Aug 16, 2002
Using a murine model of stroke, investigators in California identified an extracellular pathway whereby neuronal cell death results from S-nitrosylation of matrix metalloproteinase-9 (MMP-9). Their findings appear in the August 16th issue of Science.
Led by Dr. Stuart A. Lipton, the researchers at The Burnham Institute in La Jolla, California, observed elevated MMP activity in mouse brain parenchyma after occlusion of the middle cerebral artery for 2 hours followed by reperfusion.
Evidence suggesting the role of neuronal nitric oxide synthase (nNOS) included abrogation of MMP activation after treatment with an nNOS inhibitor and in nNOS knockout mice. MMP-9 and nNOS were found to colocalize in the ischemic cortex.
The research team generated a recombinant, truncated proMMP-9. Treatment with S-nitrosocysteine (SNOC), a physiological NO donor, led to the formation of S-nitrosothiol and activation of the recombinant proMMP-9. Treatment of cultured neurons with NO-activated MMP-9 increased apoptosis that did not take place in the presence of inactivated proMMP-9.
Dr. Lipton's team pointed out that nitrosothiols can be short-lived and that S-nitrosylation is reversible. Therefore, they looked further at the chemical nature of the NO-triggered modification of MMP-9 responsible for activation. Mass spectroscopy showed that after exposure to SNOC, a sulfonic acid derivative of the recombinant proMMP-9 was formed.
MMP-9 from rats exposed to ischemia and reperfusion also exhibited a sulfonic acid derivative similar to that found in vitro after NO activation of human MMP-9.
S-nitrosylation of one cysteine residue in MMP-9 was irreversibly oxidized to a sulfinic or sulfonic acid derivative, which led to activation of MMP-9, the researchers found. Blocking the formation of NO prevented the production of the sulfinic and sulfonic acid derivatives.
"S-Nitrosylation and subsequent oxidation of protein thiol in the prodomain of MMP-9 can thus lead to enzyme activation," the authors write, subjecting the extracellular matrix to nitrosative and oxidative stress. They suggest that other MMPs may also be activated through this pathway.
By targeting the nitrosylation of MMPs, Dr. Lipton and his associates hope that new treatments can be developed for stroke and neurodegenerative disorders, such as Alzheimer's disease, HIV-associated dementia and multiple sclerosis.
© 2002 Reuters Ltd