Echocardiography phenotyping in murine genetic reference population of BXD strains reveals significant QTLs associated with cardiac function and morphology

Abstract

Background: The genetic reference population of recombinant inbred BXD mice has been derived from crosses between C57BL/6J and DBA/2J strains. The DBA/2J parent exhibits cardiomyopathy phenotypes, while C57BL/6J has normal heart. BXD mice are sequenced for studying genetic interactions in cardiomyopathies. Objectives: The study aimed to assess cardiomyopathy traits in BXDs and investigate the quantitative genetic architecture of those traits. Methods: Echocardiography, blood pressure, and cardiomyocyte size parameters obtained from 44 strains of BXD family (N >5/sex) at 4-5 months of age were associated with heart transcriptomes and expression quantitative trait loci (eQTL) mapping was performed. Results: More than 2-fold variance in ejection fraction (EF%), fractional shortening (FS%), left ventricular volumes (LVVol), internal dimensions (LVID), mass (LVM), and posterior wall (LVPW) thickness was found among BXDs. In male BXDs, eQTL mapping identified Ndrg4 on chromosome 8 QTL to be positively correlated with LVVol and LVID and negatively associated with cardiomyocyte diameter. In female BXDs, significant eQTLs were found on chromosomes 7 and 3 to be associated with LVPW and EF% and FS%, respectively, and Josd2, Dap3 and Tmp3 were predicted as strong candidate genes. Conclusions: Our study found variable cardiovascular traits among BXD strains and identified multiple associated QTLs, suggesting an influence of genetic background on expression of echocardiographic and cardiomyocyte diameter traits. Increased LVVol and reduced EF% and FS% represented dilated cardiomyopathy, whereas increased LV mass and wall thickness indicated hypertrophic cardiomyopathy traits. The BXD family is ideal for identifying candidate genes, causal and modifier, that influence cardiovascular phenotypes.

Expression Levels of the Tnni3k Gene in the Heart Are Highly Associated with Cardiac and Glucose Metabolism-Related Phenotypes and Functional Pathways

“…We, therefore, hypothesized that the variable expression of Tnni3k in B and D alleles is correlated with the cardiac phenotypes among BXDs. To test this hypothesis, we performed association analyses between Tnni3k expression and cardiac phenotypic parameters which were previously evaluated using echocardiography and ECG tracings in BXDs [ 16 ]. Interestingly, we found Tnni3k expression to be positively correlated with heart rate ( p = 0.007, Figure 7 A, left) and left ventricular posterior wall thickness at end-diastole (LVPW; d, p = 0.033, Figure 7 A, right).…”

“…Importantly, a parental D2 strain of the BXD family of RI mice has a natural loss of Tnni3k expression compared to the other parental strain, B6. More importantly, a D2 strain has natural cardiomyopathy features relative to a B6 strain that has a normal heart [ 15 ] and diverse cardiac morphology and function traits are inherent among BXD RI lines [ 16 ]. In this study, our WGS of the BXD family identified that the T659I Tnni3k and splicing rs49812611 variants segregated among BXD strains.…”

“…Transthoracic twodimensional and Doppler echocardiography was performed to evaluate heart function and morphology using a Vevo2100 Micro-imaging System (VisualSonics Inc., Toronto, ON, Canada) as previously described [30]. Echocardiography was performed in 40 strains of BXD mice, B6 and D2 strains at 5-6 months of age (N ≥ 5 mice/strain/sex) and deposited in the GeneNetwork website (https://genenetwork.org/, accessed on 6 August 2023), as we described previously [16], and as displayed in the Supplementary Table S3. Briefly, the chest of the mice was treated with chemical hair remover the day prior.…”

“…The rs49812611 has been experimentally linked to aberrant TNNI3K protein expression in the D2 strain, which is known to display cardiomyopathy traits including cardiac hypertrophy and fibrosis [ 14 , 15 ]. Importantly, recombinant inbred (RI) mice derived from crosses of B6 and D2 strains, the so-called BXD family of murine genetic reference population (GRP) segregated those cardiomyopathy traits, suggesting a potential relation between cardiomyopathy traits and Tnni3k [ 16 ]. Knockout B6 mice and transgenic mice with overexpression of mutated kinase-dead TNNI3K demonstrated subtle cardiac hypertrophy compared to mice harboring wild-type Tnni3k transgene [ 3 ].…”

Exploring the Regulation and Function of Rpl3l in the Development of Early-Onset Dilated Cardiomyopathy and Congestive Heart Failure Using Systems Genetics Approach

“…We hypothesized that different genetic backgrounds affect the expression of RPL3L, and elucidation of gene-gene interactions using reference populations with diverse genetic backgrounds would be advantageous in understanding the regulatory mechanisms of RPL3L. In this study, we utilized the BXD family of mice derived from C57BL/6J and DBA/2J strains that has recently been demonstrated to be an ideal murine genetic reference population (GRP) for dissecting the genetic determinants and mechanisms involved in the pathogenesis of cardiomyopathies and the failing heart [18]. We employed a comparative mouse-human genetic analysis, and this analysis suggested that Rpl3l is upstream-regulated by Myl4 and Sdha.…”