Graduate School of Agriculture, Hokkaido University, Sapporo 060-8589, Japan.
Research Faculty of Agriculture, Hokkaido University, Sapporo 060-8589, Japan; Functional Biomolecules Research Group, National Agriculture and Food Research Organization, Tsukuba, Ibaraki 305-0901, Japan.
Biochem Biophys Res Commun. 2014 Jun 6;448(3):261-6. doi: 10.1016/j.bbrc.2014.04.114. Epub 2014 May 2.
Exosomes are membrane vesicles 30-120 nm in diameter that are released by many cell types and carry a cargo of proteins, lipids, mRNA, and microRNA. Cultured adipocytes reportedly release exosomes that may play a role in cell-to-cell communication during the development of metabolic diseases. However, the characteristics and function of exosomes released from adipocytes in vivo remain to be elucidated. Clearly, adipocyte-derived exosomes could exist in the circulation and may be associated with adipocyte-specific proteins such as adipocytokines. We isolated exosomes from serum of mice by differential centrifugation and analyzed adiponectin, leptin, and resistin in the exosome fraction. Western blotting detected adiponectin but no leptin and only trace amounts of resistin in the exosome fraction. The adiponectin signal in the exosome fraction was decreased by proteinase K treatment and completely quenched by a combination of proteinase K and Triton X-100. Quantitative ELISA showed that the exosome fraction contains considerable amounts of adiponectin, but not leptin or resistin. The concentration of adiponectin in the serum and the ratio of adiponectin to total protein in the exosome fraction were lower in obese mice than in lean mice. These results suggest that a portion of adiponectin exists as a transmembrane protein in the exosomes in mouse serum. We propose adiponectin as a marker of exosomes released from adipocytes in vivo.
外泌体是直径 30-120nm 的膜囊泡，由许多细胞类型释放，并携带蛋白质、脂质、mRNA 和 microRNA 等货物。据报道，培养的脂肪细胞释放的外泌体可能在代谢疾病发生过程中的细胞间通讯中发挥作用。然而，体内脂肪细胞释放的外泌体的特征和功能仍有待阐明。显然，脂肪细胞来源的外泌体可能存在于循环中，并且可能与脂肪细胞特异性蛋白（如脂肪细胞因子）相关。我们通过差速离心法从小鼠血清中分离出外泌体，并分析外泌体部分中的脂联素、瘦素和抵抗素。Western blot 检测到外泌体部分中的脂联素，但没有瘦素，只有痕量的抵抗素。外泌体部分中的脂联素信号被蛋白酶 K 处理减弱，并且被蛋白酶 K 和 Triton X-100 的组合完全淬灭。定量 ELISA 显示外泌体部分含有相当数量的脂联素，但没有瘦素或抵抗素。肥胖小鼠血清中的脂联素浓度和外泌体部分中脂联素与总蛋白的比值均低于瘦小鼠。这些结果表明，一部分脂联素以跨膜蛋白的形式存在于小鼠血清中的外泌体中。我们提出脂联素作为体内脂肪细胞释放的外泌体的标志物。
