N‐Acetyl Cysteine Regulates TNF‐α‐Inhibited Differentiation in ROS 17/2.8 Osteoblasts

Abstract

Osteoblasts play a pivotal role in bone remodeling. The alkaline phosphatase(ALPase) activity was decreased in ROS 17/2.8 osteoblast treated with TNF‐α (2, 5 or 10 ng/ml). The treatment of TNF‐α inhibited osteoblast differentiation such as ALPase activity in ROS 17/2.8 osteoblast. TNF‐α (10 ng/ml) increased NF‐κB DNA binding activity in nuclear extracts of osteoblasts. The addition of NAC (N‐acetyl cysteine), free radical scavenger, completely prevented TNF‐α‐induced activation of NF‐κB. In addition, IκBα and IκBβ were rapidly degraded, allowing the activated NF‐κB to enter the nucleus and promote gene transcription. To determine whether IκBα signal transduction pathway is important in the differentiation, we generated IκB (KD)‐stably transfected ROS 17/2.8 cells. These IκB (KD) transfectants did not show any regulation of ALPase in osteoblasts. Here, we suggest that the degradations of IκBα and IκBβ and the following activation of NF‐κB are the targets of NAC and that NF‐κB transcription factor is a pivotal clue to regulation of differentiation in TNFα‐exposed osteoblasts.