Type: dissertation
Abstract: Recent studies show that macrophages are present in the healthy myocardium and can also be recruited in response to myocardial infarction (MI).However, the specific contribution of these cells to either cardiac homeostasis or cardiac repair following injury is not fully understood.In our study, we focus on macrophages present in the heart and examine their subsets, phenotype and functional properties in the steady state and after MI.For the analysis, we developed two different mouse models of MI: cryoinjury and left anterior descending coronary artery ligation (LADligation), and we used in vivo tracing flow cytometry, state-of-the-art confocal microscopy, transcriptional and ecocardiography analysis.We identified a population of cardiac resident macrophages located in close proximity with endothelial cells and that exhibit an M2-like/tissue-homeostatic signature consistent with anti-inflammatory and pro-angiogenic activity.These findings suggest that cardiac resident macrophages found in the healthy myocardium might have a role in maintaining cardiac homeostasis and coronary vasculature integrity.After MI, we found two distinct subsets of monocytes and macrophages that sequentially appeared in the infarcted myocardium and that showed different gene expression profiles.Ly6C hi cells found soon after myocardial injury correspond to pro-inflammatory monocytes/macrophages, whereas Ly6C lo cells found at later stages represent macrophages exhibiting anti-inflammatory and pro-angiogenic activity.Notably, the gene expression profile of these cells had features of pro-angiogenic Tie2-expressing macrophages (TEMs), which are also present in tumors and ischemic tissues.We examined the presence of TEMs in the ischemic myocardium and found that these cells are recruited in response to injury and exhibit pro-angiogenic properties.These results indicate that TEMs might be involved in the revascularization of the ischemic myocardium following MI.Our findings suggest that modulation of macrophage activation in both homeostasis and cardiac disease might help to develop novel therapeutic approaches to avoid adverse cardiac remodeling and improve cardiac repair.11 RESUMEN RESUMEN 13 El corazón alberga poblaciones de macrófagos tanto en condiciones fisiológicas, como en respuesta al daño cardíaco por infarto de miocardio (IM).No obstante, la contribución específica de estas poblaciones al mantenimiento de la homeostasis y a la reparación cardíaca de corazón adulto no ha sido completamente dilucidada.Nuestro estudio se centra en la caracterización de las distintas subpoblaciones de macrófagos presentes en el corazón en homeostasis y en respuesta al IM.Para ello, se han desarrollado dos modelos distintos de inducción de IM: la criolesión y la ligación permanente coronaria y se han llevado a cabo estudios in vivo por citometría de flujo, microscopía confocal, ecocardiografía y análisis de la expresión génica.Se ha identificado la existencia de una población de macrófagos residentes cardíacos cuya localización es cercana a los pequeños y grandes vasos sanguíneos de la vasculatura coronaria.Estos macrófagos exhiben un perfil génico anti-inflamatorio caracterizado por la expresión de marcadores homeostáticos y pro-angiogénicos, lo que sugiere una función de estas células en el mantenimiento de la homeostasis cardíaca y de la integridad vascular.En respuesta al IM, se ha identificado la presencia de dos subpoblaciones de monocitos y macrófagos que aparecen de forma secuencial en el corazón y muestran distintos perfiles de expresión.La subpoblación celular Ly6C hi se compone de monocitos y macrófagos con carácter pro-inflamatorio, que se hallan presentes en fases tempranas tras el IM.En fases más tardías, se encuentra un subpoblación de macrófagos Ly6C lo que exhiben propiedades anti-inflamatorias y pro-angiogénicas similares a las mostradas por poblaciones de macrófagos Tie2 + (TEMs), previamente descritos en distintos procesos isquémicos.De acorde a este hallazgo, se ha llevado a cabo el estudio de la presencia de TEMs tras el IM.Se ha demostrado que estas células corresponden a subpoblaciones de macrófagos presentes en el miocardio dañado, que exhiben un patrón de expresión altamente pro-angiogénico y son distintas de los macrófagos Ly6C lo .Los resultados obtenidos en este estudio sugieren que en el contexto tanto de homeostasis como de enfermedad cardíaca, la modulación de la activación del macrófago puede servir como herramienta útil para el desarrollo de nuevas terapias enfocadas a la mejora de la función cardíaca.phagocytic granules, which give them a 'foamy' appearance.Macrophages have roles in almost every aspect of an organism's biology; from development, homeostasis and repair, to immune responses against pathogens.In adult mammals, macrophages are found in all tissues where they display a wide anatomical and functional diversity.Macrophages broadly consist of two classes: tissue-resident macrophages and infiltrating macrophages (Pollard 2009; Murray and Wynn 2011).Tissueresident