Matrix metalloproteinase expression in an experimentally-induced DTH model of multiple sclerosis in the rat CNS

In an experimentally-induced DTH model of MS, we examined mRNA and protein expression of a range of MMPs and of TNFα to establish the contribution that individual MMPs might make to the pathogenesis. In control rat brain, mRNA for all of the MMPs examined was detectable. However, by immunohistochemistry, only MMP-2 could be detected. In the DTH lesions, significant increases in the level of mRNA expression were observed for MMP- 7, MMP-8, MMP-12, and TNFα. Where expression of MMP mRNA was increased, there was a corresponding increase in protein expression detected by immunohistochemistry. To determine whether the upregulated MMPs could invoke destructive events in the CNS, highly purified activated MMP-7, MMP-8, and MMP-9 were stereotaxically injected into the brain parenchyma. All provoked recruitment of leukocytes and BBB breakdown. In addition, MMPs 7 and 9 induced loss of myelin staining. In conclusion, specific MMPs are upregulated in DTH lesions; for the most part, measurement of mRNA was a predictor of increased protein expression. From our injections of MMPs, it is clear that the upregulated MMPs in the DTH lesions could participate in the disruption of the BBB, leukocyte recruitment, and tissue damage.</p

Extracellular Signal-regulated Kinase Phosphorylates Tumor Necrosis Factor α-converting Enzyme at Threonine 735: A Potential Role in Regulated Shedding

The ectodomain of certain transmembrane proteins can be released by the action of cell surface proteases, termed secretases. Here we have investigated how mitogen-activated protein kinases (MAPKs) control the shedding of membrane proteins. We show that extracellular signal-regulated kinase (Erk) acts as an intermediate in protein kinase C-regulated TrkA cleavage. We report that the cytosolic tail of the tumor necrosis factor α-converting enzyme (TACE) is phosphorylated by Erk at threonine 735. In addition, we show that Erk and TACE associate. This association is favored by Erk activation and by the presence of threonine 735. In contrast to the Erk route, the p38 MAPK was able to stimulate TrkA cleavage in cells devoid of TACE activity, indicating that other proteases are also involved in TrkA shedding. These results demonstrate that secretases are able to discriminate between the different stimuli that trigger membrane protein ectodomain cleavage and indicate that phosphorylation by MAPKs may regulate the proteolytic function of membrane secretases