Localization of Microfibrillar-Associated Protein 4 (MFAP4) in Human Tissues: Clinical Evaluation of Serum MFAP4 and Its Association with Various Cardiovascular Conditions

Anders Schlosser,Vicki Nielsen,Ida Tornøe,Susanne Gjørup Sækmose,Henrik Munkholm,Helle Wulf-Johansson,Grith Lykke Sorensen,Uffe Holmskov,Niels Marcussen,Jørgen Vestbo,Anne Trommelholt Holm,Hans Mickley,Axel C. P. Diederichsen,Christian Schulz,Lars Melholt Rasmussen,Tina Svenstrup Poulsen,Sofie Lock Johansson

doi:10.1371/journal.pone.0082243

Abstract

Microfibrillar-associated protein 4 (MFAP4) is located in the extracellular matrix (ECM). We sought to identify tissues with high levels of MFAP4 mRNA and MFAP4 protein expression. Moreover, we aimed to evaluate the significance of MFAP4 as a marker of cardiovascular disease (CVD) and to correlate MFAP4 with other known ECM markers, such as fibulin-1, osteoprotegerin (OPG), and osteopontin (OPN). Quantitative real-time PCR demonstrated that MFAP4 mRNA was more highly expressed in the heart, lung, and intestine than in other elastic tissues. Immunohistochemical studies demonstrated high levels of MFAP4 protein mainly at sites rich in elastic fibers and within blood vessels in all tissues investigated. The AlphaLISA technique was used to determine serum MFAP4 levels in a clinical cohort of 172 patients consisting of 5 matched groups with varying degrees of CVD: 1: patients with ST elevation myocardial infarction (STEMI), 2: patients with non-STEMI, 3: patients destined for vascular surgery because of various atherosclerotic diseases (stable atherosclerotic disease), 4: apparently healthy individuals with documented coronary artery calcification (CAC-positive), and 5: apparently healthy individuals without signs of coronary artery calcification (CAC-negative). Serum MFAP4 levels were significantly lower in patients with stable atherosclerotic disease than CAC-negative individuals (p<0.05). Furthermore, lower serum MFAP4 levels were present in patients with stable atherosclerotic disease compared with STEMI and non-STEMI patients (p<0.05). In patients with stable atherosclerotic disease, positive correlations between MFAP4 and both fibulin-1 (ρ = 0.50; p = 0.0244) and OPG (ρ = 0.62; p = 0.0014) were found. Together, these results indicate that MFAP4 is mainly located in elastic fibers and is highly expressed in blood vessels. The present study suggests that serum MFAP4 varies in groups of patients with different cardiovascular conditions. Further studies are warranted to describe the role of serum MFAP4 as a biomarker of stable atherosclerotic disease.

Highlights

Microfibrillar-associated protein 4 (MFAP4) is a matricellular protein belonging to the fibrinogen-related protein superfamily
MFAP4 mRNA Expression in Human Tissues Quantitative Real-time PCR (qPCR) was performed in 15 different human tissues to determine MFAP4 mRNA transcript levels
Relative MFAP4 mRNA transcript levels were highest in the heart, small intestine, and lung, as shown in figure 1

Summary

Introduction

Microfibrillar-associated protein 4 (MFAP4) is a matricellular protein belonging to the fibrinogen-related protein superfamily. This family includes fibroleukin, ficolins, FIBCD1, angiopoietins, and tenascins, which play multifaceted roles in innate immunity, the development of the cardiovascular system, and the normal functioning of the endothelium [1,2,3,4,5]. MFAP4 has considerable sequence homology with the 36-kDa bovine microfibril-associated glycoprotein (MAGP-36), which was first discovered in porcine aorta and has since been detected in a wide variety of elastic tissues [9,10].

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