Arterial endoglin does not protect against arteriovenous malformations

Endothelial-to-Mesenchymal Transition in an Hereditary Hemorrhagic Telangiectasia-like Pediatric Case of Multiple Pulmonary Arteriovenous Malformations

Pulmonary arteriovenous malformations (PAVMs) are vascular anomalies resulting in abnormal connections between pulmonary arteries and veins. In 80% of cases, PAVMs are present from birth, but clinical manifestations are rarely seen in childhood. These congenital malformations are typically associated with Hereditary Hemorrhagic Telangiectasia (HHT), a rare disease that affects 1 in 5000/8000 individuals. HHT disease is frequently caused by mutations in genes involved in the TGF-β pathway. However, approximately 15% of patients do not have a genetic diagnosis and, among the genetically diagnosed, more than 33% do not meet the Curaçao criteria. This makes clinical diagnosis even more challenging in the pediatric age group. Here, we introduce an 8-year-old patient bearing a severe phenotype of multiple diffuse PAVMs caused by an unknown mutation which ended in lung transplantation. Phenotypically, the case under study follows a molecular pattern which is HHT-like. Therefore, molecular- biological and cellular-functional analyses have been performed in primary endothelial cells (ECs) isolated from the explanted lung. The findings revealed a loss of functionality in lung endothelial tissue and a stimulation of endothelial-to-mesenchymal transition. Understanding the molecular basis of this transition could potentially offer new therapeutic strategies to delay lung transplantation in severe cases.

Employment of diverse in vitro systems for analyzing multiple aspects of disease, hereditary hemorrhagic telangiectasia (HHT)

BACKGROUND

In vitro disease modeling enables translational research by providing insight into disease pathophysiology and molecular mechanisms, leading to the development of novel therapeutics. Nevertheless, in vitro systems have limitations for recapitulating the complexity of tissues, and a single model system is insufficient to gain a comprehensive understanding of a disease.

RESULTS

Here we explored the potential of using several models in combination to provide mechanistic insight into hereditary hemorrhagic telangiectasia (HHT), a genetic vascular disorder. Genome editing was performed to establish hPSCs (H9) with ENG haploinsufficiency and several in vitro models were used to recapitulate the functional aspects of the cells that constitute blood vessels. In a 2D culture system, endothelial cells showed early senescence, reduced viability, and heightened susceptibility to apoptotic insults, and smooth muscle cells (SMCs) exhibited similar behavior to their wild-type counterparts. Features of HHT were evident in 3D blood-vessel organoid systems, including thickening of capillary structures, decreased interaction between ECs and surrounding SMCs, and reduced cell viability. Features of ENG haploinsufficiency were observed in arterial and venous EC subtypes, with arterial ECs showing significant impairments. Molecular biological approaches confirmed the significant downregulation of Notch signaling in HHT-ECs.

CONCLUSIONS

Overall, we demonstrated refined research strategies to enhance our comprehension of HHT, providing valuable insights for pathogenic analysis and the exploration of innovative therapeutic interventions. Additionally, these results underscore the importance of employing diverse in vitro systems to assess multiple aspects of disease, which is challenging using a single in vitro system.

Hereditary hemorrhagic telangiectasia: from signaling insights to therapeutic advances

Hereditary hemorrhagic telangiectsia (HHT) is an inherited vascular disorder with highly variable expressivity, affecting up to 1 in 5,000 individuals. This disease is characterized by small arteriovenous malformations (AVMs) in mucocutaneous areas (telangiectases) and larger visceral AVMs in the lungs, liver, and brain. HHT is caused by loss-of-function mutations in the BMP9-10/ENG/ALK1/SMAD4 signaling pathway. This Review presents up-to-date insights on this mutated signaling pathway and its crosstalk with proangiogenic pathways, in particular the VEGF pathway, that has allowed the repurposing of new drugs for HHT treatment. However, despite the substantial benefits of these new treatments in terms of alleviating symptom severity, this not-so-uncommon bleeding disorder still currently lacks any FDA- or European Medicines Agency-approved (EMA-approved) therapies.

lncRNA CCAT2 Protects Against Cardiomyocyte Injury After Myocardial Ischemia/Reperfusion by Regulating BMI1 Expression

