Time-dependent effect of GDF-5 on protein expression of tendonogenic markers and MMP-13. Tenomodulin increased at days 3, 6, and 12; Smad-8 increased at days 3, 6, and 9; tenascin-C increased at days 3, 6, and 12 but decreased at day 9; and MMP-13 increased at days 3 and 9 but decreased at days 6 and 12.