IGF-I promotes a shift in metabolic flux in vascular smooth muscle cells

Bergenin alleviates proliferative arterial diseases by modulating glucose metabolism in vascular smooth muscle cells

BACKGROUND

Vascular smooth muscle cell (VSMC) proliferation and phenotypic switching are key mechanisms in the development of proliferative arterial diseases. Notably, reprogramming of the glucose metabolism pattern in VSMCs plays an important role in this process.

PURPOSE

The aim of this study is to investigate the therapeutic potential and the mechanism underlying the effect of bergenin, an active compound found in Bergenia, in proliferative arterial diseases.

METHODS

The effect of bergenin on proliferative arterial disease was evaluated using platelet-derived growth factor (PDGF)-stimulated VSMCs and a mouse model of carotid artery ligation. VSMC proliferation and phenotypic switching were evaluated in vitro using cell counting kit-8, 5-ethynyl-2-deoxyuridine incorporation, scratch, and transwell assays. Carotid artery neointimal hyperplasia was evaluated in vivo using hematoxylin and eosin staining and immunofluorescence. The expression of proliferation and VSMC contractile phenotype markers was evaluated using PCR and western blotting.

RESULTS

Bergenin treatment inhibited PDGF-induced VSMC proliferation and phenotypic switching and reduced neointimal hyperplasia in the carotid artery ligation model. Additionally, bergenin partially reversed the PDGF-induced Warburg-like glucose metabolism pattern in VSMCs. RNA-sequencing data revealed that bergenin treatment significantly upregulated Ndufs2, an essential subunit of mitochondrial complex I. Ndufs2 knockdown attenuated the inhibitory effect of bergenin on PDGF-induced VSMC proliferation and phenotypic switching, and suppressed neointimal hyperplasia in vivo. Conversely, Ndufs2 overexpression enhanced the protective effect of bergenin. Moreover, Ndufs2 knockdown abrogated the effects of bergenin on the regulation of glucose metabolism in VSMCs.

CONCLUSION

These findings suggest that bergenin is effective in alleviating proliferative arterial diseases. The reversal of the Warburg-like glucose metabolism pattern in VSMCs during proliferation and phenotypic switching may underlie this therapeutic mechanism.

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.

Metabolic reprogramming in atherosclerosis: Opposed interplay between the canonical WNT/β-catenin pathway and PPARγ

Atherosclerosis, a chronic inflammatory and age-related disease, is a complex mechanism presenting a dysregulation of vessel structures. During this process, the canonical WNT/β-catenin pathway is increased whereas PPARγ is downregulated. The two systems act in an opposite manner. This paper reviews the opposing interplay of these systems and their metabolic-reprogramming pathway in atherosclerosis. Activation of the WNT/β-catenin pathway enhances the transcription of targets involved in inflammation, endothelial dysfunction, the proliferation of vascular smooth muscle cells, and vascular calcification. This complex mechanism, which is partly controlled by the WNT/β-catenin pathway, presents several metabolic dysfunctions. This phenomenon, called aerobic glycolysis (or the Warburg effect), consists of a shift in ATP production from mitochondrial oxidative phosphorylation to aerobic glycolysis, leading to the overproduction of intracellular lactate. This mechanism is partially due to the injury of mitochondrial respiration and an increase in the glycolytic pathway. In contrast, PPARγ agonists downregulate the WNT/β-catenin pathway. Therefore, the development of therapeutic targets, such as PPARγ agonists, for the treatment of atherosclerosis could be an interesting and innovative way of counteracting the canonical WNT pathway.

