Overexpressed or hyperactivated Rac1 as a target to treat hepatocellular carcinoma.

Despite novel targeted and immunotherapies, the prognosis remains bleak for patients with hepatocellular carcinoma (HCC), especially for advanced and/or metastatic forms. The rapid emergence of drug resistance is a major obstacle in the success of chemo-, targeted-, immuno-therapies of HCC. Novel targets are needed. The prominent roles of the small GTPase Rac1 in the development and progression of HCC are discussed here, together with its multiple protein partners, and the targeting of Rac1 with RNA-based regulators and small molecules. We discuss the oncogenic functions of Rac1 in HCC, including the contribution of Rac1 mutants and isoform Rac1b. Rac1 is a ubiquitous target, but the protein is frequently overexpressed and hyperactivated in HCC. It contributes to the aggressivity of the disease, with key roles in cancer cell proliferation, tumor metastasis and resistance to treatment. Small molecule targeting Rac1, indirectly or directly, have shown anticancer effects in HCC experimental models. Rac1-binding agents such as EHT 1864 and analogues offer novel opportunities to combat HCC. We discuss the different modalities to repress Rac1 overactivation in HCC with small molecules and the combination with reference drugs to promote cancer cell death and to repress cell invasion. We highlight the necessity to combine Rac1-targeted approach with appropriate biomarkers to select Rac1 activated tumors. Our analysis underlines the prominent oncogenic functions of Rac1 in HCC and discuss the modalities to target this small GTPase. Rac1 shall be considered as a valid target to limit the acquired and intrinsic resistance of HCC tumors and their metastatic potential.

Essential role of smooth muscle Rac1 in severe asthma-associated airway remodelling.

BACKGROUND: Severe asthma is a chronic lung disease characterised by inflammation, airway hyperresponsiveness (AHR) and airway remodelling. The molecular mechanisms underlying uncontrolled airway smooth muscle cell (aSMC) proliferation involved in pulmonary remodelling are still largely unknown. Small G proteins of the Rho family (RhoA, Rac1 and Cdc42) are key regulators of smooth muscle functions and we recently demonstrated that Rac1 is activated in aSMC from allergic mice. The objective of this study was to assess the role of Rac1 in severe asthma-associated airway remodelling. METHODS AND RESULTS: Immunofluorescence analysis in human bronchial biopsies revealed an increased Rac1 activity in aSMC from patients with severe asthma compared with control subjects. Inhibition of Rac1 by EHT1864 showed that Rac1 signalling controlled human aSMC proliferation induced by mitogenic stimuli through the signal transducer and activator of transcription 3 (STAT3) signalling pathway. In vivo, specific deletion of Rac1 in SMC or pharmacological inhibition of Rac1 by nebulisation of NSC23766 prevented AHR and aSMC hyperplasia in a mouse model of severe asthma. Moreover, the Rac1 inhibitor prevented goblet cell hyperplasia and epithelial cell hypertrophy whereas treatment with corticosteroids had less effect. Nebulisation of NSC23766 also decreased eosinophil accumulation in the bronchoalveolar lavage of asthmatic mice. CONCLUSION: This study demonstrates that Rac1 is overactive in the airways of patients with severe asthma and is essential for aSMC proliferation. It also provides evidence that Rac1 is causally involved in AHR and airway remodelling. Rac1 may represent as an interesting target for treating both AHR and airway remodelling of patients with severe asthma.

Small G proteins in the cardiovascular system: physiological and pathological aspects.

Small G proteins exist in eukaryotes from yeast to human and constitute the Ras superfamily comprising more than 100 members. This superfamily is structurally classified into five families: the Ras, Rho, Rab, Arf, and Ran families that control a wide variety of cell and biological functions through highly coordinated regulation processes. Increasing evidence has accumulated to identify small G proteins and their regulators as key players of the cardiovascular physiology that control a large panel of cardiac (heart rhythm, contraction, hypertrophy) and vascular functions (angiogenesis, vascular permeability, vasoconstriction). Indeed, basal Ras protein activity is required for homeostatic functions in physiological conditions, but sustained overactivation of Ras proteins or spatiotemporal dysregulation of Ras signaling pathways has pathological consequences in the cardiovascular system. The primary object of this review is to provide a comprehensive overview of the current progress in our understanding of the role of small G proteins and their regulators in cardiovascular physiology and pathologies.

