Sulfur dioxide attenuates hypoxia-induced pulmonary arteriolar remodeling via Dkk1/Wnt signaling pathway

A novel tiRNA-Glu-CTC induces nanoplastics accelerated vascular smooth muscle cell phenotypic switching and vascular injury through mitochondrial damage

Nanoplastics pose several health hazards, especially vascular toxicity. Transfer RNA-derived small RNAs (tsRNAs) are novel noncoding RNAs associated with different pathological processes. However, their biological roles and mechanisms in aberrant vascular smooth muscle cell (VSMC) plasticity and vascular injury are unclear. This study investigated the potent effects of tsRNAs on vascular injury induced by short- and long-term exposure to polystyrene nanoplastics (PS-NPs). Mice were exposed to PS-NPs (100 nm) at different doses (10-100 μg/mL) for 30 or 180 days. High-throughput sequencing was used to analyze tsRNA expression patterns in arterial tissues obtained from an in vivo model. Additionally, quantitative real-time polymerase chain reaction, fluorescent in situ hybridization assays, and dual-luciferase reporter assays were performed to measure the expression and impact of tiRNA-Glu-CTC on VSMCs exposed to PS-NPs. Short-term (≥50 μg/mL, moderate concentration) and long-term (≥10 μg/mL, low concentration) PS-NP exposure induced vascular injury in vivo. Cellular experiments showed that the moderate concentration of PS-NPs induced VSMC phenotypic switching, whereas a high concentration of PS-NPs (100 μg/mL) promoted VSMC apoptosis. PS-NP induced severe mitochondrial damage in VSMCs, including overexpression of reactive oxygen species, accumulation of mutated mtDNA, and dysregulation of genes related to mitochondrial synthesis and division. Compared with the control group, 13 upregulated and 12 downregulated tRNA-derived stress-induced RNAs (tiRNAs) were observed in the long-term PS-NP (50 μg/mL) exposure group. Bioinformatics analysis indicated that differentially expressed tiRNAs targeted genes that were involved in vascular smooth muscle contraction and calcium signaling pathways. Interestingly, tiRNA-Glu-CTC was overexpressed in vivo and in vitro following PS-NP exposure. Functionally, the tiRNA-Glu-CTC inhibitor mitigated VSMC phenotypic switching and mitochondrial damage induced by PS-NP exposure, whereas tiRNA-Glu-CTC mimics had the opposite effect. Mechanistically, tiRNA-Glu-CTC mimics induced VSMC phenotypic switching by downregulating Cacna1f expression. PS-NP exposure promoted VSMC phenotypic switching and vascular injury by targeting the tiRNA-Glu-CTC/Cacna1f axis.

Advances in the research of sulfur dioxide and pulmonary hypertension

Pulmonary hypertension (PH) is a fatal disease caused by progressive pulmonary vascular remodeling (PVR). Currently, the mechanisms underlying the occurrence and progression of PVR remain unclear, and effective therapeutic approaches to reverse PVR and PH are lacking. Since the beginning of the 21st century, the endogenous sulfur dioxide (SO2)/aspartate transaminase system has emerged as a novel research focus in the fields of PH and PVR. As a gaseous signaling molecule, SO2 metabolism is tightly regulated in the pulmonary vasculature and is associated with the development of PH as it is involved in the regulation of pathological and physiological activities, such as pulmonary vascular cellular inflammation, proliferation and collagen metabolism, to exert a protective effect against PH. In this review, we present an overview of the studies conducted to date that have provided a theoretical basis for the development of SO2-related drug to inhibit or reverse PVR and effectively treat PH-related diseases.

