FGF21 attenuates hypoxia‑induced dysfunction and apoptosis in HPAECs through alleviating endoplasmic reticulum stress

Regulation of endoplasmic reticulum stress on autophagy and apoptosis of nucleus pulposus cells in intervertebral disc degeneration and its related mechanisms

Intervertebral disc degeneration (IVDD) is a common and frequent disease in orthopedics, which seriously affects the quality of life of patients. Endoplasmic reticulum stress (ERS)-regulated autophagy and apoptosis play an important role in nucleus pulposus (NP) cells in IVDD. Hypoxia and serum deprivation were used to induce NP cells. Cell counting kit-8 (CCK-8) assay was used to detect cell activity and immunofluorescence (IF) was applied for the appraisement of glucose regulated protein 78 (GRP78) and green fluorescent protein (GFP)-light chain 3 (LC3). Cell apoptosis was detected by flow cytometry and the expression of LC3II/I was detected by western blot. NP cells under hypoxia and serum deprivation were induced by lipopolysaccharide (LPS), and intervened by ERS inhibitor (4-phenylbutyric acid, 4-PBA) and activator (Thapsigargin, TP). Then, above functional experiments were conducted again and western blot was employed for the evaluation of autophagy-, apoptosis and ERS-related proteins. Finally, NP cells under hypoxia and serum deprivation were stimulated by LPS and intervened using apoptosis inhibitor z-Val-Ala-DL-Asp-fluoromethyl ketone (Z-VAD-FMK) and autophagy inhibitor 3-methyladenine (3-MA). CCK-8 assay, IF, flow cytometry and western blot were performed again. Besides, the levels of inflammatory cytokines were measured with enzyme-linked immunosorbent assay (ELISA) and the protein expressions of programmed death markers were estimated with western blot. It showed that serum deprivation induces autophagy and apoptosis. ERS was significantly activated by LPS in hypoxic and serum deprivation environment, and autophagy and apoptosis were significantly promoted. Overall, ERS affects the occurrence and development of IVDD by regulating autophagy, apoptosis and other programmed death.

HMGB1-induced activation of ER stress contributes to pulmonary artery hypertension in vitro and in vivo

BACKGROUND

HMGB1 and ER stress have been considered to participate in the progression of pulmonary artery hypertension (PAH). However, the molecular mechanism underlying HMGB1 and ER stress in PAH remains unclear. This study aims to explore whether HMGB1 induces pulmonary artery smooth muscle cells (PASMCs) functions and pulmonary artery remodeling through ER stress activation.

METHODS

Primary cultured PASMCs and monocrotaline (MCT)-induced PAH rats were applied in this study. Cell proliferation and migration were determined by CCK-8, EdU and transwell assay. Western blotting was conducted to detect the protein levels of protein kinase RNA-like endoplasmic reticulum kinase (PERK), activating transcription factor-4 (ATF4), seven in absentia homolog 2 (SIAH2) and homeodomain interacting protein kinase 2 (HIPK2). Hemodynamic measurements, immunohistochemistry staining, hematoxylin and eosin staining were used to evaluate the development of PAH. The ultrastructure of ER was observed by transmission electron microscopy.

RESULTS

In primary cultured PASMCs, HMGB1 reduced HIPK2 expression through upregulation of ER stress-related proteins (PERK and ATF4) and subsequently increased SIAH2 expression, which ultimately led to PASMC proliferation and migration. In MCT-induced PAH rats, interfering with HMGB1 by glycyrrhizin, suppression of ER stress by 4-phenylbutyric acid or targeting SIAH2 by vitamin K3 attenuated the development of PAH. Additionally, tetramethylpyrazine (TMP), as a component of traditional Chinese herbal medicine, reversed hemodynamic deterioration and vascular remodeling by targeting PERK/ATF4/SIAH2/HIPK2 axis.

CONCLUSIONS

The present study provides a novel insight to understand the pathogenesis of PAH and suggests that targeting HMGB1/PERK/ATF4/SIAH2/HIPK2 cascade might have potential therapeutic value for the prevention and treatment of PAH.