RRAD mutation causes electrical and cytoskeletal defects in cardiomyocytes derived from a familial case of Brugada syndrome.

AIMS: The Brugada syndrome (BrS) is an inherited cardiac disorder predisposing to ventricular arrhythmias. Despite considerable efforts, its genetic basis and cellular mechanisms remain largely unknown. The objective of this study was to identify a new susceptibility gene for BrS through familial investigation. METHODS AND RESULTS: Whole-exome sequencing performed in a three-generation pedigree with five affected members allowed the identification of one rare non-synonymous substitution (p.R211H) in RRAD, the gene encoding the RAD GTPase, carried by all affected members of the family. Three additional rare missense variants were found in 3/186 unrelated index cases. We detected higher levels of RRAD transcripts in subepicardium than in subendocardium in human heart, and in the right ventricle outflow tract compared to the other cardiac compartments in mice. The p.R211H variant was then subjected to electrophysiological and structural investigations in human cardiomyocytes derived from induced pluripotent stem cells (iPSC-CMs). Cardiomyocytes derived from induced pluripotent stem cells from two affected family members exhibited reduced action potential upstroke velocity, prolonged action potentials and increased incidence of early afterdepolarizations, with decreased Na+ peak current amplitude and increased Na+ persistent current amplitude, as well as abnormal distribution of actin and less focal adhesions, compared with intra-familial control iPSC-CMs Insertion of p.R211H-RRAD variant in control iPSCs by genome editing confirmed these results. In addition, iPSC-CMs from affected patients exhibited a decreased L-type Ca2+ current amplitude. CONCLUSION: This study identified a potential new BrS-susceptibility gene, RRAD. Cardiomyocytes derived from induced pluripotent stem cells expressing RRAD variant recapitulated single-cell electrophysiological features of BrS, including altered Na+ current, as well as cytoskeleton disturbances.

Synthesis and biological evaluation of 3-amino-, 3-alkoxy- and 3-aryloxy-6-(hetero)arylpyridazines as potent antitumor agents.

Various 3-amino-, 3-aryloxy- and alkoxy-6-arylpyridazines have been synthesized by an electrochemical reductive cross-coupling between 3-amino-, 3-aryloxy- or 3-alkoxy-6-chloropyridazines and aryl or heteroaryl halides. In vitro antiproliferative activity of these products was evaluated against a representative panel of cancer cell lines (HuH7, CaCo-2, MDA-MB-231, HCT116, PC3, NCI-H727, HaCaT) and oncogenicity prevention of the more efficient derivatives was highlighted on human breast cancer cell line MDA-MB 468-Luc prior establishing their interaction with p44/42 and Akt-dependent signaling pathways.

Targeting of Rac1 prevents bronchoconstriction and airway hyperresponsiveness.

BACKGROUND: The molecular mechanisms responsible for airway smooth muscle cells' (aSMCs) contraction and proliferation in airway hyperresponsiveness (AHR) associated with asthma are still largely unknown. The small GTPases of the Rho family (RhoA, Rac1, and Cdc42) play a central role in SMC functions including migration, proliferation, and contraction. OBJECTIVE: The objective of this study was to identify the role of Rac1 in aSMC contraction and to investigate its involvement in AHR associated with allergic asthma. METHODS: To define the role of Rac1 in aSMC, ex and in vitro analyses of bronchial reactivity were performed on bronchi from smooth muscle (SM)-specific Rac1 knockout mice and human individuals. In addition, this murine model was exposed to allergens (ovalbumin or house dust mite extract) to decipher in vivo the implication of Rac1 in AHR. RESULTS: The specific SMC deletion or pharmacological inhibition of Rac1 in mice prevented the bronchoconstrictor response to methacholine. In human bronchi, a similar role of Rac1 was observed during bronchoconstriction. We further demonstrated that Rac1 activation is responsible for bronchoconstrictor-induced increase in intracellular Ca2+ concentration and contraction both in murine and in human bronchial aSMCs, through its association with phospholipase C ß2 and the stimulation of inositol 1,4,5-trisphosphate production. In vivo, Rac1 deletion in SMCs or pharmacological Rac1 inhibition by nebulization of NSC23766 prevented AHR in murine models of allergic asthma. Moreover, nebulization of NSC23766 decreased eosinophil and neutrophil populations in bronchoalveolar lavages from mice with asthma. CONCLUSIONS: Our data reveal an unexpected and essential role of Rac1 in the regulation of intracellular Ca2+ and contraction of aSMCs, and the development of AHR. Rac1 thus appears as an attractive therapeutic target in asthma, with a combined beneficial action on both bronchoconstriction and pulmonary inflammation.

