Structured illumination microscopy as a diagnostic tool for nephrotic disease

Nephrotic disease is a group of debilitating and sometimes lethal diseases affecting kidney function, specifically the loss of ability to retain vital proteins in the blood while smaller molecules are removed through filtration into the urine. Treatment routes are often dictated by microscopic analysis of kidney biopsies. Podocytes within the glomeruli of the kidney have many interdigitating projections (foot processes), which form the main filtration system. Nephrotic disease is characterised by the loss of this tightly interdigitating substructure and its observation by electron microscopy (EM) is necessitated as these structures are typically 250􀀀500nm wide, with 40nm spacing. Diagnosis by EM is both expensive and time consuming; it can take up to one week to complete the preparation, imaging, and analysis of a single sample. We propose structured illumination microscopy (SIM) as an alternative, optical diagnostic tool. Our results show that SIM can resolve the structure of fluorescent probes tagged to podocin, a protein localised to the periphery of the podocyte foot processes. Three-dimensional podocin maps were acquired in healthy tissue and tissue from patients diagnosed with two different nephrotic disease states; minimal change disease and membranous nephropathy. These structures correlated well with EM images of the same structure. Preparation, imaging, and analysis could be achieved in several hours. Additionally, the volumetric information of the SIM images revealed morphological changes in disease states not observed by EM. This evidence supports the use of SIM as a diagnostic tool for nephrotic disease and can potentially reduce the time and cost per diagnosis.