The Gridlock transcriptional repressor impedes vertebrate heart regeneration by restricting expression of lysine methyltransferase

Abstract

Teleost zebrafish and neonatal mammalian hearts exhibit the remarkable capacity to regenerate through dedifferentiation and proliferation of pre-existing cardiomyocytes (CMs). Although many mitogenic signals that stimulate zebrafish heart regeneration have been identified, transcriptional programs that restrain injury-induced CM renewal are incompletely understood. Here, we report that mutations in gridlock (grl; also known as hey2), encoding a Hairy-related basic helix-loop-helix transcriptional repressor, enhance CM proliferation and reduce fibrosis following damage. In contrast, myocardial grl induction blunts CM dedifferentiation and regenerative responses to heart injury. RNA sequencing analyses uncover Smyd2 lysine methyltransferase (KMT) as a key transcriptional target repressed by Grl. Reduction in Grl protein levels triggered by injury induces smyd2 expression at the wound myocardium, enhancing CM proliferation. We show that Smyd2 functions as a methyltransferase and modulates the Stat3 methylation and phosphorylation activity. Inhibition of the KMT activity of Smyd2 reduces phosphorylated Stat3 at cardiac wounds, suppressing the elevated CM proliferation in injured grl mutant hearts. Our findings establish an injury-specific transcriptional repression program in governing CM renewal during heart regeneration, providing a potential strategy whereby silencing Grl repression at local regions might empower regeneration capacity to the injured mammalian heart.

Rewiring of 3D Chromatin Topology Orchestrates Transcriptional Reprogramming and the Development of Human Dilated Cardiomyopathy

“…SMYD2 (SET [suppressor of variegation, enhancer of zeste, trithorax] and MYND [myeloid-nervy-DEAF1] domain-containing protein 2; histone lysine methyltransferase) is robustly expressed in neonatal heart and regulates cardiac development and regeneration. 37,38 Similar to TBX5 (t-box transcription factor 5), we also found that its promoter interacted with an activated enhancer embedded in its 3rd intron in DCM hearts (Figure 3F). Other DCM-enriched E-P examples ( MEF2D [myocyte enhancer factor 2d], regulator for myogenesis 39 and cardiac stress 40 ; MYPN [myopalladin], regulator for maintaining sarcomeric integrity 41 ) are displayed in Figure S4F and S4G, respectively.…”

Foxm1 regulates cardiomyocyte proliferation in adult zebrafish after cardiac injury

“…1 G-J). Semi-qualitative analysis of the fibrotic area was performed to indicate the increased severity of the damage as shown in previous studies ( Bise et al, 2020 ; She et al, 2020 ; Sun et al, 2022 ; Xia et al, 2022 ). Acid fuchsin orange G (AFOG) staining revealed fibrotic tissue in foxm1 m/m ( Fig.…”

A novel gene-trap line reveals the dynamic patterns and essential roles of cysteine and glycine-rich protein 3 in zebrafish heart development and regeneration

“…For PCNA staining, adult zebrafish hearts were extracted and fixed in 4% paraformaldehyde for 1 h at room temperature, and subsequently dehydrated in 30% sucrose, then embedded in OCT solution and further sectioned at 10 μm thickness with a Leica cryostat. Immunostaining on cryosections was performed as previously described [ 14 ], administrated with antigen retrieval at 98 °C for 20 min in the citric acid buffer. CM proliferation index was calculated as the number of PCNA + Mef2C + cells over the number of total Mef2C + cells.…”