Benefit of Mineralocorticoid Receptor Antagonism in AKI: Role of Vascular Smooth Muscle Rac1.

AKI is a frequent complication in hospitalized patients. Unfortunately, there is no effective pharmacologic approach for treating or preventing AKI. In rodents, mineralocorticoid receptor (MR) antagonism prevents AKI induced by ischemia-reperfusion (IR). We investigated the specific role of vascular MR in mediating AKI induced by IR. We also assessed the protective effect of MR antagonism in IR-induced AKI in the Large White pig, a model of human AKI. In mice, MR deficiency in smooth muscle cells (SMCs) protected against kidney IR injury. MR blockade by the novel nonsteroidal MR antagonist, finerenone, or genetic deletion of MR in SMCs associated with weaker oxidative stress production. Moreover, ischemic kidneys had higher levels of Rac1-GTP, required for NADPH oxidase activation, than sham control kidneys, and genetic deletion of Rac1 in SMCs protected against AKI. Furthermore, genetic deletion of MR in SMCs blunted the production of Rac1-GTP after IR. Pharmacologic inhibition of MR also prevented AKI induced by IR in the Large White pig. Altogether, we show that MR antagonism, or deletion of the MR gene in SMCs, limited the renal injury induced by IR through effects on Rac1-mediated MR signaling. The benefits of MR antagonism in the pig provide a rational basis for future clinical trials assessing the benefits of this approach in patients with IR-mediated AKI.

Mesenchymal Stem Cells Induce Suppressive Macrophages Through Phagocytosis in a Mouse Model of Asthma.

Mesenchymal stem cell (MSC) immunosuppressive functions make them attractive candidates for anti-inflammatory therapy in allergic asthma. However, the mechanisms by which they ensure therapeutic effects remain to be elucidated. In an acute mouse model of house dust mite (Der f)-induced asthma, one i.v. MSC injection was sufficient to normalize and stabilize lung function in Der f-sensitized mice as compared to control mice. MSC injection decreased in vivo airway responsiveness and decreased ex vivo carbachol-induced bronchial contraction, maintaining bronchial expression of the inhibitory type 2 muscarinic receptor. To evaluate in vivo MSC survival, MSCs were labeled with PKH26 fluorescent marker prior to i.v. injection, and 1 to 10 days later total lungs were digested to obtain single-cell suspensions. 91.5 ± 2.3% and 86.6 ± 6.3% of the recovered PKH26(+) lung cells expressed specific macrophage markers in control and Der f mice, respectively, suggesting that macrophages had phagocyted in vivo the injected MSCs. Interestingly, only PKH26(+) macrophages expressed M2 phenotype, while the innate PKH26(-) macrophages expressed M1 phenotype. Finally, the remaining 0.5% PKH26(+) MSCs expressed 10- to 100-fold more COX-2 than before injection, suggesting in vivo MSC phenotype modification. Together, the results of this study indicate that MSCs attenuate asthma by being phagocyted by lung macrophages, which in turn acquire a M2 suppressive phenotype. Stem Cells 2016;34:1836-1845.

Coronin 1A promotes a cytoskeletal-based feedback loop that facilitates Rac1 translocation and activation.

The activation of the Rac1 GTPase during cell signalling entails its translocation from the cytosol to membranes, release from sequestering Rho GDP dissociation inhibitors (RhoGDI), and GDP/GTP exchange. In addition to those steps, we show here that optimal Rac1 activation during cell signalling requires the engagement of a downstream, cytoskeletal-based feedback loop nucleated around the cytoskeletal protein coronin 1A and the Rac1 exchange factor ArhGEF7. These two proteins form a cytosolic complex that, upon Rac1-driven F-actin polymerization, translocates to juxtamembrane areas where it expands the pool of activated, membrane-bound Rac1. Such activity requires the formation of an F-actin/ArhGEF7-dependent physical complex of coronin 1A with Pak1 and RhoGDIα that, once assembled, promotes the Pak1-dependent dissociation of Rac1 from the Rac1/RhoGDIα complex and subsequent Rac1 activation. Genetic evidence demonstrates that this relay circuit is essential for generating sustained Rac1 activation levels during cell signalling.

