Dysfunction of the adhesion G protein-coupled receptor latrophilin 1 (ADGRL1/LPHN1) increases the risk of obesity

Obesity is one of the diseases with severe health consequences and rapidly increasing worldwide prevalence. Understanding the complex network of food intake and energy balance regulation is an essential prerequisite for pharmacological intervention with obesity. G protein-coupled receptors (GPCRs) are among the main modulators of metabolism and energy balance. They, for instance, regulate appetite and satiety in certain hypothalamic neurons, as well as glucose and lipid metabolism and hormone secretion from adipocytes. Mutations in some GPCRs, such as the melanocortin receptor type 4 (MC4R), have been associated with early-onset obesity. Here, we identified the adhesion GPCR latrophilin 1 (ADGRL1/LPHN1) as a member of the regulating network governing food intake and the maintenance of energy balance. Deficiency of the highly conserved receptor in mice results in increased food consumption and severe obesity, accompanied by dysregulation of glucose homeostasis. Consistently, we identified a partially inactivating mutation in human ADGRL1/LPHN1 in a patient suffering from obesity. Therefore, we propose that LPHN1 dysfunction is a risk factor for obesity development.

Dose-Dependent Effects of Lipopolysaccharide on the Endothelium-Sepsis versus Metabolic Endotoxemia-Induced Cellular Senescence

The endothelium, the innermost cell layer of blood vessels, is not only a physical barrier between the bloodstream and the surrounding tissues but has also essential functions in vascular homeostasis. Therefore, it is not surprising that endothelial dysfunction is associated with most cardiovascular diseases. The functionality of the endothelium is compromised by endotoxemia, the presence of bacterial endotoxins in the bloodstream with the main endotoxin lipopolysaccharide (LPS). Therefore, this review will focus on the effects of LPS on the endothelium. Depending on the LPS concentration, the outcomes are either sepsis or, at lower concentrations, so-called low-dose or metabolic endotoxemia. Sepsis, a life-threatening condition evoked by hyperactivation of the immune response, includes breakdown of the endothelial barrier resulting in failure of multiple organs. A deeper understanding of the underlying mechanisms in the endothelium might help pave the way to new therapeutic options in sepsis treatment to prevent endothelial leakage and fatal septic shock. Low-dose endotoxemia or metabolic endotoxemia results in chronic inflammation leading to endothelial cell senescence, which entails endothelial dysfunction and thus plays a critical role in cardiovascular diseases. The identification of compounds counteracting senescence induction in endothelial cells might therefore help in delaying the onset or progression of age-related pathologies. Interestingly, two natural plant-derived substances, caffeine and curcumin, have shown potential in preventing endothelial cell senescence.

Caffeine Inhibits Oxidative Stress- and Low Dose Endotoxemia-Induced Senescence-Role of Thioredoxin-1

The maintenance of Thioredoxin-1 (Trx-1) levels, and thus of cellular redox homeostasis, is vital for endothelial cells (ECs) to prevent senescence induction. One hallmark of EC functionality, their migratory capacity, which depends on intact mitochondria, is reduced in senescence. Caffeine improves the migratory capacity and mitochondrial functionality of ECs. However, the impact of caffeine on EC senescence has never been investigated. Moreover, a high-fat diet, which can induce EC senescence, results in approximately 1 ng/mL lipopolysaccharide (LPS) in the blood. Therefore, we investigated if low dose endotoxemia induces EC senescence and concomitantly reduces Trx-1 levels, and if caffeine prevents or even reverses senescence. We show that caffeine precludes H₂O₂-triggered senescence induction by maintaining endothelial NO synthase (eNOS) levels and preventing the elevation of p21. Notably, 1 ng/mL LPS also increases p21 levels and reduces eNOS and Trx-1 amounts. These effects are completely blocked by co-treatment with caffeine. This prevention of senescence induction is similarly accomplished by the permanent expression of mitochondrial p27, a downstream effector of caffeine. Most importantly, after senescence induction by LPS, a single bolus of caffeine inhibits the increase in p21. This treatment also blocks Trx-1 degradation, suggesting that the reversion of senescence is intimately associated with a normalized redox balance.

Flavanol Consumption in Healthy Men Preserves Integrity of Immunological-Endothelial Barrier Cell Functions: Nutri(epi)genomic Analysis

SCOPE

While cocoa flavanol (CF) consumption improves cardiovascular risk biomarkers, molecular mechanisms underlying their protective effects are not understood.

OBJECTIVE

To investigate nutri(epi)genomic effects of CF and identify regulatory networks potential mediating vascular health benefits.

METHODS AND RESULTS

Twenty healthy middle-aged men consume CF (bi-daily 450 mg) or control drinks for 1 month. Microarray analysis identifies 2235 differentially expressed genes (DEG) involved in processes regulating immune response, cell adhesion, or cytoskeleton organization. Distinct patterns of DEG correlate with CF-related changes in endothelial function, arterial stiffness, and blood pressure. DEG profile negatively correlates with expression profiles of cardiovascular disease patients. CF modulated DNA methylation profile of genes implicates in cell adhesion, actin cytoskeleton organization, or cell signaling. In silico docking analyses indicate that CF metabolites have the potential of binding to cell signaling proteins and transcription factors. Incubation of plasma obtained after CF consumption decrease monocyte to endothelial adhesion and dose-dependently increase nitric oxide-dependent chemotaxis of circulating angiogenic cells further validating the biological functions of CF metabolites.

CONCLUSION

In healthy humans, CF consumption may mediate vascular protective effects by modulating gene expression and DNA methylation towards a cardiovascular protective effect, in agreement with clinical results, by preserving integrity of immunological-endothelial barrier functions.

Impact of whole thorax irradiation on cardiac remodeling and outcome after ischemia/reperfusion

Background

Thoracic irradiation is a fundamental treatment of several malignancies and has contributed to significant rise in long-term survival of cancer patients. However, a potentially increased risk of cardiac late effects, such as accelerated atherosclerosis, coronary heart disease or myocardial fibrosis, may partially diminish the therapeutic benefit and increase the risk of cardiovascular events, e.g. ischemia/reperfusion (I/R). The purpose of this project was to unravel the impact of whole thorax irradiation (WTI) on the outcome and cardiac remodeling after I/R.

Method

11-week-old male C57BL/6J mice were either exposed to WTI with a single dose (12.5 Gy) or sham-irradiation only (0 Gy) and subsequently observed over four weeks. Blood samples were taken to monitor early changes in circulating leukocytes (flow cytometry) and RNA was isolated from cardiac tissue to observe damage to mitochondria by analysis of different mitochondrial markers.

To study the impact of WTI on cardiac remodeling and outcome after I/R, mice were subjected to ischemia by occlusion of the left anterior descending artery (for 45 minutes) four weeks after WTI or sham-irradiation, followed by reperfusion for up to three weeks.

During early timepoints of cardiac remodeling, circulating immune cells and the immune cell influx in the heart were analysed (flow cytometry), ischemic area and cardiac inflammation were assessed by magnetic resonance imaging (MRI) and multiple cytokines were measured in the plasma (immunoassay).

Results

After WTI, a downregulation of leukocyte numbers was observed three days after irradiation, which recovered over four weeks. In addition, WTI resulted in a decrease in relative mRNA expression of mitochondrial fission factor (MFF) and a decrease in relative ATP levels in irradiated mice, suggesting damage of cardiac mitochondria.

The combined setup of WTI and I/R led to enhanced plasma concentration of IL-12(p70), IL-13, MCP-1 or MIP-1β and an increased ischemic area one day after I/R. Further, cardiac inflammation was increased three days post I/R in irradiated mice. Flow cytometric analysis revealed, increased amounts of circulating Ly6Chigh monocytes (% of all monocytes) and cardiac myeloid cells, specifically macrophages. Survival of irradiated mice was impaired already after one week post I/R; therefore, when analysing scar size three weeks later, no changes could be observed in the surviving mice.

Conclusion

Our data show that WTI causes early damage to cardiac mitochondrial network. While WTI also led acutely to a decrease in circulating immune cells, upon I/R, the preexisting irradiation-induced cardiac damage impacts on circulating and cardiac macrophages and monocytes resulting in increased cardiac inflammation and plasma concentration of cytokines in irradiated mice. In sum, irradiation-induced cardiac damage and subsequently altered immune response are likely contributing to the impaired survival of irradiated mice after I/R.

Funding Acknowledgement

Type of funding sources: Public grant(s) – National budget only. Main funding source(s): DFG - GRK 1739

Triiodothyronine improves contractile recovery of human atrial trabeculae after hypoxia/reoxygenation

BACKGROUND

In patients undergoing interventional or surgical coronary revascularization, subclinical hypothyroidism is common and associated with worse outcome, including the need for postoperative inotropic support. In isolated rat hearts with global ischemia/reperfusion, exogenous triiodothyronine (T3) reduces infarct size. Aim of this study was, to investigate whether or not exogenous T3 protects human myocardium from ischemia/reperfusion injury.

METHODS

Right atrial trabeculae from patients undergoing routine coronary artery bypass grafting were isolated and transferred to Tyrode's buffer. Electrically initiated (1 Hz) contractile stress (mN/mm²) was recorded for 10 min at baseline (95% O₂/ 5% CO₂, glucose). Sixty min hypoxia were induced by changing buffer gas and increasing stimulation rate (95% N₂/ 5% CO₂, choline chloride, 3 Hz) before return to reoxygenation for 30 min. T3 (500 μg/l) vs. NaOH (solvent control) was administered A) throughout (n = 11 vs. n = 9) or B) only 15 min before and during reoxygenation (n = 12 vs. n = 13). Western blot analyses of established cardioprotective signaling proteins were performed.

