Kory Lavine, M.D. Ph.D.
Project Overview:
Pediatric dilated cardiomyopathy (DCM) is an important cause of mortality and is the most common indication for heart transplantation in children. Unfortunately, outcomes for patients with pediatric DCM remain poor and clinical trials have revealed that children with heart failure do not respond to medications used in adults. In fact, despite modern therapies, there has been no improvement in outcomes for children with heart failure since the implementation of medical regimens established in the 1970s. These observations support the concept that pediatric and adult heart failure represent distinct entities and highlight the clinically unmet need to identify underlying mechanisms that contribute to the progression of pediatric cardiomyopathy, strategies to predict outcomes, and new treatments.
In Year One, we tested the hypothesis that the pathogenesis of pediatric and adult DCMs are distinct in that adverse remodeling (the target of adult heart failure therapies) occurs specifically in adult patients. Using molecular pathology techniques and deep RNA sequencing we demonstrated that adverse remodeling does not occur in children with DCM, thus providing a mechanistic rationale for why adult heart failure medications do not work in children. These observations are paradigm shifting in that they suggest that prognostic and therapeutic approaches routinely employed in adult heart failure patients may not be effective in pediatric populations.
An alternative approach to this challenging disease is to define and target the mechanisms by which specific pediatric DCM mutations result in cardiomyopathy. To accomplish this, we have developed models of pediatric DCM in zebrafish using Cas9/CRISPR based gene editing. While the zebrafish heart may be viewed as primitive, previous studies have demonstrated that zebrafish serve as effective models of human heart failure. In addition, zebrafish provide numerous advantages over traditional cell based and mouse models as they are optically translucent and thus ideal for advanced imaging applications, genetically tractable, and amenable to small molecule screens.
The goals of this proposal are to generate zebrafish models of the six most prevalent pediatric DCM mutations, perform detailed phenotypic characterization using high content imaging to define mechanistic elements that are unique to and shared by each of these mutations, and to build a platform to execute chemical and genetic screens to identify precision therapies for pediatric DCM.
Our findings clearly demonstrate that adverse remodeling does not occur on the pathological or molecular level in children with DCM. Collectively, these observations show that adverse remodeling does not govern disease progression in pediatric DCM and support the concept that pediatric and adult DCMs represent distinct disease entities.
Our observations also explain several clinical distinctions between pediatric and adult heart failure. For example, the absence of myocardial fibrosis offers a rationale for why children with DCM display substantially higher rates of cardiac recovery and lower rates of sudden cardiac death or ICD placement compared to adults. The absence of adverse remodeling in pediatric DCM may also explain why clinical outcomes for children newly diagnosed with DCM are uniformly determined within two years from their incident diagnosis. Children will either experience complete recovery of cardiac function, disease stabilization, or progressive heart failure resulting in death or need for cardiac transplantation.
In this context, early delineation of clinical outcomes strongly implies that heart failure progression in children is dictated by proximal events such as the initial cause of heart failure. Therefore, we postulate that an improved understanding of proximate disease mechanisms in children is required to develop appropriate prognostic tools and rationally designed therapies. We have chosen to take two approaches to advance prognostic and therapeutic strategies for pediatric DCM. The latter approach will serve as the focus of this application.
- To define pediatric DCM biomarkers that are predictive of clinical outcomes, we have developed a collaboration with the PCMR investigator group. This large scale biomarker discovery and validation study will utilize the newly available SOMAscan biomarker discovery platform.
- To define proximate disease mechanisms and precision therapies, we have developed a model system in zebrafish to introduce DCM variants, define disease mechanisms, and aim to utilize this tool as a platform for drug discovery.
Our findings established the feasibility of using zebrafish DCM. In addition, our observations clearly indicate that distinct DCM mutations give rise to unique heart failure pathologies and highlight the potential impact of pursuing a precision medicine strategy in the treatment of dilated cardiomyopathy. By designing therapeutics targeted based on genetic mutation and mechanism of disease, it may be feasible to develop approaches that correct the molecular underpinnings of a patient’s disease. Future experiments will focus on developing additional zebrafish models using gene editing and transgenic approaches. In addition, we will conduct chemical screens using small molecule libraries (ICCB bioactives, n=480 and DNA-encoded libraries). These experiments will be the focus of future NIH R01 and UG3 applications.
