Protective effects of desacyl ghrelin on diabetic cardiomyopathy

Ghrelin inhibits myocardial pyroptosis in diabetic cardiomyopathy by regulating ERS and NLRP3 inflammasome crosstalk through the PI3K/AKT pathway

AIMS

Endoplasmic reticulum stress(ERS) can induce inflammation mediated by NLRP3 inflammatory bodies and link inflammation with oxidative stress in myocardial tissue. Ghrelin is an endogenous growth hormone-releasing peptide that has been proven to have multiple effects, such as regulating energy metabolism and inhibiting inflammation. However, the role of ghrelin in myocardial injury in diabetic rats and the mechanism have not been reported.

RESULTS

We found that ghrelin could improve endoplasmic reticulum stress and inflammatory pyroptosis in the myocardial tissue of diabetic rats and reduce ERS and NLRP3 inflammasome crosstalk in H9C2 cardiomyocytes. Interestingly, ghrelin could activate the PI3K/AKT signalling pathway, playing a role in inhibiting endoplasmic reticulum stress and reducing the expression of pyroptosis-related proteins. However, these protective effects could be largely eliminated by LY294002.

CONCLUSIONS

In summary, we demonstrated that ghrelin inhibited myocardial pyroptosis in diabetic cardiomyopathy by regulating ERS and NLRP3 inflammasome crosstalk through the PI3K/AKT pathway. Our results provide new insights into the mechanism of diabetic myocardial injury induced by high glucose and high palmitic acid and ghrelin-mediated anti-inflammatory protection and provide potential therapeutic targets and strategies for diabetic cardiomyopathy.

N-Terminal Pro-Brain Natriuretic Peptide Correlates with Ghrelin and Acyl-Ghrelin in Pre-Dialysis Chronic Kidney Disease

Pro-B amino-terminal natriuretic peptide (NT-proBNP) is a diagnostic marker for heart failure (HF), a severe complication of chronic kidney disease (CKD). However, its significance in CKD is not clear, as other factors, such as renal function, may also have an impact. Recent studies have shown that ghrelin treatment is effective in HF in the general population, but the impact of ghrelin on cardiac function in CKD patients is still unknown. Our study aimed to investigate the factors associated with NT-proBNP in pre-dialysis CKD patients and to evaluate the correlation between NT-proBNP and ghrelin and acyl-ghrelin, molecules determined using ELISA methods. In a cross-sectional observational study, we included 80 patients with pre-dialysis CKD, with a mean age of 68 years and 50% men. The median values for NT-proBNP were 351.8 pg/mL, for acyl ghrelin 16.39 pg/mL, and for ghrelin 543.32 pg/mL. NT-proBNP was correlated with ghrelin (p = 0.034, r = 0.24), acyl-ghrelin (p = 0.033, r = -0.24), estimated glomerular filtration rate (p = 0.027, r = -0.25), serum urea (p = 0.006, r = 0.31), and ferritin (p = 0.041, r = 0.28). In multivariate analysis, ghrelin (p = 0.040) and blood urea (p = 0.040) remained significant predictors for NT-proBNP levels. NT-proBNP was a significant predictor for acyl-ghrelin (p = 0.036). In conclusion, in pre-dialysis CKD patients, a high value of NT-proBNP was associated with a high value of total ghrelin and a low value of acyl-ghrelin.

Desacyl-ghrelin, not just an inactive form of ghrelin?-A review of current knowledge on the biological actions of desacyl-ghrelin

Desacyl-ghrelin is a form of ghrelin which lacks acyl-modification of the third serine residue of ghrelin. Originally, desacyl-ghrelin was considered to be just an inactive form of ghrelin. More recently, however, it has been suggested to have various biological activities, including control of food intake, growth hormone, glucose metabolism, and gastric movement, and is involved in cell survival. In this review, we summarize the current knowledge of the biological actions of desacyl-ghrelin and the proposed mechanisms by which it exerts the effects.

Gut Molecules in Cardiometabolic Diseases: The Mechanisms behind the Story

Atherosclerotic cardiovascular disease is the most common cause of morbidity and mortality worldwide. Diabetes mellitus increases cardiovascular risk. Heart failure and atrial fibrillation are associated comorbidities that share the main cardiovascular risk factors. The use of incretin-based therapies promoted the idea that activation of alternative signaling pathways is effective in reducing the risk of atherosclerosis and heart failure. Gut-derived molecules, gut hormones, and gut microbiota metabolites showed both positive and detrimental effects in cardiometabolic disorders. Although inflammation plays a key role in cardiometabolic disorders, additional intracellular signaling pathways are involved and could explain the observed effects. Revealing the involved molecular mechanisms could provide novel therapeutic strategies and a better understanding of the relationship between the gut, metabolic syndrome, and cardiovascular diseases.

Effect of Ghrelin on the Cardiovascular System

Simple Summary

Ghrelin is an octanoylated peptide that was initially isolated from rat and human stomachs in the process of searching for an endogenous ligand to the orphan growth hormone secretagogue receptor (GHS-R), a G-protein-coupled receptor. Exogenous or endogenous ghrelin secreted from the stomach binds to GHS-R on gastric vagal nerve terminals, and the signals are transmitted to the central nervous system via the vagal afferent nerve to facilitate growth hormone (GH) secretion, feeding, sympathetic inhibition, parasympathetic activation, and anabolic effects. Ghrelin also binds directly to the pituitary GHS-R and stimulates GH secretion. Ghrelin has beneficial effects on the cardiovascular system, including cardioprotective effects such as anti-heart failure, anti-arrhythmic, and anti-inflammatory actions, and it enhances vascular activity via GHS-R-dependent stimulation of GH/IGF-1 (insulin-like growth factor-1) and modulation of the autonomic nervous system. The anti-heart failure effects of ghrelin could be useful as a new therapeutic strategy for chronic heart failure.

Abstract

Ghrelin, an n-octanoyl-modified 28-amino-acid-peptide, was first discovered in the human and rat stomach as an endogenous ligand for the growth hormone secretagogue receptor (GHS-R). Ghrelin-GHS-R1a signaling regulates feeding behavior and energy balance, promotes vascular activity and angiogenesis, improves arrhythmia and heart failure, and also protects against cardiovascular disease by suppressing cardiac remodeling after myocardial infarction. Ghrelin’s cardiovascular protective effects are mediated by the suppression of sympathetic activity; activation of parasympathetic activity; alleviation of vascular endothelial dysfunction; and regulation of inflammation, apoptosis, and autophagy. The physiological functions of ghrelin should be clarified to determine its pharmacological potential as a cardiovascular medication.

Acylated ghrelin protects against doxorubicin-induced nephropathy by activating silent information regulator 1

This study investigated the nephroprotective role of acylated ghrelin (AG) against DOX-induced nephropathy and examined whether the protection involves silent information regulator 1 (SIRT1). Rats were divided into control, control + AG, DOX, DOX + AG, DOX + AG + [D-Lys3]-GHRP-6 (a ghrelin receptor antagonist), and DOX + AG + EX-527 (a sirt1 inhibitor). DOX was given over the first 2 weeks. AG (10 ng/kg) and both inhibitors were given as 3 doses/wk for 5 weeks. AG improved the structure and the function of the kidneys; down-regulated the renal expression of TGF-β1, collagen 1A1 and α-SMA; and inhibited the renal collagen deposition in the kidneys of DOX-treated rats. Concomitantly, it reduced the renal levels of ROS, MDA, TNF-α, and IL-6 and protein levels of cytochrome-c, TGF-β1, Smad3 and α-SMA in these rats. In both the control and DOX-treated rats, AG significantly increased the renal levels of SOD and GSH, decreased the expression of cleaved caspase-3 and Bax, increased the total levels and the nuclear activity of SIRT1 and reduced the deacetylation of p53, NF-κB and FOXO-31. All the effects were abolished by the concurrent administration of EX-527 and [D-Lys3]-GHRP-6. In conclusion, AG prevents DOX-induced nephropathy in SIRT1 and GSHRa1-dependent mechanism.

