Orientadora: Profa. Dra.Marcela Sorelli Carneiro Ramos / Tese (doutorado) - Universidade Federal do ABC, Programa de Pós-Graduação em Biossistemas, 2015. / Recentemente, dados na literatura demonstram a estreita interacao patofisiologica existente entre os rins e o coracao. Conhecida como sindrome cardio-renal, essa patologia e capaz de promover hipertrofia e falencia cardiaca a partir de um quadro de lesao renal. Sabe-se que a lesao renal isquemica (LRI) promove a liberacao de diferentes citocinas inflamatorias que tem o coracao como tecido alvo e sao capazes de promover a instalacao do quadro hipertrofico, agindo, por exemplo, por meio de receptores semelhantes ao Toll (toll-like receptors - TLR). Alem de mediadores inflamatorios, trabalhos presentes na literatura ja comprovaram a direta relacao entre alteracoes no sistema renina-angiotensina (SRA) e nos niveis de Angiotensina II (Ang II) com o aumento da massa cardiaca. O presente estudo objetivou investigar o papel do SRA com a hipertrofia cardiaca (HC) induzida por um modelo experimental de LRI em camundongos tratados ou nao com bloqueadores do SRA, Losartan (Los) e Enalapril (Ena). O quadro de LRI foi induzido cirurgicamente atraves da oclusao do pediculo renal esquerdo por 60 minutos seguido de reperfusao. Apos 12, 15 ou 20 dias os tecidos foram removidos para a realizacao de analises macromorfometricas, moleculares e funcionais. Os principais resultados indicam que a cirurgia de isquemia renal e reperfusao foi capaz de gerar um quadro de falencia renal e induzir HC de maneira independente de aumento na pressao arterial. Ainda, no periodo analisado, observou-se aumento nos niveis sericos de TNF-¿¿ e Ang II, elevados niveis de expressao genica ou proteica de AT1, ECA-2, TLR-2, TLR-4 e NFk¿À, sugerindo relacao desses componentes com a HC. Os tratamentos com Los e Ena reverteram completamente a HC observada e aboliram o aumento na expressao cardiaca de TLRs, AT1R e ECA-2 e modularam diferencialmente os niveis sericos de Ang II e citocinas inflamatorias. Juntos, os dados sugerem um papel crucial do SRA na regulacao do quadro patologico neste modelo, atuando juntamente com o sistema imune inato na regulacao da patogenese da HC atraves da modulacao de seus principais componentes. / Recently published data demonstrate the close pathophysiological interaction between the kidneys and the heart. Known as cardio-renal syndrome, this pathology is capable of promoting hypertrophy and heart failure starting from renal injury. It is known that ischemic renal injury (IRI) promotes the release of various inflammatory cytokines that have the heart as a target tissue and are capable of promoting hypertrophy acting through the Toll-like receptors (TLR). In addition to inflammatory mediators, literature has extensively demonstrated the direct correlation between changes in the renin-angiotensin system (RAS) and the levels of angiotensin II (Ang II) within the increase in cardiac mass. This study aimed to investigate the role of the RAS with cardiac hypertrophy (CH) induced by an experimental model of IRI in mice treated or not with RAS blockers, Losartan (Los) and Enalapril (Ena). The IRI was surgically induced by occlusion of the left renal pedicle for 60 minutes followed by reperfusion. After 12, 15 or 20 days, tissues were removed and morphological, molecular, and functional analysis were performed. The leading results indicate that renal ischemia and reperfusion surgery was capable of generating renal failure which subsequently induced HC in a blood-pressure independent manner. Also, over this period, there was an increase in serum levels of TNF-á and Ang II, high levels of gene or protein expression of AT1, ACE-2, TLR-2, TLR-4 and NFkâ, suggesting a cross-talk within these components and CH development. Treatment with Los or Ena has completely reversed the CH and abolished the increase observed in cardiac expression of TLRs, NFkâ, ACE-2 and AT1R, and also differentially modulated Ang II and inflammatory cytokines serum levels. Together, the data suggest a critical role for RAS in the regulation of the pathological condition in this model, acting together with the innate immune system in the pathogenesis of CH through modulation of its main components.

