Transdifferentiation of myoblasts by the adipogenic transcription factors PPAR gamma and C/EBP alpha

Prmt6 represses the pro-adipogenic Ppar-gamma-C/ebp-alpha transcription factor loop

The feed-forward loop between the transcription factors Ppar-gamma and C/ebp-alpha is critical for lineage commitment during adipocytic differentiation. Ppar-gamma interacts with epigenetic cofactors to activate C/ebp-alpha and the downstream adipocytic gene expression program. Therefore, knowledge of the epigenetic cofactors associated with Ppar-gamma, is central to understanding adipocyte differentiation in normal differentiation and disease. We found that Prmt6 is present with Ppar-gamma on the Ppar-gamma and C/ebp-alpha promoter. It contributes to the repression of C/ebp-alpha expression, in part through its ability to induce H3R2me2a. During adipocyte differentiation, Prmt6 expression is reduced and the methyltransferase leaves the promoters. As a result, the expression of Ppar-gamma and C/ebp-alpha is upregulated and the adipocytic gene expression program is established. Inhibition of Prmt6 by a small molecule enhances adipogenesis, opening up the possibility of epigenetic manipulation of differentiation. Our data provide detailed information on the molecular mechanism controlling the Ppar-gamma-C/ebp-alpha feed-forward loop. Thus, they advance our understanding of adipogenesis in normal and aberrant adipogenesis.

Cell-state dependent regulation of PPAR γ signaling by ZBTB9 in adipocytes

Adipocytes play a critical role in metabolic homeostasis. Peroxisome proliferator-activated receptor- γ (PPAR γ ) is a nuclear hormone receptor that is a master regulator of adipocyte differentiation and function. ZBTB9 was predicted to interact with PPAR γ based on large-scale protein interaction experiments. In addition, GWAS studies in the type 2 diabetes (T2D) Knowledge Portal revealed associations between Z btb9 and both BMI and T2D risk. Here we show that ZBTB9 positively regulates PPAR γ activity in mature adipocytes. Surprisingly Z btb9 knockdown (KD) also increased adipogenesis in 3T3-L1 cells and human preadipocytes. E2F activity was increased and E2F downstream target genes were upregulated in Zbtb9 -KD preadipocytes. Accordingly, RB phosphorylation, which regulates E2F activity, was enhanced in Zbtb9 -KD preadipocytes. Critically, an E2F1 inhibitor blocked the effects of Zbtb9 deficiency on adipogenic gene expression and lipid accumulation. Collectively, these results demonstrate that Zbtb9 inhibits adipogenesis as a negative regulator of Pparg expression via altered RB-E2F1 signaling. Our findings reveal complex cell-state dependent roles of ZBTB9 in adipocytes, identifying a new molecule that regulates adipogenesis and adipocyte biology as both a positive and negative regulator of PPAR γ signaling depending on the cellular context, and thus may be important in the pathogenesis and treatment of obesity and T2D.

Comprehensive Analysis of Transcriptome and Metabolome Reveals Regulatory Mechanism of Intramuscular Fat Content in Beef Cattle

The intramuscular fat (IMF) content of beef determined the meat quality, and the market value of beef varies with different breeds. To provide some new approaches for improving meat quality and cattle breed improvement, 24-month-old Qinchuan cattle (Q, n = 6), Nanyang cattle (N, n = 6), and Japanese black cattle (J, n = 6) were selected. IMF content of the J group (16.92 ± 1.08%) is remarkably higher than that of indigenous Chinese cattle (Q, 13.38 ± 1.08%, and N, 12.35 ± 1.22%). Monounsaturated fatty acids and polyunsaturated fatty acids in the J group are higher than the Q and creatine, lysine, and glutamine are the three most abundant amino acids in beef, which contribute to the flavor formation. Similarly, IMF content-related genes were enriched in four vital KEGG pathways, including fatty acid metabolism, biosynthesis of unsaturated fatty acids, fatty acid elongation, and insulin resistance. Moreover, weighted genes coexpression network analysis (WGCNA) revealed that ITGB1 is the critical gene associated with the IMF content. This study compares transcriptome and metabolome of local and high-IMF cattle breeds, providing data for native cattle breeding and improvement of beef quality.

Functionally conserved PPARG exonic circRNAs enhance intramuscular fat deposition by regulating PPARG and HSL

Circular RNAs (circRNA) are a kind of endogenous biological macromolecules that play significant roles in many biological processes, including adipogenesis, a precisely orchestrated process that is mediated by a large number of factors. Among them, peroxisome proliferator-activated receptor gamma (PPARG), is undoubtedly the most important regulator of adipocyte development in all types of adipose tissue. The formation of intramuscular fat (IMF), is a key factor that influences the meat quality in livestock animals. PPARG has been demonstrated to show a positive correlation with IMF deposition although the regulatory mechanism involved is not known. This study demonstrates that PPARG mediates IMF deposition by producing multiple exonic circRNAs (circPPARGs). Three circPPARGs promote adipogenic differentiation and inhibit the proliferation of intramuscular preadipocytes and these effects are conserved across several species including buffaloes, cattle and mice. Notably, circPPARG1 interacts with PPARG protein to inhibit the transcription of hormone sensitive lipase (HSL) involved in lipolysis. In addition, the positive effects of circPPARG1 on IMF deposition were identified in mice in vivo. Thus, PPARG drives IMF deposition, not only through the common transcription factor pathway, but also by producing circRNAs. This study provides new insights into our understanding of the regulatory mechanisms of PPARG in IMF deposition.

Comparative Analysis of Porcine Adipose- and Wharton's Jelly-Derived Mesenchymal Stem Cells

Mesenchymal stem cells (MSCs) are promising candidates for tissue regeneration, cell therapy, and cultured meat research owing to their ability to differentiate into various lineages including adipocytes, chondrocytes, and osteocytes. As MSCs display different characteristics depending on the tissue of origin, the appropriate cells need to be selected according to the purpose of the research. However, little is known of the unique properties of MSCs in pigs. In this study, we compared two types of porcine mesenchymal stem cells (MSCs) isolated from the dorsal subcutaneous adipose tissue (adipose-derived stem cells (ADSCs)) and Wharton's jelly of the umbilical cord (Wharton's jelly-derived mesenchymal stem cells (WJ-MSCs)) of 1-day-old piglets. The ADSCs displayed a higher proliferation rate and more efficient differentiation potential into adipogenic and chondrogenic lineages than that of WJ-MSCs; conversely, WJ-MSCs showed superior differentiation capacity towards osteogenic lineages. In early passages, ADSCs displayed higher proliferation rates and mitochondrial energy metabolism (measured based on the oxygen consumption rate) compared with that of WJ-MSCs, although these distinctions diminished in late passages. This study broadens our understanding of porcine MSCs and provides insights into their potential applications in animal clinics and cultured meat science.

Impaired Plakophilin-2 in obesity breaks cell cycle dynamics to breed adipocyte senescence

Plakophilin-2 (PKP2) is a key component of desmosomes, which, when defective, is known to promote the fibro-fatty infiltration of heart muscle. Less attention has been given to its role in adipose tissue. We report here that levels of PKP2 steadily increase during fat cell differentiation, and are compromised if adipocytes are exposed to a pro-inflammatory milieu. Accordingly, expression of PKP2 in subcutaneous adipose tissue diminishes in patients with obesity, and normalizes upon mild-to-intense weight loss. We further show defective PKP2 in adipocytes to break cell cycle dynamics and yield premature senescence, a key rheostat for stress-induced adipose tissue dysfunction. Conversely, restoring PKP2 in inflamed adipocytes rewires E2F signaling towards the re-activation of cell cycle and decreased senescence. Our findings connect the expression of PKP2 in fat cells to the physiopathology of obesity, as well as uncover a previously unknown defect in cell cycle and adipocyte senescence due to impaired PKP2.

Circular RNA- and microRNA-Mediated Post-Transcriptional Regulation of Preadipocyte Differentiation in Adipogenesis: From Expression Profiling to Signaling Pathway

Adipogenesis is an indispensable cellular process that involves preadipocyte differentiation into mature adipocyte. Dysregulated adipogenesis contributes to obesity, diabetes, vascular conditions and cancer-associated cachexia. This review aims to elucidate the mechanistic details on how circular RNA (circRNA) and microRNA (miRNA) modulate post-transcriptional expression of targeted mRNA and the impacted downstream signaling and biochemical pathways in adipogenesis. Twelve adipocyte circRNA profiling and comparative datasets from seven species are analyzed using bioinformatics tools and interrogations of public circRNA databases. Twenty-three circRNAs are identified in the literature that are common to two or more of the adipose tissue datasets in different species; these are novel circRNAs that have not been reported in the literature in relation to adipogenesis. Four complete circRNA-miRNA-mediated modulatory pathways are constructed via integration of experimentally validated circRNA-miRNA-mRNA interactions and the downstream signaling and biochemical pathways involved in preadipocyte differentiation via the PPARγ/C/EBPα gateway. Despite the diverse mode of modulation, bioinformatics analysis shows that the circRNA-miRNA-mRNA interacting seed sequences are conserved across species, supporting mandatory regulatory functions in adipogenesis. Understanding the diverse modes of post-transcriptional regulation of adipogenesis may contribute to the development of novel diagnostic and therapeutic strategies for adipogenesis-associated diseases and in improving meat quality in the livestock industries.

