The role of telomerase reverse transcriptase in the mitochondrial protective functions of Angiotensin-(1-7) in diabetic CD34+ cells

Angiotensin (Ang)-(1-7) stimulates vasoprotective functions of diabetic (DB) CD34+ hematopoietic stem/progenitor cells partly by decreasing reactive oxygen species (ROS), increasing nitric oxide (NO) levels and decreasing TGFβ1 secretion. Telomerase reverse transcriptase (TERT) translocates to mitochondria and regulates ROS generation. Alternative splicing of TERT results in variants α-, β- and α-β-TERT, which may oppose functions of full-length (FL) TERT. This study tested if the protective functions of Ang-(1-7) or TGFβ1-silencing are mediated by mitoTERT and that diabetes decreases FL-TERT expression by inducing splicing. CD34+ cells were isolated from the peripheral blood mononuclear cells of nondiabetic (ND, n = 68) or DB (n = 74) subjects. NO and mitoROS levels were evaluated by flow cytometry. TERT splice variants and mitoDNA-lesions were characterized by qPCR. TRAP assay was used for telomerase activity. Decoy peptide was used to block mitochondrial translocation (mitoXTERT). TERT inhibitor or mitoXTERT prevented the effects of Ang-(1-7) on NO or mitoROS levels in DB-CD34+ cells. FL-TERT expression and telomerase activity were lower and mitoDNA-lesions were higher in DB cells compared to ND and were reversed by Ang-(1-7) or TGFβ1-silencing. The prevalence of TERT splice variants, with predominant β-TERT expression, was higher and the expression of FL-TERT was lower in DB cells (n = 25) compared to ND (n = 30). Ang-(1-7) or TGFβ1-silencing decreased TERT-splicing and increased FL-TERT. Blocking of β-splicing increased FL-TERT and protected mitoDNA in DB-cells. The findings suggest that diabetes induces TERT-splicing in CD34+ cells and that β-TERT splice variant largely contributes to the mitoDNA oxidative damage.

5,6-diHETE lactone (EPA-L) mediates hypertensive microvascular dilation by activating the endothelial GPR-PLC-IP3 signaling pathway

Endothelial microvascular dysfunction affects multi-organ pathologic processes that contribute to increased vascular tone and is at the base of impaired metabolic and cardiovascular diseases. The vascular dilation impaired by nitric oxide (NO) deficiency in such dysfunctional endothelium is often balanced by endothelial-derived hyperpolarizing factors (EDHFs), which play a critical role in managing vascular tone. Our latest research has uncovered a new group of lactone oxylipins produced in the polyunsaturated fatty acids (PUFAs) CYP450 epoxygenase pathway, significantly affecting vascular dilation. The lactone oxylipin, derived from arachidonic acid (5,6-diHET lactone, AA-L), has been previously shown to facilitate vasodilation dependent on the endothelium in isolated human microvessels. The administration of the lactone oxylipin derived from eicosapentaenoic acid (5,6-diHETE lactone, EPA-L) to hypertensive rats demonstrated a significant decrease in blood pressure and improvement in the relaxation of microvessels. However, the molecular signaling processes that underlie these observations were not fully understood. The current study delineates the molecular pathways through which EPA-L promotes endothelium-dependent vascular dilation. In microvessels from hypertensive individuals, it was found that EPA-L mediates endothelium-dependent vasodilation while the signaling pathway was not dependent on NO. In vitro studies on human endothelial cells showed that the hyperpolarization mediated by EPA-L relies on G-protein-coupled receptor (GPR)-phospholipase C (PLC)-IP3 signaling that further activates calcium-dependent potassium flux. The pathway was confirmed using a range of inhibitors and cells overexpressing GPR40, where a specific antagonist reduced the calcium levels and outward currents induced by EPA-L. The downstream AKT and endothelial NO synthase (eNOS) phosphorylations were non-significant. These findings show that the GPR-PLC-IP3 pathway is a key mediator in the EPA-L-triggered vasodilation of arterioles. Therefore, EPA-L is identified as a significant lactone-based PUFA metabolite that contributes to endothelial and vascular health.

Disparities in Cardiovascular Disease-Related Outcomes Among Cancer Survivors in the United States: A Systematic Review of the Literature

BACKGROUND

Cancer and cardiovascular disease (CVD) are major causes of morbidity and mortality in the United States (US). Cancer survivors have increased risks for CVD and CVD-related mortality due to multiple factors including cancer treatment-related cardiotoxicity. Disparities are rooted in differential exposure to risk factors and social determinants of health (SDOH), including systemic racism. This review aimed to assess SDOH's role in disparities, document CVD-related disparities among US cancer survivors, and identify literature gaps for future research.

METHODS

Following the Peer Review of Electronic Search Strategies (PRESS) guidelines, MEDLINE, PsycINFO, and Scopus were searched on March 15, 2021, with an update conducted on September 26, 2023. Articles screening was performed using the Preferred Reporting Items for Systematic Review and Meta-Analysis (PRISMA) 2020, a pre-defined Population, Exposure, Comparison, Outcomes, and Settings (PECOS) framework, and the Rayyan platform. A modified version of the Newcastle-Ottawa Scale was used to assess the risk of bias, and RAW Graphs for alluvial charts. This review is registered with PROSPERO under ID #CRD42021236460.

RESULTS

Out of 7,719 retrieved articles, 24 were included, and discussed diverse SDOH that contribute to CVD-related disparities among cancer survivors. The 24 included studies had a large combined total sample size (n=7,704,645; median=19,707). While various disparities have been investigated, including rural-urban, sex, socioeconomic status, and age, a notable observation is that non-Hispanic Black cancer survivors experience disproportionately adverse CVD outcomes when compared to non-Hispanic White survivors. This underscores historical racism and discrimination against non-Hispanic Black individuals as fundamental drivers of CVD-related disparities.

CONCLUSIONS

Stakeholders should work to eliminate the root causes of disparities. Clinicians should increase screening for risk factors that exacerbate CVD-related disparities among cancer survivors. Researchers should prioritise the investigation of systemic factors driving disparities in cancer and CVD and develop innovative interventions to mitigate risk in cancer survivors.

Nedd4-2 up-regulation is associated with ACE2 ubiquitination in hypertension

AIMS

Angiotensin-converting enzyme 2 (ACE2) is a critical component of the compensatory renin-angiotensin system that is down-regulated during the development of hypertension, possibly via ubiquitination. However, little is known about the mechanisms involved in ACE2 ubiquitination in neurogenic hypertension. This study aimed at identifying ACE2 ubiquitination partners, establishing causal relationships and clinical relevance, and testing a gene therapy strategy to mitigate ACE2 ubiquitination in neurogenic hypertension.