Our objective was to determine whether chronic vagus nerve stimulation (VNS) mitigates pressure overload (PO)-induced remodeling of the cardioneural interface. Guinea pigs (n = 48) were randomized to right or left cervical vagus (RCV or LCV) implant. After 2 wk, chronic left ventricular PO was induced by partial (15–20%) aortic constriction. Of the 31 animals surviving PO induction, 10 were randomized to RCV VNS, 9 to LCV VNS, and 12 to sham VNS. VNS was delivered at 20 Hz and 1.14 ± 0.03 mA at a 22% duty cycle. VNS commenced 10 days after PO induction and was maintained for 40 days. Time-matched controls (n = 9) were evaluated concurrently. Echocardiograms were obtained before and 50 days after PO. At termination, intracellular current-clamp recordings of intrinsic cardiac (IC) neurons were studied in vitro to determine effects of therapy on soma characteristics. Ventricular cardiomyocyte sizes were assessed with histology along with immunoblot analysis of selected proteins in myocardial tissue extracts. In sham-treated animals, PO increased cardiac output (34%, P < 0.004), as well as systolic (114%, P < 0.04) and diastolic (49%, P < 0.002) left ventricular volumes, a hemodynamic response prevented by VNS. PO-induced enhancements of IC synaptic efficacy and muscarinic sensitivity of IC neurons were mitigated by chronic VNS. Increased myocyte size, which doubled in PO (P < 0.05), was mitigated by RCV. PO hypertrophic myocardium displayed decreased glycogen synthase (GS) protein levels and accumulation of the phosphorylated (inactive) form of GS. These PO-induced changes in GS were moderated by left VNS. Chronic VNS targets IC neurons accompanying PO to obtund associated adverse cardiomyocyte remodeling.

No description available.

The role of T-type calcium channels (TTCCs) in the heart is unclear. TTCCs are transiently expressed throughout the neonatal heart during a period of rapid cardiac development. A few weeks postnatally, TTCCs are no longer found in ventricular myocytes (VMs) and calcium influx via TTCCs (ICa,T) is only detected in the SA node and Purkinje system. However, pathologic cardiac stress is associated with re-expression of TTCCs in VMs. Whether ICa,T in this setting promotes cardiac growth or exacerbates cardiac function is a topic of debate. The focus of this thesis work was to examine the effect of TTCC re-expression in the normal and diseased myocardium. Our experiments were performed in a transgenic mouse model with inducible, cardiac-specific expression of α1G TTCCs. While both the α1G and α1H TTCC subtypes re-appear during cardiac disease, we specifically evaluated the effects of α1G TTCCs since mRNA levels of this TTCC subtype are markedly elevated during cardiac pathology. We found that transgenic mice with α1G overexpression had robust ICa,T with biophysical properties similar to those published in previous studies. α1G mice had a small increase in cardiac function and showed no evidence of cardiac histopathology or increased mortality. These findings were in contrast to the phenotype of transgenic mice with augmented L-type calcium channel (LTCC) activity secondary to overexpression of the β2a regulatory subunit. While the magnitude of calcium influx in α1G and β2a VMs was similar, we found that cardiac contractility of β2a mice was significantly greater than α1G mice. Also, β2a mice had significant cardiac fibrosis, myocyte death, and premature lethality compared to the benign phenotype of α1G mice. We showed that the phenotypic differences are likely related to the differential spatial localization of T- and LTCCs. Whereas α1G TTCCs were principally localized to the surface sarcolemma, LTCCs were primarily found in the transverse tubules in close proximity to the sites of sarcoplasmic reticulum calcium release. We evaluated the effect of TTCC expression during cardiac disease by inducing myocardial infarction (MI) in α1G mice. Acutely (1-week post MI), α1G mice showed similar worsening of cardiac function and mortality rates compared to control post-infarct mice. However, α1G hearts had smaller infarct sizes which correlated with increased Akt and NFAT activation in α1G than control hearts. After chronic heart failure, i.e. 7- weeks post-infarction, α1G hearts had significant hypertrophic response as determined by increased HW/BW ratio, myocyte cross-sectional area, as well as NFAT and Akt activity. Finally, α1G mice had a small survival benefit than control mice, which while statistically non-significant, suggests that TTCC re-expression does not exacerbate cardiac function as hypothesized by some investigators. We conclude that TTCCs play a minimal role in cardiac function and activate pro-survival signaling pathways in the myocardium. / Physiology

No description available.

