electrocardiogram-recordings-in-anesthetized-mice-using-lead-ii

Electrocardiogram Recordings in Anesthetized Mice using Lead II

The electrocardiogram is a valuable tool for evaluating the cardiac conduction system. Animal research has helped generate novel genetic and ...

Kyung Hee University

Recent genome-wide association studies have identified 33 human genetic loci that influence blood pressure. The 15q24 locus is one such locus that has been confirmed in Asians and Europeans. There are 21 genes in the locus within a 1-Mb boundary, but a functional link of these genes to blood pressure has not been reported. We aimed to identify a causative gene for blood pressure change in the 15q24 locus.

Gene Silencing and Haploinsufficiency of Csk Increase Blood Pressure.

Blood pressure is regulated by a network of diverse physiological pathways. The C-terminal Src kinase (CSK) locus (15q24) is associated with blood pressure in various ethnic groups. It was recently reported thatCskinsufficiency increases blood pressure through Src. The mechanisms of hypertension inCskmice are examined further in this study.Methods and Results:To identify a causal component responsible for hypertension inCsk, the heart rate was measured by electrocardiogram and plasma volume by Evans blue dilution. Plasma volume increased inCskcompared with wild-types, while the heart rate did not change. Plasma sodium and aldosterone levels rose consistently inCskvs. wild-types, and spironolactone, a mineralocorticoid receptor antagonist, reduced blood pressure. The amounts of Sgk1 and Na/K-ATPase (NKA) increased in the kidney ofCskcompared with wild-types. It was also found that Cyp11b2 (aldosterone synthase) was upregulated in the adrenal glands ofCsk, and that Csk was enriched in the zona glomerulosa of adrenals, the major site of aldosterone production in the normal mouse.

Csk Regulates Blood Pressure by Controlling the Synthetic Pathways of Aldosterone.

PR interval is the period from the onset of P wave to the start of the QRS complex on electrocardiograms. A recent genomewide association study (GWAS) suggested that GAREM1 was linked to the PR interval on electrocardiograms. This study was designed to validate this correlation using additional subjects and examined the function of Garem1 in a mouse model. We analyzed the association of rs17744182, a variant in the GAREM1 locus, with the PR interval in 5646 subjects who were recruited from 2 Korean replication sets, Yangpyeong (n = 2471) and Yonsei (n = 3175), and noted a significant genomewide association by meta-analysis (P = 2.39 × 10). To confirm the function of Garem1 in mice, Garem1 siRNA was injected into mouse tail veins to reduce the expression of Garem1. Garem1 transcript levels declined by 53% in the atrium of the heart (P = 0.029), and Garem1-siRNA injected mice experienced a significant decrease in PR interval (43.27 ms vs. 44.89 ms in control, P = 0.007). We analyzed the expression pattern of Garem1 in the heart by immunohistology and observed specific expression of Garem1 in intracardiac ganglia. Garem1 was expressed in most neurons of the ganglion, including cholinergic and adrenergic cells. We have provided evidence that GAREM1 is involved in the PR interval of ECGs. These findings increase our understanding of the regulatory signals of heart rhythm through intracardiac ganglia of the autonomic nervous system and can be used to guide the development of a therapeutic target for heart conditions, such as atrial fibrillation.

GAREM1 regulates the PR interval on electrocardiograms.

Face morphology is strongly determined by genetic factors. However, only a small number of genes related to face morphology have been identified to date. Here, we performed a two-stage genome-wide association study (GWAS) of 85 face morphological traits in 7569 Koreans (5643 in the discovery set and 1926 in the replication set).

Identification of five novel genetic loci related to facial morphology by genome-wide association studies.

A variant in the  locus has been correlated with QRS duration in an electrocardiogram genome-wide association study, and the deletion of  has been implicated as a causal factor of the dilated cardiomyopathy that is linked to 1p36 deletion syndrome. We aimed to determine how a null mutation of  affects cardiac function and study the underlying mechanism of the resulting phenotype in an appropriate mouse model. We used cardiac-specific  conditional knockout mice to examine cardiac function by electrocardiography. QRS duration and QTc interval increased significantly in cardiac-specific  knockout animals compared with wild-type mice. Further, we assessed cardiomyopathy-associated features by trichrome staining, densitometry, and hydroxyproline assay. -null hearts showed greater fibrosis and cardiomyocyte hypertrophy. By quantitative real-time PCR, -null hearts upregulated extracellular matrix-related genes (, ) and α-smooth muscle actin (), a myofibroblast marker. Moreover, TGF-β signaling was activated in -null hearts, as evidenced by increased  transcript levels and phosphorylated Smad2. However, the inhibition of TGF-β receptor did not reverse the aberrations in conduction in cardiac-specific  knockout mice. To determine the underlying mechanisms, we performed RNA-seq using mouse left ventricular tissue. By functional analysis, -null hearts experienced dysregulated expression of ion channel genes, including , , , and . Mice with -null hearts develop abnormalities in cardiac conduction and cardiomyopathy-associated phenotypes, including fibrosis and cellular hypertrophy. Further, the RNA-seq findings suggest that impairments in ion homeostasis (Ca, K, and Na) may at least partially underlie the abnormal conduction in cardiac-specific  knockout mice. This is the first study that describes aberrant cardiac function and cardiomyopathy-associated phenotypes in an appropriate murine genetic model with cardiomyocyte-specific -null mutation. It is noteworthy that the correlation of  with QRS duration is replicated in a murine animal model and the potential underlying mechanism may be the impairment of ion homeostasis.

Article	Year
Gene Silencing and Haploinsufficiency of Csk Increase Blood Pressure. PloS one\| PubMed ID: 26751575	2016
Csk Regulates Blood Pressure by Controlling the Synthetic Pathways of Aldosterone. Circulation journal : official journal of the Japanese Circulation Society\| PubMed ID: 28724838	2017
GAREM1 regulates the PR interval on electrocardiograms. Journal of human genetics\| PubMed ID: 29273731	2018
Identification of five novel genetic loci related to facial morphology by genome-wide association studies. BMC genomics\| PubMed ID: 29921221	2018
Cardiac-specific inactivation of effects cardiac conduction abnormalities and cardiomyopathy-associated phenotypes. American journal of physiology. Heart and circulatory physiology\| PubMed ID: 32083975	2020

Ji-One Kang

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