensable for adipogenesis

The RNA decay pathway plays key regulatory roles in cell identities and differentiation processes. Although adipogenesis is transcriptionally and epigenetically regulated and has been thoroughly investigated, how RNA metabolism that contributes to the stability of phenotype-shaping transcriptomes participates in differentiation remains elusive. In this study, we investigated Ddx6, an essential component of processing bodies (PBs) that executes RNA decay and translational repression in the cytoplasm and participates in the cellular transition of reprogramming. Upon adipogenic induction, Ddx6 dynamically accumulated to form PBs with a binding partner, 4E-T, at the early phase prior to emergence of intracellular lipid droplets. In contrast, preadipocytes with Ddx6 knockout (KO) or 4E-T knockdown (KD) failed to generate PBs, resulting in significant suppression of adipogenesis. Transcription factors related to preadipocytes and negative regulators of adipogenesis that were not expressed under adipogenic stimulation were maintained in Ddx6-KO and 4E-T-KD preadipocytes under adipogenic induction. Elimination of Dlk1, a major negative regulator of adipogenesis, in 3T3L1 Ddx6-KO cells did not restore adipogenic differentiation capacity to any extent. Similar to murine cells, human primary mesenchymal stem cells, which can differentiate into adipocytes upon stimulation with adipogenic cocktails, required DDX6 to maturate into adipocytes. Therefore, RNA decay of the entire parental transcriptome, rather than removal of a strong negative regulator, could be indispensable for adipogenesis.

Mice lacking PLAP-1/asporin counteracts high fat diet-induced metabolic disorder and alveolar bone loss by controlling adipose tissue expansion

Adipose tissue fibrosis with chronic inflammation is a hallmark of obesity-related metabolic disorders, and the role of proteoglycans in developing adipose tissue fibrosis is of interest. Periodontal disease is associated with obesity; however, the underlying molecular mechanisms remain unclear. Here we investigated the roles of periodontal ligament associated protein-1 (PLAP-1)/asporin, a proteoglycan preferentially and highly expressed in the periodontal ligament, in obesity-related adipose tissue dysfunction and adipocyte differentiation. It was found that PLAP-1 is also highly expressed in white adipose tissues. Plap-1 knock-out mice counteracted obesity and alveolar bone resorption induced by a high-fat diet. Plap-1 knock-down in 3T3-L1 cells resulted in less lipid accumulation, and recombinant PLAP-1 enhanced lipid accumulation in 3T3-L1 cells. In addition, it was found that primary preadipocytes isolated from Plap-1 knock-out mice showed lesser lipid accumulation than the wild-type (WT) mice. Furthermore, the stromal vascular fraction of Plap-1 knock-out mice showed different extracellular matrix gene expression patterns compared to WT. These findings demonstrate that PLAP-1 enhances adipogenesis and could be a key molecule in understanding the association between periodontal disease and obesity-related metabolic disorders.

Exercise retards ongoing adipose tissue fibrosis in diet-induced obese mice

Exercise has been recommended as an important strategy to improve glucose metabolism in obesity. Adipose tissue fibrosis is associated with inflammation and is implicated in glucose metabolism disturbance and insulin resistance in obesity. However, the effect of exercise on the progression of adipose tissue fibrosis is still unknown. The aim of the present study was to investigate whether exercise retarded the progression of adipose tissue fibrosis and ameliorated glucose homeostasis in diet-induced obese mice. To do so, obesity and adipose tissue fibrosis in mice were induced by high-fat diet feeding for 12 weeks and the mice subsequently received high-fat diet and exercise intervention for another 12 weeks. Exercise alleviated high-fat diet-induced glucose intolerance and insulin resistance. Continued high-fat diet feeding exacerbated collagen deposition and further increased fibrosis-related gene expression in adipose tissue. Exercise attenuated or reversed these changes. Additionally, PPARγ, which has been shown to inhibit adipose tissue fibrosis, was observed to be increased following exercise. Moreover, exercise decreased the expression of HIF-1α in adipose fibrosis, and adipose tissue inflammation was inhibited. In conclusion, our data indicate that exercise attenuates and even reverses the progression of adipose tissue fibrosis, providing a plausible mechanism for its beneficial effects on glucose metabolism in obesity.

Adipose Tissue Macrophage Polarization in Healthy and Unhealthy Obesity

Over 650 million adults are obese (body mass index ≥ 30 kg/m²) worldwide. Obesity is commonly associated with several comorbidities, including cardiovascular disease and type II diabetes. However, compiled estimates suggest that from 5 to 40% of obese individuals do not experience metabolic or cardiovascular complications. The existence of the metabolically unhealthy obese (MUO) and the metabolically healthy obese (MHO) phenotypes suggests that underlying differences exist in both tissues and overall systemic function. Macrophage accumulation in white adipose tissue (AT) in obesity is typically associated with insulin resistance. However, as plastic cells, macrophages respond to stimuli in their microenvironments, altering their polarization between pro- and anti-inflammatory phenotypes, depending on the state of their surroundings. The dichotomous nature of MHO and MUO clinical phenotypes suggests that differences in white AT function dictate local inflammatory responses by driving changes in macrophage subtypes. As obesity requires extensive AT expansion, we posit that remodeling capacity with adipose expansion potentiates favorable macrophage profiles in MHO as compared with MUO individuals. In this review, we discuss how differences in adipogenesis, AT extracellular matrix deposition and breakdown, and AT angiogenesis perpetuate altered AT macrophage profiles in MUO compared with MHO. We discuss how non-autonomous effects of remote organ systems, including the liver, gastrointestinal tract, and cardiovascular system, interact with white adipose favorably in MHO. Preferential AT macrophage profiles in MHO stem from sustained AT function and improved overall fitness and systemic health.