Multifaceted role of ferroptosis in cardiovascular disease

Ferroptosis is a newly identified form of non-apoptotic cell death characterised primarily by iron-dependent lipid peroxidation. It differs morphologically, biochemically, and genetically from other forms of cell death, such as apoptosis, autophagy, and necrosis. Although the molecular mechanism underlying ferroptosis remains unclear, multiple biological processes, such as iron metabolism, lipid peroxides, and systems, such as the glutathione system and the tetrahydrobiopterin/coenzyme Q10 system, appear to be involved. While the contribution of ferroptotic mechanisms to human diseases is not clear, recent studies have identified a number of ferroptosis-related genes. Cardiovascular diseases are the main cause of death globally. In this review, we outline the progress regarding the emerging role of ferroptosis in the pathogenesis of cardiac pathophysiological conditions and the association of ferroptosis with cardiomyopathy, myocardial ischemia-reperfusion injury, heart failure, and atherosclerosis. We further summarise newly discovered ferroptotic targets for the development of therapies for cardiovascular diseases. Finally, we discuss the current challenges and future research directions in cardiovascular disease treatments.

Emerging roles of fibroblast growth factor 21 in critical disease

In spite of the great progress in the management of critical diseases in recent years, its associated prevalence and mortality of multiple organ failure still remain high. As an endocrine hormone, fibroblast growth factor 21 (FGF21) functions to maintain homeostasis in the whole body. Recent studies have proved that FGF21 has promising potential effects in critical diseases. FGF21 has also been found to have a close relationship with the progression of critical diseases and has a great predictive function for organ failure. The level of FGF21 was elevated in both mouse models and human patients with sepsis or other critical illnesses. Moreover, it is a promising biomarker and has certain therapeutic roles in some critical diseases. We focus on the emerging roles of FGF21 and its potential effects in critical diseases including acute lung injury/acute respiratory distress syndrome (ALI/ARDS), acute myocardial injury (AMI), acute kidney injury (AKI), sepsis, and liver failure in this review. FGF21 has high application value and is worth further studying. Focusing on FGF21 may provide a new perspective for the management of the critical diseases.

Research Progress of Fibroblast Growth Factor 21 in Fibrotic Diseases

Fibrosis is a common pathological outcome of chronic injuries, characterized by excessive deposition of extracellular matrix components in organs, as seen in most chronic inflammatory diseases. At present, there is an increasing tendency of the morbidity and mortality of diseases caused by fibrosis, but the treatment measures for fibrosis are still limited. Fibroblast growth factor 21 (FGF21) belongs to the FGF19 subfamily, which also has the name endocrine FGFs because of their endocrine manner. In recent years, it has been found that plasma FGF21 level is significantly correlated with fibrosis progression. Furthermore, there is evidence that FGF21 has a pronounced antifibrotic effect in a variety of fibrotic diseases. This review summarizes the biological effects of FGF21 and discusses what is currently known about this factor and fibrosis disease, highlighting emerging insights that warrant further research.

The integrated stress response in ischemic diseases

Ischemic disease is among the deadliest and most disabling illnesses. Prominent examples include myocardial infarction and stroke. Most, if not all, underlying pathological changes, including oxidative stress, inflammation, and nutrient deprivation, are potent inducers of the integrated stress response (ISR). Four upstream kinases are involved in ISR signaling that sense a myriad of input stress signals and converge on the phosphorylation of serine 51 of eukaryotic translation initiation factor 2α (eIF2α). As a result, translation initiation is halted, creating a window of opportunity for the cell to repair itself and restore homeostasis. A growing number of studies show strong induction of the ISR in ischemic disease. Genetic and pharmacological evidence suggests that the ISR plays critical roles in disease initiation and progression. Here, we review the basic regulation of the ISR, particularly in response to ischemia, and summarize recent findings relevant to the actions of the ISR in ischemic disease. We then discuss therapeutic opportunities by modulating the ISR to treat ischemic heart disease, brain ischemia, ischemic liver disease, and ischemic kidney disease. Finally, we propose that the ISR represents a promising therapeutic target for alleviating symptoms of ischemic disease and improving clinical outcomes.

