Proteomic study on the protective mechanism of fibroblast growth factor 21 to ischemia-reperfusion injury

Fibroblast Growth Factor 21 Suppressed Neutrophil Extracellular Traps Induced by Myocardial Ischemia/Reperfusion Injury via Adenosine Monophosphate-Activated Protein Kinase

Background

Previous investigations have established the anti-inflammatory properties of fibroblast growth factor 21 (FGF21). However, the specific mechanism through which FGF21 mitigates myocardial ischemia/reperfusion (I/R) injury by inhibiting neutrophil extracellular traps (NETs) remains unclear.

Methods

A mice model of myocardial I/R injury was induced, and myocardial tissue was stained with immunofluorescence to assess NETs. Serum NETs levels were quantified using a PicoGreen kit. In addition, the expression levels of adenosine monophosphate (AMP)-activated protein kinase (AMPK) and FGF21 were evaluated by Wes fully automated protein blotting quantitative analysis system. Moreover, a hypoxia/reoxygenation (H/R) model was established using AMPK inhibitor and agonist pretreated H9c2 cells to further explore the relationship between FGF21 and AMPK.

Results

Compared with the control group, serum NETs levels were significantly higher in I/R mice, and a large number of NETs were formed in myocardial tissues (97.63 ± 11.45 vs. 69.65 ± 3.33, P < 0.05). However, NETs levels were reversed in FGF21 pretreated mice (P < 0.05). Further studies showed that FGF21 enhanced AMPK expression, which was significantly increased after inhibition of AMPK and decreased after promotion of AMPK (P < 0.05).

Conclusions

FGF21 may exert cardioprotective effects by inhibiting I/R injury-induced NETs via AMPK.

Metabolism and bioenergetics in the pathophysiology of organ fibrosis

Fibrosis is the tissue scarring characterized by excess deposition of extracellular matrix (ECM) proteins, mainly collagens. A fibrotic response can take place in any tissue of the body and is the result of an imbalanced reaction to inflammation and wound healing. Metabolism has emerged as a major driver of fibrotic diseases. While glycolytic shifts appear to be a key metabolic switch in activated stromal ECM-producing cells, several other cell types such as immune cells, whose functions are intricately connected to their metabolic characteristics, form a complex network of pro-fibrotic cellular crosstalk. This review purports to clarify shared and particular cellular responses and mechanisms across organs and etiologies. We discuss the impact of the cell-type specific metabolic reprogramming in fibrotic diseases in both experimental and human pathology settings, providing a rationale for new therapeutic interventions based on metabolism-targeted antifibrotic agents.

Diagnostic and predictive abilities of myokines in patients with heart failure

Myokines are defined as a heterogenic group of numerous cytokines, peptides and metabolic derivates, which are expressed, synthesized, produced, and released by skeletal myocytes and myocardial cells and exert either auto- and paracrine, or endocrine effects. Previous studies revealed that myokines play a pivotal role in mutual communications between skeletal muscles, myocardium and remote organs, such as brain, vasculature, bone, liver, pancreas, white adipose tissue, gut, and skin. Despite several myokines exert complete divorced biological effects mainly in regulation of skeletal muscle hypertrophy, residential cells differentiation, neovascularization/angiogenesis, vascular integrity, endothelial function, inflammation and apoptosis/necrosis, attenuating ischemia/hypoxia and tissue protection, tumor growth and malignance, for other occasions, their predominant effects affect energy homeostasis, glucose and lipid metabolism, adiposity, muscle training adaptation and food behavior. Last decade had been identified 250 more myokines, which have been investigating for many years further as either biomarkers or targets for heart failure management. However, only few myokines have been allocated to a promising tool for monitoring adverse cardiac remodeling, ischemia/hypoxia-related target-organ dysfunction, microvascular inflammation, sarcopenia/myopathy and prediction for poor clinical outcomes among patients with HF. This we concentrate on some most plausible myokines, such as myostatin, myonectin, brain-derived neurotrophic factor, muslin, fibroblast growth factor 21, irisin, leukemia inhibitory factor, developmental endothelial locus-1, interleukin-6, nerve growth factor and insulin-like growth factor-1, which are suggested to be useful biomarkers for HF development and progression.

Mechanism of fibroblast growth factor 21 in cardiac remodeling

Cardiac remodeling is a basic pathological process that enables the progression of multiple cardiac diseases to heart failure. Fibroblast growth factor 21 is considered a regulator in maintaining energy homeostasis and shows a positive role in preventing damage caused by cardiac diseases. This review mainly summarizes the effects and related mechanisms of fibroblast growth factor 21 on pathological processes associated with cardiac remodeling, based on a variety of cells of myocardial tissue. The possibility of Fibroblast growth factor 21 as a promising treatment for the cardiac remodeling process will also be discussed.

Delayed revascularization in acute ischemic stroke patients

Stroke shares a significant burden of global mortality and disability. A significant decline in the quality of life is attributed to the so-called post-stroke cognitive impairment including mild to severe cognitive alterations, dementia, and functional disability. Currently, only two clinical interventions including pharmacological and mechanical thrombolysis are advised for successful revascularization of the occluded vessel. However, their therapeutic effect is limited to the acute phase of stroke onset only. This often results in the exclusion of a significant number of patients who are unable to reach within the therapeutic window. Advances in neuroimaging technologies have allowed better assessment of salvageable penumbra and occluded vessel status. Improvement in diagnostic tools and the advent of intravascular interventional devices such as stent retrievers have expanded the potential revascularization window. Clinical studies have demonstrated positive outcomes of delayed revascularization beyond the recommended therapeutic window. This review will discuss the current understanding of ischemic stroke, the latest revascularization doctrine, and evidence from clinical studies regarding effective delayed revascularization in ischemic stroke.

Synthetic Fibroblasts: Terra Incognita in Cardiac Regeneration

Ischemic heart disease, a major risk factor for myocardial infarction (MI), occurs when the blood vessels supplying oxygen-rich blood to the heart become partially or fully occluded by lipid-rich plaques, resulting in myocardial cell death, remodeling, and scarring. In addition, MI occurs as result of lipid-rich plaque rupture, resulting in thrombosis and vessel occlusion. Cardiac fibroblasts (CFs) and CF-derived growth factors are crucial post-MI in myocardial remodeling. Information regarding the regenerative phenotypes of CFs is scarce; however, regenerative CFs are translationally relevant in myocardial regeneration following MI. The emerging technologies in regenerative cardiology offer cutting-edge translational opportunities, including synthetic cells. In this review, we critically reviewed the current knowledge and the ongoing research efforts on application of synthetic cells for improving cardiac regeneration post-MI. Impact statement Synthetic cells offer tremendous regenerative potential in otherwise deleterious cardiac remodeling postmyocardial infarction. Understanding the role of fibroblasts in cardiac healing and the therapeutic applications of synthetic cells would open a multitude of novel cardiac regenerative approaches. The novel concept of synthetic fibroblasts that emulate native cardiac fibroblasts can provide an effective solution in cardiac healing.

The Potential Implications of Hydrogen Sulfide in Aging and Age-Related Diseases through the Lens of Mitohormesis

The growing increases in the global life expectancy and the incidence of chronic diseases as a direct consequence have highlighted a demand to develop effective strategies for promoting the health of the aging population. Understanding conserved mechanisms of aging across species is believed helpful for the development of approaches to delay the progression of aging and the onset of age-related diseases. Mitochondrial hormesis (or mitohormesis), which can be defined as an evolutionary-based adaptive response to low-level stress, is emerging as a promising paradigm in the field of anti-aging. Depending on the severity of the perceived stress, there are varying levels of hormetic response existing in the mitochondria called mitochondrial stress response. Hydrogen sulfide (H2S) is a volatile, flammable, and toxic gas, with a characteristic odor of rotten eggs. However, H2S is now recognized an important gaseous signaling molecule to both physiology and pathophysiology in biological systems. Recent studies that elucidate the importance of H2S as a therapeutic molecule has suggested its protective effects beyond the traditional understanding of its antioxidant properties. H2S can also be crucial for the activation of mitochondrial stress response, postulating a potential mechanism for combating aging and age-related diseases. Therefore, this review focuses on highlighting the involvement of H2S and its sulfur-containing derivatives in the induction of mitochondrial stress response, suggesting a novel possibility of mitohormesis through which this gaseous signaling molecule may promote the healthspan and lifespan of an organism.

