Modulation of Extracellular Matrix Production by Conditioned Medium

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Abstract
This report describes some general features of chick embryo chondrocyte cultures and some methods for measuring matrix production. It is reported that as cultures grow, the average chondrocyte acquires an increased ability to synthesize matrix components. In part this increased ability is caused by conditioning of the culture medium, since conditioned medium from chondrocyte cultures can rapidly stimulate mucopolysaccharide and collagen synthesis, but not growth. The cells condition the medium by releasing a factor that has the following characteristics: non-dialyzable, heat and trypsin-sensitive, sensitive to treatment with mercaptoethanol, p-chloromercuribenzoate, and periodate, and a molecular weight greater than 30,000 but less than 150,000. The factor is a specialized product of chondrocytes, since it is not made by unexpressed chondrocytes nor by differentiated pigmented retina cells. Conditioned medium acts rapidly (2 hr) to produce a significant stimulation of the incorporation of sulfate into hyaluronidase-sensitive material. This action is not sensitive to treatment with actinomycin D, and it is suggested that conditioned medium might act on the cell surface. The action of conditioned medium factor represents an example of positive feedback of one specialized product made by a particular cell type on the synthesis of other specialized products made by the same cell type.

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