Small Interfering RNA Reduces the Expression of Thrombospondins 1 and 2 in ST2 Cell Line In Vitro to Study Regulation of Transforming Growth Factor-β Bioavailability in Osteoblasts

Abstract

Maintenance of bone strength is controlled by the balance of bone resorption and formation. Bone resorption and formation are coupled processes regulated by osteoclasts and osteoblasts. Transforming growth factor-beta, TGF-β, influences the balance of these processes and therefore has been an important area of study in relation to the skeleton. Thrombospondins 1 and 2 (TSP1 and TSP2), are bone extracellular matrix (ECM) proteins that interact with transforming growth factor-beta (TGF-β) in other systems such as the skin and airways and so they have the potential to help regulate the availability of TGF-β in bone. Specifically, TSP1 can bind and activate latent TGF-β to help present it to its cell surface receptors. TSP2 also binds TGF-β, but it lacks the sequence required for growth factor activation. Thus, the relative proportions of TSP1 and TSP2 are a possible means by which TGF-β availability might be regulated in the skeleton. This study aims to examine osteoblast-specific regulation of TGF-β by TSP1 and TSP2. Gene expression of TSP1 and TSP2 was decreased 4 days post-transfection in ST2 cells using RNA interference (RNAi). Western blot analysis showed that 4 and 7 days post transfection, TSP1 protein was undetected and protein levels of TSP2 did not decrease. Continued research will provide insight on developing therapeutic strategies to treat diseases such as osteogenesis imperfecta where ECM-control of growth factor activity is compromised.