Irisin: Still chasing shadows

Area of Science:

• Biochemistry
• Molecular Biology
• Endocrinology

Background:

• The myokine irisin has garnered attention for its potential roles in metabolism and exercise.
• Significant questions persist regarding the accuracy and reproducibility of methods used to measure irisin levels.

Purpose of the Study:

• To evaluate the reliability of commonly used reagents and methods for quantifying circulating irisin.
• To investigate the FNDC5 gene transcription and irisin antibody specificity across species.

Main Methods:

• Assessed FNDC5 transcript patterns in humans and mice using cDNA amplification.
• Examined irisin antibody specificity and sensitivity via western blotting.
• Quantified circulating irisin using mass spectrometry with absolute quantification peptides.

Main Results:

• Identified greater human FNDC5 transcript diversity than annotated, but no evidence of truncated irisin transcripts.
• Demonstrated that irisin antibodies cross-react with non-specific serum proteins, compromising ELISA reliability.
• Highlighted uncontrollable variations in mass spectrometry-based irisin quantification due to multi-step sample preparation.

Conclusions:

• Current methods for measuring circulating irisin are unreliable and should be used with caution.
• The findings suggest that measurements of irisin using available techniques are not robust.