zDHHC9 Regulates Cardiomyocyte Rab3a Activity and Atrial Natriuretic Peptide Secretion Through Palmitoylation of Rab3gap1

Palmitoylation in cardiovascular diseases: Molecular mechanism and therapeutic potential

Cardiovascular disease is one of the leading causes of mortality worldwide, and involves complex pathophysiological mechanisms that encompass various biological processes and molecular pathways. Post-translational modifications of proteins play crucial roles in the occurrence and progression of cardiovascular diseases, among which palmitoylation is particularly important. Various proteins associated with cardiovascular diseases can be palmitoylated to enhance the hydrophobicity of their molecular subdomains. This lipidation can significantly affect some pathophysiological processes, such as metabolism, inflammation by altering protein stability, localization, and signal transduction. In this review, we narratively summarize recent advances in the palmitoylation of proteins related to cardiovascular diseases and discuss its potential as a therapeutic target.

Harnessing integrated bioinformatics to identify new diagnostic and therapeutic strategies for heart failure

Heart failure (HF) is a life-threatening condition that poses a significant challenge on public health, particularly among the elder populations. To develop new diagnostic and therapeutic strategies for HF, we analyzed large-scale transcriptome sequencing data from HF patients as an exploratory approach. We identified 18 HF-related genes and developed a robust scoring model for HF diagnosis, by applying two machine learning algorithms for data analysis. Meanwhile, we evaluated and compared the predictive abilities of three bioinformatics methods in identifying potential HF treatment drugs. Significantly, an unconventional network-based proximity analysis, integrating multidimensional drug target information, outperformed other methods in the assessment of predictive ability. To validate these findings, we tested several candidate drugs in a mouse model transitioning from acute myocardial infarction (MI) to chronic HF. Among the candidates, mirtazapine exhibited cardioprotective effects in both early (1-week) post-MI and chronic HF (4-week post-MI) settings, while cabergoline showed potential efficacy primarily in the early post-MI phase. Additionally, the screened triamterene, used as a positive control, exhibited protective effects in both early post-MI and chronic HF stages. Mechanistic studies revealed that growth factor receptor-bound protein 14 and Ras-related protein Rab-3A were critical to the observed cardioprotection. These findings provide valuable evidence and insights for exploring potential therapeutic agents for HF treatment.

Post-translational acylation of proteins in cardiac hypertrophy

Acylations are post-translational modifications in which functional groups are attached to amino acids on proteins. Most acylations (acetylation, butyrylation, crotonylation, lactylation, malonylation, propionylation and succinylation) involve lysine but cysteine (palmitoylation) and glycine (myristoylation) residues can also be altered. Acylations have important roles in physiological and pathophysiological processes, including cardiac hypertrophy and related cardiovascular diseases. These post-translational modifications influence chromatin architecture, transcriptional regulation and metabolic pathways, thereby affecting cardiomyocyte function and pathology. The dynamic interaction between these acylations and their regulatory enzymes, such as histone acetyltransferases, histone deacetylases and sirtuins, underscores the complexity of cellular homeostasis and pathological processes. Emerging evidence highlights the therapeutic potential of targeting acylations to modulate enzyme activity and metabolite levels, offering promising avenues for novel treatments. In this Review, we explore the diverse mechanisms through which acylations contribute to cardiac hypertrophy, highlighting the complexity and potential therapeutic targets in this regulatory network.

Metabolites-mediated posttranslational modifications in cardiac metabolic remodeling: Implications for disease pathology and therapeutic potential

The nonenergy - producing functions of metabolism are attracting increasing attention, as metabolic changes are involved in discrete pathways modulating enzyme activity and gene expression. Substantial evidence suggests that myocardial metabolic remodeling occurring during diabetic cardiomyopathy, heart failure, and cardiac pathological stress (e.g., myocardial ischemia, pressure overload) contributes to the progression of pathology. Within the rewired metabolic network, metabolic intermediates and end-products can directly alter protein function and/or regulate epigenetic modifications by providing acyl groups for posttranslational modifications, thereby affecting the overall cardiac stress response and providing a direct link between cellular metabolism and cardiac pathology. This review provides a comprehensive overview of the functional diversity and mechanistic roles of several types of metabolite-mediated histone and nonhistone acylation, namely O-GlcNAcylation, lactylation, crotonylation, β-hydroxybutyrylation, and succinylation, as well as fatty acid-mediated modifications, in regulating physiological processes and contributing to the progression of heart disease. Furthermore, it explores the potential of these modifications as therapeutic targets for disease intervention.

