J Korean Orthop Assoc.  1999 Oct;34(5):803-809.

Cellular Proliferation and Apoptosis during Endochondral Fracture Healing

• Im GI
• Kim DY
• Shin JH
• Han JD
• Cho WH
• Kim IS

Abstract

PURPOSE: The authors investigated the process of endochondral ossification quantitatively and objectively in respect to proliferation and apoptosis.
MATERIALS AND METHODS
Fractures were made on the left tibiae of 72 male Sprague-Dawley rats. The fracture callus was harvested at the 5th, 7th, 9th, 11th, 14th, and the 21st day after fracture. Cellular DNA content was analyzed with image cytometry, and proliferative index was determined from the data. The Ki-67 antigen expression was semiquantitatively measured by the immunohisto-chemical method. TUNEL was used for in situ localization of apoptotic cells. The expression of cell cycle inhibitors, P21 and P27, was investigated with Northern blotting.
RESULTS
The proliferation index was highest on the 5th day, then gradually decreased until the 11th day. The expression of Ki-67 antigen gradually decreased with time. Apoptotic cells increased in accordance with enhanced bone formation within chondroid callus. The expression of p21 and p27 was highest on the 11th and the 14th day.
CONCLUSIONS
These findings show that proliferative activity decreased with the reduction of mesenchymal tissue and the appearance of mature chondroid tissue. The apoptosis of hypertrophic chondrocytes occurred in accordance with enhanced bone formation. P21 and P27 had a certain role in the differentiation of chondrocytes.

Keyword

Apoptosis; Endochondral ossification; Fracture healing

MeSH Terms

Apoptosis*
Blotting, Northern
Bony Callus
Cell Cycle
Cell Proliferation*
Chondrocytes
DNA
Fracture Healing*
Humans
Image Cytometry
In Situ Nick-End Labeling
Ki-67 Antigen
Male
Osteogenesis
Rats, Sprague-Dawley
Tibia
DNA
Ki-67 Antigen