PRKAR1A deficiency impedes hypertrophy and reduces heart size

Detection of PRKAR1A gene mutations in sporadic cardiac myxomas: a study of 24 cases

The benign neoplasm cardiac myxoma represents one of the hallmarks of Carney complex (CNC), a familial multiple neoplasia syndrome. About 80% of the index cases have germline mutations in PRKAR1A encoding the RIα regulatory subunit of cAMP-dependent protein kinase A (PKA). However, the role of PRKAR1A gene mutations in the pathogenesis of non-CNC-associated sporadic cardiac myxoma is less well established. Here, we investigated the presence of PRKAR1A gene variants in a cohort of 24 sporadic cardiac myxomas using targeted next-generation sequencing. Our study shows that 14 out of 24 cases (58%) harbor PRKAR1A gene mutations, represented mostly by frameshift, nonsense, and splice site mutations (together 84%), leading to a premature stop codon predicted to be degraded via non-sense mediated mRNA decay. The other 16% of PRKAR1A genetic alterations involved missense mutations, often located in important functional domains of the regulatory subunit RIα. Notably, 64% (n = 9/14) of the cases harbored more than one PRKAR1A gene variant, suggesting compound heterozygous mutations either in cis or trans. In conclusion, PRKAR1A gene mutations associated with loss of RIα function leading to increased PKA activity were observed in ~ 60% of sporadic cardiac myxomas, strongly supporting an essential role for PKA in mediating formation of cardiac myxoma.

Essential Role of the RIα Subunit of cAMP-Dependent Protein Kinase in Regulating Cardiac Contractility and Heart Failure Development

BACKGROUND

The heart expresses 2 main subtypes of cAMP-dependent protein kinase (PKA; type I and II) that differ in their regulatory subunits, RIα and RIIα. Embryonic lethality of RIα knockout mice limits the current understanding of type I PKA function in the myocardium. The objective of this study was to test the role of RIα in adult heart contractility and pathological remodeling.

METHODS

We measured PKA subunit expression in human heart and developed a conditional mouse model with cardiomyocyte-specific knockout of RIα (RIα-icKO). Myocardial structure and function were evaluated by echocardiography, histology, and ECG and in Langendorff-perfused hearts. PKA activity and cAMP levels were determined by immunoassay, and phosphorylation of PKA targets was assessed by Western blot. L-type Ca2+ current (ICa,L), sarcomere shortening, Ca2+ transients, Ca2+ sparks and waves, and subcellular cAMP were recorded in isolated ventricular myocytes (VMs).

RESULTS

RIα protein was decreased by 50% in failing human heart with ischemic cardiomyopathy and by 75% in the ventricles and in VMs from RIα-icKO mice but not in atria or sinoatrial node. Basal PKA activity was increased ≈3-fold in RIα-icKO VMs. In young RIα-icKO mice, left ventricular ejection fraction was increased and the negative inotropic effect of propranolol was prevented, whereas heart rate and the negative chronotropic effect of propranolol were not modified. Phosphorylation of phospholamban, ryanodine receptor, troponin I, and cardiac myosin-binding protein C at PKA sites was increased in propranolol-treated RIα-icKO mice. Hearts from RIα-icKO mice were hypercontractile, associated with increased ICa,L, and [Ca2+]i transients and sarcomere shortening in VMs. These effects were suppressed by the PKA inhibitor, H89. Global cAMP content was decreased in RIα-icKO hearts, whereas local cAMP at the phospholamban/sarcoplasmic reticulum Ca2+ ATPase complex was unchanged in RIα-icKO VMs. RIα-icKO VMs had an increased frequency of Ca2+ sparks and proarrhythmic Ca2+ waves, and RIα-icKO mice had an increased susceptibility to ventricular tachycardia. On aging, RIα-icKO mice showed progressive contractile dysfunction, cardiac hypertrophy, and fibrosis, culminating in congestive heart failure with reduced ejection fraction that caused 50% mortality at 1 year.

CONCLUSIONS

These results identify RIα as a key negative regulator of cardiac contractile function, arrhythmia, and pathological remodeling.

