Transcriptomic analysis of injured axolotl hearts reveals AXL-GAS6 as potential mitogenic signal for cardiac regeneration

Cardiovascular diseases are the leading cause of death in the western world, partly due to the post-mitotic nature of adult cardiac muscle cells (CMs).

In contrast to adult mammals, the salamander Ambystoma mexicanum (axolotl) can regenerate their hearts after injury. Unlike other regenerative models, axolotls have the additional advantage of having a heart size similar to mammalian models.

Past works in the field focused on changes occurring in the CMs themselves and largely didn’t attempt to decipher the cardiac cellular-crosstalk or its contribution to regeneration.

We hypothesized that signalling events specifically at the infarct–border zone intersection enable regeneration. To identify these, we generated single nucleus RNA and ATAC-seq analysis of the regenerating axolotl heart. Leveraging the large size of the heart, we performed spatial transcriptomic analysis and obtained the first-of-its-kind, spatially resolved “atlas” of heart regeneration. We identified border zone CMs (BZ-CMs) and, using trajectory analyses, we could delineate their behaviour after injury. We analyzed which cell types are in proximity with BZ-CMs, allowing us to curate the “spatially relevant” ligand-receptor interactions. We identified conserved pro-regenerative signalling events, as well as signalling pairs which were not previously described in this context, such as Tyrosine-protein kinase receptor UFO (AXL), found solely in the injury-responsive CMs, and its ligand Growth arrest-specific protein 6 (Gas6) in endothelial cells.

Our results provide a novel atlas of axolotl cardiac cells, a comprehensive analysis of changes occurring during cardiac regeneration, and identification of novel pro-regenerative pathways.