The Rab3 GTPase cycle modulates cardiomyocyte exocytosis and atrial natriuretic peptide release

Natriuretic peptides are produced predominantly by atrial cardiomyocytes in response to cardiovascular stress and attenuate cardiac maladaptation by reducing blood pressure, blood volume, and cardiac workload primarily through activation of natriuretic peptide receptors in the kidney and vasculature. However, mechanisms underlying cardiomyocyte exocytosis and natriuretic peptide secretion remain poorly defined. Manipulation of Rab3a GTPase activity by Rab3gap1 was recently found to modulate atrial natriuretic peptide (ANP) release by cardiomyocytes. Here, we examined upstream signaling mechanisms and the role of the Rab3a GTPase cycle in exocytosis and ANP secretion by cardiomyocytes. Pharmacological inhibition of the heterotrimeric G protein subunit G⍺q suppressed ANP secretion at baseline and prevented GTP loading of Rab3a and ANP release in neonatal rat cardiomyocytes in response to phenylephrine (PE). Similar to agonist-induced activation of ANP secretion, genetic overexpression of a constitutively active, GTP-loaded Rab3a mutant (Q81L) in neonatal rat cardiomyocytes resulted in enhanced intracellular distribution of Rab3a at endomembranes peripheral to the Golgi and promotion of ANP release, indicating that enhancement of Rab3a activity is sufficient to elicit ANP secretion by cardiomyocytes. Collectively, these data indicate G⍺q signaling downstream of receptor activation and Rab3a-regulated secretory pathway activity and exocytosis facilitate ANP release by cardiomyocytes that could potentially be harnessed to antagonize hypertension and adverse cardiac remodeling in cardiovascular disease.

Rab3gap1 palmitoylation cycling modulates cardiomyocyte exocytosis and atrial natriuretic peptide release

Rab3 GTPase-activating protein 1 (Rab3gap1) hydrolyzes GTP on Rab3 to inactivate it and reinitiate the Rab3 cycle, which regulates exocytic release of neuropeptides and hormones from neuroendocrine cells and atrial natriuretic peptide (ANP) secretion by cardiomyocytes. Cysteine palmitoylation of Rab3gap1 by the Golgi-localized S-acyltransferase zDHHC9 was recently shown to hinder ANP release by impairing Rab3gap1-mediated nucleotide cycling on Rab3a. Here, we interrogate the cysteine residues of Rab3gap1 modified by palmitoylation and impacts on ANP secretion in cardiomyocytes. Although mutation of the previously identified cysteine (Cys)-678 site of Rab3gap1 alone was insufficient to elicit complete loss of Rab3gap1 palmitoylation in cardiomyocytes, combinatorial mutation of Cys-509, 510, 521, 522, and 678 (Rab3gap15CS) dramatically reduced Rab3gap1 palmitoylation. Notably, total cellular GTPase-activating protein (GAP) activity in cardiomyocytes was maintained with mutation of the Rab3gap1 palmitoylation sites as the Rab3gap15CS mutant substantially reduced steady-state Rab3a-GTP levels in cardiomyocytes similar to wild-type Rab3gap1. However, although expression of wild-type Rab3gap1 induced robust secretion of ANP and greatly enhanced phenylephrine-stimulated ANP release, the Rab3gap15CS palmitoylation-deficient mutant was incapable of promoting exocytosis and ANP release by cardiomyocytes. These data suggest Rab3gap1 cysteine palmitoylation may target Rab3gap1 to Rab3a for regulated GAP-mediated inactivation at specific intracellular membrane domains to modulate the Rab3 cycle and exocytosis. Collectively, these data support a role for Rab3gap1 palmitoylation cycling in spatiotemporal control of the Rab3 cycle to regulate exocytosis and ANP secretion by cardiomyocytes.

In Vitro Assessment of Cardiac Fibroblast Activation at Physiologic Stiffness

Cardiac fibroblasts (CF) are an essential cell type in cardiac physiology, playing diverse roles in maintaining structural integrity, extracellular matrix (ECM) synthesis, and tissue repair. Under normal conditions, these cells reside in the interstitium in a quiescent state poised to sense and respond to injury by synthesizing and secreting collagen, vimentin, hyaluronan, and other ECM components. In response to mechanical and chemical stimuli, these "resident" fibroblasts can undergo a transformation through a continuum of activation states into what is commonly known as a "myofibroblast," in a process critical for injury response. Despite progress in understanding the contribution of fibroblasts to cardiac health and disease, much remains unknown about the signaling mediating this activation, in part owing to technical challenges in evaluating CF function and activation status in vitro. Given their role in monitoring the ECM, CFs are acutely sensitive to stiffness and pressure. High basal activation of isolated CFs is common due to the super-physiologic stiffness of traditional cell culture substrates, making assays dependent on quiescent cells challenging. To overcome this problem, cell culture parameters must be tightly controlled, and the use of dishes coated with biocompatible reduced-stiffness substrates, such as 8-kPa polydimethylsiloxane (PDMS), has shown promise in reducing basal activation of fibroblasts. Here, we describe cell culture protocol for maintaining CF quiescence in vitro to enable a dynamic range for the assessment of activation status in response to fibrogenic stimuli using PDMS-coated coverslips. Our protocol provides a cost-effective tool to study fibroblast signaling and activity, allowing researchers to better understand the underlying mechanisms involved in cardiac fibrosis. © 2024 The Authors. Current Protocols published by Wiley Periodicals LLC. Basic Protocol 1: Generation of 8-kPa polydimethylsiloxane (PDMS)/gelatin-coated coverslips for cardiac fibroblast cell culture Basic Protocol 2: Isolation of adult cardiac fibroblasts and plating onto PDMS coverslips Basic Protocol 3: Assessment of cardiac fibroblast activation by α smooth muscle actin (αSMA) immunocytochemistry.