Adipose Tissue T Regulatory Cells: Implications for Health and Disease

Obesity dramatically increases the risk of numerous conditions, including type 2 diabetes mellitus and other components of the metabolic syndrome. Pro-inflammatory changes that occur in adipose tissue are critical to the pathogenesis of these obesity-induced complications. Adipose tissue is one of the body's largest endocrine organs, and the cells that comprise the adipose tissue immunoenvironment secrete multiple factors (including adipokines and cytokines) that impact systemic metabolism. In particular, immunosuppressive regulatory T cells (Tregs) decline in obesity, partly in response to its complex interaction with adipocytes, and this decline contributes to disruption of the typical homeostasis observed in lean adipose tissue. Although the regulation of Treg differentiation, function, and enrichment is incompletely understood, factors including various cell-surface co-stimulatory molecules, certain lipid species, and cytokines such as PPARγ, adiponectin, and leptin are important mediators. It is also clear that there may be depot-specific differences in Tregs, rendering adipose tissue Tregs distinct from lymphoid or circulating Tregs, with implications on maintenance and functionality. While most of these findings are derived from studies in murine models, comparatively little is known about the human adipose tissue Treg signature, which requires further investigation.

All-trans retinoic acid controls differentiation, proliferation, and lipolysis in isolated subcutaneous adipocytes from peripartal Holstein cows

Preadipocyte proliferation and differentiation are critical for normal adipose tissue development, including achieving a mature phenotype, characterized by its ability to accumulate triacylglycerol and release fatty acids. In nonruminants, it is well known that all-trans retinoic acid (ATRA), the most-active form of vitamin A, helps regulate proliferation, differentiation, and apoptosis in several types of cells including adipocytes. The purpose of this study was to evaluate the effect of ATRA on proliferation, apoptosis, differentiation, and lipolysis of primary bovine adipocytes isolated from subcutaneous adipose tissue of 5 healthy Holstein cows at 17 (±4 standard deviations) d postpartum. Cells were stimulated with increasing concentrations of ATRA (0.2, 2, and 20 nM) at the preconfluent (2 d) and postconfluent (8 d) preadipocyte stage or at the mature adipocyte stage (2 d). All concentrations of ATRA inhibited preconfluent preadipocyte proliferation with decreased proportion of S-phase cells and reduced protein abundance of cyclins (CCND1, CCND2, CCND3, CCNE1) and cyclin-dependent kinases (CDK2, CDK4, CDK6). Compared with vehicle, ATRA treatment induced apoptosis in preconfluent preadipocytes. Additionally, ATRA (0.2, 2, and 20 nM) supplementation also inhibited differentiation of postconfluent preadipocytes through downregulation of protein abundance of PPARγ and C/EBPα. After induction of differentiation, basal lipolysis in mature adipocytes increased upon treatment with all concentrations of ATRA. However, data on phosphorylated hormone-sensitive lipase or PLIN1 indicated that ATRA had no effect on epinephrine-stimulated lipolysis in mature adipocytes. Overall, these results demonstrate that ATRA might inhibit lipid accumulation by suppressing preadipocyte proliferation and differentiation, subsequently leading to apoptosis in postconfluent preadipocytes and promoting basal lipolysis in mature adipocytes. Overall, these in vitro responses provide some insights into the potential for nutritional management to modulate adipose tissue lipolysis, particularly in overconditioned cows during the dry period, which are more susceptible to suffer metabolic disorders due to excessive fat mobilization postpartum.

Widely-tunable synchronisation-free picosecond laser source for multimodal CARS, SHG, and two-photon microscopy

We demonstrate a continuous wave (CW) seeded synchronization-free optical parametric amplifier (OPA) pumped by a picosecond, 1 µm laser and show its performance when used as a simple yet powerful source for label-free coherent anti-Stokes Raman scattering (CARS), concurrent second harmonic generation (SHG), and two-photon fluorescence microscopy in an epi-detection geometry. The average power level of above 175 mW, spectral resolution of 8 cm^-1, and 2 ps pulse duration are well optimized for CARS microscopy in bio-science and bio-medical imaging systems. Our OPA is a much simpler setup than either the "gold-standard" laser and optical parametric oscillator (OPO) combination traditionally used for CARS imaging, or the more recently developed OPA systems pumped with femtosecond pulses [1]. Rapid and accurate tuning between resonances was achieved by changing the poled channels and temperature of the periodically-poled lithium niobate (PPLN) OPA crystal together with the OPA seed wavelength. The Pump-Stokes frequency detuning range fully covered the C-H stretching band used for the imaging of lipids. By enabling three multiphoton techniques using a compact, synchronization free laser source, our work paves the way for the translation of label-free multi-photon microscopy imaging from biomedical research to an imaging based diagnostic tool for use in the healthcare arena.

