Cardiac fibroblasts network organization and activation in the junctional region of the giant danio heart (543.8)

Abstract

The Giant danio (GD) and zebrafish (ZF) are small fish belonging to the diverse family of cyprinids; they both display the remarkable ability for heart regeneration. Our lab has recently described the complex junctional region (JR) at the interface of the compact and spongy myocardial layers of the ZF. However, how these two distinct layers are integrated in the GD has not been studied. Using light, scanning, and transmission electron microscopy (TEM), our study reveals that the GD possesses a complex JR with transitional cardiac myocytes (CM) linking compact heart CM and CM of the spongy heart, and that luminal and abluminal contacts are mediated through discrete membrane appositions and adherens junctions. More importantly we also found a complex network of fibroblasts (FB) with extensive cytoplasmic processes occupying the JR and investing the GD compact heart. To ascertain (FB) function, we treated GD with low dose of the antineoplastic agent Doxorubicin (DOX). Using Masson’s trichrome staining, we observed the accumulation of collagen in the compact heart. In addition, TEM shows increased level of collagen in the JR of treated hearts, as well as increase in FB endoplasmic reticulum and cytoplasmic polyribosomes suggesting a state of activation. We conclude that cardiac FB are resident in the complex JR and compact heart of the GD. Moreover our data suggest they are key to the accumulation of collagen that accompany the DOX‐induced injury response. Grant Funding Source: Supported by FDC‐DePauw University