Downregulated endogenous sulfur dioxide/aspartate aminotransferase pathway is involved in angiotensin II-stimulated cardiomyocyte autophagy and myocardial hypertrophy in mice

Persistent hypertension induces atrial remodeling and atrial fibrillation through DNA damage and ATM/CHK2/p53 signaling pathway

Atrial fibrillation (AF) is the most prevalent arrhythmia in clinical practice, with hypertension emerging as an independent risk factor. Previous literature has established associations between DNA damage response (DDR) and autophagy in relation to the pathogenesis of AF. The aim of this study was to evaluate the effect of atrial DNA damage response in persistent hypertension-induced atrial electrical and structural remodeling, and to further explore the potential therapeutic targets. Patient samples, spontaneous hypertensive rats (SHR) and angiotensin II (Ang II)-challenged HL-1 cells were employed to elucidate the detailed mechanisms. Bioinformatics analysis and investigation on human atrial samples revealed a critical role of DDR in the pathogenesis of AF. The markers of atrial DNA damage, DDR, autophagy, inflammation and fibrosis were detected by western blot, immunofluorescence, monodansyl cadaverine (MDC) assay and transmission electron microscopy. Compared with the control group, SHR exhibited significant atrial electrical and structural remodeling, abnormal increase of autophagy, inflammation, and fibrosis, which was accompanied by excessive activation of DDR mediated by the ATM/CHK2/p53 pathway. These detrimental changes were validated by in vitro experiments. Ang II-challenged HL-1 cells also exhibited significantly elevated γH2AX expression, and markers related to autophagy, inflammation as well as structural remodeling. Additionally, inhibition of ATM with KU55933 (a specific ATM inhibitor) significantly reversed these effects. Collectively, these data demonstrate that DNA damage and the subsequently overactivated ATM/CHK2/p53 pathway play critical roles in hypertension-induced atrial remodeling and the susceptibility to AF. Targeting ATM/CHK2/p53 signaling may serve as a potential therapeutic strategy against AF.

Sulfenylation of ERK1/2: A novel mechanism for SO2-mediated inhibition of cardiac fibroblast proliferation

Background

Endogenous sulfur dioxide (SO2) plays a crucial role in protecting heart from myocardial fibrosis by inhibiting the excessive growth of cardiac fibroblasts. This study aimed to investigate potential mechanisms by which SO2 suppressed myocardial fibrosis.

Methods and results

Mouse model of angiotensin II (Ang II)-induced cardiac fibrosis and cell model of Ang II-stimulated cardiac fibroblast proliferation were employed. Our findings discovered that SO2 mitigated the aberrant phosphorylation of extracellular signal-regulated kinase 1/2 (ERK1/2) induced by Ang II, leading to a reduction of fibroblast proliferation. Mechanistically, for the first time, we found that SO2 sulfenylated ERK1/2, and inhibited ERK1/2 phosphorylation and cardiac fibroblast proliferation, while a sulfhydryl reducing agent dithiothreitol (DTT) reversed the above effects of SO2. Furthermore, mutant ERK1C183S (cysteine 183 to serine) abolished the sulfenylation of ERK by SO2, thereby preventing the inhibitory effects of SO2 on ERK1 phosphorylation and cardiac fibroblast proliferation.

Conclusion

Our study suggested that SO2 inhibited cardiac fibroblast proliferation by sulfenylating ERK1/2 and subsequently suppressing ERK1/2 phosphorylation. These new findings might enhance the understanding of the mechanisms underlying myocardial fibrosis and emphasize the potential of SO2 as a novel therapeutic target for myocardial fibrosis.

Elucidating the Molecular Pathways and Therapeutic Interventions of Gaseous Mediators in the Context of Fibrosis

Fibrosis, a pathological alteration of the repair response, involves continuous organ damage, scar formation, and eventual functional failure in various chronic inflammatory disorders. Unfortunately, clinical practice offers limited treatment strategies, leading to high mortality rates in chronic diseases. As part of investigations into gaseous mediators, or gasotransmitters, including nitric oxide (NO), carbon monoxide (CO), and hydrogen sulfide (H2S), numerous studies have confirmed their beneficial roles in attenuating fibrosis. Their therapeutic mechanisms, which involve inhibiting oxidative stress, inflammation, apoptosis, and proliferation, have been increasingly elucidated. Additionally, novel gasotransmitters like hydrogen (H2) and sulfur dioxide (SO2) have emerged as promising options for fibrosis treatment. In this review, we primarily demonstrate and summarize the protective and therapeutic effects of gaseous mediators in the process of fibrosis, with a focus on elucidating the underlying molecular mechanisms involved in combating fibrosis.

