Exercise training and beta-blocker treatment ameliorate age-dependent impairment of beta-adrenergic receptor signaling and enhance cardiac responsiveness to adrenergic stimulation

The Role of Exercise on Glial Cell Activity in Neuropathic Pain Management

Chronic pain is a widespread global health problem with profound socioeconomic implications, affecting millions of people of all ages. Glial cells (GCs) in pain pathways play essential roles in the processing of pain signals. Dysregulation of GC activity contributes to chronic pain states, making them targets for therapeutic interventions. Non-pharmacological approaches, such as exercise, are strongly recommended for effective pain management. This review examines the link between exercise, regular physical activity (PA), and glial cell-mediated pain processing, highlighting its potential as a strategy for managing chronic pain. Exercise not only improves overall health and quality of life but also influences the function of GCs. Recent research highlights the ability of exercise to mitigate neuroinflammatory responses and modulate the activity of GCs by reducing the activation of microglia and astrocytes, as well as modulating the expression biomarkers, thereby attenuating pain hypersensitivity. Here, we summarize new insights into the role of exercise as a non-pharmacological intervention for the relief of chronic pain.

Exercise Preconditioning Preserves Cardiac Function and Enhances Cardiac Recovery Following Dobutamine Stimulation in Doxorubicin-Treated Rat Hearts

ABSTRACT

Exercise preconditioning has been shown to protect against doxorubicin (DOX)-induced cardiac dysfunction when hearts are maintained under resting conditions. However, it is unclear whether this exercise-induced protective effect is maintained when the heart is challenged with the β 1 -adrenergic receptor agonist dobutamine (DOB), which mimics acute exercise stress. Fischer 344 rats were randomly assigned to sedentary (SED) or voluntary wheel running (WR) groups for 10 weeks. At week 11, rats were treated with either 15 mg/kg DOX or saline. Five days later, ex vivo cardiac function was assessed using an isolated working heart model at baseline, during the infusion of 7.5 μg·kg -1 ·min -1 DOB, and during recovery. DOB infusion significantly increased left ventricular developed pressure (LVDP), maximal (dP/dt max ) and minimal (dP/dt min ) rate of left ventricular pressure development, and heart rate in all groups ( P < 0.05). SED + DOX also showed a lower baseline and recovery LVDP than WR + DOX (83 ± 12 vs. 109 ± 6 mm Hg baseline, 76 ± 11 vs. 100 ± 10 mm Hg recovery, P < 0.05). WR + DOX showed higher dP/dt max and lower dP/dt min when compared with SED + DOX during DOB infusion (7311 ± 1481 vs. 5167 ± 1436 mm Hg/s and -4059 ± 1114 vs.-3158 ± 1176 mm Hg/s, respectively). SED + DOX dP/dt max was significantly lower during baseline and during recovery when compared with all other groups ( P < 0.05). These data suggest that exercise preconditioning preserved cardiac function after DOX exposure even when the heart is challenged with DOB, and it appeared to preserve the heart's ability to recover from this functional challenge.

Rejuvenation of the Aging Heart: Molecular Determinants and Applications

In Canada and worldwide, the elderly population (ie, individuals > 65 years of age) is increasing disproportionately relative to the total population. This is expected to have a substantial impact on the health care system, as increased aged is associated with a greater incidence of chronic noncommunicable diseases. Within the elderly population, cardiovascular disease is a leading cause of death, therefore developing therapies that can prevent or slow disease progression in this group is highly desirable. Historically, aging research has focused on the development of anti-aging therapies that are implemented early in life and slow the age-dependent decline in cell and organ function. However, accumulating evidence supports that late-in-life therapies can also benefit the aged cardiovascular system by limiting age-dependent functional decline. Moreover, recent studies have demonstrated that rejuvenation (ie, reverting cellular function to that of a younger phenotype) of the already aged cardiovascular system is possible, opening new avenues to develop therapies for older individuals. In this review, we first provide an overview of the functional changes that occur in the cardiomyocyte with aging and how this contributes to the age-dependent decline in heart function. We then discuss the various anti-aging and rejuvenation strategies that have been pursued to improve the function of the aged cardiomyocyte, with a focus on therapies implemented late in life. These strategies include 1) established systemic approaches (caloric restriction, exercise), 2) pharmacologic approaches (mTOR, AMPK, SIRT1, and autophagy-targeting molecules), and 3) emerging rejuvenation approaches (partial reprogramming, parabiosis/modulation of circulating factors, targeting endogenous stem cell populations, and senotherapeutics). Collectively, these studies demonstrate the exciting potential and limitations of current rejuvenation strategies and highlight future areas of investigation that will contribute to the development of rejuvenation therapies for the aged heart.

Hallmarks of cardiovascular ageing

Normal circulatory function is a key determinant of disease-free life expectancy (healthspan). Indeed, pathologies affecting the cardiovascular system, which are growing in prevalence, are the leading cause of global morbidity, disability and mortality, whereas the maintenance of cardiovascular health is necessary to promote both organismal healthspan and lifespan. Therefore, cardiovascular ageing might precede or even underlie body-wide, age-related health deterioration. In this Review, we posit that eight molecular hallmarks are common denominators in cardiovascular ageing, namely disabled macroautophagy, loss of proteostasis, genomic instability (in particular, clonal haematopoiesis of indeterminate potential), epigenetic alterations, mitochondrial dysfunction, cell senescence, dysregulated neurohormonal signalling and inflammation. We also propose a hierarchical order that distinguishes primary (upstream) from antagonistic and integrative (downstream) hallmarks of cardiovascular ageing. Finally, we discuss how targeting each of the eight hallmarks might be therapeutically exploited to attenuate residual cardiovascular risk in older individuals.

The long-term exercise after traumatic brain injury: Reharmonizing brain by sound body

Traumatic brain injuries (TBI) refer to multiple acquired dysfunctions arising from damage to the brain caused by an external force, including rapid acceleration/deceleration and concussion. Among them, mild TBI (mTBI) accounts for most cases (up to 90%) of injuries. It is responsible for a variety of symptoms, including anxiety, depression, and cognitive impairments that remain difficult to be treated. It has been reported that regular physical activity, as well as, improving life quality, display a neuroprotective function, suggesting a possible role in post-traumatic rehabilitation. In this study, we investigated the effects of treadmill exercise in a mice mTBI model by behavioural, electrophysiological and neurochemical analysis. Daily exercise decreased anxiety, aggressive behavior, and depression in mTBI mice. Accordingly, electrophysiological and neurochemical maladaptive rearrangement occurring in the hippocampus of mTBI mice were prevented by the exercise.

