Boosting the hypoxic response in myeloid cells accelerates resolution of fibrosis and regeneration of the liver in mice

Chahrazade Kantari-Mimoun,Helene Rundqvist,Ursula Lemberger,Joachim Fandrey,Christian Stockmann,Anna-Katharina Meinecke,Thomas Mathivet,Magali Castells,Christoph Österreicher,Milos Gojkovic,Corinne Milien,Katrin Schrödter,Ralph Klose,Ewelina Krzywinska

doi:10.18632/oncotarget.14749

Abstract

We have recently shown that targeting Vascular Endothelial Growth Factor (VEGF) specifically in scar-infiltrating myeloid cells prevented remodeling of the sinusoidal vasculature and abrogated the resolution of murine liver fibrosis, thereby unmasking an unanticipated link between angiogenesis and resolution of fibrosis. In a gain of function approach, we wanted to test the impact of VEGF overexpression in myeloid cells on fibrolysis. We observe that genetic inactivation of the von Hippel Lindau protein (VHL), a negative regulator of Hypoxia-inducible factors (HIF) in myeloid cells, leads to increased VEGF expression and most importantly, accelerated matrix degradation and reduced myofibroblast numbers after CCl4 challenge. This is associated with enhanced expression of MMP-2 and -14 as well as lower expression of TIMP-2 in liver endothelial cells. In addition, we report increased expression of MMP-13 in scar-associated macrophages as well as improved liver regeneration upon ablation of VHL in myeloid cells. Finally, therapeutic infusion of macrophages nulli-zygous for VHL or treated with the pharmacologic hydroxylase inhibitor and HIF-inducer Dimethyloxalylglycine (DMOG) accelerates resolution of fibrosis. Hence, boosting the HIF-VEGF signaling axis in macrophages represents a promising therapeutic avenue for the treatment of liver fibrosis.

Highlights

Liver fibrosis is characterized by the loss of parenchyma and deposition of extracellular matrix (ECM) components by activated myofibroblasts, leading to excessive scar formation and organ failure [1, 2]
We tested the therapeutic potential of genetically inactivating the von Hippel Lindau protein (VHL), a negative regulator of Hypoxia-inducible factors (HIF) and HIF-dependent Vascular Endothelial Growth Factor (VEGF) expression [10, 11] in myeloid cells (VHLfl/fl-LysMCre+ mice) using a loxP-flanked VHL allele crossed to the lysozyme M promoter-driven Cre recombinase [14] which results in VEGF overexpression in macrophages (Figure 1A)
Mouse studies have shown that transfer of untreated cells of the monocyte-macrophage lineage is able to www.impactjournals.com/oncotarget reduce fibrosis as well to foster liver regeneration [6] and clinical testing of this approach is on the way [4]

Summary

Introduction

Liver fibrosis is characterized by the loss of parenchyma and deposition of extracellular matrix (ECM) components by activated myofibroblasts, leading to excessive scar formation and organ failure [1, 2]. The recovery process requires first, ECM degradation along with resolution of the fibrotic scar, and second, regeneration of the hepatocyte population involving the activation of liver progenitor cells [4, 5]. The monocyte-macrophage lineage plays a crucial role in the resolution of fibrosis as well as liver regeneration by driving the expansion of liver progenitor cells [6]. In this context, different macrophage subtypes have been described including antifibrotic, CD11Bhi F4/80int Ly6Clo “restorative” macrophages with crucial www.impactjournals.com/oncotarget pro-resolution properties [7]. Bone marrow cell treatment for liver cirrhosis holds considerable therapeutic potential [4, 6, 8]

Methods

Results

Conclusion