Myokine

Mass spectrometry

Chemistry

Chromatography

Blot

Extracellular matrix

FNDC5

Skeletal muscle

Gene

Endocrinology

Complementary DNA

Biology

Robustness (evolution)

Fibronectin

Computational biology

Biochemistry

Molecular Metabolism

Considerable uncertainty remains regarding the veracity of measuring myokine irisin more than seven years after its original description. Unresolved issues include the nature of transcription of the irisin precursor fibronectin type III domain containing 5 (FNDC5) gene across species, the reliability of irisin levels measured with commercial enzyme-linked immunosorbent assays (ELISAs), and the overall validity of the recently published reference values for human serum measured with quantitative mass spectrometry. We utilized multiple species and measures to evaluate the robustness of commonly used reagents and methods for reporting irisin. Amplification of cDNA was used to assess the FNDC5 transcript patterns in humans and mice. The specificity and sensitivity of different irisin antibodies were examined via western blotting. Quantification of circulating native irisin was conducted with mass spectrometry using an absolute quantification peptide for irisin. We show that there is a greater transcript diversity...

Irisin: Still chasing shadows