No abstract

No abstract

Matrix metalloproteinases (MMPs) and the tissue inhibitors of MMPs (TIMPs) are emerging as important modulators of brain physiopathology. Dramatic changes in the expression of MMPs and TIMPs occur during excitotoxic/neuroinflammatory processes. However, only the measurement of net protease activity is relevant physiologically, and the functional consequences of MMP/TIMP ratio modifications in the brain remain elusive. In order to assess MMP activity and effects in brain tissue, we combined in vivo and organotypic culture models of kainate (KA)-induced excitotoxicity to provoke selective neuronal death and neuroinflammation in the hippocampus. Using in situ zymography, we show that KA-induced excitotoxic seizures in rats increase net MMP activity in hippocampal neurons 8 h after seizures, before their death, and that this increase is neuronal activity-dependent. Three days after KA, proteolytic activity increases in blood vessels and reactive glial cells of vulnerable areas, in relation with neuroinflammation. At 7 and 15 days, proteolysis remains high in blood vessels whereas it is reduced in glia. In organotypic hippocampal cultures, which lack blood cell-mediated inflammation and extrinsic connections, a broad-spectrum inhibitor of MMPs (MMPI), but also a selective MMP-9 inhibitor, protect hippocampal neurons against KA-induced excitotoxicity. Moreover, recombinant MMP-9, but not MMP-2, induces selective pyramidal cell death in these cultures and KA-induced neuronal activity exacerbates the neuronal death promoting effects of MMP-9. These data strongly implicate MMPs, and MMP-9 in particular, in both excitotoxic neuronal damage and subsequent neuroinflammatory processes, and suggest that selective MMPIs could be therapeutically relevant in related neurological disorders.

No abstract

No abstract

We investigated in vivo the expression of the tissue inhibitor of metalloproteinases-1 (TIMP-1) in the rat CNS after kainate (KA)-induced excitotoxic seizures. In situ hybridization revealed that TIMP-1 mRNA is induced rapidly and massively in most regions of the adult forebrain after KA treatment. Neuronal activity seems to be necessary but not sufficient to trigger TIMP-1 induction, because it is not observed in seizing 10-d-old pups, unlike what is observed in 21-and 35-d-old animals after seizures. The rapid induction of TIMP-1 is not prevented by the inhibitor of protein synthesis cycloheximide, suggesting that, after seizures, TIMP-1 is induced in neurons as an immediate early gene (IEG). The initial neuronal upregulation is followed by enhanced expression in astrocytes, as assessed by double-labeling experiments. In the hippocampus rapid increases in mRNA are followed by relatively delayed (8 hr after KA) increases in TIMP-1 immunoreactivity in the perisomatic and dendro-axonic areas, suggesting secretion of the protein. At 3 d after KA treatment, strong immunoreactivity is found in astrocytes and in the cell bodies and dendro-axonic projections of resistant neurons such as the dentate granule cells. Taken together, the results suggest that TIMP-1 may be instrumental for neurons and astrocytes in coupling early cellular events triggered by seizures with the regulation of long-lasting changes involved in tissue reorganization and/or neuroprotection.

No abstract

No abstract