Screening and functional validation of lipid metabolism-related lncRNA-46546 based on the transcriptome analysis of early embryonic muscle tissue in chicken

OBJECTIVE

The study was conducted to screen differentially expressed long noncoding RNA (lncRNA) in chickens by high-throughput sequencing and explore its mechanism of action on intramuscular fat deposition.

METHODS

Herein, Rose crown and Cbb broiler chicken embryo breast and leg muscle lncRNA and mRNA expression profiles were constructed by RNA sequencing. A total of 96 and 42 differentially expressed lncRNAs were obtained in Rose crown vs Cobb broiler chicken breast and leg muscle, respectively. lncRNA-ENSGALT00000046546, with high interspecific variability and a potential regulatory role in lipid metabolism, and its predicted downstream target gene 1-acylglycerol-3-phosphate-O-acyltransferase 2 (AGPAT2), were selected for further study on the preadipocytes.

RESULTS

lncRNA-46546 overexpression in chicken preadipocyte 2 cells significantly increased (p<0.01) the expression levels of AGPAT2 and its downstream genes diacylglycerol acyltransferase 1 and diacylglycerol acyltransferase 2 and those of the fat metabolism-related genes peroxisome proliferator-activated receptor γ, CCAAT/enhancer binding protein α, fatty acid synthase, sterol regulatory element-binding transcription factor 1, and fatty acid binding protein 4. The lipid droplet concentration was higher in the overexpression group than in the control cells, and the triglyceride content in cells and medium was also significantly increased (p<0.01).

CONCLUSION

This study preliminarily concludes that lncRNA-46546 may promote intramuscular fat deposition in chickens, laying a foundation for the study of lncRNAs in chicken early embryonic development and fat deposition.

Thermal stress and selection for growth affect myogenic satellite cell lipid accumulation and adipogenic gene expression through mechanistic target of rapamycin pathway

Satellite cells (SCs) are multipotential stem cells having the plasticity to convert to an adipogenic lineage in response to thermal stress during the period of peak mitotic activity (the first week after hatch in poultry). The mechanistic target of rapamycin (mTOR) pathway, which regulates cellular function and fate of SCs, is greatly altered by thermal stress in turkey pectoralis major muscle SCs. The objective of the present study was to determine the effects of thermal stress, selection for growth, and the role of the mTOR pathway on SC intracellular lipid accumulation and expression of adipogenic regulatory genes. These effects were analyzed using SCs isolated from the pectoralis major muscle of 1-wk-old modern faster-growing commercial turkey line (NC) selected for increased growth and breast muscle yield as compared with SCs of a historic slower-growing Randombred Control Line 2 (RBC2) turkey. Heat stress (43 °C) of SCs during proliferation increased intracellular lipid accumulation (P < 0.001), whereas cold stress (33 °C) showed an inhibitory effect (P < 0.001) in both lines. Knockdown of mTOR reduced the intracellular lipid accumulation (P < 0.001) and suppressed the expression of several adipogenic regulatory genes: peroxisome proliferator-activated receptor-γ (PPARγ; P < 0.001), CCAAT/enhancer-binding protein-β (C/EBPβ; P < 0.001), and neuropeptide-Y (NPY; P < 0.001) during both proliferation and differentiation. The NC line SCs showed fewer reductions in lipid accumulation compared with the RBC2 line independent of temperature. Both intracellular lipid accumulation (P < 0.001) and PPARγ expression (P < 0.001) were greater at 72 h of proliferation than at 48 h of differentiation in both the RBC2 and NC lines independent of temperature. Thus, hot and cold thermal stress affected intracellular lipid accumulation in the pectoralis major muscle SCs, in part, through the mTOR pathway in wea growth-dependent manner. Altered intracellular lipid accumulation could eventually affect intramuscular fat deposition, resulting in a long-lasting effect on the structure and protein to fat ratio of the poultry pectoralis major muscle.

Revisiting Epithelial Carcinogenesis

The origin of cancer remains one of the most important enigmas in modern biology. This paper presents a hypothesis for the origin of carcinomas in which cellular aging and inflammation enable the recovery of cellular plasticity, which may ultimately result in cancer. The hypothesis describes carcinogenesis as the result of the dedifferentiation undergone by epithelial cells in hyperplasia due to replicative senescence towards a mesenchymal cell state with potentially cancerous behavior. In support of this hypothesis, the molecular, cellular, and histopathological evidence was critically reviewed and reinterpreted when necessary to postulate a plausible generic series of mechanisms for the origin and progression of carcinomas. In addition, the implications of this theoretical framework for the current strategies of cancer treatment are discussed considering recent evidence of the molecular events underlying the epigenetic switches involved in the resistance of breast carcinomas. The hypothesis also proposes an epigenetic landscape for their progression and a potential mechanism for restraining the degree of dedifferentiation and malignant behavior. In addition, the manuscript revisits the gradual degeneration of the nonalcoholic fatty liver disease to propose an integrative generalized mechanistic explanation for the involution and carcinogenesis of tissues associated with aging. The presented hypothesis might serve to understand and structure new findings into a more encompassing view of the genesis of degenerative diseases and may inspire novel approaches for their study and therapy.

Regulation of Adipose Tissue Biology by Long-Chain Fatty Acids: Metabolic Effects and Molecular Mechanisms

Long-chain fatty acids (LCFA) modulate metabolic, oxidative, and inflammatory responses, and the physiological effects of LCFA are determined by chain length and the degree of saturation. Adipose tissues comprise multiple cell types, and play a significant role in energy storage and expenditure. Fatty acid uptake and oxidation are the pathways through which fatty acids participate in the regulation of energy homeostasis, and their dysregulation can lead to the development of obesity and chronic obesity-related disorders, including type 2 diabetes, cardiovascular diseases, and certain types of cancer. Numerous studies have reported that many aspects of adipose tissue biology are influenced by the number and position of double bonds in LCFA, and these effects are mediated by various signaling pathways, including those regulating adipocyte differentiation (adipogenesis), thermogenesis, and inflammation in adipose tissue. This review aims to describe the underlying molecular mechanisms by which different types of LCFA influence adipose tissue metabolism, and to further clarify their relevance to metabolic dysregulation associated with obesity. A better understanding of the effects of LCFA on adipose tissue metabolism may lead to improved nutraceutical strategies to address obesity and obesity-associated diseases.

The Effects of Maternal Intake of EPA and DHA Enriched Diet During Pregnancy and Lactation on Offspring’s Muscle Development and Energy Homeostasis

EPA and DHA are n-3 long-chain polyunsaturated fatty acids with a diversity of health benefits on offspring. The objective of this study was to test the in vivo effect of maternal ingestion of EPA and DHA on fetal and offspring muscle development and energy balance. Two groups of female C57BL/6 mice were fed EPA and DHA enriched diet (FA) and diet devoid of EPA and DHA (CON) respectively throughout the entire period of gestation and lactation. Embryos at E13 and offspring at age of D1 and D21 were selected for sample collection and processing. No change in birth number and body weight were observed between groups at D1 and D21. Transient increase in the expression levels of myogenesis regulating genes was detected at D1 (p < 0.05) in FA group. Most of the expression of muscle protein synthesis regulating genes were comparable (p > 0.05) between FA and CON groups at D1 and D21. The significant increase in MHC4, and IGF-1 was not linked to increased muscle mass. A persistent increase in ISR expression (p < 0.05) but not in GLUT-4 (p > 0.05) was detected in offspring. Up-regulation of adipogenesis regulating genes was accompanied by increasing intramuscular fat accumulation in the offspring of FA group. Considerable increase in transcripts of genes regulating lipid catabolism and thermogenesis in liver (p < 0.05) was noticed in FA group at D21; whereas, only the levels of carnitine palmitoyl transferase 1A (Cpt1α) and Enoyl-CoA Hydratase And 3-Hydroxyacyl CoA Dehydrogenase (Ehhadh) increased at D1. Similarly, genes regulating lipolysis were highly expressed at D21 in FA group. EPA and DHA treatment promoted BAT development and activity by increasing the expression of BAT signature genes (p < 0.05). Also, maternal intake of EPA and DHA enriched diet enhanced browning of sWAT. Taken together, maternal ingestion of EPA/DHA may be suggested as a therapeutic option to improve body composition and counteract childhood obesity- related metabolic disorders and confer lifelong positive metabolic impact on offspring.

