Mitochondrial fission induced by platelet-derived growth factor regulates vascular smooth muscle cell bioenergetics and cell proliferation

Chronic Exercise Training Improved Aortic Endothelial and Mitochondrial Function via an AMPKα2-Dependent Manner

Chronic exercise training is known to protect the vasculature; however, the underlying mechanisms remain obscure. The present study hypothesized that exercise may improve aortic endothelial and mitochondrial function through an adenosine monophosphate-activated protein kinase α2 (AMPKα2)-dependent manner. Ten-week-old AMPKα2 knockout (AMPKα2^−/−) mice and age-matched wild-type (WT) mice were subjected to daily treadmill running for 6 weeks, and the thoracic aorta from these mice were used for further examination. Our results showed that exercise significantly promoted vasodilatation and increased expression and phosphorylation of endothelial nitric oxide synthase (eNOS), concomitant with increased AMPKα2 expression in WT mice. These effects were not observed in AMPKα2^−/− mice. Furthermore, exercise training increased thoracic aortic mitochondrial content as indicated by increased Complex I and mitochondrial DNA (mtDNA) in WT mice but not in AMPKα2^−/− mice. This may be caused by decreased mitochondrial autophagy since the expression of BH3 domain-containing BCL2 family members BNIP3-like (BNIP3L) and LC3B were decreased in WT mice with exercise. And these changes were absent with AMPKα2 deletion in mice. Importantly, exercise increased the expression of manganous superoxide dismutase (MnSOD) and catalase, suggesting that mitochondrial antioxidative capacity was increased. Notably, the improved antioxidative capacity was lost in AMPKα2^−/− mice with exercise. In conclusion, this study illustrated that AMPKα2 plays a critical role in exercise-related vascular protection via increasing endothelial and mitochondrial function in the artery.

Aspirin increases mitochondrial fatty acid oxidation

The metabolic effects of salicylates are poorly understood. This study investigated the effects of aspirin on fatty acid oxidation. Aspirin increased mitochondrial long-chain fatty acid oxidation, but inhibited peroxisomal fatty acid oxidation, in two different cell lines. Aspirin increased mitochondrial protein acetylation and was found to be a stronger acetylating agent in vitro than acetyl-CoA. However, aspirin-induced acetylation did not alter the activity of fatty acid oxidation proteins, and knocking out the mitochondrial deacetylase SIRT3 did not affect the induction of long-chain fatty acid oxidation by aspirin. Aspirin did not change oxidation of medium-chain fatty acids, which can freely traverse the mitochondrial membrane. Together, these data indicate that aspirin does not directly alter mitochondrial matrix fatty acid oxidation enzymes, but most likely exerts its effects at the level of long-chain fatty acid transport into mitochondria. The drive on mitochondrial fatty acid oxidation may be a compensatory response to altered mitochondrial morphology and inhibited electron transport chain function, both of which were observed after 24 h incubation of cells with aspirin. These studies provide insight into the pathophysiology of Reye Syndrome, which is known to be triggered by aspirin ingestion in patients with fatty acid oxidation disorders.

Inhibition of Epac1 suppresses mitochondrial fission and reduces neointima formation induced by vascular injury

Vascular smooth muscle cell (VSMC) activation in response to injury plays an important role in the development of vascular proliferative diseases, including restenosis and atherosclerosis. The aims of this study were to ascertain the physiological functions of exchange proteins directly activated by cAMP isoform 1 (Epac1) in VSMC and to evaluate the potential of Epac1 as therapeutic targets for neointima formation during vascular remodeling. In a mouse carotid artery ligation model, genetic knockdown of the Epac1 gene led to a significant reduction in neointima obstruction in response to vascular injury. Pharmacologic inhibition of Epac1 with an Epac specific inhibitor, ESI-09, phenocopied the effects of Epac1 null by suppressing neointima formation and proliferative VSMC accumulation in neointima area. Mechanistically, Epac1 deficient VSMCs exhibited lower level of PI3K/AKT signaling and dampened response to PDGF-induced mitochondrial fission and reactive oxygen species levels. Our studies indicate that Epac1 plays important roles in promoting VSMC proliferation and phenotypic switch in response to vascular injury, therefore, representing a therapeutic target for vascular proliferative diseases.