Brite Adipocyte FGF21 Attenuates Cardiac Ischemia/Reperfusion Injury in Rat Hearts by Modulating NRF2

Although the optimal therapy for myocardial infarction includes reperfusion to restore blood flow to the ischemic area, myocardial injury after ischemia/reperfusion usually leads to an inflammatory response, oxidative stress, and cardiomyocyte apoptosis. In this study, rat adipose-derived stem cells were differentiated into low-thermogenic beige adipocytes (LBACs) and high-thermogenic beige adipocytes (HBACs) to study the different cardioprotective effects of heterogeneous expression of brown adipocytes. We found that antioxidant and antiapoptotic factors in H9c2 cardiomyocytes were upregulated by high levels of secreted FGF21 in HBAC conditioned medium (HBAC-CM), whereas FGF21 in HBAC-CM did not affect antioxidative or antiapoptotic cell death in H9c2 cardiomyocytes with Nrf2 knockdown. These results show that NRF2 mediates antioxidative and antiapoptotic effects through the HBAC-secreted factor FGF21. Consistent with this finding, the expression of antioxidant and antiapoptotic genes was upregulated by highly secreted FGF21 after HBAC-CM treatment compared to LBAC-CM treatment in H9c2 cardiomyocytes via NRF2 activation. Furthermore, HBAC-CM significantly attenuated ischemic rat heart tissue injury via NRF2 activation. Based on these findings, we propose that HBAC-CM exerts beneficial effects in rat cardiac ischemia/reperfusion injury by modulating NRF2 and has potential as a promising therapeutic agent for myocardial infarction.

The role of FGF21 in the pathogenesis of cardiovascular disease

ABSTRACT

The morbidity and mortality of cardiovascular diseases (CVDs) are increasing worldwide and seriously threaten human life and health. Fibroblast growth factor 21 (FGF21), a metabolic regulator, regulates glucose and lipid metabolism and may exert beneficial effects on the cardiovascular system. In recent years, FGF21 has been found to act directly on the cardiovascular system and may be used as an early biomarker of CVDs. The present review highlights the recent progress in understanding the relationship between FGF21 and CVDs including coronary heart disease, myocardial ischemia, cardiomyopathy, and heart failure and also explores the related mechanism of the cardioprotective effect of FGF21. FGF21 plays an important role in the prediction, treatment, and improvement of prognosis in CVDs. This cardioprotective effect of FGF21 may be achieved by preventing endothelial dysfunction and lipid accumulating, inhibiting cardiomyocyte apoptosis and regulating the associated oxidative stress, inflammation and autophagy. In conclusion, FGF21 is a promising target for the treatment of CVDs, however, its clinical application requires further clarification of the precise role of FGF21 in CVDs.

The Roles of FGF21 and ALCAT1 in Aerobic Exercise-Induced Cardioprotection of Postmyocardial Infarction Mice

Aerobic exercise mitigates oxidative stress and apoptosis caused by myocardial infarction (MI) even though the precise mechanisms remain completely elusive. In this study, we investigated the potential mechanisms of aerobic exercise in ameliorating the cardiac function of mice with MI. In vivo, MI was induced by left anterior descending (LAD) coronary artery ligation in wild-type mice, alcat1 knockout, and fgf21 knockout mice. The mice were exercised under a moderate-intensity protocol for 6 weeks at one week later post-MI. In vitro, H9C2 cells were treated with lentiviral vector carrying alcat1 gene, recombinant human FGF21 (rhFGF21), PI3K inhibitor, and H₂O₂ to explore the potential mechanisms. Our results showed that aerobic exercise significantly increased the FGF21 expression and decreased the ALCAT1 expression in the hearts of mice with MI. fgf21 knockout weakened the inhibitory effects of aerobic exercise on oxidative stress, endoplasmic reticulum (ER) stress, and apoptosis in mice with MI. Both/either alcat1 knockout and/or aerobic exercise improved cardiac function by inhibiting oxidative stress and apoptosis in the MI heart. rhFGF21 inhibited both H₂O₂ and overexpression of ALCAT1-induced oxidative stress and apoptosis by activating the PI3K/AKT pathway in H9C2 cells. In conclusion, our results showed that aerobic exercise alleviated oxidative stress and apoptosis by activating the FGF21/FGFR1/PI3K/AKT pathway or inhibiting the hyperexpression of ALCAT1, which ultimately improved the cardiac function in MI mice.

Advances in Biological Functions and Clinical Studies of FGF21

Fibroblast growth factor 21 (FGF21) regulates many crucial biological processes in human and mammals, particularly metabolic modulation and protective effect after injury. Therefore, determining complex regulatory mechanisms and elucidating the signaling pathway may greatly promote the prevention, diagnosis, and treatment of related injury and metabolic diseases. This review focused on the metabolic modulation and protective effect of FGF21 and summarized the molecular mechanisms and clinical research developments.

Modulatory Effect of Myokines on Reactive Oxygen Species in Ischemia/Reperfusion

There is a growing body of evidence showing the importance of physical activity against acute ischemic events in various organs. Ischemia/reperfusion injury (I/R) is characterized by tissue damage as a result of restriction and subsequent restoration of blood supply to an organ. Oxidative stress due to increased reactive oxygen species formation and/or insufficient antioxidant defense is considered to play an important role in I/R. Physical activity not only decreases the general risk factors for ischemia but also confers direct anti-ischemic protection via myokine production. Myokines are skeletal muscle-derived cytokines, representing multifunctional communication channels between the contracting skeletal muscle and other organs through an endocrine manner. In this review, we discuss the most prominent members of the myokines (i.e., brain-derived neurotrophic factor (BDNF), cathepsin B, decorin, fibroblast growth factors-2 and -21, follistatin, follistatin-like, insulin-like growth factor-1; interleukin-6, interleukin-7, interleukin-15, irisin, leukemia inhibitory factor, meteorin-like, myonectin, musclin, myostatin, and osteoglycin) with a particular interest in their potential influence on reactive oxygen and nitrogen species formation or antioxidant capacity. A better understanding of the mechanism of action of myokines and particularly their participation in the regulation of oxidative stress may widen their possible therapeutic use and, thereby, may support the fight against I/R.

Brain-dead donor heart conservation with a preservation solution supplemented by a conditioned medium from mesenchymal stem cells improves graft contractility after transplantation

Hearts are usually procured from brain-dead (BD) donors. However, brain death may induce hemodynamic instability, which may contribute to posttransplant graft dysfunction. We hypothesized that BD-donor heart preservation with a conditioned medium (CM) from mesenchymal stem cells (MSCs) would improve graft function after transplantation. Additionally, we explored the PI3K pathway's potential role. Rat MSCs-derived CM was used for conservation purposes. Donor rats were either exposed to sham operation or brain death by inflation of a subdural balloon-catheter for 5.5 hours. Then, the hearts were explanted, stored in cardioplegic solution-supplemented with either a medium vehicle (BD and sham), CM (BD + CM), or LY294002, an inhibitor of PI3K (BD + CM + LY), and finally transplanted. Systolic performance and relaxation parameters were significantly reduced in BD-donors compared to sham. After transplantation, systolic and diastolic functions were significantly decreased, terminal deoxynucleotidyl transferase-mediated dUTP nick end-labeling (TUNEL)-positive cells and endonuclease G positive cells were increased in the BD-group compared to sham. Preservation of BD-donor hearts with CM resulted in a recovery of systolic graft function (dP/dt_max : BD + CM: 3148 ± 178 vs BD: 2192 ± 94 mm Hg/s at 110 µL, P < .05) and reduced apoptosis. LY294002 partially lowered graft protection afforded by CM in the BD group. Our data suggest that PI3K/Akt pathway is not the primary mechanism of action of CM in improving posttransplant cardiac contractility and preventing caspase-independent apoptosis.

