Obesity-induced cardiac lipid accumulation in adult mice is modulated by G protein-coupled receptor kinase 2 levels

Estradiol contributes to sex differences in resilience to sepsis-induced metabolic dysregulation and dysfunction in the heart via GPER-1-mediated PPARδ/NLRP3 signaling

BACKGROUND AND AIM

Clinically, septic males tend to have higher mortality rates, but it is unclear if this is due to sex differences in cardiac dysfunction, possibly influenced by hormonal variations. Cardiac dysfunction significantly contributes to sepsis-related mortality, primarily influenced by metabolic imbalances. Peroxisome proliferator-activated receptor delta (PPARδ) is a key player in cardiac metabolism and its activation has been demonstrated to favor sepsis outcomes. While estradiol (E2) is abundant and beneficial in females, its impact on PPARδ-mediated metabolism in the heart with regards to sex during sepsis remains unknown.

METHODS AND RESULTS

Here, we unveil that while sepsis diminishes PPARδ nuclear translocation and induces metabolic dysregulation, oxidative stress, apoptosis and dysfunction in the heart thereby enhancing mortality, these effects are notably more pronounced in males than females. Mechanistic experiments employing ovariectomized(OVX) mice, E2 administration, and G protein-coupled estrogen receptor 1(GPER-1) knockout (KO) mice revealed that under lipopolysaccharide (LPS)-induced sepsis, E2 acting via GPER-1 enhances cardiac electrical activity and function, promotes PPARδ nuclear translocation, and subsequently ameliorates cardiac metabolism while mitigating oxidative stress and apoptosis in females. Furthermore, PPARδ specific activation using GW501516 in female GPER-1-/- mice reduced oxidative stress, ultimately decreasing NLRP3 expression in the heart. Remarkably, targeted GPER-1 activation using G1 in males mirrors these benefits, improving cardiac electrical activity and function, and ultimately enhancing survival rates during LPS challenge. By employing NLRP3 KO mice, we demonstrated that the targeted GPER-1 activation mitigated injury, enhanced metabolism, and reduced apoptosis in the heart of male mice via the downregulation of NLRP3.

CONCLUSION

Our findings collectively illuminate the sex-specific cardiac mechanisms influencing sepsis mortality, offering insights into physiological and pathological dimensions. From a pharmacological standpoint, this study introduces specific GPER-1 activation as a promising therapeutic intervention for males under septic conditions. These discoveries advance our understanding of the sex differences in sepsis-induced cardiac dysfunction and also present a novel avenue for targeted interventions with potential translational impact.

USP28 Serves as a Key Suppressor of Mitochondrial Morphofunctional Defects and Cardiac Dysfunction in the Diabetic Heart

BACKGROUND

The majority of people with diabetes are susceptible to cardiac dysfunction and heart failure, and conventional drug therapy cannot correct diabetic cardiomyopathy progression. Herein, we assessed the potential role and therapeutic value of USP28 (ubiquitin-specific protease 28) on the metabolic vulnerability of diabetic cardiomyopathy.

METHODS

The type 2 diabetes mouse model was established using db/db leptin receptor-deficient mice and high-fat diet/streptozotocin-induced mice. Cardiac-specific knockout of USP28 in the db/db background mice was generated by crossbreeding db/m and Myh6-Cre+/USP28fl/fl mice. Recombinant adeno-associated virus serotype 9 carrying USP28 under cardiac troponin T promoter was injected into db/db mice. High glucose plus palmitic acid-incubated neonatal rat ventricular myocytes and human induced pluripotent stem cell-derived cardiomyocytes were used to imitate diabetic cardiomyopathy in vitro. The molecular mechanism was explored through RNA sequencing, immunoprecipitation and mass spectrometry analysis, protein pull-down, chromatin immunoprecipitation sequencing, and chromatin immunoprecipitation assay.

RESULTS

Microarray profiling of the UPS (ubiquitin-proteasome system) on the basis of db/db mouse hearts and diabetic patients' hearts demonstrated that the diabetic ventricle presented a significant reduction in USP28 expression. Diabetic Myh6-Cre+/USP28fl/fl mice exhibited more severe progressive cardiac dysfunction, lipid accumulation, and mitochondrial disarrangement, compared with their controls. On the other hand, USP28 overexpression improved systolic and diastolic dysfunction and ameliorated cardiac hypertrophy and fibrosis in the diabetic heart. Adeno-associated virus serotype 9-USP28 diabetic mice also exhibited less lipid storage, reduced reactive oxygen species formation, and mitochondrial impairment in heart tissues than adeno-associated virus serotype 9-null diabetic mice. As a result, USP28 overexpression attenuated cardiac remodeling and dysfunction, lipid accumulation, and mitochondrial impairment in high-fat diet/streptozotocin-induced type 2 diabetes mice. These results were also confirmed in neonatal rat ventricular myocytes and human induced pluripotent stem cell-derived cardiomyocytes. RNA sequencing, immunoprecipitation and mass spectrometry analysis, chromatin immunoprecipitation assays, chromatin immunoprecipitation sequencing, and protein pull-down assay mechanistically revealed that USP28 directly interacted with PPARα (peroxisome proliferator-activated receptor α), deubiquitinating and stabilizing PPARα (Lys152) to promote Mfn2 (mitofusin 2) transcription, thereby impeding mitochondrial morphofunctional defects. However, such cardioprotective benefits of USP28 were largely abrogated in db/db mice with PPARα deletion and conditional loss-of-function of Mfn2.

CONCLUSIONS

Our findings provide a USP28-modulated mitochondria homeostasis mechanism that involves the PPARα-Mfn2 axis in diabetic hearts, suggesting that USP28 activation or adeno-associated virus therapy targeting USP28 represents a potential therapeutic strategy for diabetic cardiomyopathy.

