Related Experiment Videos
Spatial distribution of CD44 and hyaluronan in the proximal tibia of the growing rat
K J Noonan1, J W Stevens, R Tammi
1Department of Orthopaedic Surgery, University of Iowa, College of Medicine, Iowa City 52242, USA.
Insights
CD44 is a cell surface receptor investigated for hyaluronan binding in rat tibia. While CD44 and hyaluronan co-localize in many connective tissues, CD44 is not the primary hyaluronan binder in growing cartilage.
Area of Science:
- Biochemistry
- Cell Biology
- Histology
Background:
- CD44 is a known cell surface hyaluronan receptor.
- Its prevalence in connective tissues containing hyaluronan is generally assumed.
- This study investigates CD44 and hyaluronan localization in the rat proximal tibia.
Purpose of the Study:
- To determine if CD44 and hyaluronan co-localize in rat proximal tibia tissues.
- To assess if CD44 functions as a major hyaluronan binding protein in these tissues.
Main Methods:
- In situ hybridization and immunohistochemistry were used to detect CD44.
- Biotinylated G1 domain of aggrecan and link protein identified hyaluronan.
- Localization was studied in various tissues of the growing rat proximal tibia.
Main Results:
- CD44 was found on osteoclasts, osteocytes, hematopoietic cells, synovial cells, and fibroblasts.
- CD44 expression was reduced on osteoblasts and osteoprogenitor cells.
- CD44 was absent in growth plate chondrocytes and meniscal fibrocartilage.
- Hyaluronan was detected in growth cartilages, synovium, connective tissues, periosteum, endosteum, osteocyte lacunae, and around blood vessels.
Conclusions:
- CD44 is a likely hyaluronan binding protein in several proximal tibia tissues.
- However, CD44 is not the predominant hyaluronan binding protein in the growing cartilages of young rats.
Abstract:
CD44 has been described as a cell surface hyaluronan receptor present on a variety of different cells, and it is generally assumed to be prevalent in most connective tissues that contain hyaluronan. A major aim of this study was to test that presumption by localizing CD44 and hyaluronan within several tissues of the proximal tibia of the growing rat. Comparison of these profiles would reveal whether CD44 and hyaluronan co-localize with high fidelity, as would be expected if CD44 were a major hyaluronan binding protein. Using in situ hybridization and immunohistochemistry, CD44 was identified on osteoclasts, chondroclasts, osteocytes, hematopoietic marrow cells, synovial cells, and connective tissue fibroblasts (ligaments, tendons, and fascia). Although the majority of osteocytes expressed CD44, reduced expression was observed for osteoblasts and ostcoprogenitor cells. Additionally. CD44 was not detected on chondrocytes from epiphyseal and metaphyseal growth cartilages or in meniscal fibrocartilage. Using biotinylated G1 domain from aggrecan and link protein, hyaluronan was observed in the maturational and hypertrophic zones of all growth cartilages, the synovium and other fibroblastic connective tissues, regional areas of the periosteum and endosteum (around osteoblasts, osteoprogenitor cells, and osteoclasts), osteocyte lacunae, and surrounding blood vessels. In regions of co-localization for CD44 and hyaluronan, it seems that CD44 is a likely hyaluronan binding protein in several tissues of the proximal tibia. However, it does not appear to be the predominant hyaluronan binding protein in growing cartilages of the weanling rat.