METHODS AND RESULTS

Bioinformatics and proteomics were combined to identify E3 ubiquitin ligases associated with ACE2 ubiquitination in chronically hypertensive mice. In vitro gain/loss of function experiments assessed ACE2 expression and activity to validate the interaction between ACE2 and the identified E3 ligase. Mutation experiments were further used to generate a ubiquitination-resistant ACE2 mutant (ACE2-5R). Optogenetics, blood pressure telemetry, pharmacological blockade of GABAA receptors in mice expressing ACE2-5R in the bed nucleus of the stria terminalis (BNST), and capillary western analysis were used to assess the role of ACE2 ubiquitination in neurogenic hypertension. Ubiquitination was first validated as leading to ACE2 down-regulation, and Neural precursor cell-expressed developmentally down-regulated protein 4-2 (Nedd4-2) was identified as a E3 ligase up-regulated in hypertension and promoting ACE2 ubiquitination. Mutation of lysine residues in the C-terminal of ACE2 was associated with increased activity and resistance to angiotensin (Ang)-II-mediated degradation. Mice transfected with ACE2-5R in the BNST exhibited enhanced GABAergic input to the paraventricular nucleus (PVN) and a reduction in hypertension. ACE2-5R expression was associated with reduced Nedd4-2 levels in the BNST.

CONCLUSION

Our data identify Nedd4-2 as the first E3 ubiquitin ligase involved in ACE2 ubiquitination in Ang-II-mediated hypertension. We demonstrate the pivotal role of ACE2 on GABAergic neurons in the maintenance of an inhibitory tone to the PVN and the regulation of pre-sympathetic activity. These findings provide a new working model where Nedd4-2 could contribute to ACE2 ubiquitination, leading to the development of neurogenic hypertension and highlighting potential novel therapeutic strategies.

Abstract P576: Disparities in Cardiovascular Disease Outcomes Among Cancer Survivors in the United States: A Systematic Review

Significance: Cardiovascular diseases (CVD) and cancer are leading causes of morbidity and mortality in the US; and cancer survivors are at increased risk for CVD. The risk for adverse CVD outcomes is not equitably distributed. Disparities exist; and some groups and/or communities that have been targeted for marginalization are more affected.

Objective: To document known disparities in CVD outcomes among cancer survivors in the US and identify literature gaps to inform future studies.

Methods: We used the Peer Review of Electronic Search Strategies (PRESS) guidelines and searched three databases: MEDLINE, PsycINFO, and Scopus on March 15 th , 2021. With a pre-defined PICOS framework, we used rayyan for articles screening and the PRISMA 2020 reporting guidelines. The Newcastle Ottawa Scale was used to assess the risk of bias. RAW Graphs were used to create alluvial charts. This review is registered with PROSPERO, ID # CRD42021236460.

Results & Discussion: From 6,000 articles retrieved, 13 articles met our pre-defined inclusion criteria. All studies investigated racial and ethnic disparities. Gender, age at diagnosis, and cancer stage at diagnosis, and sensitivity C-reactive protein disparities were respectively investigated by one study. The most prevalent outcome investigated is CVD mortality, followed by CVD risk, CVD event, hypertension, and cardiotoxicity. Non-Hispanic Black survivors are at increased risk for all outcomes investigated which might suggest root causes of disparities into historical and structural racism.

Conclusions & Implications: (1) Policy implication: There is an urgent need for stakeholders to work to eliminate root causes of disparities and all forms of injustice, by removing all systemic barriers that limit individuals’ access to essential resources needed to maintain health. (2) Clinical implication: Clinicians should increase screening for risk factors that exacerbate poor CVD outcomes. (3) Research implication: Researchers should enhance community partnerships and broaden their focus in investigating innovative approaches to reduce disparities and advance health equity and justice.

Keywords: Disparities, cancer survivors, cardiovascular disease (CVD), cardio-oncology, racism, discrimination.

Lipid phosphate phosphatase 3 maintains NO-mediated flow-mediated dilatation in human adipose resistance arterioles

Microvascular dysfunction predicts adverse cardiovascular events despite absence of large vessel disease. A shift in the mediator of flow-mediated dilatation (FMD) from nitric oxide (NO) to mitochondrial-derived hydrogen peroxide (H2 O2 ) occurs in arterioles from patients with coronary artery disease (CAD). The underlying mechanisms governing this shift are not completely defined. Lipid phosphate phosphatase 3 (LPP3) is a transmembrane protein that dephosphorylates lysophosphatidic acid, a bioactive lipid, causing a receptor-mediated increase in reactive oxygen species. A single nucleotide loss-of-function polymorphism in the gene coding for LPP3 (rs17114036) is associated with elevated risk for CAD, independent of traditional risk factors. LPP3 is suppressed by miR-92a, which is elevated in the circulation of patients with CAD. Repression of LPP3 increases vascular inflammation and atherosclerosis in animal models. We investigated the role of LPP3 and miR-92a as a mechanism for microvascular dysfunction in CAD. We hypothesized that modulation of LPP3 is critically involved in the disease-associated shift in mediator of FMD. LPP3 protein expression was reduced in left ventricle tissue from CAD relative to non-CAD patients (P = 0.004), with mRNA expression unchanged (P = 0.96). Reducing LPP3 expression (non-CAD) caused a shift from NO to H2 O2 (% maximal dilatation: Control 78.1 ± 11.4% vs. Peg-Cat 30.0 ± 11.2%; P < 0.0001). miR-92a is elevated in CAD arterioles (fold change: 1.9 ± 0.01 P = 0.04), while inhibition of miR-92a restored NO-mediated FMD (CAD), and enhancing miR-92a expression (non-CAD) elicited H2 O2 -mediated dilatation (P < 0.0001). Our data suggests LPP3 is crucial in the disease-associated switch in the mediator of FMD. KEY POINTS: Lipid phosphate phosphatase 3 (LPP3) expression is reduced in heart tissue patients with coronary artery disease (CAD). Loss of LPP3 in CAD is associated with an increase in the LPP3 inhibitor, miR-92a. Inhibition of LPP3 in the microvasculature of healthy patients mimics the CAD flow-mediated dilatation (FMD) phenotype. Inhibition of miR-92a restores nitric oxide-mediated FMD in the microvasculature of CAD patients.

New developments in translational microcirculatory research

Microvascular disease plays a critical role in systemic end-organ dysfunction, and treatment of microvascular pathologies may greatly reduce cardiovascular morbidity and mortality. The Call for Papers collection: New Developments in Translational Microcirculatory Research highlights key advances in our understanding of the role of microvessels in the development of chronic diseases as well as therapeutic strategies to enhance microvascular function. This Mini Review provides a concise summary of these advances and draws from other relevant research to provide the most up-to-date information on the influence of cutaneous, cerebrovascular, coronary, and peripheral microcirculation on the pathophysiology of obesity, hypertension, cardiovascular aging, peripheral artery disease, and cognitive impairment. In addition to these disease- and location-dependent research articles, this Call for Papers includes state-of-the-art reviews on coronary endothelial function and assessment of microvascular health in different organ systems, with an additional focus on establishing rigor and new advances in clinical trial design. These articles, combined with original research evaluating cellular, exosomal, pharmaceutical, exercise, heat, and dietary interventional therapies, establish the groundwork for translating microcirculatory research from bench to bedside. Although numerous studies in this collection are focused on human microcirculation, most used robust preclinical models to probe mechanisms of pathophysiology and interventional benefits. Future work focused on translating these findings to humans are necessary for finding clinical strategies to prevent and treat microvascular dysfunction.

The impact of greenspace or nature-based interventions on cardiovascular health or cancer-related outcomes: A systematic review of experimental studies

SIGNIFICANCE

Globally, cardiovascular disease (CVD) and cancer are leading causes of morbidity and mortality. While having different etiologies, CVD and cancer are linked by multiple shared risk factors, the presence of which exacerbate adverse outcomes for individuals with either disease. For both pathologies, factors such as poverty, lack of physical activity (PA), poor dietary intake, and climate change increase risk of adverse outcomes. Prior research has shown that greenspaces and other nature-based interventions (NBIs) contribute to improved health outcomes and climate change resilience.

