Aldehyde dehydrogenase 2 deficiency promotes atherosclerotic plaque instability through accelerating mitochondrial ROS-mediated vascular smooth muscle cell senescence

Previous evidence has indicated a beneficial role for aldehyde dehydrogenase 2 (ALDH2) in suppressing atherosclerotic plaque progression and instability. However, the underlying mechanism remains somewhat elusive. This study was designed to examine the effect of ALDH2 deficiency on high-cholesterol diet-induced atherosclerotic plaque progression and plaque vulnerability in atherosclerosis-prone ApoE knockout (ApoE^?/?) mice with a focus on foam cell formation in macrophages and senescence of vascular smooth muscle cells (VSMCs). Serum lipid profile, plaque progression, and plaque vulnerability were examined in ApoE^?/? and ALDH2/ApoE double knockout (ALDH2^?/?ApoE^?/?) mice after high-cholesterol diet intake for 8 weeks. ALDH2 deficiency increased the serum levels of triglycerides while it decreased levels of total cholesterol and high-density lipoprotein cholesterol. Unexpectedly, ALDH2 deficiency reduced the plaque area by 58.9% and 37.5% in aorta and aortic sinus, respectively. Plaque instability was aggravated by ALDH2 deficiency along with the increased necrotic core size, decreased collagen content, thinner fibrous cap area, decreased VSMC content, and increased macrophage content. In atherosclerotic lesions, ALDH2 protein was located in both macrophages and VSMCs. Further results revealed downregulated ALDH2 expression in aorta of aged ApoE^?/? mice compared with young mice. However, in vitro study suggested that ALDH2 expression was upregulated in bone marrow-derived macrophages (BMDMs) with an opposite effect in VSMCs following 80 μg/ml oxidized low-density lipoprotein (oxLDL) treatment. Interestingly, ALDH2 deficiency displayed little effect in oxLDL-induced foam cell formation from BMDMs, while ALDH2 knockdown by siRNA and ALDH2 overexpression by lentivirus infection promoted and retarded oxLDL-induced VSMC senescence, respectively. Mechanistically, ALDH2 mitigated oxLDL-induced overproduction of mitochondrial reactive oxygen species (mROS) and activation of downstream p53/p21/p16 pathway. Clearance of mROS by mitoTEMPO significantly reversed the promotive effect of ALDH2 knockdown on VSMC senescence. Taken together, our data revealed that ALDH2 deficiency suppressed atherosclerotic plaque area while facilitating plaque instability possibly through accelerating mROS-mediated VSMC senescence.This article is part of a Special Issue entitled: Genetic and epigenetic regulation of aging and longevity edited by Jun Ren & Megan Yingmei Zhang.     

Cytokines, macrophage lipid metabolism and foam cells: implications for cardiovascular disease therapy

Cardiovascular disease is the biggest killer globally and the principal contributing factor to the pathology is atherosclerosis; a chronic, inflammatory disorder characterized by lipid and cholesterol accumulation and the development of fibrotic plaques within the walls of large and medium arteries. Macrophages are fundamental to the immune response directed to the site of inflammation and their normal, protective function is harnessed, detrimentally, in atherosclerosis. Macrophages contribute to plaque development by internalizing native and modified lipoproteins to convert them into cholesterol-rich foam cells. Foam cells not only help to bridge the innate and adaptive immune response to atherosclerosis but also accumulate to create fatty streaks, which help shape the architecture of advanced plaques. Foam cell formation involves the disruption of normal macrophage cholesterol metabolism, which is governed by a homeostatic mechanism that controls the uptake, intracellular metabolism, and efflux of cholesterol. It has emerged over the last 20 years that an array of cytokines, including interferon-γ, transforming growth factor-β1, interleukin-1β, and interleukin-10, are able to manipulate these processes. Foam cell targeting, anti-inflammatory therapies, such as agonists of nuclear receptors and statins, are known to regulate the actions of pro- and anti-atherogenic cytokines indirectly of their primary pharmacological function. A clear understanding of macrophage foam cell biology will hopefully enable novel foam cell targeting therapies to be developed for use in the clinical intervention of atherosclerosis.     

