Surface Phosphatidylserine Is Responsible for the Internalization on Microvesicles Derived from Hypoxia-Induced Human Bone Marrow Mesenchymal Stem Cells into Human Endothelial Cells

Abstract

BackgroundPrevious data have proven that microvesicles derived from hypoxia-induced mesenchymal stem cells (MSC-MVs) can be internalized into endothelial cells, enhancing their proliferation and vessel structure formation and promoting in vivo angiogenesis. However, there is a paucity of information about how the MSC-MVs are up-taken by endothelial cells.MethodsMVs were prepared from the supernatants of human bone marrow MSCs that had been exposed to a hypoxic and/or serum-deprivation condition. The incorporation of hypoxia-induced MSC-MVs into human umbilical cord endothelial cells (HUVECs) was observed by flow cytometry and confocal microscopy in the presence or absence of recombinant human Annexin-V (Anx-V) and antibodies against human CD29 and CD44. Further, small interfering RNA (siRNA) targeted at Anx-V and PSR was delivered into HUVECs, or HUVECs were treated with a monoclonal antibody against phosphatidylserine receptor (PSR) and the cellular internalization of MVs was re-assessed.ResultsThe addition of exogenous Anx-V could inhibit the uptake of MVs isolated from hypoxia-induced stem cells by HUVECs in a dose- and time-dependent manner, while the anti-CD29 and CD44 antibodies had no effect on the internalization process. The suppression was neither observed in Anx-V siRNA-transfected HUVECs, however, addition of anti-PSR antibody and PSR siRNA-transfected HUVECs greatly blocked the incorporation of MVs isolated from hypoxia-induced stem cells into HUVECs.ConclusionPS on the MVs isolated from hypoxia-induced stem cells is the critical molecule in the uptake by HUVECs.

Extracellular vesicle docking at the cellular port: Extracellular vesicle binding and uptake

“…More specifically, TIM4 is a phagocytic receptor that recognizes phosphatidylserine (PS), a phospholipid that is abundant in EVs. Blocking TIM4 in macrophages reduced the uptake of leukemia cell-derived exosomes, which suggests a possible role for PS in exosome internalization [8, 9, 13, 45, 47, 62, 93]. …”

The biology of extracellular microvesicles

“…Plasma membrane bleb formation is regulated by a host of factors which modulate deformability and bending of the membrane, including the lipid composition and organization of the peripheral cytoskeleton, to alter membrane fluidity and deformability. MVs display unique lipid characteristics, such as the externalization of the phospholipid phosphatidylserine (PS), which has been demonstrated to promote uptake by recipient cells . The phospholipid lysophosphatidylcholines, the sphingolipid sphingomyelins, and acylcarnitines, the fatty acyl esters of L‐carnitine, have also been found to be enriched in MVs .…”

“…MVs display unique lipid characteristics, such as the externalization of the phospholipid phosphatidylserine (PS), 64 which has been demonstrated to promote uptake by recipient cells. 65 The phospholipid lysophosphatidylcholines, the sphingolipid sphingomyelins, and acylcarnitines, the fatty acyl esters of L-carnitine, have also been found to be enriched in MVs. 66 The prominent plasma membrane lipid cholesterol is thought to play an important role in MV formation, as its depletion reduces MV formation.…”

Recent Developments in Cellular Immunotherapy for HSCT-Associated Complications

“…This lipid has been identified on the surface of various types of EVs, derived from various types of cells, and has been described as an evolutionary conserved immunosuppressive signal which promotes tolerance and prevents the activation of the immune system (87). Recently, Wei et al have demonstrated that phosphatidylserine on the surface of MSC-derived microvesicles is essential for their uptake by human umbilical vein endothelial cells (HUVECs), however, the role of this lipid in MSC-EV-derived immunosuppression is still unexplored (88). …”