The myokine GDF-15 is a potential biomarker for myositis and associates with the protein aggregates of sporadic inclusion body myositis.
BACKGROUND
The cytokine growth differentiation factor-15 (GDF-15) has been associated with inflammatory and mitochondrial disease, warranting exploration of its expression in myositis patients.


METHODS
GDF-15 protein levels are evaluated in 35 idiopathic inflammatory myopathy (IIM) serum samples using enzyme-linked immunosorbent assays, comparing with levels in samples from healthy individuals and from patients with genetically confirmed hereditary muscular dystrophies and mitochondrial disorders. Muscle tissue expression of GDF-15 protein is evaluated using immunofluorescent staining and Western blotting.


RESULTS
GDF-15 protein levels are significantly higher in IIM sera (625 ± 358 pg/ml) than in that of healthy controls (326 ± 204 pg/ml, p = 0.01). Western blotting confirms increased GDF-15 protein levels in IIM muscle. In skeletal muscle tissue of IIM patients, GDF-15 localizes mostly to small regenerating or denervated muscle fibres. In patients diagnosed with sporadic inclusion body myositis, GDF-15 co-localizes with the characteristic protein aggregates within affected muscle fibres.


CONCLUSIONS
We describe for the first time that GDF-15 is a myokine upregulated in myositis and present the cytokine as a potential diagnostic serum biomarker.