Date Published: April 22, 2019
Publisher: Public Library of Science
Author(s): Carolina Gil-Cayuela, Alejandro López, Luis Martínez-Dolz, José Ramón González-Juanatey, Francisca Lago, Esther Roselló-Lletí, Miguel Rivera, Manuel Portolés, John Lynn Jefferies.
This study aimed to analyze changes in the expression of autophagy- and phagocytosis-related genes in patients with dilated cardiomyopathy (DCM), especially in relation to left ventricular (LV) dysfunction. Furthermore, transmission electron microscopy of the diseased tissue was carried out to investigate if the gene expression changes are translated into ultrastructural alterations. LV tissue samples from patients with DCM (n = 13) and from controls (CNT; n = 10) were analyzed by RNA-sequencing, whereupon the altered expression (P < 0.05) of 13 autophagy- and 3 phagocytosis-related genes was observed. The expression changes of the autophagy-related genes NRBP2 and CALCOCO2 were associated with cardiac dysfunction and remodeling (P < 0.05). The affected patients had a higher activity of these degradation processes, as evidenced by the greater number of autophagic structures in the DCM tissue (P < 0.001). Differences in the ultrastructural distribution were also found between the DCM and CNT tissues. These results show that in patients with DCM, the altered expression of NRBP2 and CALCOCO2 is related to LV dysfunction and remodeling. Clarification of the molecular mechanisms of cardiac autophagy would help in the future development of therapies to improve LV performance.
Dilated cardiomyopathy (DCM) is characterized by the dilation of the cardiac chambers with increases in the ventricular mass and wall thickness, impaired myocardial contractility, and ventricular dysfunction that frequently results in heart failure. It is a condition that is increasing in prevalence and carries a high mortality rate, with no curative treatment available [1,2]. The development of heart failure is known to be associated with the altered expression of genes involved in the production of various subcellular organelles and structures (e.g., the extracellular matrix [3,4], endoplasmic and sarcoplasmic reticulums , and Golgi apparatus ), which results in alterations to the cellular processes in which these structures participate. However, there are no published transcriptomic studies focused on the expression levels of genes involved in the processes of autophagy and phagocytosis. These processes play an indispensable role in the degradation of cellular structures. During phagocytosis, cells internalize and enclose surrounding microorganisms or unusable or harmful cell debris through generation of the phagosome, a single-membrane structure that merges with a lysosome to produce a phagolysosome wherein degradation takes place . In autophagy, cytoplasmic components are engulfed by a membrane structure known as the phagophore. This membranous structure enlarges either by the direct inflow of the endoplasmic reticulum or by the addition of vesicles to eventually generate a double-membranous autophagosome that closes off, thereby sequestering the cytosolic material within it . The autophagosome then merges with a lysosome, forming the autophagolysosome that executes the degradation of the autophagosome’s internal contents as well as its inner membrane .
Degradation pathways are induced in response to external stress, damage, and cell development and remodeling. They are essential for maintaining cellular homeostasis and are required for intracellular self-renewal, energy replenishment, and substrate recycling. Deregulation of the degradation pathways has been linked to various diseases, such as cancer, neurodegenerative disorders and heart failure . However, the functional role of autophagy in heart diseases remains unclear. Regulation of autophagy has been related to both protective and detrimental roles in cardiac cells . Increased autophagy has been found in hearts after ischemia and reperfusion. It has been suggested that upregulation of autophagy provides protection against cell death and improves cardiac function [18–20]; the degradation of proteins and organelles may maintain ATP production and energy homeostasis during ischemia, thus promoting survival of cardiac cells . Nevertheless, other studies have shown that increased autophagy in hypertrophied hearts might mediate the transition from stable cardiac hypertrophy to decompensated heart failure . In support of this, Matsiu et al. reported that the induction of decreased levels of autophagy in a mice model resulted in reduced apoptosis and infarct size compared to the wild type . In this regard, our study showed a new link between deregulation of the degradation pathways and cardiac dysfunction in patients with dilated cardiomyopathy.
We have found the altered expression of a total of 16 genes involved in both the autophagy (13 genes) and phagocytosis (3 genes) degradation processes. The changes in NRBP2 and CALCOCO2 expression were associated with cardiac dysfunction and remodeling. Through TEM, we observed increased tissue repair and cellular recycling mechanisms in DCM, as evidenced by the greater number of autophagic structures in the diseased tissue relative to the CNTs. Furthermore, the multivesicular bodies and lamellar structures observed were specific to DCM. Our findings suggest new targets of the cellular degradation machinery that could be used for the development of therapies to improve LV performance.