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

Duygu Elif Yilmaz,Karin Kirschner,Hasan Demirci,Nina Himmerkus,Sebastian Bachmann,Kerim Mutig

doi:10.1016/j.jbc.2022.101589

Duygu Elif Yilmaz, Karin Kirschner + Show 4 more

Open Access

https://doi.org/10.1016/j.jbc.2022.101589

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Abstract

Current immunosuppressive strategies in organ transplantation rely on calcineurin inhibitors cyclosporine A (CsA) or tacrolimus (Tac). Both drugs are nephrotoxic, but CsA has been associated with greater renal damage than Tac. CsA inhibits calcineurin by forming complexes with cyclophilins, whose chaperone function is essential for proteostasis. We hypothesized that stronger toxicity of CsA may be related to suppression of cyclophilins with ensuing endoplasmic reticulum (ER) stress and unfolded protein response (UPR) in kidney epithelia. Effects of CsA and Tac (10 µM for 6 h each) were compared in cultured human embryonic kidney 293 (HEK 293) cells, primary human renal proximal tubule (PT) cells, freshly isolated rat PTs, and knockout HEK 293 cell lines lacking the critical ER stress sensors, protein kinase RNA–like ER kinase or activating transcription factor 6 (ATF6). UPR was evaluated by detection of its key components. Compared with Tac treatment, CsA induced significantly stronger UPR in native cultured cells and isolated PTs. Evaluation of proapoptotic and antiapoptotic markers suggested an enhanced apoptotic rate in CsA-treated cells compared with Tac-treated cells as well. Similar to CsA treatment, knockdown of cyclophilin A or B by siRNA caused proapoptotic UPR, whereas application of the chemical chaperones tauroursodeoxycholic acid or 4-phenylbutyric acid alleviated CsA-induced UPR. Deletion of protein kinase RNA–like ER kinase or ATF6 blunted CsA-induced UPR as well. In summary, inhibition of cyclophilin chaperone function with ensuing ER stress and proapoptotic UPR aggravates CsA toxicity, whereas pharmacological modulation of UPR bears potential to alleviate renal side effects of CsA.

Highlights

Current immunosuppressive strategies in organ transplantation rely on calcineurin inhibitors cyclosporine A (CsA) or tacrolimus (Tac)
Cyclosporine A induces endoplasmic reticulum (ER) stress in kidney epithelia (HRPTEpCs), and freshly isolated rat proximal tubule (PT), we provide several lines of evidence in support of the hypothesis that the more pronounced toxic effects of CsA on proteostasis are rooted in the suppression of cyclophilin chaperone activity
The present results obtained in cultured cells of renal origin and isolated rat PTs demonstrate that CsA stimulates multiple unfolded protein response (UPR) pathways, as evident from enhanced levels of spliced XBP1 (sXBP1), p-IRE1α, and C/EBP homologous protein (CHOP) [8, 9, 32]

Summary

Introduction

Current immunosuppressive strategies in organ transplantation rely on calcineurin inhibitors cyclosporine A (CsA) or tacrolimus (Tac) Both drugs are nephrotoxic, but CsA has been associated with greater renal damage than Tac. CsA inhibits calcineurin by forming complexes with cyclophilins, whose chaperone function is essential for proteostasis. Cyclosporine A induces ER stress in kidney epithelia (HRPTEpCs), and freshly isolated rat PTs, we provide several lines of evidence in support of the hypothesis that the more pronounced toxic effects of CsA on proteostasis are rooted in the suppression of cyclophilin chaperone activity. Pharmacological targeting of UPR using chemical chaperones, inhibitors of translation, or autophagy enhancers has been considered as an emerging strategy to delay progression of chronic kidney disorders [9] In this context, improved understanding of UPR-related molecular pathways affected by CNI may deliver new options for managing their nephrotoxicity

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