Studies have shown that neuronal nitric oxide synthase (nNOS, NOS1) knockout mice (NOS1-/-) have increased or decreased contractility, but consistently have found a slowed rate of intracellular Ca2+ ([Ca2+]i) decline and relengthening. Contraction and [Ca2+]i decline are determined by many factors, one of which is phospholamban (PLB). The purpose of this study is to determine the involvement of PLB in the NOS1-mediated effects. Force-frequency experiments were performed in trabeculae isolated from NOS1-/- and wild-type (WT) mice. We also simultaneously measured Ca2+ transients (Fluo-4) and cell shortening (edge detection) in myocytes isolated from WT, NOS1-/-, and PLB-/- mice. NOS1-/- trabeculae had a blunted force-frequency response and prolonged relaxation. We observed similar effects in myocytes with NOS1 knockout or specific NOS1 inhibition with S-methyl-l-thiocitrulline (SMLT) in WT myocytes (i.e., decreased Ca2+ transient and cell shortening amplitudes and prolonged decline of [Ca2+]i). Alternatively, NOS1 inhibition with SMLT in PLB-/- myocytes had no effect. Acute inhibition of NOS1 with SMLT in WT myocytes also decreased basal PLB serine16 phosphorylation. Furthermore, there was a decreased SR Ca2+ load with NOS1 knockout or inhibition, which is consistent with the negative contractile effects. Perfusion with FeTPPS (peroxynitrite decomposition catalyst) mimicked the effects of NOS1 knockout or inhibition. beta-Adrenergic stimulation restored the slowed [Ca2+]i decline in NOS1-/- myocytes, but a blunted contraction remained, suggesting additional protein target(s). In summary, NOS1 inhibition or knockout leads to decreased contraction and slowed [Ca2+]i decline, and this effect is absent in PLB-/- myocytes. Thus NOS1 signaling modulates PLB serine16 phosphorylation, in part, via peroxynitrite.
INTRODUCTION: Cerebrospinal fluid (CSF) biomarkers can identify individuals withAlzheimer disease (AD) pathology (e.g., amyloid plaques, neurofibrillary tangles), but defined analyte cut-points using high-throughput automated assays are necessary for general clinical use. METHODS: CSF Aβ42, t-tau, and t-tau/Aβ42 were quantified by the LUMIPULSE platform in two test cohorts (A/B: Eisai BAN2401-201/MISSION AD E2609-301/302, n=138; C: Knight AD Research Center, n=198), and receiver operating characteristic (ROC) curve analyses defined cutpoints corresponding best to amyloid determinations using PET imaging. The best-performing cutpoint was then validated as a predictor of amyloid status in an independent cohort (D: MISSION AD E2609-301/302; n=240). RESULTS:Virtually identical t-tau/Aβ42 cut-points (~0.54) performed best in both test cohorts and with similar accuracy (areas under ROC curve [AUC] (A/B: 0.95; C: 0.94). The cut-point yielded an overall percent agreement with amyloid PET of 85.0% in validation cohort D. DISCUSSION: LUMIPULSE CSF biomarker measures with validated cut-points have clinical utility in identifying AD pathology.
Rationale: MicroRNAs (miRs) are small, non-coding RNAs that function to post-transcriptionally regulate gene expression. First transcribed as long primary miR transcripts (pri-miRs), they are enzymatically processed in the nucleus by Drosha into hairpin intermediate miRs (pre-miRs) and further processed in the cytoplasm by Dicer into mature miRs where they regulate cellular processes following activation by a variety of signals such as those stimulated by β-adrenergic receptors (βARs). Initially discovered to desensitize βAR signaling, β-arrestins are now appreciated to transduce multiple effector pathways independent of G protein-mediated second messenger accumulation, a concept known as biased signaling. We previously showed that the β-arrestin-biased βAR agonist carvedilol activates cellular pathways in the heart. Objective: Here, we tested whether carvedilol could activate β-arrestin-mediated miR maturation, thereby providing a novel potential mechanism for its cardioprotective effects. Methods and Results: In human cells and mouse hearts, carvedilol upregulates a subset of mature and pre-miRs but not their pri-miRs in β1AR-, G protein-coupled receptor kinase 5/6- and β-arrestin1-dependent manner. Mechanistically, β-arrestin1 regulates miR processing by forming a nuclear complex with hnRNPA1 and Drosha on pri-miRs. Conclusions: Our findings indicate a novel function for β1AR-mediated β-arrestin1 signaling activated by carvedilol in miR biogenesis, which may be linked, in part, to its mechanism for cell survival.