Master of Science / Department of Human Nutrition / Denis M. Medeiros / Copper deficiency has been linked with many health problems, among them cardiac hypertrophy. Because of its potential for causing oxidative damage, copper within the cell must be bound to chaperone proteins. In this thesis, we examined the role of dietary copper deficiency in the regulation of select copper chaperone proteins in cardiac tissue of rats. Sixteen weanling male Long-Evans rats were randomized into treatment groups, one group receiving a copper deficient diet (< 1 mg Cu/kg diet) and one group receiving a diet containing adequate copper (6 mg Cu/kg diet) for 5 weeks. Rats were sacrificed and a small blood sample was removed to determine hematocrit. Also, heart and liver tissues were removed for subsequent analysis. Rats fed the copper deficient diet had lower body weights but greater heart weights and heart:body weight. Hematocrit levels and liver copper concentrations were markedly decreased in copper deficient rats. These variables indicated that the copper deficient diet did in fact induce a copper deficiency in these animals. Non-myofibrillar proteins from the hearts were removed and separated by SDS-PAGE. Western Blotting was used to determine the concentrations of CTR1, CCS, Cox17, SCO1, Cox1 and Cox4. No changes were observed in the concentrations of CTR1 and Cox17. CCS and SCO1 were up-regulated as a result of copper deficiency, while Cox1 and Cox4 were both down-regulated. However, use of another antibody against Cox subunits suggested that only the nuclear encoded subunits including subunit IV were decreased, but not subunits I and II. These data provide new insight into the cardiac hypertrophy observed in copper deficiency, which suggests that select chaperone proteins may be up-regulated by a dietary copper deficiency.

Il y a 4 isoforme de p38 : α, β, δ, and γ. MK5, à l'origine identifié comme étant un régulateur de PRAK (Regulated/Activated Protein Kinase), est maintenant connu pour être activée par la protéine kinase p38 (qui est un mitogène activé par la protéine kinase, MAPK). Cette dernière est impliquée dans les mécanismes de fibrose et d'apoptose pendant l'hypertrophie cardiaque. De plus, MK5 est également activée par les MAPKs atypiques; ERK3 et ERK4. Bien qu’elles soient fortement exprimées dans le coeur, le rôle physiologique de MK5 et ERK3 demeure inconnu. Par conséquent, nous avons étudié l'effet de la constriction aortique transversale (TAC) – induisant un surcharge chronique de pression chez les souris hétèrozygotes knockout pour MK5 (MK5+/-) ou ERK3 (ERK3+/-) et pour leurs types sauvages (MK5+/+ et ERK3+/+). Deux sem post-TAC; le ratio de poids du coeur/poids corporel a été augmenté chez les 2 souris MK5+/- et MK5+/+. L'échocardiographie de la trans-thoracique démontre que la surcharge de pression a altéré la fonction diastolique du ventricule gauche chez MK5+/+, mais pas chez la souris MK5+/-. De plus, nous avons observé moins de dépôt de collagène, évalué par une coloration au trichrome de Masson, 2 et 3 sem post-TAC chez les souris MK5+/-. Parallèlement, le niveau de l’ARNm de collagène type1 alpha-1 a été significativement diminué dans les coeurs des souris MK5+/-, 2 et 3 sem post-TAC. De même, ERK3, mais pas ERK5 ni p38α, co-IP avec MK5 dans les 2 modèles des coeurs TAC; aigus ou chroniques. En revanche, l’ajout exogénique de GST-MK5 a abaissé ERK4 et p38α, mais pas ERK3 dans les lysâtes de coeur de souris. Par contre, GST-ERK3 et GST-p38α ne démontrent aucune co-IP avec MK5. Ces données suggèrent