Regulation of mitochondrial morphology by positive feedback interaction between PKCδ and Drp1 in vascular smooth muscle cell

Rotenone activates the LKB1-AMPK-ULK1 signaling pathway to induce autophagy and apoptosis in rat thoracic aortic endothelial cells

BACKGROUND

The specific mechanism by which rotenone impacts thoracic aortic autophagy and apoptosis is unknown. We aimed to investigate the regulatory effects of rotenone on autophagy and apoptosis in rat thoracic aortic endothelial cells (RTAEC) via activation of the LKB1-AMPK-ULK1 signaling pathway and to elucidate the molecular mechanisms of rotenone on autophagy and apoptosis in vascular endothelial cells.

METHODS

In vivo, 60 male SD rats were randomly selected and divided into 5 groups: control (Con), DMSO, 1, 2, and 4 mg/kg groups, respectively. After 28 days of treatment, histopathological and ultrastructural changes in each group were observed using HE and transmission electron microscopy; Autophagy, apoptosis, and LKB1-AMPK-ULK1 pathway-related proteins were detected by Western blot; Apoptosis levels in the thoracic aorta were detected by TUNEL. In vitro, RTAEC were cultured and divided into control (Con), DMSO, 20, 100, 500, and 1000 nM groups. After 24 h of intervention, autophagy, apoptosis, and LKB1-AMPK-ULK1 pathway-related factors were detected by Western blot and qRT-PCR; Flow cytometry to detect apoptosis levels; Autophagy was inhibited with 3-MA and CQ to detect apoptosis levels, and changes in autophagy, apoptosis, and downstream factors were detected by the AMPK inhibitor CC intervention.

RESULTS

Gavage in SD rats for 28 days, some degree of damage was observed in the thoracic aorta and heart of the rotenone group, as well as the appearance of autophagic vesicles was observed in the thoracic aorta. TUNEL analysis revealed higher apoptosis in the rotenone group's thoracic aorta; RTAEC cultured in vitro, after 24 h of rotenone intervention, showed increased ROS production and significantly decreased ATP production. The flow cytometry data suggested an increase in the number of apoptotic RTAEC. The thoracic aorta and RTAEC in the rotenone group displayed elevated levels of autophagy and apoptosis, and the LKB1-AMPK-ULK1 pathway proteins were activated and expressed at higher levels. Apoptosis and autophagy were both suppressed by the autophagy inhibitors 3-MA and CQ. The AMPK inhibitor CC reduced autophagy and apoptosis in RTAEC and suppressed the production of the AMPK downstream factors ULK1 and P-ULK1.

CONCLUSIONS

Rotenone may promote autophagy in the thoracic aorta and RTAEC by activating the LKB1-AMPK-ULK1 signaling pathway, thereby inducing apoptosis.

Effects of mitochondrial dysfunction on cellular function: Role in atherosclerosis

Atherosclerosis, an immunoinflammatory disease of medium and large arteries, is associated with life-threatening clinical events, such as acute coronary syndromes and stroke. Chronic inflammation and impaired lipoprotein metabolism are considered to be among the leading causes of atherosclerosis, while numerous risk factors, including arterial hypertension, diabetes mellitus, obesity, and aging, can contribute to the development of the disease. In recent years, emerging evidence has underlined the key role of mitochondrial dysfunction in the pathogenesis of atherosclerosis. Mitochondrial dysfunction is believed to result in an increase in reactive oxygen species, leading to oxidative stress, chronic inflammation, and intracellular lipid deposition, all of which can contribute to the pathogenesis of atherosclerosis. Critical cells, including endothelial cells, vascular smooth muscle cells, and macrophages, play an important role in atherosclerosis. Mitochondrial function is also involved in maintaining the normal function of these cells. To better understand the relationship between mitochondrial dysfunction and atherosclerosis, this review summarizes the findings of recent studies and discusses the role of mitochondrial dysfunction in the risk factors and critical cells of atherosclerosis. FACTS: OPEN QUESTIONS.

Mitochondrial fission inhibition protects against hypertension induced by angiotensin II

Mitochondrial dysfunction has been implicated in various types of cardiovascular disease including hypertension. Mitochondrial fission fusion balance is critical to mitochondrial quality control, whereas enhanced fission has been reported in several models of cardiovascular disease. However, limited information is available regarding the contribution of mitochondrial fission in hypertension. Here, we have tested the hypothesis that inhibition of mitochondrial fission attenuates the development of hypertension and associated vascular remodeling. In C57BL6 mice infused with angiotensin II for 2 weeks, co-treatment of mitochondrial fission inhibitor, mdivi1, significantly inhibited angiotensin II-induced development of hypertension assessed by radiotelemetry. Histological assessment of hearts and aortas showed that mdivi1 inhibited vessel fibrosis and hypertrophy induced by angiotensin II. This was associated with attenuation of angiotensin II-induced decline in mitochondrial aspect ratio seen in both the endothelial and medial layers of aortas. Mdivi1 also mitigated angiotensin II-induced cardiac hypertrophy assessed by heart weight-to-body weight ratio as well as by echocardiography. In ex vivo experiments, mdivi1 inhibited vasoconstriction and abolished the enhanced vascular reactivity by angiotensin II in small mesenteric arteries. Proteomic analysis on endothelial cell culture media with angiotensin II and/or mdivi1 treatment revealed that mdivi1 inhibited endothelial cell hypersecretory phenotype induced by angiotensin II. In addition, mdivi1 attenuated angiotensin II-induced protein induction of periostin, a myofibroblast marker in cultured vascular fibroblasts. In conclusion, these data suggest that mdivi1 prevented angiotensin II-induced hypertension and cardiovascular remodeling via multicellular mechanisms in the vasculature.

Dynamin-Related Protein 1 Binding Partners MiD49 and MiD51 Increased Mitochondrial Fission In Vitro and Atherosclerosis in High-Fat-Diet-Fed ApoE-/- Mice

Novel components of the mitochondrial fission machinery, mitochondrial dynamics proteins of 49 kDa (MiD49) and 51 kDa (MiD51), have been recently described, and their potential therapeutic targets for treating cardiovascular disease have been shown, including acute myocardial infarction (AMI), anthracycline cardiomyopathy and pulmonary arterial hypertension (PAH). Here, we examined the role of MiD49 and MiD51 in atherosclerosis. MiD49/51 expression was increased in the aortic valve endothelial cells (ECs) of high-fat diet-induced atherosclerosis in ApoE-/-mice and IL-8-induced human umbilical vein endothelial cells (HUVECs), which accelerated dynamin-related protein 1 (Drp1)-mediated mitochondrial fission. Silencing MiD49/51 reduced atherosclerotic plaque size, increased collagen content, and decreased the IL-8-induced adhesion and proliferation of HUVECs. MiD51 upregulation resulted from decreased microRNA (miR)-107 expression and increased hypoxia-inducible factor-1a (HIF-1a) expression. Treatment with miR-107 mimics decreased atherosclerotic plaque size by reducing HIF-1α and MiD51 production. Both MiD49 and MiD51 were involved in atherosclerotic plaque formation through Drp1-mediated mitochondrial fission, and the involvement of MiD51 in this process was the result of decreased miR-107 expression and increased HIF-1α expression. The miR-107-HIF-1α-MiD51 pathway might provide new therapeutic targets for atherosclerosis.

PKCδ regulates the vascular biology in diabetic atherosclerosis

Diabetes mellitus, known for its complications, especially vascular complications, is becoming a globally serious social problem. Atherosclerosis has been recognized as a common vascular complication mechanism in diabetes. The diacylglycerol (DAG)-protein kinase C (PKC) pathway plays an important role in atherosclerosis. PKCs can be divided into three subgroups: conventional PKCs (cPKCs), novel PKCs (nPKCs), and atypical PKCs (aPKCs). The aim of this review is to provide a comprehensive overview of the role of the PKCδ pathway, an isoform of nPKC, in regulating the function of endothelial cells, vascular smooth muscle cells, and macrophages in diabetic atherosclerosis. In addition, potential therapeutic targets regarding the PKCδ pathway are summarized. Video Abstract.

