Figure 3. Engineered heart tissues from patient-derived induced pluripotent stem cells exhibit reduced levels of desmoplakin.

(A) Engineered heart tissues (EHTs) were created by differentiating cardiomyocytes from patient-derived induced pluripotent stem cells (iPSCs) and seeding cells into decellularized porcine myocardial slices. Constructs were used to assess contractility and electrical conduction velocity. (B) EHTs were generated using cardiomyocytes differentiated from G(+)P(+) patient III-36 and G(–)P(–) sibling III-35, denoted as EHT_WT/R451G and EHT_WT/WT, respectively. Bright-field images of EHTs show similar matrix compaction and morphology between the 2 types. Scale bar: 1 mm. (C) Representative immunoblot of desmoplakin (DSP) protein levels in EHTs shows substantial loss in the patient-derived tissue, which was statistically significant when quantified across several samples (*P < 0.05 for 2-tailed unpaired t test; n = 5 WT and n = 7 R451G). (D) Ca²⁺ transients collected from EHT_WT/R451G and EHT_WT/WT showed no differences between the 2 tissue types. (E) Measurements of longitudinal conduction velocity in EHTs showed no differences between EHT_WT/R451G and EHT_WT/WT (unpaired t test; n = 7 and 8 respectively). (F) Protein levels of connexin-43 (Cx43) and phosphorylated (Ser368) Cx43 in EHTs normalized to sarcomeric actin reveals significantly reduced Cx43 and significantly elevated levels of phosphorylated Cx43 in EHT_WT/R451G (*P < 0.05 for 2-tailed unpaired t test, n = 3). (G) Representative force transients collected simultaneously with above Ca²⁺ transients reveal a delayed time to peak force in EHT_WT/R451G. (H) Maximal force produced by EHTs. (I) Time from stimulus to maximal force. (J) Time elapsed from point of maximal force to 50% relaxation (RT50). ***P < 0.001 for 2-tailed unpaired t test with Bonferroni correction (n = 16 EHT_WT/WT and n = 8 EHT_WT/R451G). Error bars represent SEM.