Insulin-independent GLUT4 translocation in proliferative vascular smooth muscle cells involves SM22α

HMGB2 promotes smooth muscle cell proliferation through PPAR-γ/PGC-1α pathway-mediated glucose changes in aortic dissection

BACKGROUND AND AIMS

Aortic dissection (AD) is a fatal condition with a complicated pathogenesis. High mobility group protein B2 (HMGB2) is a member of the high mobility group protein family; HMGB2 is involved in innate immunity and inflammatory diseases, but its role in AD remains unclear.

METHODS

HMGB2-/- mice were generated and treated with β-aminopropionitrile and angiotensin II (Ang II) to establish an AD model. An F12 gel containing AAV9-HMGB2 was applied to overexpress HMGB2 in mice. Pathological changes in the aorta were assessed by visualizing vascular collagen deposition and elastic fiber fracture via H&E, Masson and EVG staining. HMGB2 expression was measured by Western blotting and immunohistochemistry. MTS, CCK-8 and EdU assays were used to test cell proliferation.

RESULTS

HMGB2 expression was increased in samples from AD patients, samples from AD mouse modeland human aortic smooth muscle cells (HASMCs). HMGB2 promoted HASMC proliferation. Immunofluorescence staining and plasma membrane protein isolation revealed that HMGB2 decreased GLUT1 expression and promoted GLUT4 translocation. HMGB2 was also found to inhibit the expression of SIRT1/PGC-1α, but blocking the PPAR-γ pathway attenuated this effect. HMGB2-/- significantly reduced the incidence and mortality rates of AD, whereas treatment with AAV9-HMGB2 exacerbated AD.

CONCLUSIONS

This study suggests that HMGB2 promotes HASMC proliferation and vascular remodeling by regulating glucose metabolism through the PPAR-γ/SIRT1/PGC-1α pathway. HMGB2 knockdown reduces, while HMGB2 overexpression promotes, the occurrence of AD in mice. This study may help elucidate the underlying mechanisms and provide a new preventive target for AD.

Gamut of glycolytic enzymes in vascular smooth muscle cell proliferation: Implications for vascular proliferative diseases

Vascular smooth muscle cells (VSMCs) are the predominant cell type in the media of the blood vessels and are responsible for maintaining vascular tone. Emerging evidence confirms that VSMCs possess high plasticity. During vascular injury, VSMCs switch from a "contractile" phenotype to an extremely proliferative "synthetic" phenotype. The balance between both strongly affects the progression of vascular remodeling in many cardiovascular pathologies such as restenosis, atherosclerosis and aortic aneurism. Proliferating cells demand high energy requirements and to meet this necessity, alteration in cellular bioenergetics seems to be essential. Glycolysis, fatty acid metabolism, and amino acid metabolism act as a fuel for VSMC proliferation. Metabolic reprogramming of VSMCs is dynamically variable that involves multiple mechanisms and encompasses the coordination of various signaling molecules, proteins, and enzymes. Here, we systemically reviewed the metabolic changes together with the possible treatments that are still under investigation underlying VSMC plasticity which provides a promising direction for the treatment of diseases associated with VSMC proliferation. A better understanding of the interaction between metabolism with associated signaling may uncover additional targets for better therapeutic strategies in vascular disorders.

Deletion of SM22α disrupts the structure and function of caveolae and T-tubules in cardiomyocytes, contributing to heart failure

Aims

Smooth muscle 22-alpha (SM22α) is an actin-binding protein that plays critical roles in mediating polymerization of actin filaments and stretch sensitivity of cytoskeleton in vascular smooth muscle cells (VSMCs). Multiple lines of evidence indicate the existence of SM22α in cardiomyocytes. Here, we investigated the effect of cardiac SM22α on the membrane architecture and functions of cardiomyocytes to pressure overload.

