Stromelysin-1 also known as matrix metalloproteinase-3 (MMP-3) is an enzyme that in humans is encoded by the MMP3 gene. The MMP-3 enzyme degrades collagen types II, III, IV, IX, and X, proteoglycans, fibronectin, laminin, and elastin. In addition, MMP-3 can also activate other MMPs such as MMP-1, MMP-7, and MMP-9, rendering MMP-3 crucial in connective tissue remodeling.[3] The enzyme is also thought to be involved in wound repair, progression of atherosclerosis, and tumor initiation.

In addition to classical roles for MMP3 in extracellular space, MMP3 can enter in cellular nuclei and control transcription. MMP3 itself can enter in nuclei of cells and regulate target gene such as CTGF/CCN2 gene.

MMP-3 has been implicated in exacerbating the effects of traumatic brain injury (TBI) through its disruption of the blood-brain barrier (BBB). Different studies have shown that after the brain undergoes trauma and inflammation has begun, MMP production in the brain is increased.[21][22] In a study conducted using MMP-3 wild type (WT) and knockout (KO) mice, MMP-3 was shown to increase BBB permeability after traumatic injury.