AAV Gene Transfer to the Heart

Virally delivered CMYA5 enhances the assembly of cardiac dyads

Cardiomyocytes derived from human induced pluripotent stem cells (hiPSC-CMs) lack nanoscale structures essential for efficient excitation-contraction coupling. Such nanostructures, known as dyads, are frequently disrupted in heart failure. Here we show that the reduced expression of cardiomyopathy-associated 5 (CMYA5), a master protein that establishes dyads, contributes to dyad disorganization in heart failure and to impaired dyad assembly in hiPSC-CMs, and that a miniaturized form of CMYA5 suitable for delivery via an adeno-associated virus substantially improved dyad architecture and normalized cardiac function under pressure overload. In hiPSC-CMs, the miniaturized form of CMYA5 increased contractile forces, improved Ca2+ handling and enhanced the alignment of sarcomere Z-lines with ryanodine receptor 2, a protein that mediates the sarcoplasmic release of stored Ca2+. Our findings clarify the mechanisms responsible for impaired dyad structure in diseased cardiomyocytes, and suggest strategies for promoting dyad assembly and stability in heart disease and during the derivation of hiPSC-CMs.

Cardiomyocyte-fibroblast interaction regulates ferroptosis and fibrosis after myocardial injury

Neonatal mouse hearts have transient renewal capacity, which is lost in juvenile and adult stages. In neonatal mouse hearts, myocardial infarction (MI) causes an initial loss of cardiomyocytes. However, it is unclear which type of regulated cell death (RCD) occurs in stressed cardiomyocytes. In the current studies, we induced MI in neonatal and juvenile mouse hearts and showed that ischemic cardiomyocytes primarily undergo ferroptosis, a non-apoptotic and iron-dependent form of RCD. We demonstrated that cardiac fibroblasts (CFs) protect cardiomyocytes from ferroptosis through paracrine effects and direct cell-cell interaction. CFs show strong resistance to ferroptosis due to high ferritin expression. The fibrogenic activity of CFs, typically considered detrimental to heart function, is negatively regulated by paired-like homeodomain 2 (Pitx2) signaling from cardiomyocytes. In addition, Pitx2 prevents ferroptosis in cardiomyocytes by regulating ferroptotic genes. Understanding the regulatory mechanisms of cardiomyocyte survival and death can identify potentially translatable therapeutic strategies for MI.

Tbx5 maintains atrial identity in post-natal cardiomyocytes by regulating an atrial-specific enhancer network

Understanding how the atrial and ventricular heart chambers maintain distinct identities is a prerequisite for treating chamber-specific diseases. Here, we selectively knocked out (KO) the transcription factor Tbx5 in the atrial working myocardium to evaluate its requirement for atrial identity. Atrial Tbx5 inactivation downregulated atrial cardiomyocyte (aCM) selective gene expression. Using concurrent single nucleus transcriptome and open chromatin profiling, genomic accessibility differences were identified between control and Tbx5 KO aCMs, revealing that 69% of the control-enriched ATAC regions were bound by TBX5. Genes associated with these regions were downregulated in KO aCMs, suggesting they function as TBX5-dependent enhancers. Comparing enhancer chromatin looping using H3K27ac HiChIP identified 510 chromatin loops sensitive to TBX5 dosage, and 74.8% of control-enriched loops contained anchors in control-enriched ATAC regions. Together, these data demonstrate TBX5 maintains the atrial gene expression program by binding to and preserving the tissue-specific chromatin architecture of atrial enhancers.

A new UltraScan module for the characterization and quantification of analytical buoyant density equilibrium experiments to determine AAV capsid loading

A method for characterizing and quantifying peaks formed in an analytical buoyant density equilibrium (ABDE) experiment is presented. An algorithm is derived to calculate the concentration of the density forming gradient material at every point in the cell, provided the rotor speed, temperature, meniscus position, bottom of the cell position, and the loading concentration, molar mass, and partial specific volume of the density gradient-forming material are known. In addition, a new peak fitting algorithm has been developed which allows the user to automatically quantify the peaks formed in terms of density, apparent partial specific volume, and relative abundance. The method is suitable for both ionic and non-ionic density forming materials and can be used with data generated from the UV optical system as well as the AVIV fluorescence optical system. These methods have been programmed in a new UltraScan-III module (us_abde). Examples are shown that demonstrate the application of the new module to adeno-associated viral vector preparations and proteins.

