Accumulation of Cyclophilin A in the cardiac microenvironment promotes cardiac stiffness in failing hearts

Manuel Sigle (Tübingen)1, A.-K. Rohlfing (Tübingen)1, K. Krutzke (Tübingen)2, V. Gidlund (Tübingen)2, J. Marzi (Tübingen)3, S. von Ungern-Sternberg (Tübingen)4, A. Poso (Kuopio)5, M. Heikenwälder (Heidelberg)6, K. Schenke-Layland (Tübingen)3, T. E. Schäffer (Tübingen)2, P. Seizer (Aalen)7, K. A. L. Müller (Tübingen)4, M. Gawaz (Tübingen)4, D. Heinzmann (Tübingen)4

1Universitätsklinikum Tübingen Innere Medizin III, Kardiologie und Angiologie Tübingen, Deutschland; 2Institut für Angewandte Physik Tübingen, Deutschland; 3Institute for Biomedical Engineering Tübingen, Deutschland; 4Universitätsklinikum Tübingen Innere Medizin III, Kardiologie und Kreislauferkrankungen Tübingen, Deutschland; 5School of Pharmacy Faculty of Health Sciences Kuopio, Finnland; 6Division of Chronic Inflammation and Cancer, German Cancer Research Centre Heidelberg (DKFZ) Heidelberg, Deutschland; 7Ostalb-Klinikum Aalen Innere Medizin II, Kardiologie und Angiologie Aalen, Deutschland


Background and aims:
Cardiac hypertrophy is characterized by remodeling of the myocardium, which involves alterations of the extracellular matrix (ECM) and cardiomyocyte structure. These alterations critically contribute to impaired contractility and relaxation, ultimately leading to heart failure. Emerging evidence implicates that extracellular signaling molecules are critically involved in the pathogenesis of cardiac hypertrophy and remodeling. The immunophilin cyclophilin A (CyPA) has been identified as a potential culprit. In this study, we aimed to unravel the interplay between extracellular CyPA (eCyPA) and myocardial dysfunction and evaluate the therapeutic potential of inhibiting its extracellular accumulation to improve heart function.
We employed a multidisciplinary approach encompassing in vitro, in vivo, ex vivo and in silico experiments to decipher the interaction of CyPA and the cardiac microenvironment. Therefore, we used a mouse model of cardiac hypertrophy with high amount of reactive oxygen species (ROS), by continuously infusing Angiotensin II (Ang II) into hyperlipidemic ApoE-/- mice over 28 days. The whole heart, cardiac tissue composite and isolated cardiac cells were assessed by functional (echocardiography), structural (immunohistology, atomic force microscopy) and biomolecular (Raman spectroscopy) analyses. The effect of inhibiting eCyPA in the cardiac microenvironment was evaluated using a newly developed neutralizing anti-eCyPA monoclonal antibody tested and validated in vitro and consecutively administered in vivo.
We observed a significant accumulation of eCyPA in the extracellular space of murine failing hearts. Importantly, higher extracellular accumulation was associated with increased stiffness, enhanced fibrosis (Pearson correlation coefficient = 0.8), hypertrophy (Pearson correlation coefficient = 0.7), and contractile dysfunction (Pearson correlation coefficient = -0.73). Antibody-based inhibition of eCyPA prevented (Ang II)-induced myocardial remodeling and dysfunction in mice (P<0.0001). In vitro, CyPA enhanced cardiomyocyte stiffness by upregulation of the tubulin cytoskeleton, which was inverted by blocking CyPA in the medium. 
Our preliminary results demonstrate that the selective inhibition of extracellular CyPA reduces extracellular matrix remodeling and hereby preserves cardiac contractility. Targeting the extracellular accumulation of CyPA may therefore present a future treatment strategy to improve cardiac remodeling and heart function in patients with non-ischemic heart failure. 
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