RESULTS

At baseline, contractile stress was comparable. T3 improved the cumulative recovery of contractile stress during reoxygenation from 41 ± 16 with NaOH to 55 ± 11% of baseline with T3, when given continuously in A or from 52 ± 13 with NaOH to 63 ± 11% of baseline with T3 when given just before and during reoxygenation in B. The ratio of mitochondrial complex I matrix arm to membrane NADH:ubiquinone oxidoreductase subunits (NDUF)V2 to NDUFA9 was reduced, reflecting increased complex I activity.

CONCLUSION

T3 increases contractile recovery of human right atrial trabeculae from hypoxia/reoxygenation.

Aryl Hydrocarbon Receptor-Dependent and -Independent Pathways Mediate Curcumin Anti-Aging Effects

The aryl hydrocarbon receptor (AhR) is a ligand-activated transcription factor whose activity can be modulated by polyphenols, such as curcumin. AhR and curcumin have evolutionarily conserved effects on aging. Here, we investigated whether and how the AhR mediates the anti-aging effects of curcumin across species. Using a combination of in vivo, in vitro, and in silico analyses, we demonstrated that curcumin has AhR-dependent or -independent effects in a context-specific manner. We found that in Caenorhabditis elegans, AhR mediates curcumin-induced lifespan extension, most likely through a ligand-independent inhibitory mechanism related to its antioxidant activity. Curcumin also showed AhR-independent anti-aging activities, such as protection against aggregation-prone proteins and oxidative stress in C. elegans and promotion of the migratory capacity of human primary endothelial cells. These AhR-independent effects are largely mediated by the Nrf2/SKN-1 pathway.

Protective Effects of Curcumin in Cardiovascular Diseases—Impact on Oxidative Stress and Mitochondria

Cardiovascular diseases (CVDs) contribute to a large part of worldwide mortality. Similarly, two of the major risk factors for these diseases, aging and obesity, are also global problems. Aging, the gradual decline of body functions, is non-modifiable. Obesity, a modifiable risk factor for CVDs, also predisposes to type 2 diabetes mellitus (T2DM). Moreover, it affects not only the vasculature and the heart but also specific fat depots, which themselves have a major impact on the development and progression of CVDs. Common denominators of aging, obesity, and T2DM include oxidative stress, mitochondrial dysfunction, metabolic abnormalities such as altered lipid profiles and glucose metabolism, and inflammation. Several plant substances such as curcumin, the major active compound in turmeric root, have been used for a long time in traditional medicine and for the treatment of CVDs. Newer mechanistic, animal, and human studies provide evidence that curcumin has pleiotropic effects and attenuates numerous parameters which contribute to an increased risk for CVDs in aging as well as in obesity. Thus, curcumin as a nutraceutical could hold promise in the prevention of CVDs, but more standardized clinical trials are required to fully unravel its potential.

Role of Mitochondrial Protein Import in Age-Related Neurodegenerative and Cardiovascular Diseases

Mitochondria play a critical role in providing energy, maintaining cellular metabolism, and regulating cell survival and death. To carry out these crucial functions, mitochondria employ more than 1500 proteins, distributed between two membranes and two aqueous compartments. An extensive network of dedicated proteins is engaged in importing and sorting these nuclear-encoded proteins into their designated mitochondrial compartments. Defects in this fundamental system are related to a variety of pathologies, particularly engaging the most energy-demanding tissues. In this review, we summarize the state-of-the-art knowledge about the mitochondrial protein import machinery and describe the known interrelation of its failure with age-related neurodegenerative and cardiovascular diseases.

Mitochondrial Telomerase Reverse Transcriptase Protects from Myocardial Ischemia/reperfusion Injury by Improving Complex I Composition and Function

Background: The catalytic subunit of telomerase, Telomerase Reverse Transcriptase (TERT) has protective functions in the cardiovascular system. TERT is not only present in the nucleus, but also in mitochondria. However, it is unclear whether nuclear or mitochondrial TERT is responsible for the observed protection and appropriate tools are missing to dissect this. Methods: We generated new mouse models containing TERT exclusively in the mitochondria (mitoTERT mice) or the nucleus (nucTERT mice) to finally distinguish between the functions of nuclear and mitochondrial TERT. Outcome after ischemia/reperfusion, mitochondrial respiration in the heart as well as cellular functions of cardiomyocytes, fibroblasts, and endothelial cells were determined. Results: All mice were phenotypically normal. While respiration was reduced in cardiac mitochondria from TERT-deficient and nucTERT mice, it was increased in mitoTERT animals. The latter also had smaller infarcts than wildtype mice, whereas nucTERT animals had larger infarcts. The decrease in ejection fraction after one, two and four weeks of reperfusion was attenuated in mitoTERT mice. Scar size was also reduced and vascularization increased. Mitochondrial TERT protected a cardiomyocyte cell line from apoptosis. Myofibroblast differentiation, which depends on complex I activity, was abrogated in TERT-deficient and nucTERT cardiac fibroblasts and completely restored in mitoTERT cells. In endothelial cells, mitochondrial TERT enhanced migratory capacity and activation of endothelial NO synthase. Mechanistically, mitochondrial TERT improved the ratio between complex I matrix arm and membrane subunits explaining the enhanced complex I activity. In human right atrial appendages, TERT was localized in mitochondria and there increased by remote ischemic preconditioning. The Telomerase activator, TA-65 evoked a similar effect in endothelial cells, thereby increasing their migratory capacity, and enhanced myofibroblast differentiation. Conclusions: Mitochondrial, but not nuclear TERT, is critical for mitochondrial respiration and during ischemia/reperfusion injury. Mitochondrial TERT improves complex I subunit composition. TERT is present in human heart mitochondria, and remote ischemic preconditioning increases its level in those organelles. TA-65 has comparable effects ex vivo and improves migratory capacity of endothelial cells and myofibroblast differentiation. We conclude that mitochondrial TERT is responsible for cardioprotection and its increase could serve as a therapeutic strategy.

Endothelial hyaluronan synthase 3 aggravates acute colitis in an experimental model of inflammatory bowel disease

The association between hyaluronan (HA) accumulation and increased inflammation in the colon suggests that HA is a potential therapeutic target in inflammatory bowel disease (IBD). However, whether patients with IBD would benefit from interference with HA synthesis is unknown. Here, we used pharmacological and genetic approaches to investigate the impact of systemic and partial blockade of HA synthesis in the Dextran Sodium Sulfate (DSS)-induced colitis model. To systemically inhibit HA production, we used 4-Methylumbelliferone (4-MU), whereas genetic approaches included the generation of mice with global or inducible cell-type specific deficiency in the Hyaluronan synthase 3 (Has3). We found that 4-MU treatment did not ameliorate but exacerbated disease severity characterized by increased body weight loss and enhanced colon tissue destruction compared to control mice without colitis. In contrast, global Has3 deficiency had a profound protective effect as reflected by a low colitis score and reduced infiltration of immune cells into the colon. To get further mechanistic insight into the proinflammatory role of HAS3, we deleted Has3 in a cell-type specific manner. Interestingly, while lack of Has3 expression in intestinal epithelial and smooth muscle cells had no effect or was rather proinflammatory, mice with Has3 deficiency in the endothelium were strongly protected against acute colitis. We conclude that endothelium-derived HAS3 plays a critical role in driving experimental colitis, warranting future studies on cell type-specific therapeutic interference with HA production in human IBD.

Accessing Mitochondrial Protein Import in Living Cells by Protein Microinjection

Mitochondrial protein biogenesis relies almost exclusively on the expression of nuclear-encoded polypeptides. The current model postulates that most of these proteins have to be delivered to their final mitochondrial destination after their synthesis in the cytoplasm. However, the knowledge of this process remains limited due to the absence of proper experimental real-time approaches to study mitochondria in their native cellular environment. We developed a gentle microinjection procedure for fluorescent reporter proteins allowing a direct non-invasive study of protein transport in living cells. As a proof of principle, we visualized potential-dependent protein import into mitochondria inside intact cells in real-time. We validated that our approach does not distort mitochondrial morphology and preserves the endogenous expression system as well as mitochondrial protein translocation machinery. We observed that a release of nascent polypeptides chains from actively translating cellular ribosomes by puromycin strongly increased the import rate of the microinjected pre-protein. This suggests that a substantial amount of mitochondrial translocase complexes was involved in co-translational protein import of endogenously expressed pre-proteins. Our protein microinjection method opens new possibilities to study the role of mitochondrial protein import in cell models of various pathological conditions as well as aging processes.

Extra-Nuclear Functions of the Transcription Factor Grainyhead-Like 3 in the Endothelium-Interaction with Endothelial Nitric Oxide Synthase

We previously demonstrated that the transcription factor Grainyhead-like 3 (GRHL3) has essential functions in endothelial cells by inhibiting apoptosis and promoting migration as well as activation of endothelial nitric oxide synthase (eNOS). We now show that a large portion of the protein is localized to myo-endothelial projections of murine arteries suggesting extra-nuclear functions. Therefore, we generated various deletion mutants to identify the nuclear localization signal (NLS) of GRHL3 and assessed potential extra-nuclear functions. Several large-scale deletion mutants were incapable of activating a GRHL3-dependent reporter construct, which could either be due to deficiencies in transcriptional activation or to impaired nuclear import. One of these mutants encompassed a predicted bipartite NLS whose deletion led to the retention of GRHL3 outside the nucleus. Interestingly, this mutant retained functions of the full-length protein as it could still inhibit pathways inducing endothelial cell apoptosis. As apoptosis protection by GRHL3 depends on NO-production, we examined whether GRHL3 could interact with eNOS and showed a direct interaction, which was enhanced with the extra-nuclear GRHL3 variant. The observation that endogenous GRHL3 also interacts with eNOS in intact murine arteries corroborated these findings and substantiated the notion that GRHL3 has important extra-nuclear functions in the endothelium.

