MMP-9-Dependent Serum-Borne Bioactivity Caused by Multiwalled Carbon Nanotube Exposure Induces Vascular Dysfunction via the CD36 Scavenger Receptor

Abstract

Inhalation of multi walled carbon nanotubes (MWCNT) causes systemic effects including vascular inflammation, endothelial dysfunction, and acute phase protein expression. MWCNTs translocate only minimally beyond the lungs, thus cardiovascular effects thereof may be caused by generation of secondary biomolecular factors from MWCNT-pulmonary interactions that spill over into the systemic circulation. Therefore, we hypothesized that induced matrix metalloproteinase-9 (MMP-9) is a generator of factors that, in turn, drive vascular effects through ligand-receptor interactions with the multiligand pattern recognition receptor, CD36. To test this, wildtype (WT; C57BL/6) and MMP-9−/− mice were exposed to varying doses (10 or 40 μg) of MWCNTs via oropharyngeal aspiration and serum was collected at 4 and 24 h postexposure. Endothelial cells treated with serum from MWCNT-exposed WT mice exhibited significantly reduced nitric oxide (NO) generation, as measured by electron paramagnetic resonance, an effect that was independent of NO scavenging. Serum from MWCNT-exposed WT mice inhibited acetylcholine (ACh)-mediated relaxation of aortic rings at both time points. Absence of CD36 on the aortic rings (obtained from CD36-deficient mice) abolished the serum-induced impairment of vasorelaxation. MWCNT exposure induced MMP-9 protein levels in both bronchoalveolar lavage and whole lung lysates. Serum from MMP-9−/− mice exposed to MWCNT did not diminish the magnitude of vasorelaxation in naïve WT aortic rings, although a modest right shift of the ACh dose-response curve was observed in both MWCNT dose groups relative to controls. In conclusion, pulmonary exposure to MWCNT leads to elevated MMP-9 levels and MMP-9-dependent generation of circulating bioactive factors that promote endothelial dysfunction and decreased NO bioavailability via interaction with vascular CD36.

Thrombospondin-1 mediates multi-walled carbon nanotube induced impairment of arteriolar dilation

“…The results of this MWCNT exposure were obtained by using a powerful technique for the assessment of microvascular function in vivo combined with a well-characterized knockout model. This study also represents one of a handful of attempts to use genetically manipulated animals to investigate molecular mechanisms of nanotoxicity (Aragon et al, 2016; Bagher et al, 2011; Chen et al, 2015; Louro et al, 2014), and is the first in the area of the peripheral microcirculation.…”

“…Recently, a role for CD36 has been described in mediating vascular dysfunction following MWCNT inhalation (Aragon et al, 2016). The authors report that endothelial cells incubated in serum collected from mice post-exposure generated significantly less NO, independent of NO scavenging.…”

Serum-borne bioactivity caused by pulmonary multiwalled carbon nanotubes induces neuroinflammation via blood–brain barrier impairment

“…Inhalation of MWCNTs induces lung inflammation, as indicated by infiltration of inflammatory cells from the periphery, increased lung permeability, and fibrosis (10,11). Despite their very limited ability to translocate beyond the lung (12), MWCNTs have been shown to induce extrapulmonary toxicity through as-yet unknown pathways (13)(14)(15). Pulmonary interactions with inhaled pollutants, including MWCNTs, can generate secondary bioactive factors that spill over into the systemic circulation and are distributed throughout the body (15)(16)(17).…”

“…Despite their very limited ability to translocate beyond the lung (12), MWCNTs have been shown to induce extrapulmonary toxicity through as-yet unknown pathways (13)(14)(15). Pulmonary interactions with inhaled pollutants, including MWCNTs, can generate secondary bioactive factors that spill over into the systemic circulation and are distributed throughout the body (15)(16)(17). One consequence of these circulating factors is activation of the endothelium, characterized by the expression of adhesion molecules and recruitment/activation of circulating inflammatory cells (18).…”

Thrombospondin‐1 and microRNA‐1 expression in response to multiwalled carbon nanotubes in alveolar epithelial cells

“…In alveolar epithelial cells, MWCNT induce the expression of ECM components TGFβ and Col3A1, and remodeling zinc‐metalloproteinases MMP‐9 and MMP‐12 . In support of the in vitro studies, the in vivo studies also showed the production of TGFβ and MMP‐9 in bronchoalveolar lavage cells (BAL) or whole lung lysate of mice treated with MWCNT . In addition to activating TGFβ‐mediated fibrosis, MWCNT have been shown to also induce epithelial‐mesenchymal transition (EMT) through TGFβ‐induced Akt/GSK/Snail‐1 signaling …”