This work aims to investigate the energy metabolism in mice with restrictive cardiomyopathy induced by cardiac troponin Ⅰ (cTnI) R193H mutation. Echocardiography was used to monitor cardiac function. ATP content and ATPase activity were detected with relevant kits. The expression levels of GLUT4, FAT/CD36, and PI3K/AKT pathway proteins were detected. Proteomics and phosphorylation omics were used to analyze the differential expression and modification of cardiac proteins and related pathways, respectively. The utilization of cardiac energy substrates was investigated using relevant kits. The isovolumic relaxation time of 4-month-old cTnI193His-M mice was significantly prolonged (P < 0.01); Cardiac ATP content, ATPase activity, and mitochondrial number were significantly increased (P < 0.05, P < 0.01, and P < 0.01, respectively); GLUT4 expression level increased (P < 0.01); the expression level of CD36 decreased (P < 0.01). Proteomic results showed that the glycolytic/gluconeogenic pathway was up-regulated. Phosphorylation omics was enriched in the inositol phosphate metabolism pathway and PI3K/AKT pathway. In conclusion, at the early stage of diastolic dysfunction, cTnI193His-M mice may increase glucose uptake and metabolism through the PI3K/AKT pathway to satisfy the high energy demand, which may contribute to the development of myocardial fibrosis and heart failure.

Aging is an independent risk factor for cardiovascular diseases. Cardiac diastolic dysfunction (CDD), ultimately leading to heart failure with preserved ejection fraction (HFpEF), is prevalent among older individuals. Although therapeutics have made great progress, preventive strategies remain unmet medical needs. Green tea catechins have been shown to be effective in improving aging-related cardiovascular and cerebral disorders in animal models and patients. However, little attention has been paid to whether long-term administration of epigallocatechin gallate (EGCG), the major bioactive ingredient of green tea catechins, could prevent the onset and progression of CDD. In this study, 12-month-old female mice were orally administered 50, 100 and 200 mg EGCG mixed with drinking water for 6 months. Aged mice (18 months old) exhibited the major features of HFpEF, including CDD with pEF, cardiac fibrosis, increased cardiomyocyte apoptosis, and mitochondrial damages, as well as elevated A/B-type natriuretic peptide. Cardiac troponin I (cTnI) expression was also reduced. Long-term administration of 100 or 200 mg EGCG prevented aging-related CDD and exercise capacity decline, along with alleviating myocardial apoptosis and mitochondria damage. The transcription and protein expression of cTnI were increased, which might be achieved by inhibiting the expression and activity of histone deacetylase 1 (HDAC1), and reducing its binding level near cTnI’s promoter, thereby elevating acetylated histone 3 (AcH3) and acetylated lysine 9 on histone H3 (AcH3K9) in the aged mice. We provide a novel insight that long-term administration of EGCG is a potentially effective strategy in preventing aging-related CDD and cTnI expression decline.

In the past studies, it is shown that cardiac troponin I (cTnI, encoded by TNNI3), as a cytoplasmic protein, is an inhibitory subunit in troponin complex, and involves in cardiomyocyte diastolic regulation. Here, we assessed a novel role of cTnI as a nucleoprotein. Firstly, the nuclear translocation of cTnI was found in mouse, human fetuses and rat heart tissues. In addition, there were differences in percentage of intranuclear cTnI in different conditions. Based on weighted gene co-expression network analyses (WGCNA) and verification in cell experiments, a strong expression correlation was found between TNNI3 and Atp2a2, which encodes sarco-endoplasmic reticulum Ca²⁺ ATPase isoform 2a (SERCA2a), and involves in ATP hydrolysis and Ca²⁺ transient. TNNI3 gain and loss caused Atpa2a2 increase/decrease in a dose-dependent manner both in mRNA and protein levels, in vivo and in vitro. By using ChIP-sequence we demonstrated specific binding DNA sequences of cTnI were enriched in ATP2a2 promoter −239~–889 region and the specific binding sequence motif of cTnI was analyzed by software as "CCAT", which has been reported to be required for YY1 binding to the promoter region of YY1-related genes. Moreover, it was further verified that pcDNA3.1 (−)-TNNI3 could express cTnI proteins and increase the promoter activity of Atp2a2 through luciferase report assay. In the end, we evaluated beat frequencies, total ATP contents, Ca²⁺ transients in TNNI3-siRNA myocardial cells. These findings indicated, for the first time, cTnI may regulate Atp2a2 in cardiomyocytes as a co-regulatory factor and participate in the regulation of intracellular Ca ions.

Cardiac Troponin I (cTnI) is a subunit of the thin filament involved in regulation of heart contraction. Mutated cTnI accounts for most genetic mutations associated with restrictive cardiomyopathy (RCM). We previously found phosphodiesterase 4D (PDE4D) decreased in RCM mice with cTnIR193H mutation and the mutant cTnI might be involved in PDE4D reduction. This study aims to elucidate a novel role of cTnIR193H mutant as a gene regulator. Overexpression of cTnIR193H mutant in cardiomyocytes showed decrease in PDED4D protein expression, while the enrichment of histone deacetylase 1 (HDAC1) was increased along with decreases in acetylated lysine 4 (acH3K4) and 9 (acH3K9) levels in the PDE4D promoter. HDAC1 overexpression could also downregulate PDE4D via reducing acH3K4 and acH3K9 levels. Co-IP assays showed that cTnIR193H mutant owed increased binding ability to HDAC1 compared with wild type cTnI. EGCG as a HDAC1 inhibitor could diminish the strength of cTnIR193H-HDAC1 interactions and alleviate the reduction in PDE4D expression. Together, our data indicated that cTnIR193H mutant could repress PDE4D expression in cardiomyocytes through HDAC1 associated histone deacetylation modification. Unlike the typical function of cTnI in cytoplasm, our study suggested a novel role of cTnI mutants in nuclei in regulating gene expression.

Down syndrome (DS), as a typical genomic aneuploidy, is a common cause of various birth defects, among which is congenital heart disease (CHD). 40–60% neonates with DS have some kinds of CHD. However, the molecular pathogenic mechanisms of DS associated CHD are still not fully understood. This review summarizes available studies on DS associated CHD from seven aspects so as to provide a crucial and updated overview of what we known so far in this domain.