que dans le coeur seul ERK3, et non ERK4 ou p38α, est capable d’interagir avec, et réguler MK5. A niveau physiologique MK5 interagit entièrement avec ERK3 et par conséquent MK5 n’est pas disponible pour lier les protéines exogéniques. Les souris hétérozygotes pour ERK3 (ERK3+/-) ont également démontré une réduction ou une absence de collagène et une faible expression d’ARNm du collagène type1 alpha1, 3 sem post-TAC. Ces résultats démontrent un important rôle pro-fibrotique de la signalisation MK5-ERK3 pendant une surcharge chronique de pression.Nous avons également démontré 5 variant d'épissage de (MK5.1-5), y compris la forme originale (MK5.1). MK5.2 et MK5.5 subissent une délétion de 6 paires de base dans l’exon 12 : MK5.3 manque l'exon 12 : MK5.4 et MK5.5 manquent les exons 2-6. L'expression des ARNm des différents variant d'épissage a été vérifiée par PCR en temps réel (qPCR). Bien que l’expression est ubiquitaire, l'abondance relative de chaque variant était tissu-spécifique (coeur, rein, pancréas, muscle squelettique, poumon, foie, et cerveau). En plus, l'abondance relative des variant d’épissage varie pendant la surcharge de pression et le développement postnatal du coeur. En outre, l'immunofluorescence a indiqué que MK5.1-5.3 se localise au noyau alors que MK5.4-5.5 est situé au niveau cytoplasmic dans les cellules HEK 293 non stimulées. Suite à une stimulation avec l'anisomycin, un activateur de p38 MAPK, MK5.1-5.3 se translocalise du noyau au cytoplasme alors qu’une petite fraction de MK5.4-5.5 translocalise vers le noyau. Ces variant d'épissage peuvent diversifier la signalisation de MK5-ERK3 dans coeur, mais leur rôle exact oblige des recherches supplémentaires. Excepté l’isoforme δ, toutes les isoformes de p38 sont exprimées dans le coeur et la forme α est considérée comme étant l'isoforme dominante. L’analyse par qPCR et immunobuvardage de type western ont démontré que p38α et p38γ sont les deux isoformes prédominantes alors que p38β et p38δ sont exprimées aux mêmes niveaux dans le coeur de rat adulte. L'immunofluorescence a démontré que p38α et p38γ se trouvent dans le cytoplasme et le noyau. Cependant, suite à la surcharge par TAC, p38γ s'est accumulé dans noyau tandis que la distribution de p38α est demeurée inchangée. Ainsi, l'abondance de p38γ et sa translocalisation nucléaire suite à la surcharge de pression indique un rôle potentiel dans l'expression génique pendant le remodelage cardiaque. En conclusion, nous avons mis en évidence pour la première fois un rôle pro-fibrotique pour la signalisation MK5-ERK3 pendant une surcharge chronique de pression. D'ailleurs, les niveaux comparables d'expression de p38γ avec p38α, et la localisation différentielle de p38γ pendant la surcharge aiguë ou chronique de pression suggèrent différents rôles possibles pour ces isoformes pendant le remodelage hypertrophique cardiaque. / There are 4 isoforms of p38 MAP kinase: α, β, γ, and δ. p38 signaling has been implicated in fibrosis and apoptosis during cardiac hypertrophy. MK5, originally identified as a p38 Regulated/Activated Protein Kinase (PRAK), is known to be downstream of p38 mitogen activated protein kinase (MAPK). Although highly expressed in the heart, the physiological roles of MK5 remain unknown. To determine if MK5 plays a role in mediating detrimental effects downstream of p38, we studied the effect of transverse aortic constriction (TAC)-induced chronic pressure overload in mice heterozygous for a knockout of MK5 (MK5+/-). Moreover, as MK5 is also activated by the atypical MAPKs, ERK3 and ERK4, the