Transfer of the glycosylphosphatidylinositol‐anchored 5′‐nucleotidase CD73 from adiposomes into rat adipocytes stimulates lipid synthesis

Abstract

Background and purpose:In addition to predominant localization at detergent-insoluble, glycolipid-enriched plasma membrane microdomains (DIGs), glycosylphosphatidylinositol (GPI)-anchored proteins (GPI-proteins) have been found associated with lipid droplets (LDs) and adiposomes. Adiposomes are vesicles that are released from adipocytes in response to anti-lipolytic and lipogenic signals, such as H2O2, palmitate and the antidiabetic sulfonylurea drug, glimepiride, and harbour (c)AMPdegrading GPI-proteins, among them the 5-nucleotidase CD73. Here the role of adiposomes in GPI-protein-mediated information transfer was studied. Experimental approach: Adiposomes were incubated with isolated rat adipocytes under various conditions. Trafficking of CD73 and lipid synthesis were analysed. Key results: Upon blockade of GPI-protein trafficking, CD73 specifically associated with DIGs of small, and to a lower degree, large, adipocytes. On reversal of the blockade, CD73 appeared at cytosolic LD in time-adiposome concentration-and signal (H2O2 > glimepiride > palmitate)-dependent fashion. The salt-and carbonate-resistant association of CD73 with structurally intact DIGs and LD was dependent on its intact GPI anchor. Upon incubation with small and to a lower degree, large adipocytes, adiposomes increased lipid synthesis in the absence or presence of H2O2, glimepiride and palmitate and improved the sensitivity toward these signals. Upregulation of lipid synthesis by adiposomes was dependent on the translocation of CD73 with intact GPI anchors from DIGs to LD. Conclusions:The signal-induced transfer of GPI-anchored CD73 from adiposomes via DIGs to LD of adipocytes mediates paracrine upregulation of lipid synthesis within the adipose tissue.

Adipocyte-specific Inactivation of Acyl-CoA Synthetase Fatty Acid Transport Protein 4 (Fatp4) in Mice Causes Adipose Hypertrophy and Alterations in Metabolism of Complex Lipids under High Fat Diet

“…Phosphatidylinositol forms the precursor molecule for glycosylphosphatidylinositol as part of glycosylphosphatidylinositol-anchored proteins. A number of those glycosylphosphatidylinositol-anchored proteins on the other hand are known to regulate processes like lipolysis and lipogenesis (21,22). However, it is unlikely that adipose hypertrophy in our study arose from increased de novo lipogenesis, because the expression of major enzymes involved in the latter remained unchanged.…”

Cellular function and molecular structure of ecto-nucleotidases

“…Furthermore, eN can be released in GPI-anchored form via microvesicles or exosomes from cells [159,265] or in snake venom [266], and it can serve the transfer of the enzyme between cells, as exemplified for adipocytes [267]. It can also be released into pancreatic juice [156].…”

Oral Protein Therapy for the Future – Transport of Glycolipid-Modified Proteins: Vision or Fiction

“…The recently reported observations with adipocytes [171,172] raised the possibility for the operation of similar mechanisms of inter-and intracellular trafficking of GPI proteins between and in other tissue cells, such as pancreatic ␤ , muscle or liver cells, with their transfer from microvesicles/exosomes to plasma membrane DIGs and subsequent translocation to the surface of cytoplasmic LD. Both DIGs and LD are present in virtually all mammalian cell types studied so far, albeit at considerably varying amounts [73-79, 130-132, 195, 196] .…”

“…This complex inter-and intracellular trafficking of GPI proteins has recently been demonstrated for the adiposome-mediated transfer of the GPI-anchored (c)AMPdegrading enzymes, Gce1 and CD73, from donor to acceptor adipocytes and their subsequent translocation to cytoplasmic LD of the acceptor adipocytes [170][171][172] . The expression of Gce1 and CD73 at the LD surface with their (c)AMP-degrading catalytic domains gaining access to the cytoplasm leads to lowering of the concentration of (c)AMP at the LD surface zone ( fig.…”

“…9 ). The resulting blockade of cAMP-dependent phosphorylation causes the inhibition of hormone-sensitive lipase and activation of glycerol-3-phosphate acyltransferase in the immediate vicinity of the LD [170][171][172] . Thus, this mechanism coordinates down-regulation of lipolysis and up-regulation of esterification which both ultimately foster triacylglycerol Three putative mechanisms for the intracellular trafficking of GPI proteins from DIGs to LD.…”