Functional Effects of Cigarette Smoke-Induced Changes in Airway Smooth Muscle Mitochondrial Morphology

Long-term exposure to cigarette smoke (CS) triggers airway hyperreactivity and remodeling, effects that involve airway smooth muscle (ASM). We previously showed that CS destabilizes the networked morphology of mitochondria in human ASM by regulating the expression of mitochondrial fission and fusion proteins via multiple signaling mechanisms. Emerging data link regulation of mitochondrial morphology to cellular structure and function. We hypothesized that CS-induced changes in ASM mitochondrial morphology detrimentally affect mitochondrial function, leading to CS effects on contractility and remodeling. Here, ASM cells were exposed to 1% cigarette smoke extract (CSE) for 48 h to alter mitochondrial fission/fusion, or by inhibiting the fission protein Drp1 or the fusion protein Mfn2. Mitochondrial function was assessed via changes in bioenergetics or altered rates of proliferation and apoptosis. Our results indicate that both exposure to CS and inhibition of mitochondrial fission/fusion proteins affect mitochondrial function (i.e., energy metabolism, proliferation, and apoptosis) in ASM cells. In vivo, the airways in mice chronically exposed to CS are thickened and fibrotic, and the expression of proteins involved in mitochondrial function is dramatically altered in the ASM of these mice. We conclude that CS-induced changes in mitochondrial morphology (fission/fusion balance) correlate with mitochondrial function, and thus may control ASM proliferation, which plays a central role in airway health. J. Cell. Physiol. 232: 1053-1068, 2017. © 2016 Wiley Periodicals, Inc.

Exogenous H2S modulates mitochondrial fusion-fission to inhibit vascular smooth muscle cell proliferation in a hyperglycemic state

Aim

Vascular smooth muscle cell (VSMC) proliferation in response to hyperglycemia is an important process in the development of arterial vessel hyperplasia. The shape change of mitochondria is dynamic and closely related to fission and fusion. Hydrogen sulfide (H₂S) was confirmed to have anti-oxidative, anti-inflammatory and anti-proliferative effects. However, little it is known about its effects on mitochondrial morphology induced by hyperglycemia. The aim of the study is to demonstrate that H₂S inhibits VSMC proliferation through regulating mitochondrial fission.

Methods and results

We observe lower H₂S levels as well as higher proliferative protein expression levels for proliferative cell nuclear antigen (PCNA) and cyclin D1 and higher mitochondrial fusion–fission protein expression levels for dynamin-related protein 1 (Drp 1) in human kidney arteries and in db/db mouse aorta. Exogenous H₂S (100 μM NaHS) inhibits vascular smooth muscle cells of human pulmonary aorta(HPASMC) proliferation and migration in response to high glucose using the BrdU and scratch wound repair assays, decreases proliferative protein (PCNA and cyclin D1) expression, and reduces ROS production in the cytoplasm and mitochondria. When HPASMCs proliferate with a high glucose treatment, the mitochondria become small spheres with a short rod-shaped structure, whereas NaHS, a mitochondrial division inhibitor and siDrp prevent VSMC proliferation and maintain mitochondria as stationary and randomly dispersed with fixed structures.

Conclusion

Exogenous H₂S aids in inhibiting mitochondrial fragmentation and affects proliferation in db/db mice and HPASMCs by decreasing Drp 1 expression.

Electronic supplementary material

The online version of this article (doi:10.1186/s13578-016-0102-x) contains supplementary material, which is available to authorized users.

The entangled ER-mitochondrial axis as a potential therapeutic strategy in neurodegeneration: A tangled duo unchained

Endoplasmic reticulum (ER) and mitochondrial function have both been shown to be critical events in neurodegenerative diseases. The ER mediates protein folding, maturation, sorting as well acts as calcium storage. The unfolded protein response (UPR) is a stress response of the ER that is activated by the accumulation of misfolded proteins within the ER lumen. Although the molecular mechanisms underlying ER stress-induced apoptosis are not completely understood, increasing evidence suggests that ER and mitochondria cooperate to signal cell death. Similarly, calcium-mediated mitochondrial function and dynamics not only contribute to ATP generation and calcium buffering but are also a linchpin in mediating cell fate. Mitochondria and ER form structural and functional networks (mitochondria-associated ER membranes [MAMs]) essential to maintaining cellular homeostasis and determining cell fate under various pathophysiological conditions. Regulated Ca(2+) transfer from the ER to the mitochondria is important in maintaining control of pro-survival/pro-death pathways. In this review, we summarize the latest therapeutic strategies that target these essential organelles in the context of neurodegenerative diseases.