Myocardial ischemia/reperfusion (I/R) decreases cardiac function and efficiency. Accumulating evidence suggests that long noncoding RNAs (lncRNAs) have been linked to the cellular processes of myocardial I/R injury. The present investigation elucidated the function of lncRNA colon cancer-associated transcript 2 (CCAT2) in myocardial I/R injury and the related mechanisms.AC16 cardiomyocytes were exposed to hypoxia (16 hours) /reoxygenation (6 hours) (H/R) to mimic myocardial I/R models in vitro. CCAT2 and microRNA (miR) -539-3p expressions in AC16 cardiomyocytes were measured using real-time quantitative polymerase chain reaction. B-cell-specific Moloney murine leukemia virus insertion region 1 (BMI1) protein levels in AC16 cardiomyocytes were determined by western blotting. Cell viability, lactate dehydrogenase (LDH) leakage, reactive oxygen species (ROS) levels, mitochondrial membrane potential, and apoptosis were detected using Counting Kit-8, LDH Assay Kit, dihydroethidium assay, 5,5',6,6'-tetrachloro1,1',3,3'-tetramethylbenzimidazolylcarbocyanine iodide staining, flow cytometry, and western blotting, respectively. The interactions between the molecules were confirmed using the dual-luciferase gene reporter. The wingless/integrated/beta-catenin (Wnt/β-catenin) pathway under the H/R condition was detected by western blotting.CCAT2 and BMI1 mRNA expressions were reduced in H/R-exposed AC16 cardiomyocytes. CCAT2 overexpression exerted protective effects against H/R-induced cardiomyocyte injury, as demonstrated by increased cell viability and mitochondrial membrane potential and decreased LDH leakage, ROS levels, and apoptosis. In addition, CCAT2 positively regulated BMI1 expression by binding to miR-539-3p. CCAT2 knockdown or miR-539-3p overexpression restrained the protective effects of BMI1 against H/R-induced cardiomyocyte injury. In addition, miR-539-3p overexpression reversed the protective effects of CCAT2. Furthermore, CCAT2 activated the Wnt/β-catenin pathway under the H/R condition via the miR-539-3p/BMI1 axis.Overall, this investigation showed the protective effects of the CCAT2/miR-539-3p/BMI1/Wnt/β-catenin regulatory axis against cardiomyocyte injury induced by H/R.

Prevalence and Characteristics of Intracranial Aneurysms in Hereditary Hemorrhagic Telangiectasia

BACKGROUND AND PURPOSE

The association between hereditary hemorrhagic telangiectasia and intracranial aneurysms remains controversial. This study evaluated the prevalence and characteristics of intracranial aneurysms in patients with hereditary hemorrhagic telangiectasia with brain vascular malformations.

MATERIALS AND METHODS

Between 2007 and 2021, patients enrolled in the Brain Vascular Malformation Consortium with definite hereditary hemorrhagic telangiectasia, the presence of brain vascular malformations, and available angiographic studies of the brain were retrospectively reviewed. Angiographic features of intracranial aneurysms and their relationship to coexisting brain vascular malformations were analyzed. We also examined the association between baseline clinical features and the presence of intracranial aneurysms.

RESULTS

One hundred eighty patients were included. A total of 14 intracranial aneurysms were found in 9 (5%) patients, and 4 intracranial aneurysms were considered flow-related aneurysms. Patients with intracranial aneurysms were significantly older than patients without intracranial aneurysms (mean, 48.1 [SD, 18.2] years versus 33.5 [SD, 21.0] years; P = .042). If we excluded flow-related intracranial aneurysms, the prevalence of intracranial aneurysms was 3.3%. All intracranial aneurysms were in the anterior circulation, were unruptured, and had an average maximal diameter of 3.9 (SD, 1.5) mm. No intracranial aneurysms were found in pediatric patients with hereditary hemorrhagic telangiectasia. No statistically significant correlation was observed among other baseline demographics, hereditary hemorrhagic telangiectasia features, and the presence of intracranial aneurysms.

CONCLUSIONS

The prevalence of intracranial aneurysms in this large cohort study is comparable with that in the general population and might be increased slightly due to hemodynamic factors associated with shunting brain vascular malformations.

Pathological angiogenesis: mechanisms and therapeutic strategies

In multicellular organisms, angiogenesis, the formation of new blood vessels from pre-existing ones, is an essential process for growth and development. Different mechanisms such as vasculogenesis, sprouting, intussusceptive, and coalescent angiogenesis, as well as vessel co-option, vasculogenic mimicry and lymphangiogenesis, underlie the formation of new vasculature. In many pathological conditions, such as cancer, atherosclerosis, arthritis, psoriasis, endometriosis, obesity and SARS-CoV-2(COVID-19), developmental angiogenic processes are recapitulated, but are often done so without the normal feedback mechanisms that regulate the ordinary spatial and temporal patterns of blood vessel formation. Thus, pathological angiogenesis presents new challenges yet new opportunities for the design of vascular-directed therapies. Here, we provide an overview of recent insights into blood vessel development and highlight novel therapeutic strategies that promote or inhibit the process of angiogenesis to stabilize, reverse, or even halt disease progression. In our review, we will also explore several additional aspects (the angiogenic switch, hypoxia, angiocrine signals, endothelial plasticity, vessel normalization, and endothelial cell anergy) that operate in parallel to canonical angiogenesis mechanisms and speculate how these processes may also be targeted with anti-angiogenic or vascular-directed therapies.

