Novel cardiovascular magnetic resonance phenotyping of the myocardium

INTRODUCTION Left ventricular (LV) microstructure is unique, composed of a winding helical pattern of myocytes and rotating aggregations of myocytes called sheetlets. Hypertrophic cardiomyopathy (HCM) is a cardiovascular disease characterised by left ventricular hypertrophy (LVH), however the link between LVH and underlying microstructural aberration is poorly understood. In vivo cardiovascular diffusion tensor imaging (cDTI) is a novel cardiovascular MRI (CMR) technique, capable of characterising LV microstructural dynamics non-invasively. In vivo cDTI may therefore improve our understanding microstructural-functional relationships in health and disease. METHODS AND RESULTS The monopolar diffusion weighted stimulated echo acquisition mode (DW-STEAM) sequence was evaluated for in vivo cDTI acquisitions at 3Tesla, in healthy volunteers (HV), patients with hypertensive LVH, and HCM patients. Results were contextualised in relation to extensively explored technical limitations. cDTI parameters demonstrated good intra-centre reproducibility in HCM, and good inter-centre reproducibility in HV. In all subjects, cDTI was able to depict the winding helical pattern of myocyte orientation known from histology, and the transmural rate of change in myocyte orientation was dependent on LV size and thickness. In HV, comparison of cDTI parameters between systole and diastole revealed an increase in transmural gradient, combined with a significant re-orientation of sheetlet angle. In contrast, in HCM, myocyte gradient increased between phases, however sheetlet angulation retained a systolic-like orientation in both phases. Combined analysis with hypertensive patients revealed a proportional decrease in sheetlet mobility with increasing LVH. CONCLUSION In vivo DW-STEAM cDTI can characterise LV microstructural dynamics non-invasively. The transmural rate of change in myocyte angulation is dependent on LV size and wall thickness, however inter phase changes in myocyte orientation are unaffected by LVH. In contrast, sheetlet dynamics demonstrate increasing dysfunction, in proportion to the degree of LVH. Resolving technical limitations is key to advancing this technique, and improving the understanding of the role of microstructural abnormalities in cardiovascular disease expression.Open Acces

Computational biomechanics in the remodelling rat heart post myocardial infarction

Cardiovascular diseases account for one third of all deaths worldwide, more than 33% of which are related to ischemic heart disease, including myocardial infarction (MI). This thesis seeks to provide insight and understanding of mechanisms during different stages of MI by utilizing finite element (FE) modelling. Three-dimensional biventricular rat heart geometries were developed from cardiac magnetic resonance images of a healthy heart and a heart with left ventricular (LV) infarction two weeks and four weeks after infarct induction. From these geometries, FE models were established. To represent the myocardium, a structure-based constitutive model and a rule-based myofibre distribution were developed to simulate both passive mechanics and active contraction

3D cine DENSE MRI: ventricular segmentation and myocardial stratin analysis

Includes abstract. Includes bibliographical references

LOX and LOX-Like Proteins as Potential Therapeutic Target for Atrial Fibrillation

