RhoA-ROCK signaling is involved in contraction-mediated inhibition of SERCA2a expression in cardiomyocytes

In neonatal ventricular cardiomyocytes (NVCM), decreased contractile activity stimulates sarco-endoplasmic reticulum Ca2+-ATPase2a (SERCA2a), analogous to reduced myocardial load in vivo. This study investigated in contracting NVCM the role of load-dependent RhoA-ROCK signaling in SERCA2a regulation. Contractile arrest of NVCM resulted in low peri-nuclear localized RhoA levels relative to contracting NVCM. In arrested NVCM, ROCK activity was decreased (59%) and paralleled a loss in F-actin levels. Y-27632-induced ROCK inhibition in contracting NVCM increased SERCA2a messenger RNA expression by 150%. This stimulation was transcriptional, as evident from transfections with the SERCA2a promoter. A reciprocal effect of Y-27632 treatment on the promoter activity of atrial natriuretic factor was observed. SERCA2a transcription was not altered by co-transfection of the RhoA-ROCK-dependent serum response factor (SRF) alone or in combination with myocardin. Furthermore, GATA4, another ROCK-dependent transcription factor, induced rather than repressed SERCA2a transcription. This study shows that contractile activity suppresses SERCA2a gene expression via RhoA-ROCK-dependent transcription modulation. This modulation is likely to be accomplished by a transcription factor other than SRF, myocardin, or GATA4

Selenoprotein dio2 is a regulator of mitochondrial function, morphology and uprmt in human cardiomyocytes

Members of the fetal-gene-program may act as regulatory components to impede deleterious events occurring with cardiac remodeling, and constitute potential novel therapeutic heart failure (HF) targets. Mitochondrial energy derangements occur both during early fetal development and in patients with HF. Here we aim to elucidate the role of DIO2, a member of the fetal-gene-program, in pluripotent stem cell (PSC)-derived human cardiomyocytes and on mitochondrial dynamics and energetics, specifically. RNA sequencing and pathway enrichment analysis was performed on mouse cardiac tissue at different time points during development, adult age, and ischemia-induced HF. To determine the function of DIO2 in cardiomyocytes, a stable human hPSC-line with a DIO2 knockdown was made using a short harpin sequence. Firstly, we showed the selenoprotein, type II deiodinase (DIO2): the enzyme responsible for the tissue-specific conversion of inactive (T4) into active thyroid hormone (T3), to be a member of the fetal-gene-program. Secondly, silencing DIO2 resulted in an increased reactive oxygen species, impaired activation of the mitochondrial unfolded protein response, severely impaired mitochondrial respiration and reduced cellular viability. Microscopical 3D reconstruction of the mitochondrial network displayed substantial mitochondrial fragmentation. Summarizing, we identified DIO2 to be a member of the fetal-gene-program and as a key regulator of mitochondrial performance in human cardiomyocytes. Our results suggest a key position of human DIO2 as a regulator of mitochondrial function in human cardiomyocytes

American Thyroid Association Guide to Investigating Thyroid Hormone Economy and Action in Rodent and Cell Models

Background: An in-depth understanding of the fundamental principles that regulate thyroid hormone homeostasis is critical for the development of new diagnostic and treatment ap-proaches for patients with thyroid disease. Summary: Important clinical practices in use today for the treatment of patients with hypothy-roidism, hyperthyroidism, or thyroid cancer, are the result of laboratory discoveries made by scientists investigating the most basic aspects of thyroid structure and molecular biology. In this document, a panel of experts commissioned by the American Thyroid Association makes a se-ries of recommendations related to the study of thyroid hormone economy and action. These recommendations are intended to promote standardization of study design, which should in turn increase the comparability and reproducibility of experimental findings. Conclusions: It is expected that adherence to these recommendations by investigators in the field will facilitate progress towards a better understanding of the thyroid gland and thyroid hormone dependent processes

Cardiac thyroid-hormone deiodinative pathways in ventricular hypertrophy and heart failure

Many of the cardiac genes that are involved in contractile dysfunction following pathological ventricular remodeling are transcriptionally regulated by thyroid hormone (TH). The phenotype of the pathologically hypertrophied cardiomyocyte suggests that reduced TH signaling contributes to its development. Increased expression of the TH-degrading enzyme deiodinase type 3 (D3) in cardiomyocytes of hypertrophic left or right ventricles has recently been described for different rodent models of heart failure. At least in right ventricular failure, this was associated with a severe, cardiomyocyte-specific hypothyroid condition. D3 expression is transcriptionally stimulated by factors that are implicated in cardiomyocyte hypertrophy, e.g., mitogen-activated protein kinases (MAPK) ERK, and p38 and Smad proteins activated by transforming growth factor-β (TGFβ). Hypoxia-inducible factor 1 (HIF-1) also stimulates D3 transcription. Reduced oxygen tension and subsequent HIF-1 signaling may occur in the hypertrophic cardiomyocyte, and this appears to account for the increased D3 expression in the model of right ventricular failure. It remains to be established whether stimulation of D3 activity and the ensuing local hypothyroid condition with reduction of energy turnover are an adaptive response or contribute to the further deterioration of contractile function and heart failure

The Cardioprotective Effect of Sevoflurane Depends on Protein Kinase C Activation, Opening of Mitochondrial K+ ATP Channels, and the Production of Reactive Oxygen Species

Several studies suggest that the cardioprotective effect of sevoflurane depends on protein kinase C (PKC) activation, mitochondrial K+ ATP channel (mitoK+ ATP) opening, and reactive oxygen species (ROS). However, evidence for their involvement was obtained in separate experimental models. Here, we studied the relative roles of PKC, mitoK+ ATP, and ROS in sevoflurane-induced cardioprotection in one model. Rat trabeculae were subjected to simulated ischemia by applying metabolic inhibition (MI) through buffer containing NaCN, followed by 60-min reperfusion. Recovery of active force (Fa) was assessed as percentage of pre-MI force. In time controls, Fa amounted 60% ± 5% at the end of the experiment. The recovery of F a after MI was reduced to 28% ± 5% (P = 0.045 versus time control), whereas sevoflurane reversed the detrimental effect of MI (F a recovery, 67% ± 8%; P = 0.01 versus MI). The PKC inhibitor chelerythrine, the mitoK+ ATP inhibitor 5-hydroxy decanoic, and the ROS scavenger N-(2-mercaptopropionyl)-glycine all completely abolished the protective effect of sevoflurane (recovery of Fa, 31% ± 8%, 33% ± 8%, and 24% ± 9% for chelerythrine, 5-hydroxy decanoic, and N-(2-mercaptopropionyl)-glycine, respectively). In conclusion, PKC activation, mitoK+ ATP channel opening, and ROS production are all essential for sevoflurane-induced cardioprotection. These signaling events are arranged in series within a common signaling pathway, rather than in parallel cascades. Our findings implicate that the perioperative use of sevoflurane preserves cardiac function by preventing ischemia-reperfusion injury