Regeneration of the lizard heart after cryoinjury

Lizards are renowned for their tremendous potential to heal tissues and organs after injury, but little is known about myocardial regeneration in reptiles generally. Here, we study cardiac regeneration in the leopard gecko (Eublepharis macularius) to fill the knowledge gap between traditional models of poikilothermic (zebrafish) and homeothermic (neonatal mice) vertebrates commonly used in myocardial regenerative studies. We inflicted cryoinjury at the apex of the adult heart and used optical mapping, microCT, histology and immunohistochemistry to evaluate myocardial regeneration over the following 4 weeks. Optical mapping revealed epicardial electrical activation of the ventricle during the healing period after cryoinjury, and demonstrated that the cryoinjured area was devoid of electrical activation during the first 2 weeks. The functional recovery of signal spreading over the whole ventricular surface was completed in 21 days after cryoinjury. Morphologically, the first week was characterized by a loss of myocardial viability, the second week by a restoration of the myocardial tissue, the third week by continuation of the regenerative processes, and the fourth week by a completion of myocardial regeneration and a restoration of heart viability. In conclusion, geckos may provide novel insight into myocardial healing across the vertebrate lineages and thus help to reveal healing abilities between non-ischaemic regenerative and ischaemic reparative processes during cardiac regeneration.