Les lysyl-oxydases (LOX) et LOX-like (LOXL-1, 2, 3 et 4) influencent le remodelage de la matrice extracellulaire (MEC) lors d’anomalies cardiaques comme l’insuffisance cardiaque (IC) ou la fibrose. L’objectif principal était d’étudier les fonctions matrice-dépendantes et -indépendantes des LOX et LOXL dans la transduction des signaux favorisant la fibrose et la fibrillation atriales (FA). Dans l’oreillette gauche (OG) de chiens IC, nous avons observé une augmentation de la régulation de : LOX et LOXL-1 dans le tissue atrial, LOX et LOXL-2 dans les fibroblastes ainsi que LOX, LOXL-1, LOXL-3 et LOXL-4 dans les myocytes. Nous avons évalué le rôle des isoformes des LOX dans la signalisation de la fibrose et de la FA dans l’OG de rats avec infarctus du myocarde (IM). Chez le chien et les cellules cardiaques de rats néonataux, nous avons exploré le rôle des LOX et LOXL sur la fonction matrice-dépendante et -indépendante des fibroblastes et myocytes cardiaques, en utilisant un traitement à l’angiotensine-II (Ang II) et un knockdown par si-ARN des isoformes de LOX. L’augmentation de l’expression des ARNm de LOX et LOXL était associée à une augmentation de l’expression des ARNm de COL 1A1, FN 1, TGF-β1, CTGF, periostin, α-SMA et MMP-2 dans la zone infarcie du ventricule gauche (VG). L’expression des ARNm de LOXL-1, LOXL-3, COL 1A1, TGF-β1 et periostin était significativement augmentée dans l’OG. L’administration de β-aminopropionitrile (BAPN) post-IM a diminué significativement l’expression des ARNm de LOXL-1,2,3. Le BAPN a aussi diminué l’expression d’ARNm de marqueurs pro-fibrotiques dans l’OG. Ces changements n’étaient pas significatifs dans le VG. Le BAPN a diminué la fibrose dans l’OG ainsi que le ratio de cross-linking du collagène, mais pas significativement dans le VG. Le BAPN a réduit les remodelages structuraux et fonctionnels de l’OG sans influencer significativement ceux-ci dans le VG. L’IM était associé à une augmentation de la durée de l’onde P ainsi que la durée et l’inductibilité des FA que le BAPN a significativement réduit. Chez des rats néonataux, des fibroblastes et des myocytes de ventricule ont été mis en culture et traités à l’Ang II. Les LOX et LOXL-2 sécrétées et le ratio de cross-linking du collagène ont été augmentés; et contribueraient au remodelage de la MEC. Chez le chien, la contractilité des myocytes de l’OG a été augmentée suivant le knockdown de LOX et LOXL-1 associé à des changements de concentrations calciques. Dans les fibroblastes, le knockdown de LOXL-3 a réduit l’expression des ARNm de LOXL-2,3,4, associé à une réduction de la prolifération cellulaire et de l’expression des ARNm de COL 1A1, COL 3A1 et CCNE 2. Ces résultats suggèrent que LOXL-2,3,4 influenceraient la prolifération des fibroblastes et la synthèse du collagène. Le knockdown de LOXL-4 a augmenté ratio de l’expression en ARNm de BAX/BLC-2, ainsi LOXL-4 pourrait avoir un effet protecteur contre l’apoptose. En conclusion, les LOX et LOXL sont des médiateurs potentiels de la fibrose et la FA dans l’OG chez le rat infarci. Les LOX et LOXL seraient alors impliqués dans la régulation des fonctions des fibroblastes et myocytes cardiaques.Lysyl oxidase (LOX) and LOX-like (LOXL-1, 2, 3 and 4) proteins have a