Role of IRE1α in podocyte proteostasis and mitochondrial health

Abstract

Glomerular epithelial cell (GEC)/podocyte proteostasis is dysregulated in glomerular diseases. The unfolded protein response (UPR) is an adaptive pathway in the endoplasmic reticulum (ER) that upregulates proteostasis resources. This study characterizes mechanisms by which inositol requiring enzyme-1α (IRE1α), a UPR transducer, regulates proteostasis in GECs. Mice with podocyte-specific deletion of IRE1α (IRE1α KO) were produced and nephrosis was induced with adriamycin. Compared with control, IRE1α KO mice had greater albuminuria. Adriamycin increased glomerular ER chaperones in control mice, but this upregulation was impaired in IRE1α KO mice. Likewise, autophagy was blunted in adriamycin-treated IRE1α KO animals, evidenced by reduced LC3-II and increased p62. Mitochondrial ultrastructure was markedly disrupted in podocytes of adriamycin-treated IRE1α KO mice. To pursue mechanistic studies, GECs were cultured from glomeruli of IRE1α flox/flox mice and IRE1α was deleted by Cre–lox recombination. In GECs incubated with tunicamycin, deletion of IRE1α attenuated upregulation of ER chaperones, LC3 lipidation, and LC3 transcription, compared with control GECs. Deletion of IRE1α decreased maximal and ATP-linked oxygen consumption, as well as mitochondrial membrane potential. In summary, stress-induced chaperone production, autophagy, and mitochondrial health are compromised by deletion of IRE1α. The IRE1α pathway is cytoprotective in glomerular disease associated with podocyte injury and ER stress.

Immunosuppressive calcineurin inhibitor cyclosporine A induces proapoptotic endoplasmic reticulum stress in renal tubular cells

“…Notably, our attempts to inactivate another ER-stress sensor, IRE1α, produced no viable cell line suggesting that intact IRE1α signaling is critical to cellular proteostasis and survival (32). Indeed, deletion of IRE1α has been shown to impair protein folding, autophagy, and mitochondrial function in podocytes (46). In the present study, PERK-KO cells exhibited milder increases of CHOP and p-IRE1α in response to CsA or Tg suggesting a blunted UPR.…”

Analysis of gene expression and use of connectivity mapping to identify drugs for treatment of human glomerulopathies

“…Primary mouse GECs were generated according to previously published methods ( 12 , 31 ). These cells contain a floxed IRE1α gene, but in the absence of transduced Cre recombinase, the cells express normal levels of IRE1α, and are phenotypically normal ( 12 ). In IRE1α knockout (KO) cells, Cre recombinase has deleted IRE1α ( 12 ).…”

“…These cells contain a floxed IRE1α gene, but in the absence of transduced Cre recombinase, the cells express normal levels of IRE1α, and are phenotypically normal ( 12 ). In IRE1α knockout (KO) cells, Cre recombinase has deleted IRE1α ( 12 ). Studies were done after the cells were cultured at the differentiation temperature (37°C).…”

“…For example, mice with podocyte-specific genetic deletion of IRE1α show reduced induction of ER chaperones and autophagy that is associated with podocyte injury as the mice age, and exacerbation of injury in experimental glomerulopathies. “Preconditioning” of animals to induce the UPR or treatment of animals with chemical chaperones to reduce ER protein misfolding attenuate glomerular disease ( 7 , 12 , 13 ). Mice with podocyte-specific deletion of the key autophagy mediators ATG5 or ATG7 show age-related podocyte injury and exaggerated injury in experimental glomerulopathies ( 7 , 14 ).…”

Therapeutic Approaches Targeting Proteostasis in Kidney Disease and Fibrosis

“…In addition, albumin and high glucose administration induced the activation of ER stress in human and rodent renal tubules [86]. Furthermore, the deletion of podocyte-specific IRE1a and XBP1s in mice led to more severe cases of albuminuria, glomerular basement membrane thickening, and ER stress induction [87,88].…”