Institute for Diabetes and Obesity, Helmholtz Diabetes Center (HDC) at Helmholtz Zentrum München, German Research Center for Environmental Health (GmbH), Oberschleissheim, Germany; German Center for Diabetes Research (DZD), Oberschleissheim, Germany; Department Biology I, Genetics, Ludwig-Maximilians-Universität München, Planegg, Martinsried, Germany.
Institute for Diabetes and Obesity, Helmholtz Diabetes Center (HDC) at Helmholtz Zentrum München, German Research Center for Environmental Health (GmbH), Oberschleissheim, Germany; German Center for Diabetes Research (DZD), Oberschleissheim, Germany; Division of Metabolic Diseases, Department of Medicine, Technische Universität München, München, Germany.
Mech Ageing Dev. 2020 Sep;190:111307. doi: 10.1016/j.mad.2020.111307. Epub 2020 Jul 3.
Glycosylphosphatidylinositol (GPI)-anchored proteins (GPI-APs) are associated with the surface of eucaryotic cells only through a covalently coupled carboxy-terminal GPI glycolipid structure which is anchored at the outer leaflet of plasma membranes. This mode of membrane association may be responsible for the recent observations that full-length GPI-APs harbouring the complete GPI anchor are (i) released from isolated rat adipocytes in vitro and (ii) expressed in rat and human serum. The upregulation of the adipocyte release in response to increased cell size and blood glucose/insulin levels of the donor rats and downregulation of the expression in serum of insulin resistant and diabetic rats have been reconciled with enhanced degradation of the full-length GPI-APs released into micelle-like complexes together with (lyso) phospholipids and cholesterol by serum GPI-specific phospholipase D (GPI-PLD). Here by using a sensitive and reliable sensing method for full-length GPI-APs, which relies on surface acoustic waves propagating over microfluidic chips, the upregulation of (i) the release of the full-length GPI-APs CD73, alkaline phosphatase and CD55 from isolated adipocyte plasma membranes monitored in a "lab-on-the-chip" configuration, (ii) their release from isolated rat adipocytes into the incubation medium and (iii) the lipolytic cleavage of their GPI anchors in serum was demonstrated to increase with age (3-16 weeks) and body weight (87-477 g) of (healthy) donor rats. In contrast, the amount of full-length GPI-APs in rat serum, as determined by chip-based sensing, turned out to decline with age/body weight. These correlations suggest that age-/weight-induced alterations (in certain biophysical/biochemical characteristics) of plasma membranes are responsible for the release of full-length GPI-APs which becomes counteracted by elevated GPI-PLD activity in serum. Thus, sensitive and specific measurement of these GPI-AP-relevant parameters may be useful for monitoring of age-related cell surface changes, in general, and diseases, in particular.
糖基磷脂酰肌醇（GPI）锚定蛋白（GPI-APs）仅通过共价连接的羧基末端 GPI 糖脂结构与真核细胞表面相连，该结构锚定于质膜的外叶。这种膜结合方式可能是导致以下最近观察结果的原因：全长 GPI-AP 携带完整的 GPI 锚定结构，（i）在体外从分离的大鼠脂肪细胞中释放，（ii）在大鼠和人血清中表达。对供体大鼠细胞大小增加和血糖/胰岛素水平升高的反应中脂肪细胞释放的上调，以及胰岛素抵抗和糖尿病大鼠血清中表达的下调，与血清 GPI 特异性磷脂酶 D（GPI-PLD）增强全长 GPI-AP 的降解相一致，这些全长 GPI-AP 与（溶）磷脂和胆固醇一起释放到胶束样复合物中。在这里，我们使用一种灵敏可靠的全长 GPI-AP 检测方法，该方法依赖于在微流控芯片上传播的声表面波，检测到在“芯片上实验室”配置中，（i）全长 GPI-APs CD73、碱性磷酸酶和 CD55 从分离的脂肪细胞膜中释放，（ii）从分离的大鼠脂肪细胞中释放到孵育培养基中，以及（iii）其 GPI 锚的脂解切割在血清中增加，与（健康）供体大鼠的年龄（3-16 周）和体重（87-477g）增加有关。相比之下，通过基于芯片的检测确定的大鼠血清中全长 GPI-AP 的量随着年龄/体重的增加而减少。这些相关性表明，血浆膜的年龄/体重诱导的改变（在某些生物物理/生化特征方面）负责全长 GPI-AP 的释放，而血清中升高的 GPI-PLD 活性则对此进行拮抗。因此，这些 GPI-AP 相关参数的敏感和特异性测量可能有助于监测一般的年龄相关细胞表面变化，特别是疾病。