Exercise may alleviate age-related spatial memory impairment by rescuing β-adrenergic receptor dysregulation via both G protein-dependent and β-arrestin-dependent mechanisms in rat hippocampus

Hippocampal-dependent memory abilities including spatial memory decline with age. Exercise improves memory decline in aging brain, but, the precise mechanisms are still unknown. Learning and memory are recently hypothesized to be mediated by a β-arrestin (βArr)-dependent β-adrenergic pathway. Hence, we examined the effect of 8 weeks of treadmill exercise on hippocampal expression of β-adrenergic receptors (β-ARs; members of the G protein-coupled receptor family), and βArrs as well as spatial learning and memory in aged male rats to determine whether β-AR/βArr pathway could be involved in age-related memory decline. A total of 24 young (3-month-old) and aged (18-month-old) male Wistar rats were divided into young control, aged sedentary, and aged + exercise (n = 8 for each). Western blot for β1- and β2-ARs as well as βArr1 and βArr2 was performed. Spatial learning and memory were evaluated with the Morris water maze. The results showed significant up-regulation of β1-ARs as well as significant down-regulation of β2-AR and βArrs (βArr1 and βArr2) in the hippocampus of aged rats. Spatial memory, but not spatial learning, was impaired in aging, and treadmill exercise improved it. Notably, the improvement in spatial memory was accompanied by amelioration of β-ARs dysregulation and increase in βArr2 levels after exercise. There was a negative association between the expression of βArr2 and β1-AR, but not β2-AR, such that an increase in βArr2 by exercise was associated with reduced β1-AR expression, suggesting βArr2 may contribute to posttranslational down-regulation of β1-ARs. These data suggest that both G protein-dependent and β-arrestin-dependent β-AR pathways may regulate spatial learning and memory in aging brain.

cMyBPC phosphorylation modulates the effect of omecamtiv mecarbil on myocardial force generation

Omecamtiv mecarbil (OM), a direct myosin motor activator, is currently being tested as a therapeutic replacement for conventional inotropes in heart failure (HF) patients. It is known that HF patients exhibit dysregulated β-adrenergic signaling and decreased cardiac myosin-binding protein C (cMyBPC) phosphorylation, a critical modulator of myocardial force generation. However, the functional effects of OM in conditions of altered cMyBPC phosphorylation have not been established. Here, we tested the effects of OM on force generation and cross-bridge (XB) kinetics using murine myocardial preparations isolated from wild-type (WT) hearts and from hearts expressing S273A, S282A, and S302A substitutions (SA) in the M domain, between the C1 and C2 domains of cMyBPC, which cannot be phosphorylated. At submaximal Ca2+ activations, OM-mediated force enhancements were less pronounced in SA than in WT myocardial preparations. Additionally, SA myocardial preparations lacked the dose-dependent increases in force that were observed in WT myocardial preparations. Following OM incubation, the basal differences in the rate of XB detachment (krel) between WT and SA myocardial preparations were abolished, suggesting that OM differentially affects the XB behavior when cMyBPC phosphorylation is reduced. Similarly, in myocardial preparations pretreated with protein kinase A to phosphorylate cMyBPC, incubation with OM significantly slowed krel in both the WT and SA myocardial preparations. Collectively, our data suggest there is a strong interplay between the effects of OM and XB behavior, such that it effectively uncouples the sarcomere from cMyBPC phosphorylation levels. Our findings imply that OM may significantly alter the in vivo cardiac response to β-adrenergic stimulation.

Exercise training ameliorates adrenergic control in spontaneously hypertensive rats

The goal of this study was to examine vascular control after sympathetic stimulation by tyramine infusion in hypertensive rats submitted to swimming training. To this end, male rats were assigned to the following groups: sedentary (SN) and trained normotensive (TN), sedentary (SH) and trained hypertensive (TH). Arterial pressure (AP), heart rate (HR), HR variability (HRV), AP variability (APV), and cardiac autonomic function were recorded. Following, infusion of tyramine was administrated. The TN and TH showed a lower resting HR compared with their respective sedentary groups (p < .05). Pressure levels were less in TH than SH (p < .05). The TH showed a higher HRV together with a lower APV in comparison to SH (p < .05). The sympathetic modulation of HRV and APV was lower in TH than in SH (p < .05). Both trained groups presented an increased parasympathetic modulation of HRV compared with their respective sedentary groups (p < .05). The TN and TH groups had a higher vagal effect in comparison with their respective sedentary groups (p < .001). The sympathetic effect was lower in TH than in SH (p < .001). Pressor and HR responses to tyramine in different doses were attenuated in TH (p < .001). Further analysis showed a significant association between infusion of tyramine and normalized LF component of HRV (r = 0.84, p < .001), systolic APV (r = 0.58, p < .001) and diastolic APV (r = 0.49, p < .001). In conclusion, exercise training provokes less pressor response variation by tyramine infusion in hypertensive animals suggesting sympathetic nerve endings adjustments and decrease of the vasoconstrictor effect attenuates injury caused by hypertension improving cardiovascular autonomic dysfunction, which can be associated with sympathetic attenuation.

Exercise and cardiac health: physiological and molecular insights

The cardiac benefits of exercise have been recognized for centuries. Studies have undisputedly shown that regular exercise is beneficial for the cardiovascular system in young, old, healthy and diseased populations. For these reasons, physical activity has been recommended worldwide for cardiovascular disease prevention and treatment. Although the benefits of exercise are clear, understanding of the molecular triggers that orchestrate these effects remains incomplete and has been a topic of intense research in recent years. Here, we provide a comprehensive review of the cardiac effects of physical activity, beginning with a brief history of exercise in cardiovascular medicine and then discussing seminal work on the physiological effects of exercise in healthy, diseased and aged hearts. Later, we revisit pioneering work on the molecular mechanisms underlying the cardiac benefits of exercise, and we conclude with our view on the translational potential of this knowledge as a powerful platform for cardiovascular disease drug discovery.

Cardiomyocyte slowly activating delayed rectifier potassium channel: regulation by exercise and β-adrenergic signaling

Results demonstrate that exercise training (TRN) downregulates ventricular IKs channel current and the channel’s responsiveness to β-agonist factors mediated by TRN-induced decline in channel subunits KCNQ1 and KCNE1 and the A-kinase anchoring protein yotiao. The reduced IKs current helps explain the TRN-induced prolongation of the action potential in basal conditions and, coupled with previously reported upregulation of the KATP channel, results in a more efficient heart that is better able to respond to beat-by-beat changes in metabolism.

Androgen Effects on the Adrenergic System of the Vascular, Airway, and Cardiac Myocytes and Their Relevance in Pathological Processes

INTRODUCTION

Androgen signaling comprises nongenomic and genomic pathways. Nongenomic actions are not related to the binding of the androgen receptor (AR) and occur rapidly. The genomic effects implicate the binding to a cytosolic AR, leading to protein synthesis. Both events are independent of each other. Genomic effects have been associated with different pathologies such as vascular ischemia, hypertension, asthma, and cardiovascular diseases. Catecholamines play a crucial role in regulating vascular smooth muscle (VSM), airway smooth muscle (ASM), and cardiac muscle (CM) function and tone.

OBJECTIVE

The aim of this review is an updated analysis of the role of androgens in the adrenergic system of vascular, airway, and cardiac myocytes. Body. Testosterone (T) favors vasoconstriction, and its concentration fluctuation during life stages can affect the vascular tone and might contribute to the development of hypertension. In the VSM, T increases α1-adrenergic receptors (α ₁-ARs) and decreases adenylyl cyclase expression, favoring high blood pressure and hypertension. Androgens have also been associated with asthma. During puberty, girls are more susceptible to present asthma symptoms than boys because of the increment in the plasmatic concentrations of T in young men. In the ASM, β ₂-ARs are responsible for the bronchodilator effect, and T augments the expression of β ₂-ARs evoking an increase in the relaxing response to salbutamol. The levels of T are also associated with an increment in atherosclerosis and cardiovascular risk. In the CM, activation of α _1A-ARs and β ₂-ARs increases the ionotropic activity, leading to the development of contraction, and T upregulates the expression of both receptors and improves the myocardial performance.

CONCLUSIONS

Androgens play an essential role in the adrenergic system of vascular, airway, and cardiac myocytes, favoring either a state of health or disease. While the use of androgens as a therapeutic tool for treating asthma symptoms or heart disease is proposed, the vascular system is warmly affected.