Constitutive activation of B-Raf in the mouse germ line provides a model for human cardio-facio-cutaneous syndrome.

RASopathies are a class of developmental syndromes that result from congenital mutations in key elements of the RAS/RAF/MEK signaling pathway. A well-recognized RASopathy is the cardio-facio-cutaneous (CFC) syndrome characterized by a distinctive facial appearance, heart defects, and mental retardation. Clinically diagnosed CFC patients carry germ-line mutations in four different genes, B-RAF, MEK1, MEK2, and K-RAS. B-RAF is by far the most commonly mutated locus, displaying mutations that most often result in constitutive activation of the B-RAF kinase. Here, we describe a mouse model for CFC generated by germ-line expression of a B-RafLSLV600E allele. This targeted allele allows low levels of expression of B-RafV600E, a constitutively active B-Raf kinase first identified in human melanoma. B-Raf+/LSLV600E mice are viable and display several of the characteristic features observed in CFC patients, including reduced life span, small size, facial dysmorphism, cardiomegaly, and epileptic seizures. These mice also show up-regulation of specific catecholamines and cataracts, two features detected in a low percentage of CFC patients. In addition, B-Raf+/LSLV600E mice develop neuroendocrine tumors, a pathology not observed in CFC patients. These mice may provide a means of better understanding the pathophysiology of at least some of the clinical features present in CFC patients. Moreover, they may serve as a tool to evaluate the potential therapeutic efficacy of B-RAF inhibitors and establish the precise window at which they could be effective against this congenital syndrome.

Implication of Rac1 GTPase in molecular and cellular mitochondrial functions.

Rac1 is a member of the Rho GTPase family which plays major roles in cell mobility, polarity and migration, as a fundamental regulator of actin cytoskeleton. Signal transduction by Rac1 occurs through interaction with multiple effector proteins, and its activity is regulated by guanine nucleotide exchange factors (GEFs) and GTPase-activating proteins (GAPs). The small protein is mainly anchored to the inner side of the plasma membrane but it can be found in endocellular compartments, notably endosomes and cell nuclei. The protein localizes also into mitochondria where it contributes to the regulation of mitochondrial dynamics, including both mitobiogenesis and mitophagy, in addition to signaling processes via different protein partners, such as the proapoptotic protein Bcl-2 and chaperone sigma-1 receptor (σ-1R). The mitochondrial form of Rac1 (mtRac1) has been understudied thus far, but it is as essential as the nuclear or plasma membrane forms, via its implication in regulation of oxidative stress and DNA damages. Rac1 is subject to diverse post-translational modifications, notably to a geranylgeranylation which contributes importantly to its mitochondrial import and its anchorage to mitochondrial membranes. In addition, Rac1 contributes to the mitochondrial translocation of other proteins, such as p53. The mitochondrial localization and functions of Rac1 are discussed here, notably in the context of human diseases such as cancers. Inhibitors of Rac1 have been identified (NSC-23766, EHT-1864) and some are being developed for the treatment of cancer (MBQ-167) or central nervous system diseases (JK-50561). Their effects on mtRac1 warrant further investigations. An overview of mtRac1 is provided here.

Vav3 proto-oncogene deficiency leads to sympathetic hyperactivity and cardiovascular dysfunction.

Although much is known about environmental factors that predispose individuals to hypertension and cardiovascular disease, little information is available regarding the genetic and signaling events involved. Indeed, few genes associated with the progression of these pathologies have been discovered despite intensive research in animal models and human populations. Here we identify Vav3, a GDP-GTP exchange factor that stimulates Rho and Rac GTPases, as an essential factor regulating the homeostasis of the cardiovascular system. Vav3-deficient mice exhibited tachycardia, systemic arterial hypertension and extensive cardiovascular remodeling. These mice also showed hyperactivity of sympathetic neurons from the time of birth. The high catecholamine levels associated with this condition led to the activation of the renin-angiotensin system, increased levels of kidney-related hormones and the progressive loss of cardiovascular and renal homeostasis. Pharmacological studies with drugs targeting sympathetic and renin-angiotensin responses confirmed the causative role and hierarchy of these events in the development of the Vav3-null mouse phenotype. These observations uncover the crucial role of Vav3 in the regulation of the sympathetic nervous system (SNS) and cardiovascular physiology, and reveal a signaling pathway that could be involved in the pathophysiology of human disease states involving tachycardia and sympathetic hyperactivity with unknown etiologies.

