Active proliferation of mesenchymal cells prior to the chondrogenic repair response in rabbit full-thickness defects of articular cartilage.
OBJECTIVE
In full-thickness articular defects, fibroblast growth factor-2 (FGF-2) participates in the chondrogenic repair response which occurs in a defect-size dependent manner. Here we demonstrate that FGF-2 plays a critical role in the proliferation of pre-chondrogenic mesenchymal cells during chondrogenic induction.


METHODS
Three-millimeter- or 5-mm-diameter cylindrical defects were created in the femoral trochlea of the rabbit knee. The defects received sterile saline or FGF-2 (50 pg/h) via an osmotic pump for the initial 2 weeks. We assessed the proliferative capacity of undifferentiated mesenchymal cells in the reparative tissue with the anti-proliferating cell nuclear antigen (PCNA) monoclonal antibody. Using a total of 180 rabbits, we performed three sets of experiments.


RESULTS
In the 3-mm-diameter defects, undifferentiated mesenchymal cells spontaneously initiated chondrogenic differentiation within 2 weeks, resulting in the regeneration of surfacing articular cartilage concomitantly with the repair of subchondral bone. No evidence of chondrogenesis was seen in the 5-mm-diameter defects, whereas application of FGF-2 promoted successful regeneration of articular cartilage. In the 3-mm-diameter defects and in the FGF-2-treated 5-mm defects, PCNA immunoreactivity was widely detected in undifferentiated cells in the reparative tissue at 1 and 2 weeks after creation of the defects. In contrast, in the 5-mm-diameter defects without FGF-2 treatment, the PCNA-positive cells were found at a significantly lower incidence.


CONCLUSIONS
Active expansion of undifferentiated cell population mediated by FGF-2 is required to initiate and support a chondrogenic repair response in full-thickness defects of articular cartilage. Endogenous FGF-2 could not meet the requirements of growth signaling in the center of larger sized defects.
Mizuta
Hiroshi
H
Department of Orthopaedic and Neuro-Musculoskeletal Surgery, Faculty of Medical and Pharmaceutical Sciences, Kumamoto University, Kumamoto 860-8556, Japan.
Kudo
Satoshi
S
Nakamura
Eiichi
E
Otsuka
Yutaka
Y
Takagi
Katsumasa
K
Hiraki
Yuji
Y
D000469:Alkaline Phosphatase / Q000032:analysis; D000818:Animals; D015703:Antigens, CD / Q000032:analysis; D002358:Cartilage, Articular / Q000293:injuries / Q000503:physiopathology*; D002452:Cell Count; D002454:Cell Differentiation / Q000502:physiology; D019902:Chondrocytes / Q000502:physiology*; D002809:Chondroitin Sulfates / Q000032:analysis; D003094:Collagen / Q000032:analysis; D016222:Fibroblast Growth Factor 2 / Q000502:physiology*; D007150:Immunohistochemistry / Q000379:methods; D007632:Keratan Sulfate / Q000032:analysis; D059630:Mesenchymal Stem Cells / Q000502:physiology*; D018809:Proliferating Cell Nuclear Antigen / Q000032:analysis; D011817:Rabbits
D015703:Antigens, CD; D018809:Proliferating Cell Nuclear Antigen; D016222:Fibroblast Growth Factor 2; D002809:Chondroitin Sulfates; D003094:Collagen; D007632:Keratan Sulfate; D000469:Alkaline Phosphatase