Optimizing renal transporter immunodetection: consequences of freeze-thaw during sample preparation

Area of Science:

• Renal physiology and molecular biology
• Biochemical analysis and quantification techniques

Background:

• Renal transporters are crucial for fluid and electrolyte homeostasis and are key targets for drug development.
• Immunoblotting is a standard method for assessing renal transporter abundance, but results vary due to inconsistent sample preparation.
• Lack of standardized kidney sample preparation protocols leads to variability in immunoblotting results.

Purpose of the Study:

• To investigate the impact of freeze-thawing kidney samples on immunoblot signal detection of renal transporters.
• To assess the effect of protease inhibitors during homogenization on transporter abundance quantification.
• To determine sex-specific differences in the effects of sample preparation on immunoblot signals.

Main Methods:

• Comparison of immunoblot signals from freshly processed (Fresh) versus freeze-thawed (Frozen) rat and mouse kidneys.
• Evaluation of the impact of standard and additional protease inhibitors (Roche cOmplete Protease Inhibitor) during homogenization.
• Quantification of 15 different renal transporters using specific antibody probes.

Main Results:

• Freeze-thawing significantly reduced immunodetection signals for most transporters in female Sprague-Dawley rats (∼50%) and male C57BL/6 mice (∼25-50%).
• Additional protease inhibitors partially restored signals but did not fully recover levels to those of fresh samples in male rats.
• Signal equivalence was observed in female rats for specific transporters (claudin 2, villin, AQP1, NKCC2, NCC, ENaCβ, ENaCɣ, claudin 7, AQP2, NKAα1, NKAβ1) when comparing fresh and frozen samples with inhibitors.

Conclusions:

• Kidney sample preparation variables, including freeze-thaw cycles and protease inhibition, have significant transporter-specific effects on immunoblot quantification.
• Sex and transporter type influence the impact of sample preparation on immunoblot signal recovery.
• Standardizing and reporting sample preparation methods are critical for ensuring the rigor and reproducibility of renal transporter abundance studies.