Telomerase as a Therapeutic Target in Cardiovascular Disease

Shortened telomeres have been linked to numerous chronic diseases, most importantly coronary artery disease, but the underlying mechanisms remain ill defined. Loss-of-function mutations and deletions in telomerase both accelerate telomere shortening but do not necessarily lead to a clinical phenotype associated with atherosclerosis, questioning the causal role of telomere length in cardiac pathology. The differential extranuclear functions of the 2 main components of telomerase, telomerase reverse transcriptase and telomerase RNA component, offer important clues about the complex relationship between telomere length and cardiovascular pathology. In this review, we critically discuss relevant preclinical models, genetic disorders, and clinical studies to elucidate the impact of telomerase in cardiovascular disease and its potential role as a therapeutic target. We suggest that the antioxidative function of mitochondrial telomerase reverse transcriptase might be atheroprotective, making it a potential target for clinical trials. Graphic Abstract: A graphic abstract is available for this article.

Non-canonical functions of Telomerase Reverse Transcriptase - Impact on redox homeostasis

Telomerase consists of the catalytic subunit Telomerase Reverse Transcriptase (TERT) and the Telomerase RNA Component. Its canonical function is the prevention of telomere erosion. Over the last years it became evident that TERT is also present in tissues with low replicative potential. Important non-canonical functions of TERT are protection against apoptosis and maintenance of the cellular redox homeostasis in cancer as well as in somatic tissues. Intriguingly, TERT and reactive oxygen species (ROS) are interdependent on each other, with TERT being regulated by changes in the redox balance and itself controlling ROS levels in the cytosol and in the mitochondria. The latter is achieved because TERT is present in the mitochondria, where it protects mitochondrial DNA and maintains levels of anti-oxidative enzymes. Since numerous diseases are associated with oxidative stress, increasing the mitochondrial TERT level could be of therapeutic value.

Local Peroxynitrite Impairs Endothelial Transient Receptor Potential Vanilloid 4 Channels and Elevates Blood Pressure in Obesity

BACKGROUND

Impaired endothelium-dependent vasodilation is a hallmark of obesity-induced hypertension. The recognition that Ca2+ signaling in endothelial cells promotes vasodilation has led to the hypothesis that endothelial Ca2+ signaling is compromised during obesity, but the underlying abnormality is unknown. In this regard, transient receptor potential vanilloid 4 (TRPV4) ion channels are a major Ca2+ influx pathway in endothelial cells, and regulatory protein AKAP150 (A-kinase anchoring protein 150) enhances the activity of TRPV4 channels.

METHODS

We used endothelium-specific knockout mice and high-fat diet-fed mice to assess the role of endothelial AKAP150-TRPV4 signaling in blood pressure regulation under normal and obese conditions. We further determined the role of peroxynitrite, an oxidant molecule generated from the reaction between nitric oxide and superoxide radicals, in impairing endothelial AKAP150-TRPV4 signaling in obesity and assessed the effectiveness of peroxynitrite inhibition in rescuing endothelial AKAP150-TRPV4 signaling in obesity. The clinical relevance of our findings was evaluated in arteries from nonobese and obese individuals.

RESULTS

We show that Ca2+ influx through TRPV4 channels at myoendothelial projections to smooth muscle cells decreases resting blood pressure in nonobese mice, a response that is diminished in obese mice. Counterintuitively, release of the vasodilator molecule nitric oxide attenuated endothelial TRPV4 channel activity and vasodilation in obese animals. Increased activities of inducible nitric oxide synthase and NADPH oxidase 1 enzymes at myoendothelial projections in obese mice generated higher levels of nitric oxide and superoxide radicals, resulting in increased local peroxynitrite formation and subsequent oxidation of the regulatory protein AKAP150 at cysteine 36, to impair AKAP150-TRPV4 channel signaling at myoendothelial projections. Strategies that lowered peroxynitrite levels prevented cysteine 36 oxidation of AKAP150 and rescued endothelial AKAP150-TRPV4 signaling, vasodilation, and blood pressure in obesity. Peroxynitrite-dependent impairment of endothelial TRPV4 channel activity and vasodilation was also observed in the arteries from obese patients.

CONCLUSIONS

These data suggest that a spatially restricted impairment of endothelial TRPV4 channels contributes to obesity-induced hypertension and imply that inhibiting peroxynitrite might represent a strategy for normalizing endothelial TRPV4 channel activity, vasodilation, and blood pressure in obesity.

Increased Protein Tyrosine Phosphatase 1B (PTP1B) Activity and Cardiac Insulin Resistance Precede Mitochondrial and Contractile Dysfunction in Pressure-Overloaded Hearts

BACKGROUND

Insulin resistance in diabetes mellitus has been associated with mitochondrial dysfunction. Defects at the level of mitochondria are also characteristic of heart failure. We assessed changes in cardiac insulin response and mitochondrial function in a model of pressure overload-induced heart failure.

METHODS AND RESULTS

Rats underwent aortic banding to induce pressure overload. At 10 weeks, rats showed cardiac hypertrophy and pulmonary congestion, but left ventricular dilatation and systolic dysfunction were only evident after 20 weeks. This contractile impairment was accompanied by mitochondrial dysfunction as shown by markedly reduced state 3 respiration of isolated mitochondria. Aortic banding did not affect systemic insulin response. However, insulin-stimulated cardiac glucose uptake and glucose oxidation were significantly diminished at 10 and 20 weeks, which indicates cardiac insulin resistance starting before the onset of mitochondrial and contractile dysfunction. The impaired cardiac insulin action was related to a decrease in insulin-stimulated phosphorylation of insulin receptor β. Consistently, we found elevated activity of protein tyrosine phosphatase 1B (PTP1B) at 10 and 20 weeks, which may blunt insulin action by dephosphorylating insulin receptor β. PTP1B activity was also significantly increased in left ventricular samples of patients with systolic dysfunction undergoing aortic valve replacement because of aortic stenosis.

CONCLUSIONS

Pressure overload causes cardiac insulin resistance that precedes and accompanies mitochondrial and systolic dysfunction. Activation of PTP1B in the heart is associated with heart failure in both rats and humans and may account for cardiac insulin resistance. PTP1B may be a potential target to modulate insulin sensitivity and contractile function in the failing heart.

CDKN1B/p27 is localized in mitochondria and improves respiration-dependent processes in the cardiovascular system-New mode of action for caffeine

We show that the cyclin-dependent kinase inhibitor 1B (CDKN1B)/p27, previously known as a cell cycle inhibitor, is also localized within mitochondria. The migratory capacity of endothelial cells, which need intact mitochondria, is completely dependent on mitochondrial p27. Mitochondrial p27 improves mitochondrial membrane potential, increases adenosine triphosphate (ATP) content, and is required for the promigratory effect of caffeine. Domain mapping of p27 revealed that the N-terminus and C-terminus are required for those improvements. Further analysis of those regions revealed that the translocation of p27 into the mitochondria and its promigratory activity depend on serine 10 and threonine 187. In addition, mitochondrial p27 protects cardiomyocytes against apoptosis. Moreover, mitochondrial p27 is necessary and sufficient for cardiac myofibroblast differentiation. In addition, p27 deficiency and aging decrease respiration in heart mitochondria. Caffeine does not increase respiration in p27-deficient animals, whereas aged mice display improvement after 10 days of caffeine in drinking water. Moreover, caffeine induces transcriptome changes in a p27-dependent manner, affecting mostly genes relevant for mitochondrial processes. Caffeine also reduces infarct size after myocardial infarction in prediabetic mice and increases mitochondrial p27. Our data characterize mitochondrial p27 as a common denominator that improves mitochondria-dependent processes and define an increase in mitochondrial p27 as a new mode of action of caffeine.

Regulation of Transcription Factors by Reactive Oxygen Species and Nitric Oxide in Vascular Physiology and Pathology

SIGNIFICANCE

Cardiovascular diseases are the main cause of death worldwide and pose an immense economical burden. In most cases, the underlying problem is vascular occlusion by atherosclerotic plaques. Importantly, different cell types of the vascular wall and the immune system play crucial roles in atherosclerosis at different stages of the disease. Furthermore, atherosclerosis and conditions recognized as risk factors are characterized by a reduced availability of the vasoprotective molecule nitric oxide and an increase in reactive oxygen species, so-called oxidative stress. Transcription factors function as intracellular signal integrators and relays and thus, play a central role in cellular responses to changing conditions. Recent Advances: Work on specific transcriptional regulators has uncovered many of their functions and the upstream pathways modulating their activity in response to reactive oxygen and nitrogen species. Here, we have reviewed for a few selected examples how this can contribute not only to protection against atherosclerosis development but also to disease progression and the occurrence of clinical manifestations, such as plaque rupture.

CRITICAL ISSUES

Transcription factors have pleiotropic outputs and often also divergent functions in different cell types and tissues. Thus, in light of potential severe adverse side effects, a global activation or inhibition of particular transcriptions factors does not seem a feasible therapeutic option.

FUTURE DIRECTIONS

A further in-depth characterization of the cell- and stage-specific actions and regulation of transcription factors in atherosclerosis with respect to protein-protein interactions and target genes could open up new avenues for prevention or therapeutic interventions in this vascular disease. Antioxid. Redox Signal. 26, 679-699.

