Deficiency of vascular endothelial growth factor-D does not affect murine adipose tissue development

Identifying key genes in milk fat metabolism by weighted gene co-expression network analysis

Milk fat is the most important and energy-rich substance in milk, and its content and composition are important reference elements in the evaluation of milk quality. However, the current identification of valuable candidate genes affecting milk fat is limited. IlluminaPE150 was used to sequence bovine mammary epithelial cells (BMECs) with high and low milk fat rates (MFP), the weighted gene co-expression network (WGCNA) was used to analyze mRNA expression profile data in this study. As a result, a total of 10,310 genes were used to construct WGCNA, and the genes were classified into 18 modules. Among them, violet (r = 0.74), yellow (r = 0.75) and darkolivegreen (r =  − 0.79) modules were significantly associated with MFP, and 39, 181, 75 hub genes were identified, respectively. Combining enrichment analysis and differential genes (DEs), we screened five key candidate DEs related to lipid metabolism, namely PI4K2A, SLC16A1, ATP8A2, VEGFD and ID1, respectively. Relative to the small intestine, liver, kidney, heart, ovary and uterus, the gene expression of PI4K2A is the highest in mammary gland, and is significantly enriched in GO terms and pathways related to milk fat metabolism, such as monocarboxylic acid transport, phospholipid transport, phosphatidylinositol signaling system, inositol phosphate metabolism and MAPK signaling pathway. This study uses WGCNA to form an overall view of MFP, providing a theoretical basis for identifying potential pathways and hub genes that may be involved in milk fat synthesis.

Beyond adiponectin and leptin: adipose tissue-derived mediators of inter-organ communication

The breakthrough discoveries of leptin and adiponectin more than two decades ago led to a widespread recognition of adipose tissue as an endocrine organ. Many more adipose tissue-secreted signaling mediators (adipokines) have been identified since then, and much has been learned about how adipose tissue communicates with other organs of the body to maintain systemic homeostasis. Beyond proteins, additional factors, such as lipids, metabolites, noncoding RNAs, and extracellular vesicles (EVs), released by adipose tissue participate in this process. Here, we review the diverse signaling mediators and mechanisms adipose tissue utilizes to relay information to other organs. We discuss recently identified adipokines (proteins, lipids, and metabolites) and briefly outline the contributions of noncoding RNAs and EVs to the ever-increasing complexities of adipose tissue inter-organ communication. We conclude by reflecting on central aspects of adipokine biology, namely, the contribution of distinct adipose tissue depots and cell types to adipokine secretion, the phenomenon of adipokine resistance, and the capacity of adipose tissue to act both as a source and sink of signaling mediators.

Transgenic overexpression of VEGF-C induces weight gain and insulin resistance in mice

Obesity comprises great risks for human health, contributing to the development of other diseases such as metabolic syndrome, type 2 diabetes and cardiovascular disease. Previously, obese patients were found to have elevated serum levels of VEGF-C, which correlated with worsening of lipid parameters. We recently identified that neutralization of VEGF-C and -D in the subcutaneous adipose tissue during the development of obesity improves metabolic parameters and insulin sensitivity in mice. To test the hypothesis that VEGF-C plays a role in the promotion of the metabolic disease, we used K14-VEGF-C mice that overexpress human VEGF-C under control of the keratin-14 promoter in the skin and monitored metabolic parameters over time. K14-VEGF-C mice had high levels of VEGF-C in the subcutaneous adipose tissue and gained more weight than wildtype littermates, became insulin resistant and had increased ectopic lipid accumulation at 20 weeks of age on regular mouse chow. The metabolic differences persisted under high-fat diet induced obesity. These results indicate that elevated VEGF-C levels contribute to metabolic deterioration and the development of insulin resistance, and that blockade of VEGF-C in obesity represents a suitable approach to alleviate the development of insulin resistance.

Blockade of VEGF-C and VEGF-D modulates adipose tissue inflammation and improves metabolic parameters under high-fat diet

OBJECTIVE

Elevated serum levels of the lymphangiogenic factors VEGF-C and -D have been observed in obese individuals but their relevance for the metabolic syndrome has remained unknown.

METHODS

K14-VEGFR-3-Ig (sR3) mice that constitutively express soluble-VEGFR-3-Ig in the skin, scavenging VEGF-C and -D, and wildtype (WT) mice were fed either chow or high-fat diet for 20 weeks. To assess the effect of VEGFR-3 blockage on adipose tissue growth and insulin sensitivity, we evaluated weight gain, adipocyte size and hepatic lipid accumulation. These results were complemented with insulin tolerance tests, FACS analysis of adipose tissue macrophages, in vitro 3T3-L1 differentiation assays and in vivo blocking antibody treatment experiments.

RESULTS

We show here that sR3 mice are protected from obesity-induced insulin resistance and hepatic lipid accumulation. This protection is associated with enhanced subcutaneous adipose tissue hyperplasia and an increased number of alternatively-activated (M2) macrophages in adipose tissue. We also show that VEGF-C and -D are chemotactic for murine macrophages and that this effect is mediated by VEGFR-3, which is upregulated on M1 polarized macrophages. Systemic antibody blockage of VEGFR-3 in db/db mice reduces adipose tissue macrophage infiltration and hepatic lipid accumulation, and improves insulin sensitivity.

CONCLUSIONS

These results reveal an unanticipated role of the lymphangiogenic factors VEGF-C and -D in the mediation of metabolic syndrome-associated adipose tissue inflammation. Blockage of these lymphangiogenic factors might constitute a new therapeutic strategy for the prevention of obesity-associated insulin resistance.

