Carbon nanotubes and crystalline silica induce matrix remodeling and contraction by stimulating myofibroblast transformation in a three-dimensional culture of human pulmonary fibroblasts: role of dimension and rigidity.

Pulmonary fibrosis is a poorly understood pathologic condition. Carbon nanotubes (CNTs) are nanomaterials with potentials for broad applications. CNTs can induce pulmonary fibrosis in animals, a cause for concern for exposed workers and consumers. Given the large number of CNTs available on the market and the seemingly infinite number of ways these particles can be modified in ways that may affect toxicity, in vitro models that can be used to quickly and effectively investigate the relative fibrogenicity of CNTs are much needed. Here we analyzed the fibrogenic potentials of six CNTs of varying physical properties and crystalline silica using two- and three-dimensional (2D and 3D, respectively) in vitro models. WI38-VA13 human pulmonary fibroblasts were treated with CNTs or silica, with TGF-β1, a known inducer of fibroblast differentiation, as positive control. The cells were examined for fibrotic matrix alterations, including myofibroblast transformation, matrix remodeling, and matrix contraction. While all tested CNTs induced myofibroblast differentiation in 2D and 3D cultures, the 3D culture allowed the examination of myofibroblast clustering, collagen deposition and rearrangement, cell division, and matrix contraction in response to fibrogenic exposures, processes critical for fibrosis in vivo. At 1 µg/ml, MWCNTs elicit higher induction of myofibroblast differentiation and matrix remodeling than SWCNTs. Among MWCNTs, those with the highest and lowest aspect ratios produced the largest effects, which were comparable to those by TGF-β1 and higher than those by silica. Thus, the 3D collagen-based model enables the study of matrix fibrotic processes induced by CNTs and silica particles directly and effectively.