Effect of expression of PPARG, DNM2L, RRAD, and LINGO1 on broiler chicken breast muscle satellite cell function

Disorders affecting the breast muscle of modern commercial broiler chickens have increased in recent years. Wooden Breast (WB) myopathy is characterized by a palpably hard breast muscle with increased fat deposition. WB is a metabolic disorder with lipid accumulation considered to be a primary causal factor. The adult myoblasts, satellite cells, are a partially differentiated stem cell population and primarily function in muscle growth and regeneration. The satellite cells also express adipogenic genes. The objective of this study was to determine the expression of the adipogenic genes PPARG, DNM2L, RRAD, and LINGO1 in commercial Ross 708 (708) and Randombred (RBch) satellite cells. RBch satellite cells are from commercial 1995 broilers before WB and 708 broilers are a modern commercial line. In general, expression of these genes was different between the 708 and RBch satellite cells during proliferation and differentiation. Expression of PPARG and RRAD were both significantly increased during both proliferation and differentiation in the 708 cells (P ≤ 0.05). Knocking down the expression of these genes with small interfering RNAs did not greatly affect either proliferation or differentiation. Lipid accumulation was affected by the knockdown of these genes with significant line effects from 48 h of proliferation through 72 h of differentiation. In general, 708 satellite cells had higher lipid levels. Knockdown treatment effect was specific to each gene. The results demonstrate that lipid biosynthesis has been affected in breast muscle satellite cells which may contribute to the increased lipid deposition in modern day commercial broiler chickens.

Time-resolved Phosphoproteome and Proteome Analysis Reveals Kinase Signalling on Master Transcription Factors During Myogenesis

Myogenesis is governed by signaling networks that are tightly regulated in a time-dependent manner. Although different protein kinases have been identified, knowledge of the global signaling networks and their downstream substrates during myogenesis remains incomplete. Here, we map the myogenic differentiation of C2C12 cells using phosphoproteomics and proteomics. From these data, we infer global kinase activity and predict the substrates that are involved in myogenesis. We found that multiple mitogen-activated protein kinases (MAPKs) mark the initial wave of signaling cascades. Further phosphoproteomic and proteomic profiling with MAPK1/3 and MAPK8/9 specific inhibitions unveil their shared and distinctive roles in myogenesis. Lastly, we identified and validated the transcription factor nuclear factor 1 X-type (NFIX) as a novel MAPK1/3 substrate and demonstrated the functional impact of NFIX phosphorylation on myogenesis. Altogether, these data characterize the dynamics, interactions, and downstream control of kinase signaling networks during myogenesis on a global scale.

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Phosphoproteomic and proteomic maps of myogenic differentiation of C2C12 cells

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Myogenic kinome activity and kinase-substrates prediction using machine learning

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MAPK1/3 and MAPK8/9 inhibition unveil shared and distinctive effects on myogenesis

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Validation of NFIX phosphorylation by MAPK1/3 and its impact on myogenesis

Transdifferentiation of Myoblasts Into Adipocytes by All-Trans-Retinoic Acid in Avian

Increased adipogenesis in muscle tissues is related to metabolic syndromes and muscle weakness in humans and improvement of meat quality in animal production. With growing evidence for pro-adipogenic functions of all-trans-retinoic acid (atRA), the current study investigated whether atRA can transdifferentiate myoblasts into adipocytes using a quail myogenic cell line (QM7) and avian primary myoblasts. atRA increased cytoplasmic lipid droplet accumulation and mRNA expression for adipogenic genes in these cells. An acute induction of Pparγ expression by atRA under cycloheximide treatment indicated a direct regulation of Pparγ by atRA. In addition, the induction of Pparγ expression was mediated by retinoic acid receptors . At high levels of Pparγ by atRA, BADGE, an antagonist of Pparγ, inhibited, and rosiglitazone, an agonist of Pparγ, further enhanced atRA-induced transdifferentiation. However, at very low levels of Pparγ in the absence of atRA treatment, rosiglitazone could not induce transdifferentiation of avian myoblasts. These data suggest that the induction of Pparγ expression by atRA is an essential molecular event in myoblasts for atRA-induced transdifferentiation into adipocytes. Based on our findings, atRA can be a new transdifferentiation factor of myoblasts to adipocytes, providing a potential nutrient to enhance marbling in poultry.

Transcriptome analysis of miRNAs during myoblasts adipogenic differentiation

Intramuscular fat content is closely related to meat quality traits and has high heritability. miRNAs are a class of small non-coding RNA, which are highly conserved in animals and play important regulatory roles in adipogenesis. Therefore, they can be used as molecular markers for meat quality traits. Herein, we used in vitro model of myoblasts adipogenic differentiation to screen differential miRNAs by RNA-seq. A total of 71 differentially miRNAs were filtered, including 31 up-regulated miRNAs and 40 down-regulated miRNAs. Since, we selected 18 miRNAs for RT-qPCR validation, including some miRNAs likely miR-146a-5p, miR-210-3p, miR-199a, miR-224, and miR-214-3p that play important regulatory roles in adipogenesis. In addition, functional enrichment analysis results revealed that members of miRNA target genes were enriched into insulin signaling pathway and MAPK signaling pathway, which are closely related to adipogenesis. Taken together, these data will contribute to further investigate the function of miRNAs in intramuscular fat deposition. These differentially miRNAs can be developed as biomarkers for animal breeding.

Perspectives on scaling production of adipose tissue for food applications

With rising global demand for food proteins and significant environmental impact associated with conventional animal agriculture, it is important to develop sustainable alternatives to supplement existing meat production. Since fat is an important contributor to meat flavor, recapitulating this component in meat alternatives such as plant based and cell cultured meats is important. Here, we discuss the topic of cell cultured or tissue engineered fat, growing adipocytes in vitro that could imbue meat alternatives with the complex flavor and aromas of animal meat. We outline potential paths for the large scale production of in vitro cultured fat, including adipogenic precursors during cell proliferation, methods to adipogenically differentiate cells at scale, as well as strategies for converting differentiated adipocytes into 3D cultured fat tissues. We showcase the maturation of knowledge and technology behind cell sourcing and scaled proliferation, while also highlighting that adipogenic differentiation and 3D adipose tissue formation at scale need further research. We also provide some potential solutions for achieving adipose cell differentiation and tissue formation at scale based on contemporary research and the state of the field.

Oxidative Stress and Respiratory Diseases in Preterm Newborns

Premature infants are exposed to increased generation of reactive oxygen species, and on the other hand, they have a deficient antioxidant defense system. Oxidative insult is a salient part of lung injury that begins as acute inflammatory injury in respiratory distress disease and then evolves into chronic and structural scarring leading to bronchopulmonary dysplasia. Oxidative stress is also involved in the pathogenesis of pulmonary hypertension in newborns through the modulation of the vascular tone and the response to pulmonary vasodilators, with consequent decrease in the density of the pulmonary vessels and thickening of the pulmonary arteriolar walls. Oxidative stress has been recognized as both a trigger and an endpoint for several events, including inflammation, hypoxia, hyperoxia, drugs, transfusions, and mechanical ventilation, with impairment of pulmonary function and prolonged lung damage. Redoxomics is the most fascinating new measure to address lung damage due to oxidative stress. The new challenge is to use omics data to discover a set of biomarkers useful in diagnosis, prognosis, and formulating optimal and individualized neonatal care. The aim of this review was to examine the most recent evidence on the relationship between oxidative stress and lung diseases in preterm newborns. What is currently known regarding oxidative stress-related lung injury pathogenesis and the available preventive and therapeutic strategies are also discussed.

Familial partial lipodystrophy syndromes

Lipodystrophies are a heterogeneous group of rare conditions characterised by the loss of adipose tissue. The most common forms are the familial partial lipodystrophy (FPLD) syndromes, which include a set of disorders, usually autosomal dominant, due to different pathogenetic mechanisms leading to improper fat distribution (loss of fat in the limbs and gluteal region and variable regional fat accumulation). Affected patients are prone to suffering serious morbidity via the development of metabolic complications associated to insulin resistance and an inability to properly store lipids. Although no well-defined diagnostic criteria have been established for lipodystrophy, there are certain clues related to medical history, physical examination and body composition evaluation that may suggest FPLD prior to confirmatory genetic analysis. Its treatment must be fundamentally oriented towards the control of the metabolic abnormalities. In this sense, metreleptin therapy, the newer classes of hypoglycaemic agents and other investigational drugs are showing promising results. This review aims to summarise the current knowledge of FPLD syndromes and to describe their clinical and molecular picture, diagnostic approaches and recent treatment modalities.

