Objectives: Characterize the phenotypic features of smooth muscle cells (SMCs) in the wall of human saccular intracranial aneurysms (sIAs).
Methods and results: We investigated by means of immunohistochemistry the expression of the cytoskeletal differentiation markers α-smooth muscle actin (α-SMA), smooth muscle myosin heavy chains (SMMHCs), and smoothelin in 26 sIAs and 15 nonaneurysmal cerebral arteries. In addition, S100A4, a recently identified marker of dedifferentiated SMCs in atherosclerotic plaques, was also investigated. Six sIAs and 5 nonaneurysmal arteries were used for morphometric analysis. sIAs displayed a significant medial atrophy compared with nonaneurysmal cerebral arteries; moreover, sIA SMCs showed marked decrease of α-SMA and SMMHCs expression and disappearance of smoothelin. Unexpectedly, S100A4 was strongly up-regulated in media SMCs of sIAs.
Conclusions: In sIAs, media SMCs acquire a dedifferentiated phenotype and show de novo expression of S100A4, characteristic features of atherosclerotic plaque SMCs.
Keywords: Atherosclerosis; CD68; Smooth muscle myosin heavy chains; Smoothelin; α-smooth muscle actin.
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