Abstract
Abstract The aim of this study was to determine whether synovial fluid (SF) of dogs contains cells that have characteristics of MSCs and to describe their differentiation potential. SF adherent cells from 5 young German shepherd dogs (average 3.8 ± 0.9 years) were expanded (37°C, 5% CO2, humidified atmosphere) three weeks before their phenotype was characterized by flow-cytometry for the presence of CD90 and CD34. Population doubling time (PDT), number of CFU-F and adipogenic, osteogenic and chondrogenic potentials have been determined in vitro. In early passages PTD was 31 ± 10 hours and expansion fold after 3 sub cultivations (9 days) theoretically could be 372 ± 134. At P1, 0.55 ± 0.05% of SF cells had the ability to form CFU-F. Sixty-six percent of cells expressed CD90 and none of the cells expressed markers of hematopoietic cells. Oil Red O staining has shown accumulation of fat droplets in cells grown in adipogenic medium, while deposits of calcium in the osteogenic medium were evidenced with Alizarin red staining. SF cultured in hondrogenic and control medium in three-dimensional conditions formed a cartilage-like tissue. Alcian blue staining of pellets’ slides have shown a significant amount of glycosaminoglycans (GAGs) and immunohistochemistry analysis documented collagen type II expression. The amount of GAGs in pellets grown in both conditions showed no difference. SF cells in vitro exhibited osteogenic, adipogenic and chondrogenic differentiation potentials, suggesting the presence of different mesenchymal progenitors. These results also demonstrated that SF cells have a spontaneous chondrogenic potential that should be further explored for possible tissue engineering protocols.
Highlights
Normal synovial fluid (SF) is a hyaluronic acid rich, viscous liquid that protects diarthrodial joints and nourishes chondrocytes of avascular hyaline cartilage
In passages P1 to P3 Population doubling time (PDT) was 31 ± 10 hours and expansion fold after 3 sub cultivations was 372 ± 134 that theoretically could result in a high cell number suitable for further use (Table 1)
The main finding of this work is that cells, cultivated from SF of adult young dogs without signs of OA or inflammation, have a large proliferative potential and the possibility to differentiate toward adipocytes, osteoblasts and chondrocytes, i.e. these cells have typical in vitro characteristics of mesenchymal progenitor cells
Summary
Normal synovial fluid (SF) is a hyaluronic acid rich, viscous liquid that protects diarthrodial joints and nourishes chondrocytes of avascular hyaline cartilage. The main function of the SF leukocyte population is the immune surveillance of the joint tissue. Their transendothelial migration is similar in all tissues [1]. The function of synoviocytes in the SF is just beginning to be defined and the first data obtained in rabbits [2,3] and some very recent experimental data in porcine, rats and rabbits point that SF cells could directly differentiate into chondrocytes and meniscal cells when hyaline cartilage or meniscal injury is provoked [2,3,4,5,6]
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