Mitochondria spatially and temporally modulate VSMC phenotypes via interacting with cytoskeleton in cardiovascular diseases

Cardiovascular diseases caused by atherosclerosis (AS) seriously endanger human health, which is closely related to vascular smooth muscle cell (VSMC) phenotypes. VSMC phenotypic transformation is marked by the alteration of phenotypic marker expression and cellular behaviour. Intriguingly, the mitochondrial metabolism and dynamics altered during VSMC phenotypic transformation. Firstly, this review combs VSMC mitochondrial metabolism in three aspects: mitochondrial ROS generation, mutated mitochondrial DNA (mtDNA) and calcium metabolism respectively. Secondly, we summarized the role of mitochondrial dynamics in regulating VSMC phenotypes. We further emphasized the association between mitochondria and cytoskelton via presenting cytoskeletal support during mitochondrial dynamics process, and discussed its impact on their respective dynamics. Finally, considering that both mitochondria and cytoskeleton are mechano-sensitive organelles, we demonstrated their direct and indirect interaction under extracellular mechanical stimuli through several mechano-sensitive signaling pathways. We additionally discussed related researches in other cell types in order to inspire deeper thinking and reasonable speculation of potential regulatory mechanism in VSMC phenotypic transformation.

Mitochondrial Dysfunction in the Cardio-Renal Axis

Cardiovascular disease (CVD) frequently complicates chronic kidney disease (CKD). The risk of all-cause mortality increases from 20% to 500% in patients who suffer both conditions; this is referred to as the so-called cardio-renal syndrome (CRS). Preclinical studies have described the key role of mitochondrial dysfunction in cardiovascular and renal diseases, suggesting that maintaining mitochondrial homeostasis is a promising therapeutic strategy for CRS. In this review, we explore the malfunction of mitochondrial homeostasis (mitochondrial biogenesis, dynamics, oxidative stress, and mitophagy) and how it contributes to the development and progression of the main vascular pathologies that could be affected by kidney injury and vice versa, and how this knowledge may guide the development of novel therapeutic strategies in CRS.

Mitochondrial dynamics in vascular remodeling and target-organ damage

Vascular remodeling is the pathological basis for the development of many cardiovascular diseases. The mechanisms underlying endothelial cell dysfunction, smooth muscle cell phenotypic switching, fibroblast activation, and inflammatory macrophage differentiation during vascular remodeling remain elusive. Mitochondria are highly dynamic organelles. Recent studies showed that mitochondrial fusion and fission play crucial roles in vascular remodeling and that the delicate balance of fusion-fission may be more important than individual processes. In addition, vascular remodeling may also lead to target-organ damage by interfering with the blood supply to major body organs such as the heart, brain, and kidney. The protective effect of mitochondrial dynamics modulators on target-organs has been demonstrated in numerous studies, but whether they can be used for the treatment of related cardiovascular diseases needs to be verified in future clinical studies. Herein, we summarize recent advances regarding mitochondrial dynamics in multiple cells involved in vascular remodeling and associated target-organ damage.

Mitochondrial Dysfunction and Increased DNA Damage in Vascular Smooth Muscle Cells of Abdominal Aortic Aneurysm (AAA-SMC)

There is increasing evidence for enhanced oxidative stress in the vascular wall of abdominal aortic aneurysms (AAA). Mitochondrial damage and dysfunction are hypothesized to be actors in altered production of reactive oxygen species (ROS) and oxidative stress. However, the role of mitochondria and oxidative stress in vascular remodelling and progression of AAA remains uncertain. We here addressed whether mitochondrial dysfunction is persistently increased in vascular smooth muscle cells (VSMCs) isolated from AAA compared to healthy VSMC. AAA-derived VSMC cultures (AAA-SMC, n = 10) and normal VSMC cultures derived from healthy donors (n = 7) were grown in vitro and analysed for four parameters, indicating mitochondrial dysfunction: (i) mitochondrial content and morphology, (ii) ROS production and antioxidative response, (iii) NADP+/NADPH content and ratio, and (iv) DNA damage, in the presence or absence of angiotensin II (AngII). AAA-SMC displayed increased mitochondrial circularity (rounded shape), reduced mitochondrial area, and reduced perimeter, indicating increased fragmentation and dysfunction compared to healthy controls. This was accompanied by significantly increased O₂ ^- production, reduced NADP+/NADPH levels, a lower antioxidative response (indicated by antioxidative response element- (ARE-) driven luciferase reporter assays), more DNA damage (determined by percentage of γ-H2A.X-positive nuclei), and earlier growth arrest in AAA-SMC. Our data suggest that mitochondrial dysfunction and oxidative stress are persistently increased in AAA-SMC, emphasizing their implication in the pathophysiology of AAA.

Mitochondria as novel mediators linking gut microbiota to atherosclerosis that is ameliorated by herbal medicine: A review

Atherosclerosis (AS) is the main cause of cardiovascular disease (CVD) and is characterized by endothelial damage, lipid deposition, and chronic inflammation. Gut microbiota plays an important role in the occurrence and development of AS by regulating host metabolism and immunity. As human mitochondria evolved from primordial bacteria have homologous characteristics, they are attacked by microbial pathogens as target organelles, thus contributing to energy metabolism disorders, oxidative stress, and apoptosis. Therefore, mitochondria may be a key mediator of intestinal microbiota disorders and AS aggravation. Microbial metabolites, such as short-chain fatty acids, trimethylamine, hydrogen sulfide, and bile acids, also affect mitochondrial function, including mtDNA mutation, oxidative stress, and mitophagy, promoting low-grade inflammation. This further damages cellular homeostasis and the balance of innate immunity, aggravating AS. Herbal medicines and their monomers can effectively ameliorate the intestinal flora and their metabolites, improve mitochondrial function, and inhibit atherosclerotic plaques. This review focuses on the interaction between gut microbiota and mitochondria in AS and explores a therapeutic strategy for restoring mitochondrial function and intestinal microbiota disorders using herbal medicines, aiming to provide new insights for the prevention and treatment of AS.

Arterial remodeling: the role of mitochondrial metabolism in vascular smooth muscle cells

Arterial remodeling is a common pathological basis of cardiovascular diseases such as atherosclerosis, vascular restenosis, hypertension, pulmonary hypertension, aortic dissection, and aneurysm. Vascular smooth muscle cells (VSMCs) are not only the main cellular components in the middle layer of the arterial wall but also the main cells involved in arterial remodeling. Dedifferentiated VSMCs lose their contractile properties and are converted to a synthetic, secretory, proliferative, and migratory phenotype, playing key roles in the pathogenesis of arterial remodeling. As mitochondria are the main site of biological oxidation and energy transformation in eukaryotic cells, mitochondrial numbers and function are very important in maintaining the metabolic processes in VSMCs. Mitochondrial dysfunction and oxidative stress are novel triggers of the phenotypic transformation of VSMCs, leading to the onset and development of arterial remodeling. Therefore, pharmacological measures that alleviate mitochondrial dysfunction reverse arterial remodeling by ameliorating VSMCs metabolic dysfunction and phenotypic transformation, providing new options for the treatment of cardiovascular diseases related to arterial remodeling. This review summarizes the relationship between mitochondrial dysfunction and cardiovascular diseases associated with arterial remodeling and then discusses the potential mechanism by which mitochondrial dysfunction participates in pathological arterial remodeling. Furthermore, maintaining or improving mitochondrial function may be a new intervention strategy to prevent the progression of arterial remodeling.

Current Understanding of the Pivotal Role of Mitochondrial Dynamics in Cardiovascular Diseases and Senescence

The heart is dependent on ATP production in mitochondria, which is closely associated with cardiovascular disease because of the oxidative stress produced by mitochondria. Mitochondria are highly dynamic organelles that constantly change their morphology to elongated (fusion) or small and spherical (fission). These mitochondrial dynamics are regulated by various small GTPases, Drp1, Fis1, Mitofusin, and Opa1. Mitochondrial fission and fusion are essential to maintain a balance between mitochondrial biogenesis and mitochondrial turnover. Recent studies have demonstrated that mitochondrial dynamics play a crucial role in the development of cardiovascular diseases and senescence. Disruptions in mitochondrial dynamics affect mitochondrial dysfunction and cardiomyocyte survival leading to cardiac ischemia/reperfusion injury, cardiomyopathy, and heart failure. Mitochondrial dynamics and reactive oxygen species production have been associated with endothelial dysfunction, which in turn causes the development of atherosclerosis, hypertension, and even pulmonary hypertension, including pulmonary arterial hypertension and chronic thromboembolic pulmonary hypertension. Here, we review the association between cardiovascular diseases and mitochondrial dynamics, which may represent a potential therapeutic target.

Endothelial cell-derived tetrahydrobiopterin prevents aortic valve calcification

AIMS

Tetrahydrobiopterin (BH4) is a critical determinant of the biological function of endothelial nitric oxide synthase. The present study was to investigate the role of valvular endothelial cell (VEC)-derived BH4 in aortic valve calcification.

