Cardiomyocyte Notch1 signaling is essential for protection of the maternal heart from peripartum stress
Authors: Ricke-Hoch M , Stapel B , Pietzsch S , Erschow S , Scherr M , Viereck J , Thum T , Bauersachs J , Hilfiker-Kleiner D 
Published: May 2024

Abstract

Funding Acknowledgements
Type of funding sources: Public grant(s) – National budget only. Main funding source(s): Deutsche Forschungsgemeinschaft

Background
Peripartum cardiomyopathy (PPCM) is a life-threatening disease in women without known cardiovascular disease and is characterized by a sudden onset of heart failure (HF) before, under or after delivery. Previous studies suggest impaired endothelial to cardiomyocyte crosstalk as a major pathomechanism of the disease.

Purpose
Analyses of the role of Notch1 signaling for the endothelial-cardiomyocyte crosstalk in PPCM.

Methods and results
Serum from PPCM patients with acute HF reduced Notch1 expression in induced pluripotent stem cell derived cardiomyocytes (-20%, P&lt;0.05) compared to serum from postpartum-matched healthy controls (PP-Ctrl). Beside miRNA-146a previously described to be up-regulated in PPCM plasma (6.8-fold, P&lt;0.01), additional miRNAs targeting Notch1 signaling (miR-30a-3p, miR-34a, miR-200b-3p, miR-200c-3p, miR-429-3p, miR-449a) were up-regulated in PPCM plasma. Overexpression of these miRNAs in cardiomyocytes (CM) reduces Notch1 protein levels. Mice with a CM-restricted knockout of Notch1 (N1-KO) are born at the expected Mendelian ratio and nulli pari (NP) N1-KO female mice do not show a distinct cardiac phenotype at the age of 3 to 4 months compared to WT female mice (%FS WT: 41±5 vs N1-KO: 37±6; n= 9-12). However, they develop mild HF at the age of 6 months (%FS WT: 44±4 vs N1-KO: 31±8; n=11-14; P&lt;0.01). Mated N1-KO females displayed normal cardiac function and LV dimensions in the last week of the first pregnancy. After 3 pregnancies and nursing periods, N1-KO developed severe HF (%FS WT PP: 30±5 vs N1-KO PP: 16±5; n=8-12; P&lt;0.01), and show enhanced mortality (P&lt;0.01). N1-KO-NP and N1-KO-PP displayed significant increase in the cardiac expression of the stress markers ANP and BNP compared to respective WT-NP and WT-PP. RNA-Seq analysis of N1-KO-PP revealed 1380 transcripts (adj. P&lt;0.01) differently regulated genes, among them down-regulation of ErbB4, a known driver in PPCM onset. SiRNA-mediated knockdown of Notch1 in CM were associated with a decrease in ErbB4 protein expression. Treatment with bromocriptin (BR) was not able to improve survival and to rescue cardiac function and LV dimensions in postpartum N1-KO females (WT: 37±4, N1-KO: 23±10; n=7-8). Moreover, RNA-Seq analysis revealed that BR had no effect on the dysregulated cardiac mRNA.
In conclusion, the pathophysiology of PPCM is associated with reduced cardiac Notch1 expression, which results in part from 16-kDa-prolactin mediated upregulation of miRNAs targeting Notch1. The reduced cardiac Notch1 expression contributes to PPCM as indicated with severe postpartum HF and high mortality in N1-KO mice. Inhibition of prolactin secretion with BR failed to rescue the development of PPCM in N1-KO mice suggesting that deregulated Notch1 is downstream of the 16-kDa prolactin-miRNA pathophysiology.