Background: Peripartum cardiomyopathy (PPCM) is characterized by maternal systolic heart failure (HF) due to left ventricular (LV) dysfunction in heart-healthy women occurring between one month before and six months following delivery. Recent data from the German PPCM registry indicated that gene variants associated with the DNA damage response might promote PPCM onset. In this study, we investigated the regulation of DNA damage response (DDR) associated genes in the postpartum mouse heart, the impact of impairment in this pathway during the peripartum phase using mice heterozygous for a major regulator of these pathway Ataxia-Telangiectasia-Mutated (ATM) and determined the frequency of ATM gene variants in PPCM patients.

Methods and results: RNAseq analyses of nulli pari (NP) and postpartum (PP) wildtype (WT) mice revealed upregulation of several genes involved in the DDR (Table). Whole exome sequencing in 65 PPCM patients from the German PPCM registry identified 9 carriers of ATM gene variants, mainly classified as variant of uncertain significance (VUS), with an increased prevalence of ATM gene variants (13.9%) compared to the average western population (1-2.8%). Therefore, we investigated the role of ATM deficiency in the peripartum heart using a heterozygous ATM (ATM^+/-) mouse model generated by a targeted mutation (Atm^ins5790neo), which results in a truncated protein. ATM^+/- mice are born at the expected mendelian ratio and western blotting confirmed the reduction of ATM protein levels in ATM^+/- mice (-43%, P<0.0001). Cardiac function of NP ATM^+/- mice at 7 months of age was unchanged compared to WT female mice (fractional area change (FAC) (%): WT: 54±9 vs ATM+/-: 58±9; n=11-15, n.s.). However, ATM^+/- mice developed a reduced cardiac function after 4 pregnancies and nursing periods compared to corresponding WT-PP mice (FAC (%): WT: 53±4 vs ATM+/-: 35±7; n=6-9; P<0.001). ATM^+/--PP mice showed increased cardiac dimensions (end-diastolic area (mm²): WT: 23.3±3 vs ATM^+/-: 27±4; n=6-9; P<0.05 / end-systolic area (mm²): WT: 11±2 vs ATM^+/-: 17±4; n=6-9; P<0.0001) and weights (heart weight/tibia length: WT: 8.3±0.4 vs ATM^+/-: 9.2±1.2; n=7-9; P<0.05) compared to WT-PP. In line with these findings, ATM^+/--PP mice revealed increased cardiac mRNA expression of hypertrophic stress markers ANKRD1 (+100%; P<0.001) and ANP (+52%; P<0.05) compared to WT-PP. In contrast, ATM^+/--PP mice did not develop cardiac fibrosis (confirmed by sirius red staining and Col1a1 RNA expression) or inflammation (confirmed by CD45 staining and expression of the macrophage marker Adgre1) compared to WT-PP.

In conclusion, upregulation of DDR genes in the postpartum maternal heart suggests an important role of this pathway for protection from pregnancy associated stress. The increased prevalence of ATM gene variants in a cohort of the German PPCM cohort supports this notion and suggests a potential role of ATM mutations in the pathophysiology of PPCM. In line with these findings, reduced ATM expression causes cardiac impairment in the ATM+/-PP mice after consecutive pregnancies and nursing periods. 

 


Table: RNA-Seq data: DDR associated transcripts from  WT-NP vs. WT-PP hearts