CTRP9 Mitigates the Progression of Arteriovenous Shunt-Induced Pulmonary Artery Hypertension in Rats

The present study is aimed at investigating the molecular mechanism of C1q/TNF-related protein 9 (CTRP9) and providing a new perspective in arteriovenous shunt-induced pulmonary arterial hypertension (PAH). PAH was established by an arteriovenous shunt placement performed in rats. Adenovirus(Ad)-CTRP9 and Ad-green fluorescent protein viral particles were injected into the rats through the tail vein. Following 12 weeks, the mean pulmonary arterial pressure (mPAP) and right ventricular systolic pressure (RVSP) were measured and morphological analysis was conducted to confirm the establishment of the PAH model. The systemic elevation of CTRP9 maintained pulmonary vascular homeostasis and protected the rats from dysfunctional and abnormal remodeling. CTRP9 attenuated the pulmonary vascular remodeling in the shunt group by decreasing the mPAP and RVSP, which was associated with suppressed inflammation, apoptosis, and extracellular matrix injury. In addition, CTRP9 dramatically increased the phosphorylation of AKT and p38-MAPK in the lung tissues of shunt-operated animals. These findings suggest a previously unrecognized effect of CTRP9 in pulmonary vascular homeostasis during PAH pathogenesis.

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.

FGF21 attenuates hypoxia‑induced dysfunction and inflammation in HPAECs via the microRNA‑27b‑mediated PPARγ pathway

Pulmonary arterial hypertension (PAH), is a chronic and progressive disorder characterized by pulmonary vascular remodeling, including endothelial cell dysfunction and inflammation. MicroRNAs (miRNAs or miRs) play an important role in the development of PAH. In addition, fibroblast growth factor 21 (FGF21) has been found to have marked anti-dysfunction and anti-inflammatory properties. Therefore, the present study aimed to investigate the latent effects of FGF21 against PAH through the miR-27b/peroxisome proliferator-activated receptor γ (PPARγ) axis. Human pulmonary arterial endothelial cells (HPAECs) subjected to hypoxia were used as PAH models. The results revealed that PPARγ expression was downregulated and miR-27b expression was upregulated in the HPAECs exposed to hypoxia. Luciferase assay suggested that PPARγ was a target gene of miR-27b. Furthermore, miR-27b inhibited the expression of the PPARγ gene, thereby aggravating hypoxia-induced HPAEC dysfunction. Moreover, miR-27b activated the nuclear factor-κB signaling pathway and the expression of inflammatory factors [interleukin (IL)-1β, IL-6 and tumor necrosis factor-α] by targeting PPARγ. In addition, the expression of miR-27b decreased following treatment of the hypoxia-exposed HPAECs with FGF21. Furthermore, FGF21 alleviated hypoxia-induced HPAEC dysfunction and inflammation by inhibiting miR-27b expression and thereby promoting PPARγ expression. On the whole, the findings of the present study suggest that FGF21 may serve as a therapeutic target for managing PAH through the miR-27b-mediated PPARγ pathway.

Adipokines and Metabolic Regulators in Human and Experimental Pulmonary Arterial Hypertension

Pulmonary hypertension (PH) is associated with meta-inflammation related to obesity but the role of adipose tissue in PH pathogenesis is unknown. We hypothesized that adipose tissue-derived metabolic regulators are altered in human and experimental PH. We measured circulating levels of fatty acid binding protein 4 (FABP-4), fibroblast growth factor -21 (FGF-21), adiponectin, and the mRNA levels of FABP-4, FGF-21, and peroxisome proliferator-activated receptor γ (PPARγ) in lung tissue of patients with idiopathic PH and healthy controls. We also evaluated lung and adipose tissue expression of these mediators in the three most commonly used experimental rodent models of pulmonary hypertension. Circulating levels of FABP-4, FGF-21, and adiponectin were significantly elevated in PH patients compared to controls and the mRNA levels of these regulators and PPARγ were also significantly increased in human PH lungs and in the lungs of rats with experimental PH compared to controls. These findings were coupled with increased levels of adipose tissue mRNA of genes related to glucose uptake, glycolysis, tricarboxylic acid cycle, and fatty acid oxidation in experimental PH. Our results support that metabolic alterations in human PH are recapitulated in rodent models of the disease and suggest that adipose tissue may contribute to PH pathogenesis.

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.

