Spontaneous heart regeneration in adult MRL mice after cryo-injury

The reaction of myocardium to injury is generally characterized by a tissue repair mechanism that is initially beneficial in maintaining tissue integrity but which ultimately has a debilitating effect on cardiac function. The components of this type of wound healing response in the mammalian heart have been the subject of extensive study. Far less understood, however, are the dynamics of inflammation, ECM remodeling and scar formation at the site of injury, as well as compensatory adaptations of adjacent uninjured myocardium such as angiogenesis, cadiomyocyte hypertrophy, and apoptosis in the regenerative response to a myocardial injury. Recent observations in the MRL strain of mice indicate a capacity to heal myocardial injury with a rapid resolution of granulation tissue and little scar tissue, an increase of cardiomyocyte BrdU incorporation and restoration of myocardial architecture/function. The role of stem cells in this process remains to be elucidated for MRL mice. This response to injury, however, suggests epimorphic regeneration rather than repair.