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Description
Following cardiac injury, mammals are unable to regenerate the affected tissue and instead form a fibrotic scar to preserve mechanical function. In contrast, zebrafish possess the remarkable capacity to fully regenerate the damaged area within 30 days post-injury.
The extracellular matrix (ECM) plays an essential role in this regenerative process. Using high-resolution mechanical measurements (atomic force microscopy and nanoindentation), our group identified a gradient in ECM stiffness across the regenerating tissue. This stiffness gradient arises from variations in the crosslinking of collagen fibers in a process mediated by periostin b. These findings indicate that the mechanical properties of the ECM are dynamically regulated during zebrafish heart regeneration, potentially playing a critical role in guiding cellular behavior and tissue remodeling.
To better understand whole-heart structure and morphology without prior physical manipulation (such as decellularization or sectioning, which can disrupt native architecture), we applied synchrotron-based X-ray Phase Contrast Imaging (X-PCI) at the FAXTOR beamline of the ALBA Synchrotron facility. This technique uses highly intense X-rays to visualize soft tissues in 3D at microscopic resolution without the need for contrast agents or destructive preparation methods. We examined cardiac morphology, ECM organization, and structural differences between wild-type zebrafish (which regenerate normally) and postnb KO mutant zebrafish (which lack the postnb gene and are unable to regenerate their hearts). We analyzed adult zebrafish hearts at 7 days post ventricular amputation or sham operation (non-amputated controls), preparing formalin-fixed, paraffin-embedded (FFPE) heart blocks for imaging. Image acquisition was performed at 20 keV with a voxel size of 0.65 µm.
In our first beamtime session, we acquired high-resolution tomographic images from 9 zebrafish hearts, including WT and PostnB KO mutant animals from both non-amputated hearts and hearts at 7 dpa. Despite the modest number of successfully acquired samples, we obtained valuable preliminary results. We observed that non-amputated wildtype hearts exhibit more structured cardiomyocyte fibers/trabeculae, a thicker epicardium/cortical cardiomyocyte layer, and appear more organized overall compared to non-amputated PostnB mutant hearts. Furthermore, analysis of one heart per amputated condition showed that, at 7 dpa, the wildtype regenerating region was organized and of similar dimensions to the original myocardium, whereas the PostnB mutant heart formed a disorganized, blob-like mass and larger than the original tissue (Figure 1). Further studies are needed to fully characterize the native organization of the myocardium, as well as the precise dynamics of its regrowth.