MMP9 and intervertebral disk degenerative disorder: Compared with the OVX group, mRNA and protein levels of Aggrecan and type II collagen in the OVX+E2 and OVX+PTH groups were higher, and expression of type I collagen, MMP-3 and MMP-9 were lower, showing that oestrogen and PTH could improve disc matrix synthesis and inhibit enzymes that can degrade extracellular matrix to reverse disc degeneration caused by ovariectomy.