N-Acetyl cysteine regulates TNF-α-inhibited differentiation in ROS 17/2.8 osteoblasts

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.