effects of TAC were also studied in ERK3+/- mice. Wild-type (MK5+/+; ERK3+/+) littermates were used as controls. Two wks post-TAC, heart weight/body weight ratios were significantly and similarly increased in both MK5+/- and MK5+/+ hearts. Trans-thoracic echocardiography revealed that pressure overload impaired left ventricular diastolic function in MK5+/+, but not in MK5+/- hearts. In addition, less collagen deposition, assessed by Masson trichrome staining, was observed in MK5+/- hearts 2 and 3 wks post-TAC. Furthermore, TAC-induced increases in collagen alpha1 type1 mRNA levels were significantly lower in MK5+/- hearts at both 2 and 3 wks post-TAC. Immunoprecipitation of MK5 resulted in co-immunoprecipitation of ERK3 but not ERK4 or p38α in either acute or chronic sham-operated and TAC hearts. In contrast, exogenous GST-MK5 pulled down endogenous ERK4 and p38α, but not ERK3, from mouse heart lysates. Neither exogenous GST-ERK3 nor GST-p38α pulled down MK5. These results suggest that MK5 associates with, and is regulated by ERK3, but not ERK4 or p38α in heart. At physiological expressional levels, all MK5 was bound to ERK3 and hence not available to bind exogenous protein. Along similar lines, mice heterozygous for an ERK3 knockout (ERK3+/-) also showed reduced or absent collagen deposition and lower collagen alpha1 type1 mRNA levels 3 wks post-TAC. This data suggests an important pro-fibrotic role of MK5-ERK3 signaling during chronic pressure overload.We also demonstrated the existence of 5 splice variants of (MK5.1-5), including the originally published form (MK5.1). MK5.2 and MK5.5 had a 6 base pair deletion in exon 12: MK5.3 lacked exon 12: and MK5.4 and MK5.5 lacked exons 2-6. Subsequently, expression of the splice variants at the mRNA level was quantified by real time qPCR. Although ubiquitously expressed, the relative abundance of each variant was tissue-specific (heart, kidney, pancreas, skeletal muscle, lung, liver, and brain). Additionally, the relative abundance of MK5 splice variants changed in the heart during pressure overload and post-natal development. Furthermore, immunofluorescence revealed MK5.1-5.3 localized to the nucleus and MK5.4-5.5 to the cytoplasm in unstimulated HEK 293 cells. Upon stimulation with anisomycin, which activates p38 MAPK, MK5.1-5.3 translocated from the nucleus to the cytoplasm and small amounts of MK5.4-5.5 relocated to the nucleus. These splice variants may further diversify MK5-ERK3 signaling in the heart, but their exact role awaits further investigation. With the exception of p38δ, all p38 isoforms are expressed in the heart and α is considered to be the prominent isoform in this tissue. qPCR and western blot analysis revealed p38α and p38γ to be the predominant isoforms and p38β and p38δ are expressed at comparable levels in the adult heart. Confocal immunofluorescence studies revealed p38α and p38γ in both the cytoplasm and nucleus. However, in response to TAC, p38γ accumulated in the nucleus whereas the distribution of p38α remained unaffected. The high abundance of p38γ and its nuclear accumulation during chronic pressure overload suggest that this isoform may play a role in gene expression during pathological cardiac remodeling. In conclusion, we have shown for the first time a pro-fibrotic role for MK5-ERK3 signaling during chronic pressure overload. Moreover, comparable expression levels of p38γ with p38α, and differential localization of p38γ during acute or chronic pressure overload, suggest these isoforms play different roles during cardiac remodeling.