Long noncoding RNA Mhrt alleviates angiotensin II-induced cardiac hypertrophy phenotypes by mediating the miR-765/Wnt family member 7B pathway

Long noncoding RNAs (lncRNAs) are known to participate in the pathological process of cardiac hypertrophy. This study aimed to investigate the function of the lncRNA, myosin heavy-chain associated RNA transcript (Mhrt), in cardiac hypertrophy and its possible mechanism of action. Adult mouse cardiomyocytes were treated with angiotensin II (Ang II) and transfected with Mhrt; cardiac hypertrophy was evaluated by estimating atrial natriuretic peptide, brain natriuretic peptide, and beta-myosin heavy-chain levels, and cell surface area by reverse transcription-quantitative polymerase chain reaction, western blotting, and immunofluorescence staining. The interaction between the Mhrt/Wnt family member 7B (WNT7B) and miR-765 was assessed using a luciferase reporter assay. Rescue experiments were performed by analyzing the role of the miR-765/WNT7B pathway underlying the function of Mhrt. The results indicated that Ang II induced hypertrophy of cardiomyocytes; however, overexpression of Mhrt alleviated the Ang II-induced cardiac hypertrophy. Mhrt acted as a sponge for miR-765 to regulate the expression of WNT7B. Rescue experiments revealed that the inhibitory effect of Mhrt on myocardial hypertrophy was abolished by miR-765. Additionally, the knockdown of WNT7B reversed the suppression of myocardial hypertrophy induced by downregulating miR-765. Taken together, Mhrt alleviated cardiac hypertrophy by targeting the miR-765/WNT7B axis.

Reducing Chemo-/Radioresistance to Boost the Therapeutic Efficacy against Temozolomide-Resistant Glioblastoma

Chemo-/radioresistance is the most important reason for the failure of glioblastoma (GBM) treatment. Reversing the chemo-/radioresistance of GBM for boosting therapeutic efficacy is very challenging. Herein, we report a significant decrease in the chemo-/radioresistance of GBM by the in situ generation of SO₂ within a tumor, which was released on demand from the prodrug 5-amino-1,3-dihydrobenzo[c]thiophene 2,2-dioxide (ATD) loaded on rare-earth-based scintillator nanoparticles (i.e., NaYF₄:Ce@NaLuF₄:Nd@ATD@DSPE-PEG₅₀₀₀, ScNPs) under X-ray irradiation. Our novel X-ray-responsive ScNPs efficiently converted highly penetrating X-rays into ultraviolet rays for controlling the decomposition of ATD to generate SO₂, which effectively damaged the mitochondria of temozolomide-resistant U87 cells to lower the production of ATP and inhibit P-glycoprotein (P-gp) expression to reduce drug efflux. Meanwhile, the O⁶-methylguanine-DNA methyltransferase (MGMT) of drug-resistant tumor cells was also reduced to prevent the repair of damaged DNA and enhance cell apoptosis and the efficacy of chemo-/radiotherapy. The tumor growth was obviously suppressed, and the mice survived significantly longer than untreated temozolomide-resistant GBM-bearing mice. Our work demonstrates the potential of SO₂ in reducing chemo-/radioresistance to improve the therapeutic effect against resistant tumors if it can be well controlled and in situ generated in tumor cells. It also provides insights into the rational design of stimuli-responsive drug delivery systems for the controlled release of drugs.

Upregulation of Endothelial DKK1 (Dickkopf 1) Promotes the Development of Pulmonary Hypertension Through the Sp1 (Specificity Protein 1)/SHMT2 (Serine Hydroxymethyltransferase 2) Pathway

BACKGROUND

Pulmonary hypertension (PH) is a cancer-like proliferative disease, which has no curative treatment options. The dysfunction of pulmonary artery endothelial cells plays a key role in PH. DKK1 (Dickkopf 1) is a secretory glycoprotein that exerts proproliferative effects on tumor cells. In the present study, we aimed to identify the role and underlying mechanism of DKK1 in the development of PH, which still remain unclear.

