Myocardial Biomechanics and the Consequent Differentially Expressed Genes of the Left Atrial Ligation Chick Embryonic Model of Hypoplastic Left Heart Syndrome

Abstract

Left atrial ligation (LAL) of the chick embryonic heart is a model of the hypoplastic left heart syndrome (HLHS) where a purely mechanical intervention without genetic or pharmacological manipulation is employed to initiate cardiac malformation. It is thus a key model for understanding the biomechanical origins of HLHS. However, its myocardial mechanics and subsequent gene expressions are not well-understood. We performed finite element (FE) modeling and single-cell RNA sequencing to address this. 4D high-frequency ultrasound imaging of chick embryonic hearts at HH25 (ED 4.5) were obtained for both LAL and control. Motion tracking was performed to quantify strains. Image-based FE modeling was conducted, using the direction of the smallest strain eigenvector as the orientations of contractions, the Guccione active tension model and a Fung-type transversely isotropic passive stiffness model that was determined via micro-pipette aspiration. Single-cell RNA sequencing of left ventricle (LV) heart tissues was performed for normal and LAL embryos at HH30 (ED 6.5) and differentially expressed genes (DEG) were identified.After LAL, LV thickness increased by 33%, strains in the myofiber direction increased by 42%, while stresses in the myofiber direction decreased by 50%. These were likely related to the reduction in ventricular preload and underloading of the LV due to LAL. RNA-seq data revealed potentially related DEG in myocytes, including mechano-sensing genes (Cadherins, NOTCH1, etc.), myosin contractility genes (MLCK, MLCP, etc.), calcium signaling genes (PI3K, PMCA, etc.), and genes related to fibrosis and fibroelastosis (TGF-β, BMP, etc.). We elucidated the changes to the myocardial biomechanics brought by LAL and the corresponding changes to myocyte gene expressions. These data may be useful in identifying the mechanobiological pathways of HLHS.

Role of tissue biomechanics in the formation and function of myocardial trabeculae in zebrafish embryos

“…As FE models are not often applied to embryonic hearts, we briefly explain its assumptions and limitations. Our FE computational model uses previously established methodologies (Lashkarinia et al., 2023; Shavik et al., 2020), which utilizes previously established tissue mechanics theories and computational methods explained in these previous publications. It assumes that the myocardium has a stiffness model that is transversely isotropic and hyperelastic (Guccione et al., 1991), and that at any myocardial location there is a direction of higher stiffness that corresponds to the myofibre orientation and the direction of maximum shortening.…”

“…As our algorithm could track image features and not just cardiac structure boundaries, the tracking results could be used for computation of strains, by first computing the 3D deformational gradient tensor using spatial gradients of displacements, before computing the Green–Lagrange strain tensor according to the finite strain theory (Ren et al., 2023; Zheng et al., 2022). We have previously used the algorithm for strain calculations in microscopy and clinical cardiac images (Lashkarinia et al., 2023; Ren et al., 2023; Zheng et al., 2022). The reconstructed end‐diastolic models were meshed using ANSYS and converted into a finely detailed volume mesh and strains were evaluated at the nodes of this mesh, as a means of evaluating strains at evenly distributed locations.…”

“…The mechanical model and FE modelling of the zebrafish embryonic ventricle was adapted from previous work (Lashkarinia et al., 2023) and was performed using the open‐source library FEniCS (https://fenicsproject.org/). The source code is available at https://github.com/WeiXuanChan/heartFEM.…”