AP-1 Contributes to Chromatin Accessibility to Promote Sarcomere Disassembly and Cardiomyocyte Protrusion During Zebrafish Heart Regeneration

Abstract

Rationale: The adult human heart is an organ with low regenerative potential. Heart failure following acute myocardial infarction is a leading cause of death due to the inability of cardiomyocytes to proliferate and replenish lost cardiac muscle. While the zebrafish has emerged as a powerful model to study endogenous cardiac regeneration, the molecular mechanisms by which cardiomyocytes respond to damage by disassembling sarcomeres, proliferating, and repopulating the injured area remain unclear. Furthermore, we are far from understanding the regulation of the chromatin landscape and epigenetic barriers that must be overcome for cardiac regeneration to occur. Objective: To identify transcription factor regulators of the chromatin landscape, which promote cardiomyocyte regeneration in zebrafish, and investigate their function. Methods and Results: Using the Assay for Transposase-Accessible Chromatin coupled to high-throughput sequencing (ATAC-Seq), we first find that the regenerating cardiomyocyte chromatin accessibility landscape undergoes extensive changes following cryoinjury, and that activator protein-1 (AP-1) binding sites are the most highly enriched motifs in regions that gain accessibility during cardiac regeneration. Furthermore, using bioinformatic and gene expression analyses, we find that the AP-1 response in regenerating adult zebrafish cardiomyocytes is largely different from the response in adult mammalian cardiomyocytes. Using a cardiomyocyte-specific dominant negative approach, we show that blocking AP-1 function leads to defects in cardiomyocyte proliferation as well as decreased chromatin accessibility at the fbxl22 and ilk loci, which regulate sarcomere disassembly and cardiomyocyte protrusion into the injured area, respectively. We further show that overexpression of the AP-1 family members Junb and Fosl1 can promote changes in mammalian cardiomyocyte behavior in vitro. Conclusions: AP-1 transcription factors play an essential role in the cardiomyocyte response to injury by regulating chromatin accessibility changes, thereby allowing the activation of gene expression programs that promote cardiomyocyte dedifferentiation, proliferation, and protrusion into the injured area.

M2 macrophage-derived exosomes promote the c-KIT phenotype of vascular smooth muscle cells during vascular tissue repair after intravascular stent implantation

“…Additionally, the activation of AP-1 plays an important role in the process of aging 45 , atherosclerosis 46 , 47 , and vascular remodeling 48 - 50 . According to the latest research, AP-1 plays an essential role in the cardiomyocyte response to injury by regulating chromatin accessibility changes, thereby allowing the activation of gene expression programs that promote cardiomyocyte dedifferentiation, proliferation, and protrusion into the injured area 51 . In our study, the dedifferentiation of VSMCs after stent implantation was accompanied by the activation of AP-1.…”

What we know about cardiomyocyte dedifferentiation

“…In other words, dedifferentiation might be a prerequisite for CM proliferation. In this section, the following molecular mechanisms involved in zebrafish heart regeneration are discussed based on their effects on regulating CM dedifferentiation and J o u r n a l P r e -p r o o f Journal Pre-proof proliferation: Nrg1-ErbB [29], NF-κB [30], TGFβ/Activin-β [33], BMP-pSmad1/5/8 [31], Notch [32], AP-1 transcriptional factor [42], Let-7 miRNAs [34], Ezh2-H3K27me3 [35] and PDGF signalling pathway [38]. These mechanisms are summarised in Table 1, Figure 2 and Figure 3.…”

“…CM-specific KO of Fos (one of the subunits of AP-1) results in less proliferating CMs and embCMHC + CMs. A putative target gene of AP-1, fbxl22, contributes to cardiac sarcomere disassembly [42]. Elevated expression and activity of Let-7i is necessary to induce CM proliferation by suppressing TNFα signalling, but depletion of Let-7i activity does not disrupt CM dedifferentiation within 7 dpa, as the CMs still manifest disassembled sarcomere and activation of gata4 [34].…”

Hypoxic Preconditioning Enhances Cellular Viability and Pro-angiogenic Paracrine Activity: The Roles of VEGF-A and SDF-1a in Rat Adipose Stem Cells

“…Stem cell-based therapy has a broad application prospect for the repair and functional reconstruction of tissue or organ defects in tissue engineering (Beisaw et al, 2020). Transplanting stem cells into the target area directly is a wellestablished approach.…”