Profiling Reduced Expression of Contractile and Mitochondrial mRNAs in the Human Sinoatrial Node vs. Right Atrium and Predicting Their Suppressed Expression by Transcription Factors and/or microRNAs

(1) Background: The sinus node (SN) is the main pacemaker of the heart. It is characterized by pacemaker cells that lack mitochondria and contractile elements. We investigated the possibility that transcription factors (TFs) and microRNAs (miRs) present in the SN can regulate gene expression that affects SN morphology and function. (2) Methods: From human next-generation sequencing data, a list of mRNAs that are expressed at lower levels in the SN compared with the right atrium (RA) was compiled. The mRNAs were then classified into contractile, mitochondrial or glycogen mRNAs using bioinformatic software, RStudio and Ingenuity Pathway Analysis. The mRNAs were combined with TFs and miRs to predict their interactions. (3) Results: From a compilation of the 1357 mRNAs, 280 contractile mRNAs and 198 mitochondrial mRNAs were identified to be expressed at lower levels in the SN compared with RA. TFs and miRs were shown to interact with contractile and mitochondrial function-related mRNAs. (4) Conclusions: In human SN, TFs (MYCN, SOX2, NUPR1 and PRDM16) mainly regulate mitochondrial mRNAs (COX5A, SLC25A11 and NDUFA8), while miRs (miR-153-3p, miR-654-5p, miR-10a-5p and miR-215-5p) mainly regulate contractile mRNAs (RYR2, CAMK2A and PRKAR1A). TF and miR-mRNA interactions provide a further understanding of the complex molecular makeup of the SN and potential therapeutic targets for cardiovascular treatments.

Myristate induces mitochondrial fragmentation and cardiomyocyte hypertrophy through mitochondrial E3 ubiquitin ligase MUL1

Introduction: Cardiovascular diseases, especially metabolic-related disorders, are progressively growing worldwide due to high-fat-containing foods, which promote a deleterious response at the cellular level, termed lipotoxicity, or lipotoxic stress. At the cardiac level, saturated fatty acids have been directly associated with cardiomyocyte lipotoxicity through various pathological mechanisms involving mitochondrial dysfunction, oxidative stress, and ceramide production, among others. However, integrative regulators connecting saturated fatty acid-derived lipotoxic stress to mitochondrial and cardiomyocyte dysfunction remain elusive.

Methods: Here, we worked with a cardiomyocyte lipotoxicity model, which uses the saturated fatty acid myristate, which promotes cardiomyocyte hypertrophy and insulin desensitization.

Results: Using this model, we detected an increase in the mitochondrial E3 ubiquitin ligase, MUL1, a mitochondrial protein involved in the regulation of growth factor signaling, cell death, and, notably, mitochondrial dynamics. In this context, myristate increased MUL1 levels and induced mitochondrial fragmentation, associated with the decrease of the mitochondrial fusion protein MFN2, and with the increase of the mitochondrial fission protein DRP1, two targets of MUL1. Silencing of MUL1 prevented myristate-induced mitochondrial fragmentation and cardiomyocyte hypertrophy.

Discussion: These data establish a novel connection between cardiomyocytes and lipotoxic stress, characterized by hypertrophy and fragmentation of the mitochondrial network, and an increase of the mitochondrial E3 ubiquitin ligase MUL1.

Integrated Analysis and Validation of Autophagy-Related Genes and Immune Infiltration in Acute Myocardial Infarction

Background

Acute myocardial infarction (AMI) is one of the most critical conditions of coronary heart disease with many uncertainties regarding reduction of ischemia/reperfusion injury, medical treatment strategies, and other aspects. The inflammatory immune response has a bidirectional regulatory role in AMI and plays an essential role in myocardial remodeling after AMI. The purpose of our research was tantamount to explore possible mechanisms of AMI and to analyze the relationship with the immune microenvironment.

Methods

We firstly analyzed the expression profile of GSE61144 and HADb to identify differentially expressed autophagy-related genes (DEARGs). Then, we performed GO, functional enrichment analysis, and constructed PPI network by Metascape. A lncRNA-miRNA-mRNA ceRNA network was built, and hub genes were extracted by Cytoscape. After that, we used CIBERSORT algorithm to estimate the proportion of immunocytes, followed by correlation analysis to find relationships between hub DEARGs and immunocyte subsets. Finally, we verified those hub genes in another dataset and cellular experiments qPCR.

