A Cycle of Altered Proteasome and Reactive Oxygen Species Production in Renal Proximal Tubular Cells

Nirmala Parajul

doi:10.17140/tfmoj-4-128

Abstract

AimsAn intricate relationship exists between the mitochondrial function and proteasome activity. Our recent report showed in a rat model of renal transplantation that mitochondrial dysfunction precedes compromised proteasome function and this results in a vicious cycle of mitochondrial injury and proteasome dysfunction. In this study, we studied whether reactive oxygen species (ROS) has a role in proteasome alteration in renal cells and vice versa.MethodsWe used the genomic and pharmacologic approach on rat normal kidney proximal tubular (NRK) cell lines. First, we knocked down β5 or Rpt6 subunit of the proteasome using small interfering RNA (siRNA) in NRK cells. We also treated NRK cells with Bortezomib, a proteasome inhibitor, and peroxynitrite (a potent ROS).ResultsStudies with RNA interference showed increased mitochondrial ROS following knockdown of β5 or Rpt6 subunit in NRK cells. Similarly, pharmacological inhibition of the proteasome in NRK cells using Bortezomib also showed an increase of mitochondrial ROS in a dose-dependent manner. Next, exposing NRK cells to different concentrations of peroxynitrite provided evidence that the higher levels of peroxynitrite exposure decreased the key subunits (β5 and α3) of the proteasome in NRK cells.ConclusionOur results suggest that proteasome inhibition/downregulation increases ROS, which then impairs proteasome subunits in renal proximal tubular cells.

Highlights

The proteasome is the main machinery of the ubiquitin-proteasome system (UPS), which is essential for maintaining protein quality in all eukaryotic cells.[1,2,3]
Our results suggest that proteasome inhibition/downregulation increases reactive oxygen species (ROS), which impairs proteasome subunits in renal proximal tubular cells
We recently reported that Bortezomib (BTZ) treatment increases mitochondrial dysfunction and alteration of key respiratory subunits in normal kidney proximal tubular (NRK) cells.[11]

Summary

Introduction

The proteasome is the main machinery of the ubiquitin-proteasome system (UPS), which is essential for maintaining protein quality in all eukaryotic cells.[1,2,3]. The role of the proteasome pathway during renal ischemia-reperfusion needs to be fully elucidated.[8] Interestingly, in vitro data show that ROS exposure to mammalian cells can inhibit the proteasome function and can alter its composition.[9,10] We recently demonstrated that mitochondrial dysfunction precedes compromised proteasome function in a rat model of renal cold storage plus transplantation, and reported the existence of a functional interdependent relationship between the proteasome activity and mitochondrial function in rat kidneys/renal cells.[11] The main goal of this study was to examine a relationship between ROS and proteasome alteration in renal proximal tubular cells. Using normal rat kidney proximal tubular cell line (NRK), here, we demonstrate that proteasome inhibition increases mitochondrial ROS and exogenous ROS treatment declines proteasome subunit level

Methods

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Discussion

Conclusion