Precision Therapeutics for Pediatric Dilated Cardiomyopathy (DCM) 
(2nd Year)

Kory Lavine, M.D. Ph.D.


Project Overview:

Dilated cardiomyopathy (DCM) is the most common indication for heart transplantation in children. While it is recognized that mutations in sarcomeric and cytoskeletal genes underlie pediatric DCM, outcomes remain poor and few therapeutics exist. The goal of this proposal is to generate Zebrafish models of the six most prevalent pediatric DCM mutations, perform detailed phenotyping to define mechanistic elements that are unique to and shared by each of these mutations, and optimize experimental approaches to identify mutation specific compounds that either suppress or reverse heart failure. We envision these studies would provide the requisite information to design small molecule and genetic screens to identify novel therapies for pediatric DCM, a core mission of the LLF.

Project aims:

            Generate zebrafish models of pediatric DCM and define proximate disease mechanisms

            Design a high-throughput screening strategy to identify precision therapeutics for pediatric DCM

 

Progress Report:

One potential explanation for why adult heart failure therapeutics do not improve outcomes in the pediatric population is that adverse remodeling does not govern disease progression in children. In the previous award period, we tested the hypothesis that adverse remodeling specifically occurs in adult patients and is not present in children with DCM. Our findings have been accepted for publication (Patel et al. JCI Insight 2017).

 

Data from Previous Award Period: To test the hypothesis that adverse remodeling does not occur in children with DCM, we obtained LV myocardial specimens from the apex and lateral wall of non-failing pediatric donor controls (n=11), pediatric DCM patients (n=31), adult non-failing donor controls (n=14), and adult DCM (n=34) patients. To our knowledge, this represents the largest collection of pediatric and adult DCM tissue specimens studied to date. Control tissue was obtained from unused donors with normal cardiac function by echocardiography. DCM specimens were obtained from children and adults with advanced stage idiopathic or familial DCN at the time of cardiac transplantation or implantation of a left ventricular assist device. To evaluate the presence and extent of adverse remodeling at the tissue level, we measured cardiomyocyte and sarcomere size, myocardial fibrosis, and capillary density in pediatric and adult donor control and DCM specimens. In addition, we performed RNA sequencing on pediatric and adult DCM specimens to examine gene expression signatures of adverse remodeling and define pathways that differentiate pediatric from adult DCM. Control and DCM specimens were obtained in collaboration with the Translational Cardiovascular Biobank and Repository at Washington University, University of Colorado, and the Pediatric Cardiomyopathy Registry (PCMR) tissue repository.

 

Using a combination of quantitative histology, immunostaining, electron microscopy, and RNA sequencing, we demonstrated that adverse remodeling does not uniformly occur in children with DCM. Myocardial specimens obtained from patients with pediatric DCM display no evidence of cardiomyocyte hypertrophy or increased sarcomere thickness compared to age matched donor controls. In contrast, myocardial specimens obtained from adults with DCM, displayed robust increases in cardiomyocyte hypertrophy and sarcomere thickness. Examination of myocardial fibrosis similarly revealed no evidence of increased collagen deposition in pediatric DCM specimens compared to age matched donor controls. In contrast, myocardial specimens obtained from adults with DCM, displayed robust increases in myocardial fibrosis compared to age matched donor controls. Importantly, these findings appear to be irrespective of patient age across pediatric and adult subgroups, as both linear reqression and subgroup analyses stratifying pediatric and adult groups by patient age demonstrated that only adult DCM displayed increased cardiomyocyte hypertrophy and myocardial fibrosis across the spectrum of ages examined. Measurement of capillary density revealed coronary expansion only in pediatric DCM specimens.

 

Careful analysis of clinical and demographic information revealed several key differences between our pediatric and adult DCM cohorts including increased length of disease duration and increased frequency of hypertension, diabetes, and chronic kidney disease in the adult DCM group. As these differences may represent potential confounding variables, we examined if disease duration, hypertension, diabetes, and chronic kidney disease were associated with the extent of pathological remodeling (cardiomyocyte hypertrophy or myocardial fibrosis). Linear regression and subgroup analyses failed to demonstrate statistically significant associations between these variables, indicating that differences in adverse remodeling between pediatric and adult DCM were not due to unbalanced comorbidities or disease duration.

 

Consistent with pathology data, RNA sequencing revealed divergent gene expression profiles between pediatric and adult DCM tissue  specimens with adult specimens displaying marked induction of transcripts associated with adverse remodeling and inflammation (Fig. 3). In addition, we noted that compared to children, adult DCM specimens displayed marked increases in transcripts involved in metabolite signaling, fatty acid utilization, and oxidative metabolism. These data confirm the importance of metabolism/substrate utilization in adult heart failure and signify the relevance of innate immune activation in the pathogenesis of adult DCM. Collectively, these data demonstrate that adverse remodeling does not govern disease progression in pediatric DCM and support the innovative concept that pediatric and adult DCMs represent distinct disease entities.