Smooth muscle glucose metabolism promotes monocyte recruitment and atherosclerosis in a mouse model of metabolic syndrome

Metabolic syndrome contributes to cardiovascular disease partly through systemic risk factors. However, local processes in the artery wall are becoming increasingly recognized to exacerbate atherosclerosis both in mice and humans. We show that arterial smooth muscle cell (SMC) glucose metabolism markedly synergizes with metabolic syndrome in accelerating atherosclerosis progression, using a low-density lipoprotein receptor-deficient mouse model. SMCs in proximity to atherosclerotic lesions express increased levels of the glucose transporter GLUT1. Cytokines, such as TNF-α produced by lesioned arteries, promote GLUT1 expression in SMCs, which in turn increases expression of the chemokine CCL2 through increased glycolysis and the polyol pathway. Furthermore, overexpression of GLUT1 in SMCs, but not in myeloid cells, accelerates development of larger, more advanced lesions in a mouse model of metabolic syndrome, which also exhibits elevated levels of circulating Ly6Chi monocytes expressing the CCL2 receptor CCR2. Accordingly, monocyte tracing experiments demonstrate that targeted SMC GLUT1 overexpression promotes Ly6Chi monocyte recruitment to lesions. Strikingly, SMC-targeted GLUT1 overexpression fails to accelerate atherosclerosis in mice that do not exhibit the metabolic syndrome phenotype or monocytosis. These results reveal a potentially novel mechanism whereby arterial smooth muscle glucose metabolism synergizes with metabolic syndrome to accelerate monocyte recruitment and atherosclerosis progression.

Lactate dehydrogenase-A is indispensable for vascular smooth muscle cell proliferation and migration

The proliferation and migration of vascular smooth muscle cells (VSMCs) have been implicated in the pathogenesis of atherosclerosis. Increased aerobic glycolysis is a key feature of cellular phenotypes including cancer and immune cells. However, the role of aerobic glycolysis in the atherogenic phenotype of VSMCs remains largely unknown. Here, we investigated the role of lactate dehydrogenase-A (LDHA), which is a key enzyme for glycolysis, in the proliferation and migration of VSMCs. Activation of primary rat VSMCs with fetal bovine serum (FBS) or platelet-derived growth factor (PDGF) increased their proliferation and migration, glycolytic activity, and expression of LDHA. Wound healing and transwell migration assays demonstrated that small interfering RNA-mediated knockdown of LDHA and pharmacological inhibition of LDHA by oxamate both effectively inhibited VSMC proliferation and migration. Inhibition of LDHA activity by oxamate reduced PDGF-stimulated glucose uptake, lactate production, and ATP production. Taken together, this study shows that enhanced glycolysis in PDGF- or FBS-stimulated VSMCs plays an important role in their proliferation and migration and suggests that LDHA is a potential therapeutic target to prevent vessel lumen constriction during the course of atherosclerosis and restenosis.

Role of the hypothalamus in mediating protective effects of dietary restriction during aging

Dietary restriction (DR) can extend lifespan and reduce disease burden across a wide range of animals and yeast but the mechanisms mediating these remarkably protective effects remain to be elucidated despite extensive efforts. Although it has generally been assumed that protective effects of DR are cell-autonomous, there is considerable evidence that many whole-body responses to nutritional state, including DR, are regulated by nutrient-sensing neurons. In this review, we explore the hypothesis that nutrient sensing neurons in the ventromedial hypothalamus hierarchically regulate the protective responses of dietary restriction. We describe multiple peripheral responses that are hierarchically regulated by the hypothalamus and we present evidence for non-cell autonomous signaling of dietary restriction gathered from a diverse range of models including invertebrates, mammalian cell culture, and rodent studies.

Expression of conventional and novel glucose transporters, GLUT1, -9, -10, and -12, in vascular smooth muscle cells