Early ERK1/2 activation promotes DRP1-dependent mitochondrial fission necessary for cell reprogramming

During the process of reprogramming to induced pluripotent stem (iPS) cells, somatic cells switch from oxidative to glycolytic metabolism, a transition associated with profound mitochondrial reorganization. Neither the importance of mitochondrial remodelling for cell reprogramming, nor the molecular mechanisms controlling this process are well understood. Here, we show that an early wave of mitochondrial fragmentation occurs upon expression of reprogramming factors. Reprogramming-induced mitochondrial fission is associated with a minor decrease in mitochondrial mass but not with mitophagy. The pro-fission factor Drp1 is phosphorylated early in reprogramming, and its knockdown and inhibition impairs both mitochondrial fragmentation and generation of iPS cell colonies. Drp1 phosphorylation depends on Erk activation in early reprogramming, which occurs, at least in part, due to downregulation of the MAP kinase phosphatase Dusp6. Taken together, our data indicate that mitochondrial fission controlled by an Erk-Drp1 axis constitutes an early and necessary step in the reprogramming process to pluripotency.

Glucagon-like peptide-1 inhibits vascular smooth muscle cell dedifferentiation through mitochondrial dynamics regulation

Glucagon-like peptide-1 (GLP-1) is a neuroendocrine hormone produced by gastrointestinal tract in response to food ingestion. GLP-1 plays a very important role in the glucose homeostasis by stimulating glucose-dependent insulin secretion, inhibiting glucagon secretion, inhibiting gastric emptying, reducing appetite and food intake. Because of these actions, the GLP-1 peptide-mimetic exenatide is one of the most promising new medicines for the treatment of type 2 diabetes. In vivo treatments with GLP-1 or exenatide prevent neo-intima layer formation in response to endothelial damage and atherosclerotic lesion formation in aortic tissue. Whether GLP-1 modulates vascular smooth muscle cell (VSMC) migration and proliferation by controlling mitochondrial dynamics is unknown. In this report, we showed that GLP-1 increased mitochondrial fusion and activity in a PKA-dependent manner in the VSMC cell line A7r5. GLP-1 induced a Ser-637 phosphorylation in the mitochondrial fission protein Drp1, and decreased Drp1 mitochondrial localization. GLP-1 inhibited PDGF-BB-induced VSMC migration and proliferation, actions inhibited by overexpressing wild type Drp1 and mimicked by the Drp1 inhibitor Mdivi-1 and by overexpressing dominant negative Drp1. These results show that GLP-1 stimulates mitochondrial fusion, increases mitochondrial activity and decreases PDGF-BB-induced VSMC dedifferentiation by a PKA/Drp1 signaling pathway. Our data suggest that GLP-1 inhibits vascular remodeling through a mitochondrial dynamics-dependent mechanism.

Mitochondrial dynamics, mitophagy and cardiovascular disease

Cardiac hypertrophy is often initiated as an adaptive response to haemodynamic stress or myocardial injury, and allows the heart to meet an increased demand for oxygen. Although initially beneficial, hypertrophy can ultimately contribute to the progression of cardiac disease, leading to an increase in interstitial fibrosis and a decrease in ventricular function. Metabolic changes have emerged as key mechanisms involved in the development and progression of pathological remodelling. As the myocardium is a highly oxidative tissue, mitochondria play a central role in maintaining optimal performance of the heart. 'Mitochondrial dynamics', the processes of mitochondrial fusion, fission, biogenesis and mitophagy that determine mitochondrial morphology, quality and abundance have recently been implicated in cardiovascular disease. Studies link mitochondrial dynamics to the balance between energy demand and nutrient supply, suggesting that changes in mitochondrial morphology may act as a mechanism for bioenergetic adaptation during cardiac pathological remodelling. Another critical function of mitochondrial dynamics is the removal of damaged and dysfunctional mitochondria through mitophagy, which is dependent on the fission/fusion cycle. In this article, we discuss the latest findings regarding the impact of mitochondrial dynamics and mitophagy on the development and progression of cardiovascular pathologies, including diabetic cardiomyopathy, atherosclerosis, damage from ischaemia-reperfusion, cardiac hypertrophy and decompensated heart failure. We will address the ability of mitochondrial fusion and fission to impact all cell types within the myocardium, including cardiac myocytes, cardiac fibroblasts and vascular smooth muscle cells. Finally, we will discuss how these findings can be applied to improve the treatment and prevention of cardiovascular diseases.

