Transport and Removal of Lipofuscin from Mouse Myocardium

Fig. S1. Longitudinal section of myocardial fiber in mouse heart.

In the vertical axis of the myocardial fiber in the figure, an oval-shaped cell nucleus can be seen. A large number of densely arranged mitochondria can be seen in the cytoplasm at both ends of the nucleus, and there are multiple lipofuscin granules with high electron density among the mitochondria. These lipofuscin granules are of different sizes and uneven internal structures. Several scattered lipofuscin granules can also be seen among the myofibrils (shown by black arrows). (×15000, scale plate: 2 μm)

Fig. S2. Myocardial fibers and capillary in mouse heart.

Three lipofuscin granules with high electron density can be seen within the myocardial fiber in the right half of the picture close to the capillary wall. They protrude from the surface of the myocardial fiber covered only by a layer of sarcolemma (shown by black arrows). There is no basement membrane outside the capillary endothelium. In the deeper part of the myocardial fiber, two lipofuscin-like granules with different electron densities can be seen (shown by white arrows). (×15000, scale plate: 1 μm)

Fig. S3. Myocardial fiber and myocardial interstitium in mouse heart.

This image shows a longitudinal section of the myocardial fiber. A narrow gap can be seen between the two myocardial fibers. The sarcolemma on the surface of the myocardial fiber on the left side of the gap is clearly visible, and the walking is smooth. The surface of the myocardial fiber on the right side of the gap is uneven, and there are several capsule-like protrusions on the surface of the myocardial fiber (shown by black arrows) of different sizes, heights, and widths. In the middle region of the cytoplasm inside the larger protrusion, there are several lipofuscin granules with high electron density. (×20000, scale plate: 800 nm)

Fig. S4. Fibroblast in myocardial interstitium of mouse heart.

A fibroblast is long spindle-shaped cell that is present in the longitudinal direction of the myocardial fibers with slender ends. The cytoplasm has high density and is rich in organelles. It also contains lipofuscin granules or clumps of varying sizes. These lipofuscinous granules or clumps have uneven internal structures and different morphologies, have high electron density, and have no membrane coating on the periphery. (×12 000, scale plate: 1 μm)

Fig. S5. Capillary and fibroblast in the cardiac myocardium of mouse heart.

A complete capillary can be seen in the myocardial interstitium. The lumen of the capillary is almost filled with red blood cells, leaving a little space on the top. There are several elongated finger-like protrusions from the endothelial cell. Below the capillary, a fibroblast can be seen, with an elongated protrusion, and it is closely attached to the outer wall of the capillary. In this area, there is no basement membrane notieable, and thus, the end of the protrusion is directly attached to the endothelial cell (shown by black arrows). Above the capillary, there are two small lipofuscin-like granules (shown by white arrows). (×20000, scale plate: 800 nm) (shown by thin white arrows)

Fig. S6. Myocardial tissue around extracellular space in mouse cardiac myocardium.

In the myocardial tissue around the extracellular space, a layer of cells is often visible on the surface of the myocardial fibers. This layer of cells can have different cellular characteristics, such as fibroblastic type (shown by the white arrow) or phagocytic type (shown by the black arrow). In addition to rich organelles, the cytoplasm of these cells will contain some lipofuscin-like mass or granules with high or medium electron density. Most of the lipofuscin granules are found within the phagocytic cell. (×20000, scale plate: 800 nm)

Fig. S7. A lipofuscin-containing phagocytic cell in the extracellular space of mouse cardiac myocardium.

The image shows a lipofuscin-containing phagocyte in the myocardial space with the morphological characteristics of macrophages. The cell surface is not smooth and has many wrinkles or protrusions of various sizes. There are visible signs of wrapping and swallowing. The cell contains multiple lipofuscin particles and lumps of various sizes, which have higher electron density. Parts of the lipofuscin granules have uneven internal structures with a large difference in electron density. Some lipofuscin granules have lipid droplet-like morphological characteristics. (×10000, scale plate: 1 μm)

Fig. S8. Lipofuscin mass in myocardium of mouse heart.

In the interstitium between myocardial fiber and capillary (or lymphatic vessel), there is a large lipofuscin mass. On the periphery of this huge lipofuscinous mass, intermittent membrane wrapping can be seen only in the area below it. Most part of the lipofuscinous mass is directly exposed in the interstitium, directly with the left myocardial fiber and the capillary (or lymphatic vessel) on the right are attached. The basement membrane is not noticeable between the lipofuscin mass and capillary endothelium (shown by black arrows). At the bottom, there are two separate lipofuscin granules, which are located below the sarcolemma of the myocardial fiber (shown by white arrow). (×15000, scale plate: 1 μm)

Fig. S9. Structure of a capillary in the myocardium of the mouse heart.

It can be seen that the capillary wall is thick, structural density of the endothelial cell is low, and the number of vesicles is low. In the cytoplasm of endothelial cell, three medium-high electron density spherical lipofuscin granules (shown by black arrows), few medium-high electron density fine particles, and several medium-high electron density tubules can be seen. The left inner wall of the capillary is not smooth, and the endothelial cell membrane protrudes into the lumen, forming fine finger-like protrusions and vesicles. Membrane sacs and membrane debris-like structures are scattered throughout the capillary cavity. The exterior of the vessel wall on both sides contains cytoplasmic fragments of extramural cells attached to the exterior of the endothelial cell (shown by white arrows). ( ×20 000, scale plate: 800 nm)