Abstract 462: Expression, Phosphorylation and Interaction Partners of the Transcription Factor Grainyhead-like 3 in the Endothelium

The transcription factor Grainyhead-like 3 (GRHL3) regulates apoptosis, migration and NO-bioavailability and thus, critical functions of endothelial cell, which are impaired in many cardiovascular diseases. However, due to the lack of a good antibody, all experiments concerning the regulation of GRHL3 itself were performed on the RNA level. After establishing a new antibody, we analyzed the GRHL3 protein in aortic sections of ApoE-deficient mice fed a high fat diet, a model for atherosclerosis. The diet resulted in a reduction of GRHL3 levels in the endothelium, which was corroborated ex vivo in endothelial cells treated with LDL. This simulated high fat diet also led to a decrease in endothelial NO-synthase. As the activity of transcription factors is regulated by post-translational modifications and protein-protein interactions, we analyzed the phosphorylation of GRHL3 and identified potential interaction partners. Using a combination of immunoprecipitation and -blotting we demonstrated for the first time that GRHL3 is phosphorylated on tyrosine residues. Furthermore, this phosphorylation was NO-inducible and Src-kinase-dependent. After characterization of the modified residues, we will assess their relevance by determining the impact of phospho-mimetic and non-phosphorylatable mutants on functional parameters of endothelial cells. To identify potential interaction partners of GRHL3 we immunoprecipitated the protein and analyzed the co-precipitated proteins by mass spectrometry. We identified the DBHS-proteins NONO and SFPQ, which have been implicated in the regulation of transcription and alternative splicing. The interaction with these two proteins was validated by co-immunoprecipitation. As a next step, we will overexpress and downregulate these proteins in endothelial cells to evaluate their cross-talk with GRHL3. Taken together our findings demonstrate (i) a downregulation of GRHL3 in a disease setting, (ii) a Src-kinase dependent, NO-inducible phosphorylation and (iii) an interaction with other gene-regulatory proteins. The analysis of the functional consequences of these different aspects of GRHL3 regulation will further shed light on the GRHL3 network in the endothelium and thus, its functions in the vasculature.

The Anti-Apoptotic Properties of APEX1 in the Endothelium Require the First 20 Amino Acids and Converge on Thioredoxin-1

The APEX nuclease (multifunctional DNA repair enzyme) 1 (APEX1) has a disordered N-terminus, a redox, and a DNA repair domain. APEX1 has anti-apoptotic properties, which have been linked to both domains depending on cell type and experimental conditions.

AIMS

As protection against apoptosis is a hallmark of vessel integrity, we wanted to elucidate whether APEX1 acts anti-apoptotic in primary human endothelial cells and, if so, what the underlying mechanisms are.

RESULTS

APEX1 inhibits apoptosis in endothelial cells by reducing Cathepsin D (CatD) cleavage, potentially by binding to the unprocessed form. Diminished CatD activation results in increased Thioredoxin-1 protein levels leading to reduced Caspase 3 activation. Consequently, apoptosis rates are decreased. This depends on the first twenty amino acids in APEX1, because APEX1 (21-318) induces CatD activity, decreases Thioredoxin-1 protein levels, and, thus, increases Caspase 3 activity and apoptosis. Along the same lines, APEX1 (1-20) inhibits Caspase 3 cleavage and apoptosis. Furthermore, re-expression of Thioredoxin-1 via lentiviral transduction rescues endothelial cells from APEX1 (21-318)-induced apoptosis. In an in vivo model of restenosis, which is characterized by oxidative stress, endothelial activation, and smooth muscle cell proliferation, Thioredoxin-1 protein levels are reduced in the endothelium of the carotids.

INNOVATION

APEX1 acts anti-apoptotic in endothelial cells. This anti-apoptotic effect depends on the first 20 amino acids of APEX1.

CONCLUSION

As proper function of the endothelium during life span is a hallmark for individual health span, a detailed characterization of the functions of the APEX1N-terminus is required to understand all its cellular properties. Antioxid. Redox Signal. 26, 616-629.

Role of Telomerase in the Cardiovascular System

Aging is one major risk factor for the incidence of cardiovascular diseases and the development of atherosclerosis. One important enzyme known to be involved in aging processes is Telomerase Reverse Transcriptase (TERT). After the discovery of the enzyme in humans, TERT had initially only been attributed to germ line cells, stem cells and cancer cells. However, over the last few years it has become clear that TERT is also active in cells of the cardiovascular system including cardiac myocytes, endothelial cells, smooth muscle cells and fibroblasts. Interference with the activity of this enzyme greatly contributes to cardiovascular diseases. This review will summarize the findings on the role of TERT in cardiovascular cells. Moreover, recent findings concerning TERT in different mouse models with respect to cardiovascular diseases will be described. Finally, the extranuclear functions of TERT will be covered within this review.

Outfielders playing in the infield: functions of aging-associated "nuclear" proteins in the mitochondria

Over the past few years it has become clear that mitochondria are not merely the powerhouses of cells. Proteome-analyses of mitochondria from different organisms and organs revealed that more than 1000 proteins are localized in and/or on mitochondria. This by far exceeds the number of proteins required for classical mitochondrial functions, e.g. the respiratory chain, the tricarboxylic acid cycle, fatty acid oxidation and apoptosis. This suggests that many of these proteins have other, as yet unknown functions. Several proteins with well-described nuclear functions, like the transcription factor FoxO3A or the Telomerase Reverse Transcriptase, have recently been shown to be localized also within the mitochondria. This mini-review will focus on the description of the functions of these two proteins in the nucleus and in the mitochondria - as two examples of many more proteins, which are yet to be uncovered. It will give insights into the role of these proteins within different organelles of the cell and will reveal that the functions of the proteins are probably not the same in the nucleus and the mitochondria. Therefore, these differences have to be considered when targeting proteins for therapeutic approaches.

Critical regulators of endothelial cell functions: for a change being alternative

SIGNIFICANCE

The endothelium regulates vessel dilation and constriction, balances hemostasis, and inhibits thrombosis. In addition, pro- and anti-angiogenic molecules orchestrate proliferation, survival, and migration of endothelial cells. Regulation of all these processes requires fine-tuning of signaling pathways, which can easily be tricked into running the opposite direction when exogenous or endogenous signals get out of hand. Surprisingly, some critical regulators of physiological endothelial functions can turn malicious by mere alternative splicing, leading to the expression of protein isoforms with opposite functions.

RECENT ADVANCES

While reviewing the evidence of alternative splicing on cellular physiology, it became evident that expression of splice factors and their activities are regulated by externally triggered signaling cascades. Furthermore, genome-wide identification of RNA-binding sites of splicing regulatory proteins now offer a glimpse into the splicing code responsible for alternative splicing of molecules regulating endothelial functions.

CRITICAL ISSUES

Due to the constantly growing number of transcript and protein isoforms, it will become more and more important to identify and characterize all transcripts and proteins regulating endothelial cell functions. One critical issue will be a non-ambiguous nomenclature to keep consistency throughout different laboratories.

FUTURE DIRECTIONS

RNA-deep sequencing focusing on exon-exon junction needs to more reliably identify alternative splicing events combined with functional analyses that will uncover more splice variants contributing to or inhibiting proper endothelial functions. In addition, understanding the signals mediating alternative splicing and its regulation might allow us to derive new strategies to preserve endothelial function by suppressing or upregulating specific protein isoforms. Antioxid. Redox Signal. 22, 1212-1229.

Abstract 224: Detoxification versus Healthy Aging: Aryl Hydrocarbon Receptor Deficiency Improves Vessel Functionality and Increases Healthy Lifespan

Development of age-associated vascular diseases like atherosclerosis depends not only on genetic predisposition but also on environmental influences. Ligands of the aryl hydrocarbon receptor (AhR), a ubiquitously expressed transcription factor upregulating detoxifying enzymes, like dioxin and benzo[a]pyrene (BaP) have been shown to promote atherosclerosis. Furthermore, recovery of the blood flow after hindlimb ischemia is significantly enhanced in AhR-deficient mice demonstrating increased angiogenesis in the absence of AhR. Thus, there seems to be a link between AhR, vessel functionality and age-related cardiovascular diseases.

To investigate the role of the AhR in health span and vessel function, we analyzed AhR-deficient Caenorhabditis elegans, vessel stiffness in AhR-knockout mice and human subjects of different age and with varying levels of AhR expression as well as functional parameters in primary human endothelial cells (EC) after AhR activation.

AhR-deficient C. elegans showed not only an extended life span, but also enhanced motility. In AhR-knockout mice, we observed a reduced PWV in both old and young animals, suggesting that AhR impairs vessel function already at young age. Concomitantly, eNOS phosphorylation at serine 1178, a surrogate marker for eNOS activation, was enhanced in aortas of knockout animals. In line with this, the AhR agonist BaP increased an inhibitory phosphorylation on eNOS in EC. Moreover, BaP reduced migration of EC without changes in proliferation or apoptosis, an effect that was reversed by addition of the AhR antagonist 3’methoxy-4’nitroflavone. In human subjects we demonstrated not only a positive correlation between age and pulse wave velocity (PWV), a readout for vessel stiffness, but also between AhR expression in blood cells and PWV, again suggesting a negative impact of AhR on vessel functionality.

Our data demonstrate that loss of AhR extends life span as well as health span in C. elegans. Knockout of AhR in mice leads to improvement of vessel functionality by decreasing vessel stiffness. Finally, the PWV in humans positively correlates not only with age but also with the expression of AhR. Thus, AhR expression may be useful as a new predictor of healthy aging from nematodes to humans.

Measurement of Endothelium-Dependent Vasodilation in Mice—Brief Report

Objective—

Endothelium-dependent, flow-mediated vasodilation after an increase in shear stress at the endothelial lining of conduit arteries during reactive hyperemia after ischemia is a fundamental principle of vascular physiology adapting blood flow to demand of supplied tissue. Flow-mediated vasodilation measurements have been performed in human studies and are of diagnostic and prognostic importance, but have been impossible because of technical limitations in transgenic mice to date, although these represent the most frequently used animal model in cardiovascular research.

