Involvement of endoplasmic reticulum (ER) stress in podocyte injury induced by excessive protein accumulation.
BACKGROUND
An imbalance between protein load and folding capacity is referred to as endoplasmic reticulum (ER) stress. As a defense mechanism, cells express ER stress inducible chaperons, such as oxygen-regulated proteins 150 (ORP150) and glucose-regulated proteins (GRPs). While ER stress is important in various diseases, a pathophysiologic role for ER stress in kidney disease remains elusive. Here we investigate expression of ER stress proteins in cultured rat podocytes as well as in our recently developed animal model of abnormal protein retention within the ER of podocytes (i.e., megsin transgenic rat).


METHODS
The expression of ER stress inducible proteins (ORP150, GRP78, or GRP94) in cultured podocytes treated with tunicamycin, A23187, SNAP, hypoxia, or hyperglycemia, and the renal tissues or isolated glomeruli from megsin transgenic rats was analyzed by Western blotting analysis, immunohistochemistry, or confocal microscopy.


RESULTS
Cultured podocytes demonstrated that treatment with tunicamycin, A23187, and SNAP, but not hypoxia or hyperglycemia, up-regulate expression of ER stress proteins. Extracts of isolated glomeruli from megsin transgenic rats reveal marked up-regulation of ER stress chaperones in podocytes, which was supported by immunohistochemical analysis. Confocal microscopy revealed that ER stress in podocytes was associated with cellular injury. Podocytes of transgenic rats overexpressing a mutant megsin, without the capacity for polymerization within the ER, do not exhibit ER stress or podocyte damage, suggesting a pathogenic role of ER retention of polymerized megsin.


CONCLUSIONS
This paper implicates a crucial role for the accumulation of excessive proteins in the podocyte ER in the induction of ER stress and associated podocyte injury.
Inagi
Reiko
R
Molecular and Cellular Nephrology, Institute of Medical Sciences, Tokai University, Kanagawa, Japan.
Nangaku
Masaomi
M
Onogi
Hiroshi
H
Ueyama
Hiroshi
H
Kitao
Yasuko
Y
Nakazato
Kiyokazu
K
Ogawa
Satoshi
S
Kurokawa
Kiyoshi
K
Couser
William G
WG
Miyata
Toshio
T
D000818:Animals; D030801:Animals, Genetically Modified; D000900:Anti-Bacterial Agents / Q000494:pharmacology; D002478:Cells, Cultured; D004721:Endoplasmic Reticulum / Q000187:drug effects / Q000378:metabolism*; D000091342:Endoplasmic Reticulum Chaperone BiP; D018840:HSP70 Heat-Shock Proteins / Q000378:metabolism; D006360:Heat-Shock Proteins / Q000378:metabolism; D006801:Humans; D008565:Membrane Proteins / Q000378:metabolism; D018832:Molecular Chaperones / Q000378:metabolism; D050199:Podocytes / Q000166:cytology / Q000187:drug effects / Q000378:metabolism*; D017510:Protein Folding; D011506:Proteins / Q000737:chemistry / Q000378:metabolism*; D011507:Proteinuria / Q000378:metabolism*; D051381:Rats; D015843:Serpins / Q000235:genetics / Q000378:metabolism; D014415:Tunicamycin / Q000494:pharmacology
D000900:Anti-Bacterial Agents; D000091342:Endoplasmic Reticulum Chaperone BiP; C051684:GRP78 protein, rat; D018840:HSP70 Heat-Shock Proteins; C000717247:HSPA5 protein, human; D006360:Heat-Shock Proteins; D008565:Membrane Proteins; D018832:Molecular Chaperones; D011506:Proteins; C114170:SERPINB7 protein, human; D015843:Serpins; C018551:glucose-regulated proteins; C050087:oxygen-regulated proteins; D014415:Tunicamycin