The Particulars of Particulate Matter Induced Myofibroblast Differentiation
Craig, Nathan
2022
Abstract
Particulate matter (PM) has long been appreciated as a biologically significant component of air pollution that has major impacts on public health. Exposure to PM less than 2.5 µm in diameter (PM2.5) is associated with mortality, and increased incidence of lung diseases. While the effect that PM2.5 exposure has on many cell types, such as epithelial cells, is relatively well studied, the effect it has on mesenchymal cells, such as fibroblasts, is less understood. This study seeks to determine the effect that PM2.5 exposure has on fibroblast-to-myofibroblast differentiation, which is a critical step in pulmonary fibrosis, a disease that has been shown to be exacerbated by PM2.5 exposure. We assessed the effect that PM2.5 exposure has on fibroblast biology and myofibroblast differentiation through four research aims. In Aim 1, we delineated the conditions and determinants by which ambient PM2.5 affected fibroblast-to-myofibroblast differentiation and found that, interestingly, repeated low concentration PM2.5 exposures promoted increases in αSMA and collagen, markers of myofibroblast differentiation. Furthermore, follow-up studies utilizing pharmacological inhibitors showed that NF-κB is critical for this effect. In Aim 2, we sought to investigate the effect that PM2.5 exposure has on bone morphogenic protein (BMP)2 expression and secretion in fibroblasts. BMP2 is a cytokine that can promote or inhibit myofibroblast differentiation and can be activated by NF-κB. We found that PM2.5 exposure promoted a dose-dependent increase in BMP2 transcript and secreted protein. The role of BMP2 on PM2.5-induced increase in myofibroblast differentiation was less clear; however, as treatment with exogenous BMP2 promoted myofibroblast differentiation, while blocking endogenous BMP2 with an siRNA or inhibitory protein (noggin), also promoted myofibroblast differentiation. This implies that a certain level of BMP2 signaling is critical for fibroblasts to maintain homeostasis, but that too much signaling has deleterious effects as well. In Aim 3, we examine the effect that PM2.5 exposure has on cytokine secretion and DNA methylation in lung fibroblasts. We analyze fibroblasts exposed to PM2.5 on a DNA methylation array, as well as supernatants collected from similarly exposed fibroblasts on a Luminex cytokine kit. We found that low concentrations of PM2.5 promoted methylation changes in genes enriched in cell cycle whereas high concentrations promoted methylation changes in a completely different set of genes, including those enriched in adhesion, neuronogeneis, and cell signaling. Additionally, IL-12 was found to be significantly upregulated following low concentration exposure to PM2.5 in our Luminex experiments. We sought to determine if PM2.5 exposure in vivo increases susceptibility to pulmonary fibrosis in Aim 4. The data in our prior Aims suggest that PM2.5 exposure promotes myofibroblast differentiation, an important process in fibrogenesis. Here, we exposed mice to PM2.5 and assess their susceptibility to bleomycin-induced fibrosis. Despite promising results in a pilot experiment, where we demonstrated a trend toward higher collagen content, as measured by hydroxyproline, in the lungs of male mice exposed to PM2.5 prior to bleomycin treatment, we were unable to replicate the results in a larger study with female mice. This implies that sex may have significant effects on susceptibility to PM2.5 exposure. PM2.5 exposure results in a myriad of changes in fibroblast biology, changes that can often promote fibrosis. The exact effects of PM2.5 on fibroblasts vary depending on the duration, frequency, and concentration of exposure, demonstrating the public health significance of even low levels of air pollution.Deep Blue DOI
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Particulates Fibrosis Fibroblasts PM2.5
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