OBJECTIVE

To summarize evidence on the impact of greenspaces or NBIs on cardiovascular health and/or cancer-related outcomes and identify knowledge gaps to inform future research.

METHODS

Following the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) 2020 and Peer Review of Electronic Search Strategies (PRESS) guidelines, we searched five databases: Web of Science, Scopus, Medline, PsycINFO and GreenFile. Two blinded reviewers used Rayyan AI and a predefined criteria for article inclusion and exclusion. The risk of bias was assessed using a modified version of the Newcastle-Ottawa Scale (NOS). This review is registered with PROSPERO, ID # CRD42021231619.

RESULTS & DISCUSSION

Of 2565 articles retrieved, 31 articles met the inclusion criteria, and overall had a low risk of bias. 26 articles studied cardiovascular related outcomes and 5 studied cancer-related outcomes. Interventions were coded into 4 categories: forest bathing, green exercise, gardening, and nature viewing. Outcomes included blood pressure (BP), cancer-related quality of life (QoL) and (more infrequently) biomarkers of CVD risk. Descriptions of findings are presented as well as visual presentations of trends across the findings using RAW graphs. Overall studies included have a low risk of bias; and alluvial chart trends indicated that NBIs may have beneficial effects on CVD and cancer-related outcomes.

CONCLUSIONS & IMPLICATIONS

(1) Clinical implication: Healthcare providers should consider the promotion of nature-based programs to improve health outcomes. (2) Policy implication: There is a need for investment in equitable greenspaces to improve health outcomes and build climate resilient neighborhoods. (3) Research or academic implication: Research partnerships with community-based organizations for a comprehensive study of benefits associated with NBIs should be encouraged to reduce health disparities and ensure intergenerational health equity. There is a need for investigation of the mechanisms by which NBIs impact CVD and exploration of the role of CVD biological markers of inflammation among cancer survivors.

Emerging mitochondrial signaling mechanisms in cardio-oncology: beyond oxidative stress

Many anticancer therapies (CTx) have cardiotoxic side effects that limit their therapeutic potential and cause long-term cardiovascular complications in cancer survivors. This has given rise to the field of cardio-oncology, which recognizes the need for basic, translational, and clinical research focused on understanding the complex signaling events that drive CTx-induced cardiovascular toxicity. Several CTx agents cause mitochondrial damage in the form of mitochondrial DNA deletions, mutations, and suppression of respiratory function and ATP production. In this review, we provide a brief overview of the cardiovascular complications of clinically used CTx agents and discuss current knowledge of local and systemic secondary signaling events that arise in response to mitochondrial stress/damage. Mitochondrial oxidative stress has long been recognized as a contributor to CTx-induced cardiotoxicity; thus, we focus on emerging roles for mitochondria in epigenetic regulation, innate immunity, and signaling via noncoding RNAs and mitochondrial hormones. Because data exploring mitochondrial secondary signaling in the context of cardio-oncology are limited, we also draw upon clinical and preclinical studies, which have examined these pathways in other relevant pathologies.

Noncanonical Role of Telomerase in Regulation of Microvascular Redox Environment With Implications for Coronary Artery Disease

Telomerase reverse transcriptase (TERT) (catalytic subunit of telomerase) is linked to the development of coronary artery disease (CAD); however, whether the role of nuclear vs. mitchondrial actions of TERT is involved is not determined. Dominant-negative TERT splice variants contribute to decreased mitochondrial integrity and promote elevated reactive oxygen species production. We hypothesize that a decrease in mitochondrial TERT would increase _mtDNA damage, promoting a pro-oxidative redox environment. The goal of this study is to define whether mitochondrial TERT is sufficient to maintain nitric oxide as the underlying mechanism of flow-mediated dilation by preserving _mtDNA integrity.Immunoblots and quantitative polymerase chain reaction were used to show elevated levels of splice variants α- and β-deletion TERT tissue from subjects with and without CAD. Genetic, pharmacological, and molecular tools were used to manipulate TERT localization. Isolated vessel preparations and fluorescence-based quantification of _mtH₂O₂ and NO showed that reduction of TERT in the nucleus increased flow induced NO and decreased _mtH₂O₂ levels, while prevention of mitochondrial import of TERT augmented pathological effects. Further elevated _mtDNA damage was observed in tissue from subjects with CAD and initiation of _mtDNA repair mechanisms was sufficient to restore NO-mediated dilation in vessels from patients with CAD. The work presented is the first evidence that catalytically active mitochondrial TERT, independent of its nuclear functions, plays a critical physiological role in preserving NO-mediated vasodilation and the balance of mitochondrial to nuclear TERT is fundamentally altered in states of human disease that are driven by increased expression of dominant negative splice variants.

Endothelial dysfunction as a complication of anti-cancer therapy

Recent strides in anti-cancer therapeutics have improved longevity and led to a growing population of cancer survivors, who are increasingly likely to die of other causes. Treatment-induced cardiotoxicity is a complication of several therapeutic agents with acute and long-term consequences for cancer patients. Vascular endothelial dysfunction is a precursor and hallmark of ischemic coronary disease and may play a role in anti-cancer therapy-induced cardiotoxicity. This review summarizes clinical evidence for endothelial dysfunction following anti-cancer therapy and extends the discussion to include the impact of therapeutic agents on conduit arteries and the microcirculation. We highlight the role of innate immune system activation and cross-talk between inflammation and oxidative stress as pathogenic mechanisms underlying anti-cancer therapy-induced vascular toxicity. Understanding the impact of anti-cancer agents on the vascular endothelium will inform therapeutic approaches to prevent or reverse treatment-induced cardiotoxicity and may serve as an important tool to predict, monitor, and prevent adverse cardiovascular outcomes in patients undergoing treatment.

Abstract 105: Mitotempol Restores Endothelial Dysfunction In Placental Arterioles In Preeclampsia

Preeclampsia (PreE) is complication of pregnancy, affecting 5% of pregnancies in the United States, and presenting a significant burden to our healthcare systems. Oxidative damage and dysfunction of the placental microcirculation has been implicated. Clinical trials of antioxidant therapies to treat PreE have failed. However, none of these studies have used targeted antioxidants. Given that vascular compromise in preeclampsia may be caused by mitochondrial dysfunction, we propose that MitoTEMPOL (MT), a mitochondrial-targeted superoxide dismutase mimetic, will restore endothelium-dependent vasodilation in human placental arterioles. Arterioles from the maternal portion of the placenta of average diameter 161.1 ± 11.1 μm were cannulated on glass micropipettes and constricted with 0.1-1.5 nM endothelin-1 and flow was generated with a pressure gradient across vessel reservoirs. Flow-mediated dilation (FMD) was measured by video-microscopy presented as % maximal diameter from baseline. Smooth muscle function was evaluated by exposure to 100 μM papaverine. Vessels from normal placentas dilated to flow by 70.2% ± 3.8% (n=11), whereas vessels from PreE placentas dilated to only 47.9% ± 5.6% (n=8, p=0.005). Exposure to 10 μM of MT for 30 minutes in the organ bath restored Pre-E vessel dilation to 80.0% ± 3.9% (n=6, p=0.0003 vs PreE). FMD in normal vessels was not affected by exposure to MT (75.9% ± 7.2%, n=4, p=0.84). Significance was evaluated by 2-way ANOVA, α = 0.05. MT restores endothelium-dependent vasodilation in PreE vessels. Further evaluation of other mitochondrial-targeted antioxidants could lead to novel therapeutic options to improve vascular function in PreE.