High-fat diet causes mitochondrial damage and downregulation of mitofusin-2 and optic atrophy-1 in multiple organs

High-fat consumption promotes the development of obesity, which is associated with various chronic illnesses. Mitochondria are the energy factories of eukaryotic cells, maintaining self-stability through a fine-tuned quality-control network. In the present study, we evaluated high-fat diet (HFD)-induced changes in mitochondrial ultrastructure and dynamics protein expression in multiple organs. C57BL/6J male mice were fed HFD or normal diet (ND) for 24 weeks. Compared with ND-fed mice, HFD-fed mice exhibited increased body weight, cardiomyocyte enlargement, pulmonary fibrosis, hepatic steatosis, renal and splenic structural abnormalities. The cellular apoptosis of the heart, liver, and kidney increased. Cellular lipid droplet deposition and mitochondrial deformations were observed. The proteins related to mitochondrial biogenesis (TFAM), fission (DRP1), autophagy (LC3 and LC3-II: LC3-I ratio), and mitophagy (PINK1) presented different changes in different organs. The mitochondrial fusion regulators mitofusin-2 (MFN2) and optic atrophy-1 (OPA1) were consistently downregulated in multiple organs, even the spleen. TOMM20 and ATP5A protein were enhanced in the heart, skeletal muscle, and spleen, and attenuated in the kidney. These results indicated that high-fat feeding caused pathological changes in multiple organs, accompanied by mitochondrial ultrastructural damage, and MFN2 and OPA1 downregulation. The mitochondrial fusion proteins may become promising targets and/or markers for treating metabolic disease.

Metformin and Dapagliflozin Attenuate Doxorubicin-Induced Acute Cardiotoxicity in Wistar Rats: An Electrocardiographic, Biochemical, and Histopathological Approach

Doxorubicin is a widely used anticancer drug whose efficacy is limited due to its cardiotoxicity. There is no ideal cardioprotection available against doxorubicin-induced cardiotoxicity. This study aimed to investigate the anticipated cardioprotective potential of metformin and dapagliflozin against doxorubicin-induced acute cardiotoxicity in Wistar rats. At the beginning of the experiment, cardiac screening of experimental animals was done by recording an electrocardiogram (ECG) before allocating them into the groups. Thereafter, a total of thirty healthy adult Wistar rats (150-200 g) were randomly divided into five groups (n = 6) and treated for eight days as follows: group I (normal control), group II (doxorubicin control), group III (metformin 250 mg/kg/day), group IV (metformin 180 mg/kg/day), and group V (dapagliflozin 0.9 mg/kg/day). On the 7th day of the treatment phase, doxorubicin 20 mg/kg was administered intraperitoneal to groups II, III, IV, and V. On the 9th day (immediately after 48 h of doxorubicin administration), blood was collected from anesthetized animals for glucose, lipid profile, CK-MB & AST estimation, and ECG was recorded. Later, animals were sacrificed, and the heart was dissected for histopathological examination. We found that compared to normal control rats, CK-MB, AST, and glucose were significantly increased in doxorubicin control rats. There was a significant reversal of doxorubicin-induced hyperglycemia in the rats treated with metformin 250 mg/kg compared to doxorubicin control rats. Both metformin (180 mg/kg and 250 mg/kg) and dapagliflozin (0.9 mg/kg) significantly altered doxorubicin-induced ECG changes and reduced the levels of cardiac injury biomarkers CK-MB and AST compared to doxorubicin control rats. Metformin and dapagliflozin protected the cellular architecture of the myocardium from doxorubicin-induced myocardial injury. Current study revealed that both metformin and dapagliflozin at the FDA-recommended antidiabetic doses mitigated doxorubicin-induced acute cardiotoxicity in Wistar rats. The obtained data have opened the perspective to perform chronic studies and then to clinical studies to precisely consider metformin and dapagliflozin as potential chemoprotection in the combination of chemotherapy with doxorubicin to limit its cardiotoxicity, especially in patients with comorbid conditions like type II diabetes mellitus.

GRK2 in cardiovascular disease and its potential as a therapeutic target

Cardiovascular diseases (CVDs) represent the leading cause of death globally. Despite major advances in the field of pharmacological CVD treatments, particularly in the field of heart failure (HF) research, case numbers and overall mortality remain high and have trended upwards over the last few years. Thus, identifying novel molecular targets for developing HF therapeutics remains a key research focus. G protein-coupled receptors (GPCRs) are critical myocardial signal transducers which regulate cardiac contractility, growth, adaptation and metabolism. Additionally, GPCR dysregulation underlies multiple models of cardiac pathology, and most pharmacological therapeutics currently used in HF target these receptors. Currently-approved treatments have improved patient outcomes, but therapies to stop or reverse HF are lacking. A recent focus on GPCR intracellular-regulating proteins such as GPCR kinases (GRKs) has uncovered GRK2 as a promising target for combating HF. Current literature strongly establishes increased levels and activity of GRK2 in multiple models of CVD. Additionally, the GRK2 interactome includes numerous proteins which interact with differential domains of GRK2 to modulate both beneficial and deleterious signaling pathways in the heart, indicating that these domains can be targeted with a high level of specificity unique to various cardiac pathologies. These data support the premise that GRK2 should be at the forefront of a novel investigative drug search. This perspective reviews cardiac GPCRs, describes the structure and functions of GRK2 in cardiac function and maladaptive pathology, and summarizes the ongoing and future research for targeting this critical kinase across cellular, animal and human models of cardiac dysfunction and HF.

Pea-Resistant Starch with Different Multi-scale Structural Features Attenuates the Obesity-Related Physiological Changes in High-Fat Diet Mice

The present study compared the modulatory effects of different resistant starches (RSs) isolated from native (NP-RS), acid-hydrolyzed (AHP-RS), and pullulanase debranched (PDP-RS) pea starches on the corresponding in vivo metabolic responses in high fat (HF)-diet-induced obese mice. The biochemical studies on serum lipid profile and antioxidant enzyme activities were supported by histological and gene expression analyses, which suggested a potential therapeutic role for RS in regulating obesity, possibly through the production of short-chain fatty acids and the proliferation of some beneficial colonic bacteria, including Allobaculum, Bifidobacterium, Odoribacter, Clostridium, and Prevotella. Particularly, a more pronounced effect of AHP-RS with a higher proportion of the crystalline region and a more ordered double-helical alignment on improving the hyperlipidemic symptoms in obese mice induced by a HF diet was observed. Our analysis revealed that the RS3 samples seemed to be more effective than RS2 in terms of attenuating obesity in mice that were fed a HF diet.