Dynamic changes in P300 enhancers and enhancer-promoter contacts control mouse cardiomyocyte maturation

Cardiomyocyte differentiation continues throughout murine gestation and into the postnatal period, driven by temporally regulated expression changes in the transcriptome. The mechanisms that regulate these developmental changes remain incompletely defined. Here, we used cardiomyocyte-specific ChIP-seq of the activate enhancer marker P300 to identify 54,920 cardiomyocyte enhancers at seven stages of murine heart development. These data were matched to cardiomyocyte gene expression profiles at the same stages and to Hi-C and H3K27ac HiChIP chromatin conformation data at fetal, neonatal, and adult stages. Regions with dynamic P300 occupancy exhibited developmentally regulated enhancer activity, as measured by massively parallel reporter assays in cardiomyocytes in vivo, and identified key transcription factor-binding motifs. These dynamic enhancers interacted with temporal changes of the 3D genome architecture to specify developmentally regulated cardiomyocyte gene expressions. Our work provides a 3D genome-mediated enhancer activity landscape of murine cardiomyocyte development.

Tbx5 maintains atrial identity by regulating an atrial enhancer network

Understanding how the atrial and ventricular chambers of the heart maintain their distinct identity is a prerequisite for treating chamber-specific diseases. Here, we selectively inactivated the transcription factor Tbx5 in the atrial working myocardium of the neonatal mouse heart to show that it is required to maintain atrial identity. Atrial Tbx5 inactivation downregulated highly chamber specific genes such as Myl7 and Nppa , and conversely, increased the expression of ventricular identity genes including Myl2 . Using combined single nucleus transcriptome and open chromatin profiling, we assessed genomic accessibility changes underlying the altered atrial identity expression program, identifying 1846 genomic loci with greater accessibility in control atrial cardiomyocytes compared to KO aCMs. 69% of the control-enriched ATAC regions were bound by TBX5, demonstrating a role for TBX5 in maintaining atrial genomic accessibility. These regions were associated with genes that had higher expression in control aCMs compared to KO aCMs, suggesting they act as TBX5-dependent enhancers. We tested this hypothesis by analyzing enhancer chromatin looping using HiChIP and found 510 chromatin loops that were sensitive to TBX5 dosage. Of the loops enriched in control aCMs, 73.7% contained anchors in control-enriched ATAC regions. Together, these data demonstrate a genomic role for TBX5 in maintaining the atrial gene expression program by binding to atrial enhancers and preserving tissue-specific chromatin architecture of atrial enhancers.

Ryanodine receptor 2 (RYR2) dysfunction activates the unfolded protein response and perturbs cardiomyocyte maturation

AIMS

Calcium-handling capacity is a major gauge of cardiomyocyte maturity. Ryanodine receptor 2 (RYR2) is the pre-dominant calcium channel that releases calcium from the sarcoplasmic reticulum/endoplasmic reticulum (SR/ER) to activate cardiomyocyte contraction. Although RYR2 was previously implied as a key regulator of cardiomyocyte maturation, the mechanisms remain unclear. The aim of this study is to solve this problem.

METHODS AND RESULTS

We performed Cas9/AAV9-mediated somatic mutagenesis to knockout RYR2 specifically in cardiomyocytes in mice. We conducted a genetic mosaic analysis to dissect the cell-autonomous function of RYR2 during cardiomyocyte maturation. We found that RYR2 depletion triggered ultrastructural and transcriptomic defects relevant to cardiomyocyte maturation. These phenotypes were associated with the drastic activation of ER stress pathways. The ER stress alleviator tauroursodeoxycholic acid partially rescued the defects in RYR2-depleted cardiomyocytes. Overexpression of ATF4, a key ER stress transcription factor, recapitulated defects in RYR2-depleted cells. Integrative analysis of RNA-Seq and bioChIP-Seq data revealed that protein biosynthesis-related genes are the major direct downstream targets of ATF4.

CONCLUSION

RYR2-regulated ER homeostasis is essential for cardiomyocyte maturation. Severe ER stress perturbs cardiomyocyte maturation primarily through ATF4 activation. The major downstream effector genes of ATF4 are related to protein biosynthesis.

