Abstract
Rationale:
Established animal models of tissue and limb regeneration demonstrate a critical dependence on concurrent reinnervation by the peripheral nervous system. The abundance of autonomic nerves in the mammalian heart suggests they play a similar role in the response to cardiac injury.
Objective:
To test the hypothesis that reinnervation is required for innate neonatal cardiac regeneration.
Methods and Results:
Crossing Wnt1:cre transgenic mice with a double-tandem (td) tomato reporter strain identified all neural crest-derived cell lineages including the peripheral autonomic nerves in the heart. Whole mount epi-fluorescence microscopy facilitated the clear resolution of subepicardial autonomic nerves in the mouse ventricles providing unprecedented detail of the subepicardial neuroanatomy of the mouse heart. We confirmed that sympathetic nerve structures envelop the entire heart, and importantly, exhibit robust re-growth into the regenerating myocardium following resection of the left ventricular apex in neonatal mice. While innervated hearts regenerate with minimal scarring to the left ventricular myocardium, we report that innate cardiac regeneration was inhibited following sympathectomy, as determined by cross-sectional percentage of viable LV myocardium (n=9, 0.87±1.4% vs. n=6, 14.05±4.4% ; p<0.01).
Conclusions:
Ablation of post-ganglionic sympathetic nerves blocks the innate regenerative capacity of neonatal mouse hearts. Therefore, the innate ability of the neonatal mouse heart to undergo regeneration in response to injury is dependent on sympathetic innervation of the ventricular myocardium. This finding has significant implications for adult regeneration following myocardial infarction where nerve growth is hindered by age related influences and scar tissue.