Methods

SM22α knock-out (KO) mice were utilized to assess the role of SM22α in the heart. Echocardiography was used to evaluate cardiac function, transverse aortic constriction (TAC) was used to induce heart failure, cell shortening properties were measured by IonOptix devices in intact cardiomyocytes, Ca²⁺ sensitivity of myofilaments was measured in permeabilized cardiomyocytes. Confocal microscopy, electron microscopy, western blotting, co-immunoprecipitation (co-IP), Real-Time Quantitative Reverse Transcription PCR (qRT-PCR) techniques were used to perform functional and structural analysis.

Results

SM22α ablation did not alter cardiac function at baseline, but mRNA levels of atrial natriuretic peptide (ANP), brain natriuretic peptide (BNP) and β-myosin heavy chain (β-MHC) were increased significantly compared with wild type (WT) controls. The membrane architecture was severely disrupted in SM22α KO cardiomyocytes, with disassembly and flattening of caveolae and disrupted T-tubules. Furthermore, SM22α was co-immunoprecipitated with caveolin-3 (Cav3), and the interaction between Cav3 and actin was significantly reduced in SM22α KO cells. SM22α KO cardiomyocytes displayed asynchronized SR Ca²⁺ release, significantly increased Ca²⁺ spark frequency. Additionally, the kinetics of sarcomere shortening was abnormal, accompanied with increased sensitivity and reduced maximum response of myofilaments to Ca²⁺ in SM22α KO cardiomyocytes. SM22α KO mice were more prone to heart failure after TAC.

Conclusions

Our findings identified that SM22α may be required for the architecture and function of caveolae and T-tubules in cardiomyocytes.

Inflammation and atherosclerosis: signaling pathways and therapeutic intervention

Atherosclerosis is a chronic inflammatory vascular disease driven by traditional and nontraditional risk factors. Genome-wide association combined with clonal lineage tracing and clinical trials have demonstrated that innate and adaptive immune responses can promote or quell atherosclerosis. Several signaling pathways, that are associated with the inflammatory response, have been implicated within atherosclerosis such as NLRP3 inflammasome, toll-like receptors, proprotein convertase subtilisin/kexin type 9, Notch and Wnt signaling pathways, which are of importance for atherosclerosis development and regression. Targeting inflammatory pathways, especially the NLRP3 inflammasome pathway and its regulated inflammatory cytokine interleukin-1β, could represent an attractive new route for the treatment of atherosclerotic diseases. Herein, we summarize the knowledge on cellular participants and key inflammatory signaling pathways in atherosclerosis, and discuss the preclinical studies targeting these key pathways for atherosclerosis, the clinical trials that are going to target some of these processes, and the effects of quelling inflammation and atherosclerosis in the clinic.

Circ-Sirt1 inhibits vascular smooth muscle cells proliferation via the c-Myc/cyclin B1 axis

Vascular smooth muscle cells（VSMCs）are an important cellular component of vascular wall. Restenosis is mainly due to VSMC excessive proliferation. However, little is known about the role of circRNAs in VSMC proliferation and phenotypic switching. Herein, using FISH assay and RT-qPCR, we found that circ-Sirt1 was markedly downregulated in neointimal formation after injury and in VSMCs treated with PDGF-BB. BrdU and MTT assays confirmed the inhibitory role of circ-Sirt1 on cell proliferation. Mechanistically, circ-Sirt1 was mainly expressed in the cytoplasm of VSMCs. Through RIP and RNA pull-down assays, we found that circ-Sirt1 bound c-Myc, protein associated with proliferation of VSMCs. ChIP assay also provided evidence that the overexpression of circ-Sirt1 almost ceased PDGF-BB-induced binding of c-Myc to the promoter of cyclin B1 in VSMCs. These results indicated that circ-Sirt1 had an inhibitory effect on c-Myc activity, providing a mechanism for suppressing PDGF-BB-induced VSMC proliferation by direct interactions with c-Myc and its sequestration in the cytoplasm. Overall, our study demonstrated that a previously unrecognized circ-Sirt1/c-Myc/cyclin B1 axis in VSMCs mediates neointimal formation following injury. This article is protected by copyright. All rights reserved.

