Membrane-type 5 matrix metalloproteinase is expressed in differentiated neurons and regulates axonal growth.

Expression of membrane-type (MT) 5 matrix metalloproteinase (MMP) in the mouse brain was examined. MT5-MMP was expressed in the cerebrum in embryos, but it declined after birth. In contrast, expression in the cerebellum started to increase postnatally and continued thereafter. The cells expressing MT5-MMP were postmitotic neurons that showed gelatinolytic activities. Specific expression of MT5-MMP was observed in the neurons but not in the glial cells when embryonal mouse carcinoma P19 cells were differentiated in vitro by retinoic acid treatment. Neurons isolated from dorsal root ganglia also expressed MT5-MMP, and it was localized at the edge of growth cone. Proteoglycans inhibit neurite extension and regulate synaptogenesis. The inhibitory effect of the proteoglycans on neurite extension of dorsal root ganglia neurons was effectively eliminated by recombinant MT5-MMP. Thus, MT5-MMP expressed in neurons may play a role in axonal growth that contributes to the regulation of neural network formation