A review of fibroblast growth factor 21 in diabetic cardiomyopathy

FGF21 (fibroblast growth factor 21) is a regulator of metabolism and performs an important role in glucose and lipid metabolism and the maintenance of energy balance. FGF21 is principally expressed in the liver, but it can also be found in the pancreas, skeletal muscle, and adipose tissue. It is known that levels of serum FGF21 are significantly elevated in obese, insulin-resistant patients, and those with metabolic syndrome. Elevated levels of FGF21 in serum during the early stages of various metabolic diseases are considered a compensatory response by the organism. Therefore, FGF21 is considered a hormone in response to stress and an early diagnostic marker of disease. Diabetic cardiomyopathy is a special type of cardiac complication, characterized as a chronic myocardial disorder caused by diabetes. The pathological process includes increased oxidative stress, energy metabolism in myocardial cells, an inflammatory response, and myocardial cell apoptosis. A growing body of evidence suggests that FGF21 has the potential to be an effective drug for the treatment of diabetic cardiomyopathy. Here, we review recent progress on the characteristics of FGF21 in its protective role, especially in pathological processes such as suppressing apoptosis in the myocardium, reducing inflammation in cardiomyocytes, reducing oxidative stress, and promoting fatty acid oxidation. In addition, we explore the possibility that diabetic cardiomyopathy can be delayed through the application of FGF21, providing possible therapeutic targets of the disease.

Serum Levels of FGF21, β-Klotho, and BDNF in Stable Coronary Artery Disease Patients With Depressive Symptoms: A Cross-Sectional Single-Center Study

Background: The incidence of depressive symptoms (DS) in patients with stable coronary artery disease (SCAD) is significantly higher than those in healthy population, and that DS are independent risk factors for cardiovascular events. Previous studies have reported that fibroblast growth factor 21 (FGF21), β-klotho, mature brain-derived neurotrophic factor (mBDNF), and BDNF precursor (proBDNF) play important roles in the pathogenesis and treatment of coronary heart disease and depression. With this in mind, the present study aimed to clarify the relationship between FGF21, β-klotho, mBDNF, and proBDNF and SCAD with comorbid depression, in addition to also exploring the underlying mechanisms of these disease processes. Methods: A total of 116 patients with SCAD and 45 healthy controls were recruited. Patients with SCAD were further divided into two subgroups based on the Zung Self-Rating Depression Scale (SDS), which were characterized as those with no DS (NDS) and those with DS. Baseline data were collected, and serum levels of FGF21, β-klotho, mBDNF, and proBDNF were determined. Results: In SCAD patients, Gensini scores-denoting the degree of coronary arteriostenosis-were significantly greater in the DS group than in the NDS group. There was also a positive correlation between the Gensini scores and the SDS scores. Patients in the SCAD group demonstrated a lower serum FGF21. Serum β-klotho, mBDNF, and mBDNF/proBDNF were also significantly lower in the DS group than in the NDS group. Furthermore, β-klotho and mBDNF were negatively correlated with the SDS scores. Additionally, SCAD patients were divided into lower- and higher-level groups using hierarchical cluster analysis, with the results highlighting that patients in the lower mBDNF group had a higher incidence of DS. Conclusions: The depression score was positively correlated with the severity of coronary artery stenosis, and serum FGF21, β-klotho, mBDNF, and proBDNF were closely related to the development of DS in patients with SCAD. These observations suggest FGF21, β-klotho, mBDNF, and proBDNF as potential diagnostic and/or therapeutic targets for SCAD with co-morbid depression.

Metabolic remodeling induced by mitokines in heart failure

The prevalence rates of heart failure (HF) are greater than 10% in individuals aged >75 years, indicating an intrinsic link between aging and HF. It has been recognized that mitochondrial dysfunction contributes to the pathology of HF. Mitokines are a type of cytokines, peptides, or signaling pathways produced or activated by the nucleus or the mitochondria through cell non-autonomous responses during cellular stress. In addition to promoting the communication between the mitochondria and the nucleus, mitokines also exert a systemic regulatory effect by circulating to distant tissues. It is noteworthy that increasing evidence has demonstrated that mitokines are capable of reducing the metabolic-related HF risk factors and are associated with HF severity. Consequently, mitokines might represent a potential therapy target for HF.

Delayed recanalization at 3 days after permanent MCAO attenuates neuronal apoptosis through FGF21/FGFR1/PI3K/Caspase-3 pathway in rats

Reperfusion exceeded time window may induce ischemia/reperfusion injury, increase hemorrhagic transformation, and deteriorate neurological outcomes in ischemic stroke models. However, the increasing clinical evidences supported that reperfusion even within 6-24 h may salvage ischemic tissue and improve neurological outcomes in selected large vessel occlusion patients, without inducing serious ischemia/reperfusion injury and hemorrhagic transformation. The underlying molecular mechanisms are less clear. In present study, we demonstrated that delayed recanalization at 3 days after permanent middle cerebral artery occlusion (MCAO) decreased infarct volumes and improved neurobehavioral deficits in rats, with no increasing animal mortality and intracerebral hemorrhage. Meanwhile, we observed that endogenous neuroprotective agent fibroblast growth factor 21 (FGF21) significantly increased in serum after MCAO, but which did not synchronously increase in penumbra due to permanent MCAO. Recanalization dramatically increased the endogenous FGF21 expression on neurons in penumbra after MCAO. We confirmed that FGF21 activated the FGFR1/PI3K/Caspase-3 signaling pathway, which attenuated neuronal apoptosis in penumbra. Conversely, knockdown of FGFR1 via FGFR1 siRNA abolished the anti-apoptotic effects of FGF21, and in part abrogated beneficial effects of recanalization on neurological outcomes. These findings suggested that delayed recanalization at 3 days after MCAO improved neurological outcomes in rats via increasing endogenous FGF21 expression and activating FGFR1/PI3K/Caspase-3 pathway to attenuate neuronal apoptosis in penumbra. Delayed recanalization at 3 days after ischemic stroke onset may be a promising treatment strategy in selected patients.

New Insights Into the Comorbidity of Coronary Heart Disease and Depression

Coronary heart disease (CHD) and depression are common disorders that markedly impair quality of life and impose a great financial burden on society. They are also frequently comorbid, exacerbating patient condition, and worsening prognosis. This comorbidity strongly suggests shared pathologic mechanisms. This review focuses on the incidence of depression in patients with CHD, deleterious effects of depression on CHD symptoms, and the potential mechanisms underlying comorbidity. In addition to the existing frequent mechanisms that are well known for decades, this review summarized interesting and original potential mechanisms to underlie the comorbidity, such as endocrine substances, gut microbiome, and microRNA. Finally, there are several treatment strategies for the comorbidity, involving drugs and psychotherapy, which may provide a theoretical basis for further basic research and clinical investigations on improved therapeutic interventions.

FGF21 promotes functional recovery after hypoxic-ischemic brain injury in neonatal rats by activating the PI3K/Akt signaling pathway via FGFR1/β-klotho

Perinatal asphyxia often results in neonatal cerebral hypoxia-ischemia (HI), which is associated with high mortality and severe long-term neurological deficits in newborns. Currently, there are no effective drugs to mitigate the functional impairments post-HI. Previous studies have shown that fibroblast growth factor 21 (FGF21) has a potential neuroprotective effect against brain injury. However, the effect of FGF21 on neonatal HI brain injury is unclear. In the present study, both in vivo and in vitro models were used to assess whether recombinant human FGF21 (rhFGF21) could exert a neuroprotective effect after HI and explore the associated mechanism. The results showed that the rhFGF21 treatment remarkably reduced the infarct volume, ameliorated the body weight and improved the tissue structure after HI in neonatal rats. In addition, the rhFGF21 treatment lengthened the running endurance times in the rotarod test and decreased the mean escape latencies and increased the number of platform crossings in the Morris water maze test at 21 d post-HI insult. In contrast, the FGFR1 inhibitor PD173074 and PI3K inhibitor LY294002 partially reversed these therapeutic effects. In isolated primary cortical neurons, the rhFGF21 treatment protected primary neurons from oxygen-glucose deprivation (OGD) insult by inhibiting neuronal apoptosis and promoting neuronal survival. Both our in vivo and in vitro results reveal that rhFGF21 could inhibit neuronal apoptosis by activating the PI3K/Akt signaling pathway via FGF21/FGFR1/β-klotho complex formation. Therefore, rhFGF21 may be a promising therapeutic agent for promoting functional recovery after HI-induced neonatal brain injury.

