No abstract

Lysophosphatidic acid (LPA) is an extracellular lipid mediator involved in many physiological functions by signaling through six known G-protein-coupled receptors (LPA 1-LPA 6). In the central nervous system (CNS), LPA mediates a wide range of effects, including neural progenitor cell physiology, astrocyte and microglia activation, neuronal cell death, axonal retraction, and contributions to pain, schizophrenia and hydrocephalus. We recently reported that LPA-LPA 1 signaling mediates functional deficits and myelin loss after spinal cord injury (SCI). Here, we provide clear evidence on the deleterious contribution of another LPA receptor, LPA 2 , to myelin loss after SCI. We found that LPA 2 is constitutively expressed in the spinal cord parenchyma and its transcripts were up-regulated after contusion injury, in part, by microglial cells. We also found that the demyelinating lesion triggered by intraspinal injection of LPA into the undamaged spinal cord was markedly reduced in the lack of LPA 2. Similarly, LPA 2 deficient mice showed enhanced motor skills and myelin sparing after SCI. To gain insights into the detrimental actions of LPA 2 in spinal cord we performed cell culture studies. These experiments revealed that, similar to LPA 1 , activation of microglia LPA 2 led to oligodendrocyte cell death. Moreover, we also found that the cytotoxic effects underlaying microglial LPA-LPA 2 axis were mediated by the release of purines by microglia and the activation of P 2 X 7 receptor on oligodendrocytes. Overall, this study provides new mechanistic insights into how LPA contributes to SCI physiopathology, and suggest that targeting LPA 2 could be a novel therapeutic approach for the treatment of acute SCI.

Spinal cord injury (SCI) causes loss of neural functions below the level of the lesion due to interruption of spinal pathways and secondary neurodegenerative processes. The transplant of neural stem cells (NSCs) is a promising approach for the repair of SCI. Reprogramming of adult somatic cells into induced pluripotent stem cells (iPSCs) is expected to provide an autologous source of iPSC-derived NSCs, avoiding the immune response as well as ethical issues. However, there is still limited information on the behavior and differentiation pattern of transplanted iPSC-derived NSCs within the damaged spinal cord. We transplanted iPSC-derived NSCs, obtained from adult human somatic cells, into rats at 0 or 7 days after SCI, and evaluated motor-evoked potentials and locomotion of the animals. We histologically analyzed engraftment, proliferation, and differentiation of the iPSC-derived NSCs and the spared tissue in the spinal cords at 7, 21, and 63 days posttransplant. Both transplanted groups showed a late decline in functional recovery compared to vehicle-injected groups. Histological analysis showed proliferation of transplanted cells within the tissue and that cells formed a mass. At the final time point, most grafted cells differentiated to neural and astroglial lineages, but not into oligodendrocytes, while some grafted cells remained undifferentiated and proliferative. The proinflammatory tissue microenviroment of the injured spinal cord induced proliferation of the grafted cells and, therefore, there are possible risks associated with iPSC-derived NSC transplantation. New approaches are needed to promote and guide cell differentiation, as well as reduce their tumorigenicity once the cells are transplanted at the lesion site.