Allergic Sensitization Driving Immune Phenotyping and Disease Severity in a Mouse Model of Asthma.

PURPOSE: Asthma is a frequent chronic inflammatory bronchial disease affecting more than 300 million patients worldwide, 70% of whom are secondary to allergy. The diversity of asthmatic endotypes contributes to their complexity. The inter-relationship between allergen and other exposure and the airway microbiome adds to the phenotypic diversity and defines the natural course of asthma. Here, we compared the mouse models of house dust mite (HDM)-induced allergic asthma. Allergic sensitization was performed via various routes and associated with outcomes. METHODS: Mice were sensitized with HDM via the oral, nasal or percutaneous routes. Lung function, barrier integrity, immune response and microbiota composition were analyzed. RESULTS: Severe impairment of respiratory function was observed in the mice sensitized by the nasal and cutaneous paths. It was associated with epithelial dysfunction characterized by an increased permeability secondary to junction protein disruption. Such sensitization paths induced a mixed eosinophilic and neutrophilic inflammatory response with high interleukin (IL)-17 airway secretion. In contrast, orally sensitized mice showed a mild impairment of respiratory function. Epithelial dysfunction was mild with increased mucus production, but preserved epithelial junctions. Regarding lung microbiota, sensitization provoked a significant loss of diversity. At the genus level, Cutibacterium, Acinetobacter, Streptococcus and Lactobacillus were found to be modulated according to the sensitization pathway. An increase in theanti-inflammatory microbiota metabolites was observed in the oral-sensitization group. CONCLUSIONS: Our study highlights the strong impact of the sensitization route on the pathophysiology and the critical phenotypic diversity of allergic asthma in a mouse model.

Transcriptional factor aryl hydrocarbon receptor (Ahr) controls cardiovascular and respiratory functions by regulating the expression of the Vav3 proto-oncogene.

Aryl hydrocarbon receptor (Ahr) is a transcriptional factor involved in detoxification responses to pollutants and in intrinsic biological processes of multicellular organisms. We recently described that Vav3, an activator of Rho/Rac GTPases, is an Ahr transcriptional target in embryonic fibroblasts. These results prompted us to compare the Ahr(-/-) and Vav3(-/-) mouse phenotypes to investigate the implications of this functional interaction in vivo. Here, we show that Ahr is important for Vav3 expression in kidney, lung, heart, liver, and brainstem regions. This process is not affected by the administration of potent Ahr ligands such as benzo[a]pyrene. We also report that Ahr- and Vav3-deficient mice display hypertension, tachypnea, and sympathoexcitation. The Ahr gene deficiency also induces the GABAergic transmission defects present in the Vav3(-/-) ventrolateral medulla, a main cardiorespiratory brainstem center. However, Ahr(-/-) mice, unlike Vav3-deficient animals, display additional defects in fertility, perinatal growth, liver size and function, closure, spleen size, and peripheral lymphocytes. These results demonstrate that Vav3 is a bona fide Ahr target that is in charge of a limited subset of the developmental and physiological functions controlled by this transcriptional factor. Our data also reveal the presence of sympathoexcitation and new cardiorespiratory defects in Ahr(-/-) mice.

Expression of VAV1 in the tumour microenvironment of glioblastoma multiforme.

Even though much progress has been made towards understanding the molecular nature of glioma, the survival rates of patients affected by this tumour have not changed significantly over recent years. Better knowledge of this malignancy is still needed in order to predict its outcome and improve patient treatment. VAV1 is an GDP/GTP exchange factor for Rho/Rac proteins with oncogenic potential that is involved in the regulation of cytoskeletal dynamics and cell migration. Here we report its overexpression in 59 patients diagnosed with high-grade glioma, and the associated upregulation of a number of genes coding for proteins also involved in cell invasion- and migration-related processes. Unexpectedly, immunohistochemical experiments revealed that VAV1 is not expressed in glioma cells. Instead, VAV1 is found in non-tumoural astrocyte-like cells that are located either peritumouraly or perivascularly. We propose that the expression of VAV1 is linked to synergistic signalling cross-talk between cancer and infiltrating cells. Interestingly, we show that the pattern of expression of VAV1 could have a role in the neoplastic process in glioblastoma tumours.

