Evidence for synergy between sarcomeres and fibroblasts in an in vitro model of myocardial reverse remodeling

https://doi.org/10.1016/j.yjmcc.2021.05.005Get rights and content

Highlights

  • Reverse remodeling is a phenomenon seen in some failing hearts after unloading.

  • Engineered heart tissues exhibit reverse remodeling-like behavior after unloading.

  • The cardiac myosin inhibitor mavacamten blunted in vitro reverse remodeling.

  • An inhibitor of fibroblast activation also prevented in vitro reverse remodeling.

  • Myocardial reverse remodeling apparently requires activity of sarcomeres and fibroblasts.

Abstract

We have created a novel in-vitro platform to study reverse remodeling of engineered heart tissue (EHT) after mechanical unloading. EHTs were created by seeding decellularized porcine myocardial sections with a mixture of primary neonatal rat ventricular myocytes and cardiac fibroblasts. Each end of the ribbon-like constructs was fixed to a plastic clip, allowing the tissues to be statically stretched or slackened. Inelastic deformation was introduced by stretching tissues by 20% of their original length. EHTs were subsequently unloaded by returning tissues to their original, shorter length. Mechanical characterization of EHTs immediately after unloading and at subsequent time points confirmed the presence of a reverse-remodeling process, through which stress-free tissue length was increased after chronic stretch but gradually decreased back to its original value within 9 days. When a cardiac myosin inhibitor was applied to tissues after unloading, EHTs failed to completely recover their passive and active mechanical properties, suggesting a role for actomyosin contraction in reverse remodeling. Selectively inhibiting cardiomyocyte contraction or fibroblast activity after mechanical unloading showed that contractile activity of both cell types was required to achieve full remodeling. Similar tests with EHTs formed from human induced pluripotent stem cell-derived cardiomyocytes also showed reverse remodeling that was enhanced when treated with omecamtiv mecarbil, a myosin activator. These experiments suggest essential roles for active sarcomeric contraction and fibroblast activity in reverse remodeling of myocardium after mechanical unloading. Our findings provide a mechanistic rationale for designing potential therapies to encourage reverse remodeling in patient hearts.

Introduction

The left ventricular assist device (LVAD) has emerged as a life-saving treatment option for many advanced heart failure (HF) patients [[1], [2], [3], [4], [5]]. The shift in usage of LVAD from short-term to long-term therapy is reflected in the national statistics; among over 15,000 LVADs implanted between 2006 and 2014, the percentage of LVADs implanted for destination therapy increased from 14.7% to 45.7% [6]. Among the patients receiving an LVAD, most experience some degree of recovery in cardiac function, while a small number undergo more significant functional, structural, and cellular improvement in a process called reverse remodeling (RR) [[7], [8], [9]].

Reverse remodeling is an intrinsic tissue-level process that results in restoration of normal cardiomyocyte size and extracellular matrix composition as well as reductions in inflammation and pro-apoptotic signaling [8,10]. This recovery process enables some patients to regain sufficient cardiac function to allow LVAD explantation, prompting the notion of LVAD as bridge to recovery therapy [8,10,11]. However, the number of adult nonischemic dilated cardiomyopathy (DCM) patients experiencing recovery following LVAD support is relatively small [8,10,[12], [13], [14], [15], [16], [17]], with overall LVAD explanation rate observed to be around 5% [12,13]. Moreover, since DCM is the most common form of cardiomyopathy in children [6], LVADs have also been often used in pediatric patients with advanced HF from DCM [[18], [19], [20]]. Similar trends but higher recovery have been reported, with even better outcome observed for children <2 years old [19].

It is not fully understood why mechanical unloading leads to recovery of cardiac function and HF remission only in certain patients. A major obstacle is a lack of understanding about the mechanisms that drive reverse remodeling on a cell and tissue level. Until these mechanisms are identified and described, the path toward encouraging beneficial remodeling after myocardial unloading will remain obscure.

Here, we describe the development of a novel in vitro model that enables study of the basic phenomenon of myocardial reverse remodeling after mechanical unloading. Using our engineered heart tissue (EHT) platform and a custom stretch device, we first overloaded tissues by subjecting them to 2 days of stretch. We could then ‘unload’ EHTs and observe the reverse remodeling process in detail, enabling the identification of specific cellular and molecular contributors. These findings provide the first description of a novel platform for studying the fundamental processes involved in myocardial reverse remodeling and may inspire future therapeutic strategies for diseases that feature cardiac chamber dilation.

Section snippets

Ethical approval

Animal procedures were all approved by the Yale University Institutional Animal Care and Use Committee (Approval # 2018–11,528), and compliant with the regulations of the Animal Welfare Act, Public Health Service, the United States Department of Agriculture, and the principles and regulations of the Journal of Physiology [21]. 1–2-day old Sprague-Dawley neonatal rat litters used for this study were purchased from Charles River Laboratories (Wilmington, MA). The animals were kept under a 12-h

In vitro model validation

We sought a system in which a linear segment of artificial myocardium could first be stretched to the point of inelastic (not immediately reversible) deformation. We hypothesized that relieving tension in this over-stretched tissue would provide an opportunity to study the reverse remodeling process in detail, by monitoring biomechanical characteristics of the engineered heart tissues (EHTs), including stress-free tissue length (slack length), stiffness, and active contractile force during a

Discussion

To our knowledge, this study is the first of its kind to specifically characterize the interaction of cardiomyocytes and cardiac fibroblasts in a simple in vitro representation of myocardial reverse remodeling. A series of controlled in vitro experiments in an engineered three-dimensional tissue model revealed an essential role for both cell types in successful recovery of both active and passive tissue functions.

Reflecting on these results, we propose a mechanistic model for the processes that

Sources of funding

This work was supported by a National Science Foundation CAREER Award (1653160) and NIH 1R01HL136590 (both to S.G.C). L.R.S was supported by a Paul and Daisy Soros Fellowship for New Americans, an American Heart Association Predoctoral Fellowship, and a NIH/NIGMS Medical Scientist Training Program Grant (T32GM007205).

Disclosures

S.G.C. holds equity ownership in Propria LLC, which has licensed technology used in the research reported in this publication. L.R.S. and S.S. declare no conflicts of interest.

Data availability statement

The raw/processed data required to reproduce these findings cannot be shared at this time due to technical or time limitations.

Acknowledgement

We thank Mahammad Camara for his work on an early prototype of the EHT stretch device.

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