The inhibitory effect of dexamethasone on platelet-derived growth factor-induced vascular smooth muscle cell migration through up-regulating PGC-1α expression

Dexamethasone has been shown to inhibit vascular smooth muscle cell (VSMC) migration, which is required for preventing restenosis. However, the mechanism underlying effect of dexamethasone remains unknown. We have previously demonstrated that peroxisome proliferator-activated receptor gamma (PPARγ) coactivator-1 alpha (PGC-1α) can inhibit VSMC migration and proliferation. Here, we investigated the role of PGC-1α in dexamethasone-reduced VSMC migration and explored the possible mechanism. We first examined PGC-1α expression in cultured rat aortic VSMCs. The results revealed that incubation of VSMCs with dexamethasone could significantly elevate PGC-1α mRNA expression. In contrast, platelet-derived growth factor (PDGF) decreased PGC-1α expression while stimulating VSMC migration. Mechanistic study showed that suppression of PGC-1α by small interfering RNA strongly abrogated the inhibitory effect of dexamethasone on VSMC migration, whereas overexpression of PGC-1α had the opposite effect. Furthermore, an analysis of MAPK signal pathways showed that dexamethasone inhibited ERK and p38 MAPK phosphorylation in VSMCs. Overexpression of PGC-1α decreased both basal and PDGF-induced p38 MAPK phosphorylation, but it had no effect on ERK phosphorylation. Finally, inhibition of PPARγ activation by a PPARγ antagonist GW9662 abolished the suppressive effects of PGC-1α on p38 MAPK phosphorylation and VSMC migration. These effects of PGC-1α were enhanced by a PPARγ agonist troglitazone. Collectively, our data indicated for the first time that one of the anti-migrated mechanisms of dexamethasone is due to the induction of PGC-1α expression. PGC-1α suppresses PDGF-induced VSMC migration through PPARγ coactivation and, consequently, p38 MAPK inhibition.     

Enhanced levels of endogenous endothelin-1 contribute to the over expression of Giα protein in vascular smooth muscle cells from SHR: Role of growth factor receptor activation

We earlier showed that vascular smooth muscle cells (VSMC) from spontaneously hypertensive rats (SHR) exhibit increased expression of Gi proteins. Since the levels of endothelin-1 (ET-1) are enhanced in VSMC from SHR, we undertook the present study to examine the implication of endogenous ET-1 and the underlying mechanisms in the enhanced expression of Giα proteins in VSMC from SHR. The enhanced expression of Giα-2 and Giα-3 proteins in VSMC from SHR was inhibited by ET_A and ET_B receptor antagonists, BQ123 and BQ788 respectively. In addition, these antagonists also attenuated the enhanced inhibition of forskolin-stimulated adenylyl cyclase activity by low concentrations of GTPγS and by inhibitory hormones in VSMC from SHR compared to WKY. Furthermore, AG1295, AG1024 and PP2, inhibitors of platelet derived growth factor receptor (PDGFR), insulin-like growth factor 1 receptor (IGF-1R) and c-Src respectively, inhibited the enhanced expression of Giα protein and the enhanced phosphorylation of PDGFR and IGF-1R in VSMC from SHR to WKY levels. In addition, NAD(P)H oxidase inhibitor DPI and N-acetylcysteine (NAC), a scavenger of superoxide anion (O₂⁻) also inhibited the enhanced phosphorylation of PDGFR and IGF-1R and c-Src in VSMC from SHR to control levels. Furthermore, the augmented phosphorylation of ERK1/2 in VSMC from SHR was attenuated by BQ123 and BQ788, growth factor receptors inhibitors and PP2. These results suggest that the enhanced levels of endogenous ET-1 in VSMC from SHR increase oxidative stress, which through c-Src-mediated activation of growth factor receptors and associated MAP kinase signaling, contribute to the enhanced expression of Giα proteins.     