CMYA5 establishes cardiac dyad architecture and positioning

Cardiac excitation-contraction coupling requires dyads, the nanoscopic microdomains formed adjacent to Z-lines by apposition of transverse tubules and junctional sarcoplasmic reticulum. Disruption of dyad architecture and function are common features of diseased cardiomyocytes. However, little is known about the mechanisms that modulate dyad organization during cardiac development, homeostasis, and disease. Here, we use proximity proteomics in intact, living hearts to identify proteins enriched near dyads. Among these proteins is CMYA5, an under-studied striated muscle protein that co-localizes with Z-lines, junctional sarcoplasmic reticulum proteins, and transverse tubules in mature cardiomyocytes. During cardiac development, CMYA5 positioning adjacent to Z-lines precedes junctional sarcoplasmic reticulum positioning or transverse tubule formation. CMYA5 ablation disrupts dyad architecture, dyad positioning at Z-lines, and junctional sarcoplasmic reticulum Ca2+ release, leading to cardiac dysfunction and inability to tolerate pressure overload. These data provide mechanistic insights into cardiomyopathy pathogenesis by demonstrating that CMYA5 anchors junctional sarcoplasmic reticulum to Z-lines, establishes dyad architecture, and regulates dyad Ca2+ release.

miR-155-5p upregulation ameliorates myocardial insulin resistance via mTOR signaling in chronic alcohol drinking rats

Background

Chronic alcohol intake is associated with an increased risk of alcoholic cardiomyopathy, which may present with pathological changes such as myocardial insulin resistance, leading to ventricular dilation and cardiac dysfunction. Although a correlation between microRNA-155 (miR-155) and insulin signaling has been identified, the underlying mechanism has not been elucidated to date. The purpose of the study was to determine whether overexpression of miR-155-5p in vivo could ameliorate chronic alcohol-induced myocardial insulin resistance and cardiac dysfunction.

Material and Methods

Wistar rats were fed with either alcohol or water for 20 weeks to establish chronic alcohol intakes model. Then the alcohol group were divided into three groups: model group, miRNA-155 group and AAV-NC group. Rats undergoing alcohol treatment were injected with AAV-miRNA-155 (adeno-associated virus 9) or its negative control AAV-NC, respectively. Gene expression was determined by real-time PCR, and protein expression was determined by western blot. Echocardiography was performed to assess terminal cardiac function. Insulin responsiveness was determined through the quantification of phosphorylated insulin receptor substrate 1 (ser 307) and phosphorylated insulin receptor (Tyr 1185) levels.

Results

We found that cardiac function was attenuated in chronic alcohol intake rats, with an activated mammalian target of rapamycin (mTOR) signaling pathway, accompanied by an increase in p-IRS1(ser 307) and a decrease in p-IR (Tyr 1185) level in myocardial tissue. Also, alcohol drinking significantly up-regulated miR-155-5p level and its overexpression decreased p-IRS1 (ser 307) and increased p-IR (Tyr 1185) levels, and meanwhile inhibited the mTOR signaling pathway.

Conclusion

miR-155-5p upregulation ameliorates myocardial insulin resistance via the mTOR signaling in chronic alcohol drinking rats. We propose that miR-155 may serve as a novel potential therapeutic target for alcoholic heart disease.

Mechanotranduction Pathways in the Regulation of Mitochondrial Homeostasis in Cardiomyocytes

Mitochondria are one of the most important organelles in cardiomyocytes. Mitochondrial homeostasis is necessary for the maintenance of normal heart function. Mitochondria perform four major biological processes in cardiomyocytes: mitochondrial dynamics, metabolic regulation, Ca2+ handling, and redox generation. Additionally, the cardiovascular system is quite sensitive in responding to changes in mechanical stress from internal and external environments. Several mechanotransduction pathways are involved in regulating the physiological and pathophysiological status of cardiomyocytes. Typically, the extracellular matrix generates a stress-loading gradient, which can be sensed by sensors located in cellular membranes, including biophysical and biochemical sensors. In subsequent stages, stress stimulation would regulate the transcription of mitochondrial related genes through intracellular transduction pathways. Emerging evidence reveals that mechanotransduction pathways have greatly impacted the regulation of mitochondrial homeostasis. Excessive mechanical stress loading contributes to impairing mitochondrial function, leading to cardiac disorder. Therefore, the concept of restoring mitochondrial function by shutting down the excessive mechanotransduction pathways is a promising therapeutic strategy for cardiovascular diseases. Recently, viral and non-viral protocols have shown potentials in application of gene therapy. This review examines the biological process of mechanotransduction pathways in regulating mitochondrial function in response to mechanical stress during the development of cardiomyopathy and heart failure. We also summarize gene therapy delivery protocols to explore treatments based on mechanical stress-induced mitochondrial dysfunction, to provide new integrative insights into cardiovascular diseases.