Regulation of cardiomyocyte intracellular trafficking and signal transduction by protein palmitoylation

Despite the well-established functions of protein palmitoylation in fundamental cellular processes, the roles of this reversible post-translational lipid modification in cardiomyocyte biology remain poorly studied. Palmitoylation is catalyzed by a family of 23 zinc finger and Asp-His-His-Cys domain-containing S-acyltransferases (zDHHC enzymes) and removed by select thioesterases of the lysophospholipase and α/β-hydroxylase domain (ABHD)-containing families of serine hydrolases. Recently, studies utilizing genetic manipulation of zDHHC enzymes in cardiomyocytes have begun to unveil essential functions for these enzymes in regulating cardiac development, homeostasis, and pathogenesis. Palmitoylation co-ordinates cardiac electrophysiology through direct modulation of ion channels and transporters to impact their trafficking or gating properties as well as indirectly through modification of regulators of channels, transporters, and calcium handling machinery. Not surprisingly, palmitoylation has roles in orchestrating the intracellular trafficking of proteins in cardiomyocytes, but also dynamically fine-tunes cardiomyocyte exocytosis and natriuretic peptide secretion. Palmitoylation has emerged as a potent regulator of intracellular signaling in cardiomyocytes, with recent studies uncovering palmitoylation-dependent regulation of small GTPases through direct modification and sarcolemmal targeting of the small GTPases themselves or by modification of regulators of the GTPase cycle. In addition to dynamic control of G protein signaling, cytosolic DNA is sensed and transduced into an inflammatory transcriptional output through palmitoylation-dependent activation of the cGAS-STING pathway, which has been targeted pharmacologically in preclinical models of heart disease. Further research is needed to fully understand the complex regulatory mechanisms governed by protein palmitoylation in cardiomyocytes and potential emerging therapeutic targets.

Structure, Function, and Regulation of the Junctophilin Family

In both excitable and nonexcitable cells, diverse physiological processes are linked to different calcium microdomains within nanoscale junctions that form between the plasma membrane and endo-sarcoplasmic reticula. It is now appreciated that the junctophilin protein family is responsible for establishing, maintaining, and modulating the structure and function of these junctions. We review foundational findings from more than two decades of research that have uncovered how junctophilin-organized ultrastructural domains regulate evolutionarily conserved biological processes. We discuss what is known about the junctophilin family of proteins. Our goal is to summarize the current knowledge of junctophilin domain structure, function, and regulation and to highlight emerging avenues of research that help our understanding of the transcriptional, translational, and post-translational regulation of this gene family and its roles in health and during disease.

Palmitoylation-dependent regulation of cardiomyocyte Rac1 signaling activity and minor effects on cardiac hypertrophy

S-palmitoylation is a reversible lipid modification catalyzed by 23 S-acyltransferases with a conserved zinc finger aspartate-histidine-histidine-cysteine (zDHHC) domain that facilitates targeting of proteins to specific intracellular membranes. Here we performed a gain-of-function screen in the mouse and identified the Golgi-localized enzymes zDHHC3 and zDHHC7 as regulators of cardiac hypertrophy. Cardiomyocyte-specific transgenic mice overexpressing zDHHC3 show cardiac disease, and S-acyl proteomics identified the small GTPase Rac1 as a novel substrate of zDHHC3. Notably, cardiomyopathy and congestive heart failure in zDHHC3 transgenic mice is preceded by enhanced Rac1 S-palmitoylation, membrane localization, activity, downstream hypertrophic signaling, and concomitant induction of all Rho family small GTPases whereas mice overexpressing an enzymatically dead zDHHC3 mutant show no discernible effect. However, loss of Rac1 or other identified zDHHC3 targets Gαq/11 or galectin-1 does not diminish zDHHC3-induced cardiomyopathy, suggesting multiple effectors and pathways promoting decompensation with sustained zDHHC3 activity. Genetic deletion of Zdhhc3 in combination with Zdhhc7 reduces cardiac hypertrophy during the early response to pressure overload stimulation but not over longer time periods. Indeed, cardiac hypertrophy in response to 2 weeks of angiotensin-II infusion is not diminished by Zdhhc3/7 deletion, again suggesting other S-acyltransferases or signaling mechanisms compensate to promote hypertrophic signaling. Taken together, these data indicate that the activity of zDHHC3 and zDHHC7 at the cardiomyocyte Golgi promote Rac1 signaling and maladaptive cardiac remodeling, but redundant signaling effectors compensate to maintain cardiac hypertrophy with sustained pathological stimulation in the absence of zDHHC3/7.