Intimal hyperplasia is characterized by exaggerated proliferation of vascular smooth muscle cells (VSMCs). Enhanced VSMC growth is dependent on increased glucose uptake and metabolism. Facilitative glucose transporters (GLUTs) are comprised of conventional GLUT isoforms (GLUT1-5) and novel GLUT isoforms (GLUT6-14). Previous studies demonstrate that GLUT1 overexpression or GLUT10 downregulation contribute to phenotypic changes in VSMCs. To date, the expression profile of all 14 GLUT isoforms has not been fully examined in VSMCs. Using the proliferative and differentiated phenotypes of human aortic VSMCs, the present study has determined the relative abundance of GLUT1-14 mRNAs by quantitative real-time PCR analysis. Twelve GLUT mRNAs excluding GLUT7 and GLUT14 were detectable in VSMCs. In the proliferative phenotype, the relative abundance of key GLUT mRNAs was GLUT1 (∼43%)>GLUT10 (∼26%)>GLUT9 (∼13%)>GLUT12 (∼4%), whereas in the differentiated phenotype the relative abundance was GLUT10 (∼28%)>GLUT1 (∼25%)>GLUT12 (∼20%)>GLUT9 (∼14%), together constituting 86-87% of total GLUT transcripts. To confirm the expression of key GLUT proteins, immunoblot and immunocytochemical analyses were performed using GLUT isoform-specific primary antibodies. The protein bands characteristic of GLUT1, -9, -10, and -12 were detected in VSMCs in parallel with respective positive controls. In particular, GLUT1 protein expression showed different molecular forms representative of altered glycosylation. While GLUT1 protein displayed a predominant distribution in the plasma membrane, GLUT9, -10, and -12 proteins were mostly distributed in the intracellular compartments. The present study provides the first direct evidence for GLUT9 and GLUT12 expression in VSMCs in conjunction with the previously identified GLUT1 and GLUT10.

Role of cellular bioenergetics in smooth muscle cell proliferation induced by platelet-derived growth factor

Abnormal smooth muscle cell proliferation is a hallmark of vascular disease. Although growth factors are known to contribute to cell hyperplasia, the changes in metabolism associated with this response, particularly mitochondrial respiration, remain unclear. Given the increased energy requirements for proliferation, we hypothesized that PDGF (platelet-derived growth factor) would stimulate glycolysis and mitochondrial respiration and that this elevated bioenergetic capacity is required for smooth muscle cell hyperplasia. To test this hypothesis, cell proliferation, glycolytic flux and mitochondrial oxygen consumption were measured after treatment of primary rat aortic VSMCs (vascular smooth muscle cells) with PDGF. PDGF increased basal and maximal rates of glycolytic flux and mitochondrial oxygen consumption; enhancement of these bioenergetic pathways led to a substantial increase in the mitochondrial reserve capacity. Interventions with the PI3K (phosphoinositide 3-kinase) inhibitor LY-294002 or the glycolysis inhibitor 2-deoxy-D-glucose abrogated PDGF-stimulated proliferation and prevented augmentation of glycolysis and mitochondrial reserve capacity. Similarly, when L-glucose was substituted for D-glucose, PDGF-dependent proliferation was abolished, as were changes in glycolysis and mitochondrial respiration. Interestingly, LDH (lactate dehydrogenase) protein levels and activity were significantly increased after PDGF treatment. Moreover, substitution of L-lactate for D-glucose was sufficient to increase mitochondrial reserve capacity and cell proliferation after treatment with PDGF; these effects were inhibited by the LDH inhibitor oxamate. These results suggest that glycolysis, by providing substrates that enhance the mitochondrial reserve capacity, plays an essential role in PDGF-induced cell proliferation, underscoring the integrated metabolic response required for proliferation of VSMCs in the diseased vasculature.

GLUT1-induced cFLIP expression promotes proliferation and prevents apoptosis in vascular smooth muscle cells