Attenuated Cardiac oxidative stress, inflammation and apoptosis in Obese Mice with nonfatal infection of Escherichia coli

Obesity is a risk factor of many diseases, but could be beneficial to the individuals with bacterial infection. The present study was conducted to investigate the relationship between obesity and heart during nonfatal bacterial infection. Male normal (lean) and diet-induced obesity mice (DIO, fed with high-fat diet) were chosen to perform nasal instillation with E. coli to establish a nonfatal acute mouse model. The cardiac histopathology, inflammation and oxidative damage, as well as apoptosis were detected post-infection. The results revealed that the Escherichia coli (E.coli)-infected mice exhibited increased cardiac index, contents of IL-1β, IL-6, IL-8, TNF-α, leptin and resistin, levels of apoptotic proteins (caspase-3 and caspase-9, and bax/bcl-2 ratio), cardiac pathological changes and oxidative stress. Furthermore, these parameters were more serious in the lean mice than those in the DIO mice. In summary, our findings gave a new sight that E.coli infection impaired heart via histopathological lesions, inflammation and oxidative stress and excessive apoptosis of cardiomyocytes. Interestingly, obesity exerted attenuated effects on the heart of mice with non-fatal infection of E.coli through decreased inflammation, oxidative stress and apoptosis of cardiac tissue.

Cadmium exposure induces cardiac glucometabolic dysregulation and lipid accumulation independent of pyruvate dehydrogenase activity

CONTEXT

Suppressed glucose metabolism, elevated fatty acid metabolism and lipid deposition within myocardial cells are the key pathological features of diabetic cardiomyopathy. Studies have associated cadmium exposure with metabolic disturbances.

OBJECTIVE

To examine the effects of cadmium exposure on cardiac glucose homeostasis and lipid accumulation in male Wistar rats.

METHODS

Male Wistar rats were treated for 21 days as (n = 5): Control, cadmium chloride Cd5 (5 mg/kg, p.o.), cadmium chloride Cd30 (30 mg/kg, p.o).

RESULTS

The fasting serum insulin level in this study decreased significantly. Pyruvate and hexokinase activity reduced significantly in the Cd5 group while no significant change in lactate and glycogen levels. The activity of pyruvate dehydrogenase enzyme significantly increased with an increasing dosage of cadmium. The free fatty acid, total cholesterol and triglyceride levels in the heart increased significantly with increasing dosage of cadmium when compared with the control. Lipoprotein lipase activity in the heart showed no difference in the Cd5 group but a reduction in the activity in the Cd30 group was observed.

CONCLUSION

This study indicates that cadmium exposure interferes with cardiac substrate handling resulting in impaired glucometabolic regulation and lipid accumulation which could reduce cardiac efficiency.

Functional resilience of C57BL/6J mouse heart to dietary fat overload

Molecular mechanisms underlying cardiac dysfunction and subsequent heart failure in diabetic cardiomyopathy are incompletely understood. Initially we intended to test the role of G protein-coupled receptor kinase 2 (GRK2), a potential mediator of cardiac dysfunction in diabetic cardiomyopathy, but found that control animals on HFD did not develop cardiomyopathy. Cardiac function was preserved in both wild-type and GRK2 knockout animals fed high-fat diet as indicated by preserved left ventricular ejection fraction (LVEF) although heart mass was increased. The absence of cardiac dysfunction led us to rigorously evaluate the utility of diet-induced obesity to model diabetic cardiomyopathy in mice. Using pure C57BL/6J animals and various diets formulated with different sources of fat-lard (32% saturated fat, 68% unsaturated fat) or hydrogenated coconut oil (95% saturated fat), we consistently observed left ventricular hypertrophy, preserved LVEF, and preserved contractility measured by invasive hemodynamics in animals fed high-fat diet. Gene expression patterns that characterize pathological hypertrophy were not induced, but a modest induction of various collagen isoforms and matrix metalloproteinases was observed in heart with high-fat diet feeding. PPARα-target genes that enhance lipid utilization such as Pdk4, CD36, AcadL, and Cpt1b were induced, but mitochondrial energetics was not impaired. These results suggest that although long-term fat feeding in mice induces cardiac hypertrophy and increases cardiac fatty acid metabolism, it may not be sufficient to activate pathological hypertrophic mechanisms that impair cardiac function or induce cardiac fibrosis. Thus, additional factors that are currently not understood may contribute to the cardiac abnormalities previously reported by many groups.NEW & NOTEWORTHY Dietary fat overload (DFO) is widely used to model diabetic cardiomyopathy but the utility of this model is controversial. We comprehensively characterized cardiac contractile and mitochondrial function in C57BL6/J mice fed with lard-based or saturated fat-enriched diets initiated at two ages. Despite cardiac hypertrophy, contractile and mitochondrial function is preserved, and molecular adaptations likely limit lipotoxicity. The resilience of these hearts to DFO underscores the need to develop robust alternative models of diabetic cardiomyopathy.