crucial role in extracellular matrix (ECM) remodeling in several types of heart disease, such as heart failure (HF) and fibrosis. The main objective of this thesis was to address the matrix-dependent and matrix-independent functions of LOX and LOXL proteins in signal transduction, leading to atrial fibrosis and atrial fibrillation (AF). We noted upregulation of LOX and LOXL-1 in tissues, LOX and LOXL-2 in fibroblasts and LOX, LOXL-1, LOXL-3 and LOXL-4 in myocytes of the canine left atrium (LA) in congestive heart failure (CHF). Based on these findings, we studied the roles of LOX isoforms as upstream targets in the signaling pathways of LA fibrosis and AF in a rat model following myocardial infarction (MI). Additionally, we explored the physiological roles of LOX and LOXL proteins in matrix-dependent and matrix-independent functions of cardiac fibroblasts and myocytes through angiotensin II (Ang II) treatment and siRNA-mediated knockdown of LOX isoforms in canine and neonatal rat cells. Upregulation of the mRNA expression of LOX and LOXL was accompanied by an increase in mRNA expression of COL 1A1, FN 1, TGF-β1, CTGF, periostin, α-SMA and MMP-2 in the infarcted area of the left ventricle (LV). mRNA expression of LOXL-1, LOXL-3, COL 1A1, TGF-β1 and periostin were significantly increased in the LA post-MI. Administration of β-aminopropionitrile (BAPN) post-MI significantly reduced the mRNA expression of LOXL-1, LOXL-2 and LOXL-3 along with a decrease in the mRNA expression of several profibrotic markers in the LA without significant changes to those in the LV. Moreover, the administration of BAPN post-MI reduced LA fibrosis and the collagen cross-linking ratio without significantly changing those in the LV. BAPN administration post-MI reduced the adverse structural and functional remodeling of LA without significantly changing those in the LV. Furthermore, MI caused an increase in the P-wave duration, AF duration and AF inducibility, while the values of those parameters were significantly reduced upon BAPN administration post-MI. The protein expression of secreted LOX and LOXL-2 were increased in cultured neonatal rat ventricular fibroblasts and myocytes along with an increase in the collagen cross-linking ratio in fibroblasts upon treatment with Ang II. The secretion of LOX and LOXL-2 from cardiac fibroblasts and myocytes may contribute to ECM remodeling. Moreover, the contractility of canine LA myocytes was enhanced upon knockdown of LOX or LOXL-1 along with slight changes in Ca2+ transients. Upon knockdown of LOXL-3 in fibroblasts, LOXL-2, LOXL-3 and LOXL-4 mRNA expression levels were reduced along with reduced proliferation and mRNA expression of COL 1A1, COL 3A1 and CCNE 2. The results showed that LOXL-2, LOXL-3 and LOXL-4 may promote fibroblast proliferation and collagen synthesis. LOXL-4 knockdown increased the mRNA expression of the BAX/BCL-2 ratio, suggesting that LOXL-4 may protect against apoptosis in cardiac fibroblasts and myocytes. In conclusion, LOX and LOXL proteins are prominent mediators of LA fibrosis and AF post-MI. Additionally, these findings suggested that LOX and LOXL proteins are implicated in the regulation of various aspects of cardiac fibroblast and myocyte functions

