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. 2005 Feb;64(2):217–221. doi: 10.1136/ard.2004.022590

Increased Bcl-2/p53 ratio in human osteoarthritic cartilage: a possible role in regulation of chondrocyte metabolism

F Iannone 1, C De Bari 1, C Scioscia 1, V Patella 1, G Lapadula 1
PMCID: PMC1755345  PMID: 15647429

Abstract

Objective: To determine whether Bcl-2, p53, and Fas/CD95 help to control cartilage metabolism.

Methods: Six normal and 14 osteoarthritic (OA) cartilage samples were examined, and two zones from each sample showing the least (Min) and most (Max) anatomical damage were selected. Chondrocytes were isolated by sequential enzymatic digestion and freshly processed. Bcl-2, p53, and Fas/CD95 expression was evaluated by immunofluorescence and FACS analysis; the cell cycle was analysed using propidium iodide, and chondrocyte proliferation assessed by [3H]thymidine incorporation.

Results: Intracellular levels of Bcl-2 were significantly higher in Max (27.5%) than in Min (21%, p<0.01) OA or normal chondrocytes (18.5%, p<0.01). Intracellular p53 expression was significantly decreased in Max (25.5%) compared with Min (37%, p<0.01) OA or normal cartilage (41.5%, p<0.05). Fas/CD95 receptor expression on surface chondrocytes did not significantly differ between OA and normal cartilage. Cell cycle analysis showed that the proportion of activated chondrocytes in the S phase was significantly higher in Max (69%) than in Min (49%) OA or normal cartilage (43%). The prevalence of proliferating chondrocytes progressively increased according to the degree of OA damage (mean (SEM) Min 1247 (260), Max 2423 (460), p<0.05). Chondrocyte [3H]thymidine uptake correlated positively with Bcl-2 (rs = 0.62, p = 0.009) and correlated inversely with p53 levels (rs = –0.55, p = 0.02).

Conclusions: Bcl-2 and p53 play a part in apoptosis, but also help to regulate chondrocyte growth and differentiation. Whereas Bcl-2 promotes cell survival, p53 can arrest cell cycle. The data confirm that chondrocyte activity is enhanced in OA and suggest that the increased Bcl-2/p53 ratio sustains the metabolic boost of chondrocytes.

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Figure 1.

Figure 1

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 Photomicrographs of safranin O stained histological sections of zones with macroscopically defined minimum (left) and maximum (right) damage in typical OA cartilage (original magnification x60). A diffuse staining of the cartilage, almost entirely masking the chondrocytes, is present in the minimum zone, while in the maximum zone there is evident hypocellularity together with some clusters of chondrocytes and severe reduction of the safranin O staining.

Figure 2.

Figure 2

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 Percentage of chondrocytes expressing intracellular p53 and Bcl-2, and cell surface Fas/CD95 in six normal cartilages (No), and in the lowest (Min) and highest (Max) damaged zones of 14 OA cartilages.

Figure 3.

Figure 3

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 Fluorescence intensity for intracellular p53 and Bcl-2 and surface CD95/Fas from an OA cartilage with minimal (Min) and maximum (Max) anatomical damage, and from a normal cartilage. Negative controls (a non-binding mAb) are shown as grey overlapping histograms. The y axis shows the percentage of positive chondrocytes and the x axis the mean channel fluorescence. Protein expression of p53 is definitely lower in Max than in Min or normal cartilage, and Bcl-2 was higher in Max than in Min or normal cartilage.

Figure 4.

Figure 4

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 Global correlation of intracellular levels of p53 and Bcl-2 with chondrocyte proliferation at day 5 assessed in three normal subjects and in the least (open circles) and most (closed triangles) damaged zones of 14 OA cartilage specimens. Spearman correlation test: rs correlation coefficient; p, significance level.

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