Fibroblast growth factor-21 alleviates hypoxia/reoxygenation injury in H9c2 cardiomyocytes by promoting autophagic flux

Fibroblast growth factor (FGF)-21, a member of the family of FGFs, exhibits protective effects against myocardial ischemia and ischemia/reperfusion injury; it is also an enhancer of autophagy. However, the mechanisms underlying the protective role of FGF-21 against cardiomyocyte hypoxia/reoxygenation (H/R) injury remain unclear. The present study aimed to investigate the effect of FGF-21 on H9c2 cardiomyocyte injury induced by H/R and the mechanism associated with changes in autophagy. Cultured H9c2 cardiomyocytes subjected to hypoxia were treated with a vehicle or FGF-21 during reoxygenation. The viability of H9c2 rat cardiomyocytes was measured using Cell Counting Kit-8 and trypan blue exclusion assays. The contents of creatine kinase (CK) and creatine kinase isoenzymes (CK-MB), cardiac troponin I (cTnT), cardiac troponin T (cTnI) and lactate dehydrogenase (LDH) in culture medium were detected with a CK, CK-MB, cTnT, cTnI and LDH assay kits. The protein levels were examined by western blot analysis. Autophagic flux was detected by Ad-mCherry-GFP-LC3B autophagy fluorescent adenovirus reagent. The results indicated that FGF-21 alleviated H/R-induced H9c2 myocardial cell injury and enhanced autophagic flux during H/R, and that this effect was antagonized by co-treatment with 3-methyladenine, an autophagy inhibitor. Furthermore, FGF-21 increased the expression levels of Beclin-1 and Vps34 proteins, but not of mechanistic target of rapamycin. These data indicate that FGF-21 treatment limited H/R injury in H9c2 cardiomyocytes by promoting autophagic flux through upregulation of the expression levels of Beclin-1 and Vps34 proteins.

The Biological Role of Klotho Protein in the Development of Cardiovascular Diseases

Klotho is a membrane-bound or soluble antiaging protein, whose protective activity is essential for a proper function of many organs. In 1997, an accidental insertion of a transgene led to creation of transgenic mice with several age-related disorders. In Klotho-deficient mice, the inherited phenotypes closely resemble human aging, while in an animal model of Klotho overexpression, the lifespan is extended. Klotho protein is detected mainly in the kidneys and brain. It is a coreceptor for fibroblast growth factor and hence is involved in maintaining endocrine system homeostasis. Furthermore, an inhibition of insulin/insulin-like growth factor-1 signaling pathway by Klotho regulates oxidative stress and reduces cell death. The association between serum Klotho and the classic risk factors, as well as the clinical history of cardiovascular disease, was also shown. There are a lot of evidences that Klotho deficiency correlates with the occurrence and development of coronary artery disease, atherosclerosis, myocardial infarction, and left ventricular hypertrophy. Therefore, an involvement of Klotho in the signaling pathways and in regulation of a proper cell metabolism could be a crucial factor in the cardiac and vascular protection. It is also well established that Klotho protein enhances the antioxidative response via augmented production of superoxide dismutase and reduced generation of reactive oxygen species. Recent studies have proven an expression of Klotho in cardiomyocytes and its increased expression in stress-related heart injury. Thus, the antioxidative and antiapoptotic activity of Klotho could be considered as the novel protective factor in cardiovascular disease and heart injury.

Circulating level of fibroblast growth factor 21 is independently associated with the risks of unstable angina pectoris

There is increasing evidence that serum adipokine levels are associated with higher risks of cardiovascular diseases. As an important adipokine, fibroblast growth factor 21 (FGF21) has been demonstrated to be associated with atherosclerosis and coronary artery disease (CAD). However, circulating level of FGF21 in patients with angina pectoris has not yet been investigated. Circulating FGF21 level was examined in 197 patients with stable angina pectoris (SAP, n=66), unstable angina pectoris (UAP, n=76), and control subjects (n=55) along with clinical variables of cardiovascular risk factors. Serum FGF21 concentrations on admission were significantly increased more in patients with UAP than those with SAP (Ln-FGF21: 5.26 ± 0.87 compared with 4.85 ± 0.77, P<0.05) and control subjects (natural logarithm (Ln)-FGF21: 5.26 ± 0.87 compared with 4.54 ± 0.72, P<0.01). The correlation analysis revealed that serum FGF21 concentration was positively correlated with the levels of cardiac troponin I (cTnI) (r²  =  0.026, P=0.027) and creatine kinase-MB (CK-MB) (r²  =  0.023, P= 0.04). Furthermore, FGF21 level was identified as an independent factor associated with the risks of UAP (odds ratio (OR): 2.781; 95% CI: 1.476–5.239; P=0.002), after adjusting for gender, age, and body mass index (BMI). However, there were no correlations between serum FGF21 levels and the presence of SAP (OR: 1.248; 95% CI: 0.703–2.215; P=0.448). The present study indicates that FGF21 has a strong correlation and precise predictability for increased risks of UAP, that is independent of traditional risk factors of angina pectoris.

FGF21 protects human umbilical vein endothelial cells against high glucose-induced apoptosis via PI3K/Akt/Fox3a signaling pathway

AIMS

Diabetic macroangiopathy is the main cause of morbidity and mortality in patients with diabetes. Endothelial cell injury is a pathological precondition for diabetic macroangiopathy. Fibroblast growth factor 21 (FGF21) is a key metabolic regulator which has recently been suggested to protect cardiac myocytes and vascular cells against oxidative stress-induced injury in vitro and vivo. In this study, we aimed to investigate the protective capacity of FGF21 in human umbilical vein endothelial cells (HUVECs) against high glucose (HG)-induced apoptosis via phosphatidylinositol-3-kinase/protein kinase B (PI3K/Akt)/FoxO3a pathway.

METHODS

The cell viability was examined by CCK-8 assay, Intracellular ROS levels were measured by the detection of the fluorescent product formed by the oxidation of DCFH-DA, Apoptosis was analyzed using Hoechst 33258 nuclear staining and Flow Cytometry Analysis (FCA), the expression of protein were detected by Western blot.

RESULTS

Results show that pretreating HUVECs with FGF21 before exposure to HG increases cell viability, while decreasing apoptosis and the generation of reactive oxygen species. Western blot analysis shows that HG reduces the phosphorylation of Akt and FoxO3a, and induces nuclear localization of FoxO3a. The effects were significantly reversed by FGF21 pre-treatment. Furthermore, the protective effects of FGF21 were prevented by PI3K/Akt inhibitor LY294002.

CONCLUSIONS

Our data demonstrates that FGF21 protects HUVECs from HG-induced oxidative stress and apoptosis via the activation of PI3K/Akt/FoxO3a signaling pathway.

Protective Effects of Fibroblast Growth Factor 21 Against Amyloid-Beta1-42-Induced Toxicity in SH-SY5Y Cells

Alzheimer's disease (AD) is a neurodegenerative disorder characterized by the progressive loss of cholinergic neurons. Amyloid beta is a misfolded protein that represents one of the key pathological hallmarks of AD. Numerous studies have shown that Aβ_1-42 induces oxidative damage, neuroinflammation, and apoptosis, leading to cognitive decline in AD. Recently, fibroblast growth factor 21 (FGF21) has been suggested to be a potential regulator of oxidative stress in mammalian cells. FGF21 has been shown to improve insulin sensitivity, reduce hyperglycemia, increase adipose tissue glucose uptake and lipolysis, and decrease body fat and weight loss by enhancing energy expenditure. In this study, we investigated the effect of FGF21 Aβ_1-42 toxicity in SH-SY5Y neuroblastoma cells. Our data shows that FGF21 significantly decreased Aβ_1-42-induced toxic effects and repressed oxidative stress and apoptosis in cells exposed to Aβ_1-42 peptide. Our investigation also confirmed that FGF21 pretreatment favorably affects HSP90/TLR4/NF-κB signaling pathway. Therefore, FGF21 represents a viable therapeutic strategy to abrogate Aβ_1-42-induced cellular inflammation and apoptotic death in the SH-SY5Y neuroblastoma cells.

Comparisons of cardioprotective efficacy between fibroblast growth factor 21 and dipeptidyl peptidase-4 inhibitor in prediabetic rats

AIMS

Comparative efficacy between fibroblast growth factor 21 (FGF21) and vildagliptin on metabolic regulation, cardiac mitochondrial function, heart rate variability (HRV), and left ventricular (LV) function is not known. We hypothesized that FGF21 and vildagliptin share a similar efficacy in improving these parameters in high fat diet (HFD)-induced obese-insulin resistant rats.