METHODS AND RESULTS

Plasma and aortic valve BH4 concentrations and the BH4:BH2 ratio were significantly lower in calcific aortic valve disease patients than in controls. There was a significant decrease of the two key enzymes of BH4 biosynthesis, guanosine 5'-triphosphate cyclohydrolase I (GCH1) and dihydrofolate reductase (DHFR), in calcified aortic valves compared with the normal ones. Endothelial cell-specific deficiency of Gch1 in Apoe-/- (Apoe-/-Gch1fl/flTie2Cre) mice showed a marked increase in transvalvular peak jet velocity, calcium deposition, runt-related transcription factor 2 (Runx2), dihydroethidium (DHE), and 3-nitrotyrosine (3-NT) levels in aortic valve leaflets compared with Apoe-/-Gch1fl/fl mice after a 24-week western diet (WD) challenge. Oxidized LDL (ox-LDL) induced osteoblastic differentiation of valvular interstitial cells (VICs) co-cultured with either si-GCH1- or si-DHFR-transfected VECs, while the effects could be abolished by BH4 supplementation. Deficiency of BH4 in VECs caused peroxynitrite formation increase and 3-NT protein increase under ox-LDL stimulation in VICs. SIN-1, the peroxynitrite generator, significantly up-regulated alkaline phosphatase (ALP) and Runx2 expression in VICs via tyrosine nitration of dynamin-related protein 1 (DRP1) at Y628. Finally, folic acid (FA) significantly attenuated aortic valve calcification in WD-fed Apoe-/- mice through increasing DHFR and salvaging BH4 biosynthesis.

CONCLUSION

The reduction in endothelial-dependent BH4 levels promoted peroxynitrite formation, which subsequently resulted in DRP1 tyrosine nitration and osteoblastic differentiation of VICs, thereby leading to aortic valve calcification. Supplementation of FA in diet attenuated hypercholesterolaemia-induced aortic valve calcification by salvaging BH4 bioavailability.

Mitochondrial Implications in Cardiovascular Aging and Diseases: The Specific Role of Mitochondrial Dynamics and Shifts

Cardiovascular disease has been, and remains, one of the leading causes of death in the modern world. The elderly are a particularly vulnerable group. The aging of the body is inevitably accompanied by the aging of all its systems, and the cardiovascular system is no exception. The aging of the cardiovascular system is a significant risk factor for the development of various diseases and pathologies, from atherosclerosis to ischemic stroke. Mitochondria, being the main supplier of energy necessary for the normal functioning of cells, play an important role in the proper functioning of the cardiovascular system. The functioning of each individual cell and the organism as a whole depends on their number, structure, and performance, as well as the correct operation of the system in removing non-functional mitochondria. In this review, we examine the role of mitochondria in the aging of the cardiovascular system, as well as in diseases (for example, atherosclerosis and ischemic stroke). We pay special attention to changes in mitochondrial dynamics since the shift in the balance between fission and fusion is one of the main factors associated with various cardiovascular pathologies.

Mitochondria Lead the Way: Mitochondrial Dynamics and Function in Cellular Movements in Development and Disease

The dynamics, distribution and activity of subcellular organelles are integral to regulating cell shape changes during various physiological processes such as epithelial cell formation, cell migration and morphogenesis. Mitochondria are famously known as the powerhouse of the cell and play an important role in buffering calcium, releasing reactive oxygen species and key metabolites for various activities in a eukaryotic cell. Mitochondrial dynamics and morphology changes regulate these functions and their regulation is, in turn, crucial for various morphogenetic processes. In this review, we evaluate recent literature which highlights the role of mitochondrial morphology and activity during cell shape changes in epithelial cell formation, cell division, cell migration and tissue morphogenesis during organism development and in disease. In general, we find that mitochondrial shape is regulated for their distribution or translocation to the sites of active cell shape dynamics or morphogenesis. Often, key metabolites released locally and molecules buffered by mitochondria play crucial roles in regulating signaling pathways that motivate changes in cell shape, mitochondrial shape and mitochondrial activity. We conclude that mechanistic analysis of interactions between mitochondrial morphology, activity, signaling pathways and cell shape changes across the various cell and animal-based model systems holds the key to deciphering the common principles for this interaction.

Mangiferin Inhibits PDGF-BB-Induced Proliferation and Migration of Rat Vascular Smooth Muscle Cells and Alleviates Neointimal Formation in Mice through the AMPK/Drp1 Axis

Mangiferin is a naturally occurring xanthone C-glycoside that is widely found in various plants. Previous studies have reported that mangiferin inhibits tumor cell proliferation and migration. Excessive proliferation and migration of vascular smooth muscle cells (SMCs) is associated with neointimal hyperplasia in coronary arteries. However, the role and mechanism of mangiferin action in neointimal hyperplasia is still unknown. In this study, a mouse carotid artery ligation model was established, and primary rat smooth muscle cells were isolated and used for mechanistic assays. We found that mangiferin alleviated neointimal hyperplasia, inhibited proliferation and migration of SMCs, and promoted platelets derive growth factors-BB- (PDGF-BB-) induced contractile phenotype in SMCs. Moreover, mangiferin attenuated neointimal formation by inhibiting mitochondrial fission through the AMPK/Drp1 signaling pathway. These findings suggest that mangiferin has the potential to maintain vascular homeostasis and inhibit neointimal hyperplasia.

Association of Lectin-Like Oxidized Low-Density Lipoprotein Receptor-1 With Angiotensin II Type 1 Receptor Impacts Mitochondrial Quality Control, Offering Promise for the Treatment of Vascular Senescence

Lectin-like oxidized low-density lipoprotein (ox-LDL) causes vascular senescence and atherosclerosis. It has been reported that ox-LDL scavenger receptor-1 (LOX-1) is associated with the angiotensin II type 1 receptor (AT1R). While mitochondria play a crucial role in the development of vascular senescence and atherosclerosis, they also undergo quality control through mitochondrial dynamics and autophagy. The aim of this study was to investigate (1) whether LOX-1 associates with AT1R, (2) if this regulates mitochondrial quality control, and (3) whether AT1R inhibition using Candesartan might ameliorate ox-LDL-induced vascular senescence. We performed in vitro and in vivo experiments using vascular smooth muscle cells (VSMCs), and C57BL/6 and apolipoprotein E-deficient (ApoE KO) mice. Administration of oxidized low-density lipoprotein (ox-LDL) to VSMCs induced mitochondrial dysfunction and cellular senescence accompanied by excessive mitochondrial fission, due to the activation of fission factor Drp1, which was derived from the activation of the Raf/MEK/ERK pathway. Administration of either Drp1 inhibitor, mdivi-1, or AT1R blocker candesartan attenuated these alterations. Electron microscopy and immunohistochemistry of the co-localization of LAMP2 with TOMM20 signal showed that AT1R inhibition also increased mitochondrial autophagy, but this was not affected by Atg7 deficiency. Conversely, AT1R inhibition increased the co-localization of LAMP2 with Rab9 signal. Moreover, AT1R inhibition-induced mitochondrial autophagy was abolished by Rab9 deficiency, suggesting that AT1R signaling modulated mitochondrial autophagy derived from Rab9-dependent alternative autophagy. Inhibition of the Raf/MEK/ERK pathway also decreased the excessive mitochondrial fission, and Rab9-dependent mitochondrial autophagy, suggesting that AT1R signaling followed the Raf/MEK/ERK axis modulated both mitochondrial dynamics and autophagy. The degree of mitochondrial dysfunction, reactive oxygen species production, vascular senescence, atherosclerosis, and the number of fragmented mitochondria accompanied by Drp1 activation were all higher in ApoE KO mice than in C57BL/6 mice. These detrimental alterations were successfully restored, and mitochondrial autophagy was upregulated with the administration of candesartan to ApoE KO mice. The association of LOX-1 with AT1R was found to play a crucial role in regulating mitochondrial quality control, as cellular/vascular senescence is induced by ox-LDL, and AT1R inhibition improves the adverse effects of ox-LDL.