DHA but not EPA induces the trans-differentiation of C2C12 cells into white-like adipocytes phenotype

Muscle derived stem cells (MDSCs) and myoblast play an important role in myotube regeneration when muscle tissue is injured. However, these cells can be induced to differentiate into adipocytes once exposed to PPARγ activator like EPA and DHA that are highly suggested during pregnancy. The objective of this study aims at determining the identity of trans-differentiated cells by exploring the effect of EPA and DHA on C2C12 undergoing differentiation into brown and white adipocytes. DHA but not EPA committed C2C12 cells reprograming into white like adipocyte phenotype. Also, DHA promoted the expression of lipolysis regulating genes but had no effect on genes regulating β-oxidation referring to its implication in lipid re-esterification. Furthermore, DHA impaired C2C12 cells differentiation into brown adipocytes through reducing the thermogenic capacity and mitochondrial biogenesis of derived cells independent of UCP1. Accordingly, DHA treated groups showed an increased accumulation of lipid droplets and suppressed mitochondrial maximal respiration and spare respiratory capacity. EPA, on the other hand, reduced myogenesis regulating genes, but no significant differences were observed in the expression of adipogenesis key genes. Likewise, EPA suppressed the expression of WAT signature genes indicating that EPA and DHA have an independent role on white adipogensis. Unlike DHA treatment, EPA supplementation had no effect on the differential of C2C12 cells into brown adipocytes. In conclusion, DHA is a potent adipogenic and lipogenic factor that can change the metabolic profile of muscle cells by increasing myocellular fat.

Effect of ciglitazone on adipogenic transdifferentiation of bovine skeletal muscle satellite cells

Ciglitazone is a member of the thiazolidinedione family, and specifically binds to peroxisome proliferator-activated receptor-γ (PPARγ), thereby promoting adipocyte differentiation. We hypothesized that ciglitazone as a PPARγ ligand in the absence of an adipocyte differentiation cocktail would increase adiponectin and adipogenic gene expression in bovine satellite cells (BSC). Muscle-derived BSCs were isolated from six, 18-month-old Yanbian Yellow Cattle. The BSC were cultured for 96 h in differentiation medium containing 5 µM ciglitazone (CL), 10 µM ciglitazone (CM), or 20 µM ciglitazone (CH). Control (CON) BSC were cultured only in a differentiation medium (containing 2% horse serum). The presence of myogenin, desmin, and paired box7 (Pax7) proteins was confirmed in the BSC by immunofluorescence staining. The CL, CM, and CH treatments produced higher concentrations of triacylglycerol and lipid droplet accumulation in myotubes than those of the CON treatment. Ciglitazone treatments significantly increased the relative expression of PPARγ, CCAAT/enhancer-binding protein alpha (C/EBPα), C/EBPβ, fatty acid synthase, stearoyl-CoA desaturase, and perilipin 2. Ciglitazone treatments increased gene expression of Pax3 and Pax7 and decreased expression of myogenic differentiation-1, myogenin, myogenic regulatory factor-5, and myogenin-4 (p < 0.01). Adiponectin concentration caused by ciglitazone treatments was significantly greater than CON (p < 0.01). RNA sequencing showed that 281 differentially expressed genes (DEGs) were found in the treatments of ciglitazone. DEGs gene ontology (GO) analysis showed that the top 10 GO enrichment significantly changed the biological processes such as protein trimerization, negative regulation of cell proliferation, adipocytes differentiation, and cellular response to external stimulus. Kyoto Encyclopedia of Genes and Genomes pathway analysis showed that DEGs were involved in the p53 signaling pathway, PPAR signaling pathway, biosynthesis of amino acids, tumor necrosis factor signaling pathway, non-alcoholic fatty liver disease, PI3K-Akt signaling pathway, and Wnt signaling pathway. These results indicate that ciglitazone acts as PPARγ agonist, effectively increases the adiponectin concentration and adipogenic gene expression, and stimulates the conversion of BSC to adipocyte-like cells in the absence of adipocyte differentiation cocktail.

Targeted overexpression of PPARγ in skeletal muscle by random insertion and CRISPR/Cas9 transgenic pig cloning enhances oxidative fiber formation and intramuscular fat deposition

Peroxisome proliferator-activated receptor gamma (PPARγ) is a master regulator of adipogenesis and lipogenesis. To understand its roles in fiber formation and fat deposition in skeletal muscle, we successfully generated muscle-specific overexpression of PPARγ in two pig models by random insertion and CRISPR/Cas9 transgenic cloning procedures. The content of intramuscular fat was significantly increased in PPARγ pigs while had no changes on lean meat ratio. PPARγ could promote adipocyte differentiation by activating adipocyte differentiating regulators such as FABP4 and CCAAT/enhancer-binding protein (C/EBP), along with enhanced expression of LPL, FABP4, and PLIN1 to proceed fat deposition. Proteomics analyses demonstrated that oxidative metabolism of fatty acids and respiratory chain were activated in PPARγ pigs, thus, gathered more Ca²⁺ in PPARγ pigs. Raising of Ca²⁺ could result in increased phosphorylation of CAMKII and p38 MAPK in PPARγ pigs, which can stimulate MEF2 and PGC1α to affect fiber type and oxidative capacity. These results support that skeletal muscle-specific overexpression of PPARγ can promote oxidative fiber formation and intramuscular fat deposition in pigs.

Transcriptional networks controlling stromal cell differentiation

Stromal progenitors are found in many different tissues, where they play an important role in the maintenance of tissue homeostasis owing to their ability to differentiate into parenchymal cells. These progenitor cells are differentially pre-programmed by their tissue microenvironment but, when cultured and stimulated in vitro, these cells - commonly referred to as mesenchymal stromal cells (MSCs) - exhibit a marked plasticity to differentiate into many different cell lineages. Loss-of-function studies in vitro and in vivo have uncovered the involvement of specific signalling pathways and key transcriptional regulators that work in a sequential and coordinated fashion to activate lineage-selective gene programmes. Recent advances in omics and single-cell technologies have made it possible to obtain system-wide insights into the gene regulatory networks that drive lineage determination and cell differentiation. These insights have important implications for the understanding of cell differentiation, the contribution of stromal cells to human disease and for the development of cell-based therapeutic applications.

Effect of Temperature and Selection for Growth on Intracellular Lipid Accumulation and Adipogenic Gene Expression in Turkey Pectoralis Major Muscle Satellite Cells

As multipotential stem cells, satellite cells (SCs) have the potential to express adipogenic genes resulting in lipid synthesis with thermal stress. The present study determined the effect of temperature on intracellular lipid synthesis and adipogenic gene expression in SCs isolated from the pectoralis major (p. major) muscle of 7-day-old fast-growing modern commercial (NC) turkeys compared to SCs from unselected slower-growing turkeys [Randombred Control Line 2 (RBC2)]. Since proliferating and differentiating SCs have different responses to thermal stress, three incubation strategies were used: (1) SCs proliferated at the control temperature of 38°C and differentiated at 43° or 33°C; (2) SCs proliferated at 43° or 33°C and differentiated at 38°C; or (3) SCs both proliferated and differentiated at 43°, 38°, or 33°C. During proliferation, lipid accumulation increased at 43°C and decreased at 33°C with the NC line showing greater variation than the RBC2 line. During proliferation at 43°C, peroxisome proliferator-activated receptor-γ (PPARγ) and neuropeptide-Y (NPY) expression was reduced to a greater extent in the NC line than the RBC2 line. At 33°C, expression of PPARγ, NPY, and CCAAT/enhancer-binding protein-β (C/EBPβ) was upregulated, but only in the RBC2 line. During differentiation, both lines showed greater changes in lipid accumulation and in C/EBPβ and NPY expression if the thermal challenge was initiated during proliferation. These data suggest that adipogenic gene expression is more responsive to thermal challenge in proliferating SCs than in differentiating SCs, and that growth-selection has increased temperature sensitivity of SCs, which may significantly affect breast muscle structure and composition.

Alpha-tocopherol acetate and alpha lipoic acid may mitigate the development of wooden breast myopathy in broilers at an early age

1. The objective of this study was to identify the effects of the antioxidant alpha-tocopherol acetate (ATA) and alpha lipoic acid (ALA) which have anti-inflammatory effects on developmental onset, severity and the progression of wooden breast (WB) based on Pectoralis major (P. major) muscle morphology and expression of genes associated with WB during the first three weeks post-hatch.2. A total of 160 newly hatched Ross 708 broiler chicks were randomly assigned in a replicated trial to either a control group or three dietary treatments (ATA 160 mg/kg feed, ALA 500 mg/kg feed or in combination).3. Microscopic changes associated with WB began at one week of age in all groups. The ATA acetate and ALA fed in combination decreased WB severity at two weeks of age (P = 0.05) and ATA alone or in combination reduced severity at three weeks of age compared to the control group (P = 0.05). Expression of myogenic determination factor 1 and peroxisome proliferator-activated receptor gamma was reduced in all dietary treatments compared to the control at three weeks of age (P ≤ 0.05), which suggested reduced muscle degeneration and lipid deposition.4. ATA and ALA fed both independently and in combination had a positive effect on mitigating WB severity microscopically as early as two weeks of age.

