A Transgenic Mouse Model of Eccentric Left Ventricular Hypertrophy With Preserved Ejection Fraction Exhibits Alterations in the Autophagy-Lysosomal Pathway.

Kristin Wenzel,Stephanie Könemann,Elisabeth Krämer,Birgit Geertz,Saskia Schlossarek,Stephan B Felix,Lucie Carrier

doi:10.3389/fphys.2021.614878

Abstract

The ubiquitin-proteasome system (UPS) and the autophagy-lysosomal pathway (ALP) are the main proteolytic systems involved in cellular homeostasis. Since cardiomyocytes, as terminally differentiated cells, lack the ability to share damaged proteins with their daughter cells, they are especially reliant on these protein degradation systems for their proper function. Alterations of the UPS and ALP have been reported in a wide range of cardiac diseases, including cardiomyopathies. In this study, we determined whether the UPS and ALP are altered in a mouse model of eccentric left ventricular (LV) hypertrophy expressing both cyclin T1 and Gαq under the control of the cardiac-specific α-myosin heavy chain promoter (double transgenic; DTG). Compared to wild-type (WT) littermates, DTG mice showed higher end-diastolic (ED) LV wall thicknesses and diameter with preserved ejection fraction (EF). The cardiomyopathic phenotype was further confirmed by an upregulation of the fetal gene program and genes associated with fibrosis as well as a downregulation of genes involved in Ca2+ handling. Likewise, higher NT-proBNP levels were detected in DTG mice. Investigation of the UPS showed elevated steady-state levels of (poly)ubiquitinated proteins without alterations of all proteasomal activities in DTG mice. Evaluation of ALP key marker revealed a mixed pattern with higher protein levels of microtubule-associated protein 1 light chain 3 beta (LC3)-I and lysosomal-associated membrane protein-2, lower protein levels of beclin-1 and FYVE and coiled-coil domain-containing protein 1 (FYCO1) and unchanged protein levels of p62/SQSTM1 in DTG mice when compared to WT. At transcriptional level, a > 1.2-fold expression was observed for Erbb2, Hdac6, Lamp2, Nrg1, and Sqstm1, while a < 0.8-fold expression was revealed for Fyco1 in DTG mice. The results related to the ALP suggested overall a repression of the ALP during the initiation process, but an induction of the ALP at the level of autophagosome-lysosome fusion and the delivery of ubiquitinated cargo to the ALP for degradation.

Highlights

The adult heart undergoes distinct remodeling processes in response to acute or chronic insults, which involve myocardial hypertrophy, ventricular wall thickening and dilatation as well as cardiomyocyte apoptosis and the development of fibrosis (Frey and Olson, 2003; Dorn and Force, 2005)
Several lines of evidence indicate that alterations of the ubiquitin-proteasome system (UPS) and the autophagy-lysosomal pathway (ALP) may be involved in cardiac diseases, such as dilated and hypertrophic cardiomyopathies (Mearini et al, 2008; Zheng and Wang, 2010; Day, 2013; Zech et al, 2020)
Representative magnetic resonance imaging (MRI) images of WT and Double transgenic (DTG) hearts are shown in Supplementary Figure 1

Summary

Introduction

The adult heart undergoes distinct remodeling processes in response to acute or chronic insults, which involve myocardial hypertrophy, ventricular wall thickening and dilatation as well as cardiomyocyte apoptosis and the development of fibrosis (Frey and Olson, 2003; Dorn and Force, 2005). The highly selective degradation process by the UPS is ATP-dependent and involves the polyubiquitination of a target protein through a series of enzymatic reactions and the subsequent degradation of this (poly)ubiquitinated protein by the 26S proteasome (Ciechanover, 2007). A marked accumulation of (poly)ubiquitinated proteins has been reported as a common feature of cardiac disorders (Weekes et al, 2003; Birks et al, 2008; Predmore et al, 2010), whereas the proteasomal activities have been shown to be higher or lower depending on the status of the cardiac disease (Depre et al, 2006; Tsukamoto et al, 2006; Birks et al, 2008; Predmore et al, 2010; Schlossarek et al, 2012; Thottakara et al, 2015). A basal ALP activity is thought to be important to maintain normal cardiac function, whereas a decrease or an increase in ALP activity could mediate the adaption of the heart during stress conditions (Lavandero et al, 2013)

Methods

Results

Conclusion