Cold-pressed oil from Citrus aurantifolia inhibits the proliferation of vascular smooth muscle cells via regulation of PI3K/MAPK signaling pathways

Vascular occlusive disease is a chronic disease with significant morbidity and mortality. Although a variety of therapies and medications have been developed, the likelihood of disease re-emergence is high and this can be life-threatening. Based on a previous screening experiment related to vascular obstructive diseases using 34 types of essential oils, cold-pressed oil (CpO) from Citrus aurantifolia (lime) has been demonstrated to have the best effect for the inhibition of vascular smooth muscle cells (VSMCs) proliferation. The aim of the present study was to evaluate the effect of lime CpO on the pathological changes of VSMCs. To determine this, the effect of lime CpO on VSMC proliferation, a major cause of vascular disease, was investigated. To determine the safe concentration interval for toxicity of CpO during VSMC culture, a dilution of 1x10^-5 was determined using Cell Counting Kit-8 assay, which was confirmed to be non-toxic using a lactate dehydrogenase assay. To examine the effect of lime CpO in cellular signaling pathways, changes in phosphorylation of both the PI3K/AKT/mTOR and extracellular signal-regulated MEK/ERK signaling pathways with serum were investigated. Furthermore, lime CpO with FBS also significantly decreased the expression levels of the cell cycle regulators cyclin D1 and proliferating cell nuclear antigen. Additionally, lime CpO with FBS significantly inhibited the sprouting of VSMCs in an ex vivo culture system. These results suggested that lime CpO inhibited the abnormal proliferation of VSMCs and can be developed as a nature-based therapeutic agent for obstructive vascular disease.

Role of mitochondrial dynamics and mitophagy of vascular smooth muscle cell proliferation and migration in progression of atherosclerosis

Vascular smooth muscle cell (VSMC) proliferation and migration are critical events that contribute to the pathogenesis of vascular diseases such as atherosclerosis, restenosis, and hypertension. Recent findings have revealed that VSMC phenotype switching is associated with metabolic switch, which is related to the role of mitochondria. Mitochondrial dynamics are directly associated with mitochondrial function and cellular homeostasis. Interestingly, it has been suggested that mitochondrial dynamics and mitophagy play crucial roles in the regulation of VSMC proliferation and migration through various mechanisms. Especially, dynamin-related protein-1 and mitofusion-2 are two main molecules that play a key role in regulating mitochondrial dynamics to induce VSMC proliferation and migration. Therefore, this review describes the function and role of mitochondrial dynamics and mitophagy in VSMC homeostasis as well as the underlying mechanisms. This will provide insight into the development of innovative approaches to treat atherosclerosis.

Aorta smooth muscle-on-a-chip reveals impaired mitochondrial dynamics as a therapeutic target for aortic aneurysm in bicuspid aortic valve disease

Background:

Bicuspid aortic valve (BAV) is the most common congenital cardiovascular disease in general population and is frequently associated with the development of thoracic aortic aneurysm (TAA). There is no effective strategy to intervene with TAA progression due to an incomplete understanding of the pathogenesis. Insufficiency of NOTCH1 expression is highly related to BAV-TAA, but the underlying mechanism remains to be clarified.

Methods:

A comparative proteomics analysis was used to explore the biological differences between non-diseased and BAV-TAA aortic tissues. A microfluidics-based aorta smooth muscle-on-a-chip model was constructed to evaluate the effect of NOTCH1 deficiency on contractile phenotype and mitochondrial dynamics of human aortic smooth muscle cells (HAoSMCs).

Results:

Protein analyses of human aortic tissues showed the insufficient expression of NOTCH1 and impaired mitochondrial dynamics in BAV-TAA. HAoSMCs with NOTCH1-knockdown exhibited reduced contractile phenotype and were accompanied by attenuated mitochondrial fusion. Furthermore, we identified that mitochondrial fusion activators (leflunomide and teriflunomide) or mitochondrial fission inhibitor (Mdivi-1) partially rescued the disorders of mitochondrial dynamics in HAoSMCs derived from BAV-TAA patients.

Conclusions:

The aorta smooth muscle-on-a-chip model simulates the human pathophysiological parameters of aorta biomechanics and provides a platform for molecular mechanism studies of aortic disease and related drug screening. This aorta smooth muscle-on-a-chip model and human tissue proteomic analysis revealed that impaired mitochondrial dynamics could be a potential therapeutic target for BAV-TAA.

Funding:

National Key R and D Program of China, National Natural Science Foundation of China, Shanghai Municipal Science and Technology Major Project, Shanghai Science and Technology Commission, and Shanghai Municipal Education Commission.

To function properly, the heart must remain a one-way system, pumping out oxygenated blood into the aorta – the largest artery in the body – so it can be distributed across the organism. The aortic valve, which sits at the entrance of the aorta, is a key component of this system. Its three flaps (or ‘cusps’) are pushed open when the blood exits the heart, and they shut tightly so it does not flow back in the incorrect direction.

Nearly 1.4% of people around the world are born with ‘bicuspid’ aortic valves that only have two flaps. These valves may harden or become leaky, forcing the heart to work harder. This defect is also associated with bulges on the aorta which progressively weaken the artery, sometimes causing it to rupture.

Open-heart surgery is currently the only way to treat these bulges (or ‘aneurysms’), as no drug exists that could slow down disease progression. This is partly because the biological processes involved in the aneurysms worsening and bursting open is unclear.

Recent studies have highlighted that many individuals with bicuspid aortic valves also have lower levels of a protein known as NOTCH1, which plays a key signalling role for cells. Problems in the mitochondria – the structures that power up a cell – are also observed. However, it is not known how these findings are connected or linked with the aneurysms developing.

To answer this question, Abudupataer et al. analyzed the proteins present in diseased and healthy aortic muscle cells, confirming a lower production of NOTCH1 and impaired mitochondria in diseased tissues. They also created an ‘aorta-on-a-chip’ model where aortic muscle cells were grown in the laboratory under conditions resembling those found in the body – including the rhythmic strain that the aorta is under because of the heart beating. Abudupataer et al. then reduced NOTCH1 levels in healthy samples, which made the muscle tissue less able to contract and reduced the activity of the mitochondria. Applying drugs that tweak mitochondrial activity helped tissues from patients with bicuspid aortic valves to work better.

These compounds could potentially benefit individuals with deficient aortic valves, but experiments in animals and clinical trials would be needed first to confirm the results and assess safety. The aorta-on-a-chip model developed by Abudupataer et al. also provides a platform to screen for drugs and examine the molecular mechanisms at play in aortic diseases.

Bufalin induces mitochondrial dysfunction and promotes apoptosis of glioma cells by regulating Annexin A2 and DRP1 protein expression

Background

Glioma is a common primary central nervous system tumour, and therapeutic drugs that can effectively improve the survival rate of patients in the clinic are lacking. Bufalin is effective in treating various tumours, but the mechanism by which it promotes the apoptosis of glioma cells is unclear. The aim of this study was to investigate the drug targets of bufalin in glioma cells and to clarify the apoptotic mechanism.

Methods

Cell viability and proliferation were evaluated by CCK-8 and colony formation assays. Then, the cell cycle and apoptosis, intracellular ion homeostasis, oxidative stress levels and mitochondrial damage were assessed after bufalin treatment. DARTS-PAGE technology was employed and LC–MS/MS was performed to explore the drug targets of bufalin in U251 cells. Molecular docking and western blotting were performed to identify potential targets. siRNA targeting Annexin A2 and the DRP1 protein inhibitor Mdivi-1 were used to confirm the targets of bufalin.

Results

Bufalin upregulated the expression of cytochrome C, cleaved caspase 3, p-Chk1 and p-p53 proteins to induce U251 cell apoptosis and cycle arrest in the S phase. Bufalin also induced oxidative stress in U251 cells, destroyed intracellular ion homeostasis, and caused mitochondrial damage. The expression of mitochondrial division-/fusion-related proteins in U251 cells was abnormal, the Annexin A2 and DRP1 proteins were translocated from the cytoplasm to mitochondria, and the MFN2 protein was released from mitochondria into the cytoplasm after bufalin treatment, disrupting the mitochondrial division/fusion balance in U251 cells.

Conclusions

Our research indicated that bufalin can cause Annexin A2 and DRP1 oligomerization on the surface of mitochondria and disrupt the mitochondrial division/fusion balance to induce U251 cell apoptosis.

Graphic Abstract

Supplementary Information

The online version contains supplementary material available at 10.1186/s12935-021-02137-x.

Mitochondria Homeostasis and Vascular Medial Calcification

Vascular calcification occurs highly prevalent, which commonly predicts adverse cardiovascular events. The pathogenesis of calcification, a complicated and multifactorial process, is incompletely characterized. Accumulating evidence shows that mitochondrial dysfunction may ultimately be more detrimental in the vascular smooth muscle cells (VSMCs) calcification. This review summarizes the role of mitochondrial dysfunction and metabolic reprogramming in vascular calcification, and indicates that metabolic regulation may be a therapeutic target in vascular calcification.

