Nanoscale dysregulation of collagen structure-function disrupts mechano-homeostasis and mediates pulmonary fibrosis.

Mark G Jones ,Aiman Alzetani,Franco Conforti,Martin Kolb,Atul Bhaskar,Sumeet Mahajan,Lucy Cao,Alessandra Bonfanti,Luca Richeldi,Sanjay Jogai,Kerry Lunn,Wolfgang Jarolimek,Jack Gauldie,Regan Doherty,Kjetil Ask,James Roberts ,P.b Johnson ,Katherine Ma O’reilly ,Phillip Monk ,Victoria Tear ,Christopher J Brereton ,Sophie Fletcher ,Konstantinos N Bourdakos ,Aurélie Fabre ,Chester Lai ,Philipp J Thurner ,Patricia J Sime ,Serena Chee ,Benjamin C Johnson ,Orestis G Andriotis ,David E Smart ,Ben G Marshall ,Christian Ottensmeier ,Donna E Davies

doi:10.7554/elife.36354

Abstract

Matrix stiffening with downstream activation of mechanosensitive pathways is strongly implicated in progressive fibrosis; however, pathologic changes in extracellular matrix (ECM) that initiate mechano-homeostasis dysregulation are not defined in human disease. By integrated multiscale biomechanical and biological analyses of idiopathic pulmonary fibrosis lung tissue, we identify that increased tissue stiffness is a function of dysregulated post-translational collagen cross-linking rather than any collagen concentration increase whilst at the nanometre-scale collagen fibrils are structurally and functionally abnormal with increased stiffness, reduced swelling ratio, and reduced diameter. In ex vivo and animal models of lung fibrosis, dual inhibition of lysyl oxidase-like (LOXL) 2 and LOXL3 was sufficient to normalise collagen fibrillogenesis, reduce tissue stiffness, and improve lung function in vivo. Thus, in human fibrosis, altered collagen architecture is a key determinant of abnormal ECM structure-function, and inhibition of pyridinoline cross-linking can maintain mechano-homeostasis to limit the self-sustaining effects of ECM on progressive fibrosis.

Highlights

Fibrotic diseases are a major cause of morbidity and mortality worldwide and their prevalence is increasing with an ageing population
Whilst the exact mechanisms of progressive lung fibrosis are uncertain, idiopathic pulmonary fibrosis (IPF) is thought to result from repetitive micro-injuries to the alveolar epithelium promoting fibroblast differentiation into extracellular matrix (ECM)-producing myofibroblasts
Whilst an increase in fibrillar collagen was suggested by second harmonic generation imaging of IPF lung tissue (Figure 1D), quantitation of total collagen concentration by hydroxyproline assay showed no difference in mean total collagen in IPF tissue relative to control tissue following normalisation to either dry weight or to total protein (Figure 1E and Figure 1—figure supplement 1); in addition, no dependence of lung tissue stiffness on collagen concentration was found (Figure 1F)

Summary

Introduction

Fibrotic diseases are a major cause of morbidity and mortality worldwide and their prevalence is increasing with an ageing population. Idiopathic pulmonary fibrosis (IPF) is considered the prototypic chronic progressive fibrotic disease (Raghu et al, 2011). Whilst the exact mechanisms of progressive lung fibrosis are uncertain, IPF is thought to result from repetitive micro-injuries to the alveolar epithelium promoting fibroblast differentiation into extracellular matrix (ECM)-producing myofibroblasts. Fibrillar collagens are a major component of lung ECM that form a scaffold to support tissue architecture and are a primary determinant of tissue stiffness (Senior et al, 1975; White, 2015). The lysyl oxidase (LOX) enzymes are a family of five secreted copper-dependent amine oxidases (LOX and LOX-like (LOXL) 1 to 4) that are responsible for post-translational modification of collagen in the ECM to initiate covalent cross-linking. The type of LOX/LOXL mediated collagen cross-link is determined by the hydroxylation of telopeptidyl and helical lysine residues in collagen prior to cross-link formation (Yamauchi and Sricholpech, 2012), with increased hydroxylation of telopeptide lysine residues by lysyl hydroxylase 2/procollagen lysine,2-oxoglutarate 5-dioxygenase 2 (LH2/PLOD2) proposed to be a general fibrotic phenomenon causing increased hydroxyallysine derived pyridinoline cross-links (Brinckmann et al, 1999; van der Slot et al, 2003)

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