Enlarged adipocytes from subcutaneous vs. visceral adipose tissue differentially contribute to metabolic dysfunction and atherogenic risk of patients with obesity

Morphological characteristics and source of adipose tissue as well as adipokines may increase cardiometabolic risk. This study aimed to explore whether adipose tissue characteristics may impact metabolic and atherogenic risks. Subcutaneous Adipose Tissue (SAT), Visceral Adipose Tissue (VAT) and peripheral blood were obtained from obese patients submitted to bariatric surgery. Adipose tissue (morphometry), plasma adiponectin, TNF-α, resistin (multiplexing) and biochemical chemistry were analyzed; as well as endothelial dysfunction (Flow Mediated Dilation, FMD) and atherogenesis (Carotid Intima Media Thickness, CIMT). Subgroups divided by adipocyte size and source were compared; as well as correlation and multivariate analysis. Sixty patients 36.6% males, aged 44 years-old, BMI 46.7 kg/m² were included. SAT's adipocytes showed a lower range of size expandability than VAT's adipocytes. Independent from their source, larger adipocytes were associated with higher glucose, lower adiponectin and higher CIMT. Particularly, larger adipocytes from SAT were associated with higher blood pressure, lower insulin and HDL-cholesterol; and showed positive correlation with glucose, Hb_A1c, systolic/diastolic values, and negatively correlated with insulin and adiponectin. VAT's larger adipocytes particularly associated with lower resistin and lower FMD values. Gender and Diabetes Mellitus significantly impacted the relation of adipocyte size/source with the metabolic and atherogenic risk. Multivariable analysis suggested hypertension-resistin-Hb_A1c interactions associated with SAT's larger adipocytes; whereas potential insulin-adiponectin associations were observed for VAT's larger adipocytes. Adipocyte morphology and source are differentially related with cardiometabolic and atherogenic risk in population with obesity, which are potentially affected by gender and Diabetes Mellitus.

Dietary alpha- and gamma-tocopherol (1:5 ratio) supplementation attenuates adipose tissue expansion, hepatic steatosis, and expression of inflammatory markers in a high-fat-diet-fed murine model

OBJECTIVES

The aim of this study was to evaluate the effect of the dietary supplementation of an alpha- and gamma-tocopherol mixture (1:5 ratio) in the adipose tissue expansion, hepatic steatosis, and expression of inflammatory markers induced by consumption of a high-fat diet (HFD) in mice.

METHODS

Male C57BL/6 J mice were fed for 12 wk and divided into the following: 1) control diet (CD; 10% fat, 20% protein, 70% carbohydrates); 2) CD + TF (CD plus alpha-tocopherol: 0.7 mg/kg/d, gamma-tocopherol: 3.5 mg/kg/d); 3) HFD (60% fat, 20% protein, 20% carbohydrates); and 4) HFD + TF (HFD plus alpha-tocopherol: 0.7 mg/kg/d, gamma-tocopherol: 3.5 mg/kg/d). General parameters, adipocyte size, liver steatosis, adipose and hepatic tumor necrosis factor-α (TNF-α) and interleukin-1 β (IL-1β) expression, hepatic nuclear factor kappa B (NF-κB), and peroxisome proliferator-activated receptor α (PPAR-α) levels were evaluated.

RESULTS

Tocopherol supplementation in HFD-fed mice showed a significant decrease in the body weight (19%) and adipose tissue weight (52%), adipose tissue/body weight ratio (36%), and serum triacylglycerols (56%); a 42% decrease (P < 0.05) of adipocyte size compared to HFD; attenuation of liver steatosis by decreasing (P < 0.05) lipid vesicles presence (90%) and total lipid content (75%); and downregulation of inflammatory markers (TNF-α and IL-1β), along with an upregulation of hepatic PPAR-α expression and its downstream-regulated genes (ACOX and CAT-1), and an inhibition of hepatic NF-κB activation.

CONCLUSION

The present study suggests that alpha- and gamma-tocopherol (1:5 ratio) supplementation attenuates the adipocyte enlargement, hepatic steatosis, and metabolic inflammation induced by HFD in association with PPAR-α/NF-κB modulation.

Type VI collagen and its cleavage product, endotrophin, cooperatively regulate the adipogenic and lipolytic capacity of adipocytes

OBJECTIVE

Obesity-induced adipose tissue remodeling is closely associated with systemic insulin resistance. However, the mechanistic involvement of adipocyte-derived extracellular matrix proteins under pathophysiological conditions remains unclear. Our aim was to investigate the distinctive contributions of each chain of type VI collagens (Col6) and its cleavage protein endotrophin to adipocyte functions and insulin sensitivity.

METHODS

Col6 comprises three alpha chains: Col6a1, Col6a2, and Col6a3. We generated Col6a1-, Col6a2-, and Col6a3-deficient 3T3-L1 adipocytes using the CRISPR-Cas9 system as well as a novel Col6a3-deficient (Col6a3KO) mouse model for loss-of-function studies. Adenoviral-endotrophin and adipocyte-specific doxycycline-inducible endotrophin transgenic mice were utilized for the gain-of-function analysis.

