creation of a thrombus or a puncture wound on a murine jugular vein/femoral artery for montaged wide-area electron microscopy analysis

Puncture Wound Hemostasis and Montaged Electron Microscopy 

The formation of a puncture wound thrombus that leads to bleeding cessation is one of the most essential events in life1. Yet despite that essentiality, knowledge of what occurs structurally during thrombus formation, be it in a vein, an artery, an atherosclerotic event, or an occlusive clot, has been limited by resolution and imaging depth. Conventional light microscopy is limited in depth when compared to a fully formed puncture wound thrombus, 200 to 300 &#181;m in Z1,&#160;and in resolution level when compared to the size of platelet organelles and their spacing, often less than 30 nm2. Two-photon light microscopy can yield the needed depth of imaging but does not improve resolution significantly. The most recent advances in light microscopy, for example, super-resolution techniques, are still resolution limited, in practice ~20 nm in XY and twice that in Z, and depth limited, no more than conventional light microscopy. Furthermore, super-resolution light microscopy, like much of research light microscopy, is based on fluorescence microscopy, a technique that is inherently biased to a small set of candidate proteins for which good antibodies exist or good tagged constructs3. In conclusion, conventional scanning electron microscopy can, at most, visualize the surface of the forming platelet-rich thrombus.
To overcome these technical limitations to characterizing thrombus structure, we had three goals. First, reproducibly produce a defined puncture wound in a mouse vein or artery that could then be readily stabilized in situ by chemical fixation. Second, apply a preparative procedure that emphasizes membrane preservation, a goal consistent with the aim of defining the position of individual platelets within the forming thrombus. Third, use an unbiased visualization technique that, in a single image, could be scaled between nanometer to near millimeter scale.
Montaged, wide-area electron microscopy was chosen as a major end visualization technique for a single important reason: in electron microscope imaging, one sees a vast array of features within a cell that outlines its organelles and features within the organelles. Small objects such as ribosomes can be recognized. This range of features is seen because the electron-dense heavy metal stains, uranyl, lead, and osmium, that are used for electron microscopy to yield contrast bind to a wide range of molecules. In an electron microscope image, one sees much of what is there, while with immunofluorescence and protein tagging approaches, one only sees what lights up. This means, for example, the antigen sites present on a given individual protein species. In the case of a tagged molecule, often a protein, it is the site(s) where that protein is. All other molecules are dark and not lit up. However, is this choice of electron microscopy practical? A puncture wound thrombus has a size of 300 by 500 &#181;m and, at a pixel size of 3 nm, that is an image of 100,000 by 167,000 pixels. A high-quality electron microscope camera has 4000 by 4000 pixels. That means that approximately 1000 frames must be stitched/blended to give a single image. That is a possibility that has been present in most electron microscopes manufactured in the last 15 years. The microscope stage is computerized, and the images can be stitched together with a computer. That is the rationale that led to choices underlying the formulation of the presented protocol.
Conclusively, we present below a series of steps that give a reproducible wound in the vein or artery of mice that then, following in situ fixation steps and later embedding steps, can be visualized by montaged, wide-area transmission electron microscopy at nm scale and in the stitched image visualized at near mm scale, the scale of the actual in situ fixed thrombus. Scalability of this kind is required for understanding thrombus formation as both a problem in hematology/health and as a developmental biology system in which platelets are the major cell type. These advances deliver a major virtue of electron microscopy, namely, one sees what is there, not only what lights up. For a detailed protocol on the preparation of samples for serial block face scanning electron microscopy (SBF-SEM), the reader is directed to a recent article by Joshi et al.4.