An efficient dual-function fluorescent probe for sulfites and sulfides and its imaging application in cells

As gas signaling molecules in organisms, SO2 derivatives and H2S play crucial regulating roles in a series of physiological processes. Therefore, developing an assay that can accurately monitor the concentration of SO2 derivatives and H2S in cells is extremely important for the research and treatment of related illnesses. A bifunctional probe SN-F based on FRET mechanism for SO2 derivatives and H2S was designed. SN-F had a short response time to SO2 (2 min), excellent anti-interference capability and selectivity in the non-organic solvent system (pH = 7.4), which was suitable for the determination of SO2 derivatives in cells. SN-F had a wide linear range for H2S. Moreover, SN-F was applied in cell imaging successfully with high targeting ability to endoplasmic reticulum (ER) and could monitor endogenous and exogenous H2S in cells.

Changes in glutamic oxaloacetic transaminase 2 during rat physiological and pathological cardiomyocyte hypertrophy

BACKGROUND

Physiological and pathological cardiomyocyte hypertrophy are important pathophysiological processes of adult congenital heart disease-associated ventricular hypertrophy. Glutamic oxaloacetic transaminase (GOT) is a vital marker of myocardial injury. This study aimed to investigate the changes in GOT levels during physiological and pathological cardiomyocyte hypertrophy in rats.

METHODS

RNA-seq analysis and colorimetric methods were used to evaluate the changes in GOT mRNA and activity, respectively. GOT2 protein expression was detected by western blotting and immunofluorescence. Hematoxylin-eosin and wheat germ agglutinin methods were used to observe changes in rat cardiomyocyte morphology.

RESULTS

In juvenile rat hearts, GOT mRNA expression and activity, and GOT2 protein level increased with age-related physiological cardiomyocyte hypertrophy; however, GOT2 protein level was reduced in hypoxia-induced pathological cardiomyocyte hypertrophy.

CONCLUSIONS

GOT2 may regulate physiological and pathological myocardial hypertrophy in rats. We speculated that the low GOT2 level contributed to the rapid occurrence of pathological cardiomyocyte hypertrophy, causing strong plasticity of right ventricular cardiomyocytes in the early postnatal period and heart failure in adulthood.

Sulfur signaling pathway in cardiovascular disease

Hydrogen sulfide (H2S) and sulfur dioxide (SO2), recognized as endogenous sulfur-containing gas signaling molecules, were the third and fourth molecules to be identified subsequent to nitric oxide and carbon monoxide (CO), and exerted diverse biological effects on the cardiovascular system. However, the exact mechanisms underlying the actions of H2S and SO2 have remained elusive until now. Recently, novel post-translational modifications known as S-sulfhydration and S-sulfenylation, induced by H2S and SO2 respectively, have been proposed. These modifications involve the chemical alteration of specific cysteine residues in target proteins through S-sulfhydration and S-sulfenylation, respectively. H2S induced S-sulfhydrylation can have a significant impact on various cellular processes such as cell survival, apoptosis, cell proliferation, metabolism, mitochondrial function, endoplasmic reticulum stress, vasodilation, anti-inflammatory response and oxidative stress in the cardiovascular system. Alternatively, S-sulfenylation caused by SO2 serves primarily to maintain vascular homeostasis. Additional research is warranted to explore the physiological function of proteins with specific cysteine sites, despite the considerable advancements in comprehending the role of H2S-induced S-sulfhydration and SO2-induced S-sulfenylation in the cardiovascular system. The primary objective of this review is to present a comprehensive examination of the function and potential mechanism of S-sulfhydration and S-sulfenylation in the cardiovascular system. Proteins that undergo S-sulfhydration and S-sulfenylation may serve as promising targets for therapeutic intervention and drug development in the cardiovascular system. This could potentially expedite the future development and utilization of drugs related to H2S and SO2.

Autophagy and pressure overload-induced cardiac hypertrophy

Autophagy plays an important role in the pathogenesis of cardiovascular diseases. Dysregulation of autophagy may have a huge effect on cardiac hypertrophy induced by overload pressure although reports on autophagy and cardiac hypertrophy have been contradictory. Some studies showed that autophagy activation attenuated cardiac hypertrophy. However, others suggested that inhibition of autophagy would be protective. Different research models or different pathways involved could be responsible for it. Cardiac hypertrophy may be alleviated through regulation of autophagy. This review aims to highlight the pathways and therapeutic targets identified in the prevention and treatment of cardiac hypertrophy by regulating autophagy.

Gaseous signal molecule SO2 regulates autophagy through PI3K/AKT pathway inhibits cardiomyocyte apoptosis and improves myocardial fibrosis in rats with type II diabetes

