Dang-heng Wei

PCSK9 siRNA suppresses the inflammatory response induced by oxLDL through inhibition of NF-κB activation in THP-1-derived macrophages.

Proprotein convertase subtilisin/kexin 9 (PCSK9), a member of the protein-converting enzyme family, is highly expressed in adult hepatocytes and small intestinal enterocytes. To our knowledge, in this study, we demonstrate for the first time that PCSK9 is upregulated in a dose-dependent manner via oxidized low-density lipoprotein (oxLDL) stimulation in THP-1-derived macrophages. PCSK9 small interfering RNA (siRNA) suppresses the oxLDL-induced inflammatory cytokine expression in THP-1-derived macrophages. The exposure of macrophages to oxLDL markedly increased the expression of NF-κB protein in the nucleus. However, this effect was significantly attenuated by PCSK9 siRNA. These findings indicate that PCSK9 expression is induced by oxLDL, and that PCSK9 siRNA protects against inflammation via the inhibition of NF-κB activation in oxLDL-stimulated THP-1-derived macrophages. Our results suggest that PCSK9 may be used as a therapeutic target for the treatment of atherosclerosis since PCSK9 siRNA suppresses oxLDL-induced IκB-α degradation and NF-κB nuclear translocation into THP-1-derived macrophages.

Hydrogen sulfide prevents H₂O₂-induced senescence in human umbilical vein endothelial cells through SIRT1 activation.

The aim of the present study was to investigate the attenuation of endothelial cell senescence by H2S and to explore the mechanisms underlying the anti-aging effects of H2S. Senescence was induced in human umbilical vein endothelial cells (HUVECs) by incubation in 25 µmol/l H2O2 for 1 h. Senescence-associated β-galactosidase (SA-β-gal) activity was examined to determine the effects of H2S on senescent HUVECs. The results indicated that SA-β-gal activity in the H2O2-treated HUVECs was 11.2 ± 1.06%, which was attenuated in the NaHS group. Pretreatment with nicotinamide (NAM), a sirtuin 1 (SIRT1) inhibitor, inhibited the reduction in senescence associated with H2S. Immunoblot analyses revealed that SIRT1 levels in senescent HUVECs treated with NaHS (60 µM) were indistinguishable from controls; however, analyses of SIRT1 activity indicated that SIRT1 enzyme activity was enhanced. In addition, we found that H2S improves the function of senescent HUVECs. The present study demonstrated that H2S protects against HUVEC senescence, potentially through modulation of SIRT1 activity. Furthermore, this study establishes a novel endothelial protective effect of H2S.

Cathepsin L stimulates autophagy and inhibits apoptosis of ox-LDL-induced endothelial cells: Potential role in atherosclerosis

The activation of endothelial cells by oxidized low-density lipoprotein (ox-LDL) with subsequent increases in endothelial permeability occurs in the early stage of atherosclerosis. Cathepsin L (CATL) is one of the cysteine proteases and has been implicated in advanced atherosclerotic lesions and plaque instability. This study aimed to explore the role of CATL in ox-LDL-induced early atherosclerotic events and to delineate the underlying mechanism. Results showed that ox-LDL upregulated CATL protein levels and activation in human umbilical vein endothelial cells (ECs) in a concentration-dependent manner and stimulated EC autophagy and apoptosis and increased EC monolayer permeability. Concomitantly, VE-cadherin expression was decreased. When ECs were pretreated with a CATL inhibitor, ox-LDL-induced autophagy was inhibited while apoptosis was further increased. In addition, the VE-cadherin protein level was increased, and the EC monolayer permeability was reduced. Taken together, the present study showed that the upregulated expression and activation of CATL induced by ox-LDL, increased EC autophagy and antagonized EC apoptosis, which partly neutralized the effect of increased EC monolayer permeability mediated by the downregulation of VE-cadherin. Thus, the proatherogenic effect of CATL was partly neutralized by inducing autophagy and inhibiting apoptosis in early stages of atherosclerosis.

Upregulation of SDF-1 is Associated with Atherosclerosis Lesions Induced by LDL Concentration Polarization

Previous numerical simulations on low-density lipoprotein (LDL) concentration polarization in the arterial system indicated that LDL concentration polarization might play an important role in the genesis and development of atherosclerosis. To date, no in vivo experiments have examined this question directly, and the molecular mechanisms are unknown. In this study, ten rabbits were treated with gel–silica loop to develop a defined local stenosis in the straight segment of the left carotid artery. Both numerical simulation and experiment measurements showed that the concentration of LDL was about 35% higher at the blood/arterial wall interface than in the lumen on the distal side of the stenosis. Atherosclerotic lesions with abundant lipid deposits were observed and stromal derived factor-1 (SDF-1) was detected at the distal end of the stenosis, while the straight segment was plaque-free. In vitro studies demonstrated that LDL-induced SDF-1 expression in endothelial cells and increased monocyte adhesion to endothelial cells in a dose-dependent manner. The adhesion was suppressed when endothelial cells were pretreated with SDF-1 antibody. These results suggested LDL concentration polarization contributed to the localization of atherosclerosis and to the expression of SDF-1. In turn, SDF-1 facilitated plaque formation.