RESULTS

The holo-Col6 fibrils were found to be required for mature adipocyte differentiation. Only Col6a3-deficient 3T3-L1 adipocytes showed decreased inflammation and basal adipocyte lipolysis and prevented ER-stress-induced insulin resistance. Consistently, Col6a3KO mice showed decreased adipocyte size and fat mass of epididymal adipose tissues due to a defect in adipogenic and lipolytic capacity of adipocytes. Beyond the structural role of Col6a3, overexpression of endotrophin in obese mice further augmented insulin resistance, which was tightly associated with a significant increase in lipolysis, inflammation, and cellular apoptosis in adipose tissues, whereas this showed a limited effect on adipogenesis.

CONCLUSIONS

These novel findings corroborate our previous observations suggesting that adipose tissue extracellular matrix regulates adipocyte function and insulin sensitivity in pathophysiological conditions. Mechanistically, holo-Col6 fibrils and their signaling derivative endotrophin govern adipocyte function independently of their role as structural supports via MAPK signaling pathways, and the latter could be an important metabolic effector in obesity-related metabolic diseases.

The prebiotic fiber inulin ameliorates cardiac, adipose tissue, and hepatic pathology, but exacerbates hypertriglyceridemia in rats with metabolic syndrome

Prebiotics ameliorate dysbiosis and influence metabolism and the immune system, but their effects on cardiovascular complications in metabolic disorders remain largely unknown. We here investigated the effects of the soluble fiber inulin on cardiac, adipose tissue, and hepatic pathology as well as on metabolic disorders in DahlS.Z-Leprfa/Leprfa (DS/obese) rats, an animal model of metabolic syndrome (MetS). DS/obese rats and their homozygous lean (DahlS.Z-Lepr+/Lepr+, or DS/lean) littermate controls were fed a purified diet containing 5% or 20% inulin from 9 to 13 wk of age. The high-fiber diet ameliorated hypertension, left ventricular inflammation, fibrosis and diastolic dysfunction; attenuated adipose tissue inflammation and fibrosis; and alleviated the elevation of interleukin-6 levels, without affecting insulin resistance, in DS/obese rats. In addition, high fiber intake ameliorated lipid accumulation, inflammation, and fibrosis; attenuated the reduction in AMPK activity; upregulated sterol regulatory element-binding protein-1c gene expression; and increased the expression of microsomal triglyceride transfer protein gene in the liver of DS/obese rats. It also mitigated increases in total and non-high-density lipoprotein cholesterol levels but increased the triglyceride concentration in serum in these rats. None of these parameters were affected by high dietary fiber in DS/lean rats. The proportion of regulatory T cells in adipose tissue was influenced by dietary fiber but not by genotype. Our results indicate that inulin exacerbates hypertriglyceridemia but alleviates hypertension and cardiac injury as well as adipose tissue and hepatic pathology in MetS rats.NEW & NOTEWORTHY Prebiotics ameliorate dysbiosis and influence metabolism and the immune system, but their effects on cardiovascular complications in metabolic disorders remain largely unknown. Inulin ameliorated hypertension, cardiac injury, and diastolic dysfunction without affecting obesity or insulin resistance in a rat model of metabolic syndrome. The favorable cardiac effects of inulin may be related to inhibition of systemic inflammation associated with a reduction in circulating interleukin-6 levels. Additionally, inulin exacerbated hypertriglyceridemia but alleviates adipose tissue and hepatic pathology in these animals, as well as increased the number of regulatory T cells in adipose tissue.

Endotrophin as a novel marker in PCOS and its relation with other adipokines and metabolic parameters: a pilot study

BACKGROUND

Polycystic ovary syndrome is known to be the most common hormonal disorder in women of reproductive age. Current evidence shows that regulatory proteins secreted from the adipose tissue called adipokines may have a role in polycystic ovary syndrome. We planned to investigate the role of endotrophin that has never been researched in polycystic ovary syndrome before and its correlation with other metabolic parameters and adipokines such as adiponectin and ghrelin in patients with polycystic ovary syndrome.

METHODS

Forty-three women (n: 43) with polycystic ovary syndrome and 43 (n: 43) women as a control group were enrolled in this cross-sectional study. Serum levels of endotrophin, adiponectin, and ghrelin levels were measured with the enzyme-linked immunosorbent assay method. High-density lipoprotein cholesterol, low-density lipoprotein cholesterol, total cholesterol levels, luteinizing hormone/follicle-stimulating hormone ratio, total testosterone, and triglyceride levels were measured. Homeostasis model assessment for insulin resistance index, body mass index, Ferriman Gallwey Score, and waist-to-hip ratio were also evaluated.

RESULTS

Total testosterone, homeostasis model assessment for insulin resistance, C-reactive protein, luteinizing hormone/follicle-stimulating hormone ratio, and triglyceride levels were higher in patients with polycystic ovary syndrome (p < 0.01). No difference was detected between the groups in terms of body mass index, Ferriman Gallwey Score, waist-to-hip ratio, total cholesterol, low-density lipoprotein, and high-density lipoprotein levels (p > 0.05). We did not observe any significant difference in adiponectin and ghrelin levels between the groups (p > 0.05). Patients with polycystic ovary syndrome had significantly higher endotrophin levels (p < 0.01). According to our regression analyses [area under the curve: 0.973 (0.935-1.000), 95% confidence interval, 95.2% sensitivity, and 100% specificity], it was shown that endotrophin greater than 92 ng/ml and homeostasis model assessment for insulin resistance greater than 2.5 might be good predictors for polycystic ovary syndrome diagnosis.

