Induction of interleukin‐1 receptors on chondrocytes by fibroblast growth factor: A possible mechanism for modulation of interleukin‐1 activity

Abstract

Interleukin-1 is a polypeptide factor with profound effects on several cell types, such as chondrocytes, fibroblasts, and T-cells. The ability of interleukin-1 to induce the synthesis of matrix-degradative enzymes, as well as prostaglandin E2, suggests a pivotal role for this mediator in chronic inflammation. Previous studies have shown that the effect of human monocyte interleukin-1 on the synthesis of collagenase and neutral proteases by chondrocytes was enhanced by basic fibroblast growth factor. Using recombinant human interleukin-1B, we have examined whether the potentiation of interleukin-1 effects by fibroblast growth factor is related to changes in the number or affinity of interleukin-1 receptors. Our studies confirm that rabbit articular chondrocytes in culture contain a single class of high-affinity receptors for interleukin-1 with a Ka of 0.9-1.1 x 10(-13) M-1. While the untreated chondrocytes contain approximately 1,620 receptors per cell, fibroblast growth factor-treated cells exhibit a higher number of receptors (approximately 2,960 per cell) with no apparent change in the affinity. The increase in receptor number can be abolished by inhibitors of lysosomal function, indicating a requirement for intracellular processing of the fibroblast growth factor. Our results suggest that the potentiation of interleukin-1 catabolic effects by fibroblast growth factor may be related to its ability to induce additional interleukin-1 receptors on the chondrocyte cell surface.

Differential regulation of metalloprotease steady‐state mRNA levels by IL‐1 and FGF in rabbit articular chondrocytes

“…The relative molecular welghts were determined by comparing against high molecular weight standards from Bio-Rad. Cells treated with FGF alone did not induce any pretense (data not shown: [12]). …”

“…Chondrocytes were isolated from the tibial and femoral cartilage of 1-1.5 k/g NZW rabbits 18,12] by sequential digestion with hyaluronldase (Sigma; St. Louis), TPCK-tqpsin and collagenas¢ (Worthington, Freehold. N J).…”

“…The. ¢on~ntrafions of the ~'tok-lnes and growth factors were establi'~ed based on our previous observations [12,15], The total cellular RNA was extracted with guanidine hydrochloride, then with chloroform + n-butanol, followed by 2 ethanol Confluent monolayers of rabbit articular chondroeytcs were treated with IL-I (30 ng/ml) or FGF (10 ng/ml) or both for indicated time intervals in eerum-fre¢ DMEM. The conditioned media samples were assayed (in quadruplicate) for neutral pretense activity using [.~H]caseln as the sabstrate (Materials and Methods).…”

“…In this system, only 1L-1 was able to induce collagenase/stromelysin production, whereas growth factors modulated the IL-I activity. These growth factors, when added alone, did not induce any enzyme synthesis [12][13][14][15]. The rnetalloproteases are synthesized as precursor proteins and require activation [1][2][3][4], but very little is known about the early postreceptor events that lead to the induction of the enzymes.…”

The superficial layer of human articular cartilage is more susceptible to interleukin‐1–induced damage than the deeper layers

“…The beads were washed extensively, and the cells were released from alginate with 5 mM EDTA, recovered by centrifugation or filtration, and then bound radioactivity was measured in a gamma counter. Specific binding was calculated as the difference in binding of '251-labeled IL-I a or p alone and in the presence of a 250-fold concentration of unlabeled IL-1 a or p (54). The molar ratios of ' "I to IL-la and to IL-1 p were the same.…”