A computational study of post-infarct mechanical effects of injected biomaterial into ischaemic myocardium

Includes abstract.Includes bibliographical references.Cardiovascular diseases account for one third of all deaths worldwide, more than 33% of which are related to ischaemic heart disease, involving a myocardial infarction (MI). Emerging MI therapies involving biomaterial injections have shown some benefits; the underlying mechanisms of which remain unclear. Computational models offer considerable potential to study the biomechanics of a myocardial infarction and novel therapies. Geometrical data of a healthy human left ventricle (LV) obtained from magnetic resonance images (MRI) was used to create a finite element (FE) mesh of the LV at the end-systolic time point using Continuity® 6.3 (University of California in San Diego, US). A mesh of 96 hexahedral elements with high order basis functions was employed to adequately describe the geometry of the LV. Simulations of diastolic filling and systolic contraction were performed using a transversely isotropic exponential strain energy function and a model for active stress based on contraction at the cellular level. An anterior apical, transmural MI was modelled in the LV encompassing 16% of the LV wall volume. The infarct was modelled at acute and fibrotic stages of post-infarct LV remodelling by altering the constitutive and active stress models to best describe passive and active behaviour of the ischaemic myocardium at each time point. The geometry of the LV with the fibrotic infarct was adjusted to represent the wall thinning that occurs during LV post-MI remodelling. Hydrogel injection was modelled as layers with material properties differing from those of the surrounding myocardium while accounting for thickening of the LV wall at the injection site. The study design comprised a healthy case and two infarcted cases with and without hydrogel injection. The end-diastolic volume (EDV) increased in the acute infarct model compared to the healthy case due to the reduced stiffness in the infarct wall. An EDV increase was not observed in the fibrotic infarct model compared to the healthy case. This was partially attributed to the increase in infarct stiffness and partially due to the fact that remodelling-related dilation of the LV was not implemented in the model. Inclusion of hydrogel lowered EDV in both the acute and fibrotic models. The predicted ejection fraction (EF) decreased from 41.2% for the healthy case to 28.5% and 33.0% for the acute and fibrotic infarct models, respectively. Inclusion of hydrogel layers caused an improvement in EF in the acute model only

