1179A novel exonic variant in TRIM55 gene predisposes to heart failure
Authors: Heliste J , Chheda H , Akimov Y , Paatero I , Elenius K , Aittokallio T 
Published: October 2019

Abstract

Background/Introduction
Heart failure is a potentially lethal cardiac disorder. The genetic variants as well as the molecular signaling pathways accounting for the majority of the heritability of sporadic heart failure are unknown. Here, we screened for novel genetic variants associated with heart failure in the Finnish population. A previously uncharacterized variant in TRIM55 was selected for further validation.

Purpose
To identify and characterize heart failure-associated genetic variants.

Methods
Heart failure-associated genetic variants were screened from the FINRISK survey study data by the National Institute of Health and Welfare of Finland (genotype data available for approx. 28,000 individuals, 1,485 individuals with heart failure). A probably damaging heart failure-associated exonic variant in TRIM55 gene (rs138811034), encoding an E140K variant, was functionally characterized in HL-1 mouse cardiomyocytes using CRISPR/Cas9 technology to introduce the alteration in the endogenous locus. Variant cell lines were analyzed with RNA sequencing. The effect of the variant on cellular viability was tested with CTG assays. Hypertrophic response after isoproterenol treatment was studied by quantitating cell surface area with immunofluorescence microscopy. Western analyses of p21 expression and flow cytometry-based cell cycle analyses were carried out to assess effects on cell cycle progression. In zebrafish embryos in vivo, cardiac contractility was videomicroscopically measured after transient CRISPR-mediated knockdown of the trim55a gene.

Results
HL-1 cells harboring Trim55 E140K/− genotype demonstrated significantly reduced viability as compared to the WT/WT cell (P=0.006), similarly to the cell line with double knockout (−/−) of the gene. E140K/−, −/− and WT/− cell lines demonstrated a significant hypertrophic response to isoproterenol stimulation (P=0.007, P=0.007 and P=0.018, respectively), while the WT/WT cells did not. In the E140K/− and −/− cell lines, p21 protein expression was increased and there were significantly fewer cells in the mitotic G2/M phase of the cell cycle, as compared to the WT/WT cells (P=0.031 and P=0.024, respectively). In the E140K/− and −/− cell lines, RNA sequencing revealed systemic alterations in the genes related to cardiac contractility and stress. In zebrafish embryos with deleted trim55a gene, ejection fraction was reduced as compared to control sgRNA-injected embryos (30.8% ± 6.0% vs 43.9%± 2.2% (95% CIs), respectively, P=0.019).

Conclusions
TRIM55 E140K variant was statistically associated with heart failure in the Finnish population. In HL-1 cardiomyocytes in vitro, the variant reduced cellular viability and cell cycle progression and promoted hypertrophy. In zebrafish embryos, loss of trim55a caused a significant reduction in cardiac contractility. These findings are consistent with a novel role for TRIM55 polymorphism in predisposing to heart failure.

Acknowledgement/Funding
Finnish Cultural Foundation (Varsinais-Suomi Regional Fund), Inkeri ja Mauri Vänskän säätiö, Academy of Finland [310507], Sigrid Jusélius Foundation