Role of the Endocannabinoid System in the Adipose Tissue with Focus on Energy Metabolism

The endocannabinoid system is involved in a wide range of processes including the control of energy acquisition and expenditure. Endocannabinoids and their receptors are present in the central nervous system but also in peripheral tissues, notably the adipose tissues. The endocannabinoid system interacts with two main hormones regulating appetite, namely leptin and ghrelin. The inhibitory effect of the cannabinoid receptor 1 (CB₁) antagonist rimonabant on fat mass suggested that the endocannabinoid system can also have a peripheral action in addition to its effect on appetite reduction. Thus, several investigations have focused on the peripheral role of the endocannabinoid system in the regulation of metabolism. The white adipose tissue stores energy as triglycerides while the brown adipose tissue helps to dissipate energy as heat. The endocannabinoid system regulates several functions of the adipose tissues to favor energy accumulation. In this review we will describe the presence of the endocannabinoid system in the adipose tissue. We will survey the role of the endocannabinoid system in the regulation of white and brown adipose tissue metabolism and how the eCB system participates in obesity and metabolic diseases.

MYOD1 inhibits avian adipocyte differentiation via miRNA-206/KLF4 axis

BACKGROUND

A considerable number of muscle development-related genes were differentially expressed in the early stage of avian adipocyte differentiation. However, the functions of them in adipocyte differentiation remain largely known. In this study, the myoblast determination protein 1 (MYOD1) was selected as a representative of muscle development. We investigated its expression, function, and regulation in avian adipocyte differentiation.

RESULTS

The expression of MYOD1 decreased significantly in the early stage of avian adipocyte differentiation. CRISPR/Cas9-mediated deletion of MYOD1 induced adipocyte differentiation, whereas over-expression of MYOD1 inhibited adipogenesis. The mRNA-seq data showed that MYOD1 could perturb the lipid biosynthetic process during differentiation. Our results showed that MYOD1 directly up-regulates the miR-206 expression by binding the upstream 1200 bp region of miR-206. Then, over-expression of miR-206 can inhibit the adipogenesis. Furthermore, MYOD1 affected the expression of endogenous miR-206 and its target gene Kruppel-like factor 4 (KLF4), which is an important activator of adipogenesis. Accordingly, the inhibition of miR-206 or over-expression of KLF4 could counteract the inhibitory effect of MYOD1 on adipocyte differentiation.

CONCLUSIONS

Our results establish that MYOD1 inhibits adipocyte differentiation by up-regulating miR-206 to suppress the KLF4 expression. These findings identify a novel function of MYOD1 in adipocyte differentiation, suggesting a potential role in body-fat distribution regulation.

The Role of Lipid Sensing Nuclear Receptors (PPARs and LXR) and Metabolic Lipases in Obesity, Diabetes and NAFLD

Obesity and type 2 diabetes mellitus (T2DM) are metabolic disorders characterized by metabolic inflexibility with multiple pathological organ manifestations, including non-alcoholic fatty liver disease (NAFLD). Nuclear receptors are ligand-dependent transcription factors with a multifaceted role in controlling many metabolic activities, such as regulation of genes involved in lipid and glucose metabolism and modulation of inflammatory genes. The activity of nuclear receptors is key in maintaining metabolic flexibility. Their activity depends on the availability of endogenous ligands, like fatty acids or oxysterols, and their derivatives produced by the catabolic action of metabolic lipases, most of which are under the control of nuclear receptors. For example, adipose triglyceride lipase (ATGL) is activated by peroxisome proliferator-activated receptor γ (PPARγ) and conversely releases fatty acids as ligands for PPARα, therefore, demonstrating the interdependency of nuclear receptors and lipases. The diverse biological functions and importance of nuclear receptors in metabolic syndrome and NAFLD has led to substantial effort to target them therapeutically. This review summarizes recent findings on the roles of lipases and selected nuclear receptors, PPARs, and liver X receptor (LXR) in obesity, diabetes, and NAFLD.

Hexane Extract of Chloranthus japonicus Increases Adipocyte Differentiation by Acting on Wnt/β-Catenin Signaling Pathway

Chloranthus japonicus has been heavily investigated for the treatment of various diseases. This paper attempts to show that Chloranthus japonicus can modulate adipocyte differentiation of preadipocytes. To establish this, we investigated the effects of Chloranthus japonicus extract in peroxisome proliferator-activated receptor γ (PPARγ) expression, adipogenesis, and the underlying molecular mechanisms in C3H10T1/2 and 3T3-L1 cells. Our data showed that Chloranthus japonicus methanol extract increased lipid accumulation and promoted adipocyte differentiation. Further studies on the fractionation with various solvents led to the identification of Chloranthus japonicus hexane extract (CJHE) as the most potent inducer of adipocyte differentiation. CJHE consistently increased lipid accumulation and adipocyte marker expression including Pparγ and it acted during the early stages of adipocyte differentiation. Mechanistic studies revealed that CJHE and a Wnt inhibitor similarly stimulated adipogenesis and were active in Wnt-selective reporter assays. The effects of CJHE were inhibited by Wnt3a protein treatment and were significantly blunted in β-catenin-silenced cells, further suggesting that CJHE acted on Wnt pathways to promote adipogenesis. We also showed that Chloranthus japonicus extracts generated from different plant parts similarly promoted adipocyte differentiation. These results identified Chloranthus japonicus as a pro-adipogenic natural product and suggest its potential use in metabolic syndrome.

Comprehensive evaluation of the metabolic effects of porcine CRTC3 overexpression on subcutaneous adipocytes with metabolomic and transcriptomic analyses

BACKGROUND

Meat quality is largely driven by fat deposition, which is regulated by several genes and signaling pathways. The cyclic adenosine monophosphate (cAMP) -regulated transcriptional coactivator 3 (CRTC3) is a coactivator of cAMP response element binding protein (CREB) that mediates the function of protein kinase A (PKA) signaling pathway and is involved in various biological processes including lipid and energy metabolism. However, the effects of CRTC3 on the metabolome and transcriptome of porcine subcutaneous adipocytes have not been studied yet. Here, we tested whether porcine CRTC3 expression would be related to fat deposition in Heigai pigs (a local fatty breed in China) and Duroc×Landrace×Yorkshire (DLY, a lean breed) pigs in vivo. The effects of adenovirus-induced CRTC3 overexpression on the metabolomic and transcriptomic profiles of subcutaneous adipocytes were also determined in vitro by performing mass spectrometry-based metabolomics combined with RNA sequencing (RNA-seq).

RESULTS

Porcine CRTC3 expression is associated with fat deposition in vivo. In addition, CRTC3 overexpression increased lipid accumulation and the expression of mature adipocyte-related genes in cultured porcine subcutaneous adipocytes. According to the metabolomic analysis, CRTC3 overexpression induced significant changes in adipocyte lipid, amino acid and nucleotide metabolites in vitro. The RNA-seq analysis suggested that CRTC3 overexpression alters the expression of genes and pathways involved in adipogenesis, fatty acid metabolism and glycerophospholipid metabolism in vitro.

CONCLUSIONS

We identified significant alterations in the metabolite composition and the expression of genes and pathways involved in lipid metabolism in CRTC3-overexpressing adipocytes. Our results suggest that CRTC3 might play an important regulatory role in lipid metabolism and thus affects lipid accumulation in porcine subcutaneous adipocytes.

Adipocyte-specific deletion of zinc finger protein 407 results in lipodystrophy and insulin resistance in mice

PPARγ deficiency in humans and model organisms impairs the transcriptional control of adipogenesis and mature adipocyte function resulting in lipodystrophy and insulin resistance. Zinc finger protein 407 (ZFP407) positively regulates PPARγ target gene expression and insulin-stimulated glucose uptake in cultured adipocytes. The in vivo physiological role of ZFP407 in mature adipocytes, however, remains to be elucidated. Here we generated adipocyte-specific ZFP407 knockout (AZKO) mice and discovered a partial lipodystrophic phenotype with reduced fat mass, hypertrophic adipocytes in inguinal and brown adipose tissue, and reduced adipogenic gene expression. The lipodystrophy was further exacerbated in AZKO mice fed a high-fat diet. Glucose and insulin tolerance tests revealed decreased insulin sensitivity in AZKO mice compared to control littermates. Cell-based assays demonstrated that ZFP407 is also required for adipogenesis, which may also contribute to the lipodystrophic phenotype. These results demonstrate an essential in vivo role of ZFP407 in brown and white adipose tissue formation and organismal insulin sensitivity.