Aberrant Mitochondrial Dynamics: An Emerging Pathogenic Driver of Abdominal Aortic Aneurysm

Abdominal aortic aneurysm (AAA) is defined as a progressive segmental dilation of the abdominal aorta and is associated with high mortality. The characterized features of AAA indicate several underlying mechanisms of AAA formation and progression, including reactive oxygen species production, inflammation, and atherosclerosis. Mitochondrial functions are critical for determining cell fate, and mitochondrial dynamics, especially selective mitochondrial autophagy, which is termed as mitophagy, has emerged as an important player in the pathogenesis of several cardiovascular diseases. The PARKIN/PARIS/PGC1α pathway is associated with AAA formation and has been proposed to play a role in mitochondrial dynamics mediated by the PINK/PARKIN pathway in the pathogenesis underlying AAA. This review is aimed at deepening our understanding of AAA formation and progression, which is vital for the development of potential medical therapies for AAA.

Pathophysiological Aspects of the Development of Abdominal Aortic Aneurysm with a Special Focus on Mitochondrial Dysfunction and Genetic Associations

Abdominal aortic aneurysm (AAA) is a complex degenerative vascular disease, with considerable morbidity and mortality rates among the elderly population. The mortality of AAA is related to aneurysm expansion (the enlargement of the aortic diameter up to 30 mm and above) and the subsequent rupture. The pathogenesis of AAA involves several biological processes, including aortic mural inflammation, oxidative stress, vascular smooth muscle cell apoptosis, elastin depletion, and degradation of the extracellular matrix. Mitochondrial dysfunction was also found to be associated with AAA formation. The evidence accumulated to date supports a close relationship between environmental and genetic factors in AAA initiation and progression. However, a comprehensive pathophysiological understanding of AAA formation remains incomplete. The open surgical repair of AAA is the only therapeutic option currently available, while a specific pharmacotherapy is still awaited. Therefore, there is a great need to clarify pathophysiological cellular and molecular mechanisms underlying AAA formation that would help to develop effective pharmacological therapies. In this review, pathophysiological aspects of AAA development with a special focus on mitochondrial dysfunction and genetic associations were discussed.

Targeting mitochondrial fission as a potential therapeutic for abdominal aortic aneurysm

AIMS

Angiotensin II (AngII) is a potential contributor to the development of abdominal aortic aneurysm (AAA). In aortic vascular smooth muscle cells (VSMCs), exposure to AngII induces mitochondrial fission via dynamin-related protein 1 (Drp1). However, pathophysiological relevance of mitochondrial morphology in AngII-associated AAA remains unexplored. Here, we tested the hypothesis that mitochondrial fission is involved in the development of AAA.

METHODS AND RESULTS

Immunohistochemistry was performed on human AAA samples and revealed enhanced expression of Drp1. In C57BL6 mice treated with AngII plus β-aminopropionitrile, AAA tissue also showed an increase in Drp1 expression. A mitochondrial fission inhibitor, mdivi1, attenuated AAA size, associated aortic pathology, Drp1 protein induction, and mitochondrial fission but not hypertension in these mice. Moreover, western-blot analysis showed that induction of matrix metalloproteinase-2, which precedes the development of AAA, was blocked by mdivi1. Mdivi1 also reduced the development of AAA in apolipoprotein E-deficient mice infused with AngII. As with mdivi1, Drp1+/- mice treated with AngII plus β-aminopropionitrile showed a decrease in AAA compared to control Drp1+/+ mice. In abdominal aortic VSMCs, AngII induced phosphorylation of Drp1 and mitochondrial fission, the latter of which was attenuated with Drp1 silencing as well as mdivi1. AngII also induced vascular cell adhesion molecule-1 expression and enhanced leucocyte adhesion and mitochondrial oxygen consumption in smooth muscle cells, which were attenuated with mdivi1.

CONCLUSION

These data indicate that Drp1 and mitochondrial fission play salient roles in AAA development, which likely involves mitochondrial dysfunction and inflammatory activation of VSMCs.

Macrophage (Drp1) Dynamin-Related Protein 1 Accelerates Intimal Thickening After Vascular Injury

OBJECTIVE

Mitochondria consistently change their morphology in a process regulated by proteins, including Drp1 (dynamin-related protein 1), a protein promoting mitochondrial fission. Drp1 is involved in the mechanisms underlying various cardiovascular diseases, such as myocardial ischemia/reperfusion injury, heart failure, and pulmonary arterial hypertension. However, its role in macrophages, which promote various vascular diseases, is poorly understood. We therefore tested our hypothesis that macrophage Drp1 promotes vascular remodeling after injury.

METHOD AND RESULTS

To explore the selective role of macrophage Drp1, we created macrophage-selective Drp1-deficient mice and performed femoral arterial wire injury. In these mice, intimal thickening and negative remodeling were attenuated at 4 weeks after injury when compared with control mice. Deletion of macrophage Drp1 also attenuated the macrophage accumulation and cell proliferation in the injured arteries. Gain- and loss-of-function experiments using cultured macrophages indicated that Drp1 induces the expression of molecules associated with inflammatory macrophages. Morphologically, mitochondrial fission was induced in inflammatory macrophages, whereas mitochondrial fusion was induced in less inflammatory/reparative macrophages. Pharmacological inhibition or knockdown of Drp1 decreased the mitochondrial reactive oxygen species and chemotactic activity in cultured macrophages. Co-culture experiments of macrophages with vascular smooth muscle cells indicated that deletion of macrophage Drp1 suppresses growth and migration of vascular smooth muscle cells induced by macrophage-derived soluble factors.

CONCLUSIONS

Macrophage Drp1 accelerates intimal thickening after vascular injury by promoting macrophage-mediated inflammation. Macrophage Drp1 may be a potential therapeutic target of vascular diseases.

New perspectives on the role of Drp1 isoforms in regulating mitochondrial pathophysiology

Mitochondria are dynamic organelles constantly undergoing fusion and fission. A concerted balance between the process of mitochondrial fusion and fission is required to maintain cellular health under different physiological conditions. Mutation and dysregulation of Drp1, the major driver of mitochondrial fission, has been associated with various neurological, oncological and cardiovascular disorders. Moreover, when subjected to pathological insults, mitochondria often undergo excessive fission, generating fragmented and dysfunctional mitochondria leading to cell death. Therefore, manipulating mitochondrial fission by targeting Drp1 has been an appealing therapeutic approach for cytoprotection. However, studies have been inconsistent. Studies employing Drp1 constructs representing alternate Drp1 isoforms, have demonstrated differing impacts of these isoforms on mitochondrial fission and cell death. Furthermore, there are distinct expression patterns of Drp1 isoforms in different tissues, suggesting idiosyncratic engagement in specific cellular functions. In this review, we will discuss these inherent variations among human Drp1 isoforms and how they could affect Drp1-mediated mitochondrial fission and cell death.

Involvement of Senescence and Mitochondrial Fission in Endothelial Cell Pro-Inflammatory Phenotype Induced by Angiotensin II

Angiotensin II (AngII) has a crucial role in cardiovascular pathologies, including endothelial inflammation and premature vascular aging. However, the precise molecular mechanism underlying aging-related endothelial inflammation induced by AngII remains elusive. Here, we have tested a hypothesis in cultured rat aortic endothelial cells (ECs) that the removal of AngII-induced senescent cells, preservation of proteostasis, or inhibition of mitochondrial fission attenuates the pro-inflammatory EC phenotype. AngII stimulation in ECs resulted in cellular senescence assessed by senescence-associated β galactosidase activity. The number of β galactosidase-positive ECs induced by AngII was attenuated by treatment with a senolytic drug ABT737 or the chemical chaperone 4-phenylbutyrate. Monocyte adhesion assay revealed that the pro-inflammatory phenotype in ECs induced by AngII was alleviated by these treatments. AngII stimulation also increased mitochondrial fission in ECs, which was mitigated by mitochondrial division inhibitor-1. Pretreatment with mitochondrial division inhibitor-1 attenuated AngII-induced senescence and monocyte adhesion in ECs. These findings suggest that mitochondrial fission and endoplasmic reticulum stress have causative roles in endothelial senescence-associated inflammatory phenotype induced by AngII exposure, thus providing potential therapeutic targets in age-related cardiovascular diseases.

