Abstract
It has been shown before that exposure to nanomaterials (NMs) might promote the formation of foam cells, the key cells involved in all stages of atherosclerosis. However, to our best knowledge, previous studies, particularly in vitro studies, only investigated the transformation of macrophages into foam cells, whereas the importance of smooth muscle cells (SMCs) was overlooked. The present study investigated the toxicity of pristine multi-walled carbon nanotubes (MWCNTs; Code XFM19) and carboxylated MWCNTs (Code XFM21) to human aortic smooth muscle cells (HASMCs). The results showed that exposure to both types of MWCNTs significantly reduced mitochondrial activity but might not damage lysosomes. MWCNT exposure had minimal impact on cytokine release but significantly promoted lipid accumulation, which was significantly inhibited when the cells were pre-incubated with ER stress inhibitors or antioxidants. The mRNA levels of ER stress markers DDIT3 and XBP-1 s and protein levels of chop and p-chop were induced particularly by XFM21, accompanying with increased SREBF1 and SREBF2 mRNA as well as FASN protein, the key regulators involved in de novo lipogenesis. In addition, the mRNA levels of KLF4 and KLF5 and protein levels of KLF were induced after exposure to both types of MWCNTs, associated with an increase of CD68 protein levels. We concluded that MWCNTs might promote lipid accumulation in HASMCs through the induction of ER stress leading to de novo lipogenesis, as well as the activation of KLF pathway resulting in SMC transformation.