Proteomics in the characterization of adipose dysfunction in obesity

Mass spectrometry for the study of adipocyte cell secretome in cardiovascular diseases

Adipose tissue is classically considered the primary site of lipid storage, but in recent years has garnered appreciation for its broad role as an endocrine organ, capable of remotely signaling to other tissues to alter their metabolic program. The adipose tissue is now recognized as a crucial regulator of cardiovascular health, mediated by the secretion of several bioactive products, with a wide range of endocrine and paracrine effects on the cardiovascular system. Thanks to the development and improvement of high-throughput mass spectrometry, the size and components of the human secretome have been characterized. In this review, we summarized the recent advances in mass spectrometry-based studies of the cell and tissue secretome for the understanding of adipose tissue biology, which may help to decipher the complex molecular mechanisms controlling the crosstalk between the adipose tissue and the cardiovascular system, and their possible clinical translation.

Role of obesity related inflammation in pathogenesis of peripheral artery disease in patients of type 2 diabetes mellitus

Objective

Type 2 diabetes mellitus (T2DM) has emerged as one of the greatest global health challenges of twenty-first century. Visceral obesity is one of the most important determinant of insulin resistance (IR) as well as T2DM complications. Therefore this review focuses on the molecular mechanism of obesity induced inflammation, signaling pathways contributing to diabetes, as well as role of lifestyle interventions and medical therapies in the prevention and management of T2DM.

Method

Articles were searched on digital data base PubMed, Cochrane Library, and Web of Science. The key words used for search included Type 2 diabetes mellitus, obesity, insulin resistance, vascular inflammation and peripheral arterial disease.

Result

Visceral obesity is associated with chronic low grade inflammation and activation of immune systems which are involved in pathogenesis of obesity related IR and T2DM.

Conclusion

Metabolic dysregulation of adipose tissue leads to local hypoxia, misfolded/unfolded protein response and increased circulating free fatty acids, which in turn initiate inflammatory signaling cascades in the population of infiltrating cells. Mechanism that relates the role of adipocytokines with insulin sensitivity and glucose homeostasis might throw a light on the development of therapeutic interventions and subsequently might result in the reduction of vascular complications.

Metformin Prevents Key Mechanisms of Obesity-Related Complications in Visceral White Adipose Tissue of Obese Pregnant Mice

With the gaining prevalence of obesity, related risks during pregnancy are rising. Inflammation and oxidative stress are considered key mechanisms arising in white adipose tissue (WAT) sparking obesity-associated complications and diseases. The established anti-diabetic drug metformin reduces both on a systemic level, but only little is known about such effects on WAT. Because inhibiting these mechanisms in WAT might prevent obesity-related adverse effects, we investigated metformin treatment during pregnancy using a mouse model of diet-induced maternal obesity. After mating, obese mice were randomised to metformin administration. On gestational day G15.5, phenotypic data were collected and perigonadal WAT (pgWAT) morphology and proteome were examined. Metformin treatment reduced weight gain and visceral fat accumulation. We detected downregulation of perilipin-1 as a correlate and observed indications of recovering respiratory capacity and adipocyte metabolism under metformin treatment. By regulating four newly discovered potential adipokines (alpha-1 antitrypsin, Apoa4, Lrg1 and Selenbp1), metformin could mediate anti-diabetic, anti-inflammatory and oxidative stress-modulating effects on local and systemic levels. Our study provides an insight into obesity-specific proteome alterations and shows novel modulating effects of metformin in pgWAT of obese dams. Accordingly, metformin therapy appears suitable to prevent some of obesity’s key mechanisms in WAT.

Proteomic Signatures of Human Visceral and Subcutaneous Adipocytes

CONTEXT

Adipose tissue distribution is a key factor influencing metabolic health and risk in obesity-associated comorbidities.

OBJECTIVE

Here we aim to compare the proteomic profiles of mature adipocytes from different depots.

METHODS

Abdominal subcutaneous (SA) and omental visceral adipocytes (VA) were isolated from paired adipose tissue biopsies obtained during bariatric surgery on 19 severely obese women (body mass index > 30 kg/m2) and analyzed using state-of-the-art mass spectrometry. Differential expression analysis and weighted gene co-expression network analysis (WGCNA) were performed to investigate proteome signature properties and to examine a possible association of the protein expression with the clinical data.

RESULTS

We identified 3686 protein groups and found 1140 differentially expressed proteins (adj. P value < 0.05), of which 576 proteins were upregulated in SA and 564 in VA samples. We provide a global protein profile of abdominal SA and omental VA, present the most differentially expressed pathways and processes distinguishing SA from VA, and correlate them with clinical and body composition data. We show that SA are significantly more active in processes linked to vesicular transport and secretion, and to increased lipid metabolism activity. Conversely, the expression of proteins involved in the mitochondrial energy metabolism and translational or biosynthetic activity is higher in VA.

