Mesenchymal progenitor cell markers in human articular cartilage: normal distribution and changes in osteoarthritis.
BACKGROUND
Recent findings suggest that articular cartilage contains mesenchymal progenitor cells. The aim of this study was to examine the distribution of stem cell markers (Notch-1, Stro-1 and VCAM-1) and of molecules that modulate progenitor differentiation (Notch-1 and Sox9) in normal adult human articular cartilage and in osteoarthritis (OA) cartilage.


METHODS
Expression of the markers was analyzed by immunohistochemistry (IHC) and flow cytometry. Hoechst 33342 dye was used to identify and sort the cartilage side population (SP). Multilineage differentiation assays including chondrogenesis, osteogenesis and adipogenesis were performed on SP and non-SP (NSP) cells.


RESULTS
A surprisingly high number (>45%) of cells were positive for Notch-1, Stro-1 and VCAM-1 throughout normal cartilage. Expression of these markers was higher in the superficial zone (SZ) of normal cartilage as compared to the middle zone (MZ) and deep zone (DZ). Non-fibrillated OA cartilage SZ showed reduced Notch-1 and Sox9 staining frequency, while Notch-1, Stro-1 and VCAM-1 positive cells were increased in the MZ. Most cells in OA clusters were positive for each molecule tested. The frequency of SP cells in cartilage was 0.14 +/- 0.05% and no difference was found between normal and OA. SP cells displayed chondrogenic and osteogenic but not adipogenic differentiation potential.


CONCLUSIONS
These results show a surprisingly high number of cells that express putative progenitor cell markers in human cartilage. In contrast, the percentage of SP cells is much lower and within the range of expected stem cell frequency. Thus, markers such as Notch-1, Stro-1 or VCAM-1 may not be useful to identify progenitors in cartilage. Instead, their increased expression in OA cartilage implicates involvement in the abnormal cell activation and differentiation process characteristic of OA.
Grogan
Shawn P
SP
Department of Molecular and Experimental Medicine, The Scripps Research Institute, La Jolla, California 92037, USA. sgrogan@scripps.edu
Miyaki
Shigeru
S
Asahara
Hiroshi
H
D'Lima
Darryl D
DD
Lotz
Martin K
MK
D000293:Adolescent; D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D000954:Antigens, Surface / Q000032:analysis / Q000096:biosynthesis; D015415:Biomarkers / Q000032:analysis / Q000378:metabolism; D002358:Cartilage, Articular / Q000166:cytology / Q000378:metabolism* / Q000473:pathology*; D002452:Cell Count; D002478:Cells, Cultured; D005260:Female; D005333:Fetus / Q000166:cytology / Q000378:metabolism / Q000473:pathology; D006801:Humans; D008297:Male; D059630:Mesenchymal Stem Cells / Q000166:cytology / Q000378:metabolism* / Q000473:pathology*; D008875:Middle Aged; D010003:Osteoarthritis / Q000378:metabolism* / Q000473:pathology*; D051881:Receptor, Notch1 / Q000032:analysis / Q000096:biosynthesis; D055758:SOX9 Transcription Factor / Q000032:analysis / Q000096:biosynthesis; D019010:Vascular Cell Adhesion Molecule-1 / Q000032:analysis / Q000096:biosynthesis; D055815:Young Adult
D000954:Antigens, Surface; D015415:Biomarkers; C497761:NOTCH1 protein, human; D051881:Receptor, Notch1; D055758:SOX9 Transcription Factor; C527932:SOX9 protein, human; C525591:STRO-1 antigen, human; D019010:Vascular Cell Adhesion Molecule-1