Ghrelin inhibited pressure overload-induced cardiac hypertrophy by promoting autophagy via CaMKK/AMPK signaling pathway

Ghrelin, a novel gut hormone, has been shown to exert protective effects on cardiac dysfunction and remodeling. However, the underlying mechanisms of its protective effects remain unclear. Here, we investigated the effects of ghrelin on cardiac hypertrophy and explored the mechanisms involved. Ghrelin (30 μg.kg^-1. day^-1) was systemically administered to rats with cardiac hypertrophy induced by abdominal aortic constriction (AAC) by a mini-osmotic pump the next day after surgery continuously for 4 weeks. The AAC treated rats without ghrelin infusion showed decreased ghrelin content and expression of its receptors in the hearts. Exogenous ghrelin greatly attenuated cardiac hypertrophy as shown by heart weight to tibial length (HW/TL), hemodynamics, echocardiography, histological analyses, and expression of hypertrophic markers induced by AAC. This corresponded with decreased cardiac fibrosis and inflammation in the hearts of AAC rats treated with ghrelin. Moreover, ghrelin significantly increased the myocardial expression of autophagy markers, which was further confirmed in cultured cardiomyocytes. Concurrently, cardiomyocyte apoptosis in vivo and in vitro was ameliorated by ghrelin, which was reversed by inhibition of autophagy. The enhancement of autophagy and inhibition of apoptosis by ghrelin were eliminated on pretreatment with compound C, an AMP-activated protein kinase (AMPK) inhibitor. Furthermore, inhibition of Ca²⁺/Calmodulin-dependent protein kinase kinase (CaMKK), an upstream kinase of AMPK, made ghrelin fail to activate AMPK and simultaneously reversed ghrelin's promotion of autophagy. In conclusion, ghrelin could exert its cardioprotective effects on cardiac hypertrophy by promoting autophagy, possibly via CaMKK/AMPK signaling pathway.

Regulatory effects of ghrelin on endoplasmic reticulum stress, oxidative stress, and autophagy: Therapeutic potential

Ghrelin is a regulatory peptide that is the endogenous ligand of the growth hormone secretagogue 1a (GHS-R1a) which belongs to the G protein-coupled receptor family. Ghrelin and GHS-R1a are widely expressed in the central and peripheral tissues and play therapeutic potential roles in the cytoprotection of many internal organs. Endoplasmic reticulum stress (ERS), oxidative stress, and autophagy dysfunction, which are involved in various diseases. In recent years, accumulating evidence has suggested that ghrelin exerts protective effects by regulating ERS, oxidative stress, and autophagy in diverse diseases. This review article summarizes information about the roles of the ghrelin system on ERS, oxidative stress, and autophagy in multiple diseases. It is suggested that ghrelin positively affects the treatment of diseases and may be considered as a therapeutic drug in many illnesses.

Role of AMP-activated protein kinase on cardio-metabolic abnormalities in the development of diabetic cardiomyopathy: A molecular landscape

Cardiovascular complications associated with diabetes mellitus remains a leading cause of morbidity and mortality across the world. Diabetic cardiomyopathy is a descriptive pathology that in absence of co-morbidities such as hypertension, dyslipidemia initially characterized by cardiac stiffness, myocardial fibrosis, ventricular hypertrophy, and remodeling. These abnormalities further contribute to diastolic dysfunctions followed by systolic dysfunctions and eventually results in clinical heart failure (HF). The clinical outcomes associated with HF are considerably worse in patients with diabetes. The complexity of the pathogenesis and clinical features of diabetic cardiomyopathy raises serious questions in developing a therapeutic strategy to manage cardio-metabolic abnormalities. Despite extensive research in the past decade the compelling approaches to manage and treat diabetic cardiomyopathy are limited. AMP-Activated Protein Kinase (AMPK), a serine-threonine kinase, often referred to as cellular "metabolic master switch". During the development and progression of diabetic cardiomyopathy, a plethora of evidence demonstrate the beneficial role of AMPK on cardio-metabolic abnormalities including altered substrate utilization, impaired cardiac insulin metabolic signaling, mitochondrial dysfunction and oxidative stress, myocardial inflammation, increased accumulation of advanced glycation end-products, impaired cardiac calcium handling, maladaptive activation of the renin-angiotensin-aldosterone system, endoplasmic reticulum stress, myocardial fibrosis, ventricular hypertrophy, cardiac apoptosis, and impaired autophagy. Therefore, in this review, we have summarized the findings from pre-clinical and clinical studies and provided a collective overview of the pathophysiological mechanism and the regulatory role of AMPK on cardio-metabolic abnormalities during the development of diabetic cardiomyopathy.

Regional Differences in the Ghrelin-Growth Hormone Secretagogue Receptor Signalling System in Human Heart Disease

Background

The hormone ghrelin and its receptor, the growth hormone secretagogue receptor (GHSR) are expressed in myocardium. GHSR binding activates signalling pathways coupled to cardiomyocyte survival and contractility. These properties have made the ghrelin-GHSR axis a candidate for a biomarker of cardiac function. The dynamics of ghrelin-GHSR are altered significantly in late stages of heart failure (HF) and cardiomyopathy, when left ventricular (LV) function is failing. We examined the relationship of GHSR with ghrelin in cardiac tissue from patients with valvular disease with no detectable changes in LV function.

Methods

Biopsy samples from the left ventricle and left atrium were obtained from 25 patients with valvular disease (of whom 13 also had coronary artery disease) and preserved LV ejection fraction, and compared to control samples obtained via autopsy. Using quantitative confocal fluorescence microscopy, levels of GHSR were determined using [Dpr³(n-octanoyl),Lys¹⁹(sulfo-Cy5)]ghrelin(1-19), and immunofluorescence determined ghrelin, the heart failure marker natriuretic peptide type-B (BNP), and contractility marker sarcoplasmic reticulum ATPase pump (SERCA2a).

Results

A positive correlation between GHSR and ghrelin was apparent in only diseased tissue. Ghrelin and BNP significantly correlated in the left ventricle and strongly colocalized to the same intracellular compartment in diseased and control tissue. GHSR, ghrelin, and BNP all strongly and significantly correlated with SERCA2a in the left ventricle of diseased tissue only.

Conclusions

Our results suggest that the dynamics of the myocardial ghrelin-GHSR axis is altered in cardiovascular disease in the absence of measurable changes in heart function, and might accompany a regional shift in endocrine programming.