METHODS AND RESULTS

We found endothelial DKK1 expression was upregulated in serum and lung tissues obtained from patients with PH, mice with hypoxia-induced PH, and human pulmonary artery endothelial cells cultured under hypoxic conditions. Endothelium-specific DKK1-knockout (DKK1ECKO) mice significantly ameliorated hypoxia+Sugen5416 and hypoxia-induced PH. More importantly, neutralizing anti-DKK1 antibody treatment significantly attenuated established hypoxia+Sugen5416 PH. Results of proteome analysis of control and DKK1-knockdown human pulmonary artery endothelial cells identified a significantly differentially expressed protein, SHMT2 (serine hydroxymethyltransferase 2), a key metabolic enzyme in one-carbon metabolism, as a novel DKK1 target. DKK1 knockdown in human pulmonary artery endothelial cells cultured under hypoxic conditions decreased the cellular NADPH/NADP+ ratio, increased reactive oxygen species levels and the extent of mitochondrial DNA damage, and inhibited mitochondrial membrane hyperpolarization. In the context of this altered redox defense and mitochondrial disorder, DKK1 induced a proproliferative and antiapoptotic phenotype in endothelial cells. Furthermore, we confirmed that DKK1 regulated SHMT2 transcription through the AKT-Sp1 (specificity protein 1) signaling axis.

CONCLUSIONS

Our data provide robust evidence and molecular explanations for the associations between DKK1, redox defense, mitochondrial disorders, and PH and reveal a novel target for PH treatment.

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.

Epithelial-mesenchymal transition related genes in unruptured aneurysms identified through weighted gene coexpression network analysis

Intracranial aneurysm (IA) can cause fatal subarachnoid hemorrhage (SAH) after rupture, and identifying patients with unruptured IAs is essential for reducing SAH fatalities. The epithelial-mesenchymal transition (EMT) may be vital to IA progression. Here, identified key EMT-related genes in aneurysms and their pathogenic mechanisms via bioinformatic analysis. The GSE13353, GSE75436, and GSE54083 datasets from Gene Expression Omnibus were analyzed with limma to identify differentially expressed genes (DEGs) among unruptured aneurysms, ruptured aneurysms, and healthy samples. The results revealed that three EMT-related DEGs (ADIPOQ, WNT11, and CCL21) were shared among all groups. Coexpression modules and hub genes were identified via weighted gene co-expression network analysis, revealing two significant modules (red and green) and 14 EMT-related genes. Gene Ontology and Kyoto Encyclopedia of Genes and Genomes pathway analyses suggested that cytokine interactions were closely related. Gene set enrichment analysis revealed that unruptured aneurysms were enriched for the terms "inflammatory response" and "vascular endothelial growth". Protein-protein interaction analysis identified seven key genes, which were evaluated with the GSE54083 dataset to determine their sensitivity and specificity. In the external validation set, we verified the differential expression of seven genes in unruptured aneurysms and normal samples. Together, these findings indicate that FN1, and SPARC may help distinguish normal patients from patients with asymptomatic IAs.

Compensatory role of endogenous sulfur dioxide in nitric oxide deficiency-induced hypertension

OBJECTIVE

This study aimed to determine the communicational pattern of gaseous signaling molecules sulfur dioxide (SO2) and nitric oxide (NO) between vascular endothelial cells (VECs) and vascular smooth muscle cells (VSMCs), and elucidate the compensatory role and significance of endogenous SO2 in the development of hypertension due to NO deficiency.

APPROACH AND RESULTS

Blood pressure was monitored by the tail-cuff and implantable physiological signal telemetry in L-nitro-arginine methyl ester (l-NAME)-induced hypertensive mice, and structural alterations of mouse aortic vessels were detected by the elastic fiber staining method. l-NAME-treated mice showed decreased plasma NO levels, increased SO2 levels, vascular remodeling, and increased blood pressure, and application of l-aspartate-β-hydroxamate, which inhibits SO2 production, further aggravated vascular structural remodeling and increased blood pressure. Moreover, in a co-culture system of HAECs and HASMCs, NO from HAECs did not influence aspartate aminotransferase (AAT)1 protein expression but decreased AAT1 activity in HASMCs, thereby resulting in the inhibition of endogenous SO2 production. Furthermore, NO promoted S-nitrosylation of AAT1 protein in HASMCs and purified AAT1 protein. Liquid chromatography with tandem mass spectrometry showed that the Cys192 site of AAT1 purified protein was modified by S-nitrosylation. In contrast, dithiothreitol or C192S mutations in HASMCs blocked NO-induced AAT1 S-nitrosylation and restored AAT1 enzyme activity.