Cardiac GRK2 Protein Levels Show Sexual Dimorphism during Aging and Are Regulated by Ovarian Hormones

Cardiovascular disease (CVD) risk shows a clear sexual dimorphism with age, with a lower incidence in young women compared to age-matched men. However, this protection is lost after menopause. We demonstrate that sex-biased sensitivity to the development of CVD with age runs in parallel with changes in G protein-coupled receptor kinase 2 (GRK2) protein levels in the murine heart and that mitochondrial fusion markers, related to mitochondrial functionality and cardiac health, inversely correlate with GRK2. Young female mice display lower amounts of cardiac GRK2 protein compared to age-matched males, whereas GRK2 is upregulated with age specifically in female hearts. Such an increase in GRK2 seems to be specific to the cardiac muscle since a different pattern is found in the skeletal muscles of aging females. Changes in the cardiac GRK2 protein do not seem to rely on transcriptional modulation since adrbk1 mRNA does not change with age and no differences are found between sexes. Global changes in proteasomal or autophagic machinery (known regulators of GRK2 dosage) do not seem to correlate with the observed GRK2 dynamics. Interestingly, cardiac GRK2 upregulation in aging females is recapitulated by ovariectomy and can be partially reversed by estrogen supplementation, while this does not occur in the skeletal muscle. Our data indicate an unforeseen role for ovarian hormones in the regulation of GRK2 protein levels in the cardiac muscle which correlates with the sex-dependent dynamics of CVD risk, and might have interesting therapeutic applications, particularly for post-menopausal women.

GRK2 regulates GLP-1R-mediated early phase insulin secretion in vivo

BACKGROUND

Insulin secretion from the pancreatic β-cell is finely modulated by different signals to allow an adequate control of glucose homeostasis. Incretin hormones such as glucagon-like peptide-1 (GLP-1) act as key physiological potentiators of insulin release through binding to the G protein-coupled receptor GLP-1R. Another key regulator of insulin signaling is the Ser/Thr kinase G protein-coupled receptor kinase 2 (GRK2). However, whether GRK2 affects insulin secretion or if GRK2 can control incretin actions in vivo remains to be analyzed.

RESULTS

Using GRK2 hemizygous mice, isolated pancreatic islets, and model β-cell lines, we have uncovered a relevant physiological role for GRK2 as a regulator of incretin-mediated insulin secretion in vivo. Feeding, oral glucose gavage, or administration of GLP-1R agonists in animals with reduced GRK2 levels (GRK2+/- mice) resulted in enhanced early phase insulin release without affecting late phase secretion. In contrast, intraperitoneal glucose-induced insulin release was not affected. This effect was recapitulated in isolated islets and correlated with the increased size or priming efficacy of the readily releasable pool (RRP) of insulin granules that was observed in GRK2+/- mice. Using nanoBRET in β-cell lines, we found that stimulation of GLP-1R promoted GRK2 association to this receptor and that GRK2 protein and kinase activity were required for subsequent β-arrestin recruitment.

CONCLUSIONS

Overall, our data suggest that GRK2 is an important negative modulator of GLP-1R-mediated insulin secretion and that GRK2-interfering strategies may favor β-cell insulin secretion specifically during the early phase, an effect that may carry interesting therapeutic applications.

Myeloid GRK2 Regulates Obesity-Induced Endothelial Dysfunction by Modulating Inflammatory Responses in Perivascular Adipose Tissue

Perivascular adipose tissue (PVAT) is increasingly being regarded as an important endocrine organ that directly impacts vessel function, structure, and contractility in obesity-associated diseases. We uncover here a role for myeloid G protein-coupled receptor kinase 2 (GRK2) in the modulation of PVAT-dependent vasodilation responses. GRK2 expression positively correlates with myeloid- (CD68) and lymphoid-specific (CD3, CD4, and CD8) markers and with leptin in PVAT from patients with abdominal aortic aneurysms. Using mice hemizygous for GRK2 in the myeloid lineage (LysM-GRK2^+/−), we found that GRK2 deficiency in myeloid cells allows animals to preserve the endothelium-dependent acetylcholine or insulin-induced relaxation, which is otherwise impaired by PVAT, in arteries of animals fed a high fat diet (HFD). Downregulation of GRK2 in myeloid cells attenuates HFD-dependent infiltration of macrophages and T lymphocytes in PVAT, as well as the induction of tumor necrosis factor-α (TNFα) and NADPH oxidase (Nox)1 expression, whereas blocking TNFα or Nox pathways by pharmacological means can rescue the impaired vasodilator responses to insulin in arteries with PVAT from HFD-fed animals. Our results suggest that myeloid GRK2 could be a potential therapeutic target in the development of endothelial dysfunction induced by PVAT in the context of obesity.

Acute dapagliflozin administration exerts cardioprotective effects in rats with cardiac ischemia/reperfusion injury

BACKGROUND

A sodium-glucose co-transporter 2 (SGLT-2) inhibitor had favorable impact on the attenuation of hyperglycemia together with the severity of heart failure. However, the effects of acute dapagliflozin administration at the time of cardiac ischemia/reperfusion (I/R) injury are not established.

METHODS

The effects of dapagliflozin on cardiac function were investigated by treating cardiac I/R injury at different time points. Cardiac I/R was instigated in forty-eight Wistar rats. These rats were then split into 4 interventional groups: control, dapagliflozin (SGLT2 inhibitor, 1 mg/kg) given pre-ischemia, at the time of ischemia and at the beginning of reperfusion. Left ventricular (LV) function and arrhythmia score were evaluated. The hearts were used to evaluate size of myocardial infarction, cardiomyocyte apoptosis, cardiac mitochondrial dynamics and function.

RESULTS

Dapagliflozin given pre-ischemia conferred the maximum level of cardioprotection quantified through the decrease in arrhythmia, attenuated infarct size, decreased cardiac apoptosis and improved cardiac mitochondrial function, biogenesis and dynamics, leading to LV function improvement during cardiac I/R injury. Dapagliflozin given during ischemia also showed cardioprotection, but at a lower level of efficacy.

CONCLUSIONS

Acute dapagliflozin administration during cardiac I/R injury exerted cardioprotective effects by attenuating cardiac infarct size, increasing LV function and reducing arrhythmias. These benefits indicate its potential clinical usefulness.