Brain arteriovenous malformation in hereditary hemorrhagic telangiectasia: Recent advances in cellular and molecular mechanisms

Hereditary hemorrhagic telangiectasia (HHT) is a genetic disorder characterized by vessel dilatation, such as telangiectasia in skin and mucosa and arteriovenous malformations (AVM) in internal organs such as the gastrointestinal tract, lungs, and brain. AVMs are fragile and tortuous vascular anomalies that directly connect arteries and veins, bypassing healthy capillaries. Mutations in transforming growth factor β (TGFβ) signaling pathway components, such as ENG (ENDOGLIN), ACVRL1 (ALK1), and SMAD4 (SMAD4) genes, account for most of HHT cases. 10-20% of HHT patients develop brain AVMs (bAVMs), which can lead to vessel wall rupture and intracranial hemorrhages. Though the main mutations are known, mechanisms leading to AVM formation are unclear, partially due to lack of animal models. Recent mouse models allowed significant advances in our understanding of AVMs. Endothelial-specific deletion of either Acvrl1, Eng or Smad4 is sufficient to induce AVMs, identifying endothelial cells (ECs) as primary targets of BMP signaling to promote vascular integrity. Loss of ALK1/ENG/SMAD4 signaling is associated with NOTCH signaling defects and abnormal arteriovenous EC differentiation. Moreover, cumulative evidence suggests that AVMs originate from venous ECs with defective flow-migration coupling and excessive proliferation. Mutant ECs show an increase of PI3K/AKT signaling and inhibitors of this signaling pathway rescue AVMs in HHT mouse models, revealing new therapeutic avenues. In this review, we will summarize recent advances and current knowledge of mechanisms controlling the pathogenesis of bAVMs, and discuss unresolved questions.

An update on preclinical models of hereditary haemorrhagic telangiectasia: Insights into disease mechanisms

Endoglin (ENG) is expressed on the surface of endothelial cells (ECs) where it efficiently binds circulating BMP9 and BMP10 ligands to initiate activin A receptor like type 1 (ALK1) protein signalling to protect the vascular architecture. Patients heterozygous for ENG or ALK1 mutations develop the vascular disorder known as hereditary haemorrhagic telangiectasia (HHT). Many patients with this disorder suffer from anaemia, and are also at increased risk of stroke and high output heart failure. Recent work using animal models of HHT has revealed new insights into cellular and molecular mechanisms causing this disease. Loss of the ENG (HHT1) or ALK1 (HHT2) gene in ECs leads to aberrant arteriovenous connections or malformations (AVMs) in developing blood vessels. Similar phenotypes develop following combined EC specific loss of SMAD1 and 5, or EC loss of SMAD4. Taken together these data point to the essential role of the BMP9/10-ENG-ALK1-SMAD1/5-SMAD4 pathway in protecting the vasculature from AVMs. Altered directional migration of ECs in response to shear stress and increased EC proliferation are now recognised as critical factors driving AVM formation. Disruption of the ENG/ALK1 signalling pathway also affects EC responses to vascular endothelial growth factor (VEGF) and crosstalk between ECs and vascular smooth muscle cells. It is striking that the vascular lesions in HHT are both localised and tissue specific. Increasing evidence points to the importance of a second genetic hit to generate biallelic mutations, and the sporadic nature of such somatic mutations would explain the localised formation of vascular lesions. In addition, different pro-angiogenic drivers of AVM formation are likely to be at play during the patient’s life course. For example, inflammation is a key driver of vessel remodelling in postnatal life, and may turn out to be an important driver of HHT disease. The current wealth of preclinical models of HHT has led to increased understanding of AVM development and revealed new therapeutic approaches to treat AVMs, and form the topic of this review.

