Upregulation of myelin and lymphocyte protein (MAL) after traumatic spinal cord injury in rats

Myelin and lymphocyte protein (MAL) was identified as a tetraspan proteolipid that is highly expressed by oligodendrocytes and Schwann cells as a component of compact myelin. It has also been reported to be a tumour suppressor and induces apoptosis through the Fas pathway. However, its expression and function in spinal cord injury are still unclear, especially in gray matter. In this study, we performed a spinal cord contusion injury (SCI) model in adult rats and detected the dynamic changes of MAL expression in spinal cord. Western blot and immunohistochemistry analysis revealed that MAL was present in gray and white matter of normal spinal cord. It gradually increased, got a peak at 1 day, and then declined to basal levels after spinal cord injury. Double immunofluorescence staining showed that MAL immunoreactivity was found in neurons and oligodendrocytes. Interestingly, MAL expression was increased predominantly in neurons rather than oligodendrocytes. We also examined the expression profiles of active caspase-3, whose changes were correlated with the expression profiles of MAL. Moreover, co-localization of MAL with active caspase-3 was detected. In conclusion, this is the first description of MAL expression changes in gray matter after spinal cord injury. Our results prompted that MAL might participate in CNS pathophysiology after SCI.