Heal the heart through gut (hormone) ghrelin: a potential player to combat heart failure

Ghrelin, a small peptide hormone (28 aa), secreted mainly by X/A-like cells of gastric mucosa, is also locally produced in cardiomyocytes. Being an orexigenic factor (appetite stimulant), it promotes release of growth hormone (GH) and exerts diverse physiological functions, viz. regulation of energy balance, glucose, and/or fat metabolism for body weight maintenance. Interestingly, administration of exogenous ghrelin significantly improves cardiac functions in CVD patients as well as experimental animal models of heart failure. Ghrelin ameliorates pathophysiological condition of the heart in myocardial infarction, cardiac hypertrophy, fibrosis, cachexia, and ischemia reperfusion injury. This peptide also exerts significant impact at the level of vasculature leading to lowering high blood pressure and reversal of endothelial dysfunction and atherosclerosis. However, the molecular mechanism of actions elucidating the healing effects of ghrelin on the cardiovascular system is still a matter of conjecture. Some experimental data indicate its beneficial effects via complex cellular cross talks between autonomic nervous system and cardiovascular cells, some other suggest more direct receptor-mediated molecular actions via autophagy or ionotropic regulation and interfering with apoptotic and inflammatory pathways of cardiomyocytes and vascular endothelial cells. Here, in this review, we summarise available recent data to encourage more research to find the missing links of unknown ghrelin receptor-mediated pathways as we see ghrelin as a future novel therapy in cardiovascular protection.

Morphological characteristics in diabetic cardiomyopathy associated with autophagy

Diabetic cardiomyopathy, clinically diagnosed as ventricular dysfunction in the absence of coronary atherosclerosis or hypertension in diabetic patients, is a cardiac muscle-specific disease that increases the risk of heart failure and mortality. Its clinical course is characterized initially by diastolic dysfunction, later by systolic dysfunction, and eventually by clinical heart failure from an uncertain mechanism. Light microscopic features such as interstitial fibrosis, inflammation, and cardiomyocyte hypertrophy are observed in diabetic cardiomyopathy, but are common to failing hearts generally and are not specific to diabetic cardiomyopathy. Electron microscopic studies of biopsy samples from diabetic patients with heart failure have revealed that the essential mechanism underlying diabetic cardiomyopathy involves thickening of the capillary basement membrane, accumulation of lipid droplets, and glycogen as well as increased numbers of autophagic vacuoles within cardiomyocytes. Autophagy is a conserved mechanism that contributes to maintaining intracellular homeostasis by degrading long-lived proteins and damaged organelles and is observed more often in cardiomyocytes within failing hearts. Diabetes mellitus (DM) impairs cardiac metabolism and leads to dysregulation of energy substrates that contribute to cardiac autophagy. However, a "snapshot" showing greater numbers of autophagic vacuoles within cardiomyocytes may indicate that autophagy is activated into phagophore formation or is suppressed due to impairment of the lysosomal degradation step. Recent in vivo studies have shed light on the underlying molecular mechanism governing autophagy and its essential meaning in the diabetic heart. Autophagic responses to diabetic cardiomyopathy differ between diabetic types: they are enhanced in type 1 DM, but are suppressed in type 2 DM. This difference provides important insight into the pathophysiology of diabetic cardiomyopathy. Here, we review recent advances in our understanding of the pathophysiology of diabetic cardiomyopathy, paying particular attention to autophagy in the heart, and discuss the therapeutic potential of interventions modulating autophagy in diabetic cardiomyopathy.

The new mechanism of Ghrelin/GHSR-1a on autophagy regulation

Autophagy is associated with several diseases. In recent years, accumulating evidence has suggested that ghrelin pathway exerts a protective effect by regulating autophagy. This review aims to assess the potential role and use of ghrelin as a new treatment for obesity, cardiovascular diseases, nonalcoholic fatty liver disease (NFALD), neurodegenerative diseases, and tissue damage associated with autophagy. Ghrelin reduces the basal expression of autophagy-related genes in obesity-associated type 2 diabetes and ghrelin level changes in obesity, heart failure, and NFALD as well as altered autophagy. Ghrelin and its receptor GHSR-1 activation induce the phosphorylation of ERK1/2 and the induction of PI-3 kinase (PI3 K) and phosphorylation of Akt. In the myocardium and hypothalamic NPY/AgRP neurons, ghrelin increases levels of the intracellular energy sensor AMPK and enhances autophagy, protecting cardiac ischemia and inducing neural stem cells. Nonetheless, ghrelin activates the PI3 K/Akt/Bcl-2 pathway and inhibits the activation of autophagy, such as tissues injured by sepsis or doxorubicin. In conclusion, endogenous ghrelin system could be considered as a new target or treatment for metabolism disorders, cardiac diseases, neurodegenerative diseases, and tissue injuries.

Physiological Effect of Ghrelin on Body Systems

Ghrelin is a relatively novel multifaceted hormone that has been found to exert a plethora of physiological effects. In this review, we found/confirmed that ghrelin has effect on all body systems. It induces appetite; promotes the use of carbohydrates as a source of fuel while sparing fat; inhibits lipid oxidation and promotes lipogenesis; stimulates the gastric acid secretion and motility; improves cardiac performance; decreases blood pressure; and protects the kidneys, heart, and brain. Ghrelin is important for learning, memory, cognition, reward, sleep, taste sensation, olfaction, and sniffing. It has sympatholytic, analgesic, antimicrobial, antifibrotic, and osteogenic effects. Moreover, ghrelin makes the skeletal muscle more excitable and stimulates its regeneration following injury; delays puberty; promotes fetal lung development; decreases thyroid hormone and testosterone; stimulates release of growth hormone, prolactin, glucagon, adrenocorticotropic hormone, cortisol, vasopressin, and oxytocin; inhibits insulin release; and promotes wound healing. Ghrelin protects the body by different mechanisms including inhibition of unwanted inflammation and induction of autophagy. Having a clear understanding of the ghrelin effect in each system has therapeutic implications. Future studies are necessary to elucidate the molecular mechanisms of ghrelin actions as well as its application as a GHSR agonist to treat most common diseases in each system without any paradoxical outcomes on the other systems.

Acylated ghrelin prevents doxorubicin-induced cardiac intrinsic cell death and fibrosis in rats by restoring IL-6/JAK2/STAT3 signaling pathway and inhibition of STAT1

This study investigated if JAK/STAT signaling pathway mediates doxorubicin (DOX)-induced cell death and fibrosis in left ventricles (LVs) of rats and examined if acylated ghrelin affords protection by modulating this pathway. Male rats (120 ± 5 g) were divided into 6 groups (10 rats each) as follows: control; control + AG (10 ng/kg, s.c.); DOX (an accumulative dose 15 mg/kg, i.p.); DOX + AG, DOX + AG + AG490, a JAK2 inhibitor (5 mg/kg, i.p.); and DOX + AG + [D-Lys3]-GHRP-6; an AG receptor antagonist (3.75 mg/kg, i.p.). All treatments were carried out for 35 days. In rats' LVs, DOX significantly impaired the systolic and diastolic functions, enhanced levels of ROS and MDA, reduced levels of GSH and Bcl-2, and increased mRNA and protein levels of collagen I/III and TGF-β and cleaved caspase-3. In addition, although DOX did not affect JAK1 or JAK2 activity, it significantly increased protein levels of IL-6, decreased STAT3 and p-STAT3 (Tyr701&Ser727), and increased STAT1 and p-STAT1 (Tyr701&Ser727) levels, with a concomitant decrease in ERK1/2 activity and an increase in P38 activity. However, without affecting IL-6 and JAK1/2, AG reversed all of the observed alterations with a significant increase in the levels and activities of JAK2. Similar effects of AG were also seen in control rats. Interestingly, all the beneficial effects afforded by AG were abolished by AG490 and AG + [D-Lys3]-GHRP-6. In conclusion, DOX-induced cardiac toxicity involves stimulation of IL-6, P38, and STAT1 signaling levels whereas the protective effect afforded by AG involves the activation of ERK1/2 and JAK2/STAT3 and inhibition of STAT1.

