Nicotinamide adenine dinucleotide phosphate (NADPH) oxidases regulate production of reactive oxygen species (ROS) that cause oxidative damage to cellular components but also regulate redox signaling in many cell types with essential functions in the cardiovascular system. Research over the past couple of decades has uncovered mechanisms by which NADPH oxidase (NOX) enzymes regulate oxidative stress and compartmentalize intracellular signaling in endothelial cells, smooth muscle cells, macrophages, cardiomyocytes, fibroblasts, and other cell types. NOX2 and NOX4, for example, regulate distinct redox signaling mechanisms in cardiac myocytes pertinent to the onset and progression of cardiac hypertrophy and heart failure. Heart failure with preserved ejection fraction (HFpEF), which accounts for at least half of all heart failure cases and has few effective treatments to date, is classically associated with ventricular diastolic dysfunction, i.e., defects in ventricular relaxation and/or filling. However, HFpEF afflicts multiple organ systems and is associated with systemic pathologies including inflammation, oxidative stress, arterial stiffening, cardiac fibrosis, and renal, adipose tissue, and skeletal muscle dysfunction. Basic science studies and clinical data suggest a role for systemic and myocardial oxidative stress in HFpEF, and evidence from animal models demonstrates the critical functions of NOX enzymes in diastolic function and several HFpEF-associated comorbidities. Here, we discuss the roles of NOX enzymes in cardiovascular cells that are pertinent to the development and progression of diastolic dysfunction and HFpEF and outline potential clinical implications.

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.

Cardiac hypertrophy is a common adaptation to cardiovascular stress and often a prelude to heart failure. We examined how S -palmitoylation of the small GTPase, Ras-related C3 botulinum toxin substrate 1 (Rac1), impacts cardiomyocyte stress signaling. Mutation of the Cys-178 palmitoylation site impaired activation of Rac1 when overexpressed in cardiomyocytes. Cardiomyocyte-specific Rac1 conditional knockin (Rac1 ^cKI ) mice expressing a Rac1 ^C178S mutant protein exhibited normal cardiac structure and function but developed more severe cardiac hypertrophy in response to angiotensin II (AngII) infusion, cardiomyocyte-specific overexpression of AngII type 1 receptor (AT1R), and cardiac pressure overload. Moreover, pressure overload and AT1R overexpression evoked cardiac failure phenotypes in Rac1 ^cKI mice not observed in controls. Mechanistically, Rac1 ^cKI hearts and cardiomyocytes genetically resistant to Rac1 S -palmitoylation had a profound increase in protein kinase A (PKA) substrate phosphorylation in response to acute β-adrenergic stimulation, as did Rac1 ^cKI hearts subjected to chronic AngII treatment, AT1R overexpression, or pressure overload that correlates with more advanced heart failure phenotypes. This was not associated with increased PKA enzymatic activity, suggesting potential deficits in phosphatase activity at PKA-regulated phospho-sites. Taken together, this study suggests Rac1 S -palmitoylation dampens adrenergic drive and PKA-dependent modulation of the phospho-proteome in response to cardiovascular stress, revealing essential functions for S -acylated Rac1 in cardiac adaptation.

Adhesion G protein–coupled receptors (AGPCRs) regulate essential physiological processes through interactions between their ectodomains and adjacent cell surface proteins or extracellular matrix components (ECM). AGPCRs distinctively arrive at the plasma membrane as self-cleaved holoreceptors with noncovalently associated N-terminal (NTF) and C-terminal fragments (CTF). Canonical AGPCR signaling proceeds in three sequential steps; NTF adhesive domains bind to ligands, extracellular shear force mediates NTF and CTF dissociation, a tethered peptide agonist (TA) is exposed and binds to the CTF orthosteric site to stabilize the active state receptor. Depending on the cellular context, both autoproteolysis-deficient and perhaps, a few cleavage-capable AGPCRs may be activated without NTF dissociation or the action of the TA. To discriminate the functional consequences of these signaling modes in vivo, we created a cleavage-deficient, Gpr56 H381S knock-in mouse and investigated five distinct defective phenotypes of Gpr56 knockout mice. One prominent phenotype, brain malformation that parallels human bilateral frontoparietal polymicrogyria (BFPP) disease, is characterized by dysplasia of the cortex and cerebellum and neuron heterotopia. Brain histology analyses confirmed that Gpr56 H381S mice had comparable cerebellar structural irregularities as Gpr56 knockout mice, indicating that TA agonism is indispensable for proper cerebellar lobule formation and neuronal migration. TA-dependent signaling was also required for male mouse fertility, but not for adult cardiomyocyte homeostatic functions, platelet-dependent hemostasis, or axon myelination in the central nervous system. These findings indicate that GPR56 has multiple modes of activation and that these signaling outcomes are likely driven by NTF interactions with specific ligands including collagen and transglutaminase-2.