Chondrocyte apoptosis induced by collagen degradation: Inhibition by caspase inhibitors and IGF‐1

Abstract

The main objective of this study was to test the effectiveness of candidate apoptosis inhibitors in limiting chondrocyte apoptosis induced by collagen degradation. Primary human chondrocytes were isolated from normal articular cartilage and grown in monolayer culture. Collagenase was added to the cells in the presence and absence of caspase inhibitors and insulin like growth factor (1GF)-I . The amount of chondrocyte apoptosis was measured using an enzyme linked immunosorbent assay for nucleosomes, a specific and quantitative measure of apoptosis. Chondrocyte apoptosis was induced by collagenase treatment in both a time and dose dependent manner. The non-selective caspase inhibitor Z-VAD, the caspase-3 selective inhibitor Z-DEVD, and the growth factor insulin like growth factor (1GF)-I inhibited chondrocyte apoptosis induced by collagenase treatment. The caspase-l selective inhibitor Z-YVAD also blocked chondrocyte apoptosis under these conditions, in contrast to previous studies where caspase-1 inhibition failed to block apoptosis induced by agents such as the topoisomerase inhibitor camptothecin. These data demonstrate that the response of chondrocytes to caspase inhibition may be dependent upon the specific stimulus that initiates apoptosis. Furthermore, these findings suggest that multiple pathways involving both the initiation and execution of programmed cell death are potential targets for chondrocyte apoptosis inhibition therapy.

Binding and Release Characteristics of Insulin-Like Growth Factor-1 from a Collagen–Glycosaminoglycan Scaffold

“…40 The addition of IGF-1 to explants and monolayer cultures at concentrations of 10-200 ng/mL increased collagen type II and DNA synthesis and inhibited proteoglycan degradation, 41 whereas 200 ng/mL also inhibited chondrocyte apoptosis in vitro. 42 The optimal dose of IGF-1 required to enhance proteoglycan synthesis in osteoarthritic cartilage was 30 ng IGF-1/mL. 43 Previous research also indicated that in vitro chondrocytes do not respond any better to 1000 ng IGF-1/mL than 100 ng IGF-1/mL.…”

Chondrocyte Apoptosis: Implications for Osteochondral Allograft Transplantation

“…Although a variety of different stimuli initiate chondrocyte apoptosis [2,3,6,9,10,23,24,26,30,32], a universal feature of chondrocyte apoptosis is caspase activation [13,16,17,31,35,39,44] (Fig. 1).…”

“…Upon activation, caspase enzymes cleave a number of cellular proteins, including poly (ADPribose) polymerase, sterol regulatory element binding protein, and nuclear mitotic apparatus proteins, which ultimately lead to cell death. In particular, caspase 1 and caspase 3 are believed to play critical roles in the initiation and execution phases of chondrocyte apoptosis, making them attractive targets for intervention [31]. Caspase 9, part of the ''apoptosome'' complex that mediates mitochondrial pro-apoptotic signaling pathways, may also play an important role in chondrocyte apoptosis [35].…”

“…Blockade of the pathways responsible for the initiation and/ or execution of apoptosis may prevent chondrocyte loss associated with cartilage injury, and a series of recent studies [14,16,31,39] suggest this approach may, in fact, be quite feasible. Nuttall and colleagues [39] demonstrated that caspase 3 inhibition could block chondrocyte apoptosis and maintain biosynthetic function in cultured chondrocytes.…”

“…Nuttall and colleagues [39] demonstrated that caspase 3 inhibition could block chondrocyte apoptosis and maintain biosynthetic function in cultured chondrocytes. Other studies [14,16,31] have identified growth factors and multiple caspase inhibitors that can block chondrocyte PCD induced by matrix degradation and mechanical injury. We reported that insulin growth factor (IFG)-1, as well as peptide inhibitors of caspase 1 and caspase 3, blocked chondrocyte apoptosis induced by collagenases treatment [31].…”