Urea-associated oxidative stress and Gadd153/CHOP induction

Area of Science:

• Nephrology
• Cell Biology
• Molecular Biology

Background:

• Urea is a key solute in the renal medulla, crucial for concentrating urine.
• The cellular response to high solute concentrations, particularly urea, is not fully understood.
• Oxidative stress is implicated in various kidney diseases.

Purpose of the Study:

• To investigate the cellular response of renal medullary cells to urea treatment.
• To determine if urea induces oxidative stress and identify associated molecular pathways.
• To explore the role of oxidative stress in solute signaling within the kidney medulla.

Main Methods:

• Treatment of mouse renal medullary mIMCD3 cells with varying concentrations of urea.
• Analysis of gene and protein expression for Gadd153/CHOP, C/EBP-beta, and grp78 using mRNA and Western blot techniques.
• Reporter gene assays to assess Gadd153 and Egr-1 transcriptional activity.
• Quantification of intracellular reduced glutathione to measure oxidative stress.
• Assessment of antioxidant effects on urea-induced gene expression.

Main Results:

• Urea treatment (100-300 mM) significantly increased Gadd153/CHOP mRNA and protein levels in mIMCD3 cells.
• Other tested solutes did not induce similar changes in Gadd153/CHOP expression.
• Urea modestly enhanced Gadd153 transcription but did not affect mRNA stability.
• Urea treatment led to increased oxidative stress, evidenced by reduced intracellular glutathione.
• Antioxidant treatment partially inhibited urea-induced Egr-1 reporter gene activation.

Conclusions:

• Urea induces oxidative stress in renal medullary cells.
• Urea-mediated upregulation of Gadd153/CHOP is sensitive to oxidative stress.
• Oxidative stress represents a novel solute-signaling pathway in the kidney medulla.
• This pathway may also be relevant in other tissues exposed to high solute concentrations.