METHODS

Twenty-four male Wistar rats were fed with either a normal diet (ND) or a HFD for 12 weeks. Then, ND rats were received vehicle (NDV). Rats in the HFD group were divided into three subgroups to receive either vehicle (HFV), recombinant human FGF21 (rhFGF21, 0.1 mg/kg/d, ip; HFF), or vildagliptin (3 mg/kg/d, PO; HFVil) for 28 days.

RESULTS

HFV rats developed obese-insulin resistance, increased serum tumor necrosis factors alpha (TNF-α) level, impaired heart rate variability (HRV) together with cardiac mitochondrial dysfunction, and LV dysfunction. Cardiac apoptosis was markedly increased in HFV rats indicated by decreased B-cell lymphoma 2 (Bcl-2) with increased Bcl2-associated X-protein (Bax) and cleaved caspase 3 expression. Cardiac FGF21 signaling pathways were markedly decreased in HFV rats indicated by decreased phosphor-fibroblast growth factor receptors 1 (p-FGFR1), phosphor-extracellular signal-regulated protein kinases 1 (p-ERK1/2), proliferator-activated receptor gamma coactivator 1-alpha (PGC-1α), and carnitine palmitoyltransferase-1 (CPT-1) expression. Although both FGF21 and vildagliptin similarly attenuated these impairments, only HFF rats had decreased body weight, visceral fat, and serum TNF-α levels.

CONCLUSIONS

FGF21 exerts better metabolic regulation and inflammation reduction than vildagliptin. However, FGF21 and vildagliptin shared a similar efficacy for cardioprotection by improving HRV and LV function.

Fibroblast growth factor-21 prevents diabetic cardiomyopathy via AMPK-mediated antioxidation and lipid-lowering effects in the heart

Our previous studies showed that both exogenous and endogenous FGF21 inhibited cardiac apoptosis at the early stage of type 1 diabetes. Whether FGF21 induces preventive effect on type 2 diabetes-induced cardiomyopathy was investigated in the present study. High-fat-diet/streptozotocin-induced type 2 diabetes was established in both wild-type (WT) and FGF21-knockout (FGF21-KO) mice followed by treating with FGF21 for 4 months. Diabetic cardiomyopathy (DCM) was diagnosed by significant cardiac dysfunction, remodeling, and cardiac lipid accumulation associated with increased apoptosis, inflammation, and oxidative stress, which was aggravated in FGF21-KO mice. However, the cardiac damage above was prevented by administration of FGF21. Further studies demonstrated that the metabolic regulating effect of FGF21 is not enough, contributing to FGF21-induced significant cardiac protection under diabetic conditions. Therefore, other protective mechanisms must exist. The in vivo cardiac damage was mimicked in primary neonatal or adult mouse cardiomyocytes treated with HG/Pal, which was inhibited by FGF21 treatment. Knockdown of AMPKα1/2, AKT2, or NRF2 with their siRNAs revealed that FGF21 protected cardiomyocytes from HG/Pal partially via upregulating AMPK–AKT2–NRF2-mediated antioxidative pathway. Additionally, knockdown of AMPK suppressed fatty acid β-oxidation via inhibition of ACC–CPT-1 pathway. And, inhibition of fatty acid β-oxidation partially blocked FGF21-induced protection in cardiomyocytes. Further, in vitro and in vivo studies indicated that FGF21-induced cardiac protection against type 2 diabetes was mainly attributed to lipotoxicity rather than glucose toxicity. These results demonstrate that FGF21 functions physiologically and pharmacologically to prevent type 2 diabetic lipotoxicity-induced cardiomyopathy through activation of both AMPK–AKT2–NRF2-mediated antioxidative pathway and AMPK–ACC–CPT-1-mediated lipid-lowering effect in the heart.

The relationship of circulating fibroblast growth factor 21 levels with incident atrial fibrillation: The Multi-Ethnic Study of Atherosclerosis

BACKGROUND AND AIMS

Elevated circulating levels of fibroblast growth factor 21 (FGF21) are associated with multiple cardiovascular disease (CVD) risk factors and incident events. Previous small cross-sectional studies, mainly in Chinese populations, have suggested FGF21 may play a role in the development of atrial fibrillation (AF). We therefore investigated the relationship of FGF21 levels with incident AF in participants free of clinically apparent CVD at baseline in a large, multi-ethnic cohort.

METHODS

A total of 5729 participants of four major ethnic groups (Caucasian, African American, Hispanic American, and Chinese American) from the Multi-Ethnic Study of Atherosclerosis (MESA), who were free of AF and had plasma FGF21 levels measured by ELISA at the baseline exam, were included in the analysis. Participants were followed up for incident AF over a median period of 12.9 years. Cox proportional hazards regression analysis was used.

RESULTS

Among the 5729 participants, 778 participants developed incident AF. Participants with incident AF had significantly higher baseline FGF21 levels than those without incident AF (median = 166.0 and 142.8 pg/mL, p < 0.001). After adjusting for possible confounders, including demographic, socioeconomic and lifestyle factors, traditional CVD risk factors and circulating inflammatory markers, higher baseline FGF21 levels did not predict incident AF over the follow up period. There was no effect modification by sex or ethnicity.

CONCLUSIONS

Baseline FGF21 levels were not associated with the development of AF in an ethnically diverse population followed long-term. Our findings do not support an important role of FGF21 in AF development.

Fibroblast growth factor 21 protects rat cardiomyocytes from endoplasmic reticulum stress by promoting the fibroblast growth factor receptor 1-extracellular signal‑regulated kinase 1/2 signaling pathway

Fibroblast growth factor 21 (FGF21), as an endocrine factor, is secreted into circulation by injured cardiomyocytes. Endoplasmic reticulum (ER) stress-induced apoptosis has been proposed as an important pathophysiological mechanism for cardiomyocyte injury. However, whether the enhanced expression of FGF21 in cardiomyocytes is linked to ER stress, and the effect and underlying mechanism of FGF21 on ER stress-induced cardiomyocyte apoptosis remain unclear. In the present study, it was demonstrated that mild ER stress resulted in upregulated expression levels of FGF21 and its main receptors, as a response to cell compensation, at the induction of ≤5 µM tunicamycin (TM). However, excessive ER stress (TM ≥10 µM) activated the ER stress-mediated apoptosis signaling pathways, including PKR-like ER kinase (PERK)-eukaryotic translational initiation factor 2α (eIF2α)-activating transcription factor 4 (ATF4)-CCAAT/-enhancer-binding protein homologous protein (CHOP) and inositol-requiring kinase 1α (IRE1α)-c-Jun N-terminal kinases (JNK), as well as inhibited the expression of FGF21 and its primary receptors. In addition, FGF21 overexpression provided protection against ER stress-induced cardiomyocyte injury, as evidenced by increased cell viability and reduced apoptosis. These changes were associated with the inhibition of ER stress-mediated apoptosis signaling pathways, as well as increased phosphorylation of FGFR1 and ERK1/2. However, the protective effects of overexpressed FGF21 were abolished following treatment with FGFR1 and ERK1/2 inhibitors. Thus, mild ER stress may induce the expression of FGF21 and its primary receptors in cardiomyocytes. FGF21 inhibits ER stress-induced cardiomyocyte injury as least in part via the FGFR1-ERK1/2 signaling pathway.