Endothelial Dysfunction in Chronic Heart Failure: Assessment, Findings, Significance, and Potential Therapeutic Targets

Chronic heart failure (CHF) is a complex syndrome that results from structural and functional disturbances that affect the ability of the heart to supply oxygen to tissues. It largely affects and reduces the patient's quality of life, socio-economic status, and imposes great costs on health care systems worldwide. Endothelial dysfunction (ED) is a newly discovered phenomenon that contributes greatly to the pathophysiology of numerous cardiovascular conditions and commonly co-exists with chronic heart failure. However, the literature lacks clarity as to which heart failure patients might be affected, its significance in CHF patients, and its reversibility with pharmacological and non-pharmacological means. This review will emphasize all these points and summarize them for future researchers interested in vascular pathophysiology in this particular patient population. It will help to direct future studies for better characterization of these two phenomena for the potential discovery of therapeutic targets that might reduce future morbidity and mortality in this "at risk" population.

Heart rate during exercise: mechanisms, behavior, and therapeutic and prognostic implications in heart failure patients with reduced ejection fraction

Exercise intolerance is a typical manifestation of patients affected by heart failure with reduced ejection fraction (HFrEF); however, the relationship among functional capacity, mortality, and exercise-induced heart rate response during exercise remains unclear in either sinus rhythm or atrial fibrillation subjects. Heart rate increase during incremental load exercise has a typical pattern in normal subjects, whereas it is commonly compromised in HFrEF patients, mainly due to the imbalance of the autonomic nervous system. In the present review, we aim to describe the behavior of heart rate during exercise in normal subjects and in HFrEF patients in sinus rhythm and atrial fibrillation, understanding and explaining the mechanism leading to a different exercise performance and functional limitation. Moreover, the role of chronotropic incompetence and the need of standardizing the cutoff criteria are also discussed in order to clarify the clinical importance, the prognostic relevance, and the potential therapeutic implications of this condition. Looking into the relative contribution and interaction of heart rate response during exercise might represent an important issue to guide individualized therapeutic interventions and prognostic assessment in HFrEF patients.

β2-Adrenergic receptor signaling mediates the preferential mobilization of differentiated subsets of CD8+ T-cells, NK-cells and non-classical monocytes in response to acute exercise in humans

Acute exercise preferentially mobilizes cytotoxic T-cells, NK-cells and non-classical monocytes to the bloodstream under the influence of hemodynamic forces and/or β₂-adrenergic receptor (β₂-AR) signaling. However, the relative contribution of these mechanisms to the redeployment of the most exercise-responsive cell types is largely unknown. We determined the lymphocyte and monocyte subtypes mobilized to blood during exercise via β₂-AR signaling whilst controlling for β₁-AR mediated reductions in hemodynamic forces. In a randomized, double blind, complete cross-over design, 14 healthy cyclists exercised for 30-minutes at +10% of blood lactate threshold after ingesting: (1) a placebo, (2) a β₁-preferential antagonist (10 mg bisoprolol), or (2) a non-preferential β₁ + β₂-antagonist (80 mg nadolol) across three trials separated by >7-days. Bisoprolol was administered to reduce hemodynamic forces (heart rate and blood pressure) during exercise to levels comparable with nadolol but without blocking β₂-ARs. The mobilization of total NK-cells, terminally differentiated (CD57+) NK-cells, central memory, effector memory and CD45RA+ effector memory CD8+ T-cells; non-classical monocytes; and γδ T-cells were significantly blunted or abrogated under nadolol compared to both bisoprolol and placebo, indicating that the exercise-induced mobilization of these cell types to the blood is largely influenced by β₂-AR signaling. Nadolol failed to inhibit the mobilization of classical monocytes, CD4+ T-cells (and their subsets) or naïve CD8+ T-cells, indicating that these cell types are mobilized with exercise independently of the β₂-AR. We conclude that the preferential mobilization of NK-cells, non-classical monocytes and differentiated subsets of CD8+ T-cells with exercise is largely dependent on catecholamine signaling through the β₂-AR. These findings provide mechanistic insights by which distinct lymphocyte and monocyte subtypes are preferentially mobilized to protect the host from anticipated injury or infection in response to an acute stress response.

Alteration of β-Adrenoceptor Signaling in Left Ventricle of Acute Phase Takotsubo Syndrome: a Human Study

Accumulating evidence indicates alteration of the β-adrenoceptor (AR), such as desensitization and subtype switching of its coupling G protein, plays a role in the protection against catecholamine toxicity in heart failure. However, in human takotsubo syndrome (TTS), which is associated with a surge of circulating catecholamine in the acute phase, there is no histologic evidence of β-AR alteration. The purpose of this study was to investigate the involvement of alteration of β-AR signaling in the mechanism of TTS development. Left ventricular (LV) biopsied samples from 26 patients with TTS, 19 with normal LV function, and 26 with dilated cardiomyopathy (DCM) were studied. G protein-coupled receptor kinase 2 (GRK2) and β-arrestin2, which initiate the alteration of β-AR signaling, were more abundantly expressed in the myocardium in acute-phase TTS than in those of DCM and normal control as indicated by immunohistochemistry. The percentage of cardiomyocytes that showed positive membrane staining for GRK2 and β-arrestin2 was also significantly higher in acute-phase TTS. Sequential biopsies in the recovery-phase for two patients with TTS revealed that membrane expression of GRK2 and β-arrestin2 faded over time. This study provided the first histologic evidence of the involvement of alteration of β-ARs in the development of TTS.

New Insights in Cardiac β-Adrenergic Signaling During Heart Failure and Aging

Heart failure (HF) has become increasingly common within the elderly population, decreasing their survival and overall quality of life. In fact, despite the improvements in treatment, many elderly people suffer from cardiac dysfunction (HF, valvular diseases, arrhythmias or hypertension-induced cardiac hypertrophy) that are much more common in an older fragile heart. Since β-adrenergic receptor (β-AR) signaling is abnormal in failing as well as aged hearts, this pathway is an effective diagnostic and therapeutic target. Both HF and aging are characterized by activation/hyperactivity of various neurohormonal pathways, the most important of which is the sympathetic nervous system (SNS). SNS hyperactivity is initially a compensatory mechanism to stimulate contractility and maintain cardiac output. Unfortunately, this chronic stimulation becomes detrimental and causes decreased cardiac function as well as reduced inotropic reserve due to a decrease in cardiac β-ARs responsiveness. Therapies which (e.g., β-blockers and physical activity) restore β-ARs responsiveness can ameliorate cardiac performance and outcomes during HF, particularly in older patients. In this review, we will discuss physiological β-adrenergic signaling and its alterations in both HF and aging as well as the potential clinical application of targeting β-adrenergic signaling in these disease processes.

New Insights in Cardiac β-Adrenergic Signaling During Heart Failure and Aging

Heart failure (HF) has become increasingly common within the elderly population, decreasing their survival and overall quality of life. In fact, despite the improvements in treatment, many elderly people suffer from cardiac dysfunction (HF, valvular diseases, arrhythmias or hypertension-induced cardiac hypertrophy) that are much more common in an older fragile heart. Since β-adrenergic receptor (β-AR) signaling is abnormal in failing as well as aged hearts, this pathway is an effective diagnostic and therapeutic target. Both HF and aging are characterized by activation/hyperactivity of various neurohormonal pathways, the most important of which is the sympathetic nervous system (SNS). SNS hyperactivity is initially a compensatory mechanism to stimulate contractility and maintain cardiac output. Unfortunately, this chronic stimulation becomes detrimental and causes decreased cardiac function as well as reduced inotropic reserve due to a decrease in cardiac β-ARs responsiveness. Therapies which (e.g., β-blockers and physical activity) restore β-ARs responsiveness can ameliorate cardiac performance and outcomes during HF, particularly in older patients. In this review, we will discuss physiological β-adrenergic signaling and its alterations in both HF and aging as well as the potential clinical application of targeting β-adrenergic signaling in these disease processes.