Approach and Results—

Using high-frequency ultrasound, we visualized, quantified, and characterized for the first time endothelium-dependent dilation of the femoral artery after temporal ischemia of the lower part of the hindlimb and demonstrated that the signaling was almost exclusively dependent on stimulation of endothelial nitric oxide synthase, similar to acetylcholine, completely abolished after pharmacological or genetic inhibition of endothelial nitric oxide synthase and endothelial denudation, substantially impaired in mice of increasing age and cholesterol-fed ApoE knock outs and increased by the dietary polyphenol (−)-epicatechin. Intra- and interindividual variability were similar to the human methodology.

Conclusions—

The physiology of flow-mediated vasodilation in mice resembles that in humans underscoring the significance of this novel technology to noninvasively, serially, and reliably quantify flow-mediated vasodilation in transgenic mice.

Redox balance in the aged endothelium

The endothelium is located in a strategic anatomical position within the blood vessel wall and thus constitutes a barrier between the blood and all tissues. The integrity of the endothelial cells, which line the entire circulatory system like wallpaper, is essential to prevent the onset of cardiovascular disorders. Aging is one of the major risk factors for the development of heart and vascular diseases. However, over the past years it has become clear that the functional capacity of endothelial cells declines with age and that physiological aging occurs independently of pathological changes. One important mechanism contributing to the onset of the aging. process is the disturbance of the cellular redox homeostasis. Two key molecules involved in maintaining the delicate balance between oxidative and antioxidative systems are NADPH oxidase 4, an enzyme whose sole function is to produce reactive oxygen species and the oxidoreductase thioredoxin-1, which reduces oxidized proteins. Therefore, this review will focus on the role of these two proteins in cardiovascular aging.

Abstract 335: Carbon Nanoparticles Cause Loss of Gap Junctional Intercellular Communication and Nuclear Translocation of ß-Catenin in Endothelial Cells

Introduction: Environmental factors like industrial or consumer derived pollution are known to increase the risk for cardiovascular diseases. Previous studies demonstrated that senescent endothelial cells contribute to the onset of atherosclerosis. We have recently shown that non-toxic and non-inflammatory concentrations of carbon nanoparticles (CNP), a major component of industrial pollution, induce senescence in human primary endothelial cells (EC). However, the underlying molecular mechanisms leading to senescent EC are far from understood. Gap junctional intercellular communication (GJIC), which depends on Connexin 43 (Cx43) and β-catenin, is important for endothelial function and seems to be dysregulated during aging. Phosphorylation of Cx43 on serine 368 reduces the trafficking of Cx43 to the plasma membrane and assembly of Cx43 into gap junctional structures.

Objective: The aim of this study was to investigate whether CNP affect GJIC and β-catenin in EC.

Material and Methods: EC were treated with CNP at a measured size of 10 - 34 nm and GJIC was measured by dye transfer assay. The localization of Cx43 and β-catenin was assessed by immunofluorescence and phosphorylation and protein levels of Cx43 were by immunoblots.

Results: Two weeks incubation with CNP concentrations, which we are exposed to everyday, elevated the number of senescent EC. This was determined by increased staining for senescence-associated beta-galactosidase and the cell cycle inhibitor p21 - two established markers of senescence. The same concentrations of CNP resulted in an enhanced phosphorylation of Cx43 on serine 368. Moreover, CNP induced internalization of Cx43 and led to nuclear translocation of the Cx43 interacting protein β-catenin. This resulted in reduced GJIC, which was shown by decreased dye transfer. Thus, CNP-induced senescence is accompanied by loss of cell-cell communication.

Conclusion: These data indicate for the first time that Cx43 and β-catenin, which are essential for endothelial functionality, are affected by CNP and that loss of GJIC is involved in CNP-induced senescence. Overexpression studies will investigate whether a causal link exists between CNP-induced senescence and loss of GJIC in primary EC.

Abstract 342: The Antiapoptotic Function of APEX Nuclease (Multifunctional DNA Repair Enzyme) 1 in Endothelial Cells Is Linked to Changes in Transcription Factor Activities and Independent of Its DNA Repair Domain

APEX nuclease (multifunctional DNA repair enzyme) 1 (APEX1) has both DNA repair and redox regulatory activity. Interestingly, APEX1 is also able to modulate transcription factor reduction, a prerequisite for DNA binding, independent of its intrinsic redox activity, probably by recruiting other reducing molecules like Thioredoxin-1 (TXN). APEX1 has been shown to exert anti-apoptotic properties in different cell lines and is localized in the cytosol and in the nucleus. So far it has not been studied whether APEX1 acts anti-apoptotic in primary human endothelial cells (EC) and whether this is dependent on its nuclear or cytosolic localization.

After cloning human APEX1 and overexpression in EC we demonstrated that it inhibits not only basal but also H2O2-induced apoptosis. To further characterize the anti-apoptotic properties of APEX1 we generated mutants that lacked the C-terminal DNA repair domain (APEX1ΔC 1-127) or the N-terminal nuclear localization signal (NLS) (APEX1ΔN 21-318). We first analyzed the localization of the mutants by immunostaining. APEX1wt and APEX1ΔC 1-127 showed a predominant nuclear staining whereas APEX1ΔN 21-318 was mainly localized in the cytosol. With respect to the anti-apoptotic properties, only the mutant with intact NLS and redox domain APEX1ΔC 1-127 prevented apoptosis both under basal conditions as well as after H2O2 treatment similar to APEX1wt.

The association between nuclear localization of APEX1wt and its anti-apoptotic properties in EC suggests that this function is linked to changes in transcription factor activities. It is known that the p65 subunit of the transcription factor complex NF-kB is activated by pro-apoptotic stimuli in EC. Using a specific DNA binding assay we could show that overexpression of APEX1wt and APEX1ΔC 1-127 reduced DNA binding of p65, whereas the NLS-deficient mutant had no effect.

In conclusion, the anti-apoptotic activity of APEX1 in EC critically depends on its nuclear localization and redox-activity, is independent of its DNA repair domain and is at least partially due to suppression of NF-kB dependent, pro-apoptotic gene expression programs. In future studies we will analyze the impact of APEX1 on other transcription factors in concert with TXN.

Abstract 336: The Imbalanced Redox Homeostasis in Senescent Endothelial Cells is Due to Dysregulated Thioredoxin-1 and NADPH-Oxidase 4

Senescent endothelial cells are not only present in aged vessels, but also in atherosclerotic lesions, where they contribute to endothelial dysfunction. One hallmark of cellular senescence is an imbalanced redox homeostasis. However, the underlying mechanisms how this imbalance occurs are not completely understood. Thioredoxin-1 (Trx-1) is one of the most important redox regulators in primary human endothelial cells. It has previously been shown that Trx-1, in addition to its oxidoreductase activity has anti-apoptotic properties. Cellular generators of reactive oxygen species (ROS) are NADPH oxidases (NOXs), of which NOX4 shows highest expression levels in endothelial cells. Therefore, the aim of the study was to investigate whether and how Trx-1 and NOX4 are regulated during stress-induced premature senescence in endothelial cells, an ex vivo model mirroring the situation in aged or diseased vessels.

We treated primary human endothelial cells for two weeks with hydrogen peroxide to generate stress-induced premature senescence in these cells. Senescence induction was confirmed by an increase in senescence-associated beta-Galactosidase and nuclear p21, two established senescence markers. Moreover, cytosolic and mitochondrial reactive oxygen species formation were enhanced. Concomitantly, we observed decreased Trx-1 levels and elevated NOX4 levels, which could explain the imbalance in the cellular redox homeostasis. Moreover, the lysosomal protease Cathepsin D, known to degrade Trx-1 under short-term oxidative stress, was over-activated, providing a mechanistic basis for reduced Trx-1 protein levels. Inhibition of “over-active” Cathepsin D by the specific, cell-permeable inhibitor pepstatin A counteracted the increase in nuclear p21, ROS formation and degradation of Trx-1, thus leading to blockade of stress-induced premature senscence by stabilizing the cellular redox homeostasis. Moreover, aortic Trx-1 levels negatively correlated with NOX4 expression in NOX4 transgenic mice exclusively expressing NOX4 in the endothelium and their wildtype littermates.

Our data show that loss of Trx-1 and upregulation of NOX4 may importantly contribute to the imbalanced redox homeostasis in senescent endothelial cells ex vivo and in vivo.

The imbalanced redox status in senescent endothelial cells is due to dysregulated Thioredoxin-1 and NADPH oxidase 4

Environmental stressors as well as genetic modifications are known to enhance oxidative stress and aging processes. Mitochondrial and nuclear dysfunctions contribute to the onset of aging. One of the most important redox regulators in primary human endothelial cells is Thioredoxin-1 (Trx-1), a 12 kD protein with additional anti-apoptotic properties. Cellular generators of reactive oxygen species are NADPH oxidases (NOXs), of which NOX4 shows highest expression levels in endothelial cells. Therefore, the aim of the study was to investigate how Trx-1 and NOX4 are regulated during stress-induced premature senescence in endothelial cells. We treated primary human endothelial cells for two weeks with H2O2 to generate stress-induced premature senescence in these cells. In this model senescence-associated β-Galactosidase and nuclear p21 as senescence markers are increased. Moreover, total and mitochondrial reactive oxygen species formation is enhanced. An imbalanced redox homeostasis is detected by elevated NOX4 and decreased Trx-1 levels. This can be rescued by lentiviral expression of Trx-1. Moreover, the lysosomal protease Cathepsin D is over-activated, which results in reduced Trx-1 protein levels. Inhibition of "over-active" Cathepsin D by the specific, cell-permeable inhibitor pepstatin A abolishes the increase in nuclear p21 protein, ROS formation and degradation of Trx-1 protein, thus leading to blockade of stress-induced premature senescence by stabilizing the cellular redox homeostasis. Aortic Trx-1 levels are decreased and Cathepsin D activity is increased in NOX4 transgenic mice exclusively expressing NOX4 in the endothelium when compared to their wildtype littermates. Thus, loss of Trx-1 and upregulation of NOX4 importantly contribute to the imbalance in the redox-status of senescent endothelial cells ex vivo and in vivo.