Physicochemical and histochemical characteristics of bovine longissimus lumborum muscle defected as muscular steatosis (massive adipocyte infiltration)

To understand muscular steatosis observed in beef carcasses, physicochemical and histochemical characteristics were compared between abnormal (massive fatty replaced) and normal regions of beef striploin. Fat content in the abnormal region (48.02%) was approximately twice than that in the normal region (22.01%). However, fatty acids did not show significant (P > 0.05) differences in their compositions between the two regions. Tenderness was significantly (P < 0.05) higher in the abnormal region. However, other meat quality traits were not significantly (P > 0.05) different between the two regions. Massive accumulation of adipocytes was accompanied by muscle fiber atrophy regardless of muscle fiber types. Without a change in total muscle fiber density, oxidative fiber composition was significantly increased, whereas glycolytic fiber composition was decreased (P < 0.05). These findings suggest that adipogenic transdifferentiation and muscle fiber type switching can occur within the muscle due to muscular steatosis.

Using the novel pelvic organ prolapse histologic quantification system to identify phenotypes in uterosacral ligaments in women with pelvic organ prolapse

BACKGROUND

Pelvic organ prolapse is common, but the underlying etiologies are poorly understood, which limits our current prevention and treatment options.

OBJECTIVE

Our primary objective was to compare the uterosacral ligament histologic features in women with and without prolapse using the novel pelvic organ prolapse histologic quantification system. Our secondary aim was to determine whether composite histologic findings in uterosacral ligaments are associated with prolapse risk factors.

STUDY DESIGN

This was a prospective cohort study in which paracervical uterosacral ligament biopsies were performed at the time of hysterectomy for primary prolapse or other benign gynecologic indications and processed for histologic evaluation. The pelvic organ prolapse quantification system was used to determine the prolapse stage. In this study, 9 prominent histologic features were semiquantitatively scored using the pelvic organ prolapse histologic quantification system in a blinded fashion and compared between prolapse and control groups. Unbiased principal component analysis of these scores was independently performed to identify potential relationships between histologic measures and prolapse risk factors.

RESULTS

The histologic scores of 81 prolapse and 33 control ligaments were analyzed. Compared with the control group, women in the prolapse group were significantly older and more likely to be in the menopausal phase. There was no difference in the number of vaginal deliveries, body mass index, hormone use, or smoking status between the groups. To control for baseline differences, patients were also stratified by age over 40 years and menopausal status. Compared with the control group, the prolapse ligaments in the premenopausal group had significantly more loss of smooth muscle fibers within the fascicles (P<.001), increased inflammatory infiltrates of neutrophils within the tissue and perineural inflammatory cells (P<.01 and P=.04, respectively), and reduced neointimal hyperplasia (P=.02). Prolapse ligaments in the postmenopausal group exhibited elevated adipose content compared with that of the control group (P=.05). Amount of fibrillar collagen, total nonvascular smooth muscle, and muscle fiber vesicles of prolapse ligaments did not differ in either the premenopausal or postmenopausal group compared with that of the control group. Unbiased principal component analysis of the histologic scores separated the prolapse ligaments into 3 phenotypes: (1) increased adipose accumulation, (2) increased inflammation, and (3) abnormal vasculature, with variable overlap with controls. Posthoc analysis of these subgroups demonstrated a positive correlation between increasing number of vaginal deliveries and body mass index with increasing adipose content in the adipocyte accumulation and inflammatory phenotype and increasing neointimal hyperplasia in the vascular phenotype. However, only the relationship between vaginal delivery and adipocytes was significant in the adipose phenotype (R²=0.13; P=.04).

CONCLUSION

Histologic phenotypes exist in pelvic support ligaments that can be distinguished using the pelvic organ prolapse histologic quantification system and principle component analysis. Vaginal delivery is associated with aberrant adipose accumulation in uterosacral ligaments. Our findings support a multifactorial etiology for pelvic organ prolapse contributing to altered smooth muscle, vasculature, and connective tissue content in crucial pelvic support structures. To confirm these associations and evaluate the biomechanical properties of histologic phenotypes of prolapse, larger studies are warranted. Closing this gap in knowledge will help optimize personalized medicine and help identify targets for prevention and treatment of this complex condition.

Effect of vitamin E and alpha lipoic acid on intestinal development associated with wooden breast myopathy in broilers

Intestinal development is closely associated with inflammatory wooden breast (WB) myopathy. Vitamin E (VE) and alpha lipoic acid (ALA) with antioxidant and anti-inflammatory effects were used independently and in combination to evaluate their effects on intestinal developmental changes in ileal morphology and expression of genes related with gut nutrient transport, structure, and inflammation in broilers during the first 3 wk posthatch. A total of 160 newly hatched Ross 708 broiler chicks were randomly assigned into a control and 3 dietary treatments with 10 replicates of 4 birds each. Supplementation of VE (160 mg/kg) and ALA (500 mg/kg) independently and in combination were fed during the first 3 wk. At 1, 2, and 3 wk of age, one chick from each pen was harvested. Plasma VE concentration and ileal morphology were determined. Gene expression was measured by real-time quantitative PCR. Broilers in VE and combination of ALA and VE group had higher plasma VE concentration than the control and ALA group at 1, 2, and 3 wk of age (P < 0.01). All dietary treatments increased ileal villus height at 1 wk of age (P < 0.01) and decreased intraepithelial lymphocytes at 3 wk of age compared to the control (P ≤ 0.05). Combination of VE and ALA increased collagen type IV alpha 1 chain expression (P ≤ 0.05) and improved basement membrane structure indicating increased gut basement membrane integrity at 2 and 3 wk of age compared to the control. Expression of lipopolysaccharide-induced tumor necrosis factor-alpha factor associated with inflammation was decreased in all dietary treatments at 3 wk of age compared to the control (P < 0.01). Ileal morphology and gene expression were closely correlated with breast muscle morphology and gene expression. These results suggest that VE and ALA especially when they were combined in the diet had positive effects on mitigating intestinal inflammation and improving nutrient transport beginning at 1 wk of age, which is likely critical in reducing the severity of WB.

Factors inducing transdifferentiation of myoblasts into adipocytes

Fat infiltration in skeletal muscle is observed in several myopathies, is associated with muscular dysfunction, and is strongly correlated with insulin resistance, diabetes, obesity, and aging. In animal production, skeletal muscle fat (also known as intermuscular and intramuscular fat) is positively related to meat quality including tenderness, flavor, and juiciness. Thus, understanding the cell origin and regulation mechanism of skeletal muscle fat infiltration is important for developing therapies against human myopathies as well as for improving meat quality. Notably, age, sarcopenia, oxidative stress, injury, and regeneration can activate adipogenic differentiation potential in myoblasts and affect fat accumulation in skeletal muscle. In addition, several transcriptional and nutritional factors can directly induce transdifferentiation of myoblasts into adipocytes. In this review, we focused on the recent progress in understanding the muscle-to-adipocyte differentiation and summarized and discussed the genetic, nutritional, and physiological factors that can induce transdifferentiation of myoblasts into adipocytes. Moreover, the regulatory roles and mechanisms of these factors during the transdifferentiation process were also discussed.

Myostatin site-directed mutation and simultaneous PPARγ site-directed knockin in bovine genome

Most studies on the acquisition of advantageous traits in transgenic animals only focus on monogenic traits. In practical applications, transgenic animals need to possess multiple advantages. Therefore, multiple genes need to be edited simultaneously. CRISPR/Cas9 technology has been widely used in many research fields. However, few studies on endogenous gene mutation and simultaneous exogenous gene insertion performed via CRISPR/Cas9 technology are available. In this study, the CRISPR/Cas9 technology was used to achieve myostatin (MSTN) point mutation and simultaneous peroxisome proliferator-activated receptor-γ (PPARγ) site-directed knockin in the bovine genome. The feasibility of this gene editing strategy was verified on a myoblast model. The same gene editing strategy was used to construct a mutant myoblast model with MSTN mutation and simultaneous PPARγ knockin. Quantitative reverse-transcription polymerase chain reaction, immunofluorescence staining, and western blot analyses were used to detect the expression levels of MSTN and PPARγ in the mutant myoblast. Results showed that this strategy can inhibit the expression of MSTN and promote the expression of PPARγ. The cell counting kit-8 cell proliferation analysis, 5-ethynyl-2'-deoxyuridine cell proliferation analysis, myotube fusion index statistics, oil red O staining, and triglyceride content detection revealed that the proliferation, myogenic differentiation, and adipogenic transdifferentiation abilities of the mutant myoblasts were higher than those of the wild myoblasts. Finally, transgenic bovine embryos were obtained via somatic cell nuclear transfer. This study provides a breeding material and technical strategy to breed high-quality bovine and a gene editing method to realize the mutation of endogenous genes and simultaneous insertion of exogenous genes in genomes.

