Intrinsic Depot-Specific Differences in the Secretome of Adipose Tissue, Preadipocytes, and Adipose Tissue–Derived Microvascular Endothelial Cells

Abstract

OBJECTIVEVisceral adipose tissue (VAT) is more closely linked to insulin resistance than subcutaneous adipose tissue (SAT). We conducted a quantitative analysis of the secretomes of VAT and SAT to identify differences in adipokine secretion that account for the adverse metabolic consequences of VAT.RESEARCH DESIGN AND METHODSWe used lectin affinity chromatography followed by comparison of isotope-labeled amino acid incorporation rates to quantitate relative differences in the secretomes of VAT and SAT explants. Because adipose tissue is composed of multiple cell types, which may contribute to depot-specific differences in secretion, we isolated preadipocytes and microvascular endothelial cells (MVECs) and compared their secretomes to those from whole adipose tissue.RESULTSAlthough there were no discrete depot-specific differences in the secretomes from whole adipose tissue, preadipocytes, or MVECS, VAT exhibited an overall higher level of protein secretion than SAT. More proteins were secreted in twofold greater abundance from VAT explants compared with SAT explants (59% versus 21%), preadipocytes (68% versus 0%), and MVECs (62% versus 15%). The number of proteins in the whole adipose tissue secretome was greater than the sum of its cellular constituents. Finally, almost 50% of the adipose tissue secretome was composed of factors with a role in angiogenesis.CONCLUSIONSVAT has a higher secretory capacity than SAT, and this difference is an intrinsic feature of its cellular components. In view of the number of angiogenic factors in the adipose tissue secretome, we propose that VAT represents a more readily expandable tissue depot.

Regulation of De Novo Adipocyte Differentiation Through Cross Talk Between Adipocytes and Preadipocytes

“…Among the 98 proteins identified by mass spectrometry, adiponectin, cystatin C, resistin, adipsin, metalloproteinase inhibitor 1, chemerin, Vim, Sparc, and Vitamin D-binding protein are known adipokines (13,(26)(27)(28)(29). Taking into account which proteins have been reported to be secreted by adipocytes and adipose tissue, we identified Cpq, Got2, and Ecm1 as potential novel adipokines.…”

“…Adipokine secretion is dependent not only on adipocyte size, but also on adipose depots; for example, subcutaneous adipose tissue has been shown to secrete higher amounts of metabolically beneficial adipokines such as leptin and adiponectin, whereas proinflammatory adipokine secretion is higher in visceral adipose tissue (13).…”

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“…To make issues more complex, there is a constant turnover of cells in tissue (10% of adipocytes renew each year (Spalding et al 2008)) and an influx of macrophages from the periphery at times of adipocyte hypertrophy or stress (Sell and Eckel 2010). Different depots in the body have differing physiology (Hocking et al 2010;Ray et al 2009), most likely due to inconsistent derivations of tissue (Laharrague and Casteilla 2010;Billon et al 2007). The differences between depots are seen both chemically and physiologically.…”

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“…The most perfect approximation to the real situation is the study of the in vivo secretome. In this research line, one of the few proteomics studies was carried out by implanting capillary ultrafiltration probes into tumor masses induced in mice (Alvarez-Llamas et al, 2007;Hocking et al, 2010). However, this is not always feasible and the use of tissue explants (ex vivo approach) represents a compromise solution which gives information about secretory molecules coming from all tissue components as result of cross-talk between them and approaches the physiological situation better than the cell culture.…”

“…However, this is not always feasible and the use of tissue explants (ex vivo approach) represents a compromise solution which gives information about secretory molecules coming from all tissue components as result of cross-talk between them and approaches the physiological situation better than the cell culture. Adipose tissue secretome was investigated as a tissue model representing not only energy storage depot but, more importantly, a key organ for the regulation of energy metabolism through secretion of a variety of adipokines involved in the regulation of energy metabolism (Roelofsen et al, 2009;Hocking et al, 2010). Two key points to consider when working directly with tissue in culture are: a) the need to ensure that all detected proteins are truly coming from the tissue and not "contaminants" derived from plasma and b) validation of identified proteins as secreted.…”