New role of PCSK9 in atherosclerotic inflammation promotion involving the TLR4/NF-κB pathway

BACKGROUND AND AIMS Proprotein convertase subtilisin/kexin 9 (PCSK9) has emerged as a popular target in the development of new cholesterol-lowering drugs and therapeutic interventions for atherosclerosis. PCSK9 could accelerate atherosclerosis through mechanisms beyond the degradation of the hepatic low-density lipoprotein receptor. Several clinical studies suggested that PCSK9 is involved in atherosclerotic inflammation. Accordingly, this study aimed to explore the role of PCSK9 in vascular inflammation that promotes atherosclerotic progression. METHODS We examined whether PCSK9 silencing via transduction with the lentivirus-mediated PCSK9 shRNA (LV-PCSK9 shRNA) vector affects the formation of vascular lesions in hyperlipidemia-induced atherosclerosis in apolipoprotein E knockout (apoE KO) mice. In vitro, the effects of PCSK9 on oxLDL-induced macrophages inflammation were investigate using LV-PCSK9 and LV-PCSK9 shRNA for PCSK9 overexpression and PCSK9 silencing. RESULTS Immunohistochemical analysis showed that PCSK9 expression increased within atherosclerotic plaques in apoE KO mice. These in vivo results showed that the LV-PCSK9 shRNA group of mice developed less aortic atherosclerotic plaques compared with the control group. These lesions also had the reduced number of macrophages and decreased expression of vascular inflammation regulators, such as tumor necrosis factor-α, interleukin 1 beta, monocyte chemoattractant protein-1, toll-like receptor 4 and nuclear factor kappa B (NF-κB). We further showed that PCSK9 overexpression in macrophages in vitro increased the secretion of oxLDL-induced proinflammatory cytokines. PCSK9 overexpression upregulated TLR4 expression and increased p-IκBα levels, IkBα degradation, and NF-κB nuclear translocation in macrophages, but PCSK9 knockdown had the opposite effects in oxLDL-treated macrophages. CONCLUSIONS PCSK9 gene interference could suppress atherosclerosis directly through decreasing vascular inflammation and inhibiting the TLR4/NF-κB signaling pathway without affecting plasma cholesterol level in high-fat diet-fed apoE KO mice. PCSK9 may be an inflammatory mediator in the pathogenesis of atherosclerosis.

Ox-Lp(a) transiently induces HUVEC autophagy via an ROS-dependent PAPR-1-LKB1–AMPK–mTOR pathway

Oxidised lipoprotein(a) [oxLp(a)] is considered as a more potent arteriosclerotic factor than native Lp(a). However, the molecular mechanisms underlying this potency remain unclear. Reactive oxygen species (ROS) possibly act as intracellular second messengers that participate in autophagy stimulation. In this study, the effect of oxLp(a) on endothelial cell autophagy was determined. The mechanism and effect of autophagy on endothelial cells were also investigated. Results showed that oxLp(a) could induce autophagy depending on the generation of cellular ROS. Superoxide dismutase, an antioxidant, could inhibit oxLp(a)-induced autophagy in human umbilical vascular endothelial cells. Furthermore, poly(adenosine diphosphate-ribose) polymerase-1 (PARP-1)-liver kinase B1 (LKB1)-adenosine monophosphate-activated protein kinase (AMPK)-mammalian target of rapamycin (mTOR) and LKB1-AMPK-mTOR pathways are involved in oxLp(a)-induced autophagy. These pathways are also dependent on ROS. Thus, oxLp(a) induced autophagy via LKB1-AMPK-mTOR and PAPR-1-LKB1-AMPK-mTOR pathways, which are dependent on ROS generation.

Vitamin C down-regulate apo(a) expression via Tet2-dependent DNA demethylation in HepG2 cells

Lipoprotein(a)[Lp(a)] is a risk factor for coronary heart diseases. However, the metabolism of this protein remains poorly understood. Efficient and specific drugs that can decrease high plasma levels of Lp(a) have not been developed yet. Vitamin C is responsible for maintaining the catalytic activity of a group of iron and 2-oxoglutarate (2OG)-dependent dioxygenases and induces the generation of 5-hydroxymethylcytosine (5hmC) via Ten-eleven translocation (Tet) dioxygenases. In addition, It has been reported vitamin C deficiency induces atherosclerosis and increases Lp(a) and apo(a) plasma levels in Lp(a)+ mice. However, the mechanism is still unclear. In this study, we investigated the effects of vitamin C on apo(a) expression and the possible molecular mechanism of vitamin C that influences apolipoprotein(a) [apo(a)] biosynthesis in HepG2 cells. Results showed that vitamin C significantly inhibited the expression and secretion levels of apo(a). Vitamin C can also increase ELK1 expression and hydroxymethylation of ELK1 promoter and the globle DNA in HepG2 cells. In addition, the effects of vitamin C inhibiting the apo(a) expression were attenuated by ELK1siRNA and Tet2siRNA. These results suggested vitamin C down-regulate apo(a) expression via Tet2-dependent DNA demethylation in HepG2 cells.

