[show abstract][hide abstract] ABSTRACT: Synphilin-1 was originally identified as a binding protein of α-synuclein, a major component of Lewy bodies in Parkinson's disease. Synphilin-1 localizes mainly in the synaptic terminals and is also found in Lewy bodies. We previously demonstrated the expression of α-synuclein in vascular endothelial cells. The present study was undertaken to address the expression of synphilin-1 in endothelial cells. Synphilin-1 immunoreactivity was detected in the vessel walls, particularly in endothelial cells, in postmortem human brain. Expressions of mRNA and protein for synphilin-1 in human umbilical vein endothelial cells in culture were demonstrated by reverse-transcription polymerase-chain reaction and western blotting. Synphilin-1 is constitutively expressed in endothelial cells and may have some physiological function in the vascular wall.