Imatinib mesylate does not counteract ovarian tissue fibrosis in postnatal rat ovary

Chemotherapy may result in ovarian atrophy, a depletion of the primordial follicle pool, diminished ovarian weight, cortical and stromal fibrosis. Imatinib mesylate is an anticancer agent that inhibits competitively several receptor tyrosine kinases (RTKs). RTKs play important roles in cell metabolism, proliferation, and apoptosis. In clinic, imatinib mesylate is also known as an anti-fibrotic medicine. In the present study, the impact of imatinib on the ovarian tissue was investigated by assessing ovarian tissue fibrosis in postnatal rat administered with or without imatinib for three days. Fibrosis in the ovarian tissue was determined by histology (Picrosirius and Masson's trichrome staining) and the protein expression of vimentin and alpha-smooth muscle actin (α-SMA). Furthermore, mRNA expression of Forkhead box transcription factor O1 and O3 (FOXO1 and FOXO3), which are markers of cell proliferation was quantified. A short-term exposure to imatinib showed to increase tissue fibrosis in ovaries. This was observed by Masson's trichrome staining. Exposure to imatinib led also to a down-regulation of vimentin protein expression and up-regulation mRNA expression of FOXO3. This may indicate a role of FOXO3 in ovarian tissue fibrosis in postnatal rat ovaries.

Autophagy in cardiomyopathies

Autophagy (greek auto: self; phagein: eating) is a highly conserved process within eukaryotes that degrades long-lived proteins and organelles within lysosomes. Its accurate and constant operation in basal conditions ensures cellular homeostasis by degrading damaged cellular components and thereby acting not only as a quality control but as well as an energy supplier. An increasing body of evidence indicates a major role of autophagy in the regulation of cardiac homeostasis and function. In this review, we describe the different forms of mammalian autophagy, their regulations and monitoring with a specific emphasis on the heart. Furthermore, we address the role of autophagy in several forms of cardiomyopathy and the options for therapy.

Ghrelin attenuates myocardial fibrosis after acute myocardial infarction via inhibiting endothelial-to mesenchymal transition in rat model

Ghrelin, a peptide hormone produced in the gastrointestinal tract, has recently been found to be associated with the onset of myocardial fibrosis (MF). The exact mechanism, however, remains elusive. This study sought to identify the function and mechanism of ghrelin on MF after acute myocardial infarction (AMI). AMI was established in Spraque-Dawley rats by ligation of the left anterior descending (LAD). Ghrelin or saline was intraperitoneally injected two times per day for 8 weeks after ligation. The weight of heart (mg) and the weight ratio of heart to body (mg/g) as well as the fibrotic area were increased, while serum level of ghrelin was decreased after AMI. Ghrelin significantly ameliorated MF and decreased deposition of collagens in perivascular fibrosis area. In addition, ghrelin inhibited Endothelial-to-mesenchymal transition (EndMT), a crucial process for MF, in perivascular fibrosis area and TGF-β1-induced human coronary artery endothelial cells (HCAECs). Mechanistically, ghrelin persistently decreased the phosphorylation of Smad2/3 and enhanced the expression of Smad7 and p-AMPK in vivo and in vitro. After the abolition of Smad7, GHSR-1a and AMPK pathway, the effect of ghrelin on EndMT was significantly inhibited. In conclusion, these results presented a novel finding that ghrelin attenuated MF after AMI via regulation EndMT in a GHSR-1a/AMPK/Smad7- dependent manner.

Effect of the peptides Relaxin, Neuregulin, Ghrelin and Glucagon-like peptide-1, on cardiomyocyte factors involved in the molecular mechanisms leading to diastolic dysfunction and/or heart failure with preserved ejection fraction

Heart failure with preserved ejection fraction (HFpEF) represents an important cardiac condition because of its increasing prevalence, resistance to treatment and high associated morbidity and mortality. Two of the major mechanisms responsible for HFpEF are impaired cardiomyocyte sarcoplasmic reticulum (SR) Ca²⁺ ATPase (SERCA2a), which is responsible for calcium reuptake into the SR, and cardiac fibroblasts/myofibroblasts that produce collagen or myocardial fibrosis. Phospholamban (PLB), in the SR and endoplasmic reticulum, is the primary regulator of SERCA2a in the heart and acts as a reversible inhibitor of SERCA2a. Glucagon-like peptide-1, a 30 amino acid peptide, improves diastolic function through increasing SERCA2a expression and activity as well as by decreasing phosphorylation of Ryanodine receptors. It also enhances collagen production through enhanced procollagen IalphaI/IIIalphaI, connective tissue growth factor, fibronectin, TGF-β3 as well as Interleukin -10, -1beta, and -6 gene expression. Relaxin-2, a two chain, 53 amino acid peptide, increases Ser16- and Thr17-phosphorylation levels of PLB, thereby relieving SERCA2a of its inhibition. H3 Relaxin inhibits TGF-β1-stimulated collagen deposition through H3 relaxin-induced increases in pSmad2. Neuregulin-1, an epidermal growth factor, induces nitric oxide and PI-3 kinase activation that enhance SERCA2 activity. Neuregulin-1 was associated with less myocardial macrophage infiltration and cytokine expression reducing collagen deposition. Ghrelin, a 28 amino acid peptide, improves SERCA2a function by inducing PLB phosphorylation. Ghrelin also reduces cardiac fibrosis. In summary, Glucagon-like peptide-1, Relaxin-2, Neuregulin-1, and Ghrelin each modify calcium dynamics, collagen expression, and myocardial fibrosis through attenuation of deleterious signaling cascades, and induction of adaptive pathways, representing potential therapeutic targets for HFpEF.

Isolated perfused working hearts provide valuable additional information during phenotypic assessment of the diabetic mouse heart

Although murine models for studying the development of cardiac dysfunction in diabetes mellitus are well established, their reported cardiac phenotypes vary. These reported divergences may, in addition to the severity of different models, also be linked to the methods used for cardiac functional assessment. In the present study, we examined the functional changes using conventional transthoracic echocardiography (in vivo) and isolated heart perfusion techniques (ex vivo), in hearts from two mouse models; one with an overt type 2 diabetes (the db/db mouse) and one with a prediabetic state, where obesity was induced by a high-fat diet (HFD). Analysis of left ventricular function in the isolated working hearts from HFD-fed mice, suggested that these hearts develop diastolic dysfunction with preserved systolic function. Accordingly, in vivo examination demonstrated maintained systolic function, but we did not find parameters of diastolic function to be altered. In db/db mice, ex vivo working hearts showed both diastolic and systolic dysfunction. Although in vivo functional assessment revealed signs of diastolic dysfunction, the hearts did not display reduced systolic function. The contrasting results between ex vivo and in vivo function could be due to systemic changes that may sustain in vivo function, or a lack of sensitivity using conventional transthoracic echocardiography. Thus, this study demonstrates that the isolated perfused working heart preparation provides unique additional information related to the development of cardiomyopathy, which might otherwise go unnoticed when only using conventional echocardiographic assessment.