MicroRNA‑30a‑5p promotes proliferation and inhibits apoptosis of human pulmonary artery endothelial cells under hypoxia by targeting YKL‑40

Pulmonary arterial hypertension (PAH) is a fatal and currently incurable cardiopulmonary disease. Numerous microRNAs (miRNAs) serve important roles in the development of PAH. While the expression of miR-30a-5p was downregulated in the lung tissue of rats in a pulmonary hypertension rat model, the expression pattern and function of miR-30a-5p in human PAH remain unclear. Reverse transcription quantitative polymerase chain reaction (RT-qPCR) was used to examine miR-30a-5p and chitinase-3-like protein 1 (YKL-40) mRNA expression levels. The expression levels of YKL-40 and apoptosis-associated proteins were measured by western blot analysis. Cell proliferation assays and flow cytometry analysis were performed to examine cell proliferation and apoptosis, respectively. The association between miR-30a-5p and YKL-40 was determined by a luciferase reporter assay, RT-qPCR and western blot analysis. The relative expression levels of miR-30a-5p in plasma were increased in patients with PAH [median=13.23 (25th percentile=6.388, 75th percentile=21.91)] compared with normal controls [median=2.25 (25th percentile=1.4, 75th percentile=3.7). The expression of miR-30a-5p was significantly downregulated while the protein expression of YKL-40 was significantly upregulated in hypoxia-induced human pulmonary artery endothelial cells (HPAECs) when compared with the hypoxia-induced group at 0 h. miR-30a-5p overexpression promoted HPAEC growth and inhibited apoptosis of HPAECs under hypoxia. A miR-30a-5p mimic decreased the luciferase activity of a luciferase reporter construct containing YKL-40 3′-untranslated region and also decreased YKL-40 protein expression. YKL-40 overexpression partly alleviated the effects of miR-30a-5p upregulation on proliferation and apoptosis of HPAECs under hypoxia. In conclusion, the data indicated that miR-30a-5p promoted cell growth and inhibited apoptosis of HPAECs under hypoxia by targeting YKL-40. Therefore, the miR-30a-5p/YKL-40 axis may provide a potential target for the development of novel PAH therapies.

Mutual promotion of FGF21 and PPARγ attenuates hypoxia-induced pulmonary hypertension

IMPACT STATEMENT

In this study, we reported for the first time that FGF21 alleviated hypoxia-induced pulmonary hypertension through attenuation of increased pulmonary arterial pressure, pulmonary arterial remodeling and collagen deposition in vivo, and we confirmed the mutual promotion of FGF21 and PPARγ in hypoxia-induced pulmonary hypertension. Additionally, we found that FGF21 and PPARγ mutually promote each other's expression via the AMPK/PGC-1α pathway and KLB protein in vitro and in vivo. Pulmonary hypertension is a progressive and serious pathological phenomenon with a poor prognosis, and current therapies are highly limited. Our results provide novel insight into potential clinical therapies for pulmonary hypertension and establish the possibility of using this drug combination and potential dosage reductions in clinical settings.

Fibroblast Growth Factor 21 Attenuates Vascular Calcification by Alleviating Endoplasmic Reticulum Stress Mediated Apoptosis in Rats

Fibroblast growth factor 21 (FGF21), a hormone with multiple metabolic properties, has proven to be pleiotropic biological effects and may play pivotal role in numerous cardiovascular and metabolic diseases in the future. Vascular calcification (VC) is a concomitant pathological process of various cardiovascular and metabolic diseases. However, the effects of FGF21 on VC remain unclear. Therefore, in this research, we aimed to explore the roles and mechanisms of FGF21 in VC induced by vitamin D₃ plus nicotine (VDN) treatment rats. After 28 days VDN treatment, the calcium overload was confirmed by blood pressure, ultrasound imaging, calcium content, ALP activity and aortic pathological characteristics. In terms of FGF21, exogenous FGF21 can ameliorate the elevation of blood pressure, aortic calcification and related injury in VC rats. To investigate the mechanisms of FGF21 on VC, the endoplasmic reticulum stress (ERS) mediated apoptosis pathways were tested. As a method to detect apoptosis, the increased positive TUNEL staining cells were alleviated by FGF21 treatment. Furthermore, exogenous FGF21 can suppress the increased ERS chaperone, GRP78, in the calcified aortas. In the three pathways of ERS mediated apoptosis, we found CHOP pathway and caspase-12 pathway were involved in the treatment of FGF21, but not p-JNK/JNK pathway. Our study proved for the first time that FGF21 can inhibit the progress of VC by alleviating ERS mediated apoptosis in rats. FGF21 might be a new target for preventing and treating VC.