Tet methylcytosine dioxygenase 2 inhibits atherosclerosis via upregulation of autophagy in ApoE −/− mice

Tet methylcytosine dioxygenase 2 (TET2) mediates the conversion of 5-methylcytosine (5mC) to 5-hydroxymethylcytosine (5hmC). The loss of TET2 is associated with advanced atherosclerotic lesions. Our previous study showed that TET2 improves endothelial cell function by enhancing endothelial cell autophagy. Accordingly, this study determined the role of TET2 in atherosclerosis and potential mechanisms. In ApoE−/− mice fed high-fat diet, TET2 overexpression markedly decreased atherosclerotic lesions with uniformly increased level of 5hmC and decreased level of 5mC in genomic DNA. TET2 overexpression also promoted autophagy and downregulated inflammation factors, such as vascular cell adhesion molecule 1, intercellular adhesion molecule 1, monocyte chemotactic protein 1, and interleukin-1. Consistently, TET2 knockdown with small hairpin RNA (shRNA) in ApoE−/− mice decreased 5hmC and increased 5mC levels in atherosclerotic lesions. Meanwhile, autophagy was inhibited and atherosclerotic lesions progressed with an unstable lesion phenotype characterized by large lipid core, macrophage accumulation, and upregulated inflammation factor expression. Experiments with the cultured endothelial cells revealed that oxidized low-density lipoprotein (ox-LDL) inhibited endothelial cell autophagy. TET2 shRNA strengthened impaired autophagy and autophagic flux in the ox-LDL-treated endothelial cells. TET2 overexpression reversed these effects by decreasing the methylation level of the Beclin 1 promoter, which contributed to the downregulation of inflammation factors. Overall, we identified that TET2 was downregulated during the pathogenesis of atherosclerosis. The downregulation of TET2 promotes the methylation of the Beclin 1 promoter, leading to endothelial cell autophagy, impaired autophagic flux, and inflammatory factor upregulation. Upregulation of TET2 may be a novel therapeutic strategy for treating atherosclerosis.

TET2 Protects against oxLDL-Induced HUVEC Dysfunction by Upregulating the CSE/H2S System

Ten-eleven translocation-2 (TET2) protein is a DNA demethylase that regulates gene expression through DNA demethylation and also plays important roles in various diseases including atherosclerosis. Endothelial dysfunction represents an early key event in atherosclerotic disease. The cystathionine-γ-lyase (CSE)/hydrogen sulfide (H2S) is a key endogenous system with protective effects on endothelial functions. In this study, we examined how TET2 regulates oxidized low-density lipoprotein (oxLDL)-induced dysfunction of human umbilical vein endothelial cells (HUVECs) and determined the role of the CSE/H2S system. Treatment with oxLDL resulted in downregulation of both TET2 expression and CSE/H2S system in HUVECs. TET2 was found to have protective effects on oxLDL-induced HUVEC dysfunction, which was confirmed with TET2 overexpression plasmid or TET2 shRNA plasmid. Moreover, TET2 was found to upregulate the CSE/H2S system and inhibit NF-κB activation, leading to decreased expression of ICAM-1 and VCAM-1 and attenuated adhesion of THP-1 cells to oxLDL-activated HUVECs. The protective effect of TET2 was reduced by treatment with CSE siRNA. Further studies revealed that CSE promoter region contains a well-defined CpG island. We also showed that TET2 enhanced 5-hydroxymethylcytosine (5hmC) level and promoted DNA demethylation of CSE gene promoter, leading to an increase in CSE expression. In conclusion, TET2 has protective effects on oxLDL-induced HUVEC dysfunction, likely through upregulating the CSE/H2S system by DNA demethylation of CSE gene promoter. TET2 may become a novel therapeutic target for endothelial dysfunction-associated vascular diseases.

H2S inhibits apo(a) expression and secretion through PKCα/FXR and Akt/HNF4α pathways in HepG2 cells

Lipoprotein(a) [Lp(a)] is a strong genetic risk factor for coronary heart diseases. However, the metabolism of this protein remains poorly understood. Efficient and specific drugs that can decrease high plasma levels of Lp(a) have not been developed yet. Hydrogen sulfide (H2S), a member of the gas transmitter family, performs important biological actions, including protection against cardiovascular diseases and maintenance of the lipid metabolism equilibrium in hepatocytes and adipocytes. In this study, we investigated the possible molecular mechanism of H2S that influences apolipoprotein(a) [apo(a)] biosynthesis. We also determined the effects of H2S on apo(a) expression and secretion in HepG2 cells as well as the underlying mechanisms. Results showed that H2S significantly inhibited the expression and secretion levels of apo(a). These effects were attenuated by the PKCα inhibitor and FXR siRNA. H2S also reduced HNF4α expression and enhanced FXR expression. The Akt inhibitor partially reversed H2S‐induced inhibition of apo(a) and HNF4α expression and apo(a) secretion. This study reveals that H2S suppressed apo(a) expression and secretion via the PKCα‐FXR and PI3K/Akt‐HNF4α pathways.