Stoichiometric, adhesion, and contractile deficits in desmoplakin cardiomyopathy

Variants in the gene desmoplakin (DSP) cause an arrhythmogenic form of cardiomyopathy that leads to both lethal ventricular arrhythmias and progressive heart failure, and no treatments are available. DSP encodes a critical structural protein that transduces force from the contractile machinery to intercellular junctions. Our prior work has demonstrated that DSP cardiomyopathy is almost always caused by truncating genetic variants that we further show cause reduced DSP mRNA and protein abundance consistent with a loss of function (LoF) mechanism. Distinct to DSP cardiomyopathy, these truncating variants lead to recurrent cardiac injury episodes and ensuing fibrosis early in the disease course, preceding development of left ventricular systolic dysfunction. Based on these observations, we hypothesize that reduced DSP abundance due to truncating variants renders heart muscle tissue susceptible to injury due to an incapacity to normally handle the cardiac workload. Our primary objective is to test this mechanism while also building evidence for novel treatment strategies that can be used in patients to prevent cardiac injury in DSP patients. Our specific aims will test the following hypotheses: (Aim 1) DSP truncating variants act via LoF, disrupting desmosomal stoichiometry and leading to defective cell- cell adhesion that is potentiated by EGFR signaling; (Aim 2) DSP variants result in increased molecular tension at desmosomes leading to tensile stress-induced injury that can be reduced by contractile antagonists or afterload reduction as preventive approaches. To rigorously examine relationships between biomechanical stress and injury due to DSP variants, we will utilize bioengineered induced pluripotent stem cells (iPSC)-derived cardiac muscle bundles designed for direct visualization of cell junctions under controlled tensile stress conditions and leveraging a suite of both patient and genome engineered iPSC lines. We will determine relationships among DSP mRNA reduction, desmosomal stoichiometric disruption, and impaired biomechanical injury response through validated CRISPR-Cas9 tools that activate or repress endogenous DSP mRNA expression. Additionally, we will quantify stoichiometric effects in vivo using an allelic series of murine models with variable levels of DSP haploinsufficiency. We will leverage these models to determine the time course over which DSP haploinsufficiency disrupts desmosomes and normal cell-cell adhesion that predisposes to cardiac injury and fibrosis. Further, EGFR inhibition, contractile antagonism, and afterload reduction (using FDA- approved medications) will all be tested as in vivo approaches in a mouse model of DSP cardiomyopathy to determine whether cardiac injury can be prevented by improving cell adhesion or by reducing biomechanical stress. Taken together, this proposal will yield fundamental insights into the mechanisms by which DSP truncating variants cause cardiac injury while directly building critical preclinical data toward novel therapeutic approaches that can be translated to patients. Project Number: 1R01HL176497-01A1 | Fiscal Year: 2025 | NIH Institute/Center: National Heart Lung and Blood Institute (NHLBI) | Principal Investigator: ADAM HELMS | Institution: UNIVERSITY OF MICHIGAN AT ANN ARBOR, ANN ARBOR, MI | Award Amount: $651,349 | Activity Code: R01 | Study Section: Integrative Myocardial Physiology/Pathophysiology A Study Section [MPPA] View on NIH RePORTER: https://reporter.nih.gov/project-details/1R01HL17649701A1