Myocardial fibrosis is a key link in the occurrence and development of diabetic cardiomyopathy. Its etiology is complex, and the effect of drugs is not good. Cardiomyocyte apoptosis is an important cause of myocardial fibrosis. The purpose of this study was to investigate the effect of gaseous signal molecule sulfur dioxide (SO₂) on diabetic myocardial fibrosis and its internal regulatory mechanism. Masson and TUNEL staining, Western-blot, transmission electron microscopy, RT-qPCR, immunofluorescence staining, and flow cytometry were used in the study, and the interstitial collagen deposition, autophagy, apoptosis, and changes in phosphatidylinositol 3-kinase (PI3K)/AKT pathways were evaluated from in vivo and in vitro experiments. The results showed that diabetic myocardial fibrosis was accompanied by cardiomyocyte apoptosis and down-regulation of endogenous SO₂-producing enzyme aspartate aminotransferase (AAT)_1/2. However, exogenous SO₂ donors could up-regulate AAT1/2, reduce apoptosis of cardiomyocytes induced by diabetic rats or high glucose, inhibit phosphorylation of PI3K/AKT protein, up-regulate autophagy, and reduce interstitial collagen deposition. In conclusion, the results of this study suggest that the gaseous signal molecule SO₂ can inhibit the PI3K/AKT pathway to promote cytoprotective autophagy and inhibit cardiomyocyte apoptosis to improve myocardial fibrosis in diabetic rats. The results of this study are expected to provide new targets and intervention strategies for the prevention and treatment of diabetic cardiomyopathy.

Sulfur Dioxide: Endogenous Generation, Biological Effects, Detection, and Therapeutic Potential

Significance: Previously, sulfur dioxide (SO₂) was recognized as an air pollutant. However, it is found to be endogenously produced in mammalian tissues. As a new gasotransmitter, SO₂ is involved in regulating the structure and function of blood vessels, heart, lung, gastrointestinal tract, nervous system, etc.Recent Advances: Increasing evidence showed that endogenous SO₂ regulates cardiovascular physiological processes, such as blood pressure control, vasodilation, maintenance of the normal vascular structure, and cardiac negative inotropy. Under pathological conditions including hypertension, atherosclerosis, vascular calcification, aging endothelial dysfunction, myocardial injury, myocardial hypertrophy, diabetic myocardial fibrosis, sepsis-induced cardiac dysfunction, pulmonary hypertension, acute lung injury, colitis, epilepsy-related brain injury, depression and anxiety, and addictive drug reward memory consolidation, endogenous SO₂ protects against the pathological changes via different molecular mechanisms and the disturbed SO₂/aspartate aminotransferase pathway is likely involved in the mechanisms for the earlier mentioned pathologic processes. Critical Issues: A comprehensive understanding of the biological effects of endogenous SO₂ is extremely important for the development of novel SO₂ therapy. In this review, we summarized the biological effects, mechanism of action, SO₂ detection methods, and its related prodrugs. Future Directions: Further studies should be conducted to understand the effects of endogenous SO₂ in various physiological and pathophysiological processes and clarify its underlying mechanisms. More efficient and accurate SO₂ detection methods, as well as specific and effective SO₂-releasing systems should be designed for the treatment and prevention of clinical related diseases. The translation from SO₂ basic medical research to its clinical application is also worthy of further study. Antioxid. Redox Signal. 36, 256-274.

Sulphenylation of CypD at Cysteine 104: A Novel Mechanism by Which SO2 Inhibits Cardiomyocyte Apoptosis

Objectives: The study was designed to explore the role of endogenous gaseous signaling molecule sulfur dioxide (SO2) in the control of cardiomyocyte apoptosis and its molecular mechanisms.

Methods: Neonatal mouse cardiac myocytes (NMCMs) and H9c2 cells were used in the cell experiments. The endogenous SO2 pathway including SO2 level and the expression of SO2-generating enzyme aspartate aminotransferase 1/2 (AAT1/2) were detected in NMCMs. The apoptosis of cardiomyocytes was examined by a TUNEL assay. The cleavage and the activity of apoptotic proteins caspase9 and caspase3 were measured. The content of ATP, the opening of mitochondrial permeability transition pore (mPTP), and the cytochrome c (cytc) leakage were detected by immunofluorescence. The sulphenylation of cyclophilin-D (CypD) was detected by biotin switch analysis. The four CypD mutant plasmids in which cysteine sites were mutated to serine were constructed to identify the SO2-affected site in vitro.

Results: ISO down-regulated the endogenous SO2/AAT pathway of cardiomyocytes in association with a significant increase in cardiomyocyte apoptosis, demonstrated by the increases in apoptosis, cleaved-caspase3/caspase3 ratio, and caspase3 activity. Furthermore, ISO significantly reduced ATP production in H9c2 cells, but the supplement of SO2 significantly restored the content of ATP. ISO stimulated mPTP opening, resulting in an increase in the release of cytc, which further increased the ratio of cleaved caspase9/caspase9 and enhanced the protein activity of caspase9. While, the supplementation of SO2 reversed the above effects. Mechanistically, SO2 did not affect CypD protein expression, but sulphenylated CypD and inhibited mPTP opening, resulting in an inhibition of cardiomyocyte apoptosis. The C104S mutation in CypD abolished SO2-induced sulphenylation of CypD, and thereby blocked the inhibitory effect of SO2 on the mPTP opening and cardiomyocyte apoptosis.

Conclusion: Endogenous SO2 sulphenylated CypD at Cys104 to inhibit mPTP opening, and thus protected against cardiomyocyte apoptosis.