macrophages regulate tissue homeostasis by acting as sentinels and responding to changes in physiology as well as challenges from external environment.In contrast, infiltrating macrophages are only found in inflammatory Definitive hematopoiesis (i.e., the generation of hematopoietic cells from multipotent hematopoietic stem cells) starts at E9.5 -E10 in the Aorto-Gonado-Mesonephron (AGM) region of the embryo to continue in the fetal liver, spleen and bone marrow at later stages of development.Therefore, after birth, as the bony structures are formed the main site of hematopoiesis is the bone marrow; at this stage, the MPS is established (van Furth, Cohn et al, 1972).Wynn, Chawla et al, 2013).In addition, recent studies have described the existence of a minor population of circulating Tie-2 expressing monocytes (TEMs) that are recruited into tissues where they differentiate into Tie2-expressing macrophages which are involved in angiogenic processes (De Palma, Venneri et al, 2005).producing pro-inflammatory cytokines like IL-12, IL-1𝛽, and TNF𝛼 (Biswas and Mantovani 2010).In addition, M1 macrophages show enhanced phagocytosis of microorganisms, and act as antigen presenting cells (APC) for T cells (Sica and Mantovani 2012).Macrophages exposed to Th2-type cytokines such as IL4 and IL13, undergo alternatively activated or M2 polarization state, a process controlled by the transcription factors IRF4, STAT6 and PPAR (Ohmori and Hamilton 1997;Satoh, Takeuchi et al, 2010).These M2 macrophages have a role in protection against a continuum rather than discrete entities (Mosser and Edwards 2008;Geissmann, Manz et al, 2010).Figure 3 Macrophage activated phenotypes.In response to IFN𝛾 TNF𝛼 or LPS, macrophages undergo M1 or classically-activated phenotype, releasing several pro-inflammatory cytokines.In contrast, macrophage polarization into M2 or alternatively activation takes place in response to IL-13 or IL-4Hasleton et al, 1997;Azzawi, Kan et al, 2005).Recent work using the CX3CR1 GFP/+ transgenic mouse model, describes an abundant population of cardiac resident macrophages that appears within the normal myocardium in direct contact with endothelial cells and myocytes (Pinto, Paolicelli et al, 2012).These cells exhibit an alternative like phenotype in resting conditions.Furthermore, the existence of four different populations of cardiac resident macrophages has been recently demonstrated (Epelman, Lavine et al, 2014).It has been shown that these cells arise from yolk sac and fetal progenitors and that are maintained through local proliferation at steady state (Epelman, Lavine et al, 2014).Although these findings clearly improve our knowledge of macrophage biology in resting myocardium, it is currently unclear how cardiac resident macrophages since 2000 as an alternate means of achieving cardiac repair (Bolli, Chugh et al, 2011).Stem cell therapy through using multiple cell types to regenerate the injured heart has been tested in clinical trials.Nonetheless, its efficacy has several limitations, such as low cardiac engraftment of cells, and low cardiomyogenic potential of bone marrow cells as well as the necessity of optimizing more efficient Monocytes and macrophages initially accumulate in the infarct border zone (van der Laan, Ter Horst et al, 2014), probably because vascular access is still intact in this area.Presumably, over time, monocytes and macrophages migrate into the core of the infarct as demonstrated by human studies reporting an increase in monocyte number in the infarct core later than in the border zone (van der Laan, Ter Horst et al, 2014).Figure 5 Biphasic monocyte response after myocardial infarction.Time course of monocyte subsets recruitment and their function depicted in the lower panel.Distinct phases of cardiac healing after MI are depicted in the upper panel.Adapted from Nahrendorf et al, 2007.crosstalk between injected stem cells and macrophages (Dayan, Yannarelli et al, 2011).In this study, MSC transplantation into the infarct increases the percentage of reparative M2 macrophages in the infarcted heart of mice supporting the concept that these cells are crucial for cardiac repair and cardiac function recovery. Macrophages in myocardial angiogenesisAfter MI, neovascularization in the border zone adjacent to the ischemic region is critical to supply the healing infarct with oxygen and nutrients and thus, to preserve cardiac function and attenuate adverse left ventricular remodeling (Frangogiannis 2012).Neovascularization is orchestrated by interactions between pro-angiogenic and anti-angiogenic factors, the extracellular matrix, and endothelial cells and pericytes at the border zone (Frangogiannis, Smith et al, 2002).The new blood vessels restore perfusion to ischemic areas through connecting patent and occluded arteries.Initially, new vessels only consist of endothelial cells but acquire a more mature morphology, including a pericyt
Language: English
Subfield: Cardiology and Cardiovascular Medicine
Field: Medicine
Domain: Health Sciences
Open Access status: green
OpenAlex ID: W7005965778