CONCLUSION

Our analysis represents a valuable resource of protein expression profiles in abdominal SA and omental VA, highlighting key differences in their role in obesity.

Longitudinal liver proteome profiling in dairy cows during the transition from gestation to lactation: Investigating metabolic adaptations and their interactions with fatty acids supplementation via repeated measurements ANOVA-simultaneous component analysis

Repeated measurements analysis of variance - simultaneous component analysis (ASCA) has been developed to handle complex longitudinal omics datasets and combine novel information with existing data. Herein, we aimed at applying ASCA to 64 liver proteomes collected at 4-time points (day -21, +1, +28, and + 63 relative to parturition) from 16 Holstein cows treated from 9 wk. antepartum to 9 wk. postpartum (PP) with coconut oil (CTRL) or a mixture of essential fatty acids (EFA) and conjugated linoleic acid (CLA) (EFA + CLA). The ASCA modeled 116, 43, and 97 differentially abundant proteins (DAP) during the transition to lactation, between CTRL and EFA + CLA, and their interaction, respectively. Time-dependent DAP were annotated to pathways related to the metabolism of carbohydrates, FA, and amino acid in the PP period. The DAP between FA and the interaction effect were annotated to the metabolism of xenobiotics by cytochrome P450, drug metabolism - cytochrome P450, retinol metabolism, and steroid hormone biosynthesis. Collectively, ASCA provided novel information on molecular markers of metabolic adaptations and their interactions with EFA + CLA supplementation. Bioinformatics analysis suggested that supplemental EFA + CLA amplified hepatic FA oxidation; cytochrome P450 was enriched to maintain metabolic homeostasis by oxidation/detoxification of endogenous compounds and xenobiotics. SIGNIFICANCE: This report is among the first ones applying repeated measurement analysis of variance-simultaneous component analysis (ASCA) to deal with longitudinal proteomics results. ASCA separately identified differentially abundant proteins (DAP) in 'transition time', 'between fatty acid treatments', and 'their interaction'. We first identified the molecular signature of hepatic metabolic adaptations during postpartum negative energy balance; the enriched pathways were well-known pathways related to mobilizing fatty acids (FA) and amino acids to support continuous energy production through fatty acid oxidation, TCA cycle, and gluconeogenesis. Some of the DAP were not previously reported in transition dairy cows. Secondly, we provide novel information on the mechanisms by which supplemented essential FA and conjugated linoleic acids interact with hepatic metabolism. In this regard, FA amplified hepatic detoxifying and oxidation capacity through ligand activation of nuclear receptors. Finally, we briefly compared the strengths and weaknesses of the ASCA model with PLS-DA and outlined why these methods are complementary.

Comparative Proteomic Profiling of 3T3-L1 Adipocyte Differentiation Using SILAC Quantification

Adipocyte differentiation is a general physiological process that is also critical for metabolic syndrome. In spite of extensive study in the past two decades, adipogenesis is a still complex cellular process that is accompanied by complicated molecular mechanisms. Here, we performed SILAC-based quantitative global proteomic profiling of 3T3-L1 adipocyte differentiation. We report protein changes to the proteome profiles, with 354 proteins exhibiting significant increase and 56 proteins showing decrease in our statistical analysis. Our results show that adipocyte differentiation is involved not only in metabolic processes by increasing TCA cycle, fatty acid synthesis, lipolysis, acetyl-CoA production, antioxidants, and electron transport, but also in nicotinamide metabolism, cristae formation, mitochondrial protein import, and Ca²⁺ transport into mitochondria and ER. A search for Chromosome-Centric Human Proteome Project (C-HPP) using neXtprot highlighted one protein with a protein existence uncertain (PE5) and 17 proteins as functionally uncharacterized protein existence 1 (uPE1). This study provides quantitative information on proteome changes in adipogenic differentiation, which is helpful in improving our understanding of the processes of adipogenesis.

iTRAQ-Based Quantitative Proteomic Comparison of 2D and 3D Adipocyte Cell Models Co-cultured with Macrophages Using Online 2D-nanoLC-ESI-MS/MS