Mitochondria-targeted and FRET-based fluorescent probe for the imaging of endogenous SO2 in living cells

Sulfur dioxide (SO₂) is an important signal molecule in living systems, and plays a wide range of physiological functions. Real-time and in situ detection of the dynamic balance of SO₂ in mitochondria is of great significance to in-depth study its biological roles. Herein, we have developed a mitochondria-targeted fluorescent probe Nap-L based on the FRET mechanism to detect SO₂ in living cells. The probe Nap-L employed naphthalimide and positively charged benzopyridine as the donor and acceptor in the FRET system, and emitted green and red fluorescence under excitation. In respond to SO₂, the nucleophilic addition of bisulfite to benzopyridine and then interrupted the FRET process from naphthalimide to benzopyridine fluorophore, thereby triggering an obvious change in the fluorescence ratio. The probe Nap-L showed high selectivity to SO₂ over the biothiols (Hcy, GSH, Cys) and other biologically related species. Biological experiments suggested that the probe Nap-L mainly distributed in mitochondria, and can be successfully used to detect mitochondrial endogenous SO₂ in living cells.

A novel fluorescent probe based on triphenylamine for detecting sulfur dioxide derivatives

According to the nucleophilicity of sulfur dioxide derivatives, a reactive fluorescent probe was designed and synthesized by linking triphenylamine with benzoindole.

Sulfur Dioxide: An Endogenous Protector Against Myocardial Injury

Sulfur dioxide (SO2) was previously known as a harmful gas in air pollution. Recently, it was reported that SO2 can be endogenously generated in cardiovascular tissues. Many studies have revealed that endogenous SO2 has important physiological and pathophysiological significance and pharmacological potential. As a novel gasotransmitter, SO2 has important regulatory effects on the heart. It has a dose-dependent negative inotropic effect on cardiac function, in which L-type calcium channels are involved. SO2 can also attenuate myocardial injury caused by various harmful stimuli and play an important role in myocardial ischemia-reperfusion injury and myocardial hypertrophy. These effects are thought to be linked to its ability to reduce inflammation and as an antioxidant. In addition, SO2 regulates cardiomyocyte apoptosis and autophagy. Therefore, endogenous SO2 plays an important role in maintaining cardiovascular system homeostasis. In the present review, the literature concerning the metabolism of endogenous SO2, its cardiac toxicological effects and physiological regulatory effects, mechanisms for SO2-mediated myocardial protection and its pharmacological applications are summarized and discussed.

Endogenous SO2-dependent Smad3 redox modification controls vascular remodeling

Sulfur dioxide (SO2) has emerged as a physiological relevant signaling molecule that plays a prominent role in regulating vascular functions. However, molecular mechanisms whereby SO2 influences its upper-stream targets have been elusive. Here we show that SO2 may mediate conversion of hydrogen peroxide (H2O2) to a more potent oxidant, peroxymonosulfite, providing a pathway for activation of H2O2 to convert the thiol group of protein cysteine residues to a sulfenic acid group, aka cysteine sulfenylation. By using site-centric chemoproteomics, we quantified >1000 sulfenylation events in vascular smooth muscle cells in response to exogenous SO2. Notably, ~42% of these sulfenylated cysteines are dynamically regulated by SO2, among which is cysteine-64 of Smad3 (Mothers against decapentaplegic homolog 3), a key transcriptional modulator of transforming growth factor β signaling. Sulfenylation of Smad3 at cysteine-64 inhibits its DNA binding activity, while mutation of this site attenuates the protective effects of SO2 on angiotensin II-induced vascular remodeling and hypertension. Taken together, our findings highlight the important role of SO2 in vascular pathophysiology through a redox-dependent mechanism.

Endothelial Cell-Derived SO2 Controls Endothelial Cell Inflammation, Smooth Muscle Cell Proliferation, and Collagen Synthesis to Inhibit Hypoxic Pulmonary Vascular Remodelling

