Distinct remodeling pattern between pediatric and adult heart failure: a focus on Ca2+ signaling pathway at proteomic level
Authors: Zhang H , Kuzmanov U , Urschel S , Wang F , Wang S , Gramolini A , Oudit G.Y 
Published: November 2020

Abstract

Background
Dilated cardiomyopathy (DCM) is among the most common causes leading to end-stage heart failure with reduced ejection fraction (HF-rEF) in adult and pediatric patients. Despite similar phenotypes characterized as systolic dysfunction and eccentric ventricular dilation, pediatric DCM are biologically distinct entities with age- and development-specific features in the heart. Though underlying mechanisms may vary between the two populations, it's largely unexplored with few studies conducted to date.

Purpose
HF-rEF typically results from impaired myocardial contractility, triggered by defective cellular Ca2+ handling and cytoskeletal remodeling. Hence, we aim to integrate clinical profile and experimental data from human explanted hearts: 1) to unravel the age-dependent disparate Ca2+ signaling pathways; and 2) to identify pediatric-specific HF signatures or potential cures for precision managements.

Methods
Non-ischemic failing hearts (n=6 adult and n=6 pediatric) were procured immediately after excision via Human Explanted Heart Program. Age-matched adult non-failing control hearts (NFC, n=6) were obtained from deceased donors without cardiovascular history, while pediatric NFC (n=6) were collected from children with congenital heart defects but no primary myocardial dysfunction constituting relatively reasonable controls. Myocardial metabolic and oxidative profile were evaluated spectrophotometrically, and tissue remodeling was assessed immunohistochemically. Global proteomics and phosphoproteomics were performed on a Q-Exactive mass spectrometer, followed by network biology pathway analyses. Expression of screened proteins and kinases was validated by gel electrophoresis. Apoptosis and cellular growth signaling pathways were also incorporated into analysis.

Results
Both HF groups had remarkably lower LVEF (26.6±10.7% in pediatric vs. 26.5±9.1% in adult DCM) while compared to the NFC (both ≥60%) respectively. Histologically, adult-DCM demonstrated significantly worse fibrosis than pediatric-DCM (p&lt;0.01). It was consistent with excessive reactive oxygen species (ROS) production and perturbed anti-ROS defense noted in adult-DCM, indicative of possible reverse remodeling in the pediatric failing hearts with shorter course of illness till transplant. Mechanistically, NCX1 was elevated with SERCA2 decreased in adult-DCM versus adult-NFC (p&lt;0.05), while both pediatric groups exhibited comparable levels. Reduced p-/t-phospholamban and p-/t-CaMK in adult-DCM, unlike in pediatric-DCM, also illustrated altered phosphorylation patterns. Moreover, GSK-3β and AMPK pathways were inhibited while AKT-473 was activated in adult-DCM.

Conclusions
Pediatric DCM exhibited less adverse remodeling partially mediated by divergent Ca2+ handling and downstream signaling pathways, illustrating the fundamental differences between adult and pediatric DCM. Our findings may provide a scientific basis for the development of specific therapies for pediatric DCM.

Funding Acknowledgement
Type of funding source: Public grant(s) – National budget only. Main funding source(s): Canadian Institutes for Health Research (CIHR); Heart & Stroke Foundation (HSF)