Is autophagy associated with diabetes mellitus and its complications? A review

Diabetes mellitus (DM) is an endocrine disorder. In coming decades it will be one of the leading causes of death globally. The key factors in the pathogenesis of diabetes are cellular injuries and disorders of energy metabolism leading to severe diabetic complications. Recent studies have confirmed that autophagy plays a pivotal role in diabetes and its complications. It has been observed that autophagy regulates the normal function of pancreatic β cells and insulin-target tissues, such as skeletal muscle, liver, and adipose tissue. This review will summarize the regulation of autophagy in diabetes and its complications, and explore how this process would emerge as a potential therapeutic target for diabetes treatment.

Changes in the Cardiac GHSR1a-Ghrelin System Correlate With Myocardial Dysfunction in Diabetic Cardiomyopathy in Mice

Ghrelin and its receptor, the growth hormone secretagogue receptor 1a (GHSR1a), are present in cardiac tissue. Activation of GHSR1a by ghrelin promotes cardiomyocyte contractility and survival, and changes in myocardial GHSR1a and circulating ghrelin track with end-stage heart failure, leading to the hypothesis that GHSR1a is a biomarker for heart failure. We hypothesized that GHSR1a could also be a biomarker for diabetic cardiomyopathy (DCM). We used two models of streptozotocin (STZ)-induced DCM: group 1, adult mice treated with 35 mg/kg STZ for 3 days; and group 2, neonatal mice treated with 70 mg/kg STZ at days 2 and 5 after birth. In group 1, mild fasting hyperglycemia (11 mM) was first detected 8 weeks after the last injection, and in group 2, severe fasting hyperglycemia (20 mM) was first detected 1 to 3 weeks after the last injection. In group 1, left ventricular function was slightly impaired as measured by echocardiography, and Western blot analysis showed a significant decrease in myocardial GHSR1a. In group 2, GHSR1a levels were also decreased as assessed by Cy5-ghrelin(1–19) fluorescence microscopy, and there was a significant negative correlation between GHSR1a levels and glucose tolerance. There were significant positive correlations between GHSR1a and ghrelin and between GHSR1a and sarcoplasmic reticulum Ca²⁺-ATPase 2a (SERCA2a), a marker for contractility, but not between GHSR1a and B-type natriuretic peptide, a marker for heart failure. We conclude that the subclinical stage of DCM is accompanied by alterations in the myocardial ghrelin-GHSR1a system, suggesting the possibility of a biomarker for DCM.

Protective Effect of Unacylated Ghrelin on Compression-Induced Skeletal Muscle Injury Mediated by SIRT1-Signaling

Unacylated ghrelin, the predominant form of circulating ghrelin, protects myotubes from cell death, which is a known attribute of pressure ulcers. In this study, we investigated whether unacylated ghrelin protects skeletal muscle from pressure-induced deep tissue injury by abolishing necroptosis and apoptosis signaling and whether these effects were mediated by SIRT1 pathway. Fifteen adult Sprague Dawley rats were assigned to receive saline or unacylated ghrelin with or without EX527 (a SIRT1 inhibitor). Animals underwent two 6-h compression cycles with 100 mmHg static pressure applied over the mid-tibialis region of the right limb whereas the left uncompressed limb served as the intra-animal control. Muscle tissues underneath the compression region, and at the similar region of the opposite uncompressed limb, were collected for analysis. Unacylated ghrelin attenuated the compression-induced muscle pathohistological alterations including rounding contour of myofibers, extensive nucleus accumulation in the interstitial space, and increased interstitial space. Unacylated ghrelin abolished the increase in necroptosis proteins including RIP1 and RIP3 and attenuated the elevation of apoptotic proteins including p53, Bax, and AIF in the compressed muscle. Furthermore, unacylated ghrelin opposed the compression-induced phosphorylation and acetylation of p65 subunit of NF-kB. The anti-apoptotic effect of unacylated ghrelin was shown by a decrease in apoptotic DNA fragmentation and terminal dUTP nick-end labeling index in the compressed muscle. The protective effects of unacylated ghrelin vanished when co-treated with EX527. Our findings demonstrated that unacylated ghrelin protected skeletal muscle from compression-induced injury. The myoprotective effects of unacylated ghrelin on pressure-induced tissue injury were associated with SIRT1 signaling.

Ghrelin and autophagy

PURPOSE OF REVIEW

A compromised autophagy is associated with the onset of obesity, type 2 diabetes, nonalcoholic fatty liver disease, cardiovascular and neurodegenerative diseases. Our aim is to review the potential role of ghrelin, a gut hormone involved in energy homeostasis, in the regulation of autophagy.

RECENT FINDINGS

In the recent years, it has been demonstrated that autophagy constitutes an important mechanism by which ghrelin exerts a plethora of central and peripheral actions. Ghrelin enhances autophagy through the activation of AMP-activated protein kinase in different target organs to regulate lipid and glucose metabolism, the remodeling and protection of small intestine mucosa, protection against cardiac ischemia as well as higher brain functions such as learning and memory consolidation. Nonetheless, in inflammatory states, such as acute hepatitis, liver fibrosis or adipose tissue inflammation, ghrelin acts as an anti-inflammatory factor reducing the autophagic flux to prevent further cell injury. Interestingly, several cardiometabolic disorders, including obesity, type 2 diabetes, nonalcoholic fatty liver disease or chronic heart failure are accompanied by low ghrelin levels in addition to altered autophagy.

SUMMARY

Ghrelin represents an attractive target for development of therapeutics for prevention or treatment of metabolic, cardiac or neuronal disorders, in which autophagy is impaired.

Myocardial stress and autophagy: mechanisms and potential therapies

Autophagy is a ubiquitous cellular catabolic process responsive to energy stress. Research over the past decade has revealed that cardiomyocyte autophagy is a prominent homeostatic pathway, important in adaptation to altered myocardial metabolic demand. The cellular machinery of autophagy involves targeted direction of macromolecules and organelles for lysosomal degradation. Activation of autophagy has been identified as cardioprotective in some settings (that is, ischaemia and ischaemic preconditioning). In other situations, sustained autophagy has been linked with cardiopathology (for example, sustained pressure overload and heart failure). Perturbation of autophagy in diabetic cardiomyopathy has also been observed and is associated with both adaptive and maladaptive responses to stress. Emerging research findings indicate that various forms of selective autophagy operate in parallel to manage various types of catabolic cellular cargo including mitochondria, large proteins, glycogen, and stored lipids. In this Review, induction of autophagy associated with cardiac benefit or detriment is considered. The various static and dynamic approaches used to measure autophagy are critiqued, and current inconsistencies in the understanding of autophagy regulation in the heart are highlighted. The prospects for pharmacological intervention to achieve therapeutic manipulation of autophagic processes are also discussed.

