Physiological stress improves stem cell modeling of dystrophic cardiomyopathy

Heart failure contributes to Duchenne muscular dystrophy (DMD), which arises from mutations that ablate dystrophin, rendering the plasma membrane prone to disruption. Cardiomyocyte membrane breakdown in patients with DMD yields a serum injury profile similar to other types of myocardial injury with the release of creatine kinase and troponin isoforms. Human induced pluripotent stem cell-derived cardiomyocytes (hiPSC-CMs) are highly useful but can be improved. We generated hiPSC-CMs from a patient with DMD and subjected these cells to equibiaxial mechanical strain to mimic in vivo stress. Compared to healthy cells, DMD hiPSC-CMs demonstrated greater susceptibility to equibiaxial strain after 2 h at 10% strain. We generated an aptamer-based profile of proteins released from hiPSC-CMs both at rest and subjected to strain and identified a strong correlation in the mechanical stress-induced proteome from hiPSC-CMs and serum from patients with DMD. We exposed hiPSC-CMs to recombinant annexin A6, a protein resealing agent, and found reduced biomarker release in DMD and control hiPSC-CMs subjected to strain. Thus, the application of mechanical strain to hiPSC-CMs produces a model that reflects an in vivo injury profile, providing a platform to assess pharmacologic intervention.

Susceptibility to innate immune activation in genetically-mediated myocarditis

BACKGROUND

Myocarditis is clinically characterized by chest pain, arrhythmias, and heart failure, and treatment for myocarditis is often supportive. Mutations in DSP, a gene encoding the desmosomal protein desmoplakin, have been increasingly implicated in myocarditis with biomarkers and pathological features indistinguishable from other forms of myocarditis. DSP-associated myocarditis can progress to dilated cardiomyopathy with heightened arrhythmia risk.

METHODS

To model the cardiomyocyte aspects of DSP-associated myocarditis and assess the role of innate immunity, we generated engineered heart tissues (EHTs) from human induced pluripotent stem cell-derived cardiomyocytes (hiPSC-CMs) from patients and gene-edited healthy control hiPSC lines. Homozygous and heterozygous DSP disrupted EHTs were generated to contain 90% hiPSC-CMs and 10% healthy control human cardiac fibroblasts. We measured innate immune activation and function at baseline and in response to Toll-like receptor (TLR) stimulation in EHTs.

RESULTS

At baseline, DSP-/- EHTs displayed a transcriptomic signature of immune activation which was mirrored by EHT cytokine release. Importantly, DSP-/- EHTs were hypersensitive to TLR stimulation demonstrating greater contractile function impairment compared to isogenic controls. Compared to homozygous DSP-/- EHTs, heterozygous DSP patient-derived EHTs had less functionally impairment but also displayed heightened sensitivity to TLR stimulation. When subjected to strain, heterozygous DSP EHTs developed greater functional deficit indicating reduced contractile reserve compared to healthy control. Colchicine or NFΚB inhibitors improved baseline force production and strain-induced force deficits in DSP EHTs. Genomic correction of DSP p.R1951X using adenine base editing reduced inflammatory biomarker release from EHTs.

CONCLUSIONS

Genetic reduction of DSP renders cardiomyocytes susceptible to innate immune activation and strain-dependent contractile deficits. EHTs replicate electrical and contractile phenotypes seen in human myocarditis implicating cytokine release as a key part of the myogenic susceptibility to inflammation. This heightened innate immune activation and sensitivity is a target for clinical intervention.