Enhanced expression of the facilitative glucose transporter, GLUT1, has been shown to inhibit apoptosis in several cell systems including vascular smooth muscle cells (VSMCs). A decrease in apoptosis could lead to increased VSMC numbers in neointimal and medial arterial layers under several pathologic conditions. The hypothesis underlying these studies is that GLUT1 induces expression of antiapoptotic and prosurvival genes that increase VSMC survival. Transcriptomic analysis of A7r5 VSMCs, in which GLUT1 was acutely overexpressed, showed a 2.14-fold increase in c-FLICE inhibitory protein (cFLIP), which promotes cellular growth and prevents apoptosis through caspase 8 binding. We confirmed that overexpression of GLUT1 induced mRNA and protein expression of both the long and short isoforms of cFLIP (cFLIP(L) and cFLIP(S)) in primary and stable immortalized VSMC lines as well as in aortas from GLUT1 transgenic mice. Increased GLUT1 reduced VSMC death by more than twofold after serum withdrawal, as evidenced by decreased caspase 3 activity and Trypan blue exclusion studies. GLUT1 overexpression resulted in a greater than twofold increase in proliferating cell nuclear antigen expression and live cell numbers, consistent with augmented VSMC proliferation. Lentiviral knockdown of cFLIP(L) showed that cFLIP(L) was necessary for the proproliferative and antiapoptotic effects of GLUT1 overexpression. Taken together, these data suggest that GLUT1 induction of cFLIP(L) expression augments proliferation and prevents apoptosis in VSMCs.

Angiotensin II Decreases Glucose Uptake by Downregulation of GLUT1 in the Cell Membrane of the Vascular Smooth Muscle Cell Line A10

Recent evidence suggests a crosstalk between angiotensin II (Ang II) and insulin. However, whether this crosstalk affects glucose uptake, particularly in terms of actin filament involvement, has not yet been studied in vascular smooth muscle cells. Pretreatment of cells with either Ang II or cytochalasin D disarranged actin filaments in a time-dependent manner and inhibited glucose uptake. However, insulin increased actin reorganization and glucose uptake. Membrane fractionation studies showed that Ang II decreased GLUT-1 at the cell membrane, whereas it increased GLUT-1 in the cytoplasm, indicating that Ang II may cause internalization of GLUT-1 via actin disorganization, consequently decreasing glucose uptake. The effects of Ang II on glucose uptake and actin reorganization were blocked by AT1 receptor antagonist, but not by AT2 antagonist. Either P38 or ERK1/2 inhibitors partially reversed the Ang II-inhibited actin reorganization and glucose uptake, suggesting that MAPK signaling pathways could be involved as downstream events in Ang II signaling, and this signaling may interfere with insulin-induced actin reorganization and glucose uptake. These data imply that Ang II induces insulin resistance by decreasing glucose uptake via disarrangement of actin filaments, which provides a novel insight into understanding of insulin resistance by Ang II at the molecular level.

Autophagy: highlighting a novel player in the autoimmunity scenario

Autophagy is a physiological cellular mechanism that degrades and recycles proteins and other molecules to maintain an adequate amino acid level during nutritional starvation of the cell. Autophagy is involved in cellular homeostasis and differentiation, as well as in tissue remodeling, aging, cancer, and other diseases. Under particular environmental conditions, autophagy can also be a contributor to programmed cell death, or can act as a defense mechanism for the elimination of intracellular bacteria and viruses. According to recent experimental data, autophagy may be implicated in autoimmunity by promotion of major histocompatibility complex (MHC) class II presentation of cytosolic antigens and control of T lymphocyte homeostasis, and its induction by Th1 cytokines and perhaps by specific serum autoantibodies. We review herein the role of autophagy in immune function and its possible contribution to breakdown of tolerance and development of autoimmunity.

Insulin-like growth factor-1 and TNF-alpha regulate autophagy through c-jun N-terminal kinase and Akt pathways in human atherosclerotic vascular smooth cells

A balance between programmed cell death and survival of vascular smooth muscle cells (VSMC) in the fibrous cap, which is primarily composed of VSMC and extracellular matrix, appears to best correlate with plaque instability or stability and is controlled by growth factors and cytokines. Autophagy is also involved in programmed cell death. We assessed the effect of TNF-alpha and insulin-like growth factor-1 (IGF-1) on the expression of autophagic genes, microtubule-associated protein 1 light chain 3 (MAPLC-3) and Beclin-1 in VSMC isolated from atherosclerotic plaques. Transmission electron microscopy showed a significantly higher number of vacuolated cells in the TNF-alpha-treated VSMC and a markedly lower number in the IGF-1-treated VSMC when compared with the untreated control group. TNF-alpha-induced MAPLC-3 mRNA expression through c-jun N-terminal kinase and protein kinase B pathways and induced Beclin-1 protein expression through the c-jun N-terminal kinase pathway. Expression of MAPLC-3 and Beclin-1 correlated with autophagic cell death of plaque VSMC. IGF-1 inhibited MAPLC-3 mRNA transcripts through the Akt pathway. These findings suggest that the expression of autophagy genes can be influenced by IGF-1 and TNF-alpha through c-jun N-terminal kinase or Akt pathways and autophagy might be involved in the regulation of plaque stability.