MIR22HG Aggravates Oxygen-Glucose Deprivation and Reoxygenation-Induced Cardiomyocyte Injury through the miR-9-3p/SH2B3 Axis

Reperfusion therapy, the standard treatment for acute myocardial infarction (MI), can trigger necrotic death of cardiomyocytes and provoke ischemia/reperfusion (I/R) injury. However, molecular mechanisms that regulate cardiomyocyte death remain largely unknown. The abnormal expression of lncRNA MIR22HG has been found in types of diseases. The current study was aimed at exploring the function and mechanism of MIR22HG in I/R injury. In this study, mouse myocardial cells (HL-1) treated with oxygen-glucose deprivation and reoxygenation (OGD/R) were used as the in vitro models, and myocardial ischemia reperfusion injury (MIRI) animal models in vivo were established in male C57BL/6 mice. Experiments including CCK-8, flow cytometry, TUNEL, HE staining, RT-qPCR, western blotting, and luciferase reporter assays were performed to explore the function and potential mechanism of MIR22HG in MIRI in vitro and in vivo. Bioinformatics analysis was performed to predict the binding site between miR-9-3p and MIR22HG (or SH2B3). Our results indicated that the MIR22HG level was upregulated in cardiomyocytes after OGD/R treatment. The knockdown of MIR22HG promoted cell viability and inhibited apoptosis and extracellular matrix (ECM) production in OGD/R-treated HL-1 cells. In mechanism, MIR22HG binds to miR-9-3p, and miR-9-3p targets the SH2B3 3 ${}^{\prime }$ untranslated region (UTR). Moreover, SH2B3 expression was positively regulated by MIR22HG but negatively modulated by miR-9-3p. Rescue assays suggested that the suppressive effect of MIR22HG knockdown on cell viability, apoptosis, and ECM accumulation was reversed by the overexpression of SH2B3. The in vivo experiments demonstrated that MIR22HG knockdown alleviated cardiomyocyte apoptosis and reduced myocardial infarct size in MIRI mice. In summary, MIR22HG knockdown alleviates myocardial injury through the miR-9-3p/SH2B3 axis.

The versatility and paradox of BMP signaling in endothelial cell behaviors and blood vessel function

Blood vessels expand via sprouting angiogenesis, and this process involves numerous endothelial cell behaviors, such as collective migration, proliferation, cell–cell junction rearrangements, and anastomosis and lumen formation. Subsequently, blood vessels remodel to form a hierarchical network that circulates blood and delivers oxygen and nutrients to tissue. During this time, endothelial cells become quiescent and form a barrier between blood and tissues that regulates transport of liquids and solutes. Bone morphogenetic protein (BMP) signaling regulates both proangiogenic and homeostatic endothelial cell behaviors as blood vessels form and mature. Almost 30 years ago, human pedigrees linked BMP signaling to diseases associated with blood vessel hemorrhage and shunts, and recent work greatly expanded our knowledge of the players and the effects of vascular BMP signaling. Despite these gains, there remain paradoxes and questions, especially with respect to how and where the different and opposing BMP signaling outputs are regulated. This review examines endothelial cell BMP signaling in vitro and in vivo and discusses the paradox of BMP signals that both destabilize and stabilize endothelial cell behaviors.

Melatonin Attenuates Ischemia/Reperfusion-Induced Oxidative Stress by Activating Mitochondrial Fusion in Cardiomyocytes

Myocardial ischemia/reperfusion (I/R) injury can stimulate mitochondrial reactive oxygen species production. Optic atrophy 1- (OPA1-) induced mitochondrial fusion is an endogenous antioxidative mechanism that preserves the mitochondrial function. In our study, we investigated whether melatonin augments OPA1-dependent mitochondrial fusion and thus maintains redox balance during myocardial I/R injury. In hypoxia/reoxygenation- (H/R-) treated H9C2 cardiomyocytes, melatonin treatment upregulated OPA1 mRNA and protein expression, thereby enhancing mitochondrial fusion. Melatonin also suppressed apoptosis in H/R-treated cardiomyocytes, as evidenced by increased cell viability, diminished caspase-3 activity, and reduced Troponin T secretion; however, silencing OPA1 abolished these effects. H/R treatment augmented mitochondrial ROS production and repressed antioxidative molecule levels, while melatonin reversed these changes in an OPA1-dependent manner. Melatonin also inhibited mitochondrial permeability transition pore opening and maintained the mitochondrial membrane potential, but OPA1 silencing prevented these outcomes. These results illustrate that melatonin administration alleviates cardiomyocyte I/R injury by activating OPA1-induced mitochondrial fusion and inhibiting mitochondrial oxidative stress.

