A Potent Tartrate Resistant Acid Phosphatase Inhibitor to Study the Function of TRAP in Alveolar Macrophages

Carian E Boorsma,Don Sin,Barbro N Melgert,Maarten Van Den Berge,Göran Andersson,Yohan Bossé,Angela Casini,Anja Reithmeier,T Anienke Van Der Veen,Thais Mauad,Gyorgy Fejer,Andreia De Almeida,Kurnia S S Putri,Christina Draijer,Corry-Anke Brandsma,Peter Olinga,Wim Timens,Ke Hao

doi:10.1038/s41598-017-12623-w

Abstract

The enzyme tartrate resistant acid phosphatase (TRAP, two isoforms 5a and 5b) is highly expressed in alveolar macrophages, but its function there is unclear and potent selective inhibitors of TRAP are required to assess functional aspects of the protein. We found higher TRAP activity/expression in lungs of patients with chronic obstructive pulmonary disease (COPD) and asthma compared to controls and more TRAP activity in lungs of mice with experimental COPD or asthma. Stimuli related to asthma and/or COPD were tested for their capacity to induce TRAP. Receptor activator of NF-κb ligand (RANKL) and Xanthine/Xanthine Oxidase induced TRAP mRNA expression in mouse macrophages, but only RANKL also induced TRAP activity in mouse lung slices. Several Au(III) coordination compounds were tested for their ability to inhibit TRAP activity and [Au(4,4′-dimethoxy-2,2′-bipyridine)Cl2][PF6] (AubipyOMe) was found to be the most potent inhibitor of TRAP5a and 5b activity reported to date (IC50 1.3 and 1.8 μM respectively). AubipyOMe also inhibited TRAP activity in murine macrophage and human lung tissue extracts. In a functional assay with physiological TRAP substrate osteopontin, AubipyOMe inhibited mouse macrophage migration over osteopontin-coated membranes. In conclusion, higher TRAP expression/activity are associated with COPD and asthma and TRAP is involved in regulating macrophage migration.

Highlights

IntroductionThe function of TRAP5b in bone has been studied in relation to bone remodeling extensively, in which TRAP activity was found to mediate osteoclast migration[2,14,15]
We observed higher TRAP expression in chronic obstructive pulmonary disease (COPD) and asthma as compared to control and we found that this increase may be triggered by RANKL and/or oxidative stress, though the functional consequences of this higher expression and activity remain to be determined
This Au(III)-based compound is the most potent inhibitor of the phosphatase function of TRAP described to date and was used here to show that TRAP appears to be involved in macrophage migration

Summary

Introduction

The function of TRAP5b in bone has been studied in relation to bone remodeling extensively, in which TRAP activity was found to mediate osteoclast migration[2,14,15]. Hayman et al demonstrated potent inhibitory effects of sodium tetrachloroaurate (NaAuCl4) on TRAP activity[20] This Au(III) complex is a reactive compound prone to reduction in biological environment and has unspecific protein binding, which may interfere with many different cellular pathways. Our starting hypothesis was that TRAP activity is involved in regulation of osteopontin-dependent macrophage migration, similar to osteoclasts in bone. Alveolar macrophages express αvβ[3] integrins and we hypothesized that they may need TRAP to migrate[30]. We used AubipyOMe to investigate functional aspects of TRAP activity in macrophages, such as cell migration

Methods

Results

Conclusion