Proliferation Protein Ki-67 is Increased in PTH Exposed Primary Cartilage

Objectives: Cartilage development in the cranial base and midface is a highly regulated process that involves the coordination of intracellular signaling and extracellular protein deposition. Regional proliferation and maturation appear to be regulated, in part, by the PTH/PTHrP (PPR) receptor. We asked: How does PPR activation modulate the proliferation marker Ki-67. Methods: Day fourteen embryonic chick sterna were harvested and placed in organ culture for 8 days. The sterna were grown in a defined media with or without 10-7M PTH. On the first, fourth and eighth days, the cephalic and caudal sterna were fixed and processed for immunohistochemistry using antibodies for the antinuclear protein Ki-67. Whole mount sternal lateral plates were analyzed with confocal microscopy. Random IHC samples (n=5 per group) were used to count chondrocytes with Ki-67 staining. Results: In the cephalic region, after one day of treatment, 36.65% of the PTH-treated chondrocytes stained for Ki-67 compared to 16.92 % of controls. On day 4, 33.46% of the PTH treatment group had Ki-67 compared to 16.08% in controls. On the eighth day, the PTH groups had 36.82 % Ki-67 staining compared to 3.04% in controls. In the caudal region, on Day 1, 18.18% of the PTH-treated chondrocytes stained for Ki-67 compared to 43.03 % of controls. On day 4, 1.8% of the PTH treatment group had Ki-67 compared to 3.2% in controls. On the eighth day, the PTH groups had 6.8% Ki-67 staining compared to 17.87% in controls. Conclusions: In the cephalic region of the primary avian cartilage, activation of the PTH/PTHrP common receptor may attenuate maturation and prolong chondrocytic proliferation as indicated by the increased Ki-67 staining. However, in the caudal region, exposure to PTH has little effect on Ki-67 staining, possibly suggesting decreased PPR ligand binding. NIH/DE-446951