Fig 4. Correlation analysis of cumulative population doubling level (PDL) of nucleus pulposus chondrocytes versus (A) donor age, (B) initial telomere length, and (C) initial telomerase activity.

Telomere length and telomerase activity at the first passage are indicated as initial telomere length and initial telomerase activity. Telomere lengths are provided in kilobases (kb) and the level of telomerase activity as relative telomerase activity (RTA).