# Deletion of Ptpmt1 by αMHC-Cre in Mice Results in Left Ventricular Non-Compaction

## TL;DR

Deleting the Ptpmt1 gene in mouse hearts causes a heart defect called left ventricular non-compaction, leading to early death and abnormal heart structure.

## Contribution

This study identifies Ptpmt1 as a critical gene in regulating left ventricular compaction during heart development in mice.

## Key findings

- Cardiac-specific deletion of Ptpmt1 in mice leads to left ventricular non-compaction and early postnatal death.
- Ptpmt1 deletion reduces cardiomyocyte proliferation and disrupts heart development at embryonic stages.
- Ptpmt1 deficiency induces mitochondrial stress and alters gene expression related to heart development.

## Abstract

Background: Left ventricular non-compaction cardiomyopathy (LVNC) is a congenital heart disease characterized by abnormal prenatal development of the left ventricle that has an aberrantly thick trabecular layer and a thinner compacted myocardial layer. However, the underlying molecular mechanisms of LVNC regulated by mitochondrial phosphatase genes remain largely unresolved. Methods: We generated a mouse model with cardiac-specific deletion (CKO) of Ptpmt1, a type of mitochondrial phosphatase gene, using the αMHC-Cre, and investigated the effects of cardiac-specific Ptpmt1 deficiency on cardiac development. Morphological, histological, and immunofluorescent analyses were conducted in Ptpmt1 CKO and littermate controls. A transcriptional atlas was identified by RNA sequencing (RNA-seq) analysis. Results: We found that CKO mice were born at the Mendelian ratio with normal body weights. However, most of the CKO mice died within 24 h after birth, developing spontaneous ventricular tachycardia. Morphological and histological analysis further revealed that newborn CKO mice developed an LVNC phenotype, evidenced by a thicker trabecular layer and a thinner myocardium layer, when compared with the littermate control. We then examined the embryonic hearts and found that such an LVNC phenotype could also be observed in CKO hearts at E15.5 but not at E13.5. We also performed the EdU incorporation assay and demonstrated that cardiac cell proliferation in both myocardium and trabecular layers was significantly reduced in CKO hearts at E15.5, which is also consistent with the dysregulation of genes associated with heart development and cardiomyocyte proliferation in CKO hearts at the same stage, as revealed by both the transcriptome analysis and the quantitative real-time PCR. Deletion of Ptpmt1 in mouse cardiomyocytes also induced an increase in phosphorylated eIF2α and ATF4 levels, indicating a mitochondrial stress response in CKO hearts. Conclusions: Our results demonstrated that Ptpmt1 may play an essential role in regulating left ventricular compaction during mouse heart development.