L’hypertrophie cardiaque représente la réponse primaire du cœur dans le but d’améliorer la fonction cardiaque qui est compromise suite à un accident ischémique ou une surcharge hémodynamique. Cependant, l’hypertrophie cardiaque a pour conséquence pathologique la fibrose réactive, qui est caractérisée par la synthèse incontrôlée et le dépôt du collagène par les myofibroblastes. Ainsi, l’accumulation accrue du collagène dans le cœur hypertrophié mène à l’augmentation de la rigidité cardiaque et la détérioration progressive de la fonction contractile du cœur. Plusieurs études ont démontré que la protéine nestine, appartenant à la famille des filaments intermédiaires, est ré-exprimée dans les myofibroblastes durant la fibrose réparative et est impliquée dans la prolifération cellulaire. Basée sur ces observations, cette étude teste l’hypothèse selon laquelle nestine est induite dans les myofibroblastes suivant le développement de la fibrose réactive dans le cœur des rats ayant subi une constriction aortique supra-rénale. Deux semaines suivant une constriction aortique supra-rénale chez le rat, un patron d’hypertrophie concentrique cardiaque a été observé et associé avec une réponse de fibrose réactive caractérisée par le dépôt accru de collagène dans le tissu interstitiel et la région péri-vasculaire de nombreux vaisseaux sanguins cardiaques. De plus, les niveaux de la protéine nestine sont augmentés significativement dans les cœurs des rats hypertrophiés, et ce, de façon corrélative avec la pression artérielle moyenne et la pression systolique du ventricule gauche. Les techniques d’immunofluorescences ont révélé une apparition accrue des cellules immunoréactives à nestine, qui présentent un phénotype mésenchymateux caractérisé par la co-expression de collagène dans le tissu interstitiel et la région péri-vasculaire des cœurs hypertrophiés. Ces données suggèrent que les fibroblastes résidents peuvent exprimer la protéine nestine ou que l’expression de nestine est induite en réponse aux facteurs pro-fibrotiques impliqués dans la fibrose réactive. En effet, l’exposition des myofibroblastes normaux et des myofibroblastes isolés des cœurs hypertrophiés à l’AII, TGF-B1 et EGF augmente significativement l’expression de la protéine nestine, tandis que l’expression de l’α-SMA demeure inchangée. De plus, de manière prédominante dans le cœur hypertrophié, des cellules non-vasculaires CD31(+) ont été détectées dans le tissu interstitiel et la région péri-vasculaire. Ces cellules co-expriment nestine et collagène suggérant une transition des cellules endothéliales vers un phénotype mésenchymateux. Finalement, la protéine nestine, sous sa forme filamenteuse, a été détectée dans les cellules endothéliales de l’artère coronaire humaine et leur exposition au TGF-B1, induit l’expression de collagène. En revanche, l’expression de collagène a été détectée dans les cellules microvasculaires de rats CD31(+), alors que l’expression de nestine est absente. En réponse aux traitements de TGF-B1 et EGF, l’expression de nestine, sous sa forme non-filamenteuse, est détectée dans les cellules microvasculaires de rats. Collectivement, ces données supportent la prémisse selon laquelle la réponse de fibrose réactive dans les cœurs hypertrophiés, suite à une constriction aortique supra-rénale, est attribuée en partie à l’augmentation de l’apparition des cellules mésenchymateuses positives à l’expression de nestine qui proviennent des fibroblastes résidents du ventricule. De plus, les données in vivo et in vitro suggèrent que les cellules endothéliales déplacées représentent une source additionnelle des cellules mésenchymateuses nestine(+) dans le cœur hypertrophié et contribuent au développement de la fibrose réactive. Cibler la protéine nestine peut représenter une approche thérapeutique afin d’atténuer la réponse de fibrose réactive indépendamment de l’origine des cellules mésenchymateuses. / Cardiac hypertrophy secondary to an ischemic insult or a hemodynamic overload represents the primary response of the heart to enhance compromised cardiac function. However, a pathological consequence of cardiac hypertrophy is reactive fibrosis characterized by the uncontrolled synthesis and deposition of collagen by proliferating myofibroblasts. Furthermore, the unrestrained accumulation of collagen in the hypertrophic heart leads to increased cardiac stiffness and progressive worsening of contractile function. Previous studies have reported that the intermediate filament protein nestin was re-expressed in myofibroblasts during reparative fibrosis and played a direct role in cell proliferation. Based on these observations, the