Chronic low-intensity exercise attenuates cardiomyocyte contractile dysfunction and impaired adrenergic responsiveness in aortic-banded mini-swine

Exercise improves clinical outcomes in patients diagnosed with heart failure with reduced ejection fraction (HFrEF), in part via beneficial effects on cardiomyocyte Ca²⁺ cycling during excitation-contraction coupling (ECC). However, limited data exist regarding the effects of exercise training on cardiomyocyte function in patients diagnosed with heart failure with preserved ejection fraction (HFpEF). The purpose of this study was to investigate cardiomyocyte Ca²⁺ handling and contractile function following chronic low-intensity exercise training in aortic-banded miniature swine and test the hypothesis that low-intensity exercise improves cardiomyocyte function in a large animal model of pressure overload. Animals were divided into control (CON), aortic-banded sedentary (AB), and aortic-banded low-intensity trained (AB-LIT) groups. Left ventricular cardiomyocytes were electrically stimulated (0.5 Hz) to assess Ca²⁺ homeostasis (fura-2-AM) and unloaded shortening during ECC under conditions of baseline pacing and pacing with adrenergic stimulation using dobutamine (1 μM). Cardiomyocytes in AB animals exhibited depressed Ca²⁺ transient amplitude and cardiomyocyte shortening vs. CON under both conditions. Exercise training attenuated AB-induced decreases in cardiomyocyte Ca²⁺ transient amplitude but did not prevent impaired shortening vs. CON. With dobutamine, AB-LIT exhibited both Ca²⁺ transient and shortening amplitude similar to CON. Adrenergic sensitivity, assessed as the time to maximum inotropic response following dobutamine treatment, was depressed in the AB group but normal in AB-LIT animals. Taken together, our data suggest exercise training is beneficial for cardiomyocyte function via the effects on Ca²⁺ homeostasis and adrenergic sensitivity in a large animal model of pressure overload-induced heart failure. NEW & NOTEWORTHY Conventional treatments have failed to improve the prognosis of heart failure with preserved ejection fraction (HFpEF) patients. Our findings show chronic low-intensity exercise training can prevent cardiomyocyte dysfunction and impaired adrenergic responsiveness in a translational large animal model of chronic pressure overload-induced heart failure with relevance to human HFpEF.

The Role of Exercise in Cardiac Aging: From Physiology to Molecular Mechanisms

Aging induces structural and functional changes in the heart that are associated with increased risk of cardiovascular disease and impaired functional capacity in the elderly. Exercise is a diagnostic and therapeutic tool, with the potential to provide insights into clinical diagnosis and prognosis, as well as the molecular mechanisms by which aging influences cardiac physiology and function. In this review, we first provide an overview of how aging impacts the cardiac response to exercise, and the implications this has for functional capacity in older adults. We then review the underlying molecular mechanisms by which cardiac aging contributes to exercise intolerance, and conversely how exercise training can potentially modulate aging phenotypes in the heart. Finally, we highlight the potential use of these exercise models to complement models of disease in efforts to uncover new therapeutic targets to prevent or treat heart disease in the aging population.

Reversal of diet-induced obesity and insulin resistance by inducible genetic ablation of GRK2

Insulin resistance is a common feature of obesity and predisposes individuals to various prevalent pathological conditions. G protein (heterotrimeric guanine nucleotide-binding protein)-coupled receptor kinase 2 (GRK2) integrates several signal transduction pathways and is emerging as a physiologically relevant inhibitor of insulin signaling. GRK2 abundance is increased in humans with metabolic syndrome and in different murine models of insulin resistance. To support GRK2 as a potential drug target in type 2 diabetes and obesity, we investigated whether lowering GRK2 abundance reversed an ongoing systemic insulin-resistant phenotype, using a mouse model of tamoxifen-induced GRK2 ablation after high-fat diet-dependent obesity and insulin resistance. Tamoxifen-triggered GRK2 deletion impeded further body weight gain, normalized fasting glycemia, improved glucose tolerance, and was associated with preserved insulin sensitivity in skeletal muscle and liver, thereby maintaining whole-body glucose homeostasis. Moreover, when continued to be fed a high-fat diet, these animals displayed reduced fat mass and smaller adipocytes, were resistant to the development of liver steatosis, and showed reduced expression of proinflammatory markers in the liver. Our results indicate that GRK2 acts as a hub to control metabolic functions in different tissues, which is key to controlling insulin resistance development in vivo. These data suggest that inhibiting GRK2 could reverse an established insulin-resistant and obese phenotype, thereby putting forward this enzyme as a potential therapeutic target linking glucose homeostasis and regulation of adiposity.

Acute aerobic exercise mediates G protein-coupled receptor kinase 2 expression in human PBMCs

AIMS

G protein-coupled receptor kinase 2 (GRK2), a cytosolic enzyme desensitizing G protein-couple receptors (e.g., β-adrenergic receptors [β-ARs]), is involved in regulation of hypertension, congestive heart failure, and inflammatory response. Since cellular GRK2 levels change quickly in response to exogenous/endogenous stimuli, this study examined whether GRK2 levels in human peripheral blood mononuclear cells (PBMCs) would increase during acute aerobic exercise and be associated with plasma IL-6 and cardiorespiratory fitness levels.

MAIN METHODS

Eighteen subjects (8 men and 10 women), ages 18 to 30 years, were recruited to perform a 30-minute bout of acute aerobic exercise at 75% VO2max.

KEY FINDINGS

Our results demonstrated that women exhibited significantly greater exercise-induced GRK2 expression in PBMCs compared to men. IL-6 modulation is independent of GRK2 expression. Furthermore, the percent change in GRK2 expression was negatively correlated with cardiorespiratory fitness levels (relative VO2max), but not plasma IL-6.

SIGNIFICANCE

Acute aerobic exercise induces a greater GRK2 expression in women than men, while increased cardiorespiratory fitness is associated with exercise-induced GRK2 expression in PBMCs. Gender could be a contributor to regulate this GRK2 responsiveness to acute aerobic exercise.

Tailoring therapy for heart failure: the pharmacogenomics of adrenergic receptor signaling

Heart failure is one of the leading causes of mortality in Western countries, and β-blockers are a cornerstone of its treatment. However, the response to these drugs is variable among individuals, which might be explained, at least in part, by genetic differences. Pharmacogenomics is the study of genetic contributions to drug response variability in order to provide evidence for a tailored therapy in an individual patient. Several studies have investigated the pharmacogenomics of the adrenergic receptor system and its role in the context of the use of β-blockers in treating heart failure. In this review, we will focus on the most significant polymorphisms described in the literature involving adrenergic receptors and adrenergic receptor-related proteins, as well as genetic variations influencing β-blocker metabolism.

The autonomic nervous system and heart failure

The pathophysiology of heart failure (HF) is characterized by hemodynamic abnormalities that result in neurohormonal activation and autonomic imbalance with increase in sympathetic activity and withdrawal of vagal activity. Alterations in receptor activation from this autonomic imbalance may have profound effects on cardiac function and structure. Inhibition of the sympathetic drive to the heart through β-receptor blockade has become a standard component of therapy for HF with a dilated left ventricle because of its effectiveness in inhibiting the ventricular structural remodeling process and in prolonging life. Several devices for selective modulation of sympathetic and vagal activity have recently been developed in an attempt to alter the natural history of HF. The optimal counteraction of the excessive sympathetic activity is still unclear. A profound decrease in adrenergic support with excessive blockade of the sympathetic nervous system may result in adverse outcomes in clinical HF. In this review, we analyze the data supporting a contributory role of the autonomic functional alterations on the course of HF, the techniques used to assess autonomic nervous system activity, the evidence for clinical effectiveness of pharmacological and device interventions, and the potential future role of autonomic nervous system modifiers in the management of this syndrome.

