Relaxin stimulates MMP-2 and alpha-smooth muscle actin expression by human periodontal ligament cells

The main cells in the periodontal ligament (PDL) are the fibroblasts, which play an important role in periodontal remodelling. Matrix metalloproteinases (MMPs) are largely responsible for the degradation of extracellular matrix proteins in the PDL. Previous studies have indicated that MMP production can be stimulated by the hormone relaxin. This hormone facilitates delivery by softening the connective tissues of the reproductive tract, and it prepares the mammary gland for lactation. Periodontal remodelling takes place during orthodontic tooth movement, which might be enhanced by relaxin. Therefore, we investigated the effects of relaxin on gelatinase expression of human PDL cells. Cultures of human PDL cells were incubated with relaxin. Gelatinase (MMP-2 and -9) expression, alpha-smooth muscle actin expression (alpha-SMA), total MMP activity and DNA content were measured. Both proMMP-2 and active MMP-2 was identified in the cultures. There was a clear trend showing a dose-dependent increase of MMP-2 production, which was significant at 250 ng/ml. Total MMP activity was not affected. A stimulation of alpha-SMA expression was found at 50 ng/ml. The results indicate that relaxin activates human PDL cells by the stimulation of MMP-2 and alpha-smooth muscle actin.