α-synuclein is expressed in a variety of brain tumors showing neuronal differentiation

α-synuclein is presynaptic nerve terminal protein and its immunoreactivity has been observed in such neurodegenerative structures as senile plaques of Alzheimer's disease or Lewy bodies of Parkinson's disease. The physiological role of α-synuclein is still unknown. It is speculated that α-synuclein may be expressed in brain tumors, especially in those showing neuronal differentiation. We examined the immunohistochemical localization of α-synuclein in 77 human brain tumors. α-synuclein was widely distributed in the brain tumors showing neuronal differentiation. As a result, positive immunostaining for α-synuclein was observed in ganglioglioma, medulloblastoma, neuroblastoma, primitive neuroectodermal tumor, pineocytoma/pineoblastoma, and central neurocytoma. Compared with other neuronal markers, the positive ratio of a-synuclein was not as high as synaptophysin, microtubule-associacted protein 2, neuron-specific enolase and tau, but it was higher than neurofilament and chromogranin A. The expression of synaptophysin was diffusely observed in the cytoplasm, cellular processes and nucleus in tumors showing neuronal differentiation; however, the expression of α-synuclein was predominantly observed in the cytoplasm of the tumors as well as in the cellular processes. On the other hand, non-neuronal brain tumors such as astrocytic tumors or meningiomas were totally negative for α-synuclein. In conclusion, the appearance of an α-synuclein-positive structure was not limited to neurodegenerative diseases, but could also be detected in neoplastic cells showing neuronal differentiation.