CONCLUSION

Endothelium-derived NO inhibits AAT activity by nitrosylating AAT1 at the Cys192 site and reduces SO2 production in HASMCs. Our findings suggest that SO2 acts as a compensatory defense system to antagonize vascular structural remodeling and hypertension when the endogenous NO pathway is disturbed.

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.

PSF functions as a repressor of hypoxia-induced angiogenesis by promoting mitochondrial function

BACKGROUND

Abnormal neovascularization is the most common cause of blindness, and hypoxia alters tissue metabolism, function, and morphology. HIF-1α, the transcriptional activator of VEGF, has intricate mechanisms of nuclear translocation and activation, but its signal termination mechanisms remain unclear.

METHODS

We investigated the role of polypyrimidine tract-binding protein-associated splicing factor (PSF) in cellular energy production, migration, and proliferation by targeting HIF-1α in vivo and in vitro PSF plasmids were transfected with liposome 2000 transfection reagent. Young C57/BL6J mice were kept in a hyperoxia environment, followed by indoor air, resulting in oxygen-induced retinopathy. Oxygen-induced retinopathy (OIR) animals were randomly divided into three groups: OIR group, OIR + vector group (OIR cubs treated with rAAV vector) and OIR + PSF group (OIR cubs treated with rAAV-PSF). Age-matched C57/BL6J mice were used as controls and exposed to constant normoxic conditions. The animals were executed and their pupils were subjected to subsequent experiments. The metabolic spectrum was analyzed by Seahorse XFe96 flux analyzer, and OCR and extracellular acidification rate were quantified at the same time.

RESULTS

PSF ameliorated retinal neovascularization and corrected abnormal VEGF expression in mice with oxygen-induced retinopathy and reduced intra-retinal neovascularization in Vldlr - / - mice. PSF reprogrammed mitochondrial bioenergetics and inhibited the transition of endothelial cells after hypoxia, suggesting its involvement in pathological angiogenesis.Ectopic PSF expression inhibited hypoxia-induced HIF-1α activation in the nucleus by recruiting Hakai to the PSF/HIF-1α complex, causing HIF-1α inhibition. PSF knockdown increased hypoxia-stimulated HIF-1α reactions. These hypoxia-dependent processes may play a vital role in cell metabolism, migration, and proliferation. Thus, PSF is a potential treatment target in neovascularization-associated ophthalmopathy.

CONCLUSION

This is the first study showing that PSF inhibits HIF-1α via recruitment of Hakai, modulates mitochondrial oxidation and glycolysis, and downregulates VEGF expression under hypoxia. We propose a new HIF-1 α/Hakai regulatory mechanism that may play a vital role in the pathogenesis of neovascularization in ophthalmopathy. PSF-Hakai-HIF-1α signaling pathway under hypoxia condition. Schematic diagram showing that the PSF-Hakai-HIF-1α signaling pathway. Under hypoxia condition, PSF-Hakai complex regulate HIF-1α signaling, thus inhibiting downstream target gene VEGF, cell metabolism and angiogenesis eventually. Video Abstract: Detailed information of Materials and Methods.

Calcium-sensing receptor in the development and treatment of pulmonary hypertension

Calcium-sensing receptor (CaSR) is widely involved in the cell proliferation, differentiation, migration, adhesion and apoptosis, which can affect the vascular remodeling in the humanbody. The main ligand of CaSR is extracellular Ca²⁺. CaSR has the physiological significance in Ca²⁺ homeostasis. Pulmonary vascular remodeling is one of the main histopathological changes of pulmonary hypertension (PH). The abnormal proliferation of pulmonary artery smooth muscle cells (PASMCs) results in the pulmonary vascular remodeling. CaSR is an important regulator of [Ca²⁺]_i. [Ca²⁺]_i is the main cause of the excessive pulmonary vascular remodeling in patients with PH. In this review, it was conclued that the structure of CaSR was prone to explore the devolopment or the treatment of PH. It was found that the regulation of CaSR with some miRNA could inhibit the proliferation of PASMCs, and that CaSR could affect the occurrence of autophagy in PH. Therefore, CaSR would become a new therapeutic target to PH.

