MICRO RNAs ARE INVOLVED IN ACTIVATION OF EPICARDIUM DURING ZEBRAFISH HEART REGENERATION

Zebrafish could be an interesting translational model to understand and improve the post-infarctiontrial and possible regeneration in humans. The adult zebrafish is able to regenerate efficiently afterresecting nearly 20% of the ventricular apex. This process requires the concert activation of theepicardium and endocardium, as well as trans-differentiation of pre-existing cardiomyocytes thattogether replace the lost tissue. The molecular mechanisms involved in this activation process arenot completely clarified. In this work, in order to investigate if the down-regulation of thesemiRNAs (miRs) are linked with activation of epicardium, the expressions of miR133a and b andmiR1 during regeneration were analyzed. qPCR analyses in whole heart, or from distinct dissectedepicardial cells comparing to regenerative clot (containing cardiomyocytes, fibroblasts andendocardial cells)by laser-micro-dissector has indicated that already at 24 hrs there is adownregulation of miRs: 1) miR133a and miR1 in epicardium; 2) miR 133b and miR1 in theregenerative clot. All the miRs remain down-regulated until 7 days post-surgery. With the aim tovisualize the activations of heart component in combination with miRs, we developed immunohistochemistryusingantibodiesdirectedagainstcommon markers in mammals as well as zebrafish:Wilms Tumor 1 (WT1), a marker of epicardium; Heat Shock Protein 70 (HSP70), a chaperonactivated during regeneration, and the Cardiac Troponin T (cTnT) a marker of differentiatedcardiomyocytes.All these markers are directly or indirectly linked to the investigated miRs. WT1and HSP70 strongly marked the regeneration site just at two-three days post ventricular resection.In coherence, cTnT intensively marked the regenerative portion from 7 days onwards. miRs-1 and 133(a,b)have been strongly involved in the activation of epicardium and regenerative-clot duringthe regeneration process in zebrafish. This study can be a useful translational model to understandthe early epicardial activation in which miRs 133a and miR1 seem to play a central roleas observedin human heart.