Combination of thrombin and matrix metalloproteinase-9 exacerbates neurotoxicity in cell culture and intracerebral hemorrhage in mice.

The rapid loss of neurons is a major pathological outcome of intracerebral hemorrhage (ICH). Several mechanisms may produce the neurotoxicity observed in ICH, and these include proteolytic enzymes such as thrombin and matrix metalloproteinase-9 (MMP-9). We tested the hypothesis that thrombin and MMP-9 combine to injure neurons in culture and that they interact to promote the acute neurotoxicity that occurs in ICH in vivo. We report that human fetal neurons die when exposed to thrombin or MMP-9 in isolation and that a combination of these two enzymes increased neurotoxicity. The toxicity of thrombin involved protease-activated receptor-1 and the conversion of proMMP-9 to active MMP-9. In ICH, which was induced in mice by the intracerebral injection of autologous blood, significant areas of brain damage, neuronal death, microglia/macrophage activation, and neutrophil accumulation occurred by 24 h of injury. Importantly, these neuropathological features were reduced in MMP-9 null mice compared with wild-type controls, and the concordant antagonism of thrombin using hirudin also alleviated the injury found in MMP-9 null mice. Our collective results demonstrate that thrombin and MMP-9 collaborate to promote neuronal death in culture and in ICH. To improve the prognosis of ICH, the neurotoxic actions of thrombin and MMP-9 must be inhibited early and simultaneously after injury.

Cytotoxicity by matrix metalloprotease-1 in organotypic spinal cord and dissociated neuronal cultures.

Extracellular matrix (ECM) proteins, including collagens and laminins, are critical to the structure of the neuronal synapse and may also be involved in cell survival. In the present study, we therefore examined the possibility that select ECM degrading proteins might be toxic to organotypic spinal cord and dissociated neuronal cultures. Of those proteins tested, including MMP-1, -7, and -9, we observed that MMP-1 was toxic to spinal cord cultures as determined by release of lactic acid dehydrogenase as well as uptake of propidium iodide. Pretreatment of cell cultures with 50 microM alpha-tocopherol partially reversed these effects. We also observed that MMP-1 was toxic to human neurons grown in dissociated cultures and that increased amounts of MMP-1 were released by astrocytes following their stimulation with IL-1beta. These results suggest that further studies may be warranted to determine whether MMP-1 contributes to neurodegenerative conditions in which activated astrocytes may play a role.