Preventive effect of small-leaved Kuding tea (Ligustrum robustum) on high-diet-induced obesity in C57BL/6J mice

Small-leaved Kuding tea (SLKDT; Ligustrum robustum) is a traditional Chinese tea. We systematically investigated the effect of SLKDT extract on obesity. SLKDT-controlled weight gain in mice fed a high-fat diet. Tissue specimen results showed that the SLKDT extract alleviated liver damage and fat accumulation. Meanwhile, SLKDT extract improved dyslipidemia by decreasing total cholesterol, triglycerides, and low-density lipoprotein cholesterol levels and increasing high-density lipoprotein cholesterol levels. Furthermore, SLKDT extract reduced alanine aminotransferase, alkaline phosphatase, and aspartate transaminase levels in the serum and liver tissues; decreased inflammatory cytokines, including interleukin (IL)-1β, tumor necrosis factor-α, interferon-γ, and IL-6; and increased the anti-inflammatory cytokines, IL-4 and IL-10. The quantitative PCR results showed that SLKDT extract upregulated the mRNA expressions of peroxisome proliferator-activated receptor (PPAR)-α, lipoprotein lipase, carnitine palmitoyltransferase 1, and cholesterol 7 alpha hydroxylase and downregulated PPAR-γ and CCAAT/enhancer-binding protein-alpha mRNA expressions in the obese mouse livers to reduce adipocyte differentiation and fat accumulation, promote fat oxidation, and improve dyslipidemia, thereby inhibiting the immune response and alleviating liver injury. SLKDT shows a potential for preventing obesity and regulating obesity-related syndrome, so it is possible to be further developed as a novel treatment for fighting obesity.

Adipogenesis: A Complex Interplay of Multiple Molecular Determinants and Pathways

The formation of adipocytes during embryogenesis has been largely understudied. However, preadipocytes appear to originate from multipotent mesenchymal stromal/stem cells which migrate from the mesoderm to their anatomical localization. Most studies on adipocyte formation (adipogenesis) have used preadipocytes derived from adult stem/stromal cells. Adipogenesis consists of two phases, namely commitment and terminal differentiation. This review discusses the role of signalling pathways, epigenetic modifiers, and transcription factors in preadipocyte commitment and differentiation into mature adipocytes, as well as limitations in our understanding of these processes. To date, a limited number of transcription factors, genes and signalling pathways have been described to regulate preadipocyte commitment. One reason could be that most studies on adipogenesis have used preadipocytes already committed to the adipogenic lineage, which are therefore not suitable for studying preadipocyte commitment. Conversely, over a dozen molecular players including transcription factors, genes, signalling pathways, epigenetic regulators, and microRNAs have been described to be involved in the differentiation of preadipocytes to adipocytes; however, only peroxisome proliferator-activated receptor gamma has proven to be clinically relevant. A detailed understanding of how the molecular players underpinning adipogenesis relate to adipose tissue function could provide new therapeutic approaches for addressing obesity without compromising adipose tissue function.

Concurrent EPA and DHA Supplementation Impairs Brown Adipogenesis of C2C12 Cells

Maternal dietary supplementation of n−3 polyunsaturated fatty acids (n−3 PUFAs), especially eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA), is considered to play positive roles in fetal neuro system development. However, maternal n−3 PUFAs may induce molecular reprogramming of uncommitted fetal myoblasts into adipocyte phenotype, in turn affecting lipid metabolism and energy expenditure of the offspring. The objective of this in vitro study was to investigate the combined effects of EPA and DHA on C2C12 cells undergoing brown adipogenic differentiation. C2C12 myoblasts were cultured to confluency and then treated with brown adipogenic differentiation medium with and without 50 μM EPA and 50 μM DHA. After differentiation, mRNA and protein samples were collected. Gene expression and protein levels were analyzed by real-time PCR and western blot. General Proteomics analysis was conducted using mass spectrometric evaluation. The effect of EPA and DHA on cellular oxygen consumption was measured using a Seahorse XFP Analyzer. Cells treated with n−3 PUFAs had significantly less (P < 0.05) expression of the brown adipocyte marker genes PGC1α, DIO2, and UCP3. Expression of mitochondrial biogenesis-related genes TFAM, PGC1α, and PGC1β were significantly downregulated (P < 0.05) by n−3 PUFAs treatment. Expression of mitochondrial electron transportation chain (ETC)-regulated genes were significantly inhibited (P < 0.05) by n−3 PUFAs, including ATP5J2, COX7a1, and COX8b. Mass spectrometric and western blot evaluation showed protein levels of enzymes which regulate the ETC and Krebs cycle, including ATP synthase α and β (F1F0 complex), citrate synthase, succinate CO-A ligase, succinate dehydrogenase (complex II), ubiquinol-cytochrome c reductase complex subunits (complex III), aconitate hydratase, cytochrome c, and pyruvate carboxylase were all decreased in the n−3 PUFAs group (P < 0.05). Genomic and proteomic changes were accompanied by mitochondrial dysfunction, represented by significantly reduced oxygen consumption rate, ATP production, and proton leak (P < 0.05). This study suggested that EPA and DHA may alter the BAT fate of myoblasts by inhibiting mitochondrial biogenesis and activity and induce white-like adipogenesis, shifting the metabolism from lipid oxidation to synthesis.

Histone deacetylase 9 promoter hypomethylation associated with adipocyte dysfunction is a statin-related metabolic effect

Background

Adipogenesis, the process whereby preadipocytes differentiate into mature adipocytes, is crucial for maintaining metabolic homeostasis. Cholesterol-lowering statins increase type 2 diabetes (T2D) risk possibly by affecting adipogenesis and insulin resistance but the (epi)genetic mechanisms involved are unknown. Here, we characterised the effects of statin treatment on adipocyte differentiation using in vitro human preadipocyte cell model to identify putative effective genes.

Results

Statin treatment during adipocyte differentiation caused a reduction in key genes involved in adipogenesis, such as ADIPOQ, GLUT4 and ABCG1. Using Illumina’s Infinium ‘850K’ Methylation EPIC array, we found a significant hypomethylation of cg14566882, located in the promoter of the histone deacetylase 9 (HDAC9) gene, in response to two types of statins (atorvastatin and mevastatin), which correlates with an increased HDAC9 mRNA expression. We confirmed that HDAC9 is a transcriptional repressor of the cholesterol efflux ABCG1 gene expression, which is epigenetically modified in obesity and prediabetic states. Thus, we assessed the putative impact of ABCG1 knockdown in mimicking the effect of statin in adipogenesis. ABCG1 KD reduced the expression of key genes involved in adipocyte differentiation and decreased insulin signalling and glucose uptake. In human blood cells from two cohorts, ABCG1 expression was impaired in response to statins, confirming that ABCG1 is targeted in vivo by these drugs.

Conclusions

We identified an epigenetic link between adipogenesis and adipose tissue insulin resistance in the context of T2D risk associated with statin use, which has important implications as HDAC9 and ABCG1 are considered potential therapeutic targets for obesity and metabolic diseases.

Cerasus humilis Cherry Polyphenol Reduces High-Fat Diet-Induced Obesity in C57BL/6 Mice by Mitigating Fat Deposition, Inflammation, and Oxidation

This study aimed to determine the anti-obesity effects and mechanisms of Cerasus humilis polyphenol (CHP) in C57BL/6 obese mice and 3T3-L1 cells. High-performance liquid chromatography-electrospray ionization-tandem mass spectrometry was used for the qualitative and quantitative identification of CHP components. The obese mice, induced by feeding high-fat diet (HFD), were treated with CHP (250 mg/kg/day) by gavage for 12 weeks. Orlistat was gavaged at 15.6 mg/kg bw/day, as a positive control group. The analysis revealed that the main components of CHP were procyanidin B2, cyanidin-3-glucoside, and pelargonidin-3-glucoside. CHP dietary supplementation significantly reduced body weight and improved blood lipid measurements in HFD-fed mice (p < 0.01). Moreover, it inhibited mRNA expression of miR-122, Srebp-1c, and Cpt1a (p < 0.01) and reduced hepatic lipid deposition, as seen by hematoxylin and eosin staining. CHP downregulated the protein expression of PPARγ and C/EBPα in HFD-induced obese mice and inhibited adipocyte differentiation (p < 0.01). Compared with the HFD group, CHP supplementation had an obvious anti-inflammatory effect (decreased protein expression, such as TNF-α, IL-6, and MCP1), reducing leptin levels and TNF-α secretion in serum and cells (p < 0.01). CHP significantly inhibited the expression of miR-27a/b (53.3 and 29.9%, p < 0.01) in mice retroperitoneal white adipocytes, enhancing the expression of the target gene Prdm16 and significantly upregulating Sirt1 (105.5%, p < 0.01) compared with the HFD group. Moreover, CHP supplementation effectively improved oxidative stress (ROS, T-AOC, SOD, CAT, and GSH-Px) induced by HFD in obese mice (p < 0.01). Thus, CHP mitigates adipocyte differentiation, browning of white adipocytes, and reduction of inflammation and antioxidant activity to reduce obesity. Consequently, these results provide novel insights into the anti-obesity roles of CHP in HFD-induced obesity.

