Pseudohypoxic HIF pathway activation dysregulates collagen structure-function in human lung fibrosis

Abstract

Extracellular matrix (ECM) stiffening with downstream activation of mechanosensitive pathways is strongly implicated in fibrosis. We previously reported that altered collagen nanoarchitecture is a key determinant of pathogenetic ECM structure-function in human fibrosis (Jones et al., 2018). Here, through human tissue, bioinformatic and ex vivo studies we show that hypoxia-inducible factor (HIF) pathway activation is a critical pathway for this process regardless of oxygen status (pseudohypoxia). Whilst TGFβ increased rate of fibrillar collagen synthesis, HIF pathway activation was required to dysregulate post-translational modification of fibrillar collagen, promoting 'bone-type' cross-linking, altering collagen nanostructure, and increasing tissue stiffness. In vitro, knock down of Factor Inhibiting HIF (FIH) or oxidative stress caused pseudohypoxic HIF activation in normal fibroblasts. In contrast, endogenous FIH activity was reduced in fibroblasts from patients with lung fibrosis in association with significantly increased normoxic HIF pathway activation. In human lung fibrosis tissue, HIF mediated signalling was increased at sites of active fibrogenesis whilst subpopulations of IPF lung mesenchymal cells had increases in both HIF and oxidative stress scores. Our data demonstrate that oxidative stress can drive pseudohypoxic HIF pathway activation which is a critical regulator of pathogenetic collagen-structure function in fibrosis.

Towards an artificial human lung: modelling organ-like complexity to aid mechanistic understanding

“…Similarly, several natural biomaterials such as Matrigel®, Chitosan, gelatine, collagen and alginate, as well as other synthetic materials including polyethylene glycol (PEG), Poly(lactic-co-glycolic acid) (PLGA) and pluronic F-127, mimicking the ECM/scaffold, have successfully been used in 3D bio-printing for construction of lung tissue [16,160,161]. An alternative is the long-term culture of lung fibroblasts from human explant lung tissue under defined conditions to promote the selfassembly of a mature 3D ECM [162,163]. Such an approach can recapitulate the topology and stiffness of the lung cellular microenvironment, and permits functional assessment of tissue stiffness [162].…”