M6A methylation-mediated elevation of SM22α inhibits the proliferation and migration of vascular smooth muscle cells and ameliorates intimal hyperplasia in type 2 diabetes mellitus

Abnormal proliferation of vascular smooth muscle cells (VSMCs) induced by insulin resistance facilitates intimal hyperplasia of type 2 diabetes mellitus (T2DM) and N6-methyladenosine (m⁶A) methylation modification mediates the VSMC proliferation. This study aimed to reveal the m⁶A methylation modification regulatory mechanism. In this study, m⁶A demethylase FTO was elevated in insulin-treated VSMCs and T2DM mice with intimal injury. Functionally, FTO knockdown elevated m⁶A methylation level and further restrained VSMC proliferation and migration induced by insulin. Mechanistically, FTO knockdown elevated Smooth muscle 22 alpha (SM22α) expression and m⁶A-binding protein IGF2BP2 enhanced SM22α mRNA stability by recognizing and binding to m⁶A methylation modified mRNA. In vivo studies confirmed that the elevated m⁶A modification level of SM22α mRNA mitigated intimal hyperplasia in T2DM mice. Conclusively, m⁶A methylation-mediated elevation of SM22α restrained VSMC proliferation and migration and ameliorated intimal hyperplasia in T2DM.

Insulin-Independent and Dependent Glucose Transporters in Brain Mural Cells in CADASIL

Typical cerebral autosomal-dominant arteriopathy with subcortical infarcts and leukoencephalopathy (CADASIL) is caused by mutations in the human NOTCH3 gene. Cerebral autosomal-dominant arteriopathy with subcortical infarcts and leukoencephalopathy is characterized by subcortical ischemic strokes due to severe arteriopathy and fibrotic thickening of small vessels. Blood regulating vascular smooth muscle cells (VSMCs) appear as the key target in CADASIL but the pathogenic mechanisms remain unclear. With the hypothesis that brain glucose metabolism is disrupted in VSMCs in CADASIL, we investigated post-mortem tissues and VSMCs derived from CADASIL patients to explore gene expression and protein immunoreactivity of glucose transporters (GLUTs), particularly GLUT4 and GLUT2 using quantitative RT-PCR and immunohistochemical techniques. In vitro cell model analysis indicated that both GLUT4 and -2 gene expression levels were down-regulated in VSMCs derived from CADASIL patients, compared to controls. In vitro studies further indicated that the down regulation of GLUT4 coincided with impaired glucose uptake in VSMCs, which could be partially rescued by insulin treatment. Our observations on reduction in GLUTs in VSMCs are consistent with previous findings of decreased cerebral blood flow and glucose uptake in CADASIL patients. That impaired ability of glucose uptake is rescued by insulin is also consistent with previously reported lower proliferation rates of VSMCs derived from CADASIL subjects. Overall, these observations are consistent with the development of severe cerebral arteriopathy in CADASIL, in which VSMCs are replaced by widespread fibrosis.

Smooth muscle 22α deficiency impairs oxytocin-induced uterine contractility in mice at full-term pregnancy

Smooth muscle 22α (SM22α, namely Transgelin), as an actin-binding protein, regulates the contractility of vascular smooth muscle cells (VSMCs) by modulation of the stress fiber formation. However, little is known about the roles of SM22α in the regulation of uterine contraction during parturition. Here, we showed that contraction in response to oxytocin (OT) was significantly decreased in the uterine muscle strips from SM22α knockout (Sm22α-KO) mice, especially at full-term pregnancy, which may be resulted from impaired formation of stress fibers. Furthermore, serious mitochondrial damage such as the mitochondrial swelling, cristae disruption and even disappearance were observed in the myometrium of Sm22α-KO mice at full-term pregnancy, eventually resulting in the collapse of mitochondrial membrane potential and impairment in ATP synthesis. Our data indicate that SM22α is necessary to maintain uterine contractility at delivery in mice, and acts as a novel target for preventive or therapeutic manipulation of uterine atony during parturition.

