Tremendous efforts have been made to ameliorate and improve locomotor function after spinal cord injury (SCI) by the transplantation of various types of stem cells. However, the mechanism of action still has to be elucidated. In our study we compared the use of non-neurogenic stem cells – mesenchymal stem cells (MSCs), an immortalized stem cell line (SPCs) derived from human fetal spinal cord tissue or human induced pluripotent stem cell-derived neural precursors (iPS-NPs) – for the treatment of a balloon-induced spinal cord compression lesion. Two months post-implantation (PI), both types of NPs survived in the lesion. Compared to SPCs, which partially filled the lesion cavity, iPS-NPs interacted more with the host tissue. Besides differentiating into MAP2- , 5TH- and Dcx-positive neurons, iPS-NPs differentiated into CNPase+ oligodendrocytes. A few cells expressed Chat, while others were DARPP32+. Though, SPCs expressed mainly GFAP, two months PI we found 25% of the cells to be positive for Nkx 6.1, and at four months PI the cells were positive for ChAT and Islet2, motor neuron-specific markers. However, animals transplanted with any cell type displayed significant motor and sensory improvement compared to the controls. The improvement in functional outcome precede the differentiation and maturation of NPs and was also present after grafting of MSCs. We therefore investigate the effect of cell grafting on NF-kB activity, which is associated with inflammatory response induced by SCI. Cell transplantation resulted in significant downregulation of TNF-α production at 10 and 14 days after SCI and in strong inhibition of p65 NF-κB activity at 28 days after SCI, mainly in the gray matter. Morphometric evaluation showed that the white and grey matter was spared in all grafted animals when compared to controls. To assess the effectivity of the MSC treatment, different dosages (0.5 or 1.5 million cells) and repeated applications were compared. Cells or saline were applied intrathecally by lumbar puncture for one week only, or in three consecutive weeks after injury. Histochemical analyses revealed a gradually increasing effect of grafted cells, resulting in a significant increase in the number of GAP43+ fibers, a higher amount of spared gray matter and reduced astrogliosis. mRNA expression of macrophage markers and apoptosis was downregulated after the repeated application of 1.5 million cells.  

Our results demonstrate that the transplantation of neurogenic as well as non-neurogenic stem cells into the lesioned rat spinal cord improves functional outcome due to their strong immunomodulatory properties based on inhibition of a major signaling pathway. Reduced inflammation may have led to observed tissue sparing. Additionally, such immune response modulation could have impacted astrocyte activation resulting in reduced glial scar. The effect of MSCs on spinal cord regeneration is dose-dependent and potentiated by repeated application. Neurogenic stem cells have the ability to interact with the host tissue and differentiate into a more mature phenotype, such as motor neurons. 

Supported by: Operational Programme Research, Development and Education in the framework of the project “Center of Reconstructive Neuroscience”, registration number CZ.02.1.01/0.0./0.0/15_003/0000419, Czech Science Foundation 17-11140S and National Sustainability Program I LO1909.