Take charge during treatment: A planned exercise protocol to evaluate disparities and cardiovascular outcomes in Black and White patients with breast cancer undergoing treatment

TPS12138

Background : Cardiotoxicity is a significant challenge associated with common first-line breast cancer (BC) chemotherapy (CTx) treatments including anthracyclines (AC) and targeted therapies, such as anti-Her-2 therapy. For targeted therapies, cardiac complications typically resolve once treatment is completed or stopped. For ACs, treatment may lead to permanent long term cardiac damage, and elevated risk for major adverse cardiovascular events (MACE). Black/African American (B/AA) women are at higher risk for AC-based cardiotoxicity compared to Non-Hispanic White (NHW) women. To date, most efforts have targeted managing and defining mechanisms of large vessels and cardiac damage. However, impaired microvascular function, a powerful but clinically underused predictor of future MACE, may also be implicated. Extensive evidence shows that exercise interventions reduce systemic inflammation and possibly MACE. However, few cardio-oncology studies have utilized exercise to mitigate cardiotoxicity, and none have quantified microvascular endothelial function. A further gap in cardio-oncology research is a paucity of studies focused on understanding and addressing disparities. This research project aims to 1) test the feasibility and efficacy of an exercise intervention designed to mitigate the effects of CTx, Take Charge during Treatment (TCT) and 2) examine the influence of socio-ecological factors on endothelial function in response to an exercise intervention. Methods: B/AA (n=50) and NHW (n=50) women diagnosed with non-metastatic BC, scheduled to receive AC and/or anti-HER-2 therapy, will be recruited and randomized to participate in the TCT intervention or usual care (NCT05223322). TCT is a virtual exercise coaching program with weekly coaching sessions, six of which include supervised exercise. Assessments to assess socio-ecologic and vascular outcomes are presented in the Table. Assessments will be completed prior to treatment (T1), after treatment completion (18-24 weeks, T2), and 12-months post treatment (T3). Clinical trial information: NCT05223322. [Table: see text]

Modulation of p66Shc impairs cerebrovascular myogenic tone in low renin but not low nitric oxide models of systemic hypertension

Cerebral blood flow and perfusion are tightly maintained through autoregulation despite changes in transmural pressure. Oxidative stress impairs cerebral blood flow, precipitating cerebrovascular events. Phosphorylation of the adaptor protein p66Shc increases mitochondrial-derived oxidative stress. The effect of p66Shc gain or loss of function in nonhypertensive rats is unclear. We hypothesized that p66Shc gain of function would impair autoregulation of cerebral microcirculation under physiological and pathological conditions. Three previously established transgenic [salt-sensitive (SS) background] p66Shc rats were used, p66-Del/SS (express p66Shc with a nine-amino acid deletion), p66Shc-knockout (KO)/SS (frameshift premature termination codon), and p66Shc signaling and knock-in substitution of Ser36Ala (p66Shc-S36A)/SS (substitution of Ser36Ala). The p66Shc-Del were also bred on Sprague-Dawley (SD) backgrounds (p66-Del/SD), and a subset was exposed to a hypertensive stimulus [NG-nitro-l-arginine methyl ester (l-NAME)] for 4 wk. Active and passive diameters to increasing transmural pressure were measured and myogenic tone was calculated in all groups (SS and SD). Myogenic responses to increasing pressure were impaired in p66Shc-Del/SS rats relative to wild-type (WT)/SS and knock-in substitution of Ser36Ala (S36A; P < 0.05). p66-Del/SD rats did not demonstrate changes in active/passive diameters or myogenic tone relative to WT/SD but did demonstrate attenuated passive diameter responses to higher transmural pressure relative to p66-Del/SS. Four weeks of a hypertensive stimulus (l-NAME) did not alter active or passive diameter responses to increasing transmural pressure (P = 0.86-0.99), but increased myogenic responses relative to p66-Del/SD (P < 0.05). Collectively, we demonstrate the functional impact of p66Shc within the cerebral circulation and demonstrate that the genetic background of p66Shc rats largely drives changes in cerebrovascular function.NEW & NOTEWORTHY We demonstrate that the modulation of p66Shc signaling impairs cerebral artery myogenic tone in a low renin model of hypertension. This impairment is dependent upon the genetic background, as modulated p66Shc signaling in Sprague-Dawley rats does not impair cerebral artery myogenic tone.

Autophagy, TERT, and mitochondrial dysfunction in hyperoxia

Ventilation with gases containing enhanced fractions of oxygen is the cornerstone of therapy for patients with hypoxia and acute respiratory distress syndrome. Yet, hyperoxia treatment increases free reactive oxygen species (ROS)-induced lung injury, which is reported to disrupt autophagy/mitophagy. Altered extranuclear activity of the catalytic subunit of telomerase, telomerase reverse transcriptase (TERT), plays a protective role in ROS injury and autophagy in the systemic and coronary endothelium. We investigated interactions between autophagy/mitophagy and TERT that contribute to mitochondrial dysfunction and pulmonary injury in cultured rat lung microvascular endothelial cells (RLMVECs) exposed in vitro, and rat lungs exposed in vivo to hyperoxia for 48 h. Hyperoxia-induced mitochondrial damage in rat lungs [TOMM20, 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT)], which was paralleled by increased markers of inflammation [myeloperoxidase (MPO), IL-1β, TLR9], impaired autophagy signaling (Beclin-1, LC3B-II/1, and p62), and decreased the expression of TERT. Mitochondrial-specific autophagy (mitophagy) was not altered, as hyperoxia increased expression of Pink1 but not Parkin. Hyperoxia-induced mitochondrial damage (TOMM20) was more pronounced in rats that lack the catalytic subunit of TERT and resulted in a reduction in cellular proliferation rather than cell death in RLMVECs. Activation of TERT or autophagy individually offset mitochondrial damage (MTT). Combined activation/inhibition failed to alleviate hyperoxic-induced mitochondrial damage in vitro, whereas activation of autophagy in vivo decreased mitochondrial damage (MTT) in both wild type (WT) and rats lacking TERT. Functionally, activation of either TERT or autophagy preserved transendothelial membrane resistance. Altogether, these observations show that activation of autophagy/mitophagy and/or TERT mitigate loss of mitochondrial function and barrier integrity in hyperoxia.NEW & NOTEWORTHY In cultured pulmonary artery endothelial cells and in lungs exposed in vivo to hyperoxia, autophagy is activated, but clearance of autophagosomes is impaired in a manner that suggests cross talk between TERT and autophagy. Stimulation of autophagy prevents hyperoxia-induced decreases in mitochondrial metabolism and sustains monolayer resistance. Hyperoxia increases mitochondrial outer membrane (TOMM20) protein, decreases mitochondrial function, and reduces cellular proliferation without increasing cell death.

