Depth-varying Density and Organization of Chondrocytes in Immature and Mature Bovine Articular Cartilage Assessed by 3-D Imaging and Analysis
Kyle D. Jadin 1, Benjamin L. Wong 1, Won C. Bae 1, Kelvin W. Li 1, Amanda K. Williamson 1, Barbara L. Schumacher 1, Jeffrey H. Price 1 and Robert L. Sah 1*
1 Department of Bioengineering, University of California-San Diego, La Jolla, California
* To whom correspondence should be addressed. E-mail: rsah{at}ucsd.edu.
Submitted on August 24, 2004
Accepted on 15 March 2005
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Abstract |
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Articular cartilage is a heterogeneous tissue, varying with depth, as well as with maturation, in mechanical properties, matrix composition and orientation, and cell density and organization. The objective of the present study was to establish an automated method for localizing individual cells in three-dimensional (3-D) images of cartilage and to use this method to quantify the depth-associated variation in cellularity and cell organization at different stages of tissue growth. Three-dimensional images of fetal, calf, and adult cartilage were obtained by digital volumetric imaging, and then processed to identify cell nuclei. Accuracy of nucleus localization by the automated method was high, with 99% sensitivity relative to manual localization. Using nuclei localized as centroid positions, cellularity decreased from 290, 310, and 150 million cells per cm3 near the articular surface in fetal, calf, and adult samples, respectively, to 120, 110, and 50 million cells per cm3 at a depth of 1.0 mm. Cell organization, determined from the Euclidean Distance Transform, gave an average vector to the nearest cell nucleus with amplitude (distance) of 7.9, 7.1, and 9.1 µm near the articular surface of fetal, calf, and adult samples, increasing to 11.6, 12.0, and 19.2 µm at a depth of 0.7 mm. The angle of this vector (with respect to the transverse plane) was 30-31° throughout the full depth of fetal and calf cartilage and decreased from 31° near the surface of adult tissue, to 25° at a depth of 0.7 mm. The methodologies described here may be applied to characterize and assess the role of 3-D cellular organization during the dynamic processes of cartilage growth and maturation, as well as in aging, degeneration, and regeneration.
Key Words:
3-D imaging, cartilage, cell organization, chondrocyte, development, growth, histology, nucleus
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