Hypoxic pulmonary vascular remodelling (PVR) is the major pathological basis of aging-related chronic obstructive pulmonary disease and obstructive sleep apnea syndrome. The pulmonary artery endothelial cell (PAEC) inflammation, and pulmonary artery smooth muscle cell (PASMC) proliferation, hypertrophy and collagen remodelling are the important pathophysiological components of PVR. Endogenous sulfur dioxide (SO₂) was found to be a novel gasotransmitter in the cardiovascular system with its unique biological properties. The study was aimed to investigate the role of endothelial cell- (EC-) derived SO₂ in the progression of PAEC inflammation, PASMC proliferation, hypertrophy and collagen remodelling in PVR and the possible mechanisms. EC-specific aspartic aminotransferase 1 transgenic (EC-AAT1-Tg) mice were constructed in vivo. Pulmonary hypertension was induced by hypoxia. Right heart catheterization and echocardiography were used to detect mouse hemodynamic changes. Pathologic analysis was performed in the pulmonary arteries. High-performance liquid chromatography was employed to detect the SO₂ content. Human PAECs (HPAECs) with lentiviruses containing AAT1 cDNA or shRNA and cocultured human PASMCs (HPASMCs) were applied in vitro. SO₂ probe and enzyme-linked immunosorbent assay were used to detect the SO₂ content and determine p50 activity, respectively. Hypoxia caused a significant reduction in SO₂ content in the mouse lung and HPAECs and increases in right ventricular systolic pressure, pulmonary artery wall thickness, muscularization, and the expression of PAEC ICAM-1 and MCP-1 and of PASMC Ki-67, collagen I, and α-SMA (p < 0.05). However, EC-AAT1-Tg with sufficient SO₂ content prevented the above increases induced by hypoxia (p < 0.05). Mechanistically, EC-derived SO₂ deficiency promoted HPAEC ICAM-1 and MCP-1 and the cocultured HPASMC Ki-67 and collagen I expression, which was abolished by andrographolide, an inhibitor of p50 (p < 0.05). Meanwhile, EC-derived SO₂ deficiency increased the expression of cocultured HPASMC α-SMA (p < 0.05). Taken together, these findings revealed that EC-derived SO₂ inhibited p50 activation to control PAEC inflammation in an autocrine manner and PASMC proliferation, hypertrophy, and collagen synthesis in a paracrine manner, thereby inhibiting hypoxic PVR.

MiR-26a-5p inhibits GSK3β expression and promotes cardiac hypertrophy in vitro

Background

The role of miR-26a-5p expression in cardiac hypertrophy remains unclear. Herein, the effect of miR-26a-5p on cardiac hypertrophy was investigated using phenylephrine (PE)-induced cardiac hypertrophy in vitro and in a rat model of hypertension-induced hypertrophy in vivo.

Methods

The PE-induced cardiac hypertrophy models in vitro and vivo were established. To investigate the effect of miR-26a-5p activation on autophagy, the protein expression of autophagosome marker (LC3) and p62 was detected by western blot analysis. To explore the effect of miR-26a-5p activation on cardiac hypertrophy, the relative mRNA expression of cardiac hypertrophy related mark GSK3β was detected by qRT-PCR in vitro and vivo. In addition, immunofluorescence staining was used to detect cardiac hypertrophy related mark α-actinin. The cell surface area was measured by immunofluorescence staining. The direct target relationship between miR-26a-5p and GSK3β was confirmed by dual luciferase report.

Results

MiR-26a-5p was highly expressed in PE-induced cardiac hypertrophy. MiR-26a-5p promoted LC3II and decreased p62 expression in PE-induced cardiac hypertrophy in the presence or absence of lysosomal inhibitor. Furthermore, miR-26a-5p significantly inhibited GSK3β expression in vitro and in vivo. Dual luciferase report results confirmed that miR-26a-5p could directly target GSK3β. GSK3β overexpression significantly reversed the expression of cardiac hypertrophy-related markers including ANP, ACTA1 and MYH7. Immunofluorescence staining results demonstrated that miR-26a-5p promoted cardiac hypertrophy related protein α-actinin expression, and increased cell surface area in vitro and in vivo.

Conclusion

Our study revealed that miR-26a-5p promotes myocardial cell autophagy activation and cardiac hypertrophy by regulating GSK3β, which needs further research.

Protective Effect of a Novel Polysaccharide from Lonicera japonica on Cardiomyocytes of Mice Injured by Hydrogen Peroxide

Lonicera japonica is a traditional Chinese herbal medicine with antioxidation, anti-inflammatory, antibacterial, and immunoregulation functions. A method to isolate polysaccharides from Lonicera japonica (LJP) has been reported previously by our group. We also reported previously that LJP was consisted of 6 types of monosaccharides and had the characteristic absorption of typical polysaccharides. In this study, we investigated the protective effect of LJP on cardiomyocytes of mice injured by hydrogen peroxide (H2O2). The results showed that LJP can increase the cardiomyocyte viability and the activities of the enzyme (SOD, CAT, GSH-Px, AST, CPK, and LDH) in cardiomyocytes of mice injured by hydrogen peroxide. The results of intracellular ROS contents showed that a high dose (40 μg mL-1) of LJP had the best effects on protecting the cardiomyocytes of mice injured by H2O2. In addition, the measurement results of the cardiomyocyte apoptosis and the activity of caspase-3, caspase-8, and caspase-9 in cardiomyocytes confirmed this conclusion from another perspective.