Corylin Inhibits Vascular Cell Inflammation, Proliferation and Migration and Reduces Atherosclerosis in ApoE-Deficient Mice

Atherosclerosis is a complex disease that includes several events, including reactive oxygen species (ROS) stress, inflammation, endothelial dysfunction, lipid deposition, and vascular smooth muscle cell (VSMC) proliferation and migration, which result in atherosclerotic plaque formation. Corylin, a flavonoid compound, is known to exhibit antioxidative, anti-inflammatory and antiproliferative effects. However, it remains unknown whether corylin could modulate atherogenesis. Here, we identified the anti-inflammatory effect of corylin in tumor necrosis factor-α (TNF-α)-induced vascular cells. In human umbilical vein endothelial cells (HUVECs), corylin suppressed TNF-α-induced monocyte adhesion to the HUVECs and transmigration by downregulating the ROS/JNK/nuclear factor-kappa beta (NF-κB) p65 pathway. In VSMCs, corylin inhibited TNF-α-induced monocyte adhesion by suppressing ROS production, mitogen-activated protein kinase (MAPK) phosphorylation and NF-κB p65 translocation. In platelet-derived growth factor-BB (PDGF-BB)-induced VSMCs, corylin inhibited PDGF-BB-induced VSMC proliferation and migration through regulating the mammalian target of rapamycin (mTOR)/dynamin-1-like protein 1 (Drp1) signaling cascade. In addition, corylin treatment not only attenuated atherosclerotic lesions, ROS production, vascular cell adhesion protein-1 (VCAM-1) expression, monocyte adhesion and VSMC proliferation in apolipoprotein E (ApoE)-deficient mice but also inhibited neointimal hyperplasia in endothelial-denuded mice. Thus, corylin may be a potential prevention and treatment for atherosclerosis.

Metabolic Stress

Mitochondria regulate major aspects of cell function by producing ATP, contributing to Ca²⁺ signaling, influencing redox potential, and controlling levels of reactive oxygen species. In this review, we will discuss recent findings that illustrate how mitochondrial respiration, Ca²⁺ handling, and production of reactive oxygen species affect vascular smooth muscle cell function during neointima formation. We will review mitochondrial fission/fusion as fundamental mechanisms for smooth muscle proliferation, migration, and metabolism and examine the role of mitochondrial mobility in cell migration. In addition, we will summarize novel aspects by which mitochondria regulate apoptosis.

Complex Effects of Putative DRP-1 Inhibitors on Stress Responses in Mouse Heart and Rat Cardiomyoblasts

Dynamin-related protein-1 (DRP-1)-dependent mitochondrial fission may influence cardiac tolerance to ischemic or oxidative stress, presenting a potential "cardioprotective" target. Effects of dynamin inhibitors [mitochondrial division inhibitor 1 (MDIVI-1) and dynasore] on injury, mitochondrial function, and signaling proteins were assessed in distinct models: ischemia-reperfusion (I-R) in mouse hearts and oxidative stress in rat H9c2 cardiomyoblasts. Hearts exhibited substantial cell death [approx. 40 IU lactate dehydrogenase (LDH) efflux] and dysfunction (approx. 40 mmHg diastolic pressure, approx. 40% contractile recovery) following 25 minutes' ischemia. Pretreatment with 1 μM MDIVI-1 reduced dysfunction (30 mmHg diastolic pressure, approx. 55% recovery) and delayed without reducing overall cell death, whereas 5 μM MDIVI-1 reduced overall death at the same time paradoxically exaggerating dysfunction. Postischemic expression of mitochondrial DRP-1 and phospho-activation of ERK1/2 were reduced by MDIVI-1. Conversely, 1 μM dynasore worsened cell death and reduced nonmitochondrial DRP-1. Postischemic respiratory fluxes were unaltered by MDIVI-1, although a 50% fall in complex-I flux control ratio was reversed. In H9c2 myoblasts stressed with 400 μM H₂O₂, treatment with 50 μM MDIVI-1 preserved metabolic (MTT assay) and mitochondrial (basal respiration) function without influencing survival. This was associated with differential signaling responses, including reduced early versus increased late phospho-activation of ERK1/2, increased phospho-activation of protein kinase B (AKT), and differential changes in determinants of autophagy [reduced microtubule-associated protein 1 light chain 3b (LC3B-II/I) vs. increased Parkinson juvenile disease protein 2 (Parkin)] and apoptosis [reduced poly-(ADP-ribose) polymerase (PARP) cleavage vs. increased BCL2-associated X (BAX)/B-cell lymphoma 2 (BCL2)]. These data show MDIVI-1 (not dynasore) confers some benefit during I-R/oxidative stress. However, despite mitochondrial and metabolic preservation, MDIVI-1 exerts mixed effects on cell death versus dysfunction, potentially reflecting differential changes in survival kinase, autophagy, and apoptosis pathways. SIGNIFICANCE STATEMENT: Inhibition of mitochondrial fission is a novel approach to still elusive cardioprotection. Assessing effects of fission inhibitors on responses to ischemic or oxidative stress in hearts and cardiomyoblasts reveals mitochondrial division inhibitor 1 (MDIVI-1) and dynasore induce complex effects and limited cardioprotection. This includes differential impacts on death and dysfunction, survival kinases, and determinants of autophagy and apoptosis. Although highlighting the interconnectedness of fission and these key processes, results suggest MDIVI-1 and dynasore may be of limited value in the quest for effective cardioprotection.

Lysophosphatidylcholine-induced mitochondrial fission contributes to collagen production in human cardiac fibroblasts

Lysophosphatidylcholine (LPC) may accumulate in the heart to cause fibrotic events, which is mediated through fibroblast activation and collagen accumulation. Here, we evaluated the mechanisms underlying LPC-mediated collagen induction via mitochondrial events in human cardiac fibroblasts (HCFs), coupling application of the pharmacologic cyclooxygenase-2 (COX-2) inhibitor, celecoxib, and genetic mutations in FOXO1 on the fibrosis pathway. In HCFs, LPC caused prostaglandin E2 (PGE2)/PGE2 receptor 4 (EP4)-dependent collagen induction via activation of transcriptional activity of forkhead box protein O1 (FoxO1) on COX-2 gene expression. These responses were mediated through LPC-induced generation of mitochondrial reactive oxygen species (mitoROS), as confirmed by ex vivo studies, which indicated that LPC increased COX-2 expression and oxidative stress. LPC-induced mitoROS mediated the activation of protein kinase C (PKC)α, which interacted with and phosphorylated dynamin-related protein 1 (Drp1) at Ser616, thereby increasing Drp1-mediated mitochondrial fission and mitochondrial depolarization. Furthermore, inhibition of PKCα and Drp1 reduced FoxO1-mediated phosphorylation at Ser256 and nuclear accumulation, which suppressed COX-2/PGE2 expression and collagen production. Moreover, pretreatment with celecoxib or COX-2 siRNA suppressed WT FoxO1; mutated Ser256-to-Asp256 FoxO1-enhanced collagen induction, which was reversed by addition of PGE2 Our results demonstrate that LPC-induced generation of mitoROS regulates PKCα-mediated Drp1-dependent mitochondrial fission and COX-2 expression via a PKCα/Drp1/FoxO1 cascade, leading to PGE2/EP4-mediated collagen induction. These findings provide new insights about the role of LPC in the pathway of fibrotic injury in HCFs.

PKCδ Mediates Mineralocorticoid Receptor Activation by Angiotensin II to Modulate Smooth Muscle Cell Function

Angiotensin II (AngII) and the mineralocorticoid receptor (MR) ligand aldosterone both contribute to cardiovascular disorders, including hypertension and adverse vascular remodeling. We previously demonstrated that AngII activates MR-mediated gene transcription in human vascular smooth muscle cells (SMCs), yet the mechanism and the impact on SMC function are unknown. Using an MR-responsive element-driven transcriptional reporter assay, we confirm that AngII induces MR transcriptional activity in vascular SMCs and endothelial cells, but not in Cos1 or human embryonic kidney-293 cells. AngII activation of MR was blocked by the MR antagonist spironolactone or eplerenone and the protein kinase C-δ (PKCδ) inhibitor rottlerin, implicating both in the mechanism. Similarly, small interfering RNA knockdown of PKCδ in SMCs prevented AngII-mediated MR activation, whereas knocking down of MR blocked both aldosterone- and AngII-induced MR function. Coimmunoprecipitation studies reveal that endogenous MR and PKCδ form a complex in SMCs that is enhanced by AngII treatment in association with increased serine phosphorylation of the MR N terminus. AngII increased mRNA expression of the SMC-MR target gene, FKBP51, via an MR-responsive element in intron 5 of the FKBP51 gene. The impact of AngII on FKBP51 reporter activity and gene expression in SMCs was inhibited by spironolactone and rottlerin. Finally, the AngII-induced increase in SMC number was also blocked by the MR antagonist spironolactone and the PKCδ inhibitor rottlerin. These data demonstrate that AngII activates MR transcriptional regulatory activity, target gene regulation, and SMC proliferation in a PKCδ-dependent manner. This new mechanism may contribute to synergy between MR and AngII in driving SMC dysfunction and to the cardiovascular benefits of MR and AngII receptor blockade in humans.

