Correlation of calcium multiphoton with ultrastructural STED imaging of the slit diaphragm in the same glomerulus

Abstract In recent years functional multiphoton imaging of viable mouse tissue and STED imaging of optically cleared tissues allowed new insights into kidney biology. Here, we present a novel workflow where multiphoton imaging of calcium signals in podocytes is, in the same glomerulus, correlated with super-resolved STED imaging and analysis of the slit diaphragm (SD) morphology. Mice expressing the calcium indicator GCaMP3 exclusively in podocytes served as healthy controls and were challenged with two different doses of nephrotoxic serum (NTS). NTS-induced SD architecture damage increased in a dose-dependent manner, whereas intracellular calcium levels exhibited a wide range of variation and showed no correlation with SD damage in the same glomerulus. Our co-imaging protocol is applicable to a broad range of research questions as it is suitable for other tissues and compatible with a variety of reporters and tissue antigens. Translational statement The combination of multiphoton and super-resolution microscopy identifies the modulation of signaling pathways and resolves the changes in ultrastructure in disease states in the same glomeruli. Using our new method, we can compare functional and morphological data to investigate the degree of correlation to reveal novel underlying pathomechanism. This knowledge can improve our ability to draw conclusions from human kidney biopsies, in which the ultrastructure will be assessed more-often by routine super-resolution microscopy in the future.