PDGF/MEK/ERK axis represses Ca2+ clearance via decreasing the abundance of plasma membrane Ca2+ pump PMCA4 in pulmonary arterial smooth muscle cells

Pulmonary arterial hypertension (PAH) is a rare and lethal disease characterized by vascular remodeling and vasoconstriction, which is associated with increased intracellular calcium ion concentration ([Ca2+]i). Platelet-derived growth factor-BB (PDGF-BB) is the most potent mitogen for pulmonary arterial smooth muscle cells (PASMCs) and is involved in vascular remodeling during PAH development. PDGF signaling has been proved to participate in maintaining Ca2+ homeostasis of PASMCs; however, the mechanism needs to be further elucidated. Here, we illuminate that the expression of plasma membrane calcium-transporting ATPase 4 (PMCA4) was downregulated in PASMCs after PDGF-BB stimulation, which could be abolished by restraining the mitogen-activated protein kinase/extracellular signal-regulated kinase (MEK/ERK). Functionally, suppression of PMCA4 attenuated the [Ca2+]i clearance in PASMCs after Ca2+ entry, promoting cell proliferation and elevating cell locomotion through mediating formation of focal adhesion. Additionally, the expression of PMCA4 was decreased in the pulmonary artery of monocrotaline (MCT)- or hypoxia-induced PAH rats. Moreover, knockdown of PMCA4 could increase the right ventricular systolic pressure (RVSP) and wall thickness (WT) of pulmonary artery in rats raised under normal conditions. Taken together, our findings demonstrate the importance of the PDGF/MEK/ERK/PMCA4 axis in intracellular Ca2+ homeostasis in PASMCs, indicating a functional role of PMCA4 in pulmonary arterial remodeling and PAH development.

Effect of sulfur dioxide on vascular biology

Gasotransmitters, such as nitric oxide, carbon monoxide and hydrogen sulfide, can be generated endogenously. These gasotransmitters play important roles in vascular biology, including vasorelaxation and inhibition of vascular smooth muscle cell (VSMC) proliferation. In recent years, sulfur dioxide (SO₂) has been considered as a fourth gasotransmitter. SO₂ is present in air pollution. Moreover, SO₂ toxicity, including oxidative stress and DNA damage, has been extensively reported in previous studies. Recent studies have shown that SO₂ can be endogenously generated in various organs and vascular tissues, where it regulates vascular tone, vascular smooth cell proliferation and collagen synthesis. SO₂ can decrease blood pressure in rats, inhibit smooth muscle cell proliferation and collagen accumulation and promote collagen degradation, and improve vascular remodelling. SO₂ can decrease cardiovascular atherosclerotic plaques by enhancing the antioxidant effect and upregulating nitric oxide/nitric oxide synthase and hydrogen sulfide/cystathionine-γ-lyase pathways. SO₂ can also ameliorate vascular calcification via the transforming growth factor - β1/Smad pathway. The effect of SO₂ on vascular regulation has attracted great interest. SO₂ may be a novel mediator in vascular biology.

Screening and functional prediction of differentially expressed circRNAs in proliferative human aortic smooth muscle cells