following study tested the hypothesis that nestin was induced in myofibroblasts secondary to the development of reactive fibrosis in the heart of rats subjected to suprarenal aortic constriction. Two weeks following suprarenal aortic constriction of the adult male rat, a concentric pattern of cardiac hypertrophy was observed and associated with an overt reactive fibrotic response characterized by the increased deposition of collagen in the interstitium and perivascular region of numerous blood vessels. Nestin protein levels were significantly increased in the heart of hypertrophied rats and expression positively correlated with mean arterial pressure and left ventricular systolic pressure. Immunofluorescence approach revealed an increased appearance of nestin-immunoreactive cells in the interstitium and perivascular region of hypertrophied hearts and exhibited a mesenchymal phenotype characterized by collagen co-staining. The latter data suggests that resident fibroblasts may have expressed nestin and/or was induced in response to pro-fibrotic factors implicated in reactive fibrosis. Indeed, the exposure of normal myofibroblasts and myofibroblasts isolated from the hypertrophied heart to AII, TGF-B1 and EGF significantly increased nestin protein levels, whereas α-SMA expression remained unchanged. Moreover and predominantly in the hypertrophied heart, displaced non-vascular CD31(+) cells were detected in the interstitium and perivascular region that co-expressed nestin and collagen suggesting a transition of endothelial cells to a mesenchymal phenotype. Indeed, filamentous nestin was detected in human coronary artery endothelial cells and exposure to TGF-B1 induced collagen expression. By contrast, collagen was detected in CD31(+) rat microvascular endothelial cells whereas nestin expression was absent. In response to TGF-B1 and EGF, nestin was expressed in rat microvascular endothelial cells but the reported filamentous phenotype was not observed. Collectively, these data support the premise that the progression of the reactive fibrotic response in the hypertrophied heart secondary to suprarenal aortic constriction was attributed in part to the increased appearance of nestin(+) mesenchymal cells originating in part from resident ventricular myofibroblasts. Moreover, the in vivo and in vitro data further suggest that displaced endothelial cells may represent an additional source of nestin(+) mesenchymal cells in the hypertrophied heart contributing to the development of reactive fibrosis. Targeting nestin may represent a potential therapeutic approach to attenuate the reactive fibrotic response regardless the cellular origin of the mesenchymal cell.

O presente estudo avaliou o papel do receptor AT1 de Angiotensina II no desenvolvimento da hipertrofia dos cardiomiócitos promovida pelo T3, bem como a participação dos mecanismos intracelulares deflagrados pelo receptor AT1 neste modelo de hipertrofia cardíaca. O silenciamento do receptor AT1 com RNA de interferência preveniu totalmente o desenvolvimento da hipertrofia dos cardiomiócitos induzida pelo T3. Os cardiomiócitos tratados com T3 demonstraram uma rápida ativação da via da Akt/GSK-3/mTOR, a qual foi atenuada ou prevenida pelo silenciamento do receptor AT1. Ainda, a expressão de Angiotensina I/II no lisado celular e a expressão do receptor AT1 foram rapidamente aumentados pelo T3. Esses dados demonstram pela primeira vez que o receptor AT1 é um mediador crítico da hipertrofia dos cardiomiócitos induzida pelo T3, bem como para a ativação da via da Akt, sugerindo que a via Ang I/II-AT1-Akt/GSK-3/mTOR corresponde a um potencial mediador dos efeitos tróficos exercidos pelo T3 nessas células. / The present study investigated the role of Angiotensin type 1 receptor (AT1R) in T3-induced cardiomyocyte hypertrophy, as well as the participation of the intracellular mechanisms mediated by AT1R in this cardiac hypertrophy model. The AT1R silencing using small interfering RNA totally prevented the development of T3-induced cardiomyocyte hypertrophy. The cardiomyocytes treated with T3 demonstrated a rapid activation of Akt/GSK-3/mTOR signaling pathway, which was attenuated or prevented by the AT1R silencing. In addition, local Angiotensin I/II (Ang I/II) levels and the AT1R expression were rapidly increased by T3 treatment. These data demonstrate for the first time that the AT1R is a critical mediator to the T3-induced cardiomyocyte hypertrophy, as well as to the activation of the Akt signaling, suggesting that the Ang I/II-AT1R-Akt/GSK-3/mTOR pathway corresponds to a potential mediator of the trophic effect exerted by T3 in cardiomyocytes.

