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The lung fibroblast surface proteins PDGFRα and CDCP1 as profibrotic mediators in pulmonary fibrosis
The lung fibroblast surface proteins PDGFRα and CDCP1 as profibrotic mediators in pulmonary fibrosis
Idiopathic pulmonary fibrosis (IPF) is a chronic, irreversible, and life-threatening disease with a median survival of 3-5 years after diagnosis. The number of patients suffering from IPF is rapidly increasing, and therapeutic options are very limited. IPF is characterized by altered cellular composition and homeostasis in lung parenchyma, leading to excessive deposition of extracellular matrix (ECM), and ultimately, organ failure. Fibroblasts are the main cell types producing ECM in the lung. In general, fibroblasts play an important role in various cellular responses, including cell proliferation and migration, and therefore are essential for the processes of normal wound healing. The injury of the lung epithelium leads to the recruitment of inflammatory cells and the release of profibrotic growth factors, such as TGFβ, resulting in fibroblast to myofibroblast differentiation. Myofibroblasts represent a highly proliferating, migrating and increased ECM producing phenotype essentially participating in tissue remodeling of the fibrotic lung. Little information, however, exists regarding changes in the fibroblast surface proteome under growth factor stimulation, since the fibroblasts surface proteome is not well characterized to date. Therefore, we have initially performed a cell-surface proteome profiling of primary human lung fibroblasts (phLFs) and further analyzed the impact of TGFβ on it [Heinzelmann et al., 2016]. Here, we identified Platelet derived growth factor receptor-alpha (PDGFRα) and Cub domain containing protein 1 (CDCP1) among the top downregulated proteins. Thus, in my thesis I aimed to investigate in detail their functional role in lung fibroblasts and their impact on IPF. In the first part of this thesis, the effect of TGFβ on the total mRNA and protein expression as well as on cell surface localization of PDGFRα and CDCP1 in primary human lung fibroblasts (phLFs) was determined. We confirmed PDGFRα and CDCP1 surface localization and downregulation of expression levels by TGFβ. In the second part, functional roles of both surface proteins in phLFs were addressed. With a focus on PDGF signaling first, PDGF ligand-receptor interactions were analyzed showing that ligand PDGF-AB predominantly activates PDGFRα, whereas PDGF-DD activates PDGFRβ downstream signaling as demonstrated by increased Akt phosphorylation. Surprisingly, the expression of PDGFRβ receptor was increased in the absence of PDGFRα via siRNA-mediated knockdown. Moreover, the role of PDGF signaling in cell invasion was addressed showing that PDGF-AB-induced signaling increased invasion properties of human lung fibroblasts and this effect is mediated in a PDGFRα-dependent manner. Importantly, Nintedanib decreased TGFβ-increased αSMA and collagen V total protein expression, however, this effect was largely attenuated in PDGFRα-depleted cells. Analysis of CDCP1 regulation revealed that TGFβ downregulated CDCP1 expression in a time-dependent manner and this effect was potentially mediated via increased ubiquitin-independent proteasomal degradation of CDCP1, but not canonical or non-canonical TGFβ pathway. Interestingly, CDCP1 also affected downstream TGFβ signaling as demonstrated by increased Smad3 phosphorylation in CDCP1-depleted cells treated with TGFβ. Moreover, CDCP1 depletion enhanced TGFβ-mediated cell adhesion capacity of human lung fibroblasts. CDCP1 knockdown led to an increase in total protein expression levels of αSMA, collagen III, and collagen V in phLFs, which was independent of TGFβ. Importantly, αSMA-positive interstitial myofibroblasts located in fibroblastic foci of IPF lung sections displayed a low expression of CDCP1, whereas non-differentiated interstitial lung fibroblasts in sections of donor lungs were highly CDCP1-positive, and clearly αSMA-negative. In sum, I showed in my study that TGFβ regulates the expression of fibroblasts surface proteins, as shown here for PDGFRα and CDCP1, which in turn modulates their function in lung fibroblasts and lung disease.
