Abstract
BackgroundThe abnormal epithelial-mesenchymal restorative capacity in idiopathic pulmonary fibrosis (IPF) has been recently associated with an accelerated aging process as a key point for the altered wound healing. The advanced glycation end-products (AGEs) are the consequence of non-enzymatic reactions between lipid and protein with several oxidants in the aging process. The receptor for AGEs (RAGEs) has been implicated in the lung fibrotic process and the alveolar homeostasis. However, this AGE-RAGE aging pathway has been under-explored in IPF.MethodsLung samples from 16 IPF and 9 control patients were obtained through surgical lung biopsy. Differences in AGEs and RAGE expression between both groups were evaluated by RT-PCR, Western blot and immunohistochemistry. The effect of AGEs on cell viability of primary lung fibrotic fibroblasts and alveolar epithelial cells was assessed. Cell transformation of fibrotic fibroblasts cultured into glycated matrices was evaluated in different experimental conditions.ResultsOur study demonstrates an increase of AGEs together with a decrease of RAGEs in IPF lungs, compared with control samples. Two specific AGEs involved in aging, pentosidine and Nε-Carboxymethyl lysine, were significantly increased in IPF samples. The immunohistochemistry identified higher staining of AGEs related to extracellular matrix (ECM) proteins and the apical surface of the alveolar epithelial cells (AECs) surrounding fibroblast foci in fibrotic lungs. On the other hand, RAGE location was present at the cell membrane of AECs in control lungs, while it was almost missing in pulmonary fibrotic tissue. In addition, in vitro cultures showed that the effect of AGEs on cell viability was different for AECs and fibrotic fibroblasts. AGEs decreased cell viability in AECs, even at low concentration, while fibroblast viability was less affected. Furthermore, fibroblast to myofibroblast transformation could be enhanced by ECM glycation.ConclusionsAll of these findings suggest a possible role of the increased ratio AGEs-RAGEs in IPF, which could be a relevant accelerating aging tissue reaction in the abnormal wound healing of the lung fibrotic process.
Highlights
The abnormal epithelial-mesenchymal restorative capacity in idiopathic pulmonary fibrosis (IPF) has been recently associated with an accelerated aging process as a key point for the altered wound healing
IPF is characterized by an histologic pattern of usual interstitial pneumonia (UIP) which shows a heterogeneous distribution of dense parenchyma collagen deposition and active fibroblast foci alternating with areas of normal
IPF lung sections presented the strongest staining around the extracellular matrix (ECM) proteins (Fig. 1, B4) and the apical surface of reactive alveolar epithelial cells (AECs) (Fig. 1, B5) and bronchial epithelium (Fig. 1, B6), while no signal was seen into the fibroblast foci
Summary
The abnormal epithelial-mesenchymal restorative capacity in idiopathic pulmonary fibrosis (IPF) has been recently associated with an accelerated aging process as a key point for the altered wound healing. The advanced glycation end-products (AGEs), oxidative non-enzymatic products derived from modified lipids, proteins or nucleic acids, have been implicated in some diseases related to an accelerated aging process [6,7,8], being proposed as markers of oxidative. The involvement of AGEs in promoting ECM protein modification and cross-linking is remarkable [15, 16] In this way, some studies have related a loss of tendon viscoelasticity when incubated with AGEs [17], and an increment of arterial stiffness driven by AGEs accumulation has been described in the aortic walls [18]. A previous report from our group demonstrated stiffness changes in glycated 3D collagen matrices and fibroblast phenotypic transformation [19] This type of in vitro model would mimic the cross-links and AGEs generation. AGEs can glycate some plasmatic proteins, such as globulins or albumin, changing their physicochemical properties [20, 21]
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