Cardioprotective effects of fibroblast growth factor 21 against doxorubicin-induced toxicity via the SIRT1/LKB1/AMPK pathway

Doxorubicin (DOX) is a highly effective antineoplastic anthracycline drug; however, the adverse effect of the cardiotoxicity has limited its widespread application. Fibroblast growth factor 21 (FGF21), as a well-known regulator of glucose and lipid metabolism, was recently shown to exert cardioprotective effects. The aim of this study was to investigate the possible protective effects of FGF21 against DOX-induced cardiomyopathy. We preliminarily established DOX-induced cardiotoxicity models in H9c2 cells, adult mouse cardiomyocytes, and 129S1/SyImJ mice, which clearly showed cardiac dysfunction and myocardial collagen accumulation accompanying by inflammatory, oxidative stress, and apoptotic damage. Treatment with FGF21 obviously attenuated the DOX-induced cardiac dysfunction and pathological changes. Its effective anti-inflammatory activity was revealed by downregulation of inflammatory factors (tumor necrosis factor-α and interleukin-6) via the IKK/IκBα/nuclear factor-κB pathway. The anti-oxidative stress activity of FGF21 was achieved via reduced generation of reactive oxygen species through regulation of nuclear transcription factor erythroid 2-related factor 2 transcription. Its anti-apoptotic activity was shown by reductions in the number of TUNEL-positive cells and DNA fragments along with a decreased ratio of Bax/Bcl-2 expression. In a further mechanistic study, FGF21 enhanced sirtuin 1 (SIRT1) binding to liver kinase B1 (LKB1) and then decreased LKB1 acetylation, subsequently inducing AMP-activated protein kinase (AMPK) activation, which improved the cardiac inflammation, oxidative stress, and apoptosis. These alterations were significantly prohibited by SIRT1 RNAi. The present work demonstrates for the first time that FGF21 obviously prevented DOX-induced cardiotoxicity via the suppression of oxidative stress, inflammation, and apoptosis through the SIRT1/LKB1/AMPK signaling pathway.

FGF21 ameliorates diabetic cardiomyopathy by activating the AMPK-paraoxonase 1 signaling axis in mice

The aim of the present study is to explore the molecular mechanism of fibroblast growth factor 21 (FGF21) in protecting against diabetic cardiomyopathy (DCM). Streptozotocin/high-fat diet (STZ/HFD) was used to induced diabetes in FGF21-deficient mice and their wild-type littermates, followed by evaluation of the difference in DCM between the two genotypes. Primary cultured cardiomyocytes were also used to explore the potential molecular mechanism of FGF21 in the protection of high glucose (HG)-induced cardiomyocyte injury. STZ/HFD-induced cardiomyopathy was exacerbated in FGF21 knockout mice, which was accompanied by a significant reduction in cardiac AMP-activated protein kinase (AMPK) activity and paraoxonase 1 (PON1) expression. By contrast, adeno-associated virus (AAV)-mediated overexpression of FGF21 in STZ/HFD-induced diabetic mice significantly enhanced cardiac AMPK activity, PON1 expression and its biological activity, resulting in alleviated DCM. In cultured cardiomyocytes, treatment with recombinant mouse FGF21 (rmFGF21) counteracted HG-induced oxidative stress, mitochondrial dysfunction, and inflammatory responses, leading to increased AMPK activity and PON1 expression. However, these beneficial effects of FGF21 were markedly weakened by genetic blockage of AMPK or PON1. Furthermore, inactivation of AMPK also markedly blunted FGF21-induced PON1 expression but significantly increased HG-induced cytotoxicity in cardiomyocytes, the latter of which was largely reversed by adenovirus-mediated PON1 overexpression. These findings suggest that FGF21 ameliorates DCM in part by activation of the AMPK-PON1 axis.

Role of angiopoietin-2 in the cardioprotective effect of fibroblast growth factor 21 on ischemia/reperfusion-induced injury in H9c2 cardiomyocytes

Fibroblast growth factor 21 (FGF21) exerts a protective effect in ischemia/reperfusion (I/R)-induced cardiac injury. However, the exact molecular mechanism underlying the FGF21 action remains unclear. The present study aimed to evaluate the role of angiopoietin-2 (Angpt2) in the cardioprotective effect of FGF21. For this purpose, the H9C2 cell line was subjected to simulated I/R or aerobic conditions with or without FGF21 administration. Certain groups were also transfected with Angpt2 small interfering RNA (siRNA). Cell viability, apoptosis rate and cell migration were examined, and the expression levels of Angpt2, glucose transporter 1 (GLUT1) and caspase-3 were measured by quantitative polymerase chain reaction (qPCR) and western blot analyses. The results demonstrated that FGF21 administration suppressed apoptosis and increased the cell migration ability following I/R-induced injury. qPCR and western blot data showed a decreased level of GLUT1 after I/R-induced injury, which was reversed by FGF21 administration. Furthermore, inhibition of Angpt2 expression using siRNA enhanced the cardioprotective effect of FGF21 by upregulation of GLUT1. In conclusion, FGF21 administration protected against I/R-induced injury in cardiomyocytes, and further inhibition of Angpt2 with FGF21 administration induced the expression of GLUT1, which may promote the energy metabolism in cardiomyocytes, consequently resulting in a more efficient cardioprotective effect. These results suggested that FGF21 administration and inhibition of Angpt2 could be a novel therapeutic approach for I/R-induced cardiac injury.

Vildagliptin and caloric restriction for cardioprotection in pre-diabetic rats

Long-term high-fat diet (HFD) consumption causes cardiac dysfunction. Although calorie restriction (CR) has been shown to be useful in obesity, we hypothesized that combined CR with dipeptidyl peptidase-4 (DPP-4) inhibitor provides greater efficacy than monotherapy in attenuating cardiac dysfunction and metabolic impairment in HFD-induced obese-insulin resistant rats. Thirty male Wistar rats were divided into 2 groups to be fed on either a normal diet (ND, n = 6) or a HFD (n = 24) for 12 weeks. Then, HFD rats were divided into 4 subgroups (n = 6/subgroup) to receive just the vehicle, CR diet (60% of mean energy intake and changed to ND), vildagliptin (3 mg/kg/day) or combined CR and vildagliptin for 4 weeks. Metabolic parameters, heart rate variability (HRV), cardiac mitochondrial function, left ventricular (LV) and fibroblast growth factor (FGF) 21 signaling pathway were determined. Rats on a HFD developed insulin and FGF21 resistance, oxidative stress, cardiac mitochondrial dysfunction and impaired LV function. Rats on CR alone showed both decreased body weight and visceral fat accumulation, whereas vildagliptin did not alter these parameters. Rats in CR, vildagliptin and CR plus vildagliptin subgroups had improved insulin sensitivity and oxidative stress. However, vildagliptin improved heart rate variability (HRV), cardiac mitochondrial function and LV function better than the CR. Chronic HFD consumption leads to obese-insulin resistance and FGF21 resistance. Although CR is effective in improving metabolic regulation, vildagliptin provides greater efficacy in preventing cardiac dysfunction by improving anti-apoptosis and FGF21 signaling pathways and attenuating cardiac mitochondrial dysfunction in obese-insulin-resistant rats.

The Role of ERK1/2 in the Development of Diabetic Cardiomyopathy

Diabetes mellitus is a chronic metabolic condition that affects carbohydrate, lipid and protein metabolism and may impair numerous organs and functions of the organism. Cardiac dysfunction afflicts many patients who experience the oxidative stress of the heart. Diabetic cardiomyopathy (DCM) is one of the major complications that accounts for more than half of diabetes-related morbidity and mortality cases. Chronic hyperglycemia and hyperlipidemia from diabetes mellitus cause cardiac oxidative stress, endothelial dysfunction, impaired cellular calcium handling, mitochondrial dysfunction, metabolic disturbances, and remodeling of the extracellular matrix, which ultimately lead to DCM. Although many studies have explored the mechanisms leading to DCM, the pathophysiology of DCM has not yet been fully clarified. In fact, as a potential mechanism, the associations between DCM development and mitogen-activated protein kinase (MAPK) activation have been the subjects of tremendous interest. Nonetheless, much remains to be investigated, such as tissue- and cell-specific processes of selection of MAPK activation between pro-apoptotic vs. pro-survival fate, as well as their relation with the pathogenesis of diabetes and associated complications. In general, it turns out that MAPK signaling pathways, such as extracellular signal-regulated kinase 1/2 (ERK1/2), c-Jun N-terminal protein kinase (JNK) and p38 MAP kinase, are demonstrated to be actively involved in myocardial dysfunction, hypertrophy, fibrosis and heart failure. As one of MAPK family members, the activation of ERK1/2 has also been known to be involved in cardiac hypertrophy and dysfunction. However, many recent studies have demonstrated that ERK1/2 signaling activation also plays a crucial role in FGF21 signaling and exerts a protective environment of glucose and lipid metabolism, therefore preventing abnormal healing and cardiac dysfunction. The duration, extent, and subcellular compartment of ERK1/2 activation are vital to differential biological effects of ERK1/2. Moreover, many intracellular events, including mitochondrial signaling and protein kinases, manipulate signaling upstream and downstream of MAPK, to influence myocardial survival or death. In this review, we will summarize the roles of ERK1/2 pathways in DCM development by the evidence from current studies and will present novel opinions on "differential influence of ERK1/2 action in cardiac dysfunction, and protection against myocardial ischemia-reperfusion injury".

