Cardiac copper content and its relationship with heart physiology: Insights based on quantitative genetic and functional analyses using BXD family mice

Abstract

Background: Copper (Cu) is essential for the functioning of various enzymes involved in important cellular and physiological processes. Although critical for normal cardiac function, excessive accumulation, or deficiency of Cu in the myocardium is detrimental to the heart. Fluctuations in cardiac Cu content have been shown to cause cardiac pathologies and imbalance in systemic Cu metabolism. However, the genetic basis underlying cardiac Cu levels and their effects on heart traits remain to be understood. Representing the largest murine genetic reference population, BXD strains have been widely used to explore genotype-phenotype associations and identify quantitative trait loci (QTL) and candidate genes.

Methods: Cardiac Cu concentration and heart function in BXD strains were measured, followed by QTL mapping. The candidate genes modulating Cu homeostasis in mice hearts were identified using a multi-criteria scoring/filtering approach.

Results: Significant correlations were identified between cardiac Cu concentration and left ventricular (LV) internal diameter and volumes at end-diastole and end-systole, demonstrating that the BXDs with higher cardiac Cu levels have larger LV chamber. Conversely, cardiac Cu levels negatively correlated with LV posterior wall thickness, suggesting that lower Cu concentration in the heart is associated with LV hypertrophy. Genetic mapping identified six QTLs containing a total of 217 genes, which were further narrowed down to 21 genes that showed a significant association with cardiac Cu content in mice. Among those, Prex1 and Irx3 are the strongest candidates involved in cardiac Cu modulation.

Conclusion: Cardiac Cu level is significantly correlated with heart chamber size and hypertrophy phenotypes in BXD mice, while being regulated by multiple genes in several QTLs. Prex1 and Irx3 may be involved in modulating Cu metabolism and its downstream effects and warrant further experimental and functional validations.

Keywords: BXD; cardiac Cu homeostasis; cardiomyopathy; gene expression; genetic mapping; hypertrophy; quantitative trait loci; systems genetics.

FIGURE 1

Genetic mapping of the cardiac copper (Cu) concentration in BXD family mice. (A) Bar plot showing Cu concentration in the myocardium of BXD mice. The x-axis shows the BXD and the parental strains, and the y-axis shows Cu levels in μg/g. (B) Manhattan plot indicating the genomic loci correlated with Cu concentration across all mouse chromosomes. The x-axis indicates the genomic position, while the y-axis shows the –log(P), a measurement of the linkage between Cu level and genomic region. The blue and red dotted lines indicate suggestive (–logP of 3) and significant (–logP of 4) genome-wide thresholds, respectively. (C–H) Genomic loci correlated with Cu concentration either with a significant or suggestive threshold in specific chromosomes. The x-axis indicates the genomic position, and y-axis denotes the –log(P) value.

FIGURE 2

Number of genes within 1.5-LOD interval across the significant and suggestive QTLs. (A) Number of genes in each category for each indicated chromosome. (B) Number of exclusive and shared genes across five selection criteria.

FIGURE 3

Correlation between cardiac copper (Cu) concentration and echo phenotypes (LVID, LV.Vol, and LVPW). The x-axis indicates the Cu concentration (μg/g), and y axis denotes various echocardiography parameters. The Pearson correlation coefficient was used to determine the relationship between cardiac Cu concentration and echo phenotypes. The Pearson correlation r and P-values are indicated in the plots. LV, left ventricular; s, end-systole; d, end-diastole; LVID, LV internal diameter; LV.Vol, LV volume; LVPW, LV posterior wall.

FIGURE 4

Correlation between cardiac copper (Cu) concentration and echo phenotypes (FS%, EF%, stroke volume, CO, and IVS). The x-axis indicates the Cu concentration (μg/g), and y axis denotes the echocardiography parameters. The Pearson correlation coefficient was used to determine the relationship between cardiac Cu concentration and echo phenotypes. The Pearson correlation r and P-values are indicated in the plots. LV, left ventricular; s, end-systole; d, end-diastole; CO, cardiac output; IVS, interventricular septum.