Vascular smooth muscle cell (VSMC) proliferation is the pathological base of vascular remodelling diseases. Circular RNAs (circRNAs) are important regulators involved in various biological processes. However, the function of circRNAs in VSMC proliferation regulation remains largely unknown. This study was conducted to identify the key differentially expressed circRNAs (DEcircRNAs) and predict their functions in human aortic smooth muscle cell (HASMC) proliferation. To achieve this, DEcircRNAs between proliferative and quiescent HASMCs were detected using a microarray, followed by quantitative real-time RT-PCR validation. A DEcircRNA-miRNA-DEmRNA network was constructed, and functional annotation was performed using Gene Ontology (GO) and KEGG pathway analysis. The function of hsa_circ_0002579 in HASMC proliferation was analysed by Western blot. The functional annotation of the DEcircRNA-miRNA-DEmRNA network indicated that the four DEcircRNAs might play roles in the TGF-β receptor signalling pathway, Ras signalling pathway, AMPK signalling pathway and Wnt signalling pathway. Twenty-seven DEcircRNAs with coding potential were screened. Hsa_circ_0002579 might be a pro-proliferation factor of HASMC. Overall, our study identified the key DEcircRNAs between proliferative and quiescent HASMCs, which might provide new important clues for exploring the functions of circRNAs in vascular remodelling diseases.

Endothelin-1 Downregulates Sulfur Dioxide/Aspartate Aminotransferase Pathway via Reactive Oxygen Species to Promote the Proliferation and Migration of Vascular Smooth Muscle Cells

The regulatory mechanisms for proliferation and migration of vascular smooth muscle cells have not yet been clear. The present study was designed to investigate whether and how endothelin-1 (ET-1) impacted the generation of endogenous sulfur dioxide (SO₂) in rat vascular smooth muscle cell (VSMC) proliferation and migration. Primary VSMCs and purified aspartate aminotransferase (AAT) protein were used in this study. We found that in the presence of ET-1, the expression of PCNA and Ki-67 was upregulated and the migration of VSMCs was promoted, while the AAT activity and SO₂ levels in VSMCs were reduced without any changes in AAT1 and AAT2 expression. SO₂ supplementation successfully prevented the ET-1-facilitated expression of PCNA and Ki-67 and the migration of VSMCs. Interestingly, ET-1 significantly increased reactive oxygen species (ROS) production in association with SO₂/AAT pathway downregulation in VSMCs compared with controls, while the ROS scavenger N-acetyl-L-cysteine (NAC) and the antioxidant glutathione (GSH) significantly abolished the ET-1-stimulated downregulation of the SO₂/AAT pathway. Moreover, the AAT activity was reduced in purified protein after the treatment for 2 h. However, NAC and GSH blocked the hydrogen peroxide-induced AAT activity reduction. In conclusion, our results suggest that ET-1 results in the downregulation of the endogenous SO₂/AAT pathway via ROS generation to enhance the proliferation and migration of VSMCs.

Sulfur Dioxide Activates Cl-/HCO3 - Exchanger via Sulphenylating AE2 to Reduce Intracellular pH in Vascular Smooth Muscle Cells

Sulfur dioxide (SO₂) is a colorless and irritating gas. Recent studies indicate that SO₂ acts as the gas signal molecule and inhibits vascular smooth muscle cell (VSMC) proliferation. Cell proliferation depends on intracellular pH (pH_i). Transmembrane cystein mutation of Na⁺- independent Cl^-/HCO₃ ^- exchanger (anion exchanger, AE) affects pH_i. However, whether SO₂ inhibits VSMC proliferation by reducing pH_i is still unknown. Here, we investigated whether SO₂ reduced pH_i to inhibit the proliferation of VSMCs and explore its molecular mechanisms. Within a range of 50-200 μM, SO₂ was found to lower the pH_i in VSMCs. Concurrently, NH₄Cl pre-perfusion showed that SO₂ significantly activated AE, whereas the AE inhibitor 4,4'-diisothiocyanatostilbene- 2,20-disulfonic acid (DIDS) significantly attenuated the effect of SO₂ on pH_i in VSMCs. While 200 μM SO₂ sulphenylated AE2, while dithiothreitol (DTT) blocked the sulphenylation of AE2 and subsequent AE activation by SO₂, thereby restoring the pH_i in VSMCs. Furthermore, DIDS pretreatment eliminated SO₂-induced inhibition of PDGF-BB-stimulated VSMC proliferation. We report for the first time that SO₂ inhibits VSMC proliferation in part by direct activation of the AE via posttranslational sulphenylation and induction of intracellular acidification.