Differential Mitochondrial Adaptation in Primary Vascular Smooth Muscle Cells from a Diabetic Rat Model

Diabetes affects more than 330 million people worldwide and causes elevated cardiovascular disease risk. Mitochondria are critical for vascular function, generate cellular reactive oxygen species (ROS), and are perturbed by diabetes, representing a novel target for therapeutics. We hypothesized that adaptive mitochondrial plasticity in response to nutrient stress would be impaired in diabetes cellular physiology via a nitric oxide synthase- (NOS-) mediated decrease in mitochondrial function. Primary smooth muscle cells (SMCs) from aorta of the nonobese, insulin resistant rat diabetes model Goto-Kakizaki (GK) and the Wistar control rat were exposed to high glucose (25 mM). At baseline, significantly greater nitric oxide evolution, ROS production, and respiratory control ratio (RCR) were observed in GK SMCs. Upon exposure to high glucose, expression of phosphorylated eNOS, uncoupled respiration, and expression of mitochondrial complexes I, II, III, and V were significantly decreased in GK SMCs (p < 0.05). Mitochondrial superoxide increased with high glucose in Wistar SMCs (p < 0.05) with no change in the GK beyond elevated baseline concentrations. Baseline comparisons show persistent metabolic perturbations in a diabetes phenotype. Overall, nutrient stress in GK SMCs caused a persistent decline in eNOS and mitochondrial function and disrupted mitochondrial plasticity, illustrating eNOS and mitochondria as potential therapeutic targets.

Molecular insight and pharmacological approaches targeting mitochondrial dynamics in skeletal muscle during obesity

Obesity-associated insulin resistance is the major characteristic of the early stage of metabolic syndrome. A decline in mitochondrial function plays a role in the development of insulin resistance in obesity and type 2 diabetes. Accumulating data reveal that mitochondrial dynamics, the balance between mitochondrial fusion and fission, are an important factor in the maintenance of mitochondrial function. Thus, the mechanisms underlying the regulation of mitochondrial dynamics in obesity deserve further investigation. This review describes an overview of mitochondrial fusion and fission machineries, and discusses the mechanistic and functional aspects of mitochondrial dynamics, with a focus on skeletal muscle in obesity. Finally, we discuss current pharmacological approaches of targeting mitochondrial dynamics. Elucidating the role of mitochondrial dynamics in skeletal muscle afflicted by obesity may provide not only important clues in understanding muscle insulin resistance, but also new therapeutic targets.

Decreasing mitochondrial fission diminishes vascular smooth muscle cell migration and ameliorates intimal hyperplasia

AIMS

Vascular smooth muscle cell (VSMC) migration in response to arterial wall injury is a critical process in the development of intimal hyperplasia. Cell migration is an energy-demanding process that is predicted to require mitochondrial function. Mitochondria are morphologically dynamic, undergoing continuous shape change through fission and fusion. However, the role of mitochondrial morphology in VSMC migration is not well understood. The aim of the study is to understand how mitochondrial fission contributes to VSMC migration and provides its in vivo relevance in the mouse model of intimal hyperplasia.

METHODS AND RESULTS

In primary mouse VSMCs, the chemoattractant PDGF induced mitochondrial shortening through the mitochondrial fission protein dynamin-like protein 1 (DLP1)/Drp1. Perturbation of mitochondrial fission by expressing the dominant-negative mutant DLP1-K38A or by DLP1 silencing greatly decreased PDGF-induced lamellipodia formation and VSMC migration, indicating that mitochondrial fission is an important process in VSMC migration. PDGF induced an augmentation of mitochondrial energetics as well as ROS production, both of which were found to be necessary for VSMC migration. Mechanistically, the inhibition of mitochondrial fission induced an increase of mitochondrial inner membrane proton leak in VSMCs, abrogating the PDGF-induced energetic enhancement and an ROS increase. In an in vivo model of intimal hyperplasia, transgenic mice expressing DLP1-K38A displayed markedly reduced ROS levels and neointima formation in response to femoral artery wire injury.

CONCLUSIONS

Mitochondrial fission is an integral process in cell migration, and controlling mitochondrial fission can limit VSMC migration and the pathological intimal hyperplasia by altering mitochondrial energetics and ROS levels.

Mitochondrial metabolism and the control of vascular smooth muscle cell proliferation

Differentiation and dedifferentiation of vascular smooth muscle cells (VSMCs) are essential processes of vascular development. VSMC have biosynthetic, proliferative, and contractile roles in the vessel wall. Alterations in the differentiated state of the VSMC play a critical role in the pathogenesis of a variety of cardiovascular diseases, including atherosclerosis, hypertension, and vascular stenosis. This review provides an overview of the current state of knowledge of molecular mechanisms involved in the control of VSMC proliferation, with particular focus on mitochondrial metabolism. Mitochondrial activity can be controlled by regulating mitochondrial dynamics, i.e., mitochondrial fusion and fission, and by regulating mitochondrial calcium handling through the interaction with the endoplasmic reticulum (ER). Alterations in both VSMC proliferation and mitochondrial function can be triggered by dysregulation of mitofusin-2, a small GTPase associated with mitochondrial fusion and mitochondrial–ER interaction. Several lines of evidence highlight the relevance of mitochondrial metabolism in the control of VSMC proliferation, indicating a new area to be explored in the treatment of vascular diseases.

