Cellular Crosstalk between Pulmonary Endothelial Cells and Fibroblasts Suppresses Inflammatory and Fibrotic Responses in Acute Exacerbations of Pulmonary Fibrosis
Authors: Wyman Anne E. , Tulapurkar Mohan E. , Karki Pratap E. , Nguyen Trang T.T. , Todd Nevins W. , Luzina Irina G. , Atamas Sergei P. , Birukova Anna A. , Birukov Konstantin G. 
Published: June 2021

Pulmonary fibrosis is a severe condition with limited treatments. Contribution of the lung vasculature to disease development is not well understood. We began to study pulmonary endothelial cell and fibroblast interactions through experimental models of acute exacerbations of pulmonary fibrosis (AE‐PF). These are severe episodes of lung function decline characterized by features of acute lung injury superimposed on fibrosis. AE‐PF accelerate disease progression in patients with pulmonary fibrosis and have high mortality. The objective of this study was to investigate the effects of acute inflammatory stimuli on inflammatory and fibrotic responses in endothelial cells and fibroblasts from patients with idiopathic pulmonary fibrosis (IPF) and controls. We previously showed decreased levels of the longevity‐promoting molecules sirtuins (SIRTs) in pulmonary fibrosis, with a notable decline in SIRT7 in fibroblasts from patients compared to controls. To gain insight into aging‐related mechanisms in AE‐PF, we examined effects of SIRT manipulation in fibroblasts on inflammatory responses in endothelial cells. Normal human pulmonary artery endothelial cells (HPAEC) were cultured in conditioned media from normal human lung (NHLF) and IPF lung (IPFLF) fibroblasts or co‐cultured directly with fibroblasts. To simulate an aging phenotype in HPAEC‐fibroblast interactions, NHLF were transfected with control or SIRT7 siRNA and co‐cultured with HPAEC. NHLF and IPFLF were cultured with HPAEC‐conditioned media. HPAEC, fibroblasts, or co‐cultures were stimulated with lipopolysaccharide (LPS), TNFα, or TGFβ. ICAM1, IL8, and IL6 levels were measured by ELISA or RT‐PCR. Collagen chains COL1A1, COL1A2, and COL3A1 and alpha smooth muscle actin (α‐SMA) were measured by RT‐PCR or western blotting. In HPAEC, NHLF‐conditioned media decreased basal and LPS‐ or TNFα‐induced levels of ICAM1 by 30–50% and IL‐8 by 50–60%. Compared to NHLF, IPFLF‐conditioned media lowered ICAM1 levels by 10–20%, IL8 by 20–50%, and IL6 by ~10%. Co‐culture experiments showed similar results. Silencing SIRT7 in NHLF co‐cultured with HPAEC had similar, although more pronounced effects, with lower ICAM1, IL8, and IL6 levels. Fibroblast culture with HPAEC or HPAEC‐conditioned media attenuated LPS‐ or TGFβ‐induced increases in COL1A1, COL1A2 and COL3A1 mRNA levels by 1.5–2 fold, IL6 by 2–4 fold, and αSMA by 2–4 fold; αSMA protein levels were decreased by ~2 fold. Endothelial cells and fibroblasts engage in mutual negative feedback to limit inflammation and fibrosis in response to acute inflammatory stimuli. Structural damage and remodeling in pulmonary fibrosis may contribute to loss of protective antifibrotic effects from the vasculature. Decreased endothelial cell inflammatory responses in the presence of IPF versus normal lung fibroblasts may represent a compensatory response to limit inflammation in pulmonary fibrosis. Silencing SIRT7 in NHLF co‐cultured with endothelial cells has pronounced anti‐inflammatory effects, suggesting that an aging‐associated, senescent phenotype in IPF fibroblasts may contribute to suppressed inflammatory activation of the vascular endothelium in pulmonary fibrosis exacerbations. These potential mechanisms are currently being investigated by our group.

This abstract is from the Experimental Biology 2018 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.