Ghrelin and the Cardiovascular System

Ghrelin is a small peptide released primarily from the stomach. It is a potent stimulator of growth hormone secretion from the pituitary gland and is well known for its regulation of metabolism and appetite. There is also a strong relationship between ghrelin and the cardiovascular system. Ghrelin receptors are present throughout the heart and vasculature and have been linked with molecular pathways, including, but not limited to, the regulation of intracellular calcium concentration, inhibition of proapoptotic cascades, and protection against oxidative damage. Ghrelin shows robust cardioprotective effects including enhancing endothelial and vascular function, preventing atherosclerosis, inhibiting sympathetic drive, and decreasing blood pressure. After myocardial infarction, exogenous administration of ghrelin preserves cardiac function, reduces the incidence of fatal arrhythmias, and attenuates apoptosis and ventricular remodeling, leading to improvements in heart failure. It ameliorates cachexia in end-stage congestive heart failure patients and has shown clinical benefit in pulmonary hypertension. Nonetheless, since ghrelin's discovery is relatively recent, there remains a substantial amount of research needed to fully understand its clinical significance in cardiovascular disease.

Acute administration of acyl, but not desacyl ghrelin, decreases blood pressure in healthy humans

OBJECTIVE

To compare the effects of acyl ghrelin (AG) and desacyl ghrelin (DAG) on blood pressure (BP), heart rate (HR) and other autonomic parameters in healthy humans and to elucidate the hormonal mechanisms through which AG could exert its cardiovascular effects.

DESIGN

Seventeen healthy participants underwent frequent monitoring of systolic (sBP) and diastolic blood pressure (dBP), HR, respiratory rate (RR) and body surface temperature (Temp) during continuous infusion of AG, DAG, combined AG + DAG or saline control before and during an IV glucose tolerance test on 4 separate days. Plasma catecholamines, renin and aldosterone levels were also measured. Differences in outcome measures between treatment groups were assessed using mixed-model analysis.

RESULTS

Compared to the saline control, AG and combined AG + DAG infusions decreased sBP, dBP, mean arterial blood pressure (MAP), HR and Temp. In contrast, DAG infusion did not alter BP, RR or Temp, but did decrease HR. The AG and AG + DAG infusions also raised plasma aldosterone levels compared to saline (P < 0.001) without affecting renin or catecholamine levels.

CONCLUSIONS

The decrease in BP, HR, RR and Temp with AG infusion suggests mediation through the autonomic nervous system. The lack of response to DAG suggests that these autonomic effects require activation of the ghrelin receptor.

Acylated and desacyl ghrelin are associated with hepatic lipogenesis, β-oxidation and autophagy: role in NAFLD amelioration after sleeve gastrectomy in obese rats

Bariatric surgery improves non-alcoholic fatty liver disease (NAFLD). Our aim was to investigate the potential role of ghrelin isoforms in the resolution of hepatic steatosis after sleeve gastrectomy, a restrictive bariatric surgery procedure, in diet-induced obese rats. Male Wistar rats (n = 161) were subjected to surgical (sham operation and sleeve gastrectomy) or dietary interventions [fed ad libitum a normal (ND) or a high-fat (HFD) diet or pair-fed]. Obese rats developed hepatosteatosis and showed decreased circulating desacyl ghrelin without changes in acylated ghrelin. Sleeve gastrectomy induced a dramatic decrease of desacyl ghrelin, but increased the acylated/desacyl ghrelin ratio. Moreover, sleeve gastrectomy reduced hepatic triglyceride content and lipogenic enzymes Mogat2 and Dgat1, increased mitochondrial DNA amount and induced AMPK-activated mitochondrial FFA β-oxidation and autophagy to a higher extent than caloric restriction. In primary rat hepatocytes, the incubation with both acylated and desacyl ghrelin (10, 100 and 1,000 pmol/L) significantly increased TG content, triggered AMPK-activated mitochondrial FFA β-oxidation and autophagy. Our data suggest that the decrease in the most abundant isoform, desacyl ghrelin, after sleeve gastrectomy contributes to the reduction of lipogenesis, whereas the increased relative acylated ghrelin levels activate factors involved in mitochondrial FFA β-oxidation and autophagy in obese rats, thereby ameliorating NAFLD.

Unacylated ghrelin analog prevents myocardial reperfusion injury independently of permeability transition pore

Reperfusion injury is responsible for an important part of myocardial infarct establishment due notably to triggering cardiomyocytes death at the first minutes of reperfusion. AZP-531 is an optimized analog of unacylated ghrelin currently in clinical development in several metabolic diseases. We investigated a potential cardioprotective effect of AZP-531 in ischemia/reperfusion (IR) and the molecular underlying mechanism(s) involved in this protection. In vivo postconditioning with AZP-531 in C57BL6 mouse IR model decreased infarct size. Western blot analysis on areas at risk from the different mouse groups showed that AZP-531 activates Akt, ERK1-2 as well as S6 and 4EBP1, mTORC1 effectors. We also showed an inhibition of caspase 3 cleavage and Bax translocation to the mitochondria. AZP-531 also stimulated the expression of antioxidants and was capable of decreasing mitochondrial H₂O₂ production, contributing to the reduction of ROS accumulation. AZP-531 exhibits cardioprotective effect when administrated for postconditioning in C57BL6 mouse IR model. Treatment with AZP-531 rescued the myocardium from cell death at early reperfusion by stimulating protein synthesis, inhibiting Bax/caspase 3-induced apoptosis as well as ROS accumulation and oxidative stress-induced necrosis. AZP-531 may prove useful in the treatment of IR injury.

Ghrelin improves vascular autophagy in rats with vascular calcification

BACKGROUNDS

This study aimed to investigate whether ghrelin ameliorated vascular calcification (VC) through improving autophagy.

METHODS

VC model was induced by nicotine plus vitamin D₃ in rats and β-glycerophosphate in vascular smooth muscle cell (VSMC). Calcium deposition was detected by von Kossa staining or alizarin red S staining. ALP activity was also detected. Western blot was used to assess the protein expression.

RESULTS

Ghrelin treatment attenuated the elevation of calcium deposition and ALP activity in VC model both in vivo and in vitro. Interesting, the protein levels of autophagy markers, LC3 and beclin1 were significantly upregulated by ghrelin in VC model. An autophagy inhibitor, 3-methyladenine blocks the ameliorative effect of ghrelin on VC. Furthermore, protein expressions of phosphate-AMPK were increased by ghrelin treatment both in calcified aorta and VSMC. The effect of ghrelin on autophagy induction and VC attenuation was prevented by AMPK inhibitor, compound C.

CONCLUSIONS

Our results suggested that ghrelin improved autophagy through AMPK activation, which was resulted in VC amelioration. These data maybe throw light on prevention and therapy of VC.

H2S improves renal fibrosis in STZ-induced diabetic rats by ameliorating TGF-β1 expression

Nephropathy develops in many patients with type 1 diabetes mellitus (T1DM). However, the specific mechanisms and therapies remain unclear. For this purpose we investigated the effects of hydrogen sulfide (H₂S) on renal fibrosis in streptozotocin (STZ) induced diabetic rats and its underlying mechanisms.