Abstract P141: Downregulation Of Deletion Variants Of Telomerase Reverse Transcriptase (TERT) By Transforming Growth Factor-β1-silencing Decreases Mitochondrial ROS In Diabetic CD34 + Cells

Telomerase reverse transcriptase (TERT) modulates mitochondrial levels of reactive oxygen species (mitoROS). Deletion variants, α-, β- and αβ, are negative regulators of TERT. Increased ROS levels in diabetic CD34 + cells impair vasoreparative functions. Our recent studies showed that silencing of transforming growth factor-β1 (TGF-β1) decreased ROS levels and stimulated vasoreparative functions. This study tested the hypothesis that prevalence of TERT deletion variants is higher in diabetic CD34 + cells and that TGF-β1-silencing decreases mitoROS by downregulation of the variants.

CD34 + cells derived from either male or female nondiabetic (ND) (n=38) or diabetic (DB), both type 1 and type 2, (n=43) subjects were studied. Phosphorodiamidate morpholino oligomers (PMO) were used for TGF-β1-silencing. TERT variants were characterized by qPCR and agarose gel electrophoresis. MitoSOX-flow cytometry and ELISA were used for determining mitoROS levels and telomerase activity, respectively.

TGF-β1-silencing decreased mitoROS levels in DB-CD34+ cells (P<0.01 vs ND-cells, n=6). This effect was reversed by TERT inhibitor, BIBR1532 (1μM) (n=6) or mito-X-TERT, a decoy peptide that prevents mitochondrial translocation of TERT (n=5). TERT expression was higher in DB compared to ND cells (P<0.05, n=18) but telomerase activity was lower (P<0.05 vs ND, n=10). Prevalence of TERT deletion variants was higher among DB cells compared to ND (DB - 8/10 vs ND - 2/10 subjects have one or more of α, β, or αβ variants). TGF-β1-silencing downregulated the expression of TERT variants and increased full-length TERT that was accompanied by increased telomerase activity in DB-CD34+ cells (P<0.05 vs untreated, n=5).

This study suggests that diabetes is associated with higher prevalence of TERT variants that would impede mitochondrial functions of TERT. TGF-β1-silencing decreases mitoROS levels at least in part by downregulation of TERT variants.

Vascular effects of disrupting endothelial mTORC1 signaling in obesity

The mechanistic target of rapamycin complex 1 (mTORC1) signaling complex is emerging as a critical regulator of cardiovascular function with alterations in this pathway implicated in cardiovascular diseases. In this study, we used animal models and human tissues to examine the role of vascular mTORC1 signaling in the endothelial dysfunction associated with obesity. In mice, obesity induced by high-fat/high-sucrose diet feeding for ∼2 mo resulted in aortic endothelial dysfunction without appreciable changes in vascular mTORC1 signaling. On the other hand, chronic high-fat diet feeding (45% or 60% kcal: ∼9 mo) in mice resulted in endothelial dysfunction associated with elevated vascular mTORC1 signaling. Endothelial cells and visceral adipose vessels isolated from obese humans display a trend toward elevated mTORC1 signaling. Surprisingly, genetic disruption of endothelial mTORC1 signaling through constitutive or tamoxifen inducible deletion of endothelial Raptor (critical subunit of mTORC1) did not prevent or rescue the endothelial dysfunction associated with high-fat diet feeding in mice. Endothelial mTORC1 deficiency also failed to reverse the endothelial dysfunction evoked by a high-fat/high-sucrose diet in mice. Taken together, these data show increased vascular mTORC1 signaling in obesity, but this vascular mTORC1 activation appears not to be required for the development of endothelial impairment in obesity.

Dietary Sodium Restriction Results in Tissue-Specific Changes in DNA Methylation in Humans

[Figure: see text].

Targeting muscle-enriched long non-coding RNA H19 reverses pathological cardiac hypertrophy

AIMS

Pathological cardiac remodelling and subsequent heart failure represents an unmet clinical need. Long non-coding RNAs (lncRNAs) are emerging as crucial molecular orchestrators of disease processes, including that of heart diseases. Here, we report on the powerful therapeutic potential of the conserved lncRNA H19 in the treatment of pathological cardiac hypertrophy.

METHOD AND RESULTS

Pressure overload-induced left ventricular cardiac remodelling revealed an up-regulation of H19 in the early phase but strong sustained repression upon reaching the decompensated phase of heart failure. The translational potential of H19 is highlighted by its repression in a large animal (pig) model of left ventricular hypertrophy, in diseased human heart samples, in human stem cell-derived cardiomyocytes and in human engineered heart tissue in response to afterload enhancement. Pressure overload-induced cardiac hypertrophy in H19 knock-out mice was aggravated compared to wild-type mice. In contrast, vector-based, cardiomyocyte-directed gene therapy using murine and human H19 strongly attenuated heart failure even when cardiac hypertrophy was already established. Mechanistically, using microarray, gene set enrichment analyses and Chromatin ImmunoPrecipitation DNA-Sequencing, we identified a link between H19 and pro-hypertrophic nuclear factor of activated T cells (NFAT) signalling. H19 physically interacts with the polycomb repressive complex 2 to suppress H3K27 tri-methylation of the anti-hypertrophic Tescalcin locus which in turn leads to reduced NFAT expression and activity.

CONCLUSION

H19 is highly conserved and down-regulated in failing hearts from mice, pigs and humans. H19 gene therapy prevents and reverses experimental pressure-overload-induced heart failure. H19 acts as an anti-hypertrophic lncRNA and represents a promising therapeutic target to combat pathological cardiac remodelling.

Preclinical Models of Cancer Therapy-Associated Cardiovascular Toxicity: A Scientific Statement From the American Heart Association

Although cardiovascular toxicity from traditional chemotherapies has been well recognized for decades, the recent explosion of effective novel targeted cancer therapies with cardiovascular sequelae has driven the emergence of cardio-oncology as a new clinical and research field. Cardiovascular toxicity associated with cancer therapy can manifest as a broad range of potentially life-threatening complications, including heart failure, arrhythmia, myocarditis, and vascular events. Beyond toxicology, the intersection of cancer and heart disease has blossomed to include discovery of genetic and environmental risk factors that predispose to both. There is a pressing need to understand the underlying molecular mechanisms of cardiovascular toxicity to improve outcomes in patients with cancer. Preclinical cardiovascular models, ranging from cellular assays to large animals, serve as the foundation for mechanistic studies, with the ultimate goal of identifying biologically sound biomarkers and cardioprotective therapies that allow the optimal use of cancer treatments while minimizing toxicities. Given that novel cancer therapies target specific pathways integral to normal cardiovascular homeostasis, a better mechanistic understanding of toxicity may provide insights into fundamental pathways that lead to cardiovascular disease when dysregulated. The goal of this scientific statement is to summarize the strengths and weaknesses of preclinical models of cancer therapy-associated cardiovascular toxicity, to highlight overlapping mechanisms driving cancer and cardiovascular disease, and to discuss opportunities to leverage cardio-oncology models to address important mechanistic questions relevant to all patients with cardiovascular disease, including those with and without cancer.