Comparison of T1-maps and late gadolinium enhancement images in the detection of Myocardial Fibrosis in Hypertrophic Cardiomyopathy

Tese de Mestrado Integrado, Engenharia Biomédica e Biofísica, 2021, Universidade de Lisboa, Faculdade de CiênciasHypertrophic Cardiomyopathy (HCM) is characterized as an abnormal and heterogeneous thickening of the Left Ventricle (LV) wall. HCM is the leading cause of sudden cardiac death in children and young people, with an estimated prevalence of 1:500 in the general population. Myocardial fibrosis is the key histopathological hallmark in HCM and is presented in different patterns: interstitial diffuse fibrosis which, if not treated, evolves to replacement fibrosis. Cardiac Magnetic Resonance (CMR) imaging has been used for the detection and quantification of myocardial fibrosis. The Late Gadolinium Enhancement (LGE) technique is the primary tool for non-invasive tissue characterization, particularly for replacement fibrosis. Conversely, T1 mapping is commonly used for the detection of diffuse interstitial fibrosis, frequently missed using LGE. The clear disadvantage of LGE relies on the need to inject contrast agents that, despite being considered safe, may accumulate in the body for years and potentially cause nephrogenic systemic fibrosis in end-stage chronic kidney disease patients. The capability of native T1 mapping identifying not only diffuse interstitial but also replacement fibrosis would play a pivotal role in HCM diagnosis. The potential of native T1 mapping for a cheaper and non-contrast HCM assessment needs to be further studied. A database of 15 HCM patients, without and with fibrosis, was acquired at Hospital da Luz, Lisboa. In this project, (1) an extensive image preprocessing pipeline was applied to aim for the best possible spatial alignment of the myocardium between the two modalities (native T1 mapping and LGE); (2) the mean native T1 values of individuals without and with the presence of scarred tissue were examined; (3) a pixel-by-pixel analysis was performed to investigate if there is a correlation between fibrotic tissue in LGE and hyperintense regions in native T1 mapping; (4) a Texture Analysis (TA) was performed to study if texture information of native T1 mapping could provide differential diagnosis or prognostic information beyond mean T1 values. The first step was the most longstanding and challenging process. The registration of T1 and LGE images is difficult due to the different intensity profiles. The registration of the myocardial masks using a model with rigid, affine, and free-form deformation transformations revealed to be the best methodology. Mean native T1 values were not increased in patients with scarred tissue. Regarding the third aim, no clear intensity correlation between techniques was observed, which suggests the need for the TA. Seven features (in a total of 350) were selected to distinguish between cardiac segments without and with fibrotic tissue using a ML (Machine Learning) algorithm that finds the features that most contribute to distinguish the two groups. Four first-order features distinguish the cohorts due to the presence of scarred tissue - hyperintense zones - and three texture features suggest that the fibrotic remodeling in the myocardium of HCM patients might be associated with a more heterogeneous tissue texture. A Receiver Operating Characteristics (ROC) analysis was performed and revealed that the Cluster Prominence is the feature that best distinguishes sections without and with fibrotic tissue (accuracy of 70%) but with low sensitivity (65%) and low specifity (64%). A model with the 90th Percentile feature revealed an accuracy of 64%, sensitivity of 71% and specificity of 57%. Studying the Variance feature, the achieved accuracy was 63%, with 66% of sensitivity and 60% of specificity. The remaining features yielded lower accuracy values than the ones previously mentioned, but all of them higher than 50%. The low sensitivity and specificity of the best three models suggest that analysing these values considering these features may help cardiologists to identify focal fibrosis regions and avoid contrast injection methods but may not provide an accurate diagnosis of the presence of fibrotic tissue alone. Further research on the correlation of native T1 mapping and LGE cardiac images is highly recommended to develop a contrast-agent-free technology to replace LGE.A Cardiomiopatia Hipertrófica (do inglês, HCM) é descrita por um espessamento anormal e heterogéneo da parede do ventrículo esquerdo (do inglês, LV). A HCM é a principal causa de morte súbita cardíaca em crianças e jovens, com uma prevalência estimada de 1:500 na população em geral. Esta doença é, na sua maioria, hereditária, e causada por variantes nos genes da proteína do sarcómero (predominantemente MYH7 e MYBPC3). A fibrose do miocárdio é a principal marca histopatológica da HCM e apresenta-se em diferentes padrões: fibrose intersticial difusa que, se não tratada, evolui para fibrose focal. A fibrose é caracterizada por um aumento da deposição de colagénio, que afeta a viabilidade do miocárdio. A imagem de Ressonância Magnética Cardíaca (do inglês, CMR) tem sido usada para a deteção e quantificação de fibrose do miocárdio. A técnica de Realce Tardio (do inglês, LGE) é a principal ferramenta para caracterização não invasiva de tecidos, particularmente de fibrose focal. Em contrapartida, o mapeamento