The demand for novel three-dimensional (3D) cell culture models of adipose tissue has been increasing, and proteomic investigations are important for determining the underlying causes of obesity, type II diabetes, and metabolic disorders. In this study, we performed global quantitative proteomic profiling of three 3D-cultured 3T3-L1 cells (preadipocytes, adipocytes and co-cultured adipocytes with macrophages) and their 2D-cultured counterparts using 2D-nanoLC-ESI-MS/MS with iTRAQ labelling. A total of 2,885 shared proteins from six types of adipose cells were identified and quantified in four replicates. Among them, 48 proteins involved in carbohydrate metabolism (e.g., PDHα, MDH1/2, FH) and the mitochondrial fatty acid beta oxidation pathway (e.g., VLCAD, ACADM, ECHDC1, ALDH6A1) were relatively up-regulated in the 3D co-culture model compared to those in 2D and 3D mono-cultured cells. Conversely, 12 proteins implicated in cellular component organisation (e.g., ANXA1, ANXA2) and the cell cycle (e.g., MCM family proteins) were down-regulated. These quantitative assessments showed that the 3D co-culture system of adipocytes and macrophages led to the development of insulin resistance, thereby providing a promising in vitro obesity model that is more equivalent to the in vivo conditions with respect to the mechanisms underpinning metabolic syndromes and the effect of new medical treatments for metabolic disorders.

Peptidomic analysis reveals multiple protection of human breast milk on infants during different stages

It has been shown that human breast milk (HBM) is an important nutrient for the growth and development of newborns. Currently, peptide drugs provide promising regimes in neonatal disease treatment, especially peptides from HBM that exhibit multiple functions within cells. To explore the potential biological function peptides among the colostrum, transition and mature milk from mother of extremely low birth weight children (the samples were collected from Women's Hospital of Nanjing Medical University from December 2016 to February 2017). A total of 3,182 nonredundant peptides were identified and compared among colostrum, transitional and mature milk using liquid chromatography/mass spectrometry technology, and the numbers and fragments of peptides were various. The isoelectric point and molecular weight analysis of the differentially expressed peptides basically accord with the range of mass spectrometry identification (<3 kDa). Gene Ontology analysis and Pathway analysis, restriction sites analysis, as well as bioinformatics analysis showed that these differentially expressed peptides enriched a variety of biological processes. We identified several putative peptides that might have bioactive effects in diseases and development of newborns, which will inform further functional investigations. Our preliminary research provided a better understanding of the function of peptides during the newborn periods. Furthermore, it laid a foundation for discovering new peptide drugs in neonatal disease treatment.

Comparative Proteomic Analysis of Visceral Adipose Tissue in Morbidly Obese and Normal Weight Chinese Women

OBJECTIVE

Visceral adipose tissue (VAT) plays a central role in the balance of energy metabolism. The objective of this study was to investigate the differentially expressed proteins in VAT between morbidly obese (BMI >35 kg/m²) and normal weight Chinese women.

METHOD

Nine morbidly obese women and 8 normal weight women as controls were enrolled. Abdominal VAT was excised and analyzed by label-free one-dimensional liquid chromatography tandem mass spectrometry (1D-LC-MS/MS). Differentially expressed VAT proteins were further analyzed with Gene Ontology (GO) analysis and Ingenuity Pathway Analysis (IPA). Masson's trichrome staining and CD68 immunohistochemical staining of VAT were conducted in all subjects.

RESULT

A total of 124 differentially expressed proteins were found with a ≥2-fold difference. Forty-one proteins were upregulated, and 83 proteins were downregulated in obese individuals. These altered VAT proteins were involved in the attenuation of the liver X receptor/retinoid X receptor (LXR/RXR) signaling pathway and the activation of the acute-phase response process. Three proteins (ACSL1, HADH, and UCHL1) were validated by western blotting using the same set of VAT samples from 6 morbidly obese and 7 normal weight patients, and the results indicated that the magnitude and direction of the protein changes were in accordance with the proteomic analysis. Masson's trichrome staining and CD68 immunohistochemical staining demonstrated that there was much more collagen fiber deposition and CD68-positive macrophages in the VAT of morbidly obese patients, suggesting extensive fiber deposition and macrophage infiltration.

CONCLUSION

A number of differentially expressed proteins were identified in VAT between morbidly obese and normal weight Chinese females. These differential proteins could be potential candidates in addressing the role of VAT in the development of obesity.

