Microvascular Dysfunction Following Multiwalled Carbon Nanotube Exposure Is Mediated by Thrombospondin-1 Receptor CD47.

Abstract

Pulmonary exposure to multiwalled carbon nanotubes (MWCNTs) disrupts peripheral microvascular function. Thrombospondin-1 (TSP-1) is highly expressed during lung injury and has been shown to alter microvascular reactivity. It is unclear exactly how TSP-1 exerts effects on vascular function, but we hypothesized that the TSP-1 receptor CD47 may mediate changes in vasodilation. Wildtype (WT) or CD47 knockout (CD47 KO) C57B6/J-background animals were exposed to 50 µg of MWCNT or saline control via pharyngeal aspiration. Twenty-four hours postexposure, intravital microscopy was performed to assess arteriolar dilation and venular leukocyte adhesion and rolling. To assess tissue redox status, electron paramagnetic resonance and NOx measurements were performed, while inflammatory biomarkers were measured via multiplex assay.Vasodilation was impaired in the WT + MWCNT group compared with control (57 ± 9 vs 90 ± 2% relaxation), while CD47 KO animals showed no impairment (108 ± 8% relaxation). Venular leukocyte adhesion and rolling increased by >2-fold, while the CD47 KO group showed no change. Application of the antioxidant apocynin rescued normal leukocyte activity in the WT + MWCNT group. Lung and plasma NOx were reduced in the WT + MWCNT group by 47% and 32%, respectively, while the CD47 KO groups were unchanged from control. Some inflammatory cytokines were increased in the CD47 + MWCNT group only. In conclusion, TSP-1 is an important ligand mediating MWCNT-induced microvascular dysfunction, and CD47 is a component of this dysregulation. CD47 activation likely disrupts nitric oxide (•NO) signaling and promotes leukocyte-endothelial interactions. Impaired •NO production, signaling, and bioavailability is linked to a variety of cardiovascular diseases in which TSP-1/CD47 may play an important role.