Bicellular Localization of Tricellular Junctional Protein Angulin-3/ILDR2 Allows Detection of Podocyte Injury

Podocytes serve as part of the renal filtration unit with slit diaphragms. Although the structure of slit diaphragms between two cells is well characterized, it has remained unknown how the tricellular contact of podocytes is organized and how it changes in injured podocytes. This study focused on a tricellular junction protein, angulin-3, and its localization was analyzed in healthy podocytes as well as in developmental stage and in pathologic conditions, using a newly established monoclonal antibody. Angulin-3 was confined at tricellular junctions of primordial podocytes, then transiently localized at bicellular junctions as foot process interdigitation developed and the intercellular junctions rearranged into slit diaphragm, and eventually distributed in a sparse punctate pattern on the foot processes of adult podocytes. In the rodent podocyte injury models, angulin-3 showed bicellular localization between the foot processes, and the localization turned from punctate to dashed linear pattern along the effaced foot processes as podocyte injury progressed. Angulin-3 also accumulated between foot processes in a linear pattern in kidney biopsy samples of human nephrotic syndrome. Furthermore, it was discovered that the line length of angulin-3 staining signal correlated with risk of relapse under glucocorticoid therapy in patients with minimal change nephrotic syndrome. In this article, an image program was proposed to score the linearity of the accumulation pattern of angulin-3 to evaluate the relapse risk of patients with minimal change nephrotic syndrome.