The Hippo-signaling pathway is a mechanism implicated in cardiomyocyte cytoprotection and regeneration after a myocardial infarction. Yes-associated protein 1, the main effector protein of this pathway, acts as a co-transcriptional activator to promote cardiomyocyte proliferation and survival. However, the biological mechanisms by which yes-associated protein 1 protects the heart post-MI are currently unknown. Here, we propose that yes-associated protein 1 plays a critical role in cardiomyocyte cytoprotection after simulated ischemia-reperfusion injury. AC16 human cardiomyocytes were infected with lentiviral plasmids containing normal human yes-associated protein 1 and a constitutively active form of YAP, YAP1S127A. Cells were exposed to ischemia-reperfusion injury using a hypoxic chamber. Hippo-signaling characterization after ischemia-reperfusion injury was performed via Western blotting and reverse transcriptase polymerase chain reaction. Cell viability, apoptosis, and cellular hypertrophy were assessed as a measure of cytoprotection. The GSK3β inhibitor CHIR99021 was used to investigate cross-talk between Hippo and Wnt-signaling and their role in cytoprotection after ischemia-reperfusion-injury. Ischemia-reperfusion injury resulted in significant decreased expression of the non-phosphorylated Hippo signaling kinases MST1 and LATS1, along with decreased expression of YAP/TAZ. Overexpression of yes-associated protein 1 improved cellular viability, while reducing hypertrophy and apoptosis via the ATM/ATR DNA damage response pathway. Activation of β-catenin in YAP-infected cardiomyocytes synergistically reduced cellular hypertrophy after ischemia-reperfusion-injury. Our findings indicate that yes-associated protein 1 is cytoprotective in AC16 human cardiomyocytes after ischemia-reperfusion injury, which may be mediated by co-activation of the canonical Wnt/β-catenin pathway. Thus, activation of yes-associated protein 1 may be a novel therapeutic to repair the infarcted myocardium.Impact statement: Genetically engineering the cells of the heart after myocardial infarction to display a more regenerative phenotype is a promising therapy for heart failure patients. Here, we support a regenerative role for yes-associated protein 1, the main effector protein of the Hippo signaling pathway, in AC16 human cardiomyocytes as a potential therapeutic gene target for cardiac repair after myocardial infarction.

Acute myocardial infarction (MI) remains one of the leading causes of death worldwide with no curative therapy available. Stem cell therapies have been gaining interest as a means to repair the cardiac tissue after MI and prevent the onset of heart failure. Many in vivo reports suggest that the use of stem cells is promising, yet clinical trials suggest that the cells fail to integrate into the native tissue, resulting in limited improvements in cardiac function and repair. To battle this limitation, the combination of using stem cells embedded in a bioactive scaffold that promotes cell retention is growing in interest. Yet, a systematic review of the literature on the use of stem cells embedded in bioactive scaffolds for cardiac repair has not yet been performed. In this protocol, we outline a systematic review and meta-analysis of preclinical trials in animal MI models that utilize stem cell-embedded scaffolds for cardiac repair and compare their effects to stem cell-treated animals without the use of a scaffold. We will search the following electronic databases: Cochrane Library, MEDLINE, Embase, PubMed, Scopus and Web of Science, and gray literature: Canadian Agency for Drugs and Technologies in Health and Google Scholar. We will only include randomly controlled preclinical trials that have directly investigated the effects of stem cells embedded in a scaffold for cardiac repair in an animal MI model. Two investigators will independently review each article included in the final analysis. The primary endpoint that will be investigated is left ventricular ejection fraction. Secondary endpoints will include infarct size, end systolic volume, end diastolic volume, fractional shortening and left ventricular wall thickness. Pooled analyses will be conducted using the DerSimonian-Laird random effects and Mantel-Haenszel fixed-effect models. Between-studies heterogeneity will be quantified and determined using the Tau2 and I2 statistics. Publication bias will be assessed using visual inspection of funnel plots and complemented by Begg’s and Egger’s statistical tests. Possible sources of heterogeneity will be assessed using subgroup-meta analysis and meta-regression. To date, the use of scaffolds in myocardial repair has not yet been systematically reviewed. The results of this meta-analysis will aid in determining the efficacy of stem cell-embedded scaffolds for cardiac repair and help bring this therapy to the clinic.

Synchronized contractions of cardiomyocytes within the heart are tightly coupled to electrical stimulation known as excitation-contraction coupling. Calcium plays a key role in this process and dysregulated calcium handling can significantly impair cardiac function and lead to the development of cardiomyopathies and heart failure. Here, we describe a method and analytical technique to study myofilament-localized calcium signaling using the intensity-based fluorescent biosensor, RGECO-TnT. Dilated cardiomyopathy is a heart muscle disease that negatively impacts the heart’s contractile function following dilatation of the left ventricle. We demonstrate how this biosensor can be used to characterize 2D hiPSC-CMs monolayers generated from a healthy control subject compared to two patients diagnosed with dilated cardiomyopathy. Lastly, we provide a step-by-step guide for single-cell data analysis and describe a custom Transient Analysis application, specifically designed to quantify features of calcium transients. All in all, we explain how this analytical approach can be applied to phenotype hiPSC-CM behaviours and stratify patient responses to identify perturbations in calcium signaling.