Open Access Highly Accessed Research article

Human monocytes and macrophages differ in their mechanisms of adaptation to hypoxia

Monique Fangradt12, Martin Hahne123*, Timo Gaber124, Cindy Strehl12, Roman Rauch1, Paula Hoff12, Max Löhning12, Gerd-Rüdiger Burmester1 and Frank Buttgereit124

  • * Corresponding author: Martin Hahne hahne@drfz.de

  • † Equal contributors

Author affiliations

1 Department of Rheumatology and Clinical Immunology, Charité University Hospital, Charitéplatz 1, Berlin, 10117 Germany

2 German Rheumatism Research Center (DRFZ), Charitéplatz 1, Berlin, 10117 Germany

3 Berlin-Brandenburg School for Regenerative Therapies (BSRT), Foehrer Straße 15, Berlin, 13353 Germany

4 Berlin-Brandenburg Center for Regenerative Therapies (BCRT), Foehrer Straße 15, Berlin, 13353 Germany

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Citation and License

Arthritis Research & Therapy 2012, 14:R181  doi:10.1186/ar4011

Published: 7 August 2012

Abstract

Introduction

Inflammatory arthritis is a progressive disease with chronic inflammation of joints, which is mainly characterized by the infiltration of immune cells and synovial hyperproliferation. Monocytes migrate towards inflamed areas and differentiate into macrophages. In inflamed tissues, much lower oxygen levels (hypoxia) are present in comparison to the peripheral blood. Hence, a metabolic adaptation process must take place. Other studies suggest that Hypoxia Inducible Factor 1-alpha (HIF-1α) may regulate this process, but the mechanism involved for human monocytes is not yet clear. To address this issue, we analyzed the expression and function of HIF-1α in monocytes and macrophages, but also considered alternative pathways involving nuclear factor of kappa light polypeptide gene enhancer in B-cells (NFκB).

Methods

Isolated human CD14+ monocytes were incubated under normoxia and hypoxia conditions with or without phorbol 12-myristate 13-acetate (PMA) stimulation, respectively. Nuclear and cytosolic fractions were prepared in order to detect HIF-1α and NFκB by immunoblot. For the experiments with macrophages, primary human monocytes were differentiated into human monocyte derived macrophages (hMDM) using human macrophage colony-stimulating factor (hM-CSF). The effects of normoxia and hypoxia on gene expression were compared between monocytes and hMDMs using quantitative PCR (quantitative polymerase chain reaction).

Results

We demonstrate, using primary human monocytes and hMDM, that the localization of transcription factor HIF-1α during the differentiation process is shifted from the cytosol (in monocytes) into the nucleus (in macrophages), apparently as an adaptation to a low oxygen environment. For this localization change, protein kinase C alpha/beta 1 (PKC-α/β1 ) plays an important role. In monocytes, it is NFκB1, and not HIF-1α, which is of central importance for the expression of hypoxia-adjusted genes.

Conclusions

These data demonstrate that during differentiation of monocytes into macrophages, crucial cellular adaptation mechanisms are decisively changed.