Reactive Oxygen Species in Metabolic and Inflammatory Signaling

Reactive oxygen species (ROS) are well known for their role in mediating both physiological and pathophysiological signal transduction. Enzymes and subcellular compartments that typically produce ROS are associated with metabolic regulation, and diseases associated with metabolic dysfunction may be influenced by changes in redox balance. In this review, we summarize the current literature surrounding ROS and their role in metabolic and inflammatory regulation, focusing on ROS signal transduction and its relationship to disease progression. In particular, we examine ROS production in compartments such as the cytoplasm, mitochondria, peroxisome, and endoplasmic reticulum and discuss how ROS influence metabolic processes such as proteasome function, autophagy, and general inflammatory signaling. We also summarize and highlight the role of ROS in the regulation metabolic/inflammatory diseases including atherosclerosis, diabetes mellitus, and stroke. In order to develop therapies that target oxidative signaling, it is vital to understand the balance ROS signaling plays in both physiology and pathophysiology, and how manipulation of this balance and the identity of the ROS may influence cellular and tissue homeostasis. An increased understanding of specific sources of ROS production and an appreciation for how ROS influence cellular metabolism may help guide us in the effort to treat cardiovascular diseases.

Targeting HSP90 attenuates angiotensin II-induced adventitial remodelling via suppression of mitochondrial fission

Aims

Adventitial remodelling presenting with the phenotypic switch of adventitial fibroblasts (AFs) to myofibroblasts is reportedly involved in the evolution of several vascular diseases, including hypertension. In our previous study, we reported that heat shock protein 90 (HSP90) inhibition by 17-dime-thylaminoethylamino-17-demethoxygeldanamycin (17-DMAG) markedly attenuates angiotensin II (AngII)-induced abdominal aortic aneurysm formation by simultaneously inhibiting several key signalling and transcriptional pathways in vascular smooth muscle cells; however, little is known about its role on AFs. Given that the AF phenotypic switch is likely to be associated with mitochondrial function and calcineurin (CN), a client protein of HSP90 that mediates mitochondrial fission and function, the aim of this study was to investigate whether mitochondrial fission contributes to phenotypic switch of AF, and if it does, we further aimed to determine whether HSP90 inhibition attenuates mitochondrial fission and subsequently suppresses AF transformation and adventitial remodelling in AngII-induced hypertensive mice.

Methods and results

In primary mouse AFs, we found that CN-dependent dephosphorylation of Drp1 induced mitochondrial fission and regulated mitochondrial reactive oxygen species production, which stimulated AF proliferation, migration, and phenotypic switching in AngII-treated AFs. Moreover, AngII was found to increase the binding of HSP90 and CN in AFs, while HSP90 inhibition significantly reversed AngII-induced mitochondrial fission and AF phenotypic switching by modulating the CN-dependent dephosphorylation of Drp1. Consistent with the effects in AFs, in an animal model of AngII-induced adventitial remodelling, 17-DMAG markedly reduced mitochondrial fission, AF differentiation, vessel wall thickening, and fibrosis in the aortic adventitia, which were mediated by CN/Drp1 signalling pathways.

Conclusions

Our study suggests that CN/Drp1-dependent mitochondrial fission may be essential for understanding adventitial remodelling in hypertension and that HSP90 inhibition may serve as a novel approach for the treatment of adventitial remodelling-related diseases.

Blockade of AMPA Receptor Regulates Mitochondrial Dynamics by Modulating ERK1/2 and PP1/PP2A-Mediated DRP1-S616 Phosphorylations in the Normal Rat Hippocampus

N-Methyl-D-aspartate receptor (NMDAR) and α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid receptor (AMPAR) activations induce fast and transient mitochondrial fragmentation under pathophysiological conditions. However, it is still unknown whether NMDAR or AMPAR activity contributes to mitochondrial dynamics under physiological conditions. In the present study, MK801 (a non-competitive NMDAR antagonist) did not affect mitochondrial length in hippocampal neurons as well as phosphorylation levels of dynamin-related protein 1 (DRP1)-serine (S) 616, extracellular-signal-regulated kinase 1/2 (ERK1/2), c-Jun N-terminal kinase (JNK), p38 mitogen-activated protein kinase (p38 MAPK) and AMPAR. In contrast, perampanel (a non-competitive AMPAR antagonist) elongated mitochondrial length in neurons concomitant with diminishing phosphorylations of DRP1-S616, ERK1/2, and JNK, but not p38 MAPK. Perampanel also reduced protein phosphatase (PP) 1, PP2A and PP2B phosphorylations, indicating activations of these PPs which were unaffected by MK801. U0126 (an ERK1/2 inhibitor) elongated mitochondrial length, accompanied by the reduced DRP1-S616 phosphorylation. SP600125 (a JNK inhibitor) did not influence mitochondrial length and DRP1 phosphorylations. Okadaic acid (a PP1/PP2A inhibitor) reduced mitochondrial length with the up-regulated DRP1-S616 phosphorylation, while CsA (a PP2B inhibitor) increased it with the elevated DRP1-S637 phosphorylation. Co-treatment of okadaic acid or CsA with perampanel attenuated the reductions in DRP1-S616 and -S637 phosphorylation without changing DRP1 expression level, respectively. GYKI 52466 (another non-competitive AMPAR antagonist) showed the similar effects of perampanel on phosphorylations of DRP1, ERK1/2, JNK, PPs, and GluR1 AMPAR subunits. Taken together, our findings suggest that a blockade of AMPAR may regulate the cooperation of ERK1/2- and PP1/PP2A for the modulation of DRP1 phosphorylations, which facilitate mitochondrial fusion.

Mitochondrial Assays Using Cardiac Stem Cells

Ischemic heart disease is the leading cause of death worldwide. Stem cell therapy to repair and regenerate the infarcted myocardium is a promising approach to address this unmet medical need. However, the poor survival of transplanted cells in the hostile ischemic myocardium has been a major hurdle in achieving an effective cell therapy against myocardial infarction. As such, novel strategies to promote the survival of transplanted cells are highly sought after. Mitochondria are intimately involved in cell survival and have been the main organelles being targeted for cytoprotection. Mitochondrial morphology is linked to mitochondrial function and cell viability. Therefore, quantitative methodologies to obtain reliable and reproducible results of mitochondrial morphology and function are essential for identifying and developing new cytoprotective strategies to enhance the survival of stem cells post-transplantation. Here, we describe methods for assessing mitochondrial morphology, mitochondrial membrane potential, and mitochondrial reactive oxygen species production.

Angiotensin II Signal Transduction: An Update on Mechanisms of Physiology and Pathophysiology

The renin-angiotensin-aldosterone system plays crucial roles in cardiovascular physiology and pathophysiology. However, many of the signaling mechanisms have been unclear. The angiotensin II (ANG II) type 1 receptor (AT₁R) is believed to mediate most functions of ANG II in the system. AT₁R utilizes various signal transduction cascades causing hypertension, cardiovascular remodeling, and end organ damage. Moreover, functional cross-talk between AT₁R signaling pathways and other signaling pathways have been recognized. Accumulating evidence reveals the complexity of ANG II signal transduction in pathophysiology of the vasculature, heart, kidney, and brain, as well as several pathophysiological features, including inflammation, metabolic dysfunction, and aging. In this review, we provide a comprehensive update of the ANG II receptor signaling events and their functional significances for potential translation into therapeutic strategies. AT₁R remains central to the system in mediating physiological and pathophysiological functions of ANG II, and participation of specific signaling pathways becomes much clearer. There are still certain limitations and many controversies, and several noteworthy new concepts require further support. However, it is expected that rigorous translational research of the ANG II signaling pathways including those in large animals and humans will contribute to establishing effective new therapies against various diseases.

