This study was undertaken to analyze quantitatively the secretomes of intra-abdominal (visceral) adipose tissue (IAAT) and subcutaneous adipose tissue (SAT) to identify differences in adipokine secretion that could explain the adverse metabolic consequences of IAAT. For that purpose, they used lectin affinity chromatography to selectively enrich proteins targeted for secretion, followed by comparison of isotope-labelled amino acid incorporation rates to quantitate relative differences in the secretomes of murine IAAT and SAT. They also isolated preadipocytes and microvascular endothelial cells (MVECs) to compare their secretomes to those from the whole adipose tissue. Results showed that IAAT had a higher overall secretory capacity compared to SAT. For instance, 59% of proteins were secreted from IAAT explants compared to 21% from SAT. This upregulation of protein secretion of IAAT was also observed in cells of the stromavascular fraction, the preadipocytes (IAAT: 68% vs. SAT: 0%) and MVECs (IAAT: 62% vs. SAT: 15%). Among the proteins secreted in greater abundance from IAAT, they found members of the acute phase response and innate immune system which are involved in angiogenesis. Proteins involved in macrophage recruitment were also secreted in greater abundance from intra-abdominal MVECs. A total of 115 proteins were identified from the 3 secretomes, of which 67 were unique to adipose tissue explants, 16 were unique to MVECs, and 7 were unique to preadipocytes. The number of proteins in the whole adipose tissue secretome was greater than the sum of its cellular constituents which suggests that there is a paracrine interaction between the multiple cell types within adipose tissue.
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