Macrophage-derived sulfur dioxide is a novel inflammation regulator

Macrophage-mediated inflammation is a key pathophysiological component of cardiovascular diseases, but the underlying mechanisms by which the macrophage regulates inflammation have been unclear. In our study, we, for the first time, showed an endogenous sulfur dioxide (SO₂) production in RAW267.4 macrophages by using HPLC and SO₂-specific fluorescent probe assays. Moreover, the endogenous SO₂ generating enzyme aspartate aminotransferase (AAT) was found to be expressed by the macrophages. Furthermore, we showed that AAT2 knockdown triggered spontaneous macrophage-mediated inflammation, as represented by the increased TNF-α and IL-6 levels and the enhanced macrophage chemotaxis; these effects could be reversed by the treatment with a SO₂ donor. Mechanistically, AAT2 knockdown activated the NF-κB signaling pathway in macrophages, while SO₂ successfully rescued NF-κB activation. In contrast, forced AAT2 expression reversed AngII-induced NF-κB activation and subsequent macrophage inflammation. Moreover, treatment with a SO₂ donor also alleviated macrophage infiltration in AngII-treated mouse hearts. Collectively, our data suggest that macrophage-derived SO₂ is an important regulator of macrophage activation and it acts as an endogenous "on-off switch" in the control of macrophage activation. This knowledge might enable a new therapeutic strategy for cardiovascular diseases.

Inhibiting SLC26A4 reverses cardiac hypertrophy in H9C2 cells and in rats

Background

It has been confirmed that mutations in solute carrier family 26 member 4 (SLC26A4) contribute to pendred syndrome. However, the role of SLC26A4 in cardiac hypertrophy and the signaling pathways remain unclear.

Methods

Cardiomyocytes were treated by 200 µM phenylephrine (PE) to induce cardiac hypertrophy. Also, the expression of SLC26A4, GSK3, cardiac hypertrophy markers including atrial natriuretic peptide (ANP) and brain natriuretic peptide (BNP) was detected through real-time quantitative polymerase chain reaction (RT-qPCR). Flow cytometry assay was used to test the apoptosis of PE-induced cardiomyocytes transfected by small interfere RNA (siRNA)-SLC26A4. Furthermore, we detected the expression of autophagy-related markers including light chain 3 (LC3) and P62. Finally, we established a rat model of abdominal aortic constriction (AAC)-induced cardiac hypertrophy in vivo.

Results

RT-qPCR results showed that the mRNA expression of SLC26A4 was significantly up-regulated in PE-induced cardiac hypertrophy. After inhibiting SLC26A4, the release of ANP and BNP was significantly decreased and GSK3β was elevated in vivo and in vitro. Furthermore, inhibiting SLC26A4 promoted apoptosis of cardiac hypertrophy cells. In addition, LC3 was down-regulated and P62 was enhanced after transfection of siRNA-SLC26A4.

Conclusion

Our findings revealed that SLC26A4 increases cardiac hypertrophy, and inhibiting SLC26A4 could decrease the release of ANP/BNP and promote the expression of GSK-3β in vitro and in vivo. Moreover, SLC26A4 silencing inhibits autophagy of cardiomyocytes and induces apoptosis of cardiomyocytes. Therefore, SLC26A4 possesses potential value to be a therapeutic target of cardiac hypertrophy, and our study provides new insights into the mechanisms of cardiac hypertrophy.

Inhibitory Effects of Sulfur Dioxide on Rat Myocardial Fibroblast Proliferation and Migration

Background:

Myocardial fibrosis is an important pathological change in many heart diseases, but its pathogenesis is very complex and has not yet been fully elucidated. The study was designed to examine whether endogenous sulfur dioxide (SO₂) is a novel myocardial fibroblast proliferation and migration inhibitor.

Methods:

Primary rat myocardial fibroblasts were isolated and transfected with aspartate aminotransferase (AAT1 and AAT2) knockdown lentivirus or empty lentivirus. SO₂ content in the supernatant was determined with high-performance liquid chromatography, and the expressions of AAT1, AAT2, proliferating cell nuclear antigen (PCNA), phosphorylated extracellular signal-regulated protein kinase (p-ERK), and total ERK (T-ERK) in the cells were detected. Cell migration was detected by wound healing test. Independent sample t-test (for two groups) and one-way analysis of variance (three or more groups) were used to analyze the results.

Results:

Both AAT1 and AAT2 knockdown significantly reduced SO₂ levels (F = 31.46, P < 0.01) and AAT1/2 protein expression (AAT1, t = 12.67, P < 0.01; AAT2, t = 9.61, P < 0.01), but increased PCNA expression and Cell Counting Kit-8 (CCK-8) activity as well as the migration in rat primary myocardial fibroblasts (P < 0.01). Supplementation of SO₂ rather than pyruvate significantly inhibited the increase in proliferation and migration caused by AAT knockdown (P < 0.01). Mechanistically, the ratio of p-ERK to T-ERK was significantly increased in the AAT1/2 knockdown groups compared with that in the empty lentivirus group (AAT1, t = −7.36, P < 0.01; AAT2, t = −10.97, P < 0.01). Whereas PD98059, an inhibitor of ERK activation, successfully blocked AAT knockdown-induced PCNA upregulation (F = 74.01, P > 0.05), CCK-8 activation (F = 50.14, P > 0.05), and migration augmentation in myocardial fibroblasts (24 h, F = 37.08, P > 0.05; 48 h, F = 58.60, P > 0.05).

Conclusion:

Endogenous SO₂ might be a novel myocardial fibroblast proliferation and migration inhibitor via inhibiting the ERK signaling pathway.

