Functional heterogeneity of osteoclasts: matrix metalloproteinases participate in osteoclastic resorption of calvarial bone but not in resorption of long bone

Abstract

Data in the literature suggest that site-specific differences exist in the skeleton with respect to digestion of bone by osteoclasts. Therefore, we investigated whether bone resorption by calvarial osteoclasts (intramembranous bone) differs from resorption by long bone osteoclasts (endochondral bone). The involvement of two major classes of proteolytic enzymes, the cysteine proteinases (CPs) and matrix metalloproteinases (MMPs), was studied by analyzing the effects of selective low molecular weight inhibitors of these enzymes on bone resorption. Mouse tissue explants (calvariae and long bones) as well as rabbit osteoclasts, which had been isolated from both skeletal sites and subsequently seeded on bone slices, were cultured in the presence of inhibitors and resorption was analyzed. The activity of the CP cathepsins B and K and of MMPs was determined biochemically (CPs and MMPs) and enzyme histochemically (CPs) in explants and isolated osteoclasts. We show that osteoclastic resorption of calvarial bone depends on activity of both CPs and MMPs, whereas long bone resorption depends on CPs, but not on the activity of MMPs. Furthermore, significantly higher levels of cathepsin B and cathepsin K activities were expressed by long bone osteoclasts than by calvarial osteoclasts. Resorption of slices of bovine skull or cortical bone by osteoclasts isolated from long bones was not affected by MMP inhibitors, whereas resorption by calvarial osteoclasts was inhibited. Inhibition of CP activity affected the resorption by the two populations of osteoclasts in a similar way. We conclude that this is the first report to show that significant differences exist between osteoclasts of calvariae and long bones with respect to their bone resorbing activities. Resorption by calvarial osteoclasts depends on the activity of CPs and MMPs, whereas resorption by long bone osteoclasts depends primarily on the activity of CPs. We hypothesize that functionally different subpopulations of osteoclasts, such as those described here, originate from different sets of progenitors.

The Src Inhibitor AZD0530 Reversibly Inhibits the Formation and Activity of Human Osteoclasts

“…Osteoclasts were isolated as described before (25). Briefly, long bones were dissected from 5-d-old Chinchilla rabbits, and the periostea were removed.…”

“…In addition, AZD0530 is the first Src inhibitor to show inhibition of the Src pathway in human tumor tissue (22). Preliminary data suggest that AZD0530 could specifically affect osteoclastic bone resorption because resorption markers present in serum and urine were significantly reduced after single (volunteers) or multiple daily doses of AZD0530 (volunteers and patients with cancer), whereas markers for bone formation were not affected (23)(24)(25). AZD0530 is now being tested specifically in cancer patients with metastatic bone disease to determine its effect on bone turnover markers in this population (22).…”

The role of proteases in pathologies of the synovial joint

“…Inhibitor studies of bone resorption also suggested a distinct role for one or more MMPs which was dependent on bone type (Everts et al, 1999). Further studies have implied that MMP-mediated collagen proteolysis may be physiologically important in removing any remaining matrix from areas vacated by osteclasts at the end of the resorption cycle (Everts et al, 2002).…”

Cathepsin K and matrix metalloproteases activity in bone tissue of OXYS rats with osteoporosis development

“…Важная роль в разрушении и ремоделировании тканей отводится матриксным металлопротеазам (MMП), однако сведения об их участии в резорбции кости весьма противоречивы. Установлено, что MMП-1,-2 продуцируются остеобластами [3,8]. У мышей, нокаутированных по различным ММП, не обнаружено изменений резорбции кости [4] или найдены лишь незначительные кратковременные изменения в деградации костной ткани [3].…”

“…У мышей, нокаутированных по различным ММП, не обнаружено изменений резорбции кости [4] или найдены лишь незначительные кратковременные изменения в деградации костной ткани [3]. С другой стороны, на культуре остеокластов показано, что ММП-9 (желатиназа В) также необходима для резорбции костей черепа, как и катепсин К [8]. Вовлеченность изменений матриксных металлопротеаз в патогенез остеопороза изучена недостаточно.…”