Cellular functions of the dual-targeted catalytic subunit of telomerase, telomerase reverse transcriptase--potential role in senescence and aging

Over the last 40 years it has become clear that telomeres, the end of the chromosomes, and the enzyme telomerase reverse transcriptase (TERT), which is required to counteract their shortening, play a pivotal role in senescence and aging. However, over the last years several studies demonstrated that TERT belongs to the group of dual-targeted proteins. It contains a bipartite nuclear localization signal as well as a mitochondrial targeting sequence and, under physiological conditions, is found in both organelles in several cell types including terminally differentiated, post-mitotic cells. The canonical function of TERT is to prevent telomere erosion and thereby the development of replicative senescence and genetic instability. Besides telomere extension, TERT exhibits other non-telomeric activities such as cell cycle regulation, modulation of cellular signaling and gene expression, augmentation of proliferative lifespan as well as DNA damage responses. Mitochondrial TERT is able to reduce reactive oxygen species, mitochondrial DNA damage and apoptosis. Because of the localization of TERT in the nucleus and in the mitochondria, it must have different functions in the two organelles as mitochondrial DNA does not contain telomeric structures. However, the organelle-specific functions are not completely understood. Strikingly, the regulation by phosphorylation of TERT seems to reveal multiple parallels. This review will summarize the current knowledge about the cellular functions and post-translational regulation of the dual-targeted protein TERT.

Abstract 234: Defining Domains In The Transcription Factor Grainyhead-like 3 Required For Protective Functions In The Endothelium

Important aspects during aging of human endothelial cells (EC) are an increased apoptosis level and a reduced migratory capacity. In a screening for anti-apoptotic genes we have identified the transcription factor Grainyhead-like 3 (GRHL3) and demonstrated its anti-apoptotic and pro-migratory effects after overexpression and knockdown in EC. To define the domains in GRHL3 responsible for these - potentially also extranuclear - functions we have cloned large scale deletion mutants and mutants with deletions of putative nuclear localization signals (NLS) and analyzed them for their intracellular localization and functional properties.

Immunostaining of transfected EC were used to examine the subcellular distribution. Two mutants with deletions in a bioinformatically predicted bipartite NLS were localized predominantly in the cytoplasm. To corroborate these data, lysates of the cells were fractionated biochemically. Western blotting confirmed the immunostaining data, indicating that we have identified the major NLS in GRHL3.

To analyze the transcriptional properties of these mutants, we constructed a GRHL3-specific luciferase reporter containing a tandem GRHL3 binding sites in front of a minimal promoter and cotransfected it with expression vectors for the GRHL3 deletion mutants. Besides the previously described activation domain we identified another region required for transcriptional upregulation of target genes in the N-terminal half of the protein.

We will now use these mutants to further dissect the regions in GRHL3 necessary for its pro-migratory and anti-apoptotic activities in endothelial cells. This will also allow us to investigate if all of these functions are mediated solely by the activation of target genes or by other mechanisms coupled to a non-nuclear function of GRHL3.

Abstract 267: Opposing Functions of Two Splice Variants of the Human Transcription Factor Grainyhead-like 3 in Endothelial Cells And in vivo

Grainyhead-like 3 (GRHL3) is a member of the evolutionary conserved Grainyhead family of transcription factors. In humans, three isoforms are derived from differential first exon usage and alternative splicing, which differ only in their N-terminus. Isoform 2, the only variant also present in mouse, is required for endothelial cell (EC) migration and protects against apoptosis. The functions of the human specific isoforms 1 and 3, which are derived from an alternatively spliced pre-mRNA, have not yet been investigated, although all three isoforms are expressed in EC. Therefore, we have assessed their effects on EC migration and apoptosis.

Overexpression of the two proteins had opposite effects on EC migration, with isoform 1 acting pro-migratory. This protein also protected EC against apoptosis in an eNOS-dependent manner, whereas isoform 3 had no effect. These opposing outcomes with respect to apoptosis EC were corroborated by isoform-specific knockdowns.

With reporter assays using a GRHL3-specific luciferase reporter we demonstrated that both are active transcription factors. Microarray analyses revealed that they induce divergent target gene sets in EC. Two validated targets, Akt2 and Mxi1, which are upregulated by isoform1, are regulators of Akt1-, and thus eNOS-phosphorylation and apoptosis, which could explain the effects of this protein on these processes.

In vivo, overexpression of isoform 3 in zebrafish embryos resulted in increased lethality and severe deformations, while isoform 1 had no deleterious effect.

In conclusion, our data demonstrate that the splice variant derived isoforms 1 and 3 of the human transcription factor GRHL3 induce opposing effects in primary human endothelial cells and in a whole animal model, most likely through the induction of different target genes.

Abstract 208: Defining the functions of mitochondrial Telomerase Reverse Transcriptase

Over the last few years it has become clear that mitochondria are not only the powerhouses of the cells, having their sole function in producing ATP. Proteome-analyses of mitochondria from different organisms and organs revealed that more than 1000 proteins are localized in and or on the mitochondria. This by far exceeds the number of proteins required for classical mitochondrial functions, e.g. the respiratory chain, the tricarboxylic acid cycle, fatty acid oxidation and apoptosis. This suggests that many of these proteins have other, as yet unknown functions. We identified Telomerase Reverse Transcriptase (TERT), an enzyme that, in the nucleus, protects telomeres, the ends of the chromosomes, against shortening, also in the mitochondria. However, up to now only (TERT) deficient cells and mice or TERT overexpressing cells were used to study nuclear and mitochondrial functions of TERT. In this context, we demonstrated that reduction of endogenous TERT leads to increased reactive oxygen species (ROS) production in the cytosol as well as in the mitochondria. To analyze now specifically the functions of mitochondrial TERT, we isolated TERT deficient fibroblasts and transduced them with lentiviruses containing mitochondrially targeted TERT. We first validated these newly generated cells for transgene insertion and expression. Next, we analyzed compartment specific ROS production and apoptosis in the cells. We observed a reduction specifically in the levels of mitochondrial, but not cytosolic ROS. Moreover, apoptosis induction was significantly reduced in these cells compared to TERT deficient cells as well as cells containing endogenous TERT. Thus, mitochondrial TERT specifically reduces mitochondrially produced ROS and protects cells against apoptosis. In comparison to nuclear TERT, which has the main function to prolong telomeres, mitochondrial TERT specifically protects mitochondria from damage. Currently, we are creating mice that carry mitochondrially targeted TERT on an otherwise TERT deficient background for in vivo experiments.

Two isoforms of Sister-Of-Mammalian Grainyhead have opposing functions in endothelial cells and in vivo

OBJECTIVE

Sister-of-Mammalian Grainyhead (SOM) is a member of the Grainyhead family of transcription factors. In humans, 3 isoforms are derived from differential first exon usage and alternative splicing and differ only in their N terminal domain. SOM2, the only variant also present in mouse, induces endothelial cell migration and protects against apoptosis. The functions of the human specific isoforms SOM1 and SOM3 have not yet been investigated. Therefore we wanted to elucidate their functions in endothelial cells.

APPROACH AND RESULTS

Overexpression of SOM1 in primary human endothelial cells induced migration, phosphorylation of Akt1 and endothelial nitric oxide synthase, and protected against apoptosis, whereas SOM3 had opposite effects; isoform-specific knockdowns confirmed the disparate effects on apoptosis. After reporter assays demonstrated that both are active transcription factors, microarray analyses revealed that they induce different target genes, which could explain the different cellular effects. Overexpression of SOM3 in zebrafish embryos resulted in increased lethality and severe deformations, whereas SOM1 had no deleterious effect.

CONCLUSIONS

Our data demonstrate that the splice variant-derived isoforms SOM1 and SOM3 induce opposing effects in primary human endothelial cells and in a whole animal model, most likely through the induction of different target genes.

Interacting with thioredoxin-1--disease or no disease?

SIGNIFICANCE

Many cardiovascular disorders are accompanied by a deregulated cellular redox balance resulting in elevated levels of intracellular reactive oxygen species (ROS). One major antioxidative cellular molecule is thioredoxin-1 (Trx-1). Its indispensability is demonstrated by the embryonic lethality of Trx-1 deficient mice. Trx-1 is ubiquitously expressed in cells and has numerous, diverse functions. It not only reduces oxidized proteins or, together with peroxiredoxins, detoxifies H(2)O(2), but also binds to several proteins and thereby regulates their functions. The interaction partners of Trx-1 differ depending on its localization in the cytosol or in the nucleus.

RECENT ADVANCES/CRITICAL ISSUES

Over the past decade it has become clear that Trx-1 is not only critical for tumor functions, which has resulted in therapeutic approaches targeting this protein, but also essential for proper functions of the vasculature and the heart. Changes in post-translational modifications of Trx-1 or in its interactions with other proteins can lead to a switch from a physiologic state of cells and organs to diverse pathologies. This review provides insights into the role of Trx-1 in different physiological situations and cardiac hypertrophy, ischemia reperfusion injury, heart failure, atherosclerosis, and diabetes mellitus type 2, underscoring the central role of Trx-1 in cardiovascular health and disease.

FUTURE DIRECTIONS

Thus, the manipulation of Trx-1 activity in the heart and/or vasculature, for example, by small molecules, seems to be a promising therapeutic option in cardiovascular diseases, as general anti-oxidant treatments would not take into account interactions of Trx-1 with other proteins and also eliminate vital ROS.