Benefit of physical fitness against inflammation in obesity: role of beta adrenergic receptors

Evidence shows that both poor physical fitness and obesity are linked to low-grade inflammation and inflammatory diseases. However, their relative roles on inflammation and underlying mechanisms remain unclear. Given the inhibitory effect of catecholamines on inflammatory cytokine production, we speculated that compromised responsiveness of immune cells' beta adrenergic receptors (β-ARs) to agonists may be associated with constitutively elevated levels of inflammatory cytokines. We examined circulating levels of inflammatory cytokines TNF, IL-1β, IL-6 and β-AR sensitivity of, 70 overweight or obese compared to 26 normal-weight, otherwise healthy individuals in order to investigate the associations among obesity, physical fitness, and low-grade inflammation and to examine the role of β-ARs in these relationships. Cardiorespiratory fitness was determined by VO2peak (ml/kg/min) via a treadmill exercise. Beta-AR sensitivity was evaluated by measuring the degree of inhibition in lipopolysaccharides-stimulated monocytic intracellular TNF production by isoproterenol. In all participants, BMI, which was initially a predictor of IL-1β and IL-6 levels independent of demographic characteristics, no longer significantly predicted them after controlling for fitness levels. Among the overweight or obese participants, greater cardiorespiratory fitness was a strong predictor of lower levels of TNF and IL-1β after controlling for the covariates. When β-AR sensitivity was controlled for, however, fitness was no longer a significant predictor of those cytokines. Monocytic β-AR sensitivity was negatively associated with inflammatory marker levels and diminished in obese individuals; however, when fitness was controlled for, the significant weight group differences in β-AR sensitivity disappeared. Our findings indicate that better cardiorespiratory fitness protects against obesity-related low-grade inflammation and β-AR desensitization. Given the significance of β-AR function in pathogenesis of various diseases, clinical implications of its role in the fitness-inflammation association among the obese are profound.

Effects of physical activity on endothelial progenitor cells (EPCs)

Physical activity has a therapeutic role in cardiovascular disease (CVD), through its beneficial effects on endothelial function and cardiovascular system. Circulating endothelial progenitor cells (EPCs) are bone marrow (BM) derived cells that represent a novel therapeutic target in CVD patients, because of their ability to home to sites of ischemic injury and repair the damaged vessels. Several studies show that physical activity results in a significant increase in circulating EPCs, and, in particular, there are some evidence of the beneficial exercise-induced effects on EPCs activity in CVD settings, including coronary artery disease (CAD), heart failure (HF), and peripheral artery disease (PAD). The aim of this paper is to review the current evidence about the beneficial effects of physical exercise on endothelial function and EPCs levels and activity in both healthy subjects and patients with CVD.

β-adrenergic receptor responsiveness in aging heart and clinical implications

Elderly healthy individuals have a reduced exercise tolerance and a decreased left ventricle inotropic reserve related to increased vascular afterload, arterial-ventricular load mismatching, physical deconditioning and impaired autonomic regulation (the so called "β-adrenergic desensitization"). Adrenergic responsiveness is altered with aging and the age-related changes are limited to the β-adrenergic receptor density reduction and to the β-adrenoceptor-G-protein(s)-adenylyl cyclase system abnormalities, while the type and level of abnormalities change with species and tissues. Epidemiological studies have shown an high incidence and prevalence of heart failure in the elderly and a great body of evidence correlate the changes of β-adrenergic system with heart failure pathogenesis. In particular it is well known that: (a) levels of cathecolamines are directly correlated with mortality and functional status in heart failure, (b) β1-adrenergic receptor subtype is down-regulated in heart failure, (c) heart failure-dependent cardiac adrenergic responsiveness reduction is related to changes in G proteins activity. In this review we focus on the cardiovascular β-adrenergic changes involvement in the aging process and on similarities and differences between aging heart and heart failure.

Neuro-hormonal effects of physical activity in the elderly

Thanks to diagnostic and therapeutic advances, the elderly population is continuously increasing in the western countries. Accordingly, the prevalence of most chronic age-related diseases will increase considerably in the next decades, thus it will be necessary to implement effective preventive measures to face this epidemiological challenge. Among those, physical activity exerts a crucial role, since it has been proven to reduce the risk of cardiovascular diseases, diabetes, obesity, cognitive impairment and cancer. The favorable effects of exercise on cardiovascular homeostasis can be at least in part ascribed to the modulation of the neuro-hormonal systems implicated in cardiovascular pathophysiology. In the elderly, exercise has been shown to affect catecholamine secretion and biosynthesis, to positively modulate the renin-angiotensin-aldosterone system and to reduce the levels of plasma brain natriuretic peptides. Moreover, drugs modulating the neuro-hormonal systems may favorably affect physical capacity in the elderly. Thus, efforts should be made to actually make physical activity become part of the therapeutic tools in the elderly.

Effects of exercise training on cardiovascular adrenergic system

In heart failure (HF), exercise has been shown to modulate cardiac sympathetic hyperactivation which is one of the earliest features of neurohormonal derangement in this syndrome and correlates with adverse outcome. An important molecular alteration related to chronic sympathetic overstimulation in HF is represented by cardiac β-adrenergic receptor (β-AR) dysfunction. It has been demonstrated that exercise reverses β-AR dysfunction by restoring cardiac receptor membrane density and G-protein-dependent adenylyl cyclase activation. In particular, several evidence indicate that exercise reduces levels of cardiac G-protein coupled receptor kinase-2 (GRK2) which is known to be involved in both β1-AR and β2-AR dysregulation in HF. Similar alterations of β-AR system have been described also in the senescent heart. It has also been demonstrated that exercise training restores adrenal GRK2/α-2AR/catecholamine (CA) production axis. At vascular level, exercise shows a therapeutic effect on age-related impairment of vascular reactivity to adrenergic stimulation and restores β-AR-dependent vasodilatation by increasing vascular β-AR responsiveness and reducing endothelial GRK2 activity. Sympathetic nervous system overdrive is thought to account for >50% of all cases of hypertension and a lack of balance between parasympathetic and sympathetic modulation has been observed in hypertensive subjects. Non-pharmacological, lifestyle interventions have been associated with reductions in SNS overactivity and blood pressure in hypertension. Several evidence have highlighted the blood pressure lowering effects of aerobic endurance exercise in patients with hypertension and the significant reduction in sympathetic neural activity has been reported as one of the main mechanisms explaining the favorable effects of exercise on blood pressure control.

Risk of acute myocardial infarction after transurethral resection of prostate in elderly

Background

Benign prostatic hyperplasia is a frequent disease among elderly, and is responsible for considerable disability. Benign prostatic hyperplasia can be clinically significant due to lower urinary tract symptoms that take place because the gland is enlarged and obstructs urine flow. Transurethral resection of the prostate remains the gold standard treatment for patients with moderate or severe symptoms who need active treatment or who either fail or do not want medical therapy. Moreover, perioperative and postoperative surgery complications as cardiovascular ones still occur. The incidence of acute myocardial infarction in patients undergoing transurethral resection of the prostate is controversial. The first studies showed an increase in mortality and relative risk of death from myocardial infarction in transurethral resection of the prostate group vs open prostatectomy but these results are in contrast with more recent data.

Discussion

Given the conflicting evidence of the studies in the literature, in this review we are going to discuss the factors that may influence the risk of myocardial infarction in elderly patients undergoing prostate surgery. We analyzed the possible common factors that lead to the development of myocardial infarction and benign prostatic hyperplasia (cardiovascular and metabolic), the stressor factors related to prostatectomy (surgical and haemodynamic) and the risk factors specific of the elderly population (comorbidity and therapies).