Sweat the small stuff: The human microvasculature and heart disease

Traditionally thought of primarily as the predominant regulator of myocardial perfusion, it is becoming more accepted that the human coronary microvasculature also exerts a more direct influence on the surrounding myocardium. Coronary microvascular dysfunction (CMD) not only precedes large artery atherosclerosis, but is associated with other cardiovascular diseases such as heart failure with preserved ejection fraction and hypertrophic cardiomyopathy. It is also highly predictive of cardiovascular events in patients with or without atherosclerotic cardiovascular disease. This review focuses on this recent paradigm shift and delves into the clinical consequences of CMD. Concepts of how resistance arterioles contribute to disease will be discussed, highlighting how the microvasculature may serve as a potential target for novel therapies and interventions. Finally, both invasive and non-invasive methods with which to assess the coronary microvasculature both for diagnostic and risk stratification purposes will be reviewed.

Hypertension preserves the magnitude of microvascular flow-mediated dilation following transient elevation in intraluminal pressure

OBJECTIVE

The objective of this study was to measure flow-mediated dilation (FMD) prior to and following transient increases in intraluminal pressure (IILP) in resistance arterioles isolated from subjects with and without coronary artery disease (CAD) (CAD and non-CAD) and non-CAD subjects with hypertension.

METHODS

Arterioles were isolated from discarded surgical tissues (adipose and atrial) from patients without coronary artery disease (non-CAD; ≤1 risk factor, excluding hypertension), with CAD, and non-CAD patients with hypertension (hypertension as the only risk factor). To simulate transient hypertension, increased IILP was generated (150 mmHg, 30 min) by gravity. Arterioles were constricted with endothelin-1, followed by FMD and endothelial-independent dilation prior to and following exposure to IILP.

RESULTS

IILP reduced FMD in non-CAD and CAD arterioles relative to pre-IILP (p <.05 at 100 cmH2 O). In contrast, arterioles from non-CAD hypertensive subjects exhibited no reduction in maximal FMD following IILP (p = .84 at 100 cmH2 O). FMD was reduced by L-NAME prior to IILP in non-CAD hypertensive patients (p < .05 at 100 cmH2 O); however, following IILP, FMD was inhibited by peg-cat (p < .05 at 100 cmH2 O), indicating a switch from NO to H2 O2 as the mechanism of dilation.

CONCLUSIONS

Acute exposure (30 min) to IILP (150 mmHg) attenuates the magnitude of FMD in non-CAD and CAD resistance arterioles. The presence of clinically diagnosed hypertension in non-CAD resistance arterioles preserves the magnitude of FMD following IILP as a result of a compensatory switch from NO to H2 O2 as the mechanism of dilation.

Critical Interaction Between Telomerase and Autophagy in Mediating Flow-Induced Human Arteriolar Vasodilation

OBJECTIVE

Coronary artery disease (CAD) is associated with a compensatory switch in mechanism of flow-mediated dilation (FMD) from nitric oxide (NO) to H₂O₂. The underlying mechanism responsible for the pathological shift is not well understood, and recent reports directly implicate telomerase and indirectly support a role for autophagy. We hypothesize that autophagy is critical for shear stress-induced release of NO and is a crucial component of for the pathway by which telomerase regulates FMD. Approach and Results: Human left ventricular, atrial, and adipose resistance arterioles were collected for videomicroscopy and immunoblotting. FMD and autophagic flux were measured in arterioles treated with autophagy modulators alone, and in tandem with telomerase-activity modulators. LC3B II/I was higher in left ventricular tissue from patients with CAD compared with non-CAD (2.8±0.2 versus 1.0±0.2-fold change; P<0.05), although p62 was similar between groups. Shear stress increased Lysotracker fluorescence in non-CAD arterioles, with no effect in CAD arterioles. Inhibition of autophagy in non-CAD arterioles induced a switch from NO to H₂O₂, while activation of autophagy restored NO-mediated vasodilation in CAD arterioles. In the presence of an autophagy activator, telomerase inhibitor prevented the expected switch (Control: 82±4%; NG-Nitro-l-arginine methyl ester: 36±5%; polyethylene glycol catalase: 80±3). Telomerase activation was unable to restore NO-mediated FMD in the presence of autophagy inhibition in CAD arterioles (control: 72±7%; NG-Nitro-l-arginine methyl ester: 79±7%; polyethylene glycol catalase: 38±9%).

CONCLUSIONS

We provide novel evidence that autophagy is responsible for the pathological switch in dilator mechanism in CAD arterioles, demonstrating that autophagy acts downstream of telomerase as a common denominator in determining the mechanism of FMD.

Visualization and quantification of mitochondrial structure in the endothelium of intact arteries

AIM

To quantify the mitochondrial structure of ECs in intact arteries vs. cultured cells.

METHODS AND RESULTS

Cre-stop mito-Dendra2 mice, expressing the fluorescent protein Dendra2 in the mitochondrial matrix only, were used to label EC mitochondria using Cre-recombinase under the control of the VE-cadherin promoter. Conduit arteries, resistance arterioles and veins were fixed, mounted on glass slides and fluorescent images were obtained using a laser scanning confocal microscope (ex 488 nm; em 550 nm). ImageJ was used to calculate form factor (FF) and aspect ratio (AR) of the mitochondrial segments. Mitochondrial fragmentation count (MFC) was calculated by counting non-contiguous mitochondrial particles and dividing by the number of pixels which comprise the mitochondrial network. Primary aortic EC cultures (48 h on culture plates) were generated to compare the mitochondrial structure of cultured ECs vs. intact arteries. Aortic segments were also exposed to high glucose overnight (33 mM) ex vivo, and separate groups of mice were either infused with a high-glucose saline solution (300 mM) via tail vein catheter for 1 h or injected with streptozotocin (STZ; 50 mg/kg) to cause hyperglycaemia. Compared with cultured ECs, the mitochondria of ECs from the intact aorta were more fragmented (MFC: 6.4 ± 2.5 vs. 18.6 ± 9.4, respectively; P < 0.05). The mitochondrial segments of ECs within the aorta were more circular in shape (FF: 3.5 ± 0.75 vs. 1.8 ± 0.30, respectively; P < 0.05) and had less branching (AR: 2.9 ± 0.60 vs. 2.0 ± 0.25, respectively; P < 0.05) compared with cultured ECs. Ex vivo exposure of the intact aorta to high glucose overnight caused mitochondrial fission compared with normal glucose conditions (5 mM; MFC: 25.5 ± 11.1 high glucose vs. 11.0 ± 3.6 normal glucose; P < 0.05). Both 1-h infusion of high glucose saline (MFC: 22.4 ± 4.3) and STZ treatment (MFC: 40.3 ± 14.2) caused mitochondrial fission compared with freshly fixed aortas from control mice (MFC: 18.6 ± 9.4; P < 0.05 vs. high-glucose infusion and STZ treatment).

CONCLUSIONS

Using a novel mouse model, we were able to, for the first time, obtain high resolution images of EC mitochondrial structure in intact arteries. We reveal the endothelial mitochondrial network is more fragmented in the intact aorta compared with cultured ECs, indicating that mitochondria assume a more elongated and branched phenotype in cell culture.

BCR-ABL tyrosine kinase inhibitors promote pathological changes in dilator phenotype in the human microvasculature

OBJECTIVE

Treatment with BCR-ABL tyrosine kinase inhibitors (TKIs) is the standard of care for patients with chronic myeloid leukemia, however evidence indicates these compounds may have cardiovascular side-effects. This study sought to determine if ex vivo exposure of human adipose arterioles to the BCR-ABL TKIs imatinib and nilotinib causes endothelial dysfunction.

