Early upregulation of matrix metalloproteinases following reperfusion triggers neuroinflammatory mediators in brain ischemia in rat

Abnormal expression of matrix metalloproteinases (MMPs) has been implicated in the pathophysiology of neuroinflammatory processes that accompany most central nervous system disease. In particular, early upregulation of the gelatinases MMP-2 and MMP-9 has been shown to contribute to disruption of the blood-brain barrier and to death of neurons in ischemic stroke. In situ zymography reveals a significant increase in gelatinolytic MMPs activity in the ischemic brain hemisphere after 2-h middle cerebral artery occlusion (MCAo) followed by 2-h reperfusion in rat. Accordingly, gel zymography demonstrates that expression and activity of MMP-2 and MMP-9 are enhanced in cortex and striatum ipsilateral to the ischemic insult. The latter effect appears to be instrumental for development of delayed brain damage since administration of a broad spectrum, highly specific MMPs inhibitor, GM6001, but not by its negative control, results in a significant (50%) reduction in ischemic brain volume. Increased gelatinase activity in the ischemic cortex coincides with elevation (166% vs sham) of mature interleukin-1 beta (IL-1 beta) after 2-h reperfusion and this does not appear to implicate a caspase-1-dependent processing of pro(31 kDa)-IL-1 beta to yield mature (17 kDa) IL-1 beta. More importantly, when administered at a neuroprotective dose GM6001 abolishes the early IL-1 beta increase in the ischemic cortex and reduces the cleavage of the cytokine proform supporting the deduction that MMPs may initiate IL-1 beta processing. In conclusion, development of tissue damage that follows transient ischemia implicates a crucial interplay between MMPs and mediators of neuroinflammation (e.g., IL-1 beta), and this further underscores the therapeutic potential of MMPs inhibitors in the treatment of stroke.