Summary

Although transurethral resection of the prostate is considered at low risk for severe complications, there are several reports indicating that cardiovascular events in elderly patients undergoing this surgical operation are more common than in the general population. Several cardio-metabolic, surgical and aging-related factors may help explain this observation but results in literature are not concord, especially due to the fact that most data derive from retrospective studies in which selection bias cannot be excluded. Subsequently, further studies are necessary to clarify the incidence of acute myocardial infarction in old people.

Molecular aspects of the cardioprotective effect of exercise in the elderly

Aging is a well-recognized risk factor for several different forms of cardiovascular disease. However, mechanisms by which aging exerts its negative effect on outcome have been only partially clarified. Numerous evidence indicate that aging is associated with alterations of several mechanisms whose integrity confers protective action on the heart and vasculature. The present review aims to focus on the beneficial effects of exercise, which plays a pivotal role in primary and secondary prevention of cardiovascular diseases, in counteracting age-related deterioration of protective mechanisms that are crucially involved in the homeostasis of cardiovascular system. In this regard, animal and human studies indicate that exercise training is able: (1) to improve the inotropic reserve of the aging heart through restoration of cardiac β-adrenergic receptor signaling; (2) to rescue the mechanism of cardiac preconditioning and angiogenesis whose integrity has been shown to confer cardioprotection against ischemia and to improve post-myocardial infarction left ventricular remodeling; (3) to counteract age-related reduction of antioxidant systems that is associated to decreased cellular resistance to reactive oxygen species accumulation. Moreover, this review also describes the molecular effects induced by different exercise training protocols (endurance vs. resistance) in the attempt to better explain what kind of exercise strategy could be more efficacious to improve cardiovascular performance in the elderly population.

Adrenergic nervous system in heart failure: pathophysiology and therapy

Heart failure (HF), the leading cause of death in the western world, develops when a cardiac injury or insult impairs the ability of the heart to pump blood and maintain tissue perfusion. It is characterized by a complex interplay of several neurohormonal mechanisms that become activated in the syndrome to try and sustain cardiac output in the face of decompensating function. Perhaps the most prominent among these neurohormonal mechanisms is the adrenergic (or sympathetic) nervous system (ANS), whose activity and outflow are enormously elevated in HF. Acutely, and if the heart works properly, this activation of the ANS will promptly restore cardiac function. However, if the cardiac insult persists over time, chances are the ANS will not be able to maintain cardiac function, the heart will progress into a state of chronic decompensated HF, and the hyperactive ANS will continue to push the heart to work at a level much higher than the cardiac muscle can handle. From that point on, ANS hyperactivity becomes a major problem in HF, conferring significant toxicity to the failing heart and markedly increasing its morbidity and mortality. The present review discusses the role of the ANS in cardiac physiology and in HF pathophysiology, the mechanisms of regulation of ANS activity and how they go awry in chronic HF, methods of measuring ANS activity in HF, the molecular alterations in heart physiology that occur in HF, along with their pharmacological and therapeutic implications, and, finally, drugs and other therapeutic modalities used in HF treatment that target or affect the ANS and its effects on the failing heart.

Reduction of lymphocyte G protein-coupled receptor kinase-2 (GRK2) after exercise training predicts survival in patients with heart failure

BACKGROUND

Increased cardiac G protein-coupled receptor kinase-2 (GRK2) expression has a pivotal role at inducing heart failure (HF)-related β-adrenergic receptor (βAR) dysfunction. Importantly, abnormalities of βAR signalling in the failing heart, including GRK2 overexpression, are mirrored in circulating lymphocytes and correlate with HF severity. Exercise training has been shown to exert several beneficial effects on the failing heart, including normalization of cardiac βAR function and GRK2 protein levels. In the present study, we evaluated whether lymphocyte GRK2 levels and short-term changes of this kinase after an exercise training programme can predict long-term survival in HF patients.

METHODS

For this purpose, we prospectively studied 193 HF patients who underwent a 3-month exercise training programme. Lymphocyte GRK2 protein levels, plasma N-terminal pro-brain natriuretic peptide, and norepinephrine were measured at baseline and after training along with clinical and functional parameters (left ventricular ejection fraction, NYHA class, and peak-VO2). Cardiac-related mortality was evaluated during a mean follow-up period of 37 ± 20 months.

RESULTS

Exercise was associated with a significant reduction of lymphocyte GRK2 protein levels (from 1.29 ± 0.52 to 1.16 ± 0.65 densitometric units, p < 0.0001). Importantly, exercise related changes of GRK2 (delta values) robustly predicted survival in our study population. Interestingly, HF patients who did not show reduced lymphocyte GRK2 protein levels after training presented the poorest outcome.

CONCLUSIONS

Our data offer the first demonstration that changes of lymphocyte GRK2 after exercise training can strongly predict outcome in advanced HF.

Exercise training early after acute myocardial infarction reduces stress-induced hypoperfusion and improves left ventricular function

PURPOSE

Exercise training might exert its beneficial effects on myocardial perfusion by inducing coronary vascular adaptations or enhancing collateralization. We evaluated whether long-term exercise-based cardiac rehabilitation started early after ST-elevation acute myocardial infarction (STEMI) improves myocardial perfusion and left ventricular (LV) function.

METHODS

Forty-six patients with recent STEMI and residual inducible hypoperfusion were randomized into two groups: 25 enrolled in a 6-month outpatient exercise-based cardiac rehabilitation programme (group T) and 21 discharged with generic instructions for maintaining physical activity and correct lifestyle (group C). All patients underwent cardiopulmonary exercise test and dipyridamole rest gated myocardial perfusion single photon emission computed tomography within 1 week after STEMI and at 6-month follow-up.

RESULTS

At follow-up, group T showed an improvement in peak oxygen consumption, oxygen pulse and in the slope of increase in ventilation over carbon dioxide output (all p < 0.01) associated with a reduction of stress-induced hypoperfusion (p < 0.01) and an improvement in resting and post-stress wall motion score indexes (both p < 0.01), resting and post-stress wall thickening score indexes (both p < 0.05) and resting and post-stress LV ejection fraction (both p < 0.05). On the contrary, no changes in cardiopulmonary indexes, myocardial perfusion and LV function parameters were observed in group C at follow-up.

CONCLUSION

Exercise training started early after STEMI reduces stress-induced hypoperfusion and improves LV function and contractility. Exercise-induced changes in myocardial perfusion and function were associated with the absence of unfavourable LV remodelling and with an improvement of cardiovascular functional capacity.

Blockade of β-adrenoceptors restores the GRK2-mediated adrenal α(2) -adrenoceptor-catecholamine production axis in heart failure

BACKGROUND AND PURPOSE

Sympathetic nervous system (SNS) hyperactivity is characteristic of chronic heart failure (HF) and significantly worsens prognosis. The success of β-adrenoceptor antagonist (β-blockers) therapy in HF is primarily attributed to protection of the heart from the noxious effects of augmented catecholamine levels. β-Blockers have been shown to reduce SNS hyperactivity in HF, but the underlying molecular mechanisms are not understood. The GPCR kinase-2 (GRK2)-α(2) adrenoceptor-catecholamine production axis is up-regulated in the adrenal medulla during HF causing α(2) -adrenoceptor dysfunction and elevated catecholamine levels. Here, we sought to investigate if β-blocker treatment in HF could lower SNS activation by directly altering adrenal GRK2 levels.