T1 é a técnica mais utilizada para deteção de fibrose intersticial difusa, frequentemente não detetada usando LGE. A clara desvantagem do LGE reside na necessidade de injeção de agentes de contraste. Apesar destes agentes serem considerados seguros, frequentemente causam alergias, podem-se acumular no corpo, por anos, e podem causar fibrose sistémica nefrogénica em pacientes com doença renal crónica terminal. A capacidade do mapeamento T1 nativo identificar, não só a fibrose intersticial difusa mas também a fibrose focal, desempenharia um papel fundamental no diagnóstico da HCM. Consequentemente, é de extrema importância estudar o potencial do mapeamento T1 nativo para uma avaliação desta patologia sem contraste e, desta forma, eliminar os riscos associados à injeção de contraste e reduzir os custos e tempo de preparação associados à utilização de gadolínio. Uma base de dados de 15 pacientes com HCM, com e sem fibrose, previamente adquirida no Hospital da Luz, Lisboa, foi analisada. Neste projeto, (1) aplicou-se um extenso conjunto de passos de pré-processamento de imagem para alcançar a melhor técnica possível de alinhamento espacial do miocárdio entre as duas modalidades (mapeamento T1 nativo e Realce Tardio); (2) após a divisão do miocárdio em 6 secções, como sugerido pela American Heart Association, examinaram-se os valores médios de T1, para cada secção, de indivíduos sem e com presença de tecido cicatricial; (3) realizou-se uma análise pixel a pixel para investigar se existe uma correlação entre o tecido fibrótico em LGE e as regiões hiperintensas no mapeamento T1 nativo; (4) realizou-se uma análise de textura para estudar se a informação de textura do mapeamento T1 nativo poderia fornecer um diagnóstico diferencial ou informação prognóstica além dos valores médios de T1 nativo. A primeira etapa revelou ser o processo mais demorado e desafiante. O batimento cardíaco e o ciclo respiratório representam dois desafios no registo de imagens cardíacas. Para além dos comuns desafios em alinhamento de imagens cardíacas da mesma modalidade, alinhar imagens de diferentes modalidades torna-se um processo mais complexo. Em primeiro lugar, o registo de imagens T1 e de LGE é dificultado pelos distintos perfis de intensidade das duas modalidades. Em segundo lugar, a aquisição de imagens de Realce Tardio ocorre cerca de 7 minutos após a aquisição do mapeamento T1, e o movimento dos pacientes durante este intervalo de tempo é uma fonte adicional de erro. Diferentes softwares foram utilizados, e uma imagem sintética ponderada em T1 foi criada, com o intuito de apresentar intensidades mais similares à imagem a ser alinhada (imagem de LGE). O registo das máscaras miocárdicas por meio de um modelo com transformações rígida, afim e deformações livres mostrou ser a melhor metodologia a aplicar. Os valores médios de T1 nativo não aumentaram significativamente em pacientes com tecido cicatricial, apesar de haver um aumento dos valores de T1 nativo em determinadas secções, em cortes basais e intermédios. Relativamente ao terceiro objetivo abordado, não foi observada uma clara correlação de intensidades entre as técnicas, o que reforçou a necessidade de uma análise de textura (do inglês, TA). Esta análise revelou as sete melhores características (num total de 350) que distinguem segmentos cardíacos sem e com tecido fibrótico, aplicando um método de Machine Learning (do inglês, ML) que identificou, sequencialmente, as features que adicionavam mais informação ao modelo que distinguia os dois grupos de segmentos. Quatro características de primeira ordem distinguem os segmentos devido à presença de tecido cicatricial - zonas hiperintensas - e três características de textura sugerem que a remodelação fibrótica no miocárdio de pacientes com HCM pode estar associada a uma textura mais heterogénea. Foi implementada uma análise ao desempenho de modelos com as features selecionadas, que revelou que a Cluster Prominence é a característica que melhor distingue secções sem e com tecido fibrótico, apesar de com baixa sensibilidade (65%) e baixa especificidade (64%). Um modelo que analisa o Percentil 90 revelou uma precisão de 64%, sensibilidade de 71% e especificidade de 57%. No estudo da Variância, a precisão foi de 63%, a sensibilidade 66% e a especificidade 60%. As restantes features apresentaram valores de precisão inferiores aos mencionados mas acima de 50%. Um modelo com a combinação das sete features selecionadas não melhorou a performance do modelo (precisão de 62%, sensibilidade de 75% e 49% de especificidade). A baixa sensibilidade e especificidade sugerem que a análise desses valores nessas características pode ajudar os cardiologistas a identificar regiões focais de fibrose e evitar métodos de injeção de contraste, mas pode não fornecer um diagnóstico preciso da presença de tecido fibrótico por si só. Em futuras aquisições, encontrar valores semelhantes nas features acima mencionadas, principalmente na Cluster Prominence, em novos dados, poderia ajudar os cardiologistas a identificar regiões de fibrose focal. Desta forma, não seria necessário analisar imagens de Realce Tardio, o que se traduziria na eliminação de injeção de agentes de contraste. Pesquisas adicionais focadas na correlação do mapeamento T1 nativo e imagens cardíacas de LGE são de extrema importância para desenvolver uma tecnologia independente da injeção de agentes de contraste, que substitua o Realce Tardio

