1327045 - Matured Pluripotent Stem Cell-Derived Cardiomyocytes Have High Structural Coherence in Diffusion Tensor Imaging of Animal Infarct Model

Cardiac tissue has a limited regenerative capacity post-myocardial infarction (MI), hence novel treatment strategies are needed to improve the structure and function of the myocardium. In vitro-matured pluripotent stem cell-derived cardiomyocytes (PSC-CMs) are a promising regenerative strategy which have improved cell alignment and contractile function compared to their immature counterparts¹. Notably, imaging biomarkers are needed to monitor the associated structural and functional impacts of therapy. Diffusion Tensor Imaging (DTI) is a quantitative technique used to measure tissue anisotropy and directionality. We hypothesized that mature PSC-CMs will have improved cell alignment and anisotropic structure in DTI when compared to immature PSC-CMs in a guinea pig model of MI.



Methods:

16 guinea pigs were cryoinjured on the anterolateral wall at day 0, followed by transplantation of either 10⁶ mature polydimethylsiloxane (PDMS)-generated PSC-CMs¹ (n=6) or immature tissue culture plastic (TCP)-generated PSC-CMs (n=6) at day 10. Vehicle subjects were injected with saline (n=4), and healthy controls did not undergo treatment (n=4). Animals were sacrificed on day 38 for CMR.           
Animals were imaged ex vivo on a 7T Bruker Ascend MRI. We utilized a 3D DTI sequence (resolution 0.3mm³, b-value 700 s/mm²) to quantify structure via fractional anisotropy (FA), mean diffusivity (MD) and myocyte orientation. Contrast enhancement (CE, resolution 0.2x0.2x1mm³) was used to identify scar and graft ROIs via accumulation of gadolinium-DTPA (0.3ml/kg) injected prior to sacrifice. Images were analyzed using open source software².



Results: FA and MD of PDMS grafts demonstrated high anisotropy as they were not significantly different than the healthy control hearts (Fig 1). TCP grafts exhibited significantly higher MD than the healthy control, and trended lower than PDMS grafts. TCP grafts also showed significantly lower FA than the control and trended towards lower FA than PDMS grafts.
Helix angle transmurality (HAT) across the graft ROIs was used to determine extent of helical structure (Fig 2). The control cohort demonstrated a steep, linear helical structure from endo- to epicardium. PDMS grafts showed a moderate slope and HAT while TCP grafts demonstrated a weakly linear HAT. Myofibre alignment within the PDMS graft demonstrated more aligned myofibres than the disorganized TCP grafts. Transverse angle (TA) of healthy controls showed low variability, and hence highly aligned myofibres. PDMS grafts exhibited aligned myofibres, and were not significantly different than the healthy control while TCP grafts demonstrated some cell alignment, but was significantly different than PDMS and healthy cohort (Fig 3).

Conclusion:

Here, we have showcased evidence to support our hypothesis that mature PDMS grafts have higher anisotropy, cell alignment and helix angle transmurality than immature TCP grafts. Our findings show that CMR is a valuable tool to assess structural remodelling across regenerative therapies.