Fibrosis of the left atria during progression of heart failure is associated with increased matrix metalloproteinases in the rat

AbstractObjectivesThe purpose of this study was to determine the pathogenic factors and molecular mechanisms involved in fibrosis of the atria.BackgroundFibrosis is an important component of the pathophysiology of atrial fibrillation, especially when the arrhythmia is associated with heart failure (HF) or atrial dilation.MethodsWe used a rat model of myocardial infarction (MI) complicated by various degrees of left ventricular dysfunction and atrial dilation to study fibrosis and matrix metalloproteinase (MMP) activity in the left atrial (LA) myocardium by means of histologic, Western blot, zymographic, and immunohistologic techniques.ResultsThree months after surgical ligature of the left coronary artery, 27 rats had a large MI, 12 were in mild HF, and 15 in severe HF. Both groups had LA enlargement at the echocardiography. Masson’s trichrome and picrosirius staining of tissue sections revealed marked fibrosis at the periphery of trabeculae and also surrounding myolytic myocytes, in both mild and severe HF. In mild HF, the activity and expression of the matrilysin MMP-7 were increased (122%), whereas in severe HF, both MMP-7 (211%) and the gelatinase MMP-2 (187%) were up-regulated. There were no changes in the expression or activity of MMP inhibitors, TIMP-1, -2, and -4. Immunostaining of cryosections showed that MMP-2 was present in the interstitial spaces, whereas MMP-7 accumulated in myolytic myocytes.ConclusionsHemodynamic overload of the atria is an important pathogenic factor of fibrosis; MMP-7 appears to be involved in the early stage of this tissue remodeling process

Adult cardiac myocytes survive and remain excitable during long-term culture on synthetic supports

AbstractObjective: Cardiomyocytes can be transplanted successfully into skeletal and cardiac muscle. Our goal was to determine the feasibility of grafting cardiomyocytes onto various synthetic supports to create an excitable and viable tissue for implantation. Methods: Adult rat cardiomyocytes were cultured over an 8-week period onto different substitutes, including human glutaraldehyde-treated pericardium (n = 3), equine glutaraldehyde-treated pericardium (n = 3), polytetrafluoroethylene (n = 8), Dacron polyester (n = 16), and Vicryl polyglactin (n = 8). Results: Only the cells seeded on the Dacron survived, with the synthetic fibers colonized at 8 weeks. On the other supports, the number of myocytes progressively decreased from the first week, with their density (number of cells per square millimeter) being, after 20 days, 17 ± 2 on the polytetrafluoroethylene and 5 ± 1 on the human or equine pericardium compared with 45 ± 3 on the Dacron. After 8 weeks of culture on Dacron, the sarcomeric protein (sarcomeric α-actinin) was detected in all cells. In addition, the staining was regularly arranged and well aligned in a striated pattern. Spontaneous beating activity was obtained. Moreover, electrical stimulation of the cell preparation resulted in the generation of calcium transients, the frequency of which followed the frequency of the electrical stimulation. Conclusions: These results suggest that adult cardiac myocytes remain viable and excitable during long-term culture on a 3-dimensional Dacron support, which might constitute a new synthetic cardiac tissue. (J Thorac Cardiovasc Surg 2001;121:510-9

Microtubule polymerization state and clathrin-dependent internalization regulate dynamics of cardiac potassium channel

International audienceIon channel trafficking powerfully influences cardiac electrical activity as it regulates the number of available channels at the plasma membrane. Studies have largely focused on identifying the molecular determinants of the trafficking of the atria-specific KV1.5 channel, the molecular basis of the ultra-rapid delayed rectifier current IKur. Besides, regulated KV1.5 channel recycling upon changes in homeostatic state and mechanical constraints in native cardiomyocytes has been well documented. Here, using cutting-edge imaging in live myocytes, we investigated the dynamics of this channel in the plasma membrane. We demonstrate that the clathrin pathway is a major regulator of the functional expression of KV1.5 channels in atrial myocytes, with the microtubule network as the prominent organizer of KV1.5 transport within the membrane. Both clathrin blockade and microtubule disruption result in channel clusterization with reduced membrane mobility and internalization, whereas disassembly of the actin cytoskeleton does not. Mobile KV1.5 channels are associated with the microtubule plus-end tracking protein EB1 whereas static KV1.5 clusters are associated with stable acetylated microtubules. In human biopsies from patients in atrial fibrillation associated with atrial remodeling, drastic modifications in the trafficking balance occurs together with alteration in microtubule polymerization state resulting in modest reduced endocytosis and increased recycling. Consequently, hallmark of atrial KV1.5 dynamics within the membrane is clathrin- and microtubule- dependent. During atrial remodeling, predominance of anterograde trafficking activity over retrograde trafficking could result in accumulation ok KV1.5 channels in the plasma membrane

Contribution of CLEM to study the PAH-related pulmonary vasculary remodeling

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Myocardial cell death in fibrillating and dilated human right atria

AbstractOBJECTIVESThe aim of the present study was to determine if myocytes can die by apoptosis in fibrillating and dilated human atria.BACKGROUNDThe cellular remodeling that occurs during atrial fibrillation (AF) may reflect a degree of dedifferentiation of the atrial myocardium, a process that may be reversible.METHODSWe examined human right atrial myocardium specimens (n = 50) for the presence of apoptotic myocytes. We used immunohistochemical and Western blotting analysis to examine the expression of a final effector of programmed cell death, caspase-3 (CASP-3) and of regulatory proteins from the BCL-2 family.RESULTSSections from atria in AF contained a high percentage of large myocytes with a disrupted sarcomeric apparatus replaced by glycogen granules (64.4 ± 6.3% vs. 12.2 ± 5.8%). These abnormal myocytes, which also predominated in atria from hearts with decreased left ventricular ejection fraction (42.3 ± 10.1%), contained large nuclei, most of which were TUNEL positive, indicating a degree of DNA breakage. None of these abnormal myocytes expressed the proliferative antigen Ki-67. A small percentage of the enlarged nuclei (4.2 ± 0.8%) contained condensed chromatin and were strongly TUNEL positive. Both the pro- and activated forms of CASP-3 were detected in diseased myocardial samples, which also showed stronger CASP-3 expression than controls. Expression of the antiapoptotic BCL-2 protein was decreased in diseased atria, whereas that of the proapoptotic BAX protein remained unchanged.CONCLUSIONSIn fibrillating and dilated atria, apoptotic death of myocytes with myolysis contributes to cellular remodeling, which may not be entirely reversible

Workflow for Upscaling Wettability from the Nanoscale to Core Scale

Wettability is a key factor influencing multiphase flow in porous media. In addition to the average contact angle, the spatial distribution of contact angles throughout the porous medium is important, as it directly controls the connectivity of wetting and nonwetting phases. The controlling factors may not only relate to the surface chemistry of minerals but also to their texture, which implies that a length-scale range from nanometers to centimeters has to be considered. So far, an integrated workflow addressing wettability consistently through the different scales does not exist. In this study, we demonstrate that such a workflow is possible by combining microcomputed tomography (mu CT) imaging with atomic-force microscopy (AFM). We find that in a carbonate rock, consisting of 99.9% calcite with a dual-porosity structure, wettability is ultimately controlled by the surface texture of the mineral. Roughness and texture variation within the rock control the capillary pressure required for initializing proper crude oil-rock contacts that allow aging and subsequent wettability alteration. AFM enables us to characterize such surface-fluid interactions and to investigate the surface texture. In this study, we use AFM to image nanoscale fluid-configurations in 3D at connate water saturation and compare the fluid configuration with simulations on the rock surface, assuming different capillary pressures