ERK1/2 activation by angiotensin II inhibits insulin-induced glucose uptake in vascular smooth muscle cells

Clinical evidence suggests a relationship between hypertension and insulin resistance, and cross-talk between angiotensin II (Ang II) and insulin signaling pathways may take place. We now report the effect of Ang II on insulin-induced glucose uptake and its intracellular mechanisms in vascular smooth muscle cells (VSMC). We examined the translocation of glucose transporter-4 (GLUT-4) and glucose uptake in rat aortic smooth muscle cells (RASMC). Mitogen-activated protein (MAP) kinases and Akt activities, and phosphorylation of insulin receptor substrate-1 (IRS-1) at the serine and tyrosine residues were measured by immunoprecipitation and immunoblotting. As a result, Ang II inhibited insulin-induced GLUT-4 translocation from cytoplasm to the plasma membrane in RASMC. Ang II induced extracellular signal-regulated kinase (ERK) 1/2 and c-Jun N-terminal kinase (JNK) activation and IRS-1 phosphorylation at Ser307 and Ser616. Ang II-induced Ser307 and Ser616 phophorylation of IRS-1 was inhibited by a MEK inhibitor, PD98059, and a JNK inhibitor, SP600125. Ang II inhibition of insulin-stimulated IRS-1 tyrosyl phophorylation and Akt activation were reversed by PD98059 but not by SP600125. Ang II inhibited insulin-induced glucose uptake, which was also reversed by PD98059 but not by SP600125. It is shown that Ang II-induced ERK1/2 activation inhibits insulin-dependent glucose uptake through serine phophorylation of IRS-1 in RASMC.

A critical perspective of the use of (13)C-isotopomer analysis by GCMS and NMR as applied to cardiac metabolism

The aim of this article is to provide a guide for metabolic physiologists and bioengineers to the combined use of gas chromatography-mass spectrometry (GCMS) and nuclear magnetic resonance (NMR) in stable isotope investigations in any biological systems. Building on our past experience with these two techniques, as applied separately to the investigation of citric acid metabolism in the ex vivo perfused rat heart we initiated a collaborative study for their critical evaluation. This article, which expands on our previous work (Mol. Cel. Biol., 2003), directly compares GCMS- and NMR-determined 13C-isotopomer and flux data obtained from ex vivo rat heart perfusion studies with 13C-substrates. Overall we have found excellent agreement between the 13C-enrichments of GCMS- and NMR-determined citric acid cycle metabolites (citrate, 2-ketoglutarate, succinate and malate) and glutamate; however the unlabeled component (M) was consistently underestimated by NMR. Despite this discrepancy there was reasonably good agreement in the relative fluxes of 13C-substrates through the citric acid cycle determined by the two techniques. Nevertheless, further investigations appear necessary before maximal advantage can be taken of the complementary 13C-isotopomer and flux data of GCMS and NMR for probing the dynamics of cellular metabolism.