EXPERIMENTAL APPROACH

Four weeks after myocardial infarction-induced HF, adult rats were randomized to 10-week treatment with vehicle (HF/C) or bisoprolol (HF/B). Cardiac function and dimensions were measured. In heart and adrenal gland, GRK2 levels were assessed by RT-PCR and Western blotting and adrenoceptors studied with radioligand binding. Catecholamines and α(2) adrenoceptors in adrenal medulla chromaffin cell cultures were also measured.

KEY RESULTS

Bisoprolol treatment ameliorated HF-related adverse cardiac remodelling and reduced plasma catecholamine levels, compared with HF/C rats. Bisoprolol also attenuated adrenal GRK2 overexpression as observed in HF/C rats and increased α(2) adrenoceptor density. In cultures of adrenal medulla chromaffin cells from all study groups, bisoprolol reversed HF-related α(2) adrenoceptor dysfunction. This effect was reversed by GRK2 overexpression.

CONCLUSION AND IMPLICATIONS

Blockade of β-adrenoceptors normalized the adrenal α(2) adrenoceptor-catecholamine production axis by reducing GRK2 levels. This effect may contribute significantly to the decrease of HF-related sympathetic overdrive by β-blockers.

Myocardial β(2) -adrenoceptor gene delivery promotes coordinated cardiac adaptive remodelling and angiogenesis in heart failure

BACKGROUND AND PURPOSE

We investigated whether β(2) -adrenoceptor overexpression could promote angiogenesis and improve blood perfusion and left ventricular (LV) remodeling of the failing heart.

EXPERIMENTAL APPROACH

We explored the angiogenic effects of β(2) -adrenoceptor overexpression in a rat model of post-myocardial infarction (MI) heart failure (HF). Cardiac adenoviral-mediated β(2) -adrenoceptor overexpression was obtained via direct intramyocardial injection 4-weeks post-MI. Adenovirus(Ad)-GFP and saline injected rats served as controls. Furthermore, we extended our observation to β(2) -adrenoceptor -/- mice undergoing MI.

KEY RESULTS

Transgenes were robustly expressed in the LV at 2 weeks post-gene therapy, whereas their expression was minimal at 4-weeks post-gene delivery. In HF rats, cardiac β(2) -adrenoceptor overexpression resulted in enhanced basal and isoprenaline-stimulated cardiac contractility at 2-weeks post-gene delivery. At 4 weeks post-gene transfer, Ad-β(2) -adrenoceptor HF rats showed improved LV remodeling and cardiac function. Importantly, β(2) -adrenoceptor overexpression was associated with a markedly increased capillary and arteriolar length density and enhanced in vivo myocardial blood flow and coronary reserve. At the molecular level, cardiac β(2) -adrenoceptor gene transfer induced the activation of the VEGF/PKB/eNOS pro-angiogenic pathway. In β(2) -adrenoceptor-/- mice, we found a ~25% reduction in cardiac capillary density compared with β(2) -adrenoceptor+/+ mice. The lack of β(2) -adrenoceptors was associated with a higher mortality rate at 30 days and LV dilatation, and a worse global cardiac contractility compared with controls.

CONCLUSIONS AND IMPLICATION

β(2) -Adrenoceptors play an important role in the regulation of the angiogenic response in HF. The activation of VEGF/PKB/eNOS pathway seems to be strongly involved in this mechanism.

Cardiac aging: from molecular mechanisms to significance in human health and disease

Cardiovascular diseases (CVDs) are the major causes of death in the western world. The incidence of cardiovascular disease as well as the rate of cardiovascular mortality and morbidity increase exponentially in the elderly population, suggesting that age per se is a major risk factor of CVDs. The physiologic changes of human cardiac aging mainly include left ventricular hypertrophy, diastolic dysfunction, valvular degeneration, increased cardiac fibrosis, increased prevalence of atrial fibrillation, and decreased maximal exercise capacity. Many of these changes are closely recapitulated in animal models commonly used in an aging study, including rodents, flies, and monkeys. The application of genetically modified aged mice has provided direct evidence of several critical molecular mechanisms involved in cardiac aging, such as mitochondrial oxidative stress, insulin/insulin-like growth factor/PI3K pathway, adrenergic and renin angiotensin II signaling, and nutrient signaling pathways. This article also reviews the central role of mitochondrial oxidative stress in CVDs and the plausible mechanisms underlying the progression toward heart failure in the susceptible aging hearts. Finally, the understanding of the molecular mechanisms of cardiac aging may support the potential clinical application of several "anti-aging" strategies that treat CVDs and improve healthy cardiac aging.

Pharmacogenomics of the heptahelical receptor regulators G-protein-coupled receptor kinases and arrestins: the known and the unknown

Heptahelical G-protein-coupled receptors are the most diverse and therapeutically important family of receptors, playing major roles in the physiology of various organs and tissues. They couple their ligand binding to G-protein activation, which then transmits intracellular signals. G-protein signaling is terminated by phosphorylation of the receptor by the family of G-protein-coupled receptor kinases (GRKs), followed by arrestin (Arr) binding, which uncouples the phosphorylated receptor from the G-protein and subsequently targets the receptor for internalization. Moreover, Arrs can transmit signals in their own right during receptor internalization. Genetic polymorphisms in receptors, as well as in GRK and Arr family members per se, which affect regulation of receptor signaling and function, have just started being identified and characterized. The present review will discuss what is known so far in this evolving field of GRK/Arr pharmacogenomics, as well as highlight important areas likely to produce invaluable information in the future.

Cardiac function following prolonged exercise: influence of age

This study sought to determine the influence of age on the left ventricular (LV) response to prolonged exercise (PE; 150 min). LV systolic and diastolic performance was assessed using echocardiography (ECHO) before (pre) and 60 min following (post) exercise performed at 80% maximal aerobic power in young (28 ± 4.5 years; n = 18; mean ± SD) and middle-aged (52 ± 3.9 years; n = 18) participants. LV performance was assessed using two-dimensional ECHO, including speckle-tracking imaging, to determine LV strain (LV S) and LV S rate (LV SR), in addition to Doppler measures of diastolic function. We observed a postexercise elevation in LV S (young: −19.5 ± 2.1% vs. −21.6 ± 2.1%; middle-aged: −19.9 ± 2.3% vs. −20.8 ± 2.1%; P < 0.05) and LV SR (young: −1.19 ± 0.1 vs. −1.37 ± 0.2; middle-aged: −1.20 ± 0.2 vs. −1.38 ± 0.2; P < 0.05) during recovery in both groups. Diastolic function was reduced during recovery, including the LV SR ratio of early-to-late atrial diastolic filling (SRe/a), in young (2.35 ± 0.7 vs. 1.89 ± 0.5; P < 0.01) and middle-aged (1.51 ± 0.5 vs. 1.05 ± 0.2; P < 0.01) participants, as were conventional indices including the E/A ratio. Dobutamine stress ECHO revealed a postexercise depression in LV S in response to increasing dobutamine dose, which was similar in both young (pre-exercise dobutamine 0 vs. 20 μg·kg−1·min−1: −19.5 ± 2.1 vs. −27.2 ± 2.2%; postexercise dobutamine 0 vs. 20 μg·kg−1·min−1: −21.6 ± 2.1 vs. −23.7 ± 2.2%; P < 0.05) and middle-aged participants (pre: −19.9 ± 2.3 vs. −25.3 ± 2.7%; post: −20.8 ± 2.1 vs. −23.5 ± 2.7; P < 0.05). This was despite higher noradrenaline concentrations immediately postexercise in the middle-aged participants compared with young (4.26 ± 2.7 nmol/L vs. 3.00 ± 1.4 nmol/L; P = 0.12). These data indicate that LV dysfunction is observed following PE and that advancing age does not increase the magnitude of this response.