α1D-adrenoceptor involves the relaxation effect of farrerol in rat aortic vascular smooth muscle cells

The aim of this study was to investigate the relaxation effect of farrerol on rat aortic vascular smooth muscle cells (VSMCs) and its underlying mechanism. VSMCs were cultured primarily and were used to examine the relaxation effect of farrerol. Cells surface and length were measured by dynamic observation, or by rhodamine-phalloidin labeling and hematoxylin-eosin staining. Cells contractive activity were tested using collagen gel contraction assay. The [Ca²⁺]_in was measured with molecular probe fluo-4-AM. The mRNA and protein expression of regulatory proteins for contraction were measured. In addition, rat aortic VSMCs were transfected with lentivirus-mediated α_1D-adrenoceptor gene-shRNA, then the effect of farrerol were detected by the above experimental methods. The results revealed that 10 μΜ AngⅡ promoted cell contraction, increased [Ca²⁺]_in and enhanced collagen contraction in rat aortic VSMCs. 10 μΜ AngⅡ not only increased expression of myosin light chain kinase (MLCK) and smooth muscle protein 22α (SM22α), but also increased phosphorylation level of myosin light chain (MLC) and myosin phosphatase target subunit 1 (MYPT1). The above effects induced by AngⅡ could be significantly inhibited by farrerol in a concentration dependent manner. When the cells were transfected with lentivirus mediated α_1D-adrenoceptor gene-shRNA, the effects of farrerol on changes induced by AngⅡ in rat aortic VSMCs were markedly reversed. In conclusion, farrerol could produce relaxtion effect in rat aortic VSMCs precontracted by 10 μΜ AngⅡ, which was involved in downregulation expression of MLCK and SM22α, and inhibition phosphorylation level of MYPT1 and MLC via activating α_1D-adrenoceptor gene.

Anti-proliferative and anti-migratory effects of Scutellaria strigillosa Hemsley extracts against vascular smooth muscle cells

ETHNOPHARMACOLOGICAL RELEVANCE

The abnormal increase in vascular smooth muscle cell (VSMC) proliferation and migration are critical events in the pathogenesis of cardiovascular diseases (CVDs) including restenosis and atherosclerosis. The dried roots of Scutellaria baicalensis Georgi (common name: Huangqin in China) have been confirmed to possess beneficial effects on CVD by clinical and modern pharmacological studies. Flavonoids in Huangqin exert anti-proliferative and anti-migratory effects. Similar to Huangqin, Scutellaria strigillosa Hemsley (SSH) has been used to clear heat and damp and is especially rich in flavonoids including wogonin, wogonoside, baicalein, and baicalin. However, there have been few of reports about pharmacological activities of SSH.

AIM OF THE STUDY

To investigate the anti-proliferative and anti-migratory properties of Scutellaria strigillosa Hemsley extract (SSHE) in vitro and in vivo and explore its possible mechanism of action.

MATERIALS AND METHODS

The chemical constituents of SSHE were analyzed by ultra-high performance liquid chromatography coupled with triple time-of-flight mass spectrometry (UPLC-Triple-TOF-MS/MS). Cell proliferation and migration were investigated using BrdU incorporation assay and cell scratch test, respectively. The protein expression was determined by western blotting. In vivo, we established an artery ligation model of C57BL/6 mice and orally administered them with 50 or 100 mg/kg/day of SSHE. The carotid arteries were harvested and the intima-media thickness was examined 28 days post-ligation.

RESULTS

Twelve compounds were identified and tentatively characterized. SSHE significantly inhibited the VSMC proliferation and migration stimulated by PDGF-BB and decreased the relative protein expression of regulatory signaling intermediates. Furthermore, the expression of SM22α was significantly elevated in SSHE-pretreated VSMCs, whereas knockdown of SM22α impaired the PDGF-BB-induced proliferation and migration arrest. Meanwhile, both ROS generation and the phosphorylation of ERK decreased in SSHE-pretreated VSMCs. In carotid artery ligation mice model, SSHE treatment significantly inhibited neointimal hyperplasia.

CONCLUSIONS

SSHE significantly inhibited the PDGF-BB-induced VSMC proliferation, migration, and neointimal hyperplasia of carotid artery caused by ligation. Upregulation of SM22α expression, inhibition of ROS generation and ERK phosphorylation were, at least, partly responsible for the effects of SSHE on VSMCs.