Impact of low-flow ischemia on substrate oxidation and glycolysis in the isolated perfused rat heart

Interventions that stimulate carbohydrate oxidation appear to be beneficial in the setting of myocardial ischemia or infarction. However, the mechanisms underlying this protective effect have not been defined, in part because of our limited understanding of substrate utilization under ischemic conditions. Therefore, we used (1)H and (13)C NMR spectroscopy to investigate substrate oxidation and glycolytic rates in a global low-flow model of myocardial ischemia. Isolated male Sprague-Dawley rat hearts were perfused for 30 min under conditions of normal flow (control) and low-flow ischemia (LFI, 0.3 ml/min) with insulin and (13)C-labeled lactate, pyruvate, palmitate, and glucose at concentrations representative of the physiological fed state. Despite a approximately 50-fold reduction in substrate delivery and oxygen consumption, oxidation of all exogenous substrates plus glycogen occurred during LFI. Oxidative metabolism accounted for 97% of total calculated ATP production in the control group and approximately 30% in the LFI group. For controls, lactate oxidation was the major source of ATP; however, in LFI, this shifted to a combination of oxidative and nonoxidative glycogen metabolism. Interestingly, in the LFI group, anaplerosis relative to citrate synthase increased sevenfold compared with controls. These results demonstrate the importance of oxidative energy metabolism for ATP production, even during very-low-flow ischemia. We believe that the approach described here will be valuable for future investigations into the underlying mechanisms related to the protective effect of increasing cardiac carbohydrate utilization and may ultimately lead to identification of new therapeutic targets for treatment of myocardial ischemia.

Quantitative trait loci for insulin-like growth factor I, leptin, thyroxine, and corticosterone in genetically heterogeneous mice

Genotype information was collected at 87 loci in a group of 1,108 UM-HET3 mice bred as the progeny of [BALB/cJ x C57BL/6J]F1 mothers and [C3H/HeJ x DBA/2J]F1 fathers, for which thyroxine (T4), insulin-like growth factor I (IGF-I), and leptin levels had been measured at 4 and 15 mo of age. The data provided significant evidence for quantitative trait loci (QTL) modulating IGF-I levels on chromosomes 1, 3, 8, 10, and 17; for loci affecting T4 on chromosomes 4, 15, and 17; and for leptin on chromosome 3. Fecal levels of corticosterone at 17 mo of age were influenced by a QTL on chromosome 1. Nine other gene/hormone associations reached a nominal P < 0.01, providing suggestive but not statistical evidence for additional QTL. QTL with an influence on a given hormone were in nearly all cases additive, with little or no evidence for epistasis. Of the 12 strongest QTL, 5 had effects that were age dependent, having more effect in 15-mo-old than in 4-mo-old mice in all but one case; the other QTL had effects that were apparently age-independent. These results show that the genetic controls over late-life hormone levels are complex and dependent on effects of genes that act both early and late in the life course.

Differential modulation of glucose, lactate, and pyruvate oxidation by insulin and dichloroacetate in the rat heart

Despite the fact that lactate and pyruvate are potential substrates for energy production in vivo, our understanding of the control and regulation of carbohydrate metabolism is based principally on studies where glucose is the only available carbohydrate. Therefore, the purpose of this study was to determine the contributions of lactate, pyruvate, and glucose to energy production in the isolated, perfused rat heart over a range of insulin concentrations and after activation of pyruvate dehydrogenase with dichloroacetate (DCA). Hearts were perfused with physiological concentrations of [1-13C]glucose, [U-13C]lactate, [2-13C]pyruvate, and unlabeled palmitate for 45 min. Hearts were freeze clamped, and 13C NMR glutamate isotopomer analysis was performed on tissue extracts. Glucose, lactate, and pyruvate all contributed significantly to myocardial energy production; however, in the absence of insulin, glucose contributed only 25-30% of total pyruvate oxidation. Even under conditions where carbohydrates represented >95% of substrate entering the tricarboxylic acid (TCA) cycle, we found that glucose contributed at most 50-60% of total carbohydrate oxidation. Despite being present at only 0.1 mM, pyruvate contributed between approximately 10% and 30% of total acetyl-CoA entry into the TCA cycle. We also found that insulin and DCA not only increased glucose oxidation but also exogenous pyruvate oxidation; however, lactate oxidation was not increased. The differential effects of insulin and DCA on pyruvate and lactate oxidation provide further evidence for compartmentation of cardiac carbohydrate metabolism. These results may have important implications for understanding the mechanisms underlying the beneficial effects of increasing cardiac carbohydrate metabolism.