Persistent fibrosis and decreased cardiac function following cardiac injury in theCtenopharyngodon idella(grass carp)

Following the discovery of heart regeneration in zebrafish, several more species within the Cyprinidae family have been found to have the same capability, suggesting heart regeneration may be conserved within this family. Although gonad regeneration has been observed in grass carp ( Ctenopharyngodon idella ), one of the largest cyprinid fish, the species’ response to cardiac injury has not been characterized. Surprisingly, we found cardiomyocytes do not repopulate the injured region following cryoinjury to the ventricle, instead exhibiting unresolved fibrosis and decreased cardiac function that persists for the 8-week duration of this study. Compared to other cyprinid fish studied, infiltration of macrophages is delayed and muted in this model. Additionally, fibroblasts are depleted following injury, a phenomenon not previously described in any cardiac model. This study shows that heart regeneration is not conserved among the Cyprinidae family and suggests the important role of non-fibroblasts in chronic fibrosis. Further study of these phenomenon may reveal the underlying differences between regeneration versus unresolved fibrosis in heart disease. Summary statement Grass carp, a member of the Cyprinidae family that includes regenerative zebrafish, do not regenerate functional cardiac tissue after cryoinjury. Instead, healing progresses through collagen deposition and scar formation.