METHODS

Human adipose arterioles were incubated overnight in cell culture media containing vehicle (PBS), imatinib (10 µmol/L) or nilotinib (100 µmol/L). Arterioles were cannulated onto glass pipettes and flow mediated dilation (FMD) was assessed via video microscopy. To determine the mechanism of vasodilation, FMD was re-assessed in the presence of either the nitric oxide synthase inhibitor L-NAME (100 µmol/L) or the H₂ O₂ scavenger PEG-Catalase (500 U/mL).

RESULTS

Neither imatinib nor nilotinib affected the magnitude of FMD (max dilation = 78±17% vehicle, 80 ± 24% nilotinib, 73 ± 13% imatinib). FMD was decreased by L-NAME in vehicle-treated arterioles (max dilation = 47±29%). Conversely, L-NAME had no effect on FMD in imatinib- or nilotinib-treated vessels (max dilation = 79±14% and 80 ± 24%, respectively), rather FMD was inhibited by PEG-Catalase (max dilation = 29±11% and 29 ± 14%, respectively).

CONCLUSION

Incubating human arterioles with imatinib or nilotinib switches the mediator of FMD from vasoprotective nitric oxide to pro-inflammatory H₂ O₂ .

Detrimental effects of chemotherapy on human coronary microvascular function

Chemotherapy (CT) is a necessary treatment to prevent the growth and survival of cancer cells. However, CT has a well-established adverse impact on the cardiovascular (CV) system, even years after cessation of treatment. The effects of CT drugs on tumor vasculature have been the focus of much research, but little evidence exists showing the effects on the host microcirculation. Microvascular (MV) dysfunction is an early indicator of numerous CV disease phenotypes, including heart failure. The goal of this study was to evaluate the direct effect of doxorubicin (Dox) on human coronary MV function. To study the effect of CT on the cardiac MV function, flow-mediated dilation (FMD), pharmacologically-induced endothelial dependent dilation to acetylcholine (ACh), and smooth muscle-dependent dilation to papaverine were investigated. Vessels were freshly isolated from atrial appendages of adult patients undergoing cardiopulmonary bypass surgery or from cardiac tissue of pediatric patients, collected at the time of surgery to repair congenital heart defects. Isolated vessels were incubated in endothelial culture medium containing vehicle or Dox (100 nm, 15-20 h) and used to measure dilator function by video microscopy. Ex vivo treatment of adult human coronary microvessels with Dox significantly impaired flow-mediated dilation (FMD). Conversely, in pediatric coronary microvessels, Dox-induced impairment of FMD was significantly reduced in comparison with adult subjects. In both adult and pediatric coronary microvessels, ACh-induced constriction was reversed into dilation in the presence of Dox. Smooth muscle-dependent dilation remained unchanged in all groups tested. In vessels from adult subjects, acute treatment with Dox in clinically relevant doses caused significant impairment of coronary arteriolar function, whereas vessels from pediatric subjects showed only marginal impairment to the same stressor. This interesting finding might explain the delayed onset of future adverse CV events in children compared with adults after anthracycline therapy.NEW & NOTEWORTHY We have characterized, for the first time, human microvascular responses to acute ex vivo exposure to doxorubicin in coronary vessels from patients without cancer. Our data show an augmented impairment of endothelial function in vessels from adult subjects compared with pediatric samples.

Cancer therapy-induced cardiovascular toxicity: old/new problems and old drugs

Cardio-oncology has emerged as an exciting new field at the intersection of cardiology and oncology. While improved oncology treatment efficacy has increased survival rates in cancer patients, the long-term cardiovascular consequences of this life-saving treatment have become more clinically relevant. Both traditional and newer (targeted) cancer therapies can have cardiovascular and metabolic sequelae, resulting in heart failure, coronary artery disease, myocarditis, pericardial disease, hypertension, and vascular and metabolic perturbations (Moslehi JJ. Cardiovascular toxic effects of targeted cancer therapies. N Engl J Med 375: 1457-1467, 2016). Both acute and chronic cardiovascular toxicities have proven challenging for clinicians and patients, significantly contributing to morbidity and mortality. Although chronic cardiovascular disease affects a growing number of cancer survivors (~17 million in the United States in 2019), cardiovascular toxicities associated with cancer and cancer therapies are poorly understood mechanistically. To balance potential damage to the cardiovascular system with effective and efficient cancer treatment, novel strategies are sorely needed. This perspective focuses on an assembly of articles that discuss novel means of counteracting adverse cardiovascular events in response to anticancer therapy. In light of new clinical syndromes in cardiology due to cancer therapies, we hope to highlight promising research opportunities offered by cardio-oncology (Bellinger AM, Arteaga CL, Force T, Humphreys BD, Demetri GD, Druker BJ, Moslehi JJ. Cardio-oncology: how new targeted cancer therapies and precision medicine can inform cardiovascular discovery. Circulation 132: 2248-2258, 2015.).

Mitochondrial Oxidative Phosphorylation defect in the Heart of Subjects with Coronary Artery Disease

Coronary artery disease (CAD) is a leading cause of death worldwide and frequently associated with mitochondrial dysfunction. Detailed understanding of abnormalities in mitochondrial function that occur in patients with CAD is lacking. We evaluated mitochondrial damage, energy production, and mitochondrial complex activity in human non-CAD and CAD hearts. Fresh and frozen human heart tissue was used. Cell lysate or mitochondria were isolated using standard techniques. Mitochondrial DNA (_mtDNA), NAD + and ATP levels, and mitochondrial oxidative phosphorylation capacity were evaluated. Proteins critical to the regulation of mitochondrial metabolism and function were also evaluated in tissue lysates. PCR analysis revealed an increase in _mtDNA lesions and the frequency of mitochondrial common deletion, both established markers for impaired mitochondrial integrity in CAD compared to non-CAD patient samples. NAD⁺ and ATP levels were significantly decreased in CAD subjects compared to Non-CAD (NAD⁺ fold change: non-CAD 1.00 ± 0.17 vs. CAD 0.32 ± 0.12* and ATP fold change: non-CAD 1.00 ± 0.294 vs. CAD 0.01 ± 0.001*; N = 15, P < 0.005). We observed decreased respiration control index in CAD tissue and decreased activity of complexes I, II, and III. Expression of ETC complex subunits and respirasome formation were increased; however, elevations in the de-active form of complex I were observed in CAD. We observed a corresponding increase in glycolytic flux, indicated by a rise in pyruvate kinase and lactate dehydrogenase activity, indicating a compensatory increase in glycolysis for cellular energetics. Together, these results indicate a shift in mitochondrial metabolism from oxidative phosphorylation to glycolysis in human hearts subjects with CAD.

