Measuring hypertrophy in neonatal rat primary cardiomyocytes and human iPSC-derived cardiomyocytes

Inhibition of Cholesteryl Ester Transfer Protein Contributes to the Protection of Ginsenoside Re Against Isoproterenol-Induced Cardiac Hypertrophy

Background and objectives Ginsenoside Re (Re), a protopanaxatriol-type saponin extracted from ginseng, is known to have potential cardioprotective effects; however, the mechanisms of Re in improving cardiac hypertrophy have not been fully elucidated. This study aimed to investigate the therapeutic effects and underlying mechanism of Re on isoproterenol (ISO)-induced cardiac hypertrophy in vivo and in vitro. Methods Rats were intraperitoneally injected with ISO 30 mg/kg thrice daily for 14 consecutive days to induce cardiac hypertrophy, and these rats were treated with atorvastatin (ATC, 20 mg/kg) or Re (20 mg/kg or 40 mg/kg) once daily for three days in advance until the end of the experiment. Heart weight index, hematoxylin and eosin staining, and hypertrophy-related fetal gene expression were measured to evaluate the effect of Re on cardiac hypertrophy in vivo. Meanwhile, the rat H9c2 cardiomyocyte hypertrophy model was induced by ISO 10 μM for 24 hours. Cell surface area and hypertrophy-related fetal gene expression were determined to assess the effect of Re on ISO-induced cardiomyocyte hypertrophy in vitro. The levels of total cholesterol (TC), triglyceride (TG), low-density lipoprotein cholesterol (LDL-C), and high-density lipoprotein cholesterol (HDL-C) in both serum and cardiomyocytes were detected by enzymatic colorimetric assays. Furthermore, we chose cholesteryl ester transfer protein (CETP) as a target to explore the influence of Re on CETP expression in vivo and in vitro through real-time polymerase chain reaction, western blot, and enzyme-linked immunosorbent assay. Results Intraperitoneal administration of ISO into rats resulted in increases in cross-sectional cardiomyocyte area, the ratio of heart weight to body weight, the ratio of left ventricular weight to body weight, and the ratio of right ventricular weight to body weight, as well as reactivation of fetal genes; however, treatment with Re or ATC ameliorated most of these hypertrophic responses. Similarly, Re pronouncedly alleviated ISO-induced cardiomyocyte hypertrophy, as evidenced by a decreased cell surface area and downregulation of fetal genes. Moreover, our in vivo and in vitro data revealed that Re reduced TC, TG, and LDL-C levels, and enhanced HDL-C levels. Re improved cardiac hypertrophy mainly associated with the inhibition of mRNA level and protein expression of CETP, to an extent comparable to that of the classical CETP inhibitor, anacetrapib. Conclusions Our research found that CETP inhibition contributes to the protection of Re against ISO-induced cardiac hypertrophy, which provides evidence for the application of Re for cardiovascular disease treatments.

Comparing the signaling and transcriptome profiling landscapes of human iPSC-derived and primary rat neonatal cardiomyocytes

The inaccessibility of human cardiomyocytes significantly hindered years of cardiovascular research efforts. To overcome these limitations, non-human cell sources were used as proxies to study heart function and associated diseases. Rodent models became increasingly acceptable surrogates to model the human heart either in vivo or through in vitro cultures. More recently, due to concerns regarding animal to human translation, including cross-species differences, the use of human iPSC-derived cardiomyocytes presented a renewed opportunity. Here, we conducted a comparative study, assessing cellular signaling through cardiac G protein-coupled receptors (GPCRs) in rat neonatal cardiomyocytes (RNCMs) and human induced pluripotent stem cell-derived cardiomyocytes. Genetically encoded biosensors were used to explore GPCR-mediated nuclear protein kinase A (PKA) and extracellular signal-regulated kinase 1/ 2 (ERK1/2) activities in both cardiomyocyte populations. To increase data granularity, a single-cell analytical approach was conducted. Using automated high content microscopy, our analyses of nuclear PKA and ERK_1/2 signaling revealed distinct response clusters in rat and human cardiomyocytes. In line with this, bulk RNA-seq revealed key differences in the expression patterns of GPCRs, G proteins and downstream effector expression levels. Our study demonstrates that human stem cell-derived models of the cardiomyocyte offer distinct advantages for understanding cellular signaling in the heart.

Monitoring the maturation of the sarcomere network: a super-resolution microscopy-based approach

The in vitro generation of human cardiomyocytes derived from induced pluripotent stem cells (iPSC) is of great importance for cardiac disease modeling, drug-testing applications and for regenerative medicine. Despite the development of various cultivation strategies, a sufficiently high degree of maturation is still a decisive limiting factor for the successful application of these cardiac cells. The maturation process includes, among others, the proper formation of sarcomere structures, mediating the contraction of cardiomyocytes. To precisely monitor the maturation of the contractile machinery, we have established an imaging-based strategy that allows quantitative evaluation of important parameters, defining the quality of the sarcomere network. iPSC-derived cardiomyocytes were subjected to different culture conditions to improve sarcomere formation, including prolonged cultivation time and micro patterned surfaces. Fluorescent images of α-actinin were acquired using super-resolution microscopy. Subsequently, we determined cell morphology, sarcomere density, filament alignment, z-Disc thickness and sarcomere length of iPSC-derived cardiomyocytes. Cells from adult and neonatal heart tissue served as control. Our image analysis revealed a profound effect on sarcomere content and filament orientation when iPSC-derived cardiomyocytes were cultured on structured, line-shaped surfaces. Similarly, prolonged cultivation time had a beneficial effect on the structural maturation, leading to a more adult-like phenotype. Automatic evaluation of the sarcomere filaments by machine learning validated our data. Moreover, we successfully transferred this approach to skeletal muscle cells, showing an improved sarcomere formation cells over different differentiation periods. Overall, our image-based workflow can be used as a straight-forward tool to quantitatively estimate the structural maturation of contractile cells. As such, it can support the establishment of novel differentiation protocols to enhance sarcomere formation and maturity.