Sublytic complement C5b‐9 complexes induce thrombospondin‐1 production in rat glomerular mesangial cells via PI3‐k/Akt: association with activation of latent transforming growth factor‐β1

Summary Mesangial cell proliferation is a common cellular response to a variety of different types of glomerular injury. Complement C5b‐9 is a prime candidate to mediate mesangial cell proliferation, especially sublytic C5b‐9, which can induce the production of multiple inflammatory factors and cytokines. Transforming growth factor (TGF)‐β1 plays a major role in the accumulation of extracellular matrix (ECM), while thrombospondin (TSP)‐1 has been identified as an activator of latent TGF‐β1 in an in vitro system. Using rat glomerular mesangial cells (GMCs) as a model system, we assessed the effect of sublytic C5b‐9 on the expression of TSP‐1 and TGF‐β1 and explored the relevant pathway of signal transduction. First, we ensured the concentrations of anti‐Thy1 antibody and complement, which were regarded as a sublytic C5b‐9 dose, and examined whether the sublytic C5b‐9 induced expression of TSP‐1 in rat GMCs which, in turn, activated latent TGF‐β1 by real‐time polymerase chain reaction (PCR) and enzyme‐linked immunosorbent assay (ELISA), respectively. Then, we investigated the role of the PI3‐k/Akt pathway in sublytic C5b‐9‐induced TSP‐1 production in rat GMCs by Western blot analysis. The addition of sublytic C5b‐9 (5% anti‐Thy1 antibody and 4% normal serum) to rat GMCs induced activation of latent TGF‐β1 via TSP‐1. The addition of sublytic C5b‐9 apparently increased the protein of Akt phosphorylation, whereas PI3‐k inhibitor LY294002 could clearly reduce the increase of TSP‐1 induced by sublytic C5b‐9. These results indicate that TSP‐1 is an activator of latent TGF‐β1 in sublytic C5b‐9‐induced rat GMCs; furthermore, the PI3‐k/Akt signal transduction pathway may play a key role in sublytic C5b‐9‐induced TSP‐1 production.