Fibroblast growth factor 21 (FGF21) therapy attenuates left ventricular dysfunction and metabolic disturbance by improving FGF21 sensitivity, cardiac mitochondrial redox homoeostasis and structural changes in pre-diabetic rats

AIMS

Fibroblast growth factor 21 (FGF21) acts as a metabolic regulator and exerts cardioprotective effects. However, the effects of long-term FGF21 administration on the heart under the FGF21-resistant condition in obese, insulin-resistant rats have not been investigated. We hypothesized that long-term FGF21 administration reduces FGF21 resistance and insulin resistance and attenuates cardiac dysfunction in obese, insulin-resistant rats.

METHODS

Eighteen rats were fed on either a normal diet (n = 6) or a high-fat diet (HFD; n = 12) for 12 weeks. Then, rats in the HFD group were divided into two subgroups (n = 6 per subgroup) and received either the vehicle (HFV) or recombinant human FGF21 (rhFGF21, 0.1 mg kg(-1)  day(-1) ; HFF) injected intraperitoneally for 28 days. The metabolic parameters, inflammation, malondialdehyde (MDA), heart rate variability (HRV), left ventricular (LV) function, cardiac mitochondrial redox homoeostasis, cardiac mitochondrial fatty acid β-oxidation (FAO) and anti-apoptotic signalling pathways were determined.

RESULTS

HFV rats had increased dyslipidaemia, insulin resistance, plasma FGF21 levels, TNF-α, adiponectin and MDA, depressed HRV, and impaired LV and mitochondrial function. HFV rats also had decreased cardiac Bcl-2, cardiac PGC-1α and CPT-1 protein expression. However, FGF21 restored metabolic parameters, decreased TNF-α and MDA, increased serum adiponectin, and improved HRV, cardiac mitochondrial and LV function in HFF rats. Moreover, HFF rats had increased cardiac Bcl-2, cardiac PGC-1α and CPT-1 protein expression.

CONCLUSION

Long-term FGF21 therapy attenuates FGF21 resistance and insulin resistance and exerts cardioprotection by improving cardiometabolic regulation via activating anti-apoptotic and cardiac mitochondrial FAO signalling pathways in obese, insulin-resistant rats.

Up-regulation of Nrf2 is involved in FGF21-mediated fenofibrate protection against type 1 diabetic nephropathy

The lipid lowering medication, fenofibrate (FF), is a peroxisome proliferator-activated receptor-alpha (PPARα) agonist, possessing beneficial effects for type 2 diabetic nephropathy (DN). We investigated whether FF can prevent the development of type 1 DN, and the underlying mechanisms. Diabetes was induced by a single intraperitoneal injection of streptozotocin in C57BL/6J mice. Mice were treated with oral gavage of FF at 100mg/kg every other day for 3 and 6 months. Diabetes-induced renal oxidative stress, inflammation, apoptosis, lipid and collagen accumulation, and renal dysfunction were accompanied by significant decrease in PI3K, Akt, and GSK-3β phosphorylation as well as an increase in the nuclear accumulation of Fyn [a negative regulator of nuclear factor (erythroid-derived 2)-like 2 (Nrf2)]. All these adverse effects were significantly attenuated by FF treatment. FF also significantly increased fibroblast growth factor 21 (FGF21) expression and enhanced Nrf2 function in diabetic and non-diabetic kidneys. Moreover, FF-induced amelioration of diabetic renal damage, including the stimulation of PI3K/Akt/GSK-3β/Fyn pathway and the enhancement of Nrf2 function were abolished in FGF21-null mice, confirming the critical role of FGF21 in FF-induced renal protection. These results suggest for the first time that FF prevents the development of DN via up-regulating FGF21 and stimulating PI3K/Akt/GSK-3β/Fyn-mediated activation of the Nrf2 pathway.

Ischemic postconditioning influences electron transport chain protein turnover in Langendorff-perfused rat hearts

Ischemia postconditioning (IPo) is a promising strategy in reducing myocardial ischemia reperfusion (I/R) injury (MIRI), but its specific molecular mechanism is incompletely understood. Langendorff-perfused isolated rat hearts were subjected to global I/R and received IPo in the absence or presence of the mitochondrial ATP-sensitive potassium channel (mitoKATP) blocker 5-hydroxydecanoate (5-HD). Myocardial mitochondria were extracted and mitochondrial comparative proteomics was analyzed. IPo significantly reduces post-ischemic myocardial infarction and improved cardiac function in I/R rat hearts, while 5-HD basically cancelled IPo's myocardial protective effect. Joint application of two-dimensional polyacrylamide gel electrophoresis (2DE) and MALDI-TOF MS identified eight differentially expressed proteins between groups. Expression of cardiac succinate dehydrogenase (ubiquinone) flavoprotein subunit (SDHA) increased more than two-fold after I/R, while IPo led to overexpression of dihydrolipoyl dehydrogenase (DLD), NADH dehydrogenase (ubiquinone) flavoprotein 1 and isoform CRA_b (NDUFV1). When the mitoKATP was blocked, MICOS complex subunit Mic60 (IMMT) and Stress-70 protein (Grp75) were over expressed, while DLDH, ATPase subunit A (ATPA) and rCG44606 were decreased. Seven of the differential proteins belong to electron transport chain (ETC) or metabolism regulating proteins, and five of them were induced by closing mitoKATP in I/R hearts. We thus conclude that IPo's myocardial protective effect relies on energy homeostasis regulation. DLD, SDHA, NDUFV1, Grp75, ATPA and rCG44606 may contribute to IPo's cardial protective effect.

Physiological and Pharmacological Roles of FGF21 in Cardiovascular Diseases

Cardiovascular disease (CVD) is one of the most severe diseases in clinics. Fibroblast growth factor 21 (FGF21) is regarded as an important metabolic regulator playing a therapeutic role in diabetes and its complications. The heart is a key target as well as a source of FGF21 which is involved in heart development and also induces beneficial effects in CVDs. Our review is to clarify the roles of FGF21 in CVDs. Strong evidence showed that the development of CVDs including atherosclerosis, coronary heart disease, myocardial ischemia, cardiac hypertrophy, and diabetic cardiomyopathy is associated with serum FGF21 levels increase which was regarded as a compensatory response to induced cardiac protection. Furthermore, administration of FGF21 suppressed the above CVDs. Mechanistic studies revealed that FGF21 induced cardiac protection likely by preventing cardiac lipotoxicity and the associated oxidative stress, inflammation, and apoptosis. Normally, FGF21 induced therapeutic effects against CVDs via activation of the above kinases-mediated pathways by directly binding to the FGF receptors of the heart in the presence of β-klotho. However, recently, growing evidence showed that FGF21 induced beneficial effects on peripheral organs through an indirect way mediated by adiponectin. Therefore whether adiponectin is also involved in FGF21-induced cardiac protection still needs further investigation.

Effects of fibroblast growth factor 21 on the heart

Fibroblast growth factor 21 (FGF21) is a novel polypeptide ligand that has been shown to be involved in several physiological and pathological processes including regulation of glucose and lipids as well as reduction of arteriosclerotic plaque formation in the great vessels. It has also been shown to exert cardioprotective effects in myocardial infarction, cardiac ischemia-reperfusion injury, cardiac hypertrophy and diabetic cardiomyopathy. Moreover, FGF21 protects the myocardium and great arteries by attenuating remodeling, inflammation, oxidative stress and also promoting the energy supply to the heart through fatty acid β-oxidation. This growing evidence emphasizes the important roles of FGF21 in cardioprotection. This review comprehensively summarizes and discusses the consistent and inconsistent findings regarding the beneficial effects of FGF21 on the heart available from both basic research and clinical reports. The details of the signaling, biological and pharmacological effects of FGF21 with regard to its protection of the heart are also presented and discussed in this review.