Sulfur dioxide improves endothelial dysfunction by downregulating the angiotensin II/AT1R pathway in D-galactose-induced aging rats

The aim of this study was to investigate the protective effects of sulfur dioxide (SO₂) on the endothelial function of the aorta in D-galactose (D-gal)-induced aging rats. Sprague Dawley rats were randomized into a D-gal group, a D-gal + SO₂ group and a control group, then injected with D-gal, D-gal + SO₂ donor or equivalent volumes of saline, respectively, for 8 consecutive weeks. After 8 weeks, the mean arterial pressure was significantly increased in the D-gal group, but was lowered by SO₂. SO₂ significantly ameliorated the endothelial dysfunction induced by D-gal treatment. The vasorelaxant effect of SO₂ was associated with the elevated nitric oxide levels and upregulated phosphorylation of endothelial nitric oxide synthase. In the D-gal group, the concentration of angiotensin II in the plasma was significantly increased, but was decreased by SO₂. Moreover, levels of vascular tissue hydrogen peroxide (H₂O₂) and malondialdehyde were significantly lower in SO₂-treated groups than those in the D-gal group. Western blot analysis showed that the expressions of oxidative stress-related proteins (the angiotensin II type 1 receptor (AT₁R), and nicotinamide adenine dinucleotide phosphate oxidase subunits) were increased in the D-gal group, while they were decreased after treatment with SO₂. In conclusion, SO₂ attenuated endothelial dysfunction in association with the inhibition of oxidative stress injury and the downregulation of the angiotensin II/AT₁R pathway in D-gal-induced aging rats.

Sulfur dioxide attenuates sepsis-induced cardiac dysfunction via inhibition of NLRP3 inflammasome activation in rats

OBJECTIVE

Sulfur dioxide (SO₂) plays an important role in maintaining homeostasis of cardiovascular system. This study was aimed to investigate cardioprotective effects of SO₂ on in the rat and the underlying mechanism.

METHODS AND RESULTS

Sepsis model induced by cecal ligation and puncture (CLP) in rats were used. SO₂ donor (NaHSO₃/Na₂SO₃, 1:3 M/M) was administered intraperitoneally at a dose of 85 mg/kg. Primary neonatal rat cardiac ventricular myocytes (NRCMs) were stimulated with LPS (1 mg/mL) in presence or absence of different concentrations of SO₂ (10, 50 and 100 μmol/L). SO₂ donor could restore the decreased levels of SO₂ in plasma and heart of septic rats. SO₂ exhibited dramatic improvement in cardiac functions. At 24 h after CLP, SO₂ treatments decreased the number of TUNEL-positive cells, Bax/Bcl-2 ratio and activity of caspase-3. Moreover CLP-induced inflammatory response was also relieved by SO₂. In NRCMs, SO₂ could suppress the LPS-induced myocardial injury, leading to an increase in cell viability, a decrease in LDH and apoptotic rate. Western blot showed that the expression of TLR4, NLRP3, and Caspase-1 were obviously increased in myocardial tissue of CLP group or in NRCMs of LPS group, while SO₂ significantly inhibited the CLP-induced or LPS-induced TLR4, NLRP3, and Caspase-1 expression.

CONCLUSION

SO₂ attenuated sepsis-induced cardiac dysfunction likely in association with the inhibiting inflammation via TLR4/NLRP3 signaling pathway.

The Increased Endogenous Sulfur Dioxide Acts as a Compensatory Mechanism for the Downregulated Endogenous Hydrogen Sulfide Pathway in the Endothelial Cell Inflammation

Endogenous hydrogen sulfide (H₂S) and sulfur dioxide (SO₂) are regarded as important regulators to control endothelial cell function and protect endothelial cell against various injuries. In our present study, we aimed to investigate the effect of endogenous H₂S on the SO₂ generation in the endothelial cells and explore its significance in the endothelial inflammation in vitro and in vivo. The human umbilical vein endothelial cell (HUVEC) line (EA.hy926), primary HUVECs, primary rat pulmonary artery endothelial cells (RPAECs), and purified aspartate aminotransferase (AAT) protein from pig heart were used for in vitro experiments. A rat model of monocrotaline (MCT)-induced pulmonary vascular inflammation was used for in vivo experiments. We found that endogenous H₂S deficiency caused by cystathionine-γ-lyase (CSE) knockdown increased endogenous SO₂ level in endothelial cells and enhanced the enzymatic activity of AAT, a major SO₂ synthesis enzyme, without affecting the expressions of AAT1 and AAT2. While H₂S donor could reverse the CSE knockdown-induced increase in the endogenous SO₂ level and AAT activity. Moreover, H₂S donor directly inhibited the activity of purified AAT protein, which was reversed by a thiol reductant DTT. Mechanistically, H₂S donor sulfhydrated the purified AAT1/2 protein and rescued the decrease in the sulfhydration of AAT1/2 protein in the CSE knockdown endothelial cells. Furthermore, an AAT inhibitor l-aspartate-β-hydroxamate (HDX), which blocked the upregulation of endogenous SO₂/AAT generation induced by CSE knockdown, aggravated CSE knockdown-activated nuclear factor-κB pathway in the endothelial cells and its downstream inflammatory factors including ICAM-1, TNF-α, and IL-6. In in vivo experiment, H₂S donor restored the deficiency of endogenous H₂S production induced by MCT, and reversed the upregulation of endogenous SO₂/AAT pathway via sulfhydrating AAT1 and AAT2. In accordance with the results of the in vitro experiment, HDX exacerbated the pulmonary vascular inflammation induced by the broken endogenous H₂S production in MCT-treated rat. In conclusion, for the first time, the present study showed that H₂S inhibited endogenous SO₂ generation by inactivating AAT via the sulfhydration of AAT1/2; and the increased endogenous SO₂ generation might play a compensatory role when H₂S/CSE pathway was downregulated, thereby exerting protective effects in endothelial inflammatory responses in vitro and in vivo.