[Oxidative stress in endothelial cells and in diabetes type 2]

Reactive oxygen species (ROS) are important signaling molecules in human cells. At physiological concentrations, they can for instance protect against apoptosis and act as secondary messengers in many different signaling pathways. Disturbance of redox homeostasis, i.e., the physiological balance between ROS generation and degradation, leads to not only increased ROS levels, so-called oxidative stress, but also results in damage to macromolecules and promotes the development of diseases and accelerates the aging process. The organism has various enzyme systems at hand to eliminate excess ROS. Their inactivation or degradation under conditions of oxidative stress is tightly linked to endothelial dysfunction due to endothelial cell apoptosis, a loss of telomerase activity, and telomere shortening. Restricted endothelial function causes cardiovascular diseases and diabetes type 2.

Abstract 543: The Janus-Faced Transcription Factor Sister-of-Mammalian Grainyhead: 2 Isoforms with Opposing Effects in Endothelial Cells and in Vivo

Maintenance of apoptosis protection and migratory capacity are absolutely required for proper endothelial function. Several pathways are described, which are necessary for these processes including activation of the protein kinase B (Akt) and the endothelial nitric oxide synthase (eNOS). Recently, we identified a new player, the transcription factor sister-of-mammalian grainyhead (SOM)/Grainyhead-like 3, which demonstrated anti-apoptotic and pro-migratory properties in endothelial cells (EC).

In humans, three isoforms of SOM are expressed, two of which, SOM1 and SOM3, are derived from an alternatively spliced transcript. SOM3 lacks exon 2, described to contain the putative transactivation domain, and thus, has been suggested to be a repressor. SOM1 and SOM3 are co-expressed in numerous tissues, however, their exact cellular functions have not been investigated so far.

Here we demonstrate that SOM1 and SOM3 are expressed in primary human EC. In contrast to published data, which were based on a yeast two hybrid analysis with isolated domains, we could show that both full length proteins are transcriptional activators. Moreover, they have opposing functions in EC and in a whole animal model. Overexpression of SOM1 inhibited apoptosis and induced migration of EC. The latter effect could be due to the observed activation of eNOS and its upstream regulator Akt. On the contrary, SOM3 has no effect on apoptosis and significantly inhibits migration and eNOS activation. To assess the in vivo relevance of the opposing effects of SOM1 and SOM3, we made use of zebrafish as a whole animal model. SOM3, but not SOM1, induced severe malformations in embryos and reduced the number of normally developed embryos significantly. Microarray analyses showed that SOM1 and SOM3 have some overlapping, but an even larger number of distinct target genes.

Our data suggest that the opposing effects of the two SOM isoforms are mediated by transcriptome alterations and that a switch in isoform expression could change the cellular fate with dramatic consequences for a whole organism.

Abstract 460: Thioredoxin-1 and Its Interaction Partners Control Apoptosis in the Endothelium

In the endothelium, defense against oxidative stress as well as inhibition of apoptosis is mainly mediated by thioredoxin-1 (Trx-1). Trx-1 protein levels are reduced in aged endothelial cells (EC) in vitro and in vivo, leading to increased apoptosis sensitivity. Apoptosis is dependent on (i) cytoskeletal changes resulting in formation of stress fibers (thick bundles of actin), (ii) activation of caspase-3 and (iii) the redox status of the cell. The mechanisms how Trx-1 protects EC against apoptosis are not completely understood, but could involve protein-protein interactions.

We identified three proteins interacting with Trx-1: γ-actin, the p17 subunit of Caspase-3 and the AP-endonuclease 1/redox factor 1 (APEX1). We could show that H2O2-induced stress fiber formation in EC was prevented by exogenously applied or overexpressed Trx-1. Moreover, the interaction between Trx-1 and non-polymerized γ-actin precluded Trx-1 degradation, suggesting a mutual protection of both proteins. Secondly, we observed that Trx-1 overexpression reduces apoptosis induction by the p17 subunit of Caspase-3 in EC. This was corroborated by the identification of a disulfide bridge-dependent interaction of Trx-1 with cysteine 163 in p17 preventing association with the second subunit, p12, which is essential for full activation of Caspase-3. However, interaction of Trx-1 with other proteins is not necessarily dependent on disulfide bridge formation. We could demonstrate that APEX1 can protect EC against apoptosis. Interestingly, we found that Trx-1 and APEX1 associate with each other even after mutation of 3 (APEX1) or 2 (Trx-1) cysteines with the same efficiency as the wildtype proteins. It is conceivable that this interaction is required for the protective effect of APEX1.

Taken together, our data demonstrate the importance of Trx-1 in maintaining endothelial cell integrity mediated by interaction with other proteins, and that apoptosis protection of EC is not only due to its anti-oxidative capacity. Loss of Trx-1 in senescent EC therefore importantly contributes to the increased apoptosis sensitivity observed in during aging.

Abstract 389: Mitochondrial p27 Is Absolutely Required for Endothelial Cell Migration and ATP Production

The cell cycle inhibitor p27 has been shown to exert non-nuclear functions. Moreover, migration of fibroblasts depends on p27 expression. However, the underlying mechanisms of this phenomenon are largely unknown. Therefore, we first investigated the role of p27 in endothelial cell (EC) migration and showed that its downregulation abrogated migration. Since we previously demonstrated that migration of EC requires intact mitochondria, we analyzed whether it depends on the localization of p27 within the cell. We generated p27 variants, which are exclusively localized either in the nucleus (nucp27) or in the mitochondria (mitop27). Overexpression of mitop27 enhanced EC migration, whereas nucp27 decreased it. Along the same line, mitop27 induced ATP production, which is required for migratory processes. As a potential mechanism for the increased ATP production, we found that mitochondrial p27 interacts with prohibitin, which forms multimeric complexes thereby enhancing respiration and ATP production. Next, we analyzed, which domains in p27 are involved in these processes. Therefore, we created p27 deletion mutants and found that both the N- and the C-terminus are necessary for cell migration and ATP-production. These regions contain several phosphorylation sites, two of which (Ser 10 and Thr 187) are phosphorylated by pro-migratory stimuli. Thus, we cloned corresponding nonphosphorylatable (p27 S10A/T187A) and phosphomimetic (p27 S10D/T187D) mutants of mitop27. Overexpression of the nonphosphorylatable mutant decreased EC migration, while the phosphomimetic mutant increased it. Finally, we investigated the mitochondrial import mechanism of p27. Since p27 lacks a typical mitochondrial targeting sequence, we determined whether it interacts with cytosolic heat shock protein 60 (HSP60), which is known to import proteins into the mitochondria. Indeed, cytosolic p27 is associated with HSP60 and this association is increased under promigratory stimuli.

Taken together, these data demonstrate that mitochondrial p27 and its phosphorylation at the N- and C-termini are required for migration and ATP production and that p27 is imported into the mitochondria in a HSP60 dependent manner.

Abstract 352: Unhealthy Diet and Air Pollution Induce Cardiovascular Dysfunction

Cardiovascular diseases remain the dominant cause of deaths worldwide. Unhealthy diet and air pollution have each been described as risk factors for cardiovascular diseases. The molecular mechanisms involved in translating unhealthy diet and/or exposure to air pollution into cardiovascular dysfunctions remain yet to be identified.

First, we investigated the impact of an unhealthy diet on disease-related signaling pathways in human primary cardiovascular cells. Based on nutrition health reports on diet composition in industrialized countries, we supplemented cell culture media of human primary endothelial cells (EC), smooth muscle cells (SMC) and cardiomyocytes (CM) with 100 mg/dl LDL and replaced 1/3 of the glucose with fructose. This treatment did not induce cell death in any of the cell types. However, we observed hypertrophy in CM, enhanced proliferation in SMC and increased senescence, loss of endothelial nitric oxide synthase (eNOS) and increased nuclear localization FoxO3A in EC.

Based on several studies, which demonstrated that ultrafine particles can enter the circulation and thus directly interact with EC, we investigated the impact of ultrafine carbon black particles (ufCB), one of the major constituents of industrial and exhaust emissions, on human primary EC. Treatment with ufCB in non-toxic concentrations increased reactive oxygen species and dramatically reduced the S-NO content, a marker for NO-bioavailability. NO has been shown to increase the activation of Telomerase Reverse Transcriptase (TERT), which is required for proper endothelial cell function and is inactivated by the Src kinase under conditions of oxidative stress. ufCB significantly reduced Telomerase activity while increasing Src kinase activity. Subsequently, ufCB dramatically increased senescence of EC. To investigate whether ufCB effects also occur in vivo, we instilled ufCB in non-inflammatory concentrations into mice. Indeed, eNOS expression was reduced in the abdominal aorta of animals treated with ufCB.

Taken together, common unhealthy diet as well as low-level air pollution, which we are exposed to permanently, seem to accelerate cardiovascular diseases.