TGF-β superfamily co-receptors in cancer

Transforming growth factor-β (TGF-β) superfamily signaling via their cognate receptors is frequently modified by TGF-β superfamily co-receptors. Signaling through SMAD-mediated pathways may be enhanced or depressed depending on the specific co-receptor and cell context. This dynamic effect on signaling is further modified by the release of many of the co-receptors from the membrane to generate soluble forms that are often antagonistic to the membrane-bound receptors. The co-receptors discussed here include TβRIII (betaglycan), endoglin, BAMBI, CD109, SCUBE proteins, neuropilins, Cripto-1, MuSK, and RGMs. Dysregulation of these co-receptors can lead to altered TGF-β superfamily signaling that contributes to the pathophysiology of many cancers through regulation of growth, metastatic potential, and the tumor microenvironment. Here we describe the role of several TGF-β superfamily co-receptors on TGF-β superfamily signaling and the impact on cellular and physiological functions with a particular focus on cancer, including a discussion on recent pharmacological advances and potential clinical applications targeting these co-receptors.

Novel Insights Into the Role of Mitochondria-Derived Peptides in Myocardial Infarction

Mitochondria-derived peptides (MDPs) are a new class of bioactive peptides encoded by small open reading frames (sORFs) within known mitochondrial DNA (mtDNA) genes. MDPs may affect the expression of nuclear genes and play cytoprotective roles against chronic and age-related diseases by maintaining mitochondrial function and cell viability in the face of metabolic stress and cytotoxic insults. In this review, we summarize clinical and experimental findings indicating that MDPs act as local and systemic regulators of glucose homeostasis, immune and inflammatory responses, mitochondrial function, and adaptive stress responses, and focus on evidence supporting the protective effects of MDPs against myocardial infarction. These insights into MDPs actions suggest their potential in the treatment of cardiovascular diseases and should encourage further research in this field.

Role of Venous Endothelial Cells in Developmental and Pathologic Angiogenesis

BACKGROUND

Angiogenesis is a dynamic process that involves expansion of a preexisting vascular network that can occur in a number of physiological and pathological settings. Despite its importance, the origin of the new angiogenic vasculature is poorly defined. In particular, the primary subtype of endothelial cells (capillary, venous, arterial) driving this process remains undefined.

METHODS

Endothelial cells were fate-mapped with the use of genetic markers specific to arterial and capillary cells. In addition, we identified a novel venous endothelial marker gene (Gm5127) and used it to generate inducible venous endothelium-specific Cre and Dre driver mouse lines. Contributions of these various types of endothelial cells to angiogenesis were examined during normal postnatal development and in disease-specific setting.

RESULTS

Using a comprehensive set of endothelial subtype-specific inducible reporter mice, including tip, arterial, and venous endothelial reporter lines, we showed that venous endothelial cells are the primary endothelial subtype responsible for the expansion of an angiogenic vascular network. During physiological angiogenesis, venous endothelial cells proliferate, migrating against the blood flow and differentiating into tip, capillary, and arterial endothelial cells of the new vasculature. Using intravital 2-photon imaging, we observed venous endothelial cells migrating against the blood flow to form new blood vessels. Venous endothelial cell migration also plays a key role in pathological angiogenesis. This was observed both in formation of arteriovenous malformations in mice with inducible endothelium-specific Smad4 deletion mice and in pathological vessel growth seen in oxygen-induced retinopathy.

CONCLUSIONS

Our studies establish that venous endothelial cells are the primary endothelial subtype responsible for normal expansion of vascular networks, formation of arteriovenous malformations, and pathological angiogenesis. These observations highlight the central role of the venous endothelium in normal development and disease pathogenesis.

Defective Flow-Migration Coupling Causes Arteriovenous Malformations in Hereditary Hemorrhagic Telangiectasia

BACKGROUND

Activin receptor-like kinase 1 (ALK1) is an endothelial transmembrane serine threonine kinase receptor for BMP family ligands that plays a critical role in cardiovascular development and pathology. Loss-of-function mutations in the ALK1 gene cause type 2 hereditary hemorrhagic telangiectasia, a devastating disorder that leads to arteriovenous malformations. Here, we show that ALK1 controls endothelial cell polarization against the direction of blood flow and flow-induced endothelial migration from veins through capillaries into arterioles.

METHODS

Using Cre lines that recombine in different subsets of arterial, capillary-venous, or endothelial tip cells, we show that capillary-venous Alk1 deletion was sufficient to induce arteriovenous malformation formation in the postnatal retina.

RESULTS

ALK1 deletion impaired capillary-venous endothelial cell polarization against the direction of blood flow in vivo and in vitro. Mechanistically, ALK1-deficient cells exhibited increased integrin signaling interaction with vascular endothelial growth factor receptor 2, which enhanced downstream YAP/TAZ nuclear translocation. Pharmacologic inhibition of integrin or YAP/TAZ signaling rescued flow migration coupling and prevented vascular malformations in Alk1-deficient mice.

