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Although light microscopy is a powerful tool for the assessment of kidney physiology and pathology, it has traditionally been unable to resolve structures separated by less than the ~250 nm
diffraction limit of visible light. Here, we report on the optimization, validation, and application of a recently developed super-resolution fluorescence microscopy method, called expansion
microscopy (ExM), for volumetric interrogation of mouse and human kidney tissue with 70–75 nm lateral and ~250 nm axial spatial resolution. Using ExM with a standard confocal microscope, we
resolve fine details of structures that have traditionally required visualization by electron microscopy, including podocyte foot processes, the glomerular basement membrane, and the
cytoskeleton. This inexpensive and accessible approach to volumetric, nanoscale imaging enables visualization of fine structural details of kidney tissues that were previously difficult or
impossible to measure by conventional methodologies.
The kidney glomerulus is a compact network of capillaries, supporting tissue, and resident cells. A critical structure of the glomerulus is the three-layered glomerular filtration barrier
(GFB) that filters waste products from the blood space to the urinary space and is comprised of innermost fenestrated glomerular endothelial cells, glomerular basement membrane (GBM), and
outermost interdigitated epithelial cells called podocytes. A major limitation in imaging the GFB is that many of the structures of the GFB are too small and too densely packed to be
resolvable by the ~250 nm resolution of traditional diffraction-limited light microscopy. To date, the analysis of fine structural details of the GFB has primarily relied on electron
microscopy (EM). Although extremely powerful, EM is typically limited to thin sections (