Nkx2.2 expression in differentiation of oligodendrocyte precursor cells and inhibitory factors for differentiation of oligodendrocytes after traumatic spinal cord injury

Because successful remyelination does not occur following traumatic spinal cord injury, patients suffer from long tract dysfunction. However, demyelination is followed by remyelination in early multiple sclerosis. Oligodendrocyte precursor cells constitute a large cell population in the adult mammalian central nervous system. We demonstrated the proliferation, migration, and differentiation of oligodendrocyte precursor cells in chemically induced demyelination, a model for multiple sclerosis, and reported that Nkx2.2 expression may regulate oligodendrocyte precursor cell differentiation, making it a key factor in the differentiation. To investigate what factors disturb remyelination in spinal cord injury, we examined the oligodendrocyte precursor cell proliferation and differentiation, and the expression of Nkx2.2 using contusive injury in rats as a model for traumatic spinal cord injury. This study showed that oligodendrocyte precursor cells proliferated after contusive injury but did not subsequently differentiate. The number of Nkx2.2-positive oligodendrocyte precursor cells did not significantly change in the tissue surrounding the lesion. Within the demyelinating lesion, the peak of Nkx2.2positive oligodendrocyte precursor cell was delayed, and its level was lower than in the chemical models. No clearly recognizable oligodendrocytes were found in the demyelinating lesion throughout the observation period. To assess whether environmental changes differ between these two models, mRNA expressions of various cytokines were evaluated and compared. IL-1 beta and IL-6 mRNA significantly increased in the contusion-induced injury model, 6 h after the injury. These results suggest that environmental factors such as cytokines may affect Nkx2.2 expression or oligodendrocyte precursor cell differentiation in the contusion-induced spinal cord injury model.