Age exacerbates chronic catecholamine-induced impairments in contractile reserve in the rat

Contractile reserve decreases with advancing age and chronic isoproterenol (ISO) administration is a well-characterized model of cardiac hypertrophy known to impair cardiovascular function. This study evaluated whether nonsenescent, mature adult rats are more susceptible to detrimental effects of chronic ISO administration than younger adult rats. Rats received daily injections of ISO (0.1 mg/kg sc) or vehicle for 3 wk. ISO induced a greater impairment in contractile reserve [maximum of left ventricular pressure development (Δ+dP/dt(max))] in mature adult ISO-treated (MA-ISO) than in young adult ISO-treated rats (YA-ISO) in response to infusions of mechanistically distinct inotropes (digoxin, milrinone; 20-200 μl·kg(-1)·min(-1)), while basal and agonist-induced changes in heart rate and systolic arterial pressure (SAP) were not different across groups. ISO decreased expression of the calcium handling protein, sarco(endo)plasmic reticulum Ca(2+)-ATPase-2a, in MA-ISO compared with YA, YA-ISO, and MA rats. Chronic ISO also induced greater increases in cardiac hypertrophy [left ventricular (LV) index: 33 ± 3 vs. 22 ± 5%] and caspase-3 activity (34 vs. 5%) in MA-ISO relative to YA-ISO rats. Moreover, β-myosin heavy chain (β-MHC) and atrial natriuretic factor (ANF) mRNA expression was significantly elevated in MA-ISO. These results demonstrate that adult rats develop greater impairments in systolic performance than younger rats when exposed to chronic catecholamine excess. Reduced contractile reserve may result from calcium dysregulation, increased caspase-3 activity, or increased β-MHC and ANF expression. Although several studies report age-related declines in systolic performance in older and senescent animals, the present study demonstrates that catecholamine excess induces reductions in systolic performance significantly earlier in life.

Cardiac β-adrenergic responsiveness with exercise

Left ventricular performance is enhanced with chronic exercise training. Alterations in cardiomyocyte β-adrenergic responsiveness (BAR) may, in part, mediate this response. In this study, cardiac BAR and the expression of some key cardiac hypertrophic signaling molecules following 3 months of treadmill training were examined. Four-month old, female, Wistar Kyoto (WKY) rats were randomly assigned into either a sedentary (WKY-SED, n = 15) or an exercise-trained (WKY-TRD, n = 11) group. All rats were maintained on a 12-h light/dark cycle, and fed ad libitum. Exercise training consisted of motorized treadmill training at 25 m/min, 0% grade, 60 continuous minutes, 5 days/week for a period of 12 weeks. RT-PCR was used to establish basal cardiac calcineurin A, ANP, and AKT mRNA expression. In vitro cardiac BAR responsiveness was determined in Langendorff, isolated hearts. Following baseline, isoproterenol (ISO) was incrementally infused at concentrations ranging from 1 × 10(-10) to 1 × 10(-7) mol/L. There were no group differences for heart weight, heart to body weight ratio, calcineurin A, ANP, or AKT mRNA levels between WKY-SED and WKY-TRD. WKY-TRD showed enhanced cardiac BAR relative to WKY-SED (at ISO 1 × 10(-7) mol/L; P < 0.05). Moderate intensity treadmill exercise improved cardiac BAR responsiveness to a high concentration of isoproterenol. This adaptation was independent of training-induced alterations in cardiac hypertrophy or hypertrophic marker expression.

Adrenal GRK2 lowering is an underlying mechanism for the beneficial sympathetic effects of exercise training in heart failure

Exercise training has been reported to exert beneficial effects on cardiac function and to reduce morbidity and mortality of chronic heart failure (HF). Augmented sympathetic nervous system (SNS) activity, leading to elevated circulating catecholamine (CA) levels, is a hallmark of chronic HF that significantly aggravates this disease. Exercise training has been shown to also reduce SNS overactivity in HF, but the underlying molecular mechanism(s) remain unidentified. We recently reported that adrenal G protein-coupled receptor kinase-2 (GRK2), an enzyme that regulates the sympathoinhibitory alpha(2)-adrenoceptors (alpha(2)-ARs) present in the CA-producing adrenal medulla, is upregulated in HF, contributing to the chronically elevated CA levels and SNS activity of the disease. In the present study, we tested whether exercise training can affect the adrenal GRK2-alpha(2)-AR-CA production system in the context of HF. For this purpose, a 10-wk-long exercise training regimen of adult male Sprague-Dawley rats starting at 4 wk postmyocardial infarction (post-MI) was employed, and examination at the end of this treatment period revealed significant amelioration of beta-AR-stimulated contractility in response to exercise training, accompanied by cardiac GRK2 reduction and restoration of circulating plasma CA levels. Importantly, adrenal GRK2 expression (72 + or - 5% reduction vs. post-MI untrained) and alpha(2)-AR number were also restored after exercise training in post-MI animals. These results suggest that exercise training restores the adrenal GRK2-alpha(2)-AR-CA production axis, and this might be part of the mechanism whereby this therapeutic modality normalizes sympathetic overdrive and impedes worsening of the failing heart.

In vivo properties of the proangiogenic peptide QK

The main regulator of neovascularization is Vascular Endothelial Growth Factor (VEGF). We recently demonstrated that QK, a de novo engineered VEGF mimicking peptide, shares in vitro the same biological properties of VEGF, inducing capillary formation and organization. On these grounds, the aim of this study is to evaluate in vivo the effects of this small peptide. Therefore, on Wistar Kyoto rats, we evaluated vasomotor responses to VEGF and QK in common carotid rings. Also, we assessed the effects of QK in three different models of angiogenesis: ischemic hindlimb, wound healing and Matrigel plugs. QK and VEGF present similar endothelium-dependent vasodilatation. Moreover, the ability of QK to induce neovascularization was confirmed us by digital angiographies, dyed beads dilution and histological analysis in the ischemic hindlimb as well as by histology in wounds and Matrigel plugs. Our findings show the proangiogenic properties of QK, suggesting that also in vivo this peptide resembles the full VEGF protein. These data open to new fields of investigation on the mechanisms of activation of VEGF receptors, offering clinical implications for treatment of pathophysiological conditions such as chronic ischemia.

Coexistent chronic obstructive pulmonary disease and heart failure in the elderly

The prevalence of chronic obstructive pulmonary disease (COPD) and chronic heart failure (CHF) increases substantially with age. The coexistence of COPD and CHF is common but often unrecognized in elderly patients. To avoid overlooking COPD in elderly patients with known CHF pulmonary function tests should be routinely obtained. Likewise, to avoid overlooking CHF in elderly patients with known COPD left ventricular (LV) function should be routinely assessed. Plasma brain natriuretic peptide levels are useful to differentiate COPD exacerbation from CHF decompensation in patients presenting with acute dyspnea. Aging exacerbates skeletal muscle alterations that occur in patients with CHF and COPD. Skeletal muscle metabolic alterations and atrophy and the resulting deterioration of functional capacity progress rapidly in elderly patients with COPD and CHF. Physical conditioning reverses rapidly progressing skeletal muscle metabolic alterations and atrophy and promotes independence and life quality in the elderly. Physical conditioning is clearly an essential component of the management of elderly patients with COPD and CHF. The pharmacological management of patients with coexistent COPD and CHF should focus on not depriving these patients from long-term beta adrenergic blockade. Long-term beta adrenergic blockade has been repeatedly shown to improve survival in elderly patients with CHF due to LV systolic dysfunction and, contrary to conventional belief, is well tolerated by patients with COPD.