Surgical models for cardiac regeneration in neonatal mice

Abstract

Although amphibian and fish models of heart regeneration have existed for decades, a mammalian equivalent has long remained elusive. Our discovery of a brief postnatal window for heart regeneration in neonatal mice has led to the establishment of surgical models for cardiac regenerative studies in mammals for the first time. This protocol describes a 10-min surgical procedure to induce cardiac injury in 1-d-old neonatal mice. This allows for the analysis of cardiac regeneration after surgical amputation of the left ventricle (LV) (apical resection) and coronary artery occlusion (myocardial infarction (MI)). A comparative analysis of neonatal and adult responses to myocardial injury should enable identification of the key differences between regenerative and nonregenerative responses to cardiac injury. This protocol can also be adapted to the growing repertoire of genetic models available in the mouse, and it provides a valuable tool for unlocking the molecular mechanisms that guide mammalian heart regeneration during early postnatal life.

Figure 1

Apical resection of the neonatal mouse heart. (a) A neonatal mouse pup to be placed in ice to induce hypothermia. (b) After immobilization of the pup in the supine position using tape, skin incision is performed transversely along the chest cavity. (c) Access to the heart through intercostal muscle separation at the fourth intercostal space. (d) Apical resection of 15% of the heart is performed (piece-meal resection of small portions until the chamber is exposed). Exposing the LV chamber represents a landmark for efficient myocardial resection and surgical reproducibility.

Figure 2

MI of the neonatal mouse heart. (a) A C-1 tapered needle attached to a 6-0 Prolene suture is used for LAD ligation after thoracotomy. (b) The needle is passed out of the LV for ligation at a depth of 2–3 mm (deeper insertion of the needle is also acceptable). (c) Ligation of the LAD coronary artery. Note: this should result in blanching of the myocardium below the ligation, which is indicative of proper induction of ischemia.