Effects of activated microglia on the properties of neural stem cells in vitro

Abstract

Neural stem cell (NSC) transplantation strategy offers great potential to treat spinal cord injury (SCI). NSCs may replace lost neurons or oligodendrocytes, and act as a source of neurotrophic factors to support the survival of remaining cells. Their efficiency was limited by poor survival after transplantation, and they had more tendencies to differentiate into astrocytes, but not neurons and oligodendrocytes. This project investigated whether activated microglia is a factor that contributes to this phenomenon, and studied the potential role of minocycline, a widely used antibiotic drug, to modify the negative effects of microglia on NSCs.

In the first part of this study, we used organotypic spinal cord slice (SCS) culture to mimic in vivo local environment after SCI, and NSCs were grafted on their surface or shared culture medium with them. After specific depletion of microglia with clodronate loaded liposome, more grafted NSCs survived, and in the co-culture system, the NSC neuronal differentiation rate increased while glial differentiation rate decreased, the apoptosis rate also decreased. This suggested that activated microglia may impair NSC survival, and neuronal differentiation, but improve glial differentiation.

In the second part of this study, we first tested the direct effects of minocycline on NSC apoptosis, proliferation and differentiation in vitro, to test whether minocycline has any side effect on NSCs. The results showed that at the concentration 10μg/ml or lower, minocycline did not affect NSC survival and proliferation, but impaired neuronal differentiation. Then we treated primary microglia culture with LPS or LPS plus minocycline, and collected the conditioned mediums (CM-LPS and CM-LPSMC) to test their effects on NSC apoptosis and differentiation. The results showed that compared with CM-LPS, CM-LPSMC resulted in a significantly lower apoptotic rate of NSCs, also allowed NSC neuronal differentiation. This suggested that minocycline may impair the pro-apoptotic effect of activated microglia on NSCs.

In conclusion, our study showed that activated microglia may impair NSC survival and neuronal differentiation. This indicated that in NSC transplantation strategy for SCI, microglia would be a target to be manipulated to improve graft survival and neuronal differentiation. Although minocycline may suppress NSC differentiation towards neurons, it has the potential to protect NSCs from the toxic effects of activated microglia. This showed the therapeutic potential of minocycline in NSC transplantation strategies for SCI.