Imaging Renal Ultrastructure using a Fast and Simple Optical Clearing and Swelling Protocol

Many light-microscopy protocols have in recent years been published for visualization of ultrastructure in the kidney. These protocols present researchers with new tools to evaluate both foot process anatomy and effacement, as well as protein distributions in foot processes, the slit diaphragm and in the GBM. However, these protocols either involve the application of different complicated super-resolution microscopes or lengthy sample preparation protocols. We here present a fast and simple, 5-hour long procedure for the full three-dimensional visualization of podocyte foot processes using conventional confocal microscopy. The protocol combines and optimizes different optical clearing and tissue expansion concepts to produce a mild swelling, sufficient for resolving foot processes using a diffraction-limited confocal microscope. We further show that the protocol can be used for common visualization of large-scale renal histology, pathology, and kidney protein distributions. Thus, we believe that our fast and simple protocol can be beneficial for routine conventional microscopic evaluation of kidney tissue integrity both in research and in the clinic.