Abstract
We have recently established a culture system to study the impact of simulated microgravity on oligodendrocyte progenitor cells (OPCs) development. We subjected mouse and human OPCs to a short exposure of simulated microgravity produced by a 3D-Clinostat robot. Our results demonstrate that rodent and human OPCs display enhanced and sustained proliferation when exposed to simulated microgravity as assessed by several parameters, including a decrease in the cell cycle time. Additionally, OPC migration was examined in vitro using time-lapse imaging of cultured OPCs. Our results indicated that OPCs migrate to a greater extent after stimulated microgravity than in normal conditions, and this enhanced motility was associated with OPC morphological changes. The lack of normal gravity resulted in a significant increase in the migration speed of mouse and human OPCs and we found that the average leading process in migrating bipolar OPCs was significantly longer in microgravity treated cells than in controls, demonstrating that during OPC migration the lack of gravity promotes leading process extension, an essential step in the process of OPC migration. Finally, we tested the effect of simulated microgravity on OPC differentiation. Our data showed that the expression of mature oligodendrocyte markers was significantly delayed in microgravity treated OPCs. Under conditions where OPCs were allowed to progress in the lineage, simulated microgravity decreased the proportion of cells that expressed mature markers, such as CC1 and MBP, with a concomitant increased number of cells that retained immature oligodendrocyte markers such as Sox2 and NG2. Development of methodologies aimed at enhancing the number of OPCs and their ability to progress on the oligodendrocyte lineage is of great value for treatment of demyelinating disorders. To our knowledge, this is the first report on the gravitational modulation of oligodendrocyte intrinsic plasticity to increase their progenies.
Highlights
Myelin is essential for the efficient conduction of electrochemical messages to and from the central nervous system (CNS) and lack of myelin due to trauma and/or disease leads to CNS dysfunction
After each BrdU pulse, proliferating progenitors were identified by double immunofluorescence for BrdU and neuron-glial antigen 2 (NG2) and the relative number of NG2+/BrdU+ cells was quantified in each cell population (Figure 1B)
We didn’t find any significant difference in the expression of Sox transcription factor 9 (Sox9) but we found a significant reduction in the expression of oligodendrocyte transcription factor 2 (Olig2) and a relative increase in the number of oligodendrocyte transcription factor 1 (Olig1) and Sox transcription factor 2 (Sox2) positive human OPCs (hOPCs) under simulated microgravity (Figure 8B)
Summary
Myelin is essential for the efficient conduction of electrochemical messages to and from the central nervous system (CNS) and lack of myelin due to trauma and/or disease leads to CNS dysfunction. Effective methods to generate OPCs that would be devoid of other cell populations prior to be grafted, still need to be developed. Yuge and coworkers [3] reported that human mesenchymal stem cells cultured under 0G maintained their undifferentiated state, differentiated into hyaline cartilage after being transplanted into cartilage defective mice, and had a high survival rate. More recent work tested the effects of 0G on bone marrow stromal cells. Neural-induced mesenchymal bone marrow stromal cells cultured under 1G conditions exhibited neural differentiation, whereas those cultured under 0G did not. When these cells were administered intra-venously into a mouse model of cerebral contusion, they survived in larger numbers than cells grown in 1G [4]
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