Quantitative proteomic analysis of murine white adipose tissue for peritoneal cancer metastasis

Cancer metastasis risk increases in older individuals, but the mechanisms for this risk increase are unclear. Many peritoneal cancers, including ovarian cancer, preferentially metastasize to peritoneal fat depots. However, there is a dearth of studies exploring aged peritoneal adipose tissue in the context of cancer. Because adipose tissue produces signals which influence several diseases including cancer, proteomics of adipose tissue in aged and young mice may provide insight into metastatic mechanisms. We analyzed mesenteric, omental, and uterine adipose tissue groups from the peritoneal cavities of young and aged C57BL/6J mouse cohorts with a low-fraction SDS-PAGE gelLC-MS/MS method. We identified 2308 protein groups and quantified 2167 groups, among which several protein groups showed twofold or greater abundance differences between the aged and young cohorts. Cancer-related gene products previously identified as significant in another age-related study were found altered in this study. Several gene products known to suppress proliferation and cellular invasion were found downregulated in the aged cohort, including R-Ras, Arid1a, and heat shock protein β1. In addition, multiple protein groups were identified within single cohorts, including the proteins Cd11a, Stat3, and Ptk2b. These data suggest that adipose tissue is a strong candidate for analysis to identify possible contributors to cancer metastasis in older subjects. The results of this study, the first of its kind using uterine adipose tissue, contribute to the understanding of the role of adipose tissue in age-related alteration of oncogenic pathways, which may help elucidate the mechanisms of increased metastatic tumor burden in the aged. Graphical abstract We analyzed mesenteric, omental, and uterine adipose tissue groups from the peritoneal cavities of young and aged C57BL/6J mouse cohorts with a low-fraction SDS-PAGE gelLC-MS/MS method. These fat depots are preferential sites for many peritoneal cancers. The results of this study, the first of its kind using uterine adipose tissue, contribute to the understanding of the role of adipose tissue in age-related alteration of oncogenic pathways, which may help elucidate the mechanisms of increased metastatic tumor burden in the aged.

Identification and characterization of metformin on peptidomic profiling in human visceral adipocytes

To gain insight into the effect of metformin on losing weight from peptidomic perspective and to screen potential active peptides for reducing fat lipid deposition. After determining the proper concentration of metformin on human primary visceral adipocytes, we constructed a comparative peptidomic profiling between control and metformin treatment group (n = 3) using a stable isobaric labeling strategy involving tandem mass tag reagents, followed by liquid chromatography tandem mass spectrometry. We identified and quantified 3065 non-redundant peptides, 304 of which were differentially expressed after metformin treatment, 206 peptides were up regulated and 98 peptides were down regulated significantly. Gene ontology (GO) enrichment and pathway analysis were performed to study differentially peptides though their precursor proteins. We concluded three peptides located within the functional domains of their precursor proteins could be candidate bioactive peptides for obesity. On one hand, these results confirmed the versatile effects of metformin on adipocyte and advance our current understanding of metformin, on the other hand, these identified peptides might play putative roles in treatment of obesity.

Multi-omics Integrative Investigation of Fatty Acid Metabolism in Obese and Lean Subcutaneous Tissue

White adipose tissue (WAT) plays a central role in whole-body energy homeostasis through storage and release of fatty acids. A deeper understanding of the complex and highly integrated pathways regulating WAT fatty acid metabolism, and how they are altered with obesity, is necessary for diagnostic and therapeutic innovations in nutritional disorders. In this multi-omics study, we investigated the influence of obesity on fatty acid metabolism in human subcutaneous adipose tissue (SAT) using an approach that integrated transcriptomic, peptidomic, and fatty acid analyses. Notably, all analyses were conducted in the same adipose tissue sample from each participant, thus minimizing the chance of spurious results. In a sample of SAT from the periumbilical abdominal region of obese (n = 11, mean body mass index [BMI] = 35.0 ± 1.2 kg/m²) and lean subjects (n = 9, mean BMI = 22.1 ± 0.5 kg/m²), we found that obese SAT tended to have higher relative amounts of specific monounsaturated fatty acids and n-6 polyunsaturated fatty acids, and lower amounts of saturated fatty acids (p < 0.05). These changes were associated with differential regulation of lipogenic and lipolytic pathways in obese SAT. Fatty acid analysis showed changes in estimated fatty acid desaturase and elongase activities between lean and obese SAT (p < 0.05). Biomarkers of lipogenesis (e.g., fatty acid synthase protein) were differentially regulated between lean and obese SAT. These changes were noted in conjunction with increases in extracellular matrix remodeling proteins. Transcriptomic data revealed that the key regulators of lipolysis were reduced in obese SAT. This integrative multi-omics analysis collectively shows that obese SAT has a distinct fatty acid signature compared to lean SAT and the pathways underlying fatty acid metabolism are broadly regulated at the level of gene expression and protein abundance.

Microdialysis and proteomics of subcutaneous interstitial fluid reveals increased galectin-1 in type 2 diabetes patients

OBJECTIVE

To identify a potential therapeutic target for type 2 diabetes by comparing the subcutaneous interstitial fluid from type 2 diabetes patients and healthy men.