Studies of the role of MAP kinase-activated protein kinase-5 (MK5) in reactive and reparative fibrosis in the murine heart

MK5 est une sérine/thréonine kinase, identifiée à l'origine comme une protéine kinase régulée/activée par p38 (PRAK), activée par les p38 MAPK et MAPK atypiques ERK3 et ERK4. Bien que MK5 soit exprimée dans le cœur, sa fonction physiologique commence seulement à être étudiée. Nous avons étudié les effets de la surcharge de pression chronique induite par la constriction aortique transversale (TAC) et les effets de l'infarctus du myocarde (IM) induit par la ligature permanente de l'artère coronaire descendante antérieure gauche (LADG) chez des souris hétérozygotes (MK5+/-). Aussi, nous avons étudié in vitro le rôle de MK5 dans la fonction de fibroblaste cardiaque en utilisant des fibroblastes de génotype MK5+/+, MK5+/-, MK5-/- et des fibroblastes avec un knockdown de MK5 par siRNA (MK5-kd). À l'âge de douze semaines, les souris MK5+/- étaient plus petites que les souris MK5+/+. La fonction systolique était diminuée chez les souris MK5+/-. Deux semaines après TAC, les poids cardiaque/longueur du tibia (PC/LT) ont augmenté de manière similaire et significative dans les 2 groupes. L’augmentation de l'ARNm du collagène de type 1α1 (COL1A1) MK5+/+ était atténuée de manière significative chez les souris MK5+/-. Huit semaines après TAC, PC/LT était significativement moins chez les souris TAC-MK5+/-. La progression de l'hypertrophie était atténuée dans les cœurs MK5+/-. L’immunoréactivité de MK5 a été détectée dans les fibroblastes cardiaques mais pas dans les myocytes. Ces données suggèrent que MK5 dans les fibroblastes cardiaques joue un rôle pro-fibrotique et pro-hypertrophique important dans le remodelage cardiaque pathologique. Nous avons examiné l'effet de MK5+/- dans la fibrose réparatrice après un IM. Les taux de mortalité chez les 2 groupes avec LADG ne différaient pas 7 jours suivant l'IM mais ils étaient plus élevés chez les souris MK5+/- sur une période de 21 jours. La principale cause de décès était la rupture cardiaque. Les fonctions systolique et diastolique sont également altérées chez les 2 groupes avec LADG. La zone de cicatrice et le collagène dedans la cicatrice ont diminué dans les cœurs de MK5+/- 8 jours après l'IM. L’infiltration des cellules inflammatoires était similaire dans les deux groupes avec LADG. L’angiogenèse était significativement élevée dans la zone péri-infarctus de cœurs du MK5+/-. Ces données suggèrent que MK5 peut jouer un rôle dans la régulation de la fonction des fibroblastes cardiaques. C’est pourquoi, nous avons examiné la mobilité et la prolifération du fibroblastes qui étaient diminuées chez les fibroblasts MK5-/-. Le transcriptome pour les protéines impliquées dans le remodelage de la matrice extracellulaire différait selon le génotype des fibroblastes. La sécrétion de COL1A1 et fibronectine étaient significativement augmentée dans les fibroblastes MK5-/- et MK5-kd. La contraction du myofibroblaste a été diminuée dans les fibroblastes MK5-kd. Ces données suggèrent que MK5 est impliqué dans la régulation de multiples aspects de la fonction des fibroblasts cardiaques. En conclusion, nous avons montré un rôle de MK5 dans le remodelage cardiaque pathologique ainsi qu’un rôle de MK5 dans la fonction des fibroblastes cardiaques.MK5 is a serine/threonine kinase, originally identified as a p38 Regulated/Activated Protein Kinase (PRAK), activated by p38 MAPK and the atypical MAPKs ERK3 and ERK4. Although MK5 is expressed in the heart, its physiological function is just beginning to be studied. Herein, we studied the effects of chronic pressure overload induced by transverse aortic constriction (TAC) and the effects of myocardial infarction (MI) induced by permanent ligation of the left anterior descending coronary artery (LADL) in heterozygous mice for a functional knockout of MK5 (MK5+/-). We also studied the role of MK5 in cardiac fibroblast function and in extracellular remodeling in healthy heart in vitro using MK5 wild type (MK5+/+), haplodeficient (MK5+/-), deficient (MK5-/-), and siRNA-mediated knockdown (MK5-kd) fibroblasts. At twelve weeks of age, MK5+/- mice were smaller than age-matched wild-type littermates (MK5+/+). Left ventricular end-diastolic diameter and systolic function were reduced in MK5+/- mice. Two weeks post-TAC, heart weight/tibia length ratios (HW/TL) were similarly and significantly increased in both MK5+/+ and MK5+/- hearts. However, eight weeks post-TAC, HW/TL ratios were significantly lower in TAC-MK5+/- mice compared to TAC-MK5+/+ mice. Thus, the progression of hypertrophy in response to chronic pressure overload was attenuated in MK5+/- hearts. Furthermore, two weeks of pressure overload induced increase in collagen type 1 α 1 (COL1A1) mRNA in MK5+/+ mice and this increase was significantly attenuated in MK5+/- mice. As MK5 immunoreactivity was detected in cardiac fibroblasts but not myocytes, these findings suggest that MK5 within cardiac fibroblasts plays an important pro-fibrotic and pro-hypertrophic role in cardiac remodeling during chronic pressure overload. We then examined the effect of reduced MK5 expression on reparative fibrosis following MI. Mortality rates for MK5+/+ and MK5 +/- did not differ significantly over seven days post-MI. In contrast, mortality was higher in MK5+/- mice over twenty-one days. Systolic and diastolic functions were similarly impaired in both MK5+/+ and MK5+/- mice post-MI. Scar area and scar collagen content were reduced in MK5+/- hearts eight days post-MI. Inflammatory cell infiltration was similar in both ligated groups whereas angiogenesis was significantly greater in the peri-infarct zone in LADL-MK5+/- hearts. These results suggest that MK5 may play a role in regulating cardiac fibroblast function. Finally, we examined the effect of reduced MK5 expression on fibroblast function. Motility and proliferation were reduced in MK5-/- fibroblasts compared to MK5+/+ and MK5+/- fibroblasts. The transcriptome for proteins involved in extracellular matrix remodeling (ECM) differed depending on fibroblast genotype. Similarly, collagen 1-α1 and fibronectin secretion was increased in MK5-/- and MK5-kd fibroblasts compared with MK5+/+. In addition, knocking down MK5 decreased myofibroblast contraction. Taken together, these data suggest that MK5 is involved in regulating multiple aspects of cardiac fibroblast function. In conclusion, we have shown a role for MK5 in cardiac remodeling during chronic pressure overload and myocardial infarction. Moreover, we have demonstrated a role for MK5 in cardiac fibroblast function and extracellular matrix remodeling