Neurokinin-1 receptor, a new modulator of lymphangiogenesis in obese-asthma phenotype

AIMS

Obesity and asthma are widely prevalent and associated disorders. Recent studies of our group revealed that Substance P (SP) is involved in pathophysiology of obese-asthma phenotype in mice through its selective NK1 receptor (NK1-R). Lymphangiogenesis is impaired in asthma and obesity, and SP activates contractile and inflammatory pathways in lymphatics. Our aim was to study whether NK1-R expression was involved in lymphangiogenesis on visceral (VAT) and subcutaneous (SAT) adipose tissues and in the lungs, in obese-allergen sensitized mice.

MAIN METHODS

Diet-induced obese and ovalbumin (OVA)-sensitized Balb/c mice were treated with a selective NK1-R antagonist (CJ 12,255, Pfizer Inc., USA) or placebo. Lymphatic structures (LYVE-1+) and NK1-R expression were analyzed by immunohistochemistry. A semi-quantitative score methodology was used for NK1-R expression.

KEY FINDINGS

Obesity and allergen-sensitization together increased the number of LYVE-1+ lymphatics in VAT and decreased it in SAT and lungs. NK1-R was mainly expressed on adipocyte membranes of VAT, blood vessel areas of SAT, and in lung epithelium. Obesity and allergen-sensitization combined increased the expression of NK1-R in VAT, SAT and lungs. NK1-R antagonist treatment reversed the effects observed in lymphangiogenesis in those tissues.

SIGNIFICANCE

The obese-asthma phenotype in mice is accompanied by increased expression of NK1-R on adipose tissues and lung epithelium, reflecting that SP released during inflammation may act directly on these tissues. Blocking NK1-R affects lymphangiogenesis, implying a role of SP, with opposite physiological consequences in VAT, and in SAT and lungs. Our results provide a clue for a novel SP role in the obese-asthma phenotype.

Adipose tissue angiogenesis: impact on obesity and type-2 diabetes

The growth and function of tissues are critically dependent on their vascularization. Adipose tissue is capable of expanding many-fold during adulthood, therefore requiring the formation of new vasculature to supply growing and proliferating adipocytes. The expansion of the vasculature in adipose tissue occurs through angiogenesis, where new blood vessels develop from those pre-existing within the tissue. Inappropriate angiogenesis may underlie adipose tissue dysfunction in obesity, which in turn increases type-2 diabetes risk. In addition, genetic and developmental factors involved in vascular patterning may define the size and expandability of diverse adipose tissue depots, which are also associated with type-2 diabetes risk. Moreover, the adipose tissue vasculature appears to be the niche for pre-adipocyte precursors, and factors that affect angiogenesis may directly impact the generation of new adipocytes. Here we review recent advances on the basic mechanisms of angiogenesis, and on the role of angiogenesis in adipose tissue development and obesity. A substantial amount of data points to a deficit in adipose tissue angiogenesis as a contributing factor to insulin resistance and metabolic disease in obesity. These emerging findings support the concept of the adipose tissue vasculature as a source of new targets for metabolic disease therapies. This article is part of a Special Issue entitled: Modulation of Adipose Tissue in Health and Disease.

Lymphatic lipid transport: sewer or subway?

The lymphatics began receiving attention in the scientific community as early as 1622, when Gasparo Aselli noted the appearance of milky-white vessels in the mesentery of a well-fed dog. Since this time, the lymphatic system has been historically regarded as the sewer of the vasculature, passively draining fluid and proteins from the interstitial spaces (along with lipid from the gut) into the blood. Recent reports, however, suggest that the lymphatic role in lipid transport is an active and intricate process, and that when lymphatic function is compromised, there are systemic consequences to lipid metabolism and transport. This review highlights these recent findings, and suggests future directions for understanding the interplay between lymphatic and lipid biology in health and disease.

Whole genome microarray analysis of chicken embryo facial prominences

The face is one of the three regions most frequently affected by congenital defects in humans. To understand the molecular mechanisms involved, it is necessary to have a more complete picture of gene expression in the embryo. Here, we use microarrays to profile expression in chicken facial prominences, post neural crest migration and before differentiation of mesenchymal cells. Chip-wide analysis revealed that maxillary and mandibular prominences had similar expression profiles while the frontonasal mass chips were distinct. Of the 3094 genes that were differentially expressed in one or more regions of the face, a group of 56 genes was subsequently validated with quantitative polymerase chain reaction (QPCR) and a subset examined with in situ hybridization. Microarrays trends were consistent with the QPCR data for the majority of genes (81%). On the basis of QPCR and microarray data, groups of genes that characterize each of the facial prominences can be determined.

Angiogenesis and development of adipose tissue

Obesity is a common disorder and related diseases, such as diabetes, atherosclerosis, hypertension, cardiovascular disease and cancer, are a major cause of mortality and morbidity in Western-type societies. Development of obesity is associated with substantial modulation of adipose tissue structure. The plasticity of the adipose tissue is reflected by its remarkable ability to expand or to reduce in size throughout adult lifespan. The expansion of adipose tissue is linked to the development of its vasculature. Indeed, adipogenesis is tightly associated with angiogenesis, as shown by the findings that adipose tissue explants trigger blood vessel formation, whereas in turn adipose tissue endothelial cells promote preadipocyte differentiation. Different components have been identified that play a role in adipose tissue associated angiogenesis. Modulation of angiogenesis may have the potential to impair adipose tissue development and thus may provide a novel therapeutic approach for prevention and treatment of obesity.