CONCLUSION

We demonstrated that endotrophin level is higher in patients with polycystic ovary syndrome and may have predicted polycystic ovary syndrome with increased homeostasis model assessment for insulin resistance index. There was no significant difference in adiponectin and ghrelin levels in the polycystic ovary syndrome group. Endotrophin may have a role in polycystic ovary syndrome etiology rather than other adipokines.

The Mineralocorticoid Receptor Antagonist Eplerenone Suppresses Interstitial Fibrosis in Subcutaneous Adipose Tissue in Patients With Type 2 Diabetes

Activation of the mineralocorticoid receptor (MR) may promote dysfunctional adipose tissue in patients with type 2 diabetes, where increased pericellular fibrosis has emerged as a major contributor. The knowledge of the association among the MR, fibrosis, and the effects of an MR antagonist (MRA) in human adipocytes remains very limited. The present substudy, including 30 participants, was prespecified as part of the Mineralocorticoid Receptor Antagonist in Type 2 Diabetes (MIRAD) trial, which randomized patients to either high-dose eplerenone or placebo for 26 weeks. In adipose tissue biopsies, changes in fibrosis were evaluated by immunohistological examination and by the expression of mRNA and protein markers of fibrosis. Treatment with an MRA reduced pericellular fibrosis, synthesis of the major subunits of collagen types I and VI, and the profibrotic factor α-smooth muscle actin compared with placebo in subcutaneous adipose tissue. Furthermore, we found decreased expression of the MR and downstream molecules neutrophil gelatinase-associated lipocalin, galectin-3, and lipocalin-like prostaglandin D2 synthase with an MRA. In conclusion, we present original data demonstrating reduced fibrosis in adipose tissue with inhibition of the MR, which could be a potential therapeutic approach to prevent the extracellular matrix remodeling of adipose tissue in type 2 diabetes.

GATA-3 as a Potential Therapeutic Target for Insulin Resistance and Type 2 Diabetes Mellitus

Impaired adipogenesis plays an important role in the development of obesity-associated insulin resistance and type 2 diabetes as it leads to ectopic fat deposition. The anti-adipogenic transcription factor GATA-3 was identified as one of the potential molecular targets responsible for the impairment of adipogenesis. The expression of GATA-3 is higher in insulinresistant obese individuals compared to BMI-matched insulin-sensitive counterparts. Adipose tissue inflammation is a crucial mediator of this process. Hyperglycemia mediates the activation of the immune system, partially through upregulation of GATA- 3, causing exacerbation of the inflammatory state associated with obesity. This review discusses the evidence supporting the inhibition of GATA-3 as a useful therapeutic strategy in obesity-associated insulin resistance and type 2 diabetes, through up-regulation adipogenesis and amelioration of the immune response.

The Epithelial-to-Mesenchymal Transition as a Possible Therapeutic Target in Fibrotic Disorders

Fibrosis is a chronic and progressive disorder characterized by excessive deposition of extracellular matrix, which leads to scarring and loss of function of the affected organ or tissue. Indeed, the fibrotic process affects a variety of organs and tissues, with specific molecular background. However, two common hallmarks are shared: the crucial role of the transforming growth factor-beta (TGF-β) and the involvement of the inflammation process, that is essential for initiating the fibrotic degeneration. TGF-β in particular but also other cytokines regulate the most common molecular mechanism at the basis of fibrosis, the Epithelial-to-Mesenchymal Transition (EMT). EMT has been extensively studied, but not yet fully explored as a possible therapeutic target for fibrosis. A deeper understanding of the crosstalk between fibrosis and EMT may represent an opportunity for the development of a broadly effective anti-fibrotic therapy. Here we report the evidences of the relationship between EMT and multi-organ fibrosis, and the possible therapeutic approaches that may be developed by exploiting this relationship.

Glycosaminoglycan Modification of Decorin Depends on MMP14 Activity and Regulates Collagen Assembly

Proper processing of collagens COL1 and COL6 is required for normal function of adipose tissue and skeletal muscle. Proteoglycan decorin (DCN) regulates collagen fiber formation. The amino-terminus of DCN is modified with an O-linked glycosaminoglycan (GAG), the function of which has remained unclear. Previously, non-glycanated DCN (ngDCN) was identified as a marker of adipose stromal cells. Here, we identify MMP14 as the metalloprotease that cleaves DCN to generate ngDCN. We demonstrate that mice ubiquitously lacking DCN GAG (ngDCN mice) have reduced matrix rigidity, enlarged adipocytes, fragile skin, as well as skeletal muscle hypotrophy, fibrosis, and dysfunction. Our results indicate that DCN deglycanation results in reduced intracellular DCN—collagen binding and increased production of truncated COL6 chains, leading to aberrant procollagen processing and extracellular localization. This study reveals that the GAG of DCN functions to regulate collagen assembly in adipose tissue and skeletal muscle and uncovers a new mechanism of matrix dysfunction in obesity and aging.