CONCLUSIONS

Our study reveals ALK1 as an essential driver of flow-induced endothelial cell migration and identifies loss of flow-migration coupling as a driver of arteriovenous malformation formation in hereditary hemorrhagic telangiectasia disease. Integrin-YAP/TAZ signaling blockers are new potential targets to prevent vascular malformations in patients with hereditary hemorrhagic telangiectasia.

Thresholds of Endoglin Expression in Endothelial Cells Explains Vascular Etiology in Hereditary Hemorrhagic Telangiectasia Type 1

Hereditary Hemorrhagic Telangiectasia type 1 (HHT1) is an autosomal dominant inherited disease characterized by arteriovenous malformations and hemorrhage. HHT1 is caused by mutations in ENDOGLIN, which encodes an ancillary receptor for Transforming Growth Factor-β/Bone Morphogenetic Protein-9 expressed in all vascular endothelial cells. Haploinsufficiency is widely accepted as the underlying mechanism for HHT1. However, it remains intriguing that only some, but not all, vascular beds are affected, as these causal gene mutations are present in vasculature throughout the body. Here, we have examined the endoglin expression levels in the blood vessels of multiple organs in mice and in humans. We found a positive correlation between low basal levels of endoglin and the general prevalence of clinical manifestations in selected organs. Endoglin was found to be particularly low in the skin, the earliest site of vascular lesions in HHT1, and even undetectable in the arteries and capillaries of heterozygous endoglin mice. Endoglin levels did not appear to be associated with organ-specific vascular functions. Instead, our data revealed a critical endoglin threshold compatible with the haploinsufficiency model, below which endothelial cells independent of their tissue of origin exhibited abnormal responses to Vascular Endothelial Growth Factor. Our results support the development of drugs promoting endoglin expression as potentially protective.

LATS2 Deletion Attenuates Myocardial Ischemia-Reperfusion Injury by Promoting Mitochondrial Biogenesis

Reperfusion therapy is the most effective treatment for acute myocardial infarction, but it can damage cardiomyocytes through a mechanism known as myocardial ischemia/reperfusion injury (MIRI). In this study, we investigated whether the large tumor suppressor kinase 2 (LATS2) contributes to the development of myocardial MIRI by disrupting mitochondrial biogenesis. Our in vitro data demonstrate that cardiomyocyte viability was reduced and apoptosis was increased in response to hypoxia/reoxygenation (H/R) injury. However, suppression of LATS2 by shRNA sustained cardiomyocyte viability by maintaining mitochondrial function. Compared to H/R-treated control cardiomyocytes, cardiomyocytes transfected with LATS2 shRNA exhibited increased mitochondrial respiration, improved mitochondrial ATP generation, and more stable mitochondrial membrane potential. LATS2 suppression increased cardiomyocyte viability and mitochondrial biogenesis in a manner dependent on PGC1α, a key regulator of mitochondrial metabolism. These results identify LATS2 as a new inducer of mitochondrial damage and myocardial MIRI and suggest that approaches targeting LATS2 or mitochondrial biogenesis may be beneficial in the clinical management of cardiac MIRI.

Melatonin Attenuates Cardiac Ischemia-Reperfusion Injury through Modulation of IP3R-Mediated Mitochondria-ER Contact

Although the interplay between mitochondria and ER has been identified as a crucial regulator of cellular homeostasis, the pathogenic impact of alterations in mitochondria-ER contact sites (MERCS) during myocardial postischemic reperfusion (I/R) injury remains incompletely understood. Therefore, in our study, we explored the beneficial role played by melatonin in protecting cardiomyocytes against reperfusion injury via stabilizing mitochondria-ER interaction. In vitro exposure of H9C2 rat cardiomyocytes to hypoxia/reoxygenation (H/R) augmented mitochondrial ROS synthesis, suppressed both mitochondrial potential and ATP generation, and increased the mitochondrial permeability transition pore (mPTP) opening rate. Furthermore, H/R exposure upregulated the protein content of CHOP and caspase-12, two markers of ER stress, and enhanced the transcription of main MERCS tethering proteins, namely, Fis1, BAP31, Mfn2, and IP3R. Interestingly, all the above changes could be attenuated or reversed by melatonin treatment. Suggesting that melatonin-induced cardioprotection works through normalization of mitochondria-ER interaction, overexpression of IP3R abolished the protective actions offered by melatonin on mitochondria-ER fitness. These results expand our knowledge on the cardioprotective actions of melatonin during myocardial postischemic reperfusion damage and suggest that novel, more effective treatments for acute myocardial reperfusion injury might be achieved through modulation of mitochondria-ER interaction in cardiac cells.