Abstract P047: A Novel Antiapoptotic Function of Thioredoxin-1 Is Mediated by Interaction with Caspase 3

Thioredoxin-1 (Trx-1) is one of the most important redox regulators in endothelial cells (EC). It is an oxidoreductase with anti-oxidative and anti-apoptotic properties. In EC not only the active site cysteines 32 and 35 but also the cysteine 69 are required for its anti-apoptotic function. Trx-1 has several interaction partners, but this list is far from complete. The underlying molecular mechanisms in apoptosis protection by Trx-1 are not completely understood. The most important apoptosis executor protein in EC is Caspase 3. Therefore, the aim of this study was to investigate whether Trx-1 interferes with Caspase 3 function. We first analyzed if Trx-1 is associated with Caspase 3. Coimmunoprecipitation revealed an interaction between both proteins, which was only found under non-reducing conditions, suggesting involvement of a disulfide bridge. To get insights into the functional relevance of the association between Trx-1 and Caspase 3, we investigated whether Trx-1 can directly interact with the catalytic subunit p17 of Caspase 3. After coexpression of p17 and Trx-1, coimmunoprecipitation experiments under non-reducing conditions revealed that p17 associates with Trx-1. Analysis of Trx-1 mutants demonstrated that the interaction depends on cysteine 32 and/or 69 in Trx-1. To assess the functional relevance of the Trx-1/Caspase 3 interaction in EC, we induced apoptosis by overexpression of p17 and investigated the influence Trx-1 wildtype (wt) and mutants in which single or multiple cysteine residues were replaced by serines thereby preventing disulfide bridge formation. Apoptosis induction by p17 was significantly reduced by Trx-1 wt (p17+lacZ 16.99±1.35% vs. p17+Trxwt 8.60±1.31% apoptotic cells). Interestingly, overexpression of Trx-1 with mutations of cysteines 32 and 69 enhanced apoptosis induction by Caspase 3 p17 (23.42±2.84% apoptotic cells). On the contrary, no increase in apoptosis was observed when only cysteine 32 or 69 were mutated, suggesting that both residues can scavenge p17 via disulfide bridge formation thereby preventing its association with the second Caspase 3 subunit p12 and thus activation of the enzyme. These data suggest that Trx-1 has a novel anti-apoptotic function by binding the apoptosis executing Caspase 3.

Abstract P349: Ambient Air Pollution Compromises Nitric Oxide Bioavailability, Leading to Accelerated Endothelial Cell Senescence

Particulate matter (PM) pollution is a burden to public health. Although PM causes a health risk to the lung, the overall evidence indicates that the majority of the PM effects are upon the cardiovascular system. Several studies demonstrated that ultrafine particles can directly enter the circulation and thus may interact with endothelial cells. However, intracellular mechanisms affected by non-cytotoxic, in vivo relevant concentrations of particles have not been investigated in endothelial cells in vitro and in vivo. Therefore, this study aims for the first time to analyze the effects of ultrafine and fine particles of different materials in non-toxic concentrations on human endothelial cells (EC) and in animals. We incubated EC with ultrafine and fine Carbon Black (ufCB and fCB) particles as well as Titaniumdioxide (ufTiO2 and fTiO2) and determined the non-toxic concentrations. MTT measurements revealed that 0.1 and 1 µg/cm2 did not reduce endothelial cell viability. To test whether these concentrations influence endothelial cell function, we measured nitric oxide (NO) bioavailability, which is important for vessel function. Only ultrafine particles reduced the S-NO content of EC, whereas fine particles had no effect at the same concentrations. Interestingly, the effects observed with ufCB and ufTiO2 were more pronounced than with the known reducer of NO bioavailability, H2O2. We previously demonstrated that NO increases activation of Telomerase Reverse Transcriptase (TERT), an enzyme essential for telomere maintenance. TERT activation is required to protect EC from apoptosis and the onset of senescence and TERT is inactivated by the Src kinase under conditions of oxidative stress. Therefore, we investigated the effects of ufCB and ufTiO2 on TERT and Src activation. ufCB and ufTiO2 significantly reduced TERT and increased Src kinase activation. To investigate whether ufCB show also effects in vivo, we instilled ufCB into rats and determined eNOS and TERT expression in the aorta. ufCB reduced eNOS and TERT expression in the abdominal aorta of animals treated with ufCB. Thus, ultrafine nanoparticles, which we inhale every day, seem to reduce endothelial function and thus should be considered a risk factor for cardiovascular disease.

Abstract P314: Grainyhead-like 3 Plays an Essential Role in Endothelial Cell Function in a NO-Dependent Manner

Aging of human endothelial cells (EC) is associated with reduced nitric oxide (NO) bioavailability, decreased migratory capacity and an increase in Src kinase activation and apoptosis sensitivity. We recently identified the transcription factor grainyhead-like 3 (GRHL3) as a pro-migratory transcription factor in EC. A role for GRHL3 in aging processes was suggested by reduced expression in brains from old mice. Therefore, we wanted to investigate the regulation of GRHL3 by NO and Src kinase and GRHL3 effects on NO-bioavailabilty, apoptosis and migration. We treated EC either with physiological concentrations of NO or the Src kinase inhibitor PP2. In both cases GRHL3 expression was increased (3.75 fold and 4.50 fold, respectively). In addition, both treatments induced migration and inhibited apoptosis. Interestingly, overexpression of GRHL3 activated endothelial nitric oxide synthase (eNOS), its upstream regulator Akt and subsequently increased the S-NO content of EC. This demonstrates that GRHL3 enhances NO-bioavailability in EC, which is inseparably tied to apoptosis protection and migration. Along this line, GRHL3 overexpression reduced apoptosis of EC (1.89 fold reduction of basal apoptosis vs. empty vector transfected cells). Interestingly, this anti-apoptotic effect was dependent on NO synthesis by eNOS, since the eNOS inhibitor L-NMMA completely abrogated the protective effect of GRHL3. Having demonstrated a pro-migratory effect of GRHL3, we wanted to know whether this effect is mediated by induction of vascular endothelial growth factor (VEGF) expression. Surprisingly, GRHL3 overexpression did not change VEGF protein levels. To exclude a bystander effect of GRHL3 in EC migration, we knocked down expression with shRNA. Reduction of GRHL3 mRNA levels decreased basal and NO-induced EC migration (scr: 73 +/− 16 migrated cells; shGRHL3: 26 +/− 12 migrated cells; scr+NO: 149 +/− 19 migrated cells; shGRHL3+NO: 36 +/− 10 migrated cells) demonstrating an essential role in this process. Taken together, these data suggest that GRHL3 is essential for EC functions compromised during aging.

Abstract P257: Isoform-Specific Effects of the Transcription Factor Sister-of-Mammalian Grainyhead on Endothelial Cells and in Vivo

Apoptosis and reduced migratory capacity of human endothelial cells (EC) are hallmarks for the development of atherosclerosis. TNFalpha has been described as one apoptotic stimulus, which is increased during cardiovascular disease. However, recent findings support the hypothesis that TNFalpha can induce survival genes before committing cells to apoptosis. In a screen for anti-apoptotic genes regulated by TNFalpha we have identified the transcription factor Sister-of-Mammalian Grainyhead/Grainyhead-like 3 (SOM/GRHL3). In humans two RNAs are transcribed from the gene, one of which is alternatively spliced, yielding the protein isoforms SOM1 and SOM3, the latter being an N-terminally truncated version. We have found that both isoforms are expressed in EC. Since nothing is known about the function of these proteins in EC, we investigated their functional properties and role in migration and apoptosis. To analyze their transcription factor activity we established a SOM-dependent reporter system by inserting tandem SOM binding sites and corresponding mutants upstream of a minimal promoter driving luciferase expression. To assess transcriptional activation by SOM1 and SOM3 we cotransfected these reporters with expression vectors for both proteins. In contrast to previously published work, in which isolated SOM domains fused to a Gal4 DNA binding domain were used, we found that both full length proteins are active transcription factors. We next investigated the influence of SOM1 and SOM3 on EC functions. Surprisingly, overexpression of isoform 1 induced migration and inhibited apoptosis, whereas isoform 3 had opposite effects. Along the same lines, SOM1, but not SOM3 activated endothelial nitric oxide synthase and Akt. To investigate whether these isoforms have different functions also in vivo, we overexpressed them in zebrafish embryos. SOM3 but not SOM1 overexpression led to increased lethality, a strong reduction in normal phenotype and a 10 fold higher frequency in heavy deformations. The effects observed on EC migration and apoptosis as well as on zebrafish development suggest that these isoforms activate different sets of target genes, which we are currently identifying by microarray analysis.

Abstract P316: Cysteine-Independent Interactions of Thioredoxin-1 and Apex1: Implications for Endothelial Cell Apoptosis and Aging?

Aging processes are associated with increased intracellular formation of reactive oxygen species. One redox regulator is the ubiquitously expressed oxidoreductase Thioredoxin-1 (Trx). It contains two active site cysteines and has anti-oxidative and anti-apoptotic properties. Trx levels are reduced in senescent endothelial cells (EC), leading to increased apoptosis sensitivity. Several functions of Trx are enhanced by its interaction with AP-endonuclease 1 (APEX1). APEX1 is a multifunctional protein and in concert with Trx-1 a reductive activator of e.g. the transcription factor AP-1, suggesting at least an interaction of Trx and APEX1 in vivo. Recent evidence suggests that also APEX1 levels are decreased in senescent cells. Therefore, the aim of this study is to understand the function of APEX1 in concert with Trx in EC. We first investigated whether APEX1, similar to Trx has anti-apoptotic properties in EC. Indeed, overexpression of APEX1 inhibited apoptosis. To analyze where the Trx/APEX1 interaction occurs, we performed fluorescence microscopy demonstrating a colocalization throughout the whole cell. To study the interaction in more detail, we carried out coimmunoprecipitations from nuclear and cytosolic extracts and demonstrated their association in both fractions. To determine whether disulfide bridges are involved in the Trx/APEX1 association, we mutated APEX1 cysteines 65, 93 and 310 previously shown to interact with cysteines in other proteins, to serines. This mutant bound Trx in the nucleus and cytosol of EC with the same efficiency as APEX1 wildtype. Moreover, a Trx mutant with serine mutations of active site cysteines (Trx(C32S/C35S)) was still able to bind to endogenous APEX1. These data demonstrate that the Trx/APEX-1 interaction is independent of disulfide bridge formation. We are currently analyzing a set of APEX1 deletion mutants for their interaction with Trx-1 and a potential loss of anti-apoptotic properties Exact delineation of the Trx/APEX1 interaction surface will in the future allow the development of small peptides containing the interaction domains of Trx or APEX1 respectively, in order to enhance transcription factor activity and bypass the loss of antioxidative capacity during aging processes.