Experimental rats were randomly divided into four groups: Control group (normal rats), DM group (diabetes rats), DM + NaHS group [diabetes rats treated with sodium hydrosulfide (NaHS)], and NaHS group (normal rats treated with NaHS). The diabetic models were established by intraperitoneal injection of STZ. The NaHS-treated rats were injected with NaHS as an exogenous donor of H₂S. At the same time, control group and DM group were administrated with equal doses of normal saline (NS). After eight weeks, the rats’ urine samples were collected to measure the renal hydroxyproline content by basic hydrolysis method with a hydroxyproline detection kit. Collagen I and III content was detected by immunohistochemical method, and the pathology morphology of kidney was analyzed by Masson staining. Protein expressions of transforming growth factor beta 1 (TGF-β1), ERK1/2, TIMP1, TIMP2, MMP-2, MMP-7, MMP-8, MMP-11, and MMP-14 were assessed by western blotting. The results showed that significant fibrosis occurred in the kidney of diabetes rats. NaHS treatment downregulated TGF-β1, ERK1/2, TIMP1, TIMP2, MMP-2, MMP-7, MMP-8, MMP-11, and MMP-14 expressions in the kidney of these diabetes rats (p<.01). This result suggests that NaHS treatment could attenuate renal fibrosis by TGF-β1 signaling, and its mechanisms may be correlated with ERK1/2 expression and modulation of MMPs/TIMPs expression. Therefore, H₂S may provide a promising option for defensing against diabetic renal fibrosis through TGF-β1 signaling, equilibrating the balance between profibrotic and antifibrotic mediators.

Ghrelin gene products rescue cultured adult rat hippocampal neural stem cells from high glucose insult

Adult hippocampal neurogenesis is decreased in type 2 diabetes, and this impairment appears to be important in cognitive dysfunction. Previous studies suggest that ghrelin gene products (acylated ghrelin (AG), unacylated ghrelin (UAG) and obestatin (OB)) promote neurogenesis. Therefore, we hypothesize that ghrelin gene products may reduce the harmful effects of high glucose (HG) on hippocampal neural stem cells (NSCs). The aim of this study was to investigate the role of these peptides on the survival of cultured hippocampal NSCs exposed to HG insult. Treatment of hippocampal NSCs with AG, UAG or OB inhibited HG-induced cell death and apoptosis. Exposure of cells to the growth hormone secretagogue receptor 1a antagonist abolished the protective effects of AG against HG toxicity, whereas those of UAG or OB were preserved. All three peptides attenuated HG-induced decrease in BrdU-labeled and phosphohistone-H3-labeled cells. We also investigated the effects of ghrelin gene products on the regulation of apoptosis at the mitochondrial level. AG, UAG or OB rescued hippocampal NSCs from HG insult by inhibiting intracellular and mitochondrial reactive oxygen species generation and stabilizing mitochondrial transmembrane potential. In addition, cells treated with ghrelin gene products showed an increased Bcl-2 and decreased Bax levels, thereby increasing the Bcl-2/Bax ratio, inhibiting cytochrome c release and preventing caspase-3 activation. Finally, AG-, UAG- or OB-mediated protection was dependent on the activities of adenosine monophosphate-activated protein kinase/uncoupling protein 2 pathway. Our data indicate that ghrelin gene products may act as survival factors that preserve mitochondrial function and inhibit oxidative stress-induced apoptosis.

S100A8 and S100A9 Are Associated with Doxorubicin-Induced Cardiotoxicity in the Heart of Diabetic Mice

Cardiomyopathy is a clinical problem that occurs in the hearts of type 2 diabetic patients as well as cancer patients undergoing doxorubicin chemotherapy. The number of diabetic cancer patients is increasing but surprisingly the cardiac damaging effects of doxorubicin, a commonly used chemotherapeutic drug, on diabetic hearts have not been well-examined. As the signaling mechanisms of the doxorubicin-induced cardiomyopathy in type 2 diabetic heart are largely unknown, this study examined the molecular signaling pathways that are responsible for the doxorubicin-induced cardiotoxicity in type 2 diabetic hearts. Male 14- to 18-week-old db/db mice were used as the type 2 diabetic model, and age-matched non-diabetic db/+ mice served as controls. The db/+ non-diabetic and db/db diabetic mice were randomly assigned to the following groups: db/+CON, db/+DOX-5d, db/+DOX-7d, db/dbCON, db/dbDOX-5d, and db/dbDOX-7d. Mice assigned to doxorubicin (DOX) group were exposed to an intraperitoneal (i.p.) injection of DOX at a dose of 15 mg/kg to induce cardiomyopathy. Mice in control (CON) groups were i.p. injected with the same volume of saline instead of DOX. Mice were euthanized by overdose of ketamine and xylazine 5 or 7 days after the DOX injection. Microarray analysis was adopted to examine the changes of the whole transcriptional profile in response to doxorubicin exposure in diabetic hearts. Ventricular fractional shortening was examined as an indicator of cardiac function by transthoracic echocardiography. The presence of diabetic cardiomyopathy in db/db mice was evident by the reduction of fractional shortening. There was a further impairment of cardiac contractile function 7 days after the DOX administration in db/db diabetic mice. According to our microarray analysis, we identified a panel of regulatory genes associated with cardiac remodeling, inflammatory response, oxidative stress, and metabolism in the DOX-induced cardiac injury in diabetic heart. The microarray results of selected genes were confirmed by real time PCR. Notably, S100A8 and S100A9 were found to have a unique specific expression pattern that was coincident with the DOX-induced cardiomyopathy in diabetic hearts. Correspondingly, NF-κB expression in diabetic hearts was increased together with the elevation of S100A8/9 and activation of p38 MAPK signaling after DOX administration, which induced cardiac inflammation as demonstrated by the elevation of cardiac IL-6 level. These findings provide novel pre-clinical information for revealing the S100A8/A9-associated molecular signaling pathways that mediate the doxorubicin-induced cardiotoxicity in diabetic hearts.

Doxorubicin Induces Inflammatory Modulation and Metabolic Dysregulation in Diabetic Skeletal Muscle

Anti-cancer agent doxorubicin (DOX) has been demonstrated to worsen insulin signaling, engender muscle atrophy, trigger pro-inflammation, and induce a shift to anaerobic glycolytic metabolism in skeletal muscle. The myotoxicity of DOX in diabetic skeletal muscle remains largely unclear. This study examined the effects of DOX on insulin signaling, muscle atrophy, pro-/anti-inflammatory microenvironment, and glycolysis metabolic regulation in skeletal muscle of db/db diabetic and db/+ non-diabetic mice. Non-diabetic db/+ mice and diabetic db/db mice were randomly assigned to the following groups: db/+CON, db/+DOX, db/dbCON, and db/dbDOX. Mice in db/+DOX and db/dbDOX groups were intraperitoneally injected with DOX at a dose of 15 mg per kg body weight whereas mice in db/+CON and db/dbCON groups were injected with the same volume of saline instead of DOX. Gastrocnemius was immediately harvested, weighed, washed with cold phosphate buffered saline, frozen in liquid nitrogen, and stored at -80°C for later analysis. The effects of DOX on diabetic muscle were neither seen in insulin signaling markers (Glut4, pIRS1Ser(636∕639), and pAktSer(473)) nor muscle atrophy markers (muscle mass, MuRF1 and MAFbx). However, DOX exposure resulted in enhancement of pro-inflammatory favoring microenvironment (as indicated by TNF-α, HIFα and pNFκBp65) accompanied by diminution of anti-inflammatory favoring microenvironment (as indicated by IL15, PGC1α and pAMPKβ1Ser108). Metabolism of diabetic muscle was shifted to anaerobic glycolysis after DOX exposure as demonstrated by our analyses of PDK4, LDH and pACCSer(79). Our results demonstrated that there might be a link between inflammatory modulation and the dysregulation of aerobic glycolytic metabolism in DOX-injured diabetic skeletal muscle. These findings help to understand the pathogenesis of DOX-induced myotoxicity in diabetic muscle.

