Involvement of tissue inhibition of metalloproteinases-1 in learning and memory in mice

Tissue inhibitor of metalloproteinases (TIMP-1) is one of the four-member family (TIMPs-1-4) of multifunctional proteins that inhibit matrix metalloproteinases (MMPs). Its expression in the hippocampus is neuronal-activity-dependent and dramatically induced by stimuli leading to long-term potentiation (LTP), suggesting that TIMP-1 is a candidate plasticity protein potentially involved in learning and memory processes. We tested this hypothesis in a hippocampus-dependent task using the new olfactory tubing maze, with mice carrying a null mutation for TIMP-1 (TIMP-1 KO) and mice overexpressing TIMP-1 (TIMP-1 (tg)). The TIMP-1 KO mice were significantly impaired in making correct odor-reward associations when compared with their respective wild type (WT) littermates, while TIMP-1 overexpressing mice performed better than their WT controls. Both genetically modified mice learned the paradigm and the timing of the task, like their respective WTs, and no olfactory dysfunctioning was observed. These data suggest that TIMP-1 is involved in learning and memory processes related to the hippocampus, and support the hypothesis that the MMP/TIMP ratio, and hence MMP activity, modulates neuronal plasticity in normal learning and memory processes, while altered proteolytic activity could impair cognitive functions.