Author Spotlight: Revealing Platelet Dynamics Through Advances in Structural Hematology

Puncture Wound Hemostasis and Preparation of Samples for Montaged Wide-Area Electron Microscopy Analysis

We're a lab that does volume EM, structural work, to say how do platelets activate, how do they aggregate? How do they form a thrombus that causes bleeding cessation and how in the case of over stimulation, they bring about occlusive clotting. In doing this, the premise is that if we know the structure, we can then better target drugs and bring about better outcomes.We use mouse models in our research, as many researchers do, and we all have the challenge of establishing how our findings in mice and in our case in the arteries and veins in mice, carry over to the mechanisms in the much larger arteries and veins in humans. We all hope that the principles are the same in mice and humans. If you take our work and using volume EM approaches, the big things that we've contributed are one, to say that platelets are not just suicide bombers.They retain granules. They do things in response to signaling. They have stable states, and these stable states are part of a normal thrombus and they're also part of an inclusive clot.Two, we've brought the sense that there is really structure to the thrombus that forms, it's not just simply a pile of bricks, but rather it's an ordered structure in which platelets are ordered with respect to their activation, et cetera. And three, we've brought the sense that one should be able to apply and understand from structure what needs to be either stimulated to get a good outcome or what needs to be suppressed to give a outcome that will protect people from bad outcomes. We collect sequential images at near nanometer scale of a near millimeter distances.We assemble those into the single montaged image. Hence, we can observe any given spot within the image at a scale of near nanometers to near millimeter, which is sufficient to place individual features inside of the whole thrombus. Researchers now have a powerful tool, and they can ask the new question, how do coagulation cascades and cellular signals or drugs act spatially at local to global levels in thrombi?

Creation of a Thrombus or a Puncture Wound on a Murine Jugular Vein/Femoral Artery for Montaged Wide-Area Electron Microscopy Analysis

To begin, with a pair of scissors and blunt forceps, lift and cut the skin of an anesthetized mouse over the right jugular vein. Cut a round window in the skin large enough to expose the jugular vein and some of the surrounding tissue. Gently push aside the adipose tissue, lymph nodes, and connective tissue using the blunt dissection technique.Next, fill a 20 milliliter syringe with normal saline warmed to 37 degrees Celsius. Load the syringe into the syringe infusion pump. Then attach a 27 gauge butterfly needle and associated tubing to the syringe.Set the syringe pump to a flow rate of 0.5 milliliters per minute to wash away blood from the punctured vein or artery. Position the stream of saline a few milliliters to the side of the puncture site and not directly over it. Once the jugular vein has been cleaned, start the timer.Obtain 30 gauge and 33 gauge hypodermic needles for the jugular vein and the femoral artery respectively. Turn the bevel to face upwards. Then position the needle at a 25 degree angle over the jugular vein or femoral artery.After noting the time, quickly puncture the top of the vessel. Note the time taken for the bleeding to stop completely. Wait for the formation of a thrombus before starting perfusion fixation.Once perfusion has been completed, dissect the part of the jugular vein with the puncture site and thrombus. Use a pair of sharp scissors to make a diagonal cut across the distal end of the vessel segment and make a straight cut across the proximal end of the vessel segment. Next, place the fixed tissue at four degrees Celsius for 24 hours.The next day, pour sodium cacodylate buffer solution into a 35 millimeter culture dish containing a five millimeter thick silicone mat. Carefully transfer the tissue into the buffer, ensuring that it is submerged in the buffer. With stainless steel minutien pins and a pair of fine forceps, carefully pin each end of the vessel to the mat.Carefully clean the jugular vein. With a pair of micro scissors, cut the vessel wall opposite the puncture site lengthwise. Gently open the vessel, then pin it to the silicone mat with the intraluminal side facing up.Remove the buffer solution from the dish. Then add 1%paraformaldehyde to submerge the vessel. Immediately place the lid on the dish to prevent drying out.

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Research

JoVE Journal

Medicine

22 次观看. 首先，用一把剪刀和钝钳，提起并切开右颈静脉上麻醉小鼠的皮肤。在皮肤上切一个足够大的圆窗，以暴露颈静脉和一些周围组织。使用钝性解剖技术轻轻推开脂肪组织、淋巴结和结缔组织。接下来，在20毫升注射器中加入加热至37摄氏度的生理盐水。将注射器装入注射器输液泵中。然后将 27 号蝶针和相关管路连接到注射器上。将注射泵设...