β-adrenergic receptors (βARs) are critical regulators of acute cardiovascular physiology. In response to elevated catecholamine stimulation during development of congestive heart failure (CHF), chronic activation of G s -dependent β 1 AR and G i -dependent β 2 AR pathways leads to enhanced cardiomyocyte death, reduced β 1 AR expression, and decreased inotropic reserve. β-blockers act to block excessive catecholamine stimulation of βARs to decrease cellular apoptotic signaling and normalize β 1 AR expression and inotropy. Whereas these actions reduce cardiac remodeling and mortality outcomes, the effects are not sustained. Converse to G-protein-dependent signaling, β-arrestin-dependent signaling promotes cardiomyocyte survival. Given that β 2 AR expression is unaltered in CHF, a β-arrestin-biased agonist that operates through the β 2 AR represents a potentially useful therapeutic approach. Carvedilol, a currently prescribed nonselective β-blocker, has been classified as a β-arrestin-biased agonist that can inhibit basal signaling from βARs and also stimulate cell survival signaling pathways. To understand the relative contribution of β-arrestin bias to the efficacy of select β-blockers, a specific β-arrestin-biased pepducin for the β 2 AR, intracellular loop (ICL)1-9, was used to decouple β-arrestin-biased signaling from occupation of the orthosteric ligand-binding pocket. With similar efficacy to carvedilol, ICL1-9 was able to promote β 2 AR phosphorylation, β-arrestin recruitment, β 2 AR internalization, and β-arrestin-biased signaling. Interestingly, ICL1-9 was also able to induce β 2 AR-and β-arrestin-dependent and Ca 2+ -independent contractility in primary adult murine cardiomyocytes, whereas carvedilol had no efficacy. Thus, ICL1-9 is an effective tool to access a pharmacological profile stimulating cardioprotective signaling and inotropic effects through the β 2 AR and serves as a model for the next generation of cardiovascular drug development.B eta-antagonists, also known as β-blockers, have been indicated for the treatment of pathological cardiac diseases, including congestive heart failure (CHF) and high blood pressure, for decades (1, 2). A select number of these agents, including the clinically used carvedilol, have been identified as β-arrestinbiased agonists of β-adrenergic receptors based on their ability to promote β-arrestin-dependent signaling over G-protein activation (3, 4). It is believed that the β-arrestin activation may provide additional cardioprotection based on its ability to mediate antiapoptotic signaling. As these are orthosteric ligands, there have been no means to decouple the activation of receptor-dependent β-arrestin signaling from the occupation of the orthosteric ligandbinding pocket to study their independent contribution to its efficacy as these properties appear inherently linked.Recently, we described the characterization of a library of modulators of the β 2 -adrenergic receptor (β 2 AR) known as pepducins (5). Pepducins are lipidated peptides derived from the intracel...
Background Immune cell-mediated inflammation is an essential process for mounting a repair response following myocardial infarction (MI). The sympathetic nervous system is known to regulate immune system function through β-adrenergic receptors (βAR), however their role in regulating immune cell responses to acute cardiac injury is unknown. Methods Wild-type (WT) mice were irradiated followed by isoform-specific βARKO or WT bone-marrow transplantation (BMT) and after full reconstitution underwent myocardial infarction (MI) surgery. Survival was monitored over time and alterations in immune cell infiltration following MI were examined using immunohistochemistry. Alterations in splenic function were identified through the investigation of altered adhesion receptor expression. Results β2ARKO BMT mice displayed 100% mortality resulting from cardiac rupture within 12 days post-MI compared to ~20% mortality in WT BMT mice. β2ARKO BMT mice displayed severely reduced post-MI cardiac infiltration of leukocytes with reciprocally enhanced splenic retention of the same immune cell populations. Splenic retention of the leukocytes was associated with an increase in VCAM-1 expression, which was itself regulated via β-arrestin-dependent β2AR signaling. Further, VCAM-1 expression in both mouse and human macrophages was sensitive to β2AR activity, and spleens from human tissue donors treated with β-blocker showed enhanced VCAM1 expression. The impairments in splenic retention and cardiac infiltration of leukocytes following MI were restored to WT levels via lentiviral-mediated re-expression of β2AR in β2ARKO BM prior to transplantation, which also resulted in post-MI survival rates comparable to WT BMT mice. Conclusions Immune cell-expressed β2AR plays an essential role in regulating the early inflammatory repair response to acute myocardial injury by facilitating cardiac leukocyte infiltration.