Rac1 as a Target to Treat Dysfunctions and Cancer of the Bladder.

Bladder pathologies, very common in the aged population, have a considerable negative impact on quality of life. Novel targets are needed to design drugs and combinations to treat diseases such as overactive bladder and bladder cancers. A promising new target is the ubiquitous Rho GTPase Rac1, frequently dysregulated and overexpressed in bladder pathologies. We have analyzed the roles of Rac1 in different bladder pathologies, including bacterial infections, diabetes-induced bladder dysfunctions and bladder cancers. The contribution of the Rac1 protein to tumorigenesis, tumor progression, epithelial-mesenchymal transition of bladder cancer cells and their metastasis has been analyzed. Small molecules selectively targeting Rac1 have been discovered or designed, and two of them-NSC23766 and EHT 1864-have revealed activities against bladder cancer. Their mode of interaction with Rac1, at the GTP binding site or the guanine nucleotide exchange factors (GEF) interaction site, is discussed. Our analysis underlines the possibility of targeting Rac1 with small molecules with the objective to combat bladder dysfunctions and to reduce lower urinary tract symptoms. Finally, the interest of a Rac1 inhibitor to treat advanced chemoresistance prostate cancer, while reducing the risk of associated bladder dysfunction, is discussed. There is hope for a better management of bladder pathologies via Rac1-targeted approaches.

Rac1 as a therapeutic anticancer target: Promises and limitations.

Small molecule inhibitors of GTPases are increasingly considered for the treatment of multiple human pathologies. The GTPase Rac1 (Ras-related C3 botulinum toxin substrate 1) plays major roles in vital cellular processes, notably in the control cell motility and dynamic, the regulation of oxidative stress, and in inflammatory and immune surveillance. As such, Rac1 is viewed as a potential target to combat cancers but also diverse inflammatory, metabolic, neurodegenerative, respiratory, cardiovascular, viral, and parasitic diseases. Potent and selective Rac1 inhibitors have been identified and designed, such as compounds GYS32661 and MBQ-167 both in preclinical development for the treatment of advanced solid tumors. The pleiotropic roles and ubiquitous expression of the protein can be viewed as limitations for anticancer approaches. However, the frequent overexpression and/or hyperactivation of the Rac1 in difficult-to-treat chemoresistant cancers, make Rac1 an attractive target in oncology. The key roles of Rac1 in multiple cellular pathways, together with its major implications in carcinogenesis, tumor proliferation and metastasis, support the development of small molecule inhibitors. The challenge is high and the difficulty shall not be underestimated, but the target is innovative and promising in combination with chemo- and/or immuno-therapy. Opportunities and challenges associated with the targeting of Rac1 are discussed.

Smooth muscle Rac1 contributes to pulmonary hypertension.

BACKGROUND AND PURPOSE: Pulmonary hypertension (PH) is a multifactorial chronic disease characterized by an increase in pulmonary artery (PA) resistance leading to right ventricle (RV) failure. Endothelial dysfunction and alteration of NO/cGMP signalling in PA plays a major role in PH. We recently described the involvement of the Rho protein Rac1 in the control of systemic blood pressure through its involvement in NO-mediated relaxation of arterial smooth muscle cell (SMC). The aim of this study was to analyse the role of SMC Rac1 in PH. EXPERIMENTAL APPROACH: PH is induced by exposure of control and SMC Rac1-deficient (SM-Rac1-KO) mice to chronic hypoxia (10% O2 , 4 weeks). PH is assessed by the measurement of RV systolic pressure and hypertrophy. PA reactivity is analysed by isometric tension measurements. PA remodelling is quantified by immunofluorescence in lung sections and ROS are detected using the dihydroethidium probe and electronic paramagnetic resonance analysis. Rac1 activity is determined by immunofluorescence. KEY RESULTS: Rac1 activation in PA of hypoxic mice and patients with idiopathic PH. Hypoxia-induced rise in RV systolic pressure, RV hypertrophy and loss of endothelium-dependent relaxation were significantly decreased in SM-Rac1-KO mice compared to control mice. SMC Rac1 deletion also limited hypoxia-induced PA remodelling and ROS production in pulmonary artery smooth muscle cells (PASMCs). CONCLUSION AND IMPLICATIONS: Our results provide evidence for a protective effect of SM Rac1 deletion against hypoxic PH. Rac1 activity in PASMCs plays a causal role in PH by favouring ROS-dependent PA remodelling and endothelial dysfunction induced by chronic hypoxia.