Long-Term Administration of Fibroblast Growth Factor 21 Prevents Chemically-Induced Hepatocarcinogenesis in Mice

PURPOSE

In this study, we explored whether treatment with FGF-21 could prevent diethylnitrosamine (DEN) induced hepatocarcinogenesis in mice.

METHODS & RESULTS

Hepatoma was induced by injection of DEN every three days for 18 weeks. For the prophylactic experiment, mice were firstly injected with FGF-21 for 2 weeks, then FGF-21 was administered to the mice once daily in association with DEN injection till the end of the experiment. The hepatoma incidence of mice treated with FGF-21 was 13.3%, while the incidence of mice treated with saline was 61.5%. To understand the mechanisms, we compared the expression of βklotho (KLB) and oxidative stress level in the livers between the mice treated with FGF-21 and saline. We found that FGF-21 could suppress DEN-induced oxidative stress and up-regulate the expression of KLB in the livers. To confirm these results, we compared the expression of KLB in L02 cells stimulated with or without FGF-21. Besides, we established DEN-induced oxidative stress cell model to affirm the relationship between FGF-21 and DEN-induced oxidative stress in vitro. Results showed that FGF-21 increased the expression of KLB and diminished the DEN-induced oxidative stress in vitro in a dose dependent manner.

CONCLUSION

Systemic administration of FGF-21 can prevent DEN-induced hepatocarcinogenesis via suppressing oxidative stress and increasing the expression of KLB.

Fibroblast growth factors in cardiovascular disease: The emerging role of FGF21

Early detection of risk factors for enhanced primary prevention and novel therapies for treating the chronic consequences of cardiovascular disease are of the utmost importance for reducing morbidity. Recently, fibroblast growth factors (FGFs) have been intensively studied as potential new molecules in the prevention and treatment of cardiovascular disease mainly attributable to metabolic effects and angiogenic actions. Members of the endocrine FGF family have been shown to increase metabolic rate, decrease adiposity, and restore glucose homeostasis, suggesting a multiple metabolic role. Serum levels of FGFs have been associated with established cardiovascular risk factors as well as with the severity and extent of coronary artery disease and could be useful for prediction of cardiovascular death. Furthermore, preclinical investigations and clinical trials have tested FGF administration for therapeutic angiogenesis in ischemic vascular disease, demonstrating a potential role in improving angina and limb function. FGF21 has lately emerged as a potent metabolic regulator with multiple effects that ultimately improve the lipoprotein profile. Early studies show that FGF21 is associated with the presence of atherosclerosis and may play a protective role against plaque formation by improving endothelial function. The present review highlights recent investigations suggesting that FGFs, in particular FGF21, may be useful as markers of cardiovascular risk and may also serve as protective/therapeutic agents in cardiovascular disease.

Minireview: Roles of Fibroblast Growth Factors 19 and 21 in Metabolic Regulation and Chronic Diseases

Fibroblast growth factor (FGF)19 and FGF21 are hormones that regulate metabolic processes particularly during feeding or starvation, thus ultimately influencing energy production. FGF19 is secreted by the intestines during feeding and negatively regulates bile acid synthesis and secretion, whereas FGF21 is produced in the liver during fasting and plays a crucial role in regulating glucose and lipid metabolism, as well as maintaining energy homeostasis. FGF19 and FGF21 are regarded as late-acting hormones because their functions are only used after insulin and glucagon have completed their actions. Although FGF19 and FGF21 are activated under different conditions, they show extensively functional overlap in terms of improving glucose tolerance, insulin sensitivity, weight loss, and lipid, and energy metabolism, particularly in pathological conditions such as diabetes, obesity, metabolic syndrome, and cardiovascular and renal diseases. Most patients with these metabolic diseases exhibit reduced serum FGF19 levels, which might contribute to its etiology. In addition, the simultaneous increase in serum FGF21 levels is likely a compensatory response to reduced FGF19 levels, and the 2 proteins concertedly maintain metabolic homeostasis. Here, we review the physiological and pharmacological cross talk between FGF19 and FGF21 in relation to the regulation of endocrine metabolism and various chronic diseases.

Fibroblast growth factor 21 protects the heart from apoptosis in a diabetic mouse model via extracellular signal-regulated kinase 1/2-dependent signalling pathway

AIMS/HYPOTHESIS

This study investigated fibroblast growth factor 21 (FGF21)-mediated cardiac protection against apoptosis caused by diabetic lipotoxicity and explored the protective mechanisms involved.

METHODS

Cardiac Fgf21 mRNA expression was examined in a diabetic mouse model using real-time PCR. After pre-incubation of palmitate-treated cardiac H9c2 cells and primary cardiomyocytes with FGF21 for 15 h, apoptosis and Fgf21-induced cell-survival signalling were investigated using small interfering (si)RNA and/or pharmacological inhibitors. We also examined the cardiac apoptotic signalling and structural and functional indices in wild-type and Fgf21-knockout (Fgf21-KO) diabetic mice.

RESULTS

In a mouse model of type 1 diabetes, cardiac Fgf21 expression was upregulated about 40-fold at 2 months and 3-1.5-fold at 4 and 6 months after diabetes. FGF21 significantly reduced palmitate-induced cardiac apoptosis. Mechanistically, palmitate downregulated, but FGF21 upregulated, phosphorylation levels of extracellular signal-regulated kinase (ERK)1/2, mitogen-activated protein kinase 14 (p38 MAPK) and AMP-activated protein kinase (AMPK). Inhibition of each kinase with its inhibitor and/or siRNA revealed that FGF21 prevents palmitate-induced cardiac apoptosis via upregulating the ERK1/2-dependent p38 MAPK-AMPK signalling pathway. In vivo administration of FGF21, but not FGF21 plus ERK1/2 inhibitor, to diabetic or fatty-acid-infused mice significantly prevented cardiac apoptosis and reduced inactivation of ERK1/2, p38 MAPK and AMPK and prevented cardiac remodelling and dysfunction. The Fgf21-KO mice were more susceptible to diabetes-induced cardiac apoptosis, and this could be prevented by administration of FGF21. Deletion of Fgf21 did not further exacerbate cardiac dysfunction.

CONCLUSIONS/INTERPRETATION

These results demonstrate that FGF21 prevents lipid- or diabetes-induced cardiac apoptosis by activating the ERK1/2-p38 MAPK-AMPK pathway. FGF21 may be a therapeutic target for the treatment of diabetes-related cardiac damage.

The protective effect of FGF21 on diabetes-induced male germ cell apoptosis is associated with up-regulated testicular AKT and AMPK/Sirt1/PGC-1α signaling

Fibroblast growth factor 21 (FGF21) is a metabolic regulator that is required for normal spermatogenesis and protects against diabetes-induced germ cell apoptosis. Here, we tried to define whether diabetes-induced germ cell apoptosis that is predominantly due to increased oxidative stress was associated with impaired glucose and fatty acid metabolism, by examining the effects of Fgf21 gene knockout (FGF21-KO) or FGF21 treatment on the glucose and fatty acid metabolic pathways in streptozotocin-induced diabetic mice. Western blottings revealed that protein kinase B (AKT)-mediated glucose signaling was down-regulated in diabetic testes and further decreased in FGF21-KO diabetic group both 10 days and 2 months after diabetes onset, reflected by reduced glycogen synthase (GS) kinase (GSK)-3β phosphorylation and increased GS phosphorylation. Deletion of the Fgf21 gene also inactivated fatty acid metabolism-related factors, AMP-activated protein kinase (AMPK), sirtuin 1 (Sirt1), and peroxisome proliferator-activated receptor-γ coactivator 1α (PGC-1α), along with exacerbating diabetes-induced testicular oxidative stress and damage. Treatment with recombinant FGF21 partially prevented these diabetic effects. In FGF21-KO nondiabetic mice, testicular AMPK/Sirt1/PGC-1α signaling was down-regulated and AKT1 and murine double minute 2 were inactivated along with the increased p53 expression but not AKT2, GSK-3β, and GS. These results suggest that the role of FGF21 in maintaining spermatogenesis is associated with its activation of AKT1 and inhibition of p53. Deletion of the Fgf21gene significantly exacerbates diabetes-induced down-regulation of testicular AKT/GSK-3β/GS and AMPK/Sirt1/PGC-1α pathways and testicular oxidative stress and cell apoptosis.