A high-content, in vitro cardiac fibrosis assay for high-throughput, phenotypic identification of compounds with anti-fibrotic activity

A key feature in the pathogenesis of heart failure is cardiac fibrosis, but effective treatments that specifically target cardiac fibrosis are currently not available. A major impediment to progress has been the lack of reliable in vitro models with sufficient throughput to screen for activity against cardiac fibrosis. Here, we established cell culture conditions in micro-well format that support extracellular deposition of mature collagen from primary human cardiac fibroblasts - a hallmark of cardiac fibrosis. Based on robust biochemical characterization we developed a high-content phenotypic screening platform, that allows for high-throughput identification of compounds with activity against cardiac fibrosis. Our platform correctly identifies compounds acting on known cardiac fibrosis pathways. Moreover, it can detect anti-fibrotic activity for compounds acting on targets that have not previously been reported in in vitro cardiac fibrosis assays. Taken together, our experimental approach provides a powerful platform for high-throughput screening of anti-fibrotic compounds as well as discovery of novel targets to develop new therapeutic strategies for heart failure.

Autophagy mediates hepatic GRK2 degradation to facilitate glucagon-induced metabolic adaptation to fasting

The liver plays a key role during fasting to maintain energy homeostasis and euglycemia via metabolic processes mainly orchestrated by the insulin/glucagon ratio. We report here that fasting or calorie restriction protocols in C57BL6 mice promote a marked decrease in the hepatic protein levels of G protein-coupled receptor kinase 2 (GRK2), an important negative modulator of both G protein-coupled receptors (GPCRs) and insulin signaling. Such downregulation of GRK2 levels is liver-specific and can be rapidly reversed by refeeding. We find that autophagy, and not the proteasome, represents the main mechanism implicated in fasting-induced GRK2 degradation in the liver in vivo. Reducing GRK2 levels in murine primary hepatocytes facilitates glucagon-induced glucose production and enhances the expression of the key gluconeogenic enzyme Pck1. Conversely, preventing full downregulation of hepatic GRK2 during fasting using adenovirus-driven overexpression of this kinase in the liver leads to glycogen accumulation, decreased glycemia, and hampered glucagon-induced gluconeogenesis, thus preventing a proper and complete adaptation to nutrient deprivation. Overall, our data indicate that physiological fasting-induced downregulation of GRK2 in the liver is key for allowing complete glucagon-mediated responses and efficient metabolic adaptation to fasting in vivo.

Beta-blockers: Historical Perspective and Mechanisms of Action

Beta-blockers are widely used molecules that are able to antagonize β-adrenergic receptors (ARs), which belong to the G protein-coupled receptor family and receive their stimulus from endogenous catecholamines. Upon β-AR stimulation, numerous intracellular cascades are activated, ultimately leading to cardiac contraction or vascular dilation, depending on the relevant subtype and their location. Three subtypes have been described that are differentially expressed in the body (β₁-, β₂- and β₃-ARs), β₁ being the most abundant subtype in the heart. Since their discovery, β-ARs have become an important target to fight cardiovascular disease. In fact, since their discovery by James Black in the late 1950s, β-blockers have revolutionized the field of cardiovascular therapies. To date, 3 generations of drugs have been released: nonselective β-blockers, cardioselective β-blockers (selective β₁-antagonists), and a third generation of these drugs able to block β₁ together with extra vasodilation activity (also called vasodilating β-blockers) either by blocking α₁- or by activating β₃-AR. More than 50 years after propranolol was introduced to the market due to its ability to reduce heart rate and consequently myocardial oxygen demand in the event of an angina attack, β-blockers are still widely used in clinics.

Soluble Receptor for Advanced Glycation End Products: A Protective Molecule against Intramyocardial Lipid Accumulation in Obese Zucker Rats?

Most of the obesity-related complications are due to ectopic fat accumulation. Recently, the activation of the cell-surface receptor for advanced glycation end products (RAGE) has been associated with lipid accumulation in different organs. Nevertheless, the role of RAGE and sRAGE, the soluble form that prevents ligands to activate RAGE, in intramyocardial lipid accumulation is presently unknown. To this aim, we analyzed whether, in obesity, intramyocardial lipid accumulation and lipid metabolism-related transcriptome are related to RAGE and sRAGE. Heart and serum samples were collected from 10 lean (L) and 10 obese (OB) Zucker rats. Oil red staining was used to detect lipids on frozen heart sections. The lipid metabolism-related transcriptome (84 genes) was analyzed by a specific PCR array. Heart RAGE expression was explored by real-time RT-PCR and Western blot analyses. Serum levels of sRAGE (total and endogenous secretory form (esRAGE)) were quantified by ELISA. Genes promoting fatty acid transport, activation, and oxidation in mitochondria/peroxisomes were upregulated in OB hearts. Intramyocardial lipid content did not differ between OB and L rats, as well as RAGE expression. A slight increase in epicardial adipose tissue was observed in OB hearts. Total sRAGE and esRAGE concentrations were significantly higher in OB rats. sRAGE may protect against obesity-induced intramyocardial lipid accumulation by preventing RAGE hyperexpression, therefore allowing lipids to be metabolized. EAT also played a protective role by working as a buffering system that protects the myocardium against exposure to excessively high levels of fatty acids. These observations reinforce the potential role of RAGE pathway as an interesting therapeutic target for obesity-related complications, at least at the cardiovascular level.

G Protein-Coupled Receptor Kinase 2 (GRK2) as a Potential Therapeutic Target in Cardiovascular and Metabolic Diseases

G protein-coupled receptor kinase 2 (GRK2) is a central signaling node involved in the modulation of many G protein-coupled receptors (GPCRs) and also displaying regulatory functions in other cell signaling routes. GRK2 levels and activity have been reported to be enhanced in patients or in preclinical models of several relevant pathological situations, such as heart failure, cardiac hypertrophy, hypertension, obesity and insulin resistance conditions, or non-alcoholic fatty liver disease (NAFLD), and to contribute to disease progression by a variety of mechanisms related to its multifunctional roles. Therefore, targeting GRK2 by different strategies emerges as a potentially relevant approach to treat cardiovascular disease, obesity, type 2 diabetes, or NAFLD, pathological conditions which are frequently interconnected and present as co-morbidities.