Adipose tissue in health and disease

Adipose, or fat, tissue (AT) was once considered an inert tissue that primarily existed to store lipids, and was not historically recognized as an important organ in the regulation and maintenance of health. With the rise of obesity and more rigorous research, AT is now recognized as a highly complex metabolic organ involved in a host of important physiological functions, including glucose homeostasis and a multitude of endocrine capabilities. AT dysfunction has been implicated in several disease states, most notably obesity, metabolic syndrome and type 2 diabetes. The study of AT has provided useful insight in developing strategies to combat these highly prevalent metabolic diseases. This review highlights the major functions of adipose tissue and the consequences that can occur when disruption of these functions leads to systemic metabolic dysfunction.

Age-associated changes in the transcriptomes of non-cultured adipose-derived stem cells from young and old mice assessed via single-cell transcriptome analysis

Adipose-derived stem cells (ASCs) exhibit self-renewal and pluripotency. The differentiation potency of ASCs has been reported to deteriorate with aging; however, relevant studies used ASCs that were isolated and subcultured several times. It is still unclear whether subcultured ASCs accurately reflect the in vivo state. To address this question, we used freshly isolated stromal vascular fractions (SVFs) and performed comprehensive single-cell transcriptome analysis. In this study, we identified three cell populations as putative ASC candidates in SVFs and three novel ASC-related genes: Adamts7, Snai2, and Tgfbr1, that are reported to be negative regulators of cell differentiation. Moreover, we identified age-associated high gene expression levels of Adamts7, Egfr, and Igfbp4 in the earliest differentiation stage of ASCs. These results suggest that aging may make it impossible to maintain the stringency of the regulation of the expression of some genes related to ASC differentiation.

COL6A3 expression in adipose tissue cells is associated with levels of the homeobox transcription factor PRRX1

Fibrillar collagen COL6α3 in adipose tissue has been associated with obesity, inflammation, insulin resistance and cancer. We here aimed to identify novel transcriptional regulators of COL6A3 expression. Based on a transcriptome dataset of adipose tissue, we identified strong correlations for 56 genes with COL6A3 mRNA, including targets of TGF-β/SMAD signaling. Among the identified candidates, the homeobox transcription factor PRRX1 showed a particularly striking co-expression with COL6A3, validated across several different cohorts, including patients with extreme obesity, insulin sensitive and resistant obesity (subcutaneous and omental), after profound fat loss (subcutaneous), and lean controls (subcutaneous). In human and mouse adipose cells, PRRX1 knockdown reduced COL6A3 mRNA and PRRX1 overexpression transactivated a reporter construct with the endogenous human COL6A3 promoter. Stable PRRX1 overexpression in 3T3-L1 cells induced Col6a3 mRNA threefold specifically after adipogenic induction, whereas TGF-β1 treatment upregulated Col6a3 mRNA also in the preadipocyte state. Interestingly, pro-inflammatory stimulus (i.e., TNF-α treatment) decreased PRRX1-mediated Col6a3 transactivation and mRNA expression, supporting a role for this mechanism in the regulation of adipose tissue inflammation. In conclusion, we identified the homeobox factor PRRX1 as a novel transcriptional regulator associated with COL6A3 expression, providing new insight into the regulatory mechanisms of altered adipose tissue function in obesity and insulin resistance.

Control of Adipose Cell Browning and Its Therapeutic Potential

Adipose tissue is the largest endocrine organ in humans and has an important influence on many physiological processes throughout life. An increasing number of studies have described the different phenotypic characteristics of fat cells in adults. Perhaps one of the most important properties of fat cells is their ability to adapt to different environmental and nutritional conditions. Hypothalamic neural circuits receive peripheral signals from temperature, physical activity or nutrients and stimulate the metabolism of white fat cells. During this process, changes in lipid inclusion occur, and the number of mitochondria increases, giving these cells functional properties similar to those of brown fat cells. Recently, beige fat cells have been studied for their potential role in the regulation of obesity and insulin resistance. In this context, it is important to understand the embryonic origin of beige adipocytes, the response of adipocyte to environmental changes or modifications within the body and their ability to transdifferentiate to elucidate the roles of these cells for their potential use in therapeutic strategies for obesity and metabolic diseases. In this review, we discuss the origins of the different fat cells and the possible therapeutic properties of beige fat cells.

Stiffness of the extracellular matrix regulates differentiation into beige adipocytes

Beige/brite adipocytes, which express high levels of uncoupling protein 1 (UCP1) to generate heat using stored triglycerides, are induced under specific stimuli such as cold exposure in inguinal white adipose tissue (iWAT). Although extracellular microenvironments such as extracellular matrix (ECM) stiffness are known to regulate cell behaviors, including cell differentiation into adipocytes, the effect on iWAT cells is unknown. In this study, we show that rigid ECM promotes the cell spreading of iWAT-derived preadipocytes. Furthermore, the expression of UCP1 and other thermogenic genes in iWAT cells is promoted when the cells are cultured on rigid ECM. The expression of mTOR, a kinase known to regulate the differentiation to beige adipocytes, is decreased on rigid substrates. These results suggest that ECM stiffness plays an important role in the differentiation to beige adipocytes.

