MMP9 and ulcer disease: The higher activity of MMP-2 and MMP-9 in diabetic mice wounds is similar to that of hard-to-heal wounds caused by ulcers or burns (41), and subsequently studies have identified MMP-8 and MMP-9 from diabetic wounds and demonstrated that MMP-8 inhibits apoptosis and favors wound healing, while conversely MMP-9 promotes apoptosis and renders wounds unhealable in mice (42).