AMPK in cardiac fibrosis and repair: Actions beyond metabolic regulation

Fibrosis is a general term encompassing a plethora of pathologies that span all systems and is marked by increased deposition of collagen. Injury of variable etiology gives rise to complex cascades involving several cell-types and molecular signals, leading to the excessive accumulation of extracellular matrix that promotes fibrosis and eventually leads to organ failure. Cardiac fibrosis is a dynamic process associated notably with ischemia, hypertrophy, volume- and pressure-overload, aging and diabetes mellitus. It has profoundly deleterious consequences on the normal architecture and functioning of the myocardium and is associated with considerable mortality and morbidity. The AMP-activated protein kinase (AMPK) is a ubiquitously expressed cellular energy sensor and an essential component of the adaptive response to cardiomyocyte stress that occurs during ischemia. Nevertheless, its actions extend well beyond its energy-regulating role and it appears to possess an essential role in regulating fibrosis of the myocardium. In this review paper, we will summarize the main elements and crucial players of cardiac fibrosis. In addition, we will provide an overview of the diverse roles of AMPK in the heart and discuss in detail its implication in cardiac fibrosis. Lastly, we will highlight the recently published literature concerning AMPK-targeting current therapy and novel strategies aiming to attenuate fibrosis.

Ghrelin Attenuates Liver Fibrosis through Regulation of TGF-β1 Expression and Autophagy

Ghrelin is a stomach-derived growth hormone secretagogue that promotes various physiological effects, including energy metabolism and amelioration of inflammation. The purpose of this study was to investigate the protective mechanism of ghrelin against liver fibrosis. Liver fibrosis was induced in C57BL/6 mice by intraperitoneal injection of CCl₄ (2.0 mL/kg of 10% CCl₄v/v solution in peanut oil) two times per week for eight weeks. Ghrelin (10 μg/kg) was intraperitoneally injected two times per week for eight weeks. A second murine liver fibrosis model was induced by bile duct ligation (BDL) and concurrent ghrelin administration for four weeks. Hematoxylin eosin (H&E), and Masson’s trichrome were used to detect pathological changes to liver tissue. Western blotting was used to detect protein levels of transforming growth factor (TGF)-β1, phosphorylated Smad3 (p-Smad3), I-collage, α-smooth muscle actin (α-SMA), matrix metalloproteinases (MMPs) 2, tissue inhibitor of matrix metalloproteinases (TIMPs) 1, phosphorylated NF-κB (p-NF-κB), and microtubule-associated protein light chain 3 (LC3). In addition, qRT-PCR was used to detect mRNA levels of TGF-β1, I-collage, α-SMA, MMP2, TIMP1 and LC3, while levels of TGF-β1, p-Smad3, I-collage, α-SMA, and LC3 were detected immunohistochemically. Levels of aspartate aminotransferase and alanine aminotransferase were significantly decreased by ghrelin treatment. Ghrelin administration also significantly reduced the extent of pathological changes in both murine liver fibrosis models. Expression levels of I-collage and α-SMA in both models were clearly reduced by ghrelin administration. Furthermore, ghrelin treatment decreased protein expression of TGF-β1 and p-Smad3. The protein levels of NF-κB and LC3 were increased in the CCl₄- and BDL-treatment groups but were significantly reduced following ghrelin treatment. In addition, ghrelin inhibited extracellular matrix formation by decreasing NF-κB expression and maintaining the balance between MMP2 and TIMP1. Our results demonstrated that ghrelin attenuates liver fibrosis via inhibition of the TGF-β1/Smad3 and NF-κB signaling pathways, as well as autophagy suppression.

Myocardial autophagic energy stress responses--macroautophagy, mitophagy, and glycophagy

An understanding of the role of autophagic processes in the management of cardiac metabolic stress responses is advancing rapidly and progressing beyond a conceptualization of the autophagosome as a simple cell recycling depot. The importance of autophagy dysregulation in diabetic cardiomyopathy and in ischemic heart disease - both conditions comprising the majority of cardiac disease burden - has now become apparent. New findings have revealed that specific autophagic processes may operate in the cardiomyocyte, specialized for selective recognition and management of mitochondria and glycogen particles in addition to protein macromolecular structures. Thus mitophagy, glycophagy, and macroautophagy regulatory pathways have become the focus of intensive experimental effort, and delineating the signaling pathways involved in these processes offers potential for targeted therapeutic intervention. Chronically elevated macroautophagic activity in the diabetic myocardium is generally observed in association with structural and functional cardiomyopathy; yet there are also numerous reports of detrimental effect of autophagy suppression in diabetes. Autophagy induction has been identified as a key component of protective mechanisms that can be recruited to support the ischemic heart, but in this setting benefit may be mitigated by adverse downstream autophagic consequences. Recent report of glycophagy upregulation in diabetic cardiomyopathy opens up a novel area of investigation. Similarly, a role for glycogen management in ischemia protection through glycophagy initiation is an exciting prospect under investigation.

Targeting metabolic disturbance in the diabetic heart

Diabetic cardiomyopathy is defined as ventricular dysfunction initiated by alterations in cardiac energy substrates in the absence of coronary artery disease and hypertension. In addition to the demonstrated burden of cardiovascular events associated with diabetes, diabetic cardiomyopathy partly explains why diabetic patients are subject to a greater risk of heart failure and a worse outcome after myocardial ischemia. The raising prevalence and accumulating costs of cardiovascular disease in diabetic patients underscore the deficiencies of tertiary prevention and call for a shift in medical treatment. It is becoming increasingly clearer that the effective prevention and treatment of diabetic cardiomyopathy require measures to regulate the metabolic derangement occurring in the heart rather than merely restoring suitable systemic parameters. Recent research has provided deeper insight into the metabolic etiology of diabetic cardiomyopathy and numerous heart-specific targets that may substitute or reinforce current strategies. From both experimental and translational perspectives, in this review we first discuss the progress made with conventional therapies, and then focus on the need for prospective metabolic targets that may avert myocardial vulnerability and functional decline in next-generation diabetic care.

Antifibrotic activity of acylated and unacylated ghrelin

Fibrosis can affect almost all tissues and organs, it often represents the terminal stage of chronic diseases, and it is regarded as a major health issue for which efficient therapies are needed. Tissue injury, by inducing necrosis/apoptosis, triggers inflammatory response that, in turn, promotes fibroblast activation and pathological deposition of extracellular matrix. Acylated and unacylated ghrelin are the main products of the ghrelin gene. The acylated form, through its receptor GHSR-1a, stimulates appetite and growth hormone (GH) release. Although unacylated ghrelin does not bind or activate GHSR-1a, it shares with the acylated form several biological activities. Ghrelin peptides exhibit anti-inflammatory, antioxidative, and antiapoptotic activities, suggesting that they might represent an efficient approach to prevent or reduce fibrosis. The aim of this review is to summarize the available evidence regarding the effects of acylated and unacylated ghrelin on different pathologies and experimental models in which fibrosis is a predominant characteristic.