Transglutaminases and Obesity in Humans: Association of F13A1 to Adipocyte Hypertrophy and Adipose Tissue Immune Response

Transglutaminases TG2 and FXIII-A have recently been linked to adipose tissue biology and obesity, however, human studies for TG family members in adipocytes have not been conducted. In this study, we investigated the association of TGM family members to acquired weight gain in a rare set of monozygotic (MZ) twins discordant for body weight, i.e., heavy-lean twin pairs. We report that F13A1 is the only TGM family member showing significantly altered, higher expression in adipose tissue of the heavier twin. Our previous work linked adipocyte F13A1 to increased weight, body fat mass, adipocyte size, and pro-inflammatory pathways. Here, we explored further the link of F13A1 to adipocyte size in the MZ twins via a previously conducted TWA study that was further mined for genes that specifically associate to hypertrophic adipocytes. We report that differential expression of F13A1 (ΔHeavy-Lean) associated with 47 genes which were linked via gene enrichment analysis to immune response, leucocyte and neutrophil activation, as well as cytokine response and signaling. Our work brings further support to the role of F13A1 in the human adipose tissue pathology, suggesting a role in the cascade that links hypertrophic adipocytes with inflammation.

The MMP14-caveolin axis and its potential relevance for lipoedema

Lipoedema is associated with widespread adipose tissue expansion, particularly in the proximal extremities. The mechanisms that drive the development of lipoedema are unclear. In this Perspective article, we propose a new model for the pathophysiology of lipoedema. We suggest that lipoedema is an oestrogen-dependent disorder of adipose tissue, which is triggered by a dysfunction of caveolin 1 (CAV1) and subsequent uncoupling of feedback mechanisms between CAV1, the matrix metalloproteinase MMP14 and oestrogen receptors. In addition, reduced CAV1 activity also leads to the activation of ERα and impaired regulation of the lymphatic system through the transcription factor prospero homeobox 1 (PROX1). The resulting upregulation of these factors could effectively explain the main known features of lipoedema, such as adipose hypertrophy, dysfunction of blood and lymphatic vessels, the overall oestrogen dependence and the associated sexual dimorphism, and the mechanical compliance of adipose tissue.

YAP and TAZ protect against white adipocyte cell death during obesity

The expansion of the white adipose tissue (WAT) in obesity goes along with increased mechanical, metabolic and inflammatory stress. How adipocytes resist this stress is still poorly understood. Both in human and mouse adipocytes, the transcriptional co-activators YAP/TAZ and YAP/TAZ target genes become activated during obesity. When fed a high-fat diet (HFD), mice lacking YAP/TAZ in white adipocytes develop severe lipodystrophy with adipocyte cell death. The pro-apoptotic factor BIM, which is downregulated in adipocytes of obese mice and humans, is strongly upregulated in YAP/TAZ-deficient adipocytes under HFD, and suppression of BIM expression reduces adipocyte apoptosis. In differentiated adipocytes, TNFα and IL-1β promote YAP/TAZ nuclear translocation via activation of RhoA-mediated actomyosin contractility and increase YAP/TAZ-mediated transcriptional regulation by activation of c-Jun N-terminal kinase (JNK) and AP-1. Our data indicate that the YAP/TAZ signaling pathway may be a target to control adipocyte cell death and compensatory adipogenesis during obesity.

Expansion and inflammation of white adipose tissue - focusing on adipocyte progenitors

Adipose tissue is an important organ in our body, participating not only in energy metabolism but also immune regulation. It is broadly classified as white (WAT) and brown (BAT) adipose tissues. WAT is highly heterogeneous, composed of adipocytes, various immune, progenitor and stem cells, as well as the stromal vascular populations. The expansion and inflammation of WAT are hallmarks of obesity and play a causal role in the development of metabolic and cardiovascular diseases. The primary event triggering the inflammatory expansion of WAT remains unclear. The present review focuses on the role of adipocyte progenitors (APS), which give rise to specialized adipocytes, in obesity-associated WAT expansion, inflammation and fibrosis.

Insulin-sensitizing effects of vitamin D repletion mediated by adipocyte vitamin D receptor: Studies in humans and mice

Objective

Adipose tissue inflammation and fibrosis appear to contribute to insulin resistance in obesity. Vitamin D receptor (Vdr) genes are expressed by adipocytes, macrophages, and fibroblasts, all of which could potentially play a role in adipose tissue inflammation and fibrosis. As vitamin D has been shown to have direct anti-inflammatory effects on adipocytes, we determined whether specific vitamin D receptor-mediated effects on adipocytes could impact adipose tissue inflammation and fibrosis and ultimately insulin resistance.

Methods

We examined the effects of repleting vitamin D in 25(OH)D-deficient, insulin resistant, overweight-to-obese human subjects (n = 19). A comprehensive assessment of whole-body insulin action was undertaken with stepped euglycemic (∼90 mg/dL) hyperinsulinemic clamp studies both before and after the administration of vitamin D or placebo. Adipose tissue fibrosis and inflammation were quantified by real-time rt-PCR and immunofluorescence in subcutaneous abdominal adipose tissue.