Níveis elevados de hormônios tireoidianos (HTs) são comumente associados à ativação do sistema renina angiotensina local e ao desenvolvimento da hipertrofia cardíaca. O envolvimento do receptor de angiotensina II tipo 1 (AT1R) nos efeitos hipertróficos dos HTs fora descrito previamente. No entanto, os mecanismos subjacentes a essa interação ainda são desconhecidos. O AT1R pertence à família dos receptores acoplados à proteína G e, portanto, promove a transdução de sinal por mecanismos dependentes e independentes de proteína G. Recentemente, a sinalização dependente de beta-arrestinas (independente de proteína G) tem sido descrita por contribuir com a resposta hipertrófica em diferentes modelos experimentais. Assim, no presente estudo investigou-se o envolvimento da sinalização dependente de beta-arrestinas nos efeitos hipertróficos dos HTs, mediados pelo AT1R, bem como a participação de ERK&#189; nesse processo. Culturas primárias de cardiomiócitos foram estimuladas com T3 (triiodotironina; 15nM) para indução da hipertrofia. O tratamento dos cardiomiócitos com T3 por tempos rápidos (5-30 min) resultou na ativação transiente de ERK&#189;, a qual foi parcialmente atenuada quando da administração de Losartan (1&#181;M), antagonista do AT1R. A contribuição de ERK&#189; na hipertrofia dos cardiomiócitos foi verificada através do uso de PD98059 (20&#181;M), inibidor de MEK&#189;, o qual preveniu a transcrição de marcadores hipertróficos. Ensaios de imunoprecipitação revelaram o aumento da interação entre AT1R e beta-arrestina 2 sob estímulo do T3, sugerindo o recrutamento de beta-arrestina 2 e, possível, internalização do AT1R. Através de ensaios de imunofluorescência e fracionamento subcelular, foi demonstrado que o T3 estimula a translocação do AT1R, amentando sua expressão no núcleo dos cardiomiócitos. Além disso, tanto a ativação de ERK&#189; quanto a hipertrofia cardiomiocítica mostraram-se sensíveis à inibição da endocitose, a qual foi avaliada através de Concanavalina A (0,5&#181;g/ml). Ensaios de silenciamento gênico por RNA de interferência foram eficientes em demonstrar o envolvimento de beta-arrestina 2 na ativação de ERK&#189; e na hipertrofia cardiomiocítica induzida por T3. Desta forma, os resultados evidenciam o envolvimento da sinalização dependente de beta-arrestina 2 na ativação de ERK&#189;, através do AT1R, a qual contribui com a hipertrofia cardiomiocítica promovida pelo T3. / Elevated levels of thyroid hormones (THs) are commonly associated with activation of the local renin angiotensin system and the development of cardiac hypertrophy. The involvement of the angiotensin II receptor type 1 (AT1R) in the hypertrophic effects of the THs was previously described. However, the mechanisms underlying this interaction are still unknown. AT1R belongs to the G-protein coupled receptor family and promotes its signal transduction by G-protein dependent and independent mechanisms. Recently, beta-arrestin signaling (G-protein independent) has been described as contributing to the hypertrophic response in different experimental models. Thus, the present study investigated the involvement of beta-arrestin signaling in the hypertrophic effects of THs mediated by AT1R, as well as the participation of ERK&#189; in this process. Primary cardiomyocytes cultures were stimulated with T3 (triiodothyronine; 15nM) for the induction of hypertrophy. Cardiomyocytes acutely treated with T3 (5-30 min) resulted in transient activation of ERK&#189;, which was partially attenuated upon Losartan (1&#181;M) administration, an AT1R antagonist. The contribution of ERK&#189; to cardiomyocyte hypertrophy was verified by using PD98059 (20&#181;M), a MEK&#189; inhibitor, which prevented the transcription of hypertrophic markers. Immunoprecipitation assays revealed increased interaction between AT1R and beta-arrestin 2 under T3 stimulation, suggesting the recruitment of beta-arrestin 2 and, possibly, the internalization of AT1R. Through immunofluorescence and subcellular fractionation assays, T3 has been shown to stimulate AT1R translocation, enhancing its expression in the cardiomyocyte nucleus. In addition, both ERK&#189; activation and cardiomyocyte hypertrophy were sensitive to the inhibition of endocytosis, which was assessed by Concanavalin A (0.5&#181;g/ml). Interfering RNA assays were efficient in demonstrating the involvement of beta-arrestin 2 in ERK&#189; activation and in T3-induced cardiomyocyte hypertrophy. Therefore, the results evidenced the involvement of beta-arrestin-2-dependent signaling in the activation of ERK&#189;, through the AT1R, which contributes to the cardiomyocyte hypertrophy promoted by T3.