Hyper-aldosteronism is associated with myocardial dysfunction including induction of cardiac fibrosis and maladaptive hypertrophy. Mechanisms of these cardiotoxicities are not fully understood. Here we show that mineralocorticoid receptor (MR) activation by aldosterone leads to pathological myocardial signalling mediated by mitochondrial G protein-coupled receptor kinase 2 (GRK2) pro-death activity and GRK5 pro-hypertrophic action. Moreover, these MR-dependent GRK2 and GRK5 non-canonical activities appear to involve cross-talk with the angiotensin II type-1 receptor (AT1R). Most importantly, we show that ventricular dysfunction caused by chronic hyper-aldosteronism in vivo is completely prevented in cardiac Grk2 knockout mice (KO) and to a lesser extent in Grk5 KO mice. However, aldosterone-induced cardiac hypertrophy is totally prevented in Grk5 KO mice. We also show human data consistent with MR activation status in heart failure influencing GRK2 levels. Therefore, our study uncovers GRKs as targets for ameliorating pathological cardiac effects associated with high-aldosterone levels.
Heart failure (HF) is a global epidemic with the highest degree of mortality and morbidity of any disease presently studied. G protein-coupled receptors (GPCRs) are prominent regulators of cardiovascular function. Activated GPCRs are “turned off” by GPCR kinases (GRKs) in a process known as “desensitization”. GRKs 2 and 5 are highly expressed in the heart, and known to be upregulated in HF. Over the last 20 years, both GRK2 and GRK5 have been demonstrated to be critical mediators of the molecular alterations that occur in the failing heart. In the present review, we will highlight recent findings that further characterize "non-canonical" GRK signaling observed in HF. Further, we will also present potential therapeutic strategies (i.e. small molecule inhibition, microRNAs, gene therapy) that may have potential in combating the deleterious effects of GRKs in HF.
Following cardiac injury, early immune cell responses are essential for initiating cardiac remodeling and tissue repair. We previously demonstrated the importance of β2-adrenergic receptors (β2ARs) in the regulation of immune cell localization following acute cardiac injury, with deficient leukocyte infiltration into the damaged heart. The purpose of this study was to investigate the mechanism by which immune cell-expressed β2ARs regulate leukocyte recruitment to the heart following acute cardiac injury. Chemokine receptor 2 (CCR2) expression and responsiveness to C-C motif chemokine ligand 2 (CCL2)-mediated migration were abolished in β2AR knockout (KO) bone marrow (BM), both of which were rescued by β2AR reexpression. Chimeric mice lacking immune cell-specific CCR2 expression, as well as wild-type mice administered a CCR2 antagonist, recapitulated the loss of monocyte/macrophage and neutrophil recruitment to the heart following myocardial infarction (MI) observed in mice with immune cell-specific β2AR deletion. Converse to β2AR ablation, β2AR stimulation increased CCR2 expression and migratory responsiveness to CCL2 in BM. Mechanistically, G proteindependent β2AR signaling was dispensable for these effects, whereas β-arrestin2-biased β2AR signaling was required for the regulation of CCR2 expression. Additionally, activator protein 1 (AP-1) was shown to be essential in mediating CCR2 expression in response to β2AR stimulation in both murine BM and human monocytes. Finally, reconstitution of β2ARKO BM with rescued expression of a β-arrestin-biased β2AR in vivo restored BM CCR2 expression as well as cardiac leukocyte infiltration following MI. These results demonstrate the critical role of β-arrestin2/AP-1-dependent β2AR signaling in the regulation of CCR2 expression and recruitment of leukocytes to the heart following injury.β2-adrenergic receptor | leukocyte | C-chemokine receptor 2 | cardiac injury | β-arrestin
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