To determine whether vitamin D's effects are mediated through adipocytes, we conducted hyperinsulinemic clamp studies (4 mU/kg/min) and adipose tissue analysis using an adipocyte-specific vitamin D receptor knockout (VDR-KO) mouse model (adiponectin-Cre + VDR+/fl) following high-fat diet feeding for 12 weeks.

Results

25(OH)D repletion was associated with reductions in adipose tissue expression of pro-inflammatory and pro-fibrotic genes, decreased collagen immunofluorescence, and improved hepatic insulin sensitivity in humans. Worsening trends after six months on placebo suggest progressive metabolic effects of 25(OH)D deficiency. Ad-VDR-KO mice mirrored the vitamin D-deficient humans, displaying increased adipose tissue fibrosis and inflammation and hepatic insulin resistance.

Conclusions

These complementary human and rodent studies support a beneficial role of vitamin D repletion for improving hepatic insulin resistance and reducing adipose tissue inflammation and fibrosis in targeted individuals, likely via direct effects on adipocytes. These studies have far-reaching implications for understanding the role of adipocytes in mediating adipose tissue inflammation and fibrosis and ultimately impacting insulin sensitivity.

•

Vitamin D repletion improved hepatic insulin sensitivity in obese insulin-resistant and vitamin D deficient human.

•

Correcting vitamin D deficiency concomitantly reduced adipose tissue expression of pro-inflammatory and pro-fibrotic genes.

•

Worsening trends in these metabolic parameters were observed following 6 months of uncorrected vitamin D deficiency.

•

Adipocyte-specific depletion of VDR in mice induced adipose tissue inflammation and fibrosis and hepatic insulin resistance.

The effects of obesity on the human body, part I: Skin and musculoskeletal

Obesity is a worldwide issue that many global health authorities consider a growing epidemic. Having a positive correlation between increases in the industrialization of processed foods and sedentary occupations as well as a lack of access to healthcare in poorer socioeconomic areas, obesity is a multifactorial disease affecting several organ systems. The tendency for obesity to cause detrimental changes to the human body is a focal point for healthcare providers to establish more effective clinical treatment and management plans. Implementing comprehensive global educational programs to decrease the prevalence of this unforgiving disease is imperative for a healthier future. Herein, we have provided a comprehensive review of the health effects of obesity upon the human body for the interest of many practicing clinicians managing this health crisis.

Multi-omics Analysis Reveals Adipose-tumor Crosstalk in Patients with Colorectal Cancer

Obesity and obesity-driven cancer rates are continuing to rise worldwide. We hypothesize that adipocyte-colonocyte interactions are a key driver of obesity-associated cancers. To understand the clinical relevance of visceral adipose tissue in advancing tumor growth, we analyzed paired tumor-adjacent visceral adipose, normal mucosa, and colorectal tumor tissues as well as presurgery blood samples from patients with sporadic colorectal cancer. We report that high peroxisome proliferator-activated receptor gamma (PPARG) visceral adipose tissue expression is associated with glycoprotein VI (GPVI) signaling-the major signaling receptor for collagen-as well as fibrosis and adipogenesis pathway signaling in colorectal tumors. These associations were supported by correlations between PPARG visceral adipose tissue expression and circulating levels of plasma 4-hydroxyproline and serum intercellular adhesion molecule 1 (ICAM1), as well as gene set enrichment analysis and joint gene-metabolite pathway results integration that yielded significant enrichment of genes defining epithelial-to-mesenchymal transition-as in fibrosis and metastasis-and genes involved in glycolytic metabolism, confirmed this association. We also reveal that elevated prostaglandin-endoperoxide synthase 2 (PTGS2) colorectal tumor expression is associated with a fibrotic signature in adipose-tumor crosstalk via GPVI signaling and dendritic cell maturation in visceral adipose tissue. Systemic metabolite and biomarker profiling confirmed that high PTGS2 expression in colorectal tumors is significantly associated with higher concentrations of serum amyloid A and glycine, and lower concentrations of sphingomyelin, in patients with colorectal cancer. This multi-omics study suggests that adipose-tumor crosstalk in patients with colorectal cancer is a critical microenvironment interaction that could be therapeutically targeted.See related spotlight by Colacino et al., p. 803.

Collagen: quantification, biomechanics, and role of minor subtypes in cartilage

Collagen is a ubiquitous biomaterial in vertebrate animals. Although each of its 28 subtypes contributes to the functions of many different tissues in the body, most studies on collagen or collagenous tissues have focussed on only one or two subtypes. With recent developments in analytical chemistry, especially mass spectrometry, significant advances have been made toward quantifying the different collagen subtypes in various tissues; however, high-throughput and low-cost methods for collagen subtype quantification do not yet exist. In this Review, we introduce the roles of collagen subtypes and crosslinks, and describe modern assays that enable a deep understanding of tissue physiology and disease states. Using cartilage as a model tissue, we describe the roles of major and minor collagen subtypes in detail; discuss known and unknown structure-function relationships; and show how tissue engineers may harness the functional characteristics of collagen to engineer robust neotissues.