Results

Compared with controls, we identified 44 DEARGs and then filtered the genes of MCODE by constructing PPI network for further analysis. A total of 45 lncRNAs, 24 miRNAs, 19 mRNAs, 162 lncRNA-miRNA pairs, and 37 mRNA-miRNA pairs were used to construct a ceRNA network, and 4 hub DEARGs (BCL2, MAPK1, RAF1, and PRKAR1A) were extracted. We then estimated 5 classes of immunocytes that differed between AMI and controls. According to the results of correlation analysis, these 4 hub DEARGs may play modulatory effects in immune infiltrating cells, notably in CD8+ T cells and neutrophils. Finally, the same results were verified in GSE60993 and qPCR experiments.

Conclusion

Our findings suggest that those hub DEARGs (BCL2, MAPK1, RAF1, and PRKAR1A) and immunocytes probably play functions in the progression of AMI, providing potential diagnostic markers and new perspectives for treatment of AMI.

STK25 inhibits PKA signaling by phosphorylating PRKAR1A

In the heart, protein kinase A (PKA) is critical for activating calcium handling and sarcomeric proteins in response to beta-adrenergic stimulation leading to increased myocardial contractility and performance. The catalytic activity of PKA is tightly regulated by regulatory subunits that inhibit the catalytic subunit until released by cAMP binding. Phosphorylation of type II regulatory subunits promotes PKA activation; however, the role of phosphorylation in type I regulatory subunits remain uncertain. Here, we utilize human induced pluripotent stem cell cardiomyocytes (iPSC-CMs) to identify STK25 as a kinase of the type Iα regulatory subunit PRKAR1A. Phosphorylation of PRKAR1A leads to inhibition of PKA kinase activity and increased binding to the catalytic subunit in the presence of cAMP. Stk25 knockout in mice diminishes Prkar1a phosphorylation, increases Pka activity, and augments contractile response to beta-adrenergic stimulation. Together, these data support STK25 as a negative regulator of PKA signaling through phosphorylation of PRKAR1A.

Transcriptomics of angiotensin II-induced long noncoding and coding RNAs in endothelial cells

OBJECTIVE

Angiotensin II (Ang II)-induced endothelial dysfunction plays an important role in the pathogenesis of cardiovascular diseases such as systemic hypertension, cardiac hypertrophy and atherosclerosis. Recently, long noncoding RNAs (lncRNAs) have been shown to play an essential role in the pathobiology of cardiovascular diseases; however, the effect of Ang II on lncRNAs and coding RNAs expression in endothelial cells has not been evaluated. Accordingly, we sought to evaluate the expression profiles of lncRNAs and coding RNAs in endothelial cells following treatment with Ang II.

METHODS

Human umbilical vein endothelial cells (HUVECs) were cultured and treated with Ang II (10-6 mol/l) for 24 h. The cells were then profiled for the expression of lncRNAs and mRNAs using the Arraystar Human lncRNA Expression Microarray V3.0.

RESULTS

In HUVECs following Ang II treatment, from a total of 30 584 lncRNA targets screened, 25 targets were significantly upregulated, while 69 were downregulated. In the same HUVECs samples, from 26 106 mRNA targets screened, 28 targets were significantly upregulated and 67 were downregulated. Of the differentially expressed lncRNAs, RP11-354P11.2 and RP11-360F5.1 were the most upregulated (11-fold) and downregulated (three-fold) lncRNAs, respectively. Assigning the differentially regulated genes into functional groups using bioinformatics reveals numerous genes involved in the nucleotide excision repair and ECM-receptor interaction.

CONCLUSION

This is the first study to profile the Ang II-induced differentially expressed lncRNAs and mRNAs in human endothelial cells. Our results reveal novel targets and substantially extend the list of potential candidate genes involved in Ang II-induced endothelial dysfunction and cardiovascular diseases.

PRKAR1A and SDCBP Serve as Potential Predictors of Heart Failure Following Acute Myocardial Infarction

Background and Objectives

Early diagnosis of patients with acute myocardial infarction (AMI) who are at a high risk of heart failure (HF) progression remains controversial. This study aimed at identifying new predictive biomarkers of post-AMI HF and at revealing the pathogenesis of HF involving these marker genes.

