# Nppa and Nppb Deficiency Drives Ventricular Hypertrophy and Subendocardial Gene Deregulation in the Mouse Heart

## TL;DR

Deleting Nppa and Nppb genes in mice leads to heart enlargement and changes in gene activity in the heart's inner layers.

## Contribution

This study reveals the role of Nppa and Nppb in maintaining heart structure and gene regulation in mice.

## Key findings

- Nppa–Nppb−/− mice show heart hypertrophy and QRS prolongation.
- Subendocardial gene expression changes suggest conduction system disruption.
- Tbx5 down-regulation indicates a feedback loop involving Nppa/Nppb.

## Abstract

The natriuretic peptides A and B, encoded by NPPA and NPPB, respectively, have complementary and redundant functions in cardiovascular homeostasis. To establish their coordinated roles, we analyzed the cardiac phenotype of a mouse line in which the Nppa–Nppb cluster was deleted from the genome. At 8 weeks of age, Nppa–Nppb−/− mice (HOM) had significantly larger hearts and cardiomyocytic hypertrophy compared to wild-type and heterozygous mice. Electrocardiogram comparisons showed QRS prolongation in HOM mice. Hypertrophy was confirmed by echocardiography, which further indicated preservation of left ventricular systolic function. Bulk-transcriptomic analysis revealed moderate changes in gene expression of the left ventricle. Genes involved in fatty acid metabolism, ion handling and conductivity, including genes marking the ventricular conduction system, were down-regulated. Spatial transcriptomic analysis revealed the greatest changes in gene expression in the subendocardial wall, where the ventricular conduction system is located. Tbx5, the encoding dosage-sensitive T-box transcription factor Tbx5 that is essential for the expression of ventricular conduction system genes and for Nppa and Nppb, was down-regulated in the ventricles of HOM mice, indicating that a positive feedback loop normally maintains Tbx5 expression. We conclude that homozygous Nppa–Nppb deficiency in mice causes cardiac hypertrophy, including a likely perturbation of the ventricular conduction system.