Intracellular cAMP Sensor EPAC: Physiology, Pathophysiology, and Therapeutics Development

This review focuses on one family of the known cAMP receptors, the exchange proteins directly activated by cAMP (EPACs), also known as the cAMP-regulated guanine nucleotide exchange factors (cAMP-GEFs). Although EPAC proteins are fairly new additions to the growing list of cAMP effectors, and relatively "young" in the cAMP discovery timeline, the significance of an EPAC presence in different cell systems is extraordinary. The study of EPACs has considerably expanded the diversity and adaptive nature of cAMP signaling associated with numerous physiological and pathophysiological responses. This review comprehensively covers EPAC protein functions at the molecular, cellular, physiological, and pathophysiological levels; and in turn, the applications of employing EPAC-based biosensors as detection tools for dissecting cAMP signaling and the implications for targeting EPAC proteins for therapeutic development are also discussed.

YiQiFuMai Powder Injection Protects against Ischemic Stroke via Inhibiting Neuronal Apoptosis and PKCδ/Drp1-Mediated Excessive Mitochondrial Fission

YiQiFuMai (YQFM) powder injection has been reported to be used in cardiovascular and nervous system diseases with marked efficacy. However, as a treatment against diseases characterized by hypoxia, lassitude, and asthenia, the effects and underlying mechanisms of YQFM in neuronal mitochondrial function and dynamics have not been fully elucidated. Here, we demonstrated that YQFM inhibited mitochondrial apoptosis and activation of dynamin-related protein 1 (Drp1) in cerebral ischemia-injured rats, producing a significant improvement in cerebral infarction and neurological score. YQFM also attenuated oxidative stress-induced mitochondrial dysfunction and apoptosis through increasing ATP level and mitochondria membrane potential (Δψm), inhibiting ROS production, and regulating Bcl-2 family protein levels in primary cultured neurons. Moreover, YQFM inhibited excessive mitochondrial fission, Drp1 phosphorylation, and translocation from cytoplasm to mitochondria induced by oxidative stress. We provided the first evidence that YQFM inhibited the activation, association, and translocation of PKCδ and Drp1 upon oxidative stress. Taken together, we demonstrate that YQFM ameliorates ischemic stroke-induced neuronal apoptosis through inhibiting mitochondrial dysfunction and PKCδ/Drp1-mediated excessive mitochondrial fission. These findings not only put new insights into the unique neuroprotective properties of YQFM associated with the regulation of mitochondrial function but also expand our understanding of the underlying mechanisms of ischemic stroke.

Mdivi-1 Protects Human W8B2+ Cardiac Stem Cells from Oxidative Stress and Simulated Ischemia-Reperfusion Injury

Cardiac stem cell (CSC) therapy is a promising approach to treat ischemic heart disease. However, the poor survival of transplanted stem cells in the ischemic myocardium has been a major impediment in achieving an effective cell-based therapy against myocardial infarction. Inhibiting mitochondrial fission has been shown to promote survival of several cell types. However, the role of mitochondrial morphology in survival of human CSC remains unknown. In this study, we investigated whether mitochondrial division inhibitor-1 (Mdivi-1), an inhibitor of mitochondrial fission protein dynamin-related protein-1 (Drp1), can improve survival of a novel population of human W8B2⁺ CSCs in hydrogen peroxide (H₂O₂)-induced oxidative stress and simulated ischemia-reperfusion injury models. Mdivi-1 significantly reduced H₂O₂-induced cell death in a dose-dependent manner. This cytoprotective effect was accompanied by an increased proportion of cells with tubular mitochondria, but independent of mitochondrial membrane potential recovery and reduction of mitochondrial superoxide production. In simulated ischemia-reperfusion injury model, Mdivi-1 given as a pretreatment or throughout ischemia-reperfusion injury significantly reduced cell death. However, the cytoprotective effect of Mdivi-1 was not observed when given at reperfusion. Moreover, the cytoprotective effect of Mdivi-1 in the simulated ischemia-reperfusion injury model was not accompanied by changes in mitochondrial morphology, mitochondrial membrane potential, or mitochondrial reactive oxygen species production. Mdivi-1 also did not affect mitochondrial bioenergetics of intact W8B2⁺ CSCs. Taken together, these experiments demonstrated that Mdivi-1 treatment of human W8B2⁺ CSCs enhances their survival and can be employed to improve therapeutic efficacy of CSCs for ischemic heart disease.

Assessing the effects of mitofusin 2 deficiency in the adult heart using 3D electron tomography

The effects of mitofusin 2 (MFN2) deficiency, on mitochondrial morphology and the mitochondria-junctional sarcoplasmic reticulum (jSR) complex in the adult heart, have been previously investigated using 2D electron microscopy, an approach which is unable to provide a 3D spatial assessment of these imaging parameters. Here, we use 3D electron tomography to show that MFN2-deficient mitochondria are larger in volume, more elongated, and less rounded; have fewer mitochondria-jSR contacts, and an increase in the distance between mitochondria and jSR, when compared to WT mitochondria. In comparison to 2D electron microscopy, 3D electron tomography can provide further insights into mitochondrial morphology and the mitochondria-jSR complex in the adult heart.

To mdivi-1 or not to mdivi-1: Is that the question?

The fission/division and fusion of mitochondria are fundamental aspects of mitochondrial biology. The balance of fission and fusion sets the length of mitochondria in cells to serve their physiological requirements. The fission of mitochondria is markedly induced in many disease states and in response to cellular injury, resulting in the fragmentation of mitochondria into dysfunctional units. The mechanism that drives fission is dependent on the dynamin related protein 1 (Drp1) GTPase. mdivi-1 is a quinazolinone originally described as a selective inhibitor of Drp1, over other dynamin family members, and reported to inhibit mitochondrial fission. A recent study has challenged the activity of mdivi-1 as an inhibitor of Drp1. This study raises serious issues regarding the interpretation of data addressing the effects of mdivi-1 as reflective of the inhibition of Drp1 and thus fission. This commentary considers the evidence for and against mdivi-1 as an inhibitor of Drp1 and presents the following considerations; (1) the activity of mdivi-1 toward Drp1 GTPase activity requires further biochemical investigation, (2) as there is a large body of literature using mdivi-1 in vitro with effects as predicted for inhibition of Drp1 and mitochondrial fission, reviewed herein, the evidence is in favor of mdivi-1's originally described bioactivity, and (3) until the issue is resolved, experimental interpretations for the effects of mdivi-1 on inhibition of fission in cell and tissue experiments warrants stringent positive controls directly addressing the effects of mdivi-1 on fission. © 2017 Wiley Periodicals, Inc. Develop Neurobiol 77: 1260-1268, 2017.

Atheroma Susceptible to Thrombosis Exhibit Impaired Endothelial Permeability In Vivo as Assessed by Nanoparticle-Based Fluorescence Molecular Imaging

BACKGROUND

The role of local alterations in endothelial functional integrity in atherosclerosis remains incompletely understood. This study used nanoparticle-enhanced optical molecular imaging to probe in vivo mechanisms involving impaired endothelial barrier function in experimental atherothrombosis.

METHODS AND RESULTS

Atherosclerosis was induced in rabbits (n=31) using aortic balloon injury and high-cholesterol diet. Rabbits received ultrasmall superparamagnetic iron oxide nanoparticles (CLIO) derivatized with a near-infrared fluorophore (CyAm7) 24 hours before near-infrared fluorescence imaging. Rabbits were then either euthanized (n=9) or underwent a pharmacological triggering protocol to induce thrombosis (n=22). CLIO-CyAm7 nanoparticles accumulated in areas of atheroma (P<0.05 versus reference areas). On near-infrared fluorescence microscopy, CLIO-CyAm7 primarily deposited in the superficial intima within plaque macrophages, endothelial cells, and smooth muscle cells. Nanoparticle-positive areas further exhibited impaired endothelial barrier function as illuminated by Evans blue leakage. Deeper nanoparticle deposition occurred in areas of plaque neovascularization. In rabbits subject to pharmacological triggering, plaques that thrombosed exhibited significantly higher CLIO-CyAm7 accumulation compared with nonthrombosed plaques (P<0.05). In thrombosed plaques, nanoparticles accumulated preferentially at the plaque-thrombus interface. Intravascular 2-dimensional near-infrared fluorescence imaging detected nanoparticles in human coronary artery-sized atheroma in vivo (P<0.05 versus reference segments).

CONCLUSIONS

Plaques that exhibit impaired in vivo endothelial permeability in cell-rich areas are susceptible to subsequent thrombosis. Molecular imaging of nanoparticle deposition may help to identify biologically high-risk atheroma.