Retina-derived endogenous sulfur dioxide might be a novel anti-apoptotic factor

Endogenous sulfur dioxide (SO2) was found to be generated from the enzymatic reaction catalysed by aspartate transference 1 (AAT1) in the mammals and play importantly biological effects. In the present study, we explored the existence of endogenous SO2 pathway in mouse retinal tissues and 661w photoreceptor cell and investigated its possible pathophysiological role in the hydrogen peroxide (H2O2)-induced mouse photoreceptor cell apoptosis. The data showed that endogenous SO2 pathway including AAT1 expression and SO2 content was found to be presented in mouse photoreceptor cells. AAT1 protein and SO2 were mainly distributed in the cytoplasm, while a small amount of AAT1 protein and SO2 was found in the nucleus of 661W photoreceptor cells. H2O2 significantly decreased the SO2 content and AAT1 expression, but increased the cleaved caspase-3 protein level and the apoptotic index, and the number of TUNEL-positive cells in the 661W photoreceptor cells. Moreover, an AAT inhibitor HDX treatment inhibited SO2 synthesis and mimicked H2O2-induced apoptosis in 661W cells. In conclusion, the endogenous SO2/AAT1 pathway is firstly found to be present in mouse photoreceptor cells, and might play an important role in the prevention from mouse photoreceptor cell apoptosis.

Gaseous signalling molecule SO2 via Hippo‑MST pathway to improve myocardial fibrosis of diabetic rats

Recent studies have indicated the existence of an endogenous sulfur dioxide (SO2)‑generating system in the cardiovascular system. The present study aimed to discuss the function and regulatory mechanism of gaseous signal molecule SO2 in inhibiting apoptosis and endoplasmic reticulum stress (ERS) via the Hippo‑MST signaling pathway to improve myocardial fibrosis of diabetic rats. A total of 40 male Sprague‑Dawley rats were randomly divided into four groups (10 rats per group): Normal control group (control group), diabetic rats group [streptozotocin (STZ) group], SO2 intervention group (STZ+SO2 group) and diabetes mellitus rats treated with L‑Aspartic acid β‑hydroxamate (HDX) group (HDX group). Diabetic rats models were established by intra‑peritoneal injection of STZ (40 mg/kg) Following model establishment, intra‑peritoneal injection of Na2SO3/NaHSO3 solution (0.54 mmol/kg) was administered in the STZ+SO2 group, and HDX solution (25 mg/kg/week) was administered in the HDX group. A total of 4 weeks later, echocardiography was performed to evaluate rats' cardiac function; Masson staining, terminal deoxynucleotidyl transferase dUTP nick end labeling staining and transmission electron microscopy examinations were performed to observe myocardial morphological changes. ELISA was employed to determine the SO2 content. Western blot analysis was performed to detect the expression of proteins associated with apoptosis, ERS and the Hippo‑MST signalling pathway. Compared with the control group, the STZ group and HDX group had a disordered arrangement of myocardial cells with apparent myocardial fibrosis, and echocardiography indicated that the cardiac function was lowered, there was an obvious increase of apoptosis in myocardial tissue, the expression levels of apoptosis‑associated protein B‑cell lymphoma associated protein X, caspase‑3 and caspase‑9 were upregulated, and Bcl‑2 expression was downregulated. The expression of ERS and Hippo‑MST pathway‑associated proteins, including CHOP, GRP94, MST1 and MST2, were significantly upregulated. By contrast, these above‑mentioned changes were reversed by SO2 treatment. Compared with STZ group, the HDX group had a further increase of myocardial fibrosis and apoptosis, while there were no statistically significant differences in the expression of Bax/Bcl‑2, caspase‑3, caspase‑9 and ERS and Hippo‑MST pathway‑associated proteins. The results of the present study demonstrated that the gaseous signal molecule SO2 can effectively improve the myocardial fibrosis of diabetic rats, and its mechanism may be associated with reduced apoptosis and ERS by downregulated Hippo‑MST pathway.