METHODS

Proteomics was performed on the interstitial fluid of subcutaneous adipose tissue obtained by microdialysis from 7 type 2 diabetes patients and 8 healthy participants. 851 proteins were detected, of which 36 (including galectin-1) showed significantly altered expression in type 2 diabetes. We also measured galectin-1 expression in: (1) adipocytes isolated from adipose tissue biopsies from these participants; (2) subcutaneous adipose tissue of 24 obese participants before, during and after 16weeks on a very low calorie diet (VLCD); and (3) adipocytes isolated from 6 healthy young participants after 4weeks on a diet and lifestyle intervention to promote weight gain. We also determined the effect of galectin-1 on glucose uptake in human adipose tissue.

RESULTS

Galectin-1 protein levels were elevated in subcutaneous dialysates from type 2 diabetes compared with healthy controls (p<0.05). In agreement, galectin-1 mRNA expression was increased in adipocytes from the type 2 diabetes patients (p<0.05). Furthermore, galectin-1 mRNA expression was decreased in adipose tissue after VLCD (p<0.05) and increased by overfeeding (p<0.05). Co-incubation of isolated human adipocytes with galectin-1 reduced glucose uptake (p<0.05) but this was independent of the insulin signal.

CONCLUSION

Proteomics of the interstitial fluid in subcutaneous adipose tissue in vivo identified a novel adipokine, galectin-1, with a potential role in the pathophysiology of type 2 diabetes.

Expression, regulation and functional assessment of the 80 amino acid Small Adipocyte Factor 1 (Smaf1) protein in adipocytes

The gene for Small Adipocyte Factor 1, Smaf1 (also known as adipogenin, ADIG), encodes a ∼600 base transcript that is highly upregulated during 3T3-L1 in vitro adipogenesis and markedly enriched in adipose tissues. Based on the lack of an obvious open reading frame in the Smaf1 transcript, it is not known if the Smaf1 gene is protein coding or non-coding RNA. Using a peptide from a putative open reading frame of Smaf1 as antigen, we generated antibodies for western analysis. Our studies prove that Smaf1 encodes an adipose-enriched protein which in western blot analysis migrates at ∼10 kDa. Rapid induction of Smaf1 protein occurs during in vitro adipogenesis and its expression in 3T3-L1 adipocytes is positively regulated by insulin and glucose. Moreover, siRNA studies reveal that expression of Smaf1 in adipocytes is wholly dependent on PPARγ. On the other hand, use of siRNA for Smaf1 to nearly abolish its protein expression in adipocytes revealed that Smaf1 does not have a major role in adipocyte triglyceride accumulation, lipolysis or insulin-stimulated pAkt induction. However, immunolocalization studies using HA-tagged Smaf1 reveal enrichment at adipocyte lipid droplets. Together our findings show that Smaf1 is a novel small protein endogenous to adipocytes and that Smaf1 expression is closely tied to PPARγ-mediated signals and the adipocyte phenotype.

Recent advances in proteomic studies of adipose tissues and adipocytes

Obesity is a chronic disease that is associated with significantly increased levels of risk of a number of metabolic disorders. Despite these enhanced health risks, the worldwide prevalence of obesity has increased dramatically over the past few decades. Obesity is caused by the accumulation of an abnormal amount of body fat in adipose tissue, which is composed mostly of adipocytes. Thus, a deeper understanding of the regulation mechanism of adipose tissue and/or adipocytes can provide a clue for overcoming obesity-related metabolic diseases. In this review, we describe recent advances in the study of adipose tissue and/or adipocytes, focusing on proteomic approaches. In addition, we suggest future research directions for proteomic studies which may lead to novel treatments of obesity and obesity-related diseases.

[Bardet-Biedl syndrome: cilia and obesity - from genes to integrative approaches]

The primary cilium is a specialized organelle, present at the surface of most eukaryotic cells, whose main function is to detect, integrate and transmit intra- and extra-cellular signals. Its dysfunction usually results in a group of severe clinical manifestations nowadays termed ciliopathies. The latter can be of syndromic nature with multi-organ dysfunctions and can also be associated with a morbid obese phenotype, like it is the case in the iconic ciliopathy, the Bardet Biedl syndrome (BBS). This review will discuss the contribution of the unique context offered by the emblematic BBS for understanding the mechanisms leading to obesity via the involvement of the primary cilium together with identification of novel molecular players and signaling pathways it has helped to highlight. In the current context of translational medicine and system biology, this article will also discuss the potential benefits and challenges posed by these techniques via multi-level approaches to better dissect the underlying mechanisms leading to the complex condition of obesity.