The Impact of Cardiac Lipotoxicity on Cardiac Function and Mirnas Signature in Obese and Non-Obese Rats with Myocardial Infarction

Cardiac lipotoxicity is involved in the cardiac functional consequences associated with obesity. Therefore, the aim of this study was to explore whether changes in the mitochondrial lipid cardiac profile could reflect differences in cardiac function and structure in obese and non-obese rats with myocardial infarction (MI). Whether these changes can also be reflected in a specific plasma miRNA signature as markers of cardiac damage was also evaluated. Rats were fed with either standard (3.5% fat) or high fat diet (35% fat) for 6 weeks before the induction of MI and sacrificed 4 weeks later. MI showed cardiac lipotoxicity independently of the presence of obesity, although obese and non-obese rats did not present the same cardiac lipid profile at mitochondrial level. Several cardiac lipid species in mitochondria, including cardiolipins and triglycerides, were associated with myocardial fibrosis, with mitochondrial triglyceride levels being independently associated with it; this supports that lipotoxicity can affect cardiac function. MI down-regulated plasma levels of miRNA 15b-5p and 194-5p in obese and non-obese animals, which were associated with cardiac function, mitochondrial lipids and myocardial fibrosis, with miRNA 15b-5p levels being independently associated with cardiac fibrosis. This could support that lipotoxicity could affect heart function by modulating plasma miRNAs.

Restricting mitochondrial GRK2 post-ischemia confers cardioprotection by reducing myocyte death and maintaining glucose oxidation

Increased abundance of GRK2 [G protein-coupled receptor (GPCR) kinase 2] is associated with poor cardiac function in heart failure patients. In animal models, GRK2 contributes to the pathogenesis of heart failure after ischemia-reperfusion (IR) injury. In addition to its role in down-regulating activated GPCRs, GRK2 also localizes to mitochondria both basally and post-IR injury, where it regulates cellular metabolism. We previously showed that phosphorylation of GRK2 at Ser⁶⁷⁰ is essential for the translocation of GRK2 to the mitochondria of cardiomyocytes post-IR injury in vitro and that this localization promotes cell death. Here, we showed that mice with a S670A knock-in mutation in endogenous GRK2 showed reduced cardiomyocyte death and better cardiac function post-IR injury. Cultured GRK2-S670A knock-in cardiomyocytes subjected to IR in vitro showed enhanced glucose-mediated mitochondrial respiratory function that was partially due to maintenance of pyruvate dehydrogenase activity and improved glucose oxidation. Thus, we propose that mitochondrial GRK2 plays a detrimental role in cardiac glucose oxidation post-injury.

Involvement of G protein-coupled receptor kinase 2 (GRK2) in the development of non-alcoholic steatosis and steatohepatitis in mice and humans

Insulin resistance (IR) and obesity are important risk factors for non-alcoholic fatty liver disease (NAFLD). G protein-coupled receptor kinase 2 (GRK2) is involved in the development of IR and obesity in vivo. However, its possible contribution to NAFLD and/or non-alcoholic steatohepatitis (NASH) independently of its role on IR or fat mass accretion has not been explored. Here, we used wild-type (WT) or GRK2 hemizygous (GRK2±) mice fed a high-fat diet (HFD) or a methionine and choline-deficient diet (MCD) as a model of NASH independent of adiposity and IR. GRK2± mice were protected from HFD-induced NAFLD. Moreover, MCD feeding caused an increased in triglyceride content and liver-to-body weight ratio in WT mice, features that were attenuated in GRK2± mice. According to their NAFLD activity score, MCD-fed GRK2± mice were diagnosed with simple steatosis and not overt NASH. They also showed reduced expression of lipogenic and lipid-uptake markers and less signs of inflammation in the liver. GRK2± mice preserved hepatic protective mechanisms as enhanced autophagy and mitochondrial fusion and biogenesis, together with reduced endoplasmic reticulum stress. GRK2 protein was increased in MCD-fed WT but not in GRK2± mice, and enhanced GRK2 expression potentiated palmitic acid-triggered lipid accumulation in human hepatocytes directly relating GRK2 levels to steatosis. GRK2 protein and mRNA levels were increased in human liver biopsies from simple steatosis or NASH patients in two different human cohorts. Our results describe a functional relationship between GRK2 levels and hepatic lipid accumulation and implicate GRK2 in the establishment and/or development of NASH.

Potential mechanisms responsible for cardioprotective effects of sodium-glucose co-transporter 2 inhibitors

Diabetes mellitus currently affects over 350 million patients worldwide and is associated with many deaths from cardiovascular complications. Sodium-glucose co-transporter 2 (SGLT-2) inhibitors are a novel class of antidiabetic drugs with cardiovascular benefits beyond other antidiabetic drugs. In the EMPA-REG OUTCOME trial, empagliflozin significantly decreases the mortality rate from cardiovascular causes [38% relative risk reduction (RRR)], the mortality rate from all-causes (32% RRR) and the rate of heart failure hospitalization (35% RRR) in diabetic patients with established cardiovascular diseases. The possible mechanisms of SGLT-2 inhibitors are proposed to be systemic effects by hemodynamic and metabolic actions. However, the direct mechanisms are not fully understood. In this review, reports concerning the effects of SGLT-2 inhibitors in models of diabetic cardiomyopathy, heart failure and myocardial ischemia from in vitro, in vivo as well as clinical reports are comprehensively summarized and discussed. By current evidences, it may be concluded that the direct effects of SGLT-2 inhibitors are potentially mediated through their ability to reduce cardiac inflammation, oxidative stress, apoptosis, mitochondrial dysfunction and ionic dyshomeostasis.