Not available
Noskovičová, Nina
2018
English
Universitätsbibliothek der Ludwig-Maximilians-Universität München
Noskovičová, Nina (2018): The lung fibroblast surface proteins PDGFRα and CDCP1 as profibrotic mediators in pulmonary fibrosis. Dissertation, LMU München: Faculty of Medicine
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Abstract

Idiopathic pulmonary fibrosis (IPF) is a chronic, irreversible, and life-threatening disease with a median survival of 3-5 years after diagnosis. The number of patients suffering from IPF is rapidly increasing, and therapeutic options are very limited. IPF is characterized by altered cellular composition and homeostasis in lung parenchyma, leading to excessive deposition of extracellular matrix (ECM), and ultimately, organ failure. Fibroblasts are the main cell types producing ECM in the lung. In general, fibroblasts play an important role in various cellular responses, including cell proliferation and migration, and therefore are essential for the processes of normal wound healing. The injury of the lung epithelium leads to the recruitment of inflammatory cells and the release of profibrotic growth factors, such as TGFβ, resulting in fibroblast to myofibroblast differentiation. Myofibroblasts represent a highly proliferating, migrating and increased ECM producing phenotype essentially participating in tissue remodeling of the fibrotic lung. Little information, however, exists regarding changes in the fibroblast surface proteome under growth factor stimulation, since the fibroblasts surface proteome is not well characterized to date. Therefore, we have initially performed a cell-surface proteome profiling of primary human lung fibroblasts (phLFs) and further analyzed the impact of TGFβ on it [Heinzelmann et al., 2016]. Here, we identified Platelet derived growth factor receptor-alpha (PDGFRα) and Cub domain containing protein 1 (CDCP1) among the top downregulated proteins. Thus, in my thesis I aimed to investigate in detail their functional role in lung fibroblasts and their impact on IPF. In the first part of this thesis, the effect of TGFβ on the total mRNA and protein expression as well as on cell surface localization of PDGFRα and CDCP1 in primary human lung fibroblasts (phLFs) was determined. We confirmed PDGFRα and CDCP1 surface localization and downregulation of expression levels by TGFβ. In the second part, functional roles of both surface proteins in phLFs were addressed. With a focus on PDGF signaling first, PDGF ligand-receptor interactions were analyzed showing that ligand PDGF-AB predominantly activates PDGFRα, whereas PDGF-DD activates PDGFRβ downstream signaling as demonstrated by increased Akt phosphorylation. Surprisingly, the expression of PDGFRβ receptor was increased in the absence of PDGFRα via siRNA-mediated knockdown. Moreover, the role of PDGF signaling in cell invasion was addressed showing that PDGF-AB-induced signaling increased invasion properties of human lung fibroblasts and this effect is mediated in a PDGFRα-dependent manner. Importantly, Nintedanib decreased TGFβ-increased αSMA and collagen V total protein expression, however, this effect was largely attenuated in PDGFRα-depleted cells. Analysis of CDCP1 regulation revealed that TGFβ downregulated CDCP1 expression in a time-dependent manner and this effect was potentially mediated via increased ubiquitin-independent proteasomal degradation of CDCP1, but not canonical or non-canonical TGFβ pathway. Interestingly, CDCP1 also affected downstream TGFβ signaling as demonstrated by increased Smad3 phosphorylation in CDCP1-depleted cells treated with TGFβ. Moreover, CDCP1 depletion enhanced TGFβ-mediated cell adhesion capacity of human lung fibroblasts. CDCP1 knockdown led to an increase in total protein expression levels of αSMA, collagen III, and collagen V in phLFs, which was independent of TGFβ. Importantly, αSMA-positive interstitial myofibroblasts located in fibroblastic foci of IPF lung sections displayed a low expression of CDCP1, whereas non-differentiated interstitial lung fibroblasts in sections of donor lungs were highly CDCP1-positive, and clearly αSMA-negative. In sum, I showed in my study that TGFβ regulates the expression of fibroblasts surface proteins, as shown here for PDGFRα and CDCP1, which in turn modulates their function in lung fibroblasts and lung disease.