Intracellular glutathione pools are heterogeneously concentrated

Area of Science:

• Cell Biology
• Biochemistry
• Redox Biology

Background:

• Glutathione (GSH) is a critical cellular antioxidant, present in millimolar concentrations.
• Its precise distribution across intracellular compartments, particularly the endoplasmic reticulum (ER), is not well understood.
• Understanding compartment-specific glutathione levels is crucial for cellular redox homeostasis.

Purpose of the Study:

• To investigate and quantify glutathione levels within the endoplasmic reticulum (ER) of intact cells.
• To determine the glutathione redox ratio ([GSH]:[GSSG]) specifically in the ER.
• To compare ER glutathione concentration with the overall intracellular concentration.

Main Methods:

• Utilized a genetically encoded glutaredoxin sensor (sCGrx1pER) designed to equilibrate with the ER's glutathione redox couple.
• Measured the [GSH]:[GSSG] ratio in the ER of intact HeLa cells.
• Calculated total glutathione concentration ([GStot]) based on measured ratios and known equilibrium constants.

Main Results:

• The [GSH]:[GSSG] ratio in the ER of HeLa cells was determined to be less than 7:1.
• This ratio, combined with a previously established [GSH](2):[GSSG] value of 83 mM for the ER, indicates a total glutathione concentration ([GStot]) exceeding 15 mM in the ER.
• This ER concentration is significantly higher than the integrated intracellular [GStot] of approximately 7 mM.

Conclusions:

• A concentration gradient of total glutathione ([GStot]) exists across the ER membrane, with higher levels in the ER compared to the cytosol.
• The ER environment exhibits a distinct, high [GStot] compared to the extracellular space.
• A potential homeostatic mechanism involving glutathione trapping within the ER is proposed.