Bronchial smooth muscle cell in asthma: where does it fit?

Asthma is a frequent respiratory condition whose pathophysiology relies on altered interactions between bronchial epithelium, smooth muscle cells (SMC) and immune responses. Those leads to classical hallmarks of asthma: airway hyper-responsiveness, bronchial remodelling and chronic inflammation. Airway smooth muscle biology and pathophysiological implication in asthma are now better understood. Precise deciphering of intracellular signalling pathways regulating smooth muscle contraction highlighted the critical roles played by small GTPases of Rho superfamily. Beyond contractile considerations, active involvement of airway smooth muscle in bronchial remodelling mechanisms is now established. Not only cytokines and growth factors, such as fibroblats growth factor or transforming growth factor-ß, but also extracellular matrix composition have been demonstrated as potent phenotype modifiers for airway SMC. Although basic science knowledge has grown significantly, little of it has translated into improvement in asthma clinical practice. Evaluation of airway smooth muscle function is still limited to its contractile activity. Moreover, it relies on tools, such as spirometry, that give only an overall assessment and not a specific one. Interesting technics such as forced oscillometry or specific imagery (CT and MRI) give new perspectives to evaluate other aspects of airway muscle such as bronchial remodelling. Finally, except for the refinement of conventional bronchodilators, no new drug therapy directly targeting airway smooth muscle proved its efficacy. Bronchial thermoplasty is an innovative and efficient therapeutic strategy but is only restricted to a small proportion of severe asthmatic patients. New diagnostic and therapeutic strategies specifically oriented toward airway smooth muscle are needed to improve global asthma care.

The Endothelial Dysfunction Could Be a Cause of Heart Failure with Preserved Ejection Fraction Development in a Rat Model.

50% of patients with heart failure have a preserved ejection fraction (HFpEF). Numerous studies have investigated the pathophysiological mechanisms of HFpEF and have shown that endothelial dysfunction plays an important role in HFpEF. Yet no studies answered whether endothelial dysfunction could be the cause or is the consequence of HFpEF. Recently, we have shown that the endothelial overexpression of human ß 3-adrenoreceptor (Tgß 3) in rats leads to the slow development of diastolic dysfunction over ageing. The aim of the study is to decipher the involvement of endothelial dysfunction in the HFpEF development. For that, we investigated endothelial and cardiac function in 15-, 30-, and 45-week-old wild-type (WT) and Tgß 3 rats. The aortic expression of • NO synthase (NOS) isoforms was evaluated by Western blot. Finally, electron paramagnetic resonance measurements were performed on aortas to evaluate • NO and O2 •- production. Vascular reactivity was altered as early as 15 weeks of age in response to isoproterenol in Tgß 3 aortas and mesenteric arteries. NOS1 (neuronal NOS) expression was higher in the Tgß 3 aorta at 30 and 45 weeks of age (30 weeks: WT: 1.00 ± 0.21; Tgß 3: 6.08 ± 2.30; 45 weeks: WT: 1.00 ± 0.12; Tgß 3: 1.55 ± 0.17; p < 0.05). Interestingly, the endothelial NOS (NOS3) monomer form is increased in Tgß 3 rats at 45 weeks of age (ratio NOS3 dimer/NOS3 monomer; WT: 1.00 ± 0.37; Tgß 3: 0.13 ± 0.05; p < 0.05). Aortic •NO production was increased by NOS2 (inducible NOS) at 15 weeks of age in Tgß 3 rats (+52% vs. WT). Aortic O2 •- production was increased in Tgß 3 rats at 30 and 45 weeks of age (+75% and+76%, respectively, vs. WT, p < 0.05). We have shown that endothelial dysfunction and oxidative stress are present as early as 15 weeks of age and therefore conclude that endothelial dysfunction could be a cause of HFpEF development.