Lysyl oxidases regulate fibrillar collagen remodelling in idiopathic pulmonary fibrosis

Abstract

Idiopathic pulmonary fibrosis (IPF) is a progressive scarring disease of the lung with few effective therapeutic options. Structural remodelling of the extracellular matrix [i.e. collagen cross-linking mediated by the lysyl oxidase (LO) family of enzymes (LOX, LOXL1-4)] might contribute to disease pathogenesis and represent a therapeutic target. This study aimed to further our understanding of the mechanisms by which LO inhibitors might improve lung fibrosis. Lung tissues from IPF and non-IPF subjects were examined for collagen structure (second harmonic generation imaging) and LO gene (microarray analysis) and protein (immunohistochemistry and western blotting) levels. Functional effects (collagen structure and tissue stiffness using atomic force microscopy) of LO inhibitors on collagen remodelling were examined in two models, collagen hydrogels and decellularized human lung matrices. LOXL1/LOXL2 gene expression and protein levels were increased in IPF versus non-IPF. Increased collagen fibril thickness in IPF versus non-IPF lung tissues correlated with increased LOXL1/LOXL2, and decreased LOX, protein expression. β-Aminoproprionitrile (β-APN; pan-LO inhibitor) but not Compound A (LOXL2-specific inhibitor) interfered with transforming growth factor-β-induced collagen remodelling in both models. The β-APN treatment group was tested further, and β-APN was found to interfere with stiffening in the decellularized matrix model. LOXL1 activity might drive collagen remodelling in IPF lungs. The interrelationship between collagen structural remodelling and LOs is disrupted in IPF lungs. Inhibition of LO activity alleviates fibrosis by limiting fibrillar collagen cross-linking, thereby potentially impeding the formation of a pathological microenvironment in IPF.

Targeting Lysyl oxidase-like 2 in Idiopathic Pulmonary Fibrosis

“…Thus, our data were consistent with previous reports in which it was observed that LOXL2 transcript levels were increased in IPF 10,22 .…”

“…2A) but the expression of LOXL2 was almost exclusively extracellular in explanted lung samples ( Fig 2B). The latter finding was consistent with previous findings that this enzyme is secreted and predominately localizes to the ECM in the IPF lung 22 .…”

“…Studies in a bleomycin-induced pulmonary fibrosis model strongly suggested that LOXL2 was an attractive target in fibrosis 16 Collagen cross-linking mediated by the LO family of enzymes, most notably LOXL2, has been examined in various in vitro studies and the role of these enzymes in this process appears to be firmly established. Specifically, previous studies had indicated that limiting the process of fibrillar collagen cross-linking was likely to correct the pathological microenvironment present in IPF 22 .…”

Lysyl Oxidase Like‐2 (LOXL2): An Emerging Oncology Target

“…This in vivo experiment suggested that BAPN has a role in tumor stroma or surrounding epithelium as LOX does not have a direct impact on tumor cell viability . BAPN has also been tested in IPF, reducing stiffness and returning collagen remodeling to baseline levels (Table , Entry 3) . Furthermore, LOX, LOXL2, and LOXL3 were identified at higher levels in human donor vessels of those diagnosed with idiopathic pulmonary arterial hypertension .…”

Human lung extracellular matrix hydrogels resemble the stiffness and viscoelasticity of native lung tissue

“…The absence of cells in the dECM hydrogels would mean there were no new covalent cross-links established within the hydrogels. The greater degree of matrix organization in the IPF tissue (26) and the stiffer fibroblasts within these tissues (14) would also contribute to the differences in stress relaxation.…”