Clinical Investigations of Myorcardial Perfusion using Oxygen-15-labeled Water and Positron Emission Tomography

Lammertsma, A.A. [Promotor]Visser, F.C. [Promotor]Boellaard, R. [Copromotor]Götte, M.J.W. [Copromotor

New Insights in Morphology and Pathophysiology of Hypertrophic Cardiomyopathy by Magnetic Resonance Imaging

Rossum, A.C. van [Promotor]Götte, M.J.W. [Copromotor

Enabling Studies to Optimize Biomaterials for the Treatment of Myocardial Infarction

The canonical mechanism of wound healing is disrupted following a myocardial infarction (MI), manifesting as an unregulated response that negatively impacts left ventricular (LV) function. This mechanism, termed post-MI remodeling, culminates in an outcome that favors progression to a systolic heart failure state and death for the patient. Therapeutic approaches following the occurrence of a MI are designed to modulate the natural remodeling process and mitigate the loss of cardiac function. The mechanics and structure of the healing infarct have been the focus of numerous pre-clinical and clinical investigations, leading to the impending clinical introduction of material injections as a means to favorably alter remodeling outcomes. However, to date there is no body of work that provides a coherent framework for evaluation of targeted material therapies. To form a basis for optimization of material-based MI treatments, we have integrated measurements of MI regional mechanics, the morphology of the local extracellular matrix, and the biophysical impact of material injections into the MI region in a porcine model of MI. The combined findings of this study have enhanced a mechanistic understanding of material-based post-MI interventions, elucidated the relationship between MI regional mechanics and LV function throughout the natural and attenuated history of LV remodeling, and has developed mechanical metrics of value to move forth towards future developments of a generalizable computational tools for screening and evaluation of new strategies for MI injections