Biochemical and Ultrastructural Cardiac Changes Induced by High-Fat Diet in Female and Male Prepubertal Rabbits

Early weight gain induced by high-fat diet has been identified as a predictor for cardiac disease, one of the most serious public health problems. Our goal is to study the influence of a HFD on biochemical, oxidant stress parameters, and the cardiac ultrastructure in both male and female prepubertal models. Experiments were carried on 24 prepubertal New Zealand white rabbits, randomly assigned to male and female control (MC and FC, resp.) or HFD (MHFD and FHFD, resp.) groups (n = 6) for 3 months. Body and heart weights and some biochemical and oxidative stress parameters such as lipids, calcium, CKMB, MDA, uric acid, ascorbic acid, and AOA are evaluated in plasma and the left ventricle. Under HFD effect, plasma parameters, such as lipids (TL, PL, and LDL-C), MDA, and CK-MB, increase more significantly in male than in female groups, when AA decreases. Some cardiac parameters such as TG and UA increase, when AA and AOA decrease; these variations are more significant in FHFD. In both male and female rabbits, HFD caused changes in heart ultrastructure, junctional complexes, mitochondria size and form, and so on. Early HFD feeding induced overweight, oxidative stress, and metabolic alterations in plasma and the heart of prepubertal rabbits, whereas lipotoxicity has especially a negative impact on male plasma but affects more the female heart ultrastructure.

Inhibition of galectin-3 ameliorates the consequences of cardiac lipotoxicity in a rat model of diet-induced obesity

Obesity is accompanied by metabolic alterations characterized by insulin resistance and cardiac lipotoxicity. Galectin-3 (Gal-3) induces cardiac inflammation and fibrosis in the context of obesity; however, its role in the metabolic consequences of obesity is not totally established. We have investigated the potential role of Gal-3 in the cardiac metabolic disturbances associated with obesity. In addition, we have explored whether this participation is, at least partially, acting on mitochondrial damage. Gal-3 inhibition in rats that were fed a high-fat diet (HFD) for 6 weeks with modified citrus pectin (MCP; 100 mg/kg/day) attenuated the increase in cardiac levels of total triglyceride (TG). MCP treatment also prevented the increase in cardiac protein levels of carnitine palmitoyl transferase IA, mitofusin 1, and mitochondrial complexes I and II, reactive oxygen species accumulation and decrease in those of complex V but did not affect the reduction in ¹⁸F-fluorodeoxyglucose uptake observed in HFD rats. The exposure of cardiac myoblasts (H9c2) to palmitic acid increased the rate of respiration, mainly due to an increase in the proton leak, glycolysis, oxidative stress, β-oxidation and reduced mitochondrial membrane potential. Inhibition of Gal-3 activity was unable to affect these changes. Our findings indicate that Gal-3 inhibition attenuates some of the consequences of cardiac lipotoxicity induced by a HFD since it reduced TG and lysophosphatidyl choline (LPC) levels. These reductions were accompanied by amelioration of the mitochondrial damage observed in HFD rats, although no improvement was observed regarding insulin resistance. These findings increase the interest for Gal-3 as a potential new target for therapeutic intervention to prevent obesity-associated cardiac lipotoxicity and subsequent mitochondrial dysfunction.

Summary: Inhibition of Gal-3 activity reduced the excessive cardiac accumulation of lipids in rats fed a high fat diet. This was accompanied by the amelioration of mitochondria damage observed in obese rats.

Cardioprotection of dapagliflozin and vildagliptin in rats with cardiac ischemia-reperfusion injury

Sodium-glucose cotransporter 2 inhibitor (SGLT2-i) effects on cardiac ischemia/reperfusion (I/R) injury are unclear. Unlike SGLT2-i, dipeptidyl peptidase 4 inhibitors (DPP4-i) have shown effective cardioprotection in cardiac I/R injury. We aimed to investigate whether SGLT2-i reduces myocardial dysfunction and myocardial injury to a greater extent than DPP4-i in obese insulin-resistant rats with/without cardiac I/R injury. The high-fat (HF) diet-induced obese insulin-resistant rats were divided into 4 groups and received the following treatments for 28 days: vehicle (HFV); vildagliptin at a dosage of 3 mg/kg/day (HFVil); dapagliflozin at a dosage of 1 mg/kg/day (HFDa) and combination drugs (HFDaVil). At the end, I/R injury was induced by a 30-min left anterior descending coronary occlusion and 120-min reperfusion. Dapagliflozin showed a greater efficacy than vildagliptin in improving the metabolic impairments, low frequency/high frequency (LF/HF) ratio, systolic blood pressure and left ventricular (LV) function in comparison to HFV rats. In cardiac I/R injury, dapagliflozin had a greater efficacy than vildagiptin in decreasing mitochondrial DRP1, cleaved caspase 3, LV dysfunction and infarct size in comparison to HFV rats. However, the combined therapy showed the greatest efficacy in attenuating LV dysfunction, mitochondrial DRP1 and infarct size in comparison to HFV rats. In conclusion, dapagliflozin has a more pronounced effect than vildagliptin in obese insulin-resistant rats for the improvement of LV function. In rats with cardiac I/R injury, although dapagliflozin had a greater efficacy on cardioprotection than vildagliptin, the combined therapy exerted the highest cardioprotective effects potentially by reducing mitochondrial fission.

Myocyte membrane and microdomain modifications in diabetes: determinants of ischemic tolerance and cardioprotection