Circular RNA SAMD4A controls adipogenesis in obesity through the miR-138-5p/EZH2 axis

A growing body of evidence has suggested that circular RNAs (circRNAs) are crucial for the regulation of gene expression and their dysregulation is implicated in several diseases. However, the function of circRNAs in obesity remains largely unexplored.

Methods: Global changes in the circRNA expression patterns were detected in adipose tissues derived from obese and lean individuals. In particular, circSAMD4A was identified as significantly differentially upregulated and was functionally analyzed, both in vitro and in vivo, using various approaches.

Results: CircSAMD4A overexpression was correlated with a poor prognosis in obese patients. By contrast, circSAMD4A knockdown inhibited differentiation in isolated preadipocytes. In high-fat diet (HFD) -induced obese mice, circSAMD4A knockdown reversed the associated weight gain, reduced food intake, lower body fat, and increased energy expenditure. These mice also exhibited increased insulin sensitivity and glucose tolerance. Furthermore, in vitro experiments indicated that circSAMD4A affected differentiation by binding to miR-138-5p and regulating EZH2 expression.

Conclusions: CircSAMD4A regulated preadipocyte differentiation by acting as a miR-138-5p sponge, and thus increasing EZH2 expression. These results suggested that circSAMD4A can serve as a potential target for obesity treatments and/or as a potential prognostic marker for obese patients following bariatric surgery.

Low- and high-thermogenic brown adipocyte subpopulations coexist in murine adipose tissue

Brown adipose tissue (BAT), as the main site of adaptive thermogenesis, exerts beneficial metabolic effects on obesity and insulin resistance. BAT has been previously assumed to contain a homogeneous population of brown adipocytes. Utilizing multiple mouse models capable of genetically labeling different cellular populations, as well as single-cell RNA sequencing and 3D tissue profiling, we discovered a brown adipocyte subpopulation with low thermogenic activity coexisting with the classical high-thermogenic brown adipocytes within the BAT. Compared with the high-thermogenic brown adipocytes, these low-thermogenic brown adipocytes had substantially lower Ucp1 and Adipoq expression, larger lipid droplets, and lower mitochondrial content. Functional analyses showed that, unlike the high-thermogenic brown adipocytes, the low-thermogenic brown adipocytes have markedly lower basal mitochondrial respiration, and they are specialized in fatty acid uptake. Upon changes in environmental temperature, the 2 brown adipocyte subpopulations underwent dynamic interconversions. Cold exposure converted low-thermogenic brown adipocytes into high-thermogenic cells. A thermoneutral environment had the opposite effect. The recruitment of high-thermogenic brown adipocytes by cold stimulation is not affected by high-fat diet feeding, but it does substantially decline with age. Our results revealed a high degree of functional heterogeneity of brown adipocytes.

Oleic acid in the absence of a PPARγ agonist increases adipogenic gene expression in bovine muscle satellite cells1

We hypothesized that oleic acid (OA) in the absence of a thiazolidinedione (i.e., a synthetic peroxisome proliferator-activated receptorγ [PPARγ] agonist) would increase adipogenic gene expression in bovine muscle satellite cells (BSC). The BSC were cultured in differentiation medium containing 10 µM ciglitazone (CI), 100 µM OA, or 100 µM OA plus 10 µM CI (CI-OA). Control (CON) BSC were cultured only in differentiation media (containing 2% horse serum). The presence of myogenin, desmin, and paired box 7 proteins was confirmed in the BSC by immunofluorescence staining, demonstrating that we had isolated myogenic cells. The OA BSC had lesser paired box 3 (Pax3) and myogenic differentiation 1 expression but greater Pax7 and mygogenin (MYOG) expression (P < 0.05), than the CON BSC. The CI BSC had greater Pax3, Pax7, and MYOG expression than CON BSC (P < 0.05), suggesting that CI would promote BSC myogenesis under pro-myogenic conditions (i.e., when cultured with horse serum). However, both the OA and CI treatments upregulated the expression of PPARγ, CCAAT/enhancer-binding protein alpha (C/EBPα) and C/EBPß, sterol regulatory element-binding protein 1, lipoprotein lipase, and glycerol-3-phosphate acyltransferase 3 gene expression, as well as media adiponectin concentration (P < 0.05). The CI, OA, and CI-OA treatments also increased triacylglycerol and lipid droplet accumulation, in spite of upregulation (relative to CON BSC) of adenosine monophosphate-activated protein kinase alpha-1, perilipin 2 (PLIN2), and PLIN3 in BSC and downregulation of G protein-coupled protein receptor 43, acyl-CoA synthetase long chain family member 3, and stearoyl-CoA desaturase (P < 0.05). These results indicate that OA in the absence of a synthetic PPARγ agonist can effectively increase adipogenic gene expression in BSC.

What lipodystrophies teach us about the metabolic syndrome

Lipodystrophies are the result of a range of inherited and acquired causes, but all are characterized by perturbations in white adipose tissue function and, in many instances, its mass or distribution. Though patients are often nonobese, they typically manifest a severe form of the metabolic syndrome, highlighting the importance of white fat in the "safe" storage of surplus energy. Understanding the molecular pathophysiology of congenital lipodystrophies has yielded useful insights into the biology of adipocytes and informed therapeutic strategies. More recently, genome-wide association studies focused on insulin resistance have linked common variants to genes implicated in adipose biology and suggested that subtle forms of lipodystrophy contribute to cardiometabolic disease risk at a population level. These observations underpin the use of aligned treatment strategies in insulin-resistant obese and lipodystrophic patients, the major goal being to alleviate the energetic burden on adipose tissue.

Comparison of LncRNA Expression Profiles during Myogenic Differentiation and Adipogenic Transdifferentiation of Myoblasts

Myoblasts could transdifferentiate into adipocytes or adipocyte-like cells, which have the capability of producing and storing intracellular lipids. Long-chain non-coding RNAs (lncRNAs) have many important physiological functions in eukaryotes, which include regulating gene expression, chromosome silencing, and nuclear transport. However, changes in the expression of lncRNAs in muscle cells during adipogenic transdifferentiation have not been investigated to date. Here, C2C12 myoblasts were seeded and then induced to undergo myogenic and adipogenic transdifferentiation. The expression profiles of lncRNAs in various differentiated cells were analyzed and then compared by digital gene expression (DGE) RNA sequencing. A total of 114 core lncRNAs from 836 differentially expressed lncRNAs in adipogenic cells were identified. Further investigation by in silico analysis revealed that the target genes of core lncRNAs significantly enriched various signaling pathways that were related to glucose and lipid metabolism and muscle growth. The lncRNA-GM43652 gene was a potential regulator of adipogenesis in muscle cells. It showed the highest levels of expression in adipogenic cells, and the knocking down lncRNA-GM43652 negatively influenced lipid deposition in transdifferentiated myoblasts. This study has identified the novel candidate regulators that may be assessed in future molecular studies on adipogenic conversion of muscle cells.

Flow cytometry-based FRET identifies binding intensities in PPARγ1 protein-protein interactions in living cells

PPARγ is a pharmacological target in inflammatory and metabolic diseases. Upon agonistic treatment or following antagonism, binding of co-factors is altered, which consequently affects PPARγ-dependent transactivation as well as its DNA-independent properties. Therefore, establishing techniques to characterize these interactions is an important issue in living cells. Methods: Using the FRET pair Clover/mRuby2, we set up a flow cytometry-based FRET assay by analyzing PPARγ1 binding to its heterodimerization partner RXRα. Analyses of PPARγ-reporter and co-localization studies by laser-scanning microscopy validated this system. Refining the system, we created a new readout to distinguish strong from weak interactions, focusing on PPARγ-binding to the co-repressor N-CoR2. Results: We observed high FRET in cells expressing Clover-PPARγ1 and mRuby2-RXRα, but no FRET when cells express a mRuby2-RXRα deletion mutant, lacking the PPARγ interaction domain. Focusing on the co-repressor N-CoR2, we identified in HEK293T cells the new splice variant N-CoR2-ΔID1-exon. Overexpressing this isoform tagged with mRuby2, revealed no binding to Clover-PPARγ1, nor in murine J774A.1 macrophages. In HEK293T cells, binding was even lower in comparison to N-CoR2 constructs in which domains established to mediate interaction with PPARγ binding are deleted. These data suggest a possible role of N-CoR2-ΔID1-exon as a dominant negative variant. Because binding to N-CoR2-mRuby2 was not altered following activation or antagonism of Clover-PPARγ1, we determined the effect of pharmacological treatment on FRET intensity. Therefore, we calculated flow cytometry-based FRET efficiencies based on our flow cytometry data. As with PPARγ antagonism, PPARγ agonist treatment did not prevent binding of N-CoR2. Conclusion: Our system allows the close determination of protein-protein interactions with a special focus on binding intensity, allowing this system to characterize the role of protein domains as well as the effect of pharmacological agents on protein-protein interactions.