Shank2 Regulates Renal Albumin Endocytosis

• Published in: Physiological reports 2015-09, Vol.3 (9), p.e12510-n/a
• Main Authors: Dobrinskikh, Evgenia, Lewis, Linda, Doctor, R. Brian, Okamura, Kayo, Lee, Min Goo, Altmann, Christopher, Faubel, Sarah, Kopp, Jeffrey B., Blaine, Judith
• Format: Article
• Language: English
• Subjects: Advanced imaging; Albumin; albuminuria; Caveolin; Endocytosis; Kidney diseases; Localization; Microscopy; Original Research; Physiology; Postsynaptic density; Proteins; Proteinuria; Renal tubules; Rodents; scaffolding proteins; Signal transduction; Statistical analysis; Urine
• ISSN: 2051-817X; 2051-817X
• DOI: 10.14814/phy2.12510

Albuminuria is a strong and independent predictor of kidney disease progression but the mechanisms of albumin handling by the kidney remain to be fully defined. Previous studies have shown that podocytes endocytose albumin. Here we demonstrate that Shank2, a large scaffolding protein originally identified at the neuronal postsynaptic density, is expressed in podocytes in vivo and in vitro and plays an important role in albumin endocytosis in podocytes. Knockdown of Shank2 in cultured human podocytes decreased albumin uptake, but the decrease was not statistically significant likely due to residual Shank2 still present in the knockdown podocytes. Complete knockout of Shank2 in podocytes significantly diminished albumin uptake in vitro. Shank2 knockout mice develop proteinuria by 8 weeks of age. To examine albumin handling in vivo in wild‐type and Shank2 knockout mice we used multiphoton intravital imaging. While FITC‐labeled albumin was rapidly seen in the renal tubules of wild‐type mice after injection, little albumin was seen in the tubules of Shank2 knockout mice indicating dysregulated renal albumin trafficking in the Shank2 knockouts. We have previously found that caveolin‐1 is required for albumin endocytosis in cultured podocytes. Shank2 knockout mice had significantly decreased expression and altered localization of caveolin‐1 in podocytes suggesting that disruption of albumin endocytosis in Shank2 knockouts is mediated via caveolin‐1. In summary, we have identified Shank2 as another component of the albumin endocytic pathway in podocytes. This article describes the role of Shank2, a large scaffolding protein originally identified at the neuronal postsynaptic density, in albumin endocytosis in the kidney. We find that lack of Shank2 significantly impairs albumin uptake in podocytes in vitro and, using intravital multiphoton imaging, that lack of Shank2 also impairs albumin uptake in proximal renal tubular cells. In addition, we find that lack of Shank2 alters the expression and localization of caveolin‐1, a protein required for albumin uptake in podocytes. Thus, we have identified Shank2 as another component of the albumin endocytosis pathway.