Cardiovascular disease, predominantly ischemic heart disease (IHD), is the leading cause of death in diabetes mellitus (DM). In addition to eliciting cardiomyopathy, DM induces a ‘wicked triumvirate’: (i) increasing the risk and incidence of IHD and myocardial ischemia; (ii) decreasing myocardial tolerance to ischemia–reperfusion (I–R) injury; and (iii) inhibiting or eliminating responses to cardioprotective stimuli. Changes in ischemic tolerance and cardioprotective signaling may contribute to substantially higher mortality and morbidity following ischemic insult in DM patients. Among the diverse mechanisms implicated in diabetic impairment of ischemic tolerance and cardioprotection, changes in sarcolemmal makeup may play an overarching role and are considered in detail in the current review. Observations predominantly in animal models reveal DM-dependent changes in membrane lipid composition (cholesterol and triglyceride accumulation, fatty acid saturation vs. reduced desaturation, phospholipid remodeling) that contribute to modulation of caveolar domains, gap junctions and T-tubules. These modifications influence sarcolemmal biophysical properties, receptor and phospholipid signaling, ion channel and transporter functions, contributing to contractile and electrophysiological dysfunction, cardiomyopathy, ischemic intolerance and suppression of protective signaling. A better understanding of these sarcolemmal abnormalities in types I and II DM (T1DM, T2DM) can inform approaches to limiting cardiomyopathy, associated IHD and their consequences. Key knowledge gaps include details of sarcolemmal changes in models of T2DM, temporal patterns of lipid, microdomain and T-tubule changes during disease development, and the precise impacts of these diverse sarcolemmal modifications. Importantly, exercise, dietary, pharmacological and gene approaches have potential for improving sarcolemmal makeup, and thus myocyte function and stress-resistance in this ubiquitous metabolic disorder.

GRK2 as a therapeutic target for heart failure

INTRODUCTION

G protein-coupled receptor (GPCR) kinase-2 (GRK2) is a regulator of GPCRs, in particular β-adrenergic receptors (ARs), and as demonstrated by decades of investigation, it has a pivotal role in the development and progression of cardiovascular disease, like heart failure (HF). Indeed elevated levels and activity of this kinase are able to promote the dysfunction of both cardiac and adrenal α- and β-ARs and to dysregulate other protective signaling pathway, such as sphingosine 1-phospate and insulin. Moreover, recent discoveries suggest that GRK2 can signal independently from GPCRs, in a 'non-canonical' manner, via interaction with non-GPCR molecule or via its mitochondrial localization. Areas covered: Based on this premise, GRK2 inhibition or its genetic deletion has been tested in several disparate animal models of cardiovascular disease, showing to protect the heart from adverse remodeling and dysfunction. Expert opinion: HF is one of the leading cause of death worldwide with enormous health care costs. For this reason, the identification of new therapeutic targets like GRK2 and strategies such as its inhibition represents a new hope in the fight against HF development and progression. Herein, we will update the readers about the 'state-of-art' of GRK2 inhibition as a potent therapeutic strategy in HF.

Insulin and β Adrenergic Receptor Signaling: Crosstalk in Heart

Recent advances show that insulin may affect β adrenergic receptor (βAR) signaling in the heart to modulate cardiac function in clinically relevant states, such as diabetes mellitus (DM) and heart failure (HF). Conversely, activation of βAR regulates cardiac glucose uptake and promotes insulin resistance (IR) in HF. Here, we discuss the recent characterization of the interaction between the cardiac insulin receptor (InsR) and βAR in the myocardium, in which insulin stimulation crosstalks with cardiac βAR via InsR substrate (IRS)-dependent and G-protein receptor kinase 2 (GRK2)-mediated phosphorylation of β₂AR. The insulin-induced phosphorylation promotes β₂AR coupling to G_i and expression of phosphodiesterase 4D, which both inhibit cardiac adrenergic signaling and compromise cardiac contractile function. These recent developments could support new approaches for the effective prevention or treatment of obesity- or DM-related HF.

Insulin receptor substrate signaling controls cardiac energy metabolism and heart failure

The heart is an insulin-dependent and energy-consuming organ in which insulin and nutritional signaling integrates to the regulation of cardiac metabolism, growth and survival. Heart failure is highly associated with insulin resistance, and heart failure patients suffer from the cardiac energy deficiency and structural and functional dysfunction. Chronic pathological conditions, such as obesity and type 2 diabetes mellitus, involve various mechanisms in promoting heart failure by remodeling metabolic pathways, modulating cardiac energetics and impairing cardiac contractility. Recent studies demonstrated that insulin receptor substrates 1 and 2 (IRS-1,-2) are major mediators of both insulin and insulin-like growth factor-1 (IGF-1) signaling responsible for myocardial energetics, structure, function and organismal survival. Importantly, the insulin receptor substrates (IRS) play an important role in the activation of the phosphatidylinositide-3-dependent kinase (PI-3K) that controls Akt and Foxo1 signaling cascade, regulating the mitochondrial function, cardiac energy metabolism and the renin-angiotensin system. Dysregulation of this branch in signaling cascades by insulin resistance in the heart through the endocrine system promotes heart failure, providing a novel mechanism for diabetic cardiomyopathy. Therefore, targeting this branch of IRS→PI-3K→Foxo1 signaling cascade and associated pathways may provide a fundamental strategy for the therapeutic and nutritional development in control of metabolic and cardiovascular diseases. In this review, we focus on insulin signaling and resistance in the heart and the role energetics play in cardiac metabolism, structure and function.

Targeting GPCR-Gβγ-GRK2 signaling as a novel strategy for treating cardiorenal pathologies

The pathologic crosstalk between the heart and kidney is known as cardiorenal syndrome (CRS). While the specific mechanisms underlying this crosstalk remain poorly understood, CRS is associated with exacerbated dysfunction of either or both organs and reduced survival. Maladaptive fibrotic remodeling is a key component of both heart and kidney failure pathogenesis and progression. G-protein coupled receptor (GPCR) signaling is a crucial regulator of cardiovascular and renal function. Chronic/pathologic GPCR signaling elicits the interaction of the G-protein Gβγ subunit with GPCR kinase 2 (GRK2), targeting the receptor for internalization, scaffolding to pathologic signals, and receptor degradation. Targeting this pathologic Gβγ-GRK2 interaction has been suggested as a possible strategy for the treatment of HF. In the current review, we discuss recent updates in understanding the role of GPCR-Gβγ-GRK2 signaling as a crucial mediator of maladaptive organ remodeling detected in HF and kidney dysfunction, with specific attention to small molecule-mediated inhibition of pathologic Gβγ-GRK2 interactions. Further, we explore the potential of GPCR-Gβγ-GRK2 signaling as a possible therapeutic target for cardiorenal pathologies.