Correlation between SIRT1 mRNA expression, donor age, and Pfirrmann degeneration grade. (a) Correlation between mRNA expression of silent mating type information regulator 2 homolog 1 (SIRT1) and donor age in nucleus pulposus cells derived from the disc tissues of 19 patients with lumbar spinal stenosis, lumbar disc herniation, or idiopathic scoliosis. (b) Relationship of SIRT1 mRNA expression with the Pfirrmann intervertebral disc degeneration grade from magnetic resonance imaging (MRI). *P <0.05. GAPDH, glyceraldehyde 3-phosphate dehydrogenase.