Overexpression of SERCA2a Alleviates Cardiac Microvascular Ischemic Injury by Suppressing Mfn2-Mediated ER/Mitochondrial Calcium Tethering

Our previous research has shown that type-2a Sarco/endoplasmic reticulum Ca²⁺-ATPase (SERCA2a) undergoes posttranscriptional oxidative modifications in cardiac microvascular endothelial cells (CMECs) in the context of excessive cardiac oxidative injury. However, whether SERCA2a inactivity induces cytosolic Ca²⁺ imbalance in mitochondrial homeostasis is far from clear. Mitofusin2 (Mfn2) is well known as an important protein involved in endoplasmic reticulum (ER)/mitochondrial Ca²⁺ tethering and the regulation of mitochondrial quality. Therefore, the aim of our study was to elucidate the specific mechanism of SERCA2a-mediated Ca²⁺ overload in the mitochondria via Mfn2 tethering and the survival rate of the heart under conditions of cardiac microvascular ischemic injury. In vitro, CMECs extracted from mice were subjected to 6 h of hypoxic injury to mimic ischemic heart injury. C57-WT and Mfn2^KO mice were subjected to a 1 h ischemia procedure via ligation of the left anterior descending branch to establish an in vivo cardiac ischemic injury model. TTC staining, immunohistochemistry and echocardiography were used to assess the myocardial infarct size, microvascular damage, and heart function. In vitro, ischemic injury induced irreversible oxidative modification of SERCA2a, including sulfonylation at cysteine 674 and nitration at tyrosine 294/295, and inactivation of SERCA2a, which initiated calcium overload. In addition, ischemic injury-triggered [Ca²⁺]c overload and subsequent [Ca²⁺]m overload led to mPTP opening and ΔΨm dissipation compared with the control. Furthermore, ablation of Mfn2 alleviated SERCA2a-induced mitochondrial calcium overload and subsequent mito-apoptosis in the context of CMEC hypoxic injury. In vivo, compared with that in wild-type mice, the myocardial infarct size in Mfn2^KO mice was significantly decreased. In addition, the findings revealed that Mfn2^KO mice had better heart contractile function, decreased myocardial infarction indicators, and improved mitochondrial morphology. Taken together, the results of our study suggested that SERCA2a-dependent [Ca²⁺]c overload led to mitochondrial dysfunction and activation of Mfn2-mediated [Ca²⁺]m overload. Overexpression of SERCA2a or ablation of Mfn2 expression mitigated mitochondrial morphological and functional damage by modifying the SERCA2a/Ca²⁺-Mfn2 pathway. Overall, these pathways are promising therapeutic targets for acute cardiac microvascular ischemic injury.

Hot and Cold Tumors: Is Endoglin (CD105) a Potential Target for Vessel Normalization?

Tumors are complex masses formed by malignant but also by normal cells. The interaction between these cells via cytokines, chemokines, growth factors, and enzymes that remodel the extracellular matrix (ECM) constitutes the tumor microenvironment (TME). This TME can be determinant in the prognosis and the response to some treatments such as immunotherapy. Depending on their TME, two types of tumors can be defined: hot tumors, characterized by an immunosupportive TME and a good response to immunotherapy; and cold tumors, which respond poorly to this therapy and are characterized by an immunosuppressive TME. A therapeutic strategy that has been shown to be useful for the conversion of cold tumors into hot tumors is vascular normalization. In this review we propose that endoglin (CD105) may be a useful target of this strategy since it is involved in the three main processes involved in the generation of the TME: angiogenesis, inflammation, and cancer-associated fibroblast (CAF) accumulation. Moreover, the analysis of endoglin expression in tumors, which is already used in the clinic to study the microvascular density and that is associated with worse prognosis, could be used to predict a patient's response to immunotherapy.

Vessel Enlargement in Development and Pathophysiology

From developmental stages until adulthood, the circulatory system remodels in response to changes in blood flow in order to maintain vascular homeostasis. Remodeling processes can be driven by de novo formation of vessels or angiogenesis, and by the restructuration of already existing vessels, such as vessel enlargement and regression. Notably, vessel enlargement can occur as fast as in few hours in response to changes in flow and pressure. The high plasticity and responsiveness of blood vessels rely on endothelial cells. Changes within the bloodstream, such as increasing shear stress in a narrowing vessel or lowering blood flow in redundant vessels, are sensed by endothelial cells and activate downstream signaling cascades, promoting behavioral changes in the involved cells. This way, endothelial cells can reorganize themselves to restore normal circulation levels within the vessel. However, the dysregulation of such processes can entail severe pathological circumstances with disturbances affecting diverse organs, such as human hereditary telangiectasias. There are different pathways through which endothelial cells react to promote vessel enlargement and mechanisms may differ depending on whether remodeling occurs in the adult or in developmental models. Understanding the molecular mechanisms involved in the fast-adapting processes governing vessel enlargement can open the door to a new set of therapeutical approaches to be applied in occlusive vascular diseases. Therefore, we have outlined here the latest advances in the study of vessel enlargement in physiology and pathology, with a special insight in the pathways involved in its regulation.

