Proceedings of The Physiological Society

Europhysiology 2018 (London, UK) (2018) Proc Physiol Soc 41, PCA045

Poster Communications

The cardiovascular role of proprotein convertase subtilisin/kexin 9 (PCSK9)

A. Wolf1, R. Schreckenberg1, M. Weber1, R. Schulz1, S. Rohrbach1, L. Ling1, G. Lochnit2, K. Schlueter1

1. Dept. of Physiology, Justus-Liebig-University, Giessen, Germany. 2. Department of Biochenistry, Justus-Liebig-University, Giessen, Germany.

Hypercholesteremia and hypertension belong to the most severe risk factors of cardiac disease. Proprotein converatse subtilisin/kexin 9 (PCSK9) regulates hepatic LDL receptor expression and furthermore participates in oxLDL-dependent effects on adult rat ventricular cardiomyocytes. The molecular mechanisms by which PCSK9 exerts its function in cardiomyocytes remained unclear. The current study was performed to clarify whether oxLDL causes the release of PCSK9 from cardiomyocytes, whether PCSK9 affects cardiac function via an autocrine mechanism, whether PCSK9 has intracellular functions in terminal differentiated myocytes, and whether PCSK9 also affects other pathways that reduce cardiac function such as that of angiotensin II (Ang.II). To address these questions, adult rat ventricular cardiomyocytes (ARVC) were cultured for 24 h and exposed to oxLDL (0-30 µg/ml), Ang-II (100 nM), siRNA directed against PCSK9 (xx), hPCSK9 and combinations thereof. Release of PCSK9 was quantified by ELISA, cell function by load-free cell shortening. Intracellular PCSK9 was induced independent from oxLDL by transfection of cardiomyocytes. Binding partners of PCSK9 in cardiomyocytes were identified by MALDI-TOF. oxLDL, but not Ang-II, increased the amount of extracellular PCSK9 in a concentration-dependent way (566±220 to 2804±305 pg/ml). Administration of extracellular PCSK9 and Ang-II but not transfection of cardiomyocytes with PCSK9 reduced load-free cell shortening (%-cell shortening: 7.21±3.67; 7.01±3.10; 9.31±3.20; n=90 cells, 10 culture dishes, 2 preparations). siRNA directed against PCSK9 inhibited the effect on load-free cell shortening caused by oxLDL and Ang-II (%-cell shortening: 7.01±3.10 vs. 10.64±2.62). A receptor antagonist directed against the Ang-II receptor type 1 attenuated the effect of hPCSK9. None of these treatments regimes altered significantly the steady-state expression of PCSK9 in cardiomyocytes. Upon immunoprecipitation of PCSK9, alpha-crystallin B, myosin, and actin were identified. Finally, changes in mRNA expression of PCSK9 affected the mRNA expression of alpha-crystallin B. Silencing of crystalline-B potentiated reduced cell shortening. In conclusion, oxLDL acts via release of PCSK9 and extracellular PCSK9 seems to interacts with Ang-II receptors. Intracellular mRNA levels of PCSK9 affect the steady-state of alpha-crystallin B expression and thereby reducing PCSK9 mRNA expression helps to withstand Ang-II-dependent effects on cell function.

Where applicable, experiments conform with Society ethical requirements