运动训练对大鼠主动脉应力和NF-κB及c-fos表达的影响

目的：探讨不同强度运动训练对大鼠主动脉应力和NF-κB及c-fos表达的影响。方法：采用跑台训练方式,建立大鼠有氧运动和疲劳运动模型,运用免疫组织化学SABC法研究不同强度运动训练对大鼠主动脉VEC和VSMC中NF-κB及c-fos表达的影响。结果：胸主动脉血压的变化与对照组比较,有氧训练和疲劳训练均显著性升高（P〈0．05）,但有氧训练与疲劳训练之间差异不显著。与对照组比较,有氧训练大鼠VEC和VSMC中NF-κB和c-fos均显著性下调表达,胸主动脉张开角显著性升高（P〈0．05）,疲劳训练大鼠VEC和VSMC中NF-κB和c-fos均显著性上调表达（P〈0．05）。与有氧运动组比较,疲劳运动大鼠VEC和VSMC中NF-κB和c-fos表达与胸主动脉张开角升高均具有显著性差异（P〈0．05）。表明不同强度运动大鼠主动脉VEC中NF-κB和c-fos表达变化趋势不同,疲劳训练组表达的增加趋势更显著。结论：运动可引起大鼠主动脉VEC和VSMC NF-κB及c-fos表达的变化,且与运动强度关系密切。有氧训练引起的慢性剪切应力变化可使主动脉VEC和VSMC NF-κB加及c-fos显著性下调表达,与VEC和VSMC维持血管功能的稳态有关;疲劳训练可导致壁面摩擦剪切力、周向应力增加,过度的剪切力作用可引起主动脉VEC和VSMC NF-κB及c-fos显著性上调表达,血管张开角显著增加,血管发生非均匀生长,引起血管结构与功能的重塑。     

Sphingosine 1-phosphate transactivates c-Met as well as epidermal growth factor receptor (EGFR) in human gastric cancer cells

Receptor tyrosine kinases (RTKs) are transactivated by the stimulation of G protein-coupled receptors (GPCRs). Sphingosine 1-phosphate (S1P), a ligand of GPCR, is known as a tumor-promoting lipid, but its signaling pathways are not fully understood. We here demonstrated that S1P induces rapid and transient tyrosine phosphorylation of epidermal growth factor receptor (EGFR) and c-Met in gastric cancer cells, both of which have been proposed as prognostic markers of gastric cancers. The pathway of S1P-induced c-Met transactivation is Gi-independent and matrix metalloproteinase-independent, which differs from that of EGFR transactivation. Our results indicate that S1P acts upstream of various RTKs and thus may act as a potent stimulator of gastric cancer.     

Temporary membrane distortion of vascular smooth muscle cells is responsible for their apoptosis induced by platelet-activating factor-like oxidized phospholipids and their degradation product, lysophosphatidylcholine

To obtain information about the mechanism of apoptosis induced by oxidized low density lipoproteins (oxLDL) in atherosclerotic plaques, we examined the effects of lysophosphatidylcholine (LPC) and platelet-activating factor (PAF)-like lipids (PAF-LL), which can be derived from oxLDL, on rat vascular smooth muscle cells (VSMC). All the lipids with different structures examined induced apoptosis of VSMC, so we studied the mechanism of induction of apoptosis by LPC. LPC-induced apoptosis was inhibited by alpha-tocopherol (alpha-T) and cholesterol (Chol), but not by other antioxidants such as palmitoyl ascorbic acid and PAF receptor antagonist. The cells temporarily became spherical and highly permeable before induction of apoptosis, and their change in shape was prevented by alpha-T and Chol. From these results, we suggest that the apoptosis induced by oxLDL-derived phospholipids in VSMC is caused by temporary membrane distortion, not through specific receptors.     

Osteopontin stimulates vascular smooth muscle cell migration by inducing FAK phosphorylation and ILK dephosphorylation

Focal adhesion kinase (FAK) and integrin-linked kinase (ILK) are both involved in integrin-mediated cell migration. However, the molecular mechanism, and the relationship between FAK and ILK activity in signaling transduction for the osteopontin (OPN)-induced migration of vascular smooth muscle cells (VSMCs) remain unclear. Here, we show that treating VSMCs with OPN could result in the dissociation of FAK with ILK by inducing phosphorylation of the former and dephosphorylation of the latter. Furthermore, we demonstrate that FAK phosphorylation induced by OPN is coupled with ILK dephosphorylation. We also provide evidence that ILK acts downstream of FAK in the signaling pathways that mediate OPN-induced VSMC migration. These findings suggest that FAK phosphorylation and ILK dephosphorylation play important roles in VSMC migration induced by OPN.