Methods and Results

A transcriptomic dataset of whole blood cells from AMI patients with HF progression (post-AMI HF, n = 16) and without progression (post-AMI non-HF, n = 16) was analyzed using the weighted gene co-expression network analysis (WGCNA). The results indicated that one module consisting of 720 hub genes was significantly correlated with post-AMI HF. The hub genes were validated in another transcriptomic dataset of peripheral blood mononuclear cells (post-AMI HF, n = 9; post-AMI non-HF, n = 8). PRKAR1A, SDCBP, SPRED2, and VAMP3 were upregulated in the two datasets. Based on a single-cell RNA sequencing dataset of leukocytes from heart tissues of normal and infarcted mice, PRKAR1A was further verified to be upregulated in monocytes/macrophages on day 2, while SDCBP was highly expressed in neutrophils on day 2 and in monocytes/macrophages on day 3 after AMI. Cell-cell communication analysis via the "CellChat" package showed that, based on the interaction of ligand-receptor (L-R) pairs, there were increased autocrine/paracrine cross-talk networks of monocytes/macrophages and neutrophils in the acute stage of MI. Functional enrichment analysis of the abovementioned L-R genes together with PRKAR1A and SDCBP performed through the Metascape platform suggested that PRKAR1A and SDCBP were mainly involved in inflammation, apoptosis, and angiogenesis. The receiver operating characteristic (ROC) curve analysis demonstrated that PRKAR1A and SDCBP, as well as their combination, had a promising prognostic value in the identification of AMI patients who were at a high risk of HF progression.

Conclusion

This study identified that PRKAR1A and SDCBP may serve as novel biomarkers for the early diagnosis of post-AMI HF and also revealed their potentially regulatory mechanism during HF progression.

Loss of PKA regulatory subunit 1α aggravates cardiomyocyte necrosis and myocardial ischemia/reperfusion injury

Reperfusion therapy, the standard treatment for acute myocardial infarction, can trigger necrotic death of cardiomyocytes and provoke ischemia/reperfusion (I/R) injury. However, signaling pathways that regulate cardiomyocyte necrosis remain largely unknown. Our recent genome-wide RNAi screen has identified a potential necrosis suppressor gene PRKAR1A, which encodes PKA regulatory subunit 1α (R1α). R1α is primarily known for regulating PKA activity by sequestering PKA catalytic subunits in the absence of cAMP. Here, we showed that depletion of R1α augmented cardiomyocyte necrosis in vitro and in vivo, resulting in exaggerated myocardial I/R injury and contractile dysfunction. Mechanistically, R1α loss downregulated the Nrf2 antioxidant transcription factor and aggravated oxidative stress following I/R. Degradation of the endogenous Nrf2 inhibitor Keap1 through p62-dependent selective autophagy was blocked by R1α depletion. Phosphorylation of p62 at Ser349 by mammalian target of rapamycin complex 1 (mTORC1), a critical step in p62-Keap1 interaction, was induced by I/R, but diminished by R1α loss. Activation of PKA by forskolin or isoproterenol almost completely abolished hydrogen-peroxide-induced p62 phosphorylation. In conclusion, R1α loss induces unrestrained PKA activation and impairs the mTORC1-p62-Keap1-Nrf2 antioxidant defense system, leading to aggravated oxidative stress, necrosis, and myocardial I/R injury. Our findings uncover a novel role of PKA in oxidative stress and necrosis, which may be exploited to develop new cardioprotective therapies.

Physiological And Pathological Roles Of Protein Kinase A In The Heart

Protein kinase A (PKA) is a central regulator of cardiac performance and morphology. Myocardial PKA activation is induced by a variety of hormones, neurotransmitters and stress signals, most notably catecholamines secreted by the sympathetic nervous system. Catecholamines bind β-adrenergic receptors to stimulate cAMP-dependent PKA activation in cardiomyocytes. Elevated PKA activity enhances Ca2+ cycling and increases cardiac muscle contractility. Dynamic control of PKA is essential for cardiac homeostasis, as dysregulation of PKA signaling is associated with a broad range of heart diseases. Specifically, abnormal PKA activation or inactivation contributes to the pathogenesis of myocardial ischemia, hypertrophy, heart failure, as well as diabetic, takotsubo, or anthracycline cardiomyopathies. PKA may also determine sex-dependent differences in contractile function and heart disease predisposition. Here, we describe the recent advances regarding the roles of PKA in cardiac physiology and pathology, highlighting previous study limitations and future research directions. Moreover, we discuss the therapeutic strategies and molecular mechanisms associated with cardiac PKA biology. In summary, PKA could serve as a promising drug target for cardioprotection. Depending on disease types and mechanisms, therapeutic intervention may require either inhibition or activation of PKA. Therefore, specific PKA inhibitors or activators may represent valuable drug candidates for the treatment of heart diseases.