Telomerase Deficiency Predisposes to Heart Failure and Ischemia-Reperfusion Injury

Introduction: Elevated levels of mitochondrial reactive oxygen species (ROS) contribute to the development of numerous cardiovascular diseases. TERT, the catalytic subunit of telomerase, has been shown to translocate to mitochondria to suppress ROS while promoting ATP production. Acute overexpression of TERT increases survival and decreases infarct size in a mouse model of myocardial infarct, while decreased telomerase activity predisposes to mitochondrial defects and heart failure. In the present study, we examined the role of TERT on cardiac structure and function under basal conditions and conditions of acute or prolonged stress in a novel rat model of TERT deficiency. Methods: Cardiac structure and function were evaluated via transthoracic echocardiogram. Langendorff preparations were used to test the effects of acute global ischemia reperfusion injury on cardiac function and infarction. Coronary flow and left ventricular pressure were measured during and after ischemia/reperfusion (I/R). Mitochondrial DNA integrity was measured by PCR and mitochondrial respiration was assessed in isolated mitochondria using an Oxygraph. Angiotensin II infusion was used as an established model of systemic stress. Results: No structural changes (echocardiogram) or coronary flow/left ventricle pressure (isolated hearts) were observed in TERT^-/- rats at baseline; however, after I/R, coronary flow was significantly reduced in TERT^-/- compared to wild type (WT) rats, while diastolic Left Ventricle Pressure was significantly elevated (n = 6 in each group; p < 0.05) in the TERT^-/-. Interestingly, infarct size was less in TERT^-/- rats compared to WT rats, while mitochondrial respiratory control index decreased and mitochondrial DNA lesions increased in TERT^-/- compared to WT. Angiotensin II treatment did not alter cardiac structure or function; however, it augmented the infarct size significantly more in TERT^-/- compared to the WT. Conclusion: Absence of TERT activity increases susceptibility to stress like cardiac injury. These results suggest a critical role of telomerase in chronic heart disease.

Lysophosphatidic acid acts on LPA1 receptor to increase H2 O2 during flow-induced dilation in human adipose arterioles

BACKGROUND AND PURPOSE

NO produces arteriolar flow-induced dilation (FID) in healthy subjects but is replaced by mitochondria-derived hydrogen peroxide (mtH2 O2 ) in patients with coronary artery disease (CAD). Lysophosphatidic acid (LPA) is elevated in patients with risk factors for CAD, but its functional effect in arterioles is unknown. We tested whether elevated LPA changes the mediator of FID from NO to mtH2 O2 in human visceral and subcutaneous adipose arterioles.

EXPERIMENTAL APPROACH

Arterioles were cannulated on glass micropipettes and pressurized to 60 mmHg. We recorded lumen diameter after graded increases in flow in the presence of either NOS inhibition (L-NAME) or H2 O2 scavenging (Peg-Cat) ± LPA (10 μM, 30 min), ±LPA1 /LPA3 receptor antagonist (Ki16425) or LPA2 receptor antagonist (H2L5186303). We analysed LPA receptor RNA and protein levels in human arterioles and human cultured endothelial cells.

KEY RESULTS

FID was inhibited by L-NAME but not Peg-Cat in untreated vessels. In vessels treated with LPA, FID was of similar magnitude but inhibited by Peg-Cat while L-NAME had no effect. Rotenone attenuated FID in vessels treated with LPA indicating mitochondria as a source of ROS. RNA transcripts from LPA1 and LPA2 but not LPA3 receptors were detected in arterioles. LPA1 but not LPA3 receptor protein was detected by Western blot. Pretreatment of vessels with an LPA1 /LPA3 , but not LPA2 , receptor antagonist prior to LPA preserved NO-mediated dilation.

CONCLUSIONS AND IMPLICATIONS

These findings suggest an LPA1 receptor-dependent pathway by which LPA increases arteriolar release of mtH2 O2 as a mediator of FMD.

Detection of hydrogen peroxide production in the isolated rat lung using Amplex red

The objectives of this study were to develop a robust protocol to measure the rate of hydrogen peroxide (H₂O₂) production in isolated perfused rat lungs, as an index of oxidative stress, and to determine the cellular sources of the measured H₂O₂ using the extracellular probe Amplex red (AR). AR was added to the recirculating perfusate in an isolated perfused rat lung. AR's highly fluorescent oxidation product resorufin was measured in the perfusate. Experiments were carried out without and with rotenone (complex I inhibitor), thenoyltrifluoroacetone (complex II inhibitor), antimycin A (complex III inhibitor), potassium cyanide (complex IV inhibitor), or diohenylene iodonium (inhibitor of flavin-containing enzymes, e.g. NAD(P)H oxidase or NOX) added to the perfusate. We also evaluated the effect of acute changes in oxygen (O₂) concentration of ventilation gas on lung rate of H₂O₂ release into the perfusate. Baseline lung rate of H₂O₂ release was 8.45 ± 0.31 (SEM) nmol/min/g dry wt. Inhibiting mitochondrial complex II reduced this rate by 76%, and inhibiting flavin-containing enzymes reduced it by another 23%. Inhibiting complex I had a small (13%) effect on the rate, whereas inhibiting complex III had no effect. Inhibiting complex IV increased this rate by 310%. Increasing %O₂ in the ventilation gas mixture from 15 to 95% had a small (27%) effect on this rate, and this O₂-dependent increase was mostly nonmitochondrial. Results suggest complex II as a potentially important source and/or regulator of mitochondrial H₂O₂, and that most of acute hyperoxia-enhanced lung rate of H₂O₂ release is from nonmitochondrial rather than mitochondrial sources.

Hyperoxia Causes Mitochondrial Fragmentation in Pulmonary Endothelial Cells by Increasing Expression of Pro-Fission Proteins

OBJECTIVE

We explored mechanisms that alter mitochondrial structure and function in pulmonary endothelial cells (PEC) function after hyperoxia.

APPROACH AND RESULTS

Mitochondrial structures of PECs exposed to hyperoxia or normoxia were visualized and mitochondrial fragmentation quantified. Expression of pro-fission or fusion proteins or autophagy-related proteins were assessed by Western blot. Mitochondrial oxidative state was determined using mito-roGFP. Tetramethylrhodamine methyl ester estimated mitochondrial polarization in treatment groups. The role of mitochondrially derived reactive oxygen species in mt-fragmentation was investigated with mito-TEMPOL and mitochondrial DNA (mtDNA) damage studied by using ENDO III (mt-tat-endonuclease III), a protein that repairs mDNA damage. Drp-1 (dynamin-related protein 1) was overexpressed or silenced to test the role of this protein in cell survival or transwell resistance. Hyperoxia increased fragmentation of PEC mitochondria in a time-dependent manner through 48 hours of exposure. Hyperoxic PECs exhibited increased phosphorylation of Drp-1 (serine 616), decreases in Mfn1 (mitofusion protein 1), but increases in OPA-1 (optic atrophy 1). Pro-autophagy proteins p62 (LC3 adapter-binding protein SQSTM1/p62), PINK-1 (PTEN-induced putative kinase 1), and LC3B (microtubule-associated protein 1A/1B-light chain 3) were increased. Returning cells to normoxia for 24 hours reversed the increased mt-fragmentation and changes in expression of pro-fission proteins. Hyperoxia-induced changes in mitochondrial structure or cell survival were mitigated by antioxidants mito-TEMPOL, Drp-1 silencing, or inhibition or protection by the mitochondrial endonuclease ENDO III. Hyperoxia induced oxidation and mitochondrial depolarization and impaired transwell resistance. Decrease in resistance was mitigated by mito-TEMPOL or ENDO III and reproduced by overexpression of Drp-1.

CONCLUSIONS

Because hyperoxia evoked mt-fragmentation, cell survival and transwell resistance are prevented by ENDO III and mito-TEMPOL and Drp-1 silencing, and these data link hyperoxia-induced mt-DNA damage, Drp-1 expression, mt-fragmentation, and PEC dysfunction.