Autophagy influences glomerular disease susceptibility and maintains podocyte homeostasis in aging mice
Björn Hartleben, Markus Gödel, Catherine Meyer-Schwesinger, Shuya Liu, Theresa Ulrich, Sven Köbler, Thorsten Wiech, Florian Grahammer, Sebastian J. Arnold, Maja T. Lindenmeyer, Clemens D. Cohen, Hermann Pavenstädt, Dontscho Kerjaschki, Noboru Mizushima, Andrey S. Shaw, Gerd Walz, Tobias B. Huber
Björn Hartleben, Markus Gödel, Catherine Meyer-Schwesinger, Shuya Liu, Theresa Ulrich, Sven Köbler, Thorsten Wiech, Florian Grahammer, Sebastian J. Arnold, Maja T. Lindenmeyer, Clemens D. Cohen, Hermann Pavenstädt, Dontscho Kerjaschki, Noboru Mizushima, Andrey S. Shaw, Gerd Walz, Tobias B. Huber
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Research Article Nephrology

Autophagy influences glomerular disease susceptibility and maintains podocyte homeostasis in aging mice

Abstract

Injury and loss of podocytes are leading factors of glomerular disease and renal failure. The postmitotic podocyte is the primary glomerular target for toxic, immune, metabolic, and oxidant stress, but little is known about how this cell type copes with stress. Recently, autophagy has been identified as a major pathway that delivers damaged proteins and organelles to lysosomes in order to maintain cellular homeostasis. Here we report that podocytes exhibit an unusually high level of constitutive autophagy. Podocyte-specific deletion of autophagy-related 5 (Atg5) led to a glomerulopathy in aging mice that was accompanied by an accumulation of oxidized and ubiquitinated proteins, ER stress, and proteinuria. These changes resulted ultimately in podocyte loss and late-onset glomerulosclerosis. Analysis of pathophysiological conditions indicated that autophagy was substantially increased in glomeruli from mice with induced proteinuria and in glomeruli from patients with acquired proteinuric diseases. Further, mice lacking Atg5 in podocytes exhibited strongly increased susceptibility to models of glomerular disease. These findings highlight the importance of induced autophagy as a key homeostatic mechanism to maintain podocyte integrity. We postulate that constitutive and induced autophagy is a major protective mechanism against podocyte aging and glomerular injury, representing a putative target to ameliorate human glomerular disease and aging-related loss of renal function.

Authors

Björn Hartleben, Markus Gödel, Catherine Meyer-Schwesinger, Shuya Liu, Theresa Ulrich, Sven Köbler, Thorsten Wiech, Florian Grahammer, Sebastian J. Arnold, Maja T. Lindenmeyer, Clemens D. Cohen, Hermann Pavenstädt, Dontscho Kerjaschki, Noboru Mizushima, Andrey S. Shaw, Gerd Walz, Tobias B. Huber

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Figure 2

Atg5-dependent autophagy is dispensable for glomerular development.

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Atg5-dependent autophagy is dispensable for glomerular development. ...
(A) Immunofluorescence staining of kidney sections derived from newborn GFP-LC3–transgenic mice identified autophagosomes during late podocyte differentiation in the late capillary loop stage. WT1 served as a marker for podocyte nuclei. Podocin served as a marker for podocyte foot processes. Arrows indicate GFP-LC3–positive autophagosomes. (B) Western blot analysis confirmed Atg5 deficiency in kidneys from Atg5–/– mice by demonstrating the absence of Atg5 and the lack of LC3 conversion. (C and D) No morphological abnormalities of glomerular differentiation were detected in histology (C) or electron microscopy (D) of samples derived from fetal kidneys of Atg5–/– mice. (E) Western blot analysis of isolated glomeruli from Atg5Δpodocyte mice confirmed the absence of Atg5 and displayed the abrogated conversion of LC3-I. (F) Atg5Δpodocyte mice were crossed with GFP-LC3–transgenic mice to confirm the functional ablation of autophagy. In these triple-transgenic mice, glomerular GFP-LC3–positive vesicles were completely absent and GFP-LC3 was diffusely distributed in the cytoplasm (arrows indicate cytosolic GFP signal). (G) No differences in the total number of glomeruli were detected in kidneys of Atg5Δpodocyte mice or control littermates (P = 0.78, 2-tailed Student’s t test, n = 5 for each condition). Scale bars: 5 μm (A and F, middle and right), 20 μm (C and F, left), 2 μm (D, top), 500 nm (D, bottom).