Hypothalamic GPCR Signaling Pathways in Cardiometabolic Control

Obesity is commonly associated with sympathetic overdrive, which is one of the major risk factors for the development of cardiovascular diseases, such as hypertension and heart failure. Over the past few decades, there has been a growing understanding of molecular mechanisms underlying obesity development with central origin; however, the relative contribution of these molecular changes to the regulation of cardiovascular function remains vague. A variety of G-protein coupled receptors (GPCRs) and their downstream signaling pathways activated in distinct hypothalamic neurons by different metabolic hormones, neuropeptides and monoamine neurotransmitters are crucial not only for the regulation of appetite and metabolic homeostasis but also for the sympathetic control of cardiovascular function. In this review, we will highlight the main GPCRs and associated hypothalamic nuclei that are important for both metabolic homeostasis and cardiovascular function. The potential downstream molecular mediators of these GPCRs will also be discussed.

GRKs and Epac1 Interaction in Cardiac Remodeling and Heart Failure

β-adrenergic receptors (β-ARs) play a major role in the physiological regulation of cardiac function through signaling routes tightly controlled by G protein-coupled receptor kinases (GRKs). Although the acute stimulation of β-ARs and the subsequent production of cyclic AMP (cAMP) have beneficial effects on cardiac function, chronic stimulation of β-ARs as observed under sympathetic overdrive promotes the development of pathological cardiac remodeling and heart failure (HF), a leading cause of mortality worldwide. This is accompanied by an alteration in cAMP compartmentalization and the activation of the exchange protein directly activated by cAMP 1 (Epac1) signaling. Among downstream signals of β-ARs, compelling evidence indicates that GRK2, GRK5, and Epac1 represent attractive therapeutic targets for cardiac disease. Here, we summarize the pathophysiological roles of GRK2, GRK5, and Epac1 in the heart. We focus on their signalosome and describe how under pathological settings, these proteins can cross-talk and are part of scaffolded nodal signaling systems that contribute to a decreased cardiac function and HF development.

Association Between the European Society of Cardiology/European Society of Hypertension Heart Rate Thresholds for Cardiovascular Risk and Neuroadrenergic Markers

The recent European Society of Cardiology/European Society of Hypertension hypertension guidelines identify resting heart rate (HR) values >80 bpm as predictors of cardiovascular risk, with the unproven assumption that this might reflect the presence of a sympathetic overdrive. In the present study, we tested this hypothesis throughout the use of direct and indirect sympathetic markers. In 193 untreated moderate essential hypertensives aged 50.4±0.6 years (mean±SEM), we measured clinic and ambulatory blood pressure and corresponding HR, venous plasma norepinephrine (high performance liquid chromatography), and muscle sympathetic nerve traffic (microneurography). We then subdivided the study population into 2 groups according to HR < or >80 bpm. Eighty-four patients displayed resting HR >80 bpm, which was this cutoff value in the remaining 109 patients, the 2 groups showing superimposable age, and sex distribution. Clinic and ambulatory blood pressure were similar in the 2 groups, whereas left ventricular mass index was significantly greater in the group with HR >80 bpm. Muscle sympathetic nerve traffic values were also significantly greater in this latter group (72.77±0.9 versus vs 36.83±1.3 bursts/min, P <0.0001); this being the case also for norepinephrine (293.0±8.7 versus 254.1±8.9 pg/mL, P <0.002). In the whole population, there was a significant direct relationship between muscle sympathetic nerve traffic, norepinephrine, left ventricular mass index, and HR values. Similar results were obtained when 24-hour HR values were analyzed. Thus patients with hypertension displaying HR >80 bpm are characterized by a marked sympathetic overdrive, particularly when direct adrenergic markers are used. This finding suggests that cardiac and peripheral sympathetic activation are involved in the increased cardiovascular risk detected in this group of patients.