Endothelial cells respond to hyperglycemia by increasing the LPL transporter GPIHBP1

In diabetes, when glucose uptake and oxidation are impaired, the heart is compelled to use fatty acid (FA) almost exclusively for ATP. The vascular content of lipoprotein lipase (LPL), the rate-limiting enzyme that determines circulating triglyceride clearance, is largely responsible for this FA delivery and increases following diabetes. Glycosylphosphatidylinositol-anchored high-density lipoprotein-binding protein [GPIHBP1; a protein expressed abundantly in the heart in endothelial cells (EC)] collects LPL from the interstitial space and transfers it across ECs onto the luminal binding sites of these cells, where the enzyme is functional. We tested whether ECs respond to hyperglycemia by increasing GPIHBP1. Streptozotocin diabetes increased cardiac LPL activity and GPIHBP1 gene and protein expression. The increased LPL and GPIHBP1 were located at the capillary lumen. In vitro, passaging EC caused a loss of GPIHBP1, which could be induced on exposure to increasing concentrations of glucose. The high-glucose-induced GPIHBP1 increased LPL shuttling across EC monolayers. GPIHBP1 expression was linked to the EC content of heparanase. Moreover, active heparanase increased GPIHBP1 gene and protein expression. Both ECs and myocyte heparan sulfate proteoglycan-bound platelet-derived growth factor (PDGF) released by heparanase caused augmentation of GPIHBP1. Overall, our data suggest that this protein "ensemble" (heparanase-PDGF-GPIHBP1) cooperates in the diabetic heart to regulate FA delivery and utilization by the cardiomyocytes. Interrupting this axis may be a novel therapeutic strategy to restore metabolic equilibrium, curb lipotoxicity, and help prevent or delay heart dysfunction that is characteristic of diabetes.

FAM3A promotes vascular smooth muscle cell proliferation and migration and exacerbates neointima formation in rat artery after balloon injury

The biological function of FAM3A, the first member of family with sequence similarity 3 (FAM3) gene family, remains largely unknown. This study aimed to determine its role in the proliferation and migration of vascular smooth muscle cells (VSMCs). Immunohistochemical staining revealed that FAM3A protein is expressed in the tunica media of rodent arteries, and its expression is reduced with an increase in prostaglandin E receptor 2 (EP2) expression after injury. In vitro, FAM3A overexpression promotes proliferation and migration of VSMCs, whereas FAM3A silencing inhibits these processes. In vivo, FAM3A overexpression results in exaggerated neointima formation of rat carotid artery after balloon injury. FAM3A activates Akt in a PI3K-dependent manner. In contrast, FAM3A induces ERK1/2 activation independent of PI3K. FAM3A protein is subcellularly located in mitochondria, where it affects ATP production and release. Activation of EP2 represses FAM3A expression, leading to impaired ATP production and release in VSMCs. FAM3A-induced activation of Akt and ERK1/2 pathways, proliferation and migration of VSMCs are inhibited by P2 receptor antagonist suramin. Furthermore, inhibition or knockdown of P2Y1 receptor inihibits FAM3A-induced proliferation and migration of VSMCs. In conclusion, FAM3A promotes proliferation and migration of VSMCs via P2Y1 receptor-mediated activation of Akt and ERK1/2 pathways. In injured vessels, FAM3A was repressed by upregulated EP2 expression, leading to the attenuation of ATP-P2Y1 receptor signaling, which is beneficial for preventing excessive proliferation and migration of VSMCs.

Comprehensive measurement of respiratory activity in permeabilized cells using extracellular flux analysis

Extracellular flux (XF) analysis has become a mainstream method for measuring mitochondrial function in cells and tissues. Although this technique is commonly used to measure bioenergetics in intact cells, we outline here a detailed XF protocol for measuring respiration in permeabilized cells. Cells are permeabilized using saponin (SAP), digitonin (DIG) or recombinant perfringolysin O (rPFO) (XF-plasma membrane permeabilizer (PMP) reagent), and they are provided with specific substrates to measure complex I- or complex II-mediated respiratory activity, complex III+IV respiratory activity or complex IV activity. Medium- and long-chain acylcarnitines or glutamine may also be provided for measuring fatty acid (FA) oxidation or glutamine oxidation, respectively. This protocol uses a minimal number of cells compared with other protocols and does not require isolation of mitochondria. The results are highly reproducible, and mitochondria remain well coupled. Collectively, this protocol provides comprehensive and detailed information regarding mitochondrial activity and efficiency, and, after preparative steps, it takes 6-8 h to complete.