TNF‐α and IL‐1β Suppress N‐Cadherin Expression in MC3T3‐E1 Cells

Excessive production of tumor necrosis factor (TNF) and interleukin‐1 (IL‐1) secondary to estrogen deficiency have been implicated as the cause of osteoporosis in postmenopausal woman. These cytokines appear to stimulate osteoclast precursor proliferation and activate mature osteoclast formation directly and possibly indirectly via osteoblasts. To investigate the other possible roles that these cytokines may play in stimulating the bone resorption process, we examined the effect of TNF‐α and IL‐1β on cell–cell adhesion molecules, cadherins, in osteoblastic MC3T3‐E1 cells. In this study, we investigated cadherin expression and the effect of TNF‐α, IL‐1β, and parathyroid hormone (PTH) on the expression of cadherins in MC3T3‐E1 cells. Confluent cultures of MC3T3‐E1 cells were challenged with recombinant human TNF‐α (1–100 U/ml), recombinant human IL‐1β (1–100 ng/ml) and human PTH(1–34) (1–100 ng/ml), respectively. The results show that MC3T3‐E1 cells express functional cadherin molecules, N‐cadherin and OB‐cadherin. TNF‐α (10–100 U/ml) and IL‐1β (10–100 ng/ml) suppressed N‐cadherin without changing OB‐cadherin expression, while PTH (1–100 ng/ml) had no effect on cadherin expression. These results raise the possibility that TNF‐α and IL‐1β may compromise the cell–cell adhesion of osteoblasts which cover the bone surface. The ensuing compromised cell–cell adhesion of osteoblasts may in turn facilitate the direct adhesion of osteoclasts on the calcified bone matrix surface. These results implicate an indirect role for osteoblasts in the promotion of bone resorption by TNF‐α and IL‐1β.