Coronary Endothelium No-Reflow Injury Is Associated with ROS-Modified Mitochondrial Fission through the JNK-Drp1 Signaling Pathway

Coronary artery no-reflow is a complex problem in the area of reperfusion therapy, and the molecular mechanisms underlying coronary artery no-reflow injury have not been fully elucidated. In the present study, we explored whether oxidative stress caused damage to coronary endothelial cells by inducing mitochondrial fission and activating the JNK pathway. The hypoxia/reoxygenation (H/R) model was induced in vitro to mimic coronary endothelial no-reflow injury, and mitochondrial fission, mitochondrial function, and endothelial cell viability were analyzed using western blotting, quantitative polymerase chain reaction (qPCR), enzyme-linked immunosorbent assay (ELISA), and immunofluorescence. Our data indicated that reactive oxygen species (ROS) were significantly induced upon H/R injury, and this was followed by decreased endothelial cell viability. Mitochondrial fission was induced and mitochondrial bioenergetics were impaired in cardiac endothelial cells after H/R injury. Neutralization of ROS reduced mitochondrial fission and protected mitochondrial function against H/R injury. Our results also demonstrated that ROS stimulated mitochondrial fission via JNK-mediated Drp1 phosphorylation. These findings indicate that the ROS-JNK-Drp1 signaling pathway may be one of the molecular mechanisms underlying endothelial cell damage during H/R injury. Novel treatments for coronary no-reflow injury may involve targeting mitochondrial fission and the JNK-Drp1 signaling pathway.

Dynamic changes in endoglin expression in the developing mouse heart

Endoglin (ENG) is essential for cardiovascular development and is expressed in the heart from its earliest developmental stages. ENG expression has been reported in the cardiac crescent, endocardium, valve mesenchyme and coronary vascular endothelial cells. However, its expression in these cell types is non-uniform and the dynamic changes in ENG expression during heart development have not been systematically studied. Using immunofluorescent staining we tracked ENG protein expression in mouse embryonic hearts aged from 11.5 to 17.5 days, and in postnatal and adult hearts. ENG is expressed in the endocardium and in venous endothelial cells throughout these developmental stages. ENG protein is down-regulated by approximately two-fold as a subset of early coronary veins reprogram to form arteries within the developing myocardium from E13.5. This two-fold higher ratio of ENG protein in veins versus arteries is maintained throughout cardiac development and in the adult heart. ENG is also down-regulated two-fold following mesenchymal transition of endocardial cells to form cardiac valve mesenchyme, whilst expression of the pan-endothelial marker CD31 is completely lost. A subset of epicardial cells (which do not express ENG protein) delaminate and undergo a similar mesenchymal transition to form epicardially derived cells (EPDCs). This transient intra-myocardial mesenchymal cell population expresses low levels of ENG protein, similar to valve mesenchyme. In conclusion, ENG shows dynamic changes of expression in vascular endothelial cells, endocardial cells and mesenchymal cells in the developing heart that vary according to cardiovascular cell type.

Endothelial sprouting, proliferation, or senescence: tipping the balance from physiology to pathology

Therapeutic modulation of vascular cell proliferation and migration is essential for the effective inhibition of angiogenesis in cancer or its induction in cardiovascular disease. The general view is that an increase in vascular growth factor levels or mitogenic stimulation is beneficial for angiogenesis, since it leads to an increase in both endothelial proliferation and sprouting. However, several recent studies showed that an increase in mitogenic stimuli can also lead to the arrest of angiogenesis. This is due to the existence of intrinsic signaling feedback loops and cell cycle checkpoints that work in synchrony to maintain a balance between endothelial proliferation and sprouting. This balance is tightly and effectively regulated during tissue growth and is often deregulated or impaired in disease. Most therapeutic strategies used so far to promote vascular growth simply increase mitogenic stimuli, without taking into account its deleterious effects on this balance and on vascular cells. Here, we review the main findings on the mechanisms controlling physiological vascular sprouting, proliferation, and senescence and how those mechanisms are often deregulated in acquired or congenital cardiovascular disease leading to a diverse range of pathologies. We also discuss alternative approaches to increase the effectiveness of pro-angiogenic therapies in cardiovascular regenerative medicine.