Wall shear stress on vascular smooth muscle cells exerts angiogenic effects on extracranial arteriovenous malformations

BACKGROUND: In addition to vascular endothelial cells, vascular smooth muscle cells (VSMCs) are subject to continuous shear stress because of blood circulation. The angiogenic properties of VSMCs in extracranial arteriovenous malformations (AVMs) may exceed those of normal blood vessels if the body responds more sensitively to mechanical stimuli. This study was performed to investigate the hypothesis that rapid angiogenesis may be achieved by mechanical shear stress. METHODS: VSMCs were obtained from six patients who had AVMs and six normal controls. The target genes were set to angiopoietin-2 (AGP2), aquaporin-1 (AQP1), and transforming growth factor-beta receptor 1 (TGFBR1). Reverse-transcriptase polymerase chain reaction (RT-PCR) and real-time PCR were implemented to identify the expression levels for target genes. Immunofluorescence was also conducted. RESULTS: Under the shear stress condition, mean relative quantity values of AGP2, AQP1, and TGFBR1 in AVM tissues were 1.927±0.528, 1.291±0.031, and 2.284±1.461 when compared with neutral conditions. The expression levels of all three genes in AVMs were higher than those in normal tissue except for AQP1 under shear stress conditions. Immunofluorescence also revealed increased staining of shear stress-induced genes in the normal tissue and in AVM tissue. CONCLUSIONS: Shear stress made the VSMCs of AVMs more sensitive. Although the pathogenesis of AVMs remains unclear, our study showed that biomechanical stimulation imposed by shear stress may aggravate angiogenesis in AVMs.