Pitx2 maintains mitochondrial function during regeneration to prevent myocardial fat deposition

Abstract

Loss of the paired-like homeodomain transcription factor 2 (Pitx2) in cardiomyocytes predisposes mice to atrial fibrillation and compromises neonatal regenerative capacity. In addition, Pitx2 gain-of-function protects mature cardiomyocytes from ischemic injury and promotes heart repair. Here, we characterized the longterm myocardial phenotype following myocardial infarction (MI) in Pitx2 conditional-knockout (Pitx2 CKO) mice. We found adipose-like tissue in Pitx2 CKO hearts 60 days after MI induced surgically at postnatal day 2 but not at day 8. Molecular and cellular analyses showed the onset of adipogenic signaling in mutant hearts after MI. Lineage tracing experiments showed a non-cardiomyocyte origin of the de novo adipose-like tissue. Interestingly, we found that Pitx2 promotes mitochondrial function through its gene regulatory network, and that the knockdown of a key mitochondrial Pitx2 target gene, Cox7c, also leads to the accumulation of myocardial fat tissue. Single-nuclei RNA-seq revealed that Pitx2-deficient hearts were oxidatively stressed. Our findings reveal a role for Pitx2 in maintaining proper cardiac cellular composition during heart regeneration via the maintenance of proper mitochondrial structure and function.

An Important Role for DNMT3A-Mediated DNA Methylation in Cardiomyocyte Metabolism and Contractility

“…Because DNMT3A has previously been described to be involved in regulating the methylome of mitochondrial DNA, 56 the observed mitochondrial impairment could in part be a direct effect of DNMT3A knockout, although further research will have to be conducted on this. It is interesting that Li et al 57 have observed lipid accumulations similar to what we saw in our EHTs in mice harboring a conditional cardiomyocyte-specific knockout of Pitx2. Although at a first glance this seems to be contradictory to the higher PITX2 expression we observed, Li et al found the fat-accumulating cells in their knockout model to be of noncardiomyocyte origin, whereas in the EHTs lipid droplets were located inside cardiomyocytes.…”

A cellular atlas of Pitx2-dependent cardiac development

“…We found that several clusters of cells displayed unequal composition between the two genotypes. To determine which clusters were statistically different we performed a chi-square-based cluster composition test on the scRNA-seq dataset (Li et al, 2018;Xiao et al, 2018). We found that EpiCs, EndoCs, CPs, MΦs and CM-LV cells were more prevalent in Pitx2-deficient animals, whereas CM-OFT, mesenchymal cells, atrial CMs and epithelial-mesenchymal transition (EMT) cells decreased in Pitx2 mutants compared with controls ( Fig.…”

“…The scRNA data was analyzed as previously described with minor modifications (Li et al, 2018). Briefly, raw sequencing data were handled using the 10x Genomics Cell Ranger software (www.10xgenomics.com).…”

“…For pseudotemporal analysis, the normalized data from selected clusters were then passed directly into Monocle2, in which density peak clustering and downstream analysis were performed. Chi-square statistical analysis between clusters was performed and visualized as previously described (Li et al, 2018). PAGA was implemented through Scanpy (version 1.4.1) with the threshold set to 0.1 (Wolf et al, 2018).…”

Cardiomyocyte proliferation, a target for cardiac regeneration

“…In this study, Pitx2-induced cardiac regeneration requires physical PITX2 interaction with YAP in order to cooperatively activate ROS scavengers [65]. In addition, PITX2 has been recently reported to be required to maintain, during heart regeneration, proper mitochondrial structure and function [66]. Overall these studies highlight the importance of environmental O 2 contents and subsequently metabolism status in the regulation of cardiomyocyte proliferation and ultimately heart regeneration (Fig.…”